Analysis of glucocorticoid receptor activation by high resolution two-dimensional electrophoresis of affinity-labeled receptor

To determine if activation of the glucocorticoid receptor involves covalent charge modification of the steroid-binding protein, unactivated and activated IM-9 cell glucocorticoid receptors were examined by high resolution two-dimensional gel electrophoresis. As previously reported (Smith, A. C., and Harmon, J. M. (1985) Biochemistry 24, 4946-4951), two-dimensional electrophoresis of immunopurified, [3H]dexamethasone mesylate-labeled, steroid-binding protein from unactivated receptors resolves two 92-kDa isoforms (pI congruent to 5.7 and 6.0-6.5). After activation, the apparent pI of neither isoform was altered, indicating that there had been no covalent charge modification of the steroid-binding protein. Thus, the physicochemical changes observed after activation of the steroid receptor cannot be explained by dephosphorylation or other models which involve covalent charge modification of the steroid-binding protein. This conclusion was consistent with the observation that treatment of immunopurified, affinity-labeled receptors with calf intestine alkaline phosphatase did not alter the apparent pI values or distribution of the steroid-binding protein isoforms. However, chromatography of activated steroid-receptor complexes on DNA-cellulose revealed that only the more basic of the two steroid-binding protein isoforms bound to DNA. Therefore, the charge heterogeneity of the steroid-binding protein may be important in regulating the ability of the steroid-binding protein to interact with DNA.

Cleavage of the rat intestinal 1,25-dihydroxyvitamin D3 receptor by an endogenous protease to a form with defective DNA binding

In this report we describe a form of the 1,25(OH)2D3 receptor which no longer binds to DNA. The defective form of the receptor was produced by the action of an endogenous protease. Rat intestinal receptors, obtained by a two-step procedure of a low salt homogenization followed by extraction of the chromatin pellet with high salt, fail to bind to DNA-cellulose. Inclusion of various serine protease inhibitors during the preparation protects against the loss of DNA binding. Sedimentation analysis in sucrose gradients indicates that the defective receptor is measurably smaller than the native receptor and is unable to aggregate normally under low salt conditions. The size difference, as determined by gel chromatography, is approximately 9,000 Da (56,000 for the protected receptor, 47,000 for the cleaved form). The elution from DEAE-cellulose indicates that the overall charge of both intact and cleaved receptor forms is very similar. Cell fractionation and mixing experiments suggest the enzyme may be located in the lysosomal compartment, organelles which are susceptible to breakage during the extraction procedure. The results demonstrate that an endogenous enzyme preferentially cleaves the 1,25(OH)2D3 DNA binding site resulting in a receptor with altered characteristics. Such an enzymatic activity has not been previously described for the 1,25(OH)2D3 receptor from other tissues or species. Since rat intestine is a classically studied target organ, these findings have additional relevance in receptor purification or other studies to characterize the receptor.

Specific binding of estrogen receptor to sites upstream and within the transcribed region of the chicken ovalbumin gene

By means of the DNA-cellulose competitive binding assay, the interaction of estrogen receptor complexed to 17 beta-estradiol with fragments of a cloned DNA region of the estrogen responsive chicken ovalbumin gene spanning from 1343 bps upstream to 373 bps within the transcribed region of the gene (p0V 1.7) was investigated. Only DNA fragments including either the 5'-flanking region from -21 to -140 bps or the region within the gene from +41 to +143 bps showed binding affinity for the estrogen receptor higher than calf thymus DNA. DNA fragments from human alpha 1-globin gene and glucocorticoid responsive murine mammary tumor provirus corresponding to the same DNA region investigated for ovalbumin showed affinity for the estrogen receptor no higher than that of calf thymus DNA. These results suggest that two specific binding sites for estrogen receptor are located upstream and within the ovalbumin gene, near the start-site of transcription. These receptor binding sites overlap with the 'estrogen response element' identified by Dean et al. (1) and the DNase I Hypersensitive region I found by Kaye et al. (2).

Characterization of the partially purified, ligand-free glucocorticoid receptor

A new method was developed to synthesize a cortexolone-substituted affinity matrix, based on the fast, mild and quantitative reaction between alpha-ketomesylates and thiols. The resulting cortexolone-Sepharose absorbed easily the cytosolic chick thymus glucocorticoid receptor. Owing to the relatively fast dissociation of the glucocorticoid receptor-cortexolone complex, glucocorticoid receptor could be eluted with cortexolone as well as with triamcinolone acetonide from the affinity gel with similarly good yields. We obtained 75-150-fold purification factors (yield: 20-30%) using this column procedure. The partially purified glucocorticoid receptor was obtained in non-activated form. It had a Stokes radius of 6.2 +/- 0.1 nm. It could be activated to DNA-cellulose binding form by heat or 0.3 M KCl. KCl treatment activated 30-50% of the partially purified glucocorticoid receptor. Heat activation, however, was rather poor. Cortexolone-complexed, partially purified glucocorticoid receptor dissociated easily, and partially purified free glucocorticoid receptor, capable of steroid binding, could be obtained. Binding properties of the partially purified glucocorticoid receptor were then analyzed using different steroids. Dissociation rate constants were similar to those of the cytosolic glucocorticoid complexes. Association rate constants were consistently smaller than in the case of cytosolic glucocorticoid receptor, but the relative order of rates for different steroids was basically the same for glucocorticoid receptor in the two studied systems.

Solubilization of 1,25-dihydroxyvitamin D3 receptor with pyridoxal 5'-phosphate from hen intestinal mucosa

1,25-Dihydroxyvitamin D3(1,25-(OH)2D3) receptor was solubilized in cytosol fractions upon homogenization of hen intestinal mucosa with pyridoxal 5'-phosphate contained in a low ionic strength buffer. Pyridoxal 5'-phosphate did not inhibit the binding of 1,25-(OH)2D3 to its receptor. The receptor solubilized with pyridoxal 5'-phosphate was similar to the KCl-solubilized receptor in its binding affinity to the hormone and sedimentation coefficient. A majority (greater than 90%) of the mucosal 1,25-(OH)2D3 receptors were obtained as associating with crude chromatin which was prepared with a low ionic strength buffer, and this fraction of the receptor was solubilized with pyridoxal 5'-phosphate. Ten millimolar pyridoxal 5'-phosphate was as effective as approx 0.2 M KCl in solubilizing the receptor from the crude chromatin. Pyridoxal 5'-phosphate also showed a potency to dissociate the 1,25-(OH)2D3-receptor complex previously bound to DNA-cellulose. Pyridoxal 5'-phosphate-related compounds such as pyridoxamine 5'-phosphate and pyridoxal did not show this potency. These results suggest that pyridoxal 5'-phosphate reduced the interaction of 1,25-(OH)2D3 receptor with its nuclear binding components without inhibiting the binding of the receptor to the hormone.

Steroid hormone receptor regulation by various hormonal factors during mammary development and growth in the normal mouse

The studies described herein are focused on the nature and regulation of estrogen receptors in normal mammary tissue, with the rationale that manipulation of these receptors is the sole basis for endocrine therapy of human breast cancer. Various features of this complex system have been uncovered by our studies. The presence of different forms of cytosol estrogen receptor, fluctuating in unison with glandular stimulation, results in differential responsiveness of the cells. Tissue that is relatively estrogen-starved presents its receptors in a form that avidly attract the limited available ligands and can hastily put them to use in the nucleus. In contrast, the receptor system in the highly stimulated state displays a sort of refractoriness to estrogen, being relatively sluggish in its responsiveness. Once formed, however, these latter complexes are probably far more effective in terms of eliciting estrogenic responses, since they have an enhanced affinity for DNA and a prolonged half-life. (Table; see text) Prolactin is clearly a very important mediator of the action of estrogen on the mammary gland estrogen receptors, presenting a tissue-specific difference in comparison with the regulation of the uterine estrogen-receptor system. An odd finding was that prolactin inhibits nuclear retention of the estrogen receptor (and probably the progesterone receptor), an effect that is counterproductive to its very strong positive action on the level of intracellular receptor. Perhaps prolactin is the gross effector of receptor fluctuation, allowing estrogen the privilege of dictating the degree of receptor function; indeed our data on the dose-responsiveness of estrogen action and the effects of bromocriptine indicate that a portion of the estrogenic stimulation is not mediated by prolactin. An interesting sidelight of these studies was the finding that high levels of bromocriptine, pharmacologic in terms of prolactin suppression, exhibited an inhibitory effect on nuclear retention of estrogen receptors that was independent of, and did not prevent subsequent elicitation of, the action of prolactin on the receptors. The role of prolactin in tumorigenesis is well established in experimental animals, but its role in the human disease is not clear. Although prolactin receptors have been measured in human breast cancer, there does not appear to be any distinguishable correlation with the presence of estrogen or progesterone receptors. While it is a bit premature to draw conclusions, initial trials of bromocriptine usage have not been supportive of beneficial effects of such treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Physical-chemical properties of the estrogen receptor released by deoxyribonuclease I

The physical-chemical properties of the nuclear estrogen receptor released by DNase I were characterized. Nuclei were isolated from MCF-7 cells previously exposed to 10-nM-[3H]estradiol. The parameters determined were: sedimentation coefficients (S) on a sucrose gradient, Stokes radii (Rs) by gel filtration on a Sephadex G-200 column and the binding ability to a DNA-cellulose column. The molecular weights (Mr) and frictional ratios (f/fo) were calculated from the S and Rs values. The properties of the receptor released by DNase I obtained from Worthington were compared to the properties of the receptor released by DNase I obtained from Sigma. Digestion with DNase I (Worthington) excised a receptor form which could be solubilized from nuclei by EDTA. This form sedimented at 5.2S with a Rs = 7.08 nm and a calculated Mr = 152.000. About 40% of this receptor form bound to a DNA-cellulose column. 0.4 M KCl dissociated this receptor form into a smaller form sedimenting at 4.2S with Rs = 4.64 nm and a calculated Mr = 80.000. The properties of the receptor solubilized by micrococcal nuclease followed by DNase I (Worthington) digestion were identical to the properties of the DNase I (Worthington) released receptor. Digestion with DNase I (Sigma) released a 3.2S receptor form, which diffused through the nuclear membrane and a 4-5S form which could be extracted from nuclei by EDTA. The 3.2S receptor had a Rs = 2.41 nm, a calculated Mr = 32.000 and less than 5% of it bound to a DNA-cellulose column. Digestion with micrococcal nuclease followed by DNase I (Sigma) solubilized a receptor form with identical properties to the 3.2S receptor. These results suggest that DNase I (Worthington) released a receptor form still associated with some molecules, probably chromatin proteins, which complexed it to DNA, while DNase I (Sigma) released the estradiol binding fragment of the receptor (meroreceptor) as a result of a proteolytic activity present in this preparation.

1 alpha,25-Dihydroxyvitamin D3-binding macromolecules in human B lymphocytes: effects on immunoglobulin production

Previous studies have indicated that upon in vitro activation with mitogenic lectins, human peripheral blood T lymphocytes express receptors for the steroid hormone 1 alpha, 25-dihydroxyvitamin D3(1,25(OH)2D3). Furthermore, the hormone can inhibit interleukin 2 production by the activated cells. In this investigation, we report that human peripheral B lymphocytes activated in vitro with the B lymphotropic Epstein-Barr virus (EBV) also express 1,25(OH)2D3 receptor-like macromolecules. These receptors are localized in the cell nucleus and exhibit properties similar to those found in classical target tissues for 1,25(OH)2D3. They sediment on sucrose gradients at 3.3 S, display a dissociation constant (Kd) of 4 X 10(-10) M, and can bind to DNA. In addition to the 1,25(OH)2D3 receptors, however, EBV-activated lymphocytes express a second class of 1,25(OH)2D3-binding proteins that appear to occur mainly in the cell cytosol and exhibit distinct biochemical properties from the receptor, including higher sedimentation coefficients (3.7 S to 4 S) and the lack of ability to bind to DNA. The addition of 1,25(OH)2D3 to cultures of EBV-infected cells inhibited the production of IgM and IgG by the B cells. The vitamin D3 analog 24,25(OH)2D3 did not inhibit Ig production, thus suggesting that the effect is probably mediated through the high affinity receptor macromolecule localized in the nucleus. Because the EBV-induced Ig production is independent of T cell participation, the data also suggest that the effects of 1,25(OH)2D3 are exerted directly on the B cell. The present results add to the evidence of the importance of 1,25(OH)2D3 as an immunoregulatory hormone.

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.

Characterization of the calf uterine androgen receptor and its activation to the deoxyribonucleic acid-binding state

The androgen receptor (AR) from calf uterine cytosol has been studied in terms of steroid-binding affinity, hormone dissociation kinetics, and DNA-cellulose-binding capacity. The binding affinity for three androgens, analyzed under conditions where binding to progesterone receptor did not occur, decreased in the order: methyltrienolone greater than 5 alpha-dihydrotestosterone greater than testosterone. Activation of the receptor to the DNA-binding state involved the following changes of the receptor: decrease in dissociation rate for the steroid, disaggregation of the receptor, and increase in affinity for DNA. Dissociation studies with methyltrienolone and 5 alpha-dihydrotestosterone revealed that the AR can exist in two affinity states which differ 13- to 30-fold in their affinity for the steroid. Molybdate (10-20 mM) prevented the formation of the high affinity state. The high affinity state receptor was formed in the absence of molybdate or after ammonium sulfate precipitation (0-40% saturation) of the molybdate-stabilized low affinity state receptor. During formation of the high affinity state, the sedimentation coefficient of the receptor in low ionic strength buffer decreased from 8-9S to 4.5S, indicating receptor disaggregation. DNA-cellulose binding capacity increased from 3 to 65% upon formation of the high affinity state. The DNA-binding form could be eluted from DNA-cellulose at 0.14 M NaCl. After elution the DNA-binding form maintained its sedimentation coefficient of 4.5S and chromatographed as a protein with a Stokes radius of 44 A. From these results it can be concluded that the activated, DNA-binding form of the AR in calf uterus is a protein with a molecular mass of approximately 85,000, which acquires a higher affinity for the ligand upon its formation.

Ribonuclease-induced transformation of progesterone receptor from rabbit uterus

The effect of RNase on the transformation of progesterone receptor from rabbit uterus was studied by density-gradient centrifugation and DNA-cellulose binding assay. The 7S form of the receptor in crude cytosol was RNase sensitive, and converted to the 4S form after RNase treatment. This reaction was prevented by an RNase inhibitor and reversed by the addition of ribosomal RNA. RNase treatment also caused a two-fold increase in the DNA binding of cytosolic receptor, and reduced the time required for heat-induced transformation. However, sucrose-gradient-purified progesterone receptor (7S) did not undergo transformation by warming unless exogenous RNase was added, thereby suggesting that a cytosolic factor, which might be endogenous RNase, is necessary for the heat-induced transformation of progesterone receptor. Furthermore, degradation of the receptors which occurred after prolonged warming at 25 degrees C in the presence of RNase could be prevented by the addition of DNA-cellulose to the reaction mixture. These results indicate that RNA is associated with the 7S form of progesterone receptor, and that its hydrolysis by RNase might be involved in the transformation of this receptor.

Nuclear interactions of zearalanol-oestrogen receptor complexes in rat liver: a comparison with oestradiol-17 beta

Nuclear interactions of alpha-zearalanol (P-1496) and oestradiol-17 beta (E2) were compared following binding of these compounds to cytosolic oestrogen receptor. A single dose of P-1496 (400 micrograms) or E2 (25 micrograms) given subcutaneously to ovariectomized female rats resulted in two peaks of nuclear oestrogen-receptor concentrations at approx. 0.5 and 4.5 h and showed no qualitative differences between the two compounds. Under in vitro cell-free conditions, [3H]P-1496 was also able to cause oestrogen receptor retention by liver nuclei. Moreover, analysis of salt-extracted nuclear-bound receptor on sucrose gradients gave similar results to those obtained using [3H]E2 with a main peak of radioactivity sedimenting at 5S. Using [3H]P-1496, the time-course of nuclear retention was examined in both males and females. These studies showed no sex difference with nuclear-bound radioactivity reaching a plateau between 20-30 min. The ability of oestrogen-receptor complexes to bind to DNA was examined by DNA-cellulose chromatography. Using either [3H]E2 or [3H]P-1496 as the ligand, qualitative sex differences were shown in the number of peaks present. A comparison of chromatographic patterns obtained with the two ligands suggested close similarities in non-covalent DNA binding between the two compounds, in both males and females. These studies indicate that P-1496 is capable of causing retention of oestrogen receptor by liver nuclei and it binds to DNA in a manner similar to E2. Hence, our data do not explain the marked difference in oestrogenic activity observed in vivo between E2 and P-1496.

Receptor-positive hereditary resistance to 1,25-dihydroxyvitamin D: chromatography of hormone-receptor complexes on deoxyribonucleic acid-cellulose shows two classes of mutation

We used cultured skin fibroblasts from patients with hereditary resistance to 1,25-dihydroxyvitamin D [1,25-(OH)2D] and normal hormone binding to soluble extract from cells [i.e. receptor-positive resistance to 1,25-(OH)2D] to characterize DNA binding of the receptor for 1,25-(OH)2D. Occupied receptor was generated by incubating soluble extracts from cells with [3H]1,25-(OH)2D3; occupied receptor was applied to columns of DNA-cellulose and then eluted with linear gradients of KCl. Occupied receptors of cells from other sources eluted as a single peak at 0.20-0.26 M KCl; this elution pattern was independent of tissue (skin, breast cancer, or osteosarcoma) or species (human or rat) of origin of the receptors. With cells from two kindreds in whom there was mildly decreased localization of the hormone-receptor complex to the nucleus in vitro, occupied receptor interacted abnormally with DNA-cellulose (elution at 0.09-0.13 M KCl vs. normal at 0.20-0.26 M KCl); this suggested mutation(s) that affected a DNA-binding domain of the receptor in these two kindreds. With receptor-positive cells from two other kindreds in whom there was unmeasurable hormone localization to the nucleus, the elution pattern of occupied receptors from DNA-cellulose was normal; this suggested mutation(s) which did not affect the same DNA-binding site. We conclude that our demonstration of two distinct elution profiles from DNA-cellulose reflects two independent classes of mutation, either of which can cause receptor-positive resistance to 1,25-(OH)2D.

Physicochemical characterization of a new glucocorticoid receptor

A new glucocorticoid-binding protein (Peak C) eluted with 0.14 M NaCl on DEAE-cellulose chromatography was identified previously in the rats subjected to stress or treated with glucocorticoid (100 micrograms/100 g body wt.), while the 'classic' glucocorticoid receptor (Peak B) eluted with 0.07 M NaCl was found predominantly in untreated rats. The new glucocorticoid-binding protein, Peak C, was characterized by Scatchard analysis and competition with other steroids as a glucocorticoid receptor. The saturation curve of Peak C for dexamethasone was sigmoidal, whereas that of Peak B was hyperbolic. The Hill coefficient was 1.0 for Peak B and 3.1 for Peak C. These results show that Peak C has multiple binding sites. Peak C bound specifically to only natural or synthetic glucocorticoids, whereas Peak B bound not only to glucocorticoids but also to progesterone and aldosterone. Peak C was far more labile than Peak B, its binding activity decreasing 80% when it was incubated for 30 min at 25 degrees C. The molecular sizes of these two peaks (B and C) were similar, being about 90 000-100 000 as determined by Sepharose 6B column chromatography at high ionic strength (0.34 M KCl). The hormone-receptor complex of Peak C bound to rat liver chromatin specifically, but did not bind to calf thymus DNA. The complex of Peak B bound to not only the chromatin but also calf thymus DNA. Peak B reacted well with antiserum to the 'classic' glucocorticoid receptor, but Peak C did not react with this antiserum. These results indicate that Peak C is a different glucocorticoid receptor protein from Peak B, or classic glucocorticoid receptor, and plays physiologically important roles as a glucocorticoid receptor mediating the action of the hormone at a high level.

Estrogen receptors in the wobbler mouse

Recent research has raised the interesting possibility that the neurological mutant mouse, wobbler (wr/wr), possesses an estrogen receptor deficit analogous to the androgen receptor deficiency found in androgen-resistant mice with testicular feminization. In the present report we examined estrogen-binding activity in cytosolic extracts of kidney, liver, and brain from wobbler mice, littermate control animals, and C57BL/6J mice, using DNA-cellulose chromatography. Estrogen binding components exhibiting properties of estrogen receptors were present in all tissues examined. Estrogen receptors adhered to DNA, displayed characteristic elution profiles from DNA-cellulose, and showed high affinity and limited capacity for estradiol, in contrast to non-receptor entities which bind estradiol. The qualitative elution patterns for estrogen receptors did not differ among groups within each tissue studied, and were similar to those reported previously in mouse kidney and brain. While estrogen receptors have been shown in mouse liver by other techniques, this is the first demonstration of putative estrogen receptors in mouse liver by DNA-cellulose chromatography. No consistent deficits in estrogen receptor concentration were found in wobblers compared to littermates. Thus, the data do not support the hypothesis that the wobbler mouse is an estrogen receptor-deficient mutant.

Characterization of the purified molybdate-stabilized glucocorticoid receptor from rat liver. An in vitro transformable complex

Rat liver glucocorticoid receptor was purified in the presence of molybdate by a three-step procedure comprising protamine sulfate precipitation, affinity chromatography on a dexamethasone matrix and high-performance size-exclusion chromatography (HPSEC) on a TSK G 3000 SW column. The [3H]triamcinolone-acetonide-receptor complex was obtained in 20% yield with an overall 11 800-fold purification. The dissociation rate constant of this complex was 1.6 X 10(-4) min-1. The purified receptor sedimented at 8.3 S in high-salt and 9.4 S in low-salt sucrose gradients containing molybdate. A 7.0-nm Stokes radius was determined by HPSEC on a TSK G 4000 column in high-salt buffer. The calculated Mr was 278000. Dodecyl sulfate/polyacrylamide gel electrophoresis revealed an almost homogeneous 90 000-Mr band. Three minor bands with Mr of 78 000, 72 000 and 48 000 were also inconstantly seen. An apparent pI = 5.1 was observed for the [3H]steroid complex by isoelectric focusing in agarose gel. Furthermore high-performance ion-exchange chromatography of the purified complex on a DEAE 545 LKB column (DEAE HPLC) yielded a sharp peak eluted at a 315 mM potassium ion concentration. This peak was shown to contain almost all the 90 000-Mr protein. Moreover the purified receptor complex appeared to be transformable to a DNA-binding state after molybdate removal followed by warming 30 min at 25 degrees C in presence of 0.2% bovine serum albumin: 50-78% transformation yield could be demonstrated by DNA-cellulose chromatography. Partial transformation could also be obtained at 0 degrees C in the absence of any added protein and was followed by DEAE HPLC. The transformed complex was eluted by 180 mM potassium.

DNA methyltransferases: activity minigel analysis and determination with DNA covalently bound to a solid matrix

We describe two methods that facilitate detection and characterization of DNA methyltransferases: activity gel analysis and the use of DNA-cellulose or DNA-Sepharose in DNA methylation reactions. The first permits identification of catalytic subunits, determination of the influence of proteolysis, and evolutionary or developmental studies. The second allows accurate and fast determination of DNA methyltransferase activities in crude extracts and during purification.

Conversion from 4S androgen receptor from rat submandibular gland to higher molecular form and the effect of sodium molybdate

The androgen receptor from rat submandibular gland was transformed by exposure to ATP at 0 degrees C. The transformed 4 S receptor converted to a higher molecular weight form in a low-salt glycerol gradient centrifugation when ATP was removed from the sample. The sedimentation coefficient of the converted receptor was similar in the absence or presence of 20 mM molybdate; 7.8 +/- 0.5 S without molybdate and 7.6 +/- 0.3 S with molybdate. However, the receptor converting in the presence of molybdate could markedly bind to DNA-cellulose, while an entity without molybdate could not. These results suggest that molybdate directly interacts with the DNA-binding domain on the 4 S androgen receptor and prevents this domain from being concealed by conversion in low-salt conditions.

Immunorecognition of the active form of the oestrogen receptor by using a monoclonal antibody

In previous studies, two forms (alpha and beta) of the oestrogen receptor, with different immunological characteristics, were observed in the cytosol fraction of fetal guinea-pig uterus, by using a monoclonal antibody to the human oestrogen receptor (D547Sp gamma). Only the alpha form was recognized by the antibody, shifting its sedimentation coefficient in high-salt sucrose gradients. The present work investigated the effect of several factors (time, temperature, high salt concentrations and Na2MoO4) on the interconversion of these two forms. Only the beta form was observed when cytosol was incubated with oestradiol for only 2-3 h, but 20 h later, 40-60% of the total oestradiol-receptor complexes were found as the alpha form. The transformation from the beta to the alpha form was accelerated by temperature (25 degrees C, 15 min) and exposure to high salt concentrations (0.4 M-KCl). On the other hand, Na2MoO4 completely blocked the transformation induced by time and temperature, but had little effect on that induced by KCl. The appearance of the alpha form always correlated with an increase in receptor binding to nuclei and DNA-cellulose. Finally, it was found that the isolated beta form, recovered from the gradient, was transformed into the alpha form after overnight dialysis under reduced pressure. The present data suggest that the alpha form, which is recognized by the monoclonal antibody, is the activated form of the oestrogen receptor.

Modulation of DNA binding of glucocorticoid receptor by aurintricarboxylic acid

Effects of aurintricarboxylic acid (ATA) were examined on the DNA binding properties of rat liver glucocorticoid-receptor complex. The DNA-cellulose binding capacity of the glucocorticoid-receptor complex was completely abolished by a pretreatment of receptor preparation with 0.1-0.5 mM ATA at 4 degrees C. The half-maximal inhibition (i.d.50) in the DNA binding of [3H]triamcinolone acetonide-receptor complex [( 3H]TARc) was observed at 130- and 40 microM ATA depending upon whether the inhibitor was added prior to or following the receptor activation. The entire DNA-cellulose bound [3H]TARc could be extracted in a concentration-dependent manner by incubation with 2-100 microns ATA. The [3H]TARc remained intact under the above conditions, the receptor in both control and ATA-treated preparations sedimented in the same region in salt-containing 5-20% sucrose gradients. The action of ATA appeared to be on the receptor and not on DNA-cellulose. The DNA-binding capacity of ATA-treated receptor preparations could be recovered upon exhaustive dialysis. The treatment with ATA did not appear to change the ionic behavior of heat activated GRc; the receptor in both control and the ATA-treated preparations showed similar elution profiles. Therefore, ATA appears to alter the binding to and dissociation of glucocorticoid-receptor complex from DNA. The use of ATA should offer a good chemical probe for analysis of the DNA binding domain(s) of the glucocorticoid receptor.

Effect of ribonuclease on the physico-chemical properties of estrogen receptor

Estrogen receptors (ER) from rat and rabbit uterine cytosol were examined for their sensitivity to ribonuclease (RNase). After RNase treatment, a major part of rabbit uterine ER was converted from the 7S to 3-4S form, and its binding to DNA-cellulose was increased by 40%. Similar treatment on rat uterine ER showed a shift from 7S to 4.5S, and the DNA-cellulose binding was stimulated by 20%. Measurement of endogenous RNase levels showed that lower RNase concentration in rabbit uterine cytosol coincided with larger stimulation of DNA-cellulose binding by exogenous RNase. These results indicate that a major part of 7S ER is susceptible to RNase, and cleavage of bound RNA seems to uncover additional binding sites for DNA. In contrast to the general thinking that 4S to 5S transformation is essential for nuclear binding, we have observed that RNase-treated rat uterine ER did not undergo such a transformation by warming at 25 degrees C, while DNA-cellulose binding of the receptors increased. Thus, temperature activation could occur independent of 4S to 5S transformation.

Characterization of non-liganded glucocorticoid receptor in rat liver cytosol using indirect competitive enzyme-linked immunosorbent assay

We have previously shown that the purified or unfractionated cytosolic, activated glucocorticoid receptor of rat liver consists of a polypeptide with a Stokes radius of approximately 6 nm, a sedimentation coefficient of 4S and a molecular mass of approximately 90,000 Daltons. We have confirmed previous observations by other authors that if sodium molybdate is introduced into the cytosol preparation buffer the non-activated glucocorticoid receptor appears as an 8 nm, 9S species with an apparent molecular mass of 330,000 Daltons. In order to study the physicochemical parameters of the glucocorticoid receptor prior to ligand binding, we have used an enzyme-linked immunosorbent assay (ELISA) based on antibodies raised in rabbits against the purified activated glucocorticoid receptor. In isotonic buffer, the non-liganded glucocorticoid receptor was shown to have a Stokes radius of 6 nm in the absence and 8 nm in the presence of molybdate. Furthermore, experimental conditions known to result in activation of the glucocorticoid receptor complex (increased ionic strength, increased temperature) did not lead to activation of the 6 nm non-liganded glucocorticoid receptor as judged from the lack of binding of the treated, non-liganded receptor to DNA-cellulose. The existence of both 6 and 8 nm forms of nonactivated, non-liganded glucocorticoid receptor in vitro suggests that dissociation of an 8 nm form to a 6 nm form, if it occurs in vivo, is probably not the only molecular event constituting the activation of the glucocorticoid receptor.

Purification and preliminary characterization of a macromolecular inhibitor of glucocorticoid receptor binding to DNA

Rat liver cytosol contains a heat-labile macromolecule that inhibits the binding of the transformed glucocorticoid-receptor complex to nuclei or DNA-cellulose (Milgrom, E., and Atger, M. (1975) J. Steroid Biochem. 6, 487-492; Simons, S. S., Jr., Martinez, H. M., Garcea, R. L., Baxter, J. D., and Tomkins, G. M. (1976) J. Biol. Chem. 251, 334-343. We have developed a quantitative assay for the inhibitor and have purified it 600-700-fold by ammonium sulfate precipitation, ethanol precipitation, and phosphocellulose and Sephacryl S-300 chromatography. The inhibitory activity copurifies with a Mr = 37,000 protein doublet. Under low salt conditions, both the inhibitory activity and the 37-kDa protein doublet behave as high Mr aggregates that subsequently dissociate in the presence of salt. The inhibitor is positively charged at physiological pH, and it is not affected by digestion with several serine proteases or RNase. The inhibitor does not affect the transformation process, and it does not cause the release of steroid-receptor complexes that have been prebound to DNA-cellulose. The inhibitor preparation does not cleave receptors in L-cell cytosol that are covalently labeled with the site-specific affinity steroid [3H]dexamethasone 21-mesylate. If the steroid-receptor complex is first separated from the great majority of cytosol protein by transforming it and binding it to DNA-cellulose, addition of the inhibitor preparation results in receptor cleavage. Under these conditions, cleavage can be blocked with 1-chloro-3-tosylamido-7-amino-L-2-heptanone and antipain, but protease inhibitors do not affect the inhibition of DNA binding that occurs in whole cytosol. The inhibitor acts through an interaction with the receptor, not with DNA. We suggest that the inhibitor may prove to be a useful tool for studying the interaction of the steroid-receptor complex with DNA or nuclei and speculate that it may be important in determining normal events of the receptor cycle as they occur in the intact cell.

Molybdate and the 1,25-dihydroxyvitamin D3 receptor from chick intestine

The nature of the 1,25-dihydroxyvitamin D3 receptor from chick intestine was examined in regard to its response to sodium molybdate. Sodium molybdate (10 mM) stabilized the receptor from crude nuclear extract but not that from the supernatant or cytoplasmic fraction, suggesting the molybdate may act by binding to the DNA binding region of the receptor. At a concentration of 50 mM, sodium molybdate prevented aggregation of the nuclear receptor. This concentration of sodium molybdate also inhibited the receptor from binding to DNA cellulose while the same ionic strength KCl (90 mM) did not. These properties also suggest that molybdate interacts with the DNA binding region. Purification of the receptor using DNA cellulose chromatography has also been improved by using a sodium molybdate gradient (0-0.2 M) instead of the KCl gradient used previously.