Regulation of human involucrin promoter activity by novel protein kinase C isoforms

Human involucrin (hINV) mRNA level and promoter activity increase when keratinocytes are treated with the differentiating agent, 12-O-tetradecanoylphorbol-13-acetate (TPA). This response is mediated via a p38 mitogen-activated protein kinase-dependent pathway that targets activator protein 1 (Efimova, T., LaCelle, P. T., Welter, J. F., and Eckert, R. L. (1998) J. Biol, Chem. 273, 24387-24395), In the present study we examine the role of various PKC isoforms in this regulation. Transfection of expression plasmids encoding the novel PKC isoforms delta, epsilon, and eta increase hINV promoter activity. In contrast, neither conventional PKC isoforms (alpha, beta, and gamma) nor the atypical isoform (zeta) regulate promoter activity. Consistent with these observations, promoter activity is inhibited by the PKC delta-selective inhibitor, rottlerin, but not by Go-6976, an inhibitor of conventional PRC isoforms, and novel PKC isoform-dependent promoter activation is inhibited by dominant-negative PKC delta. This regulation appears to be physiologically important, as transfection of keratinocytes with PKC delta, -epsilon, or -eta increases expression of the endogenous hINV gene. Synergistic promoter activation (greater than or equal to 100-fold) is observed when PKC epsilon- or -eta-transfected cells are treated with TPA. In contrast, the PKC delta-dependent response is more complex as either activation or inhibition is observed, depending upon PKC delta concentration.