The platelet-derived growth factor receptor-β phosphorylates and activates g protein-coupled receptor kinase-2

G protein- coupled receptor kinase- 2 ( GRK2) serinephosphorylates the platelet- derived growth factor receptor-beta ( PDGFR beta), and thereby diminishes signaling by the receptor. Because activation of GRK2 may involve phosphorylation of its N- terminal tyrosines by cSrc, we tested whether the PDGFR beta itself could tyrosine-phosphorylate and activate GRK2. To do so, we used wild type ( WT) and Y857F mutant PDGFR beta s in HEK cells, which lack endogenous PDGFRs. The Y857F PDGFR beta autophosphorylates normally but does not phosphorylate exogenous substrates. Although PDGF-stimulated Y857F and WT PDGFR beta s activated c- Src equivalently, the WT PDGFR beta tyrosine- phosphorylated GKR2 60- fold more than the Y857F PDGFR beta in intact cells. With purified GRK2 and either WT or Y857F PDGFR beta s immunoprecipitated from HEK cells, GRK2 tyrosyl phosphorylation was PDGF- dependent and required the WT PDGFR beta, even though the WT and Y857F PDGFR beta s autophosphorylated equivalently. This PDGFR beta- mediated GRK2 tyrosyl phosphorylation enhanced GRK2 activity: GRK2- mediated seryl phosphorylation of the PDGFR beta was 9- fold greater for the WT than for the Y857F in response to PDGF, but equivalent when GRK2 was activated by sequential stimulation of beta(2)- adrenergic and PDGF- beta receptors. Furthermore, both PDGFR beta- mediated GRK2 tyrosyl phosphorylation and GRK2- mediated PDGFR beta seryl phosphorylation were reduced similar to 50% in intact cells by mutation to phenylalanine of three tyrosines in the N- terminal domain of GRK2. We conclude that the activated PDGFR beta itself phosphorylates GRK2 tyrosyl residues and thereby activates GRK2, which then serine- phosphorylates and desensitizes the PDGFR beta.