Expression of protein kinase C β1 confers resistance to TNFα- and paclitaxel-induced apoptosis in HT-29 colon carcinoma cells

The expression of different protein kinase C (PKC) isoenzymes has been shown to vary with proliferation rates, differentiation or apoptosis in normal colon crypts. In addition, the activity of some PKC isoenzymes appears to be reduced in colorectal cancer. The aim of the present work was to determine whether modulation of PKC expression would affect the susceptibility of a p53-defective colon carcinoma cell line to different apoptotic treatments. HT-29 cells exhibited sensitivity to paclitaxel (Taxol) and tumor necrosis factor α (TNFα) in a dose- and time-dependent manner but were relatively resistant to etoposide. Inhibition of PKC activity augmented the susceptibility of HT-29 cells to apoptosis, and phorbol ester induction of PKC reduced such susceptibility. Transfected HT-29^PKC cells, hyper-expressing the β I isoform of PKC, were less sensitive to TNFα and paclitaxel than the normal counterpart. The present data I) indicate that the expression of PKC influences the susceptibility of HT-29 colon cancer cells to apoptotic drugs apparently regardless of their mechanism of action, and 2) suggest paclitaxel as a potential candidate for the treatment of colon cancer, possibly in association with inhibitors of PKC (α and β) at doses not cytotoxic per se.