Expression and Subcellular Distribution of the β-Isoform of the Human Glucocorticoid Receptor1

Alternative splicing of the human glucocorticoid receptor (hGR) primary transcript produces two highly homologous protein isoforms, termed hGRα and hGRβ, that differ at their carboxy-termini. In contrast to the well characterized hGRα isoform, which modulates gene expression in a hormone-dependent fashion, the biological significance of hGRβ has only recently begun to emerge. We and others have shown that the hGRβ messenger RNA transcript is widely expressed in human tissues and that the hGRβ protein functions as a dominant negative inhibitor of hGRα in transfected cells. Unfortunately, these initial studies did not determine whether the hGRβ protein was made in vivo. Such analyses are hindered because available anti-hGR antibodies cannot discriminate between the similarly sized hGRα and hGRβ proteins. Therefore, to investigate the expression of the hGRβ protein, we have produced an antipeptide, hGRβ-specific antibody termed BShGR. This antibody was made against the unique 15-amino acid peptide at the carboxy-terminus of hGRβ and recognizes both the native and denatured conformations of hGRβ, but does not cross-react with hGRα. Using BShGR on Western blots and in immunoprecipitation experiments, we detected the hGRβ protein in a variety of human cell lines and tissues. Immunocytochemistry was then performed with BShGR on HeLa S3 and CEM-C7 cells and on tissue sections prepared from lung, thymus, and liver to assess the cellular and subcellular distribution of hGRβ. In all immunopositive cells, hGRβ was found in the nucleus independent of glucocorticoid treatment. Within tissues, the hGRβ protein was expressed most abundantly in the epithelial cells lining the terminal bronchiole of the lung, forming the outer layer of Hassall’s corpuscle in the thymus, and lining the bile duct in the liver. As a potential in vivo inhibitor of hGRα activity, expression of hGRβ may be an important factor regulating target cell responsiveness to glucocorticoids.