Characterization of glucocorticoid receptors in S49 mouse lymphoma cells by affinity labeling with [3H]dexamethasone 21-mesylate

Glucocorticoid receptors in wild type and mutant S49 mouse lymphoma cells were affinity labeled with 3H]dexamethasone 21-mesylate and analyzed directly by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The molecular weight of receptors in cytosol from wild type cells and nuclear transfer decreased (nt-) mutants was 97,000 (97 kDa). The molecular weight of receptors in cytosol from nuclear transfer increased (nti) mutants was 48 kDa. The 97 kDa receptor in cytosol from wild type cells was digested by chymotrypsin to a 40 kDa steroid-binding receptor fragment but the 48 kDa receptor in cytosol from nti mutants was resistant to digestion by chymotrypsin. In addition to the 48 kDa receptor, cytosol from nti mutants contained 40 and 18 kDa receptor fragments. Cytosol from the nt- mutants also contained 18 kDa receptor fragments. The 40 and 18 kDa receptor fragments were present in multiple subclones of a nti mutant cell line. Formation of these receptor fragments was not prevented by protease inhibitors and was not increased by extended incubation of cytosol samples. Both 48 and 40 kDa forms of the receptor, but not the 18 kDa form, could be activated and bound by DNA-cellulose.