| Protein Kinase Cdelta (PKCdelta) has been implicated both as a tumor suppressor and as a positive regulator of cell cycle progression. PKCdelta has also been shown to both negatively and positively regulate apoptotic programs. To further complicate the picture, PKCdelta has been shown to be involved in the promotion of migration of some cells. These studies have led to conflicting hypotheses regarding the role of PKCdelta in tumorigenesis. In an attempt to clarify the mechanism by which PKCdelta might influence such diverse processes, we employed phorbol esters, which have been shown to down regulate PKC isoforms upon prolonged exposure. Using this approach, we show that treatment of MCF-7 cells with PMA depleted these cells of PKCdelta. Further, PMA induced multiple effects including secretion of Matrix Metal loproteinase-9 (MMP-9), up-regulation of Extracellular Matrix Metalloproteinase Inhibitor (EMMPRIN), activation of c-Src and up-regulation of the level of the Epidermal Growth Factor Receptor (EGFR). Treatment of MCF-7 cells with PMA also induced migration in a Boyden Chamber Assay, with kinetics that was consistent with depletion of PKCdelta. Further, Bryostatin-1 a compound shown to retain PKCdelta in cells blocked the PMA induced migration. Co-treatment of MCF-7 cells with PMA and Bryostatin-1 blocked the PMA induced activation of c-Src and induction of EGFR protein level. Mouse Embryo Fibroblasts from PKCdelta null mice, migrate at a rate that is three fold higher than that of their wild type counterparts. These data taken together suggest a role for PKCdelta in the inhibition of migration and metastasis in breast cancer cell lines.; PKCdelta has been implicated in proliferation and survival of breast cancer cells, often with conflicting results; we investigated the role of PKCdelta in these processes in MDA-MB-231 cells. We found that MDA-MB-231 cells subjected to growth restrictive conditions and Rapamycin underwent apoptosis. Transforming Growth Factor Beta-1 (TGFbeta1) but not Insulin-like Growth factor-1 (IGF-1) inhibited rapamycin induced apoptosis in MDA-MB-231 cells. To implicate PKCdelta, we used siRNA mediated knockdown of PKCdelta. Transfection of MDA-MB-231 cells with PKCdelta siRNA restored the rapamycin induced cell death in the presence of TGF-beta1. Therefore, PKCdelta mediated TGF-beta1 blockade of apoptosis by a Smad dependent induction of p21. |
