Gβγ Mediate Differentiation of Vascular Smooth Muscle Cells

H Peter Reusch,Michael Schaefer,Claudia Plum,Günter Schultz,Martin Paul

doi:10.1074/jbc.m101963200

Abstract

Proliferation and subsequent dedifferentiation of vascular smooth muscle (VSM) cells contribute to the pathogenesis of atherosclerosis and postangioplastic restenosis. The dedifferentiation of VSM cells in vivo or in cell culture is characterized by a loss of contractile proteins such as smooth muscle-specific alpha-actin and myosin heavy chain (SM-MHC). Serum increased the expression of contractile proteins in neonatal rat VSM cells, indicating a redifferentiation process. RNase protection assays defined thrombin as a serum component that increases the abundance of SM-MHC transcripts. Additionally, serum and thrombin transiently elevated cytosolic Ca(2+) concentrations, led to a biphasic extracellular signal-regulated kinase (ERK) phosphorylation, up-regulated a transfected SM-MHC promoter construct, and induced expression of the contractile proteins SM-MHC and alpha-actin. Pertussis toxin, N17-Ras/Raf, and PD98059 prevented both the serum- and thrombin-induced second phase ERK phosphorylation and SM-MHC promoter activation. Constitutively active Galpha(q), Galpha(i), Galpha(12), and Galpha(13) failed to up-regulate SM-MHC transcription, whereas Gbetagamma concentration-dependently increased the SM-MHC promoter activity. Furthermore, the Gbetagamma scavenger beta-adrenergic receptor kinase 1 C-terminal peptide abolished the serum-mediated differentiation. We conclude that receptor-mediated differentiation of VSM cells requires Gbetagamma and an intact Ras/Raf/MEK/ERK signaling.

Highlights

Differentiated, contractile vascular smooth muscle (VSM)1 cells are major determinants of blood pressure and flow
In this study we describe a receptor-mediated signaling pathway leading to differentiation of VSM cells
Because coexpression of G␤␥ subunits mimicked and ␤ARK1ct abrogated the activation of the SM-MHC promoter in response to serum components, we conclude that G␤␥ mediate the agonist-induced differentiation of VSM cells

Summary

Introduction

Contractile vascular smooth muscle (VSM) cells are major determinants of blood pressure and flow. In chronic vascular diseases such as hypertension and atherosclerosis, VSM cells proliferate and undergo a phenotypic modulation characterized by local matrix degradation and a loss of contractile function [1]. Similar to pathological proliferation during vascular disease, VSM cells down-regulate SM-1/2 expression in primary culture. Depending on extracellular matrix composition, cultured VSM cells can either proliferate or differentiate in response to mechanical strain [11]. These findings were corroborated recently by applying mechanical forces to cultured whole vessels [12]. The receptor-mediated proliferation and differentiation involves the extracellular signal-regulated kinase (ERK) subfamily of MAP kinases [13, 14]. Transactivation of receptor tyrosine kinases has been demonstrated to participate in signaling from G protein-coupled receptors to ERKs (16 –18)

Methods

Results

Conclusion