A role for AP-1 in apoptosis: the case for and against

M. Ameyar, M. Wisniewska, J.B. Weitzman *

Unit of Gene Expression and Disease, Department of Developmental Biology, Fernbach Building, Institut Pasteur,25, rue du Docteur-Roux, 75724 Paris cedex 15, France

Received 15 April 2003; accepted 4 September 2003

Abstract

The nuclear transcription factor AP-1, composed of dimers of Fos and Jun proteins, has been linked to a startling breadth of cellular eventsincluding cell transformation, proliferation, differentiation and apoptosis. AP-1 is often portrayed as a general, nuclear decision-maker thatdetermines life or death cell fates in response to extracellular stimuli. However, it is increasingly clear that the cellular context is critical fordetermining the contribution of AP-1 to cellular fates, and the role of AP-1 in apoptosis should be considered within the context of a complexnetwork of nuclear factors that respond simultaneously to a wide range of signal transduction pathways. We take a closer look at the evidencefor and against a role for AP-1 in inducing apoptosis, drawing on examples of studies in neurons, lymphocytes and hepatocytes. Although AP-1activation is associated with a large number of apoptotic scenarois, its role in ensuring cell survival seems equally important. It is, therefore,difficult to convict AP-1 as a killer without taking into account the cellular and extracellular context within which it is functioning. Definingthe target genes regulated by AP-1 in these different contexts will help to decipher the contribution of AP-1 to cell fate decisions.

© 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.

Keywords: Apoptosis; AP-1; Jun; JNK

1. Introduction

So much has been written about the role of the AP-1transcription factor in determining cell death, that one mightexpect the evidence linking AP-1 to apoptosis to be over-whelmingly convincing. However, if one plunges into theliterature, however, a complex picture emerges in whichAP-1 can function to induce apoptosis in some cellular sys-tems, but is required for cell survival in others. AP-1 issometimes portrayed as a nuclear decision-maker that deter-mines life or death cell fates [1,2]. It is increasingly clear,however, that the cellular context is critical for determiningthe contribution of AP-1 to cellular fates, and the role of AP-1in apoptosis should be considered within the context of acomplex network of nuclear factors that respond simulta-neously to a wide range of signal transduction pathways.Deciphering the molecular mechanisms by which AP-1 acti-vation leads to apoptosis, or survival, remains a formidablechallenge and we have only begun to determine the AP-1-regulated target genes that contribute to the apoptotic pro-

gram. We refer the reader to earlier reviews that describeAP-1 regulation and function in more comprehensive detail[3–5]. Here, we have chosen to focus on a number of casestudies to highlight the challenge of uncovering the role ofAP-1 in apoptosis. These examples from different cell sys-tems illustrate how the problem has been tackled and presentthe case for and against a role for AP-1 in inducing apoptosis.The jury is still out, and we leave the reader to consider theevidence for and against.

The complexity of the problem begins with AP-1 itself.For AP-1 is not a single protein, but a mixture of dimers thatare composed of members of the Jun family (c-Jun, JunB andJunD) of basic leucine-zipper (bZIP) proteins associatedwith related proteins of the Fos (c-Fos, FosB, Fra1 and Fra2)or ATF families. Each of these proteins is differently ex-pressed and regulated, so that every cell contains a complexmixture of AP-1 dimers with subtly different functions. Theoutcome of AP-1 activation is dependent on the complexcombinatorial of AP-1 dimers. The AP-1 complex binds to apalindromic DNA motif (5′-TGAG/CTCA-3′) to regulategene expression. AP-1 activity is induced by a startlinglybroad range of extracellular stimuli including mitogens, hor-mones, extracellular matrix and genotoxic agents. Many of

* Corresponding author. Tel.: +33-1-45-68-85-15;fax: +33-1-40-61-30-33.

E-mail address: jonathan.weitzman@pasteur.fr (J.B. Weitzman).

Biochimie 85 (2003) 747–752

www.elsevier.com/locate/biochi

© 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.doi:10.1016/j.biochi.2003.09.006

these stimuli activate the c-Jun N-terminal kinases (JNKs)leading to the phosphorylation of Jun proteins and enhancedtranscriptional activity. Increases in the levels of Jun and Fosproteins and JNK activity have been reported in many sce-narios in which cells undergo apoptosis [6–8]. We havefocused our discussion primarily on the Jun family and at-tempt to highlight examples that provide a mechanistic andconceptual insight.

1.1. Case 1: neuronal apoptosis: the mitochondrialconnection

About half of the original population of neurons is elimi-nated by apoptosis during development of the nervous sys-tem. This cell death is critical for ensuring the correct con-nections in the developing brain and deregulated cell deathcontributes to the pathology of human neurodegenerativedisorders. The balance between pro- and anti-apoptotic Bcl-2members seems important for neuronal survival during de-velopment. The disruption of genes encoding components ofBcl-2/cytochrome c/Apaf-1/caspases pathway clearly dem-onstrated that the mitochondrial death pathway is importantin neuronal apoptosis [9].

When neurons are deprived of nerve growth factor (NGF),they die by apoptosis. Early experiments showed that NGFwithdrawal leads to increased c-Jun levels and c-Jun phos-phorylation in neurons in culture [6,7]. Microinjection of adominant-negative c-Jun isoform blocks cell death, indicat-ing that AP-1 activity is necessary for neural cell death [6].Moreover, the essential role of c-Jun in NGF withdrawal-induced cell death was recently confirmed, using a Cre-loxsystem, which allowed the conditional deletion of c-jun insympathic neurons in vitro [10]. Numerous subsequent stud-ies have provided further evidence regarding the essentialrole of JNK and c-Jun activation in neural cell death inducedby diverse stimuli (withdrawal of trophic support, DNA dam-age, oxidative stress, b-amyloid exposure, and excitotoxicstress). The functional importance of c-Jun and JNK in neu-ral cell death was confirmed in vivo using mice lacking thebrain-specific jnk3 gene or in JunAA mice in which theendogenous gene encoding c-Jun was replaced with a mutantjun allele lacking the Ser 63/73 JNK phospho-acceptor sites[11,12]. In both cases, mice were resistant to epileptic sei-zures and neural apoptosis in the hippocampal CA3 regioninduced by kainic acid, an excitotoxic glutamate-receptoragonist. Thus, the case for Jun and JNK as inducers ofneuronal cell death seems relatively clear-cut. However,studies of other AP-1 components offer a cautionary note.c-Fos and JunD are induced during light-induced apoptosisof retinal photoreceptors. Photoreceptor death is impaired inc-Fos-deficient mice, but is unaffected in JunD-deficient ani-mals [13,14]. Also, although c-Fos is induced by kainic acid,mice lacking c-Fos expression in the hippocampus exhibitincreased neuronal dell death during kainate-induced sei-zures [15].

One important issue to be resolved is the determination ofthe specific signaling cascades that lead to c-Jun/JNK activa-

tion and culminate in transcriptional regulation of death-associated genes. One such cascade implicates the sequentialactivation of Rac1/Cdc42, mixed lineage kinases (MLK),MKK4 and 7, and JNK. Recently, an elegant mechanism ofactivation was elucidated by Xu et al. [16] who demonstratedthat the multidomain POSH protein is an upstream activatorof this pathway and acts as a scaffold protein to induceJNK-mediated neural cell death. Overexpression of POSHinduced neural cell death is caspase-dependent and seems tobe associated with cytochrome c release. However, it shouldbe noted that JNK has additional substrates that may affectneuronal function independently of AP-1 activation.

JNK activation is known to be required for the regulationof stress-induced mitochondrial death pathway. JNK defi-ciency in primary MEF leads to a defect in the mitochondrialapoptotic pathway after ultraviolet (UV) treatment, includingthe failure to release cytochrome c [17]. JNK is also known tophosphorylate Bcl-2 and Bcl-xl, but it is unclear whether thisphosphorylation inactivates their anti-apoptotic functions.Gene disruption studies also demonstrated that pro-apoptoticmembers of the Bax protein subfamily are essential for JNKinduced apoptosis in murine fibroblasts [18]. Among themost exciting recent results, are those demonstrating thatsome BH3-only Bcl-2 family members, such as Bim andDP5/Hrk, induce neural cell death by a mechanism depen-dent on the JNK/Jun pathway [19–21]. Ectopic expression ofa dominant-negative mutant of c-Jun in sympathic neuronsdeprived of NGF prevents the release of cytochrome c andreduced the amount of Bim transcripts [19]. In cerebellargranular neurons undergoing apoptosis induced by potas-sium or NGF deprivation, Bim and DP5/Hrk mRNA areinduced in a manner that is clearly JNK-dependent. Interest-ingly, it was recently shown that UV irradiation induced JNKphosphorylation of Bim, as well as another BH3-only Bcl-2family member Bmf, in 293T kidney cells. This phosphory-lation released these two proteins from dynein and myosin Vmotor complexes, where they were sequestered, and mightinduce the apoptotic mitochondrial pathway via Bax/Bafactivation [21]. It will be interesting to see if similar mecha-nisms occur in neuronal cell death. However, it is importantto distinguish the apoptotic program induced by JNK infibroblasts and in neurons. In the former, UV-induced apop-tosis may be dependent on post-transcriptional regulation ofpro-apoptotic members of the Bax subfamily, whereas theapoptotic program induced by NGF withdrawal seems to beregulated by induction of c-Jun and Bim at the transcriptionallevel [12,18,19].

The importance of neuronal cell death control is under-scored by the numerous pathologies associated with deregu-lated apoptosis. It was recently demonstrated that the neuro-toxic b-amyloid peptide (Ab), an important protein in thepathogenesis of Alzheimer’s disease, induced apoptosis ofcerebral endothelial cells via AP-1 activation and subsequentBim induction [22]. Thus, one can comfortably argue thatAP-1/Bim may represent a strategic axis during the neuronalapoptotic cascade and offers a potential therapeutic approach

748 M. Ameyar et al. / Biochimie 85 (2003) 747–752

by targeting the JNK/c-Jun/Bim pathway to promote neu-ronal cell survival.

1.2. Case 2: life in the Fas lane in lymphoid cells

Cell death induced by Fas ligand (FasL) is a classic ex-ample of apoptosis induced by an external signal [23]. TheFas cell membrane protein belongs to the tumor necrosisfactor receptor (TNF) family, or so called “death receptors”.The Fas/FasL system is specifically important for the properaction of the immune system and immune cell homeostasis,although is not limited to lymphoid cells. This system isinvolved in activation induced cell death (AICD) during thedeletion of peripheral lymphocytes, as well as in T-cell medi-ated cytotoxicity. It is also implicated in establishing theimmune privilege that delineates forbidden zones for lym-phocytes, like the eye and testes, and that helps some tumorsto counterattack the immune system. Finally, the Fas/FasLsystem is often turned on in various cell-types by stressconditions, such as heat-shock, genotoxic insult, UV orc-irradiation and by growth factor withdrawal. Fas is ex-pressed in most tissues and is activated by its inducible ligandFasL. Fas/FasL cross-linking leads to activation of caspase8 activation and subsequent death. Although the execution ofFasL-mediated apoptosis does not seem to depend on proteinsynthesis, the initiation of this process is one of the fewwell-understood examples of transcription factors regulatingapoptosis. In contrast to the ubiquitously expressed Fas, theFasL gene is only expressed in certain cell-types or uponstimulation. The regulation of FasL transcription is a key stepin the induction of apoptosis and there is evidence that AP-1is an important player in the Fas team.

Kasibhatla et al. [24] observed activation of JNK andAP-1in Jurkat cells after exposure to DNA-damaging chemicals.JNK activation appeared to be upstream of Fas/FasL interac-tion and a dominant-negative MEKK1 mutant could inhibitboth apoptosis and FasL promoter expression. Mutation of aputative AP-1 binding site abrogated DNA damage-inducedFasL promoter activity. The same series of events—JNKactivation, c-Jun phosphorylation and subsequent FasLexpression—was observed by Le Niculescu et al. [25] duringapoptosis of MEKK1 overexpressing neuronal PC12 cells.The importance of c-Jun phosphorylation in the nervoussystem was demonstrated by the fact that expression of thec-JunAA phosphorylation-defective mutant decreased celldeath [11]. Promotor analysis in T cell lines and hepatomacells has identified several AP-1 binding sites in the FasLpromoter [24,26,27] and one AP-1-like site that bound toc-Jun and ATF2 in super-shift assays [28]. Together thesedata reveal a role for c-Jun in regulating FasL expression,implicating AP-1 in FasL-mediated cell death. Kolbus et al.[29] provided further evidence that AP-1, or at least c-Jun, isindispensable for FasL-mediated cell death. They usedc-jun–/– mouse fibroblasts to study the apoptosis inducedby genotoxic stress. Unlike wild-type cells, c-Jun-deficient fibroblasts were resistant to apoptosis and this wasaccompanied by impaired expression of FasL. Recombinant

FasL could restore sensitivity to DNA damage-induce death.These results showed that c-Jun is crucial for FasL expres-sion and the initiation of stress-induced FasL-mediated celldeath.

Regulation of peripheral T cells population seems to bethe major role of FasL-mediated apoptosis in vivo. It isdisappointing that the involvement of AP-1 in this physi-ological cell death process remains elusive. In vitro studieson AICD and JNK/AP-1 have provided contradictory results.Ionomycin + PMA-induced FasL promotor activity in Jurkatcells does not seem to be AP-1-dependent. The promotor isnot activated by ectopic c-Jun/c-Fos expression, neitheralone nor in combination with NFAT transcription factor, apotential AP-1 partner [30], and DN-MEKK1 failed to in-hibit the FasL promotor [24]. Experiments using more physi-ological stimulation with anti-CD3 gave opposite results.DN-JNK2 inhibits both TCR-induced FasL expression andAICD in the DO11.10 T cell hybrydoma line [31]. Further-more, expression of a DN-c-Jun mutant blocked TCR-induced apoptosis of Jurkat cells [32]. It has been proposedthat AP-1 does not act alone after TCR-stimulation, butaffects FasL expression in cooperation with NFAT in the caseof AICD [33].

Thus, the potential role of AP-1 in AICD in vitro appearsto depend on the type of stimulation, and its involvement inAICD in vivo is far from established. Some light is shed onthe question by studies conducted on JNK2-deficient andDN-JNK transgenic mice [34,35]. In fact, AICD of periph-eral T cells is not impaired in these animals, but they dodisplay a minor defect in thymocyte negative selection and invivo anti-CD3 treatment. However, although negative selec-tion in the thymus is a type of AICD, the involvement of FasLdoes not seem to be crucial. Moreover, Fas-mediated thy-mocyte apoptosis is not impaired in JNK2-deficient orJunAA mutant mice [34,36]. These data question the signifi-cance of the link between AP-1, c-Jun phosphorylation andFasL-mediated AICD.

Further confusion is added by experiments suggesting thatc-Jun may be involved in Fas promoter inhibition, implyingthat AP-1 can also have a protective effect in some particularcases. Downregulation of Fas is frequently observed duringtumor progression. Ivanov et al. demonstrated that ectopicexpression of dominant-negative mutant of c-Jun (TAM67)led to increased Fas promoter activity and Fas mRNA levelin melanoma cells. They also showed that cjun–/– fibroblastsexhibit an increase in Fas expression and forced c-Jun ex-pression in these cells to reduced Fas levels. Interestingly,c-Jun may form a complex with the STAT3 transcriptionfactor to drive Fas promoter inhibition [37].

1.3. Case 3: Lessons from liver: the link with p53

The examples discussed above demonstrate that a case canclearly be made for a role for AP-1 in inducing apoptosis. Jun

749M. Ameyar et al. / Biochimie 85 (2003) 747–752

and JNK signaling are capable of regulating genes encodingdeath receptors (extrinsic death pathway) and Bcl-2-familymembers (intrinsic mitochondrial pathway) in the immuneand nervous systems. These examples show that Jun/JNKactivation can lead to the upregulation of pro-apoptotic genesin some conditions. But a closer look at studies in differenttissues suggests that it may be difficult, if not perhaps impos-sible, to generalize a pro-apoptotic role to other cell-types.Indeed, an emerging scenario is that AP-1 functions areheavily dependent on the specific Fos and Jun subunits con-tributing to AP-1 dimers and the cellular context. Severalrecent results challenge the simple models that have beendeveloped to describe the role of AP-1 in apoptosis.

Knockout mice offer an attractive alternative to overex-pression strategies to investigate AP-1 functions in apoptosis.c-jun was the first jun family gene to be inactivated in miceby homologous recombination. Embryos lacking c-Jun die atmidgestation and exhibit defects in hepatogenesis. There is adramatic increase in apoptosis in fetal livers in the absence ofc-Jun [38]. Inactivating c-jun gene expression in adult liverprimarily affected cell cycle progression, suggesting thatc-Jun may regulate a survival response that is linked to thedifferentiation state of the cell [39]. Interestingly, the fetalliver apoptosis could be rescued by a c-Jun allele (cJunAA)in which the major JNK phosphorylation sites were mutated,or even by a JunB knock-in allele [11,40]. Mice lacking therelated JunD gene are viable and appear relatively healthy.But the lack of JunD renders animals sensitive to LPS-induced apoptosis in the liver [41]. These genetic experi-ments seem to suggest that Jun/AP-1 has a survival role inliver cells. Identifying the AP-1-regulated genes required forsurvival functions is likely to be as challenging as findingpro-apoptotic AP-1 target genes.

It is tempting to speculate about the relationship betweenAP-1 and the tumor suppressor protein p53 in the context ofapoptosis. Both AP-1 and p53 are nuclear transcription fac-tors, both are regulated post-translationally by stress signal-ing pathways, both can induce apoptosis in response to geno-toxic agents, and both activate extrinsic and mitochondrialdeath pathway components. Furthermore, JNK can phospho-rylate p53 and induces protein stabilization. The parallels arestriking. Several recent observations have linked AP-1 tomodulation of the p53 pathway to explain the role of AP-1 incell survival.

Genetic experiments in mice have shown that Jun proteinscan inhibit p53-dependent apoptosis in a number of situa-tions, but the molecular mechanisms are not entirely clear.Mouse embryonic fibroblast cells lacking JunD display ap53-dependent growth arrest and are exquisitely sensitive toapoptosis induced by stress stimuli such as UV irradiation orcytotoxic cytokines, such as tumor necrosis factor-a (TNF-a)[41]. This phenotype is associated with an upregulation ofthe p19Arf protein that stabilizes p53. Our experiments sug-gest that specific AP-1 dimers can regulate expression of themouse and human p14/p19Arf genes (M. Ameyar and J.B.Weitzman, unpublished data). These experiments place AP-1

upstream of the p19Arf/p53 family in the cellular stress re-sponse. c-Jun has also been shown to modulate p53 byrepressing transcription of the tp53 gene promoter. Mousefibroblasts lacking c-Jun exhibit upregulated p53 mRNA andprotein levels, leading to decreased proliferation [42]. Fur-thermore, impaired cell-cycle re-entry following UV irradia-tion of c-Jun null cells is due to regulation of the binding ofp53 to the promoter of the p21/Cip1 gene [43].

A recent study has provided compelling evidence that theoncogenic properties of c-Jun may be linked to antagonismof the pro-apoptotic activity of p53. Liver-specific inactiva-tion of the c-Jun gene demonstrated an essential role in thedevelopment of chemically induced hepatocellular carcino-mas (HCCs) [44]. Tumors that developed in the absence ofhepatic c-Jun expression had increased levels of apoptosis.And c-Jun null hepatocytes were sensitized to TNF-a-induced apoptosis. The absence of c-Jun in HCC tumors waslinked to elevated levels of p53 and it is pro-apoptotic targetgene, Noxa (without affecting other pro-apoptotic p53 tar-gets) [44].

Thus, a series of experiments with genetically modifiedmice and cells lacking Jun proteins have shown that AP-1 canplay a role in promoting cell survival. The link betweenJun/AP-1 and p53 pathways appears complex, but it is pos-sible that AP-1 factors have developed multiple ways ofregulating p53, either by modulating the p53-regulatorp14/p19Arf, by inhibiting transcription of the p53 gene or byregulating p53 activity and promoter binding or selectivity.We also have evidence that p53 activity can lie upstream ofJNK signaling and Jun activation (J.B. Weitzman, unpub-lished data), adding further complexity to the network ofAP-1/p53 interactions. And under some circumstances p53can induce expression of the genes encoding different AP-1components, such as c-Fos [45].

The study of Jun function in mouse livers and embryonicfibroblasts cells derived from knockout mice has highlightedthat AP-1 can have an important role in cell survival. AP-1has been functionally linked to the p53. Understanding thecomplex interactions between AP-1 and p53-regulated net-works will be critical to understanding their distinct andoverlapping functions in apoptosis and tumorigenesis.

2. The verdict

The examples cited above highlight how difficult it is toextract clear conclusions about the role of AP-1 in apoptosis.It seems likely that AP-1 can be pro-apoptotic in certaincell-types and pro-survival in others. Defining the precisedevelopmental and stage-specific apoptotic events in vivo,will deepen our understanding of the relevance of much ofthe conflicting data from studies in cell cultures. There arestill only a handful of characterized AP-1-regulated targetgenes that may account for its apoptotic functions. Identify-ing more target genes and investigating their promoters islikely provide insights into how AP-1 cooperates with othertranscription factors, in a cell-type specific manner, to deter-

750 M. Ameyar et al. / Biochimie 85 (2003) 747–752

mine when and how cells die or survive. Ultimately, it will beimportant to attempt to link changes in AP-1 activity tohuman diseases, such as cancer or neurodegenerative disor-ders, in which normal apoptosis is deregulated.

Acknowledgements

Work in our laboratory is supported by the Center Na-tional pour la Recherche Scientifique (CNRS), the Associa-tion for International Cancer Research (AICR), the EuropeanUnion, l’Association pour la Recherche Contre le Cancer(ARC). A.M. was supported by grants from the PasteurInstitute and La Ligue Nationale Contre Le Cancer. M.W.was supported by grants from AICR and La Fondation PourLa Recherche Médicale (FRM). We thank Moshe Yaniv forhis endless encouragement and support, and members of theYaniv laboratory for lively discussions.

References

[1] E. Shaulian, M. Karin, AP-1 in cell proliferation and survival, Onco-gene 20 (2001) 2390–2400.

[2] J.B. Weitzman, Life and death in the Jungle, Trends Mol. Med. 7(2001) 141–142.

[3] F. Mechta-Grigoriou, D. Gerald, M. Yaniv, The mammalian Junproteins: redundancy and specificity, Oncogene 20 (2001) 2378–2389.

[4] W. Jochum, E. Passegue, E.F. Wagner, AP-1 in mouse developmentand tumorigenesis, Oncogene 20 (2001) 2401–2412.

[5] E. Shaulian, M. Karin, AP-1 as a regulator of cell life and death, Nat.Cell Biol. 4 (2002) E131–E136.

[6] J. Ham, C. Babij, J. Whitfield, C.M. Pfarr, D. Lallemand, M. Yaniv,L.L. Rubin, A c-Jun dominant negative mutant protects sympatheticneurons against programmed cell death, Neuron 14 (1995) 927–939.

[7] S. Estus, W.J. Zaks, R.S. Freeman, M. Gruda, R. Bravo,E.M. Johnson Jr, Altered gene expression in neurons during pro-grammed cell death: identification of c-jun as necessary for neuronalapoptosis, J. Cell. Biol. 127 (1994) 1717–1727.

[8] E. Bossy-Wetzel, L. Bakiri, M. Yaniv, Induction of apoptosis by thetranscription factor c-Jun, EMBO J. 16 (1997) 1695–1709.

[9] D. Nijhawan, N. Honarpour, X. Wang, Apoptosis in neural develop-ment and disease, Annu. Rev. Neurosci. 23 (2000) 73–87.

[10] M. Palmada, S. Kanwal, N.J. Rutkoski, C. Gustafson-Brown,R.S. Johnson, R. Wisdom, B.D. Carter, c-jun is essential for sympa-thetic neuronal death induced by NGF withdrawal but not by p75activation, J. Cell. Biol. 158 (2002) 453–461.

[11] A. Behrens, M. Sibilia, E.F. Wagner, Amino-terminal phosphorylationof c-Jun regulates stress-induced apoptosis and cellular proliferation,Nat. Genet. 21 (1999) 326–329.

[12] D.D. Yang, C.Y. Kuan, A.J. Whitmarsh, M. Rincon, T.S. Zheng,R.J. Davis, P. Rakic, R.A. Flavell, Absence of excitotoxicity-inducedapoptosis in the hippocampus of mice lacking the Jnk3 gene, Nature389 (1997) 865–870.

[13] F. Hafezi, C. Grimm, A. Wenzel, H. Weitzman, M. Abegg, M. Yaniv,Retinal photoreceptors are apoptosis-competent in the absence ofJunD/AP-1, Cell Death Differ. 6 (1999) 934–936.

[14] K.A. Rich,Y. Zhan, J.C. Blanks, Aberrant expression of c-Fos accom-panies photoreceptor cell death in the rd mouse, J. Neurobiol. 32(1997) 593–612.

[15] J. Zhang, D. Zhang, J.S. Mcquade, M. Behbehani, J.Z. Tsien, M. Xu,c-fos regulates neuronal excitability and survival, Nat. Genet. 30(2002) 416–420.

[16] Z. Xu, N.V. Kukekov, L.A. Greene, POSH acts as a scaffold for amultiprotein complex that mediates JNK activation in apoptosis,EMBO J. 22 (2003) 252–261.

[17] C. Tournier, P. Hess, D.D. Yang, J. Xu, T.K. Turner, A. Nimnual,D. Bar-Sagi, S.N. Jones, R.A. Flavell, R.J. Davis, Requirement ofJNK for stress-induced activation of the cytochrome c-mediated deathpathway, Science 288 (2000) 870–874.

[18] K. Lei, A. Nimnual, W.X. Zong, N.J. Kennedy, R.A. Flavell,C.B. Thompson, D. Bar-Sagi, R.J. Davis, The Bax subfamily ofBcl2-related proteins is essential for apoptotic signal transduction byc-Jun NH(2)-terminal kinase, Mol. Cell. Biol. 22 (2002) 4929–4942.

[19] J. Whitfield, S.J. Neame, L. Paquet, O. Bernard, J. Ham, Dominant-negative c-Jun promotes neuronal survival by reducing BIM expres-sion and inhibiting mitochondrial cytochrome c release, Neuron 29(2001) 629–643.

[20] C.A. Harris, E.M. Johnson Jr, BH3-only Bcl-2 family members arecoordinately regulated by the JNK pathway and require Bax to induceapoptosis in neurons, J. Biol. Chem. 276 (2001) 37754–37760.

[21] K. Lei, R.J. Davis, JNK phosphorylation of Bim-related members ofthe Bcl2 family induces Bax-dependent apoptosis, Proc. Natl. Acad.Sci. USA 100 (2003) 2432–2437.

[22] K.J.Yin, J.M. Lee, S.D. Chen, J. Xu, C.Y. Hsu, Amyloid-beta inducesSmac release via AP-1/Bim activation in cerebral endothelial cells, J.Neurosci. 22 (2002) 9764–9770.

[23] P.H. Krammer, CD95’s deadly mission in the immune system, Nature407 (2000) 789–795.

[24] S. Kasibhatla, T. Brunner, L. Genestier, F. Echeverri, A. Mahboubi,D.R. Green, DNA damaging agents induce expression of Fas ligandand subsequent apoptosis in T lymphocytes via the activation ofNF-kappa B and AP-1, Mol. Cell 1 (1998) 543–551.

[25] H. Le-Niculescu, E. Bonfoco, Y. Kasuya, F.X. Claret, D.R. Green,M. Karin, Withdrawal of survival factors results in activation of theJNK pathway in neuronal cells leading to Fas ligand induction and celldeath, Mol. Cell. Biol. 19 (1999) 751–763.

[26] S.T. Eichhorst, M. Muller, M. Li-Weber, H. Schulze-Bergkamen,P. Angel, P.H. Krammer, A novel AP-1 element in the CD95 ligandpromoter is required for induction of apoptosis in hepatocellularcarcinoma cells upon treatment with anticancer drugs, Mol. Cell. Biol.20 (2000) 7826–7837.

[27] K. Matsui, S. Xiao, A. Fine, S.T. Ju, Role of activator protein-1 inTCR-mediated regulation of the murine fasl promoter, J. Immunol.164 (2000) 3002–3008.

[28] M. Faris, K.M. Latinis, S.J. Kempiak, G.A. Koretzky, A. Nel, Stress-induced Fas ligand expression in T cells is mediated through a MEKkinase 1-regulated response element in the Fas ligand promoter, Mol.Cell. Biol. 18 (1998) 5414–5424.

[29] A. Kolbus, I. Herr, M. Schreiber, K.M. Debatin, E.F. Wagner, P.Angel,c-Jun-dependent CD95-L expression is a rate-limiting step in theinduction of apoptosis by alkylating agents, Mol. Cell. Biol. 20 (2000)575–582.

[30] C.J. Holtz-Heppelmann, A. Algeciras, A.D. Badley, C.V. Paya, Tran-scriptional regulation of the human FasL promoter-enhancer region, J.Biol. Chem. 273 (1998) 4416–4423.

[31] J. Zhang, J.X. Gao, K. Salojin, Q. Shao, M. Grattan, C. Meagher,D.W. Laird, T.L. Delovitch, Regulation of fas ligand expression dur-ing activation-induced cell death in T cells by p38 mitogen-activatedprotein kinase and c-Jun NH2-terminal kinase, J. Exp. Med. 191(2000) 1017–1030.

[32] S. Baumann, J. Hess, S.T. Eichhorst, A. Krueger, P. Angel, P.H. Kram-mer, S. Kirchhoff, An unexpected role for FosB in activation-inducedcell death of T cells, Oncogene 22 (2003) 1333–1339.

[33] F. Macian, C. Garcia-Rodriguez, A. Rao, Gene expression elicited byNFAT in the presence or absence of cooperative recruitment of Fosand Jun, EMBO J. 19 (2000) 4783–4795.

751M. Ameyar et al. / Biochimie 85 (2003) 747–752

[34] K. Sabapathy, Y. Hu, T. Kallunki, M. Schreiber, J.P. David,W. Jochum, E.F. Wagner, M. Karin, JNK2 is required for efficientT-cell activation and apoptosis but not for normal lymphocyte devel-opment, Curr. Biol. 9 (1999) 116–125.

[35] M. Rincon, A. Whitmarsh, D.D. Yang, L. Weiss, B. Derijard,P. Jayaraj, R.J. Davis, R.A. Flavell, The JNK pathway regulates the Invivo deletion of immature CD4(+)CD8(+) thymocytes, J. Exp. Med.188 (1998) 1817–1830.

[36] A. Behrens, K. Sabapathy, I. Graef, M. Cleary, G.R. Crabtree,E.F. Wagner, Jun N-terminal kinase 2 modulates thymocyte apoptosisand T cell activation through c-Jun and nuclear factor of activated Tcell (NF-AT), Proc. Natl. Acad. Sci. USA 98 (2001) 1769–1774.

[37] V.N. Ivanov, A. Bhoumik, M. Krasilnikov, R. Raz, L.B. Owen-Schaub, D. Levy, C.M. Horvath, Z. Ronai, Cooperation betweenSTAT3 and c-jun suppresses Fas transcription, Mol. Cell 7 (2001)517–528.

[38] R. Eferl, M. Sibilia, F. Hilberg, A. Fuchsbichler, I. Kufferath,B. Guertl, R. Zenz, E.F. Wagner, K. Zatloukal, Functions of c-Jun inliver and heart development, J. Cell. Biol. 145 (1999) 1049–1061.

[39] A. Behrens, M. Sibilia, J.P. David, U. Mohle-Steinlein, F. Tronche,G. Schutz, E.F. Wagner, Impaired postnatal hepatocyte proliferationand liver regeneration in mice lacking c-jun in the liver, EMBO J. 21(2002) 1782–1790.

[40] E. Passegue, W. Jochum, A. Behrens, R. Ricci, E.F. Wagner, JunB cansubstitute for Jun in mouse development and cell proliferation, Nat.Genet. 30 (2002) 158–166.

[41] J.B. Weitzman, L. Fiette, K. Matsuo, M. Yaniv, JunD protects cellsfrom p53-dependent senescence and apoptosis, Mol. Cell 6 (2000)1109–1119.

[42] M. Schreiber, A. Kolbus, F. Piu, A. Szabowski, U. Mohle-Steinlein,J. Tian, M. Karin, P. Angel, E.F. Wagner, Control of cell cycle progres-sion by c-Jun is p53 dependent, Genes Dev. 13 (1999) 607–619.

[43] E. Shaulian, M. Schreiber, F. Piu, M. Beeche, E.F. Wagner, M. Karin,The mammalian UV response: c-Jun induction is required for exitfrom p53-imposed growth arrest, Cell 103 (2000) 897–907.

[44] R. Eferl, R. Ricci, L. Kenner, R. Zenz, J.P. David, M. Rath, E.F. Wag-ner, Liver tumor development. c-Jun antagonizes the proapoptoticactivity of p53, Cell 112 (2003) 181–192.

[45] A. Elkeles, T. Juven-Gershon, D. Israeli, S. Wilder, A. Zalcenstein,M. Oren, The c-fos proto-oncogene is a target for transactivation bythe p53 tumor suppressor, Mol. Cell. Biol. 19 (1999) 2594–2600.

752 M. Ameyar et al. / Biochimie 85 (2003) 747–752