Mutational Analysis of the Mouse Glucocorticoid Receptor¹

We have cloned the mouse glucocorticoid receptor (GR) from both wild-type and glucocorticoid-resistant variants of the mouse lymphoma cell lines WEHI-7 and S49. Mapping of the mutations present in the variant receptors, together with deletion analysis of wild-type receptor, reveals that the receptor has three clearly defined domains. The COOH-terminal domain contains the hormone-binding site. Within this domain is a small region which is important for the suppression of receptor activity in the absence of hormone. The large NH₂-terminal domain is essential for full receptor activity and contains within it a highly acidic region that potentiates receptor activity. The presence of this acidic region reduces nonspecific DNA binding and may therefore be crucial in the discrimination between specific and nonspecific DNA-binding sites by the receptor. A small centrally located domain contains all the information necessary to bind specifically to DNA and to activate transcription. Although this region is absolutely conserved in the GR of different species, many mutations introduced in vitro give rise to functional receptor. In addition, part of this region in the GR can be substituted for by the corresponding sequence in the estrogen receptor to give a GR with the DNA-binding and transcriptional specificity of an estrogen receptor. Lastly, we have succeeded in obtaining stable high-level expression of wild-type and mutant GR in transfected Chinese hamster ovary cells.