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

PKCϵ (protein kinase Cϵ) 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, PKCϵ undergoes autophosphorylation at three novel sites, Ser²³⁴, Ser³¹⁶ and Ser³⁶⁸, 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 PKCϵ at residue Ser³⁶⁸ controls an established PKCϵ scaffold interaction. Thus our current findings identify three new phosphorylation sites that contribute to the isoform-specific function of PKCϵ and highlight a novel and direct means of cross-talk between different members of the PKC superfamily.