The structure of the human glucocorticoid receptor and its gene

The human glucocorticoid receptor (hGR) is a ubiquitous, phosphorylated protein of Mr about 95,000, as determined by PAGE or other physical methods. It is found intracellularly, and current immunocytochemical studies suggest that, in the absence of ligand, it is predominantly cytoplasmic. Limited proteolysis shows that the protein can be divided into steroid-binding, DNA-binding and strongly antigenic regions, roughly one-third each of the molecule. Recently, the hGR gene has been cloned and sequenced, and analysis of the gene has confirmed and extended this general description of the protein. The DNA-binding region is cysteine-rich, and the carboxy-terminal end of the molecule is the steroid-binding region. Analysis of CEM cells, a line of human leukemic lymphoblasts, has resulted in isolation of three classes of resistant cells: receptor-site deficient (r-), receptor activation labile (r act/l), and wild-type receptor but lysis-defective (r+ly-). Monoclonal antibodies to the hGR have been produced and used to show that the r- clone does contain immunoreactive receptor. Northern blots of the RNA of these cells, probed with the full-length hGR cDNA, reveal that the r- cells have mRNA for hGR of normal size but somewhat less in amount than normal r+ cells. Previous somatic cell hybrids had shown failure to complement in crosses between r- and r act/l mutants, but dominance of the sensitive phenotype in r+ x r- and r+ x r act/l hybrids. We now show, however, that the r+ly- clone does complement the receptor-site deficient (r-) mutant. Hybrids between the two are completely steroid sensitive.