Purification and properties of progesterone receptors from chick oviduct

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.

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.

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.

Monoclonal antibody to chicken oviduct progesterone receptor

Antibodies to molybdate-stabilized chicken oviduct progesterone receptor were raised in a Wistar rat and detected by interaction with homogeneous radioiodinated progesterone receptor. Spleen cells of this rat were then fused with mouse Sp2/0-Ag14 myeloma cells and the antibodies produced by the hybrid cells were detected by double immunoprecipitation using the 125I-labeled receptor. Cells of one of the positive cultures were then cloned by limiting dilution and one hybridoma cell line was studied. The monoclonal antibody produced was an IgG2b, and it reacted with the molybdate-stabilized "8-9S" form of the chicken oviduct progesterone receptor, labeled with either [3H]progesterone or [3H]ORG 2058 (a high-affinity synthetic progestin). Kd for the 8-9S progesterone receptor was approximately equal to 1 nM. Progesterone receptor-monoclonal antibody complexes were labeled with radioactive progesterone, suggesting that antibody does not prevent hormone binding. By using a [35S]methionine-labeled antibody, we were able to detect the progesterone receptor independently of its characteristic function of binding radioactive hormone. No crossreaction with human progesterone receptor was detected.

Antibodies against progesterone receptor from chick oviduct. Cross-reactivity with mammalian progesterone receptors

The highly purified, molybdate-stabilized '8-9-S' form of the chick oviduct progesterone receptor complexed with [3H]progesterone (Specific activity approximately equal to 10-12 nmol bound steroid/mg protein) was prepared according to the three-step method [Renoir et al. (1982) Eur. J. Biochem. 127,71-79] and 50-90 micrograms samples were injected into a goat and a rabbit. Specific antibodies were observed as early as 2 weeks following the first booster injection and increased considerably 12 weeks later after further booster injections. Results were similar in the two animals, with higher titers observed in the goat. Antibodies cross-reacted with the 'transformed' 4-S form of the chick oviduct progesterone receptor. They also cross-reacted with molybdate-stabilized 8-9-S progesterone receptors of mammalian species (obtained from MCF-7 human breast cancer cells and from rabbit and mouse uteri), suggesting some evolutionary conservation of steroid hormone receptors. No cross-reaction was observed with chick oviduct oestradiol receptor and with chick plasma transcortin (a non-receptor progesterone-binding protein).

Interaction of the chick oviduct progesterone receptor with deoxyribonucleic acid

The purified DNA binding component (receptor A) of the chick oviduct progesterone receptor has been analyzed for its ability to bind to the cloned ovalbumin gene and to plasmid DNA of various structural compositions. The rapid equilibrium filter adsorption assay of Riggs et al. [Riggs, A. D., Suzuki, H., & Bourgeois, S. (1970) J. Mol. Biol. 48, 67] has been used to demonstrate high affinity binding of the protein to DNA (Kdiss = 10(-10) M at 50 mM KCl, pH 7.2). Studies of association rates are consistent with equilibrium measurements (t 1/2 = 40-80 min). Association of purified receptor with DNA and the kinetics of the interaction have been verified independently by velocity sedimentation techniques. Direct binding assays were performed with the ovalbumin structural gene (cDNA), the entire natural ovalbumin gene containing seven intervening sequences, and various ovalbumin gene fragments coding for the 5' end of the nuclear precursor RNA, intron-exon junctions, and the 3'-noncoding region of the gene. No DNA-sequence specificity was identified for the binding of the receptor protein to any region of ovalbumin gene DNA. In contrast, the structural integrity of the DNA template greatly affected receptor binding. The poorest affinity was to supercoiled DNA and to blunt end, linear duplex gene fragments. The receptor bound saturably to DNA containing limited nicks but became nonsaturable as nicks were increased. Binding of the protein to double-stranded DNA increased susceptibility of the DNA to digestion by the enzyme S1, a single strand specific nuclease. On the basis of preferential receptor binding to single-stranded DNA, a possible mechanism involving DNA helix destabilization is discussed.

Inhibition by protease inhibitors of binding of adrenal and sex steroid hormones

Binding of steroid hormones is inhibited by protease inhibitors and substrates. The protease inhibitors phenylmethyl sulphonylfluoride, tosyl-lysine chloromethyl ketone, and tosylamide-phenylethyl-chloromethyl ketone and the protease substrates tosyl arginine methyl ester and tryptophan methyl ester eliminate specific binding of aldosterone, dexamethasone, dihydrotestosterone, estrogen, and progesterone to their respective receptors. These protease inhibitors and substrates also inhibit binding of progesterone to the 20,000 molecular weight mero-receptor formed from the progesterone receptor in chick oviduct. The binding of estradiol to rat alpha-fetoprotein is inhibited by the protease inhibitors and substrates but not by tryptophan or tryptophan amide, indicating the importance of an ester structure in the inhibition of steroid binding. Our results suggest that all steroid hormone receptors have a site with both common structural features and a role in the regulation of steroid hormone binding.