Exploring Flexibility of Progesterone Receptor Ligand Binding Domain Using Molecular Dynamics.

Progesterone receptor (PR), a member of nuclear receptor (NR) superfamily, plays a vital role for female reproductive tissue development, differentiation and maintenance. PR ligand, such as progesterone, induces conformation changes in PR ligand binding domain (LBD), thus mediates subsequent gene regulation cascades. PR LBD may adopt different conformations upon an agonist or an antagonist binding. These different conformations would trigger distinct transcription events. Therefore, the dynamics of PR LBD would be of general interest to biologists for a deep understanding of its structure-function relationship. However, no apo-form (non-ligand bound) of PR LBD model has been proposed either by experiments or computational methods so far. In this study, we explored the structural dynamics of PR LBD using molecular dynamics simulations and advanced sampling tools in both ligand-bound and the apo-forms. Resolved by the simulation study, helix 11, helix 12 and loop 895-908 (the loop between these two helices) are quite flexible in antagonistic conformation. Several residues, such as Arg899 and Glu723, could form salt-bridging interaction between helix 11 and helix 3, and are important for the PR LBD dynamics. And we also propose that helix 12 in apo-form PR LBD, not like other NR LBDs, such as human estrogen receptor α (ERα) LBD, may not adopt a totally extended conformation. With the aid of umbrella sampling and metadynamics simulations, several stable conformations of apo-form PR LBD have been sampled, which may work as critical structural models for further large scale virtual screening study to discover novel PR ligands for therapeutic application.

Progesterone action in human tissues: regulation by progesterone receptor (PR) isoform expression, nuclear positioning and coregulator expression.

Progesterone is a critical regulator of normal female reproductive function, with diverse tissue-specific effects in the human. The effects of progesterone are mediated by its nuclear receptor (PR) that is expressed as two isoforms, PRA and PRB, which are virtually identical except that PRA lacks 164 amino acids that are present at the N-terminus of PRB. Considerable in vitro evidence suggests that the two PRs are functionally distinct and in animals, tissue-specific distribution patterns of PRA and PRB may account for some of the diversity of progesterone effects. In the human, PRA and PRB are equivalently expressed in most target cells, suggesting that alternative mechanisms control the diversity of progesterone actions. PR mediates the effects of progesterone by association with a range of coregulatory proteins and binding to specific target sequences in progesterone-regulated gene promoters. Ligand activation of PR results in redistribution into discrete subnuclear foci that are detectable by immunofluorescence, probably representing aggregates of multiple transcriptionally active PR-coregulator complexes. PR foci are aberrant in cancers, suggesting that the coregulator composition and number of complexes is altered. A large family of coregulators is now described and the range of proteins known to bind PR exceeds the complement required for transcriptional activation, suggesting that in the human, tissue-specific coregulator expression may modulate progesterone response. In this review, we examine the role of nuclear localization of PR, coregulator association and tissue-specific expression in modulating progesterone action in the human.

Presencia de Receptores de Estrógenos y de Progesterona en el Endometrio de Ovejas Prepúberes: Estudio Inmunocitoquímico / Presence of Estrogen and Progesterone Receptors in Endometrium of Prepubertal Sheeps: Immunocitochemistry Study

Los receptores esteroidales endometriales tienen un papel esencial en la fisiología reproductiva, siendo ellos determinantes del estado morfuncional del tracto genital y especialmente del endometrio en el cual se implantará el embrión. Se estudió la presencia de receptores de estrógenos y progesterona en el endometrio de ovejas Rommey Marsh prepúberes (n= 3). Se obtuvieron muestrasde pared uterina para estudios histológico e inmunocitoquímico.El endometrio de la oveja prepúber muestra histológicamente carúnculas, áreas aglandulares de estroma denso rico en fibroblastos que se convertirán en puntos de inserción placentaria durante la gestación y áreas intercarunculares constituidas por endometrio glandular proliferativo de estroma compacto y vasos poco prominentes. La inmunocitoquímica reveló, para los receptores de estrógenos, inmumnoreactividad positiva moderada en el estroma endometrial ymuy aisladamente en el epitelio glandular,noencontrándose diferencias entre zona caruncular e intercaruncular. Losreceptores de progesteronapresentaron positividad estromal siendo algo más intensa en la zona intercaruncular. Concluimos que la oveja Rommey Marsh presentareceptores de estrógenos y progesterona fisiológicamente activos en su endometrio ya en etapa prepúber, o sea, antes de comenzar sus ciclos ováricos, los que podrían ser inducidos y regulados por hormonas exógenas, con el fin de aumentar la eficiencia y prevenir disfunciones reproductivas.

The endometrial esteroid receptors play an essential paper in the reproductive physiology being them decisive on the morophuncional state of the genital tract and especially of the endometrium in which the embryo will be implanted. We studied the presence of estrogens and progesterone receptors in the endometrium of Rommey Marsh prepubertal sheep (n=3) samples of uterine wall were obtained for histologycal and and Inmunocitochemestry study. The endometrium of the prepubertal sheep shows histologycaly caruncles, aglandulares areas of dense estroma rich in fibroblastos, that will become points of placental insertation during the gestation and intercarunculares areas constituted by endometrium glandular proliferative of compact estroma and not very prominent vessels. The Inmunocitochemestry revealed for the estrogens receptors inmumnoreactivity positive moderated in the estroma endometrial and very scattered in the glandular epithelium, not being differences between area caruncular and intercaruncular. The progesterone receptors presented positive inmunoreactivity estromal being more intense in the intercaruncular area We conclude that the sheep Rommey Marsh shows estrogens and progesterone receptors physiologically active in its endometrium already in prepubertal stage this is before beginning its ovarian cycles, those could be induced and regulated by exogenous hormones with the purpose of to increase the efficiency and to prevent reproductive disfunctiones.

Ependimoma de ovario: comunicación de un caso con receptores de estrógenos y progestágenos / Ovarian ependymoma: A case with estrogen and progestin receptors

Los tres primeros casos de ependimomas puros de ovario se describieron en 1984. En la actualidad al menos se encuentran 12 casos descritos en la literatura inglesa. Presentamos un nuevo caso de ependimoma puro ovárico diagnosticado como hallazgo incidental en una paciente de 44 años de edad a quien se realizó una histerectomía total y anexectomía bilateral por leiomiomas uterinos múltiples. Material y métodos: Sobre la superficie del ovario izquierdo se encontró un nódulo de 2x1,5x1,5 cm, de consistencia sólida y coloración amarillenta. Se realizaron estudios de inmunohistoquímica y microscopia electrónica en el tejido fijado en formol e incluido en parafina. Resultados: El diagnóstico de ependimoma se basó en los hallazgos microscópicos similares a los de los ependimomas papilares dei sistema nervioso central, inmunohistoquimicos como la positividad para GFPA y ultraestructurales como la presencia de microfilamentos intracitoplasmáticos, microvellosidades, cilios y complejos de unión en la superficie. Además, como en los casos descritos previamente, el tumor mostró positividad para receptores de estrógenos y progesterona. Conclusiones: El diagnóstico de ependimoma de ovario puede ser establecido por el patólogo mediante los hallazgos morfológicos e inmunohistoquimicos. La presencia de receptores hormonales ha permitido sugerir la administración de un tratamiento hormonal en los raros casos que se acompañen de recidiva (AU)

Progesterone-induced acrosome reaction in stallion spermatozoa is mediated by a plasma membrane progesterone receptor.

The aim of the present study was to investigate whether the induction of stallion sperm acrosome reaction (AR) by progesterone is mediated by binding of progesterone to a receptor on the sperm plasma membrane or to an intracellular progesterone receptor. Progesterone-BSA conjugate labeled with fluorescein isothiocyanate (P-BSA-FITC) in combination with a vital stain, ethidium homodimer, was applied to visualize the presence of the progesterone receptor on living spermatozoa. Alternatively, an indirect immunofluorescence technique employing a monoclonal antibody (C-262) against human intracellular progesterone receptor was conducted to validate the presence of the progesterone receptor. Immunogold labeling techniques enabled ultrastructural localization of P-BSA-FITC or C-262 with transmission electron microscopy. The dynamic changes in labeling patterns were monitored for sperm cells, using fluorescence microscopy and flow cytometry during a 5-h capacitation period. An increasing number of viable cells showed affinity for P-BSA-FITC or C-262 at the acrosomal plasma membrane region of the sperm head, while a decreasing number of viable cells were not labeled. In contrast, almost all deteriorated cells were labeled in the cytosol of the postequatorial region of the sperm head. Incubation with P-BSA-FITC resulted in the induction of AR but to a lesser extent than that for sperm incubated with free progesterone. Therefore, coupling of progesterone to its receptor on the sperm plasma membrane appears to be an important step in the induction of the AR.

16 alpha-substituted analogs of the antiprogestin RU486 induce a unique conformation in the human progesterone receptor resulting in mixed agonist activity.

Previously, we have shown that agonists and antagonists interact with distinct, though overlapping regions within the human progesterone receptor (hPR) resulting in the formation of structurally different complexes. Thus, a link was established between the structure of a ligand-receptor complex and biological activity. In this study, we have utilized a series of in vitro assays with which to study hPR pharmacology and have identified a third class of hPR ligands that induce a receptor conformation which is distinct from that induced by agonists or antagonists. Importantly, when assayed on PR-responsive target genes these compounds were shown to exhibit partial agonist activity; an activity that was influenced by cell context. Thus, as has been shown previously for estrogen receptor, the overall structure of the ligand-receptor complex is influenced by the nature of the ligand. It appears, therefore, that the observed differences in the activity of some PR and estrogen receptor ligands reflect the ability of the cellular transcription machinery to discriminate between the structurally different complexes that result following ligand interaction. These data support the increasingly favored hypothesis that different ligands can interact with different regions within the hormone binding domains of steroid hormone receptors resulting in different biologies.

Quantitative imaging of estrogen and progesterone receptors, estrogen-regulated protein, and growth fraction: immunocytochemical assays in 52 meningiomas. Correlation with clinical and morphological data.

Quantitative imaging of estrogen receptors (ER's), progesterone receptors (PR's), estrogen-regulated protein (pS2), and growth fraction (Ki67) immunocytochemical assays were performed in 52 meningiomas. The results were correlated with clinical (age, sex, hormonal status, and tumor volume and location) and morphological (histological types and grades) data. The authors observed a lack of ER's in all meningiomas but the presence of PR's in 53% of these meningiomas. The immunoreactivity was restricted to tumor cell nuclei. The PR immunocytochemical assay was correlated with tumor location, histological type, histological grade, and pS2 immunocytochemical assay, but not with Ki67 immunocytochemical assay; high PR content was observed in cisternae, transitional, meningothelial, and low-grade meningiomas. Only 11 meningiomas showed more than 1% Ki67 immunoreactive nuclei. These meningiomas were usually located in the convexity and were of high histological grade. Estrogen-regulated protein immunoreactivity was observed in 34 meningiomas but the number of immunoreactive nuclei was low. The pS2 immunocytochemical assay was not related to clinicopathological features but was preferentially observed in PR-negative meningiomas. The results of this study are compared with those previously reported, and the function and regulation of PR's in meningiomas is discussed. The results indicate that 1) regulation of PR's and pS2 proteins in meningiomas differs from regulation in estrogen-dependent tissues such as breast or endometrium; 2) interruption of hormonal therapy in women presenting with a meningioma is not absolutely necessary; 3) meningiomas have different biological properties according to their clinicopathological features; and 4) future studies of hormonal clinical trials should be performed on well-defined meningioma subgroups.

Ligand-dependent conformational changes in the progesterone receptor are necessary for events that follow DNA binding.

Hormones and antihormones induce related, but distinct, conformational changes in the progesterone receptor [Allan, G. F., Leng, X., Tsai, S. Y., Weigel, N. L., Edwards, D. P., Tsai, M.-J. & O'Malley, B. W. (1992) J. Biol. Chem. 267, 19513-19520]. In both cases the conformational change precedes the dissociation of heat shock proteins and binding to DNA. We have now investigated the steps in hormone action which are dependent upon this conformational change. We show that in the absence of ligand, monoclonal antibodies directed against different regions of the progesterone receptor can induce high-affinity binding to its response element in vitro. This antibody-induced DNA binding is presumably facilitated by enhanced dimerization of receptor monomers. However, antibodies do not induce the hormone-specific conformational change in the progesterone receptor and do not induce in vitro transcription by the receptor. In contrast, the antiprogestin ZK98299, which inhibits receptor binding to DNA, fully induces the antihormone-specific conformational change. Thus, our data imply that steroids induce a conformational change in their receptors which is necessary for events subsequent to DNA binding, most likely for transactivation.

Heterotetrameric structure of the human progesterone receptor.

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

Hormone and antihormone induce distinct conformational changes which are central to steroid receptor activation.

Antihormones are potent antagonists of hormone action in vivo, but the mechanism underlying this antagonism is not understood. Several steroid hormones transform (activate) their receptors from a cytosolic, non-DNA binding 8 S sedimentation form to a nuclear, DNA binding 4 S form. Transformation is accompanied by the loss of associated heat shock proteins. We have previously demonstrated that an additional hormone-dependent step, separate from heat shock protein removal, is required for activation of the human progesterone receptor. We have devised an assay in which the human progesterone receptor translated in vitro binds to its specific response element in a hormone-dependent manner. As assessed by limited proteolytic digestion, hormone treatment of the nascent receptor induces a dramatic conformational change within the protein. The conformational change occurs in the absence of DNA and renders the entire ligand binding domain resistant to digestion by proteases. A number of antiprogestins, including RU486, induce an equally dramatic, but distinct, structural alteration of the ligand binding domain. The distinction centers upon the final 30 to 40 amino acids at the carboxyl terminus. The conformational change can be induced by ligand prior to dissociation of the 8 S complex and is not induced by heat shock protein removal in the absence of hormone. Remarkably, virtually identical hormone-induced conformational changes were detected following proteolytic analysis of in vitro translated retinoic acid receptors. Our data indicate that the sole necessary event in the activation of steroid receptors is conformational modification by the ligand. Furthermore, we conclude that transcriptional inactivation of steroid receptors by antihormones involves the induction of an inappropriate structural conformation at the extreme carboxyl terminus of the ligand binding domain.

Sexual dimorphism characterizes baboon myocardial androgen receptors but not myocardial estrogen and progesterone receptors.

Using biochemical methods we established that estrogen receptor content and distribution and progesterone receptor content in female and male baboon myocardium did not differ between sexes. In contrast, myocardial androgen receptor distribution between cytosolic and nuclear compartments was sexually dimorphic. Female baboon myocardial androgen receptors were restricted to the cytosolic compartment, whereas male myocardial androgen receptors were distributed between the cytosolic and nuclear compartments. Using human estrogen receptor cDNA we showed that baboon aorta, myocardium and uterus contain a 6.3 kb estrogen receptor transcript. Analyses performed with human progesterone receptor cDNA established that baboon aorta and uterus contain an 8 kb progesterone receptor transcript; however, progesterone receptor transcripts were not demonstrable in baboon myocardial RNA preparations. Because relative hybridization signal intensity reflected known uterine and aortic progesterone receptor content, failure to detect progesterone receptor transcripts in myocardial preparations may reflect sensitivity limitations and the fact that aortic progesterone receptor content is 5-fold greater than that of myocardium. Immunocytochemical analyses demonstrated that baboon myocardial progesterone receptors were present in greater than 25% of myocytes and generally absent from other myocardial cells. Our studies establish that: (1) gonadal steroid hormone receptor gene transcription occurs in cells of the baboon cardiovasculature, (2) these steroid hormone receptors may be physiologically functional, and (3) gonadal steroid hormone receptors may be restricted to specialized cells of the cardiovasculature.

Steroid hormone-dependent interaction of human progesterone receptor with its target enhancer element.

We investigated the requirement of steroid hormone for the specific binding of progesterone receptor to its cognate progesterone responsive element (PRE) in cell-free experiments. We prepared unfractionated nuclear extracts from human breast cancer (T47D) cells which are rich in progesterone receptors and used a gel retardation assay to monitor receptor-DNA complex formation. Exposure of receptor to either progesterone, R5020, or the antiprogestin RU38 486 in vivo or in vitro led to the formation of two protein-DNA complexes (1 and 2) which were not detected in nuclear extracts unexposed to hormone. Similar treatment with cortisol or estradiol failed to induce the formation of these complexes. The complexes were specific for PRE, since they could be competed efficiently in binding competition experiments by oligonucleotides containing PRE. A monoclonal antibody which recognizes both A and B forms of human progesterone receptor, interacted with both complexes 1 and 2 and shifted them to slower migrating forms. Another antibody which only recognizes the B form interacted with only complex 1 but not with complex 2, establishing that the complexes 1 and 2 were indeed formed by progesterone receptor forms B and A, respectively. We conclude from the above studies that in vivo or in vitro treatment of nuclear progesterone receptor with either progesterone or R5020 or RU38 486 alone can lead to detection of high affinity complexes formed between the PRE and the receptor present in unpurified nuclear extracts.

Progestin and estrogen receptors: characterization and localization in rat submandibular glands, with special reference to epidermal growth factor.

By using progestin (P) and estrogen (E), the localization and characterization of both steroid receptors were examined in the submandibular gland (SMG) of 6-week-old immature castrated rats, with special reference to localization of epidermal growth factor (EGF). In the castrated male and female rats, both 3H-estradiol-17 beta (3H-E2 beta) and 3H-promegestone (3H-R5020) bound to SMG cytosol with high affinity and low capacity. These values were similar to those reported for other tissues. However, E-treatment after castration inhibited the specific binding. In sucrose density gradient ultracentrifugation, it was found that P receptors in both castrated males and females had a sedimentation coefficient of 7S, whereas E receptors had sedimentation coefficients of 4S and 7S. A histochemical study of the SMG of castrated male and female rats showed that the E-peroxidase complex (EPC)- and P-peroxidase complex (PPC)-stained cells were predominantly located in the epithelium of the duct system including the excretory duct and the granular convoluted tubules. Few cells were located in the intercalated duct, and none were found in the acinus. EGF-immunoreactive cells were also located in the epithelium of the same tissue region as in PPC- and EPC-stained sections. Moreover, E-treatment after castration inhibited the intensity of staining and immunoreactivity. These results clearly suggest that rat SMG contains specific P and E receptors which are mainly located in the epithelial cells of the duct system in which EGF-containing cells are identified. We discussed the possibility that P and E might affect EGF immunoreactivity, which reflects EGF production, through their receptors in the epithelium of the duct system.