The Role of Asp-462 in Regulating Akt Activity (2002)

Protein kinase Akt, an important downstream target of phosphatidylinositol 3-kinase, is one of the major survival factors in mammalian cells. It has been shown that phosphorylation of the C-terminal hydrophobic motif is required for Akt activation. The activated Akt then phosphorylates several pro-apoptotic proteins and prevents apoptosis mediated by caspases and the mitochondria. Interestingly, Akt has also been implicated to be a direct substrate of caspases in apoptotic cells induced by Fas (Widmann, C., Gibson, S., and Johnson, G. L. (1998) J. Biol. Chem. 273, 7141–7147) and anoikis (Bachelder, R. E., Wendt, M. A., Fujita, N., Tsuruo, T., and Mercurio, A. M. (2001) J. Biol. Chem. 276, 34702–34707). In this study we showed that cytokine withdrawal resulted in Akt degradation by caspases as well. Furthermore, we demonstrated residue Asp-462 of Akt1 which is just upstream of the hydrophobic motif to be the primary cleavage site. The Akt1 mutant (D462N) that prevented caspase cleavage was more stable during factor withdrawal and enhanced cell survival. The Akt truncation mutant mimicking the caspase cleavage product lost its kinase activity and functioned as a dominant negative to promote cell death. Our results suggest that the balance between Akt and caspase activity controls cell survival. In particular, caspases are able to render Akt inactive and dominantly inhibit the Akt pathway by cleaving off the C-terminal hydrophobic motif. Consequently, the survival signal is quickly down-regulated to allow apoptosis to occur. Protein kinase Akt, an important downstream target of phosphatidylinositol 3-kinase, is one of the major survival factors in mammalian cells. It has been shown that phosphorylation of the C-terminal hydrophobic motif is required for Akt activation. The activated Akt then phosphorylates several pro-apoptotic proteins and prevents apoptosis mediated by caspases and the mitochondria. Interestingly, Akt has also been implicated to be a direct substrate of caspases in apoptotic cells induced by Fas (Widmann, C., Gibson, S., and Johnson, G. L. (1998) J. Biol. Chem. 273, 7141–7147) and anoikis (Bachelder, R. E., Wendt, M. A., Fujita, N., Tsuruo, T., and Mercurio, A. M. (2001) J. Biol. Chem. 276, 34702–34707). In this study we showed that cytokine withdrawal resulted in Akt degradation by caspases as well. Furthermore, we demonstrated residue Asp-462 of Akt1 which is just upstream of the hydrophobic motif to be the primary cleavage site. The Akt1 mutant (D462N) that prevented caspase cleavage was more stable during factor withdrawal and enhanced cell survival. The Akt truncation mutant mimicking the caspase cleavage product lost its kinase activity and functioned as a dominant negative to promote cell death. Our results suggest that the balance between Akt and caspase activity controls cell survival. In particular, caspases are able to render Akt inactive and dominantly inhibit the Akt pathway by cleaving off the C-terminal hydrophobic motif. Consequently, the survival signal is quickly down-regulated to allow apoptosis to occur. Cell survival and apoptosis are tightly regulated processes in multicellular organisms, the disruption of which may lead to diseases such as cancer. The serine/threonine kinase Akt (also referred to as PKB or RAC-PK) has proven to be a critical player in cell survival pathways. Originally identified as the cellular homologue of the retroviral oncogene v-akt (3Bellicose A. Test J.R. Staal S.P. Tsichlis P.N. Science. 1991; 254: 274-277Crossref PubMed Scopus (786) Google Scholar), Akt is conserved throughout evolution. The activation of Akt occurs through a cascade of events and is thought to be directly downstream of phosphatidylinositol 3-kinase (4Alessi D.R. Andjelkovic M. Caudwell B. Cron P. Morrice N. Cohen P. Hemmings B.A. EMBO J. 1996; 15: 6541-6551Crossref PubMed Scopus (2493) Google Scholar, 5Franke T.F. Kaplan D.R. Cantley L.C. Cell. 1997; 88: 435-437Abstract Full Text Full Text PDF PubMed Scopus (1512) Google Scholar, 6Stephens L. Anderson K. Stokoe D. Erdjument-Bromage H. Painter G.F. Holmes A.B. Gaffney P.R. Reese C.B. McCormick F. Tempst P. Coadwell J. Hawkins P.T. Science. 1998; 279: 710-714Crossref PubMed Scopus (909) Google Scholar, 7Datta S.R. Brunet A. Greenberg M.E. Genes Dev. 1999; 13: 2905-2927Crossref PubMed Scopus (3704) Google Scholar). A number of studies (8Franke T.F. Yang S.I. Chan T.O. Datta K. Kazlauskas A. Morrison D.K. Kaplan D.R. Tsichlis P.N. Cell. 1995; 81: 727-736Abstract Full Text PDF PubMed Scopus (1817) Google Scholar, 9Dudek H. Datta S.R. Franke T.F. Birnbaum M.J. Yao R. Cooper G.M. Segal R.A. Kaplan D.R. Greenberg M.E. Science. 1997; 275: 661-665Crossref PubMed Scopus (2212) Google Scholar, 10Songyang Z. Baltimore D. Cantley L.C. Kaplan D.R. Franke T.F. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 11345-11350Crossref PubMed Scopus (322) Google Scholar, 11Ahmed N.N. Grimes H.L. Bellacosa A. Chan T.O. Tsichlis P.N. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 3627-3632Crossref PubMed Scopus (486) Google Scholar, 12Kulik G. Klippel A. Weber M.J. Mol. Cell. Biol. 1997; 17: 1595-1606Crossref PubMed Scopus (964) Google Scholar) have shown that many growth and survival factors, such as nerve growth factor, platelet-derived growth factor, insulin-like growth factor-1 and cytokines, can activate Aktin vivo. Akt contains an N-terminal pleckstrin homology domain (PH) 1The abbreviations used are: PH domain, pleckstrin homology domain; IL-3, interleukin-3; PDK1, 3-phosphoinositide-dependent protein kinase-1; PARP-1, poly(ADP-ribose) polymerase 1; FKHRs, forkhead related transcription factors; HA, hemagglutinin. 1The abbreviations used are: PH domain, pleckstrin homology domain; IL-3, interleukin-3; PDK1, 3-phosphoinositide-dependent protein kinase-1; PARP-1, poly(ADP-ribose) polymerase 1; FKHRs, forkhead related transcription factors; HA, hemagglutinin. and a C-terminal kinase domain. The PH domain binds to phosphatidylinositols (thereby recruiting Akt to the plasma membrane where PDK1 is located) (13Franke T.F. Kaplan D.R. Cantley L.C. Toker A. Science. 1997; 275: 665-668Crossref PubMed Scopus (1291) Google Scholar). Phosphorylation of both Thr-308 and Ser-473 is required for fully activating Akt (4Alessi D.R. Andjelkovic M. Caudwell B. Cron P. Morrice N. Cohen P. Hemmings B.A. EMBO J. 1996; 15: 6541-6551Crossref PubMed Scopus (2493) Google Scholar). Thr-308 is believed to be phosphorylated by PDK1 (14Alessi D.R. Deak M. Casamayor A. Caudwell F.B. Morrice N. Norman D.G. Gaffney P. Reese C.B. MacDougall C.N. Harbison D. Ashworth A. Bownes M. Curr. Biol. 1997; 7: 776-789Abstract Full Text Full Text PDF PubMed Scopus (613) Google Scholar, 15Downward J. Curr. Opin. Cell Biol. 1998; 10: 262-267Crossref PubMed Scopus (1180) Google Scholar, 16Brazil D.P. Hemmings B.A. Trends Biochem. Sci. 2001; 26: 657-664Abstract Full Text Full Text PDF PubMed Scopus (1028) Google Scholar), although the kinase that phosphorylates the Ser-473 site still remains unclear (17Chan, T. O., and Tsichlis, P. N. (2001) stke.sciencemag.org/cgi/content/full/ oc_sigtrans;2001/66/pe/.Google Scholar). Interestingly, Ser-473 is within the hydrophobic motif (FXX(F/Y)(S/T)(F/Y)) in the C-terminal tail of Akt. This hydrophobic motif is also conserved among the AGC family of kinases. Basal phosphorylation of the Ser-473 site is important for the activation of Akt (4Alessi D.R. Andjelkovic M. Caudwell B. Cron P. Morrice N. Cohen P. Hemmings B.A. EMBO J. 1996; 15: 6541-6551Crossref PubMed Scopus (2493) Google Scholar), presumably necessary for maintaining the proper conformation of the kinase domain and docking to PDK1 (18Biondi R.M. Cheung P.C. Casamayor A. Deak M. Currie R.A. Alessi D.R. EMBO J. 2000; 19: 979-988Crossref PubMed Scopus (246) Google Scholar). A recent report (19Maira S.M. Galetic I. Brazil D.P. Kaech S. Ingley E. Thelen M. Hemmings B.A. Science. 2001; 294: PubMed Scopus Google Scholar) has also identified a protein that is of to the C-terminal domain of Akt and its to the important of the C-terminal of in which may and family transcription factors S.R. H. S., H. Greenberg M.E. Cell. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, L. M. R. G. Science. 1997; PubMed Scopus Google Scholar, G. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar, A. A. M.J. Anderson M.J. J. Greenberg M.E. Cell. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). Phosphorylation of and to of its apoptotic activity L. M. R. G. Science. 1997; PubMed Scopus Google Scholar). It has also been that Akt can and in that Akt may cells apoptosis by caspases N. Franke T.F. E. S. Science. 1998; PubMed Scopus Google Scholar). Interestingly, Akt was to be during apoptosis induced by Fas and and of caspase activity prevented its degradation S. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, N. T. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, S. N. T. J. Cell. 2000; PubMed Scopus Google Scholar). results suggest a negative between Akt and caspases that may to the balance between cell survival and is still unclear Akt and caspases may in cell death. The where caspase cleavage may in and this cleavage may Akt survival activity to be In this we the caspase cleavage in Akt in and in and we identified a primary cleavage site between the kinase domain and the hydrophobic motif. of this site caspase cleavage and enhanced Akt survival activity cytokine The Akt cleavage product that the C-terminal tail lost its kinase activity and as a dominant negative in cells. in to phosphorylation of Thr-308 and the activity of Akt is also regulated by has been to be down-regulated during apoptosis induced by Fas or anoikis S. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, N. T. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). In this we demonstrated that Akt also be down-regulated during cell and is mediated by In we of Akt cytokine degradation is the of apoptosis in as of the cells between and Furthermore, of a Akt degradation in cells that in Akt and a of residue Asp-462 to was able to Akt cleavage and degradation both in and in vivo. Interestingly, the enhanced Akt survival activity in by Akt its kinase activity or caspase cleavage and Akt have been N. T. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, S. N. T. J. Cell. 2000; PubMed Scopus Google Scholar), the of of in suggest that the Asp-462 site is the primary cleavage site. cleavage this site has been It is that in studies the Asp-462 site may have been cleavage Asp-462 results in a in the of Akt and to C-terminal tail of Akt downstream of the kinase domain contains a hydrophobic motif conserved in of the AGC family D.R. Cohen P. Curr. Opin. Dev. 1998; PubMed Scopus Google Scholar). Phosphorylation of the Ser-473 residue this motif an as is thought to Akt PDK1 which then phosphorylates site Thr-308 in the activation of Akt (4Alessi D.R. Andjelkovic M. Caudwell B. Cron P. Morrice N. Cohen P. Hemmings B.A. EMBO J. 1996; 15: 6541-6551Crossref PubMed Scopus (2493) Google Scholar, D.R. Cohen P. Curr. Opin. Dev. 1998; PubMed Scopus Google Scholar). This hydrophobic motif a in Akt this we that this tail is necessary for the kinase activity of Akt The mutant that this tail an kinase domain. we that this protein lost its kinase activity in and cells apoptosis in vivo. It has been shown that the hydrophobic of several AGC family protein directly PDK1 (18Biondi R.M. Cheung P.C. Casamayor A. Deak M. Currie R.A. Alessi D.R. EMBO J. 2000; 19: 979-988Crossref PubMed Scopus (246) Google Scholar, R.M. A. Currie R.A. Deak M. Alessi D.R. EMBO J. 2001; PubMed Scopus Google Scholar). that the of the hydrophobic motif by caspase cleavage Asp-462 may have prevented PDK1 docking and phosphorylation of the of the tail may have between the tail and of Akt, its The of protein kinase and Akt that the of the hydrophobic a that the kinase domain D.R. Science. 1991; PubMed Scopus Google Scholar, J. Cron P. D. Hemmings B.A. D. Mol. Cell. Full Text Full Text PDF PubMed Scopus Google Scholar). In of recent is also that such cleavage may the of Akt proteins through the Akt tail (19Maira S.M. Galetic I. Brazil D.P. Kaech S. Ingley E. Thelen M. Hemmings B.A. Science. 2001; 294: PubMed Scopus Google study has is that by caspases is for of Akt. A of of Akt that several caspase are the of Asp-462 and this the signal the that the Akt that Akt are also the C-terminal tail during of a cell is by the balance between and pro-apoptotic The that activated Akt caspases and caspases in Akt a in cell survival and cells Akt Akt can inhibit pro-apoptotic factors such as transcription factor FKHRs, and the cells to the the of caspase activity can be such that survival factors Akt can be the cells to this cleavage of Akt Asp-462 was which is also the cells to It is that cleavage of Akt may have during the we the in Akt the or C-terminal is that Akt protein Akt In of this the Akt protein in cells a In results suggest that cells the primary cleavage of Akt by caspases Asp-462 the hydrophobic is able to Akt survival activity is have shown that the Akt cleavage product as a dominant Interestingly, Akt cleavage cleavage have also been to as dominant negative of Akt and the apoptotic N. T. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google S. N. T. J. Cell. 2000; PubMed Scopus Google Scholar). are N-terminal to the kinase domain, and cleavage is to the PH domain. cleavage of Akt results in the survival signal quickly down-regulated the cells to Cell survival and apoptosis are tightly regulated processes in multicellular organisms, the disruption of which may lead to diseases such as cancer. The serine/threonine kinase Akt (also referred to as PKB or RAC-PK) has proven to be a critical player in cell survival pathways. Originally identified as the cellular homologue of the retroviral oncogene v-akt (3Bellicose A. Test J.R. Staal S.P. Tsichlis P.N. Science. 1991; 254: 274-277Crossref PubMed Scopus (786) Google Scholar), Akt is conserved throughout evolution. The activation of Akt occurs through a cascade of events and is thought to be directly downstream of phosphatidylinositol 3-kinase (4Alessi D.R. Andjelkovic M. Caudwell B. Cron P. Morrice N. Cohen P. Hemmings B.A. EMBO J. 1996; 15: 6541-6551Crossref PubMed Scopus (2493) Google Scholar, 5Franke T.F. Kaplan D.R. Cantley L.C. Cell. 1997; 88: 435-437Abstract Full Text Full Text PDF PubMed Scopus (1512) Google Scholar, 6Stephens L. Anderson K. Stokoe D. Erdjument-Bromage H. Painter G.F. Holmes A.B. Gaffney P.R. Reese C.B. McCormick F. Tempst P. Coadwell J. Hawkins P.T. Science. 1998; 279: 710-714Crossref PubMed Scopus (909) Google Scholar, 7Datta S.R. Brunet A. Greenberg M.E. Genes Dev. 1999; 13: 2905-2927Crossref PubMed Scopus (3704) Google Scholar). A number of studies (8Franke T.F. Yang S.I. Chan T.O. Datta K. Kazlauskas A. Morrison D.K. Kaplan D.R. Tsichlis P.N. Cell. 1995; 81: 727-736Abstract Full Text PDF PubMed Scopus (1817) Google Scholar, 9Dudek H. Datta S.R. Franke T.F. Birnbaum M.J. Yao R. Cooper G.M. Segal R.A. Kaplan D.R. Greenberg M.E. Science. 1997; 275: 661-665Crossref PubMed Scopus (2212) Google Scholar, 10Songyang Z. Baltimore D. Cantley L.C. Kaplan D.R. Franke T.F. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 11345-11350Crossref PubMed Scopus (322) Google Scholar, 11Ahmed N.N. Grimes H.L. Bellacosa A. Chan T.O. Tsichlis P.N. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 3627-3632Crossref PubMed Scopus (486) Google Scholar, 12Kulik G. Klippel A. Weber M.J. Mol. Cell. Biol. 1997; 17: 1595-1606Crossref PubMed Scopus (964) Google Scholar) have shown that many growth and survival factors, such as nerve growth factor, platelet-derived growth factor, insulin-like growth factor-1 and cytokines, can activate Aktin vivo. Akt contains an N-terminal pleckstrin homology domain (PH) 1The abbreviations used are: PH domain, pleckstrin homology domain; IL-3, interleukin-3; PDK1, 3-phosphoinositide-dependent protein kinase-1; PARP-1, poly(ADP-ribose) polymerase 1; FKHRs, forkhead related transcription factors; HA, hemagglutinin. 1The abbreviations used are: PH domain, pleckstrin homology domain; IL-3, interleukin-3; PDK1, 3-phosphoinositide-dependent protein kinase-1; PARP-1, poly(ADP-ribose) polymerase 1; FKHRs, forkhead related transcription factors; HA, hemagglutinin. and a C-terminal kinase domain. The PH domain binds to phosphatidylinositols (thereby recruiting Akt to the plasma membrane where PDK1 is located) (13Franke T.F. Kaplan D.R. Cantley L.C. Toker A. Science. 1997; 275: 665-668Crossref PubMed Scopus (1291) Google Scholar). Phosphorylation of both Thr-308 and Ser-473 is required for fully activating Akt (4Alessi D.R. Andjelkovic M. Caudwell B. Cron P. Morrice N. Cohen P. Hemmings B.A. EMBO J. 1996; 15: 6541-6551Crossref PubMed Scopus (2493) Google Scholar). Thr-308 is believed to be phosphorylated by PDK1 (14Alessi D.R. Deak M. Casamayor A. Caudwell F.B. Morrice N. Norman D.G. Gaffney P. Reese C.B. MacDougall C.N. Harbison D. Ashworth A. Bownes M. Curr. Biol. 1997; 7: 776-789Abstract Full Text Full Text PDF PubMed Scopus (613) Google Scholar, 15Downward J. Curr. Opin. Cell Biol. 1998; 10: 262-267Crossref PubMed Scopus (1180) Google Scholar, 16Brazil D.P. Hemmings B.A. Trends Biochem. Sci. 2001; 26: 657-664Abstract Full Text Full Text PDF PubMed Scopus (1028) Google Scholar), although the kinase that phosphorylates the Ser-473 site still remains unclear (17Chan, T. O., and Tsichlis, P. N. (2001) stke.sciencemag.org/cgi/content/full/ oc_sigtrans;2001/66/pe/.Google Scholar). Interestingly, Ser-473 is within the hydrophobic motif (FXX(F/Y)(S/T)(F/Y)) in the C-terminal tail of Akt. This hydrophobic motif is also conserved among the AGC family of kinases. Basal phosphorylation of the Ser-473 site is important for the activation of Akt (4Alessi D.R. Andjelkovic M. Caudwell B. Cron P. Morrice N. Cohen P. Hemmings B.A. EMBO J. 1996; 15: 6541-6551Crossref PubMed Scopus (2493) Google Scholar), presumably necessary for maintaining the proper conformation of the kinase domain and docking to PDK1 (18Biondi R.M. Cheung P.C. Casamayor A. Deak M. Currie R.A. Alessi D.R. EMBO J. 2000; 19: 979-988Crossref PubMed Scopus (246) Google Scholar). A recent report (19Maira S.M. Galetic I. Brazil D.P. Kaech S. Ingley E. Thelen M. Hemmings B.A. Science. 2001; 294: PubMed Scopus Google Scholar) has also identified a protein that is of to the C-terminal domain of Akt and its to the important of the C-terminal of Akt. Akt in which may and family transcription factors S.R. H. S., H. Greenberg M.E. Cell. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, L. M. R. G. Science. 1997; PubMed Scopus Google Scholar, G. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar, A. A. M.J. Anderson M.J. J. Greenberg M.E. Cell. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). Phosphorylation of and to of its apoptotic activity L. M. R. G. Science. 1997; PubMed Scopus Google Scholar). It has also been that Akt can and in that Akt may cells apoptosis by caspases N. Franke T.F. E. S. Science. 1998; PubMed Scopus Google Scholar). Interestingly, Akt was to be during apoptosis induced by Fas and and of caspase activity prevented its degradation S. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, N. T. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, S. N. T. J. Cell. 2000; PubMed Scopus Google Scholar). results suggest a negative between Akt and caspases that may to the balance between cell survival and is still unclear Akt and caspases may in cell death. The where caspase cleavage may in and this cleavage may Akt survival activity to be In this we the caspase cleavage in Akt in and in and we identified a primary cleavage site between the kinase domain and the hydrophobic motif. of this site caspase cleavage and enhanced Akt survival activity cytokine The Akt cleavage product that the C-terminal tail lost its kinase activity and as a dominant negative in cells. in to phosphorylation of Thr-308 and the activity of Akt is also regulated by has been to be down-regulated during apoptosis induced by Fas or anoikis S. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, N. T. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). In this we demonstrated that Akt also be down-regulated during cell and is mediated by In we of Akt cytokine degradation is the of apoptosis in as of the cells between and Furthermore, of a Akt degradation in cells that in Akt and a of residue Asp-462 to was able to Akt cleavage and degradation both in and in vivo. Interestingly, the enhanced Akt survival activity in by Akt its kinase activity or caspase cleavage and Akt have been N. T. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, S. N. T. J. Cell. 2000; PubMed Scopus Google Scholar), the of of in suggest that the Asp-462 site is the primary cleavage site. cleavage this site has been It is that in studies the Asp-462 site may have been cleavage Asp-462 results in a in the of Akt and to C-terminal tail of Akt downstream of the kinase domain contains a hydrophobic motif conserved in of the AGC family D.R. Cohen P. Curr. Opin. Dev. 1998; PubMed Scopus Google Scholar). Phosphorylation of the Ser-473 residue this motif an as is thought to Akt PDK1 which then phosphorylates site Thr-308 in the activation of Akt (4Alessi D.R. Andjelkovic M. Caudwell B. Cron P. Morrice N. Cohen P. Hemmings B.A. EMBO J. 1996; 15: 6541-6551Crossref PubMed Scopus (2493) Google Scholar, D.R. Cohen P. Curr. Opin. Dev. 1998; PubMed Scopus Google Scholar). This hydrophobic motif a in Akt this we that this tail is necessary for the kinase activity of Akt The mutant that this tail an kinase domain. we that this protein lost its kinase activity in and cells apoptosis in vivo. It has been shown that the hydrophobic of several AGC family protein directly PDK1 (18Biondi R.M. Cheung P.C. Casamayor A. Deak M. Currie R.A. Alessi D.R. EMBO J. 2000; 19: 979-988Crossref PubMed Scopus (246) Google Scholar, R.M. A. Currie R.A. Deak M. Alessi D.R. EMBO J. 2001; PubMed Scopus Google Scholar). that the of the hydrophobic motif by caspase cleavage Asp-462 may have prevented PDK1 docking and phosphorylation of the of the tail may have between the tail and of Akt, its The of protein kinase and Akt that the of the hydrophobic a that the kinase domain D.R. Science. 1991; PubMed Scopus Google Scholar, J. Cron P. D. Hemmings B.A. D. Mol. Cell. Full Text Full Text PDF PubMed Scopus Google Scholar). In of recent is also that such cleavage may the of Akt proteins through the Akt tail (19Maira S.M. Galetic I. Brazil D.P. Kaech S. Ingley E. Thelen M. Hemmings B.A. Science. 2001; 294: PubMed Scopus Google study has is that by caspases is for of Akt. A of of Akt that several caspase are the of Asp-462 and this the signal the that the Akt that Akt are also the C-terminal tail during of a cell is by the balance between and pro-apoptotic The that activated Akt caspases and caspases in Akt a in cell survival and cells Akt Akt can inhibit pro-apoptotic factors such as transcription factor FKHRs, and the cells to the the of caspase activity can be such that survival factors Akt can be the cells to this cleavage of Akt Asp-462 was which is also the cells to It is that cleavage of Akt may have during the we the in Akt the or C-terminal is that Akt protein Akt In of this the Akt protein in cells a In results suggest that cells the primary cleavage of Akt by caspases Asp-462 the hydrophobic is able to Akt survival activity is have shown that the Akt cleavage product as a dominant Interestingly, Akt cleavage cleavage have also been to as dominant negative of Akt and the apoptotic N. T. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google S. N. T. J. Cell. 2000; PubMed Scopus Google Scholar). are N-terminal to the kinase domain, and cleavage is to the PH domain. cleavage of Akt results in the survival signal quickly down-regulated the cells to Akt has been to be down-regulated during apoptosis induced by Fas or anoikis S. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, N. T. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). In this we demonstrated that Akt also be down-regulated during cell and is mediated by In we of Akt cytokine degradation is the of apoptosis in as of the cells between and Furthermore, of a Akt degradation in cells that in Akt and a of residue Asp-462 to was able to Akt cleavage and degradation both in and in vivo. Interestingly, the enhanced Akt survival activity in by Akt its kinase activity or caspase cleavage and Akt have been N. T. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, S. N. T. J. Cell. 2000; PubMed Scopus Google Scholar), the of of in suggest that the Asp-462 site is the primary cleavage site. cleavage this site has been It is that in studies the Asp-462 site may have been cleavage Asp-462 results in a in the of Akt and to Akt. The C-terminal tail of Akt downstream of the kinase domain contains a hydrophobic motif conserved in of the AGC family D.R. Cohen P. Curr. Opin. Dev. 1998; PubMed Scopus Google Scholar). Phosphorylation of the Ser-473 residue this motif an as is thought to Akt PDK1 which then phosphorylates site Thr-308 in the activation of Akt (4Alessi D.R. Andjelkovic M. Caudwell B. Cron P. Morrice N. Cohen P. Hemmings B.A. EMBO J. 1996; 15: 6541-6551Crossref PubMed Scopus (2493) Google Scholar, D.R. Cohen P. Curr. Opin. Dev. 1998; PubMed Scopus Google Scholar). This hydrophobic motif a in Akt this we that this tail is necessary for the kinase activity of Akt The mutant that this tail an kinase domain. we that this protein lost its kinase activity in and cells apoptosis in vivo. It has been shown that the hydrophobic of several AGC family protein directly PDK1 (18Biondi R.M. Cheung P.C. Casamayor A. Deak M. Currie R.A. Alessi D.R. EMBO J. 2000; 19: 979-988Crossref PubMed Scopus (246) Google Scholar, R.M. A. Currie R.A. Deak M. Alessi D.R. EMBO J. 2001; PubMed Scopus Google Scholar). that the of the hydrophobic motif by caspase cleavage Asp-462 may have prevented PDK1 docking and phosphorylation of the of the tail may have between the tail and of Akt, its The of protein kinase and Akt that the of the hydrophobic a that the kinase domain D.R. Science. 1991; PubMed Scopus Google Scholar, J. Cron P. D. Hemmings B.A. D. Mol. Cell. Full Text Full Text PDF PubMed Scopus Google Scholar). In of recent is also that such cleavage may the of Akt proteins through the Akt tail (19Maira S.M. Galetic I. Brazil D.P. Kaech S. Ingley E. Thelen M. Hemmings B.A. Science. 2001; 294: PubMed Scopus Google Scholar). study has is that by caspases is for of Akt. A of of Akt that several caspase are the of Asp-462 and this the signal the that the Akt that Akt are also the C-terminal tail during The of a cell is by the balance between and pro-apoptotic The that activated Akt caspases and caspases in Akt a in cell survival and cells Akt Akt can inhibit pro-apoptotic factors such as transcription factor FKHRs, and the cells to the the of caspase activity can be such that survival factors Akt can be the cells to this cleavage of Akt Asp-462 was which is also the cells to It is that cleavage of Akt may have during the we the in Akt the or C-terminal is that Akt protein Akt In of this the Akt protein in cells a In results suggest that cells the primary cleavage of Akt by caspases Asp-462 the hydrophobic is able to Akt survival activity is have shown that the Akt cleavage product as a dominant Interestingly, Akt cleavage cleavage have also been to as dominant negative of Akt and the apoptotic N. T. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google S. N. T. J. Cell. 2000; PubMed Scopus Google Scholar). are N-terminal to the kinase domain, and cleavage is to the PH domain. cleavage of Akt results in the survival signal quickly down-regulated the cells to and for