Nitric oxide-induced downregulation of cdk2 activity and cyclin A gene transcription in vascular smooth muscle cells

Background-Nitric oxide (NO) inhibits vascular smooth muscle cell (VSMC) proliferation and neointima formation after balloon injury. However, the molecular mechanisms underlying NO-mediated growth arrest are poorly understood. In the present study, we examined the effects of the NO donors sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP) on cell cycle activity in VSMCs. Methods and Results-Stimulation of quiescent rat VSMCs with serum leads to an increase in cyclin-dependent kinase (cdk)2 kinase activity that correlates with a marked induction of cyclin A protein expression The addition of SNP or SNAP to VSMC cultures at the time of serum stimulation abrogates the induction of cdk2 activity without suppressing protein levels of cdk2 or cyclin E. These NO donors block serum-stimulated upregulation of cyclin A mRNA and protein and repress the serum induction of cyclin A promoter activity in VSMCs. Conclusions-The addition of the nitric oxide donors SNP or SNAP to mitogen-stimulated VSMCs prevents activation of cdk2, a key regulator of the G(1) and S phases of the cell cycle. These NO donors do not affect the expression of cdk2 protein but block the mitogen-induced expression of cyclin A, an activating subunit of cdk2. SNP and SNAP also repress the mitogen-stimulated activation of the cyclin A promoter, These data suggest that the antiproliferative effect of NO on VSMCs results, at least in part, from the repression of cyclin A gene transcription.