Agonist-dependent modulation of G protein-coupled receptor kinase 2 by mitogen-activated protein kinases

A variety of G protein-coupled receptors (GPCRs) are phosphorylated by G pr otein-coupled receptor kinase 2 (GRK2). This event promotes the binding of regulatory proteins termed beta-arrestins to GPCRs, leading to uncoupling f rom G proteins and receptor internalization. Recent data indicate that GRK2 and beta-arrestins also play an important role in the stimulation of the e xtracellular signal-regulated kinases (ERK)/mitogen-activated protein kinas e (MAPK) cascade by GPCRs. In this report, we have investigated the existen ce of functional interactions between GRK2 and MAPK. We show that activatio n of beta(2)-adrenergic receptors (beta(2)-AR) promotes the rapid associati on of GRK2 and MAPK in living cells, as assessed by coimmunoprecipitation e xperiments in COS-7 cells transfected with beta(2)-AR, GRK2, and an epitope -tagged MAPK. Coimmunoprecipitation of MAPK and GRK2 is blocked by inhibiti on of the MAPK cascade and is not observed upon activation of MAPK in the a bsence of beta(2)-AR stimulation, thus indicating that both an active MAPK and agonist occupancy of GPCR are required for the association to occur. In terestingly, we have found that purified ERK1/MAPK can directly phosphoryla te the C-terminal domain of GRK2, and that the phosphorylation process is f avored by the presence of G beta gamma-subunits or an activated receptor. F urthermore, GRK2 phosphorylation by MAPK leads to a decreased activity of G RK2 toward GPCR. Taken together, our results suggest that stimulation of GP CRs promotes the rapid association of GRK2 and MAPK leading to modulation o f GRK2 functionality, thus putting forward a new feedback mechanism for the regulation of GPCR signaling.