P21(CIP1)-MEDIATED INHIBITION OF CELL-PROLIFERATION BY OVEREXPRESSIONOF THE GAX HOMEODOMAIN GENE

gax, a diverged homeobox gene expressed in vascular smooth muscle cell s (VSMCs), is down-regulated in vitro by mitogen stimulation and in vi vo in response to vascular injury that lends to cellular proliferation . Recombinant Gax protein microinjected into VSMCs and fibroblasts inh ibited the mitogen-induced entry into S-phase when introduced either d uring quiescence or early stages of G(1). Overexpression of gax with a replication-defective adenovirus vector resulted in G(0)/G(1) cell cy cle arrest of VSMCs and fibroblasts. The gax-induced growth inhibition correlated with a p53-independent up-regulation of the cyclin-depende nt kinase inhibitor p21. Gax overexpression also led to an association of p21 with cdk2 complexes and a decrease in cdk2 activity. Fibroblas ts deficient in p21 were not susceptible to a reduction in cdk2 activi ty or growth inhibition by gax overexpression. Localized delivery of t he virus to denuded rat carotid arteries significantly reduced neointi ma formation and luminal narrowing. These data indicate that gax overe xpression can inhibit cell proliferation in a p21-dependent manner and can modulate injury-induced changes in vessel wall morphology that re sult from excessive cellular proliferation.