Deletion experiments have defined two stretches of DNA (genetic elements), lying close to the promoter for a human gene for metallothionein, that separately mediate the induction of the gene by heavy metal ions, particularly cadmium, and by glucocorticoid hormones. The element responsible for induction by cadmium is duplicated, yet a single copy is fully functional; the element responsible for induction by glucocorticoid hormones is coincident with the DNA-binding site for the glucocorticoid hormone receptor.

Glucocorticoids are known to induce the transcription of integrated proviral mouse mammary tumour virus (MMTV) genes in a variety of cell lines derived from mouse mammary tumours. Chimaeric genes in which selectable markers are linked to the long terminal repeat (LTR) region of MMTV can be induced by the synthetic glucocorticoid dexamethasone after introduction into mouse fibroblasts. This suggests that the regulatory elements required for hormonal induction are located within the cloned LTR fragments. The idea is supported by the observation that glucocorticoid receptors bind to certain cloned fragments of MMTV DNA in vitro. Using filter binding studies and monoclonal antibodies to the glucocorticoid receptor we have now delimited the receptor binding region to a DNA segment of 152 base pairs (bp) that has been shown to be relevant for hormonal induction. In nuclease protection experiments we have identified partially homologous receptor binding sequences located in this region, all of which share the hexanucleotide 5'-TGTTCT-3'.

In contrast to its behavior as naked DNA, the MMTV promoter assembled in minichromosomes can be activated synergistically by the progesterone receptor and NF1 in a process involving ATP-dependent chromatin remodeling. The DNA-binding domain of NF1 is required and sufficient for stable occupancy of all receptor-binding sites and for functional synergism. Activation of purified minichromosomes is observed in the absence of SWI/SNF and can be enhanced by recombinant ISWI. Receptor binding to minichromosomes recruits ISWI and NURF38, but not brahma. We propose a two-step synergism in which the receptor triggers a chromatin remodeling event that facilitates access of NF1, which in turn stabilizes an open nucleosomal conformation required for efficient binding of further receptor molecules and full transactivation.

In several rodent cell lines, glucocorticoids increase the transcription of murine mammary tumour virus (MMTV) proviral DNA in a process mediated by the glucocorticoid receptor. To investigate whether a direct interaction between the receptor and specific sequences on the induced genes can be implicated in the hormonal regulation of transcription, filter binding studies were performed with partially purified glucocorticoid receptor of rat liver and eight cloned MMTV proviral probes. Both the 40 000 and the 90 00 mol. wt. forms of the receptor do bind preferentially to restriction fragments containing the right 400‐500 nucleotides of the MMTV long terminal repeat units (LTR). Using LTR deletion mutants, we confirm that the right end of the LTR contains at least one binding site for the glucocorticoid receptor. In addition, the receptor binds preferentially to the mouse genomic sequences flanking at least three endogenous proviral copies, and to sequences within the env genes in some of the endogenous and exogenous proviruses. These findings are compatible with the hypothesis that steroid hormones regulate specific gene expression through a direct interaction of the hormone‐receptor complex with DNA sequences in and around the induced genes.

The localization of glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) was determined in the rabbit kidney by immunohistochemistry with the use of a monoclonal, anti-GR antibody and a monoclonal, anti-idiotypic, anti-MR antibody. Immunostaining was performed on serial histological sections from normal and adrenalectomized rabbits. The specificity of immunostaining was assessed for MR by in situ competition studies with steroids and for GR by presaturation of the antibody with GR preparation. Immunostaining by both the anti-MR and the anti-GR antibodies was present in all parts of the distal nephron (beyond proximal tubule) and absent in the glomerulus and proximal tubule. The absence of staining by the anti-GR antibody in the proximal tubule suggests that the effects of glucocorticoids in this structure involve either a GR different from that of distal structures or a non-receptor mediated mechanism of action. MR immunostaining predominates in the distal and all along the collecting tubule in its cortical, medullary, and papillary portions. GR immunostaining was most abundant in the medullary ascending limb and distal tubule. Immunostaining by both antibodies was present in papillary interstitial cells and cells of the epithelium lining the papilla. Fifteen to twenty percent of the cells of the cortical collecting tubule, presumably intercalated cells, were devoid of MR and GR immunostaining. Immunostaining was present in both nuclear and cytoplasmic cell compartments. No clear difference was observed between normal and adrenalectomized rabbits. This study is the first report on renal immunolocalization of GR compared with MR. In addition, we show evidence for new targets for corticosteroid hormones such as papillary interstitial cells and papillary epithelium.

Although the expression of the uteroglobin gene in the lung is regulated by glucocorticoids, no binding sites for the glucocorticoid receptor are found in the promoter region nor can they be observed in the coding sequences. Instead a fragment situated 2.6 kb upstream from the start of transcription of the uteroglobin gene shows a high affinity for the receptor.Deoxyribonuclease I and methylation protection studies show three contiguous binding sites located within this fragment. All three sites show homology to the glucocorticoid receptor binding sites described for other genes. Two of them encompass the hexanucleotide 5' -TGTTCT-3', and the other binding site contains the homologue hexanucleotide, 5'-AGTCCT-3', but the contacts between the receptor and the hexanucleotides are equivalent to those found in other functional regulatory elements for glucocorticoids. These elements may therefore be responsible for the glucocorticoid regulation of uteroglobin gene expression by acting over a relatively long stretch of nucleotide sequences.

Quantitative in vitro autoradiography, cytosol receptor assay in punched brain tissue, and immunocytochemistry have revealed that the glucocorticoid receptor is present in the rat supraoptic nucleus (SON). Based on its binding characteristics the receptor appears to be the type II glucocorticoid receptor. With the use of a monoclonal antibody against purified liver glucocorticoid receptor, immunostaining was found in magnocellular neurosecretory neurons in the SON, but not in magnocellular neurons in the paraventricular nucleus. Immunoreactive cells seem to be concentrated in ventral parts of the SON where vasopressin cells were previously shown to be located. One to 2 weeks after bilateral adrenalectomy, there was a substantial decrease in glucocorticoid receptor immunostaining in magnocellular as well as other types of neurons in various brain regions. Administration of synthetic glucocorticoids (RU 28362 or dexamethasone) induced a robust increase in the intensity of immunostaining in cell nuclei of neurosecretory cells. The presence of glucocorticoid receptors in the SON suggests that glucocorticoids may affect vasopressin synthesis or/and secretion through a direct action on magnocellular neurons.

Monoclonal antibodies against the 90 000 mol. wt. form of the activated rat liver glucocorticoid receptor were generated from mice immunized with a partially purified receptor preparation. The screening assay was based on the precipitation of liver cytosol, labelled with [3H]triamcinolone acetonide, with monoclonal antibodies bound to immobilized rabbit anti‐mouse IgG. Out of 102 hybridomas obtained, 76 produced immunoglobulin and eight of them were found to react with the receptor molecule. Only one of the positive clones secreted IgG whereas the other seven produced IgM. The complexes of receptor and antibodies were identified by sucrose density gradient centrifugation. All seven monoclonal antibodies tested reacted with the 90 000 mol. wt. form of the receptor but not with the 40 000 mol. wt. form that contains the steroid and DNA binding domains. None of the monoclonal antibodies interfered with the binding of the receptor to DNA cellulose, thus suggesting that the antigenic determinants are located in a region of the receptor that is not directly implicated in either steroid binding or DNA binding. These antigenic determinants were common to glucocorticoid receptors from several tissues of the rat, whereas glucocorticoid receptors from other species react only with some of the antibodies.