Nucleocytoplasmic Trafficking of Steroid-free Glucocorticoid Receptor*
- From the Departments of ‡Medicine and§Biochemistry, Microbiology, and Immunology and the¶Graduate Program in Biochemistry, University of Ottawa, The Loeb Health Research Institute at the Ottawa Hospital, Ottawa, Ontario K1Y 4E9, Canada
Abstract
Glucocorticoid receptor (GR) recycles between an inactive form complexed with heat shock proteins (hsps) and localized to
the cytoplasm and a free liganded form that regulates specific gene transcription in the nucleus. We report here that, contrary
to previous assumptions, association of GR into hsp-containing complexes is not sufficient to prevent the shuttling or trafficking
of the GR across the nuclear membrane. Following the withdrawal of treatment with cortisol or the hormone antagonist RU486,
GRs recycled rapidly into hsp-associated, hormone-responsive complexes. However, cortisol-withdrawn receptors redistributed
to the cytoplasm very slowly (t
= 8–9 h) and RU486-withdrawn receptors not at all. Persistent localization of these GRs to the nucleus was not due to a gross
defect in export, since in both instances the complexed nuclear GRs transferred efficiently between heterokaryon nuclei. Moreover,
the addition of a nuclear retention signal to the N terminus of GR induced the transfer of naive receptor to the nucleus in
the absence of steroid. These results suggest that the localization of GR to the cytoplasm is determined by fine control of
the rates of transfer of GR across the nuclear membrane and/or by active retention that occurs independently from the association
of GR with hsps.
Footnotes
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↵* This work was funded by a grant from the Medical Research Council of Canada (to Y. A. L.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‖ To whom correspondence should be addressed: The Ottawa Hospital Loeb Research Institute, 725 Parkdale Ave., Ottawa, Ontario K1Y 4E9, Canada. Tel.: 613-761-5142; Fax: 613-761-5036; E-mail:lefebvre{at}civich.ottawa.on.ca.
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↵2 R. J. G. Haché, R. Tse, T. Reich, J. G. A. Savory, and Y. A. Lefebvre, unpublished observation.
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↵3 Savory, J. G. A., Hsu, B., Laquain, I. R., Giffin, W., Reich, T., Haché, R. J. G., and Lefebvre, Y. A. (1999) Mol. Cell. Biol., in press.
- Abbreviations:
- hsp
-
heat shock protein
- GR
-
glucocorticoid receptor
- ER
-
estrogen receptor
- PR
-
progesterone receptor
- MMTV
-
mouse mammary tumor virus
- IIF
-
indirect immunofluorescence
- NLS
-
nuclear localization signal
- CAT
-
chloramphenicol acetyl- transferase
- DMEM
-
Dulbecco’s modified Eagle’s medium
- BSA
-
bovine serum albumin
- WT
-
wild type.
-
- Received September 10, 1998.
- Revision received October 26, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
