Phorbol esters, by activating protein kinase C (PKC), induce the expression of the urokinase-type plasminogen activator (uPA) gene and the proto-oncogene c-fos in LLC-PK1 (PK1) porcine kidney epithelial cells. To investigate the role of PKC in the regulation of these two 12-O-tetradecanoylphorbol-13-acetate (TPA)-inducible genes, the α-type PKC, the predominant subtype present in the PK1 cells, was overexpressed in this cell line. Two clonal PK1 derivatives overexpressing the αPKC 15- and 20-fold, respectively, were established. Compared with the parental and control cells, only a modest but substantially sustained (2- to 3-fold) increase in the accumulation of uPA as well as c-fos mRNAs were observed by TPA in these cells. These results indicate that the extent of induction of these genes mediated by TPA was not proportional to the amounts of α-type PKC stably overexpressed in these cells, suggesting that factor(s) downstream of the activation of the αPKC appear to be rate limiting for the induction of both TPA-inducible genes in PK1 cells.