Expression of the PCPH oncogene enhances the invasiness of prostate cancer cells by a PKCδ-dependent mechanism. Free

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Previous studies showed that PCPH, a gene that is frequently either mutated or deregulated in animal and human tumors, is not expressed in normal prostate epithelia, but it is highly expressed in prostatic intraepithelial neoplasia (PIN) and remains expressed in most prostate carcinoma cells. In addition, we also described that ectopic expression of PCPH enhanced the invasive ability of prostate cancer cell lines. Overexpression of the PCPH oncogene in PC-3 cells, which express low endogenous levels of PCPH, increased their invasive ability, whereas downregulation of PCPH expression by shRNA in LNCaP cells, which express high PCPH levels, decreased their invasiveness. In this study, we report on the characterization of the mechanism by which PCPH regulates the invasive ability of prostate cancer cells. In LNCaP cells, the downregulation of PCPH by shRNA produced marked morphologic changes, but these changes were prevented when the cells were cultured in the presence of type-I collagen. Consistently, we observed that the mRNA levels of type-I collagen were reduced in cells transfected with a PCPH-targeted shRNA. Conversely, the mRNA levels of type-I collagen increased in PC-3 cells after transfection with the PCPH oncogene (mt-PCPH) relative to the levels in mock-transfected cells and in cells transfected with the PCPH proto-oncogene. Additional results showed that PCPH regulated the expression of type I collagen by a mechanism involving PKCδ. The levels of PKCδ decreased in LNCaP cells transfected with PCPH shRNA relative to untransfected cells and to cells transfected with a non-specific shRNA control. Downregulation of PKCδ by PCPH shRNA as well as by rottlerin, a PKCδ specific inhibitor, decreased the levels of COL1A1 and COL1A2 mRNA and consequently inhibited the invasive ability of LNCaP cells. This report shows that the mechanism by which PCPH regulates PKCδ expression is a process that involves the transforming growth factor-beta (TGF-β)/Smad pathway. Results showed that Smad7, an inhibitory Smad, is overexpressed in LNCaP cells transfected with PCPH shRNA and, conversely, Smad7 is downregulated in PC-3 cells transfected with mt-PCPH. Taken together, our results suggest that the expression level and/or mutational status of PCPH contribute to determine the invasiveness of prostate cancer cells through a mechanism that involves PKCδ.