The success of gene therapy using a RNA interference approach relies on small interfering RNA (siRNA) expression from a highly tissue-specific RNA polymerase II promoter rather than from ubiquitous RNA polymerase III. Accordingly, we have developed a prostate-specific vector that expresses siRNAs from the human prostate-specific antigen promoter, a RNA polymerase II promoter. Our data demonstrate androgen-dependent and tissue-specific siRNA-mediated gene silencing in the androgen-responsive prostate cancer cell line, LNCaP. The biological significance was evidenced by altered apoptotic activity through the inhibition of the apoptosis-related regulatory gene. These results demonstrate that siRNA-mediated gene silencing from a tissue-specific RNA polymerase II promoter could be a potential tool for tissue-specific gene therapy.