The identification and characterization of novel PKC epsilon phosphorylation sites provide evidence for functional cross-talk within the PKC superfamily

PKC epsilon (protein kinase C epsilon) is a phospholipid-dependent serine/threonine kinase that has been implicated in a broad array of cellular processes, including proliferation, survival, migration, invasion and transformation. Here we demonstrate that, in vitro, PKC epsilon undergoes autophosphorylation at three novel sites, Ser(234), Ser(316) and Ser(368), each of which is unique to this PKC isoform and is evolutionarily conserved. We show that these sites are phosphorylated over a range of mammalian cell lines in response to a number of different stimuli. Unexpectedly, we find that, in a cellular context, these phosphorylation events can be mediated in-trans by cPKC (classical PKC) isoforms. The functional significance of this cross-talk is illustrated through the observation that the cPKC-mediated phosphorylation of PKC epsilon at residue Set(368) controls an established PKC epsilon scaffold interaction. Thus our current findings identify three new phosphorylation sites that contribute to the isoform-specific function of PKC epsilon and highlight a novel and direct means of cross-talk between different members of the PKC superfamily.