Administration of glucocorticoid, estrogen, and progesterone is followed by changes in human adipose tissue distribution, morphology, and function. Therefore, specific receptors for these hormones were determined in different regions of human adipose tissue using ligand techniques, with separation of bound and free hormone by chromatography, absorption techniques, or isoelectric focusing, as well as protein quantitation with monoclonal antibodies against human estrogen and progesterone receptors. Furthermore, mRNAs were measured by solubilization hybridization technique with glucocorticoid, estrogen, and progesterone receptor cRNA probes for human receptors. Saturable specific cytosolic glucocorticoid binding was found. Quantitative analyses indicated more binding sites and mRNAs in intraabdominal than sc adipose tissue samples. In contrast, neither specific estrogen or progesterone binding, cytosolic or nuclear receptor protein, nor mRNAs for these receptors could be identified in abdominal, femoral, or omental adipose tissues. Parallel control experiments confirmed the presence of both estrogen and progesterone receptors in rat adipose tissues. It was concluded that while glucocorticoid receptors are clearly present in human adipose tissues, female sex hormone receptors are not present in quantities detectable with presently available methods. Effects of these hormones on human adipose tissue might, therefore, be mediated via a minute nondetectable quantity of receptors, the glucocorticoid receptor, or indirect mechanisms.

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Alternative splicing of the human glucocorticoid receptor (hGR) primary transcript generates two receptor isoforms, hGR␣ and hGR␤, with different carboxyl termini diverging at amino acid 727. By reverse transcriptase-polymerase chain reactions it was previously demonstrated that the hGR␤ message had a widespread tissue distribution. To demonstrate the presence of hGR␤ as protein we produced specific rabbit antisera to hGR␤, as well as a hGR␤-specific mouse monoclonal IgM antibody, by peptide immunizations. By SDS-polyacrylamide gel electrophoresis and Western immunoblotting we showed that hGR␤ is endogenously expressed at the protein level in HeLa cells and human lymphatic leukemia cells. Using an antibody directed against an epitope shared by both isoforms we showed a relatively lower expression of the hGR␤ form. We also showed that hGR␤ bound to hsp90 by immunoprecipitation of in vitro translated hGR␤ in reticulocyte lysate with hsp90-specific antibodies, a coprecipitation occurring also in the presence of dexamethasone. We could not demonstrate that hGR␤ inhibited the effects of dexamethasone-activated hGR␣ on a glucocorticoid-responsive reporter gene. In conclusion, low hGR␤ expression levels and hGR␤-hsp90 interaction maintained in the presence of ligand and lack of inhibition of hormone-activated hGR␣ effects challenge the concept of the hGR␤ isoform as a proposed dominant negative inhibitor of hGR␣ activity.