title: Hsp27 promotes insulin-like growth factor-I survival signaling in prostate cancer via p90Rsk-dependent phosphorylation and inactivation of BAD.
abstract: Hsp27 is highly expressed in castrate-resistant prostate cancer. Although its overexpression confers resistance to androgen ablation and chemotherapy, the mechanisms by which Hsp27 inhibits treatment-induced apoptosis are incompletely defined. Castrate-resistance often correlates with increased activity of autocrine and/or paracrine growth/survival stimulatory loops including the mitogen-activated protein kinase (MAPK) and Akt pathways and insulin-like growth factor (IGF) axis components. Because Hsp27 can be activated by both MAPK and Akt pathways, it is possible that interactions between IGF-I signaling and Hsp27 phosphoactivation function to promote castrate-resistant progression. Here, we report that Hsp27 expression and phosphorylation levels correlate with IGF-I signaling and castrate-resistant progression in human prostate cancer specimens and cell lines. IGF-I induces Hsp27 phosphorylation in a time- and dose-dependent manner via p90Rsk, which interacts directly with and phosphorylates Hsp27 in vitro and in vivo. Conversely, p90Rsk inhibition using short interfering RNA or a dominant negative mutant abolishes IGF-I-induced Hsp27 phosphorylation. Hsp27 overexpression increases IGF-I-induced phosphorylation of Erk, p90Rsk, and Akt. Conversely, Hsp27 knockdown abrogates IGF-I-induced phosphorylation of Erk, p90Rsk, and Akt, thereby destabilizing Bad/14-3-3 complexes and increasing apoptotic rates. These data elucidate the interactions between Hsp27 phosphorylation and the IGF-I receptor signaling pathway and support targeting Hsp27 as a therapeutic strategy for castrate-resistant prostate cancer.
authors.affiliation: Department of Urologic Sciences, The Vancouver Prostate Centre, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Amina
authors.initials: A
authors.lastname: Zoubeidi
authors.forename: Anousheh
authors.initials: A
authors.lastname: Zardan
authors.forename: Romina M
authors.initials: RM
authors.lastname: Wiedmann
authors.forename: Jennifer
authors.initials: J
authors.lastname: Locke
authors.forename: Eliana
authors.initials: E
authors.lastname: Beraldi
authors.forename: Ladan
authors.initials: L
authors.lastname: Fazli
authors.forename: Martin E
authors.initials: ME
authors.lastname: Gleave
mesh_terms: D048948:14-3-3 Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D048708:Cell Growth Processes / Q000502:physiology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D055551:HSP27 Heat-Shock Proteins / Q000096:biosynthesis / Q000378:metabolism*; D006360:Heat-Shock Proteins; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D008297:Male; D051379:Mice; D018832:Molecular Chaperones; D010766:Phosphorylation; D011471:Prostatic Neoplasms / Q000378:metabolism* / Q000473:pathology; D011485:Protein Binding; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism*; D015398:Signal Transduction; D051025:bcl-Associated Death Protein / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D048948:14-3-3 Proteins; C494819:BAD protein, human; D055551:HSP27 Heat-Shock Proteins; C057725:HSPB1 protein, human; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D051025:bcl-Associated Death Protein; D007334:Insulin-Like Growth Factor I; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D048049:Extracellular Signal-Regulated MAP Kinases