Inhibition of the p53 tumor suppressor gene results in growth of human aortic vascular smooth muscle cells - Potential role of p53 in regulation of vascular smooth muscle cell growth

Loss of activity of the p53 tumor suppressor gene product has been postulat ed in the pathogenesis of human restenosis. Although the antioncogenes p53 and retinoblastoma (Rb) susceptibility gene have been reported to play a pi votal role in cell cycle progression in various cells, the role of p53 and Rb in the growth of human vascular smooth muscle cells (VSMC) has not yet b een clarified. We used antisense strategy against p53 and Rb genes by the v iral envelope-liposomal method. Transfection of antisense p53 oligodeoxynuc leotides (ODN) alone resulted in an increase in DNA synthesis compared with control (P < 0.01). Similarly, transfection of antisense Rb ODN alone resu lted in a higher DNA synthesis rate than control (P < 0.01). Moreover, incr ease in VSMC number was only induced by transfection of antisense p53 ODN a lone or cotransfection of p53/Rb ODN (P < 0.01), whereas a single transfect ion of antisense Rb ODN had little effect on cell number. Therefore, we hyp othesized that this discrepancy is due to the induction of apoptosis mediat ed by p53. Interestingly, apoptotic cells were markedly increased in VSMC t ransfected with antisense Rb ODN alone, accompanied by the induction of p53 protein. The number of apoptotic cells was attenuated by cotransfection of antisense p53 ODN (P < 0.01). We finally examined the molecular mechanisms of apoptosis induced by the absence of Rb. In VSMC transfected with antise nse Rb ODN, bax, a promoter of apoptosis, was significantly increased in VS MC transfected with antisense Rb ODN (P < 0.01), whereas bcl-2 and Fas did not Flay a pivotal role in the induction of apoptosis. Overall, these data first demonstrated that the antioncogenes p53 and Rb negatively regulated t he cell cycle in VSMC, suggesting that the modulation of their activity may mediate VSMC growth such as that in restenosis and atherosclerosis. The pr esence of p53 plays a pivotal I role in the regulation of apoptosis in huma n VSMC growth, probably through the bar pathway. These results provide evid ence that p53 is a functional link between cell growth and apoptosis in VSM C.