TI - Suppression of the raptor signaling pathway by the inhibitor of heat shock protein 90 geldanamycin . AB - Heat shock protein 90 ( Hsp90 ) was co-immunoprecipitated with raptor , the binding partner of the mammalian target of rapamycin ( mTOR ) from HEK293 cells . Hsp90 was detected in the raptor antibody immunoprecipitates prepared from the cell extract by immunoblot analysis using the anti-Hsp90 antibody , and the association of these two proteins was confirmed by immunoprecipitation from the cells co-expressing Hsp90 and raptor as epitope-tagged molecules . Geldanamycin , a potent inhibitor of Hsp90 , disrupted the in vivo binding of Hsp90 to raptor without affecting the association of raptor and mTOR , and suppressed the phosphorylation by mTOR of the downstream translational regulators p70 S6 kinase ( S6K ) and eukaryotic initiation factor 4E-binding protein 1 ( 4E-BP1 ) . The protein kinase activity of S6K as well as the phosphorylation of the substrate , 40S ribosomal protein S6 , were lowered in the geldanamycin-treated cells . These results indicate that Hsp90 is involved in the regulation of protein translation by facilitating the phosphorylation reaction of 4E-BP1 and S6K catalyzed by the raptor complex through the association with raptor , and that the mTOR signaling pathway is a novel target of geldanamycin .