Oxidative stress decreases G protein-coupled receptor kinase 2 in lymphocytes via a calpain-dependent mechanism

G protein-coupled receptor kinase (GRK) 2 plays a crucial role in regulating the extent of desensitization and resensitization of G protein-coupled receptors (GPCRs). We have shown that the expression level of GRK2 in lymphocytes decreases during inflammatory diseases such as arthritis. Reactive oxygen species play an important role in a variety of inflammatory conditions, including arthritis. We demonstrate herein that oxidative stress, induced by exposure of lymphocytes to H₂O₂, results in a 50% reduction in GRK2 protein levels and GRK activity with no changes in mRNA expression. Treatment of lymphocytes with the tyrosine kinase inhibitor genistein partially reverses the effect of H₂O₂ on GRK2 levels, although we did not detect direct tyrosine phosphorylation of GRK2. Inhibition of the non-proteasomal protease calpain by calpeptin can prevent the H₂O₂-induced GRK2 decrease. In vitro experiments confirm that GRK2 is partially digested by m-calpain in a calcium-dependent way. Functionally, H₂O₂-induced decrease in GRK2 levels is associated with an ∼70% decrease in agonist-induced β₂-adrenergic receptor sequestration. We describe oxidative stress as a novel mechanism for regulation of the intracellular level of GRK2 during inflammatory processes. Moreover, our data demonstrate that oxidative stress may change the functioning of GPCRs via calpain-dependent regulation of GRK2 levels.