Glucocorticoid-resistant (CR), in contrast to glucocorticoid-sensitive (CS), mouse lymphoma P1798 was shown to lack antiglucocorticoid receptor immunoactivity. Antibodies raised against the purified rat liver glucocorticoid receptor (GR) cross-reacted with the GR from CS, but not with the GR from CR, P1798 lymphoma. Using highly specific antisera against the GR in an indirect competitive enzyme-linked immunosorbent assay, it was demonstrated that α-chymotrypsin digestion of the GR from CS P1798 lymphoma caused a separation of a “resistant-like” nonimmunogenic steroid and DNA-binding domain (Stockes' radius, 3.3 nm) from an immunoactive domain (Stokes' radius, 2.6 nm). In contrast to CS P1798 lymphoma, neither before nor after α-chymotrypsin digestion, immunoactivity could be found in the cytosol from CR P1798 lymphoma. This was assayed after chromatography on DNA-cellulose or gel filtration on Agarose A (0.5 m). These results suggest that the domain of the CS GR containing the immunoactive determinant(s), normally removed by limited proteolysis by α-chymotrypsin, appears to be missing in CR P1798 lymphoma cytosol. It seems that this domain plays an important role in the mechanism of action of glucocorticoids. This might suggest that a mutation has occurred affecting the genome resulting in defective transcription of the receptor gene(s) in CR P1798 lymphoma.
The project was supported by funds provided in part by the Swedish Medical Research Council (Nos. 13X-2819 and 13X-06245).