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 δ, ε, and η increase hINV promoter activity. In contrast, neither conventional PKC isoforms (α, β, and γ) nor the atypical isoform (ξ) regulate promoter activity. Consistent with these observations, promoter activity is inhibited by the PKCδ- selective inhibitor, rottlerin, but not by Go-6976, an inhibitor of conventional PKC isoforms, and novel PKC isoform-dependent promoter activation is inhibited by dominant-negative PKCΣ. This regulation appears to be physiologically important, as transfection of keratinocytes with PKCδ, -ε, or -η increases expression of the endogenous hINV gene. Synergistic promoter activation (≥100-fold) is observed when PKCε- or -η-transfected cells are treated with TPA. In contrast, the PKCδ-dependent response is more complex as either activation or inhibition is observed, depending upon PKCδ concentration.