Regulation of Protein Kinase Cν by the B-cell Antigen Receptor

Diacylglycerol-dependent signaling plays an important role in signal transduction through T- and B-lymphocyte antigen receptors. Recently, a novel serine-threonine kinase of the protein kinase C (PKC) family has been described and designated as PKCν. PKCν has two putative diacylglycerol binding C1 domains, suggesting that it may participate in a novel diacylglycerol-mediated signaling pathway. Here we show that both endogenous and recombinant PKCν are trans-located to the plasma membrane and activated by the diacylglycerol mimic phorbol 12-myristate 13-acetate. Mutational analysis demonstrates that PKCν activation is dependent on trans-phosphorylation of two conserved activation loop serine residues. We also find that PKCν is an important physiologic target of the B-cell receptor (BCR), because PKCν is found to be abundantly expressed in chicken and human B-cell lines and, in addition, exhibits robust activation after BCR engagement. Genetic and pharmacologic analyses of BCR-mediated PKCν activation indicate that it requires intact phospholipase Cγ and PKC signaling pathways. Furthermore, in co-transfection assays, PKCν can be trans-phosphorylated by the novel PKC isozymes PKCε, PKCη, or PKCθ but not the classical PKC enzyme, PKCα. Taken together, these results suggest that PKCν is an important component of signaling pathways downstream from novel PKC enzymes after B-cell receptor engagement.