POLYOMAVIRUS LARGE T-ANTIGEN OVERCOMES P53 DEPENDENT GROWTH ARREST

Polyomavirus transforms cells in culture and induces tumors in mice wi thout apparent interaction with or inactivation of the p53 tumor suppr essor protein. In this report we investigate the ability of polyomavir us T antigens to overcome the growth suppression function of p53. A te mperature sensitive p53 gene was introduced into mouse embryo fibrobla sts derived from a p53 null mouse, resulting in expression of a protei n with a mutant conformation at 37 degrees C and a functionally wild-t ype conformation at 32 degrees C. We found that expression of p53 at 3 2 degrees C induced the cyclin-dependent kinase inhibitor p21/WAF1 and arrested cell growth in the G(1)/G(0) phase of the cell cycle. Only t he under-phosphorylated form of the retinoblastoma tumor suppressor pr otein (pRB) was detected in these growth arrested cells. We introduced both polyomavirus large T (LT) and middle T (MT) antigens into this c ell line and showed that LT overcame p53-dependent growth arrest, whil e MT did not. In cells grown at 32 degrees C, LT expession led to cell proliferation and phosphorylation of pRB in the presence of p21. A mu tant LT containing a defective pRB binding domain failed to overcome t he growth arrest, indicating that interaction of LT with RE proteins i s required to override p53 function. Although the polyomavirus T antig ens do not interact with p53 directly, our results indicate that the v irus, through LT, is able to interfere with the growth suppressive act ivity of p53.