CGMP-ELEVATING AGENTS SUPPRESS PROLIFERATION OF VASCULAR SMOOTH-MUSCLE CELLS BY INHIBITING THE ACTIVATION OF EPIDERMAL GROWTH-FACTOR SIGNALING PATHWAY

Background Abnormal proliferation of vascular smooth muscle cells (VSM C) is a key event in the pathogenesis of atherosclerosis and many vasc ular diseases. It is known that nitric oxide released from the endothe lium participates in the regulation of VSMC proliferation via a cyclic 3',5'-guanosine monophosphate (cGMP)-mediated mechanism. In a series of experiments, sodium nitroprusside (SNP) and A02131-1 were evaluated for their antiproliferative effect and the mechanism of their cGMP-el evating action. Methods and Results The effect of SNP and A02131-1 on epidermal growth factor (EGF)-stimulated proliferation of rat aortic s mooth muscle cells (VSMC) was examined. Cell proliferation was measure d in terms of [H-3]thymidine incorporation, Bow cytometry, and the cel l number. Further, their effect on the EGF-activated signal transducti on pathway was assessed by measuring mitogen-activated protein kinases (MAPK), MAPK kinase (MEK), Raf-1 activity, and the formation of activ e form of Ras. SNP and A02131-1 inhibited EGF-induced DNA synthesis an d subsequent proliferation of VSMC. These two increased cGMP but only a little cAMP in VSMC. A similar antiproliferative effect was observed with 8-bromo-cGMP. The antiproliferative effect of the two was revers ed by KT5823 but not by dideoxyadenosine nor Rp-cAMPS. SNP and A02131- 1 blocked the EGF-inducible cell cycle progression at the G1/S phase. Further experiments indicated that the two cGMP-elevating agents prima rily blocked the activation of Raf-1 by EGF-activated Ras. Conclusions These results demonstrate that cGMP-elevating agents inhibit [H-3]thy midine incorporation and thus the growth of VSMC; and this inhibition appears to attenuate EGF-activated signal transduction pathway by prev enting Ras-dependent activation of Raf-1.