Role of protein kinase C in transforming growth factor‐β1 induction of carcinoembryonic antigen in human colon carcinoma cells

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Abstract
Transforming growth factor-β1 (TGF-β1) regulates the expression of the carcinoembryonic antigen (CEA) gene family in the human colon carcinoma cell line Moser. The mechanisms through which it acts, however, are unknown. In this communication, several lines of evidence are presented to show that the induction of CEA expression and secretion (collectively called CEA responses) by TGF-β1 is associated with protein kinase C (PKC) pathway of signal transduction. Treatment of intact cells with the PKC-specific inhibitor calphostin C downmodulated cellular PKC phosphotransferase activity and blocked the induction of the CEA responses by TGF-β1. Depletion of PKC by treatment of intact cells with phorbol ester also blocked the action of TGF-β1. The induction of the CEA responses by TGF-β1 was also blocked by the protein kinase inhibitor 1-(isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), which also inhibited cellular PKC activity. However, TGF-β1 did induce the CEA responses in intact cells treated with the calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7), the calmodulin-dependent phosphodiesterase inhibitor calmidazolium, the diacylglycerol kinase inhibitor R59 022, and the G-protein inhibitors cholera toxin and pertussis toxin. Treatment of intact cells with TGF-β1 induced a rapid and transient increase in PKC phosphotransferase activity. TGF-β1, however, was unable to induce PKC enzymatic activity in cells pretreated with calphostin C. Therefore, it is concluded that TGF-β1 regulates the CEA responses through a signal transducing pathway associated with PKC.