title: Akt phosphorylation and stabilization of X-linked inhibitor of apoptosis protein (XIAP).
abstract: Akt negatively regulates apoptotic pathways at a premitochondrial level through phosphorylation and modulation of proteins such as Bad, Forkhead proteins, and GSK-3beta. Akt has also been shown to protect cell death at a post-mitochondrial level, although its downstream targets have not been well documented. Here, we demonstrate that Akt, including AKT1 and AKT2, interacts with and phosphorylates X-linked inhibitor of apoptosis protein (XIAP) at residue serine-87 in vitro and in vivo. Phosphorylation of XIAP by Akt protects XIAP from ubiquitination and degradation in response to cisplatin. Moreover, autoubiquitination of XIAP is also inhibited by Akt. Consistent with this, an XIAP mutant introduced into cells which mimics the Akt-phosphorylated form (i.e. XIAP-S87D) displays reduced ubiquitination and degradation as compared with wild type XIAP. The greater stability of XIAP-S87D in cells translated to increased cell survival after cisplatin treatment. Conversely, a mutant that could not be phosphorylated by Akt (XIAP-S87A) was more rapidly degraded and showed increased cisplatin-induced apoptosis. Furthermore, suppression of XIAP by either siRNA or adenovirus of antisense of XIAP induced programmed cell death and inhibited Akt-stimulated cell survival in ovarian cancer cells. These data identify XIAP as a new downstream target of Akt and a potentially important mediator of the effect of Akt on cell survival.
authors.affiliation: Departments of Pathology and Interdisciplinary Oncology, University of South Florida College of Medicine and H. Lee Moffitt Cancer Center, Tampa, Florida 33612, USA.
authors.forename: Han C
authors.initials: HC
authors.lastname: Dan
authors.forename: Mei
authors.initials: M
authors.lastname: Sun
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kaneko
authors.forename: Richard I
authors.initials: RI
authors.lastname: Feldman
authors.forename: Santo V
authors.initials: SV
authors.lastname: Nicosia
authors.forename: Hong-Gang
authors.initials: HG
authors.lastname: Wang
authors.forename: Benjamin K
authors.initials: BK
authors.lastname: Tsang
authors.forename: Jin Q
authors.initials: JQ
authors.lastname: Cheng
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D019556:COS Cells; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D045744:Cell Line, Tumor; D002470:Cell Survival; D002945:Cisplatin / Q000494:pharmacology; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D020287:In Situ Nick-End Labeling; D051379:Mice; D009097:Multienzyme Complexes / Q000378:metabolism; D009154:Mutation; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D046988:Proteasome Endopeptidase Complex; D014176:Protein Biosynthesis; D017346:Protein Serine-Threonine Kinases; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012694:Serine / Q000737:chemistry; D014158:Transcription, Genetic; D025801:Ubiquitin / Q000378:metabolism; D051636:X-Linked Inhibitor of Apoptosis Protein
chemical_list: D009097:Multienzyme Complexes; D016376:Oligonucleotides, Antisense; D011506:Proteins; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D011993:Recombinant Fusion Proteins; D025801:Ubiquitin; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D012694:Serine; D005982:Glutathione Transferase; C494918:AKT1 protein, human; C494921:AKT2 protein, human; C494920:Akt1 protein, rat; C494922:Akt2 protein, mouse; C494923:Akt2 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D002945:Cisplatin