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Molecular chaperones function as steroid receptor nuclear mobility factors
Cem Elbi *,
Dawn A. Walker *,
William P. Sullivan,
David O. Toft,
Gordon L. Hager *, and
Donald B. DeFranco
*Laboratory of Receptor Biology and Gene Expression, Building 41, Room B602, National Cancer Institute, Bethesda, MD 20892-5055; Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261; and Department of Biochemistry and Molecular Biology, Mayo Graduate School, Rochester, MN 55905
Communicated by Jack Gorski, University of Wisconsin, Madison, WI, January 8, 2004
Received for publication November 20, 2003.
Live cell imaging has revealed the rapid mobility of steroidhormone receptors within nuclei and their dynamic exchange attranscriptionally active target sites. Although a number ofother proteins have been shown to be highly mobile within nuclei,the identity of soluble factors responsible for orchestratingnuclear trafficking remains unknown. We have developed a previouslyundescribed in situ subnuclear trafficking assay that generatestranscriptionally active nuclei, which are depleted of solublefactors required for the nuclear mobility of glucocorticoid(GR) and progesterone receptors (PR). Using this system anda fluorescence recovery after photobleaching technique, we demonstratethat nuclear mobility of GR recovered on incubation with reticulocytelysate was inhibited by geldanamycin, a drug that blocks thechaperone activity of heat-shock protein 90. Direct proof ofmolecular chaperone involvement in steroid receptor subnucleartrafficking was provided by the ATP-dependent recovery of nuclearmobility of GR and PR on incubation with various combinationsof purified chaperone and/or cochaperone proteins. Additionally,for both receptors, the inclusion of hormone during the recoveryperiod leads to a retardation of nuclear mobility. Thus, ourresults provide a description of soluble nuclear mobility factorsand furthermore demonstrate a previously unrecognized role formolecular chaperones in the regulation of steroid receptor functionwithin the nucleus.