Regulation of growth factor receptors on rat intestinal epithelial (RIE-1) cells by protein kinase C

The regulation of growth factor receptors by protein kinase C was investigated in rat intestinal epithelial (RIE-1) cells. Short-term treatment of the cells with the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate, was employed to activate the kinase and longer-term exposure to the agent was used to assess the effects of protein kinase C depletion. Phorbol ester concentrations as low as 30 nM were found to down-regulate immunoreactive protein kinase C over 6 h, which correlated with the rapid loss of functional kinase activity. Whereas protein kinase C reduced the binding of 125I-labelled EGF, it increased the binding of 125I-labelled angiotensin II to RIE-1 cells. However, the kinase simultaneously inhibited the activation by angiotensin receptors of phosphatidylinositol 4,5 bisphosphate hydrolysis.