Purification and characterization of the chick oviduct progesterone receptor A subunit

Identification and properties of steroid-binding proteins in nesting Chelonia mydas plasma

We report for the first time the presence of a sex steroid-binding protein in the plasma of green sea turtles Chelonia mydas, which provides an insight into reproductive status. A high affinity, low capacity sex hormone steroid-binding protein was identified in nesting C. mydas and its thermal profile was established. In nesting C. mydas testosterone and oestradiol bind at 4 degrees C with high affinity (K (a) = 1.49 +/- 0.09 x 10(9) M(-1); 0.17 +/- 0.02 x 10(7) M(-1)) and low binding capacity (B (max) = 3.24 +/- 0.84 x 10(-5) M; 0.33 +/- 0.06 x 10(-4) M). The binding affinity and capacity of testosterone at 23 and 36 degrees C, respectively were similar to those determined at 4 degrees C. However, oestradiol showed no binding activity at 36 degrees C. With competition studies we showed that oestradiol and oestrone do not compete for binding sites. Furthermore, in nesting C. mydas plasma no high-affinity binding was observed for adrenocortical steroids (cortisol and corticosterone) and progesterone. Our results indicate that in nesting C. mydas plasma temperature has a minimal effect on the high-affinity binding of testosterone to sex steroid-binding protein, however, the high affinity binding of oestradiol to sex steroid-binding protein is abolished at a hypothetically high (36 degrees C) sea/ambient/body temperature. This suggests that at high core body temperatures most of the oestradiol becomes biologically available to the tissues rather than remaining bound to a high-affinity carrier.

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)

Turtle oviduct progesterone receptor: radioligand and immunocytochemical studies of changes during the seasonal cycle

In order to determine the regulation of the oviduct progesterone receptor inChrysemys picta, radioligand binding studies were performed to determine changes in the high and lower affinity binding sites during the seasonal cycle. Lower affinity sites were present in both cytosolic and nuclear fractions during the cycle and peaked during the peri-ovulatory/early luteal periods. The high affinity sites, present exclusively in the nuclear fraction, increased following the preovulatory peak in plasma estradiol, remained elevated during the early luteal phase following the post-ovulatory peak in progesterone, and declined to non-detectable levels just before egg-laying. DNA-cellulose affinity chromatography showed that both high and low affinity binding sites were integral to both progesterone receptor B and A isoforms. Western blot analysis confirmed the binding studies and showed that PR-B (115 kDa) was present in greatest amounts during the peri-ovulatory and luteal periods, whereas PR-A (88 kDa) increased during those periods and was present following egg-laying. Immunocytochemical analysis revealed increased progesterone receptor immunostaining from the winter to the peri-ovulatory period in the three major zones (luminal epithelium, submucosal glands and the myometrium) following the preovulatory peak in estradiol, a decrease in all three zones, especially the myometrium, in the late luteal period following the post-ovulatory peak in progesterone, and an increase again during fall recrudescence. Competition studies demonstrated that progesterone was the most effective competitor followed by pregnenolone, R5020 and deoxycorticosterone. RU 486 does not bind to the high affinity site, but binds quite well to the lower affinity site. This study suggests that progesterone receptor isoforms in the turtle oviduct may be under the regulation of changing estrogen/progesterone ratios during the cycle.

Characterization of a 1,25-dihydroxy-vitamin D3 receptor in FRTL-5 cells. Evidence for an inhibitory effect of 1,25-dihydroxy-vitamin D3 on thyrotropin-induced iodide uptake

When FRTL-5 cell cytosol was incubated with increasing amounts of [3H]1,25-dihydroxy-vitamin D3 [( 3H]1,25-(OH)2D3), saturation of specific hormone binding occurred. Scatchard analysis of specific binding of [3H]1,25-(OH)2D3 to the macromolecule yielded an apparent Kd value of 0.41 +/- 0.08 X 10(-10) M and a single maximum binding capacity of 42.8 +/- 8.8 fmol/mg protein. Sucrose gradient analysis revealed substantial [3H]1,25-(OH)2D3 association with a macromolecule sedimentating slightly faster than ovalbumin (3.7 S). [3H]1,25-(OH)2D3 was completely displaced by excess 1,25-(OH)2D3. The 1,25-(OH)2D3-receptor complex bound to DNA cellulose columns in low salt buffer, and eluted as a single peak at 0.15-0.20 M KCl. Thus, we have shown for the first time the existence of a functional 1,25-(OH)2D3 receptor in thyroid follicular cells. Furthermore, 1,25-(OH)2D3 inhibited the thyrotropin (TSH)-stimulated iodide uptake in a dose-dependent manner, indicating that 1,25-(OH)2D3 has an effect on the physiological function of rat thyroid follicular cells in culture.

Steroid hormone receptors

In the three decades since the original discovery of receptors for steroid hormones, much has been learned about the biochemical processes by which these regulatory agents exert their effects in target tissues. The intracellular receptor proteins are potential transcription factors, needed for optimal gene expression in hormone-dependent cells. They are present in an inactive form until association with the hormone converts them to a functional state that can react with target genes. Transformation of the receptor protein to the nuclear binding form appears to involve the removal of both macromolecular and micromolecular factors that act to keep the receptor form reacting with DNA. Much of the native receptor is present in the nucleus, loosely bound and readily extractable, but for some and possibly all steroid hormones, some receptor is in the cytoplasm, perhaps in equilibrium with a nuclear pool. Methods have been developed for the stabilization, purification, and characterization of receptor proteins, and through cloning and sequencing of their cDNAs, primary structures for these receptors are now known. This has led to the recognition of structural similarities among the family of receptors for the different steroid hormones and to the identification of regions in the protein molecule responsible for the various aspects of their function. Monoclonal antibodies recognizing specific molecular domains are available for most receptors. Despite the knowledge that has been acquired, many important questions remain unsolved. How does association with the steroid remove factors keeping the receptor protein in its native state, and how does binding of the transformed receptor to the response element in the promoter region enhance gene transcription? Once it has converted the receptor to the nuclear binding state, is there a further role for the steroid in modulating transcription? Still not entirely clear is the involvement of phosphorylation and/or dephosphorylation in hormone binding, receptor transformation, and transcriptional activation. Less vital to basic understanding but important in the overall picture is whether the native receptors for gonadal hormones are entirely confined to the nucleus or whether there is an intracellular distribution equilibrium. With the effort now being devoted to this field, and with the application of new experimental techniques, especially those of molecular biology, our understanding of receptor function is progressing rapidly. The precise mechanism of steroid hormone action should soon be completely established.

Interaction of the chicken progesterone receptor with heat shock protein (HSP) 90

The chicken progesterone receptor A (PRA) was expressed from cDNA by in vitro transcription and translation and also by transient transfection of receptor-negative COS M6 cells. These receptors synthesized from cDNA exhibited functional properties similar to those of oviduct PRA. The ability of PRA to form an 8S complex and to bind to DNA was studied. PRA, synthesized by either expression system, formed an 8S complex which was dissociated by incubation in vitro with 0.4 M NaCl or 20 nM progesterone to generate a 4S species able to bind to DNA-cellulose. The presence of HSP 90 in the PRA 8S complex was confirmed by use of an HSP 90-specific antibody, AC-7. Expression constructs coding for various receptor deletions were studied in order to identify the site of interaction of PRA with HSP 90. Deletions of 290 amino acids from the C-terminus resulted in the loss of ability to form an 8S complex. Truncated receptor proteins lacking 153 amino acids from the C-terminus or 369 amino acids from the N-terminus were able to interact with HSP 90. These data suggest that the site of interaction between PRA and HSP 90 responsible for 8S complex formation may be in this region (amino acid 369-506). However, small internal amino acid deletions in this region of PRA did not result in the loss of interaction of mutant receptor proteins with HSP 90. Thus, it appears that there may be more than one site of interaction between PRA and HSP 90 in this region.

Molecular interactions of steroid hormone receptor with its enhancer element: evidence for receptor dimer formation

A steroid hormone responsive element (GRE/PRE), sufficient to confer glucocorticoid and progesterone inducibility when linked to a reporter gene, was used in band-shift assays to examine its molecular interactions with steroid hormone receptors. Both progesterone and glucocorticoid receptors bound directly and specifically to the GRE/PRE. The purine contact sites for both form A and form B chicken progesterone receptor, as well as those for rat glucocorticoid receptor, are identical. A peptide fragment produced in bacteria that primarily contain the DNA binding domain of the glucocorticoid receptor binds first to the TGTTCT half-site of the GRE/PRE, and a second molecule binds subsequently to the TGTACA (half-site) of the GRE/PRE in a cooperative manner. Utilizing the peptide fragment and the protein A-linked fragment, we demonstrated that the receptor interacts with its cognate enhancer as a dimer.

Purification of the intact monomeric 110 kDa form of the androgen receptor from calf uterus to near homogeneity

In the present study, calf uterine tissue has been used for isolation of androgen receptors. This tissue appeared to be a favourable source for large-scale purification of androgen receptors, because of the relatively high level of androgen receptors and the low concentration of proteolytic enzymes. The purification involved differential phosphocellulose and DNA affinity chromatography as first steps. The non-transformed receptor was passed through these matrices in order to remove contaminating DNA-binding proteins. After a transformation step to the DNA-binding state, the receptor was bound to DNA cellulose and subsequently eluted with MgCl2. A 0.5% pure androgen receptor preparation was obtained. Photoaffinity labelling with [3H]R1881 (methyltrienolone) was used to determine the size of the receptor at this stage of purification and during the following steps. Subsequently, isoelectric focussing of the partially purified androgen receptor preparation in an aqueous glycerol gradient was performed. In this step, the progesterone receptor, which is copurified with the androgen receptor protein during the first part of the purification procedure, focussed at pH 5.5 while the androgen receptor could be isolated at pH 5.8. The isoelectric focussing procedure could be applied in a preparative way for further purification of androgen receptors. After this step an approx. 8% pure preparation was obtained. Polyacrylamide gel electrophoresis of S-carboxymethylated androgen receptor was used as the final purification step. The [3H]methyltrienolone labelled androgen receptor from calf uterus was purified to homogeneity and consisted of one polypeptide with a molecular mass of 110 kDa.

High-resolution separation of molybdate-stabilized progestin receptors using high-performance liquid chromatography

Molecular heterogeneity of the human uterine progestin receptor was investigated employing sucrose density gradient centrifugation and high-performance liquid chromatography (HPLC) in size-exclusion (HPSEC), ion-exchange (HPIEC) and chromatofocusing (HPCF) modes. Synthetic progestomimetic ligands, [3H]R5020 and [3H]ORG-2058, were used to identify these receptors. Rapid centrifugation with a vertical tube rotor showed both 8-9 S and 4-5 S receptor species in the presence of 10 mM sodium molybdate with a 90-96% recovery. [3H]R5020 displayed greater nonspecific binding than [3H]ORG-2058. When separated receptor preparations were labeled, each with a different ligand, mixed and separated on optimized gradients, at least two receptor isoforms were identified in the components sedimenting at 8-9 S. HPSEC confirmed the presence of receptor isoforms displaying different molecular size and shape dependent upon the progestin ligand used. When the surface charge properties were examined by HPIEC using AX-1000, two distinct species were observed irrespective of the radioactive ligand. The first peak appeared in the void volume similar to the position of free steroid, indicating the possibility of ligand stripping by the column. The second peak bound steroid specifically and eluted with 100 mM phosphate. If either 8-S or 4-S progestin receptors were first separated by gradient centrifugation then by HPIEC, both receptor isoforms eluted with 60 mM phosphate. Re-chromatography of these on HPIEC also gave the isoform eluting at 60 mM phosphate. HPCF of ligand-bound receptors on AX-500 columns also identified one isoform eluting at pH 5.6-6.1. Using a combination of HPLC techniques and sucrose gradient centrifugation, heterogeneity of the progestin receptor has been demonstrated.

Rat antibodies as probes for the characterization of progesterone receptor A and B proteins from laying hen oviduct cytosol

The chicken oviduct contains two different hormone binding forms of the progesterone receptor, A and B. We have prepared rat antisera against both forms of the receptor partially purified from laying hen oviduct. The anti-progesterone receptor A antiserum reacts with both receptor forms on Western blots, while the anti-progesterone receptor B antiserum reacts mainly with the B form. Both antisera also react with the native progesterone receptor proteins as shown by sedimentation analysis of the antibody-receptor complexes. Receptors A and B are recognized on Western blots of total protein from dissolved tissue, indicating that both forms are likely to be physiological components. Epitope mapping experiments show that immunogenicity of both receptor molecules is restricted to structurally related protein domains of 28 kDa in receptor A and of 52 kDa in receptor B.

Purification and characterization of the untransformed androgen receptor in rat prostate

The isolation and characterization of the untransformed form of androgen receptors has not yet been successful, owing to their inherent lability as well as to their ready proteolysis. In this study, we have stabilized rat prostate androgen receptors by sodium molybdate and by rapid filtration on phosphocellulose. Proteases were inhibited by bacitracin, aprotinin, leupeptin and PMSF. Under these conditions the untransformed complex was purified approx 3000-fold, corresponding to 18% yield, by differential chromatography on DEAE cellulose and phosphocellulose gels. The partially purified receptor has the same ionic characteristics as the original untransformed receptor of crude cytosol; in addition, it possesses a Stokes' radius of 75 A, as determined by Sephacryl S-300 gel filtration, a sedimentation coefficient of 8.8S, a calculated molecular weight of 275 kDa and a friction coefficient of 1.6. The [3H]R1881 receptor complex was specific to androgens since unlabelled R1881 and dihydrotestosterone were able to completely displace bound [3H]R1881, whereas estradiol, cortisol, and triamcinolone acetonide did not compete. The purified complex was a multimer dissociable by 0.6 M KCl, resulting in a form migrating in the 4S area on sucrose density gradient. After treatment with 0.5% formaldehyde, three forms were obtained, migrating in the areas of 8-9, 5-6 and 3-4S respectively, of a sucrose density gradient containing 0.6 M KCl. This is the first step towards the purification to homogeneity of the untransformed androgen receptor.

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)

High-yield high-performance liquid chromatographic analysis of steroid hormone receptors on glass columns

The HPLC characteristics of extensively purified chicken oviduct progesterone receptors were compared on TSK 3000 SW size-exclusion and DEAE-5-PW media packed in either glass or stainless-steel columns. Recoveries of [3H]progesterone-labeled receptor from size exclusion were 75-95% in glass columns and less than 10% in stainless-steel columns. Similarly, recoveries from DEAE were greater than 90% in glass columns but only approximately 45% in stainless-steel columns. Recoveries in glass columns were similar on several HPLC systems. Thus, the requisite component for high yields from extensively purified receptor preparations was the glass column itself. While receptor B exhibited ionic strength-dependent mobility similar to several standard proteins on size-exclusion glass column HPLC, receptor A was very peculiar. Resolution of receptors A and B was superior to previous reports using size exclusion open-end chromatography. We also resolved functionally active proteolytic fragments. Finally, the generality of glass column size-exclusion HPLC was demonstrated by high-yield analysis of different steroid hormone receptors from different tissues and species.

Properties of an intermediate-sized androgen receptor: association with RNA

This study identifies an intermediate-sized androgen receptor and characterizes its relationship with the 9.1S and 4.4S receptor forms. Under low ionic conditions, at 2-4 degrees C, there exists a 9.1S (+/- 0.17) (n = 30) oligomeric form which does not bind to DNA. Under high ionic conditions, this form dissociates to a 4.4S (+/- 0.08) (n = 18) monomeric form. When the salt concentration is lowered, the 4.4S monomer converts to a species with an intermediate sedimentation coefficient of 7.7S (+/- 0.15) (n = 17) which binds to DNA. Unlike the 9.1S oligomer the 7.7S form is not maintained by sodium molybdate under high ionic conditions but rather dissociates to the 4.4S monomer. To determine whether these forms were associated with RNA, the 7.7S form was incubated with RNase A and analyzed by density gradient centrifugation. The 7.7S form was digested fully by RNase to the 4.4S monomer. The 7.7S form demonstrated a buoyant density of 1.2459 +/- 0.014 g/cm3 (n = 6) in metrizamide gradients, suggesting a ribonucleoprotein component. The sedimentation coefficient of the 9.1S form was unaffected by RNase. These data suggest that the intermediate 7.7S receptor form is composed of 4.4S monomer associated with a ribonucleoprotein molecule(s).

Involvement of a non-hormone-binding 90-kilodalton protein in the nontransformed 8S form of the rabbit uterus progesterone receptor

Nontransformed 8S progesterone receptor (8S-PR) was purified by hormone-specific affinity chromatography from rabbit uterine low-salt cytosol containing 20 mM molybdate. In the eluate obtained with radioactive progestin, sodium dodecyl sulfate-polyacrylamide electrophoresis (SDS-PAGE) showed the presence of several bands, including three that corresponded to approximately 90-, approximately 120-, and approximately 85-kDa proteins. None of these three proteins was found in the eluate of the affinity column when the molybdate-containing cytosol was chromatographed in the presence of nonradioactive progesterone ("mock purification"). Subsequent purification of the affinity eluate by DEAE-Sephacel chromatography gave a single radioactive receptor peak at 0.15 M KCl (approximately 20% yield, 19% purity on the basis of one binding site per approximately 100 kDa) with a sedimentation coefficient of 8.5 S. Silver staining after SDS-PAGE revealed that this purified 8S-PR fraction contained mainly the 120-, 90-, and 85-kDa proteins. [3H]R5020-labeled 8S-PR purified by DEAE-Sephacel column chromatography was UV irradiated, and after SDS-PAGE the 120- and 85-kDa proteins were revealed, but the 90-kDa protein was not.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for a single steroid-binding protein in the rabbit progesterone receptor

The rabbit uterine progesterone receptor copurifies as two molecular weight (Mr) forms of about 105,000 and 78,000. To investigate whether these are different proteins, we have used protease digestion, reversible denaturation, and photoaffinity labeling in studies on the steroid-binding domain of the receptor. Digestion of the Mr 105,000 and 78,000 forms, photoaffinity labeled with [3H]R5020, with Staphylococcus aureus V8 protease revealed identical peptide fragments of Mr 43,000, 39,000, and 27,000-30,000. When receptor in cytosol was denatured, separated by electrophoresis, and then reconstituted, [3H]progesterone bound specifically to a single form at about Mr 105,000. After partial purification, the reversible denaturation procedure revealed both the larger and the smaller progesterone-binding species similar to the photoaffinity-labeled species in this preparation. Receptor in uterine cytosol prepared under mild conditions appeared as a predominant large molecular weight form on photoaffinity labeling with [17 alpha-methyl-3H]R5020, [6,7-3H]R5020, or [3H]RU27987. Further purification of this cytosol showed the generation of a smaller labeled species. These results from three different approaches reinforce the view that the rabbit progesterone receptor contains a single steroid-binding protein.

Identification of a putative progesterone receptor in the oviduct of a viviparous watersnake (Nerodia)

The steroid hormone progesterone is of particular interest in reproductive tract adaptations associated with the processing of embryonic materials in the evolution of viviparity. To further understand the mechanisms of action of this steroid, a progesterone receptor-like moiety was partially characterized in the oviduct of the viviparous snake Nerodia. Using DNA-cellulose and LH-20 column chromatography, a binding component was identified which exhibits high affinity (KA = 1.5 X 10(9) M-1) and low capacity (approximately 10(-11) M) binding of the synthetic progestin, R5020. In addition, the binding exhibited physiological steroid specificity, and was only identified in reproductive structures considered targets of progesterone action. These characteristics are consistent with the primary characteristics associated with steroid-receptor binding and are similar in both cytosolic and nuclear extract preparations.

Assessment of progestin receptor polymorphism by various synthetic ligands using HPLC

Tritiated R5020 and [3H]ORG-2058 were utilized to investigate apparent polymorphism of progestin receptors by vertical-tube gradient centrifugation and HPLC in size exclusion (HPSEC), ion-exchange (HPIEC) and chromatofocusing (HPCF) modes. Rapid centrifugation (3 h) following molybdate stabilization (1 h) showed mainly 8-9S receptor species with 90-96% recovery. [3H]R5020 appeared to associate with a receptor isoform sedimenting faster than that bound to [3H]ORG-2058. Excess unlabeled R5020 did not eliminate all of the [3H]R5020 binding by the 8-9S component suggesting some nonspecific association while excess unlabeled ORG-2058 suppressed this binding by either ligand. Separate labeling of cytosol with each ligand and mixing prior to gradient separation showed at least two receptor species isoforms sedimenting in the 8-9S region with mol. wt of 190,000 and 173,000 D. Sephacryl S-300 chromatography revealed two radioactive peaks with either ligand but with slight molecular weight differences. HPSEC confirmed the presence of isoforms with different molecular size and shape as a function of the radioactive ligand employed. HPIEC showed the presence of two labeled receptor species irrespective of the ligand used. The first peak appeared at the void volume of the column (10 mM), co-eluted with free ligand, indicating the possibility of ligand stripping by the column. The second peak bound both steroids specifically and eluted with 100 mM phosphate. HPCF identified a single specific receptor eluting at a pH of 5.6-6.1, but with free steroid in the void volume irrespective of the ligand used. [3H]ORG-2058 appeared to be less prone to the stripping phenomenon than was [3H]R5020. These data suggest these ligands either bind to different progestin receptor species or they modify receptor characteristics in a fashion that allows separation based upon size and shape.

Reversible dissociation of chick oviduct progesterone receptor subunits

We report here the reversible dissociation of chick oviduct progesterone receptor subunits by pyridoxal 5'-phosphate. This agent has been reported to inhibit binding of steroid hormone receptors to DNA and nuclei (Cake et al., 1978). We have found that pyridoxal 5'-phosphate inhibits binding of chick oviduct progesterone receptors to DNA-cellulose, and also dissociates 6-8S cytosolic receptor aggregates to 4S monomers. Both of these effects are shown to be reversible if pyridoxal phosphate is removed, allowing in vitro reconstitution of receptor aggregates. Fidelity of reconstitution has been assessed by testing the reconstituted aggregate for binding to DNA-cellulose, phosphocellulose, and by studies using sedimentation velocity measurements. By these three criteria, the reconstituted product is indistinguishable from the native cytosol complex from which the monomers were derived. The reconstitution reaction shows an absolute requirement for the presence of both receptor monomers A and B. Titration experiments show a molar ratio of 1:1 for A and B in the reconstituted aggregates. These reconstitution studies confirm our hypothesis (originally based upon dissociation experiments) that native receptor aggregates are composed of the A and B proteins as subunits.

Molecular properties of the androgen receptor in rat ventral prostate

Results from these studies demonstrate that we have purified a protein from rat prostate cytosol that is similar to the beta-protein (complex II) but different from the alpha-protein (complex I) reported by Liao et al. The purified receptor was different from androgen binding protein (ABP) in that ABP has a faster dissociation rate (6 min), a lower pI value (4.6), and requires higher concentrations of ammonium sulfate for precipitation (40-50%) than the prostatic androgen receptor. It is not likely that we have purified a serum sex-steroid binding protein since no such protein is found in rat serum. This report presents a rapid and efficient procedure for the purification of androgen receptor from rat ventral prostate. However, the present procedure only allowed us to obtain a limited quantity of purified receptor from each preparation. It is obvious that we need to scale up the purification of the receptor in order to study in detail its physicochemical properties and to produce monospecific antibodies against the protein. This work is in progress. In addition, we have demonstrated that two affinity labels can be used to bind covalently to the androgen receptor. Most importantly, these compounds can be used to characterize androgen receptors under both nondenaturing and denaturing conditions and represent useful tools for future work with androgen receptor proteins and androphilic proteins in general.

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)

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.

Purification by affinity chromatography and immunological characterization of a 110kDa component of the chick oviduct progesterone receptor

A 110kDa component of the chick oviduct progesterone receptor (PR) has been purified to homogeneity according to electrophoretic criteria and specific activity (assuming one progestagen-binding site/110kDa). The procedure involved affinity chromatography of 0.3 M-KCl-prepared cytosol, followed by DEAE-Sephacel chromatography (elution at 0.2 M-KCl). The final yield was about 12% in terms of binding activity. Properties of the 110kDa component indicate that it is identical with the 'B' subunit described previously [Stokes radius approximately 6.1 nm; sedimentation coefficient, (S20, w) approximately 4S; frictional ratio approximately 1.77]. It reacted with the IgG-G3 polyclonal antibody, but not with BF4 monoclonal antibody raised against the 8S molybdate-stabilized chick oviduct PR and reacting with its 90kDa component. Another progesterone-binding component, corresponding to the 'A' subunit, also previously described, was eluted from the DEAE-Sephacel column at approximately 0.08 M-KCl, and contained a peptide of molecular mass approx. 75-80kDa, which had S20, w approximately 4S in a sucrose gradient. This component was also recognized by IgG-G3, but not by BF4; it was very unstable in terms of hormone-binding activity.

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.

Progesterone receptor binding to DNA: studies by sedimentation velocity methods

Chicken oviduct progesterone receptor subunit A (Mr = 79000) was partially purified as a hormone-receptor complex labeled with [3H]progesterone. These complexes adsorb to DNA-cellulose; sucrose gradient ultracentrifugation showed a sedimentation coefficient of 3.6 S. Receptors were mixed with [32P]DNA fragments of various types derived from bacterial plasmid pBR322. DNA structures tested included linear double-stranded and single-stranded molecules as well as supercoiled intact plasmids. [3H]Receptors were mixed in various molar ratios with [32P]DNA (nominal sed. coeff. = 18 S) and the mixtures were analyzed by sedimentation velocity ultracentrifugation performed in 5-20% sucrose gradients. In the presence of excess DNA, all of the [3H]receptor sedimented with the DNA fraction. Titrations revealed an apparent Kdiss between 1 and 5 nM. Distribution of receptor counts over the slower-sedimenting edge of the DNA peaks allowed estimation of the half-life of these complexes, which was in excess of 35 min at 0 degree C. Double-label counting of [3H]receptor-[32P]DNA complexes revealed an increase in the sedimentation coefficient of linear double-stranded DNA as increasing receptor input was used. Analysis of this S-value shift showed evidence for cooperative receptor binding isotherms, causing dramatic compaction (or other topological constraints) on the DNA. A speculative schematic model of receptor A-DNA interaction is presented, consistent with the experimental results.

Resolution of the effects of sulfhydryl-blocking reagents on hormone- and DNA-binding activities of the chick oviduct progesterone receptor

The differential effects of sulfhydryl (SH)-blocking agents on hormone and DNA binding by the chick oviduct progesterone receptor were investigated. Previous studies have demonstrated inhibition of steroid-receptor interaction by SH-blocking agents and protection against inhibition by bound hormone. The present results indicate that the SH group required for steroid binding is within or near the hormone-binding site itself, and that a second SH group (or groups) is involved in the binding of receptor to DNA. Three findings relate to the site of action of SH-blocking agents on hormone binding. First, glycerol decreased the rate of hormone dissociation and the rate of hormone displacement by mercurial reagents by 75 to 90%. Second, mercurial reagents displaced [3H]progesterone bound to the mero-receptor, a Mr 23,000 proteolytic fragment containing the hormone-binding site, but not the site of interaction with DNA. Third, hormone displacement was still present after a 10,000-fold purification of the progesterone receptor. Mercurial reagents also inhibited binding of progesterone receptor to DNA, whereas the SH-alkylating agents N-ethylmaleimide and iodoacetamide had no effect. It is likely that distinct sulfhydryl groups are required for steroid receptor interaction with hormone and with DNA, since brief treatment with mercurial reagents blocked DNA binding, but caused only a slight displacement of bound hormone. The SH group required for hormone binding probably lies within or near the hormone-binding site, is sensitive to mercurials, alkylating agents, and 5,5'-dithiobis(2-nitrobenzoate) (DTNB), and is protected by bound hormone. The SH group required for DNA binding, in contrast, is sensitive to mercurials but not to alkylating agents, is only partially sensitive to DTNB, and is not protected by bound hormone.

Rat uterine progesterone receptor: stabilization of hormone-binding components for biochemical analyses

A method was developed for quantitative recovery of the labile rat uterine progesterone receptor hormone-binding components. Initial conditions were established by the sucrose gradient procedure. Upon centrifugation through low-salt 5-20% sucrose gradients prepared in 10% glycerol, the well-known 6-8 S progesterone receptor components were observed either when cytosol was prelabeled with [3H]17,21-dimethyl-19-nor-4,9-pregnadiene-3,20-dione [( 3H]R5020) or when prelabeled with [3H]progesterone followed by postlabeling the fractions collected after centrifugation with either [3H]progesterone or [3H]R5020. Recovery of progesterone receptor binding was improved by prelabeling with [3H]R5020, by adding 1.5 mM ethylene glycol bis(beta-aminoethylether)N,N'-tetraacetic acid (EGTA) to all buffers, and at high tissue concentrations. Under these conditions quantitative conversion of the receptor to specific [3H]R5020-binding 4S components was achieved with 150 or 400 mM KCl. Similar conditions proved unsuitable for receptor analysis by gel filtration (Bio-Rad agarose A0.5M or A1.5M), apparently due to [3H]R5020 dissociation from the receptor in the large volume of elution buffer. However, excellent receptor recovery (97.2 +/- 6.7%) was achieved by including 10 nM unlabeled progesterone in all preparation and elution buffers. Receptors were then detected by the addition of 5 nM [3H]R5020 to the column fractions, exchange incubation for 3-6 h at 4 degrees C, and subsequent separation of bound and free steroid by the hydroxyapatite assay. This method resulted in a consistent elution pattern suggestive of receptor heterogeneity. Identity of the peak(s) as progesterone receptor components(s) was confirmed by the lack of competition by 2 microM cortisol when added either to cytosol or during the postlabeling-exchange process. Neither the qualitative nor quantitative results of the column profiles were changed substantially in the presence of 20 mM molybdate. Although the receptor structure has yet to be established, both statistical analysis of the column profiles by computer curve-fitting procedures and rechromatography of peak fractions suggested that the rat uterine progesterone receptor may be composed of multiple components. This ligand-stabilization/postlabeling-exchange procedure provides a method for further studies of progesterone receptor biochemistry in mammalian systems. Additionally, similar procedures may stabilize other labile ligand-binding proteins for biochemical analyses and/or purification.

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.

How do steroid hormones function to induce the transcription of specific genes?

On the whole, the question as to how steroid hormones act to induce the transcription of specified genes is not much more understood today than it was 15 years ago, but considerable progress has been made during this time to bring us a step closer to unravelling the mysteries surrounding the mechanism of hormonal gene activation. Hopefully, further studies in the three fields described (i.e. DNA/receptor binding experiments, gene-transfer experiments, and in vitro transcriptional studies) will bring in enough information for a complete story to be told one day. As to the questions asked in the introduction of this review, there appear to be sequences around inducible genes that render them sensitive to hormone administration. These sequences could be arranged in appropriate chromosomal structures flanking the gene region particularly at the 5′ end. As to whether these sequences bind the hormone/receptor complex, the experiments with the MMTV proviral DNA (17, 21–23) and the ovalbumin gene (27) appear to provide an affirmative answer. But the answer to whether this binding is responsible for the gene activation must await future experimentation. In vitro transcriptional studies specially designed with the hormone/receptor/DNA complex may be useful in answering this question.

DNA sequence preference of the progesterone receptor

Highly purified hen oviduct progesterone receptor A subunit was tested for binding to several chicken gene DNAs. Sequence preference detected by nitrocellulose filter adsorption of [32P]DNA fragments obtained from recombinant plasmids revealed a marked retention of certain DNA fragments. About a 10-fold preference was seen for DNA fragments flanking the 5' end of the steroid-regulated genes ovalbumin and gene Y. No preference was seen with analogous DNA fragments from chicken beta-globin and alpha-actin genes. Restriction endonuclease mapping suggests the presence of multiple receptor interaction sites flanking the 5' terminus of the ovalbumin gene. One of these preferential binding sites was localized between -135 and -247 base pairs upstream from the start of transcription. This region contains an 18-base-pair A + T-rich sequence, a likely candidate for the binding site itself, because earlier studies had shown receptor A to have marked preference for A + T-rich DNA.

Oligodeoxynucleotide base recognition by steroid hormone receptors

Oligodeoxynucleotides covalently linked to cellulose were used as probes of the DNA-binding domains of mouse steroid holoreceptors. With uterine cytosol estrogen receptor (E2R) the relative binding order, in prior studies, was oligo(dG) greater than oligo(dT) greater than or equal to oligo(dC) much greater than oligo(dA) greater than oligo(dI). The binding reactions were salt-sensitive with an optimal KCl concentration of 0.1-0.2 M. There was no enhancement of binding by activation, either temperature- or salt-induced. In the present study, using the oligomer ligands at a lower concentration, oligo(dT) binding was greater than that to oligo(dC). Quantitative differences in oligodeoxynucleotide binding were elicited by a number of inhibitors. These differences are again seen by exposure of E2R to chaotropic salts such as SCN-, ClO-4 and NO3- as well as to putative modifiers of receptor amino acids, ie, iodoacetamide, 1,2 cyclohexanedione, and Rose Bengal. These results, and the quantitative differences following heat and purification, led to a designation of two types of subsites within the DNA-binding domain of uterine E2R. These are stable G sites, which interact with oligo(dG); and labile N sites, which bind to oligo(dT), oligo(dC) and oligo(dA). Stimulation of binding to N sites and stabilization of the holoreceptor was effected by histones H2A and H2B. However, the differential response to incubation at 37 degrees C was not altered by addition of H2B. Treatment of uterine E2R by limited proteolysis also eliminated the stimulatory response to H2B. The above data, as well as prior studies, indicate that steroid holoreceptors can discriminate between the structural features of deoxynucleotide bases and this recognition process can be modulated by accessory proteins.

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.

Receptors for 1,25-dihydroxyvitamin D3 in chick pancreas: a partial physical and functional characterization

1,25-Dihydroxyvitamin D3(1,25-(OH)2D3) receptors from the rachitic chick pancreas have been partially characterized. Analyses of these receptors by isokinetic gradient centrifugation and analytical gel filtration reveal a sedimentation coefficient (S) of 3.3-3.7, a molecular weight (Mr) of 58,500-68,000, and a calculated Stokes molecular radius (Rs) of 34-36 A. Polyethylenimine-ammonium sulfate precipitation of pancreatic cytosol partially purifies aporeceptor and reduces nonspecific binding (in part, 5.8S DBP), thus providing material more amenable to kinetic analyses, Binding studies incorporating this fractionated cytosol reveal an equilibrium dissociation constant (K4) of approximately 0.112 nM at 2 degrees C for the 1,25-(OH)2D3-receptor interaction. Competition studies further demonstrate a particular preference for 1,25-(OH)2D3 over 1,24(R),25-trihydroxyvitamin D3, 24(R),25-dihydroxyvitamin C3, and 25-hydroxyvitamin D3. The pancreatic receptor also binds to immobilized group-selective affinity ligands such as DNA, cibacron blue, and heparin, and can be eluted as a single macromolecular species during standard linear KCl gradients. Its interaction with these ligands supports the premise that the 1,25-(OH)2D3 receptors' fundamental mode of action is at the level of the cellular genome. Salt-dependent nuclear uptake and chromatin localization studies with this receptor in vitro also support this potential site of action. Significantly, a physiologic dose of 1,25-(OH)2[3H]D3 to rachitic chicks leads to the in vivo formation of a receptor-hormone complex as identified by DNA-cellulose chromatography. These observations provide further evidence that the pancreatic protein is a biologically relevant component of the chick pancreas which functions to accumulate hormone intracellularly under physiologic situations.

Purification of chicken intestinal receptor for 1 alpha, 25-dihydroxyvitamin D3 to apparent homogeneity

The chicken intestinal 1 alpha, 25-dihydroxyvitamin D3 receptor-like protein has been purified to apparent homogeneity as determined by sodium dodecyl sulfate gel electrophoresis. The techniques employed for the purification include selective precipitation of the receptor by Polymin P (polyethyleneimine) and (NH4)2SO4 and batch adsorption to and selective elution from hydroxylapatite, followed by gel exclusion and DEAE-cellulose chromatography. Finally, the labeled receptor was eluted at a pH of approximately 6.0 on a chromatofocusing column. The protein was purified 6100-fold and the receptor was obtained in 9% yield.