title: Involvement of Hsp90 in signaling and stability of 3-phosphoinositide-dependent kinase-1.
abstract: Serine/threonine kinase Akt is thought to mediate many biological actions toward anti-apoptotic responses. Screening of drugs that could interfere with the Akt signaling pathway revealed that Hsp90 inhibitors (e.g. geldanamycin, radicicol, and its analogues) induced Akt dephosphorylation, which resulted in Akt inactivation and apoptosis of the cells. Hsp90 inhibitors did not directly affect Akt kinase activity in vitro. Thus, we examined the effects of Hsp90 inhibitors on upstream Akt kinases, phosphatidylinositide-3-OH kinase (PI3K) and 3-phosphoinositide-dependent protein kinase-1 (PDK1). Hsp90 inhibitors had no effect on PI3K protein expression. In contrast, treatment of the cells with Hsp90 inhibitors decreased the amount of PDK1 without directly inhibiting PDK1 kinase activity. We found that the kinase domain of PDK1 was essential for complex formation with Hsp90 and that Hsp90 inhibitors suppressed PDK1 binding to Hsp90. PDK1 degradation mechanisms revealed that inhibition of PDK1 binding to Hsp90 caused proteasome-dependent degradation of PDK1. Treatment of proteasome inhibitors increased the amount of detergent-insoluble PDK1 in Hsp90 inhibitor-treated cells. Therefore, the association of PDK1 with Hsp90 regulates its stability, solubility, and signaling. Because Akt binding to Hsp90 is also involved in the maintenance of Akt kinase activity, Hsp90 plays an important role in PDK1-Akt survival signaling pathway.
authors.affiliation: Institute of Molecular and Cellular Biosciences, University of Tokyo, Tokyo 113-0032, Japan.
authors.forename: Naoya
authors.initials: N
authors.lastname: Fujita
authors.forename: Saori
authors.initials: S
authors.lastname: Sato
authors.forename: Atsushi
authors.initials: A
authors.lastname: Ishida
authors.forename: Takashi
authors.initials: T
authors.lastname: Tsuruo
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D019556:COS Cells; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival; D003546:Cysteine Endopeptidases / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D003902:Detergents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D009097:Multienzyme Complexes / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D011487:Protein Conformation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D064413:3-Phosphoinositide-Dependent Protein Kinases; D020169:Caspases; D003546:Cysteine Endopeptidases; D018076:DNA, Complementary; D003902:Detergents; D004791:Enzyme Inhibitors; D018841:HSP90 Heat-Shock Proteins; D009097:Multienzyme Complexes; D019869:Phosphatidylinositol 3-Kinases; D046988:Proteasome Endopeptidase Complex; D017346:Protein Serine-Threonine Kinases; C578562:PDPK1 protein, human