© 2006 The Japanese Biochemical Society.
Regular Paper |
Suppression of the mTOR-Raptor Signaling Pathway by the Inhibitor of Heat Shock Protein 90 Geldanamycin
1 Biosignal Research Center, Kobe University, Kobe 657-8501; 2 CREST, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama 332-0012; and 3 Division of Internal and Geriatric Medicine, Department of Development and Aging, Kobe University Graduate School of Medicine, Kobe 650-0017
To whom correspondence should be addressed. Tel: +81-78-803-5964, Fax: +81-78-803-5972, E-mail: ukikkawa{at}kobe-u.ac.jp
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 anti-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 mTOR/raptor complex through the association with raptor, and that the mTOR signaling pathway is a novel target of geldanamycin.
* These authors contributed for this work equally.
Present address: Biochemistry Department, Faculty of Medicine, Brawijaya University, Malang 65145, Indonesia.
Deceased July 8, 2005.
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