Both Gs and Gi Proteins Are Critically Involved in Isoproterenol-induced Cardiomyocyte Hypertrophy

Yunzeng Zou,Issei Komuro,Tsutomu Yamazaki,Sumiyo Kudoh,Hiroki Uozumi,Takashi Kadowaki,Yoshio Yazaki

doi:10.1074/jbc.274.14.9760

Abstract

Activation of beta-adrenoreceptors induces cardiomyocyte hypertrophy. In the present study, we examined isoproterenol-evoked intracellular signal transduction pathways leading to activation of extracellular signal-regulated kinases (ERKs) and cardiomyocyte hypertrophy. Inhibitors for cAMP and protein kinase A (PKA) abolished isoproterenol-evoked ERK activation, suggesting that Gs protein is involved in the activation. Inhibition of Gi protein by pertussis toxin, however, also suppressed isoproterenol-induced ERK activation. Overexpression of the Gbetagamma subunit binding domain of the beta-adrenoreceptor kinase 1 and of COOH-terminal Src kinase, which inhibit functions of Gbetagamma and the Src family tyrosine kinases, respectively, also inhibited isoproterenol-induced ERK activation. Overexpression of dominant-negative mutants of Ras and Raf-1 kinase and of the beta-adrenoreceptor mutant that lacks phosphorylation sites by PKA abolished isoproterenol-stimulated ERK activation. The isoproterenol-induced increase in protein synthesis was also suppressed by inhibitors for PKA, Gi, tyrosine kinases, or Ras. These results suggest that isoproterenol induces ERK activation and cardiomyocyte hypertrophy through two different G proteins, Gs and Gi. cAMP-dependent PKA activation through Gs may phosphorylate the beta-adrenoreceptor, leading to coupling of the receptor from Gs to Gi. Activation of Gi activates ERKs through Gbetagamma, Src family tyrosine kinases, Ras, and Raf-1 kinase.

Highlights

These results suggest that cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) activation probably through Gs is required for ISO-induced activation of extracellular signalregulated kinases (ERKs) in cardiac myocytes
A previous report indicated that down-regulation of Gs␣ abolishes ISO-induced ERK activation in human endothelial cells [25], suggesting that Gs␣ is required for activation of ERKs by ␤-AR
Our previous [7] and present studies showed that ISO activates ERKs through cAMP/PKA in cardiac myocytes, supporting that Gs protein plays an essential role in the activation of ERKs

Summary

Introduction

We examined further the role of Src family tyrosine kinases in ISO-induced ERK activation in cardiac myocytes. The pretreatment with these inhibitors alone did not affect the basal level of protein incorporation significantly (Fig. 8A), an ISO-induced increase in protein synthesis was suppressed significantly by all of these inhibitors (Fig. 8B), indicating that ISO enhanced protein synthesis through cAMP/PKA, Gi, tyrosine kinases, and Ras. These results suggest that the signal transduction pathway leading to activation of ERKs is important for ISO-induced protein synthesis in cardiac myocytes.

Results

Conclusion