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Phosphorylation of Epac1 by GRK2 inhibits Epac1‐Rap1 signaling and prevents chronic pain (802.7)

Chronic pain is a major health issue that severely affects the quality of life of patients and it financially burdens the society. The understanding of molecular mechanisms that cause transition from acute to chronic pain remains a challenge and is critical for development of new interventions. G‐protein coupled receptor Kinase 2 (GRK2) is a key molecule in pain signaling. We recently described that GRK2 deficiency in nociceptors promotes transition to chronic inflammatory pain via an Exchange protein directly activated by cAMP (Epac) dependent pathway. The objective of this study was to investigate the mechanism via which GRK2 regulates cAMP induced Epac1 signaling. Using co‐immunoprecipitation studies we show that GRK2 binds Epac1 in neuronal cells. Epac1 specifically interacts with the kinase domain of GRK2. In vitro kinase assays revealed that GRK2 is an Epac1 kinase. Overexpression of GRK2, but not of GRK2 kinase dead mutant significantly reduced Epac‐to‐Rap1 signaling. Furthermore, we identified the Epac1 residue that is phosphorylated by GRK2 and this phosphorylation inhibits Epac1‐to‐Rap1 signaling. We conclude that GRK2 acts as an endogenous inhibitor of Epac1‐to‐Rap1 signaling by phosphorylating Epac1. In vivo, GRK2 kinase activity is required to inhibit transition to chronic pain. Thus, we uncovered a novel regulatory mechanism that is critical for regulating the pain response.