Chemical differentiation of type I and type II receptors for adrenal steroids in brain cytosol

Studies outlined here compare the properties of mineralocorticoid (Type I) and glucocorticoid (Type II) receptors in cytosol from adrenalectomized mouse brain. Pretreating cytosol with dextran-coated charcoal (DCC) produced a 4.7-fold increase in the subsequent macromolecular binding of the mineralocorticoid, [3H]aldosterone (20 nM ALDO, in the presence of a 50-fold molar excess of the highly specific synthetic glucocorticoid, RU 26988), whereas it produced a 55% decrease in the binding of the glucocorticoid, [3H]triamcinolone acetonide (20 nM TA). Scatchard analyses revealed that DCC pretreatment had no effect on the affinity or maximal binding of Type I receptors for [3H]ALDO (in the presence of a 0-, 50- or 500-fold excess of RU 26988), whereas it produced a 3- to 6-fold increase in the Kd, and an 8-43% decrease in the maximal binding, of Type II receptors for [3H]TA and [3H]dexamethasone. Optimal stability of unoccupied Type I receptors at 0 degree C was found to be achieved in buffers containing glycerol, but lacking molybdate. Although the addition of molybdate was found to reduce the loss in Type I receptor binding observed after incubating unlabelled cytosol at 12 or 22 degrees C, this stabilization was accompanied by a concentration-dependent reduction in the binding of [3H]ALDO at 0 degree C. Scatchard analyses showed that this reduction was due to a shift in the maximal binding, and not the affinity, of the Type I receptors for [3H]ALDO. The presence or absence of dithiothreitol in cytosol appeared to have little effect on the stability of Type I receptors. In contrast to our finding for Type I receptors, it was possible to stabilize the binding capacity of unoccupied Type II receptors, even after 2-4 h at 12 or 22 degrees C, if the glycerol containing buffers were supplemented with both molybdate and dithiothreitol. In summary, these results indicate distinct chemical differences between Type I and Type II receptors for adrenal steroids.

Structure of the mouse glucocorticoid receptor: rapid analysis by size-exclusion high-performance liquid chromatography

Gel-exclusion high-performance liquid chromatography (HPLC) has been used to separate the untransformed from the transformed glucocorticoid receptor (GC-R) extracted from mouse AtT-20 cells. With 200 mM potassium phosphate as the eluent, an efficient separation of the forms of the GC-R is attained in 15-20 min. The untransformed cytosolic GC-R elutes from the column with a Stokes radius (Rs) of 8.2-8.6 nm, as do the molybdate-stabilized GC-R, the purified untransformed GC-R, and the cross-linked cytosolic GC-R. GC-R transformed in vitro by either ammonium sulfate precipitation, KCl treatment, or G-25 chromatography elutes with an Rs of 5.7-6 nm. Also, GC-R extracted from the nucleus with either 0.3 M KCl or 2 mM sodium tungstate, or purified by two cycles of DNA-cellulose chromatography, has an Rs of 5.5-6.3 nm. The data are identical either in the presence or in the absence of 20 mM Na2MoO4, suggesting that molybdate is not causing aggregation to produce a larger Rs value than that of the native receptor. Vertical tube rotor sucrose gradient ultracentrifugation of cytosol produces three forms of the GC-R: 9.1 S, 5.2 S, and 3.8 S. Sequential analysis of the GC-R forms by HPLC and vertical tube rotor ultracentrifugation and vice versa allows for the hydrodynamic determination of molecular weight within a very short time period (2-3 h total).(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclic AMP-dependent protein kinase promotes glucocorticoid receptor function

Murine lymphoma cell lines such as WEHI-7 exhibit a cytolytic response to both cAMP and glucocorticoids. We have exploited this behavior to ask if cyclic AMP-dependent protein kinase plays a role in regulating glucocorticoid receptor function. We have found that cAMP-resistant cell lines containing a defective cAMP-dependent protein kinase activity give rise to spontaneous steroid-resistant variants at a high frequency (approximately 10(-7)) relative to wild type cells (less than 10(-10)). Unlike previous results with wild type cells, nearly complete loss of glucocorticoid receptor function was observed in a single selection using unmutagenized cAMPr derivatives of WEHI-7. Thus, the initial selection of the cAMPr phenotype serves as a permissive step toward the acquisition of glucocorticoid resistance in WEHI-7. In addition, cAMP was found to increase the levels of steroid binding in these cell lines, and the dose response was dependent upon the phenotype of the cyclic AMP-dependent protein kinase. The results demonstrate an important role for cAMP in regulating glucocorticoid receptor activity and strongly suggest that this novel two-step selection scheme leads to the isolation of new forms of glucocorticoid resistance.

Glucocorticoid regulation of hepatic cytosolic glucocorticoid receptors in vivo and its relationship to induction of tyrosine aminotransferase

Regulation of rat hepatic cytosolic glucocorticoid receptors was studied using our newly developed exchange assay. Injecting 1 mg of dexamethasone or corticosterone into 150-250 g adrenalectomized rats caused a rapid decline in glucocorticoid receptor binding. Glucocorticoid receptor levels were depressed 80-90% in less than 15 min after hormone treatment, and remained low for about 24-48 h after glucocorticoid administration. 80-90% of glucocorticoid receptor binding was regenerated by 48 h, and complete binding was recovered by 72 h. Regenerated glucocorticoid receptor binding (48-72 h after first hormone injection) could be re-depressed by a second injection of the hormone. Similar results were obtained using normal (intact) rats. Optimum induction of tyrosine aminotransferase activity was obtained within 2 h following the first hormonal injection. Induction of tyrosine aminotransferase activity (measured 2 h after a second injection of the glucocorticoid) correlated with glucocorticoid receptor levels. Thus, 1 mg of dexamethasone or corticosterone greatly enhanced the liver tyrosine aminotransferase activity in the adrenalectomized rats (not previously hormone treated) and in adrenalectomized rats previously injected (48-72 h) with 1 mg of the glucocorticoid hormone. Enhancement of tyrosine aminotransferase activity was lowest 16-24 h after the first hormone injection (when receptor levels were extremely low). These results indicate that the induction of liver tyrosine aminotransferase activity by glucocorticoid hormones is correlated with cytosolic glucocorticoid receptor levels.

Properties and dynamics of glucocorticoid binding capacity in rat skin

[3H]Dexamethasone binding was detected in cytosol prepared from rat skin only in the presence of dithiothreitol (DTT). Simultaneous supplement of sodium molybdate (Mo) induced synergistic enhancement of the binding. In the presence of DTT and Mo the dissociation constant was approximately 1 nM, the number of maximum binding sites was approximately 100-200 fmol/mg protein, and only steroids that possessed glucocorticoid activity competed with [3H]dexamethasone binding. [3H]Dexamethasone-receptor complexes in dermal cytosol were able to bind to DNA-cellulose after brief heating, and receptors were eluted from DEAE-cellulose with 0.2 M KCl. These observations showed that [3H]dexamethasone binding sites observed in dermal cytosols have similar binding characteristics to glucocorticoid receptors in other glucocorticoid target tissues. Binding capacity in dermal cytosols was depleted after in vivo administration of all 4 glucocorticoids used in the present study. Both the extent and the duration of depletion were dose-dependent in all instances. Non-fluorinated glucocorticoids required higher doses to induce a profound depletion than did fluorinated ones and the duration of depletion induced by the former was shorter than by the latter. Since fluorinated glucocorticoids usually have higher anti-inflammatory potency than non-fluorinated ones, we concluded that the pattern of depletion and replenishment of the dermal cytosol binding capacity was correlated with glucocorticoid biopotency.

Relationships between mammary estrogen receptor and estrogenic sensitivity. Molecular properties of cytoplasmic receptor and its binding to deoxyribonucleic acid

The cytoplasmic estrogen receptors (ER) from mammary glands of estrogen-responsive nulliparous and estrogen-resistant lactating mice have been studied to delineate various relationships between the molecular properties of ER and estrogenic sensitivity. These studies indicate that there are essentially no differences in the hydrodynamic parameters of native ER isolated in hypotonic buffer; the ER from both tissues have a stokes radius of 80-85 A, sedimentation coefficient of 9-10S, and mol wt of 300,000-340,000. However, while 60-80% of the total ER in mammary glands of nulliparous mice, upon exposure to 400 mM KC1 is able to bind to DNA, under identical experimental conditions only approximately 20% of total ER from lactating mammary glands binds to DNA. Analyses of ER in buffers containing 400 mM KC1 reveal that the ER in lactating mammary glands have a larger mol wt (100,000-130,000) as compared to ER in mammary glands of nulliparous mice (70,000). The ER in lactating mammary glands also appear to be more acidic when analyzed by diethylaminoethyl cellulose chromatography. Experiments performed with mixed cytosol reveal that lactating mammary cytosol contains factors which can impede the ability of ER to bind to DNA subsequent to exposure to KC1. The possible significance of the observed differences in the properties of ER from estrogen-responsive and unresponsive mammary glands has been discussed.

Circadian and seasonal variations of glucocorticoid receptors in normal human lymphocytes

Circulating human lymphocytes are known to contain specific glucocorticoid receptors. Using a competitive binding whole cell assay, we have examined the binding of [3H] dexamethasone to peripheral lymphocytes of normal male subjects. Lymphocytes were found to contain 2000-10000 glucocorticoid receptor sites/cell and the Kd value was in the range of 0.5-9 X 10(-9) M. The number and affinity of glucocorticoid receptors did not change throughout a 1-year observation time. In contrast, there was a significant diurnal variation in receptor content (38% higher at 11 p.m. than at 8 a.m.), while receptor affinity did not change.

Phosphorylation of L-cell glucocorticoid receptors in immune complexes: evidence that the receptor is not a protein kinase

Two phosphoproteins are absorbed to protein A-Sepharose when cytosol from 32P-labeled L-cells is incubated with a monoclonal antibody against the glucocorticoid receptor: one is a 98K phosphoprotein that contains the steroid binding site, and the other is a 90K non-steroid-binding phosphoprotein that is associated with the molybdate-stabilized receptor [Housley, P. R., Sanchez, E. R., Westphal, H. M., Beato, M., & Pratt, W. B. (1985) J. Biol. Chem. 260, 13810-13817]. In this paper we have incubated L-cell cytosol with rabbit antiserum against the mouse glucocorticoid receptor and show that incubation of protein A-Sepharose-bound immune complexes with [gamma-32P]ATP and Mg2+ results in phosphorylation of the 98K steroid-binding protein but not of the 90K receptor-associated protein. Phosphorylation occurs regardless of whether the receptor is unoccupied or is present as the untransformed or transformed steroid-receptor complex. No phosphorylation occurs in the presence of Ca2+ instead of Mg2+. If protein A-Sepharose-bound immune complexes prepared with a monoclonal antibody against the receptor are incubated with [gamma-32P]ATP and Mg2+, neither protein is phosphorylated. If the protein A-Sepharose pellet is obtained from molybdate-stabilized cytosol that has been incubated both with monoclonal antibody to provide the 98K receptor and its 90K associated protein and with preimmune rabbit serum, which causes the nonspecific adsorption of an L-cell protein kinase, then incubation with [gamma-32P]ATP and Mg2+ causes receptor phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of dithiothreitol on the kinetics of dissociation of dexamethasone from the non-transformed mammary cytosolic glucocorticoid receptor

Sulfhydryl reducing agents such as dithiothreitol are required for maximum binding of dexamethasone to the mammary cytosolic glucocorticoid receptor, but little is known concerning the effects of dithiothreitol on the kinetics of the binding reaction. In this report we have examined the influence of dithiothreitol on the dissociation kinetics of dexamethasone from the non-transformed glucocorticoid-receptor complex at 0-4 degrees C under various experimental conditions. Without dithiothreitol, the rate of dissociation of dexamethasone remains essentially the same (t1/2 approximately 17 h) regardless of the method chosen to monitor dissociation. With dithiothreitol, however, there is a marked acceleration in the rate of dissociation of receptor-bound dexamethasone when an excess of unlabeled dexamethasone is used to study dissociation (t1/2 approximately 5 h) but not when dissociation is investigated by removal of free labeled dexamethasone by charcoal adsorption (t1/2 approximately 21 h); dithiothreitol also accelerates the observed rate of dissociation when a combination of these methods is used. An acceleration in the rate of receptor-bound dexamethasone is also observed when an excess of the synthetic progestin, R5020, is used in the dissociation assay. The possible reasons and importance underlying these findings have been discussed.

Uptake kinetics and receptor binding of glucocorticosteroids in head injury: an experimental study in a rat brain oedema model

The uptake of dexamethasone (DM), as well as the glucocorticoid receptors binding sites (GCR) were studied in normal rat brain and in the rat brain after cold lesion of the right hemisphere. DM was taken up at a rate of 5.05 nmol/mg prot./min. by isolated cells of normal brain. This uptake was concentration (saturation at 10(-4) DM) and time dependent (linear up to 10 min), but was not temperature dependent. Isolated cells derived from the cold lesioned brain demonstrated a process, which is unsaturable (diffusion like) and not time nor temperature dependent. The brains of adrenalectomized rats were assayed for the GCR. There was no marked difference in the GCR content of the cortex, white matter and brain stem. Within 6 h after the cold lesion the GCR concentration in the lesioned hemisphere increased significantly (p less than 0.05). This increase was followed by a slow-levelling-off within 2 days, to reach the control values again in 7 days. At the trauma site itself, the GCR were decreased (p less than 0.10), whereas the GCR were markedly increased in the remaining homolateral hemisphere (p less than 0.001). These results favour the use of steroids in the treatment of brain oedema following severe head injury despite the controversial results of various clinical trials.

Sex differences in the distribution and regulation of glucocorticoid receptors in cardiac tissues of rats

We compared the binding of [3H]-dexamethasone in cytosols prepared from atria and ventricles. The effects of steroid treatment and adrenalectomy on receptor concentration were measured in both male and female rats. In male rats the distribution of receptors was similar in atria and ventricles. In contrast, the atria of female rats in all treatment groups had twice the number of receptors as did the ventricles. Adrenalectomy in females resulted in receptor up-regulation, but dexamethasone treatment, which was effective in reducing binding in males and in the ventricles of females, failed to alter atrial binding in females. These results suggest that the atria of female rats may be more responsive than ventricles to the effects of circulating glucocorticoids.

Tissue differences in the up-regulation of glucocorticoid-binding proteins in the rat

The magnitude of increase in glucocorticoid receptor concentration and transcortin-like binding was examined in a variety of peripheral tissues and brain structures after adrenalectomy. Glucocorticoid binding was assayed in liver, heart, kidney, pituitary, hippocampus, cerebral cortex, amygdala-entorhinal area, and hypothalamus. Glucocorticoid receptor concentration, measured using [3H]dexamethasone as ligand, increased in all eight tissues, but the magnitude of this increase varied 30-fold among tissues. The largest increase was shown by kidney cytosol, followed by amygdala-entorhinal cortex, hippocampus, liver, cerebral cortex, hypothalamus, pituitary, and heart. These increases were not due to a selective enhancement of mineralocorticoid receptors. The increase in transcortin in peripheral tissues was variable and exceeded the increase in plasma transcortin by an order of magnitude. It was concluded that up-regulation of the glucocorticoid receptor after adrenalectomy is a response common to most, if not all, glucocorticoid target tissues. However, the magnitude of this response was tissue specific and was not directly related to initial receptor density. The marked increase in tissue transcortin ([3H]corticosterone binding in the presence of excess dexamethasone) suggested that plasma transcortin is sequestered by peripheral tissues in substantial amounts in the acutely adrenalectomized rat. The increase in transcortin uptake by tissues and the increases in cytosolic receptor number are apparently subject to different regulatory control.

Drug intake and the dexamethasone suppression test

The dexamethasone suppression test (DST) is being used clinically as a diagnostic laboratory test for depression. Drug histories collected from 336 psychiatric inpatients revealed that 60% were taking one or more drugs suspected of altering DST results in either a false-positive or false-negative manner. Practical limitations of the DST as a biologic marker of affective syndromes in relation to patient drug use are discussed.

Glucocorticoids and the isolated rat hepatocyte

Following incubation at 37 degrees C with tritiated glucocorticoids isolated hepatocytes prepared from non-adrenalectomized rats show rapid uptake of label. Uptake is non-saturable, and non-linear over the first 60 sec of exposure to steroids. HPLC separation of aqueous extracts of cells and incubation medium shows that polar metabolites of the natural steroid, corticosterone, appear within 10 sec, whereas the synthetic glucocorticoid, dexamethasone, is not altered. Our results suggest that diffusion is the most important process by which glucocorticoids enter liver cells, and that the predominant fate of corticosterone is rapid metabolism.

Corticosteroid receptor in type II pneumocytes of the rat

Glucocorticoid receptor in rat type II pneumocytes has been characterized. The Scatchard plot analysis of 3H-dexamethasone binding to type II cells showed a single class of binding sites. The apparent Kd of 3H-dexamethasone binding by a whole cell assay was 9.1 nM and the maximal binding capacity was 78.0 f mol/10(6) cells (0.31 pmol/mg cytosol protein).

Demonstration of specific high affinity receptors for aldosterone in cytosol of rat colon

Since both aldosterone and glucocorticoids increase cation transport in rat distal colon, and a specific glucocorticoid high affinity cytosolic receptor has been identified in this tissue, it was possible that the action of aldosterone was dependent on interaction with the glucocorticoid receptor. Studies were, therefore, performed to determine whether a specific high affinity receptor for aldosterone was present in rat distal colon. At 4 C, aldosterone binding was saturable and exhibited a high affinity site with an apparent Kd of 6.2 +/- 0.9 X 10(-10) M and a calculated number of binding sites of 57.2 +/- 10.8 fmol/mg cytosol protein. Scatchard plot analysis also revealed a low affinity site with a Kd of 5.9 +/- 1.1 X 10(-8) M and 961 +/- 191 fmol/mg cytosol protein-binding sites. Competitive binding studies demonstrated that the high affinity binding protein was specific for aldosterone, compared to either dexamethasone or RU-28362. Since a specific high affinity receptor protein for aldosterone is present in rat distal colon, these data are consistent with a direct action of aldosterone that is independent of the glucocorticoid receptor system.

Dexamethasone binding sites and steroid-dependent stimulation of glycogenesis by insulin in cultured fetal hepatocytes

The binding of [3H]dexamethasone and the effect of insulin on [14C]glucose incorporation into glycogen were studied in cultures of fetal rat hepatocytes transplanted from 15 and 18 days of gestation, i.e. before and just at the critical stage of glucocorticoid-dependent maturation of the rat fetus. Both types of cell cultures contained approximately 50,000 specific glucocorticoid receptors per cell, with an affinity of 6 nM. Glycogenesis was hardly stimulated by insulin at the time of transplantation, especially in 15-day-old fetal hepatocytes. The stimulatory effect of insulin increased in the presence of dexamethasone (100 nM) to reach, after 40 h of treatment, 270% and 440% of the control values in 15- and 18-day-old fetal hepatocytes, respectively. A shortening of the exposure time to steroid necessary to trigger the insulin response was observed with 18-day-old cells (20 h). The half-maximal insulin-induced stimulation of glycogenesis was obtained with a lower concentration of dexamethasone in 18-day-old than in 15-day-old hepatocytes (3.2 +/- 0.32 vs. 7.9 +/- 0.29 nM, n = 5; P less than 0.001). Although high affinity dexamethasone binding sites exist in fetal rat hepatocytes before the critical stage of glucocorticoid influences, some maturation occurs between the 15th and the 18th day of gestation, which is associated with an increase in cell sensitivity to dexamethasone and in the amplitude of the steroid-induced glycogenic response to insulin.

High plasma steroid levels in the squirrel monkey: deficient receptors or metabolism?

Many New World primates such as the squirrel monkey have extraordinarily high plasma steroid hormone levels as compared to humans and Old World primates. To clarify the mechanism(s) underlying this apparent steroid resistance, glucocorticoid and androgen binding to putative receptors in genital skin fibroblasts from several species was investigated. Differences in either affinity and/or number of binding sites were found but these were small compared to the very large differences in total or free plasma steroid concentrations between Old and New World primate species. In contrast, when the ability of fibroblasts to metabolize testosterone was compared, squirrel monkey cells were devoid of 5 alpha-reductase activity which was readily demonstrated in human cells. Together with other data indicating that squirrel monkeys excrete little if any 5 alpha- or 5 beta-reduced urinary steroid metabolites, these results suggest that inefficient metabolism rather than receptor binding abnormalities may account for the elevated plasma hormone levels in the squirrel monkey.

Cross-reactivity of a monoclonal antiglucocorticoid receptor antibody BuGR1 with glucocorticoid and mineralocorticoid receptors of various species

The reactivity of a monoclonal antibody BuGR1, raised against glucocorticoid receptors of rat liver, with glucocorticoid and mineralocorticoid receptors of mammalian (rabbit) and amphibian (A6 cells) origin was examined. The glucocorticoid receptors of rabbit kidney and liver and of A6 cells were labeled with tritiated dexamethasone. The mineralocorticoid receptors were labeled with tritiated aldosterone in the presence or absence of RU26988, depending on whether aldosterone was bound to glucocorticoid receptors (A6 cells) or not (rabbit kidney), in addition to its binding to mineralocorticoid receptors. BuGR1 did not recognize mineralocorticoid receptors of A6 cells and rabbit kidney. BuGR1 cross-reacted with glucocorticoid receptors of rabbit liver and kidney but not of A6 cells, suggesting that the domain of glucocorticoid receptors recognized by BuRG1 could be present only in the mammalian species. The findings indicate that BuGR1 shows species differences as well as receptor class specificity.

Antagonism of glucocorticoid induction of Epstein-Barr virus early antigens by different steroids in Daudi lymphoma cells

Four antiglucocorticoids, RU38486, RU5020, RU25055 and progesterone were found to antagonize the induction of latent Epstein-Barr virus (EBV) information by dexamethasone. The dose response studies show that the antagonization was more prominent with the synthetic steroids than with the natural hormone. Specific binding characteristics of dexamethasone measured in whole cells indicate the presence of glucocorticoid receptors. Total cellular receptor contents deduced from binding data give values similar to those reported for B-lymphoblasts. Competition experiments between dexamethasone and RU38436 strongly suggest that RU38486 binds to two distinct sites in the whole cell; one is the glucocorticoid receptor but the nature of the other site is unknown. Inhibition by antiglucocorticoids differs from antagonism by 12-O-tetradecanoyl-phorbol-13-acetate (TPA) since the latter does not compete for any sites interacting with RU38486.

Transplacental metabolism of dexamethasone and cortisol in the late gestational age rhesus monkey (Macaca mulatta)

The synthetic glucocorticoid dexamethasone (DEX) and endogenous cortisol were compared in 2 groups of pregnant monkeys of gestational age 143-148 days. In group I, a fetal intraplacental vein and a maternal femoral vessel were catheterized. 3H-Cortisol and 14C-DEX were administered intravenously along with 0.2 mg/kg unlabelled DEX to the mother. Blood and tissue samples were collected to 3 h and urine and feces to 96 h. In group II, 4 of the 7 animals were predosed with DEX 10 mg/kg s.c. for 3 days prior to surgery. The fetus was removed by cesarean section and the in situ placenta was perfused via the umbilical arteries at 15 ml/min X 8 min with 3H-cortisol/14C-DEX in Hanks' balanced salt solution. Samples were taken from the umbilical vein and uterine vein. In group I, HPLC analysis of paired maternal and fetal plasma samples taken at 10, 20, 60, 120 and 180 min after dosing indicated that the F/M DEX ratio was significantly greater than the F/M cortisol ratio. In fetal lung and liver tissues analyzed, less than 2% of the cortisol remained unmetabolized by 3 h, whereas greater than or equal to 76% DEX remained as parent compound. There was no significant difference between the percentage of DEX (83 +/- 7%) and cortisol (73 +/- 3%) recovery in maternal urine and feces. In group II, HPLC analysis of paired umbilical vein and uterine vein samples at 2, 4 and 8 min showed that by 8 min 24% of cortisol was converted to cortisone by the uteroplacenta, but only 2.5% of DEX was converted to a metabolite. In DEX-pretreated animals both uterine vein and umbilical vein samples indicated an increase in cortisol to cortisone conversion. A significant increase in DEX metabolism was evident in the uterine vein samples but not the umbilical vein. These data indicate that the fetus is exposed to a higher proportion of DEX than cortisol and that the uteroplacenta plays a larger role in cortisol than in DEX metabolism. In addition, these data suggest that DEX pretreatment enhances the ability of the uteroplacenta to convert cortisol to cortisone.

Regulatory changes in glucocorticoid receptors in the skeletal muscle of immature and mature male rats

Specific binding of [3H]dexamethasone to cytosol and translocation of bound receptor complexes to purified nuclei were studied in the skeletal muscle of immature (3-week) and mature (26-week) Long-Evans male rats. A marked decrease (57%) in the specific binding sites with no apparent change in dissociation constant (Kd) was observed in the skeletal muscle of mature rats compared to immature. Heat activation (25 degrees C for 45 min) significantly enhances the nuclear binding of steroid-receptor complexes in the skeletal muscle of rats of both the ages at almost similar level. Cross-mixing experiments (i.e. binding of activated cytosol from mature rats to nuclei of immature and vice-versa) gave similar values. Interestingly, Ca2+-activated (0 degree C for 45 min with 20 mM Ca2+) nuclear translocation was significantly higher (27%) in the skeletal muscle of immature rats compared to mature. Our results indicate that glucocorticoid receptor level and some physicochemical properties change with age in the skeletal muscle of rats.

The molybdate-stabilized glucocorticoid binding complex of L-cells contains a 98-100 kdalton steroid binding phosphoprotein and a 90 kdalton nonsteroid-binding phosphoprotein that is part of the murine heat-shock complex

This paper summarizes our work performed with glucocorticoid-binding complexes in molybdate-stabilized cytosol prepared from 32P-labeled L-cells. In our early work, we showed that cytosol prepared from 32P-labeled L-cells contains two phosphoproteins (a 90 and a 98-100 kdalton protein) that elute from an affinity resin of deoxycorticosterone agarose in a manner consistent with the predicted behavior of the glucocorticoid receptor. Both phosphoproteins are immunoadsorbed onto protein-A-Sepharose from molybdate-stabilized cytosol incubated with a monoclonal antibody against the receptor. The 98-100 kdalton phosphoprotein binds steroid and the 90 kdalton phosphoprotein is a structurally different, nonsteroid-binding protein that is bound to the untransformed, molybdate-stabilized glucocorticoid receptor. The 90 kdalton protein reacts on Western blots with a monoclonal antibody raised against a 90 kdalton protein from the water mold Achlya ambisexualis. This antibody recognizes an epitope that is conserved in 90 kdalton phosphoproteins from rodent and human cells, and it reacts with the 90 kdalton phosphoprotein that copurifies with the molybdate-stabilized, untransformed chick oviduct progesterone receptor. The 90 kdalton nonsteroid-binding phosphoprotein is an abundant cytosolic protein that dissociates from the glucocorticoid receptor when it is transformed, and unlike the steroid-binding protein, it does not bind to DNA. The 90 kdalton phosphoprotein determines the acidic behavior of the untransformed glucocorticoid receptor on DEAE-cellulose. This abundant cytosolic 90 kdalton phosphoprotein reacts with rabbit antiserum raised against the gel purified 89 kdalton chicken heat-shock protein (hsp89). This antiserum recognizes 90 kdalton heat-shock proteins in human, rodent, frog and Drosophila cells. Immunoadsorption of molybdate-stabilized cytosol with antibody directed against the 98-100 kdalton steroid receptor results in the immune-specific adsorption of a 90 kdalton phosphoprotein that reacts with anti-hsp89 antibody on Western blots. These observations suggest that, like the transforming proteins from several avian sarcoma viruses, the untransformed glucocorticoid receptor exists in a complex with the 90 kdalton heat-shock protein.