Activation of the human glucocorticoid receptor: evidence for a two-step model.
The relationship between glucocorticoid receptor subunit dissociation and activation was investigated by DEAE-cellulose and DNA-cellulose chromatography of monomeric and multimeric [3H]triamcinolone acetonide ([3H]TA)-labeled IM-9 cell glucocorticoid receptors. Multimeric (7-8 nm) and monomeric (5-6 nm) complexes were isolated by Sephacryl S-300 chromatography. Multimeric complexes did not bind to DNA-cellulose and eluted from DEAE-cellulose at a salt concentration (0.2 M KCl) characteristic of unactivated steroid-receptor complexes. Monomeric [3H]TA-receptor complexes eluted from DEAE-cellulose at a salt concentration (20 mM KCl) characteristic of activated steroid-receptor complexes. However, only half of these complexes bound to DNA-cellulose. This proportion could not be increased by heat treatment, addition of bovine serum albumin, or incubation with RNase A. Incubation of monomeric complexes with heat inactivated cytosol resulted in a 2-fold increase in DNA-cellulose binding. Unlike receptor dissociation, this increase was not inhibited by the presence of sodium molybdate. Fractionation of heat inactivated cytosol by Sephadex G-25 chromatography demonstrated that the activity responsible for the increased DNA binding of monomeric [3H]TA-receptor complexes was macromolecular. These results are consistent with a two-step model for glucocorticoid receptor activation, in which subunit dissociation is a necessary but insufficient condition for complete activation. They also indicate that conversion of the steroid-receptor complex to the low-salt eluting form is a reflection of receptor dissociation but not necessarily acquisition of DNA-binding activity.
Harmon
J M
JM
Department of Pharmacology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814-4799.
Elsasser
M S
MS
Urda
L A
LA
Eisen
L P
LP
D002460:Cell Line; D002846:Chromatography, Affinity; D002848:Chromatography, DEAE-Cellulose; D002850:Chromatography, Gel; D006801:Humans; D046911:Macromolecular Substances; D008962:Models, Theoretical; D011965:Receptors, Glucocorticoid / Q000302:isolation & purification / Q000378:metabolism*; D014222:Triamcinolone Acetonide / Q000378:metabolism
D046911:Macromolecular Substances; D011965:Receptors, Glucocorticoid; D014222:Triamcinolone Acetonide