Intracellular Localization of the Glucocorticoid Receptor: Evidence for Cytoplasmic and Nuclear Localization*

Abstract

Using a monospecific, monoclonal antibody against the glucocorticoid receptor (GR), an immunocytochemical study was performed to investigate the intracellular localization of GR both in the presence or absence of ligand. With all fixation methods tested (paraformaldehyde, acetic acid in ethanol, Bouin's fixative, and bensochinone in PBS), it was possible to obtain specific GR staining. Fixation with paraformaldehyde was chosen for further studies on the effect of permeabilization, using several concentrations of Triton X-100 or saponin. A rat Rueber hepatoma (H-4-II-E) and a human uterus carcinoma (NHIK 3025) cell line were used as well as cultured hepatocytes from normal rat. The accessibility of the different cell compartments after fixation and permeabilization was tested for by using antibodies against cellular constituents with known locations (i.e. core-nucleosome proteins and tubulin), in combination with the anti-GR antibody in double immunofluorescence staining experiments. The specific GR stain obtained with the indirect peroxidase antiperoxidase technique or with fluorescein isothiocyanate-labeled second antibodies was shown to be present both in the cytoplasm and in the nucleus. Staining of all cellular compartments was abolished (peroxidase antiperoxidase) or diminished (fluorescein isothiocyanate) if the monoclonal antibody was preincubated with a 90% pure GR preparation. These findings are in contrast to recently reported immunocytochemical studies, where a strict nuclear existence of the estrogen and progestin receptors has been reported. Consequently, generalizations with regard to steroid receptor localization cannot be made. Furthermore, an in vitro model is described, where the effect of dexamethasone administration upon the localization of receptor staining in H-4-II-E cells can be studied.