Protein kinase Cε may act as EGF-inducible scaffold protein for phospholipase Cγ1

Abstract Phospholipase Cγ1 (PLCγ1) represents a major downstream signalling component of the epidermal growth factor (EGF) receptor (EGFR) and is activated by tyrosine phosphorylation. Here we show for the first time that cellular knockdown of protein kinase Ce (PKCe) leads to decreased activation of PLCγ1 by EGF and that EGF induces tyrosine phosphorylation of PKCe as well as association of PKCe with both EGFR and PLCγ1. Using several mutants, co-immunoprecipitation and phosphopeptide-based pull-down experiments we found that in dependency on c-Src and EGF-stimulation PKCe may bind to the c-Src-specific phosphorylation site pY845-EGFR. Furthermore, we identified a single tyrosine residue, PKCe-Y573, within a consensus binding sequence of the C-terminal SH2 domain of PLCγ1 which is critical for both tyrosine phosphorylation of PKCe and its association with PLCγ1. Thus, in particular cells and independent of the kinase activity PKCe may form a signalling module with EGFR and PLCγ1. Thereby the tyrosine phosphorylation of PLCγ1 via the EGFR may be facilitated. This is a novel function of PKCe upstream of PLCγ1 and a novel paradigm for the EGF-induced formation of multi-protein complexes.