Small-interfering RNA–induced androgen receptor silencing leads to apoptotic cell death in prostate cancer

• Published in: Molecular cancer therapeutics 2005-04, Vol.4 (4), p.505-515
• Main Authors: Liao, Xinbo, Tang, Siqing, Thrasher, J Brantley, Griebling, Tomas L, Li, Benyi
• Format: Article
• Language: English
• Subjects: androgen receptor; Annexin A5 - metabolism; Apoptosis; bcl-X Protein; Blotting, Western; Caspase 3; Caspase 6; Caspases - metabolism; Cell Death; Cell Line, Tumor; Cell Survival; Dose-Response Relationship, Drug; Enzyme Activation; Flow Cytometry; Gene Silencing; Humans; Male; Membrane Potentials; Mitochondria - metabolism; Poly(ADP-ribose) Polymerases - metabolism; prostate cancer; Prostatic Neoplasms - genetics; Prostatic Neoplasms - pathology; Protein Binding; Proteins - metabolism; Proto-Oncogene Proteins c-bcl-2 - metabolism; Receptors, Androgen - genetics; Reverse Transcriptase Polymerase Chain Reaction; RNA Interference; RNA, Messenger - metabolism; RNA, Small Interfering - metabolism; small interfering RNA; Time Factors; Transfection
• ISSN: 1535-7163; 1538-8514
• DOI: 10.1158/1535-7163.MCT-04-0313

Prostate cancer is the second leading cause of cancer death in the United States and, thus far, there has been no effective therapy for the treatment of hormone-refractory disease. Recently, the androgen receptor (AR) has been shown to play a critical role in the development and progression of the disease. In this report, we showed that knocking down the AR protein level by a small interfering RNA (siRNA) approach resulted in a significant apoptotic cell death as evidenced by an increased annexin V binding, reduced mitochondrial potential, caspase-3/6 activation, and DFF45 and poly(ADP-ribose) polymerase cleavage. The apoptotic response was specifically observed in those siRNA-transfected cells that harbor a native AR gene. No cell death was found in the AR-null prostate cancer cell PC-3 or its subline that has been reconstituted with an exogenous AR gene, as well as two breast cancer cell lines that are AR positive. Moreover, in parallel with the siRNA-induced AR silencing, the antiapoptotic protein Bcl-xL was significantly reduced, which might account for the apoptotic cell death because ectopic enforced expression of Bcl-xL protein partially inhibited apoptosis after AR silencing. Taken together, our data showed that knocking down the AR protein level in prostate cancer cells leads to apoptosis by disrupting the Bcl-xL–mediated survival signal downstream of AR-dependent survival pathway.