p53-independent association between SV40 large T antigen and the major cytosolic heat shock protein, HSP90.
The simian double strand DNA tumor virus SV40 encodes the 90-kDa multi-functional protein, large T antigen (LT). LT functions by binding to DNA, as well as to many cellular target proteins such as p53 and retinoblastoma protein (pRB). We report here the identification of a cellular heat shock protein, HSP90, as a previously undescribed LT-associated protein. Immunoprecipitates by anti-HSP90 antibodies from LT-expressing cell lysates contained LT protein, as revealed by Western blotting. Conversely, anti-LT antibody co-immunoprecipitated HSP90. Co-immunoprecipitation of HSP90 and LT was observed even after complete immuno-depletion of p53, indicating that the association of LT with HSP90 is p53-independent. LT-HSP90 complexes can be reconstituted from purified HSP90 and unfolded-LT in vitro in an ATP-independent manner but not from HSP90 and native LT, suggesting that non-mature conformation of LT is required for the efficient association with HSP90. Moreover, geldanamycin, an anti-tumor drug that specifically binds and inhibits HSP90, reduced the intracellular concentration of LT by destabilizing newly synthesized LT. The above results suggest that HSP90 associates with immature forms of LT both in vivo and in vitro, and thus might assist LT in the formation of a functional, mature structure.