Feedback inhibition of G protein-coupled receptor kinase 2 (GRK2) activityby extracellular signal-regulated kinases

G protein-coupled receptor kinase (GRK)-mediated receptor phosphorylation a nd beta-arrestin binding uncouple G protein-coupled receptors (GPCRs) from their respective G proteins and initiates the process of receptor internali zation. In the case of the beta(2)-adrenergic receptor and lysophosphatidic acid receptor, these processes can lead to ERK activation. Here we identif y a novel mechanism whereby the activity of GRK2 is regulated by feedback i nhibition. GRK2 is demonstrated to be a phosphoprotein in cells. Mass spect rometry and mutational analysis localize the site of phosphorylation on GRK 2 to a carboxyl-terminal serine residue (Ser(670)). Phosphorylation at Ser6 70 impairs the ability of GRK2 to phosphorylate both soluble and membrane-i ncorporated receptor substrates and dramatically attenuates G beta gamma-me diated activation of this enzyme, Ser(670) is located in a peptide sequence that conforms to an ERK consensus phosphorylation sequence, and in vitro, in the presence of heparin, ERK1 phosphorylates GRK2, Inhibition of ERK act ivity in HEK293 cells potentiates GRK2 activity, whereas, conversely, ERK a ctivation inhibits GRK2 activity. The discovery that ERK phosphorylates and inactivates GRK2 suggests that ERK participates in a feedback regulatory l oop. By negatively regulating GRK-mediated receptor phosphorylation, beta-a rrestin-mediated processes such as Src recruitment and clathrin-mediated in ternalization, which are required for GPCR-mediated ERK activation, are inh ibited, thus dampening further ERK activation.