Receptor properties of corticosteroid binder IB

Glucocorticoid receptor concentrations in muscle biopsies from patients with neuromuscular diseases

Increases in circulating glucocorticoids promote catabolism, particularly in skeletal muscle. The sensitivity of the muscle to glucocorticoids can be altered by a change in the number of glucocorticoid receptors in the muscle, or by a change in the proportions of activated receptors (between binders IB and II). We have investigated the concentration of glucocorticoid receptors, and the proportions of types IB and II, in healthy and diseased muscle. We found significantly reduced concentrations of glucocorticoid receptors in the group of inflammatory myopathies (51% reduction; P < 0.05, Wilcoxon signed rank test). No significant changes in the relative proportions of binders IB and II were found in pathological muscle, although the proportion of binder IB tended towards elevated values (especially in the diabetic neuropathies, with a 17% increase). We conclude that the sensitivity of muscle to glucocorticoids can be reduced in neuromuscular diseases, especially in myositis, by a reduction in the number of glucocorticoid receptors in the tissue, but that no relevant shift in the relation between activated receptor types is present. This could be important in relation to the risk of a secondary steroid myopathy and catabolism of skeletal muscle in the treatment of inflammatory myopathies with glucocorticoids.

Stress affects the activated form of the corticosteroid-receptor complex in the rat brain

Glucocorticoid actions in the brain, particularly in the hippocampus and the hypothalamus, are critically involved in the response of the organism to stress. The key molecules in this process are the corticosteroid receptors, which upon activation, migrate and act in the nucleus. We have investigated the effect of stress on the activated form of the cytosolic glucocorticoid receptor from the above brain areas, using anion exchange chromatography. Exposure of rats to chronic stress resulted in the disappearance of the chromatographic peak, which corresponds to the activated form (DE II) of the hormone-receptor complex. For this phenomenon to occur, 1) the animal must be exposed to chronic, and not to acute stress, and 2) the adrenals of the animal must be intact. The disappearance of the activated form of the hormone-receptor complex (DE II) following chronic stress is most probably due to proteolysis of the receptor molecule, since it is specifically inhibited by the protease inhibitor leupeptin. This phenomenon may represent an adaptive mechanism which helps the organism cope with a repeated stressor.

Evidence for the presence of specific binding sites for corticoids in mouse liver plasma membranes

The specific binding of [3H]cortisol to plasma membranes purified from mouse liver, studied by the ultrafiltration method, shows the existence of specific binding sites for cortisol. The kinetic parameters of this binding are KD = 4.4 nM and Bmax = 685 fmol/mg protein in presence of 1 microM of corticosterone. With respect to the binding of 4 nM [3H]cortisol to the membrane, the affinities of the steroids decreased in the following order: deoxycorticosterone greater than corticosterone greater than progesterone greater than cortisol greater than prednisolone greater than testosterone greater than 20 beta-hydroxyprogesterone greater than cortisone. Estradiol, dexamethasone, ouabain and triamcinolone acetonide do not have affinity for this binding site. Neither Ca2+ nor Mg2+ affected the binding of [3H]cortisol to the plasma membranes. Likewise, the presence of agonists and antagonists of alpha and beta-adrenergic receptors did not modify the binding of [3H]cortisol. The results suggest that the plasma membrane binding site characterized is more specific for corticoids and is different from nuclear glucocorticoid and progesterone receptors.

Glucocorticoid receptor activation in isolated perfused rat hearts

The formation of unactivated and activated glucocorticoid receptor complexes was studied in intact, isolated, perfused rat hearts in the presence of [3H]triamcinolone acetonide. Receptor activation, as quantified by the DNA-cellulose-binding assay, began to increase within 30 s of perfusion and reached a final steady-state level (t 1/2 = 4.6 min) with 46% of the steroid-receptor complexes bound to DNA-cellulose. With the use of a linear potassium phosphate (KP) gradient (5-400 mM), unactivated receptors eluted from DEAE-cellulose anion exchange columns at approximately 250 mM KP. Two activated receptor forms appeared, which eluted either in the wash fraction (binder IB) or between 50 and 100 mM KP (binder II) and occurred with half times of 1.3 and 2.7 min, respectively. Postperfusion cytosol preparation did not markedly influence the results as receptor binding was reduced by 10% or less when a 100-fold excess of unlabeled triamcinolone acetonide was included in the homogenizing buffer. We conclude from these results that glucocorticoids are able to exert a direct effect on the heart through binding to their own receptor in the absence of endogenous hormones. The time dependency of receptor activation supports a physiological role for this process. However, activation rates, determined from conformational changes associated with altered DEAE-cellulose elution profiles and appearance of activated receptor forms, occur earlier and may not be coordinated with the rate of activation as quantified by DNA-cellulose binding.

Generation of corticosteroid binder IB from binder II by a sulfhydryl dependent renal cytosolic factor

It has long been debated whether binder IB represents a unique form of the glucocorticoid receptor or is derived from the larger molecular weight form, binder II, by limited proteolysis. Transformed glucocorticoid receptors in kidney, liver and mixed kidney/liver cytosols were examined using anion exchange and gel filtration chromatography. The transformed receptor in liver cytosols chromatographs as binder II on DEAE-Sephadex A-50 anion exchange columns and has a Stokes radius of approx 6.0 nm. The transformed receptor in kidney cytosols chromatographs as binder IB on DEAE-Sephadex A-50 anion exchange columns and has a Stokes radius of 3.0-4.0 nm (3.2 nm on agarose; 3.0-4.0 nm on Sephadex G-100). Using cytosols prepared from mixed homogenates (2 g kidney plus 8 g liver tissue), our experiments show that binder II is converted to a lower molecular weight form (Rs = 3.2 nm on agarose; Rx = 3.9 nm on Sephadex G-100) that is identical to binder IB in its elution position from DEAE-Sephadex anion exchange resin. Identical results are obtained using kidney/liver/cytosols mixed in vitro in which only the hepatic receptor, binder II, is labelled with [3H]TA. These results support the hypothesis that the renal receptor, binder IB, is a proteolytic fragment of binder II and does not represent a polymorphic form of the glucocorticoid receptor. The renal converting activity is dependent on free-SH for full activity but is insensitive to the protease inhibitors leupeptin, antipain, and PMSF. The conversion of hepatic binder II to binder IB in in vitro mixing experiments can be prevented if kidney cytosol is gel filtered on Sephadex G-25 and the eluted macromolecular fraction is adjusted to 10 mM EGTA (or EDTA) prior to mixing with the [3H]TA labelled hepatic cytosol.

Specificity of activated glucocorticoid receptor expression in heart and skeletal muscle types

Muscle metabolic responses to glucocorticoids are specific to fiber type. The present study revealed that a definite pattern exists in the formation of the two thermally activated glucocorticoid receptor complexes among the different types of muscle. Fiber types that enlarge from glucocorticoids (heart) contained the highest relative distribution of binder II and lowest content of binder IB. Fibers that atrophy from glucocorticoids (white muscle) contained negligible content of binder II and the highest appearance of binder IB. The formation of binder IB could not be explained by differences in proteolysis among the cell types. These results are consistent with the hypothesis that specific receptor forms may regulate the glucocorticoid induction of muscle hypertrophy and atrophy.

Murine glucocorticoid receptors: new evidence for a discrete receptor influenced by H-2

The glucocorticoid receptor contents in the lungs of females of two congenic strains of mice, B10.A (H-2a) and B10 (H-2b), differing only in the H-2 histocompatibility region of chromosome 17, have been measured by the dextran-charcoal method and by our previously described methods of molecular sieving and ion exchange chromatography [M. Katsumata, C. Gupta, and A. S. Goldman (1985) Arch. Biochem. Biophys. 243, 385-395]. As reported, two receptors, II and IB, are demonstrable by each column chromatographic method, and 5,5-diphenylhydantoin binds to receptor IB but not to receptor II. Receptor IB cannot be detected unless molybdate is added in cytosols prepared with hypotonic buffer [10 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid and 10 mM dithiothreitol, pH 7.35) according to S. L. Liu, J. F. Grippo, R. P. Erickson, and W. B. Pratt (1984) J. Steroid Biochem. 21, 633-637], a method which has been reported to give maximal receptor levels. Using hypotonic buffer containing 10 mM molybdate we observed a small but significantly higher content of receptor IB in B10.A mice than that in B10 mice, but no significant difference in receptor II or total receptor content. On the other hand, cytosols prepared with isotonic buffer (50 mM Tris-HCl, 120 mM NaCl, 1 mM EDTA, 10 mM dithiothreitol, and 10 mM molybdate, a modification of the buffer used in our previous report) contained significantly higher levels of receptor IB and of total binding in pulmonary cytosols of B10.A as compared to those of B10. There was no difference in receptor II content. Molybdate stabilizes receptor IB in both buffers. These results explain the apparent contradiction between our results and those of Liu et al. by showing that the hypotonic buffer used by them allows for determination of maximal levels of receptor II, but permits selective destruction of receptor IB. However, the use of isotonic buffer gives maximal values of both receptors II and IB. With isotonic buffer, it is demonstrated that only the level of receptor IB is influenced by H-2-linked genes.

Glucocorticoid receptor IB: mediator of anti-inflammatory and teratogenic functions of both glucocorticoids and phenytoin

We studied the glucocorticoid receptor complexes of pulmonary and thymic cytosols of female A/J and CD-1 mice and of hepatoma G2 cells by two column-chromatographic systems, using both [3H]dexamethasone (DEX) and [3H]phenytoin (DPH) as ligands. Three DNA-cellulose adsorbable [3H]DEX-receptor complexes were separated in each system. Molecular sieving gave a 7-, a 5.4-, and a 3.5-nm complex (Stokes radii), and DEAE-Sephadex A-50 chromatography gave a complex eluting in the wash, one at 0.14 M KCl, and one at 0.20 M KCl by a KCl gradient. DPH blocked the binding of the 7- and 3.5-nm, wash, and 0.14 M KCl [3H]DEX complexes. Only two DNA-cellulose adsorbable [3H]DPH complexes, each blocked by DEX, were obtained in each system: a 7- and a 3.5-nm, a wash, and a 0.14 M KCl complex. Thus, there is a common receptor for both DPH and DEX. This receptor has two properties which distinguish it from the 5.4-nm DEX-specific receptor: (i) it binds with a variety of steroids other than glucocorticoids and DPH, and (ii) it rebinds new [3H]DEX or [3H]DPH after loss of ligand during chromatographic separation. These results indicate that DPH binds to receptor IB and not to receptor II of Litwack. [G. Litwack, 1976, in Glutathion: Metabolism and Function (Arias, I.M., and Jakoby, W.B., eds.), pp. 285-299, Raven Press, New York]. We have also found that hepatoma G2 cells have only receptor II. DPH affects neither the induction of tyrosine aminotransferase by DEX nor the basal level of this enzyme in these cells. Moreover, neither DEX nor DPH inhibits the release of [3H]arachidonic acid prelabeled in these cells, as they do in thymocytes which have the common receptor. Thus, it appears that glucocorticoid receptor IB binds DEX and DPH as glucocorticoid agonists mediating the anti-inflammatory and teratogenic action of these drugs, while receptor II apparently is responsible for the induction of tyrosine aminotransferase by DEX.

Purification, characterization, and activation of the glucocorticoid-receptor complex from rat kidney cortex

The unactivated molybdate-stabilized glucocorticoid receptor (GcR) was purified from rat kidney cortex cytosol (RKcC) by using a modification of the procedure previously described by this laboratory for rat hepatic receptor. The purification includes affinity chromatography, gel filtration, and ion-exchange chromatography. The final preparation (approximately 1000-fold pure as determined from specific radioactivity) was used in subsequent physicochemical and functional analyses. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed a single heavily Coomassie-stained band at 90 kilodaltons. Density gradient ultracentrifugation indicated a sedimentation coefficient of 10.5 +/- 0.05 S (n = 2). Chromatography on an analytical gel filtration column produced a Stokes radius (Rs) of 6.4 +/- 0.07 nm (n = 5). The Rs was unchanged when the molybdate-stabilized GcR was analyzed in the presence of 400 mM KCl or when analyzed in the unpurified (cytosolic) state. In contrast, the hepatic GcR was observed to exist as a larger form in cytosol (7.7 +/- 0.2 nm). Following purification, or upon gel filtration analysis under hypertonic conditions, the Rs was similar to that of the unpurified RKcC GcR. Following removal of molybdate from RKcC GcR and thermal activation (25 degrees C/30 min), DNA-cellulose binding increased 1.5-2-fold over the unheated control. Addition of RKcC or hepatic cytosol (endogenous receptors thermally denatured at 90 degrees C/30 min or presaturated with 10(-7) M radioinert ligand) during thermal activation increased DNA-cellulose binding an additional 2-6-fold beyond the heated control.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino acid sequence homology between the C3 chain of rat prostatic steroid binding protein and human alpha 2-macroglobulin

Using a computer program designed to detect evolutionary relationships between proteins, I find that exon 2 of the C3 chain of rat prostatic steroid binding protein has amino acid sequence homology with residues 1058-1119 of the protease inhibitor alpha 2-macroglobulin. This finding suggests interesting approaches for studying the functions of these proteins.

Glucocorticoid receptors in developing rat brain and liver

Dexamethasone receptors were measured by conventional equilibrium steroid binding studies in rat liver and brain cytosol, during late prenatal and postnatal development, Receptor binding could be detected in both cytosol preparations as early as the 17th day of gestation. Receptor levels in the cytosol from intact animals reached adult values by the 1st day after birth in both tissues. Using adrenalectomized animals an increase which reached adult values was observed during the first postnatal week for liver and the second postnatal week for brain. At physiological concentrations of endogenous glucocorticoids depletion of receptor from the cytosol of intact animals was minimal at postnatal day 1 and reached adult levels by day 7. Chromatographic analysis in DEAE-Sephadex A50 minicolumns of unactivated and activated receptor constituents revealed the same pattern as that of adult animals. Glucocorticoid receptor complex from developing liver and brain was shown to be capable of binding to isolated adult liver nuclei after in vitro activation. However full capacity, for nuclear binding was observed in vivo, after injection of inducing doses of [3H]dexamethasone: By the end of the first week after birth adult nuclear binding capacity was observed in experiments in vivo while values peaked during the second week, in both tissues studied.

Comparison of corticosteroid binder IB with the alpha-chymotrypsin- and RNase-treated hepatic glucocorticoid receptors

Rat liver and kidney cytosolic extracts contain the glucocorticoid receptor (binder II) and corticosteroid binder IB, both of which possess the steroid- and DNA-binding domains. Since it has been speculated that the smaller binder IB may be generated from binder II by proteolysis, the chymotrypsin-produced receptor fragment in rat liver cytosol has been compared with binder IB in terms of charge, size and DNA binding characteristics. The [3H]triamcinolone acetonide-receptor complex is converted to a smaller fragment by short term digestion (10 degrees C, 30 min) with 100 micrograms/ml alpha-chymotrypsin. Although the chymotrypsin fragment produced from previously heat-activated binder II and binder IB both exhibit DNA-binding capability, they differ in charge and size. Whereas the alpha-chymotrypsin-treated receptor has a Stokes radius of 30 A and elutes from DEAE-cellulose at 0.06 M potassium phosphate in a linear salt gradient, binder IB has a Stokes radius of 20 A and elutes in the buffer wash of the DEAE-cellulose column. Thus, while binder IB can be resolved from the heat-activated form of the [3H]TA-receptor on DEAE, the heat activated alpha-chymotrypsin product elutes from the anion exchange resin at the same ionic strength as intact activated binder II (i.e. at 0.05 M potassium phosphate), and the unactivated intact receptor elutes at about 0.20 M potassium phosphate. A more extended digestion with alpha-chymotrypsin (24 h, 0 degrees C) results in elimination of the DNA binding site without further reduction of the Stokes radius or change in the elution pattern from DEAE-cellulose. Furthermore, molybdate completely blocks formation of binder IB but does not inhibit the production of the receptor fragment by alpha-chymotrypsin. Treatment of the hepatic [3H]TA-receptor complex with RNase has no effect on the charge, size or DNA binding properties of the bound receptor. These results suggest that RNase does not activate the [3H]TA-receptor complex nor does it produce a IB-like component in the liver cytosol. The present results are consistent with the hypothesis that binder IB is formed in vitro by a process which may not involve proteolytic cleavage or RNase-induced modification of the glucocorticoid receptor (binder II).

Heterogeneity of the glucocorticoid receptors: molecular transformations during activation, detected by electrofocusing

Isoelectric focusing (IEF) of glucocorticoid receptor (GR) of the neural retina of the 14-day chick embryo was conducted under conditions that yielded quantitative recovery of binding activity. IEF of the cytosol, equilibrated with [3H]triamcinolone acetonide (TA) at 0-2 degrees C yielded three major TA-GR components with apparent isoelectric points (pI') of 5.4 +/- 0.3, 6.5 +/- 0.2, and 7.6 +/- 0.3, designated as I, II, and III, respectively. During temperature-induced activation (incubation at 30 degrees C for 60 min, in the presence of free [3H]TA and 0.15 M KCl), approximately 25% of the specifically bound TA was irreversibly lost. IEF reveals that this loss is accounted for by the complete loss of binding from I. During activation, II also decreases but correspondingly III increases, i.e., the sum of II and III remains unchanged. Only the bound TA of I is sensitive to the addition of KCl (a promoter of activation). This sensitivity of I is temperature dependent. Molybdate (an inhibitor of activation) protects the bound TA of I and suppresses the formation of III. These two effects of molybdate diminish simultaneously when the temperature is increased to 30 degrees C. III preferentially exhibits binding activity to nuclei. The data suggest that (i) the glucocorticoid-free cytosol contains two GRs, I and II, with possibly two different functions; (ii) activation involves the loss of bound TA from I and the transformation of II to III with increased pI; (iii) these two molecular events in GR activation are interdependent.

In vitro production of corticosteroid binder IB in the presence of proteolytic inhibitors

The effect of proteolytic inhibitors on the temperature-dependent formation of corticosteroid binder IB in rat kidney cytosol was examined. Antipain increased the apparent binding of [3H]-triamcinolone acetonide in the cytosol. Leupeptin, chymostatin, soya bean trypsin inhibitor and lima bean trypsin inhibitor did not affect total binding, while L-1-tosylamide-2-phenylethyl chloromethyl ketone, N alpha-p-tosyl-L-lysine chloromethyl ketone and phenylmethylsulfonyl fluoride markedly reduced the charcoal resistant steroid binding. However, none of the inhibitors added during tissue homogenization, steroid binding or activation affected the extent of heat-dependent conversion of the [3H]-triamcinolone acetonide-receptor complexes to the IB form, which was characterized by its exclusion from DEAE-Sephadex ion exchanger. In contrast, sodium molybdate (10 mM) effectively inhibits IB formation without inhibiting protease activity of rat kidney cytosol. These observations indicate that the temperature-dependent formation of corticosteroid binder IB in vitro does not involve proteolytic transformation of unbound or steroid-bound cytosolic proteins. Addition of antipain (3 mM) to the cytosol markedly increased the radioactivity in the buffer prewash of DEAE-cellulose columns (apparent IB) only when the inhibitor was added prior to charcoal adsorption. However, a similar peak in the prewash also was obtained with receptor-free cytosol. Antipain had no effect on the rate of dissociation of performed [3H]-triamcinolone-acetonide-receptor complexes nor did it increase the amount of receptor adsorbed to hydroxylapatite. Chromatography on Sephadex G-25 and P-2 columns showed that the increased activity in the charcoal-resistant fraction in the presence of antipain is due to unbound steroid. Thus, antipain interferes with the ability of charcoal to remove unbound steroid from the cytosol.