Progesterone-binding components of chick oviduct. Receptor B subunit protein purified to apparent homogeneity from laying hen oviducts

Cistrome and transcriptome analysis identifies unique androgen receptor (AR) and AR-V7 splice variant chromatin binding and transcriptional activities

The constitutively active androgen receptor (AR) splice variant, AR-V7, plays an important role in resistance to androgen deprivation therapy in castration resistant prostate cancer (CRPC). Studies seeking to determine whether AR-V7 is a partial mimic of the AR, or also has unique activities, and whether the AR-V7 cistrome contains unique binding sites have yielded conflicting results. One limitation in many studies has been the low level of AR variant compared to AR. Here, LNCaP and VCaP cell lines in which AR-V7 expression can be induced to match the level of AR, were used to compare the activities of AR and AR-V7. The two AR isoforms shared many targets, but overall had distinct transcriptomes. Optimal induction of novel targets sometimes required more receptor isoform than classical targets such as PSA. The isoforms displayed remarkably different cistromes with numerous differential binding sites. Some of the unique AR-V7 sites were located proximal to the transcription start sites (TSS). A de novo binding motif similar to a half ARE was identified in many AR-V7 preferential sites and, in contrast to conventional half ARE sites that bind AR-V7, FOXA1 was not enriched at these sites. This supports the concept that the AR isoforms have unique actions with the potential to serve as biomarkers or novel therapeutic targets.

Combinatorial control of gene expression by nuclear receptors and coregulators

The nuclear receptor (NR) superfamily of transcription factors regulates gene expression in response to endocrine signaling, and recruitment of coregulators affords these receptors considerable functional flexibility. We will place historical aspects of NR research in context with current opinions on their mechanism of signal transduction, and we will speculate upon future trends in the field.

Steroid receptor interactions with heat shock protein and immunophilin chaperones

We have provided a historical perspective on a body of steroid receptor research dealing with the structure and physiological significance of the untransformed 9S receptor that has often confused both novice and expert investigators. The frequent controversies and equivocations of earlier studies were due to the fact that the native, hormone-free state of these receptors is a large multiprotein complex that resisted description for many years because of its unstable and dynamic nature. The untransformed 9S state of the steroid and dioxin receptors has provided a unique system for studying the function of the ubiquitous, abundant, and conserved heat shock protein, hsp90. The hormonal control of receptor association with hsp90 provided a method of manipulating the receptor heterocomplex in a manner that was physiologically meaningful. For several steroid receptors, binding to hsp90 was required for the receptor to be in a native hormone-binding state, and for all of the receptors, hormone binding promoted dissociation of the receptor from hsp90 and conversion of the receptor to the DNA-binding state. Although the complexes between tyrosine kinases and hsp90 were discovered earlier, the hormonal regulation or steroid receptor association with hsp90 permitted much more rapid and facile study of hsp90 function. The observations that hsp90 binds to the receptors through their HBDs and that these domains can be fused to structurally different proteins bringing their function under hormonal control provided a powerful linkage between the hormonal regulation of receptor binding to hsp90 and the initial step in steroid hormone action. Because the 9S receptor hsp90 heterocomplexes could be physically stabilized by molybdate, their protein composition could be readily studied, and it became clear that these complexes are multiprotein structures containing a number of unique proteins, such as FKBP51, FKBP52, CyP-40, and p23, that were discovered because of their presence in these structures. Further analysis showed that hsp90 itself exists in a variety of native multiprotein heterocomplexes independent of steroid receptors and other 'substrate' proteins. Cell-free systems can now be used to study the formation of receptor heterocomplexes. As we outlined in the scheme of Fig. 1, the multicomponent receptor-hsp90 heterocomplex assembly system is being reconstituted, and the importance of individual proteins, such as hsp70, p60, and p23, in the assembly process is becoming recognized. It should be noted that our understanding of the mechanism and purpose of steroid receptor heterocomplex assembly is still at an early stage. We can now speculate on the roles of receptor-associated proteins in receptor action, both as individuals and as a group, but their actual functions are still vague or unknown. We can make realistic models about the chaperoning and trafficking of steroid receptors, but we don't yet know how these processes occur, we don't know where chaperoning occurs in the cell (e.g. Is it limited to the cytoplasm? Is it a diffuse process or does chaperoning occur in association with structural elements?), and, with the exception of the requirement for hormone binding, we don't know the extent to which the hsp90-based chaperone system impacts on steroid hormone action. It is not yet clear how far the discovery of this hsp90 heterocomplex assembly system will be extended to the development of a general understanding of protein processing in the cell. Because this assembly system is apparently present in all eukaryotic cells, it probably performs an essential function for many proteins. The bacterial homolog of hsp90 is not an essential protein, but hsp90 is essential in eukaryotes, and recent studies indicate that the development of the cell nucleus from prokaryotic progenitors was accompanied by the duplication of genes for hsp90 and hsp70 (698). (ABSTRACT TRUNCATED)

Characterization of chromatin binding sites for different forms of uterine progesterone receptor

We tested hamster uterine progesterone receptor (Rp) forms for binding to different chromatin preparations. Similar forms of chick oviduct Rp were used for comparison. Hamster Rp elutes from DEAE-Sephacel in the two peaks, peak I at 115 mM KCl and peak II at 205 mM KCl. Chick Rp peaks I and II elute at 125 mM and 300 mM KCl, respectively. Both chick and hamster peak I displayed a higher level of binding to SDS-stripped chromatin (DNA) than to crude chromatin or 4 M guanidine hydrochloride (GuHCl)-extracted (nucleoacidic protein, NAP) chromatin while peak II bound 50% better to the NAP chromatin than to crude chromatin or DNA. 10 mM molybdate was used to stabilize Rp and to increase Rp recovery. Molybdate-stabilized hamster Rp elutes from DEAE at the peak II position and like peak II, binds poorly to DNA. Since molybdate prevents receptor activation, DNA-Rp interactions require activated Rp. Because molybdate did not prevent Rp binding to NAP chromatin, we conclude that both activated and unactivated Rp bind well to that matrix. Activated hamster Rp could be extracted from crude chromatin, NAP chromatin and DNA with 200 mM KCl. Unactivated Rp was extracted from NAP only with 6 M GuHCl or NaSCN, whereas KCl, glycerol or pyridoxal 5'-phosphate were not able to remove unactivated Rp from NAP. Various Rp forms did not compete with [3H]ORG 2058-Rp for binding to NAP but BSA did compete. Thus a large portion of Rp binding to NAP may represent nonspecific binding rather than binding to a finite number of Rp acceptor sites. These results suggest that the binding of activated Rp to crude chromatin may represent the actual acceptor sites in target cell nuclei. Since the high level of Rp binding sites in NAP chromatin may be an extraction artifact, the involvement of proposed masking proteins in regulating the availability of acceptor sites should be reconsidered. As an alternative to acceptor site regulation, changes in the Rp molecule itself may be important. Rp isolated from hamster uteri on days 1-4 of the estrous cycle was incubated with crude chromatin, NAP chromatin and DNA. The apparent level of Rp binding to chromatin and NAP chromatin increased 2.5-fold from day 1 to day 4, but Rp binding to DNA remained constant. This suggests that ovarian cycle-dependent changes occur in the unactivated Rp which affect its interactions with chromatin, and these changes disappear when receptor is activated.(ABSTRACT TRUNCATED AT 400 WORDS)

HPLC analysis of estrogen receptor by a multidimensional approach

Previously we demonstrated the polymorphism of estrogen receptors (ER) in cytosol of various tissues based upon properties of size, shape and surface charge. This study describes the application of a multidimensional approach utilizing HPLC for characterization of ER. Cytosols from human uterus and endometrial carcinomas were characterized sequentially by high performance size exclusion chromatography (HPSEC) on Spherogel TSK-3000 SW, and high performance ion-exchange chromatography (HPIEC) using SynChropak AX-1000 anion exchange columns. Using HPSEC, specific estrogen binding was exhibited by a 30 A isoform and by one appearing after the V0 (approximately 60 A) in human uterus. However, in endometrial carcinoma other smaller binding components with Stoke's radii of less than 20 A were observed also. In buffers containing 400 mM KCl, predominantly a 28-30 A species was observed by HPSEC. Further characterization of the 28-30 A isoform from low and high salt elution from HPSEC was accomplished with an AX-1000 column. With either condition, 2 forms were eluted on HPIEC, 1 in the column wash (retention time 8-9 min), and the other at 50-70 mM phosphate. The elution profile of the larger species (approximately 60 A by HPSEC) on the ion-exchange column was time dependent. Immediate analysis (within 15 min) showed a profile similar to that of the original cytosol which contained minor components eluting in wash buffer and at 50-70 mM phosphate and a major isoform at 180 mM phosphate. However delayed analysis (after 2 h) of the 60 A isoform showed a similar profile (components in buffer wash and at 50-70 mM phosphate) obtained with the 30 A species. This time dependent change was not observed for the 30 A species or for the original cytosol. Estrogen receptors in cytosol sedimented at 10S and 4S in low ionic strength gradients and at 4S in sucrose gradients containing 400 mM KCl. The 28-30 A and 60 A species recovered from HPSEC sedimented at 3.5S. This multidimensional approach indicates that native estrogen receptors dissociated into a number of smaller molecular isoforms, which were distinguishable by different surface charge properties.

The physicochemical nature of 37 degrees C cytoplasmic glucocorticoid receptors in HeLa S3 cells

The physicochemical properties of size, shape and surface charge have been determined for the soluble fraction of cytoplasmic glucocorticoid receptors which are located in the HeLa S3 cell cytoplasm after incubation of whole cells with glucocorticoid at 37 degrees C. Under hypotonic buffer conditions approximately 80% of the total recovered [3H]triamcinolone acetonide receptor complexes sedimented through a 5-20% density gradients to the tube bottom, and approximately 90% eluted from a Sephacryl S-300 gel exclusion column in the void volume. Increasing the [KCl] of the buffer in the sucrose density gradients, and gel exclusion columns to 0.15 M caused a reduction in the percentage of this large aggregate to approximately 64% and approximately 75%, respectively. Further increases in the [KCl] during analysis to 0.4 M reduced the percentage of rapidly sedimenting receptors to approximately 62%, and shifted the sedimentation coefficient of the slower sedimenting receptors from approximately 5.2 S to 3.9 S. These conditions also decreased the fraction of receptor in the void volume of gel exclusion columns to 67%. Ion exchange analysis of receptor binding to DEAE cellulose, hydroxylapatite, phosphocellulose, and DNA cellulose revealed heterogenous populations of receptor species; comprising both "unactivated" and "activated" receptor forms. The ratios of unactivated/activated receptors was highly dependent on the matrix employed and differed substantially among those evaluated. For example, by the criteria of DEAE cellulose and phosphocellulose chromatography approximately 60% of the total 37 degrees C cytoplasmic receptors were in the "activated" state. A large fraction of these receptors, however, failed to bind to DNA cellulose. These results demonstrate that the glucocorticoid receptors which remain in the HeLa S3 cytoplasm at 37 degrees C do not bind to ion exchange materials, which are used as indexes of receptor "activation," in a uniform manner. We hypothesize that the diminished DNA binding capability of these receptors accounts for their cellular localization in the HeLa S3 cell cytoplasm at 37 degrees C.

Structural analysis of chicken oviduct progesterone receptor using monoclonal antibodies to the subunit B protein

Two monoclonal antibodies against the B subunit (Mr 108 000) of chick oviduct progesterone receptor (PgR) were produced by immunizing rats and fusing spleen cells with NS-1 mouse myeloma cells. The hybridoma lines designated 9G10 and 3E8 produce rat IgG2a and IgG2b, respectively. Antibody-receptor interactions were demonstrated under protein denaturing conditions. Previous studies by Weigel et al. [Weigel, N. L., Tash, J. S., Means, A. R., Schrader, W. T., & O'Malley, B. W. (1981) Biochem. Biophys. Res. Commun. 102, 513-519] have shown that chick PgR can be phosphorylated in vitro. Both antibodies, 9G10 and 3E8, were shown to displace partially denatured 32P-labeled PgR from its characteristic 4S position on high salt sucrose density gradients to a form with a higher sedimentation coefficient. Further specificity and sensitivity were demonstrated by protein immunoblotting experiments. In partially purified as well as electrophoretically pure receptor B subunit preparations antibodies reacted with the Mr 108 000 receptor B band. By immunoblot assay 9G10 was 20-fold more sensitive than 3E8, the former detecting down to 5 ng of receptor and the latter 100 ng. Because of its sensitivity 9G10 was able to detect the Mr 108 000 receptor as a single band in a crude oviduct fraction and did not cross-react with any other contaminating proteins. Receptor antigenic determinants were localized by immunoblot assay of receptor proteolytic digests.(ABSTRACT TRUNCATED AT 250 WORDS)

Isoforms of estrogen receptors by high-performance ion-exchange chromatography

SynChropak AX-300, AX-500 and AX-1000 columns were used to separate ionic forms of estrogen receptors by high-performance ion-exchange chromatography. Cytosols from hormone-responsive tissues were incubated for 4-10 h with 3-4 nM [16 alpha-125I]iodoestradiol-17 beta, cleared of unbound ligand and applied to an anion-exchange column. Components were eluted at pH 7.4 using a gradient of phosphate buffer at 4-6 degrees C. Non-specific binding components were identified by chromatographing, the identical cytosol, incubated with [125I]iodoestradiol and a 500-fold excess of diethylstilbestrol, which blocks specific binding sites. [125I]Iodoestradiol was applied to the column in the absence of cytosol and eluted normally to determine the behavior of free ligand. Each column exhibited a different elution pattern for the estrogen receptor. The various isoforms of estrogen receptor were eluted differently from each column usually in the 15-120 mM and 180-250 mM region of the gradient. Often one non-specific binding component was not retained whereas other non-specific species were retained and eluted from the column in a salt-dependent manner; their position in the gradient varied from column to column. Similarly, free [125I]iodoestradiol was eluted at different positions in the gradients, dependent upon which column was employed. In general, the high flow-rates, reproducibility, good recovery and the apparent differential selectivity of each of the columns appear valuable in the investigation of the nature and subunit composition of the estrogen receptor molecule.

Chick oviduct progesterone receptor: structure, immunology, function

Analysis of the purified chick oviduct progesterone receptor using biochemical and immunological approaches indicates that while the 'activated' receptor ('4S') is a mixture of two progestin-binding polypeptides, 'A' (Mr approximately 79 kDa) and 'B' (Mr approximately 110 kDa), the non-activated receptor ('8S') is a population of complexes containing a hormone-binding polypeptide (A or B, but probably not both) bound to a non-hormone-binding protein (Mr approximately 90 kDa). Two molecules of the 90 kDa protein appear to be present in each '8S' receptor molecule. The 90 kDa protein is also associated with the non-activated forms of receptors of other steroid hormones in the chick. Molybdate stabilizes the non-activated receptors, probably by forming weak coordination bonds with radicals provided by the subunits of the '8S' structure. Activation implies separation of the subunits, without a change in their primary structure, and does not require intervention of any protein other than those present in the '8S' receptor form. The presence of ligand at the binding site accelerates the activation process but, in vitro, is not necessary for it to occur. Unlike the non-activated form, activated receptors bind to the cell nuclei. However, histological studies with anti-progesterone receptor antibodies indicate that in the non-hormone-exposed tissue the (non-activated) receptors could be localized in the nuclei.

Antibodies against highly purified B-subunit of the chick oviduct progesterone receptor

A rabbit was immunized with the highly purified B-subunit (110kDa) (20 to 50 micrograms per injection) of the chick oviduct progesterone receptor (PR). Specific antibodies (IgG-RB) were observed 2 weeks after the first booster injection and high antibody titers in the serum were found after the second and third booster injections (with Kdeq of interaction integral of 2 nM). IgG-RB were tested by immunoprecipitation, immunoblotting, density gradient ultracentrifugation and protein A-sepharose assay methods. They recognized not only the B-subunit but also the A-subunit (79K), the nuclear PR, the mero-receptor (proteolytic cleavage product) and the "non-activated" molybdate-stabilized "8S" PR. However, IgG-RB did not interact with the 90K non hormone-binding component of this 8S-PR. IgG-RB did not affect the binding of the hormone to PR, whether incubated with the receptor before or after labelling with tritiated progesterone. They did not cross-react with glucocorticosteroid receptor of the chick oviduct. Weak interaction was observed with estrogen receptor of the chick oviduct and with KC1 activated "4S" forms of the rabbit and human uterus PR.

The avian progesterone receptor: isolation and characterization of phosphorylated forms

Methods have been developed for isolation of the avian progesterone receptor in the nontransformed, molybdate-stabilized state. The final step in this procedure. DEAE-Sephadex chromatography, resolves the receptor into two forms, components I and II. Analysis of these components by polyacrylamide gel electrophoresis under denaturing conditions shows that both contain a peptide with Mr = 90,000. These peptides contain phosphorylated serine residues, as shown by [32P]orthophosphate incorporation studies. When the cytosol receptor is treated with alkaline phosphatase, its steroid binding capacity is abolished. These studies show that the nontransformed progesterone receptor is a phosphoprotein and indicate that receptor phosphorylation may be important to the maintenance of steroid binding capacity.

Purification to homogeneity of the nuclear estrogen receptor from chick liver

The nuclear estradiol receptor from chick liver was purified to apparent homogeneity by using a combination of ammonium sulfate precipitation and affinity gel chromatography. The purified receptor migrated as a single band on an SDS-polyacrylamide gel with a molecular weight of 55000 and it exhibited a sedimentation coefficient of 4 S, a dissociation constant of 1.13 nM and a steroid specificity resembling that of the receptor in crude extracts.

The isolation and characterization of specific 3-methylcholanthrene-binding proteins from rat liver cytosol

The major proteins to which 3-methylcholanthrene specifically binds have been purified over 480-fold with a 45% yield compared to a rat liver 100,000g supernate. The procedure involved a batch ion-exchange technique together with hydrophobic gel filtration and chromatofocusing chromatography. The multiple, specific 3-methylcholanthrene-binding proteins obtained from this protocol had apparent isoelectric points of pH 6.3, 6.0, 5.7, and 5.5 on elution from a chromatofocusing column. They all shared a common sedimentation coefficient as determined by sucrose gradient analysis of 4.4 S. Gel filtration on Sephadex G-75 gave a common Stokes radius of 27 A. An analysis of these chromatofocusing peaks by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed those which eluted at pH 6.3 and 6.0 to contain two major protein bands of Mr 32,000 and 34,000, together with several contaminating proteins. In contrast, the peaks from chromatofocusing which eluted at pH 5.7 and 5.5 contained three major proteins of Mr 40,000, 25,000, and 14,000. The specific binding capability of these chromatofocusing peaks was found to be unstable to temperatures of -30 degrees C and below. Competition studies showed that these proteins were not steroid receptors, and that only polycyclic aromatic hydrocarbons which could induce cytochrome P-450c were able to displace 3-methylcholanthrene from the binding site. A marked preference was noted for polycyclic aromatic hydrocarbons with four to five benzene rings arranged in a nonlinear fashion, suggesting the stereochemical requirements of the protein binding site. The stability of the noncovalent interaction between the proteins and 3-methylcholanthrene was in the range of pH 7 to 9.

Protein kinase activity of purified components of the chicken oviduct progesterone receptor

Preparations of the 90K and 110K components of the chick oviduct progesterone receptor (PR) purified to near homogeneity were tested for protein kinase activity. The 90K component was shown to incorporate radioactive phosphate from [gamma-32P]-ATP in the presence of Ca2+ but not of Mg2+ ions, while the 110K component was phosphorylated in the presence of Mg2+, but not of Ca2+. The enzymatic activity of the 90K polypeptide appeared selective, since added proteins (histones) did not become phosphorylated. However, all proteins present in the 110K preparations were phosphorylated in the presence of Mg2+. These data suggest that components of the chick oviduct PR display protein kinase activity.

Purification of the receptor for 1 alpha,25-dihydroxyvitamin D3 from chicken intestine

Methods were investigated for use in the purification of the chicken intestinal receptor for 1 alpha,25-dihydroxyvitamin D3. The techniques investigated include column isoelectric focusing, gel exclusion, polyacrylamide gel electrophoresis, and DNA-cellulose, DEAE-cellulose, and hydroxylapatite chromatography. For the starting receptor preparation, a nuclear extract of chicken intestinal mucosa was found to be enriched above cytosol preparations and a plentiful source of receptor. A five-step purification scheme that resulted in the purification of the receptor protein by 5800-fold with 8% yield has been described. Analysis of the purified proteins on polyacrylamide gel electrophoresis containing sodium dodecyl sulfate suggests homogeneity. Analysis using two-dimensional polyacrylamide electrophoresis characterized the purified protein as having a molecular weight of approximately 63 000 and a pI of 6.0-6.2. Furthermore, assessment of protein purity by 125I iodination followed by sucrose gradient analysis revealed that approximately 90% of the iodinated macromolecules have the same sedimentation coefficient as the titrated 1 alpha,25-dihydroxyvitamin D3 receptor complex. The final purified receptor that bound tritiated 1 alpha,25-dihydroxyvitamin D3 retained affinity for DNA-cellulose and possesses a 3.7S sedimentation coefficient. The receptor has an estimated Stokes radius of 37 A.

Progestin binding in mammary tissue of prepartum, nonlactating and postpartum, lactating cows

Binding of [3H]R5020 (17,21-dimethyl-19-nor-4,9-pregnadiene-3, 20-=dione) to bovine mammary cytosol indicated the presence of progestin binding sites of high-affinity and low-capacity in tissue from prepartum, nonlactating and from postpartum, lactating cows. To prevent binding of [3H]R5020 to glucocorticoid binding sites, a 200-fold molar excess of nonradioactive cortisol was included during all incubations, thus specific binding was limited to progestin binding sites. Nonradioactive R5020 and progesterone effectively inhibited [3H]R5020 binding to progestin binding sites, while estradiol-17 beta, dihydrotestosterone (17 beta-hydroxy-5 alpha-androstan-3-one), dexamethasone (9-fluoro-11 beta, 17, 21-trihydroxy-16 alpha methyl-1,4-pregnadiene-3,20-dione) or additional cortisol were ineffective. Dissociation constants for especially bound [3H]R5020 in cytosol from mammary tissue of nonlactating and lactating cows were nearly identical, averaging 1.9 (+/- 0.3) and 0.8 (+/- 0.2) x 10(-9)M, respectively. However, binding capacities (fmol/mg cytosolic protein) were greater in cytosol from prepartum, nonlactating (179 +/- 53) than postpartum, lactating (41 +/- 15) cows. Specific binding components in cytosol from lactating cows sedimented iun the 6-7S region on linear sucrose density gradients. When subjected to isoelectric focusing, specific binders with isoelectric points (pI) of approximately 6.1, 7.9 and 8.3 were resolved. The decrease in number of binding sites during lactation was due to the virtual absence of the anionic binding species, suggesting that their presence is necessary for progesterone to inhibit milk secretion.

Progesterone receptor from chick oviduct: purification of molybdate-stabilized form and preliminary characterization

A molydate-stabilized, 'non-activated' form of the progesterone receptor from the cytosol of oestrogen-stimulated chick oviduct has been purified to homogeneity by a three-step procedure. The first step, affinity chromatography using a N-(12-amino-dodecyl)-3-oxo-4-androsten-17 beta-carboxamide-substituted Sepharose gel, purified the receptor 1500-2700-fold with approximately equal to 50% recovery. In the second step, ion-exchange chromatography through a DEAE-cellulose column, progesterone receptor was eluted as a single peak at 0.1 M KCl. Purification after this step was greater than 6700-fold. The third step was filtration through Ultrogel AcA 34, resulting in overall purification approximately equal to 7400-fold with overall recovery approximately equal to 25% of pure receptor on the basis of 1 binding site/molecule of Mr 85000. The purified molybdate-stabilized receptor had a sedimentation coefficient approximately equal to 7.9S +/- 0.1 (n = 4) in 0.15 M or 0.4 M KCl containing sucrose 5-20% gradient and approximately equal to 8.9S +/- 0.2 (n = 6) in 0.15 M KCl containing glycerol 10-35% gradient, and its Stokes radius was 7.05 +/- 0.10 nm (n = 3) (calculated Mr between 240000 and 280000). Binding specificity of the purified receptor was the same as that found in crude cytosol. SDS-PAGE revealed a single band migrating as a polypeptide of Mr approximately equal to 85000 +/- 2300 (n = 9). PAGE under non-denaturing conditions at total acrylamide concentrations 5%, 7% and 9% showed a single [3H]ORG 2058-protein band (ORG 2058 is a high-affinity analogue more suitable than progesterone for electrophoretic studies). The data suggest that the high molecular weight molybdate-stabilized progesterone receptor purified from oestrogen-primed chick oviduct is composed of only approximately equal to 85000-Mr polypeptide chains.

Oviduct progesterone receptor: physical and chemical studies

Chicken oviduct progesterone receptor has been purified to homogeneity. The protein consists of two dissimilar hormone-binding subunits, A and B, present in equal amounts in the complex. They have molecular weights of 79,000 and 108,000, respectively, as shown by both SDS-gel electrophoresis of the purified proteins and photoaffinity labeling of both with a labeled synthetic progestin. The two subunits show considerable homology (or identity) of structure at the hormone-binding domain, located at the N-terminus of the proteins. Considerable divergence of sequence must exist elsewhere in A and B, as shown by tryptic peptide mapping and by the fact that subunit A has a strong DNA-binding site lacking in B. Both are phosphorylated in vitro by cAMP-dependent protein kinase; this phosphorylation appears to be responsible for creation of a second, weaker progesterone-binding site on each subunit.

Physicochemical properties of the cytoplasmic glucocorticoid receptor complex in HeLa S3 cells

The physiochemical properties, size, shape, and surface charge, have been determined for the cytoplasmic glucocorticoid receptor complex (GR) in randomly growing HeLa S3 cells. Sucrose density gradient and gel exclusion chromatographic analysis have shown GR to undergo a marked reduction in size and shape when analyzed under increasing KCl concentration conditions. Analysis of GR prepared in a hypotonic buffer solution revealed a large, 7-8 S species with Ve/Vo ratio of 1.15, and a Stokes radius of congruent to 95 A. Increasing the KCl concentration in the analysis buffer to 0.15 resulted in reduction in GR size and shape to a 4.5 S species with the following properties: Ve/Vo = 1.38. Stokes radius = 69 A. and calculated Svedberg molecular weight = 132,000. A limit to the observed decrease in GR size and shape was obtained under hypertonic, 0.4 M KCl, conditions; a 3.75 S form was observed to elute from the gel exclusion column with a Ve/Vo = 1.40. Stokes radius = 65 A. and a calculated Svedburg molecular weight = 102,000. Exposure to higher KCl conditions, 0.6 M and 0.8 M, resulted in no further decrease in GR size or shape. Ion exchange chromatographic analysis of cytoplasmic GR revealed heterogeneous populations of GR with apparent differences in surface charge. GR binding to DEAE cellulose revealed a predominant form which eluted at 0.15 M KCl (Form I). Under both hypotonic and hypertonic conditions small populations of GR forms were observed to elute from DEAE at or approximately 0.1 M KCl (Form III), and or approximately 0.3 M KCl (Form II), respectively. Binding of GR to hydroxylapatite (HAP) confirmed the heterogenous nature of GR. Cytoplasmic GR partitioned into at least 3 forms om HAP. The predominant GR form eluted from HAP at 0.1 M K2HPO4 (Form I); secondary, and tertiary forms eluted at 0.125 M (Form II), and 0.15 M K2POH4 (Form III), respectively. Glucocorticoid receptors were observed to elute from columns of phosphocellulose, and DNA cellulose in the void volume. Two receptor forms were observed with isoelectric focusing of HeLa S3 cytoplasm in Sephadex IEF G-75 gels. The primary, and secondary species had pI values of 7.5 and 6.3, respectively. These results demonstrate that randomly growing HeLa S3 cells contain heterogeneous population of GR in the cytoplasmic compartment. Randomly growing HeLa S3 cell cytoplasm appears to contain two "unactivated" receptor species (Forms I and II) that differ in their overall surface charge properties; a third activated species (Form III) appears to arise from heat induced "activation" during cell homogenization, and is more basic in nature.

Problems associated with dose response in steroid-hormone activation of structural genes

A typical target cell for a sex steroid hormone contains 10 000--20 000 specific high-affinity receptors for that hormone. However full physiological responses can be achieved with only 2000 of these receptors involved in hormone--receptor complex interaction with the nucleus. The number of nuclear acceptor sites that must be filled before responses occur maybe even less. This implies that multiple occupation of nuclear acceptor sites by hormone--receptor may occur permitting co-operative induction of transcription of selected genes. The numbers of sites of initiation of RNA synthesis seem excessively high (about 70 000 per cell). Although this may be an artifact of the isolation procedures the proportion of initiation sites under hormonal control (equivalent to about 30 000 per cell) is still large. The numbers of mRNA species under hormonal control varies greatly depending on the particular hormone and target tissue. The extent to which these different observations can be incorporated into a unifying theory is discussed.

Partial purification of the nuclear estrogen receptor from chicken liver by affinity chromatography

The crude nuclear extract from the liver of estrogenized chickens contains 0.3-1 pmol/g tissue of the estrogen receptor. The receptor has been partially purified by ammonium sulphate precipitation and affinity chromatography on 17 beta-estradiol-17-hemisuccinyl-ovalbumin-Sepharose 4B. A 12% pure receptor preparation (2700-fold purification) with a yield of 17% could be obtained. The partially purified receptor has retained most properties which it displayed in cruder preparations, e.g. the dissociation constant of 10(-9)-10(-10) M, the hormone specificity and the sedimentation coefficient of 3.9 S. The size (Stokes radius, 2.9 nm; molecular weight, 49 000) and the asymetry (f/f0 = 1.10) of the receptor molecule, however, appear slightly reduced after the purification.

Structural relationships between the chick oviduct progesterone receptor A and B proteins

The chick oviduct contains two distinct forms of the progesterone receptor, termed progestophilins A (Mr = 79,000) and B (Mr = 117,000). Although these two hormone-binding proteins differ significantly in physico-chemical characteristics, a good deal of similarity exists between these two molecules. Thus, both proteins display identical hormone-binding kinetics and steroid specificity. The hormone-binding fragments obtained after the action of an endogenous oviduct Ca2+-activated protease are indistinguishable as analyzed by gel filtration chromatography. Both the A and B proteins are capable of binding to DNA-cellulose, although they elute at very different salt concentrations when subjected to gradient elution. In spite of these similarities all attempts to demonstrate the conversion of progestophilin B to A or to show a common precursor to both have been unsuccessful. Therefore, either the A and B receptor proteins are separate products of closely related genes or the conversion of one form to another occurs very rapidly either in vivo or in vitro.

Effects of progestins on the progesterone receptor in guinea pig uterus

We examined the effects of progesterone and some synthetic progestins and other steroids on the physical properties of the progesterone receptor of guinea pig uterine cytosol and on the binding of the receptor by nuclei. Progestational potency seemed to correlate with the ability to keep the receptor in the 7S form and to prevent dissociation into smaller subunits. The rate of activation prior to nuclear binding was slower with steroids of increasing progestational activity. Therefore activation in vitro may be unrelated to biological activity. Concentration of the cytosol led to a decrease in the equilibrium association constant. The extent of the decrease was less with progesterone than with its metabolite, 5 alpha-pregnanedione. When cytosol and nuclei were incubated in the absence of ligand measureable progesterone receptor was bound by the nuclei. The uncomplexed nuclear receptor bound [3H]-progesterone of [3H]-R5020 rapidly at 0 degrees, but progesterone-receptor complexes exchanged [3H]-progestin slowly at 0 degrees. Progesterone increased the amount of nuclear receptor at concentrations of 10(-9) and 10(-8)M, but decreased binding at higher concentrations. 5 alpha-Pregnanedione had the same effect as progesterone, but other metabolites of progesterone that had little affinity for the 7S progesterone receptor in cytosol had no effect on nuclear binding at any concentration. Glucocorticoids, testosterone and estradiol-17 beta increased the nuclear binding of the progesterone receptor when present at concentration of 10(-8)M and greater.

Factors influencing association of glucocorticoid receptor-steroid complexes with nuclei, chromatin, and DNA: interpretation of binding data

Attempts to reconstruct, in a test tube, the steroid-hormone system of a responsive cell are fraught with enumerable difficulties. In this chapter I have attempted to point out some of the factors that affect receptor-steroid complexes and their interactions with acceptors. In most cases there is a quantitative influence of these factors on the level of steroid complex binding to acceptors. In some cases, selected experimental designs that neglect these factors and methods of presenting the observed data may lead to artifactual conclusions. Several of these problems should disappear when the prospect of pure receptor-steroid complexes [127, 147, 150, 181, 247, 248] becomes a common occurrence. Nevertheless much has already been learned about the interactions of complexes with acceptors, which in turn have been used to help formulate models of steroid-hormone action.