p53, p21(WAF1/CIP1), and MDM2 involvement in proliferation and apoptosis in an in vitro model of conditionally immortalized human vascular smooth muscle cells

Using an in vitro model of a conditionally immortalized cell line, we inves tigated how human vascular smooth muscle cells (VSMCs) are affected by the expression of simian virus 40 (SV40) large T antigen (CT antigen), which bi nds to cell cycle regulators, such as the tmmor suppressor protein p53. Cel ls were obtained after infection of saphenous vein-derived VSMCs with a non replicative retroviral vector containing a temperature-sensitive (ts) mutan t of SV40 LT antigen and were shown to have maintained some characteristics and responses of VSMCs, Under permissive temperature conditions (36 degree s), the increased rate of cell proliferation was shown to be associated wit h expression of LT antigen and with LT-antigen binding to and inactivation of p53. p53 inactivation failed to block: apoptosis induced by serum withdr awal or by UV irradiation. Downregulation of LT-antigen expression at the n onpermissive temperature (39 degrees C) was shown to be associated with gro wth arrest, increased expression of the cell cycle inhibitor p21(WAF1/CIP1) increased MDM2-promoter activity, and differential expression of MDM2 gene products, suggesting that p53-induced transcription/transactivation may be involved in VSMC cell cycle control but nor necessarily apoptosis. The est ablished SMC Line HVTs-SM1 may be a useful model for the study of processes involved in myointimal hyperplasia, and cellular aging, as well as for the study of cell cycle control in general.