Physical-chemical analysis of steroid hormone receptors

Activated Ha-Ras but not TPA induces transcription through binding sites for activating transcription factor 3/Jun and a novel nuclear factor

We report the identification of a 20-base pair sequence mediating induced transcription in response to an activated Ha-ras gene and epidermal growth factor (EGF) but not 12-O-tetradecanoylphorbol-13-acetate stimulation. This signal-specific nuclear target is present in the long terminal repeat of a mouse VL30 retrotransposon expressed in epidermis. Functional studies and in vitro binding analyses using cultured keratinocytes (Balb/MK) reveal that the response element is composed of two cooperating sequence motifs in juxtaposed position, both of which are targets for induced binding activity 1-2 h after EGF stimulation. Of many different activating transcription factor/cAMP-responsive element binding protein/activating protein 1 factors tested, one part of the sequence selectively binds endogenous proteins immunologically related to activating transcription factor 3 (ATF3) and Jun isotypes. The other sequence is a target for a nuclear factor showing binding specificity unrelated to factors known to mediate EGF- or ras-induced transcription as determined by its sequence specificity and by antibody experiments. This component has been characterized and partially purified by gel filtration chromatography and velocity centrifugation revealing a Stokes radius of 43.6 A and a sedimentation coefficient of 9.7 S in solution. Based on these parameters, a molecular mass of 178,000 Da was calculated. The results indicate that the specific binding of ATF3/Jun and a previously uncharacterized factor account for signal-specific transcription in response to EGF or an activated Ha-ras gene in a cell type in which the cooperative action of an activated Ha-ras gene and 12-O-tetradecanoylphorbol-13-acetate cause tumor growth.

Subunit structure of the nonactivated human estrogen receptor

The nonactivated estrogen receptor of human MCF-7 mammary carcinoma cells was investigated with respect to stoichiometry of protein subunits. The native receptor complex stabilized by molybdate had a molecular mass of approximately 300 kDa. Chemical cross-linking with several bifunctional reagents resulted in complete stabilization of the same receptor form of approximately 300 kDa and was achieved both in cell extracts and in intact cells. Incubation of the cross-linked receptor with a receptor-specific monoclonal IgG1 antibody increased the molecular mass by approximately 135 kDa--i.e., no more than one immunoglobulin molecule bound to the complex. Partial and progressive cross-linking of affinity-labeled receptors revealed patterns of labeled bands upon denaturing gel electrophoresis indicative of a heteromeric structure. The completely cross-linked receptor was purified to homogeneity and analyzed for protein components. In addition to the receptor polypeptide of approximately 65 kDa, we detected the heat shock proteins hsp90 and p59; the hsp90 band was roughly twice as intense as the p59 band. The heat shock protein hsp70 and the 40-kDa cyclophilin were not detected as components of the highly purified cross-linked receptor of approximately 300 kDa. We suggest a heterotetrameric structure consisting of one receptor polypeptide, two hsp90 molecules, and one p59 subunit, for which the molecular mass adds up to approximately 300 kDa. Thus, the nonactivated estrogen receptor has a molecular architecture homologous to those of glucocorticoid and progesterone receptors, even though phylogenetically the estrogen receptor gene forms a distinct subgroup within the gene family of nuclear hormone receptors.

Purification and characterization of p68/70, regeneration-associated proteins from goldfish brain

Two acidic proteins (p68/70) previously shown to be associated with regeneration of the goldfish optic nerve were purified 887-fold from brain homogenates of Carassius auratus. Purification to homogeneity was achieved by sequential chromatography of a 100,000 g brain supernatant fraction on DEAE-Sephacel, Cu(2+)-charged iminodiacetic acid agarose, and gel filtration. The Stokes radius of the doublet was determined to be 5.8 nm, and the sedimentation coefficient calculated to be 5.2. From these values a molecular mass of 128 kDa and a frictional coefficient ratio of 1.6 were calculated. Chromatofocusing on a high-resolution DEAE column resolved the protein doublet into three dimeric species of p68, p68/70, and p70. These results indicate that the proteins are highly elongated and associate as homodimers or as a heterodimer. Subcellular localization and membrane extraction experiments indicated p68/70 to be a component of the plasma membrane associated primarily through hydrophobic interactions. p68/70 demonstrated biphasic behavior in phase partition experiments using Triton X-114. Analysis of hydrolytic products indicated p68/70 to be a glycoprotein, containing 11% carbohydrate.

Heterotetrameric structure of the human progesterone receptor

Nonactivated progesterone receptors in extracts of human T47D mammary carcinoma cells were investigated. Chemical cross-linking with dimethyl suberimidate resulted in complete stabilization of the A and B receptors with an average molecular mass of 340 kDa. For analyzing the subunit structure, we concentrated on the larger B receptor, which was separated from the A form by immunoaffinity chromatography. Progressive cross-linking of the photoaffinity-labeled receptor resulted in patterns of labeled bands in SDS gels, which are indicative of a heterotetrameric structure. It consists of one receptor polypeptide in association with two 90-kDa subunits and one polypeptide of approximately 60 kDa. The completely cross-linked B receptor has a molecular mass of approximately 390 kDa. To identify the subunits, the oligomeric B receptor was cross-linked with a cleavable bisimidate, highly purified by immunoaffinity chromatography, and analyzed by gel electrophoresis and immunoblotting. The receptor polypeptide has a mass of 116.5 kDa. The 90-kDa band was identified as the heat shock protein hsp90 and was roughly twice as intense as the receptor polypeptide. By use of specific antibodies, we identified the fourth receptor subunit as a 59-kDa protein (p59); we did not obtain any evidence for the heat shock protein hsp70 being a receptor component. We suggest an analogous heterotetrameric structure for the nonactivated A receptor.

The action of calcitonin on the TM4 Sertoli cell line and on rat Sertoli cell-enriched cultures

The effects of synthetic salmon calcitonin on primary Sertoli cell-enriched cultures and on an established cell line (TM4 cells, derived from immature mouse Sertoli cells) were studied. Synthetic salmon calcitonin stimulated the conversion of [3H]adenine to [3H]cyclic AMP in both cell systems. In addition, this peptide stimulated the secretion of rABP in primary Sertoli cell-enriched cultures prepared from rat testis. Calcitonin also increased the total concentration of both androgen and estrogen receptors in TM4 cells. Because cAMP analogs decreased androgen and estrogen receptor concentrations, the effect of calcitonin on sex steroid receptors may not be mediated by its effect on cyclic AMP in these cells. The possibility that the action of synthetic salmon calcitonin on the receptors might be mediated by a change in cellular Ca2+ was investigated. Lowering extracellular Ca2+ concentrations from 1.5 mM to less than 0.01 mM markedly reduced the concentration of androgen and estrogen receptors; restoration of Ca2+ to 1.5 mM returned receptor levels to normal. When the receptor concentrations were decreased by lowering extracellular Ca2+ concentrations to 0.5 mM, treatment with the calcium ionophore, A23187, restored receptor levels to normal. Although the calcium channel blocker, verapamil, decreased receptor levels, calcitonin partially counteracted its effect. Trifluoperazine, an inhibitor of calmodulin, also diminished androgen and estrogen receptor, levels in the cytosol of TM4 cells. It was concluded that calcitonin stimulates the formation of cyclic AMP and the secretion of rABP by Sertoli cells. This peptide also increases the concentration of androgen and estrogen receptors, possibly by a mechanism that is, in part, Ca2+ -mediated. These results, along with those on Leydig cells, suggest that calcitonin could be a regulator of testicular function.

Characterization of estrogen receptor from human liver

Characterization of the estrogen receptor in cytosol from human male liver was undertaken to further understanding of the molecular basis of estrogen action in this tissue. By analysis of estrogen binding data of crude cytosol, saturable estrogen binding showed a Kd = 4.7 X 10(-10) M. High levels of nonsaturable binding were also detected. The estrogen-binding activities detected could be distinguished by their steroid specificity, hydrodynamic parameters, ionic properties, and sensitivity to proteolytic attack. Our findings also confirmed that the moderate-affinity estrogen binders found in rodent liver cannot be detected in human tissue. We concluded that the properties of estrogen receptor of human liver cytosol allow its separation from nonsaturable estrogen-binding components.

Study of the heteromeric structure of the untransformed glucocorticoid receptor using chemical cross-linking and monoclonal antibodies against the 90K heat-shock protein

The untransformed rat glucocorticoid receptor is assumed to be a hetero-oligomeric complex, containing a non-steroid binding component, the 90K heat-shock protein (HSP 90). Direct measurement of its molecular weight by chemical cross-linking provides new evidence for a trimeric structure with a Mr of ca. 270,000. Resorting to an anti HSP 90 probe (AC 88), we show that the native dimeric HSP 90 possess two accessible epitopes for this monoclonal antibody, while when bound to the steroid-binding subunit, only one epitope remains accessible. These data clearly suggest that the untransformed rat glucocorticoid receptor is an asymmetrical hetero-oligomeric complex.

Genes coding for RNA polymerase beta subunit in bacteria. Structure/function analysis

The nucleotide sequence of the rpoB gene of Salmonella typhimurium has been determined in this work. It was compared with known sequences of the gene from other sources and the conservative regions were detected. This allowed some interesting conclusions to be made about the distribution of the functional domains in bacterial RNA polymerase and about the three-dimensional structure of its beta subunit.

Phycocyanin aggregation. A small angle neutron scattering and size exclusion chromatographic study

The influence of environmental factors on the aggregation properties of phycocyanin from Synechocystis 6701 was studied by small angle neutron scattering and high-pressure size-exclusion liquid chromatography. Phycocyanin was found to exist in a reversible equilibrium between the monomer, trimer and hexamer forms. The distribution of the protein between these oligomers is determined by the pH, buffer composition and ionic strength of the medium, and protein concentration. Phycocyanin was in a stable hexameric state at pH 5.0 to 6.0 at a concentration of 1 to 10 mg/ml, and was primarily in a trimeric state at pH 8.0 at a concentration of about 5 mg/ml. Comparison of the small angle scattering data with the computed scattering curve for a hollow cylinder was used to determine the dimensions of the best-fit model by a least-squares fitting procedure. The outer radius, inner radius and height of the phycocyanin hexamer were found to be 54.1, 12.0 and 61.4 A (1 A = 0.1 nm), respectively, and the corresponding dimensions for the trimer were 54.5, 14.0 and 33.0 A. The molecular weight ratio for phycocyanin hexamer was determined to be 217,000. The dimensions and molecular weight ratios of phycocyanin from Synechocystis 6701 obtained by solution scattering are similar to the values for Mastigocladus laminosus obtained by X-ray crystallography.

Transformation of the glucocorticoid receptor in the cell-free cytosol of the neural retina of the chick embryo: changes in the size and charge of the receptor complex during transformation suggest a multistage process

The physicochemical properties of the glucocorticoid receptors (GR), and the molecular changes induced during their transformation in the cell-free cytosol of the neural retina of the chick embryo, were investigated. The surface charge of the various size forms of the GR complex was determined on gel filtration and/or glycerol density gradient-isolated GR, by electrofocusing under nondenaturing conditions. The nontransformed molybdate-stabilized GR in hypotonic buffer (containing PMSF) appears as a 350 kilodalton (kDa) complex (Rs = 8.6 nm, S = 9.5), with an apparent pI value (pI') of 4.4 +/- 0.1. The GRs in heat or salt-activated cytosols appear as a 90 kDa hormone-receptor complex (Rs = 5.6 +/- 0.2, S = 3.9 +/- 0.1), which is resolved as a major peak with a pI' value of 6.2 +/- 0.1 and a minor peak with a pI' value of 5.4. The transformation of the 350 kDa oligomer to the 90 kDa monomer occurs in three stages. Two distinct dissociation steps were induced by 0.4 M KCl: (a) the dissociation of the 350 kDa complex to a 170 kDa complex (Rs = 7.8 +/- 0.2, S = 5.1 +/- 0.2), exhibiting a pI' value of 5.6 +/- 0.2, induced by salt and not inhibited by molybdate; and (b) the dissociation of the 170 kDa complex to the 102 kDa complex (Rs = 5.6 +/- 0.2, S = 4.4), also exhibiting a pI' value of 5.6 +/- 0.2, which is blocked by molybdate. The third step, the transition of the 102 kDa complex to the activated (nuclear-like), 90 kDa form, is dependent on cytosolic factors. It is induced in the isotonic milieu by physiological temperatures, and in the cold by exposing the crude cytosol to 0.4 M KCl. The nature of this cytosolic processing step is unknown. It occurs in the presence of PMSF, which presumably inhibits proteolytic GR degradation in the cytosol of the neural retina. Activated GR complexes tend to aggregate. Molybdate inhibits activation-induced GR-aggregation.

Subunit dissociation and activation of wild-type and mutant glucocorticoid receptors

Apparent molecular weights of wild-type and nti ('increased nuclear transfer') mutant glucocorticoid receptors were obtained from Stokes radii and sedimentation coefficients. At low salt concentrations molecular forms of Mr 328,000 and 298,000 of the wild-type and mutant, respectively, were predominant. Increasing ionic strength resulted in receptor dissociation. Dissociated forms of Mr 130,000 and 63,000 of the wild-type and mutant, respectively, were obtained at 300 mM KCl and above. Some metal oxi-anions prevented dissociation. Receptor activation to allow DNA binding produced the dissociated forms which could be separated from non-activated receptors by filtration through DNA-cellulose or by DEAE-cellulose chromatography. Non-activated wild-type and nti receptors eluted from DEAE-cellulose under identical conditions while activated wild-type and nti receptors eluted differently. Partially proteolyzed wild-type receptors behaved identically to nti receptors. We conclude that the large forms of wild-type and nti receptors are heteromeric and contain only one hormone-building polypeptide per complex.

Improved Stokes radius measurement of the glucocorticoid receptor using TSK G4000SW and TSK G3000SW high-performance size-exclusion columns. Analytical and preparative applications

The Stokes radius of the rat liver glucocorticoid receptor was determined using TSK G3000SW and TSK G4000SW high-performance size-exclusion columns. The accuracy of the calibration graph for proteins larger than 6 nm on the TSK G4000SW column allowed the resolution of a heterogeneous structure for the cytosolic untransformed receptor, giving two forms with Rs values of 8.3 and 7.1 nm, whereas the transformed receptor elutes with an Rs value of 4.7-5.3 nm. The 8.3 nm form was not observed for the highly purified untransformed receptor. Parallel analyses of the cytosolic untransformed receptor on conventional gravity-fed Bio-Gel A 1.5-m or Ultrogel AcA-22 size-exclusion columns could not resolve two components. The resolution efficiencies of high-performance size-exclusion chromatography and open-column size-exclusion chromatography were compared. Further, owing to its rapidity, high-performance chromatography allowed the characterization of steroid-receptor complexes having half-lives as short as 90 min and very unstable receptor forms could be detected. Specific applications are considered, such as the resort to a small TSK GSWP guard column for the rapid separation of affinity-purified [3H]TA-receptor complexes from free eluting steroid, and to a preparative TSK G4000SW column for the fractionation of significant amounts of the two untransformed receptor forms.

In vitro characterization of possible mechanisms underlying the selective in vivo accumulation of the PCB metabolite 4,4'-bis(methylsulphonyl)-2,2',5,5'-tetrachlorobiphenyl in the lung

In vivo, the polychlorinated biphenyl (PCB) metabolite 4,4'-bis(methylsulphonyl)-2,2',5,5'- tetrachlorobiphenyl--(MeSO2)2TCB--selectively accumulates in the Clara cells of the bronchiolar epithelium and in the secretory contents of the bronchiolar lumen. In vitro characterization of the interaction of tritiated (MeSO2)2TCB with the lung suggests that this selective accumulation is due to the presence of a secreted ([3H]MeSO2)2TCB-binding protein in the respiratory tract of rats, mice and man. The protein appears to be an almost globular, low-molecular-weight acidic protein which binds ([3H]MeSO2)2TCB and certain other methylsulphonyl PCBs with high affinity. Because of the pathway outlined for accumulation, it is suggested that methylsulphonyl PCBs should be included in studies designed to elucidate the mechanism(s) of PCB-induced lung toxicity.

"Defective" receptors in steroid-resistant conditions may be proteolytic artifacts

The specific question addressed in this report is whether the resistance to steroid treatment of certain tissues or tumors which appear to contain a normal quantity of steroid-binding sites may be due to structural defects in the receptors. This question may be seen as part of the more general question of whether there are intrinsic variations in the structures of receptors for a given class of steroids in different healthy tissues, in healthy vs. malignant tissues or in different types of tumors. Our experimental approach to these questions has involved the stabilization and precise physicochemical characterization of the receptors. To date, we have studied the estrogen and progestin receptors from human breast cancers and benign and malignant gynecologic specimens and the glucocorticoid receptors from several healthy and malignant rodent tissues and from normal human lymphocytes and various types of leukemic cells. Chromatographic and ultracentrifugal analyses in buffers of low ionic strength, containing 20 mM Na2MoO4 as the stabilizer, have revealed each of these receptors to be a large, oligomeric complex, characterized by remarkably similar values of the Stokes radius, sedimentation coefficient, molecular weight and axial ratio. In the absence of adequate stabilization, however, we found that the receptors for three classes of steroids in extracts of some healthy, steroid-responsive tissues, such as rat kidney and human uterine endometrium, are invariably degraded by endogenous proteinases. The extent of such cleavage is increased considerably by freezing the tissues prior to homogenization. Studies designed to distinguish the intact receptors from the products of proteolysis have included the characterization of receptors in cytosols prepared from mixtures of rat liver and kidney. The results strongly support the interpretation that the smaller size of the receptors detected in kidney cytosol reflects their cleavage by the more active proteinases in that tissue. The sizes and shapes of the receptors in cytosols from various tissues were found to be correlated with the activities of specific endopeptidases, assayed fluorometrically with peptidyl derivatives of 7-amino-4-methylcoumarin (AMC). These studies suggested that the receptors are vulnerable to cleavage by "lysine-specific" endopeptidases, detected with t-butyloxycarbonyl-L-valyl-L-leucyl-L-lysyl-AMC. An enzyme of this specificity was partially purified from rat kidney cytosol and tested for its ability to digest the glucocorticoid receptors from rat liver cytosol.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Resolution of non-activated and activated androgen receptors based on differences in their hydrodynamic properties

This study shows that cytosolic androgen receptor of rat ventral prostate sediments at 10-11 S on conventional low salt sucrose density gradients (SDG), and at 4.6 S on high salt SDG, whether it is activated or not; inclusion of 10 mM Na2MoO4 in all buffers does not alter these sedimentation coefficients. In the presence of 50 mM Na2MoO4 non-activated and activated androgen receptors sediment in high salt SDG at 7-8 S and 4.6 S, respectively. Thus the presence of high concentrations of molybdate during centrifugation inhibits the KCl induced disaggregation of receptor into subunits. Similar effects are observed on Sephacryl-S200 gel filtration; in 50 mM MoO2-4 and 0.4 M KCl non-activated receptor has an estimated Stokes radius of 67 A; this value decreases to 52 A upon activation in the presence of proteolysis inhibitors; omission of molybdate during chromatography yielded 52 A and 27 A entities. Estimated mol. wts are 198,000 Daltons for the non-activated 67 A form and 98,000 Daltons for the activated 52 A receptor. Sodium molybdate (50 mM) prevents temperature (18 degrees C) and high ionic strength (0.4 M KCl) induced receptor activation. This inhibition was overcome by removing molybdate by centrifugal gel filtration, or by increasing the KCl concentration to 0.8 M. The inhibitory effects of molybdate on salt induced receptor disaggregation into activated subunits are no longer observed at pH greater than 7.4 or after chemical modification of sulfhydryl groups. Once androgen receptor has been disaggregated into its activated subunits the activated state is maintained even upon reassociation to 10-11 S aggregates in low salt. The relative concentrations of KCl and molybdate are critical; thus, 10 mM Na2MoO4/0.4 M KCl and 50 mM Na2MoO4/0.8-1.2 M KCl did not differentiate activated from non-activated androgen receptor based on their hydrodynamic properties. In the presence of 0.4 M KCl and 50 mM molybdate, however, the hydrodynamic properties of androgen receptor can be correlated with receptor activation.

Heteromeric nature of glucocorticoid receptors

The wild-type and a mutant receptor of S49.1 lymphoma cells have been shown by photoaffinity labelling to contain steroid-binding polypeptides of Mr 94 000 and 40 000, respectively. We investigated the molybdate-stabilized forms of these receptors and obtained Mr 325 000 and 285 000, respectively, by gel filtration and sedimentation analysis. Mild chymotrypsin treatment of the large wild-type receptor resulted in a form of about Mr 290 000 which contained a steroid-binding polypeptide of Mr 40 000. The data suggest that the high -Mr forms of glucocorticoid receptors are heteromeric in nature and contain one steroid-binding polypeptide per complex.

Hydrodynamic and biochemical correlates of the activation of the glucocorticoid-receptor complex

Possible changes in the size and shape of the glucocorticoid-receptor complex (GRC) following activation remain poorly documented, due to the lability and possible activation of the receptor during the determination of these hydrodynamic parameters. In the present study molybdate was used to stabilize the GRC, thus preventing these uncontrolled transformations. Cytosol prepared from mouse whole brains was incubated for 18 h at 0-2 degrees C with [3H]triamcinolone acetonide (+/- molybdate). Activation was then initiated by incubation at 22 degrees C for variable times and quenched at 0 degree C by adding molybdate. The Stokes radius and sedimentation coefficient of the GRC declined from 77 A and 9.2 S before activation to 58 A and 3.8 S after activation. These measurements remained consistent after recycling GRC between sedimentation and gel filtration procedures and correspond to a 3-fold reduction in the relative molecular mass. The loss and formation of the 297 and 92 kDa species, respectively, after different durations of activation correlated nearly perfectly with increased binding of GRC to DNA-cellulose (DNA-C). The observed size change also correlated well with decreased adsorption to DEAE-cellulose filters (DE-81) and increased adsorption to glass fiber filters (GF/C). The increased adsorption to GF/C may reflect an increase in hydrophobicity which, with extended durations of activation, leads to increased aggregation and reduced binding to DNA-C, but not to a change in adsorption to DE-81. We propose that during activation the 297 kDa form of the GRC splits to form a 92 kDa species that displays an increased affinity for DNA.

Temperature-dependent kinetic correlates of the activation of the glucocorticoid-receptor complex

The effects of temperature on the kinetics of activation were studied in [3H]triamcinolone acetonide[( 3H]TA)-labeled cytosol preparations from mouse whole brain. After removal of unbound [3H]TA and molybdate (which prevents activation) from the unactivated steroid-receptor complex by gel exclusion chromatography, activation was initiated by incubation at 6-30 degrees C for 0.75-24 min and then rapidly quenched at -5 degrees C with Na2MoO4 (20 mM final concentration). The loss of the 9.2S (unactivated) form of the [3H]TA-receptor complex and the concomitant formation of the 3.8S (activated) form increased dramatically with increases in the activation temperature. These hydrodynamic changes were correlated directly with rapid time- and temperature-dependent increases in the binding of [3H]TA-labeled cytosol to DNA-cellulose (DNA-C). Further analyses of these data revealed a greater than 50-fold increase in the apparent first-order rate constant for the increased binding to DNA-C as the activation temperature was increased from 6 degrees C to 30 degrees C. An Arrhenius plot of these temperature-dependent kinetic constants revealed an energy of activation of 116 kJ. These data support a proposed model for activation of the glucocorticoid-receptor complex that includes the splitting of a 297 kDa, unactivated species into a 92 kDa, activated species.

Androgen receptor in human foreskin. II. Characterization of the receptor from hypospadiac tissue

Hypospadias represents a spectrum of disorders known as androgen insensitivity syndromes, which are characterized by a nonresponsiveness of an androgen target tissue to the steroid. The basic defect in this disorder is unknown. This article presents results of studies of the androgen receptor with use of human foreskin from normal neonates undergoing circumcision and from patients undergoing urethroplasty necessitated by hypospadias. It is speculated that a defect in receptor level or function might explain this disorder. The androgen receptors from both normal and hypospadiac tissue were stabilized with a buffer containing 50 mM Tris hydrochloride, 1 mM ethylenediaminetetraacetic acid, 12 mM monothioglycerol, 10% (v/v) glycerol, and 10 mM sodium molybdate plus 1 mM phenylmethylsulfonylfluoride (pH 7.5). The receptors were characterized by Scatchard analysis, competitive binding assays, sedimentation analysis, molecular sieve chromatography, and isoelectric focusing techniques. Specific R 1881 binding to soluble proteins from normal human foreskin was shown to be high affinity (dissociation constant = 0.5 nM), low capacity (6 fmol/mg of protein), and steroid specific. Sedimentation analysis by sucrose density gradients demonstrated the 8S-to-4S shift from low- to high-salt treatments. The receptor from the foreskins of hypospadiac patients also contained androgen receptor in a concentration similar to that in the foreskins of normal persons. The affinity for steroid binding and sedimentation profiles or sucrose gradients of the androgen receptor between normal persons and hypospadiac patients were also similar. However, the androgen receptor from hypospadiac patients displayed different patterns of molecular sieve chromatography from those displayed by the receptor of normal persons. The reason for this difference is not known but may reflect a defective receptor and explain the basic mechanism of this disorder.

Characterization of the glucocorticoid receptor in human skin

Because of the profound importance glucocorticoids have in dermatologic therapy, we studied the glucocorticoid receptor in human skin. A cytosol fraction was prepared from frozen skin by homogenization and centrifugation. When reacted with [3H]dexamethasone, this cytosol contained saturable, low-capacity binding. The glucocorticoid binding was stabilized by a protease inhibitor, phenylmethylsulfonylfluoride, and by sodium molybdate and was destroyed by trypsin. Sedimentation analysis of the glucocorticoid binding protein showed an 8S to 4S transition in high salt, a property of many known steroid hormone receptors. The binding was steroid specific, supporting the conclusion that this binding protein was a glucocorticoid receptor. The receptor molecule had a frictional ratio of 1.60 and a Mr of about 226,000 under low-salt conditions (0.05 M KCl) and a frictional ratio of 1.86 and a Mr of about 100,000 under high-salt conditions (0.3 M KCl) consistent with a nonglobular, elongated molecule. Isoelectric focusing showed that the receptor had 2 molecular species with isoelectric points of approximately 5.8 and 7.5. Quantitation of receptor in human skin showed 4-7 times more receptors in the epidermis and papillary dermis than in the lower dermis and nearly equal numbers in epidermis and papillary dermis. The concentration of receptors varied in different anatomic areas, with male foreskin showing the highest concentration, followed by female face, breast, and abdominal skin. Interestingly, the concentration of glucocorticoid receptors also varied with age; the highest levels were present at the extremes of life and a significantly lower level at midlife.

Limited proteolysis of the mouse liver glucocorticoid receptor

Activation of the mouse liver glucocorticoid receptor resulted in the generation of a protein of very different characteristics from that found previously in the mouse AtT-20 pituitary tumor cell line [Vedeckis, W. V. (1981) Biochemistry 20, 7237-7245]. Ion-exchange and adsorption chromatography showed that the activated liver receptor was a more basic protein--it eluted earlier from a DEAE-cellulose column, while a later elution was observed upon phosphocellulose and DNA-cellulose chromatography. Further experiments showed that this was due to proteolysis of the liver receptor to a smaller form (3.2 S; Rs = 3.9 nm; Mr = 53 000; f/f0 = 1.45) after activation. Mero-receptor (2.4 S; Rs = 2.4 nm; Mr = 24 000; f/f0 = 1.15) was detectable when cytosol was chromatographed on hydroxylapatite or was treated with trypsin. These proteolytic fragments are similar to those obtained for various other steroid hormone receptors. Mixing experiments with liver cytosol showed that the AtT-20 glucocorticoid receptor could also be cleaved to these fragments. Endogenous proteases are apparently in low concentration in this cell line. Finally, activation appears to result in the exposure of the protease-sensitive regions, since sodium molybdate, which prevents receptor activation, also renders the receptor resistant to proteolysis.

Subunit dissociation as a possible mechanism of glucocorticoid receptor activation

For the elucidation of the mechanism of steroid hormone receptor activation, the hydrodynamic properties of the unactivated and activated forms of the nonproteolyzed glucocorticoid receptor from the mouse AtT-20 pituitary tumor cell line were determined. The unactivated, molybdate-stabilized receptor has the following properties: sedimentation coefficient = 9 S; Rs = 8.3 nm; Mr = 317 000; f/f0 = 1.70; axial ratio (prolate ellipsoid) = 14. The activated monomeric receptor has a sedimentation coefficient of 3.2 S, a Stokes radius of 6 nm, a molecular weight of 81 000, a frictional ratio of 1.93, and an axial ratio (prolate ellipsoid) of 18. A receptor species of intermediate size was detected when the analysis was performed in buffer containing both 0.3 M KCl and 20mM Na2MoO4. Its characteristics are as follows: sedimentation coefficient = 5 S; Rs = 8.3 nm; Mr = 176 000; f/f0 = 2.06; axial ratio (prolate ellipsoid) = 22. A preliminary study seemed to indicate that this is an activated form of the receptor. On the basis of the molecular weights, it is likely that the unactivated receptor is a tetramer of identical hormone-binding subunits (Mr = 81 000) while the intermediate form is a homodimer. Alternatively, non-hormone-binding components (receptor-binding factors) may be involved in forming the multimeric, nonactivated receptor complex. In either case, the dissociation of a multimeric, nonactivated receptor into subunits appears to be a possible mechanism of receptor activation. Finally, the addition of high concentrations of 1-thioglycerol promoted activation. Thus, sulfhydryl groups may be involved in receptor subunit interaction.

Activation of the chick oviduct progesterone receptor by heparin in the presence or absence of hormone

Activation (transformation) of the chick oviduct progesterone receptor was found to be induced at 0 degrees C by heparin free in solution as well as by chromatography on a column of heparin linked to acrylamide/agarose. The transformed molecule displayed properties of the activated form of [3H]progesterone-receptor complex obtained by heat treatment or by high ionic strength: smaller size (s20,w = 3.9 S, Stokes radius = 5.2 nm), lower rate of dissociation (t 1/2 approx. 50 h at 0 degrees C compared with approx. 20 h for the 'native' form) and increased binding to phosphocellulose. In all cases, molybdate was an effective inhibitor of transformation and stabilized a large 'native' form (s20,w = 7.9 S, Stokes radius = 7.6 nm). Transformation by neither KCl nor heparin depended on the presence of ligand bound to the receptor, and the properties of the receptor molecule produced by treatment of ligand-free receptor with high ionic strength or with heparin were identical with those of the activated progesterone-receptor complex, demonstrating that receptor activation can be obtained experimentally in the absence of hormone. Our data are compatible with a model in which activation implies separation of the 4 S units, which compose the approx. 8 S 'native' form.

Tissue distribution and biochemical properties of an interspecific tumour-associated gamma foetal antigen

A late-gestation neonatal antigen (gamma foetal antigen; gamma-FA) immunologically and biochemically unrelated to murine alpha-foetoprotein, was identified in several spontaneous and carcinogen-induced sarcomas and hepatic carcinomas of the mouse and rat. An approximate mol. wt of 35,000 for gamma-FA from both foetus and tumour was obtained by molecular-sieve chromatography and sucrose-gradient centrifugation. Radial immunodiffusion analyses of organ extracts indicated that gamma-FA could be found in several neonatal tissues, the highest concentration occurring in the spleen. In the 2-month-old mouse, only splenic tissue contained gamma-FA and at much lower levels than in the organ of the newborn mouse.

Glucocorticoid receptor cleavage by leupeptin-sensitive enzymes in rat kidney cytosol

The proteolytic origin of small fragments of both the glucocorticoid and mineralocorticoid receptors in rat kidney cytosol was inferred from the effects of leupeptin, a bacterial tripeptide that inhibits many proteases [Sherman, M.R. et al., (1978). Federation Proc. 37:167--173]. In the present study, the smallest fragment of the glucocorticoid receptor containing the steroid-binding site, the mero-receptor, was characterized with respect to the Stokes radius (RS = 23 +/- 3 A) and the isoelectric point (pI = 5.9 at 4 degrees). Chromatography of cytosol labeled with [3H]triamcinolone acetonide on Sephadex LH-20 (Pharmacia) in aqueous buffer resolved the steroid-receptor complex from the unmodified free steroid and from steroid metabolites and contaminants. This technique facilitated analyses of the leupeptin-stabilized receptor form by isoelectric focusing (pU = 5.9 at 4 degrees) and centrifugation in glycerol gradients (s20,w = 9--11 S in 50mM KCl). When this large complex in fresh cytosol was analyzed on Agarose (Bio-Rad) at a high flow rate, it had RS congruent to 60 A in 50 mM KCl and RS congruent to 30 A in 400 mM KCl. These analytical studies with leupeptin indicate the need for inexpensive, irreversible inhibitors of proteolytic enzymes for the purification of intact receptors, holo-receptors, from kidney and other tissues. Specific proteases can then be applied to dissect the holo-receptor into the globular mero-receptor, proximal to the steroid-binding site, and the asymmetric region(s), distal segment(s), that may be involved in the nuclear interactions.

Oestrogen receptors in relation to human breast cancer

Work leading to the concept of hormone responsiveness of human breast cancer and current views of the mode of action of oestrogens in target tissues are reviewed. Results of oestrogen receptor assays are considered in relation to clinical response to tumours to endocrine therapy and difficulties encountered in the interpretation of receptor determinations are discussed. Recent work on the distribution of different forms of the oestrogen receptors in human tumours and their relation to clinical response may lead to better selection of patients for endocrine therapy. Results of receptor assays in male patients with breast cancer, in benign breast tumours and in malignant tumours at sites other than breast are reviewed, and work on receptors for hormones other than oestrogens is discussed briefly. Further work is needed on the integrity of the receptor mechanism in tumour cells and on the effects of hormone treatment. Methods for the separation and estimation of oestrogen receptors in human tumour tissue are reviewed and discussed. Errors arising during collection, storage and analysis are considered. Different ways of calculating and expressing results of these assays are mentioned. It is suggested that more accurate determinations of oestrogen receptors may lead to better discrimination between hormone responsive and unresponsive human breast tumours.

Multiple forms of oviduct progesterone receptors analyzed by ion exchange filtration and gel electrophoresis

Resolution of the multiple forms of steroid receptors in small samples has been improved by two new techniques: preparative ion exchange filtration and electrophoresis in highly cross-linked polyacrylamide gels of varied concentration. These techniques were used in conjunction with protamine precipitation, gel filtration, and density gradient centrifugation to separate five forms of the progesterone receptor of chick oviduct cytosol. These complexes, numbered I to V in order of elution from agarose gel columns, have been characterized with respect to apparent molecular weight, shape, and relative net charge. Form I, which is eluted in the void volume after gel filtration of cytosol in hypotonic media, is heterodisperse with respect to sedimentation coefficient and electrophoretic mobility (Rf). Form I is converted to form III by KC1. Form II has the highest axial ratio and the highest Rf at pH 10.2. This 4.2S complex can be extracted from DEAE filters, but not from protamine-precipitated cytosol, by 0.3 to 0.5 M KC1. Form III is slightly smaller (3.9S) and less asymmetric than form II. It is relased from DEAE filters and protamine-precipitated cytosol by 0.15 M KC1 and displays increased Rf upon purification. Forms II and III correspond to the B and A components described by W. T. Schrader and B. W. O'Malley ((1972), J. Biol. Chem 247, 51). Form IV may result from the proteolytic cleavage of forms II and/or III. Form V is a globular polypeptide obtained in the presence of certain divalent cations. This complex has been named the "mero-receptor" since it is the smallest part or fragment of the receptor that contains the steroid-binding site.