In vitro modulation of rat liver glucocorticoid receptor by urea

Interaction of cycloalkanoprogesterones with mammalian progesterone receptor: binding of pregna-D'-pentaranes in the calf uterine cytosol

Pregna-D'-pentaranes (pentaranes) are modified progesterones with demonstrable progestational activity and contraceptive effect. We have examined the steroid binding characteristics of the two newly synthesized progesterone analogs, Pentarane A (16 alpha, 17 alpha-cyclohexanoprogesterone) and Pentarane B (6 alpha-methyl, 16 alpha, 17 alpha-cyclohexanoprogesterone), and studied the nature of their interaction with progesterone receptor (PR) from the chicken oviduct and the calf uterine cytosols. Pregna-D'-pentaranes exhibited no affinity for the chick PR but interacted with the calf uterine PR as did R5020. The pentaranes, however, bound PR less tightly. R5020- or pentarane-bound PR sedimented as an 8S moiety in 8-30% linear glycerol gradients. Thermal transformation of receptor resulted in the reduction of the 8S form, and caused an increase in the binding of R5020- and progesterone-bound PR complexes to DNA-cellulose. The pentarane-bound PR bound poorly, if at all, to DNA-cellulose. Our data suggest that pentaranes exhibit both similarities and differences with natural and synthetic progestins with respect to their interaction with calf uterine PR. The lack of pentarane binding to chicken PR is reminiscent of the general phenomenon that antiprogestins (RU486, ZK98299, and Org 31710 and Org 31806) do not interact with chicken PR. Pentaranes, therefore, represent unique steroid analogs to investigate the molecular mechanism of steroid hormone action.

ZK98299--a new antiprogesterone: biochemical characterization of steroid binding parameters in the calf uterine cytosol

We have examined steroid binding characteristics of a newly synthesized antisteroid, ZK98299 [onapristone, 11 beta-(4-dimethylaminophenyl)-17 alpha-hydroxy-17 beta-(3-hydroxypropyl)- 13 alpha-methyl-4,9-gonadien-3-one], in the calf uterus cytosol and compared the nature of this interaction with the binding of progesterone receptor (PR) agonist R5020 [promegestone, 17,21-dimethylpregna-4,9-diene-3,20-dione]. In the freshly prepared cytosol, [3H]ZK98299 interacted specifically with a macromolecule: the binding was abolished in the presence of excess progestins (R5020 and progesterone) and the antiprogesterone ZK98299. The high affinity (Kd = 2.5 nM) interaction between [3H]ZK98299 and PR was temperature- and time-dependent, reaching an optimum by 2-3 h at 0 degrees C, and was facilitated by 20 mM Na2MoO4. Under nontransforming conditions, [3H]ZK98299-receptor complexes sedimented as 8 S species in 8-30% linear glycerol gradients. Upon salt or thermal transformation, there was a loss of the 8 S form, with only a small fraction of total complexes (5-7%) binding to DNA-cellulose. In contrast, transformed [3H]R5020-receptor complexes exhibited a greater extent of binding (25-55%) to DNA-cellulose. [3H]ZK98299-receptor complexes could be resolved into two ionic species over DEAE-Sephacel following incubation of the complexes at 0 or 23 degrees C. [3H]ZK98299 binding was sensitive to sulfhydryl group modification as beta-mercaptoethanol increased the extent of steroid binding. Although treatment with iodoacetamide (IA) abolished [3H]R5020 binding, there was a significant (nearly twofold) increase in the [3H]ZK98299 binding. The results of this study point to similarities and differences between the steroid binding properties of the uterine PR occupied by R5020 and ZK98299: both steroids appear to bind the same 8 S receptor but exhibit differential DNA binding and sensitivity to IA. The reported antagonist properties of ZK98299 may, therefore, be explained on the basis of a distinct receptor conformation induced by the antisteroid.

Progesterone binding in a clinical isolate of Pseudomonas aeruginosa

We have undertaken the characterization of progestin binding component(s) in the cytosol prepared from Pseudomonas aeruginosa isolated from an immunocompromised patient. Incubation of P. aeruginosa cytosol aliquots at 0 degrees C with 20 nM [3H]R5020 (a synthetic progestin) revealed the presence of saturable binding. The [3H]R5020 binding reached an equilibrium after 1 h at 0 degrees C and showed saturation at 30-50 nM with a Kd value of 7.7 nM. At 0 degrees C, beta-mercaptoethanol increased the [3H]R5020 binding by 20% but sodium molybdate had no effect. The [3H]R5020-macromolecular complex was stable for up to 4 h at 37 degrees C. Steroid binding specificity analysis revealed that [3H]R5020 binding could be eliminated in the presence of 2 microM progesterone, estradiol, or dihydrotestosterone but that the synthetic glucocorticoid, triamcinolone acetonide, did not compete. Postlabeling of the cytosol fractions obtained after 10-30% glycerol gradient analysis demonstrated association of the radioactivity with a molecule that sedimented as a 6-8 S protease-sensitive moiety which was unaltered in the presence of RNase or DNase. When cells were grown in the presence of 100 nM progesterone, a 50% inhibition in the number of resulting colonies was observed. In addition to its evolutionary significance, the presence of this steroid binding molecule suggests a potential in the endocrine manipulation in the treatment of infections caused by P. aeruginosa.

Interaction of rat liver glucocorticoid receptor with a newly synthesized antisteroid ZK98299

Steroid receptor antagonists are important biochemical probes for understanding the mode of steroid hormone action. We have studied the interaction between rat liver glucocorticoid receptor and a newly synthesized antisteroid ZK98299 (13-antigestagen; [11-beta-(4-dimethylaminophenyl)-17a-hydroxy-17 beta-(3- hydroxypropyl)-13 alpha-methyl-4,9-gonadien-3-one]). Glucocorticoid receptor from freshly prepared hepatic cytosol bound [3H]ZK98299 with affinity approximately equal to that of [3H]triamcinolone acetonide. The binding of both steroids reached a maximum at 4 h at 0 degrees C. Both ligands were able to compete for the steroid binding site but progesterone, estradiol and dihydrotestosterone (DHT) failed to compete for the [3H]ZK98299 and [3H]triamcinolone acetonide binding. While [3H]ZK98299 binding to glucocorticoid receptor could occur in the presence of iodoacetamide and N-ethylmaleimide (NEM), [3H]triamcinolone acetonide binding capacity was completely abolished following such treatments. The [3H]ZK98299-receptor complexes sedimented as 9 S and 4 S molecules under control (4 degrees C) and receptor transforming (23 degrees C) conditions, and exhibited a faster rate of dissociation at 23 degrees C when compared with [3H]triamcinolone acetonide-receptor complexes. These results indicate that ZK98299 interacts with hepatic glucocorticoid receptor. The differential effects of iodoacetamide and NEM on the interaction of glucocorticoid receptor with ZK98299 and triamcinolone acetonide, and the faster rate of dissociation of [3H]ZK98299-receptor complexes suggest that treatment with these agents (NEM and iodoacetamide) results in distinct conformational changes in glucocorticoid receptor structure with respect to triamcinolone acetonide and ZK98299 binding. Alternatively, ZK98299 may be interacting with a site which is distinct from one which accepts triamcinolone acetonide.

Hepatic glucocorticoid receptor behaves differently when its hormone binding site is occupied by agonist (triamcinolone acetonide) or antagonist (RU486) steroid ligands

We have examined the influence of sulfhydryl (SH)-group modifying agents on the interaction of the rat liver glucocorticoid receptor (GR) with its known agonist triamcinolone acetonide (TA) and the newly synthesized antagonist mifepristone (RU486). In the freshly prepared cytosol, [3H]TA or [3H]RU486 bound to macromolecule(s) which sediment as 8-9 moieties: the binding of either ligand can be competed with radioinert TA or RU486. The presence of 2-10 mM dithiothreitol (DTT), beta-mercaptoethanol (beta-MER), and monothioglycerol (MTG) caused a 2-3 fold increase in the [3H]TA and [3H]RU486 binding to GR. Iodoacetamide (IA) and N-ethylmaleimide (NEM) decreased the agonist binding significantly. In contrast, the [3H]RU486 binding to GR increased by 50 percent in the presence of IA. IA and NEM inhibited the binding of the heat-transformed [3H]TA-receptor complex to DNA-cellulose by 70-90 percent whereas DNA binding of [3H]RU486-bound GR was inhibited only slightly. These results indicate that either a) the interaction of GR with the agonist or antagonist steroid ligands causes differential structural alterations, which are more readily detectable in the presence of SH-modifying agents or b) the agonist and the antagonist interact with distinct steroid binding sites.

Transformation of human progesterone receptor in the presence of the progestin (R5020) and the antiprogestin (RU486)

We have examined and compared the binding characteristics and transformation in vitro of human uterine cytosolic progesterone receptor (PR) bound to either the progestin agonist, R5020 or the antiprogestin, RU486. Incubation of cytosol with 5-20 nM [3H]R5020 and [3H]RU486 yielded macromolecular complexes that sedimented in the 4S and 8S regions in 10-35% glycerol gradients. The 8S peaks of radioactivity due to macromolecular-bound [3H]R5020 or [3H]RU486 could be eliminated by a preincubation of the uterine cytosol with 1-2 microM progesterone or RU486. The [3H]R5020 binding in the 4S peak was not competable with either steroid. In contrast, the binding of [3H]RU486 in the 4S peak could be abolished by a pretreatment of uterine cytosol with excess RU486, but not progesterone. Selective fractionation of the cytosol with ammonium sulfate, in the presence of sodium molybdate, eliminated the non-specific 4S [3H]R5020 binder. The thermal (23 degrees C) transformation of the [3H]RU486-receptor complex, as a function of the loss of the area under the 8S peak, appeared to be comparable to that achieved with [3H]R5020-receptor complex. The 8S [3H]RU486 peak was reduced by only 46% compared to the [3H]R5020 peak, which was reduced by 60%. These results demonstrate that in human uterine cytosol, R5020 and RU486 bind in a specific and saturable manner to an 8S PR, which is susceptible to thermal 8S to 4S transformation. In addition, [3H]R5020 also interacts with a nonsaturable 4S macromolecule, whereas the 4S [3H]RU486 binder is saturable and specific for RU486. The above observations indicate the heterogeneity of the steroid binding components present in the human uterine cytosol, and suggest that caution should be taken when interpreting data which shows the presence of different molecular forms of the steroid receptors.

Transformation of the [3H]aldosterone-type I receptor complex to a DNA-binding species

For most steroid receptor complexes, the transformation to a DNA-binding species can be achieved readily in vitro by incubation at elevated temperatures and/or salt concentrations. Although the aldosterone-Type I receptor complex forms a clear exception to this generalization, a marked increase in its transformation can be achieved by incubation with the chaotropic anion, thiocyanate. Time and concentration-response analyses with brain cytosol revealed that over 40% of the complexes were retained in DNA-cellulose assays after a 15 min pre-incubation at 0 degree C with 100 mM thiocyanate. As expected, molybdate prevented this transformation; however, in contrast to results with heat- and/or salt-induced transformation of other steroid receptors, the molybdate effect was only partially removed by gel filtering the cytosol prior to thiocyanate addition. Thiocyanate-induced transformation should prove useful in the biochemical characterization and purification of non-transformed and transformed aldosterone-Type I receptor complexes.