Protein Kinase Cδ (PKCδ): Activation Mechanisms and Functions

Protein kinase C (PKC)δ was the first new/novel PKC isoform to be identified by the screening of mammalian cDNA libraries, based on the structural homology of its nucleotide sequences with those of classical/conventional PKC isoforms. PKCδ is expressed ubiquitously among cells and tissues. It is activated by diacylglycerol produced by receptor-mediated hydrolysis of membrane inositol phospholipids as well as by tumor-promoting phorbol ester through the binding of these compounds to the C1 region in its regulatory domain. It is also cleaved by caspase to generate a catalytically active fragment, and it is converted to an active form without proteolysis through the tyrosine phosphorylation reaction. Various lines of evidence indicate that PKCδ activated in distinct ways plays critical roles in cellular functions such as the control of growth, differentiation, and apoptosis. This article briefly summarizes the regulatory mechanisms of PKCδ activity and its functions in cell signaling.