Phospholipase C-ϵ Augments Epidermal Growth Factor-dependent Cell Growth by Inhibiting Epidermal Growth Factor Receptor Down-regulation

The down-regulation of the epidermal growth factor (EGF) receptor is critical for the termination of EGF-dependent signaling, and the dysregulation of this process can lead to oncogenesis. In the present study, we suggest a novel mechanism for the regulation of EGF receptor down-regulation by phospholipase C-ϵ. The overexpression of PLC-ϵ led to an increase in receptor recycling and decreased the down-regulation of the EGF receptor in COS-7 cells. Adaptor protein complex 2 (AP2) was identified as a novel binding protein that associates with the PLC-ϵ RA2 domain independently of Ras. The interaction of PLC-ϵ with AP2 was responsible for the suppression of EGF receptor down-regulation, since a perturbation in this interaction abolished this effect. Enhanced EGF receptor stability by PLC-ϵ led to the potentiation of EGF-dependent growth in COS-7 cells. Finally, the knockdown of PLC-ϵ in mouse embryo fibroblast cells elicited a severe defect in EGF-dependent growth. Our results indicated that PLC-ϵ could promote EGF-dependent cell growth by suppressing receptor down-regulation.