Glucocorticoid receptor (GR) recycles between an inactive form complexed wi
th heat shock proteins (hsps) and localized to the cytoplasm and a free Lig
anded form that regulates specific gene transcription in the nucleus. We re
port here that, contrary to previous assumptions, association of GR into hs
p-containing complexes is not sufficient to prevent the shuttling or traffi
cking of the GR across the nuclear membrane. Following the withdrawal of tr
eatment with cortisol or the hormone antagonist RU486, GRs recycled rapidly
into hsp associated, hormone-responsive complexes. However, cortisol-withd
rawn receptors redistributed to the cytoplasm very slowly (t(1/2) = 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and RU486-withdrawn receptors not at all.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 i
nstances the complexed nuclear GRs transferred efficiently between heteroka
ryon 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 t
he cytoplasm is determined by fine control of the rates of transfer of GR a
cross the nuclear membrane and/or by active retention that occurs independe
ntly from the association of GR with hsps.