A role for protein kinase Cε in the inhibitory effect of epidermal growth factor on calcium-stimulated chloride secretion in human colonic epithelial cells

Epidermal growth factor (EGF) inhibits carbachol-induced chloride secretion in T-84 colonic epithelial cells and has been shown to activate phosphatidylinositol (PI) 3-kinase, leading to inhibition of a basolateral potassium conductance. We asked whether the inhibitory effect of EGF on secretion is due to activation of specific isoforms of protein kinase C (PKC) by PI 3-kinase. Western analysis revealed that PKC alpha, gamma, epsilon, eta, mu, lambda/iota, and zeta were expressed in T-84 cells. Ro318220 (an inhibitor active against PKC epsilon, 10 mu M) but not Go6983 (an inhibitor active against PKC zeta; 10 mu M) reversed the inhibitory effect of EGF (100 ng/ml) on carbachol-stimulated chloride secretion. EGF induced the rapid translocation of PKC epsilon from the cytoplasm to the membrane. Wortmannin (50 mu M) and LY294002 (20 nM), which are PI 3-kinase inhibitors that by themselves had no effect on PKC epsilon activity, significantly suppressed PKC epsilon translocation activated by EGF. LY294002 also reversed the inhibitory action of EGF on chloride secretion. PI (3,4)P-2 increased membrane-associated PKC epsilon and reduced carbachol-induced Rb-86(+) efflux. Antisense oligonucleotides against PKC epsilon decreased PKC epsilon mass and prevented the inhibitory effect of EGF on carbachol-induced Rb-86(+) afflux. Thus, the inhibitory effect of EGF on carbachol-induced chloride secretion involves the activation of PKC epsilon mediated by PI 3-kinase. Our findings contribute to the understanding of the cellular mechanisms that control chloride secretion.