The unliganded glucocorticoid receptor is localized in the nucleus, not in the cytoplasm.

Abstract

The glucocorticoid receptor (GR) is often described to be localized in the cytoplasm in the absence of hormone and to translocate to the nucleus upon binding of the hormone. This apparently different behavior of the GR compared to that of other members of the steroid receptor superfamily is unexpected because similarities in the molecular structures of steroid hormone receptors would predict similarities in their working mechanisms. The absence of the unliganded GR from the nuclear compartment may be due to an artefactual redistribution, occurring during the immunocytochemical procedure. We systematically studied the effects of various fixation and permeabilization procedures on the distribution of the GR in hepatoma cells that were incubated in steroid-free or steroid-containing medium. Immunofluorescent labeling of the GR in formaldehyde-fixed and detergent-permeabilized cells resulted in the almost complete absence of immunoreactivity of cells when the receptor was in its unliganded form, whereas the liganded receptor was detected mainly in the nucleus. On the other hand, labeling of cryosectioned glutaraldehyde/formaldehyde-fixed cells demonstrated that receptor antigenicity is present in the nucleus in the absence as well as the presence of steroid. We conclude that the results obtained with the cryosectioning procedure reflect the receptor distribution in the living cell, since glutaraldehyde fixation of the cells prevented the washout of loosely bound receptor. The predominantly nuclear location of the unliganded GR in hepatoma cells and the absence of changes in distribution after steroid stimulation imply that the nuclear translocation model is not true for the GR.

Morphometric studies of the localization of the glucocorticoid receptor in mammalian cells and of glucocorticoid hormone-induced effects.

“…The average relative n/w GR distribution was about the same for both fixations. However, F/T yielded a much stronger GR signal, indicating a large degree of GR extraction by M. The similarity in GR distribution after both cross-linking and precipitating fixations strongly indicates that we observe the actual intracellular GR distribution and not an artifactual redistribution of receptor followed by recapture by cytoplasmic components, as suggested by Brink et al (10).…”

Mineralocorticoid and glucocorticoid receptors in the brain. Implications for ion permeability and transmitter systems

“…The DNA binding domain of the GR also contains a second nuclear translocation signal. It is probably due to this second translocation signal that, in the absence of corticosterone, GRs are detected in the cytosolic compartment (Picard and Yamamoto, 1987), in addition to the nuclear compartment (Brink et al, 1992). Still, even in the absence of the ligand, binding to DNA is possible but the efficacy and kinetics of this process are much reduced (Becker et al, 1986;Willmann and Beato, 1986;Schauer et al, 1989;Power et al, 1992).…”

“…Pronounced changes in receptor density have been described during senescence in rats and other species (de Kloet, 1992). The alterations for the two receptor types partly depend on the rat strain that was used for the studies.…”

Differential roles of heat shock protein 70 in the in vitro nuclear import of glucocorticoid receptor and simian virus 40 large tumor antigen.

“…Our in vitro results recapitulate hormone-dependent nuclear import of GR observed in 'I'ag XGR VOL. 14,1994 on March 30, 2019 by guest http://mcb.asm.org/ Downloaded from vivo in many cell types and challenge the notion that differential localization of unliganded GR in some systems reflects artifactual cell permeabilization and fixation conditions (7). Like other steroid receptors (8,21), GR has the capacity to shuttle between the nuclear and cytoplasmic compartments (36) and most likely preferentially accumulates within a specific subcellular compartment as a result of rate limitations on either the nuclear import or export process.…”