PCPH expression in human prostate carcinoma cells confers resistance to cisplatin-induced apoptosis through a mechanism that involves PKC alpha and Bcl-2

C80 Prostate cancer is one of the malignant tumor types that frequently exhibit resistance to anticancer drugs, a phenomenon that typically results, at least in part, from enhanced antiapoptotic response mechanisms developed by the cancer cells. Understanding drug resistance mechanisms should, therefore, facilitate the design of optimized chemotherapy protocols against prostate cancer. Recently, we described that the PCPH protein is highly expressed in human specimens of prostatic intraepithelial neoplasia (PIN) and prostate cancer (PCa), and that PCPH enhanced protein kinase C (PKCδ) expression, which up-regulated type I collagen production and, consequently, contributed to increase the invasiveness of human PCa cell lines. We now report that PCPH expression confers resistance to cisplatin-induced apoptosis. LNCaP cells expressing a specific shRNA against PCPH were about 70% more sensitive to cisplatin-induced apoptosis than LNCaP expressing a non-specific, scrambled shRNA control. Furthermore, PC-3 cells expressing a truncated, oncogenic PCPH variant protein (mt-PCPH) were found to be significantly more resistant to cisplatin-induced apoptosis when compared to PC-3 cells expressing the normal PCPH protein or to cells transfected with DNA of the corresponding empty vector as control. Additional experiments showed that PCPH expression resulted in elevated levels of phosphorylated PKCα and, simultaneously, enhanced the expression of the antiapoptotic protein Bcl-2. Moreover, inhibition of PKCα expression, but not that of PKCδ or PKCβ, sensitized prostate cell lines to cisplatin-induced apoptosis. Consistently, shRNA-mediated Bcl-2 knockdown increased the sensitivity of LNCaP and PC-3 cells to cisplatin treatment and, more importantly, resulted in the reversion of the sensitivity to cisplatin of PC-3 cells expressing the mt-PCPH oncoprotein to the level characteristic of untransfected cells. Re-expression of Bcl-2 in LNCaP cells in which PCPH had been previously knocked down by stable expression of a specific shRNA reversed the sensitivity to cisplatin-induced apoptosis produced by PCPH knockdown. Taken together results from this study suggest that targeting PCPH expression in combination with chemotherapeutic treatment may improve the outcome of protocols currently used for prostate cancer treatment.