Protein kinase A-mediated phosphorylation of naked cuticle homolog 2 stimulates cell-surface delivery of transforming growth factor- for epidermal growth factor receptor transactivation

The classic mode of G protein-coupled receptor (GPCR)-mediated transactivation of the receptor tyrosine kinase epidermal growth factor receptor (EGFR) transactivation occurs via matrix metalloprotease (MMP)-mediated cleavage of plasma membrane-anchored EGFR ligands. Herein, we show that the Gs-activating GPCR ligands vasoactive intestinal peptide (VIP) and prostaglandin E-2 (PGE(2)) transactivate EGFR through increased cell-surface delivery of the EGFR ligand transforming growth factor- (TGF) in polarizing madin-darby canine kidney (MDCK) and Caco-2 cells. This is achieved by PKA-mediated phosphorylation of naked cuticle homolog 2 (NKD2), previously shown to bind TGF and direct delivery of TGF-containing vesicles to the basolateral surface of polarized epithelial cells. VIP and PGE(2) rapidly activate protein kinase A (PKA) that then phosphorylates NKD2 at Ser-223, a process that is facilitated by the molecular scaffold A-kinase anchoring protein 12 (AKAP12). This phosphorylation stabilized NKD2, ensuring efficient cell-surface delivery of TGF and increased EGFR activation. Thus, GPCR-triggered, PKA/AKAP12/NKD2-regulated targeting of TGF to the cell surface represents a new mode of EGFR transactivation that occurs proximal to ligand cleavage by MMPs.