title: Activated α2-macroglobulin binding to cell surface GRP78 induces T-loop phosphorylation of Akt1 by PDK1 in association with Raptor.
abstract: PDK1 phosphorylates multiple substrates including Akt by PIP3-dependent mechanisms. In this report we provide evidence that in prostate cancer cells stimulated with activated α2-macroglobulin (α2M*) PDK1 phosphorylates Akt in the T-loop at Thr(308) by using Raptor in the mTORC1 complex as a scaffold protein. First we demonstrate that PDK1, Raptor, and mTOR co-immunoprecipitate. Silencing the expression, not only of PDK1, but also Raptor by RNAi nearly abolished Akt phosphorylation at Akt(Thr308) in Raptor-immunoprecipitates of α2M*-stimulated prostate cancer cells. Immunodepleting Raptor or PDK from cell lysates of cells treated with α2M* drastically reduced Akt phosphorylation at Thr(308), which was recovered by adding the supernatant of Raptor- or PDK1-depleted cell lysates, respectively. Studies of insulin binding to its receptor on prostate cancer cells yielded similar results. We thus demonstrate that phosphorylating the T-loop Akt residue Thr(308) by PDK1 requires Raptor of the mTORC1 complex as a platform or scaffold protein.
authors: Department of Pathology, Duke University Medical Center, Durham, North Carolina, United States of America.
authors: Uma Kant
authors: UK
authors: Misra
authors: Department of Pathology, Duke University Medical Center, Durham, North Carolina, United States of America.
authors: Salvatore Vincent
authors: SV
authors: Pizzo
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D002457:Cell Extracts; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D008297:Male; D008819:Mice, Nude; D008954:Models, Biological; D010766:Phosphorylation; D010769:Phosphothreonine / Q000378:metabolism; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000737:chemistry* / Q000378:metabolism*; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D012330:RNA, Double-Stranded / Q000378:metabolism; D000076223:Regulatory-Associated Protein of mTOR; D014162:Transfection; D000511:alpha-Macroglobulins / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002457:Cell Extracts; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; C000631429:PDK1 protein, human; C000631433:Pdk1 protein, mouse; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D012330:RNA, Double-Stranded; C463659:RPTOR protein, human; D000076223:Regulatory-Associated Protein of mTOR; D000511:alpha-Macroglobulins; D010769:Phosphothreonine; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt