Progesterone-induced activation of membrane-bound progesterone receptors in murine macrophage cells

Mitogen-Activated Protein Kinase and Nuclear Hormone Receptor Crosstalk in Cancer Immunotherapy

The three major MAP-kinase (MAPK) pathways, ERK1/2, p38 and JNK/SAPK, are upstream regulators of the nuclear "hormone" receptor superfamily (NHRSF), with a prime example given by the estrogen receptor in breast cancer. These ligand-activated transcription factors exert non-genomic and genomic functions, where they are either post-translationally modified by phosphorylation or directly interact with components of the MAPK pathways, events that govern their transcriptional activity towards target genes involved in cell differentiation, proliferation, metabolism and host immunity. This molecular crosstalk takes place not only in normal epithelial or tumor cells, but also in a plethora of immune cells from the adaptive and innate immune system in the tumor-stroma tissue microenvironment. Thus, the drugability of both the MAPK and the NHRSF pathways suggests potential for intervention therapies, especially for cancer immunotherapy. This review summarizes the existing literature covering the expression and function of NHRSF subclasses in human tumors, both solid and leukemias, and their effects in combination with current clinically approved therapeutics against immune checkpoint molecules (e.g., PD1).

Evidence for progesterone acting as an inhibitor of stress axis via stimulating pituitary neuropeptide B/W receptor 2 (NPBWR2) expression in chickens

In vertebrates, the hypothalamus-pituitary-adrenal gland (HPA) axis is the main endocrine pathway regulating the stress response, thus also called the stress axis. It has been well-accepted that the stress axis is tightly controlled by both hypothalamic stimulators and inhibitors [e.g. corticotropin (ACTH)-releasing inhibitory factor (CRIF)]. However, the identity of authentic CRIF remains unclear for decades. Recently, neuropeptide W (NPW) was proved to be the physiological CRIF in chickens. Together with its functional receptor (NPBWR2), they play critical roles in attenuating the activity of the chicken stress axis. Because increasing pieces of evidence suggested that sex steroids could regulate the stress axis, using chicken as a model, we investigated whether the newly identified CRIF and its receptor are under the control of sex steroids in this study. Our results showed that: (1) expression of NPW-NPBWR2 in the hypothalamus-pituitary axis was sexually dimorphic and developmental stage-dependent; (2) progesterone (P₄), rather than 17β-estradiol (E₂) and dihydrotestosterone (DHT), could dose- and time-dependently upregulate NPBWR2 expression, which was accompanied with the decrease of ACTH synthesis and secretion, in cultured pituitary cells; (3) intraperitoneal injection of P₄ could elevate the mRNA level of pituitary NPBWR2; (4) P₄-stimulated NPBWR2 expression was relevant to both nPR-mediated genomic action and mPRs-triggered nongenomic route associated with MEK/ERK, PI3K/AKT cascade, and calcium influx. To our knowledge, our results discover a novel route of sex steroids in modulating the stress axis of chickens, which lays a foundation to reveal the complicated interaction network between reproduction and stress axes in chickens.

Role of progesterone on dexamethasone-induced alterations in placental vascularization and progesterone receptors in rats†

BACKGROUND

Intrauterine growth restriction (IUGR) is manifested by lower maternal progesterone levels, smaller placental size, and decreased placental vascularity indicated by lower expression of vascular endothelial growth factor (VEGF). Studies showed that progesterone increases angiogenesis and induces VEGF expression in different tissues. Therefore, the aim of the present study is to evaluate the effect of progesterone on placental vascular bed and VEGF expression and the modulation of nuclear and membranous progesterone receptors (PR) in dexamethasone-induced rat IUGR model.

METHODS

Pregnant Sprague-Dawley rats were allocated into four groups and given intraperitoneal injections of either saline, dexamethasone, dexamethasone, and progesterone or progesterone. Injections started on gestation day (DG) 15 and lasted until the days of euthanization (19 and 21 DG). Enzyme-linked immunosorbent assay was used to evaluate plasma progesterone levels. Real-time PCR and western blotting were used to evaluate gene and protein expressions of VEGF, and PR in labyrinth and basal placental zones. Immunohistochemistry was used to locate VEGF and different PRs in placental cells. Immunofluorescence was used to monitor the expression of blood vessel marker (αSMA).

RESULTS

Dexamethasone decreased the vascular bed fraction and the expression of VEGF in both placental zones. Progesterone co-treatment with dexamethasone prevented this reduction. Nuclear and membrane PRs showed tissue-specific expression in different placental zones and responded differently to both dexamethasone and progesterone.

CONCLUSIONS

Progesterone treatment improves the outcomes in IUGR pregnancy. Progesterone alleviated DEX-induced IUGR probably by promoting placental VEGF and angiogenesis.

Functions of Membrane Progesterone Receptors (mPRs, PAQRs) in Nonreproductive Tissues

Gender differences in a wide variety of physiological parameters have implicated the ovarian hormones, estrogens and progesterone, in the regulation of numerous nonreproductive tissue functions. Rapid, nongenomic (nonclassical) progesterone actions mediated by membrane progesterone receptors (mPRs), which belong to the progestin and adipoQ receptor family, have been extensively investigated in reproductive and nonreproductive tissues since their discovery in fish ovaries 20 years ago. The 5 mPR subtypes (α, β, γ, δ, ε) are widely distributed in vertebrate tissues and are often expressed in the same cells as the nuclear progesterone receptor (PR) and progesterone receptor membrane component 1, thereby complicating investigations of mPR-specific functions. Nevertheless, mPR-mediated progesterone actions have been identified in a wide range of reproductive and nonreproductive tissues and distinguished from nuclear PR-mediated ones by knockdown of these receptors with siRNA in combination with a pharmacological approach using mPR- and PR-specific agonists. There are several recent reviews on the roles of the mPRs in vertebrate reproduction and cancer, but there have been no comprehensive assessments of mPR functions in nonreproductive tissues. Therefore, this article briefly reviews mPR functions in a broad range of nonreproductive tissues. The evidence that mPRs mediate progesterone and progestogen effects on neuroprotection, lordosis behavior, respiratory control of apnea, olfactory responses to pheromones, peripheral nerve regeneration, regulation of prolactin secretion in prolactinoma, immune functions, and protective functions in vascular endothelial and smooth muscle cells is critically reviewed. The ubiquitous expression of mPRs in vertebrate tissues suggests mPRs regulate many additional nonreproductive functions that remain to be identified.

Membrane Progesterone Receptors (mPRs, PAQRs): Review of Structural and Signaling Characteristics

The role of membrane progesterone receptors (mPRs), which belong to the progestin and adipoQ receptor (PAQR) family, in mediating rapid, nongenomic (non-classical) progestogen actions has been extensively studied since their identification 20 years ago. Although the mPRs have been implicated in progestogen regulation of numerous reproductive and non-reproductive functions in vertebrates, several critical aspects of their structure and signaling functions have been unresolved until recently and remain the subject of considerable debate. This paper briefly reviews recent developments in our understanding of the structure and functional characteristics of mPRs. The proposed membrane topology of mPRα, the structure of its ligand-binding site, and the binding affinities of steroids were predicted from homology modeling based on the structures of other PAQRs, adiponectin receptors, and confirmed by mutational analysis and ligand-binding assays. Extensive data demonstrating that mPR-dependent progestogen regulation of intracellular signaling through mPRs is mediated by activation of G proteins are reviewed. Close association of mPRα with progesterone membrane receptor component 1 (PGRMC1), its role as an adaptor protein to mediate cell-surface expression of mPRα and mPRα-dependent progestogen signaling has been demonstrated in several vertebrate models. In addition, evidence is presented that mPRs can regulate the activity of other hormone receptors.

Progesterone and Inflammatory Response in the Oviduct during Physiological and Pathological Conditions

Progesterone has been shown to be a potent suppressor of several inflammatory pathways. During pregnancy, progesterone levels increase, allowing for normal pregnancy establishment and maintenance. The dysregulation of progesterone, as well as inflammation, leads to poor pregnancy outcomes. However, it is unclear how progesterone imbalance could impact inflammatory responses in the oviduct and subsequently result in early pregnancy loss. Therefore, in this review, we describe the role of progesterone signaling in regulating the inflammatory response, with a focus on the oviduct and pathological conditions in the Fallopian tubes.

Cytotoxic Effects of the Selective Ligands of Membrane Progesterone Receptors in Human Pancreatic Adenocarcinoma Cells BxPC3

Progesterone and its synthetic analogues act on cells through different types of receptors, affecting proliferation and apoptosis. These compounds exert their effect through the nuclear receptors and the insufficiently studied membrane progesterone receptors (mPRs) belonging to the progestin and adiponectin Q receptor (PAQR) family. We have identified two selective ligands of mPRs that activate only this type of progesterone receptors - 19-hydroxypregn-4-en-20-one (LS-01) and 19-hydroxy-5β-pregn-3-en-20-one (LS-02). The goal of this work is to study the effect of these compounds on proliferation and death of human pancreatic adenocarcinoma cells BxPC3 and involvement of the two kinases (p38 MAPK and JNK) in signaling pathways activated by progestins through mPRs. It was shown that progesterone and the compound LS-01 significantly (p < 0.05) inhibited the BxPC3 cell viability, with JNK serving as a mediator. The identified targets of these two steroids are the genes of the proteins Ki67, cyclin D1, PCNA, and p21. Progesterone and the compound LS-01 significantly (p < 0.05) stimulate DNA fragmentation, enhancing the cell death. The p38 mitogen-activated protein kinase (MAPK) is a key mediator of this process. The BCL2A1 protein gene was identified as a target of both steroids. The compound LS-02 significantly (p < 0.05) alters membrane permeability and changes the exposure of phosphatidylserine on the outer membrane leaflet, also enhancing the cell death. This compound acts on these processes by activating both kinases, JNK and p38 MAPK. The compound LS-02 targets the genes encoding the proteins HRK, caspase 9, and DAPK.

Inflammatory Basis of Atherosclerosis: Modulation by Sex Hormones

Atherosclerosis-related cardiovascular diseases (CVDs) are the leading cause of death globally. Several lines of evidence are supportive of the contributory role of vascular inflammation in atherosclerosis. Diverse immune cell types, including monocytes/macrophages, T-cells and neutrophils, as well as specialized proresolving lipid mediators, have been successfully characterized as key players in vascular inflammation. The increased prevalence of atherosclerotic CVD in men in comparison to age-matched premenopausal women and the abolition of sex differences in prevalence during menopause strongly suggest a pivotal role of sex hormones in the development of CVD. Indeed, many animal and human studies conclusively implicate sex hormones as a crucial component in driving the immune response. This is further corroborated by the effective identification of sex hormone receptors in vascular endothelial cells, vascular smooth muscle cells and immune cells. Collectively, these findings suggest a cellular communication between sex hormones and vascular or immune cells underlying the vascular inflammation in atherosclerosis. The aim of this review is to provide an overview of vascular inflammation as a causal cue underlying atherosclerotic CVDs within the context of the modulatory effects of sex hormones. Moreover, the cellular and molecular signaling pathways underlying the sex hormones- immune system interactions as potential culprits for vascular inflammation are highlighted with detailed and critical discussion. Finally, the review concludes by speculations on the potential sex-related efficacy of currently available immunotherapies in mitigating vascular inflammation. Conceivably, a deeper understanding of the immunoregulatory influence of sex hormones on vascular inflammation-mediated atherosclerosis permits sex-based management of atherosclerosis-related CVDs.

PAQR7: An intermediary mediating nongenomic progesterone action in female reproductive tissue

Progestin and adipoQ receptor 7 (PAQR7) as an indispensable member of membrane progestin receptors in the Progestin and adipoQ receptor (PAQR) family that mediates nongenomic progesterone actions, initiated rapidly at the cell surface. Previous research demonstrated the distribution of PAQR7, which was mainly expressed in reproductive tissues, including ovary and testis. In the male reproductive system, PAQR7 is involved in progestin-induced sperm hypermotility. However, reports studying PAQR7 in female reproductive tissue mainly concentrate on oocyte maturation in fish, its expression in the ovary and gestational tissue, and regulation of uterine functions in mammals. Despite recent advances, many aspects of progestin signaling through PAQR7 are still unclear, especially in female reproductive tissue. Therefore, we reveal the structure and characteristics of PAQR7 and conclude the putative progestin-induced action mediated by PAQR7 in female reproductive tissue, such as the development of ovarian follicles, apoptosis of granulosa cells, oocyte maturation, and development of certain diseases, among others, to review the function of PAQR7 in the female reproductive system in detail.

Steroid hormone bioavailability is controlled by the lymphatic system

The steroid hormone progesterone accounts for immune tolerance in pregnancy. Enhanced progesterone metabolism to 6α-OH-pregnanolone occurs in complicated pregnancies such as in preeclampsia with preterm delivery or intrauterine growth restriction, and in cancer. As lymphatic endothelial cells (LECs) promote tumor immunity, we hypothesized that human LECs modify progesterone bioavailability. Primary human LECs and mice lymph nodes were incubated with progesterone and progesterone metabolism was analyzed by thin layer chromatography and liquid chromatography-mass spectrometry. Expression of steroidogenic enzymes, down-stream signal and steroid hormone receptors was assessed by Real-time PCR. The placental cell line HTR-8/SV neo was used as reference. The impact of the progesterone metabolites of interest was investigated on the immune system by fluorescence-activated cell sorting analysis. LECs metabolize progesterone to 6α-OH-pregnanolone and reactivate progesterone from a precursor. LECs highly express 17β-hydroxysteroid dehydrogenase 2 and are therefore antiandrogenic and antiestrogenic. LECs express several steroid hormone receptors and PIBF1. Progesterone and its metabolites reduced TNF-α and IFN-γ production in CD4+ and CD8+ T cells. LECs modify progesterone bioavailability and are a target of steroid hormones. Given the global area represented by LECs, they might have a critical immunomodulatory control in pregnancy and cancer.

Antisclerothic effect of tibolone by reducing proinflammatory cytokines expression, ROS production and LDL-ox uptake in THP-1 macrophages

BACKGROUND

Cardiovascular disease is more frequent in menopausal women, which has been related to factor such as weight gain, altered fat distribution, and increased inflammation markers including adipokines (MCP-1, TNF-α, IL-6) and cytokines (IL-1, IL-6, TNF-α) produced by macrophages. In addition to their phagocytic activity, macrophages secrete cytokines and chemokines that induces cell recruitment, which is a process related to vascular damage that favors the formation of atheromatous plaques. Tibolone (Tb) therapy is used to reduce the symptoms of menopause as well as osteoporosis and it has been shown to decreases the risk of fractures.

METHODS

To investigate the effect of tibolone in macrophage enzymatic activity, gene expression of cytokines, and its effect on foam cells formation. We use phorbol-12-myristate-13-acetate (PMA)-differentiated THP-1 cells. The cells were incubated 24 h and 48 h using pre and post-treatment schemes. We evaluated total ROS determination by NBT assay, expression of cytokines (IL-1β, IL-6, TNF-α, NOS2, ARG1, TGFβ) by RT-qPCR and foam cell formation in THP-1 differentiated macrophages stimulated with PMA.

RESULTS

It was observed that the minor levels of total ROS determination were obtained with tibolone at 48 h in post-treatment scheme. Also, in a long term we found decrease the proinflammatory cytokines (IL-1β, IL-6 and TNF-α). Finally, with treatment for 24 h with P4 y Tb we observed fewer LDL vesicles into macrophages cytoplasm.

CONCLUSIONS

These results suggest that tibolone reduces the inflammatory process, also inhibits the foam cells formation; suggesting a possible role in reducing cardiovascular risk.

Progesterone inhibits cytokine/TNF-α production by porcine CL macrophages via the genomic progesterone receptor

In pigs, luteolytic sensitivity to PGF-2α (=LS) is delayed until d 13 of the estrous cycle. While the control of LS is unknown, it is temporally associated with macrophage (MAC; which secretes tumor necrosis factor [TNF]-α) infiltration into the corpora lutea (CL), and previous studies have shown that TNF-α induces LS in porcine luteal cells (LCs) in culture. This study was designed to explore the control of LS by CL macrophage (CL MAC)/TNF-α by progesterone (P4), and to examine the hypothesis that P4 acting via the genomic P4 receptor (PGR) inhibits CL MAC TNF-α and thus plays a key role in regulating LS during the pig estrous cycle. In experiment 1, the effects of LCs on CL MAC cytokine/TNF-α mRNA expression in co-culture were examined (MID cycle; ~d 7-12; no LS); results showed that LC was inhibitory to cytokine/TNF-α. In experiment 2, the effects of P4 or R5020 (PGR-agonist) on CL MAC cytokine/TNF-α mRNA expression were examined (MID cycle; ~d 7-12; no LS); results showed that both P4 and R5020 dose-dependently inhibited TNF-α. In experiment 3, CL MACs were isolated from CL at MID (~d 7-12; no LS) and LATE (~d 13-18; + LS) cycle, and TNF-α/PGR mRNA measured. Results indicated that while TNF-α mRNA was 4.2-fold greater in CL MACs from LATE vs MID cycle, PGR mRNA was 4.5-fold greater in CL MACs from MID vs LATE cycle. These data support our hypothesis and suggest that progesterone, acting via PGR, plays a critical physiological role in the control of TNF-α production by CL MACs and LS during the pig estrous cycle.

Prenatal two-hit stress affects maternal and offspring pregnancy outcomes and uterine gene expression in rats: match or mismatch?

Maternal stress and inflammation excesses can lead to adverse pregnancy outcomes and offspring development. We evaluated whether distinct prenatal stressors affect pregnancy, maternal and offspring outcomes, and uterine gene expression differently when combined than either alone. Long-Evans dams were exposed to psychological or/and (two-hit) immune stress (interleukin-1 beta [IL-1β]), on gestational days 12-18 and 17-delivery, respectively. Gestational length, maternal weight gain, glycaemia and corticosterone levels, offspring weight, and gender effects were recorded. Maternal and offspring uteri were collected at weaning and on postnatal day 160 correspondingly. Uterine expression of genes involved in local progesterone metabolism, neuroendocrine and immune systems were analyzed using quantitative real-time polymerase chain reaction. Maternal two-hit stress increased gestational length variation and the occurrence of adverse pregnancy outcomes while reducing gestational weight gain. Pup weight was negatively affected by prenatal stressors in a gender-specific way. In dams, IL-1β upregulated gene expression of neuroendocrine (Crh, Crhr1) and cytokine genes (Il1b, Il1rn, Il6, and Il10). Conversely, transcriptional patterns in offspring uteri were more variable with gene-specific up- or downregulation by each stressor separately, while exposure to both extensively reduced the expression of neuroendocrine (Hsd11b1), cytokine (Il1a, Il1rn, Il6), and IL-1 receptor genes. In conclusion, maternal stress affects physiological and molecular processes in dams and their offspring; two hits have different effects than single stressors. Outcomes appear generation-, gender-, and stressor-specific. Dampening of offspring uterine gene expression after exposure to multiple stressors could fit within the match/mismatch hypothesis of perinatal programming, with offspring preparing for a stressful life.

Steroids, Pregnancy and Fetal Development

Maternal glucocorticoids critically rise during pregnancy reaching up to a 20-fold increase of mid-pregnancy concentrations. Concurrently, another steroid hormone, progesterone, increases. Progesterone, which shows structural similarities to glucocorticoids, can bind the intracellular glucocorticoid receptor, although with lower affinity. Progesterone is essential for the establishment and continuation of pregnancy and it is generally acknowledged to promote maternal immune tolerance to fetal alloantigens through a wealth of immunomodulatory mechanisms. Despite the potent immunomodulatory capacity of glucocorticoids, little is known about their role during pregnancy. Here we aim to compare general aspects of glucocorticoids and progesterone during pregnancy, including shared common steroidogenic pathways, plasma transporters, regulatory pathways, expression of receptors, and mechanisms of action in immune cells. It was recently acknowledged that progesterone receptors are not ubiquitously expressed on immune cells and that pivotal features of progesterone induced- maternal immune adaptations to pregnancy are mediated via the glucocorticoid receptor, including e.g., T regulatory cells expansion. We hypothesize that a tight equilibrium between progesterone and glucocorticoids is critically required and recapitulate evidence supporting that their disequilibrium underlie pregnancy complications. Such a disequilibrium can occur, e.g., after maternal stress perception, which triggers the release of glucocorticoids and impair progesterone secretion, resulting in intrauterine inflammation. These endocrine misbalance might be interconnected, as increase in glucocorticoid synthesis, e.g., upon stress, may occur in detriment of progesterone steroidogenesis, by depleting the common precursor pregnenolone. Abundant literature supports that progesterone deficiency underlies pregnancy complications in which immune tolerance is challenged. In these settings, it is largely yet undefined if and how glucocorticoids are affected. However, although progesterone immunomodulation during pregnancy appear to be chiefly mediated glucocorticoid receptors, excess glucocorticoids cannot compensate by progesterone deficiency, indicating that additional und still undercover mechanisms are at play.

Neuroprotection and immunomodulation of progesterone in the gut of a mouse model of Parkinson's disease

Gastrointestinal symptoms appear in Parkinson's disease patients many years before motor symptoms, suggesting the implication of dopaminergic neurones of the gut myenteric plexus. Inflammation is also known to be increased in PD. We previously reported neuroprotection with progesterone in the brain of mice lesioned with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and hypothesised that it also has neuroprotective and immunomodulatory activities in the gut. To test this hypothesis, we investigated progesterone administered to adult male C57BL/6 mice for 10 days and treated with MPTP on day 5. In an additional experiment, progesterone was administered for 5 days following MPTP treatment. Ilea were collected on day 10 of treatment and microdissected to isolate the myenteric plexus. Dopaminergic neurones were reduced by approximately 60% and pro-inflammatory macrophages were increased by approximately 50% in MPTP mice compared to intact controls. These changes were completely prevented by progesterone administered before and after MPTP treatment and were normalised by 8 mg kg^-1 progesterone administered after MPTP. In the brain of MPTP mice, brain-derived neurotrophic peptide (BDNF) and glial fibrillary acidic protein (GFAP) were associated with progesterone neuroprotection. In the myenteric plexus, increased BDNF levels compared to controls were measured in MPTP mice treated with 8 mg kg^-1 progesterone started post MPTP, whereas GFAP levels remained unchanged. In conclusion, the results obtained in the present study show neuroprotective and anti-inflammatory effects of progesterone in the myenteric plexus of MPTP mice that are similar to our previous findings in the brain. Progesterone is non-feminising and could be used for both men and women in the pre-symptomatic stages of the disease.

Estradiol replacement therapy regulates innate immune response in ovariectomized arthritic mice

Neuroendocrine changes are essential factors contributing to the progression and development of rheumatoid arthritis. However, the role of estrogen in the innate immunity during arthritis development is still controversial. Here, we evaluated the effect of estrous cycle, ovariectomy, estradiol replacement therapy and treatment with estrogen receptor (ER)α and ERβ specific agonists on joint edema formation, neutrophil recruitment, and articular levels of cytokines/chemokines in murine zymosan-induced arthritis. Our results showed that articular inflammation of proestus/estrus was similar to metaestus/diestrus animals indicating that the inflammatory response in acute arthritis is not affected by the estrous cycle. However, ovariectomy increased joint swelling, neutrophil migration, and TNF-α level. Treatment for six consecutive days with estradiol cypionate re-established the acute inflammation in ovariectomized arthritic mice to responses similar to those in SHAM-proestrus/estrus or naive mice. Moreover, treatment with propylpyrazoletriol and diarylpropionitrile, two ERα and ERβ selective agonists, respectively, inhibited both edema and neutrophil recruitment. Finally, the non-genomic properties of estradiol were analyzed with an acute treatment with β-estradiol-water soluble, which reduced the edema only. In the present study, estradiol replacement therapy improves the innate immune responses in ovariectomized arthritic mice by activating nuclear estrogen receptors. These results suggest that estradiol can induce a protective anti-inflammatory effect in arthritis during ovaries failure, as observed in the menopause.

Immunomodulatory effects of progesterone and selective ligands of membrane progesterone receptors

Progesterone (P4) and its analogues regulate various reproductive processes, such as ovulation, implantation, pregnancy maintenance and delivery. In these processes, an important role is played by the immune cells recruited to the female reproductive organs and tissues, where they are exposed to the action of P4. Progestins regulate cellular processes, acting through nuclear steroid receptors (nSRs), membrane P4 receptors (mPRs), and through the sensors. It remains unclear, what type of receptors is used by P4 and its derivatives to exert their effect on the immune cells and how similar their effects are in different types of these cells. We have previously synthesized new progesterone derivatives, among which two selective mPRs ligands, not interacting with nSRs were identified. The objective of this study was to examine the effects of P4 and new selective mPRs ligands on the expression of pro- and anti-inflammatory cytokines in activated human peripheral blood mononuclear cells (PBMCs), THP-1 monocyte cells, and Jurkat T cells. It was demonstrated that the action of P4 and selective ligands was unidirectional, but in different types of the immune cells, their effects were different, and sometimes even opposite. In PBMCs, exposure to these steroids resulted in the increase of mRNA and secreted protein levels of IL-1β, TNFα, and IL-6 cytokines, as well as in the increase of INFγ mRNA level, decrease of IL-2 mRNA level, increase of TGFβ mRNA level, and decrease of IL-4 mRNA and IL-10 secreted protein levels. In monocytes, similarly to PBMCs, expression of IL-1β and TNFα mRNA was increased, but expression of IL-10 was also increased, and the TGFβ expression statistically significantly remained the same. In Jurkat T cells, expression of IL-2 and TNFα mRNA decreased, while expression of IL-10 increased, and expression of TGFβ did not change. Thus, progestins act on the immune cells through mPRs and have both pro- and anti-inflammatory effects, depending on the phenotypes of these cells. The data obtained are important for understanding the complexity of the immune system regulation by progestins, which depends on the type of the immune cells and individual characteristics of the immune system.

Progesterone-Related Immune Modulation of Pregnancy and Labor

Pregnancy involves a complex interplay between maternal neuroendocrine and immunological systems in order to establish and sustain a growing fetus. It is thought that the uterus at pregnancy transitions from quiescent to laboring state in response to interactions between maternal and fetal systems at least partly via altered neuroendocrine signaling. Progesterone (P4) is a vital hormone in maternal reproductive tissues and immune cells during pregnancy. As such, P4 is widely used in clinical interventions to improve the chance of embryo implantation, as well as reduce the risk of miscarriage and premature labor. Here we review research to date that focus on the pathways through which P4 mediates its actions on both the maternal reproductive and immune system. We will dissect the role of P4 as a modulator of inflammation, both systemic and intrinsic to the uterus, during human pregnancy and labor.

IL-33 facilitates proliferation of colorectal cancer dependent on COX2/PGE2

Background

Interleukin-33 (IL-33) participates in various types of diseases including cancers. Previous studies of this cytokine in cancers mainly focused on its regulation on immune responses by which IL-33 modulated cancer progression. The IL-33 triggered signals in cancer cells remain unclear.

Methods

We analyzed IL-33 gene expression in human colorectal cancer (CRC) tissues and carried out gene enrichment analysis with TCGA Data Portal. We studied CRC proliferation in vivo by inoculating MC38 tumors in IL-33 transgenic mice. We investigated the cell proliferation in vitro with primary CRC cells isolated from fresh human CRC tissues, human CRC cell line HT-29 and mouse CRC cell line MC38. To evaluate the proliferation modulating effects of recombinant IL-33 incubation and other administrated factors, we measured tumor growth, colony formation, cell viability, and the expression of Ki67 and proliferating cell nuclear antigen (PCNA). We used several inhibitors, prostaglandin E2 (PGE₂) neutralizing antibody, ST2 blocking antibody and specific shRNA expressing plasmid to study the pathway mediating IL-33-induced CRC proliferation. The IL-33 receptor ST2 in human CRC tissues was detected by immunohistochemistry staining and western blotting. The ST2-positive or negative subsets of primary CRC cells were acquired by flow cytometry sorting.

Results

We found that IL-33 expression was correlated with the gene signature of cell proliferation in 394 human CRC samples. The MC38 tumors grew more rapidly and the tumor Ki67 and PCNA were expressed at higher levels in IL-33 transgenic mice than in wild-type mice. IL-33 promoted cell growth, colony formation and expression of Ki67 and PCNA in primary CRC cells as well as CRC cell lines. IL-33 activated cycloxygenase-2 (COX2) expression and increased PGE₂ production, whereas the COX2 selective inhibitor and PGE₂ neutralizing antibody abolished the proliferation promoting effect of IL-33. ST2 blockade, ST2-negative sorting, NF-κB specific inhibitor and NF-κB specific shRNA (shP65) abrogated the COX2 induction caused by IL-33.

Conclusion

IL-33 facilitates proliferation of colorectal cancer dependent on COX2/PGE₂. IL-33 functions via its receptor ST2 and upregulates COX2 expression through NF-κB signaling. Understanding the IL-33 signal transduction in CRC cells provides potential therapeutic targets for clinical treatment.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0839-7) contains supplementary material, which is available to authorized users.

Sex Hormones Regulate Innate Immune Cells and Promote Sex Differences in Respiratory Virus Infection

Sex differences in the incidence and severity of respiratory virus infection are widely documented in humans and murine models and correlate with sex biases in numbers and/or functional responses of innate immune cells in homeostasis and lung infection. Similarly, changes in sex hormone levels upon puberty, pregnancy, and menopause/aging are associated with qualitative and quantitative differences in innate immunity. Immune cells express receptors for estrogens (ERα and ERβ), androgens (AR), and progesterone (PR), and experimental manipulation of sex hormone levels or receptors has revealed that sex hormone receptor activity often underlies sex differences in immune cell numbers and/or functional responses in the respiratory tract. While elegant studies have defined mechanistic roles for sex hormones and receptors in innate immune cells, much remains to be learned about the cellular and molecular mechanisms of action of ER, PR, and AR in myeloid cells and innate lymphocytes to promote the initiation and resolution of antiviral immunity in the lung. Here, we review the literature on sex differences and sex hormone regulation in innate immune cells in the lung in homeostasis and upon respiratory virus infection.

Expression and Clinical Significance of NOD-Like Receptor Protein 3 (NLRP3) and Caspase-1 in Fetal Membrane and Placental Tissues of Patients with Premature Rupture of Membrane

Background

In this study, we aimed to investigate the expression of NOD-like receptor protein 3 (NLRP3) and caspase-1 in fetal membrane and placental tissues of patients with premature rupture of membrane (PROM), and to explore their role in PROM.

Material/Methods

Ninety women participated in this study: a control group of 30 healthy pregnant women, 30 with PPROM, and 30 with TPROM. Immunohistochemistry streptavidin-peroxidase (SP) assay was used to detect the protein expression of NLRP3 and caspase-1 in the fetal membrane and placental tissues. RT-PCR was used to detect the mRNA expression of NLRP3 and caspase-1 in fetal membrane and placental tissues.

Results

The results of SP showed that NLRP3 and caspase-1 were mainly expressed in the cytoplasm of epithelial cells, mesenchymal cells, and trophoblast cells in fetal membranes, and the cytoplasm of placental syncytiotrophoblasts and vascular endothelial cells in placental tissues. The expression of NLRP3 and caspase-1 in the TPROM group was significantly higher than that in the PPROM group and control group (p<0.05), and there was a significant difference between the PPROM group and the control group. The results of RT-PCR showed that the mRNA expression level of NLRP3 and caspase-1 in the TPROM group was significantly higher than that in the PPROM group and control group (p<0.05), and the expression of NLRP3 mRNA and caspase-1 mRNA in the PPROM group was significantly different from that in the control group (p>0.05).

Conclusions

The increased expression of NLRP3 and caspase-1 in fetal membrane and placental tissues may be associated with the development of PROM.

In an in-vitro model using human fetal membranes, 17-α hydroxyprogesterone caproate is not an optimal progestogen for inhibition of fetal membrane weakening

BACKGROUND

The progestogen 17-α hydroxyprogesterone caproate (17-OHPC) is 1 of only 2 agents recommended for clinical use in the prevention of spontaneous preterm delivery, and studies of its efficacy have been conflicting. We have developed an in-vitro model to study the fetal membrane weakening process that leads to rupture in preterm premature rupture of the fetal membranes (pPROM). Inflammation/infection associated with tumor necrosis factor-α (TNF-α) induction and decidual bleeding/abruption associated thrombin release are leading causes of preterm premature rupture of the fetal membranes. Both agents (TNF-α and thrombin) cause fetal membrane weakening in the model system. Furthermore, granulocyte-macrophage colony-stimulating factor (GM-CSF) is a critical intermediate for both TNF-α and thrombin-induced fetal membrane weakening. In a previous report, we demonstrated that 3 progestogens, progesterone, 17-alpha hydroxyprogesterone (17-OHP), and medroxyprogesterone acetate (MPA), each inhibit both TNF-α- and thrombin-induced fetal membrane weakening at 2 distinct points of the fetal membrane weakening pathway. Each block both the production of and the downstream action of the critical intermediate granulocyte-macrophage colony-stimulating factor.

OBJECTIVE

The objective of the study was to characterize the inhibitory effects of 17-OHPC on TNF-α- and thrombin-induced fetal membrane weakening in vitro.

STUDY DESIGN

Full-thickness human fetal membrane fragments from uncomplicated term repeat cesarean deliveries were mounted in 2.5 cm Transwell inserts and cultured with/without 17-alpha hydroxyprogesterone caproate (10^-9 to 10^-7 M). After 24 hours, medium (supernatant) was removed and replaced with/without the addition of tumor necrosis factor-alpha (20 ng/mL) or thrombin (10 U/mL) or granulocyte-macrophage colony-stimulating factor (200 ng/mL). After 48 hours of culture, medium from the maternal side compartment of the model was assayed for granulocyte-macrophage colony-stimulating factor and the fetal membrane fragments were rupture strength tested.

RESULTS

Tumor necrosis factor-alpha and thrombin both weakened fetal membranes (43% and 62%, respectively) and increased granulocyte-macrophage colony-stimulating factor levels (3.7- and 5.9-fold, respectively). Pretreatment with 17-alpha hydroxyprogesterone caproate inhibited both tumor necrosis factor-alpha- and thrombin-induced fetal membrane weakening and concomitantly inhibited the induced increase in granulocyte-macrophage colony-stimulating factor in a concentration-dependent manner. However, contrary to our prior reports regarding progesterone and other progestogens, 17-alpha hydroxyprogesterone caproate did not also inhibit granulocyte-macrophage colony-stimulating factor-induced fetal membrane weakening.

CONCLUSION

17-Alpha hydroxyprogesterone caproate blocks tumor necrosis factor-alpha- and thrombin-induced fetal membrane weakening by inhibiting the production of granulocyte-macrophage colony-stimulating factor. However, 17-alpha hydroxyprogesterone caproate did not also inhibit granulocyte-macrophage colony-stimulating factor-induced weakening. We speculate that progestogens other than 17-alpha hydroxyprogesterone caproate may be more efficacious in preventing preterm premature rupture of the fetal membranes-related spontaneous preterm birth.

The role of female hormonal factors in the development of rheumatoid arthritis

RA is the most common chronic systemic autoimmune disease, with a higher prevalence in women, suggesting female hormonal factors play a role in the development of the disease. However, many controversies still exist. The aim of this review was to appraise data from recent research concerning female hormonal factors and their association with RA disease development. The study of female hormonal factors is challenging because serum levels may differ throughout a woman's lifetime and interact with various environmental, immunological, genetic and endocrine factors influencing the development of autoimmunity. As some female hormonal factors may be potentially modifiable, understanding their impact on RA development is clinically relevant and may result in specific preventive interventions in high-risk populations.

Recent development of signaling pathways inhibitors of melanogenesis

Human skin, eye and hair color rely on the production of melanin, depending on its quantity, quality, and distribution, Melanin plays a monumental role in protecting the skin against the harmful effect of ultraviolet radiation and oxidative stress from various environmental pollutants. However, an excessive production of melanin causes serious dermatological problems such as freckles, solar lentigo (age spots), melasma, as well as cancer. Hence, the regulation of melanin production is important for controlling the hyper-pigmentation. Melanogenesis, a biosynthetic pathway to produce melanin pigment in melanocyte, involves a series of intricate enzymatic and chemical catalyzed reactions. Several extrinsic factors include ultraviolet radiation and chemical drugs, and intrinsic factors include molecules secreted by surrounding keratinocytes or melanocytes, and fibroblasts, all of which regulate melanogenesis. This article reviews recent advances in the development of melanogenesis inhibitors that directly/indirectly target melanogenesis-related signaling pathways. Efforts have been made to provide a description of the mechanism of action of inhibitors on various melanogenesis signaling pathways.

Progesterone-Mediated Non-Classical Signaling

Progesterone is essential for pregnancy maintenance and menstrual cycle regulation. Hormone action has been primarily ascribed to the well-characterized classical signaling pathway involving ligand binding, activation of nuclear progesterone receptors (PRs), and subsequent activation of genes containing progesterone response elements (PREs). Recent studies have revealed progesterone actions via non-classical signaling pathways, often mediated by non-genomic signaling. Progesterone signaling, in conjunction with growth factor signaling, impacts on the function of growth factors and regulates important physiological actions such as cell growth and remodeling, as well as apoptosis. This review focuses on non-classical progesterone signaling pathways, both including and excluding PR, and highlights how research in this area will provide a better understanding of progesterone actions and may inform novel therapeutic strategies.

Selective progesterone receptor modulators (SPRMs): progesterone receptor action, mode of action on the endometrium and treatment options in gynecological therapies

Introduction: The progesterone receptor plays an essential role in uterine physiology and reproduction. Selective progesterone receptor modulators (SPRMs) have emerged as a valuable treatment option for hormone dependent conditions like uterine fibroids, which have a major impact on women’s quality of life. SPRMs offer potential for longer term medical treatment and thereby patients may avoid surgical intervention.

Areas covered: The authors have reviewed the functional role of the progesterone receptor and its isoforms and their molecular mechanisms of action via genomic and non-genomic pathways. The current knowledge of the interaction of the PR and different SPRMs tested in clinical trials has been reviewed. The authors focused on pharmacological effects of selected SPRMs on the endometrium, their anti-proliferative action, and their suppression of bleeding. Potential underlying molecular mechanisms and the specific histological changes in the endometrium induced by SPRMs (PAEC; Progesterone receptor modulator Associated Endometrial Changes) have been discussed. The clinical potential of this compound class including its impact on quality of life has been covered.

Expert Opinion: Clinical studies indicate SPRMs hold promise for treatment of benign gynecological complaints (fibroids, heavy menstrual bleeding; HMB). There however remains a knowledge gap concerning mechanism of action.

Sex steroids regulate skin pigmentation through nonclassical membrane-bound receptors

The association between pregnancy and altered cutaneous pigmentation has been documented for over two millennia, suggesting that sex hormones play a role in regulating epidermal melanocyte (MC) homeostasis. Here we show that physiologic estrogen (17β-estradiol) and progesterone reciprocally regulate melanin synthesis. This is intriguing given that we also show that normal primary human MCs lack classical estrogen or progesterone receptors (ER or PR). Utilizing both genetic and pharmacologic approaches, we establish that sex steroid effects on human pigment synthesis are mediated by the membrane-bound, steroid hormone receptors G protein-coupled estrogen receptor (GPER), and progestin and adipoQ receptor 7 (PAQR7). Activity of these receptors was activated or inhibited by synthetic estrogen or progesterone analogs that do not bind to ER or PR. As safe and effective treatment options for skin pigmentation disorders are limited, these specific GPER and PAQR7 ligands may represent a novel class of therapeutics.

DOI:http://dx.doi.org/10.7554/eLife.15104.001

Factors controlling pigment production in skin are complex and poorly understood. Cells called melanocytes produce a pigment called melanin, which makes the skin darker. It has been known for a long time that skin color often changes during pregnancy, which suggests that sex hormones may be involved. However, the specific hormones and signaling mechanisms responsible for the changes have remained largely undefined.

Estrogen and progesterone are two of the main female sex hormones. Natale et al. now show that estrogen increases pigment production in human melanocytes, and progesterone decreases it.

For hormones to signal to cells, they must bind to and activate particular receptor proteins. Further investigation by Natale et al. revealed that estrogen and progesterone regulate pigment production by binding to receptors that belong to a family called G protein-coupled receptors. These receptors can signal rapidly once activated by sex hormones, and may serve as therapeutic targets for treating pigmentation disorders.

Skin diseases that cause inflammation often also cause changes in skin color. Natale et al. noticed several other G protein-coupled receptors that are likely to control pigmentation through similar mechanisms. Future analyses of the roles that these other receptors perform in melanocytes may therefore reveal how inflammation-based pigmentation changes occur.

DOI:http://dx.doi.org/10.7554/eLife.15104.002

The physiology of fetal membrane weakening and rupture: Insights gained from the determination of physical properties revisited

Rupture of the fetal membranes (FM) is precipitated by stretch forces acting upon biochemically mediated, pre-weakened tissue. Term FM develop a para-cervical weak zone, characterized by collagen remodeling and apoptosis, within which FM rupture is thought to initiate. Preterm FM also have a weak region but are stronger overall than term FM. Inflammation/infection and decidual bleeding/abruption are strongly associated with preterm premature FM rupture (pPROM), but the specific mechanisms causing FM weakening-rupture in pPROM are unknown. There are no animal models for study of FM weakening and rupture. Over a decade ago we developed equipment and methodology to test human FM strength and incorporated it into a FM explant system to create an in-vitro human FM weakening model system. Within this model TNF (modeling inflammation) and Thrombin (modeling bleeding) both weaken human FM with concomitant up regulation of MMP9 and cellular apoptosis, mimicking the characteristics of the spontaneous FM rupture site. The model has been enhanced so that test agents can be applied directionally to the choriodecidual side of the FM explant consistent with the in-vivo situation. With this enhanced system we have demonstrated that the pathways involving inflammation/TNF and bleeding/Thrombin induced FM weakening overlap. Furthermore GM-CSF production was demonstrated to be a critical common intermediate step in both the TNF and the Thrombin induced FM weakening pathways. This model system has also been used to test potential inhibitors of FM weakening and therefore pPROM. The dietary supplement α-lipoic acid and progestogens (P4, MPA and 17α-hydroxyprogesterone) have been shown to inhibit both TNF and Thrombin induced FM weakening. The progestogens act at multiple points by inhibiting both GM-CSF production and GM-CSF action. The use of a combined biomechanical/biochemical in-vitro human FM weakening model system has allowed the pathways of fetal membrane weakening to be delineated, and agents that may be of clinical use in inhibiting these pathways to be tested.

Vaginal progesterone, but not 17α-hydroxyprogesterone caproate, has antiinflammatory effects at the murine maternal-fetal interface

OBJECTIVE

Progestogen (vaginal progesterone or 17-alpha-hydroxyprogesterone caproate [17OHP-C]) administration to patients at risk for preterm delivery is widely used for the prevention of preterm birth (PTB). The mechanisms by which these agents prevent PTB are poorly understood. Progestogens have immunomodulatory functions; therefore, we investigated the local effects of vaginal progesterone and 17OHP-C on adaptive and innate immune cells implicated in the process of parturition.

STUDY DESIGN

Pregnant C57BL/6 mice received vaginal progesterone (1 mg per 200 μL, n = 10) or Replens (control, 200 μL, n = 10) from 13 to 17 days postcoitum (dpc) or were subcutaneously injected with 17OHP-C (2 mg per 100 μL, n = 10) or castor oil (control, 100 μL, n = 10) on 13, 15, and 17 dpc. Decidual and myometrial leukocytes were isolated prior to term delivery (18.5 dpc) for immunophenotyping by flow cytometry. Cervical tissue samples were collected to determine matrix metalloproteinase (MMP)-9 activity by in situ zymography and visualization of collagen content by Masson's trichrome staining. Plasma concentrations of progesterone, estradiol, and cytokines (interferon [IFN]γ, interleukin (IL)-1β, IL-2, IL-4, IL-5, IL-6, IL-10, IL-12p70, keratinocyte-activated chemokine/growth-related oncogene, and tumor necrosis factor-α) were quantified by enzyme-linked immunosorbent assays. Pregnant mice pretreated with vaginal progesterone or Replens were injected with 10 μg of an endotoxin on 16.5 dpc (n = 10 each) and monitored via infrared camera until delivery to determine the effect of vaginal progesterone on the rate of PTB.

RESULTS

The following results were found: (1) vaginal progesterone, but not 17OHP-C, increased the proportion of decidual CD4+ regulatory T cells; (2) vaginal progesterone, but not 17OHP-C, decreased the proportion of decidual CD8+CD25+Foxp3+ T cells and macrophages; (3) vaginal progesterone did not result in M1→M2 macrophage polarization but reduced the proportion of myometrial IFNγ+ neutrophils and cervical active MMP-9-positive neutrophils and monocytes; (4) 17OHP-C did not reduce the proportion of myometrial IFNγ+ neutrophils; however, it increased the abundance of cervical active MMP-9-positive neutrophils and monocytes; (5) vaginal progesterone immune effects were associated with reduced systemic concentrations of IL-1β but not with alterations in progesterone or estradiol concentrations; and (6) vaginal progesterone pretreatment protected against endotoxin-induced PTB (effect size 50%, P = 0.011).

CONCLUSION

Vaginal progesterone, but not 17OHP-C, has local antiinflammatory effects at the maternal-fetal interface and the cervix and protects against endotoxin-induced PTB.

Oxytocin-secreting system: A major part of the neuroendocrine center regulating immunologic activity

Interactions between the nervous system and immune system have been studied extensively. However, the mechanisms underlying the neural regulation of immune activity, particularly the neuroendocrine regulation of immunologic functions, remain elusive. In this review, we provide a comprehensive examination of current evidence on interactions between the immune system and hypothalamic oxytocin-secreting system. We highlight the fact that oxytocin may have significant effects in the body, beyond its classical functions in lactation and parturition. Similar to the hypothalamo-pituitary-adrenal axis, the oxytocin-secreting system closely interacts with classical immune system, integrating both neurochemical and immunologic signals in the central nervous system and in turn affects immunologic defense, homeostasis, and surveillance. Lastly, this review explores therapeutic potentials of oxytocin in treating immunologic disorders.

Progesterone inhibits in vitro fetal membrane weakening

OBJECTIVE

Inflammation/infection and abruption are leading causes of preterm premature rupture of the membranes. Recently, we identified granulocyte-macrophage colony-stimulating factor (GM-CSF) as a critical mediator of both tumor necrosis factor-α- (TNF; modeling inflammation) and thrombin-induced (modeling abruption) weakening of the fetal membranes. We found that (1) TNF and thrombin both induced GM-CSF in the choriodecidua, (2) blockade of GM-CSF action with neutralizing antibodies inhibited both TNF- and thrombin-induced fetal membrane weakening, and (3) GM-CSF alone induced fetal membrane weakening. GM-CSF is thus part of an overlap of the inflammation and abruption-induced fetal membrane weakening pathways. The effects of progesterone analogs on the pathways by which fetal membranes are weakened have not been investigated. We examined the effects of progesterone, medroxyprogesterone acetate (MPA) and 17α-hydroxyprogesterone (HP) on TNF- and thrombin-induced fetal membrane weakening.

STUDY DESIGN

Full-thickness fetal membranes from uncomplicated term repeat cesarean deliveries were mounted in Transwell inserts in Minimum Essential Medium alpha and incubated at 37°C in 5% CO2. The choriodecidua side of the fetal membrane fragments were preincubated with progesterone, MPA, HP, or vehicle for 24 hours. Fetal membranes were then exposed to TNF, thrombin, or GM-CSF on the choriodecidua side for an additional 48 hours. The fetal membrane tissues were then strength tested, and medium from the choriodecidua and amnion compartments was assayed for GM-CSF content.

RESULTS

TNF and thrombin both weakened fetal membranes and elevated media GM-CSF levels on the choriodecidua side of the fetal membrane. Pretreatment with progesterone, MPA, or HP inhibited both TNF- and thrombin-induced fetal membrane weakening and also inhibited the induced increase in GM-CSF. GM-CSF decreased fetal membrane rupture strength by 68%, which was inhibited by progestogen pretreatment with a potency order: progesterone <MPA <HP.

CONCLUSION

Progestogen pretreatment blocks TNF- and thrombin-induced fetal membrane weakening by inhibiting both the production and action of GM-CSF. These findings are consistent with the administration of progestogens in the prevention of preterm premature rupture of the membranes.

Expression and Purification of Human Membrane Progestin Receptor α (mPRα)

Membrane progestin receptors (mPRs) are responsible for mediating the rapid, nongenomic activity of progestins and belong to the G protein-coupled receptor (GPCR) family. mPRs are also considered as attractive proteins to draw a new medicinal approach. In this study, we optimized a procedure for the expression and purification of recombinant human mPRα protein (hmPRα) by a methylotropic yeast, Pichia pastoris, expression system. The protein expressed in crude membrane fractions exhibited a binding affinity of Kd = 3.8 nM and Bmax = 288.8 fmol/mg for progesterone. These results indicated that the hmPRα expressed in yeast was active. Solubilized hmPRα was purified through three column chromatography steps. A nickel-nitrilotriacetic acid (Ni-NTA) column was first used, and the mPRα proteins were then bound to cellulose resin with free amino groups (Cellufine Amino) and finally passed through an SP-Sepharose column. The optimization of expression and purification conditions resulted in a high yield of purified hmPRα (1.3–1.5 mg from 1 L culture). The purified hmPRα protein demonstrated progesterone binding (Kd = 5.2 nM and Bmax = 111.6 fmol/mg). The results indicated that we succeeded in solubilizing and purifying hmPRα in an active form. Sufficient amount of active hmPRα protein will support the establishment of applications for the screening of ligands for mPRα.