THE FUNCTION OF STEROID-HORMONE RECEPTORS IS INHIBITED BY THE HSP90-SPECIFIC COMPOUND GELDANAMYCIN

The ansamycin antibiotic geldanamycin, which specifically interacts wi th the heat shock protein hsp90, was used to study the function of hsp 90 in steroid hormone receptors, We observed inhibition of glucocortic oid-specific gene induction in several responsive cell systems, Hormon e binding abilities of receptors for glucocorticoid, progestin, androg en, and estrogen were inhibited upon exposing intact cells to geldanam ycin, Inhibition was only seen when geldanamycin was applied to cell c ultures under growth conditions or was present during in vitro synthes is; presynthesized receptors in cell extracts were not affected, Upon withdrawal of geldanamycin, glucocorticoid binding ability was re gain ed; this was partially independent of de novo protein synthesis. Gelda namycin caused decreased levels of immunoreactive glucocorticoid recep tors in wild-type cells with enhanced degradation occurring through th e ubiquitin-proteasome pathway. Analysis of receptors from treated cel ls revealed a heteromeric structure of normal size in which the recept or polypeptide is complexed with normal amounts of hsp90 and the immun ophilin p59, These data support the view that hsp90 actively participa tes in steroid-induced signal transduction, and they suggest that geld anamycin affects receptor action without disrupting hsp90-containing h eterocomplexes per se. Nevertheless, complexes synthesized and assembl ed in vitro in the presence of geldanamycin differ from receptors of c ellular origin.