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A novel signaling pathway for β‐adrenergic receptor‐mediated activation of PI3K in H9c2 cardiomyocytes
Author(s) -
Tseng YiTang,
Yano Naohiro,
Ianus Vlad,
Tseng Andy,
Zhao Ting C,
Padbury James F
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.6.a1259-b
Subject(s) - transactivation , pi3k/akt/mtor pathway , proto oncogene tyrosine protein kinase src , phosphorylation , protein kinase b , tyrosine kinase , signal transduction , tyrosine phosphorylation , microbiology and biotechnology , receptor tyrosine kinase , phosphoinositide 3 kinase , chemistry , wortmannin , biology , biochemistry , gene expression , gene
Stimulation of cardiac β‐adrenergic receptors (βAR) activates both G s ‐and G i ‐coupled signaling cascades, including the PI3K pathway, that have important physiological implications. Multiple isoforms of PI3K are found in the heart. The goals of the current study were to examine the intracellular signaling pathways linking βAR to PI3K andto identify the PI3K isoform mediating this transactivation in a cardiac context. Acute βAR stimulation with isoproterenol (ISO) resulted in increased tyrosine kinase‐associated PI3K activity and phosphorylation of Akt and p70S6K in H9c2 cardiomyocytes. Co‐treatment with ICI 118,551, but not CGP 20712, abolished ISO‐induced increase in PI3K activity, suggesting a β2AR‐mediated event. The increase in PI3K activity was also abrogated by co‐treatment with PP2, a selective inhibitor of the Src‐family tyrosine kinases, and by AG 1296, a selective inhibitor of PDGFR, but not by inhibitors of G αi , PKA, PKC, Ras, adenylyl cyclase, EGFR or IGF‐1R. Consistent with these results, βAR‐induced increases in tyrosine phosphorylation of PDGFR and Src, which can be abolished by siRNA specific for Src. Moreover, H9c2 cardiomyocytes stably transfected with a vector expressing a G βγ sequestrant peptide derived from the C‐terminus of βAR kinase‐1 failed to activate PI3K after βAR stimulation, suggesting G βγ is required for the transactivation. More important, acute βAR stimulation in vivo resulted in increases in tyrosine kinase‐sensitive PI3K and PI3Kα activities but not the activities of other isoforms (PI3Kβ, ‐δ, ‐γ) in adult mouse heart. Taken together, these data provide in vitro and in vivo evidence for a novel mechanism of βAR‐mediated transactivation of cardiac PI3Kα via sequential involvement of G βγ , Src and PDGFR. (Supported by NIH 1 P20 RR018728)