Proliferation and subsequent dedifferentiation of vascular smooth muscle (V
SM) cells contribute to the pathogenesis of atherosclerosis and postangiopl
astic restenosis, The dedifferentiation of VSRI cells in vivo or in cell cu
lture is characterized by a loss of contractile proteins such as smooth mus
cle-specific Lu-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 se
rum component that increases the abundance of SRI-MHC transcripts. Addition
ally, serum and thrombin transiently elevated cytosolic Ca2+ concentrations
, led to a biphasic extracellular signal-regulated kinase (ERK) phosphoryla
tion, up-regulated a transfected SRI-MHC promoter construct, and induced ex
pression of the contractile proteins SM-MHc and ol-actin, Pertussis toxin,
N17-Ras/Raf, and PD98059 prevented both the serum- and thrombin-induced sec
ond phase ERK phosphorylation and SM-MHc promoter activation. Constitutivel
y active G alpha (q), G alphai, G alpha (12), and G alpha (13) failed to up
-regulate SRI-MHC transcription, whereas G beta gamma concentration-depende
ntly increased the SM-MHC promoter activity. Furthermore, the G beta gamma
scavenger beta -adrenergic receptor kinase 1 C-terminal peptide abolished t
he serum-mediated differentiation. We conclude that receptor-mediated diffe
rentiation of VSM cells requires G beta gamma and an intact Ras/Raf/MEK/ERK
signaling.