Binding of progesterone to cell surfaces of human granulosa-lutein cells

Membrane Progesterone Receptors (mPRs/PAQRs) Are Going beyond Its Initial Definitions

Progesterone (PRG) is a key cyclical reproductive hormone that has a significant impact on female organs in vertebrates. It is mainly produced by the corpus luteum of the ovaries, but can also be generated from other sources such as the adrenal cortex, Leydig cells of the testes and neuronal and glial cells. PRG has wide-ranging physiological effects, including impacts on metabolic systems, central nervous systems and reproductive systems in both genders. It was first purified as an ovarian steroid with hormonal function for pregnancy, and is known to play a role in pro-gestational proliferation during pregnancy. The main function of PRG is exerted through its binding to progesterone receptors (nPRs, mPRs/PAQRs) to evoke cellular responses through genomic or non-genomic signaling cascades. Most of the existing research on PRG focuses on classic PRG-nPR-paired actions such as nuclear transcriptional factors, but new evidence suggests that PRG also exerts a wide range of PRG actions through non-classic membrane PRG receptors, which can be divided into two sub-classes: mPRs/PAQRs and PGRMCs. The review will concentrate on recently found non-classical membrane progesterone receptors (mainly mPRs/PAQRs) and speculate their connections, utilizing the present comprehension of progesterone receptors.

miR-23b-3p inhibits chicken granulosa cell proliferation and steroid hormone synthesis via targeting GDF9

MicroRNAs (miRNAs) are ∼22 nt RNAs that direct post-transcriptional repression of mRNA targets in diverse eukaryotic lineages. Granulosa cells (GCs) are the earliest differentiated follicular somatic cells. From the initiation of primordial follicles, their differentiation and growth are closely related to the development of follicles. The research on follicular development mostly focused on the granular layer, as well as the hormone synthesis induced by granulosa cell differentiation before and after follicular selection. In this study, we evaluated the effects of miR-23b-3p on chicken granulosa cells, including granulosa cell proliferation and steroid hormone synthesis. Elevated expression of miR-23b-3p significantly inhibited granulosa cell proliferation and steroid hormone synthesis, but did not affect apoptosis. Furthermore, it was observed that the forecast growth differentiation factor 9 (GDF9) is a target gene of miR-23b-3p and miR-23b-3p can down-regulate expression of GDF9. Overall, this study demonstrated that miR-23b-3p can regulate the proliferation and steroid hormone synthesis of chicken granulosa cells by inhibiting the expression of GDF9.

Progesterone-induced blocking factor (PIBF) influences the expression of membrane progesterone receptors (mPRs) on peripheral CD4+ T lymphocyte cells in normal fertile females

PURPOSE

Progesterone-induced blocking factor (PIBF) is a protein secreted by lymphocytes exposed to progesterone (P4). P4 and PIBF have immunomodulatory effects on peripheral CD4⁺ T cells during normal pregnancy. Membrane progesterone receptors (mPRs) may correlate with the immunomodulatory properties of P4 on T cells. Variation in expression of mPRs may influence P4 regulatory performance during pregnancy. On the other hand, PIBF increases in pregnant normal women compared to women who have experienced abortion. The present study aimed to determine whether PIBF, in addition to having a direct influence on the immune system, can affect P4 performance through its effect on mPR expression. Such novel research findings demonstrate the importance of PIBF in the maintenance of pregnancy.

METHODS

Isolated peripheral blood mononuclear cells (PBMCs) from 30 healthy women were stimulated with the mitogen phytohemagglutinin (PHA). Cells were either exposed to various concentrations of PIBF or had no exposure at all in a culture medium at 37 °C for 3 days. The mean fluorescence intensity (MFI) of mPRα and mPRβ was evaluated using polyclonal and monoclonal antibodies on CD4⁺ T cells.

RESULTS

PIBF was able to significantly increase mPR expression on the surface of peripheral CD4⁺ T cells (p ≤ 0.05).

CONCLUSION

This study characterized the effects of PIBF on mPR expression on peripheral CD4⁺ T cells of healthy fertile women. Thus, a decrease in PIBF concentration during abnormal pregnancy can modulate mPR expression and regulatory performance of P4 on T cells. Future research into this issue is likely to open up a new understanding of the etiology of abortion.

Role of nuclear progesterone receptor isoforms in uterine pathophysiology

BACKGROUND

Progesterone is a key hormonal regulator of the female reproductive system. It plays a major role to prepare the uterus for implantation and in the establishment and maintenance of pregnancy. Actions of progesterone on the uterine tissues (endometrium, myometrium and cervix) are mediated by the combined effects of two progesterone receptor (PR) isoforms, designated PR-A and PR-B. Both receptors function primarily as ligand-activated transcription factors. Progesterone action on the uterine tissues is qualitatively and quantitatively determined by the relative levels and transcriptional activities of PR-A and PR-B. The transcriptional activity of the PR isoforms is affected by specific transcriptional coregulators and by PR post-translational modifications that affect gene promoter targeting. In this context, appropriate temporal and cell-specific expression and function of PR-A and PR-B are critical for normal uterine function.

METHODS

Relevant studies describing the role of PRs in uterine physiology and pathology (endometriosis, uterine leiomyoma, endometrial cancer, cervical cancer and recurrent pregnancy loss) were comprehensively searched using PubMed, Cochrane Library, Web of Science, and Google Scholar and critically reviewed.

RESULTS

Progesterone, acting through PR-A and PR-B, regulates the development and function of the endometrium and induces changes in cells essential for implantation and the establishment and maintenance of pregnancy. During pregnancy, progesterone via the PRs promotes myometrial relaxation and cervical closure. Withdrawal of PR-mediated progesterone signaling triggers menstruation and parturition. PR-mediated progesterone signaling is anti-mitogenic in endometrial epithelial cells, and as such, mitigates the tropic effects of estrogen on eutopic normal endometrium, and on ectopic implants in endometriosis. Similarly, ligand-activated PRs function as tumor suppressors in endometrial cancer cells through inhibition of key cellular signaling pathways required for growth. In contrast, progesterone via PR activation appears to increase leiomyoma growth. The exact role of PRs in cervical cancer is unclear. PRs regulate implantation and therefore aberrant PR function may be implicated in recurrent pregnancy loss (RPL). PRs likely regulate key immunogenic factors involved in RPL. However, the exact role of PRs in the pathophysiology of RPL and the use of progesterone for therapeutic benefit remains uncertain.

CONCLUSIONS

PRs are key mediators of progesterone action in uterine tissues and are essential for normal uterine function. Aberrant PR function (due to abnormal expression and/or function) is a major cause of uterine pathophysiology. Further investigation of the underlying mechanisms of PR isoform action in the uterus is required, as this knowledge will afford the opportunity to create progestin/PR-based therapeutics to treat various uterine pathologies.

Progesterone signals through membrane progesterone receptors (mPRs) in MDA-MB-468 and mPR-transfected MDA-MB-231 breast cancer cells which lack full-length and N-terminally truncated isoforms of the nuclear progesterone receptor

The functional characteristics of membrane progesterone receptors (mPRs) have been investigated using recombinant mPR proteins over-expressed in MDA-MB-231 breast cancer cells. Although these cells do not express the full-length progesterone receptor (PR), it is not known whether they express N-terminally truncated PR isoforms which could possibly account for some progesterone receptor functions attributed to mPRs. In the present study, the presence of N-terminally truncated PR isoforms was investigated in untransfected and mPR-transfected MDA-MB-231 cells, and in MDA-MB-468 breast cancer cells. PCR products were detected in PR-positive T47D Yb breast cancer cells using two sets of C-terminus PR primers, but not in untransfected and mPR-transfected MDA-MB-231 cells, nor in MDA-MB-468 cells. Western blot analysis using a C-terminal PR antibody, 2C11F1, showed the same distribution pattern for PR in these cell lines. Another C-terminal PR antibody, C-19, detected immunoreactive bands in all the cell lines, but also recognized α-actinin, indicating that the antibody is not specific for PR. High affinity progesterone receptor binding was identified on plasma membranes of MDA-MB-468 cells which was significantly decreased after treatment with siRNAs for mPRα and mPRβ. Plasma membranes of MDA-MB-468 cells showed very low binding affinity for the PR agonist, R5020, ≤1% that of progesterone, which is characteristic of mPRs. Progesterone treatment caused G protein activation and decreased production of cAMP in MDA-MB-468 cells, which is also characteristic of mPRs. The results indicate that the progestin receptor functions in these cell lines are mediated through mPRs and do not involve any N-terminally truncated PR isoforms.

Characterization and expression of the nuclear progestin receptor in zebrafish gonads and brain

The zebrafish nuclear progestin receptor (nPR; official symbol PGR) was identified and characterized to better understand its role in regulating reproduction in this well-established teleost model. A full-length cDNA was identified that encoded a 617-amino acid residue protein with high homology to PGRs in other vertebrates, and contained five domains characteristic of nuclear steroid receptors. In contrast to the multiplicity of steroid receptors often found in euteleosts and attributed to probable genome duplication, only a single locus encoding the full-length zebrafish pgr was identified. Cytosolic proteins from pgr-transfected cells showed a high affinity (K(d) = 2 nM), saturable, single-binding site specific for a native progestin in euteleosts, 4-pregnen-17,20 beta-diol-3-one (17,20 beta-DHP). Both 17,20 beta-DHP and progesterone were potent inducers of transcriptional activity in cells transiently transfected with pgr in a dual luciferase reporter assay, whereas androgens and estrogens had little potency. The pgr transcript and protein were abundant in the ovaries, testis, and brain and were scarce or undetectable in the intestine, muscle, and gills. Further analyses indicate that Pgr was expressed robustly in the preoptic region of the hypothalamus in the brain; proliferating spermatogonia and early spermatocytes in the testis; and in follicular cells and early-stage oocytes (stages I and II), with very low levels within maturationally competent late-stage oocytes (IV) in the ovary. The localization of Pgr suggests that it mediates progestin regulation of reproductive signaling in the brain, early germ cell proliferation in testis, and ovarian follicular functions, but not final oocyte or sperm maturation.

Estrogen and progesterone modulate [35S]GTPgammaS binding to nociceptin receptors

Sex steroids modulate reproduction by altering the response of steroid-activated opioid circuits in the hypothalamus and limbic system, by inducing release of endogenous opioids and activation of their cognate receptors. Many studies have concentrated on steroid regulation of exogenous opioid peptides, but steroids also have important actions on opioid receptors inducing receptor trafficking. Opioid receptors are G protein-coupled receptors and their activation catalyzes the exchange of GTP for GDP initiating intracellular signaling cascades. Kinetics of G protein activation were studied using [(35)S]GTPgammaS binding. Catalytic amplification, the number of G proteins activated per occupied receptor, was used as a measure of receptor/transducer amplification. The present study examined whether estrogen and progesterone treatment altered the kinetics of nociceptin opioid receptor (ORL1) in plasma membranes from the medial preoptic area and mediobasal hypothalamus. These hypothalamic regions are important in the gonadal steroid hormone regulation of sexual receptivity. In the mediobasal hypothalamus, estrogen increased ORL1 (B(max)) receptor number 2-fold and maximal GTPgammaS binding (E(max)) 3.9-fold. Subsequent progesterone treatment further increased ORL1 E(max )6.9-fold above baseline, despite a 2-fold decrease in the catalytic amplification factor. In the medial preoptic area, estrogen alone did not increase E(max), but both estrogen and progesterone were able to increase ORL1 B(max) 2.2-fold and E(max) 3-fold, despite having a 3-fold decrease in the catalytic amplification factor. These effects are interesting because they indicate actions of steroids that increase the number of ORL1 but decrease the catalytic amplification suggesting that the steroid effects on opioid receptors are complex and may involve modulation by other signals.