Showing papers by "Allan Munck published in 1979"

Activation of steroid hormone–receptor complexes in intact target cells in physiological conditions

Abstract: AT physiological temperatures glucocorticoids1–5, in common with other steroid hormones6, initially interact with normal target cells such as the rat thymocyte by forming hormone–receptor complexes that seem first to be located in the cytoplasm and then rapidly become bound to the nucleus. At low temperatures (0–4 °C) the hormones, when incubated either with target cells or with cytosols from such cells, form ‘non-activated’ complexes that do not bind to nuclei; subsequent warming of the cells1–5, or of the cytosols together with nuclei2,7–11, leads to the formation of nuclear-bound complexes. As shown originally with oestrogens12 and later with glucocorticoids2,7–10,13, if cytosols with non-activated complexes formed at 0–4 °C are warmed to 20–37 °C in the absence of nuclei, the complexes become ‘activated’, and will then bind to nuclei even at low temperatures. Activation, which can also be brought about by increased ionic strength7–9,13, gel filtration, dilution and other treatments14, has been studied extensively and is known to be accompanied by several changes other than enhanced affinity for nuclei. For glucocorticoid–receptor complexes the changes include enhanced affinity for DNA7,10,13–15 and altered mobility on phosphocellulose16, DEAE-Sephadex17 and DEAE-cellulose18 columns. This last property is the one we have used in our experiments. Despite the many published studies on activation, formation of non-activated complexes and subsequent activation have apparently never been demonstrated in cells or cytosols exposed to steroids at normal body temperatures only. Consequently, it is not known whether non-activated complexes and activation have any significant role in physiological conditions, and at least one well known scheme of steroid hormone action19 does not include the activation step. It is therefore possible that when steroid hormones bind to cytoplasmic receptors at physiological temperatures they immediately form activated complexes. The results described here show that for glucocorticoids this alternative can be excluded: when these steroids interact with receptors in rat thymus cells at 37 °C they initially form non-activated complexes, and subsequently give rise to activated complexes.

Glucocorticoids inhibit expression of Fc receptors on the human granulocytic cell line HL-60.

Abstract: GLUCOCORTICOIDS decrease levels of circulating peripheral lymphocytes and immunoglobulins, inhibit mitogen- and antigen-induced blastogenesis of cultured lymphocytes and decrease bactericidal activity of granulocytes and other phagocytic cells1–4. Fc receptors on granulocytes are thought to play a vital part in adherence of antibody-coated particles to the surfaces of these cells, a step which initiates phagocytosis5. Factors which regulate the expression of the Fc receptor could therefore influence phagocytic capability, and it has been suggested that glucocorticoids might act in such a way6,7. We report here that glucocorticoids inhibit expression of the Fc receptor on the human promyelocytic cell line HL-60 (ref. 8). This inhibition is not accompanied by increased cell death, reduced proliferation or a general reduction in protein synthesis.

Glucocorticoids and immune responses

Abstract: We describe a series of investigations on mechanisms of antiinflammatory and immunosuppressive actions of glucocorticoids. Glucocorticoid receptors and primary mechanisms of action have been studied with isolated rat thymus cells. When added to these cells glucocorticoids immediately form cytoplasmic hormone-receptor complexes which after activation bind to the nuclei where they apparently induce mRNA for specific proteins that rapidly inhibit glucose transport and acetate incorporation into lipids. Protein and RNA metabolism are inhibited more slowly and eventually the cells die. With normal peripheral human lymphocytes, similar but slower effects are produced. A dramatic increase in receptor sites per cell is seen in lymphocytes stimulated with concanavalin A or antigen. This increase is probably associated with preparation for mitosis. We do not find, contrary to widespread belief, that these stimulated cells are insensitive to glucocorticoids. Such insensitivity has been invoked to explain the insensitivity to glucocorticoid suppression of secondary compared to primary immune responses. An alternative explanation emerges from our experiments with T-cell growth factor. T-cell growth factor, produced by mitogen or antigen stimulated spleen cells, is necessary for the proliferation of T-lymphocytes in culture and may be responsible for clonal expansion of antigen-responsive T-cells. Treatment of Con A-stimulated rat spleen cells or human peripheral mononuclear cells with 100 nM dexamethasone inhibits the production of the growth factor by 95%. This effect is specific for glucocorticoids. Addition of T-cell growth factor completely reverses the inhibition by glucocorticoid of mitogen-induced blastogenesis. We propose that the inhibitory actions of glucocorticoids on antigen- or mitogen-induced T-cell blastogenesis are related to inhibition of production of T-cell growth factor and that the reason the primary immune response is more sensitive to glucocorticoids is that by inhibiting production of T-cell growth factor, glucocorticoids block the clonal expansion necessary to amplify the primary response. We have also studied effects of glucocorticoids on Fc receptors, which play important roles in phagocytosis and other aspects of immune responses. Treatment of the human progranulocytic cell line HL-60 with dexamethasone for 72 hours reduces by 35-50% the Fc receptors per cell with no effect on cell viability or proliferation and slight increase in leucine incorporation. The effect is specific for glucocorticoids. These findings indicate that an important component in glucocorticoid-induced immunosuppression may be a reduction in Fc receptors, and with the results on T-cell growth factor, suggest that glucocorticoids regulate immune processes via effects on lymphokines and other immunologically important proteins.

Glucocorticoid receptors and actions in rat thymocytes and immunologically stimulated human peripheral lymphocytes.

Abstract: After reviewing briefly our earlier studies on glucocorticoid receptors and mechanisms in thymus cells, we have outlined results from the following two areas of current interest in our laboratories: the "life-cycle" of glucocorticoid receptors and complexes in thymus cells, and the levels of glucocorticoid receptors and sensitivity in immunologically stimulated human peripheral lymphocytes. Several of our results on energetics and kinetics of hormone binding to glucocorticoid receptors in rat thymus cells seem to require extension of the simplest model of hormone-receptor transformations in intact cells. ATP-depletion experiments suggest the existence of a nonbinding form of the receptor; "chase" experiments suggest reaction of hormone directly with nuclear-bound receptor; experiments on depletion and replenishment of cytoplasmic receptor using cortisol and dexamethasone suggest the existence of at least two subpopulations of nuclear-bound hormone-receptor complex. We have found that mitogen or immunologic stimulation of human peripheral lymphocytes in culture leads within 24 h or so to a striking increase in the number of glucocorticoid receptor sites per cell. We believe this increase may be due to partial synchronization of the cell population in a phase of the cell cycle in which receptor content is high. Contrary to the widely held view that mitogen-stimulated cells become insensitive to glucocorticoids, our experiments show that with respect to inhibition of thymidine and uridine incorporation and glucose uptake, the cells are highly sensitive to dexamethasone at 24, 48, and 72 h after stimulation with concanavalin A.