title: Down-regulation of suppressor of cytokine signaling-3 causes prostate cancer cell death through activation of the extrinsic and intrinsic apoptosis pathways.
abstract: Suppressor of cytokine signaling-3 (SOCS-3) acts as a negative feedback regulator of the Janus-activated kinase/signal transducers and activators of transcription factors signaling pathway and plays an important role in the development and progression of various cancers. To better understand the role of SOCS-3 in prostate cancer, SOCS-3 expression was down-regulated in DU-145, LNCaP-IL-6+, and PC3 cells by consecutive SOCS-3 small interfering RNA transfections. SOCS-3 mRNA and protein expression as measured by quantitative reverse transcription-PCR and Western blot, respectively, were decreased by approximately 70% to 80% compared with controls. We observed a significant decrease in cell proliferation and viability in all SOCS-3-positive cell lines but not in the parental LNCaP cell line, which is SOCS-3 negative. In this study, we show that down-regulation of SOCS-3 leads to an increased cell death in prostate cancer cell lines. We found a considerable increase in the activation of the proapoptotic caspase-3/caspase-7, caspase-8, and caspase-9. A significant up-regulation of cleaved poly(ADP-ribose) polymerase and inhibition of Bcl-2 expression was observed in all SOCS-3-positive cell lines. Overexpression of Bcl-2 could rescue cells with decreased SOCS-3 levels from going into apoptosis. Tissue microarray data prove that SOCS-3 is highly expressed in castration-refractory tumor samples. In conclusion, we show that SOCS-3 is an important protein in the survival machinery in prostate cancer and is overexpressed in castration-resistant tumors. SOCS-3 knockdown results in an increase of cell death via activation of the extrinsic and intrinsic apoptosis pathways.
authors.affiliation: Department of Urology, Innsbruck Medical University, Innsbruck, Austria.
authors.forename: Martin
authors.initials: M
authors.lastname: Puhr
authors.forename: Frédéric R
authors.initials: FR
authors.lastname: Santer
authors.forename: Hannes
authors.initials: H
authors.lastname: Neuwirt
authors.forename: Martin
authors.initials: M
authors.lastname: Susani
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Nemeth
authors.forename: Alfred
authors.initials: A
authors.lastname: Hobisch
authors.forename: Lukas
authors.initials: L
authors.lastname: Kenner
authors.forename: Zoran
authors.initials: Z
authors.lastname: Culig
mesh_terms: D017209:Apoptosis / Q000502:physiology; D020169:Caspases / Q000378:metabolism; D015536:Down-Regulation; D004789:Enzyme Activation; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism; D008297:Male; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D050794:STAT1 Transcription Factor / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D014162:Transfection
chemical_list: D015850:Interleukin-6; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; C106644:SOCS3 protein, human; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D011065:Poly(ADP-ribose) Polymerases; D020169:Caspases