Functional divergence of protein kinase C (PKC) family members. PKC gamma differs from PKC alpha and -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 transcriptional activation of a set of genes in response to PKC activators such as 12-O-tetradecanoylphorbol 13-acetate (TPA). When monitored by the expression of a reporter gene containing the chloramphenicol acetyltransferase gene fused downstream of a synthetic TPA response element (TRE) or a serum response element (SRE), the overexpression of cPKC alpha and -beta II or nPKC epsilon all resulted in the enhancement of transcriptional activation through both TRE and SRE. On the other hand, PKC gamma activates TRE only very weakly, although it activates SRE in a similar manner to the other PKC members examined. The overexpression of cPKC alpha and -beta II or nPKC epsilon, but not cPKC gamma, resulted in the enhanced expression of the endogenous c-jun gene, which contains TRE in the 5'-upstream, promoter region. The gel mobility shift assay showed that the activation of PKC gamma, as well as PKC alpha and -beta II and nPKC epsilon, causes the increase in TRE-binding proteins, suggesting that transcriptional activation through TRE requires an additional step, which is not activated by PKC gamma, 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, but also permits the dissection of the complex cellular signaling cascade involving PKC family members.