Characterization of the glucocorticoid receptor. Comparison of wild type and variant receptors

We have measured the size of the glucocorticoid receptors from two murine lymphoid cell lines, one displaying a wild type cytolytic response to hormone, the other a resistant variant. Using radiation inactivation and target analysis, we first compared the nuclear and cytoplasmic forms of the steroid receptors in a wild type line, WEHI 7.1 (W7). Within the variation expected for this type of measurement (+/- 14%), the nuclear and cytoplasmic forms have the same size, 75,000 and 79,000 daltons, respectively. We have also measured the size of the receptor in a hormone-insensitive "nuclear transfer-increased" (nti) variant (S49 143R). In contrast to reports indicating that the nti phenotype is associated with a much smaller cytoplasmic receptor, we found little or no difference in sizes of translocated receptor in wild type and nti cells. We have found significant differences, however, in the release of wild type and nti receptors from nuclei by nuclease digestion, salt, and spermidine. Approximately 80% of the nti receptor was readily released from nuclei incubated with micrococcal nuclease, while only 40-50% of the wild type receptor was released under similar conditions. The wild type nuclei also contained a fraction of receptor (approximately 30%) which was resistant to extraction by NaCl and spermidine. This fraction was greatly diminished in the nti nuclei. Thus, a portion of the wild type receptors appears to be stabilized within the nuclei, possibly through a type of interaction which cannot be sustained by the nti receptor.