Inhibition of thymocyte RNA synthesis by natural adrenal steroids and their 1,4-diene analogs. Structure-activity correlations using 13C-n.m.r. spectroscopy

Differences in nuclear retention characteristics of agonist-activated glucocorticoid receptor may determine specific responses

We studied the glucocorticoid response to the synthetic steroid pregna-1,4-diene-11beta-ol-3,20-dione (DeltaHOP) in several cell types and correlated its biological effect with the ability of the glucocorticoid receptor (GR) to be retained in the nuclear compartment. We observed that the DeltaHOP-transformed GR was diffusely distributed in the nucleus compared to the discrete structures observed for the dexamethasone (DEX)-transformed GR. Despite the fact that the receptor was entirely nuclear upon binding of each steroid and exhibited identical nuclear export rates, a greater amount of DeltaHOP-transformed GR was recovered in the cytoplasmic fraction after hypotonic cell lysis. Furthermore, accelerated nuclear export of GR was evidenced in digitonin-permeabilized cells treated with ATP and molybdate. Inasmuch as limited trypsinization of DEX-GR and DeltaHOP-GR complexes yielded different proteolytic products, we conclude that GR undergoes a differential conformational change upon binding of each ligand. We propose that these conformational differences may consequently lead to changes of stability in the interaction of the GR with chromatin. Therefore, the dynamic exchange of liganded GR with chromatin is likely to have significant consequences for the observed pleiotropic physiological responses triggered by glucocorticoid ligands, not only in different tissues but also in the same cell type.

The glucocorticoid properties of the synthetic steroid pregna-1,4-diene-11beta-ol-3,20-dione (deltaHOP) are not entirely correlated with the steroid binding to the glucocorticoid receptor

The natural steroid 11beta-hydroxyprogesterone is not only a modulator of 11beta-hydroxy-steroid dehydrogenase activity, but also an efficient inducer of tyrosine aminotransferase activity in hepatocytes. In contrast with the low affinity for the mineralocorticoid receptor. 11beta-hydroxyprogesterone binds well to both the glucocorticoid receptor and the carrier protein transcortin. It is accepted that the introduction of a 1:ene double bond into 3-keto 4:ene steroids increases the glucocorticoid potency, so that 3-keto-1,4:diene steroids show improved chemical stability and are more potent glucocorticoids than their respective 4:ene analogs. The steroid pregna-1,4-diene-11beta-ol-3,20-dione (deltaHOP) had previously been described as an anti-inflamatory compound and an inhibitor of macromolecular biosynthesis in thymocytes and lymphocytes. In such studies, deltaHOP also exhibited some particular glucocorticoid properties which made it attractive as a tool for the study of the mechanism of action of glucocorticoids. In the present paper we show that deltaHOP possesses some classical biological actions of glucocorticoids such as deposition of glycogen in rat liver, induction of TAT activity in hepatocytes, and inhibition of the uptake of leucine and thymidine by thymocytes. It also exhibits minimal sodium-retaining properties. Consistent with these biological effects, deltaHOP shows a 70 times lower relative binding affinity for the mineralocortioid receptor than aldosterone, but a reasonable affinity for the glucocorticoid receptor, and is as efficient as dexamethasone in dissociating the 90 kDa heat shock protein from the glucocorticoid receptor heterocomplex. However, the inhibition of the uptake of amino acids and nucleotides observed in the presence of deltaHOP is not efficiently blocked when thymocytes are coincubated in the presence of steroids with known antiglucocorticoid activity. deltaHOP is similarly inefficient in inducing chloramphenicol-acetyl transferase activity in cells transfected with a plasmid that possesses two canonical glucocorticoid-responsive elements. Unlike most glucocorticoids, deltaHOP does not induce the fragmentation of DNA in a regular pattern characteristic of apoptosis and it does not reduce thymus weight. This unusual dissociation of glucocorticoid parameters makes deltaHOP a useful tool to discriminate between mechanisms of action by which steroids can exert their biological effects.

Inhibition of glucocorticoid receptor binding by nitric oxide

Septic shock is a dangerous condition with high mortality rates. In sepsis, the inducible form of nitric oxide (NO) synthase is induced, releasing high amounts of NO. Glucocorticoids have potent anti-inflammatory properties and are very effective in inhibiting the induction of this enzyme if administered before the shock onset. It is known that glucocorticoid receptor (GR) has critical cysteine residues for steroid binding in its hormone-binding and DNA-binding domains. It has also been reported that NO reacts with ---SH groups, forming S-nitrosothiols. Therefore, we examined the potential effect of NO on the ligand-binding ability of GR. NO donors (S-nitroso-acetyl-DL-penicillamine, S-nitroso-DL-penicillamine, or S-nitroso-glutathione) decreased, in a time- and dose-dependent manner, the binding of [3H]triamcinolone to immunoprecipitated GR from mouse L929 fibroblasts. The nonnitrosylated parent molecules, N-acetyl-DL-penicillamine, and reduced gluthatione were without effect. Scatchard plots revealed that the number of ligand binding sites and Kd were reduced (50%) by NO donors. Western blot analysis ruled out the possibility that dissociation of GR/heat shock protein 90 heterocomplex or decrease in GR protein would account for the inhibitory effect of NO. Decreased ligand binding to GR was found when NO donors were incubated with intact fibroblasts. Incubation with NO donors also decreased the steroid-induced reduction in [3H]uridine incorporation into RNA. All of these NO effects were inhibited by the thiol-protecting agent dithiothreitol. Therefore, S-nitrosylation of critical ---SH groups in GR by NO with consequent decreases in binding and affinity may be the mechanisms which explain the failure of glucocorticoids to exert their anti-inflammatory effects in septic shock.

Influence of calf serum on glucocorticoid-responses of certain progesterone derivatives

The following in vitro glucocorticoid (GC) parameters of progesterone (P), 1-ene progesterone (deltaP), 11beta-hydroxyprogesterone (HOP), 11beta-1-ene progesterone (deltaHOP) and dexamethasone (Dexa) were assayed in the presence or absence of bovine calf serum (BCS): binding to thymus cytosol, dissociation of the glucocorticoid receptor (GR)-heat shock protein 90 (hsp90) complex (diss.), tyrosine aminotransferase (TAT) induction in hepatocytes and the inhibition of 3H-uridine and 35S-methionine uptake by thymocytes. Without BCS, steroids were in most cases active in this general order: Dex > deltaHOP > HOP > deltaP > P. BCS abolished all activities in P and deltaP, but left them unaltered in all other steroids, except diss. in HOP, which diminished intermediately. Binding of P, deltaP, HOP and deltaHOP to GR and CBG paralleled their in vivo activating effects on glycogen deposition.

CONCLUSIONS

in this steroid series, BCS, but not CBG, inhibits GC responses of P and deltaP. 11-Beta hydroxylation frees those molecules from the inhibitory effects of BCS.

Inhibitory effect of 11 beta-hydroxypregna-1,4-diene-3,20-dione (delta HOP) on lymphocyte proliferation

We have compared the immunosuppressive effect of delta HOP and glucocorticoids on lymphocyte proliferation and IL-1 secretion. The new synthetic steroid only inhibited proliferation of phytohaemagglutinin (PHA)-stimulated human lymphocyte at high concentrations and the effect did not persist after washing out the steroid. In contrast, glucocorticoids produced the classical dose-response inhibition and the effect persisted when they were removed from the cultured medium. Although both steroids decreased IL-1 secretion from human monocytes stimulated with lipopolysaccharide (LPS), they exert the same effect through a different mechanism. The experiments we report suggest that the decrease of IL-1 synthesis produced by delta HOP could be caused by inhibition of LPS phagocytosis. These results support our hypothesis that delta HOP exerts its immunosuppressive and anti-inflammatory effect by a non-genomic mechanism.

Electron impact induced fragmentations of the 1,4-diene analogues of steroid hormones and related steroids

The electron impact induced fragmentations observed in the mass spectra of eight 1,4-diene-3-ketopregnane steroids are described. The effect of hydroxyl substituents in positions 11 beta, 17 alpha and 21, on the typical fragmentation pattern is analysed; in particular the 'long range' effect of the 17 alpha-hydroxy group on the relative abundance of the ions m/z 121 and 122 is confirmed using specific deuterium labelling.

Dissociation of glucocorticoid effects of C-21 steroids at high concentrations in thymocytes

A dissociation between inhibition of RNA synthesis and cell lysis was observed when thymocytes of adrenalectomized rats were incubated with high concentrations of pregn-4-ene-11 beta-ol-3,20-dione and pregna-1,4-diene-11 beta-ol-3,20-dione. In contrast, no dissociation of these effects was found with the typical glucocorticoids cortisol and corticosterone, nor with their 1,4-diene analogs under the same conditions.