The original publication is available at http://www.journals.elsevier.com/steroids/Glucocorticoid receptor (GR) concentrations and the ability of the GR to dimerize are factors which influence
sensitivity to glucocorticoids. Upon glucocorticoid binding, the GR is actively transported into the
nucleus, a crucial step in determining GR function. We examined the effects of GR concentration and
the ability to dimerize on GR nuclear import, export and nuclear distribution using both live cell microscopy
of GFP-tagged GR and immunofluorescence of untagged GR, with both wild type GR (GRwt) and
dimerization deficient GR (GRdim). We found that the observed rate of GR nuclear import increases significantly
at higher GR concentrations, at saturating concentrations of dexamethasone (10¯ 6 M) using
GFP-tagged GR, while with untagged GR it is only discernable at sub-saturating ligand concentrations
(10 ¯10 -10 ¯ 9 M). Loss of dimerization results in a slower observed rate of nuclear import (2.5- to 3.3-fold
decrease for GFP-GRdim) as well as a decreased extent of GR nuclear localization (18–27% decrease for
untagged GRdim). These results were linked to an increased rate of GR export at low GR concentrations
(1.4- to 1.6-fold increase for untagged GR) and where GR dimerization is abrogated (1.5- to 1.7-fold
increase for GFP-GRdim). Furthermore, GR dimerization was shown to be required for the appearance
of discrete GC-dependent GR nuclear foci, the loss of which may explain the increased rate of GR export
for the GRdim. The reduction in the observed rate of nuclear import and increased rate of nuclear export
displayed at low GR concentrations and by the GRdim could explain the lowered glucocorticoid response
under these conditions.Post-prin
