The Anti-apoptotic Effect of Notch-1 Requires p56 -dependent, Akt/PKB-mediated Signaling in T Cells

The Notch family of transmembrane receptors have been implicated in a variety of cellular decisions in different cell types. Here we investigate the mechanism underlying Notch-1-mediated anti-apoptotic function in T cells using model cell lines as the experimental system. Ectopic expression of the intracellular domain of Notch-1/activated Notch (AcN1) increases expression of anti-apoptotic proteins of the inhibitors of apoptosis (IAP) family, the Bcl-2 family, and the FLICE-like inhibitor protein (FLIP) and inhibits death triggered by multiple stimuli that activate intrinsic or extrinsic pathways of apoptosis in human and murine T cell lines. Numb inhibited the AcN1-dependent induction of anti-apoptotic proteins and anti-apoptotic function. Using pharmacological inhibitors and dominant-negative approaches, we describe a functional role for phosphatidylinositol 3-kinase (PI3K)-dependent activation of the serine-threonine kinase Akt/PKB in the regulation of AcN1-mediated anti-apoptotic function and the expression of FLIP and IAP family proteins. Using a cell line deficient for the T cell-specific, Src family protein, the tyrosine kinase p56lck and by reconstitution approaches we demonstrate that p56lck is required for the Notch-1-mediated activation of Akt/PKB function. Furthermore, the Src tyrosine kinase inhibitor, PP2, abrogated ectopically expressed AcN1-mediated anti-apoptotic function and phosphorylation of p56lck. We present evidence that endogenous Notch-1 associates with p56lck and PI3K but that Akt/PKB does not co-immunoprecipitate with the Notch1·p56lck·PI3K complex. Finally, we demonstrate that the Notch1·p56lck·PI3K complex is present in primary T cells that have been activated in vitro and sustained in culture with the cytokine interleukin-2. The Notch family of transmembrane receptors have been implicated in a variety of cellular decisions in different cell types. Here we investigate the mechanism underlying Notch-1-mediated anti-apoptotic function in T cells using model cell lines as the experimental system. Ectopic expression of the intracellular domain of Notch-1/activated Notch (AcN1) increases expression of anti-apoptotic proteins of the inhibitors of apoptosis (IAP) family, the Bcl-2 family, and the FLICE-like inhibitor protein (FLIP) and inhibits death triggered by multiple stimuli that activate intrinsic or extrinsic pathways of apoptosis in human and murine T cell lines. Numb inhibited the AcN1-dependent induction of anti-apoptotic proteins and anti-apoptotic function. Using pharmacological inhibitors and dominant-negative approaches, we describe a functional role for phosphatidylinositol 3-kinase (PI3K)-dependent activation of the serine-threonine kinase Akt/PKB in the regulation of AcN1-mediated anti-apoptotic function and the expression of FLIP and IAP family proteins. Using a cell line deficient for the T cell-specific, Src family protein, the tyrosine kinase p56lck and by reconstitution approaches we demonstrate that p56lck is required for the Notch-1-mediated activation of Akt/PKB function. Furthermore, the Src tyrosine kinase inhibitor, PP2, abrogated ectopically expressed AcN1-mediated anti-apoptotic function and phosphorylation of p56lck. We present evidence that endogenous Notch-1 associates with p56lck and PI3K but that Akt/PKB does not co-immunoprecipitate with the Notch1·p56lck·PI3K complex. Finally, we demonstrate that the Notch1·p56lck·PI3K complex is present in primary T cells that have been activated in vitro and sustained in culture with the cytokine interleukin-2. The Notch family of transmembrane receptors are important regulators of cell fate determination events in different cell types. Upon activation by ligands usually located on the surface of neighboring cells, Notch undergoes intramembrane proteolysis and release of an intracellular region resulting in signaling (1.Artavanis-Tsakonas S. Rand M.D. Lake R.J. Science. 1999; 284: 770-776Crossref PubMed Scopus (5026) Google Scholar). The mechanism of Notch-1 signaling is incompletely understood even in well characterized genetic models like Drosophila or the worm. There is recent evidence of the interaction of Notch together with T cell antigen receptor in determination of cell fate within the T cell lineage (2.Robey E. Chang D. Itano A. Cado D. Alexander H. Lans D. Weinmaster G. Salmon P. Cell. 1996; 87: 483-492Abstract Full Text Full Text PDF PubMed Scopus (452) Google Scholar, 3.Washburn T. Schweighoffer E. Gridley T. Chang D. Fowlkes B.J. Cado D. Robey E. Cell. 1997; 88: 833-843Abstract Full Text Full Text PDF PubMed Scopus (368) Google Scholar). Furthermore, Notch-1 has been shown to protect against anoikis (apoptosis induced by matrix withdrawal) or p53-mediated apoptosis in immortalized epithelial cells (4.Rangarajan A. Syal R. Selvarajah S. Chakrabarti O. Sarin A. Krishna S. Virology. 2001; 286: 23-30Crossref PubMed Scopus (140) Google Scholar, 5.Nair P. Somasundaram K. Krishna S. J. Virol. 2003; 77: 7106-7112Crossref PubMed Scopus (146) Google Scholar), T cell receptor-induced apoptosis in mature cells (6.Jehn B.M. Bielke W. Pear W.S. Osborne B.A. J. Immunol. 1999; 162: 635-638PubMed Google Scholar), and dexamethasone-mediated apoptosis in thymocytes (7.Deftos M.L. He Y.W. Ojala E.W. Bevan M.J. Immunity. 1998; 9: 777-786Abstract Full Text Full Text PDF PubMed Scopus (319) Google Scholar). In mammalian cells apoptosis is initiated via extracellular receptor-mediated apoptotic signaling (8.Ashkenazi A. Dixit V.M. Science. 1998; 281: 1305-1308Crossref PubMed Scopus (5206) Google Scholar, 9.Wallach D. Varfolomeev E.E. Malinin N.L. Goltsev Y.V. Kovalenko A.V. Boldin M.P. Annu. Rev. Immunol. 1999; 17: 331-367Crossref PubMed Scopus (1138) Google Scholar) or death pathways that converge on the mitochondrion (10.Green D.R. Reed J.C. Science. 1998; 281: 1309-1312Crossref PubMed Google Scholar). Both pathways culminate in the activation of caspases, a family of proteases that mediate the orderly dismantling of cells. Death receptors of the tumor necrosis factor (TNF) 1The abbreviations used are: TNF, tumor necrosis factor; FLIP, FLICE inhibitor protein; IAP, inhibitors of apoptosis; PI3K, phosphatidylinositol 3-kinase; GFP, green fluorescent protein; LC, loading control; PP2, 4-amino-5-(4-chlorophenyl-7-(t-butyl)pyrazolo[3,4-d]pyrmidine; TRAIL, TNF-related apoptosis-inducing ligand; WBA, Western blot analysis. receptor superfamily trigger apoptosis principally via the activation of procaspase 8/10 (8.Ashkenazi A. Dixit V.M. Science. 1998; 281: 1305-1308Crossref PubMed Scopus (5206) Google Scholar, 9.Wallach D. Varfolomeev E.E. Malinin N.L. Goltsev Y.V. Kovalenko A.V. Boldin M.P. Annu. Rev. Immunol. 1999; 17: 331-367Crossref PubMed Scopus (1138) Google Scholar), whereas mitochondrial signaling activates caspase-9. Caspase-induced apoptosis is regulated by endogenous antagonists like FLICE-like inhibitor protein (FLIP) that prevent processing and anti-apoptotic proteins of the inhibitors of apoptosis protein (IAP) family that block function (11.Deveraux Q.L. Reed J.C. Genes Dev. 1999; 13: 239-252Crossref PubMed Scopus (2303) Google Scholar). The release of intermediates from the mitochondrial intermembrane space that occurs as an initial step is blocked by anti-apoptotic members of the Bcl-2 family (12.Gottlieb E. Vander Heiden M.G. Thompson C.B. Mol. Cell. Biol. 2000; 20: 5680-5689Crossref PubMed Scopus (314) Google Scholar). Mature T cells develop from immature precursors through complex but ordered processes (13.Goldrath A.W. Bevan M.J. Nature. 1999; 402: 255-262Crossref PubMed Scopus (724) Google Scholar). There is considerable evidence that Notch signaling regulates the earliest stages of T cell commitment and promotes differentiation in the T cell lineage (14.Izon D.J. Punt J.A. Pear W.S. Curr. Opin. Immunol. 2002; 14: 192-199Crossref PubMed Scopus (48) Google Scholar, 15.Radtke F. Wilson A. Ernst B. MacDonald H.R. Immunol. Rev. 2002; 187: 65-74Crossref PubMed Scopus (67) Google Scholar, 16.Schmitt T.M. Zúñiga-Pflücker J.C. Immunity. 2002; 17: 749-756Abstract Full Text Full Text PDF PubMed Scopus (929) Google Scholar). During T cell development, negative selection ensures deletion of autoreactive thymocytes and allows maturation of CD4+ or CD8+ T cells (13.Goldrath A.W. Bevan M.J. Nature. 1999; 402: 255-262Crossref PubMed Scopus (724) Google Scholar). Notch involvement in Bcl-2-dependent survival signaling in immature T cells was first reported in this model (7.Deftos M.L. He Y.W. Ojala E.W. Bevan M.J. Immunity. 1998; 9: 777-786Abstract Full Text Full Text PDF PubMed Scopus (319) Google Scholar). Thymic maturation into CD4+ or CD8+ subsets of mature T cells is accompanied by the emigration of these cells to peripheral lymphoid organs. Mature T cells remain susceptible to varied apoptotic stimuli, many of which are regulated via pathways distinct from those in thymocytes (17.Boehme S.A. Lenardo M.J. J. Immunol. 1996; 156: 4075-4078PubMed Google Scholar, 18.Kuida K. Haydar T.F. Kuan C.Y. Gu Y. Taya C. Karasuyama H. Su M.S. Rakic P. Flavell R.A. Cell. 1998; 94: 325-337Abstract Full Text Full Text PDF PubMed Scopus (1468) Google Scholar, 19.Yoshida H. Kong Y.Y. Yoshida R. Elia A.J. Hakem A. Hakem R. Penninger J.M. Mak T.W. Cell. 1998; 94: 739-750Abstract Full Text Full Text PDF PubMed Scopus (1016) Google Scholar). In this study we ask if Notch-1 regulates apoptosis in model T cell lines and have attempted to identify the molecular mechanism of Notch-1 dependent anti-apoptotic function. We show that ectopic expression of the intracellular domain of Notch-1 (AcN1) confers protection against diverse stimuli that trigger intrinsic and extrinsic pathways of death in model T cell lines. This anti-apoptotic function, we suggest, can result from the AcN1-induced elevated expression of IAP-2, Bcl-xL and FLIP, which represent three major families of anti-apoptotic proteins. The protective effect of AcN1 was attenuated by the Notch antagonist Numb and disruption of Akt/PKB-dependent signaling. Furthermore, we show that loss of function of the T cell-specific, Src family, non-receptor tyrosine kinase p56lck compromised Akt/PKB phosphorylation and anti-apoptotic function. This allows us to propose a functional hierarchy of interactions between Notch-1, PI3K, and p56lck that might operate in T cells. Cells and Reagents—Jurkat, a T lymphoblastoid cell line of human origin, and 2B4, a murine T cell hybridoma, were used in all experiments. The J.CaM1.6 mutant was obtained from ATCC (Manassas, VA). Activated T cells were generated by stimulation in vitro as described before and sustained in interleukin-2 (20.Sarin A. Wu M.L. Henkart P.A. J. Exp. Med. 1996; 184: 2445-2450Crossref PubMed Scopus (150) Google Scholar). Activated T cells were used on day 5 after stimulation. All reagents were obtained from Calbiochem unless specified otherwise. The mitochondrial dye JC-1 was obtained from Molecular Probes (Eugene, OR). Recombinant TNF, TRAIL, and antibodies to Bid, Bcl-2, Bcl-xL, and FLIP were obtained from R & D Systems (Minneapolis, MN). Antibodies to Akt, BIM, IAP-1, IAP-2, Jagged, p38MAPK, p56lck, PI3K, and GFP were from Santa Cruz Biotechnology (Santa Cruz, CA), antibodies to phosphorylated p56lck or Akt were obtained from Cell Signaling Technology (Beverly, MA) and the monoclonal antibody to GFP was from Clontech, BD Biosciences. Antibodies to the various domains of Notch and their sources are as follows: Notch-1 intracellular domain referred to as NICDHB (clone C17.9C6) and to Notch-1 intracellular domain nucleotides 6658–7131 (clone bTan 20) were obtained from the Developmental Studies Hybridoma Bank (Iowa City, IA); Notch-1 carboxyl terminus referred to as NICDSC (M-20) and to the Notch-1 extracellular domain, residues 20–150, referred to as Notch-1 ECSC (H-131), were from Santa Cruz Biotechnology and to residues 1299–1492 in the extracellular domain of Notch-1, referred to as Notch-1 ECUB (clone 8G10), was from Upstate Biotechnology (Lake Placid, NY). Plasmids and Transfections—The AcN encoding plasmid pcDNA3-ICTX (AcN1; Ref. 21.Aster J.C. Robertson E.S. Hasserjian R.P. Turner J.R. Kieff E. Sklar J. J. Biol. Chem. 1997; 272: 11336-11343Abstract Full Text Full Text PDF PubMed Scopus Google Scholar) was a of J. This was used to was a from for In we generated the for which the AcN1 region was using the and and into and of All three which principally the intracellular domain of Notch-1, the in and functional The dominant-negative mutant of Akt, was obtained from The Bcl-2 plasmid was a of S. of The for Numb W. 1996; 17: Full Text Full Text PDF PubMed Scopus Google Scholar) was obtained from The was obtained from ATCC (Manassas, VA). The of was and into the and of the expression (Santa Cruz The of the used for the are and The of all was by cell lines AcN1 or Bcl-2 were generated by with of of by cells were for in with for of cells. cells were not of of have been in these experiments. were as described H. Sarin A. J. Immunol. 2003; PubMed Scopus Google Scholar). usually in from and were in experiments. was a of three unless otherwise. of cell and mitochondrial were as described H. Sarin A. J. Immunol. 2003; PubMed Scopus Google Scholar). All was on a BD was in cells as described before H. Sarin A. J. Immunol. 2003; PubMed Scopus Google Scholar). were in cell were in and and for Cell was by for and the resulting was into with for with antibody and the with but with an antibody as a were by and with proteins were by for were in on and the proteins by Western blot analysis. In using p56lck, a antibody to Akt in from the was used as negative In the antibody to Notch intracellular domain was a antibody in and from the was used as the In and have been used as negative with In GFP was with a monoclonal to GFP, monoclonal was used as a Western of of cells were by and by the were used for Western blot of Bcl-xL, FLIP, and were by using was used to of loading in and Akt or was used as the loading for The has been used to these proteins in the various Western The murine T cell and the human lymphoblastoid cell line have been used in all experiments. All have been using the and expression of AcN1 in these cell lines. of and were as described of the in the were from or in different experiments. AcN1 and of T cell has been used in many as a model to the regulation of apoptosis in mature T cells Y. 1997; PubMed Google Scholar, A. Henkart P.A. J. Exp. Med. PubMed Scopus Google Scholar). of cells the intracellular domain of Notch-1 (AcN1) referred to as of the anti-apoptotic proteins Bcl-xL, and Bcl-2 expression is in cells and was not in cells in with cells with the elevated of these proteins with functional apoptotic was in cells or or cells or with or on to trigger signaling In all cells were from apoptotic to were obtained on of AcN1 not AcN1 in that the described were not a of the hybridoma, we ectopically expressed AcN1 in a human lymphoblastoid T cell This in elevated of Bcl-xL and proteins in cells with AcN1 as with cells with the plasmid FLIP expression is in in the in protein expression induced by AcN1 was in cell lines. Bcl-2 on the was not in cells, and expression not induced by We that Bcl-2 protein by the protein in cells that The with the cell line that AcN1 regulated apoptotic signaling. many apoptotic signaling pathways have been characterized in the cell we used the cell line to AcN1 regulated apoptosis triggered by extrinsic pathways of death as and cells were for to apoptosis induced by the death receptor ligands or was triggered by with and referred to as in all analysis. cells were from apoptotic loss of mitochondrial transmembrane which is a of mitochondrial or cell not AcN1 cells from different of apoptosis a to that by Bcl-2 in these cells Furthermore, on with cells were from apoptosis triggered by or the inhibitor, but not the of In D and cells are by and cells with GFP by ectopic expression of AcN1 in expression of anti-apoptotic proteins and protection from diverse apoptotic We attempted to identify the mechanism by which AcN1 these AcN1 have shown that Notch-1 through the PI3K to trigger survival in epithelial cells (4.Rangarajan A. Syal R. Selvarajah S. Chakrabarti O. Sarin A. Krishna S. Virology. 2001; 286: 23-30Crossref PubMed Scopus (140) Google Scholar). a mechanism in T cells, in intermediates of this in AcN1 ectopic We used pharmacological inhibitors of PI3K and a dominant-negative inhibitor of the serine-threonine kinase Akt to the functional interactions between Notch signaling and the PI3K in T cells. We phosphorylation with in of Akt in or cell lines with AcN1 In functional of a pharmacological inhibitor of PI3K J. Biol. Chem. Full Text PDF PubMed Google Scholar) the anti-apoptotic function of AcN1 in cells apoptosis is in cells as with apoptosis in cells Both and the distinct inhibitor H. S. K. Y. Y. Y. Y. J. Biol. Chem. Full Text PDF PubMed Google Scholar) attenuated AcN1 of apoptosis In the a inhibitor of was apoptosis was in cells that and in Bcl-2 cells as with cells that were with the protective effect of AcN1 but not Bcl-2 of death We that was not to cells and In we used a dominant-negative of Akt to the of disruption of Akt signaling on of induced by is in cells that AcN1 with those In this the of attenuated the anti-apoptotic effect of AcN1 that Akt signaling with the anti-apoptotic function of Ectopic expression of in cells blocked AcN1-mediated induction of and FLIP but not the of Bcl-xL cells with for were for the expression of anti-apoptotic proteins. blocked Akt phosphorylation and expression of Bcl-xL expression was not by these using genetic and pharmacological approaches that AcN1 triggered activation of a PI3K signaling that in the expression of the anti-apoptotic proteins FLIP and Bcl-xL expression to regulated of Akt signaling. Numb AcN1-induced Signaling in T used the Notch antagonist Numb to that the in the of were initiated by Notch signaling. shown in of Numb AcN1 of or in the cell Ectopic expression of Numb apoptosis by the in the cell line and apoptosis in cells Furthermore, Numb blocked AcN1-mediated induction of Bcl-xL, IAP-2, and FLIP in cell lines D and and the phosphorylation of Akt Using the of AcN1 we that AcN1 is principally to the and this was not in cells that Numb p56lck a in the AcN1-mediated of that AcN1 via the PI3K to activate Akt in cell is the between Notch-1 and Akt p56lck is a of the family of non-receptor tyrosine with T cell receptor signaling. p56lck is activated or are and and activates intracellular as Akt via Ectopic expression of AcN1 in phosphorylation of p56lck in and cells the functional of this if we used the cell line that was for p56lck In J.CaM1.6 cells AcN1 not phosphorylation of Akt or expression of or FLIP induction of and phosphorylation of Akt that the J.CaM1.6 cell line was not in the of these proteins if The cell line was to AcN1-mediated of apoptosis reconstitution with p56lck the of AcN1 to block apoptotic in these cells In with the Src kinase inhibitor, PP2, abrogated the anti-apoptotic effect of AcN1 in cells Furthermore, after that abrogated the anti-apoptotic function of blocked AcN1-induced phosphorylation of p56lck Notch-1 with PI3K and p56lck in and T AcN1 is principally PI3K is a signaling as is p56lck. We that if is a interaction of the complex with the Notch-1 the endogenous The were to this an antibody to GFP was used to from cells, to PI3K The AcN1 protein can by the antibody (clone C17.9C6) to the Notch-1 intracellular region The protein not by antibody to the intracellular The NICDSC endogenous protein a to the from the endogenous protein endogenous p56lck from cells and a complex that the of PI3K but not or Akt these are in the cell The NICDSC which does not that endogenous Notch-1 is in with PI3K and p56lck was for PI3K or Notch-1 on of p56lck in J.CaM1.6 cells, as these cells not p56lck first and In we that endogenous Notch-1 using NICDSC a complex that p56lck and PI3K but not Akt from cells from these we that endogenous Notch-1 associates with PI3K and p56lck. The complex does not with Akt or p56lck in with endogenous Notch-1 and in cells, p56lck associates with PI3K and Notch-1, the of Notch-1 are in these cells the phosphorylation of Akt and p56lck is on AcN1 and cells are from we that AcN1 the interaction by expression of endogenous mechanism has been reported in B. J.C. Hasserjian R.P. F. Sklar J. Mol. Cell. Biol. 1997; 17: PubMed Scopus Google Scholar, A. E. M.S. S. F. Dev. Biol. 2002; PubMed Scopus Google Scholar). the of p56lck, PI3K, or Akt are not in AcN1 cells, but the that AcN1 an in expression of endogenous Notch-1 was in experiments. cells with of a Notch-1 that is using an antibody that an in the Notch-1 extracellular domain Furthermore, the Notch-1 Jagged, was elevated in these cells which the of Notch signaling via the endogenous receptor in cells. We the extracellular domain of Notch-1 is present in the complex with p56lck and shown in in that the used for and p56lck a complex that the Notch-1 extracellular domain using antibodies to the extracellular region of Notch-1 ECUB and Notch-1 PI3K and are present in this complex. we Notch-1, PI3K, and p56lck in T cells. We for this in activated T cells sustained in culture with interleukin-2. The cytokine is important for T cell and survival and of these are dependent on signaling through In activated T cells we that endogenous Notch-1 p56lck and PI3K from in vitro activated T cells sustained in culture with the cytokine interleukin-2. Mature T cells are to anti-apoptotic proteins to protect from diverse apoptotic stimuli that in the of their T cells are for survival death with proteins as FLIP and members of the Bcl-2 family that to from various apoptotic stimuli (13.Goldrath A.W. Bevan M.J. Nature. 1999; 402: 255-262Crossref PubMed Scopus (724) Google Scholar). We propose that the Notch-1 receptor can mediate the induction of anti-apoptotic proteins. We show that ectopic expression of AcN1 in the of anti-apoptotic proteins and cells from diverse apoptotic that the anti-apoptotic function of Notch-1 not to to pathways but to protection to diverse apoptotic We identify PI3K as intracellular of anti-apoptotic and pharmacological inhibitors of PI3K Akt signaling AcN1 function Akt as an to this A. Genes Dev. 1999; 13: PubMed Scopus Google Scholar). In T cells, PI3K can activated by like F. R. A. J. J. D. Nature. PubMed Scopus Google Scholar), cell as C. J. S. S. A. 1998; PubMed Scopus Google Scholar), the intracellular that activates Src S. Y. T. Immunity. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar) or via F. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). In this study we a mutant cell line to demonstrate that the T non-receptor tyrosine kinase p56lck is of the by which Notch-1 activates PI3K signaling. We this by that p56lck Notch-1 and PI3K in T cell lines and T cells. We show that the anti-apoptotic effect of Notch-1 is blocked by the Src kinase inhibitor PP2, that Notch-1 with Src p56lck. Akt does not co-immunoprecipitate with the does Akt with the The of by the interaction mechanism that activates is the of which with the complex and with Akt to signaling. of the of signaling pathways to apoptosis of the of these We demonstrate that and Notch-1 are present as a complex in T cells. This is with the that disruption of of these pathways as Akt or p56lck in to apoptotic signaling J. Immunol. 2001; PubMed Scopus Google Scholar, W.S. K. M.L. K. T. W. R. K. T. Genes Dev. 2001; PubMed Scopus Google Scholar). p56lck is expressed in T cells and with and has been implicated in activation resulting from T cell receptor p56lck is in T cells, and this kinase is for the of T cells B. G. P. R. Science. 2000; PubMed Scopus Google Scholar). p56lck PI3K and the tyrosine B. Y. S. R. J. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). Furthermore, p56lck and are implicated in the of with PI3K and S. A. PubMed Scopus Google Scholar), which is to signaling T cell many of T cells, not to but as regulators of T cell In of the of Notch-1 signaling in T cell are required to the of Notch-1 interaction with PI3K and p56lck in T cell with the is that Notch as of cytokine signaling to cell survival in in T cell an antigen T cells are by Science. 1998; PubMed Scopus Google Scholar). to the loss of the of T cells is of the J. Annu. Rev. Immunol. 2002; 20: PubMed Scopus Google Scholar). initial events resulting in the of survival of T cells is dependent on by S. T. S. A. Immunity. 1998; 9: Full Text Full Text PDF PubMed Scopus Google Scholar). proteins like Bcl-2 and Bcl-xL are for and their expression is to cytokine signaling in T cells D.R. J.C. Thompson C.B. Immunol. 2002; PubMed Scopus Google Scholar). a functional between Notch-1, p56lck, and activation of Akt, that are intermediates in T cell of the mechanism by which Notch and PI3K signaling events that T cell stimulation to the regulation of apoptotic and survival of T cells into molecular underlying T cell We are to of and for and The monoclonal and by were obtained from the Developmental Studies Hybridoma Bank the of the of and by The of of City, The of of this were in by the of This in with to this