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

Intracellular glucocorticoid receptors in spleen, but not skin, vary seasonally in wild house sparrows (Passer domesticus)

Over the short-term and at physiological doses, acute increases in corticosterone (CORT) titres can enhance immune function. There are predictable seasonal patterns in both circulating CORT and immune function across many animal species, but whether CORT receptor density in immune tissues varies seasonally is currently unknown. Using radioligand binding assays, we examined changes in concentrations of glucocorticoid receptors (GR) and mineralocorticoid receptors (MR) in spleen and skin in wild-caught house sparrows in Massachusetts during six different life-history stages: moult, early winter, late winter, pre-egg-laying, breeding and late breeding. Splenic GR and MR binding were highest during the pre-laying period. This may help animals respond to immune threats through increased lymphocyte proliferation and/or an increase in delayed-type hypersensitivity reactions, both of which CORT can stimulate and in which spleen is involved. A decrease in splenic GR and MR during the late breeding period coincides with low baseline and stress-induced CORT, suggesting immune function in spleen may be relatively CORT-independent during this period. We saw no seasonal patterns in GR or MR in skin, suggesting skin's response to CORT is modulated primarily via changes in circulating CORT titres and/or via local production of CORT in response to wounding and other noxious stimuli.

Higher-Order Structural Determinants for Expression of the Ovalbumin Gene Family

The ovalbumin gene and the ovalbumin-related X and Y genes are expressed in the chicken oviduct in response to steroid hormones. These three genes are linked within a 100 kb domain of DNA which is preferentially sensitive to DNase I digestion in oviduct cell nuclei. No such preferential sensitivity to DNase is observed in nuclei isolated from other chicken tissues in which these genes are not transcribed. Thus, the DNase I sensitivity observed is correlated with the capacity for these genes to be expressed in oviduct. We have asked the question: are there specific signals in the DNA which are responsible for defining this domain or for conferring upon it the active, DNase I-sensitive, conformation? We have located DNA sequences belonging to a single repetitive DNA family, termed CR1, which are preferentially located in or near the boundary regions of the 100 kb domain. Therefore, these CR1 sequences are possible candidates for such a function. We have also searched for, but have not observed, any tissue-specific rearrangements of the DNA in the boundary regions of the domain. It is therefore unlikely that DNA rearrangements are involved in establishing the DNase I-sensitive domain in oviduct cells. However, we do note that a region at the far 3' end of the domain exhibits a cytidine methylation pattern which is highly variable among different chicken tissues. In particular, this region, which is approximately 30 kb downstream from the ovalbumin gene, is undermethylated in oviduct as compared to other hen tissues, and thus could be a control region involved in domain activation.

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)

Phosphorylation of chicken oviduct progesterone receptor by cAMP-dependent protein kinase

Phosphorylation of immunopurified chicken oviduct progesterone receptor (PR) was studied in intact cells and under cell-free conditions. Cytosol PR was isolated by incubation with anti-PR monoclonal antibody alpha PR22 adsorbed to protein A-Sepharose and suspended in a reaction mixture containing 10 mM Mg2+, 0.1 mM [gamma-32P]ATP, and the catalytic subunit of cAMP-dependent protein kinase (cAMP-PK) from bovine heart. All three major proteins of avian PR (PR-A, 79 kDa; PR-B, 110 kDa; 90 kDa) incorporated 32P-radioactivity on serine residues. The phosphorylation reaction was inhibited by synthetic inhibitors of protein kinases, H-8 and 20-residue peptide IP20. A 40 degrees C preexposure of PR oligomer increased phosphorylation of the 90-kDa protein, known to be a heat-shock protein (hsp-90). The extent of the phosphorylation reaction was temperature-dependent as the 32P-incorporation into PR-A and PR-B increased gradually, showing a maximum at 37 degrees C. Multiple phosphopeptides (4-7) were resolved by two-dimensional electrophoresis chromatography following cleavage of 32P-labeled peptides with trypsin. Both A and B forms of receptor showed similar phosphorylation patterns with B receptor digestion exhibiting two to three additional peptides. Under physiological conditions, preincubation of oviduct mince with forskolin, a regulator of intracellular cAMP levels, caused a greater extent of phosphorylation of PR-A and PR-B proteins. The results of this study demonstrate that chicken oviduct PR is an excellent substrate for the action of cAMP-PK in vitro and that this enzyme may be a physiological regulator of progesterone action in the oviduct.

Demonstration of steroid hormone receptors and steroid action in primary cultures of rat glial cells

Primary cultures of rat glial cells were established from newborn rat forebrains. A mixed population of oligodendrocytes and astrocytes was obtained, as confirmed by indirect immunofluorescence staining with specific markers for each cell type. Receptors were measured 3 weeks after primary culture in glial cells cultured in the presence or not of 50 nM estradiol and we have identified progesterone, glucocorticoid, estrogen, and androgen receptors (PR, GR, ER and AR), but only PR was inducible by the estrogen treatment. This estrogen-induction of PR was more dramatic in glial cells derived from female offsprings than from males, as measured by binding studies and by immunohistochemical techniques with the KC 146 anti-PR monoclonal antibody. The antiestrogen tamoxifen inhibited the estrogen induction, but had no effect by itself on PR concentration. Specific binding sites for PR, GR, ER and AR were measured by whole cell assays after labeling cells with, respectively, [3H]R5020, [3H]dexamethasone, [3H]OH-tamoxifen or [3H]R1881. PR and GR were also analyzed by ultracentrifugation and after exposure of cells to agonists, both receptors were recovered from cytosol as a 9S form, and from the nuclear high-salt, tungstate ions-containing fraction as a 4-6S form. In contrast, when the antiprogestin- and antiglucocorticosteroid RU486 was used as a ligand, a non-activated 8.5S receptor complex was found for both receptors in this nuclear fraction. The 8.5S complex of the GR was further analyzed in the presence of specific antibodies and, in addition to GR, the presence of the heat shock protein hsp90 and of a 59 kDa protein was found. During primary culture, the effects of progesterone (P) and estradiol (E2) were tested on glial cell multiplication, morphology and differentiation. Cell growth was inhibited by P and stimulated by E2. Both hormones induced dramatic morphologic changes in oligodendrocytes and astrocytes and increased synthesis of the myelin basic protein in oligodendrocytes and of the glial fibrillary acidic protein in astrocytes.

Steroid hormone binding in the Harderian gland of birds: characteristics of the androgen, estrogen, and progestin receptors of Anas platyrhynchos and Gallus domesticus

A series of experiments was carried out in immature female chicks and ducks to establish whether the avian Harderian gland contains specific receptors for sex steroids. Cytosol preparations of Harderian glands were submitted to hormone saturation analysis using radiolabeled estradiol, ORG-2058, and dimethylnortestosterone as ligands. In addition, the sedimentation characteristics of the hormone-receptor complexes were studied by ultracentrifugation of linear sucrose gradients. The presence of high affinity binding sites for estrogens (Kd = 2.4 and 1.6 nM), progestins (0.8 and 1.0 nM), and androgens (1.0 and 1.0 nM) was indicated in the chick and duck glands, respectively. The sedimentation coefficients were 7-7.5 S, 7-8 S, and 8 S for estrogen, progestin, and androgen receptor-ligand complexes, respectively. The concentration of the androgen receptor was significantly higher in chick than in duck Harderian glands whereas the estrogen and progestin receptor concentrations were similar in both species. A striking finding was the presence of progestin receptors, which apparently do not exist in the glands of many mammals. Priming with estrogens did not modify the concentration of ORG-2058 binding sites in either species studied, indicating that gland progestin receptor is not estrogen-regulated. Overall the data suggest intracellular mechanisms whereby circulating gonadal hormones regulate avian Harderian gland function.

Estrogen-inducible progesterone receptor in primary cultures of rat glial cells

The presence of an estrogen-inducible progesterone receptor was demonstrated in primary cultures of newborn rat glial cells by biochemical and immunohistochemical techniques. The progesterone receptor (PR) was measured 3-4 weeks after primary culture in estradiol-containing or control medium. Cells were labeled with the synthetic progestin [3H]R5020 followed by ultracentrifugation analysis of the cellular extracts. A "9 S" PR was observed in the cytosol and a "4-5 S" PR was found in the nuclear high salt, tungstate ions containing extract of estradiol-treated cells. When the antiprogestin [3H]RU486 was used instead of [3H]R5020 as a ligand, a 9 S PR was also found in the cytosol, but a nonactivated "8.5 S" receptor complex was identified in the high salt nuclear fraction in presence of tungstate ions. The levels of PR, as measured by whole cell assay, were significantly increased when glial cells were cultured in the presence of 50 nM estradiol, as compared to nonestradiol-treated controls. The estrogen induction of PR was suppressed by the antiestrogen tamoxifen, but tamoxifen by itself had no effect on PR concentration. When the glucocorticosteroid receptor and PR were measured in parallel after estradiol treatment of the same primary culture, only the levels of PR were increased. The PR was visualized inside glial cells by immunohistochemical studies with a monoclonal antibody specific for the B-form of PR (KC 146), which was recognized by fluorescein-linked or biotinylated secondary antibodies. Strong staining was observed in estradiol-treated cultures, when compared to a weaker staining in control cultures. This is the first demonstration of PR in rat glial cells, and we present evidence of its induction by estradiol in primary cultures.

Isolation of untransformed bovine estrogen receptor without molybdate stabilization

A low concentration estrogen-derivatized affinity resin has been used in a rapid, single step purification of the untransformed estrogen receptor from calf uterine cytosols prepared without sodium molybdata. The procedure isolates the Mr 65,000 estrogen receptor in association with the bovine heat shock protein hsp90. Small amounts of proteolyzed receptor ranging in size from Mr 50,000 to 60,000 are also present in the purified extracts. Results from affinity chromatography of receptor cytosols either untreated or presaturated with estradiol suggest that two proteins of Mr 22,000 and 38,000 are co-purified with the untransformed receptor complex and may represent additional nonhormone-binding components of the native receptor form. Some indication of the stability of protein-protein interactions within the oligomeric complex has been derived from differential salt elution studies with heparin-sepharose and affinity gel-immobilized untransformed receptor. On size exclusion high performance liquid chromatography the untransformed complex eluted with a Stokes radius of 75 +/- 2 A (n = 18), but was shown to be sensitive to extended ultracentrifugal analysis dissociating to the receptor homodimer, sedimentation coefficient 5.3 +/- 0.3 s (n = 5). Preliminary data on urea- and heat-induced transformation of the isolated receptor to the DNA-binding state is presented.

Studies on the characterization of rat prostate androgen receptors

In the presence of sodium molybdate and protease inhibitors, two forms of androgen-receptor complexes were observed which sedimented in the areas of 8-9S and 5-7S by SDG centrifugation. The intermediary 5-7S form was better seen when complexes were incubated at low KCl concentrations. The sedimentation coefficient of this form fluctuated between 5 and 7S depending on the KCl concentration. At high ionic strength (0.6M KCl) in all media, one form only was observed having a sedimentation coefficient value of 4.3S. By gel exclusion chromatography, we also observed two specific entities at 75A and 68A; in the presence of 0.6M KCl, however, two entities were found at 68A and 43A. The constant presence of protease inhibitors in all buffers was necessary to separate the intermediary 68A form. We calculated molecular weights of about 270 kDa, 190 kDa, and 80 kDa respectively for these three forms. [3H]R1881-receptor complexes bound to DEAE-cellulose and were eluted in the absence of glycerol at 0.1M and 0.2M KCl. Material found at 0.1M KCl sedimented in the areas of 5-7S and 8-9S in nearly equal proportion, and that found at 0.2M KCl sedimented in the 8-9S area only. When the cytosol was chromatographed at a fast flow rate (4 ml/min), untransformed 8-9S receptors did not bind to phosphocellulose, but transformed complexes were retained, could be eluted with 0.4M KCl and sedimented in the 4S area on KCl free SDG centrifugation. When the excluded untransformed 8-9S complexes were re-chromatographed at a slow flow rate (1 ml/min), they were retained on phosphocellulose, and could be eluted with 0.3M KCl.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical characterization and subunit structure of quail oviduct progesterone receptor

The cytosolic quail oviduct progesterone receptor (PR) was studied under conditions that lead either to its stabilization or activation. Sedimentation coefficients and Stokes radii were respectively 7.8 +/- 0.2 S and 7.6 +/- 0.8 nm for the non transformed receptor (8S PR) and 3.9 +/- 0.4S and 4.8 +/- 0.6 nm for the transformed receptor (4S PR). The calculated molecular weight was 261 +/- 29 KDa for the 8S PR and 83 +/- 10 KDa for the 4S PR. Density gradient centrifugation analyses showed that the monoclonal antibody BF4, directed against the 90 KDa hsp of the chick oviduct, cross-reacted with the quail 8S PR but not with the 4S PR. In contrast, polyclonal IgG-G6 antibodies, raised against the purified non transformed chick PR, cross-reacted with the non transformed as well as the transformed quail PR. The quail 8S PR was partially purified using NADAc-Sepharose affinity chromatography and DEAE-Sephacel chromatography from cytosol prepared with protease inhibitors. The subunit structure of the purified quail and chick 8S PR were compared using SDS-PAGE, photoaffinity labeling and western immunoblotting. The quail PR was composed of two different proteins: a non-hormone binding protein (Mr approximately 90 KDa) which exhibited the same properties as the 90 KDa hsp protein of the chick oviduct and a single hormone binding subunit (Mr approximately 101 KDa). Based on its binding and immunological properties, this protein corresponded to the "B" form of the chick PR but was significantly smaller. In the quail cytosol or in purified PR preparations the "A" form of the PR was virtually absent; this observation is discussed.

The antiprogesterone RU486 stabilizes the heterooligomeric, non-DNA-binding, 8S-form of the rabbit uterus cytosol progesterone receptor

The salt-induced (0.3 M KCl) transformation of the non-transformed, heterooligomeric 8S-form of the rabbit uterus cytosol progesterone receptor (PR) was analyzed by density gradient ultracentrifugation (8S----4S conversion) and DNA-cellulose chromatography (non-binding----binding forms). After 1 h treatment at 2 C, greater than 90% of agonist (R5020 or Org2058)-PR complexes were transformed, contrary to antagonist (RU486)-PR complexes, which did not undergo any transformation. Thus, there is stabilization of the non-transformed receptor form by RU486 as compared to the effect of agonist binding. The hydrodynamic parameters of both agonist- and antagonist-bound non-transformed receptors were similar and the calculated Mr were approximately 283,000 and approximately 293,000, respectively. In both cases, purification indicated the presence of a 90-kD non-hormone-binding protein associated with the hormone binding unit(s). Transformation of RU486-PR complexes occurred after exposure to high salt at increased temperature and was correlated to the dissociation of the 90-kD protein from the receptor. Both agonist- and antagonist-bound transformed forms of PR had apparent similar affinities for DNA-cellulose. Molybdate-stabilized and KCl-treated RU486-PR complexes were more stable, as assessed by steroid binding, than the corresponding R5020-PR complexes, arguing in favor of a stabilizing effect of both the 90-kD protein and RU486 against inactivation. These cell-free experiments support the concept that RU486 in the rabbit uterus system stabilizes the 8S non-DNA binding, non-transformed form of the receptor at low temperature. The possibility that impaired dissociation of the heterooligomeric receptor form is involved in the antiprogesterone activity of RU486 is discussed.

Characterization of progesterone receptor subunits in breast cancer cell line, CAMA-1N

In order to study whether cytosolic progesterone receptor (PRc) is involved in progesterone-induced proliferative arrest of breast cancer cells (CAMA-1N), subunit composition of PRc in these cells was characterized. In the TSK G3000 high-performance liquid chromatography (HPLC) column, molybdate-stabilized PRc eluted as a single sharp peak immediately following the void volume. PRc from this peak had a sedimentation coefficient of 7.6 S and was eluted at 0.22 M salt from a linear gradient (0.1 to 0.4 M NaCl) in a DEAE column. When covalently labeled with [3H]R5020, analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and visualized by fluorography, PRc from crude cytosol exhibited two major protein bands with molecular weights of 105 +/- 2.1 and 83 +/- 3.2 kD, respectively. However, HPLC-purified PRc showed only one major band of 105 kD. These results show that PRc in CAMA-1N cells has steroid-binding components similar to other target tissues and provides a basis for further quantitative and qualitative analyses of PRc during cell proliferation and progesterone-induced growth arrest of CAMA cells.

Steroid hormone antagonists at the receptor level: a role for the heat-shock protein MW 90,000 (hsp 90)

Antisteroid hormones compete for hormone binding at the receptor level and prevent the hormonal response. A new concept is proposed for explaining the antiglucocorticosteroid activity of RU 486 in the chick oviduct system. It is based on the ability of the antisteroid to stabilize the hetero-oligomeric 8S-form of the glucocorticosteroid receptor (GR), which involves the interaction of the 94k-receptor and heat-shock protein MW 90,000 (hsp 90). It is proposed that hsp 90 caps the DNA binding site of the receptor, and this prevents it from binding to the DNA of hormone regulatory elements (HRE) and increasing transcription of regulated genes. This paper reviews other antiglucocorticosteroid and antiestrogen systems with reference to this hypothesis and also describes a four-step analysis of the molecular mechanism of antisteroid hormone action at the receptor level.

Transformation of glucocorticoid and progesterone receptors to the DNA-binding state

This brief review explores some recent observations relating to the structure of untransformed glucocorticoid and progesterone receptors and the mechanism by which the receptors are transformed to the DNA-binding state. In their molybdatestabilized, untransformed state, progesterone and glucocorticoid receptors exist as a heteromeric 8-9S complex containing one unit of steroid binding phosphoprotein and one or two units of the 90 kD heat shock protein hsp90. When the receptors are transformed, the steroid-binding protein dissociates from hsp90. In cytosol preparations, temperature-mediated dissociation proceeds much more rapidly in the presence of hormone. The dissociated receptor binds to DNA with high affinity, regardless of whether it is in the hormone-bound or the hormone-free state. These observations raise the possibility that the primary, and perhaps the only, role for the hormone is to promote dissociation of the receptor-hsp90 complex. Molybdate, vanadate, and tungstate inhibit receptor transformation to the DNA-binding form, an effect that appears to reflect the ability of these transition metal oxyanions to stabilize the complex between the steroid receptor and hsp90. By promoting the formation of disulfide bonds, hydrogen peroxide also stabilizes the glucocorticoid receptor-hsp90 complex and prevents receptor transformation. A small, heat-stable factor present in all cytosol preparations inhibits receptor transformation, and, when the factor is removed, glucocorticoid receptors are rapidly transformed. This ubiquitous factor has the physical properties of a metal anion, and it is proposed that molybdate and vanadate affect steroid receptor complexes by interacting with a metal anion-binding site that is normally occupied by this endogenous receptor-stabilizing factor.

A progesterone receptor affinity chromatography reagent: 17 alpha-hexynyl nortestosterone sepharose

Several affinity chromatography reagents have been proposed for purification of progesterone receptor (PgR), and significant results have been achieved with some of these. None, however, have approached the results achieved in affinity chromatography of estrogen receptor. We have therefore synthesized a number of new 19-nortestosterone derivatives capable of chemically stable linkage with Sepharose beads, and have identified one with very high PgR affinity for further study. We first synthesized the epoxides of 17 alpha-allyl nortestosterone, by analogy with the estradiol derivatization of Greene and Jensen. The relative affinity of these epoxides for PgR from T47D human breast cancer cells, however, was only around 5% that of R5020, and affinity beads prepared from them bound very little PgR. We then reacted appropriately protected 17 alpha-ethynyl-nortestosterone with a series of diiodo alkanes, and found that 17 alpha-(6'-iodohex-1'-ynyl)nortestosterone had an affinity of 22% relative to R5020, equal to the affinity of progesterone itself. Reaction with Thiopropyl-Sepharose 6B yielded hexynyl-nortestosterone-Sepharose beads with a ligand density of about 7 micromoles/ml beads. One-hundred microliter of these beads adsorbed 71% of the PgR present in 1 ml of cytosol from T47D cells. This adsorption was inhibited by 10 microM progesterone but not cortisol, indicating the specificity of the binding. Comparisons with NADAC and Sterogel, other affinity beads used for PgR purification, show that the former takes up much less receptor, while the latter takes up and releases similar amounts of receptor but more extraneous protein, and is less stable. We therefore believe that hexynyl-nortestosterone-Sepharose, having a high density of a high affinity ligand, and having chemically and biochemically stable covalent bonds, should be a good reagent for affinity purification of PgR.

Chick oviduct progesterone receptor phosphorylation: characterization of a copurified kinase and phosphorylation in primary cultures

A protein kinase activity was copurified with the chick oviduct progesterone receptor. The enzyme is magnesium dependent and can use the B subunit of progesterone receptor or histones as substrates. The physiochemical parameters of the kinase were determined [pI approximately 5.3; Stokes radius approximately 7.2 nm; sedimentation coefficient (S 20,w) approximately 5.6] and compared to those of the purified B subunit. The results were consistent with the presence of an unique enzyme distinct from the receptor itself. The physiological significance of receptor phosphorylation was investigated in oviduct cells grown in primary culture. Cells were labeled with [32P]orthophosphate in presence or absence of progesterone and the receptor components were immunoprecipitated with a specific polyclonal antibody. Although progesterone treatment lead to the attachment of most of the receptor (approximately 80%) to nuclear structures, the 32P-labeled B subunit was only recovered in the cytosol fraction. Different procedures to extract the nuclear receptor did not allow detection of any 32P-labeled form in the nuclear-soluble fractions, suggesting that the B subunit was not further phosphorylated upon the exposure of cells to progesterone.

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.

Affinity of corticosteroids for mineralocorticoid and glucocorticoid receptors of the rabbit kidney: effect of steroid substitution

Corticosteroid derivatives coupled in the C3, C7 or C17 position with a long aliphatic chain were synthesized in order to select a suitable ligand for the preparation of a biospecific affinity adsorbent for mineralocorticoid receptor purification. The affinity of these derivatives for mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) was explored in rabbit kidney cytosol. In this model, aldosterone bound to a single class of receptors with high affinity (Kd 1 nM) and mineralocorticoid specificity. RU26988, a highly specific ligand for GR, did not compete for these sites. The C7 and C17 positions were found to be of crucial importance in the steroid's interaction with the mineralocorticoid receptors, since the linkage of a long side chain in these positions induced complete loss of affinity. Hence, deoxycorticosterone no longer bound to MR after 17 beta substitution with a 9-carbon aliphatic chain. This loss of affinity was not observed for glucocorticoids. The 17 beta nonylamide derivative of dexamethasone still competed for GR. Increasing the length of the C7 side of the spirolactone SC26304 suppressed its affinity for MR. Finally, C3 was an appropriate position for steroid substitution. The 3-nonylamide of carboxymethyloxime deoxycorticosterone bound to MR but not to GR, and therefore constitutes a suitable ligand for the preparation of a mineralocorticoid adsorbent.

Transformation and phosphorylation of purified molybdate-stabilized chicken oviduct progesterone receptor

The non-transformed, molybdate-stabilized chick oviduct cytosol progesterone receptor was purified approx. 7000-fold using biospecific affinity resin (NADAC-Sepharose), DEAE-Sephacel chromatography and gel filtration on Bio-Gel A-0.5m agarose. The purified preparation contained progesterone receptor which sedimented as a 7.9S molecule, had a Stokes' radius of 7.5 nm, was composed of three major peptides corresponding to Mr 108,000, 90,000 and 79,000. Upon removal of molybdate, the purified [3H]progesterone-receptor complex could be transformed from the 8S form to a 4S form by exposure to 23 degrees C or by an incubation with 10 mM ATP at 0 degrees C. The purified thermally transformed receptor could be adsorbed to columns of ATP-Sepharose. No cytosol factor(s) appeared to be required for the 8S to 4S transformation of purified receptor or for its subsequent binding to ATP-Sepharose. Incubation of purified non-transformed receptor preparation with [gamma-32P]ATP and cAMP-dependent protein kinase led to incorporation of radioactivity in all the three major peptides at serine residues. The results of this study show for the first time that purified 8S progesterone receptor can be phosphorylated in vitro by a cAMP-dependent protein kinase, and that it can be transformed to a 4S form by 0 degrees C incubation with 10 mM ATP.

Progesterone receptor assays in low-protein cytosols: a modified charcoal-gelatin procedure

Quantitative measurement of steroid receptors including progesterone receptor (PgR) is usually accomplished by the dextran-coated charcoal (DCC) assay. At protein concentrations below about 1 mg/ml, however, serious underestimation of receptor content by DCC occurs, presumably because of adsorption of receptor to the charcoal and possibly to assay tubes, etc. We have therefore developed a modified charcoal-gelatin (MCG) procedure which largely avoids receptor losses even in samples with extremely low protein concentrations. In this MCG procedure, 0.1% gelatin is added to both sample and charcoal suspension, the charcoal content is increased to 1%, and dextran is no longer necessary. Comparison of the MCG procedure with the standard DCC and several other methods at decreasing protein concentrations shows that MCG retains acceptable efficiency for PgR at much lower protein than the others, even as low as 10 micrograms/ml. This MCG procedure will be useful in determining receptors for prognosis in very small human breast cancer biopsies, as shown here, but also for receptor determination in very small tissues such as specific brain regions, and for receptor assay during purification.

Biochemical characterization of the progesterone receptor in the chick bursa of Fabricius

In a previous work we demonstrated estrogen-inducible progesterone binding sites in the bursa of Fabricius. In the present study these were characterized and compared to the progesterone receptor (PR) in the chick oviduct. When the size of the binding sites was analyzed with sucrose gradient centrifugation, 2 peaks of bound progesterone were obtained. The sedimentation coefficients of the peaks were 8-9 S and 3-4 S. In size exclusion HPLC only 1 peak was seen with a size corresponding to the 8-9 S in the sucrose gradient. The Stokes radius was 7.7 nm. When the ionic strength was elevated or CaCl2 was added, smaller steroid binding forms were detected. The sizes of these progesterone binding molecules at low and high ionic strength and in the presence of CaCl2 were equal in bursa and oviduct when analyzed with HPLC. The Stokes radii of these forms were 5.6 nm in high salt and 2.1 nm with CaCl2. The steroid binding components in the bursa cytosol eluated as 2 peaks from the DEAE column with KCl gradient. The peaks corresponded to the so-called A and B components in the chick oviduct. In the presence of molybdate, bound progesterone eluated as one peak from DEAE in both oviduct and bursa. The progesterone binding capacity was shown to be heat labile with equal half-lives in the bursa and the oviduct. Progesterone and ORG 2058 had a high affinity for the binding site and their binding was specific for progestins. It is concluded that the estrogen-inducible progesterone binding site in the bursa of Fabricius resembles the oviductal progesterone receptor in structural and binding properties.

Affinity labelling of steroid hormone receptors

Affinity labelling techniques have proved indispensable for the study of reversible biological recognition systems, since they conserve ligand-receptor interaction by covalent linkage. Using photo- and electrophilic labelling, it has become possible to unequivocally identify steroid hormone receptors and their proteolytic degradation products and it is simple to establish receptor peptide maps even in crude receptor preparations. The isolation of receptor proteins has been greatly simplified, as their integrity can be analyzed at any step of a purification protocol by SDS-PAGE analysis after crosslinking. Moreover, affinity-labelled receptors can be purified under denaturing conditions, e.g., in high-resolving preparative SDS-PAGE, and the material obtained can be efficiently used to generate anti-receptor antibodies. Peptide mapping after crosslinking of related receptors has been used to assess the degree of structural homology between different forms of steroid hormone receptors and receptors of different species. Peptide sequence analysis of purified crosslinked receptor protein and anti-receptor antibodies have provided the basis for cloning corresponding genes. Techniques have been established to demonstrate--via crosslinking--that the cloned DNA sequences correspond to the receptor gene binding the correct ligand. The analytical and preparative crosslinking methods developed for steroid receptors are potentially important for the study of any system in which signal transduction proceeds via the reversible interaction between biological macromolecules.

Steroid-bovine serum albumin conjugates: molecular characterization and their interaction with androgen and estrogen receptors

Conjugates of testosterone-3-carboxymethyloxime (T-3-CMO), testosterone-17-hemisuccinate (T-17-HS), 17 beta-estradiol-6-carboxymethyloxime (E-6-CMO), or 17 beta-estradiol-17-hemisuccinate (E-17-HS) and bovine serum albumin (BSA) with varying steroid:protein ratios were prepared using the mixed anhydride method. Dialysis followed by molecular filtration yielded monomer steroid-BSA conjugates with a molecular weight of 70,000 dalton, and polymer conjugates with molecular weights of 140,000 dalton and higher. When conjugates were prepared with increasing initial steroid:BSA molar ratios the ratio of the obtained conjugates increased, in parallel with a decrease in the relative amount of monomers and an increase in the mean molecular size of polymers. The molecular properties of these conjugates were studied further by polyacrylamide gel electrophoresis (PAGE) in native and denaturing conditions. In native PAGE the monomer fractions showed one main band with a mobility slightly lower than BSA and a faint band corresponding with BSA-dimers. The polymer fractions consisted of a heterogeneous population of protein oligomers with molecular weights varying from 140,000 to over a million dalton. In the presence of sodium dodecylsulphate part of the polymers dissociated into monomers. In buffered aqueous solutions the bulk of the conjugate preparation retained its molecular size and composition, although the generated covalent bonds were found to be liable to spontaneous hydrolysis. Steroid-protein conjugates were shown to contain appreciable amounts of non protein-bound steroids. Binding of T-BSA to androgen receptors in rat ventral prostate cytosol was assayed using LH-20 chromatography and sucrose gradient centrifugation analysis. Binding of E-BSA to estrogen receptors was analysed with rat uterus cytosol using the dextran coated charcoal assay and the sucrose gradient centrifugation technique. Relative binding affinities (RBA) were analyzed in competition experiments using radiolabeled ligands. It was found that the molecular size of the conjugate does not influence its interaction with steroid receptors. Steroid coupled via the 17-position show a higher RBA to receptors than the T-3 or E-6 derivatives. The RBA of T-3-BSA, T-3-CMO, T-17-BSA and T-17-HS appeared to be very low, i.e. between 0.1 and 1.7% of the RBA of dihydrotestosterone. Consequently, high concentrations of conjugate are required to saturate androgen receptor binding sites. Under these conditions involvement of type II and eventually type III binding sites, which show less ligand specificity and lower affinity, may be anticipated preventing exclusive detection of androgen receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of two forms of progesterone receptor from chick oviduct cytosol using non-denaturing gel electrophoresis

Non-denaturing polyacrylamide gel electrophoresis and non-denaturing agarose gel electrophoresis have been used to resolve [3H]R5020-binding components from chick oviduct cytosol. From both gel systems 2 peaks of bound radioactivity are resolved which display these properties of authentic progesterone receptor: binding of R5020: steroid specificity, saturability, and restriction to target tissues. The two peaks are approximately equal in magnitude, and there is no evidence for interconversion of the 2 peaks. The presence or absence of 10-20 mM sodium molybdate during cytosol preparation had no effect on the magnitude or mobility of either peak. Neither peak contains salt-dissociable components which affect its electrophoretic properties, suggesting a possible alteration of native receptor forms during electrophoresis.

Structural analyses of progesterone receptors

Progesterone receptors of T47Dco human breast cancer cells consist of two equimolar hormone-binding proteins of mol. wt approximately 85,000 (A protein) and 115,000 (B protein). Both proteins can be demonstrated in intact cells by in situ photoaffinity labeling; that is, in cells treated with the synthetic progestin [3H]R5020, irradiated 2 min with 300 nm u.v., solubilized directly in SDS and subjected to electrophoresis under denaturing conditions. These proteins are 6000-10,000 dalton heavier than the corresponding proteins of chick oviducts. This difference has been measured by direct comparison of photolabeled chick and human receptors on SDS-PAGE and by immunoblotting with the 9G10 antibody prepared against chick protein B. The antibody binds to a protein of mol. wt approximately 106,000 in human cells that is smaller than the hormone-bound B protein and larger than the hormone-bound A. In T47Dco cells, in situ photolabeled, untransformed receptors, as well as transformed nuclear-bound receptors, have equimolar amounts of A and B proteins. This ratio remains stable during a 1 h 37 degrees C in vitro incubation. Analysis of the in situ labeled receptors on gradient gels shows that the untransformed B protein exists as a doublet of mol. wt approximately 115,000 and 119,000 while the A protein is a singlet. After [3H]R5020 treatment, nuclear receptors change further: during the first 30 min in the nucleus the B protein shifts entirely to the heavier, mol. wt = 119,000 form. Between 30 and 60 min after nuclear binding, the A protein first becomes a doublet of 85,000 and 89,000 dalton then shifts entirely to the 4000 dalton heavier form. Later, nuclear processing leads to the simultaneous disappearance of both proteins without generation of smaller molecular weight fragments. Cleveland mapping studies show that the A and B proteins are closely related; despite the initial difference in the molecular weight of A and B, digestion with S. aureaus V8 protease yields identical fragmentation patterns for each, with sequential peptides of mol. wt approximately 49,000, 39,000, 26,000 and 14,000.(ABSTRACT TRUNCATED AT 400 WORDS)

Transformation of the chick oviduct progesterone receptor in the absence of hormone

Chicken oviduct progesterone receptor in cytosol was found to be transformed from the 8S to 4S form by incubation at 25 degrees C as well as by 0.3 M KCl in the absence of hormone. Heat transformation of ligand-free receptor took place at a much slower rate than that of ligand-bound receptor. The eventual percentage of transformation, however, was almost the same. The 4S form of the receptor transformed by KCl in the absence of hormone could bind to DNA-cellulose, but not to nuclei. However, upon exposure it acquired the ability to bind to nuclei. It was shown that the transformed ligand-free receptor could bind to progesterone to form the normal activated steroid-receptor complex. Conversely, when activated 4S progesterone-receptor complex was treated with DCC to peel off the hormone, a resulting ligand-free receptor was formed which behaved just like the KCl-transformed receptor in the absence of hormone.

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

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

Chick oviduct glucocorticosteroid receptor. Specific binding of the synthetic steroid RU 486 and immunological studies with antibodies to chick oviduct progesterone receptor

The glucocorticosteroid receptor (GR) has been studied in oviduct cytosol prepared from estrogen-primed, 4-week-withdrawn chicken. The equilibrium dissociation constant was 6 nM for dexamethasone, and 18 300 receptor sites/cell were measured assuming that all cells contain identical concentrations of GR. Dexamethasone, used in most studies investigating glucocorticosteroid action, was found not to be the best GR ligand. The affinities of several natural and synthetic glucocorticosteroids for GR increased in the following order: cortisol less than deoxycorticosterone less than dexamethasone less than corticosterone less than triamcinolone acetonide. The synthetic steroid RU 486 was the most specific ligand of GR (its affinity was approximately equal to 10-fold higher than that of triamcinolone acetonide), while it did not bind either to plasma transcortin (which binds dexamethasone nor, surprisingly, to progesterone receptor (PR), contrary to what occurs in mammalian species. The molybdate-stabilized, 8-S form of GR was prepared from withdrawn chick oviduct, whole chick embryo or cultured chick embryo fibroblasts (which do not contain PR), and was labeled with either [3H]dexamethasone or [3H]RU 486. The sedimentation coefficient of radioactive ligand--8-S GR complexes was shifted towards heavier forms after incubation with polyclonal (IgG-G3) or monoclonal (BF4) antibodies generated against the molybdate-stabilized, 8-S form of the chick oviduct PR. Since neither IgG-G3 nor BF4 interacted with the steroid binding 4-S form of GR, it is suggested that these antibodies recognized a non-steroid binding protein common to molybdate-stabilized, 8-S forms of GR and PR.

Binding of activated progesterone receptor to microsomes

Specific binding of steroid hormones to microsomes has been reported for several tissues. In the hen oviduct, this receptor appears to be very similar to activated cytosolic receptor. The microsomal receptor is readily solubilized, and resembles the cytosolic receptor in all physico-chemical characteristics: sedimentation coefficient approximately 4 S, Stokes radius 5.5 nm, slow dissociation rate of the complex, adsorption to polyanions. It is precipitated by an antibody to the cytosolic receptor. Microsomes display saturable binding of cytosolic receptor, with a Bmax of approximately 300 fmol/mg protein. This binding is also observed using microsomes from non-target tissues, and is decreased by treatment with RNase. It seems likely that microsomal binding is due to the high affinity of activated cytosolic receptor for RNA.

Progesterone receptor in the chick oviduct: an immunohistochemical study with antibodies to distinct receptor components

We performed immunohistochemical studies of chicken oviduct after different fixation procedures, by using antibodies against the progesterone receptor: polyclonal antibodies IgG-G3 against the "8S" form (an oligomere containing progesterone-binding and nonprogesterone-binding units), polyclonal antibodies IgG-RB against the progesterone-binding B subunit, and monoclonal BF4 against the non-progesterone-binding 90,000-mol-wt protein component. Chickens were immature animals with or without estrogen priming, and with or without progesterone treatment. The antibodies were revealed by means of an immunoperoxidase technique that used the avidin-biotin-peroxidase complex, and controls were performed by presaturation of antibodies with the purified 8S-progesterone receptor, the B subunit, and 90,000-mol-wt protein. The progesterone receptor was detected not only in well-characterized target tissues, i.e., in glands and luminal epithelium, but also in stromal cells (some displayed the strongest reaction), in mesothelium, and in fibers of smooth muscles. Only in cell nuclei, whether or not the animals received an injection of progesterone was an antigen revealed corresponding to the B subunit (and/or to the A subunit, because there is immunoreactivity of IgG-RB with both hormone-binding subunits A and B). The 90,000-mol-wt protein was revealed in both cytoplasm and nuclei. These immunohistological data suggest that the concept of steroid action that necessarily involves the original formation of the hormone-receptor complexes in the cytoplasm before translocation to the nucleus, may have to be revised.

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.

Heparin-mediated inactivation and transformation of mammary cytoplasmic glucocorticoid receptor

Glucocorticoid receptor of lactating mouse mammary gland cytosol was exposed to heparin when the receptor was either steroid-free or steroid-bound. Heparin caused a dose-dependent and time-dependent loss of steroid binding activity (inactivation) of the steroid-free receptor; this heparin-induced inactivation was inhibited by molybdate. In contrast, steroid-bound receptor maintained its steroid binding capacity in the presence of heparin but the heparin caused transformation of receptor as detected by increased binding to DNA-cellulose and ATP-Sepharose. Heparin also converted steroid-bound receptor from the 7-8S form to the 4S form. Molybdate inhibited both the heparin-induced transformation and associated conversion to the 4S form.

Common non-hormone binding component in non-transformed chick oviduct receptors of four steroid hormones

Steroid hormones produce a response in target cells by binding to hormone-specific soluble receptors, which undergo a transformational change, leading to their interaction with chromatin and to modified gene expression. In a previous paper, we described a monoclonal antibody, BF4, that specifically recognizes and binds the non-transformed '8S' form of chicken oviduct progesterone receptor (8S-PR). We now show that BF4 does not form an immune complex with the 4S transformed form of 3H-progestin-labelled progesterone receptor, but does interact with the 8S non-transformed forms of the oestrogen, androgen and glucocorticosteroid receptors. Our results suggest that the antigenic determinant recognized by BF4 is present on a non-hormone binding unit, which we identify as a polypeptide of molecular weight (MW) 90,000 in the case of the progesterone receptor, and that this unit is common to other 8S non-transformed chicken steroid receptors.

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.

Progesterone receptor subunits are high-affinity substrates for phosphorylation by epidermal growth factor receptor

Purified preparations of epidermal growth factor (EGF) receptor were used to test hen oviduct progesterone receptor subunits as substrates for phosphorylation catalyzed by EGF receptor. Both the 80-kilodalton (kDa) (A) and the 105-kDa (B) progesterone receptor subunits were phosphorylated in a reaction that required EGF and EGF receptor. No phosphorylation of progesterone receptor subunits was observed in the absence of EGF receptor, even when Ca2+ was substituted for Mg2+ and Mn2+. Phospho amino acid analysis revealed phosphorylation at tyrosine residues, with no phosphorylation detectable at serine or threonine residues. Two-dimensional maps of phosphopeptides generated from phosphorylated 80- or 105-kDa subunits by tryptic digestion revealed similar patterns, with resolution of two major, several minor, and a number of very minor phosphopeptides. The Km of progesterone receptor for phosphorylation by EGF-activated EGF receptor was 100 nM and the Vmax was 2.5 nmol/min per mg of EGF receptor protein at 0 degrees C. The stoichiometry of phosphorylation/hormone binding for progesterone receptor subunits was 0.31 at ice-bath temperature and approximately 1.0 at 22 degrees C.