title: Akt attenuation of the serine protease activity of HtrA2/Omi through phosphorylation of serine 212.
abstract: The serine protease HtrA2/Omi is released from the mitochondria into the cytosol following apoptosis stimuli, leading to the programmed cell death in caspase-dependent and -independent manners. The function of HtrA2/Omi closely relates to its protease activity, which is required for cleavage of its substrate such as the members of the X-linked inhibitor of apoptotic protein family. However, the regulation of HtrA2/Omi by signaling molecule has not been documented. Here we report that serine/threonine kinases Akt1 and Akt2 phosphorylate mitochondria-released HtrA2/Omi on serine 212 in vivo and in vitro, which results in attenuation of its serine protease activity and pro-apoptotic function. Abolishing HtrA2/Omi phosphorylation by Akt through mutation of serine 212 to alanine (HtrA2/Omi-S212A) retains its serine protease activity and induces more apoptosis as compared with wild-type HtrA2/Omi. Conversely, HtrA2/Omi-S212D, a mutant mimicking phosphorylation, lost the protease activity and failed to induce the programmed cell death. Furthermore, the phosphorylated HtrA2/Omi fails to cleave X-linked inhibitor of apoptotic protein without interfering with their complex formation. In addition, Akt inhibits the release of HtrA2/Omi from the mitochondria into the cytoplasm in response to cisplatin treatment. These data reveal for the first time that HtrA2/Omi is directly regulated by Akt and provide a mechanism by which Akt induces cell survival at post-mitochondrial level.
authors.affiliation: Department of Pathology and Cell Biology and Molecular Oncology Program, H. Lee Moffitt Cancer Center and College of Medicine, University of South Florida, Tampa, Florida 33612, USA.
authors.forename: Lin
authors.initials: L
authors.lastname: Yang
authors.forename: Mei
authors.initials: M
authors.lastname: Sun
authors.forename: Xia-meng
authors.initials: XM
authors.lastname: Sun
authors.forename: George Z
authors.initials: GZ
authors.lastname: Cheng
authors.forename: Santo V
authors.initials: SV
authors.lastname: Nicosia
authors.forename: Jin Q
authors.initials: JQ
authors.lastname: Cheng
mesh_terms: D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D003593:Cytoplasm / Q000201:enzymology; D015536:Down-Regulation; D015971:Gene Expression Regulation, Enzymologic; D000074923:High-Temperature Requirement A Serine Peptidase 2; D006801:Humans; D051379:Mice; D008928:Mitochondria / Q000201:enzymology; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D012694:Serine / Q000235:genetics / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D024101:Mitochondrial Proteins; D012694:Serine; D051057:Proto-Oncogene Proteins c-akt; D012697:Serine Endopeptidases; C000615914:HTRA2 protein, human; D000074923:High-Temperature Requirement A Serine Peptidase 2; C000615915:Htra2 protein, mouse