Overexpressed androgen receptor linked to p21(WAF1) silencing may be responsible for androgen independence and resistance to apoptosis of a prostate cancer cell line

An androgen-independent (AI) prostate cancer cell line, derived recently fr om an LNCaP cell line maintained in androgen-poor conditions has properties resembling a subgroup of advanced prostate cancers in that it has an overe xpressed androgen receptor (AR), undetectable levels of p21(WAF1) and prost ate-specific antigen, and is resistant to apoptosis. Th loss of prostate-sp ecific antigen expression but not the p21(WAF1) is attributable to gene sil encing by hypermethylation. The high AR and undetectable p21(WAF1) of Al ce lls, and lower AR but highly expressed p21(WAF1) of androgen-dependent pare ntal LNCaP cells, suggest a possibility of functional link between these tw o proteins. Therefore, we examined th impact the modulation of AR will have on the expression of p21(WAF1) Treatment of androgen-dependent cells with an androgen agonist, R1881 increased the AR protein level, whereas it simul taneously reduced th endogenous p21(WAF1)-protein 8-fold and the activity o f a transiently trans fected p21-promoter-reporter 10-fold. The down-regula tion of p21(WAF1) promoter appeared to be ARE mediated, dependent on AR, an d no cell-type specific. Furthermore, a reduction of the AR level in Al cel ls by AR-antisense oligonucleotide increased the p21(WAF1) promoter-reporte r activity by similar to4-fold, confirming a functional link between these two pro teins. A strong, direct induction of p21(WAF1) expression achieved by treat ment of AI cells with trichostatin A produced a partial reversion of the A phenotype evidenced by increased sensitivity of these cells to pac litaxel- induced apoptosis. Moreover, a reduction of AR level by antisense treat ment, which also increased p21(WAF1) expression, partially restored t h androgen dependence of AI cells for growth. The functional link between A R dosage and p21(WAF1) expression suggests that therapeutic reduction of AR protein in advanced prostate cancers with elevated AR levels ma re-establi sh their hormone dependence and improve therapeutic response to repeated ho rmonal ablation and/or induction of apoptosis.