Oncogenes and human cancer

REVIEW ARTICLE

Oncogenes and Human Cancer

Enrique Pimentel

INTRODUCTION

Oncogenes, or tumor genes, are genes with potential properties for the induct ion of neoplastic transformation in either natural or experimental conditions. Most oncogenes have been isolated from acute transforming retroviruses, which act as oncogene transducers [1], although these viruses do not usual ly transmit cancer under natural condit ions in any animal species. The existence of potentially transforming sequences in the genome of vertebrates was postulated as a possible general mechanism for the process of oncogenesis in the viral oncogene hypothesis [2, 3]. Ac- cording to this hypothesis, all vertebrates would contain in their DNA endogenous genetic information related to nncleot ide sequences present in RNA tumor viruses. These sequences were named virogenes, and the activation of a portion of the vi- rogene, named oncogene, would be responsible for transforming a normal cell into a tumor cell. Various exogenous agents (radiation, chemical carcinogens, viruses) would be capable of activating the endogenous oncogenic information. However, the viral oncogene hypothesis postulated a genetic linkage between the oncogene sequence and endogenous viral sequences, which was not confirmed in later studies. The existence of a cellular tumor gene, named the Tu gene, was postulated in experiments of selective crosses of Xiphophorus fishes [4-7]. Furthermore, in some experiments the Tu gene was successfully transferred into fish embryos, where its heritable expression was observed [8]. Regrettably, the structure of both the Tu gene and its putative product, as well as their respective normal functions, has not been elucidated. Furthermore, the distr ibution of the Tu gene among the animal kingdom remains undetermined, and it is not known if a homolog gene exists, for example, in the human genome. A viral counterpart of Tu is also unknown, and consequently, it is still uncer ta in as to whether Tu can be considered a true oncogene in the usual meaning of this word or if it merely acts through regulatory actions on one or more cellular oncogenes present in the fish cells. Other investigators detected an unexpected presence of avian tumor virus RNA and proteins in un in - fected chicken embryo cells [9-11]. Furthermore, cellular DNA and RNA sequences homologous to acute transforming retroviruses (Kirsten and Harvey strains of murine sarcoma viruses) were found in rat tumors as well as in rat normal tissues [12, 13]. More recently, it was demonstrated that the cells of uninfected chickens con-

From the National Center of Genetics, Caracas, Venezuela.

Address requests for reprints to Dr. Enrique Pimentel, Centro Nacional de Gen~tica Hu- mana y Experimental, Instituto de Medicina Experimental, Apartado Postal 50587, Caracas 1050A, Venezuela.

Received February 3, 1984; accepted March 5, 1984.

347

© 1985 by Elsevier Science Publishing Co., Inc. Cancer Genetics and Cytogenetics 14, 347-368 (1985) 52 Vanderbilt Ave., New York, NY 10017 0165-4608/85/$03.30

348 E. Pimentel

tain in their genome nucleot ide sequences that are homologous to the transforming gene of avian sarcoma viruses but that are not l inked to endogenous viral sequences [14, 15]. Since that t ime, cel lular oncogenes have been found in all vertebrate species s tudied so far [16-18], as well as in insects such as Drosophi la [19]. Appar- ently, oncogenes are present in all mul t ice l lu lar animals, but they are absent in protozoans and plants [20]. Oncogenes have been isolated from acute t ransforming retroviruses of avian, rodent, feline and pr imate origin, but they are genes of eukaryotic cel lular origin, not of viral origin (i.e., these viruses act only as oncogene transducers). The presence of oncogenes in such viruses is general ly at t r ibuted to recombinat ional events that occurred between retroviruses and eukaryotic cells. Cellular oncogenes are also named protooncogenes or c - o n c genes, whereas their viral counterparts are named v-onc genes. Each oncogene is represented by a three- letter symbol related to the name of the retrovirus from which it was original ly defined. More than 20 different oncogenes have been detected so far in normal and tumor cells from humans and other animals (for reviews see [21-30]). The associat ion of oncogenes with human tumors is discussed in the present review.

NUMBER AND LOCATION OF HUMAN ONCOGENES

Oncogenes are l imited in number. A litt le more than 20 different oncogenes have been detected in vertebrates so far, inc luding humans, and there are probably not many more. Most oncogenes were original ly isolated from acute t ransforming viruses that act as cel lular oncogene transducers, but a few oncogenes apparent ly are not present in these viruses and have been detected by means of DNA transfection/ t ransformation exper iments and/or by molecular hybr id iza t ion procedures [30]. A list of oncogenes with their respective isolat ion origin appears in Table 1. At least twelve different oncogenes have been assigned to specific human chromosomes and, more recently, the sublocal izat ion of some of them in the human chromosomes has been determined (Table 2). A precise knowledge of the chromosomal sublocalization of human oncogenes is impor tant for unders tanding the possible role of oncogene act ivi ty in human cancer. It is known that specific chromosomal rearrangements are associated with several kinds of human mal ignant diseases [47-50], and it is impor tant to compare the chromosomal break points occurring in such neoplasias with the precise local izat ion of oncogenes wi th in chromosomes in the neoplast ic cell populat ions. In fact, it has been proposed that chromosomal rearrangements are associated with certain forms of human neoplas ia through translocat ion-related activation of specific oncogenes [51].

STRUCTURE OF HUMAN ONCOGENES

Complete or part ial nucleot ide sequences of several human oncogenes have been reported, inc luding c-mos [52], c-H-ras [53-56], c-K-ras [57, 58], c-N-ras [59], c-sis [66], and c - m y c [61-63]. The complete coding sequences of c-src have been determined in the chicken [64], and homologous sequences have been detected on human chromosome #20 [44]. The structure of cel lular oncogenes is s imilar to that of their viral counterparts . An important difference is the presence of introns or inter- vening sequences (IVS) in the cel lular oncogenes, such sequences being absent in viruses. In addi t ion, v-onc and c-onc homologous genes may have differences in nucleot ide sequences, al though such differences are usual ly small. The human c-H- ras gene, for example, differs from the viral v-H-ras gene (derived from rat) at only 3 of 189 amino acid posit ions, and the human c-K-ras gene differs from the viral v- K-ras gene (also derived from rat) at only 7 of 189 posi t ions [57]. Moreover, certain

Oncogenes and H u m a n Cancer 349

Table 1 N o m e n c l a t u r e and or igin of oncogenes

Oncogene symbol Isolate origin Prototype virus strain

abl rodent (mouse) ets avian (chicken) erbA avian (chicken) erbB avian (chicken) fes (=fps) feline (cat) fgr feline (cat)

fins feline (cat) fos rodent (mouse) mht avian (chicken) mos rodent (mouse) myb avian (chicken) mye avian (chicken) raf rodent (mouse) H-ros rodent (rat) K-ras rodent (rat) N-ras primate (human) re/ avian (turkey) ros avian (chicken) sis primate (woolly monkey) ski avian (chicken) src avian (chicken) yes avian (chicken)

Abelson murine leukemia virus avian leukemia virus E26 avian erythroblastosis virus avian erythroblastosis virus Snyder-Theilen feline sarcoma virus Gardner-Rasheed feline sarcoma

virus McDonough feline sarcoma virus FBJ murine osteosarcoma virus Mill Hill 2 avian carcinoma virus Moloney routine sarcoma virus avian myeloblastosis virus MC29 avial myelocytomatosis virus 3611 murine sarcoma virus Harvey murine sarcoma virus Kirsten mnrine sarcoma virus no viral origin ° avian reticuloendotheliosis virus Rochester URII avian sarcoma virus simian sarcoma virus SKV770 avian virus Rous sarcoma virus Yamaguchi avian sarcoma virus

°Cloned from human tumor cell lines.

" c o n s t a n t " regions of these oncogenes are more p re se rved in s t ructure than o ther "va r i ab l e " regions. The sequences of oncogene cod ing regions (exons) are h igh ly conse rved even in d i s tan t ly re la ted species , w h i c h suggests the evo lu t i ona ry impor - tance of thei r r e spec t ive p o l y p e p t i d e products . The p roduc t of the c-src gene is the pro te in pp60 src H u m a n pp60 src and mouse pp60 src are bo th c lose ly re la ted in thei r

Table 2 C h r o m o s o m a l loca l i za t ion of h u m a n oncogenes

Chromosome Chromosome Oncogene assignment sublocalization Reference

c-N-ras 1 lp3200-*cen [31] c-fins 5 5q34 [32, 33] c-myb 6 6q22-24 [34, 35] c-K-rasl a 6 6pter-~q13 [36, 36, 174] c-erbB 7 7pter-~q22 [175] c-myc 8 8q24 [37] c-mos 8 8q22 [37, 38] c-abl 9 9q34--*qter [39, 40] c-H-rasl 11 11p14.1 [41, 42] c-K-ras2 12 12q11.1 or 12q24.2 [42, 43] c-fes (=c-fps) 15 15q25-26 [33, 35, 39] c-src 20 [44] c-sis 22 22qll-~qter [45, 46] c-H-ras2 a X [36]

°Probably a pseudogene.

3 5 0 E. Pimentel

primary structures to chicken pp60 Sr~ [17]. On the other hand, the size of oncogenes, even of menbers of the same family, may show great variation. For example, the c- H-rasl oncogene is contained in a 4.5 kilobase pair (kbp) DNA sequence, whereas, the c-K-ras2 oncogene, also of human origin, is nmch larger, spanning 35-40 kbp and containing four exons interrupted by IVSs [58]. In spite of these remarkable structural differences, the protein products, p21 ras, of both oncogenes are similar in size.

EXPRESSION OF ONCOGENES

Cellular oncogenes are genes that seem to participate in normal developmental processes. The expression of oncogenes is variable, depending on the tissue, the cell type, the stage of differentiation, and the general or local physiologic conditions. In the mouse, a stage- and tissue-specific expression of cellular oncogenes has been observed. Whereas, the oncogene c-rues has been found to be apparently inactive in normal mouse cells and tissues, even during prenatal development [65], the oncogenes c-H-ras, c-abl, and c-los are widely expressed in pre- and postnatal tissues [66]. The gene c-H-ras is expressed at all stages of mouse prenatal development, and it is also expressed in various tissues of 10-day-old mice. The activity of this oncogene may increase markedly during liver regeneration induced in rodents by partial hepatectomy or administration of carbon tetrachloride [67, 68]. The gene c- ab1 is expressed at high levels in the mouse embryo, especially at days 10-11, and it is also expressed in apparently all postnatal mouse tissues, although several-fold differences in c-abl expression are observed between different mouse organs and tissues. Compared with the RNAs of other cellular oncogenes (c-myb, c-myc, and c- src) the levels of c-abl transcripts, in general, are much higher [69]. The gene c-los is expressed at high levels in prenatal mice, especially in the placenta and during the later stages of development (after day 16 of gestation), and it is also expressed, although at lower levels, in all postnatal tissues investigated so far [66].

The expression of different human oncogen~s also depends on the tissue, and the stage of development and differentiation. When the transcriptional activity of different oncogenes is tested in normal human tissues, for example, in hematopoietic ceils, it becomes apparent that these genes may be classified in three groups [22]: (a) oncogenes that are almost universally active in different cells and different stages of differentiation (c-abl, c-myc, c-ras); (b) oncogenes that are active only in certain cells and in certain stages of differentiation (c-myb); and (c) oncogenes that are apparently inactive in most cells (c-fes, c-sis). The oncogene c-src is active in most normal human tissues [70]. The protein product of this gene, pp60 src, is present in normal human tissues, with highest levels being observed in brain, followed by kidney, lung, muscle, and connective tissue. The levels in human fetal muscle are two- or threefold higher than in adult muscle, and they were also found to be increased in about one-third of 30 human tumors examined [70]. The expression of c-los and c-fins was studied in human tissues at different stages of differentiation [71]. The levels of c-los transcripts are 100-fold greater in human amniotic and chorionic cells than in other normal human tissues and cells (kidney, liver, lymph nodes, lung). The levels of expression of c-fos and c-fms are greater in human term placenta than in other normal human tissues. In contrast, the expression of c-ras and c-myc does not seen to be modulated in different human tissues [71]. The mechanisms related to regulation of oncogene activation or inactivation under different conditions are poorly understood. DNA hypermethylation may be associated with transcriptional silence of some oncogenes [65, 72], whereas, hypomethylat ion may be associated with oncogene activation [73].

Oncogenes and Human Cancer 3 51

FUNCTIONS OF ONCOGENE PROTEIN PRODUCTS

The universal presence of oncogenes in vertebrates, and probably in all metazoans [20], as well as their high conservation in evolution [16, 17], indicate the biologic importance of their protein products. Unfortunately, the normal functions of the protein products of cellular oncogenes are little known. It has been postulated that oncogenes are involved in the normal processes of cellular differentiation and proliferation, especially during embryogenesis, and that they would participate in cell transformation only when they are expressed at inappropriate stages of cell differentiation [74].

The best characterized oncogene polypeptide product is pp60 Src, a protein produced by either the oncogene of the Rous sarcoma virus or its respective cellular hamolog [75]. pp60 src is a phosphoprotein with cyclic AMP-independent kinase activity, and this activity is specific for phosphorylation of tyrosine residues on protein substrates, pp60 src tryosine-specific protein kinase activity is present in normal tissues of many animal species, including human tissues, where organ-specific variations in the levels of activity have been described [70]. A similar type of activity is present in products of oncogenes other than src, including yes, fps, fes, ros, and abl [30]. These oncogenes may be members of a superfamily of genes with distantly related protein products [19]. However, tyrosine-specific protein kinase activity is not an exclusive property of oncogene products. A similar activity is elicited by the action of insulin and several growth factors (epidermal growth factor, platelet-derived growth factor) [76]. Moreover, high levels of tyrosine-specific protein kinase activity are also present in nonproliferating, terminally differentiated normal human blood cells [77]. It seems clear, thus, that high levels of this type of activity cannot be considered a characteristic of oncogene action or cell malignant transformation.

Protein kinase activity is absent from some oncogene products, including the protein products of myb, myc, mos, and ras [22, 30]. It is also absent in p28 s~s, a 28,000-dalton protein encoded by the simian sarcoma virus (SSV) oncogene and its cellular homolog [78]. It has been observed that a striking degree of sequence homology exists between p28 sis and a cellular growth factor, the platelet-derived growth factor (PDGF), which is present in normal human blood [79-81]. Moreover, there is strong evidence indicating that the cellular actions of the v-sis gene are mediated by a PDGF-like molecule [82]. Although the physiologic role of PDGF is not yet defined, it is known to be released from platelets during blood clotting, and has been recognized as an important mitogen present in serum, being required for the growth of cells of mesenchymal origin maintained in tissue culture [83]. In general, the normal functions of oncogene protein products are not understood, but some of these products are localized in the cytoplasm or the plasma membrane, whereas, others are found in the nucleus [30].

NEOPLASTIC POTENTIAL OF ONCOGENES

Oncogenes are normal components of the genome in probably all of the metazoan species. Their possible role in the origin and/or maintenance of malignant cell transformation is supported by the following experimental observations [22-30]: (A) the infection of cultured normal cells by acute transforming viruses (which contain oncogenes of cellular origin) results in the appearance of a transformed phenotype. (B) The infection of animals with acute transforming viruses results in development of malignant tumors within a few weeks after inoculation of the virus. (C) The transfection of DNA extracted from tumor cells to NIH 3T3 cells (which are

3 5 2 E. Pimentel

nononcogenic cells of murine origin) results in the product ion of foci of transformed cells, whereas, DNA transfection from normal cells do not induce such foci. (D) The transfection to NIH 3T3 cells of DNA extracted from cells t ransformed by chemical carcinogens induces the appearance of foci of cells wi th t ransformed phenotype and, more important , the previous t reatment of the DNA with different restr ict ion endonucleases suggests that the same transforming genes are transferred in all cases. (E) The transfection to normal cul tured cells of DNA containing an oncogene with a promoter long terminal repeat (LTR) at posi t ion 5' results in the efficient and rapid induct ion of a mal ignant phenotype. (F) The induct ion of tumors in mice by means of defined chemical carcinogens is associated with act ivat ion of oncogenes in the tumor cells. (G) The injection of a c loned oncogene (v-src) to suscept ible animals (chickens) results in the effective induct ion of mal ignant tumors (sarcomas) wi th in weeks after inject ion [84]. (H) The systematic dele t ion of oncogene sequences by exper imental procedures indicates that wi th in oncogenes there are regions specifical ly involved in their t ransformation abi l i ty [85]. (I) The exper imental induct ion of s i te-directed point mutat ion in a viral oncogene (the v- src gene) may abol ish its potent ial t ransforming propert ies [86], a l though other mutation sites are d ispensable for t ransformation [87]. (J) Some par t icular point mutations may produce a marked increase in the transforming abi l i ty of an oncogene on NIH 3T3 cells [53-57]. The above ment ioned ensemble of exper imenta l results strongly supports the hypothesis that oncogenes are genes wi th defined potent ial for the induct ion of cell t ransformation. It is apparent , however, that they do not prove that oncogenes are causal ly related to spontaneous tumors occurring in humans and other animals. Notwithstanding, several studies suggest that at least some human tumors may be associated with oncogene action.

ONCOGENES IN HUMAN CANCER

Since oncogenes are potent ia l ly t ransforming genes, and since they are present in all human cells, it is conceivable that act ivat ion of oncogenes might be associated with the origin and/or growth of human neoplast ic cell populat ions . However, this associat ion should not be a s imple one because there are more than 15 different human oncogenes and their respect ive t ranscr ipt ional activit ies are frequently different in different human tissues, and even in different stages of cel lular differentiation. Thus, the assumed associat ion between oncogene act ivi ty and human neoplastic diseases must have some kind of specifici ty for both the oncogene and the tumor. The presence of active oncogenes in some, but not all, human tumors be- came apparent through the posi t ive results obtained al ready in the first exper iments with transfection of DNA extracted from different human tumor cell l ines [88-90]. In such experiments , as in many consecutive ones [91], it was found that DNA extracted from different types of human tumor cell l ines contain a gene (or genes) capable of t ransforming NIH 3T3 cells. The donor cell l ines s tudied by transfection assays were of varied origin, inc luding carcinomas from different sites (urinary bladder , lung, colon, pancreas, mammary gland), as well as tumors of the nervous system and hematopoie t ic malignancies. The same gene, or closely related ones, are responsible for posi t ive results, as may be deduced by digest ion of I donor DNA wi th restr ict ion enzymes, i

Oncogenes of the c-ras family (c-H-ras, c-K-ras, c-N-ras) may be active in human carcinoma cell l ines, as well as in pr imary human tumor specimens of several sites, such as colon, lung, gall bladder , ur inary bladder, and pancreas, and also in rhab- domyosarcoma [92, 93]. Members of the same oncogene family may be active in human hematopoie t ic neoplasms, inc luding pr imary acute myelogenous leukemia and cell l ines der ived from acute lymphocyt ic leukemias, T-cell leukemias, and

Oncogenes and Human Cancer 3 5 3

chronic myelogenous leukemia [94, 95]. The findings demonstrated "that different oncogenes can be activated in lymphoid tumor cells at the same stage of hemato, poietic cell differentiation," and "that the hematopoietic oncogenes detected in the NIH 3T3 transfection assay are not specific to a given stage of cell differentiation or tissue type" [94]. However, the biological meaning of positive results obtained in such transfection assays is not clear because NIH 3T3 cells are not normal cells, and the molecular events associated with the acquisition of a transformed phenotype in these cells remains uncharacterized. When other cell systems are used, consistent negative results for transformation of the recipient cells are obtained. The NIH 3T3 cell system is apparently biased for detection of oncogenes of the c-raS family and, most important, it remains to be established that the transforming genes detected in the system are critically involved in the origin and/or development of the respective tumor under natural conditions. Many human tumors give negativ~ results for the presence of active oncogenes in transfection/transformation assays with the NIH 3T3 system [91], and consistent negative results are obtained with the same system by screening of normal cells from patients with high cancer risk syndromes [96].

Before discussing the mechanisms potentially related to oncogene activation in human tumors, the possibility of oncogene deletions should be mentioned. Hypo- thetically, deletion of specific oncogenes could produce derangements in the regulation of cell functions and, depending on the cell type and its stage of differentiation, an unbalanced activity of oncogenes could result in neoplastic transformation of the cell. However, no evidence exists for supporting this possibility. A deletion of chromosome #11, region 11p13--~11p14, has been observed in a rare congenital anomaly, the aniridia-Wilms' tumor association (AWTA) [97, 98]. The oncogene c-: H-rasl is situated in close proximity to this region but it is not deleted in patients with the AWTA anomaly [99, 100]. It is conceivable, however, that the expressio~ of c-H-ras 1 could be altered as a consequence of the abovementioned chromosome deletion. A deletion of chromosome #13, region 13p14, is observed in less than 5% of cases of human retinoblastoma [101]. However, the deletion may be present in higher proportion of retinoblastoma patients because it can occur at a submicro'o scopic level [102], but no oncogenes have been assigned to human chromosome #13. Hypothetically, the deleted region on this chromosome would contain not an oncogene but, on the contrary, a tumor-suppressing gene [102]. Increased chromosome fragility is found in several clinical syndromes associated with increasedl cancer risk [103], and it has also been found in patients with sporadic unilatera!i retinoblastoma [104]. A possible relationship between chromosome fragility and neoplastic diseases may be anticipated if this fragility results either in loss or alteration of genome segments involved in the transcriptional control of oncogenes: or in deletion of tumor-suppressing genes.

Four basic types of mechanisms may be associated with activation of oncogene~ in human cancer: increased transcriptional activity of oncogenes, amplification o[ oncogenes, translocation of oncogenes, and mutation of oncogenes. In the following~ these mechanisms are discussed.

Transcriptional Activity of Oncogenes in Human Tumors

The transcriptional activity of one or more oncogene may be increased in malignant cells, compared with their normal counterparts. This activation can be appraised by direct determination of the levels of the respective RNA or protein oncogene products in the tumor cells. Increased mRNA levels corresponding to transcription of c-sis and c-myc oncogenes has been found in some cell lines derived from dif~ ferent human tumors [105, 106]. Transcripts of the c-sis gene were detected in 8 or

354 E. Pimentel

23 human tumor cell l ines derived from sarcomas and glioblastomas, al though the levels showed marked variat ion among different lines; c-sis t ranscripts were not detected in cell l ines der ived from carcinomas, melanomas, or other human tumors, and also were undetectable in human embryonic fibroblasts [105]. Variable levels of c-myc t ranscripts were detected in cell l ines der ived from human sarcomas, carcinomas and lymphomas , as well as in normal human fibroblasts and hematopoie t ic cells [105]. There was no apparent correlat ion between c-sis and c-myc t ranscrip- t ion rates in different human tumor cell lines. Complex pat terns of t ranscr ip t ion of several oncogenes, inc luding c-H-ras and c-abl, were observed in many different human tumor cell l ines, as well as in normal human fibroblasts [105, 106]. Onco- gene transcripts with different sizes were detected in both mal ignant and normal human hematopoie t ic cells, but a consistent pat tern of t ranscr ipt ion could not be discerned. In general, human tumor cell l ines show great variat ion in the levels of expression of different oncogenes, and in some lines the levels may be normal.

The s tudy of oncogene activi ty in b iopsy specimens of human tumors may be more informative than the s tudy of cell l ines, since many of these l ines have been mainta ined for years in an artificial envi ronment and their b iochemical propert ies may be different from those existing in pr imary tumors. When the t ranscr ipt ional act ivi ty of different oncogenes (c-myc, c-myb, c-H-ras, c-re/, c-erb, and c-src) is tested in b iopsy specimens or fresh cells from a variety of human leukemias and lymphomas , no consis tent differences are observed between the tumor cells and their normal counterpar ts [107, 108]. Al though it is conceivable that some kind of hierarchical act ivat ion of different oncogenes could cri t ical ly par t ic ipate in the origin and/or deve lopment of human mal ignant diseases, the results 9btained in several s tudies do not lend suppor t to the existence of such a phenomenon. The inter- pretat ion of findings related to levels of RNA and/or protein oncogene products in either pr imary tumors or tumor cell l ines may be difficult, especia l ly when the increases are of small magnitude. Even when marked increases are observed, the levels of oncogene expression may be s imply s imilar to those occurr ing in em- bryonal or fetal stages of deve lopment of the respect ive cell or tissue. Reexpression of sets of deve lopment phase-specif ic genes is observed in cancer cells under either natural or exper imenta l condi t ions [109]. The increased levels of oncogene products could correspond, at least in some cases, to a general phenomenon of dedifferentia- t ion or retrodifferent iat ion occurring in the tumor cells. Thus, it may be s imilar to the reexpression or increased expression of oncofetal antigens and other biochem- ical changes occurring in many types of human tumors, as well as in t issue and organ regenerative processes. Furthermore, both the general physiologic condi t ions of the patient or the local condi t ions of the tumor t issue may have influence on the expression of genes present in the tumor cells, inc luding the oncogenes. However, oncogenes could part ic ipate in the complex, mult is tage processes related to tumorigenesis, which are associated with manifold changes in the express ion of different genomic functions. In any case, consis tent ly increased t ranscr ipt ional act ivi ty of a par t icular oncogene, or a set of oncogenes, is apparent ly not a universal characteristic of specific types of human tumors or of human tumors in general.

Amplification of Oncogenes in Human Tumors

Oncogene amplif icat ion has been suggested as a model for the general process of carcinogenesis [110]. This phenomenon would occur through a series of unequal sister chromat id exchanges in different cell cycles. Ampli f ica t ion of oncogenes, or other cel lular genes, might be related to same stages of the oncogenic process, because during the process of gene amplif icat ion mul t ip le DNA rearrangements occur that generate new combinat ions of DNA sequences [111]. Each amplif ied unit has a


unique structure and, at the time of formation of the units, pieces of DNA from different parts of the genome are joined together to form novel structures. Thus, gene amplification could contribute to the production of DNA molecular rearrangements that occur in many tumor cells.

Amplification of c-myc, or comyc-related sequences, has been found in a human myeloid leukemia cell line [112], in human neuroblastoma cell lines and a neuroblastoma tumor specimen [113, 114], and in human lung cancer cell lines [115]. In the latter study, of 18 human lung cancer cell lines tested, 8 showed c -myc amplification, and 5 of them, which had a high degree of c -myc DNA amplification 20 to 76-fold) and greatly increased levels of c -myc RNA, were derived from patients with a variant class of small-cell lung carcinoma with very malignant behavior. Ampli- fication of c -myc and c-K-ras 2 genes was observed in cell lines derived from human colon carcinomas [116, 117], and amplification of c-abl, as well as of adjacent sequences corresponding to the gene for immunoglobulin light chain constant region (CM, has been detected in a human chronic myeloid leukemia cell line [40]. In some of these tumor cell lines, numerous double minute (DM) chromosomes and homogeneously staining regions (HSR) of chromosomes were observed. Since such cytogenetic abnormalities are present in a number of human tumor cell lines, as well as in direct preparations of tumor specimens from some human tumors [118-122], they might correspond to amplification of certain oncogenes, and perhaps also of other genes. In fact, the c -myc gene was found to be amplified in cell lines derived from human neuroblastomas, and by means of in situ molecular hybridization it was demonstrated that HSRs are the chromosomal sites of amplified DNA [113]. However, the degree of amplification varied considerably between different human neuroblastoma cell lines (from 5 to 8-fold to 120 to 140-fold); in one cell line, no such amplification was detected (it was also not detected in cell lines derived from human melanoma, retinoblastoma, and colon carcinoma). Moreover, whereas the c- m y c gene is normally located on chromosome 8q, the detected amplified sequences, which included a domain distantly related to comyc, occupied different chromosomal locations [112]. Thus, amplification of unidentified genes, which may or may not be oncogenes, or may be pseudogenes, is associated with the development of some human tumor cells. However, only a minority of human tumors would be associated with amplification of specific oncogenes, and this amplification could represent only a consequence of different genetic and/or epigenetic changes that could have occurred in the process of cell transformation or during cell culture. It is conceivable that amplification of specific oncogenes, or other genes, could be involved in the development and/or progression of certain tumors when these genes confer some selective advantages for tumor growth. In any case, oncogene amplification is not found exclusively in malignant cells. The oncogenes c-H-ras and c-K-ras have been found to be amplified in normal animals from several rodent species, and some of these species contain about 10 copies of a given oncogene in their genome [123].

Translocation of Oncogenes in Human Tumors

Malignant diseases in humans, as in all animals, are characterized by the almost universal presence of cytogenetic abnormalities, including aneuploidy and structural chromosome aberrations [47]. Some human malignancies, especially leukemias and lymphomas, are characterized by the regular presence of translocations, not only between specific chromosomes but, more important, between specific regions within chromosomes. In the last few years, the study of these rearrangements and their possible relation to oncogene changes yielded very interesting observations. Some definite relationships between specific chromosomal rearrangements

3 5 6 E. Pimentel

and neoplastic diseases, especially diseases of the hematopoietic system, are emerging [48-51, 124, 125]. Chromosome regions corresponding to the localization of certain oncogenes, especially of c-myc, c-mos, and c-abl, are most frequently involved in rearrangements associated with malignant hematologic diseases.

The first structural chromosome abnormality described in human malignant diseases was the Philadelphia chromosome (Phi), which is present in most patients with chronic myelocytic leukemia (CML). The translocation occurs between the long arms of chromosome #22 and some other chromosome, most frequently chromosome #9, in particular t(9;22)(q34;q11) [126]. In the words of Sandberg [47], "To date, CML is the only malignant disease in which a characteristic consistent kary- otypic finding, i.e., the Philadelphia chromosome (Phi), has been established. Since its description by Nowell and Hungerford in 1960, the Ph 1 remains the most signif- icant and interesting, but also the most puzzling and perplexing chromosomal finding in human and experimental oncology. It is the only chromosome anomaly closely related to a specific type of neoplastic disease, i.e., CML, and, hence, by far the strongest argument in favor of the theory that chromosomal changes are related to neoplasia." According to this statement, it is most intriguing that, more recently, it has been demonstrated that the Ph 1 involves a reciprocal translocation, where the oncogene c-abl, normally located on human chromosome #9 [39], is translocated to chromosome 2 2 q - [127]. The Ph ~ translocation could alter the structure and/or expression of the c-abl gene, as well as the expression of the C~ immunoglobulin light chain gene, which is adjacent to the translocation site on the long arms of chromosome #22 [40]. Furthermore, the oncogene c-sis, which is normally located on the long arms of human chromosome #22 [46], may be translocated to chromosome 9q in the Ph ~ translocation [128]. However, whereas c-abl is universally active in human hematopoietic cells at all stages of differentiation, c-sis is inactive in these cells although, exceptionally, it is expressed in some T-cell lymphoma cell lines containing a unique human T-cell leukemia retrovirus (HTLV) [106]. The site of breakage is variable among different cases of Phi-positive CML [40]. In Phl-neg - ative cases c-abl is not translocated [129], which reinforces the suggestion that Ph ~- positive and Phi-negative CML are different clinical entities, the latter group of cases having a poorer prognosis [130]. It is apparent, however, that CML may result from mechanisms independent of the c-abl translocation. The precise relationship between the Ph 1 translocation and the origin of CML is not understood. The Ph 1 chromosome may be present in hematologic malignancies other than CML, and the target cell for the Phi-positive leukemia is a multipotential cell, i.e., a stem cell [50].

Regular chromosomal recombinations also occur in hematologic malignant diseases other than CML. A segment of human chromosome 21q may be translocated to chromosome 9q in acute myeloblastic leukemia, and a segment of human chromosome 17q may be translocated to chromosome 15q in acute promyelocytic leukemia [124]. Again, it is intriguing to observe that the long arms of human chromosome #8 contain two oncogenes, c-myc and c-mos [37, 38], and the long arms of human chromosome #15 contains another oncogene, cores [33, 35, 39]. However, the behavior of these oncogenes in the mentioned neoplasms is still poorly understood [94]. High levels of c-myc transcripts are present in a human promyelocytic leukemia cell line, HL60 [106], but the transcriptional activity of c-myc in uncul- tured cells from different types of childhood leukemia is usually normal [107].

Several studies revealed an association between the c-myc gene, the loci corresponding to immunoglobulin genes, and the development of human lymphomas, especially B-cell lymphomas [49-51, 131]. The human genes coding for immunoglobulin heavy, light kappa and light lambda chains are located on specific regions of chromosomes #14, #2 and #22, respectively, and these regions are involved in chromosome translocations occurring in malignant B-lymphocytes [132,133]. In the


tumor cells of virtually all patients with Burkitt's lymphoma, a small region from the long arms of chromosome #8 (8q24-~qter), containing the c-myc oncogene, is translocated to either chromosome #14 (in about 90% of patients), or to chromosomes #2 or #22 (in about 10% of patients) and, furthermore, the translocation involves the regions of chromosomes #14, #2, and #22 containing immunoglobulin genes [134-136]. A similar type of translocations, involving the c-myc gene and immunoglobulin genes, is also observed in mouse plasmocytoma cells [135, 137, 138]. In the most frequent type of translocation observed in human B-cell lymphoma, i.e., t(8;14), there is marked variability among patients in the chromosome breakpoints on both chromosomes #8 and #14 [136]. In some of the corresponding human cell lines, variable portions of the distal part of the long arm of chromosome #14, cantaining the genes coding for the variable segment of immunoglobulin heavy chains (VH), are translocated to the broken distal part of chromosome 8 q - [139]. In other Burkitt's lymphoma cell lines, characterized by t(8;22), the constant region of the lambda light chain immunoglobulin gene is translocated from chromosome #22 to chromosome #8 [140]. The breakpoint may lie within the immunoglobulin genes, but different cases have different breakpoints. The c-myc locus itself is rearranged at the 5' side in one-third of the examined human B-cell lymphoma lines [136], which may result in a 5'-to-5' ("head-to-head") position with respect to the immunoglobulin constant p. region of the gene. During the rearrangement, the 5' end of the c-myc gene occasionally remains on chromosome #8 [63].

The relationship between these changes and lymphomagenesis is not clear. B- cell lymphomas apparently are not the consequence of a simple activation mechanism of the translocated c-myc oncogene. In some human and mouse lymphomas c-myc-related RNAs are present in normal or only slightly elevated concentrations [106, 137, 141] although, in other similar cell lines, high levels of c-myc transcripts are observed [139, 142, 143]. Transcripts related to the c-mos gene were not detected in several Burkitt's lymphoma cell lines [141]. When biopsy specimens or fresh blood ceils (not cell lines) of human B-cell malignancies are studied, only a few or none of the total neoplasms show high levels of c-myc transcripts [107, 108]. In general, the transcriptional rate of the translocated c-myc gene is variable [13], but only the translocated c-myc gene is transcribed in Burkitt's lymphoma cells, the untranslocated c-myc gene being silent on the normal chromosome #8 [144]. Un- translocated and unrearranged c-myc genes may occur in some Burkitt's lymphoma cell lines, and they may be transcriptionally activated by translocation of a immunoglobulin C)~ locus [145], although in some cases the rearranged c-myc gene is placed so that it cannot utilize immunoglobulin promoter or enhancer elements [131]. On the other hand, in some cases the translocated c-myc gene may induce a transcriptional activation of immunoglobulin heavy chain genes [146], and may produce structural changes in these loci [62]. The translocated c-myc gene itself may also show structural changes [147], although in some cases the coding sequence of the rearranged c-myc gene is identical to that of the normal gene [131]. Truncated c-myc-related RNAs may be produced as a consequence of c-myc gene breakages occurring during the process of translocation.

High levels of transcripts of the 5' exon of the decapitated c-myc oncogene re- maining on chromosome 8 q - are produced by some human lymphoma cells [144]. Interestingly, DNA sequences with homology to those contained in the 5' half of the c-myc gene have been detected in human cytomegalovirus (HCMV) [148], a virus with potential oncogenic properties that has been implicated as a possible agent involved in the etiology of several types of human tumors, including Kaposi's sarcoma occurring in patients with the acquired immunodeficiency syndrome (AIDS) [149]. However, the possible role of HCMV, as well as that of other viruses with oncogenic potential, in the etiology of human cancer remains poorly under-

3 5 8 E. Pimentel

stood [150]. In avian bursal lymphoma cell lines, the sizes of c-myc-re lated products are highly variable, and it has been suggested that transformation-associated polypeptides may be truncated versions of the normal c-myc gene product [151]. A multiplicity of Cc~-immunoglobulin- and c-myc-related RNA species also are produced in mouse lymphoma cell lines, and many of these RNA species apparently are active in protein synthesis [146]. In at least some human malignant B-cell lines, however, the protein product of the c-myc gene is of normal size and structure [62, 153].

The diversity of both the quantitative and qualitative changes of c-myc RNA and protein products occurring in B-cells on c-myc translocation probably makes any single detailed model to account for the various possible consequences of this phenomenon unrealistic [153]. The relationship between the c-myc gene, its RNA and protein products, and the origin of B-cell neoplastic transformation is difficult to assess at present. The normal function(s) of the c-myc protein product is still unknown. In transfection experiments, plasmocytoma DNA can transform NIH 3T3 cells, but the transforming activity is spared by digestion with a restriction endo- nuclease (HindIII) that cuts the c-myc gene [154]. Most probably, the origin of B- cell neoplasms is complex, involving some critical steps in addition to c-myc translocation. A possible synergistic or cooperative action of other oncogenes, in addition to c-myc, should be considered [155]. However, no simple or clear-cut relationships have been established between oncogene translocations or rearrangements and oncogene activation, in order to allow the construction of a sound hypothesis on the origin of human hematopoietic neoplasms. Further studies are required in order to achieve a better understanding of the genomic phenomena involved in the origin and development of human hematologic malignant diseases.

Mutation of Oncogenes in Human Tumors

The hypothesis that the origin of neoplastic transformation involves somatic cell mutation has been widely accepted, but specific genes responsible for the transformation phenomenon have not been identified. Recently, much interest has arisen from the possibility that altered polypeptides produced by mutant oncogenes could be related to the origin of some human tumors, particularly urinary bladder, lung, and colon cancer. A biologically active oncogene, with high potential for inducing transformation in DNA transfection experiments with the NIH 3T3 assay system, has been detected in some human bladder carcinoma cell lines, the T24 and EJ cell lines [156-158]. The oncogene was cloned in molecular vectors and was identified as c-ras or c-bas, cellular homologs of the Harvey- and BALB-murine sarcoma virus oncogenes [159,160]. A better characterization demonstrated that the 21,000-dalton (p21) polypeptide product of the human urinary bladder carcinoma oncogene is different from the respective oncogene product present in normal human cells, the difference consisting of substitution of a single amino acid. Whereas normal human p21 r~s has a glycine at position 12, EJ° and T24-p21 ras has valine at this position, which would correspond to a single G-~T nucleotide change at the DNA level [53, 54, 161]. This nucleotide change was later confirmed by DNA sequence analysis [55, 56, 162]. The complete nucleotide sequence of the T24 oncogene was determined and a single point mutation residing within the first exon distinguished the coding region of this gene from the sequence of its normal counterpart, c-H-rasl. A marked functional alteration of the mutant polypeptide product is predicted from three-dimensional models of the protein [162-164]. Similar qualitative changes were also detected in c-ras genes from some human lung and colon carcinoma cell lines [165-167]. The activated transforming gene of these lines corresponds to the gene c-K-ras2 and, most interestingly, their mutational change determine single

Oncogenes and Human Cancer 359

amino acid substitutions at position 12 (i.e., at the same position as c-H-rasl, p21). Thus, single amino acid substitutions at residue 12 of p21 may represent a common mechanism of transforming activation, depending on mutation of the c-ras genes, and detected by transfection into NIH 3T3 cells [167]. In such DNA transfection assays, the cloned mutant c - r a s genes have a transforming potency that is several orders of magnitude higher than that of cloned nonmutant c-ras; a hypothetical model for explaining the detected enhanced activity has been proposed [164]. Mu- tation of the c-N-ras gene determining amino acid substitution as position 61 of the protein product has been detected in a human neuroblastoma cell line [59], and mutations at two different exon sites of the c-H-ras gene, determining single amino acid substitutions at positions 12 and 61 of the respective p21 product, are associated with enhanced capability for transformation in DNA transfection assays [165]. Furthermore, at least two different mutational changes of the c-K-ras oncogene have been observed in two human lung tumors propagated in nude mice and introduced into NIH 3T3 cells by DNA transfection experiments, and these mutations also determine amino acid substitutions at positions 12 and 61 of the p21 product [168, 169]. The c-K-ras gene of a human lung carcinoma cell line differs from its normal counterpart by amino acid substitutions at positions 12 and 31 of the p21 product [57]. Thus, it seems clear that positions 12, 31, and 61 are hot spots for mutagenesis, resulting in the acquisition of enhanced transforming capability by the encoded protein products, at least when NIH 3T3 cells are used as a test system.

The possible relationship between the abovementioned qualitative changes observed in human cell lines and the origin of human tumors is not understood. The identity of human tumor cell lines is difficult to establish after many years of culture, and cross-contamination of cell cultures is a persistent problem in laboratories [170]. Moreover, since changed oncogenes are cloned from transformed cell lines, specific point mutations could have been selected for growth in tissue culture and, therefore, may be an artifact of cell culture systems [171]. Furthermore, the NIH 3T3 assay system used in transfection experiments is apparently biased for the detection of altered products from mutant c-ras genes, and there is evidence that some oncogene mutations may be induced during some experimental manipulations in vitro. Spontaneous activation of the human oncogene c-ras, associated with a point mutation at position 35 of the first exon, occurred during a transfection experiment [162]. Interestingly, the mutation produced a change of aspartic acid instead of glycine at position 12 of the c-ras-encoded p21 protein (i.e., at the same position altered in T24 and EJ human bladder carcinoma cell lines). On the other hand, it seems likely that most oncogene mutations at different points would result in loss of oncogene biologic activity. In any case, mutant p21 ras products, as well as mutant products of other oncogenes, apparently are unable to induce neoplastic transformation by themselves, since immortality of the fibroblasts used for tests in vitro is a prerequisite for the occurrence of such transformation [172]. A preliminary study of 29 patients with bladder, lung, and colon cancer, including analysis of 20 primary tumor tissues (biopsy specimens), was negative for the presence of mutations producing substitutions of the 12th amino acid in the p21 product of the c-H-rasl gene [173]. It seems unlikely, thus, that mutations of the c-ras genes are involved in the origin and/or development of most cases of common human cancers.

CONCLUSION

Oncogenes are genes of cellular origin, not of viral origin. Although their normal functions are little understood, they may be related to important biologic processes because oncogenes are present in all metazoan species tested so far. At least some oncogenes seem to be involved in normal developmental processes, as well as in

3 6 0 E. Pimentel

processes of cell differentiat ion and/or proliferat ion occurring under specific physiologic condi t ions, inc luding regenerative processes of damaged tissnes. Oncogenes can d isp lay transforming activities under certain exper imental condi t ions, such as infection of cells by acute t ransforming viruses (which act as oncogene t ransducers , but do not t ransmit cancer under natural condit ions) or in transfection assays of DNA segments of animal genomic origin (which contain oncogenes) to certain cultured cells, specifically, NIH 3T3 cells. Al though the latter cells are nontumori - genic, they are immortal and, consequently, cannot be considered as normal cells. Furthermore, they seem to be cells with a very special k ind of alteration, because many other types of cul tured cells tested are consis tent ly resistant to t ransformat ion in DNA transfection assays.

The possible role of oncogenes in the origin and/or deve lopment of tumors occurring under natural condi t ions, especial ly human tumors, is unknown. Four basic types of mechanisms could be involved in the putat ive action of oncogenes: (a) increased t ranscr ipt ional act ivi ty at unscheduled times, (b) oncogene amplif icat ion, (c) oncogene t ranslocat ion and/or rearrangement, and (d) oncogene mutat ion. Of these four mechanisms, only t ranslocat ion of oncogenes, in par t icular of c-abl and c-myc, is consis tent ly found in certain human hematopoie t ic neoplasms (chronic myelocyt ic leukemia and B-cell lymphomas , respectively). However, these translocations and rearrangements are complex at the molecular level, and they inc lude genomic segments other than oncogenes; in particular, they include parts of the immunoglobul in genes. Moreover, the translocat ions may also be present in non- mal ignant cells of the same patients. Increased t ranscr ipt ional activity, amplification, and mutat ion of oncogenes have been observed mainly in human tumor cell l ines under the artificial condi t ions of cell culture in vitro; their presence in uncul- tured cells from pr imary human tumors is irregular and unpredictable . Thus, li t t le evidence exists indicat ing that these last three types of oncogene al terat ions are cr i t ical ly involved in the origin and/or deve lopment of common human tumors. At most, they could part icipate, in concort wi th many other factors, as components of the complex mult is tage processes involved in tumorigenesis . Fur ther s tudies are required in order to achieve a better character izat ion of the possible role of oncogenes in human cancer. On the grounds of the available evidence, however, it seems unl ikely that oncogenes represent a kind of critical, indispensable , and universa l pa thway leading to the origin of human tumors.

REFERENCES

1. Duesberg PH (1980): Transforming genes of retroviruses. Cold Spring Harbor Symp Quant Biol 44:13-29.

2. Huebner RJ, Todaro GJ (1969): Oncogenes of RNA tumor viruses as determinants of cancer. Proc Natl Acad Sci, USA 64:1087-1094.

3. Todaro GJ, Huebner RJ (1972): The viral oncogene hypothesis: New evidence. Proc Natl Acad Sci, USA 69:1009-1015.

4. Anders F, Anders A, Vielkind U (1974): Regulation of tumor expression in the Gordon- Kosswig melanoma system and the origin of malignancy. Abst XI Int Cancer Congr (Flor- ence) 3:305.

5. Anders A, Anders F (1978): Etiology of cancer as studied in the platyfish-swordtail system. Biochim Biophys Acta 516:61-95.

6. Anders F (1983): The biology of an oncogene, based upon studies on neoplasia in Xiph- ophorus. Haematol Blood Trans 28:186-206.

7. Ozato K, Wakamatsu Y (1983): Multi-step genetic regulation of oncogene expression in fish hereditary melanoma. Differentiation 24:181-190.

8. Vielkind J, Haas-Andela H, Anders F (1976): DNA-mediated transformation of the platyfish-swordtail melanoma system. Experientia 32:1043-1044.

O n c o g e n e s a n d H u m a n C a n c e r 361

9. Leong J, Garapin A, Jackson N, Fanshier L, Levinson W, Bishop JM (1972): Virus-specific ribonucleic acid in cells producing Rous sarcoma virus: Detection and characterization. J Virol 9:891-902.

10. Hayward WS, Hanafusa H (1973): Detection of avian tumor virus RNA in uninfected chicken embryo cells. J Virol 11:157-167.

11. Chen JH, Hayward WS, Hanafusa H (1974): Avian tumor virus proteins and RNA in uninfected chicken embryo cells. J Virol 14:1419-1429.

12. Anderson GR, Robbins KC (1976): Rat sequences of the Kirsten and Harvey murine sarcoma virus genomes: Nature, origin, and expression in rat tumor RNA. J Virol 17: 335-351.

13. Scolnick EM, Goldberg RJ, Williams D (1976): Characterization of rat genetic sequences of Kirsten sarcoma virus: Distinct class of endogenous rat type C viral sequences. J Virol 18:559-566.

14. Stehelin D, Varmus HE, Bishop JM, Vogt PK (1976): DNA related to the transforming gene(s) of avian sarcoma viruses is present in normal avian DNA. Nature (London) 260:170-173.

15. Bishop JM (1978): Retroviruses. Ann Rev Biochem 47:35-88.

16. Spector DH, Varmus HE, Bishop JM (1978}: Nucleotide sequences related to the transforming gene of avian sarcoma virus are present in the DNA of uninfected vertebrates. Proc Natl Acad Sci, USA 75:4100-4106.

17. Sefton BM, Hunter T, Beemon K (1980): Relationship of polypeptide products of the transforming gene of Rous sarcoma virus and the homologous gene of vertebrates. Proc Natl Acad Sci, USA 77:2059-2063.

18. Ellis RW, DeFeo D, Shih TY, Gonda MA, Young HA, Tsuchida N, Lowy DR, Scolnick EM (1981): The p21 src genes of Harvey and Kirsten sarcoma viruses originate from divergent members of a family of normal vertebrate genes. Nature (London) 292:506-511.

19. Hoffmann FM, Fresco LD, Hoffman-Falk H, Shilo BZ (1983): Nucleotide sequences of the Drosophila src and abl homologs: Conservation and variability in the src family of oncogenes. Cell 35:393-401.

20. Schartl M, Barnekow A (1982): The expression in eukaryotes of a tyrosine kinase which is reactive with pp60 ~s~ antibodies. Differentiation 23:109-114.

21. Graf T, Stehelin D (1982): Avian leukemia viruses: oncogenes and genome structure. Biochim Biophys Acta 651:245-271.

22. Gallo RC, Wong-Staal F (1982): Retroviruses as etiologic agents of some animal and human leukemias and lymphomas and as tools for elucidating the molecular mechanisms of leukemogenesis. Blood 60:545-557.

23. Robinson HL (1982): Retroviruses and cancer. Rev Infect Dis 4:1015-1025.

24. Weinberg RA (1982): Oncogenes of spontaneous and chemically induced tumors. Adv Cancer Res 36:149-163.

25. Cooper GM (1982): Cellular transforming genes. Science 217:801-806.

26. Bishop JM (1983): Cellular oncogenes and retroviruses. Ann Rev Biochem 52:301-354.

27. Aaronson SA (1983): Unique aspects of the interaction of retroviruses with vertebrate cells. Cancer Res 43:1-5.

28. Baluda MA, Perbal B, Rushlow KE, Papas TS (1983): Avian myeloblastosis virus: A model for the generation of viral oncogenes from potentially oncogenic cellular genetic elements. Folio Biol (Praha) 29:18-34.

29. Duesberg PH (1983): Retroviral transforming genes in normal cells? Nature (London) 304:219-226.

30. Land H, Parada LF, Weinberg RA (1983): Cellular oncogenes and multistep carcinogenesis. Science 222:771-778.

31. de Martinville B, Cunningham JM, Murray MJ, Francke U (1983): The N-ras oncogene assigned to the short arm of human chromosome 1. Nucl. Acid Res 11:5267-5275.

32. Groffen J, Heisterkamp N, Spurr N, Dana S, Wasmuth JJ, Stephenson JR (1983): Chromo- somal localization of the human c-fms oncogene. Nucl Acid Res 11:6331-6340.

33. Roussel MF, Sherr CJ, Barker PE, Ruddle FH (1983): Molecular cloning of the c-fins locus and its assignment to human chromosome 5. J Virol 48:770-773.

34. Dalla-Favera R, Franchini G, Martinotti S, Wong-Staal F, Gallo RC, Croce CM (1982):

3 6 2 E. Pimentel

Chromosomal assignment of the human homologues of feline sarcoma virus and avian myeloblastosis virus onc genes. Proc Natl Acad Sci, USA 79:4714-4717.

35. Harper ME, Franchini G, Love J, Simon MI, Gallo RC, Wong-Staal F (1983): Chromosomal sublocalization of human c-myb and c-fes cellular onc genes. Nature 304:169-171.

36. O'Brien SJ, Nash WG, Goodwin JL, Lowy DR, Chang EH (1983): Dispersion of the ras family of transforming genes to four different chromosomes in man. Nature (London) 302:839-842.

37. Neel BG, Jhanwar SC, Chaganti RSK, Hayward WS (1982): Two human c-onc genes are located on the long arm of chromosome 8. Proc Natl Acad Sci, USA 79:7842-7846.

38. Prakash K, McBride OW, Swan DC, Devare SG, Tronick SR, Aaronson SA (1982): Molec- ular cloning and chromosomal mapping of a human locus related to the transforming gene of Moloney murine sarcoma virus. Proc Natl Acad Sci, USA 79:5210-5214.

39. Heisterkamp N, Groffen J, Stephenson JR, Spurr NK, Goodfellow PN, Solomon E, Carritt B, Bodmer WF (1982): Chromosomal localization of human cellular homologues of two viral oncogenes. Nature (London) 299:747-749.

40. Heisterkamp N, Stephenson JR, Groffen J, Hansen PF, de Klein A, Bartram CR, Grosveld G (1983): Localization of the c-abl oncogene adjacent to a translocation break point in chronic myelocytic leukaemia. Nature (London) 306:239-242.

41. McBride OW, Swan DC, Santos E, Barbacid M, Tronick SR, Aaronson SA (1982): Local- ization of the normal allele of T24 human bladder carcinoma oncogene to chromosome 11. Nature (London) 300:773-774.

42. Jhanwar SC, Neel BG, Hayward WS, Chaganti RSK (1983): Localization of c-ras oncogene family on human germ-line chromosomes. Proc Natl Acad Sci, USA 80:4794-4797.

43. Sakaguchi AY, Naylor SL, Shows TB, Toole JJ, McCoy M, Weinberg RA (1983): Human c-Ki-ras2 proto-oncogene on chromosome 12. Science 219:1081-1083.

44. Sakaguchi AY, Naylor SL, Shows TB ( 1983): A sequence homologous to Rous sarcoma virus v-src is on human chromosome 20. Progr Nucl Acid Res Mol Biol 29:279-282.

45. Swan DC, McBride OW, Robbins KC, Keithley DA, Reddy EP, Aaronson SA (1982): Chro- mosomal mapping of the simian sarcoma virus onc gene analogue in human cells. Proc Natl Acad Sci, USA 79:4691-4695.

46. Dalla Favera R, Gallo RC, Giallongo A, Croce CM (1982): Chromosomal localization of the human homolog (c-sis) of the simian sarcoma virus onc gene. Science 218:686-688.

47. Sandberg AA (1980): The Chromosomes in Human Cancer and Leukemia. Elsevier North- Holland, New York.

48. Sandberg AA (1983): A chromosomal hypothesis of oncogenesis. Cancer Genet Cytogenet 8:277-285.

49. Yunis JJ (1983): The chromosomal basis of human neoplasia. Science 221:227-236.

50. Chaganti RSK (1983): Significance of chromosome change to hematopoietic neoplasms. Blood 62:515-524.

51. Klein G (1983): Specific chromosomal translocations and the genesis of B-cell-derived tumors in mice and men. Cell 32:311-315.

52. Watson R, Oskarsson M, Vande Woude GF (1982): Human DNA sequence homologous to the transforming gene (mos) of Moloney murine sarcoma virus. Proc Natl Acad Sci, USA 79:4078-4082.

53. Tabin CJ, Bradley SM, Bargmann CI, Weinberg RA, Papageorge AG, Scolnick EM, Dhar R, Lowy DR, Chang EH (1982): Mechanism of activation of a human oncogene. Nature (Lon- don) 300:143-149.

54. Reddy EP, Reynolds RK, Santos E, Barbacid M (1982): A point mutat ion is responsible for the acquisition of transforming properties by the T24 human bladder carcinoma oncogene. Nature (London) 300:149-152.

55. Capon DJ, Chen EY, Levinson AD, Seeburg PH, Goeddel DV (1983): Complete nfmleotide sequences of the T24 human bladder carcinoma oncogene and its normal homologue. Nature (London) 301:33-37.

56. Reddy EP (1983): Nucleotide sequence analysis of the T24 human bladder carcinoma oncogene. Science 220:1061-1063.

57. Shimizu K, Birnbaum D, Ruley MA, Fasano O, Suard Y, Edlund L, Taparowsky E, Gold- farb M, Wigler M (1983): Structure of the Ki-ras gene of the human lung carcinoma cell line Calu-1. Nature (London) 304:497-500.


58. McGrath JP, Capon DJ, Smith DH, Chen EY, Seeburg PH, Goeddel DV, Levinson AD (1983): Structure and organization of the human Ki-ras proto-oncogene and a related processed pseudogene. Nature (London) 304:501-506.

59. Taparowsky E, Shimizu K, Goldfarb M, Wigler M (1983): Structure and activation of the human N-ras gene. Cell 34:581-586.

60. Josephs SF, Dalla Favera R, Gelmann EP, Gallo RC, Wong-Staal F (1983): 5' viral and human cellular sequences corresponding to the transforming gene of simian sarcoma virus. Science 219:503-505.

61. Watson DK, Psallidopoulos MC, Samuel KP, Dalla-Favera R, Papas TS (1983): Nucleotide sequence analysis of human c-myc locus, chicken homologue, and myelocytomatosis virus MC29 transforming gene reveals a highly conserved gene product. Proc Natl Acad Sci, USA 80:3642-3645.

62. Battey J, Moulding C, Taub R, Murphy W, Stewart T, Potter H, Lenoir G, Leder P (1983): The human c-myc oncogene: Structural consequences of translocation into the IgH locus in Burkitt lymphoma. Cell 34:779-787.

63. Watt R, Nishikura K, Sorrentino J, ar-Rushdi A, Croce CM, Rovera G (1983): The structure and nucleotide sequence of the 5' end of the human c-myc oncogene. Proc Natl Acad Sci, USA 80:6307-6311.

64. Takeya T, Hanafusa H (1983): Structure and sequence of the cellular gene homologous to the RSV src gene and the mechanism for generating the transforming virus. Cell 32:881-890.

65. Gattoni S, Kirschmeier P, Weinstein IB, Escobedo J, Dina D (1982): Cellular Moloney murine sarcoma (c-mos) sequences are hypermethylated and transcriptionally silent in normal and transformed cells. Mol Cell Biol 2:42-51.

66. M~iller R, Slamon DJ, Tremblay JM, Cline MJ, Verma IM (1982): Differential expression of cellular oncogenes during pre- and postnatal development of the mouse. Nature (Lon- don) 299:640-644.

67. Goyette M, Petropoulos CJ, Shank PR, Fausto N (1983): Expression of a cellular oncogene during liver regeneration. Science 219:510-512.

68. Fausto N, Shank PR (1983): Oncogene expression in liver regeneration and hepatocarcin- ogenesis. Hepatology 3:1016-1023.

69. Wang JYJ, Baltimore D (1983): Cellular RNA homologous to the Abelson murine leukemia virus transforming gene: Expression and relationship to the viral sequence. Mol Cell Biol 3:773-779.

70. Jacobs C, R~3bsamen H (1983): Expression of pp60 °~rc protein kinase in adult and fetal human tissue: high activities in some sarcomas and mammary carcinomas. Cancer Res 43:1696-1702.

71. M~iller R, Tremblay JM~ Adamson ED, Verma IM (1983): Tissue and cell type-specific expression of two human c-onc genes. Nature (London) 304:454-456.

72. Groffen J, Heisterkamp N, Blennerhassett G, Stephenson JR (1983): Regulation of viral and cellular oncogene expression by cytosine methylation. Virology 127:213-227.

73. Feinberg AP, Vogelstein B (1983): Hypomethylation of ras oncogenes in primary human cancers. Biochem Biophys Res Comm 111:47-54.

74. Bishop JM (1981): Enemies within: The genesis of retrovirus oncogenes. Cell 23:5-6.

75. Bauer H, Barnekow A, Rose G (1982): The transforming protein of Rous sarcoma virus, pp6OSrc: Growth and cell proliferation inducing properties. Horm Cell Regul 6: 187-205.

76. Hollenberg MD (1982): Receptor mediated phosphorylat ion reactions. Trends Pharmacol Sci 3:271-273.

77. Tuy FPD, Henry J, Rosenfeld C, Kahn A (1983): High tyrosine kinase activity in normal nonproliferating cells. Nature (London) 305:435-438.

78. Robbins KC, Devare SG, Reddy EP, Aaronson SA (1982): In vivo identification of the transforming gene product of simian sarcoma virus. Science 218:1131-1133.

79. Waterfield MD, Scrace GT, Whittle N, Stroobant P, Johnsson A, Wasteson A, Westermark B, Heldin CH, Huang JS, Deuel TF (1983): Platelet-derived growth factor is structurally related to the putative transforming protein p28 s~ of simian sarcoma virus. Nature (Lon- don) 304:35-39.

80. Doolittle RF, Hunkapiller MW, Hood LE, Devare SG, Robbins KC, Aaronson SA, Anton-

3 6 4 E. Pimentel

iades HN (1983): Simian sarcoma virus o n c gene, v-sis, is derived from the gene (or genes) encoding a platelet-derived growth factor. Science 221:275-277.

81. Robbins KC, Antoniades HN, Devare SG, Hunkapiller MW, Aaronson SA (1983): Struc- tural and immunological similarities between simian sarcoma virus gene product(s) and human platelet-derived growth factor. Nature (London) 305:605-608.

82. Deuel TF, Huang JS, Huang SS, Stroobant P, Waterfield MD (1983): Expression of a platelet- derived growth factor-like protein in simian sarcoma virus transformed cells. Science 221:1348-1350.

83. Antoniades HN, Williams LT (1983): Human platelet-derived growth factor: Structure and function. Fed Proc 42:2630-2634.

84. Fung YKT, Crittenden LB, Fadly AM, Kung HJ (19831: Tumor induction by direct injection of cloned v-src DNA into chickens. Proc Natl Acad Sci, USA 80:353-357.

85. Prywes R, Foulkes JG, Rosenberg N, Baltimore D (1983): Sequences of the A-MuLV protein needed for fibroblast and lymphoid cell transformation. Cell 34:569-579.

86. Bryant D, Parsons JT (1983): Site-directed point mutation in the src gene of Rous sarcoma virus results in an inactive src gene product. J Virol 45:1211-1216.

87. Cross FR, Hanafusa H (1983): Local mutagenesis of Rous sarcoma virus: the major sites of tyrosine and serine phosphorylation of p60 ~r~ are dispensable for transformation. Cell 34:597-607.

88. Shih C, Padhy LC, Murray M, Weinberg RA (1981): Transforming genes of carcinomas and neuroblastomas introduced into mouse fibroblasts. Nature (London) 290:261-264.

89. Krontiris TG, Cooper GM (1981): Transforming activity of human tumor DNAs. Proc Natl Acad Sci, USA 78:1181-1184.

90. Perucho M, Goldfarb M, Shimizu K, Lama C, Fogh J, Wigler M (1981): Human-tumor- derived cell lines contain common and different transforming genes. Cell 27:467-476.

91. Krontiris TG (1983): The emerging genetics of human cancer. N Engl J Med 309:404-409.

92. Der CJ, Krontiris TG, Cooper GM (1982): Transforming genes of human bladder and lung carcinoma cell lines are homologous to the ras genes of Harvey and Kirsten sarcoma viruses. Proc Natl Acad Sci, USA 79:3637-3640.

93. Pulciani S, Santos E, Lauver AV, Long LK, Aaronson SA, Barbacid M (1982): Oncogenes in solid human tumours. Nature (London) 300:539-542.

94. Eva A, Tronick SR, Gol RA, Pierce JH, Aaronson SA (1983): Transforming genes of human hematopoietic tumors: Frequent detection of ras-related oncogenes whose activation appears to be independent of tumor phenotype. Proc Natl Acad Sci, USA 80:4926-4930.

95. Souyri M, Fleissner E (1983): Identification by transfection of transforming sequences in DNA of human T-cell leukemias. Proc Natl Acad Sci, USA 80:6676-6679.

96. Needleman SW, Yuasa Y, Srivastava S, Aaronson SA (1983): Normal cells of patients with high cancer risk syndromes lack transforming activity in the NIH/3T3 transfection assay. Science 222:173-175.

97. Yunis JJ, Ramsay NKC (1980): Familial occurrence of the aniridia-Wilms' tumor syndrome with deletion 11p13--~14.1 J Pediat 96:1027-1030.

98. Kaneko Y, Egues MC, Rowley JD (1981}: Interstitial deletion of short arm of chromosome 11 limited to Wilms' tumors cells in a patient without aniridia. Cancer Res 41:4577- 4578.

99. Huerre C, Despoisse S, Gilgenkrantz DS, Lenoir GM, Junien C (1983): c-Ha-rasl is not deleted in aniridia-Wilms' tumour association. Nature 305:638-641.

100. de Martinville B, Francke U (1983): The c-Ha-rasl, insulin and ~-globin loci map outside the deletion associated with aniridia-Wilms' tumour. Nature 305:641-643.

101. Vogel F (1979): Genetics of retinoblastoma. Hum Genet 52:1-54.

102. Benedict WF, Murphree AL, Banerjee A, Spina CA, Sparkes MC, Sparkes RS (1983): Patient with 13 chromosome deletion: Evidence that the retinoblastoma gene is a reces- sive cancer gene. Science 219:973-975.

103. Schroeder TM (1982): Genetically determined chromosome instability syndromes. Cyto- genet Cell Genet 33:119-132.

104. de Nufiez M, Penchaszadeh V, Pimentel E (1984): Chromosome fragility in patients with sporadic unilateral retinoblastoma. Cancer Genet Cytogenet 11:139-142.

105. Eva A, Robbins KC, Andersen PR, Srinivasan A, Tronick SR, Reddy EP, Ellmore NW,


Galen AT, Lautenberger JA, Papas TS, Westin EH, Wong-Staal F, Gallo RC, Aaronson SA (1982): Cellular genes analogous to retroviral onc genes are transcribed in human tumour cells. Nature (London) 295:116-119.

106. Westin EH, Wong-Staal F, Gelmann EP, Dalla Favera R, Papas TS, Lautenberger JA, Eva A, Reddy EP, Tronick SR, Aaronson SA, Gallo RC (1982): Expression of cellular homologues of retroviral onc genes in human hematopoietic cells. Proc Natl Acad Sci, USA 79:2490-2494.

107. Rosson D, Tereba A (1983): Transcription of hematopoietic-associated oncogenes in childhood leukemia. Cancer Res 43:3912-3918.

108. Roy-Burman P, Devi BG, Parker JW (1983): Differential expression of c-erbB, c-myc and c-myb oncogene loci in human lymphomas and leukemias. Int J Cancer 32:185-191.

109. Nozawa S, Engvall E, Kano S, Kurihara S, Fishman WH (1983): Sodium butyrate pro- duces concordant expression of "early placental" alkaline phosphatase, pregnancy- specific betal°glycoprotein and human chorionic gonadotropin beta-subunit in a newly established uterine cervical cancer cell line (SKG-IIIa). Int J Cancer 32:267-272.

110. Pall ML (1981): Gene-amplification model of carcinogenesis. Proc Natl Acad Sci, USA 78:2465-2468.

111. Caizzi R, Bostock CJ (1982): Gene amplification in methotrexate-resistant mouse cells. IV. Different sequences are amplified in different resistant lines. Nucl Acid Res 10:6597- 6618.

112. Collins S, Groudine M (1982): Amplification of endogenous myc-related DNA sequences in a human myeloid leukaemia cell line. Nature (London) 298:679-681.

113. Schwab M, Alitalo K, Klempnauer KH, Varmus HE, Bishop JM, Gilbert F, Brodeur G, Goldstein M, Trent J (1983): Amplified DNA with limited homology to myc cellular oncogene is shared by human neuroblastoma cell lines and a neuroblastoma tumour. Na- ture (London) 305:245-248.

114. Montgomery KT, Biedler JL, Spengler BA, Melera PW (1983): Specific DNA sequence amplification in human neuroblastoma cells. Proc Natl Acad Sci, USA 80:5724-5728.

115. Little CD, Nau MM, Carney DN, Gazdar AF, Minna JD (1983): Amplification and expression of the c-myc oncogbne in human lung cancer cell lines. Nature (London) 306:194- 196.

116. Alitalo K, Schwab M, Lin CC, Varmus HE, Bishop JM (1983): Homogeneously staining chromosomal regions contain amplified copies of an abundant ly expressed cellular oncogene (c-myc) in malignant neuroendocrine cells from a human colon carcinoma. Proc Natl Acad Sci, USA 80:1707-1711.

117. McCoy MS, Toole JJ, Cunningham JM, Chang EH, Lowy DR, Weinberg RA (1983): Char- acterization of a human colon/lung carcinoma oncogene. Nature (London) 302:79-82.

118. Barker PE (1982): Double minutes in human tumor cells. Cancer Genet Cytogenet 5:81- 94.

119. Casartelli C (1982): Cancer and chromosomes: A review. Rev Brasil Genet 5:595-618.

120. Bahr G, Gilbert F, Balaban G, Engler W (1983): Homogeneously staining regions and double minutes in a human cell line: Chromatin organization and DNA content. J Natl Cancer Inst 71:657-661.

121. Li YS (1983): Double minutes in acute myeloid leukemia. Int J Cancer 32:455-460.

122. Gebhart E, Tulusan AH, Maillot KV, Mulz D (1983): Double minutes: New markers in cells of human solid tumors. J G6n6t Hum 31:45-47.

123. Chattopadhyay SK, Chang EH, Lander MR, Ellis RW, Scolnick EM, Lowy DR (1982): Amplification and rearrangement of onc genes in mammalian species. Nature (London) 296:361-363.

124. Rowley JD (1982): Identification of the constant chromosome regions involved in human hematologic malignant disease. Science 216:749-751.

125. Passarge E (1983): Beziehungen zwischen Chromosomenver~inderung und Tumorenste- hung. Deut Med Wochenschr 108:28-34.

126. Rowley JD (1973): A new consistent chromosomal abnormality in chronic myelogenous leukaemia identified by quinacrine fluorescence and Giemsa staining. Nature (London) 243:290-293.

127. de Klein A, van Kessel AG, Grosveld G, Bartram CR, Hagemeijer A, Bootsma D, Spurr NK, Heisterkamp N, Groffen J, Stephenson JR (1982): A cellular oncogene is translocated

3 6 6 E. Pimentel

to the Philadelphia chromosome in chronic myelocytic leukaemia. Nature (London) 300:765-767.

128. Groffen J, Heisterkamp N, Stephenson JR, van Kessel AG, de Klein A, Grosveld G, Boots- man D (1983): c-sis is translocated from chromosome 22 to chromosome 9 in chronic myelocytic leukemia. J Exp Med 158:9-15.

129. Bartram CR, de Klein A, Hagemeijer A, van Agthoven T, van Kessel AG, Bootsman D, Grosveld G, Ferguson-Smith MA, Davies T, Stone M, Heisterkamp N, Stephenson JR, Groffen J (1983): Trans|ocation of c-abl oncogene correlates with the presence of a Phil- adelphia chromosome in chronic myelocytic leukaemia. Nature (London) 306:277-280.

130. Koeffler HP, Golde DW (1981): Chronic myelogenous leukemia: New concepts. N Engl J Med 304:1201-1209, 1269-1274.

131. Leder P, Battey J, Lenoir G, Moulding C, Murphy W, Potter H, Stewart T, Taub R (1983): Translocations among antibody genes in human cancer. Science 222:765-771.

132. Kirsch IR, Morton CC, Nakahara K, Leder P (1982): Human immunoglobulin heavy chain genes map to a region of translocations in malignant B lymphocytes. Science 216:301- 303.

133. Erikson J, Finan J, Nowell PC, Croce CM (1982): Translocation of immunoglobulin VH genes in Burkitt lymphoma. Proc Natl Acad Sci, USA 79:5611-5615.

134. Dalla-Favera R, Bregni M, Erikson J, Patterson D, Gallo RC, Croce CM (1982): Human c- m y c onc gene is located in the region of chromosome 8 that is translocated in Burkitt lymphoma cells. Proc Natl Acad Sci, USA 79:7824-7827.

135. Taub R, Kirsch I, Morton C, Lenoir G, Swan D, Tronick S, Aaronson SA, Leder P (1982): Translocation of the c-myc gene into the immunoglobulin heavy chain locus in human Burkitt lymphoma and murine plasmocytoma cells. Proc Natl Acad Sci, USA 79:7837- 7841.

136. Dalla-Favera R, Martinotti S, Gallo RC, Erikson J, Croce CM (1983): Translocation and rearrangements of the c-myc oncogene locus in human undifferentiated B-cell lymphomas. Science 219:963-967.

137. Shen-Ong GLC, Keath EJ, Piccoli SP, Cole MD (1982): Novel m y c oncogene RNA from abortive immunoglobulin-gene recombination in mouse plasmocytomas. Cell 31:443- 452.

138. Sakaguchi AY, Lalley PA, Naylor SL (1983): Human and mouse cellular m y c protooncogenes reside on chromosomes involved in numerical and structural aberrations in cancer. Somat Cell Genet 9:391-405.

139. Erikson J, ar-Rushdi A, Drwinga HL, Nowell PC, Croce CM (1983): Transcriptional activation of the translocated c-myc oncogene in Burkitt lymphoma. Proc Natl Acad Sci, USA 80:820-824.

140. de la Chapelle A, Lenoir G, Bou~ J, Bou~ A, Gallano P, Huerre C, Szajner MF, Jeanpierre M, Lalouel JM, Kaplan JC (1983): Lampbda Ig constant region genes are translocated to chromosome 8 in Burkitt's lymphoma with t(8;22). Nucl Acid Res 11:1133-1142.

141. Maguire RT, Robins TS, Thorgeirsson SS, Heilman CA (1983): Expression of cellular myc and mos genes in undifferentiated B cell lymphomas of Burkitt and non-Burkitt types. Proc Natl Acad Sci, USA 80:1947-1950.

142. Marcu KB, Harris LJ, Stanton LW, Erikson J, Watt R, Croce CM (1983): Transcriptionally active c-myc oncogene is contained within NIARD, a DNA sequence associated with chromosome translocations in B-cell neoplasia. Proc Natl Acad Sci, USA 80:519-523.

143. Nishikura K, ar-Rushdi A, Erikson J, Watt R, Rovera G, Croce CM (1983): Differential expression of the normal and of the translocated human c-myc oncogenes in B cells. Proc Natl Acad Sci, USA 80:4822-4826.

144. ar-Rushdi A, Nishikura K, Erikson J, Watt R, Rovera G, Croce CM (1983): Differential expression of the translocated and the untranslocated c-myc oncogene in Burkitt lymphoma. Science 222:390-393.

145. Croce CM, Thierfelder W, Erikson J, Nishikura K, Finan J, Lenoir GM, Nowell PC (1983): Transcriptional activation of an unrearranged and untranslocated c -myc oncogene by translocation of a CA locus in Burkitt lymphoma cells. Proc Natl Acad Sci, USA 80:6922- 6926.

146. Dean M, Kent RB, Sonenshein GE (1983): Transcriptional activation of immunoglobulin heavy-chain genes by translocation of the c-myc oncogene. Nature (London) 305:443-

446.


147. Rabbitts TH, Hamlyn PH, Baer R (1983): Altered nucleotide sequences of a translocated c-myc gene in Burkitt lymphoma. Nature (London) 306:760-765.

148. Gelmann EP, Clanton DJ, Jariwalla RJ, Rosenthal LJ (1983): Characterization and location of myc homologous sequences in human cytomegalovirus DNA. Proc Natl Acad Sci, USA 80:5107-5111.

149. Gottlieb MS, Groopman JE, Weinstein WM, Pahey JL, Detels R (1983): The acquired immunodeficiency syndrome. Ann Int Med 99:208-220.

150. Pimentel E (1979): Human oncovirology. Biochim Biophys Acta 560:169-216.

151. Pachl C, Schubach W, Eisenman R, Linial M (1983): Expression of c-myc RNA in bursal lymphoma cell lines: Identification of c-myc-encoded proteins by hybrid-selected trans- lation. Cell 33:335-344.

152. Giallongo A, Appella E, Ricciardi R, Rovera G, Croce CM (1983): Identification of the c- myc oncogene product in normal and malignant B cells. Science 222:430-432.

153. Perry RP (1983): Consequences of myc invasion of immunoglobulin loci: Facts and spec- ulation. Cell 33:647-649.

154. Adams JM, Gerondakis S, Webb E, Corcoran LM, Cory S (1983): Cellular myc oncogene is altered by chromosome translocation to an immunoglobul in locus in murine plasma- cytomas and is rearranged similarly in human Burkitt lymphomas. Proc Natl Acad Sci, USA 80:1982-1986.

155. Murray MJ, Cunningham JM, Parada LF, Dautry F, Lebowitz P, Weinberg RA (1983): The HL-60 transforming sequence: A ras oncogene coexisting with altered myc genes in hematopoietic tumors. Cell 33:749-757.

156. Goldfarb M, Shimizu K, Perucho M, Wigler M (1982): Isolation and preliminary characterization of a human transforming gene from T24 bladder carcinoma ceils. Nature (Lon- don) 296:404-409.

157. Pulciani S, Santos E, Lauver AV, Long LK, Robbins KC, Barbacid M (1982): Oncogenes in human tumor cell lines: Molecular cloning of a transforming gene from human bladder carcinoma cells. Proc Natl Acad Sci, USA 79:2845-2849.

158. Shih C, Weinberg RA (1982): Isolation of a transforming sequence from a human bladder carcinoma cell line. Cell 29:161-169.

159. Parada LF, Tabin CJ, Shih C, Weinberg RA (1982): Human EJ bladder carcinoma oncogene is homologue of Harvey sarcoma virus ras gene. Nature (London) 297:474-479.

160. Santos E, Tronick SR, Aaronson SA, Pulciani S, Barbacid M (1982): T24 human bladder carcinoma oncogene is an activated form of the normal human homologue of BALB- and Harvey-MSV transforming genes. Nature (London) 298:343-347.

161. Taparowsky E, Suard Y, Fasano O, Shimizu K, Goldfarb M, Wigler M (1982): Activation of the T24 bladder carcinoma transforming gene is linked to a single amino acid change. Nature (London) 300:762-765.

162. Santos E, Reddy EP, Pulciani S, Feldmann RJ, Barbacid M (1983): Spontaneous activation of a human proto-oncogene. Proc Natl Acad Sci, USA 80:4679-4683.

163. Wierenga RK, Hol WGJ (1983): Predicted nucleotide-binding properties of p21 protein and its cancer-associated variant. Nature (London) 302:842-844.

164. Pincus MR, van Renswoude J, Harford JB, Chang EH, Carty RP, Klausner RD (1983): Prediction of the three-dimensional structure of the transforming region of the EJ/T24 human oncogene product and its normal cellular homologue. Proc Natl Acad Sci, USA 80:5253-5257.

165. Der CJ, Cooper GM (1983): Altered gene products are associated with activation of cellular ras k genes in human lung and colon carcinomas. Cell 32:201-208.

166. Yuasa Y, Srivastava SK, Dunn CY, Rhim JS, Reddy EP, Aaronson SA (1983): Acquisit ion of transforming properties by alternative point mutations with c-bas/has human proto- oncogene. Nature (London) 303:775-779.

167. Capon DJ, Seeburg PH, McGrath JP, Hayflick JS, Edman U, Levinson AD, Goeddel DV (1983): Activation of Ki-ras2 gene in human colon and lung carcinomas by two different point mutations. Nature (London) 304:507-513.

168. Nakano H, Yamamoto F, Neville C, Evans D, Mizuno T, Perucho M (1984): Isolation of transforming sequences of two human lung carcinomas: Structural and functional analysis of the activated c-K-ras oncogenes. Proc Natl Acad Sci, USA 81:71-75.

169. Nakano H, Neville C, Yamamoto F, Garcia JL, Fogh J, Perucho M (1984): Structure and

368 E. Pimentel

mechanisms of activation of the c-K-ras oncogene from two human lung tumors. Cold Spring Harbor Conf Cell Prolif Cancer (in press).

170. O'Toole CM, Povey S, Hepburn P, Franks LM (1983): Identity of some human bladder cancer cell lines. Nature (London) 301:429-430.

171. Muschel RJ, Khoury G, Lebowitz P, Koller R, Dhar R (1983): The human c-rasl H oncogene: A mutation in normal and neoplastic tissue from the same patient. Science 219:853-856, 220:336.

172. Newbold RF, Overell RW (1983): Fibroblast immortality is a prerequisite for transformation by EJ c-Ha-ras oncogene. Nature (London) 304:648-652.

173. Feinberg AP, Vogelstein B, Droller MJ, Baylin SB, Nelkin BD (1983): Mutation affecting the 12th amino acid of the c-Ha-ras oncogene product occurs infrequently in human cancer. Science 220:1175-1177.

174. McBride OW, Swan DC, Tronick SR, Gol R, Klimanis D, Moore DE, Aaronson SA (1983): Regional chromosomal localization of N-ras, K-ras-1, K-ras-2 and myb oncogenes in human cells. Nucl Acid Res 11:8221-8236.

175. Spurr NK, Solomon E, Jansson M, Sheer D, Goodfellow PN, Bodmer WF, Vennstrom B (1984): Chromosomal localization of the human homologues to the oncogenes erbA and B. EMBO J 3:159-164.

176. Downward J, Yarden Y, Mayes E, Scrace G, Totty N, Stockwell P, Ullrich A, Schlessinger J, Waterfield MD (1984): Close similarity of epidermal growth factor receptor and v-erb- B oncogene protein sequences. Nature (London) 307:521-527.

177. Kondo I, Shimizu N (1983): Mapping of the human gene for epidermal growth factor receptor (EGFR) on the p13-*q22 region of chromosome 7. Cytogenet Cell Genet 35:9-14.

A D D E N D U M

Recently, a striking structural homology has been observed between the putative transforming protein of the v-erbB oncogene and the epidermal growth factor (EGF) receptor protein purified from a human epidermoid carcinoma cell line (A431) and human normal placenta [176]. Tyrosine phosphorylat ion sites would lie wi thin the cytoplasmic domain of the EGF receptor, which is contained in the sequence shared with the v-erbB protein. Furthermore, both the c-erbB gene and the EGF receptor gene are located in the same region of human chromosome #7 [175, 177], which indicates their possible identity. These important results suggest that some oncogene products are related to the mechanisms of action of normal cellular growth factors, such as PDGF and EGF.

Documents

Oncogenes and human cancer