Regulation of the platelet-derived growth factor receptor-β by G protein-coupled receptor kinase-5 in vascular smooth muscle cells involves the phosphatase Shp2

Smooth muscle cell (SMC) proliferation and migration are substantially controlled by the platelet-derived growth factor receptor-beta(PDGFR beta), which can be regulated by the Ser/Thr kinase G protein-coupled receptor kinase-2 (GRK2). In mouse aortic SMCs, however, we found that prolonged PDGFR beta activation engendered down-regulation of GRK5, but not GRK2; moreover, GRK5 and PDGFR beta were coordinately up-regulated in SMCs from atherosclerotic arteries. With SMCs from GRK5 knock-out and cognate wild type mice (five of each), we found that physiologic expression of GRK5 increased PDGF-promoted PDGFR beta seryl phosphorylation by 3-fold and reduced PDGFR beta-promoted phosphoinositide hydrolysis, thymidine incorporation, and overall PDGFR beta tyrosyl phosphorylation by similar to 35%. Physiologic SMC GRK5 activity also increased PDGFR beta association with the phosphatase Shp2 (8-fold), enhanced phosphorylation of PDGFR beta Tyr(1009) (the docking site for Shp2), and reduced phosphorylation of PDGFR beta Tyr(1021). Consistent with having increased PDGFR beta-associated Shp2 activity, GRK5-expressing SMCs demonstrated greater PDGF-induced Src activation than GRK5-null cells. GRK5-mediated desensitization of PDGFR beta inositol phosphate signaling was diminished by Shp2 knock-down or impairment of PDGFR beta/Shp2 association. In contrast to GRK5, physiologic GRK2 activity did not alter PDGFR beta/Shp2 association. Finally, purified GRK5 effected agonist-dependent seryl phosphorylation of partially purified PDGFR beta s. We conclude that GRK5 mediates the preponderance of PDGF-promoted seryl phosphorylation of the PDGFR beta in SMCs, and, through mechanisms involving Shp2, desensitizes PDGFR beta inositol phosphate signaling and enhances PDGFR beta-triggered Src activation.