beta-Adrenoceptor stimulation potentiates insulin-stimulated PKB phosphorylation in rat cardiomyocytes via cAMP and PKA
AuthorsStuenaes, Jorid T.
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Background and purpose: Genetic approaches have documented protein kinase B (PKB) as a pivotal regulator of heart function. Insulin strongly activates PKB, whereas adrenaline is not considered a major physiological regulator of PKB in heart. In skeletal muscles, however, adrenaline potentiates insulin-stimulated PKB activation without having effect in the absence of insulin. The purpose of the present study was to investigate the interaction between insulin and beta-adrenergic stimulation in regulation of PKB phosphorylation. Experimental approach: Cardiomyocytes were isolated from adult rats by collagenase, and incubated with insulin, isoprenaline, and other compounds. Protein phosphorylation was evaluated by Western blot and phospho-specific antibodies. Key results: Isoprenaline increased insulin-stimulated PKB Ser473 and Thr308 phosphorylation more than threefold in cardiomyocytes. Isoprenaline alone did not increase PKB phosphorylation. Isoprenaline also increased insulin-stimulate...d GSK-3 beta Ser9 phosphorylation approximately twofold, supporting that PKB phosphorylation increased kinase activity. Dobutamine (beta(1)-agonist) increased insulin-stimulated PKB phosphorylation as effectively as isoprenaline (more than threefold), whereas salbutamol (beta(2)-agonist) only potentiated insulin-stimulated PKB phosphorylation by approximately 80%. Dobutamine, but not salbutamol, increased phospholamban Ser16 phosphorylation and glycogen phosphorylase activation (PKA-mediated effects). Furthermore, the cAMP analogue that activates PKA (dibutyryl-cAMP and N6-benzoyl-cAMP) increased insulin-stimulated PKB phosphorylation by more than threefold without effect alone. The Epac-specific activator 8-(4-chlorophenylthio)-2-O-methyl-cAMP (007) increased insulin-stimulated PKB phosphorylation by approximately 50%. Db-cAMP and N6-benzoyl-cAMP, but not 007, increased phospholamban Ser16 phosphorylation. Conclusions and implications: beta-adrenoceptors are strong regulators of PKB phosphorylation via cAMP and PKA when insulin is present. We hypothesize that PKB mediates important signalling in the heart during beta-adrenergic receptors stimulation.
Keywords:Heart / Akt / GSK-3 / phosphorylation / phosphatidylinositol 3-kinase / phoshodiesterase / phospholamban / hypertrophy / rolipram / ERK
Source:British Journal of Pharmacology, 2010, 160, 1, 116-129
- Novo Nordisk Foundation, European Commission [COST BM0602]