Androgen receptor-independent regulation of PSA by p300 in prostate cancer cells chronically treated with interleukin-6

3755

Prostate cancer (PCa) is the most frequent cancer in men. Although the precise mechanisms of PCa progression are not totally defined, the androgen receptor (AR) has been shown to play an important role. The AR is expressed at both early and late stages of PCa, and AR-regulated pathways are thought to be active evidenced by elevated levels of prostate specific antigen (PSA). Several coregulatory proteins of the AR, as well as cytokines, have been shown to be involved in PCa progression. Some of these coactivators and cytokines can act together to regulate AR activity. Indeed, we have shown previously that the coactivator p300 is critical for the activation of the AR by interleukin-6 (IL-6), a cytokine involved in late-stage PCa. In addition, we have shown that p300 expression correlates with PCa progression. In this study, we investigated the effect of p300 in LNCaP cells treated chronically with IL-6. This treatment was intended to mimic the environment found in late-stage PCa. These cells have been characterized previously, and they show a more aggressive behavior. Through reporter-based assays we found that p300 transfection induced activation of PSA in the IL-6-treated cells, and that the HAT activity of p300 was necessary for this activation. Interestingly, this effect was independent of the presence of androgens or anti-androgens in the media. In addition, we found that p300 had similar effects on the androgen response element III (ARE-III), which plays a major role in the AR-mediated activation of PSA. Real time and semi-quantitative PCR showed that mRNA levels of the AR were significantly reduced in these IL-6-treated cells. Moreover, by Western Blot and immuno-cytochemistry we found that AR protein was almost undetectable, indicating that the p300-mediated effects could be bypassing the AR. Finally, we found that p300 transfection up-regulates the expression levels of PSA mRNA and protein, indicating regulation of the endogenous PSA in the IL-6-treated cells. A similar effect of p300 was found on the mRNA levels of NKX3.1, an androgen-regulated gene. Conversely, p300 had no effect on the mRNA or protein levels of AR. Our findings reveal a new insight in the AR-regulated pathways in late-stage PCa. Moreover, our data suggest that coactivators such as p300 play a major role in PCa and could regulate AR-dependent genes in the absence, or substantially low levels, of AR. This work was supported by NIH grants DK60920, CA91956, the T.J. Martell Foundation, the Prostate Cancer foundation, and the Austrian National Bank grant 9581.