title: A novel signaling pathway for beta-adrenergic receptor-mediated activation of phosphoinositide 3-kinase in H9c2 cardiomyocytes.
abstract: Stimulation of cardiac beta-adrenergic receptors (beta-AR) activates both the G(s)- and G(i)-coupled signaling cascades, including the phosphoinositide 3 kinase (PI3K) pathway, that have important physiological implications. Multiple isoforms of PI3K exist in the heart. The goals of this study were to examine the intracellular signaling pathways linking beta-AR to PI3K and to identify the PI3K isoform mediating this transactivation in a cardiac context. Acute beta-AR stimulation with isoproterenol resulted in increased tyrosine kinase-associated PI3K activity and phosphorylation of Akt and p70S6K in H9c2 cardiomyocytes. Cotreatment with ICI-118,551, but not CGP-20712, abolished the increase in PI3K activity, suggesting a beta(2)-AR-mediated event. PI3K activation was also abrogated by cotreatment with pertussis toxin, 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolol[3,4-d]pyrimidine (PP2, a selective Src-family tyrosine kinases inhibitor), or AG-1296 [selective platelet-derived growth factor receptor (PDGFR) inhibitor] but not with an inhibitor for protein kinase A, protein kinase C, Ras, adenylyl cyclase, epidermal growth factor receptor, or insulin-like growth factor-1 receptor. beta-AR stimulation induced an increase in tyrosine phosphorylation of PDGFR, which was abolished by inhibition of Src either by PP2 or small interfering RNA. Moreover, H9c2 cardiomyocytes stably transfected with a vector expressing a Gbetagamma sequestrant peptide derived from the COOH-terminus of beta-AR kinase-1 failed to activate PI3K after beta-AR stimulation, suggesting Gbetagamma is required for the transactivation. Furthermore, acute beta-AR stimulation in vivo resulted in increases in PDGFR-associated PI3K and PI3Kalpha isoform activities but not the activities of other isoforms (PI3Kbeta, -delta, -gamma) in adult mouse heart. Taken together, these data provide in vitro and in vivo evidence for a novel mechanism of beta-AR-mediated transactivation of cardiac PI3Kalpha via sequential involvement of Galpha(i)/Gbetagamma, Src, and PDGFR.
authors: Department of Pediatrics, Women and Infants Hospital of Rhode Island, Brown Medical School, 101 Dudley Street, Providence, RI 02905, USA.
authors: Naohiro
authors: N
authors: Yano
authors: Vlad
authors: V
authors: Ianus
authors: Ting C
authors: TC
authors: Zhao
authors: Andy
authors: A
authors: Tseng
authors: James F
authors: JF
authors: Padbury
authors: Yi-Tang
authors: YT
authors: Tseng
mesh_terms: D000818:Animals; D002460:Cell Line; D032383:Myocytes, Cardiac / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D011943:Receptors, Adrenergic, beta; D019869:Phosphatidylinositol 3-Kinases