NITRIC-OXIDE-INDUCED DOWN-REGULATION OF CDK2 ACTIVITY AND CYCLIN-A GENE-TRANSCRIPTION IN VASCULAR SMOOTH-MUSCLE CELLS

Background-Nitric oxide (NO) inhibits vascular smooth muscle cell (VSM C) proliferation and neointima formation after balloon injury. However , the molecular mechanisms underlying NO-mediated growth arrest are po orly understood. In the present study, we examined the effects of the NO donors sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillami ne (SNAP) on cell cycle activity in VSMCs. Methods and Results-Stimula tion 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 t o VSMC cultures at the time of serum stimulation abrogates the inducti on of cdk2 activity without suppressing protein levels of cdk2 or cycl in 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 d onors do not affect the expression of cdk2 protein but block the mitog en-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 g ene transcription.