CD98 at the crossroads of adaptive immunityand cancer
Joseph M. Cantor1 and Mark H. Ginsberg1,*Department of Medicine, University of California San Diego, La Jolla, CA 92093, USA
*Author for correspondence ([email protected])
Journal of Cell Science 125, 1373–1382� 2012. Published by The Company of Biologists Ltddoi: 10.1242/jcs.096040
SummaryAdaptive immunity, a vertebrate specialization, adds memory and exquisite specificity to the basic innate immune responses present in
invertebrates while conserving metabolic resources. In adaptive immunity, antigenic challenge requires extremely rapid proliferation ofrare antigen-specific lymphocytes to produce large, clonally expanded effector populations that neutralize pathogens. Rapid proliferationand resulting clonal expansion are dependent on CD98, a protein whose well-conserved orthologs appear restricted to vertebrates. Thus,
CD98 supports lymphocyte clonal expansion to enable protective adaptive immunity, an advantage that could account for the presenceof CD98 in vertebrates. CD98 supports lymphocyte clonal expansion by amplifying integrin signals that enable proliferation and preventapoptosis. These integrin-dependent signals can also provoke cancer development and invasion, anchorage-independence and the rapidproliferation of tumor cells. CD98 is highly expressed in many cancers and contributes to formation of tumors in experimental models.
Strikingly, vertebrates, which possess highly conserved CD98 proteins, CD98-binding integrins and adaptive immunity, also displaypropensity towards invasive and metastatic tumors. In this Commentary, we review the roles of CD98 in lymphocyte biology and cancer.We suggest that the CD98 amplification of integrin signaling in adaptive immunity provides survival benefits to vertebrates, which, in
turn, bear the price of increased susceptibility to cancer.
Key words: CD98, Cell adhesion, Cell proliferation, Immunity, Integrin
IntroductionThe crucial role of clonal expansion in vertebrate
adaptive immunity
All multicellular eukaryotic organisms initiate immune responses
after recognizing common pathogen-associated molecular
patterns (PAMPs) on the surface of invading microbes
(Medzhitov and Janeway, 1997). Pattern recognition receptors
(PRRs), including toll-like receptors (TLRs), nucleotide
oligomerization domain (NOD)-like receptors (NLRs) and
retinoic-acid-inducible gene I (RIG-I)-like receptors (RLRs;
RIG-I is also known as DDX58), generate signals that activate
‘innate’ immune cells (Kumar et al., 2011) to neutralize or
destroy viruses and bacteria either through reactive chemicals
[reactive oxygen species (ROS), reactive nitrogen species (RNS)
etc.], complement or enzymatic digestion (lysozyme, etc.) (Tosi,
2005; Leclerc and Reichhart, 2004). This process must be
repeated every time the organism is exposed to the same
pathogen. However, many pathogens that infect higher organisms
can overcome innate immunity and thus maintain infections that
result in serious damage to the host.
Vertebrates utilize an additional powerful weapon against
pathogens, namely, adaptive immunity. Adaptive immune
responses provide long-lasting, flexible and specific protection
to a wider variety of pathogens than innate immunity alone
(Boehm, 2011). Lymphocytes or lymphocyte-like cells are the
central adaptive immune cell. They each express unique antigen
receptors of a single specificity on their surface. As they develop
from lymphoid progenitor cells in the bone marrow, lymphocytes
randomly rearrange gene segments that encode three antigen
receptor components (V, D and J) through the action of
recombination-activating gene (RAG) enzymes (Hsu, 2009).
This recombination mechanism generates tremendous diversity
(Kuby, 1997) because there are many alleles for each V, D or J
gene segment [or variable lymphocyte receptor (VLR)-A and
VLR-B gene regions (Saha et al., 2010; Herrin and Cooper, 2010)
in the case of agnathans (jawless fish), discussed below], with
random nucleotide addition by terminal deoxynucleotidyl
transferase (TdT) also adding junctional diversity.
Possessing such a large repertoire of randomly generated
antigen specificities has obvious benefits (Murphy et al., 2011).
First, the greater diversity of antigen receptors enables the
neutralization of a correspondingly larger diversity of pathogens
and makes evasion of their neutralizing effects more challenging
for pathogens. Second, greater diversity combined with efficient
deletion of self-reactive cells (Fig. 1) enables more specific
targeting of pathogens rather than host tissues. Third, increased
specificity combined with expansion of pathogen-specific
lymphocytes allows for formation of specific recall or
‘memory’ responses (Sprent and Surh, 2002). Maintaining a
few memory cells that rapidly expand in response to previously
experienced antigen conserves resources that would otherwise be
expended in maintaining a large population of cells that
encompass the entire repertoire of recognition specificities
(Murphy et al., 2011). The stimulation of this memory
mechanism by vaccines underlies the protection that has saved
millions of lives. For these reasons, the vertebrate immune
system is usually viewed as more complex and potent than that of
invertebrates with respect to diversity, specificity and memory
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(Boehm, 2011). These benefits depend on the rapid proliferation
of lymphocytes that results in clonal expansion, which thus
functions as a keystone of adaptive immunity (Fig. 1), allowing
vertebrates to take advantage of the striking specificity and
diversity of adaptive immunity, while conserving metabolic
resources.
Clonal expansion requires resting lymphocytes to enter the cell
cycle rapidly upon receiving the appropriate activation signals
from antigen receptors, co-receptors, co-stimulatory molecules and
cytokines. Extremely rapid cellular proliferation must then follow
(with doubling times of less than 5 hours) in order to differentiate
and generate sufficient effector cells in time (typically in less 5
days) (Abbas, 2003). For B cells, this rapid proliferation phase
can also occur several times, with accompanying somatic
hypermutation of receptor genes to increase affinity for antigen,
and thus can last up to 3 weeks (Murphy et al., 2011). Both B and T
cell clonal expansion rely on the capacity of lymphocytes to
accelerate from a resting state to sustained rapid proliferation.
Several molecules and mechanisms assist in this process, including
growth cytokines or receptors (Nelson and Willerford, 1998;
Weaver et al., 2007), adhesion molecules (Mitchell and Williams,
2010), anti-apoptotic proteins (Hildeman et al., 2007) and the
vertebrate-specific transmembrane protein CD98 (Cantor et al.,
2009; Cantor et al., 2011).
CD98: more than a lymphocyte activation marker
The CD98 heterodimer consists of a type II single-pass
transmembrane heavy chain (CD98hc, also known as 4F2
Lymphoid progenitor cell
Memory B cell
IgG
IgA
IgM
Diverse resting B cells
Self-reactive B cellsare destroyed
Pathogens
Free virusExtracellular bacteriaParasites
Virus-infected cellsTumor cellsIntracellular bacteria
Thymus
Bone marrow
Diverseresting T cells
MemoryCD4+ T cell
‘Helper’ T cells
Self-reactive T cells are destroyed
CD4+
CD8+ Cytotoxic(CTL)
‘killer’ T cells
Antigen-presenting cell (APC)
Cytokine ‘help’ for B cells
Cytokine ‘help’ for CTL s
‘‘k
CCyyyyyyyyyyyyytttttttokkooookokoo ii
s MemoryCD8+ T cell
B cell antigen receptors
light chain VJ rearrangement
heavy chain VDJ rearrangement
T cell antigen receptors
alpha chain VJ rearrangement
beta chain VDJ rearrangement
Clonalexpansion
Spleen, lymph nodes Plasmacells
Infected host cell
Fig. 1. Vertebrate adaptive immunity. Antigen diversity in jawed vertebrates is generated by somatic recombination of the V, D and J regions (variable,
diversity and joining immunoglobulin gene regions) in both immunoglobulin (Ig, B-cell receptor) and TCR (T-cell receptor) chains. After their development in
bone marrow (and thymus for T cells), the clones that express self-reactive antigen receptors are deleted. Very few mature resting B and T cells are maintained for
each specific antigen (indicated with different colors), thus conserving valuable metabolic resources. Upon antigen exposure in the periphery, the appropriate
lymphocyte clone(s) are expanded quickly through rapid proliferation to generate large numbers of antigen-specific effector cells (clonal expansion, illustrated by
the green triangles). Effector B cells secrete soluble receptors (antibodies, i.e. IgG, IgA and IgM) that can neutralize or eliminate extracellular pathogens.
Cytotoxic (CD8+) T cells scan host cells for the presence of virus or intracellular bacteria, killing any cells that are infected. Helper (CD4+) T cells secrete
cytokines that boost both cytotoxic T cells and effector B cells for efficient class-switched antibody responses. Most effector cells die after pathogen clearance,
leaving only small numbers of memory B and T cells that are poised for a more rapid clonal expansion upon a secondary exposure (illustrated by the pink
triangles). Thus, adaptive immunity utilizes clonal expansion to provide long-lasting specific protection against a wide variety of pathogens while minimizing
nutrient cost to the host. IgG, immunoglobulin c; IgA, immunoglobulin a; IgM, immunoglobulin m.
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antigen heavy chain or FRP-1; encoded by the genes SLC3A2 and
Slc3a2 for human and mouse, respectively) of ,80–85 kDa that
is disulfide-linked with a multi-pass light chain of ,40 kDa
(Deves and Boyd, 2000) (Fig. 2). Well-conserved orthologues of
CD98 are expressed in both jawed and jawless vertebrates but not
in invertebrates (Uinuk-Ool et al., 2002). Heterodimeric amino
acid transporters containing a single-pass transmembrane heavy
chain have been found in Drosophila and in schistosomes, but
these do not appear to have all the functions of CD98 described
below (Krautz-Peterson et al., 2007; Reynolds et al., 2009).
CD98hc was discovered in 1981 when anti-leukocyte monoclonal
antibodies were prepared under the theory that ‘‘lymphocyte
differentiation antigens exist and reflect various
immunoregulatory functions’’ (Haynes et al., 1981b). The 4F2
monoclonal antibody (mAb) bound to all monocytes, weakly to
resting lymphocytes, but strongly to activated human B and T
cells (Haynes et al., 1981b), and the 4F2 antigen comprises an
,80–85-kDa heavy chain and a ,40-kDa light chain (Hemler
and Strominger, 1982). Mouse leukocytes express a similar
protein (Bron et al., 1986; Quackenbush et al., 1986), and the
human and mouse 4F2 antigens were given the systematic
CD designation CD98, with 4F2 mAb recognizing CD98hc
(Gottesdiener et al., 1988; Lumadue et al., 1987; Quackenbush et
al., 1987). Following its discovery, CD98 was used as an
activation marker for both B and T cells during normal and
disease states (Hafler et al., 1985; Kehrl et al., 1984; Konttinen
et al., 1985; Moretta et al., 1981; Patterson et al., 1984). CD98hc
was also designated ‘fusion regulatory protein’ (FRP-1) to reflect
its function in cell fusion events that lead to multinucleated giant
cells such as osteoclasts or in viral-induced syncitia (Mori et al.,
2001; Mori et al., 2004; Ohgimoto et al., 1996; Suga et al., 1997;Tsurudome and Ito, 2000).
CD98 has two known biochemical functions (Fenczik et al.,2001). The heavy chain binds to cytoplasmic tails of integrin-bchains (Miyamoto et al., 2003; Prager et al., 2007; Zent et al.,2000) and mediates adhesive signals that control cell spreading,survival and growth (Fenczik et al., 1997; Feral et al., 2005;
Rintoul et al., 2002; Zent et al., 2000). The CD98 light chain canbe any one of six permease-type amino acid transporters and isbound to CD98hc by disulfide bond. The light chain functions inamino acid transport (Deves and Boyd, 2000; Verrey, 2003);
some of the light chains have broad specificity, but the largeneutral amino acid transporters LAT-1 and LAT-2 (encoded bySLC7A6 and SLC7A8), which are the best-studied, have
preference for importing certain essential amino acids,particularly leucine, isoleucine and arginine (LAT-1), inexchange for glutamine (Bertran et al., 1992; Palacin, 1994;
Pineda et al., 1999; Torrents et al., 1998; Verrey, 2003; Verreyet al., 2000). Indeed, through this nutrient function, CD98 cancontribute to the survival and growth of many cell types (Cho
et al., 2004; Reynolds et al., 2007). Importantly, surfaceexpression of the light chain is dependent on the presence ofthe heavy chain, whereas the isolated heavy chain can beexpressed without light chains (Cantor et al., 2009; Cantor et al.,
2011; Mastroberardino et al., 1998; Teixeira et al., 1987). Thus,CD98hc functions in amplifying integrin signaling and in thetransport of amino acids; both of these functions can contribute to
cell survival and proliferation. This Commentary will summarizehow CD98 enables vertebrate adaptive immunity through supportof clonal expansion; however, CD98 also contributes to
pathological clonal expansion in the form of cancer.
CD98 in adaptive immunityDiscovery of CD98 in immune cells
Although CD98 was first identified in lymphocytes (Haynes et al.,1981b), its function in immunity has only recently beenestablished. Early studies using antibody blockade and/or CD98
crosslinking suggested that CD98 could function in B and T cellactivation, proliferation or effector functions (Diaz et al., 1997;Freidman et al., 1994; Gerrard et al., 1984; Komada et al., 2006;
Nakao et al., 1993; Spagnoli et al., 1991; Warren et al., 1996),perhaps by acting as a type of co-stimulatory receptor. However,depending on the conditions used, the effects on proliferation
varied (Gerrard et al., 1984). The role of CD98 in integrinsignaling, cell survival and proliferation in non-lymphoid cells(Fenczik et al., 1997; Feral et al., 2005; Rintoul et al., 2002; Zent
et al., 2000), and in amino acid transport (Bertran et al., 1992;Palacin, 1994; Pineda et al., 1999; Torrents et al., 1998; Verrey,2003; Verrey et al., 2000), provoked studies that examined thebiochemistry and functions of CD98 in lymphocytes upon
selective deletion of the Slc3a2 gene followed by reconstitutionwith mutants that support only one of the biochemical functionsof CD98.
CD98 in T lymphocyte function
To examine the function of CD98hc in adaptive immunity, ourgroup generated a conditional knockout for CD98hc by flankingpart of the Slc3a2 gene with LoxP sites using homologous
recombination in mouse embryonic stem cells (Feral et al., 2007),and bred it with dLck-Cre mice (Zhang et al., 2005), in which Crerecombinase deletes CD98 in the late single-positive stage in
CD98 heavy chain (4F2 Ag, FRP-1)
CD98 light chain(amino acid exchanger)
S-S
N
CN
CD98 heterodimer
CD98hc region required for integrin signaling
C
Fig. 2. Schematic illustration of CD98. The CD98 heavy chain (known as
CH98hc, 4F2 Ag or FRP-1) is encoded by the Slc3a2 gene in mice and
SLC3A2 in humans. CD98hc is a type II transmembrane protein with a large,
heavily glycosylated extracellular domain, and a short transmembrane domain
and cytoplasmic tail. The extracellular, or ecto-, domain was crystallized, and
a ribbon representation of the structure is shown (Fort et al., 2007). The CD98
heterodimer is formed by disulfide bonds between the membrane-proximal
section of the CD98hc extracellular domain and any one of at least six
possible CD98 light chains (the amino acid transporters LAT-1 or LAT-2,
etc.). The integrin signaling function of CD98hc is dependent on the
transmembrane and cytoplasmic domains. CD98 is an unusual protein in that
it combines adhesive signaling and amino acid transport functions.
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both CD4+ and CD8+ T cell lineages (Cantor et al., 2011).CD98hc-null T cells populate secondary lymphoid tissue in
normal numbers, form immunological synapses with antigen-presenting cells (APC) normally and are activated by antigen toexpress activation markers. These cells have moderately impairedhomeostatic proliferation in vivo but exhibit markedly defective
polyclonal and monoclonal antigen receptor-driven proliferationboth in vitro and in vivo (Cantor et al., 2011). Effector functionssuch as cytokine secretion and cytotoxic target lysis appear to be
normal. These data establish a crucial role for CD98hc in theclonal expansion stage of T cell immune responses and show thatCD98hc is required for T-cell-dependent adaptive immunity.
Given that clonally expanding T cells would have increasedmetabolic demands, one might expect amino acid transport to bethe crucial function of CD98 in T cells. However, reconstitutionof CD98hc-null T cells with CD98 mutants shows that the portion
of CD98hc required for amino acid transport is not absolutelyrequired, but that the region that is involved in integrin signalingis crucial for T cell proliferation (Cantor et al., 2011). The
importance of CD98hc in T cell immune responses is also seen inautoimmune disease. Here, loss of T cell CD98 prevents diseasedevelopment in two models of T-cell-mediated autoimmunity,
type 1 diabetes (T1D) and multiple sclerosis (Cantor et al., 2011).This raises the possibility that CD98hc could serve as atherapeutic target for blocking inappropriate adaptive immune
responses.
On the basis of these recent observations, several questions cannow be raised regarding CD98hc function in T cells, such as whatare the effects an antigen-activated CD98-null T cell might have
on the overall immune response? Cytokine secretion and thecapacity to differentiate to regulatory-type Foxp3+ T cells arestill intact in the absence of CD98hc (Cantor et al., 2011). The
ability of a regulatory T cell to suppress inflammatory T cellresponses might be less dependent on clonal expansion than theeffector functions of an inflammatory subset (Gavin and
Rudensky, 2002; Takahashi et al., 1998; Taams et al., 1998).Thus, there is the potential to modulate the quality of an immuneresponse through interfering with CD98hc function. The secondquestion is how partial or transient loss of CD98hc might differ
from its complete deletion. Another unresolved issue is whetherT cells require CD98hc for secondary responses to the samepathogen. In other words, what is the function of CD98hc in
memory CD4 or CD8 T cells? This might have implications indesigning intervention strategies that target CD98hc.
CD98 in B lymphocyte function
Until recently, only one study had examined CD98 function in Bcells using inhibition with the 4F2 antibody, with confusingresults that included both inhibition and enhancement of B cell
functions (Gerrard et al., 1984). To address this issue, our groupgenetically deleted CD98hc in B cells using CD19-Cre (Cantoret al., 2009). Similar to the results in T cells, CD98hc is not
required for B cell compartmentalization or their initialactivation, but is crucial for B cell clonal expansion (Cantoret al., 2009). CD98-null B cells display strikingly reduced
proliferation after stimulation with strong mitogens, and thus areunable to differentiate into plasma cells. Consequently, micelacking CD98hc in B cells have strongly impaired antibody
responses following immunization, and class-switching to IgG, ahallmark of mature antibody responses, is dramatically impaired.Because CD98hc-null B cells lack antigen-driven proliferation,
the direct role of CD98 in B cell effector function (e.g. antibodysecretion) cannot be examined directly. The apparently differing
degrees by which T and B cells depend on CD98hc remainpuzzling. One possibility is that the intensely competitive natureof B cell clonal expansion in germinal centers (Allen et al., 2007;Pritchard-Briscoe et al., 1977) renders CD98-null B cell unable to
compete for available anchorage or nutrients within theenvironment of a germinal center. Nevertheless, taken together,these studies demonstrate that CD98hc is required for both
humoral and cell-mediated adaptive immunity because it isessential for clonal expansion (Fig. 3).
Mechanism of action for CD98 in lymphocyte proliferation
Although the cellular role of CD98hc in lymphocytes has becomefairly clear, the biochemical mechanism by which this proteindrives clonal expansion is not fully understood. There are at least
three indications that the integrin signaling function of CD98hcis required for rapid lymphocyte proliferation. First, CD98hcmutants that exclusively support integrin signaling can
reconstitute proliferation, whereas those that only supportamino acid transport do not. Second, CD98-null B cells showdefective integrin functions in that they are unable to adhere
firmly and spread on anti-aLb2-integrin-coated solid surfaces.More importantly, mitogen-induced early (,30 min) mitogen-activated protein kinase (MAPK) signaling is intact in CD98-nullB cells as indicated by a normal initial wave of extracellular-
signal-regulated kinase (ERK1/2) phosphorylation. However,loss of CD98hc abrogates sustained secondary phosphorylationof ERK and downregulation of cyclin-dependent kinase (CDK)
inhibitors. This loss of sustained ERK activation anddownregulation of CDK inhibitors resembles the effects of theloss of integrin signals that support growth factor stimulation of
fibroblasts (Assoian and Schwartz, 2001; Schwartz and Assoian,2001; Walker and Assoian, 2005). These data raise the questionof which integrin ligands support B and T cell proliferation. One
possibility is that there is a ligand-independent function ofintegrins in sustaining ERK signaling, which supports cell cycleprogression. Another possibility is that CD98hc-dependentintegrins recognize cell-associated ligands during cell–cell
interactions (Nguyen et al., 2008) that occur during lymphocytelocalization and synapse formation within lymph nodes. Whereasmorphological synapse formation appears grossly normal in
CD98-null T cells in vitro, it is possible that the quality andduration of contacts is defective in vivo, perhaps preventing Tcell polarization (Chang et al., 2007). Additional hints that
CD98hc functions in cell–cell contacts comes from itsdocumented roles in cell fusion, and in monocyte or B cellaggregation (Cho et al., 2001; Cho et al., 2004; Mori et al., 2001;
Mori et al., 2004; Ohgimoto et al., 1996; Suga et al., 1997;Tsurudome and Ito, 2000). Further study is needed to understandthe details of how CD98hc and integrins might cooperate tosupport lymphocyte proliferation and adaptive immunity.
Given that highly conserved CD98 orthologs are present onlyin vertebrates (Prager et al., 2007; Uinuk-Ool et al., 2002) and arerequired for adaptive immunity, they should be found in all
adaptive immune systems. Jawless fish (agnathans), which havean alternative adaptive immune system with a unique set of genesthat form VLRs (Herrin and Cooper, 2010; Pancer et al., 2005)
still rely on clonal expansion of lymphocyte-like cells (Mariuzzaet al., 2010) and possess an unambiguous CD98hc orthologue(Uinuk-Ool et al., 2002). This fact adds additional compelling
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evidence for the absolute requirement of CD98hc for the abilityof lymphocytes to mount adaptive immune responses.
CD98 and invasive cancers: the turbochargergone awryCD98 expression in tumors
The capacity for rapid proliferation, especially without firmanchorage, can be dangerous in malignant cells, and a large body
of evidence implicates CD98 in cancer (Table 1). Many tumorsexpress CD98hc, and its expression correlates with poor
prognosis in B cell lymphomas (Holte et al., 1987; Holte et al.,1989; Salter et al., 1989). Furthermore, nearly all studies that
have examined the expression of CD98hc or CD98 light chains insolid tumors show that their expression is correlated with
progressive or metastatic tumors (Esteban et al., 1990; Kairaet al., 2009a; Kaira et al., 2009b; Kaira et al., 2009c; Kaira et al.,
2008; Kaira et al., 2009d; Kobayashi et al., 2008; Nawashiroet al., 2002; Nawashiro et al., 2006; Oleinik et al., 2005;
Powlesland et al., 2009; Shennan et al., 2003; Xiao et al., 2005).
CD98 depletion and overexpression studies in cancer
Genetic modulation of CD98 expression in human cell lines
and in animal models has established a causal link between CD98and cancer; CD98 promotes transformation and tumor growth
(Feral et al., 2005; Ohkawa et al., 2011). Furthermore, CD98overexpression drives both anchorage independence and
tumorigenesis (Nguyen et al., 2011; Hara et al., 1999;Henderson et al., 2004; Shishido et al., 2000), and the degree
of transformation correlates with the level of CD98hc present inthe cells (Hara et al., 1999). An early report showed that the
transforming ability of CD98hc is lost in a mutant that ablates theability to form disulfide bonds with the light chain and thus
abolishes its amino acid transport function (Shishido et al., 2000).However, this mutation also affects the ability of CD98hc to bind
integrins (Kolesnikova et al., 2001), making this result difficult to
interpret. Moreover, a later study using CD98hc chimeras, in
which its amino acid transport is separated from its integrinsignaling function (Fenczik et al., 2001), has shown that the
CD98 domain that is involved in integrin signaling is required for
transforming Chinese hamster ovary (CHO) cells (Henderson
et al., 2004) and for the development of embryonic stem cellteratomas in mice (Feral et al. 2005). Taken together, these
genetic studies show that CD98hc expression is important, and
that its overexpression is sufficient for cellular transformation.
CD98 blockade in tumors
The third line of evidence for the importance of CD98 in cancer
comes from a number of studies that used CD98 inhibitors in avariety of tumor cells; these have resulted in the inhibition of
cellular proliferation and tumor growth both in vitro and in vivo
(Imai et al., 2010; Nawashiro et al., 2006; Oda et al., 2010;Shennan and Thomson, 2008; Yamauchi et al., 2009). One
particular study used anti-CD98 antibodies specific for the heavy
chain and showed that the growth of human tumor cells is
inhibited in vitro (Yagita et al., 1986). Overall, these studiesindicate that CD98 might constitute a target for therapeutic
intervention in cancer. In fact, a microRNA that modulates CD98
expression during intestinal epithelial differentiation was recently
identified, raising the possibility of an additional approach toalter CD98 expression (Nguyen et al., 2010).
CD98 amino acid transport in cancer
The mechanism by which CD98 promotes tumorigenesis is an
important area of current research. Significant questions remain
Selectiveexpansion ofAg-specific
clone
2 Proliferation
3 Differentiation/effector function
Targetcell
Celldeath
Antigen
1 Activation
APC
Cytokines
CD98requirement
4 Contraction/memory formation
(> 30 days) Expansion ofmemory cells
5 Secondary (memory)response
CD98?
CD4+CD8+
Early MAPKsignals
SecondaryMAPK signaling
Fig. 3. The role of CD98hc in cell-mediated adaptive immunity. Upon immune challenge, a rare antigen-specific naive T cell (shown in blue) is activated by
peptide antigen (Ag) on an antigen-presenting cell (APC) and rapidly proliferates to expand into a large number of antigen-specific effector T cells. After
expansion and differentiation, effector CD4+ ‘helper’ cells secrete cytokines to direct the adaptive immune response, and CD8+ cytotoxic ‘killer’ T cells kill
infected target cells. After pathogen clearance, effector T cells die to leave only a few ‘memory’ T cells that are primed for a rapid secondary response. Following
secondary exposure to the same antigen, memory T cells re-expand to eliminate the pathogen. CD98hc is required for rapid clonal expansion, but appears
dispensable for antigen recognition, activation and effector functions. Whether or not CD98hc is necessary for secondary expansion is an open question.
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unanswered, such as whether CD98hc allows tumor growth by
boosting the transport of nutrients or by augmenting integrin
signaling, and if so, how would each of these roles be fulfilled. The
rapidly dividing tumor cell has intense metabolic demands, often
under conditions of diminishing nutrient availability within a solid
tumor. CD98hc could therefore support tumor growth through its
association with the amino acid transporter light chain and the
subsequent increased supply of amino acids. Under conditions of
limited amino acid availability, CD98 light chains such as LAT-1
are upregulated and their expression can be dysregulated in tumor
cells (Campbell et al., 2000). LAT-1 and LAT-2 are amino acid
exchangers and can import essential amino acids (EAA), such as
leucine, isoleucine and arginine in exchange for the export of
glutamine that has been imported by other transporters such as
through system A transporters (Verrey, 2003). Furthermore, this
CD98-mediated exchange of glutamine in the presence of EAAs is
a rate-limiting step in the activation of mammalian target of
rapamycin (mTOR) (Nicklin et al., 2009), which regulates cell
growth and proliferation, providing another pathway through
which CD98 could stimulate tumor growth. Cancer cells are
heavily dependent on glutamine, not merely as an ingredient for
nucleotide and amino acid biosynthesis, but also to promote
increased uptake of EAAs through this exchange mechanism
(Wise and Thompson, 2010). Interestingly, T lymphocytes are
another cell type that is particularly dependent on glutamine (Carr
et al., 2010). Thus, it appears probable that high expression levels
of CD98hc could allow for rapid proliferation of lymphocytes and
tumors by stimulating the exchange of glutamine for limiting
EAAs (Fig. 4, left-hand panel).
CD98 integrin signaling function in cancer
CD98hc can also contribute to transformation by amplifying
integrin signaling that results in reduced anchorage dependence.
Integrins themselves have been implicated in invasive cancers
because the ‘outside-in’ signals they transduce control cell
proliferation and survival (Huck et al., 2010; Lahlou et al., 2007;
Desgrosellier and Cheresh, 2010; Harburger and Calderwood,
2009). Integrins act as mechanotransducers that sense the
stiffness of the extracellular matrix (ECM). Increased ECM
stiffness drives tumor progression through clustering of integrins,
which leads to adhesive signaling through focal adhesion kinase
(FAK) and phosphatidylinositol 3-kinase (PI3K) (Levental et al.,
2009). These signals can also direct the proliferation of micro-
metastases in the lungs through b1 integrin (Shibue and
Weinberg, 2009). In a softer matrix, such as one with larger
amounts of flexible ECM components (elastin, etc.), high
expression of CD98hc could permit integrin signaling that
would promote cell growth and survival. Thus, the expression
level of CD98hc would fine-tune the capacity of the cell to sense
the compliance of the matrix. Indeed, CD98hc is important in
Table 1. Studies examining the role of CD98hc in cancers
Cell type Observations Reference(s)
Cutaneous T cell lymphoma (CTCL) All malignant CTCL T cells are CD98+; fewnormal T cells are
(Haynes et al., 1981a)
Bladder cancer cells (transitional epithelium) Anti-CD98 antibody treatment inhibits proliferationof human tumor cells
(Yagita et al., 1986)
B cell lymphomas CD98 expression on lymphomas can identify patientswith poor prognosis
(Holte et al., 1987; Holte et al., 1989; Salteret al., 1989; Powlesland et al., 2011)
Oral squamous cell carcinoma CD98 histological expression pattern within a tumoris a significant indicator of progression and metastasis
(Esteban et al., 1990; Kim et al., 2004)
Childhood acute lymphoblastic leukemia CD98 expression level correlates with durationof complete remission
(Taskov et al., 1996)
(Mouse) fibroblast (3T3 cell line) CD98 overexpression leads to transformation (Hara et al., 1999; Henderson et al., 2004;Shishido et al., 2000)
Astrocytic neoplasms CD98 light chain (LAT-1) expression is increasedin astrocytic cancers
(Nawashiro et al., 2002)
Human glioblastoma(and rat C6 glioma model)
High LAT1 expression correlates with poor survival;LAT1 inhibition decreases glioma tumor cell growth
(Nawashiro et al., 2006)
Breast cancer cell lines LAT-1 inhibitors suppress tumor cell growth andmetabolism
(Shennan and Thomson, 2008; Shennan et al.,2003)
(Mouse) Embryonic stem cell teratomas Genetic deletion of CD98hc blocks tumor growth (Feral et al., 2005)
Blood proteins during lung cancer High soluble CD98 and two other blood proteins maybe a tumor biomarker
(Xiao et al., 2005)
Breast tissue RNA Expression of CD98-encoding mRNAs correlateswith poor prognosis
(Esseghir et al., 2006)
Multiple CD98hc and LAT-1 expression is higher in metastaticthan primary tumor sites
(Kaira et al., 2008)
(Mouse) Glioma cells Overexpression of CD98 light chain LAT-1enhances tumor growth rate in vivo
(Kobayashi et al., 2008)
Pulmonary tumors CD98 expression predicts poor prognosis (Kaira et al., 2009a; Kaira et al., 2009b; Kairaet al., 2009c)
Renal cell cancer CD98 histological expression correlates directlywith malignancy grade
(Prager et al., 2009)
Squamous cell carcinoma lines CD98 light chain LAT-1 inhibitor improves efficacyof cisplatin treatment
(Yamauchi et al., 2009)
Non-small cell lung cancer LAT-1 inhibitor BCH reduces viability of tumor cellsex vivo
(Imai et al., 2010)
Chicken cell line and HeLa cells Genetic disruption or inhibition of LAT-1 blockstumor cell growth in vitro and in vivo
(Ohkawa et al., 2011)
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allowing a cell to exert force on the ECM through integrin-driven
RhoA signaling (Feral et al., 2007), which is a key element in the
sensing of stiffness (Samuel et al., 2011).
Anchorage independence (i.e. independence of integrin signals
provided by adhesion to ECM) is another hallmark of cellular
transformation, and CD98hc is important for anchorage
independence (Feral et al., 2005). CD98hc co-immunoprecipitates
with integrins (Henderson et al., 2004; Rintoul et al., 2002), and
binds to the b1 and b3 integrin cytoplasmic domains in a purified
system (Prager et al., 2007). Overexpression or crosslinking of
CD98hc stimulates FAK and AKT phosphorylation (Cai et al.,
2005; Rintoul et al., 2002) (Fenczik et al., 1997), and deletion of
CD98hc impairs integrin signaling (Feral et al., 2005). This integrin
signaling function of CD98hc is dependent on the transmembrane
and cytoplasmic domains (Fenczik et al., 2001), the same region that
is crucial for lymphocyte proliferation (Cantor et al., 2009; Cantor
et al., 2011) and for cellular transformation caused by overexpression
of CD98hc (Henderson et al., 2004). CD98hc can thus regulate
integrin signaling, and integrins are crucial for tumor progression
through mechanotransduction and control of anchorage-independent
growth. Therefore CD98hc might control tumorigenesis by
governing integrin signaling (Fig. 4, right-hand panel).
CD98hc might also contribute to other pathologies. For
example, in addition to autoimmunity disorders (Cantor et al.,
2011), CD98hc overexpression could lead to other adaptive
immunopathologies. Arterial restenosis and intestinal villous
inflammation are dependent on CD98hc in animal models
(Fogelstrand et al., 2009; Nguyen et al., 2011). Vertebrates
have stratified squamous epithelium containing rapidly-dividing
keratinocytes, which express high levels of CD98hc (Fernandez-
Herrera et al., 1989; Lemaitre et al., 2005; Lemaitre et al., 2011;
Patterson et al., 1984). The role of CD98hc in pathologic states in
these tissues requires further study.
ConclusionsHere, we have summarized the central importance of rapid
proliferation for clonal expansion in the vertebrate-specific
adaptive immune system. CD98hc enables lymphocyte clonal
expansion and adaptive immune responses, probably in part
through its effects on integrin signaling. CD98hc is also
important in cancer, which is probably mediated through
increased transport of amino acids and/or by boosting integrin
signals that allow growth in soft ECM or without anchorage.
Importantly, clonal expansion is the nexus at which CD98 acts in
adaptive immunity, and clonal expansion of tumor cells is also a
central feature of many cancers. CD98hc and the integrins that
bind to it are vertebrate-specific, as is adaptive immunity, and it
is noteworthy that vertebrates appear to be particularly prone to
developing invasive and metastatic cancers. This confluence of
adaptive immunity, and the expression of CD98hc and CD98-
binding integrins (Prager et al., 2007), coincident with increased
invasive cancer, in vertebrates, suggests that CD98hc provides
vertebrates with the benefit of adaptive immunity, but that this
comes with a price: increased susceptibility to invasive cancers.
CD98 amino acid transport in cancer CD98 integrin signaling in cancer
S-S
CD98hc
CD98 light chain (LAT-1, LAT-2, etc.)
AKTp130CAS
FAK
� Survival� Anchorage-independence
� Metastasis
mTORactivation
� Survival� Growth
Essentialamino acids
Glutamine
Glutamine
Unidirectionaltransporter
Autophagy
S-S
Integrin
CD98hc
CD98 light chain (LAT-1, LAT-2, etc.)
Leucine
Fig. 4. Roles of CD98 in cancer. CD98 has two main biochemical functions, amino acid transport and integrin signaling; both appear important in tumor growth
and metastasis. Left panel: CD98 amino acid transport in cancer. LAT-1 and LAT-2, the most commonly studied CD98 light chains, are system L bi-directional
transporters of large neutral amino acids. Unidirectional transporters (such as system A or N transporters) import the non-essential amino acid glutamine into a
rapidly growing cell. LAT-1 or LAT-2 can then export glutamine in exchange for importing EAAs. EAAs then activate the mTOR pathway, blocking
autophagy and promoting cell growth and protein synthesis. Right panel: CD98 integrin signaling in cancer. CD98hc interacts with integrins and mediates
integrin-dependent signals that promote tumorigenesis. CD98-dependent integrin signaling through proteins such as AKT, p130CAS (also known as BCAR1) and
focal adhesion kinase (FAK) allow tumor cell survival and proliferation without anchorage.
CD98, cancer and immunity 1379
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One could speculate that other vertebrate-specific genes that are
involved in clonal expansion must exist and are maintained
because of the survival benefits they provide through adaptive
immunity. Such genes might, like those encoding CD98, be
upregulated in activated lymphocytes and could be therapeutic
targets for autoimmunity diseases or cancer. Going forwards, it is
key for this field to define the specific molecular mechanisms by
which CD98 contributes to adaptive immunity and cancer.
Second, the dramatic effects of CD98 loss on tumors and on
lymphocyte clonal expansion demands that we make efforts to
define the therapeutic potential of CD98 inhibition in cancer and
autoimmune diseases.
FundingWork in our laboratories was supported by grants from the NationalInstitutes of Health [grant numbers HL31950, HL 57900, AR 27214,and HL 078784 to M.H.G.]. J.M.C. is supported by the MultipleSclerosis Society and an NIH K01 grant [grant numberK01DK090416]. Deposited in PMC for release after 12 months.
ReferencesAbbas, A. K. (2003). Cellular and molecular immunology. Philadelphia, PA: Saunders.
Allen, C. D., Okada, T., Tang, H. L. and Cyster, J. G. (2007). Imaging of germinal
center selection events during affinity maturation. Science 315, 528-531.
Assoian, R. K. and Schwartz, M. A. (2001). Coordinate signaling by integrins and
receptor tyrosine kinases in the regulation of G1 phase cell-cycle progression. Curr.
Opin. Genet. Dev. 11, 48-53.
Bertran, J., Magagnin, S., Werner, A., Markovich, D., Biber, J., Testar, X.,
Zorzano, A., Kuhn, L. C., Palacin, M. and Murer, H. (1992). Stimulation of system
y(+)-like amino acid transport by the heavy chain of human 4F2 surface antigen in
Xenopus laevis oocytes. Proc. Natl. Acad. Sci. USA 89, 5606-5610.
Boehm, T. (2011). Design principles of adaptive immune systems. Nat. Rev. Immunol.
11, 307-317.
Bron, C., Rousseaux, M., Spiazzi, A. L. and MacDonald, H. R. (1986). Structural
homology between the human 4F2 antigen and a murine cell surface glycoprotein
associated with lymphocyte activation. J. Immunol. 137, 397-399.
Cai, S., Bulus, N., Fonseca-Siesser, P. M., Chen, D., Hanks, S. K., Pozzi, A. and
Zent, R. (2005). CD98 modulates integrin beta1 function in polarized epithelial cells.
J. Cell Sci. 118, 889-899.
Campbell, W. A., Sah, D. E., Medina, M. M., Albina, J. E., Coleman, W. B. and
Thompson, N. L. (2000). TA1/LAT-1/CD98 light chain and system L activity, but
not 4F2/CD98 heavy chain, respond to arginine availability in rat hepatic cells. Loss
of response in tumor cells. J. Biol. Chem. 275, 5347-5354.
Cantor, J., Browne, C. D., Ruppert, R., Feral, C. C., Fassler, R., Rickert, R. C. and
Ginsberg, M. H. (2009). CD98hc facilitates B cell proliferation and adaptive humoral
immunity. Nat. Immunol. 10, 412-419.
Cantor, J., Slepak, M., Ege, N., Chang, J. T. and Ginsberg, M. H. (2011). Loss of T
cell CD98 H chain specifically ablates T cell clonal expansion and protects from
autoimmunity. J. Immunol. 187, 851-860.
Carr, E. L., Kelman, A., Wu, G. S., Gopaul, R., Senkevitch, E., Aghvanyan, A.,
Turay, A. M. and Frauwirth, K. A. (2010). Glutamine uptake and metabolism are
coordinately regulated by ERK/MAPK during T lymphocyte activation. J. Immunol.
185, 1037-1044.
Chang, J. T., Palanivel, V. R., Kinjyo, I., Schambach, F., Intlekofer, A. M.,
Banerjee, A., Longworth, S. A., Vinup, K. E., Mrass, P., Oliaro, J. et al. (2007).
Asymmetric T lymphocyte division in the initiation of adaptive immune responses.
Science 315, 1687-1691.
Cho, J. Y., Fox, D. A., Horejsi, V., Sagawa, K., Skubitz, K. M., Katz, D. R. and
Chain, B. (2001). The functional interactions between CD98, beta1-integrins, and
CD147 in the induction of U937 homotypic aggregation. Blood 98, 374-382.
Cho, J. Y., Kim, A. R., Joo, H. G., Kim, B. H., Rhee, M. H., Yoo, E. S., Katz, D. R.,
Chain, B. M. and Jung, J. H. (2004). Cynaropicrin, a sesquiterpene lactone, as a new
strong regulator of CD29 and CD98 functions. Biochem. Biophys. Res. Commun. 313,
954-961.
Desgrosellier, J. S. and Cheresh, D. A. (2010). Integrins in cancer: biological
implications and therapeutic opportunities. Nat. Rev. Cancer 10, 9-22.
Deves, R. and Boyd, C. A. (2000). Surface antigen CD98(4F2): not a single membrane
protein, but a family of proteins with multiple functions. J. Membr. Biol. 173, 165-177.
Diaz, L. A., Jr, Friedman, A. W., He, X., Kuick, R. D., Hanash, S. M. and Fox, D. A.
(1997). Monocyte-dependent regulation of T lymphocyte activation through CD98.
Int. Immunol. 9, 1221-1231.
Esseghir, S., Reis-Filho, J. S., Kennedy, A., James, M., O’Hare, M. J., Jeffery, R.,
Poulsom, R. and Isacke, C. M. (2006). Identification of transmembrane proteins as
potential prognostic markers and therapeutic targets in breast cancer by a screen for
signal sequence encoding transcripts. J. Pathol. 210, 420-430.
Esteban, F., Ruiz-Cabello, F., Concha, A., Perez Ayala, M., Delgado, M. and
Garrido, F. (1990). Relationship of 4F2 antigen with local growth and metastaticpotential of squamous cell carcinoma of the larynx. Cancer 66, 1493-1498.
Fenczik, C. A., Sethi, T., Ramos, J. W., Hughes, P. E. and Ginsberg, M. H. (1997).
Complementation of dominant suppression implicates CD98 in integrin activation.Nature 390, 81-85.
Fenczik, C. A., Zent, R., Dellos, M., Calderwood, D. A., Satriano, J., Kelly, C. and
Ginsberg, M. H. (2001). Distinct domains of CD98hc regulate integrins and aminoacid transport. J. Biol. Chem. 276, 8746-8752.
Feral, C. C., Nishiya, N., Fenczik, C. A., Stuhlmann, H., Slepak, M. and Ginsberg,
M. H. (2005). CD98hc (SLC3A2) mediates integrin signaling. Proc. Natl. Acad. Sci.
USA 102, 355-360.
Feral, C. C., Zijlstra, A., Tkachenko, E., Prager, G., Gardel, M. L., Slepak, M. and
Ginsberg, M. H. (2007). CD98hc (SLC3A2) participates in fibronectin matrix
assembly by mediating integrin signaling. J. Cell Biol. 178, 701-711.
Fernandez-Herrera, J., Sanchez-Madrid, F. and Diez, A. G. (1989). Differential
expression of the 4F2 activation antigen on human follicular epithelium in hair cycle.J. Invest. Dermatol. 92, 247-250.
Fogelstrand, P., Feral, C. C., Zargham, R. and Ginsberg, M. H. (2009). Dependenceof proliferative vascular smooth muscle cells on CD98hc (4F2hc, SLC3A2). J. Exp.
Med. 206, 2397-2406.
Fort, J., de la Ballina, L. R., Burghardt, H. E., Ferrer-Costa, C., Turnay, J., Ferrer-
Orta, C., Uson, I., Zorzano, A., Fernandez-Recio, J., Orozco, M. et al. (2007). Thestructure of human 4F2hc ectodomain provides a model for homodimerization and
electrostatic interaction with plasma membrane. J. Biol. Chem. 282, 31444-31452.
Freidman, A. W., Diaz, L. A., Jr, Moore, S., Schaller, J. and Fox, D. A. (1994). The
human 4F2 antigen: evidence for cryptic and noncryptic epitopes and for a role of 4F2in human T lymphocyte activation. Cell Immunol. 154, 253-263.
Gavin, M. A. and Rudensky, A. Y. (2002). Dual TCR T cells: gaining entry into theperiphery. Nat. Immunol. 3, 109-110.
Gerrard, T. L., Jurgensen, C. H. and Fauci, A. S. (1984). Modulation of human B cell
responses by a monoclonal antibody to an activation antigen 4F2. Clin. Exp. Immunol.
57, 155-162.
Gottesdiener, K. M., Karpinski, B. A., Lindsten, T., Strominger, J. L., Jones, N. H.,
Thompson, C. B. and Leiden, J. M. (1988). Isolation and structural characterizationof the human 4F2 heavy-chain gene, an inducible gene involved in T-lymphocyte
activation. Mol. Cell. Biol. 8, 3809-3819.
Hafler, D. A., Hemler, M. E., Christenson, L., Williams, J. M., Shapiro, H. M.,
Strom, T. B., Strominger, J. L. and Weiner, H. L. (1985). Investigation of in vivoactivated T cells in multiple sclerosis and inflammatory central nervous systemdiseases. Clin. Immunol. Immunopathol. 37, 163-171.
Hara, K., Kudoh, H., Enomoto, T., Hashimoto, Y. and Masuko, T. (1999). Malignanttransformation of NIH3T3 cells by overexpression of early lymphocyte activationantigen CD98. Biochem. Biophys. Res. Commun. 262, 720-725.
Harburger, D. S. and Calderwood, D. A. (2009). Integrin signalling at a glance. J. Cell
Sci. 122, 159-163.
Haynes, B. F., Bunn, P., Mann, D., Thomas, C., Eisenbarth, G. S., Minna, J. and
Fauci, A. S. (1981a). Cell surface differentiation antigens of the malignant T cell in
Sezary syndrome and mycosis fungoides. J. Clin. Invest. 67, 523-530.
Haynes, B. F., Hemler, M. E., Mann, D. L., Eisenbarth, G. S., Shelhamer, J.,
Mostowski, H. S., Thomas, C. A., Strominger, J. L. and Fauci, A. S. (1981b).
Characterization of a monoclonal antibody (4F2) that binds to human monocytes andto a subset of activated lymphocytes. J. Immunol. 126, 1409-1414.
Hemler, M. E. and Strominger, J. L. (1982). Characterization of antigen recognized bythe monoclonal antibody (4F2): different molecular forms on human T and Blymphoblastoid cell lines. J. Immunol. 129, 623-628.
Henderson, N. C., Collis, E. A., Mackinnon, A. C., Simpson, K. J., Haslett, C., Zent,
R., Ginsberg, M. and Sethi, T. (2004). CD98hc (SLC3A2) interaction with beta 1integrins is required for transformation. J. Biol. Chem. 279, 54731-54741.
Herrin, B. R. and Cooper, M. D. (2010). Alternative adaptive immunity in jawlessvertebrates. J. Immunol. 185, 1367-1374.
Hildeman, D., Jorgensen, T., Kappler, J. and Marrack, P. (2007). Apoptosis and thehomeostatic control of immune responses. Curr. Opin. Immunol. 19, 516-521.
Holte, H., Davies, C. D., Kvaloy, S., Smeland, E. B., Foss-Abrahamsen, A., Kaalhus,
O., Marton, P. F. and Godal, T. (1987). The activation-associated antigen 4F2
predicts patient survival in low-grade B-cell lymphomas. Int. J. Cancer 39, 590-594.
Holte, H., de Lange Davies, C., Beiske, K., Stokke, T., Marton, P. F., Smeland, E. B.,
Hoie, J. and Kvaloy, S. (1989). Ki67 and 4F2 antigen expression as well as DNA
synthesis predict survival at relapse/tumour progression in low-grade B-celllymphoma. Int. J. Cancer 44, 975-980.
Hsu, E. (2009). V(D)J recombination: of mice and sharks. Adv. Exp. Med. Biol. 650,166-179.
Huck, L., Pontier, S. M., Zuo, D. M. and Muller, W. J. (2010). beta1-integrin isdispensable for the induction of ErbB2 mammary tumors but plays a critical role inthe metastatic phase of tumor progression. Proc. Natl. Acad. Sci. USA 107, 15559-
15564.
Imai, H., Kaira, K., Oriuchi, N., Shimizu, K., Tominaga, H., Yanagitani, N.,
Sunaga, N., Ishizuka, T., Nagamori, S., Promchan, K. et al. (2010). Inhibition of L-
type amino acid transporter 1 has antitumor activity in non-small cell lung cancer.Anticancer Res. 30, 4819-4828.
Kaira, K., Oriuchi, N., Imai, H., Shimizu, K., Yanagitani, N., Sunaga, N., Hisada,
T., Tanaka, S., Ishizuka, T., Kanai, Y. et al. (2008). l-type amino acid transporter 1
Journal of Cell Science 125 (6)1380
Journ
alof
Cell
Scie
nce
and CD98 expression in primary and metastatic sites of human neoplasms. Cancer
Sci. 99, 2380-2386.
Kaira, K., Ohde, Y., Endo, M., Nakagawa, K., Okumura, T., Takahashi, T.,Murakami, H., Tsuya, A., Nakamura, Y., Naito, T. et al. (2009a). Expression of4F2hc (CD98) in pulmonary neuroendocrine tumors. Oncol. Rep. 26, 931-937.
Kaira, K., Oriuchi, N., Imai, H., Shimizu, K., Yanagitani, N., Sunaga, N., Hisada,
T., Ishizuka, T., Kanai, Y., Nakajima, T. et al. (2009b). Prognostic significance ofL-type amino acid transporter 1 (LAT1) and 4F2 heavy chain (CD98) expression instage I pulmonary adenocarcinoma. Lung Cancer 66, 120-126.
Kaira, K., Oriuchi, N., Imai, H., Shimizu, K., Yanagitani, N., Sunaga, N., Hisada,T., Kawashima, O., Kamide, Y., Ishizuka, T. et al. (2009c). CD98 expression isassociated with poor prognosis in resected non-small-cell lung cancer with lymphnode metastases. Ann. Surg. Oncol. 16, 3473-3481.
Kaira, K., Oriuchi, N., Shimizu, K., Ishikita, T., Higuchi, T., Imai, H., Yanagitani,
N., Sunaga, N., Hisada, T., Ishizuka, T. et al. (2009d). Evaluation of thoracictumors with (18)F-FMT and (18)F-FDG PET-CT: a clinicopathological study. Int. J.
Cancer 124, 1152-1160.
Kehrl, J. H., Muraguchi, A. and Fauci, A. S. (1984). Differential expression of cellactivation markers after stimulation of resting human B lymphocytes. J. Immunol.
132, 2857-2861.
Kim, D. K., Ahn, S. G., Park, J. C., Kanai, Y., Endou, H. and Yoon, J. H. (2004).Expression of L-type amino acid transporter 1 (LAT1) and 4F2 heavy chain (4F2hc)in oral squamous cell carcinoma and its precusor lesions. Anticancer Res. 24, 1671-1675.
Kobayashi, K., Ohnishi, A., Promsuk, J., Shimizu, S., Kanai, Y., Shiokawa, Y. and
Nagane, M. (2008). Enhanced tumor growth elicited by L-type amino acid transporter1 in human malignant glioma cells. Neurosurgery 62, 493-504.
Kolesnikova, T. V., Mannion, B. A., Berditchevski, F. and Hemler, M. E. (2001).Beta1 integrins show specific association with CD98 protein in low densitymembranes. BMC Biochem. 2, 10.
Komada, H., Imai, A., Hattori, E., Ito, M., Tsumura, H., Onoda, T., Kuramochi, M.,Tani, M., Yamamoto, K., Yamane, M. et al. (2006). Possible activation of murine Tlymphocyte through CD98 is independent of interleukin 2/interleukin 2 receptorsystem. Biomed. Res. 27, 61-67.
Konttinen, Y., Bergroth, V. and Nykanen, P. (1985). Lymphocyte activation inrheumatoid arthritis synovial fluid in vivo. Scand. J. Immunol. 22, 503-507.
Krautz-Peterson, G., Camargo, S., Huggel, K., Verrey, F., Shoemaker, C. B. and
Skelly, P. J. (2007). Amino acid transport in schistosomes: Characterization of thepermeaseheavy chain SPRM1hc. J. Biol. Chem. 282, 21767-21775.
Kuby, J. (1997). Immunology. New York: W. H. Freeman.
Kumar, H., Kawai, T. and Akira, S. (2011). Pathogen recognition by the innateimmune system. Int. Rev. Immunol. 30, 16-34.
Lahlou, H., Sanguin-Gendreau, V., Zuo, D., Cardiff, R. D., McLean, G. W., Frame,
M. C. and Muller, W. J. (2007). Mammary epithelial-specific disruption of the focaladhesion kinase blocks mammary tumor progression. Proc. Natl. Acad. Sci. USA 104,20302-20307.
Leclerc, V. and Reichhart, J. M. (2004). The immune response of Drosophilamelanogaster. Immunol. Rev. 198, 59-71.
Lemaitre, G., Gonnet, F., Vaigot, P., Gidrol, X., Martin, M. T., Tortajada, J. and
Waksman, G. (2005). CD98, a novel marker of transient amplifying humankeratinocytes. Proteomics 5, 3637-3645.
Lemaitre, G., Stella, A., Feteira, J., Baldeschi, C., Vaigot, P., Martin, M. T.,Monsarrat, B. and Waksman, G. (2011). CD98hc (SLC3A2) is a key regulator ofkeratinocyte adhesion. J. Dermatol. Sci. 61, 169-179.
Levental, K. R., Yu, H., Kass, L., Lakins, J. N., Egeblad, M., Erler, J. T., Fong, S. F.,Csiszar, K., Giaccia, A., Weninger, W. et al. (2009). Matrix crosslinking forcestumor progression by enhancing integrin signaling. Cell 139, 891-906.
Lumadue, J. A., Glick, A. B. and Ruddle, F. H. (1987). Cloning, sequence analysis,and expression of the large subunit of the human lymphocyte activation antigen 4F2.Proc. Natl. Acad. Sci. USA 84, 9204-9208.
Mariuzza, R. A., Velikovsky, C. A., Deng, L., Xu, G. and Pancer, Z. (2010).Structural insights into the evolution of the adaptive immune system: the variablelymphocyte receptors of jawless vertebrates. Biol. Chem. 391, 753-760.
Mastroberardino, L., Spindler, B., Pfeiffer, R., Skelly, P. J., Loffing, J., Shoemaker,
C. B. and Verrey, F. (1998). Amino-acid transport by heterodimers of 4F2hc/CD98and members of a permease family. Nature 395, 288-291.
Medzhitov, R. and Janeway, C. A., Jr (1997). Innate immunity: the virtues of anonclonal system of recognition. Cell 91, 295-298.
Mitchell, D. M. and Williams, M. A. (2010). An activation marker finds a function.Immunity 32, 9-11.
Miyamoto, Y. J., Mitchell, J. S. and McIntyre, B. W. (2003). Physical association andfunctional interaction between beta1 integrin and CD98 on human T lymphocytes.Mol. Immunol. 39, 739-751.
Moretta, L., Mingari, M. C., Sekaly, P. R., Moretta, A., Chapuis, B. and Cerottini,
J. C. (1981). Surface markers of cloned human T cells with various cytolyticactivities. J. Exp. Med. 154, 569-574.
Mori, K., Miyamoto, N., Higuchi, Y., Nanba, K., Ito, M., Tsurudome, M., Nishio,
M., Kawano, M., Uchida, A. and Ito, Y. (2001). Cross-talk between RANKL andFRP-1/CD98 Systems: RANKL-mediated osteoclastogenesis is suppressed by aninhibitory anti-CD98 heavy chain mAb and CD98-mediated osteoclastogenesis issuppressed by osteoclastogenesis inhibitory factor. Cell Immunol. 207, 118-126.
Mori, K., Nishimura, M., Tsurudome, M., Ito, M., Nishio, M., Kawano, M., Kozuka,
Y., Yamashita, Y., Komada, H., Uchida, A. et al. (2004). The functional interaction
between CD98 and CD147 in regulation of virus-induced cell fusion and osteoclast
formation. Med. Microbiol. Immunol. 193, 155-162.
Murphy, K., Travers, P., Walport, M. and Janeway, C. (2011). Janeway’s
immunobiology. New York: Garland Science.
Nakao, M., Kubo, K., Hara, A., Hirohashi, N., Futagami, E., Shichijo, S., Sagawa,
K. and Itoh, K. (1993). A monoclonal antibody (H227) recognizing a new epitope of
4F2 molecular complex associated with T cell activation. Cell Immunol. 152, 226-
233.
Nawashiro, H., Otani, N., Shinomiya, N., Fukui, S., Nomura, N., Yano, A., Shima,
K., Matsuo, H. and Kanai, Y. (2002). The role of CD98 in astrocytic neoplasms.
Hum. Cell 15, 25-31.
Nawashiro, H., Otani, N., Shinomiya, N., Fukui, S., Ooigawa, H., Shima, K.,
Matsuo, H., Kanai, Y. and Endou, H. (2006). L-type amino acid transporter 1 as a
potential molecular target in human astrocytic tumors. Int. J. Cancer 119, 484-492.
Nelson, B. H. and Willerford, D. M. (1998). Biology of the interleukin-2 receptor. Adv.
Immunol. 70, 1-81.
Nguyen, H. T., Dalmasso, G., Yan, Y., Obertone, T. S., Sitaraman, S. V. and Merlin,
D. (2008). Ecto-phosphorylation of CD98 regulates cell-cell interactions. PLoS ONE
3, e3895.
Nguyen, H. T., Dalmasso, G., Yan, Y., Laroui, H., Dahan, S., Mayer, L., Sitaraman,
S. V. and Merlin, D. (2010). MicroRNA-7 modulates CD98 expression during
intestinal epithelial cell differentiation. J. Biol. Chem. 285, 1479-1489.
Nguyen, H. T., Dalmasso, G., Torkvist, L., Halfvarson, J., Yan, Y., Laroui, H.,
Shmerling, D., Tallone, T., D’Amato, M., Sitaraman, S. V. et al. (2011). CD98
expression modulates intestinal homeostasis, inflammation, and colitis-associated
cancer in mice. J. Clin. Invest. 121, 1733-1747.
Nicklin, P., Bergman, P., Zhang, B., Triantafellow, E., Wang, H., Nyfeler, B., Yang,
H., Hild, M., Kung, C., Wilson, C. et al. (2009). Bidirectional transport of amino
acids regulates mTOR and autophagy. Cell 136, 521-534.
Oda, K., Hosoda, N., Endo, H., Saito, K., Tsujihara, K., Yamamura, M., Sakata, T.,
Anzai, N., Wempe, M. F., Kanai, Y. et al. (2010). L-type amino acid transporter 1
inhibitors inhibit tumor cell growth. Cancer Sci. 101, 173-179.
Ohgimoto, S., Tabata, N., Suga, S., Tsurudome, M., Kawano, M., Nishio, M.,
Okamoto, K., Komada, H., Watanabe, N. and Ito, Y. (1996). Regulation of human
immunodeficiency virus gp160-mediated cell fusion by antibodies against fusion
regulatory protein 1. J. Gen. Virol. 77, 2747-2756.
Ohkawa, M., Ohno, Y., Masuko, K., Takeuchi, A., Suda, K., Kubo, A., Kawahara,
R., Okazaki, S., Tanaka, T., Saya, H. et al. (2011). Oncogenicity of L-type amino-
acid transporter 1 (LAT1) revealed by targeted gene disruption in chicken DT40 cells:
LAT1 is a promising molecular target for human cancer therapy. Biochem. Biophys.
Res. Commun. 406, 649-655.
Oleinik, E. K., Shibaev, M. I. and Oleinik, V. M. (2005). [Expression of lymphocyte
activation markers in patients with gastrointestinal tumors at different stages]. Vopr.
Onkol. 51, 571-574.
Palacin, M. (1994). A new family of proteins (rBAT and 4F2hc) involved in cationic
and zwitterionic amino acid transport: a tale of two proteins in search of a transport
function. J. Exp. Biol. 196, 123-137.
Pancer, Z., Saha, N. R., Kasamatsu, J., Suzuki, T., Amemiya, C. T., Kasahara, M.
and Cooper, M. D. (2005). Variable lymphocyte receptors in hagfish. Proc. Natl.
Acad. Sci. USA 102, 9224-9229.
Patterson, J. A., Eisinger, M., Haynes, B. F., Berger, C. L. and Edelson, R. L.
(1984). Monoclonal antibody 4F2 reactive with basal layer keratinocytes: studies in
the normal and a hyperproliferative state. J. Invest. Dermatol. 83, 210-213.
Pineda, M., Fernandez, E., Torrents, D., Estevez, R., Lopez, C., Camps, M.,
Lloberas, J., Zorzano, A. and Palacin, M. (1999). Identification of a membrane
protein, LAT-2, that Co-expresses with 4F2 heavy chain, an L-type amino acid
transport activity with broad specificity for small and large zwitterionic amino acids.
J. Biol. Chem. 274, 19738-19744.
Powlesland, A. S., Hitchen, P. G., Parry, S., Graham, S. A., Barrio, M. M., Elola,
M. T., Mordoh, J., Dell, A., Drickamer, K. and Taylor, M. E. (2009). Targeted
glycoproteomic identification of cancer cell glycosylation. Glycobiology 19, 899-909.
Powlesland, A. S., Barrio, M. M., Mordoh, J., Hitchen, P. G., Dell, A., Drickamer,
K. and Taylor, M. E. (2011). Glycoproteomic characterization of carriers of the
CD15/Lewisx epitope on Hodgkin’s Reed-Sternberg cells. BMC Biochem. 12, 13.
Prager, G. W., Feral, C. C., Kim, C., Han, J. and Ginsberg, M. H. (2007). CD98hc
(SLC3A2) interaction with the integrin beta subunit cytoplasmic domain mediates
adhesive signaling. J. Biol. Chem. 282, 24477-24484.
Prager, G. W., Poettler, M., Schmidinger, M., Mazal, P. R., Susani, M., Zielinski,
C. C. and Haitel, A. (2009). CD98hc (SLC3A2), a novel marker in renal cell cancer.
Eur. J. Clin. Invest. 39, 304-310.
Pritchard-Briscoe, H., McDougall, C. and Inchley, C. J. (1977). Influence of
antigenic competition on the development of antibody-forming cell clones. Clin. Exp.
Immunol. 27, 328-334.
Quackenbush, E. J., Linsley, P. and Letarte, M. (1986). Mouse L cells express a
molecular complex carrying the human epitopes recognized by monoclonal antibodies
44D7 and 44H7 after DNA-mediated gene transfer. J. Immunol. 137, 234-239.
Quackenbush, E., Clabby, M., Gottesdiener, K. M., Barbosa, J., Jones, N. H.,
Strominger, J. L., Speck, S. and Leiden, J. M. (1987). Molecular cloning of
complementary DNAs encoding the heavy chain of the human 4F2 cell-surface
antigen: a type II membrane glycoprotein involved in normal and neoplastic cell
growth. Proc. Natl. Acad. Sci. USA 84, 6526-6530.
CD98, cancer and immunity 1381
Journ
alof
Cell
Scie
nce
Reynolds, B., Laynes, R., Ogmundsdottir, M. H., Boyd, C. A. and Goberdhan, D. C.
(2007). Amino acid transporters and nutrient-sensing mechanisms: new targets fortreating insulin-linked disorders? Biochem. Soc. Trans. 35, 1215-1217.
Reynolds, B., Roversi, P., Laynes, R., Kazi, S., Boyd, C. A. and Goberdhan, D. C.
(2009). Drosophila expresses a CD98 transporter with an evolutionarily conservedstructure and amino acid-transport properties. Biochem. J. 420, 363-372.
Rintoul, R. C., Buttery, R. C., Mackinnon, A. C., Wong, W. S., Mosher, D., Haslett,
C. and Sethi, T. (2002). Cross-linking CD98 promotes integrin-like signaling andanchorage-independent growth. Mol. Biol. Cell 13, 2841-2852.
Saha, N. R., Smith, J. and Amemiya, C. T. (2010). Evolution of adaptive immunerecognition in jawless vertebrates. Semin. Immunol. 22, 25-33.
Salter, D. M., Krajewski, A. S., Sheehan, T., Turner, G., Cuthbert, R. J. and
McLean, A. (1989). Prognostic significance of activation and differentiation antigenexpression in B-cell non-Hodgkin’s lymphoma. J. Pathol. 159, 211-220.
Samuel, M. S., Lopez, J. I., McGhee, E. J., Croft, D. R., Strachan, D., Timpson, P.,
Munro, J., Schroder, E., Zhou, J., Brunton, V. G. et al. (2011). Actomyosin-mediated cellular tension drives increased tissue stiffness and beta-catenin activationto induce epidermal hyperplasia and tumor growth. Cancer Cell 19, 776-791.
Schwartz, M. A. and Assoian, R. K. (2001). Integrins and cell proliferation: regulationof cyclin-dependent kinases via cytoplasmic signaling pathways. J. Cell Sci. 114,2553-2560.
Shennan, D. B. and Thomson, J. (2008). Inhibition of system L (LAT1/CD98hc)reduces the growth of cultured human breast cancer cells. Oncol. Rep. 20, 885-889.
Shennan, D. B., Thomson, J., Barber, M. C. and Travers, M. T. (2003). Functionaland molecular characteristics of system L in human breast cancer cells. Biochim.
Biophys. Acta. 1611, 81-90.
Shibue, T. and Weinberg, R. A. (2009). Integrin beta1-focal adhesion kinase signalingdirects the proliferation of metastatic cancer cells disseminated in the lungs. Proc.
Natl. Acad. Sci. USA 106, 10290-10295.
Shishido, T., Uno, S., Kamohara, M., Tsuneoka-Suzuki, T., Hashimoto, Y.,
Enomoto, T. and Masuko, T. (2000). Transformation of BALB3T3 cells causedby over-expression of rat CD98 heavy chain (HC) requires its association with lightchain: mis-sense mutation in a cysteine residue of CD98HC eliminates itstransforming activity. Int. J. Cancer 87, 311-316.
Spagnoli, G. C., Ausiello, C., Palma, C., Bellone, G., Ippoliti, G., Letarte, M. and
Malavasi, F. (1991). Functional effects of a monoclonal antibody directed against adistinct epitope on 4F2 molecular complex in human peripheral blood mononuclearcell activation. Cell Immunol. 136, 208-218.
Sprent, J. and Surh, C. D. (2002). T cell memory. Annu. Rev. Immunol. 20, 551-579.
Suga, S., Tsurudome, M., Ito, M., Ohgimoto, S., Tabata, N., Nishio, M., Kawano,
M., Komada, H., Ito, M., Sakurai, M. et al. (1997). Human immunodeficiency virustype-1 envelope glycoprotein gp120 induces expression of fusion regulatory protein(FRP)-1/CD98 on CD4+ T cells: a possible regulatory mechanism of HIV-inducedsyncytium formation. Med. Microbiol. Immunol. 185, 237-243.
Taams, L. S., van Rensen, A. J., Poelen, M. C., van Els, C. A., Besseling, A. C.,
Wagenaar, J. P., van Eden, W. and Wauben, M. H. (1998). Anergic T cellsactively suppress T cell responses via the antigen-presenting cell. Eur. J. Immunol. 28,2902-2912.
Takahashi, T., Kuniyasu, Y., Toda, M., Sakaguchi, N., Itoh, M., Iwata, M., Shimizu,
J. and Sakaguchi, S. (1998). Immunologic self-tolerance maintained byCD25+CD4+ naturally anergic and suppressive T cells: induction of autoimmunedisease by breaking their anergic/suppressive state. Int. Immunol. 10, 1969-1980.
Taskov, H., Pashov, A., ffmitrova, E., Yordanova, M. and Serbinova, M. (1996).Levels of CAF7 (CD98) expression correlate with the complete remission duration inchildhood acute leukemia. Leuk. Res. 20, 75-79.
Teixeira, S., Di Grandi, S. and Kuhn, L. C. (1987). Primary structure of the human4F2 antigen heavy chain predicts a transmembrane protein with a cytoplasmic NH2terminus. J. Biol. Chem. 262, 9574-9580.
Torrents, D., Estevez, R., Pineda, M., Fernandez, E., Lloberas, J., Shi, Y. B.,
Zorzano, A. and Palacin, M. (1998). Identification and characterization of amembrane protein (y+L amino acid transporter-1) that associates with 4F2hc toencode the amino acid transport activity y+L. A candidate gene for lysinuric proteinintolerance. J. Biol. Chem. 273, 32437-32445.
Tosi, M. F. (2005). Innate immune responses to infection. J. Allergy Clin. Immunol. 116,241-250.
Tsurudome, M. and Ito, Y. (2000). Function of fusion regulatory proteins (FRPs) inimmune cells and virus-infected cells. Crit. Rev. Immunol. 20, 167-196.
Uinuk-Ool, T., Mayer, W. E., Sato, A., Dongak, R., Cooper, M. D. and Klein, J.
(2002). Lamprey lymphocyte-like cells express homologs of genes involved inimmunologically relevant activities of mammalian lymphocytes. Proc. Natl. Acad.
Sci. USA 99, 14356-14361.Verrey, F. (2003). System L: heteromeric exchangers of large, neutral amino acids
involved in directional transport. Pflugers Arch. 445, 529-533.Verrey, F., Meier, C., Rossier, G. and Kuhn, L. C. (2000). Glycoprotein-associated
amino acid exchangers: broadening the range of transport specificity. Pflugers Arch.
440, 503-512.Walker, J. L. and Assoian, R. K. (2005). Integrin-dependent signal transduction
regulating cyclin D1 expression and G1 phase cell cycle progression. Cancer
Metastasis Rev. 24, 383-393.Warren, A. P., Patel, K., McConkey, D. J. and Palacios, R. (1996). CD98: a type II
transmembrane glycoprotein expressed from the beginning of primitive and definitivehematopoiesis may play a critical role in the development of hematopoietic cells.Blood 87, 3676-3687.
Weaver, C. T., Hatton, R. D., Mangan, P. R. and Harrington, L. E. (2007). IL-17family cytokines and the expanding diversity of effector T cell lineages. Annu. Rev.
Immunol. 25, 821-852.Wise, D. R. and Thompson, C. B. (2010). Glutamine addiction: a new therapeutic
target in cancer. Trends Biochem. Sci. 35, 427-433.Xiao, T., Ying, W., Li, L., Hu, Z., Ma, Y., Jiao, L., Ma, J., Cai, Y., Lin, D., Guo, S.
et al. (2005). An approach to studying lung cancer-related proteins in human blood.Mol. Cell. Proteomics 4, 1480-1486.
Yagita, H., Masuko, T. and Hashimoto, Y. (1986). Inhibition of tumor cell growth invitro by murine monoclonal antibodies that recognize a proliferation-associated cellsurface antigen system in rats and humans. Cancer Res. 46, 1478-1484.
Yamauchi, K., Sakurai, H., Kimura, T., Wiriyasermkul, P., Nagamori, S., Kanai, Y.
and Kohno, N. (2009). System L amino acid transporter inhibitor enhances anti-tumor activity of cisplatin in a head and neck squamous cell carcinoma cell line.Cancer Lett. 276, 95-101.
Zent, R., Fenczik, C. A., Calderwood, D. A., Liu, S., Dellos, M. and Ginsberg, M. H.(2000). Class- and splice variant-specific association of CD98 with integrin betacytoplasmic domains. J. Biol. Chem. 275, 5059-5064.
Zhang, D. J., Wang, Q., Wei, J., Baimukanova, G., Buchholz, F., Stewart, A. F.,
Mao, X. and Killeen, N. (2005). Selective expression of the Cre recombinase in late-stage thymocytes using the distal promoter of the Lck gene. J. Immunol. 174, 6725-6731.
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