ROLE OF PROTEIN-KINASE-C IN GROWTH-STIMULATION OF PRIMARY MOUSE COLONIC EPITHELIAL-CELLS

The phorbol ester, 12-0-tetradecanoylphorbol-13-acetate (160 nM) and the secondary bile acid, deoxycholic acid (50 mu M) stimulated DNA synthesis in quiescent primary epithelial cells from the normal mouse colon as measured by autoradiographic analysis of [H-3]thymidine incorporation. The purpose of the present study was to investigate the involvement of protein kinase C in the proliferative response of the normal colonic cells. The protein kinase C inhibitor, bisindolyl-maleimide GF 109203X, efficiently blocked the proliferative response of the cells to the phorbol ester and caused a dose-dependent decrease in the response to deoxycholic acid. While the phorbol ester-induced proliferation was unaffected by another inhibitor, H-7, the response of the cells to deoxycholic acid was blocked. Pretreatment of the cells with the phorbol ester (160 nM) for 24 h blocked the proliferative response to deoxycholic acid. Measurement of the intracellular distribution of protein kinase C activity showed a time-dependent and significant translocation of the enzyme activity from the soluble to the particulate cell fractions after exposure to 12-0-tetradecanoylphorbol-13-acetate. While exposure to the bile acid indicated a similar time-dependent translocation of the enzyme activity, the effect was not significant. The phorbol ester induced a time-dependent accumulation of c-fos mRNA and protein as measured by solution hybridization and immunocytochemistry, respectively. No effect of deoxycholic acid on c-fos expression could be observed in the present study. The data support a role for protein kinase C in the growth stimulating effect of physiological concentrations of deoxycholic acid on normal colonic epithelial cells. However, differences in the mechanisms underlying phorbol ester- and bile acid-induced proliferation are indicated.