Members of the protein kinase C (PKC) family play a key regulatory role in a variety of cellular functions including cell growth and differentiation, gene expression, hormone secretion and membrane function. PKCs were originally identified as serine/threonine protein kinases whose activity was dependent on calcium and phospholipids. Diacylglycerols (DAG) and tumor promoting phorbol esters bind to and activate PKC. Protein kinase D (PKD), also called PKCμ, is a serine/threonine kinase whose activation is dependent on the phosphorylation of two activation loop sites, Ser744 and Ser748, via a PKC-dependent signaling pathway. In addition to the two activation loop sites, the carboxy-terminal Ser916 has been identified as an autophosphorylation site for PKD/PKCμ. Phosphorylation at Ser916 correlates with PKD/PKCμ catalytic activity.
