Protein Kinase C delta (PKC delta) is a 78 kDa member of the novel group (nPKCs: sensitive to diacylglycerol, phosphatidylserine, and phorbol esters) of the PKC family of serine/threonine kinases that are involved in a wide range of physiological processes including mitogenesis, cell survival and transcriptional regulation. PKC delta is an ubiquitously expressed PKC isozyme that has been implicated in the regulation of multiple cellular processes including cell cycle progression and apoptosis. Autophosphorylation of serine 664 (serine 662 in mouse and rat) contributes to PKC delta activity. Serum dependent phosphorylation of serine 664 is mediated by mTOR pathway, is protected from dephosphorylation by phosphorylated threonine 505 in the activation loop, and is implicated in prolactin signaling.