NFκB Controls the Balance between Fas and Tumor Necrosis Factor Cell Death Pathways during T Cell Receptor-induced Apoptosis Via the Expression of Its Target Gene A20

Abstract

Activation-induced cell death (AICD), a term originally coined for the anti-CD3-induced apoptosis of T cell hybridomas and thymocytes, is predominantly driven by death receptors and has been involved in the control of autoreactive T cells in the periphery. In the Do-11.10 T cell hybridoma model of AICD, activation of the T cell receptor (TCR) results in Fas-dependent apoptosis. Here, we show that inhibition of the transcription factor nuclear factor κB (NFκB) in Do-11.10 cells resulted in increased sensitivity to TCR-mediated apoptosis, correlating with defective induction of the anti-apoptotic NFκB target gene A20. Stable expression of the zinc finger protein A20 in NFκB-negative Do-11.10 cells rescued the phenotype. TCR activation in NFκB-deficient Do-11.10 cells resulted predominantly in tumor necrosis factor (TNF) receptor 2 (TNFR2)-dependent bystander cell death rather than classical Fas-dependent AICD. Strikingly, A20 blocked TNF-mediated apoptosis and simultaneously restored TCR-induced Fas-dependent AICD. In addition, NFκB downstream of TNFR was required for up-regulation of Fas expression by endogenous TNF secreted in response to TCR stimulation. Together, these results suggest that NFκB can play both pro- and anti-apoptotic roles during AICD. We propose that NFκB controls the balance between Fas and TNF cell death pathways during AICD via the expression of the zinc finger protein A20. Activation-induced cell death (AICD), a term originally coined for the anti-CD3-induced apoptosis of T cell hybridomas and thymocytes, is predominantly driven by death receptors and has been involved in the control of autoreactive T cells in the periphery. In the Do-11.10 T cell hybridoma model of AICD, activation of the T cell receptor (TCR) results in Fas-dependent apoptosis. Here, we show that inhibition of the transcription factor nuclear factor κB (NFκB) in Do-11.10 cells resulted in increased sensitivity to TCR-mediated apoptosis, correlating with defective induction of the anti-apoptotic NFκB target gene A20. Stable expression of the zinc finger protein A20 in NFκB-negative Do-11.10 cells rescued the phenotype. TCR activation in NFκB-deficient Do-11.10 cells resulted predominantly in tumor necrosis factor (TNF) receptor 2 (TNFR2)-dependent bystander cell death rather than classical Fas-dependent AICD. Strikingly, A20 blocked TNF-mediated apoptosis and simultaneously restored TCR-induced Fas-dependent AICD. In addition, NFκB downstream of TNFR was required for up-regulation of Fas expression by endogenous TNF secreted in response to TCR stimulation. Together, these results suggest that NFκB can play both pro- and anti-apoptotic roles during AICD. We propose that NFκB controls the balance between Fas and TNF cell death pathways during AICD via the expression of the zinc finger protein A20. T lymphocytes are highly specialized cells of the adaptive immune system. Individual T cells express distinct T cell receptors (TCRs) 1The abbreviations used are: TCR, T cell receptor; AICD, activation-induced cell death; FasL, Fas ligand; mAb, monoclonal antibody; NFκB, nuclear factor κB; TNF, tumor necrosis factor; TNFR, tumor necrosis factor receptor; PMA, phorbol 12-myristate 13-acetate; RT, reverse transcriptase; FCS, fetal calf serum; Ab, antibody; EMSA, electrophoretic mobility shift assay; HRP, horseradish peroxidase. able to recognize a particular antigen and initiate a properly directed immune response. The clonal deletion of auto-reactive T cells in thymus is essential for the discrimination between self and non-self (1Robey E. Fowlkes B.J. Annu. Rev. Immunol. 1994; 12: 675-705Crossref PubMed Scopus (450) Google Scholar, 2Nossal G.J.V. Cell. 1994; 76: 229-239Abstract Full Text PDF PubMed Scopus (723) Google Scholar). This “central tolerance” is, however, incomplete, and healthy individuals harbor self-reactive T cells in the periphery (3Walker L.S. Abbas A.K. Nat. Rev. Immunol. 2002; 2: 11-19Crossref PubMed Scopus (453) Google Scholar). Normally, such self-reactive T cells fail to induce autoimmunity as a result of “peripheral tolerance” mechanisms, which involve either induction of anergy or apoptosis in self-reactive T cells. Peripheral deletion by induction of apoptosis is a major mechanism of controlling self-reactive T cells, and two distinct molecular pathways are now recognized, which result in the induction of apoptosis in lymphocytes destined to die. Activation-induced cell death (AICD) is an antigen-dependent cell-autonomous process, which involves TCR-mediated sensitization to apoptosis followed by death receptor-dependent cell death (4Combadiere B. Reis e Sousa C. Trageser C. Zheng L.X. Kim C.R. Lenardo M.J. Immunity. 1998; 9: 305-313Abstract Full Text Full Text PDF PubMed Scopus (53) Google Scholar). AICD is insensitive to action of anti-apoptotic Bcl-2 family proteins and does not rely on cytochrome c released from mitochondria. The second pathway of peripheral T cell deletion has recently been termed activated T cell autonomous cell death (5Hildeman D.A. Zhu Y. Mitchell T.C. Kappler J. Marrack P. Curr. Opin. Immunol. 2002; 14: 354-359Crossref PubMed Scopus (217) Google Scholar). In contrast to AICD, activated T cell autonomous cell death can be blocked by Bcl-2, is independent of death receptors, such as Fas, and is promoted by the pro-apoptotic Bcl-2 homologue Bim. An important question in molecular immunology is the mechanism by which TCR induces apoptosis during AICD. T cell hybridomas represent a model system to study AICD in vitro (6Lenardo M. Chan K.M. Hornung F. McFarland H. Siegel R. Wang J. Zheng L. Annu. Rev. Immunol. 1999; 17: 221-253Crossref PubMed Scopus (847) Google Scholar). In this system TCR signaling triggers up-regulation of Fas ligand (FasL) at the cell surface, which leads to the engagement of Fas, followed by cell-autonomous cell death. Several transcription factors, such as c-Myc, NF-AT, Egr, and Nur77 (7Shi Y. Glynn J.M. Guilbert L.J. Cotter T.G. Bissonnette R.P. Green D.R. Science. 1992; 257: 212-214Crossref PubMed Scopus (673) Google Scholar, 8Rengarajan J. Mittelstadt P.R. Mages H.W. Gerth A.J. Kroczek R.A. Ashwell J.D. Glimcher L.H. Immunity. 2000; 12: 293-300Abstract Full Text Full Text PDF PubMed Scopus (147) Google Scholar, 9Woronicz J.D. Calnan B. Ngo V. Winoto A. Nature. 1994; 367: 277-281Crossref PubMed Scopus (507) Google Scholar, 10Weih F. Ryseck R.-P. Chen L. Bravo R. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 5533-5538Crossref PubMed Scopus (127) Google Scholar), have been shown to participate in the TCR-mediated FasL up-regulation and induction of apoptosis in T cells. Nuclear factor κB (NFκB) transcription factors are also involved in the regulation of TCR-induced cell death (11Dudley E. Hornung F. Zheng L. Scherer D. Ballard D. Lenardo M. Eur. J. Immunol. 1999; 29: 878-886Crossref PubMed Scopus (82) Google Scholar, 12Kasibhatla S. Genestier L. Green D.R. J. Biol. Chem. 1999; 274: 987-992Abstract Full Text Full Text PDF PubMed Scopus (239) Google Scholar, 13Hettmann T. DiDonato J. Karin M. Leiden J.M. J. Exp. Med. 1999; 189: 145-158Crossref PubMed Scopus (186) Google Scholar) but the molecular mechanisms by which Rel/NFκB proteins regulate TCR-induced apoptosis are still poorly understood. NFκB constitutes a family of evolutionary closely related transcription factors with important roles in immune and stress responses, inflammation, and cancer (14Ghosh S. May M.J. Kopp E.B. Annu. Rev. Immunol. 1998; 16: 225-260Crossref PubMed Scopus (4610) Google Scholar, 15Hatada E.N. Krappmann D. Scheidereit C. Curr. Opin. Immunol. 2000; 12: 52-58Crossref PubMed Scopus (314) Google Scholar, 16Karin M. Cao Y. Greten F.R. Li Z.W. Nature Rev. Cancer. 2002; 2: 301-310Crossref PubMed Scopus (2258) Google Scholar). Five members have been identified in vertebrates: p50, p52, RelA (p65), RelB, and c-Rel. DNA binding activity of Rel/NFκB complexes is regulated by members of the IκB family, and several distinct IκB molecules with conserved ankyrin repeats have been described. In most cell types, Rel/NFκB proteins are trapped in the cytoplasm by the IκB inhibitors. A wide range of stimuli activates the IκB kinase complex, resulting in phosphorylation, ubiquitination, and degradation of IκBs. Consequently, Rel/NFκB proteins translocate to the nucleus and bind to so-called κB sequence motifs in regulatory regions of target genes (17Karin M. Ben-Neriah Y. Annu. Rev. Immunol. 2000; 18: 621-663Crossref PubMed Scopus (4084) Google Scholar, 18Pahl H.L. Oncogene. 1999; 18: 6853-6866Crossref PubMed Scopus (3448) Google Scholar). Abundant evidence has Rel/NFκB transcription factors also in the control of apoptosis M. Oncogene. 1999; 18: PubMed Scopus Google Scholar, M. A. Nat. Immunol. 2002; PubMed Scopus Google Scholar). is that NFκB is required for from tumor necrosis factor cell death in T cells, and cell M. A. Nat. Immunol. 2002; PubMed Scopus Google Scholar, D. Science. 1996; 274: PubMed Scopus Google Scholar, U. Li Z.W. V. Karin M. Immunity. 14: Full Text Full Text PDF PubMed Scopus Google Scholar). NFκB activation in response to TNF receptor for results in the induction of anti-apoptotic which at with the the TNFR M. A. Nat. Immunol. 2002; PubMed Scopus Google Scholar). to TCR-mediated apoptosis, most an anti-apoptotic for NFκB, but in NFκB can also TCR-induced cell death S. Genestier L. Green D.R. J. Biol. Chem. 1999; 274: 987-992Abstract Full Text Full Text PDF PubMed Scopus (239) Google Scholar, 13Hettmann T. DiDonato J. Karin M. Leiden J.M. J. Exp. Med. 1999; 189: 145-158Crossref PubMed Scopus (186) Google Scholar). Here, we show that in a used T cell hybridoma model of AICD NFκB downstream of TCR is to the control of the anti-apoptotic zinc finger protein A20. In the of NFκB, hybridoma cells predominantly in a cell and and of A20 this phenotype. We propose that during AICD NFκB controls the balance between Fas and TNF cell death pathways via the expression of cells to clonal of AICD. and of T cell hybridoma Do-11.10 was from the in with and at and in TNF was from induction of apoptosis, with of monoclonal to in at with and cells in of and cells with cells in cell 2 death was by the of cells with a and results cells for not and the of to the at the of the 2 2 and protein was used at was from was from and are F. D. Bravo R. Oncogene. 1994; 9: Google Scholar). and from A20 the of A20 was by with for and the and The was of which resulted in an of the A20 to A20 was in induction with for protein was on to from the was 2 and used for Stable and of Do-11.10 at and was the of via Do-11.10 cells cells in of at in a and in of cells and in at in and for NFκB induction in response to with A20 D. R. R. J. Biol. 1999; PubMed Scopus Google Scholar) by and was the of M. F. D. A. Eur. J. Immunol. 1999; 29: PubMed Scopus Google Scholar) by via The cell A. M. S. D. S. T. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar) by and was with or 2 and a Do-11.10 cells in 2 of of cells in and for at at in of and in at in and for protein expression by Green for A20 expression by or for to apoptosis. of used for of of and as F. J. Immunol. PubMed Scopus Google Scholar). and are and in with of cell and by was as F. D. Bravo R. Oncogene. 1994; 9: Google Scholar). of as mobility shift and as F. D. Bravo R. Oncogene. 1994; 9: Google Scholar). and of T H. M. B. F. B. J.D. Eur. J. Immunol. PubMed Scopus Google Scholar) by used for and with and in the of the of and to and in FCS, at a of 2 Five of cell activated in for and at a of 2 in with and cells for an used for of NFκB by a in to TCR-induced the of NFκB in the T cell hybridoma model of AICD, we blocked NFκB nuclear by the expression of a S. Ryseck R.-P. M. F. Eur. J. Immunol. PubMed Scopus Google Scholar) in Do-11.10 cells. Several and termed and not show expression of the and used as controls in termed and expression with a in endogenous The of NFκB inhibition was in with nuclear from cells. NFκB was in control cells NFκB binding with the of In control cells, the of NFκB binding was of complexes and in control but not in cells of NFκB activity downstream of TCR, Do-11.10 cells with and induction of the classical NFκB target gene was by of was in control cells with NFκB binding as in In induction of was in NFκB-negative the of NFκB in the regulation of AICD, TCR-induced cell death was in and cells. resulted in increased sensitivity to AICD in cells in control apoptosis was cell death in cells of the in Do-11.10 hybridoma cells results in a of NFκB activation downstream of the TCR and in increased sensitivity to TCR-induced apoptosis. TCR of the A20 is a of genes cells from TNF-mediated apoptosis M. Oncogene. 1999; 18: PubMed Scopus Google Scholar, M. A. Nat. Immunol. 2002; PubMed Scopus Google Scholar). We the increased TCR-induced apoptosis in NFκB-deficient Do-11.10 cells with expression of NFκB target of and activated with or and of anti-apoptotic NFκB target genes by of the which is in an was as a control for TCR the genes and on and A20 both and on NFκB a on NFκB was for the expression of the genes and and In addition, induction of gene expression was in of the of anti-apoptotic NFκB target genes in Do-11.10 T cell by either or increased on NFκB was by and by not was not as a by was on increased by was on either or increased on NFκB was by and was not as a increased not by was on in a has recently been shown to also pro-apoptotic Y. Ashwell J.D. Nature. 2002; PubMed Scopus Google Scholar), we on A20 as a anti-apoptotic the that A20 expression was by TCR signaling was a of TCR-induced A20 in the induction in cells, and a of this is shown in that A20 induction also results in increased A20 protein we directed the of A20. that A20 protein of in control but not in NFκB-negative Do-11.10 cells TCR also induces A20 expression in T we T cell from that TCR signaling A20 expression on both and protein results with and T cell not that TCR signaling also induces A20 expression independent of TNF, we T cell from which are in TNFR ligand H. M. B. F. B. J.D. Eur. J. Immunol. PubMed Scopus Google Scholar). A20 between and T cell that activation of the TCR induces A20 independent of TNFR signaling Together, these that TCR-induced A20 expression is a of T cells and that this response is, at in Do-11.10 cells, NFκB of A20 in NFκB-negative Do-11.10 AICD and to A20 cells from increased sensitivity to AICD, we both and with either or a A20 with from cell M. A. Nat. Immunol. 2002; PubMed Scopus Google Scholar, D. Science. 1996; 274: PubMed Scopus Google Scholar), we that cells to apoptosis and A20 rescued this This result that A20 in cells for from We also the of A20 on AICD. of A20 on AICD in cells. In cells, however, with A20 TCR-induced apoptosis to to the in control cells A20 not apoptosis, that apoptosis is not blocked in this system not We that expression of A20 in cells is to both TNF sensitivity and AICD in response to TCR A20 protein at the of AICD in and The of A20 protein in control cells was than in cells with an A20 increased of in the of We also increased of endogenous A20 protein in but not in that TCR signaling increased A20 protein the of A20 was not not has been that of A20 NFκB M. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: PubMed Scopus Google Scholar), we activation of NFκB in cells A20. of NFκB in cells was in the of this the cells not NFκB-negative but a with NFκB at and with of NFκB in Do-11.10 in a from to AICD, by A20 the Do-11.10 T cell hybridoma model of AICD, TCR signaling results in apoptosis. cells increased sensitivity to TCR-induced cell death with cells than in we cell death by a molecular mechanism in with cells. the of death receptors from the TNFR with FasL as of cell death in Do-11.10 also the of AICD in Do-11.10 cell by and not In contrast to cells, AICD in cells was by but blocked by cells A20 AICD to cells with cells with A20 also AICD from controls results in the of NFκB, the pathway and cells by endogenous the on the pathway can be restored by A20 in cells, that A20 is a major target of NFκB downstream of the The of TNF in AICD of Do-11.10 cells was hybridomas to rely on the Fas and not the TNFR pathway R. L. J. M. Y. J. Immunol. PubMed Scopus Google Scholar). however, suggest that TNF hybridoma cells to apoptosis J.M. R. J. J. Immunol. PubMed Scopus Google Scholar). We Do-11.10 cells with TNF and of these was of apoptosis cell death the resulted in cell death TNF is of the Fas an for the of endogenous TNF on AICD in Do-11.10 hybridoma cells. Do-11.10 cells express both and not which TNFR is Do-11.10 cells with in the and of In as as in cells, of a that the of TNF signaling The of in AICD model be the result of the that is of of TNF M. A. Chen Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). NFκB of Fas in Do-11.10 but This for Fas-dependent the question of cells Fas-dependent cell we FasL and Fas which are both NFκB target genes S. Genestier L. Green D.R. J. Biol. Chem. 1999; 274: 987-992Abstract Full Text Full Text PDF PubMed Scopus (239) Google Scholar, M. Eur. J. Immunol. 2000; PubMed Scopus Google Scholar, F. Li M. J. Exp. Med. 1999; 189: PubMed Scopus Google Scholar). of NFκB not anti-CD3-induced FasL or FasL expression A and Fas expression was also anti-CD3-induced up-regulation of Fas and Fas expression was in with cells A and endogenous TNF to the regulation of AICD in system and TNF induces Fas in Y. F. P. V. S. J. Immunol. PubMed Scopus Google Scholar), we the of endogenous TNF in Fas regulation by or and during AICD of cells to induction of Fas and a of anti-CD3-induced Fas up-regulation on the cell with of anti-CD3-induced up-regulation of Fas in Do-11.10 cells is by secreted TNF and on We to the of Fas induction was for the apoptosis in cells. We of the that cells and cells with A20 Fas-dependent AICD that A20 not the anti-CD3-induced up-regulation of Fas in cells AICD, that Fas expression is for AICD in Do-11.10 cells. NFκB of TCR and TNFR for A20 of the anti-CD3-induced NFκB activity was on endogenous TNF, Do-11.10 cells with in the and of and nuclear in of both that the of NFκB induction 2 of was by endogenous TNF, was also NFκB which was and not the NFκB induction with control of however, resulted in a NFκB and of A20 is a classical gene J. Biol. Chem. Full Text PDF PubMed Google Scholar). the of endogenous TNF to the induction of A20 control Do-11.10 cells in the or of anti-CD3-induced A20 In the of mAb, the of was for a major of in this system Together, these results that during AICD NFκB is by both and a of that regulate AICD. The of NFκB in apoptosis has been in but the molecular mechanisms by which gene expression TCR-mediated cell death are still We have anti-apoptotic NFκB target genes in the Do-11.10 T cell hybridoma model of AICD. and NFκB-deficient Do-11.10 we that TCR signaling A20 and genes in an the NFκB are either not by TCR signaling or in the of is important to that A20 expression is also by TCR signaling in T cell but not in or T cells M. J. Immunol. Google Scholar) not anti-CD3-induced expression of and is not on NFκB and induction by is blocked in cells results show that so-called NFκB target genes are on NFκB and that on NFκB has to be in the of target and T cell In contrast to anti-apoptotic has been that NFκB can also play a in TCR-induced death of T cell hybridomas S. Genestier L. Green D.R. J. Biol. Chem. 1999; 274: 987-992Abstract Full Text Full Text PDF PubMed Scopus (239) Google Scholar) or T. DiDonato J. Karin M. Leiden J.M. J. Exp. Med. 1999; 189: 145-158Crossref PubMed Scopus (186) Google Scholar). In in TCR-mediated apoptosis was in T cells from or Y. F. P. V. S. J. Immunol. PubMed Scopus Google Scholar). TCR signaling induces Rel/NFκB proteins B. C. P. D. J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar), the of a Rel/NFκB family not result in a phenotype. the T cells from and show activation-induced to AICD Y. F. P. V. S. J. Immunol. PubMed Scopus Google Scholar) not that in AICD in T cell from also increased apoptosis in response to TCR signaling (11Dudley E. Hornung F. Zheng L. Scherer D. Ballard D. Lenardo M. Eur. J. Immunol. 1999; 29: 878-886Crossref PubMed Scopus (82) Google Scholar). show that in Do-11.10 cells inhibition of NFκB results in increased sensitivity to TCR-mediated apoptosis. This is, however, a of the mechanism of apoptosis both increased apoptosis and cell death in NFκB-deficient Do-11.10 cells. in contrast to either or roles for NFκB, these results for both and pro-apoptotic of NFκB downstream of the A20 NFκB during AICD of T in hybridoma cells results in to AICD and sensitivity to in response to secreted of the zinc finger protein A20 this is that A20 also a TNF-mediated apoptosis and at the TCR-induced apoptosis. has been that A20 apoptosis by of and to the in T cells Biol. 2002; PubMed Scopus Google Scholar). In NFκB-deficient Do-11.10 cells, is the receptor apoptosis and A20 this cell death. was also to apoptosis in T cells B. Immunity. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar), is that A20 apoptosis in Do-11.10 cells by of to both and The that A20 AICD in Do-11.10 cells is is to the action of A20 on AICD activated T cells TNF and A20 is required to from cell death. We not of A20 on the expression of both FasL and Fas, that A20 this cell death pathway downstream of The of A20 in TCR-induced apoptosis is important in the of that of the classical anti-apoptotic NFκB target genes can also cell death. has been to degradation of the anti-apoptotic protein Y. Ashwell J.D. Nature. 2002; PubMed Scopus Google Scholar). In addition, has been to apoptosis by Fas the pro-apoptotic of at but expression result in from apoptosis Y. A. S. J. 2002; PubMed Scopus Google Scholar). the of a and NFκB as to apoptosis be a rather than an A20 does not bind to death signaling molecules or death receptors, but can be to the via with IκB kinase M. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: PubMed Scopus Google Scholar, Biol. 2002; PubMed Scopus Google Scholar, A. D. Immunity. 2000; 12: Full Text Full Text PDF PubMed Scopus Google Scholar). Several proteins with D. R. R. J. Biol. 1999; PubMed Scopus Google Scholar), S. F. D. R. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar), and D. M. R. R. Oncogene. 1999; 18: PubMed Scopus Google Scholar). the of A20 and these proteins is still poorly a molecular of the of A20 in TCR-induced apoptosis In with the of A20 on NFκB activation M. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: PubMed Scopus Google Scholar), we also induction of NFκB binding in Do-11.10 cells A20. This result does not with to AICD a of a can be rescued by A20 that as as A20 is by NFκB downstream of the TCR AICD of TNF and in Fas-dependent during AICD of Do-11.10 that endogenous TNF is for AICD of Do-11.10 cells is an for the system was for the hybridoma model of AICD R. L. J. M. Y. J. Immunol. PubMed Scopus Google Scholar). is that hybridomas show sensitivity apoptosis. In with was shown that apoptosis of Do-11.10 cells and T cell with TNF and J.M. R. J. J. Immunol. PubMed Scopus Google Scholar, A. J. Immunol. 2000; PubMed Scopus Google Scholar). In addition, of T cells with results in sensitivity to Fas J.M. R. J. J. Immunol. PubMed Scopus Google Scholar). these results suggest a of TNF and on the Fas is evidence that is the major TNF receptor in T cells, in particular for the induction of apoptosis B. Immunity. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar, L. J. Lenardo M.J. Nature. PubMed Scopus Google Scholar). This the that TNFR which also a death and have been as apoptosis to participate in the regulation of apoptosis. the of has been shown that NFκB is essential for up-regulation of Fas F. Li M. J. Exp. Med. 1999; 189: PubMed Scopus Google Scholar, Y. F. P. V. S. J. Immunol. PubMed Scopus Google Scholar). We that a also in T cells, that Fas up-regulation during AICD to apoptosis by the of Fas engagement on the cell This however, by the that Fas on T cell hybridoma are for AICD, that TNF-mediated sensitization to AICD downstream of TCR A20 at and induction of A20 expression downstream of both TCR and TNF is with in the A20 A. J. Biol. Chem. 1992; Full Text PDF PubMed Google Scholar). The regulation of A20 protein by the TCR, however, A20 are 2 of TCR A20 protein is not at this A20 but not from a also TCR This is not and with increased A20 as by not A20 gene expression is at both and A of regulation has been for anti-apoptotic NFκB target M. C. C. T. Nat. Biol. 1999; PubMed Scopus Google Scholar), that regulation of genes controlling apoptosis is than of NFκB in suggest a model in which NFκB activated by the TCR and by secreted TNF induces of A20. a A20 cell death and at the apoptosis, both and pro-apoptotic roles in AICD AICD is involved in both of activated T cells an immune response and in of T cells during the activation (6Lenardo M. Chan K.M. Hornung F. McFarland H. Siegel R. Wang J. Zheng L. Annu. Rev. Immunol. 1999; 17: 221-253Crossref PubMed Scopus (847) Google Scholar). This is the T cell has and a particular T cell not the immune response. AICD in antigen-dependent that T cells apoptosis. In the of NFκB, however, TNF secreted by cells NFκB-deficient cells in This so-called bystander cell in which also T cells is highly the of AICD NFκB via the expression of target gene A20 to the of clonal during AICD. We and for and We are to for the and for the cell as as and for the A20 We also for and on this for and the in the at the of and with