title: Androgens repress Bcl-2 expression via activation of the retinoblastoma (RB) protein in prostate cancer cells.
abstract: The oncogene Bcl-2 is upregulated frequently in prostate tumors following androgen ablation therapy, and Bcl-2 overexpression may contribute to the androgen-refractory relapse of the disease. However, the molecular mechanism underlying androgenic regulation of Bcl-2 in prostate cancer cells is understood poorly. In this study, we demonstrated that no androgen response element (ARE) was identified in the androgen-regulated region of the P1 promoter of Bcl-2 gene, whereas, we provided evidence that the androgenic effect is mediated by E2F1 protein through a putative E2F-binding site in the promoter. We further demonstrated that retinoblastoma (RB) protein plays a critical role in androgen regulation of Bcl-2. The phosphorylation levels of RB at serine residues 780 and 795 were decreased in LNCaP cells treated with androgens. Ectopic expression of a constitutively active form of RB inhibited expression of Bcl-2. Knockdown of endogenous RB protein by an Rb small inference RNA (siRNA) induced an increase in Bcl-2 levels. Most importantly, the effect of androgens on Bcl-2 was abolished completely by specific inhibition of RB function with a mutated E1A. Finally, androgen treatment of LNCaP cells upregulated specifically levels of the cyclin-dependent kinase inhibitors (CDKIs) p15INK4B and p27KIP1. Ectopic expression of p15INK4B and/or p27KIP1 inhibited Bcl-2 expression. Knockdown of endogenous p15INK4B or p27KIP1 protein with a pool of siRNAs diminished androgen-induced downregulation of Bcl-2 expression. Therefore, our data indicate that androgens suppress Bcl-2 expression through negatively modulating activities of the E2F site in the Bcl-2 promoter by activating the CDKI-RB axis.
authors.affiliation: Department of Urology, Mayo Clinic/Foundation, Rochester, MN 55905, USA.
authors.forename: Haojie
authors.initials: H
authors.lastname: Huang
authors.forename: Ofelia L
authors.initials: OL
authors.lastname: Zegarra-Moro
authors.forename: Douglas
authors.initials: D
authors.lastname: Benson
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Tindall
mesh_terms: D000728:Androgens / Q000378:metabolism* / Q000494:pharmacology; D045744:Cell Line, Tumor; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D017930:Genes, Reporter; D006801:Humans; D008297:Male; D015741:Metribolone / Q000494:pharmacology; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors* / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection
chemical_list: D000728:Androgens; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D016160:Retinoblastoma Protein; D015741:Metribolone; D012694:Serine