Effect of sulfhydryl reagents on mevalonate kinase partially purified from chicken liver

Unlike other vertebrate mevalonate kinase, the enzyme partially purified from neonatal chick liver was not activated by the -SH group protectors reduced glutathione, cysteine, dithiothreitol and beta-mercaptoethanol at any concentrations assayed (0.01-10.00 mM). However, the activity was found to be sensitive to thiol group binding reagents. p-Hydroxymercuribenzoate was the most active inhibitor. At 0.1 mM concentration, p-HMB completely abolished the enzyme activity. N-ethylmaleimide (0.01-1.00 mM) was practically ineffective. Inhibition by p-HMB was temperature dependent, being more potent at 37 degrees C than at 4 degrees C.     

Changes in the sedimentation properties of cytosolic androgen receptors associated with activation in vitro and in vivo

In cell-free systems androgen receptor (AR) labeled with (3H)DHT at 0 degrees C in the presence of 50mM molybdate remains unactivated (less than 3% binding to nuclei) and untransformed (7-8S on sucrose density gradients containing 0.4M KCl and 50mM molybdate). In the absence of molybdate, however, these complexes undergo activation and transformation even at 0 degrees C, albeit, very slowly. Incubation of unactivated, untransformed AR complexes at 18 degrees C, or at 0 degrees C in the presence of 0.4M KCl, greatly accelerated both activation and transformation. Activation and transformation are also associated with formation of high affinity (3H)DHT-receptor complexes as indicated by decreased rates of (3H)DHT dissociation from the receptor. Cytosolic AR complexes labeled with (3H)DHT in tissue slices at 37 degrees C, or in vivo, undergo rapid activation, transformation and nuclear translocation. The data suggest that activation and transformation of cytosolic AR in cell-free systems is associated with changes in the physicochemical properties of AR similar to those occurring upon hormone binding in intact cells and in vivo.     

Transformation of calf uterine progesterone receptor: analysis of the process when receptor is bound to progesterone and RU38486

Effects of different transforming agents were examined on the sedimentation characteristics of calf uterine progesterone receptor (PR) bound to the synthetic progestin [3H]R5020 or the known progesterone antagonist [3H]RU38486 (RU486). [3H]R5020-receptor complexes [progesterone-receptor complexes (PRc)] sedimented as fast migrating 8S moieties in 8-30% linear glycerol gradients containing 0.15 M KCl and 20 mM Na2MoO4. Incubation of cytosol containing [3H]PRc at 23 degrees C for 10-60 min, or at 0 degrees C with 0.15-0.3 M KCl or 1-10 mM ATP, caused a gradual transformation of PRc to a slow sedimenting 4S form. This 8S to 4S transformation was molybdate sensitive. In contrast, the [3H]RU486-receptor complex exhibited only the 8S form. Treatment with all three activation agents caused a decrease in the 8S form but no concomitant transformation of the [3H]RU486-receptor complex into the 4S form. PR in the calf uterine cytosol incubated at 23 or at 0 degrees C with 0.3 M KCl or 10 mM ATP could be subsequently complexed with [3H]R5020 to yield the 4S form of PR. However, the cytosol PR transformed in the absence of any added ligand failed to bind [3H]RU486. Heat treatment of both [3H]R5020- and [3H]RU486-receptor complexes caused an increase in DNA-cellulose binding, although the extent of this binding was lower when RU486 was bound to receptors. An aqueous two-phase partitioning analysis revealed a significant change in the surface properties of PR following both binding to ligand and subsequent transformation. The partition coefficient (Kobsd) of the heat-transformed [3H]R5020-receptor complex increased about 5-fold over that observed with PR at 0 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)     

Activation of [3H]estradiol--and [3H]H1285-receptor complexes: effect of salt versus ATP on molybdate-stabilized estrogen receptors

The activation by salt or ATP of [3H]estradiol- and [3H]H1285-receptor complexes from rabbit uterus and their binding capacity to DNA-cellulose, phosphocellulose and ATP-Sepharose has been studied. The estrogen-receptor was prepared in 1 mM molybdate which stabilized the receptor; but both salt- and ATP-transformation of estrogen receptors occurred. The binding of molybdate-stabilized cytosol [3H]estradiol-receptor complexes to the various resins revealed that salt-activation by 0.3 M KCl caused the greatest binding (5-6-fold) to DNA-cellulose as compared to other resins. However, 5 mM ATP-dependent activation of receptor-complexes resulted in preferential binding to ATP-Sepharose. Activated cytosol [3H]H1285-receptor complexes bound all the resins to a lesser degree when compared to [3H]estradiol-receptor complexes. Partially purified receptor complexes also showed different resin-binding patterns for salt- and ATP-mediated activation. These findings suggest that salt-activation is different than ATP-activation. Further, the differential magnitude of [3H]estradiol- and [3H]H1285-receptor activation suggests that estrogen-receptor complexes are "fully" activated as compared to "partially" activated antiestrogen-receptor complexes.     

Characterization of the parameters affecting covalent binding stoichiometry in binary and ternary complexes of thymidylate synthase

Covalent binding stoichiometries for both the enzyme:5-fluoro-2'-deoxyuridine 5'-monophosphate (FdUMP) binary complex and the enzyme:FdUMP:5,10-methylenetetrahydrofolate (inhibitory ternary) complex at equilibrium were measured by the trichloroacetic acid precipitation assay and shown to be a function of temperature, time, pH, salt concentration, buffer composition and thiol concentration. Incubation at 37 degrees C yielded the maximum covalent binding ratio (mol FdUMP/mol enzyme) for the latter binary (0.7) and ternary (1.7) complexes. In most buffers studied, the maximum covalent binding ratio (1.5-1.7) for the inhibitory ternary complex occurred over a broad pH range (4.5-8.0), while the optimum covalent binding ratio for binary complex was observed at a much narrower region centered between pH 5.5-6.5. In the presence of increasing concentrations of phosphate buffer, the maximum binding ratio for the covalent binary complex decreased from 0.63 in the absence of phosphate to 0.1 in the presence of 225 mM phosphate, while that for the inhibitory ternary complex was unchanged. When a ternary complex was formed with enzyme, FdUMP and (+/-)-tetrahydrofolate in the absence of phosphate, the FdUMP:enzyme covalent binding ratio was 1.8, while in the presence of 75 mM phosphate, the binding ratio was only 1.0. When exogenous thiol was removed by centrifugal column chromatography, the maximum binding stoichiometry of the resulting inhibitory ternary complex was 1.7 and was independent of added thiol over a 2 h incubation period at 37 degrees C. When extensive dialysis at 5 degrees C was used to remove the thiol, the maximum binding stoichiometry of the resulting inhibitory ternary complex was found to be dependent on both the concentration of added thiol and the time of incubation at 37 degrees C and did not exceed a value of 1.0.     

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.     

Relationship between glucocorticoid receptor steroid-binding capacity and association of the Mr 90,000 heat shock protein with the unliganded receptor

Treatment of rat liver cytosol with hydrogen peroxide (H2O2) or sodium molybdate (MoO4(2-)) inhibits thermal inactivation of glucocorticoid receptor steroid-binding capacity at 25 degrees C. Dithiothreitol (DTT) prevents the stabilization of receptors by H2O2. Heating (25 degrees C) of immune pellets formed by immunoadsorption of L-cell murine glucocorticoid receptor complexes to protein-A-Sepharose with an anti-receptor monoclonal antibody (BuGR2) results in dissociation of the M 90,000 heat shock protein (hsp90) from the steroid binding protein. Such thermal-induced dissociation of hsp90 is inhibited by H2O2. Pretreatment of immunoadsorbed receptor complexes with the thiol derivatizing agent, methyl methanethiosulfonate (MMTS) prevents the ability of H2O2 to stabilize the hsp90-receptor interaction. These data suggest a role for hsp90 in maintaining an active steroid-binding conformation of the glucocorticoid receptor.     

Interaction of the radiolabelled high-affinity anti-oestrogen [3H]H1285 with the cytoplasmic oestrogen receptor.

The high-affinity triarylethylene anti-oestrogen H1285 [4-(NN-diethylaminoethoxy)-beta-ethyl-alpha-(p-hydroxyphenyl) -4'-methoxystilbene] was tritiated to high specific radioactivity (35 Ci/mmol). Competition experiments between [3H]H1285 and H1285 or oestradiol demonstrated that both compounds would compete with [3H]H1285 for oestrogen-specific binding sites in rat uterine cytosol. [3H]H1285 had at least 10 times the affinity for the receptor compared with oestradiol at the 50% competition level. [3H]H1285 appeared to have at least twice the association rate for the oestrogen receptor compared with [3H]oestradiol. In addition, the dissociation half-life (t1/2) of specific binding of [3H]H1285 to oestrogen receptors at 0 degrees C was about 220 h compared with a value of 60 h for [3H]oestradiol. Because of the extremely slow dissociation of [3H]H1285 from the oestrogen receptor, we were able to compare the sedimentation profiles of [3H]H1285-receptor complexes with those of [3H]oestradiol-receptor complexes in the presence of 0.4 M-KCl on 5-20% sucrose density gradients. [3H]Oestradiol-receptor complexes had a major peak at 4.4 S with a smaller peak at 5.6 S, whereas with [3H]H1285-receptor complexes the 5.6 S peak was always higher than the 4.4 S peak. There was significant variation between the dissociation behaviour at 20 degrees C of [3H]H1285-receptor complexes and [3H]oestradiol-receptor complexes pre-activated at 25 degrees C for 30 min in the presence and in the absence of 10 mM-sodium molybdate. The dissociation t1/2 of [3H]oestradiol-receptor complexes at 20 degrees C decreased from 1.5 h to 0.5 h when molybdate was present during heat treatment whereas the dissociation t1/2 for [3H]H1285-receptor complexes was 5 h for both conditions. These observations indicate that there are fundamental differences in the initial interaction of H1285 and oestradiol with the oestrogen receptor.     

Characterization of mevalonate-activating enzymes in the neonatal chick liver.

1. The 5-phosphomevalonate (MVAP) and 5-pyrophosphomevalonate (MVAPP) formation by cell-free extracts from 7-10 days chick liver shows an absolute nucleotide requirement, ATP being the most effective phosphate donor, though ITP and UTP can be used less effectively. 2. Mn2+ is a better activator than Mg2+ at low concentrations (0.1-5.0 mM). At higher concentrations (10.0 mM) Mn2+ produces a clear decrease in the MVAP formation, whereas the maximum MVAPP formation occurs in the presence of 10.0 mM Mg2+. 3. Mevalonate-activating enzymes maintain their activities for 48 hr at 4 degrees C and 24 hr at 37 degrees C. No MVAP is formed when the extracts are heated to 65 degrees C for 10 min. 4. Unlike other vertebrate mevalonate and phosphomevalonate kinases, these enzymes from chick liver are not activated by -SH group protectors as dithiothreitol, reduced glutathione, cysteine or beta-mercaptoethanol. However, the enzymes are found to be sensitive to thiol binding reagents p-hydroxymercuribenzoate and 5,5'-dithiobis-(2-nitrobenzoic acid).     

Binding of [3H]estradiol- and [3H]H1285-receptor complexes to rabbit uterine chromatin

In the present study we investigated the binding characteristics of estrogen and antiestrogen-receptor complexes to rabbit uterine chromatin. Activated or nonactivated estrogen receptors were partially purified by DEAE-cellulose chromatography using low (1 mM) or high (10 mM) concentrations of sodium molybdate. Activated [³H]estradiol-receptor complexes showed enhanced binding to chromatin acceptor sites unmasked by 1 M, 4 M and 6 M guanidine hydrochloride. We also examined the chromatin-binding characteristics of the estrogen receptors when bound by the high-affinity triphenylethylene antiestrogen, H1285. The acceptor site activity for the [³H]H1285-receptor complexes was markedly decreased at sites unmasked by 4 M and 6 M guanidine hydrochloride. Further, the nonactivated receptor complexes showed very low binding to deproteinized chromatin. The estrogen-receptor chromatin-acceptor sites were tissue specific and saturable. These chromatin acceptor sites differ in their affinity and capacity (number of binding sites per cell) for the estrogen- and antiestrogen-receptor complexes. Thus, we suggest that the differences in the physiological and physicochemical properties of estrogens and antiestrogens may be related to their differential interaction with uterine chromatin subfractions.     

Binding of [3H]triamcinolone acetonide-receptor complexes to chromatin from the B-cell leukemia line, BCL1

The binding characteristics of partially purified glucocorticoid receptor complexes from hormone sensitive, non-differentiating BCL1 cells to sequentially deproteinized BCL1 chromatin-cellulose was investigated. [3H]Triamcinolone acetonide (TA)-receptor complexes were purified (approx. 30-fold) from DEAE-cellulose columns by salt elution which allowed receptor activation only in the absence of molybdate. Addition of 10 mM molybdate completely blocked salt activation. The binding pattern of the activated [3H]TA-receptor complexes to chromatin-cellulose extracted with 0-8 M guanidine hydrochloride revealed three regions of increased binding activity (acceptor sites), at 2, 5 and 7 M guanidine hydrochloride. Acceptor site binding was markedly reduced for chromatin extracted with 3, 6 and 8 M guanidine hydrochloride. Non-activated receptor complexes demonstrated very low binding to deproteinized chromatin. It was also shown that chromatin binding required glucocorticoid receptors and that free ligand or ligand bound to other proteins did not bind significantly to chromatin. In addition, binding of [3H]TA-receptor complexes to partially deproteinized chromatin was competable by unlabeled TA-receptor complexes. Scatchard analysis demonstrated that chromatin from non-differentiating BCL1 cells possesses multiple, high-affinity binding sites which differ in their affinity for the glucocorticoid receptor. Partially deproteinized chromatin from lipopolysaccharide-stimulated BCL1 cells demonstrated a different pattern of receptor binding, i.e., receptor binding was significantly greater to chromatin previously extracted with 6-8 M guanidine hydrochloride. These results suggest that differentiation alters the state of chromatin and the interaction of non-histone protein/DNA acceptor sites with glucocorticoid receptors. These alterations may play a role in the acquisition of hormone resistance.     

In vitro activation of rat cardiac glucocorticoid antagonist- versus agonist-receptor complexes

The synthetic antiglucocorticoid RU 38486 interacts with cardiac cytoplasmic glucocorticoid receptors and competes for in vitro binding with the potent agonist triamcinolone acetonide. In addition to binding to receptors with high affinity, RU 38486 also facilitates the in vitro conformational change in the receptor which is a consequence of the physiologically relevant activation step during which the receptor is converted from a non DNA- to a DNA-binding form. This ability of RU 38486 to promote receptor activation is reflected by both the appropriate shift in the elution profile of [3H]RU 38486-receptor complexes from DEAE-cellulose as well as by an increased binding of these complexes to DNA-cellulose. Although less effective than triamcinolone acetonide, RU 38486 promotes in vitro receptor activation under a variety of experimental conditions, including incubation of labeled cardiac cytosols at 25 degrees C for 30 min or at 15 degrees C for 30 min in the presence of 5 mM pyridoxal 5'-phosphate. Once thermally activated, the cardiac [3H]triamcinolone acetonide and [3H]RU 38486-receptor complexes bind to nonspecific DNA-cellulose with the same relative affinities, as evidenced by the fact that 50% of both activated complexes are eluted at approx. 215-250 mM NaCl. Thus, this pure antiglucocorticoid does promote, at least to some extent, many of the crucial in vitro events including high-affinity binding, activation, and DNA binding which have been shown to be required to elicit a physiological response in vivo.     

Interaction of the antiestrogen [3H]H1285 with the two forms of the molybdate-stabilized calf uterine estrogen receptor

The high affinity antiestrogen [3H]H1285 bound to the cytosol calf uterine estrogen receptor dissociated very slowly (t 1/2 approx 30 h at 20 degrees C) and did not demonstrate a change in dissociation rate in the presence of molybdate, which is characteristic of [3H]estradiol-receptor complexes. [3H]H1285-Receptor complexes sediment at approx 6S on 5-20% sucrose density gradients containing 0.3M KCl with or without 10 mM molybdate. This is in contrast to [3H]estradiol-receptor complexes which sedimented at approx 4.5S without molybdate and at approx 6S with molybdate. These results suggest a physicochemical difference in the estrogen receptor when occupied by antiestrogens versus estrogens. We recently reported that the cytoplasmic uterine estrogen receptor, when bound by estradiol and prepared in 10 mM molybdate, eluted from DEAE-Sephadex columns as Peak I (0.21 M KCl) & Peak II (0.25 M KCl). However, [3H]H1285 bound to the estrogen receptor eluted only as one peak at 0.21 M KCl, also suggesting that the initial interaction of antiestrogens with the estrogen receptor is different. We have extended these studies and report that H1285 can compete with [3H]estradiol for binding to both forms of the estrogen receptor and [3H]H1285 can bind to both forms if the unoccupied receptor is first separated by DEAE-Sephadex chromatography. However, if the receptor is first bound by unlabeled H1285, eluted from the column and post-labeled by exchange with [3H]estradiol, only one peak is measured. Thus, it appears that H1285 binding alters the properties of the receptor such that all receptor components seem to elute as one form. These partially purified [3H]H1285-receptor complexes obtained from DEAE-Sephadex columns sedimented as 5.5S in sucrose density gradients in contrast to the sedimentation values for the [3H]estradiol-receptor components eluting as Peak I (4.5S) and Peak II (6.3S). These differences in the physicochemical characteristics of the estrogen receptor when bound by estrogen versus antiestrogens may be related to some of the biological response differences induced by these ligands.     

Activation of cytosol aldosterone receptors in rat kidney

Cytosolic aldosterone-protein complexes are isolated from rat kidney slices after incubation with [3H]aldosterone and dexamethasone. Activated and unactivated forms of the complex are characterized by gel electrophoresis and hydroxyapatite chromatography after incubation at 4 degrees C and 25 degrees C respectively. It is found that the activated form reaches a maximum after 30 min at 25 degrees C and can be separated as an homogeneous peak by electrophoresis. Intermediate forms can also be identified. In the presence of 10 mM ATP, activation immediately occurs at 4 degrees C and is almost complete. In the presence of 10 mM molybdate, the activation is strongly enhanced and the increase in activated form may be about fifteen-fold whether molybdate is added during kidney homogenization or just before incubation at 25 degrees C. On the other hand molybdate reduces to one third the binding of the aldosterone-receptor complexes to nuclei. In the presence of the steroid RU 26988 which is a pure glucocorticoid, experiments done on aldosterone-receptors complexes and their binding to nuclei are confirmed. This proves that aldosterone is specific for mineralocorticoid sites. The general pattern of the mineralocorticoid receptor activation is discussed and its resemblance to the case of other steroid hormones is emphasized.     

Stabilization of soluble active rat liver glucagon receptor

Active glucagon receptor was solubilized with 3-(3-cholamidopropyl)dimethylammonio-1-propanesulfonate (Chaps) from rat liver plasma membranes but rapidly (less than 8 h) lost activity. Either inclusion of 1X Hanks' balanced salt solution in the 3 mM Chaps solubilization buffer or its addition after solubilization increased the percentage of total binding attributable to specific glucagon binding from approximately 10 to greater than 80%; of great importance, it increased the stability from near zero binding at 8 h to 50% binding at 48 h (4 degrees C). Of the Hanks' solution components, either NaCl (137 mM) or CaCl2 (1.26 mM) was effective in increasing specific binding to approximately 70 and 60% respectively: Mg salts were ineffective. Soluble receptor binding activity was assayed by dextran-coated charcoal adsorption of free hormone. The assay is rapid, simple, and reproducible. It is suitable for monitoring receptor activity during purification and molecular characterization. Competition binding studies gave an IC50 value of 10-20 nM (slope factor approximately 1), with or without GTP. Dissociation assays revealed GTP sensitivity when receptors were solubilized either as glucagon-receptor complexes or free receptor. Active glucagon-receptor complexes could be eluted from wheat germ lectin-agarose: neither concanavalin A-agarose nor soybean agglutinin-agarose bind receptor. A glucagon degrading activity which co-solubilized with the receptor but did not require detergent for extraction was distinguishable from the soluble receptor not only by solubility but also by its heat stability (30 degrees C), its inhibition by bacitracin, its affinity for glucagon, its retention of activity for at least 1 week at 4 degrees C, and its size.     

Mammalian progesterone receptor shows differential sensitivity to sulfhydryl group modifying agents when bound to agonist and antagonist ligands

Modulation of calf uterine progesterone receptor (PR), in relation to its binding to synthetic steroids with known agonist (R5020) and antagonist (RU486) properties, was studied in the presence of iodoacetamide (IA), N-ethylmaleimide (NEM), beta-mercaptoethanol (MER), and dithiothreitol (DTT). Pretreatment of uterine cytosol at 4 degrees C with NEM (4-10 mM) reduced the binding of [3H]RU486 to PR by 40%, but [3H] R5020 binding was completely abolished. Whereas IA (2-10 mM) treatment did not affect [3H]RU486 binding, [3H]R5020 binding was totally eliminated. DTT or MER increased the binding of both steroids slightly (15%). [3H]R5020- or [3H]RU486-receptor complexes (Rc) migrated in the 8 S region and were eliminated upon pretreatment with NEM. At 23 degrees C, DTT increased the amount of 4 S [3H]R5020-Rc, but had no effect on the [3H]RU486-Rc. In the control, [3H]RU486 binding to the 8 S PR could be competed with radioinert R5020 or RU486, but R5020 failed to compete in the presence of IA. The heat-treated [3H]R5020- and [3H]RU486-Rc showed reduced binding to DNA-cellulose in the presence of NEM and IA. The results of our study suggest that SH group modifications differentially influence the properties of mammalian PR complexed with either R5020 or RU486. In the presence of IA, the [3H]RU486-Rc remained in the 8 S form when incubated at 23 degrees C, indicating that RU486 binding causes conformational changes in PR which are distinct from those that result upon R5020 binding.     

Evidence that the 90-kDa heat shock protein is necessary for the steroid binding conformation of the L cell glucocorticoid receptor

Using L cell glucocorticoid receptors that have been immunopurified by adsorption to protein A Sepharose with a monoclonal antireceptor antibody, we have developed an assay to study the requirements for maintenance of steroid-binding capacity. After rapid purification by immunoadsorption, heteromeric receptor complexes retain the ability to bind glucocorticoid hormone. When the receptor complexes are warmed at 20 degrees C, steroid-binding capacity is lost, and the 90-kDa heat shock protein (hsp90) dissociates from the receptor. The rates of both temperature- and salt-dependent dissociation of hsp90 parallel the rates of loss of hormone-binding activity. Molybdate and hydrogen peroxide stabilize the hsp90-receptor complex against temperature-dependent dissociation. Molybdate, however, is much more effective in stabilizing steroid-binding capacity than peroxide. Receptors that have been inactivated in the absence of molybdate or peroxide cannot be reactivated. Inactivation of steroid-binding capacity occurs in the presence or absence of reducing agent, and inactivation is not accompanied by receptor cleavage or dephosphorylation. Under no conditions does an hsp90-free receptor bind steroid. Receptor bound to hsp90 can be cleaved to the 27-kDa meroreceptor in the presence of molybdate with retention of both hsp90 and steroid-binding activity. These observations lead us to propose that hsp90 is necessary but not sufficient for maintaining a competent high affinity glucocorticoid-binding site. Although the 27-kDa meroreceptor fragment is not itself sufficient for a competent binding site, it is sufficient when it is associated with hsp90.     

Characterization of R5020 and RU486 binding to progesterone receptor from calf uterus

We have examined and compared the binding characteristics of the progesterone agonist R5020 [promegestone, 17,21-dimethylpregna-4,9(10)-diene-3,20-dione] and the progesterone antagonist RU486 [mifepristone, 17 beta-hydroxy-11 beta-[4-(dimethylamino) phenyl]-17 alpha-(prop-1-ynyl)-estra-4,9-dien-3-one] in calf uterine cytosol. Both steroids bound cytosol macromolecule(s) with high affinity, exhibiting Kd values of 5.6 and 3.6 nM for R5020 and RU486 binding, respectively. The binding of the steroids to the macromolecule(s) was rapid at 4 degrees C, showing saturation of binding sites at 1-2 h for [3H]progesterone and 2-4 h for both [3H]R5020 and [3H]RU486. Addition of molybdate and glycerol to cytosol increased the extent of [3H]R5020 binding. The extent of [3H]RU486 binding remained unchanged in the presence of molybdate, whereas glycerol had an inhibitory effect. Molybdate alone or in combination with glycerol stabilized the [3H]R5020- and [3H]RU486-receptor complexes at 37 degrees C. Although the rate of association of [3H]RU486 with the cytosolic macromolecule was slower than that of [3H]R5020, its dissociation from the ligand-macromolecule complex was significantly slower than [3H]R5020. Competitive steroid binding analysis revealed that [3H]progesterone, [3H]R5020, and [3H]RU486 compete for the same site(s) in the uterine cytosol, suggesting that all three bind to the progesterone receptor (PR). Sedimentation rate analysis showed that both steroids were bound to a molecule that sediments in the 8S region. The 8S [3H]R5020 and [3H]RU486 peaks were abolished by excess radioinert progesterone, RU486, or R5020.(ABSTRACT TRUNCATED AT 250 WORDS)     

Binding of [3H]triamcinolone acetonide-receptor complexes to chromatin from the B-cell leukemia line,BCL1

The binding characteristics of partially purified glucocorticoid receptor complexes from hormone sensitive, non-differentiating BCL₁ cells to sequentially deproteinized BCL₁ chromatin-cellulose was investigated. [³H]Triamcinolone acetonide (TA)-receptor complexes were purified (approx. 30-fold) from DEAF-cellulose columns by salt elution which allowed receptor activation only in the absence of molybdate. Addition of 10 mM molybdate completely blocked salt activation. The binding pattern of the activated [³H]TA-receptor complexes to chromatin-cellulose extracted with 0–8 M guanidine hydrochloride revealed three regions of increased binding activity (acceptor sites), at 2, 5 and 7 M guanidine hydrochloride. Acceptor site binding was markedly reduced for chromatin extracted with 3, 6 and 8 M guanidine hydrochloride. Non-activated receptor complexes demonstrated very low binding to deproteinized chromatin. It was also shown that chromatin binding required glucocortical receptors and that free ligand or ligand bound to other proteins did not bind significantly to chromatin. In addition, binding of [³H]TA-receptor complexes to partially deproteinized chromatin was competable by unlabeled TA-receptor complexes. Scatchard analysis demonstrated that chromatin from non-differentiating BCL₁ cells possesses multiple, high-affinity binding sites which differ in their affinity for the glucocorticoid receptor. Partially deproteinized chromatin from lipopolysaccharide-stimulated BCL₁ cells demonstrated a different pattern of receptor binding, i.e., receptor binding was significantly greater to chromatin previously extracted with 6–8 M guanidine hydrochloride. These results suggest that differentiation alters the state of chromatin and the interaction of non-histone protein/DNA acceptor sites with glucocorticoid receptors. These alterations may play a role in the acquisition of hormone resistance.     

Inhibition of phosphate transport in human erythrocytes by 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl)

Treatment of intact human erythrocytes with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) leads to inhibition of anion transport as measured by [32P]phosphate exchange for intracellular chloride. Inhibition is rapid at 37 degrees C (80% inhibition, 1.7 mM NBD-Cl, 3 min, pH 6.9) and not reversed by washing the cells with 1% bovine serum albumin in isotonic sucrose citrate buffer. Pretreatment of cells with N-ethylmaleimide and p-chloromercuribenzenesulfonic acid enhanced transport inhibition by NBD-Cl. Transport inhibition caused by brief incubations of erythrocytes with NBD-Cl could be almost completely reversed with dithiothreitol or beta-mercaptoethanol. Prolonged incubation (60 min, 37 degrees C, pH 6.4, sucrose-citrate buffer) following NBD-Cl treatment leads to partial reversal of transport inhibition. The residual inhibition is then only partially reversed by dithiothreitol treatment. Reversal of transport inhibition of dithiothreitol or beta-mercaptoethanol may be prevented by incubation of the erythrocytes with sodium dithionite. Phosphate transport was readily inhibited by other tyrosine-directed reagents, tetranitromethane (55% inhibition, 1.6 mM, 3 min, 37 degrees C, pH 8.3 in sucrose-citrate medium) and p-nitrobenzene sulfonyl fluoride (31% inhibition, 1.8 mM, 3 min, 37 degrees C, pH 8.1 in sucrose-citrate medium) but not by N-acetylimidazole (10% inhibition, 37.5 mM, 30 min, 37 degrees C, pH 7.5). These results suggest that NBD-Cl inhibits anion exchange by two mechanisms; a rapid inhibition reversible by sulfhydryl reagents, possibly due to modification of a tyrosine residue(s), and a slower irreversible inhibition due to modification of an essential amino group in the transporter.