Activation of protein kinase C augments butyrate-induced differentiation and turnover in human colonic epithelial cells in vitro

As the colonic epithelium is physiologically exposed to butyrate and to act ivators of protein kinase C, we examined the effect of the protein kinase C signalling pathway on butyrate-induced expression of markers of differenti ation. Activators and inhibitors of protein kinase C were used in combinati on with butyrate and effects on the expression of markers of differentiatio n examined ill colon cancer cell lines. When the protein kinase C activator phorbol myristate acetate (100 nM) was added for 24 h prior to the additio n of 2 mM butyrate, there was a synergistic increase in alkaline phosphatas e activity (153 +/- 11% above that for butyrate alone, P = 0.003) in a conc entration- and time-dependent manner. Butyrate-induced expression of carcin oembryonic antigen and interleukin-8, dome formation and cell turnover were also markedly augmented by pre-treatment with phorbol myristate acetate, A similar effect was observed with propionate or acetate (but not other diff erentiating agents), when phorbol myristate acetate and butyrate were added concurrently, or when other protein kinase C activators were used. Pharmac ological inhibition of protein kinase C activity did not alter butyrate-ind uced alkaline phosphatase activity, but abrogated the augmentation induced by phorbol myristate acetate, We conclude that protein kinase C does not me diate the differentiating effects of butyrate on colon cancer cells, but it s activation regulates butyrate-induced cellular differentiation.