FUNCTIONAL DIVERGENCE OF PROTEIN-KINASE-C (PKC) FAMILY MEMBERS - PKC-GAMMA DIFFERS FROM PKC-ALPHA AND PKC-BETA-II AND NPKC-EPSILON IN ITS COMPETENCE TO MEDIATE-12-O-TETRADECANOYL PHORBOL 13-ACETATE (TPA)-RESPONSIVE TRANSCRIPTIONAL ACTIVATION THROUGH A TPA-RESPONSE ELEMENT

We have established an assay system where overexpression of a specific protein kinase C (PKC) type caused by introduction of the respective cDNA results in the enhancement of a cell response: the transcriptiona l activation of a set of genes in response to PKC activators such as 1 2-O-tetradecanoylphorbol 13-acetate (TPA). When monitored by the expre ssion of a reporter gene containing the chloramphenicol acetyltransfer ase gene fused downstream of a synthetic TPA response element (TRE) or a serum response element (SRE), the overexpression of cPKCalpha and b etaII or nPKCepsilon all resulted in the enhancement of transcriptiona l activation through both TRE and SRE. On the other hand, PKCgamma act ivates TRE only very weakly, although it activates SRE in a similar ma nner to the other PKC members examined. The overexpression of cPKCalph a and -betaII or nPKCepsilon, but not cPKCgamma, resulted in the enhan ced expression of the endogenous c-jun gene, which contains TRE in the 5'-upstream, promoter region. The gel mobility shift assay showed tha t the activation of PKCgamma, as well as PKCalpha and -betaII and nPKC epsilon, causes the increase in TRE-binding proteins, suggesting that transcriptional activation through TRE requires an additional step, wh ich is not activated by PKCgamma, such as a qualitative change in TRE- binding or in TRE-associating proteins. This finding provides not only a rationale to explain the presence of multiple PKC family members, b ut also permits the dissection of the complex cellular signaling casca de involving PKC family members.