G??q-mediated Activation of GRK2 by Mechanical Stretch in Cardiac Myocytes: THE ROLE OF PROTEIN KINASE C* |
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Authors: | Ricky Malhotra Karen M D'Souza Michelle L Staron Konstantin G Birukov Ilona Bodi and Shahab A Akhter |
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Institution: | From the ‡Department of Surgery, Section of Cardiac and Thoracic Surgery, and ;§Department of Medicine, Section of Pulmonary/Critical Care, University of Chicago Medical Center, Chicago, Illinois 60637 and ;the ¶Institute for Molecular Pharmacology and Biophysics, University of Cincinnati, Cincinnati, Ohio 45267 |
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Abstract: | G protein-coupled receptor kinase-2 (GRK2) is a critical regulator of β-adrenergic receptor (β-AR) signaling and cardiac function. We studied the effects of mechanical stretch, a potent stimulus for cardiac myocyte hypertrophy, on GRK2 activity and β-AR signaling. To eliminate neurohormonal influences, neonatal rat ventricular myocytes were subjected to cyclical equi-biaxial stretch. A hypertrophic response was confirmed by “fetal” gene up-regulation. GRK2 activity in cardiac myocytes was increased 4.2-fold at 48 h of stretch versus unstretched controls. Adenylyl cyclase activity was blunted in sarcolemmal membranes after stretch, demonstrating β-AR desensitization. The hypertrophic response to mechanical stretch is mediated primarily through the Gαq-coupled angiotensin II AT1 receptor leading to activation of protein kinase C (PKC). PKC is known to phosphorylate GRK2 at the N-terminal serine 29 residue, leading to kinase activation. Overexpression of a mini-gene that inhibits receptor-Gαq coupling blunted stretch-induced hypertrophy and GRK2 activation. Short hairpin RNA-mediated knockdown of PKCα also significantly attenuated stretch-induced GRK2 activation. Overexpression of a GRK2 mutant (S29A) in cardiac myocytes inhibited phosphorylation of GRK2 by PKC, abolished stretch-induced GRK2 activation, and restored adenylyl cyclase activity. Cardiac-specific activation of PKCα in transgenic mice led to impaired β-agonist-stimulated ventricular function, blunted cyclase activity, and increased GRK2 phosphorylation and activity. Phosphorylation of GRK2 by PKC appears to be the primary mechanism of increased GRK2 activity and impaired β-AR signaling after mechanical stretch. Cross-talk between hypertrophic signaling at the level of PKC and β-AR signaling regulated by GRK2 may be an important mechanism in the transition from compensatory ventricular hypertrophy to heart failure. |
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Keywords: | Cardiac Hypertrophy G Protein-coupled Receptors (GPCR) Protein Kinase C (PKC) Protein-Protein Interactions Receptor Desensitization Signal Transduction |
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