Induction of 12-lipoxygenase expression by epidermal growth factor is mediated by protein kinase C in A431 cells

Epidermal growth factor (EGF) increases 12-lipoxygenase mRNA by about 2-fold with a lag period of 4 to 8 hr, which precedes the increase in 12-lipoxygenase activity by 2 to 4 hr in human epidermoid carcinoma A431 cells. Induction of 12-lipoxygenase expression in human erythroleukemia cells by phorbol 12-myristate 13-acetate (PMA) has been reported previously. The present report describes a study of the involvement of protein kinase C (PKC) in EGF-induced 12-lipoxygenase expression in A431 cells. EGF-induced 12-lipoxygenase expression was inhibited by methyl 2,5-dihydroxycinnamate, a tyrosine kinase inhibitor. Staurosporine and calphostin C, which are two PKC inhibitors, inhibited EGF-induced enzyme activity and mRNA expression of 12-lipoxygenase. 1,2-Dioctanoyl-sn-glycerol (a membrane-permeant diacylglycerol) and PMA significantly induced enzyme activity and mRNA expression. Simultaneous treatment of cells with EGF and PMA did not exhibit an additive effect, suggesting that EGF and PMA share a common biochemical pathway in 12-lipoxygenase induction. Expression of mRNA for PKC alpha, delta and zeta was detected in A431 cells, whereas no mRNA expression for PKC beta 1, gamma and epsilon was observed. Taken together, these results suggest that EGF-induced 12-lipoxygenase expression is at least in part mediated by the PKC signal transduction pathway.