Androgen Receptor Expression in Androgen-independent Prostate Cancer Is Associated with Increased Expression of Androgen-regulated Genes1

The human prostate cancer (CaP) xenograft, CWR22, mimics human CaP. CWR22 grows in testosterone-stimulated nude mice, regresses after castration, and recurs after 5-6 months in the absence of testicular androgen. Like human CaP that recurs during androgen deprivation therapy, the recurrent CWR22 expresses high levels of androgen receptor (AR). Immunohistochemical, Western, and Northern blot analyses dem onstrated that AR expression in the androgen-independent CWR22 is similar to AR expression in the androgen-dependent CYYR22 prior to castration. Expression of prostate-specific antigen and human kallikrein-2 mRNAs, two well-characterized androgen-regulated genes in human CaP, was androgen dependent in CYVR22. Despite the absence of testicular androgen. prostate-specific antigen and human kallikrein-2 niRNA levels in recurrent CVVR22 were higher than the levels in regressing CWR22 tumors from 12-day castrate mice and similar to those in the androgenstimulated CWR22. Other AR-regulated genes followed a similar pattern of expression. Differential expression screening identified androgen reg ulation of a-enolase and ct-tubulin as well as other unknown mRNAs. Insulin-like growth factor binding protein-5, the homeobox gene \k.\ 3.1, the AR coactivator ARA-70, and cell cycle genes (tiki and Cdk2 were androgen regulated in CWR22. In recurrent CYVR22, the steady-state levels of all these AR-dependent mRNAs were similar to those in the androgen-stimulated CYVR22, despite the absence of testicular androgen. Expression of AR and AR-regulated genes in the androgen-deprived recurrent CWR22 at levels similar to the androgen-stimulated CWR22 suggests that AR is transcriptionally active in recurrent CWR22. Induc tion of these AR-regulated genes may enhance cellular proliferation in relative androgen absence but through an AR-dependent mechanism. Alternatively, in androgen-independent tumors, induced expression of the AR-regulated gene network might result from a non-AR transcription control mechanism common to these genes.