Geldanamycin prevents nuclear translocation of mutant p53.

p53 is a tumor suppressor protein that acts in the nucleus to effect cell cycle arrest and apoptosis. In some cells p53 is located in the cytoplasm, perhaps as a means of downregulating its activity. We recently showed that hsp90 forms a complex with the cytoplasmically localized mutant p53 (TSp53vall35) within transformed cells (Sepehrnia et al., J. Biol. Chem. 271, 15084, 1996). The present study was undertaken to determine the p53 conformation bound to hsp90 and the role of hsp90 in p53 nuclear translocation. We show that hsp90 binds both a native and a denatured form of p53 as determined by conformation-specific antibodies. hsp90 does not bind p53 in a spatial-specific manner because it remains bound to p53 when induced to translocate to the nucleus by the protein synthesis inhibitor cycloheximide (CHX). Treatment of transformed cells with geldanamycin (GA), a small molecule that binds hsp90, causes a rapid destabilization of p53 by 50%. Residual p53 that survives GA treatment is incapable of translocating to the nucleus. GA does not destabilize p53 in cells where p53 is genotypically wild type. Although GA appears to dramatically alter the translocating properties of mutant p53 it does not dissociate the p53-hsp90 complex. We suggest that a second chaperone protein, called p23, which we show also binds p53, may play an important role in these GA-mediated effects.