Characterization of the purified activated glucocorticoid receptor from rat liver cytosol

The activated glucocorticoid receptor (GR) from rat liver cytosol was purified by sequential chromatography on DNA-cellulose and DEAE-Sepharose. Analysis by sodium dodecyl sulfate-gel electrophoresis demonstrated a main band with Mr = 94,000 (94K band). Two minor bands with Mr = 79,000 (79K band) and 72,000 (72K band) were also seen in this preparation. Photoaffinity labeling showed that the hormone is bound to the 94K and 79K components but not to the 72K component. Immunoblotting using antibodies raised against the 94K protein demonstrated cross-reactivity between the 94K and 79K components but not with the 72K species. The 72K species could be partially separated from the 94K and 79K components by density gradient centrifugation. Limited proteolysis of the purified GR with trypsin or alpha-chymotrypsin led to degradation of the 94K and 79K components and appearance of a 39K fragment which still retained the hormone and could be bound to DNA-cellulose. The 72K component was not affected by digestion with trypsin or alpha-chymotrypsin. However, chromatography on DNA-cellulose of the alpha-chymotrypsin-treated GR resulted in elution of the 72K component in the flow-through of the column while the 39K fragment was retained on the column and eluted with 0.18 M NaCl. In the control experiment where no alpha-chymotrypsin treatment was performed, the 72K component could not be detected in the flow-through fraction but was eluted together with the 94K and 79K components at 0.18 M NaCl. These results suggest that the 72K protein might be bound to the 94K and/or 79K component. The 39K fragment did not bind antibodies raised against the 94K protein. The 39K fragment was further degraded by trypsin but not by alpha-chymotrypsin to a 27K and a 25K fragment while both still retained the ligand. These data obtained with limited proteolysis of the purified GR are in agreement with previous findings on proteolysis of the GR in crude cytosol (Wrange, O., and Gustafsson, J.-A. (1978) J. Biol. Chem. 253, 856-865; Carlstedt-Duke, J., Okret, S., Wrange, O., and Gustafsson, J.-A. (1982) Proc. Natl. Acad. Sci. U.S.A. 79, 4260-4264).