In vitro binding of cortisol-1,2-3H by a substance in the supernatant fraction of P1798 mouse lymphosarcoma

Das gestresste Immunsystem und Autoimmunität

Über einen möglichen Zusammenhang zwischen psychologischem Stress, Immunsystem und Autoimmunität wird schon lange debattiert. Erkenntnisse aus der Grundlagen- und epidemiologischen Forschung, die das Verständnis für diesen komplexen Zusammenhang erhöhen werden in dieser kurzen Übersicht zusammengestellt. Zunächst werden bekannte anatomisch-physiologische Grundlagen für einen Zusammenhang zwischen psychologischem Stress und Immunsystem dargestellt. Es wird beschrieben, dass die Interaktion zwischen Gehirn über autonomes Nervensystem und Hormonsystem bis zur Immunzelle mit entsprechenden Rezeptoren für Neurotransmitter und Hormone mittlerweile bis auf die molekulare Ebene gut beschrieben ist. Im Rahmen der akuten Stressreaktion treten charakteristische Veränderungen im Immunsystem auf, die ebenfalls gut dokumentiert sind. In einem zweiten Teil wird dann beschrieben welche Veränderungen im Rahmen einer chronischen Stressbelastung am Immunsystem auftreten können und zuletzt wird diskutiert inwiefern diese Veränderungen auch für pathophysiologische Zustände des Immunsystems, z. B. im Rahmen von Autoimmunerkrankungen, relevant sein könnten. Zusammenfassend führt akuter Stress, im Sinne der optimalen Vorbereitung einer fight&flight Situation, zu einer Steigerung der Immunfunktion v. a. der humoralen Immunität, wohingegen die Auswirkungen von chronischem Stress weniger klar definiert sind und es eher zu einer Immundysregulation mit verminderter basaler Immunfunktion, v. a. der zytotoxischen Funktion aber einer gesteigerten Reaktion nach Aktivierung, v. a. im angeborenen Immunschenkel kommt. Epidemiologische Daten belegen gut, dass chronischer Stress zu einer erhöhten Suzeptibilität für Autoimmunerkrankungen führt. Erste klinische Anwendungen, wie beispielsweise die gezielte neuronale Stimulation des N. vagus sind in Erprobung, für einen breiteren klinischen Einsatz sollten aber die biologischen Netzwerkstrukturen noch besser verstanden werden, um die besten Angriffspunkte zu finden.

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.

Glucocorticoid receptors of normal and leukemic cells: role of proliferation conditions

A published whole-cell binding assay of 3H-dexamethasone (3H-DEX) was combined with cell sedimentation analysis to investigate various factors influencing specific binding of glucocorticoids by leukemic lymphoblasts. Studies with mouse L1210 and human HL-60 cell lines revealed that glucocorticoid (GC) receptors accumulate during G1 phase of the cell cycle. In human lymphoblastic leukemia, the per cell receptor number was highest in cells in S and G2 phase and lowest in small, noncycling cells. In normal human white blood cells, GC receptor content was maximal in large lymphocytes and monocytes while no receptors were present in small lymphocytes. However, the receptor density of large lymphocytes was still 3-4 fold lower than of leukemic lymphoblasts of similar size. In L1210 cells the number of GC receptors decreased considerably in stationary cultures or following inhibition of cell cycle progression by dibutyryl cyclic AMP (dbc-AMP). Receptor content was also reduced in cells growing as ascites tumors in hosts with terminal disease. Accordingly, the receptor content in leukemic blasts appeared highly dependent on cell cycle distribution and on the proliferative status of the tumor cells. These findings may in part explain the large interpatient variation and the conflicting views regarding GC receptor content and prognosis in acute lymphoblastic leukemia.

Glucocorticoid receptors

Glucocorticoid receptors are found in most mammalian tissues and have been studied in detail in a number of tissue culture systems. With cells that have not been exposed to steroids, the receptors are found in the cytoplasmic fraction from which they can be isolated and studied. Methods for studying glucocorticoid receptors depend on their high-affinity specific binding of radioactive steroids. The reversible interaction is intracellular. It follows Michaelian kinetics, at least in cell-free cytosol, and involves a thermodynamically homogeneous population of about 10 000 sites per cell. The receptor is an asymmetric, slightly acidic protein of about 100 000 daltons. It is very labile, especially in the unbound form. Binding activity depends on the integrity of thiol groups and perhaps on phosphorylation of amino acid residues. Although indirect, the evidence is overwhelmingly convincing that this protein is the physiologic glucocorticoid receptor. The time-kinetics of binding and dissociation are consistent with the sequence of events in glucocorticoid action. Various steroid analogs display binding characteristics predictable from their glucocorticoid activity. Loss of the binding protein from certain cultured cell lines is accompanied by unresponsiveness to glucocorticoids. The extensive tissue distribution of receptors parallels the extensive role of glucocorticoids in regulation. Finally, there is a strong correlation between nuclear binding of receptors and nuclear effects of the steroid. The glucocorticoid receptor can be distinguished from other glucocorticoid-binding proteins, based on their steroid specificity and physicochemical properties. There is no clear-cut demonstration that the receptor differs from tissue to tissue, and it is in fact very similar in various species. Unlike in other systems, receptor concentration does not seem to be regulated by its ligand or by other hormones. However, certain cases of hypo- as well as hypersensitivity to glucocorticoids appear to result from changes at the receptor level. The data indicate that the receptor can exist in inactive and active forms. The former predominate in the absence of steroid or when an angatonist is bound. Glucocorticoid agonists bind the active form, allowing it to be "activated" and subsequently bound to the nucleus. All of the receptors in isolated cytosol do not appear to be available for immediate occupancy by an agonist and this may be due to the time required for conversion of the receptors from inactive to active forms. The correlations between receptor binding and the glucocorticoid response indicate that the receptor is a rate-limiting factor in the magnitude and kinetics of the response, and this finding has important implications regarding mechanisms.

Isolation and characterization of L-cell variants with altered sensitivity to glucocorticoids

Stable glucocorticoid-resistant receptor-containing (R+) variants of L cells have been obtained and characterized. Five clones of such cells were obtained after chemical mutagenesis of the A9HT cell line. These clones and an additional, spontaneously resistant subclone of the LB82 cell line all contain glucocorticoid receptors which appear normal with regard to quantity, affinity for steroids, and in vivo localization in subcellular compartments. Somatic cell hybrids were formed between two of these R+-resistant clones, a previously isolated R-resistant clone, and three different sensitive L cell parents. In no case was steroid resistance dominant. Thus, these resistant L cells appear to be candidates for complementation analysis. The R+-resistant clones may be hindered in as yet undefined steps of glucocorticoid action.

Chronic lymphatic leukaemia: cellular effects of glucocorticoids in vitro

Glucocorticoid receptor levels and steroid induced inhibition of nucleic acid precursors have been examined in lymphocytes from 27 patients at different stages of chronic lymphatic leukaemia. No correlation can be found between the level of glucocorticoid receptors and the stage of the disease. On the other hand, a significant difference (P less than 0.02) was found between stage O and stage III/IV patients, in terms of the in vitro effect of dexamethasone on [3H] uridine incorporation.

Glucocorticoid receptors in corticosensitive and corticoresistant thymocyte subpopulations. I. characterization of glucocorticoid receptors and isolation of a corticoresistant subpopulation

1. Separation of mouse thymocytes by centrifugation on a discontinuous bovine serum albumin gradient leads to the isolation of four subpopulations of cells. 2. The study of I13H]uridine incorporation in vitro by these subpopulation in the presence of steroid shows that one of them is corticoresistant. 3. However, the binding capacity of these subpopulations measured by incubation with [3H]dexamethasone is very similar. 4. It is therefore concluded that in mouse thymus, in contrast with lymphoma cells, corticoresistance may not be explained by a defect of cytoplasmic glucocorticoid receptors.

Effects of prednisolone metasulfabenzoate on the induction of DNase II in comparison to alkaline phosphatase and acid phosphatase activities in cultures of HeLa S3 cells

Cultures of HeLa S3 cells were treated with prednisolone metasulfobenzoate (Na), a derivative of prednisolone which is readily soluble in water. The steroid induced an increase in DNase II, a lysosomal enzyme which was not used previously in enzyme induction by steroids. Alkaline phosphatase, a known inducible enzyme by other steroids and acid phosphatase, a known uninducible enzyme by other steroids, were included for comparative reasons.

Glucocorticoid action on hybrid clones derived from cultured myeloma and lymphoma cell lines

Cells of a cloned myeloma line from a Balb/c mouse contain specific cytoplasmic glucocorticoid receptors and are killed by dexamethasone. Cells of a lymphoma line (from mouse strain C57BL) also contain specific glucocorticoid receptors but are resistant to the steroid. Cells of two hybrid clones with widely differing chromosome numbers, derived by fusion between the resistant lymphoma and the sensitive myeloma, contain specific glucocorticoid receptors with similar binding properties as the parental receptors and are killed by dexamethasone. Since the lethal effect of the steroid is expressed in the hybrid cells, failure of the parent lymphoma line to be affected by dexamethasone is probably not due to an inhibitor of the lethal reaction.

Glucocorticoid receptors in lymphoma cells in culture: relationship to glucocorticoid killing activity

Mouse lymphoma cells in culture which are killed by adrenal steroids contain specific cortisol receptors that may be involved in the initial events of hormone action. The similarity of these receptors to those in hepatoma tissue culture cells, where adrenal steroids induce tyrosine aminotransferase, suggests that certain aspects of steroid action are similar in the two systems. In three steroid-resistant lymphoma cell populations specific binding was less than in the parent lines, suggesting that conversion to steroid resistance may be associated with changes in specific steroid binding.