The transformed glucocorticoid receptor has a lower steroid-binding affinity than the nontransformed receptor

High-salt treatment of cytosolic glucocorticoid receptor (GR) preparations reduces the steroid-binding ability of the receptor and induces the conversion of the receptor from a nontransformed (non-DNA-binding) 9S form to a transformed (DNA-binding) 4S entity. Therefore, we decided to investigate the possible relationship between these two phenomena. Steroid-free GR was converted from a 9S to a 4S form by exposure to 0.4 M NaCl. The binding of [3H]triamcinolone acetonide [( 3H]TA) to the 9S form was almost saturated at a concentration of 20 nM, whereas [3H]TA was hardly bound to the 4S form at this concentration. The 4S form was efficiently labeled at 200 nM. Scatchard analysis of the GR exposed to 0.4 M NaCl in the presence of 10 mM molybdate showed the presence of two types of binding sites with apparent dissociation constants of 0.52 +/- 0.07 and 64.1 +/- 16.2 nM, respectively. In the absence of molybdate, the ratio of the lower affinity site was increased, but the total number of binding sites was not modified. The GR with the low [3H]TA-binding affinity bound to DNA-cellulose even in its unliganded state, whereas the form with the high affinity did not. Immunoblot analysis using anti-GR monoclonal antibody revealed no difference in molecular size (Mr 94000) between the high- and low-affinity entities. These results indicate that the transformed GR has a reduced [3H]TA-binding affinity as compared to the nontransformed GR.(ABSTRACT TRUNCATED AT 250 WORDS)