Characterization and immunocytochemical demonstration of glucocorticoid receptor using antisera specific to transformed receptor

Mitochondrial localization of glucocortocoid receptor in glial (Müller) cells in the salamander retina

Glucocorticoid hormones regulate the transcription of nuclear genes by way of their receptors. In addition, these hormones modulate mitochondrial gene transcription by mechanisms that remain poorly understood. Using immunofluorescence labeling in isolated Müller and photoreceptor cells and in intact salamander retina, we found that the glucocorticoid receptor (GR) is localized in both cell types. Confocal laser scanning microscopy and double staining with cytochrome oxidase (COX) showed that GR is localized in the mitochondria of Müller cells, but not in the mitochondria of photoreceptors. GR also colocalizes with glutamine synthetase (GS) in the cytoplasm of Müller cells. GR is also localized in the microvilli of the distal process of Müller cells and in the synaptic terminal of photoreceptors. Pre-incubation of Müller cells with 1 microM dexamethasone (DEX) for 7 h led to greater than 50% inhibition of the glutamate-induced increase in mitochondrial NADH. This late effect of glucocorticoids on glutamate metabolism could be ascribed, in part, to a direct action of steroid hormones on mitochondrial metabolism.

Neuroendocrine control of thymus physiology

The thymus gland is a central lymphoid organ in which bone marrow-derived T cell precursors undergo differentiation, eventually leading to migration of positively selected thymocytes to the peripheral lymphoid organs. This differentiation occurs along with cell migration in the context of the thymic microenvironment, formed of epithelial cells, macrophages, dendritic cells, fibroblasts, and extracellular matrix components. Various interactions occurring between microenvironmental cells and differentiating thymocytes are under neuroendocrine control. In this review, we summarize data showing that thymus physiology is pleiotropically influenced by hormones and neuropeptides. These molecules modulate the expression of major histocompatibility complex gene products by microenvironmental cells and the extracellular matrix-mediated interactions, leading to enhanced thymocyte adhesion to thymic epithelial cells. Cytokine production and thymic endocrine function (herein exemplified by thymulin production) are also hormonally controlled, and, interestingly in this latter case, a bidirectional circuitry seems to exist since thymic-derived peptides also modulate hormonal production. In addition to their role in thymic cell proliferation and apoptosis, hormones and neuropeptides also modulate intrathymic T cell differentiation, influencing the generation of the T cell repertoire. Finally, neuroendocrine control of the thymus appears extremely complex, with possible influence of biological circuitry involving the intrathymic production of a variety of hormones and neuropeptides and the expression of their respective receptors by thymic cells.

Steroid hormone receptors

In the three decades since the original discovery of receptors for steroid hormones, much has been learned about the biochemical processes by which these regulatory agents exert their effects in target tissues. The intracellular receptor proteins are potential transcription factors, needed for optimal gene expression in hormone-dependent cells. They are present in an inactive form until association with the hormone converts them to a functional state that can react with target genes. Transformation of the receptor protein to the nuclear binding form appears to involve the removal of both macromolecular and micromolecular factors that act to keep the receptor form reacting with DNA. Much of the native receptor is present in the nucleus, loosely bound and readily extractable, but for some and possibly all steroid hormones, some receptor is in the cytoplasm, perhaps in equilibrium with a nuclear pool. Methods have been developed for the stabilization, purification, and characterization of receptor proteins, and through cloning and sequencing of their cDNAs, primary structures for these receptors are now known. This has led to the recognition of structural similarities among the family of receptors for the different steroid hormones and to the identification of regions in the protein molecule responsible for the various aspects of their function. Monoclonal antibodies recognizing specific molecular domains are available for most receptors. Despite the knowledge that has been acquired, many important questions remain unsolved. How does association with the steroid remove factors keeping the receptor protein in its native state, and how does binding of the transformed receptor to the response element in the promoter region enhance gene transcription? Once it has converted the receptor to the nuclear binding state, is there a further role for the steroid in modulating transcription? Still not entirely clear is the involvement of phosphorylation and/or dephosphorylation in hormone binding, receptor transformation, and transcriptional activation. Less vital to basic understanding but important in the overall picture is whether the native receptors for gonadal hormones are entirely confined to the nucleus or whether there is an intracellular distribution equilibrium. With the effort now being devoted to this field, and with the application of new experimental techniques, especially those of molecular biology, our understanding of receptor function is progressing rapidly. The precise mechanism of steroid hormone action should soon be completely established.

Compared intracellular localization of the glucocorticosteroid and progesterone receptors: an immunocytochemical study

The intracellular distribution of the glucocorticosteroid and progesterone receptors (GR and PR, respectively) was studied immunohistochemically. In control adrenalectomized (Adx) rat liver, immunostaining of paraffin sections revealed GR in cell nuclei, with a wide range of intensity between individuals. Following dexamethasone (Dex) treatment, the nuclear staining was uniformly high in all animals; the cytoplasmic staining was always weak and remained unchanged after Dex treatment. In frozen sections, the GR immunoreactivity in cell nuclei was weak in the absence and very strong in the presence of Dex, while no GR-specific cytoplasmic staining was observed. In frozen sections fixed in vapor of formaldehyde to avoid any artifactual redistribution of the receptor, some GR immunostaining was observed in the cytoplasm and the nucleus. In contrast, in paraffin as well as in frozen sections of chick oviduct, fixed by immersion or in vapor, PR was exclusively nuclear, including in the absence of progesterone, and the intensity of immunostaining was not modified by progesterone treatment. In order to verify if loss of nuclear receptors during tissue preparation could explain the differences in nuclear immunostaining observed between hormone-free and hormone-occupied GR, and between GR and PR, frozen sections of Adx rat liver and chick oviduct were preincubated at 4 degrees C in buffer solutions before the fixation procedure. It was found that hormone-free GR diffused out of the nucleus faster than hormone-occupied GR nuclei, and that nuclear GR diffused faster than nuclear PR. Based on these results, we propose that, during the fixation procedure, the fraction of nuclear GR which diffuses out of the nucleus is much smaller in the presence than in the absence of Dex. This lesser loss of nuclear GR after Dex treatment results in an increase of immunostaining after hormonal administration, which might have been erroneously interpreted as a sign of translocation from cytoplasm to nucleus. That the nuclear PR detection is not modified by progesterone treatment may be explained by its reduced diffusibility as compared to nuclear GR. This hypothesis does not rule out the existence of some cytoplasmic GR, whose significance remains unclear, but it offers a unified mechanism of action for all steroid hormone receptors. In the case of glucocorticosteroids, as already proposed for estradiol and progesterone, no step of cytoplasm to nucleus translocation would be required for hormone action, and transformation-activation would occur in the nucleus, resulting in tighter binding of the hormone receptor complexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogeny of adrenergic fibers in rat spinal cord in relationship to adrenal preganglionic neurons

Adrenergic neurons in the C1 cell group in the rostral ventrolateral medulla oblongata contain epinephrine, as well as its biosynthetic enzyme, phenylethanolamine N-methyltransferase (PNMT). These neurons send axons to regions of the central nervous system known to regulate autonomic function, including the sympathetic preganglionic nuclei of thoracic and upper lumbar spinal cord. Previous studies have shown that PNMT is expressed in neurons located in the medulla oblongata on embryonic day 14; however, the development of the projections from these cells has not been studied. With the aid of high-performance liquid chromatography (HPLC) to determine levels of catecholamines and immunocytochemistry to demonstrate PNMT, the ontogeny of the adrenergic bulbospinal pathway in the embryonic, postnatal, and adult rat has been studied. In addition, the relationship between PNMT-immunoreactive (IR) fibers and retrogradely labeled sympathetic preganglionic neurons projecting to adrenal medulla are described. PNMT-IR fibers were first observed in the caudal medulla oblongata and lateral funiculus of spinal cord on gestational day 15(E15). On E16, PNMT-IR fibers in the thoracic spinal cord were observed in the intermediate gray matter at the level of the lateral horn. Epinephrine was measureable in spinal cord on E20. Both the density of PNMT-IR fibers and the levels of epinephrine increased to a maximum during the second postnatal week and then declined to adult levels. These observations suggest that a period of adrenergic hyperinnervation of spinal sympathetic nuclei occurs during the neonatal period. PNMT-IR terminals in spinal cord were observed, primarily, although not exclusively, in sympathetic nuclei of thoracic cord and parasympathetic nuclei of upper sacral cord. Adrenergic fibers in the intermediolateral nucleus (IML) and the central autonomic nucleus (CAN) dorsal to the central canal were particularly dense during the second postnatal week in both midthoracic and upper sacral segments. In the neonate, a "ladder-like" pattern of PNMT-IR fiber staining was observed which represented transverse fiber bundles connecting IML with CAN and extensive longitundinal fiber bundles along the border of the funiculus in IML. At all spinal levels, adrenergic fibers were also observed adjacent to the ependyma dorsal or lateral to the central canal. The relationship between adrenal preganglionic neurons and PNMT-IR fibers in IML was examined on postnatal days 4, 15, and 60. With retrograde labeling from adrenal medulla, it was demonstrated that PNMT-IR fibers are associated with adrenal preganglionic neurons throughout postnatal development.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunocytochemical localization of glucocorticoid receptors in cells, cytoplasts, and nucleoplasts

A monoclonal antibody has been used to assess the intracellular localization of the glucocorticoid receptor in rodent L-929 fibroblasts and GH3 pituitary tumor cells. Whole cells from both cell lines showed immunoreactivity in the cytoplasm and nucleus. However, when cytoplasts and nucleoplasts of these cells were examined, only L-cells showed strong antibody binding in both fractions; in contrast, GH3 cells exhibited nuclear staining and slight cytoplasmic staining. These results are discussed in terms of the current findings regarding the intracellular location of steroid hormone receptors.

Glucocorticoid mechanism of action: monoclonal antibodies as experimental tools

In order to provide a further insight into glucocorticoid receptor (GR)-mediated action of glucocorticoid hormones, we produced ten monoclonal antibodies against rat GR. In studies combining physicochemical separation methods with antibody methodology, we established that the molybdate-stabilised GR contains one steroid-binding monomer. Using a monoclonal anti-GR antibody-based immunoaffinity chromatographic procedure, we purified two non-ligand-binding proteins, with molecular weights of 80,000 and 90,000, present in the molybdate-stabilised GR complex. These proteins are not recognised by monoclonal antibodies directed against GR. The possible relation of these two proteins to heat shock proteins remains to be established. Immunohistochemical studies of GR in the central nervous system of the rat provided new information on the distribution of GR, particularly in the hypothalamus. Studies of intracellular receptor localisation in rat brain after endocrine manipulations gave results in support of the classical concept of translocation of GR from cytoplasm to cell nucleus. Studies with a cell culture system also supported the existence of GR in the cytoplasm as well as in the cell nucleus.

Evidence for differences in the steroid binding domains of the glucocorticoid receptor versus the idiotype antibody

Triamcinolone acetonide (TA), coupled to bovine serum albumin, was used to obtain a polyclonal anti-TA antibody in the rabbit. This idiotype differed from rat glucocorticoid receptor and transcortin in several respects. RU 38486, a synthetic antagonist with high affinity for the receptor, could neither bind the anti-TA antibody nor displace the idiotype bound 3H-TA. Similarly, corticosterone, the natural rodent ligand, had no affinity for the idiotype. These results imply differences in the conformation and topology of the corticoid binding domains, contrary to the current notion where all agonists and antagonists would saturate an identical configuration.

Ultrastructural localization of the progesterone receptor by an immunogold method: effect of hormone administration

The progesterone receptor has been localized in the rabbit uterus by immunocytochemistry at the electron microscopic level, using monoclonal antibodies and the protein A-gold technique. The progesterone receptor in uterine stromal cells was mainly localized in the nucleus; however, a small fraction of antigen was present in the cytoplasm, where it was associated with the rough endoplasmic reticulum and with free ribosomes. The plasma membrane was not labeled. In the nucleus, the receptor was always associated with condensed chromatin or areas surrounding condensed chromatin, whereas the nuceolus was not labeled. In the chromatin, receptor distribution varied according to the hormonal state: in the absence of progesterone, the receptor was randomly scattered over the clumps of condensed chromatin; after administration of the progestin R5020, it was mainly detected in the border regions between condensed chromatin and nucleoplasm and, to a lesser extent, over dispersed chromatin in the nucleoplasm. These areas have been shown to be the most active sites of gene transcription.