Lovastatin induces p21WAF1/Cip1 in human vascular smooth muscle cells:: Influence on protein phosphorylation, cell cycle, induction of apoptosis, and growth inhibition

Morbidity, mortality and the incidence of myocardial revascularisation procedures can be reduced by simvastatin, an inhibitor of the HMG-CoA reductase (EC 1.1.1.34). It was hypothesised that inhibition of isoprenylation of signalling proteins by HMG-CoA reductase inhibitors (vastatins), especially of the p21(ras) proteins could be causative for suppression of vascular smooth muscle cell (SMC) proliferation. The primary pharmacological mechanism of vastatins on human vascular SMG still remains unexplained. To analyse the influence of vastatins, SMC grown in presence of endothelial cell growth supplement (ECGS) were exposed to different concentrations of lovastatin. At 10 mu M concentration, inhibition of SMC proliferation was associated with induction of apoptosis in a large fraction of cells as at the 1 mu M level apoptosis was induced only in a minority of SMC. Protein phosphorylation on tyrosine, serine and threonine residues demonstrated no differences to untreated controls. Lovastatin induced arrest of cells in G(0)/G(1) phase of the cell cycle and DNA synthesis was reduced. Western blot analysis demonstrated a significant induction of p21(WAF1/Cip1) protein expression. This led to strong inhibition of cyclin dependent kinases (cdks) resulting in a cell cycle arrest. Our study provides evidence for a pharmacological explanation for the inhibition of EGGS-driven proliferation of human SMC by lovastatin.