Mechanism of hydrogen peroxide-induced cell cycle arrest in vascular smooth muscle.

Reactive oxygen species such as hydrogen peroxide (H(2)O(2)) can positively and negatively modulate vascular smooth muscle cell (VSMC) growth. To investigate these paradoxical effects of H(2)O(2), we examined its effect on apoptosis, cell cycle progression, and cell cycle proteins. High concentrations of H(2)O(2) (500 microM to 1 mM) induced apoptosis, whereas moderate concentrations (100 microM) caused cell cycle arrest in G1. H(2)O(2) (100 microM) blocked serum-stimulated cyclin-dependent kinase-2 (CDK2) activity, but not CDK4 activity, suggesting that cell cycle arrest occurred in part by inhibiting CDK2 activity. The serum-induced increase in cyclin A mRNA was also completely suppressed by H(2)O(2), whereas cyclin D1 mRNA was not affected. In addition, H(2)O(2) caused a dramatic increase in expression of the cell cycle inhibitor p21 mRNA (9.67 +/- 0.94-fold at 2 h) and protein (8.75 +/- 0.08-fold at 8 h), but no change in p27 protein. Finally, H(2)O(2 )transiently increased p53 protein levels (3.16 +/- 1.2-fold at 2 h). Thus, whereas high levels of H(2)O(2) induce apoptosis, moderate concentrations of H(2)O(2) coordinate a set of molecular events leading to arrest of VSMCs at the G1/S checkpoint of the cell cycle. These results provide insight into the mechanisms underlying positive and negative regulation of VSMC growth by H(2)O(2) in vascular disease.