Phosphatidylinositol 3-kinase functionally compartmentalizes the concurrent G(s) signaling during beta2-adrenergic stimulation.
Compartmentation of intracellular signaling pathways serves as an important mechanism conferring the specificity of G protein-coupled receptor (GPCR) signaling. In the heart, stimulation of beta2-adrenoceptor (beta2-AR), a prototypical GPCR, activates a tightly localized protein kinase A (PKA) signaling, which regulates substrates at cell surface membranes, bypassing cytosolic target proteins (eg, phospholamban). Although a concurrent activation of beta2-AR-coupled G(i) proteins has been implicated in the functional compartmentation of PKA signaling, the exact mechanism underlying the restriction of the beta2-AR-PKA pathway remains unclear. In the present study, we demonstrate that phosphatidylinositol 3-kinase (PI3K) plays an essential role in confining the beta2-AR-PKA signaling. Inhibition of PI3K with LY294002 or wortmannin enables beta2-AR-PKA signaling to reach intracellular substrates, as manifested by a robust increase in phosphorylation of phospholamban, and markedly enhances the receptor-mediated positive contractile and relaxant responses in cardiac myocytes. These potentiating effects of PI3K inhibitors are not accompanied by an increase in beta2-AR-induced cAMP formation. Blocking G(i) or Gbetagamma signaling with pertussis toxin or betaARK-ct, a peptide inhibitor of Gbetagamma, completely prevents the potentiating effects induced by PI3K inhibition, indicating that the pathway responsible for the functional compartmentation of beta2-AR-PKA signaling sequentially involves G(i), Gbetagamma, and PI3K. Thus, PI3K constitutes a key downstream event of beta2-AR-G(i) signaling, which confines and negates the concurrent beta2-AR/G(s)-mediated PKA signaling.
Laboratory of Cardiovascular Science, Gerontology Research Center, National Institute on Aging, National Institute of Health, Baltimore, Md 21224, USA.
Su-Hyun
SH
Jo
Veronique
V
Leblais
Ping H
PH
Wang
Michael T
MT
Crow
Rui-Ping
RP
Xiao
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism; D048429:Cell Size / Q000187:drug effects; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004983:Ethanolamines / Q000494:pharmacology; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism*; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism; D007093:Imidazoles / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D018343:Receptors, Adrenergic, beta-2 / Q000187:drug effects / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D000077191:Wortmannin; D000099211:Phospholamban
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D000730:Androstadienes; D002118:Calcium; D002135:Calcium-Binding Proteins; D002867:Chromones; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D004791:Enzyme Inhibitors; D004983:Ethanolamines; D019205:GTP-Binding Protein alpha Subunits, Gs; D020962:Heterotrimeric GTP-Binding Proteins; D007093:Imidazoles; D007334:Insulin-Like Growth Factor I; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D018343:Receptors, Adrenergic, beta-2; D012694:Serine; D000077191:Wortmannin; D000099211:Phospholamban; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C002904:zinterol; C049763:CGP 20712A