Cloning and tissue expression of two putative steroid membrane receptors

A progesterone derivative linked to a stable phospholipid activates breast cancer cell response without leaving the cell membrane

In hormone-responsive breast cancer cells, progesterone (P4) has been shown to act via its nuclear receptor (nPR), a ligand-activated transcription factor. A small fraction of progesterone receptor is palmitoylated and anchored to the cell membrane (mbPR) forming a complex with estrogen receptor alpha (ERα). Upon hormone exposure, either directly or via interaction with ERα, mbPR activates the SRC/RAS/ERK kinase pathway leading to phosphorylation of nPR by ERK. Kinase activation is essential for P4 gene regulation, as the ERK and MSK1 kinases are recruited by the nPR to its genomic binding sites and trigger chromatin remodeling. An interesting open question is whether activation of mbPR can result in gene regulation in the absence of ligand binding to intracellular progesterone receptor (iPR). This matter has been investigated in the past using P4 attached to serum albumin, but the attachment is leaky and albumin can be endocytosed and degraded, liberating P4. Here, we propose a more stringent approach to address this issue by ensuring attachment of P4 to the cell membrane via covalent binding to a stable phospholipid. This strategy identifies the actions of P4 independent from hormone binding to iPR. We found that a membrane-attached progestin can activate mbPR, the ERK signaling pathway leading to iPR phosphorylation, initial gene regulation and entry into the cell cycle, in the absence of detectable intracellular progestin.

Progesterone Signaling and Mammalian Ovarian Follicle Growth Mediated by Progesterone Receptor Membrane Component Family Members

How progesterone influences ovarian follicle growth is a difficult question to answer because ovarian cells synthesize progesterone and express not only the classic nuclear progesterone receptor but also members of the progestin and adipoQ receptor family and the progesterone receptor membrane component (PGRMC) family. Which type of progestin receptor is expressed depends on the ovarian cell type as well as the stage of the estrous/menstrual cycle. Given the complex nature of the mammalian ovary, this review will focus on progesterone signaling that is transduced by PGRMC1 and PGRMC2 specifically as it relates to ovarian follicle growth. PGRMC1 was identified as a progesterone binding protein cloned from porcine liver in 1996 and detected in the mammalian ovary in 2005. Subsequent studies focused on PGRMC family members as regulators of granulosa cell proliferation and survival, two physiological processes required for follicle development. This review will present evidence that demonstrates a causal relationship between PGRMC family members and the promotion of ovarian follicle growth. The mechanisms through which PGRMC-dependent signaling regulates granulosa cell proliferation and viability will also be discussed in order to provide a more complete understanding of our current concept of how progesterone regulates ovarian follicle growth.

E2 + norethisterone promotes the PI3K-AKT pathway via PGRMC1 to induce breast cancer cell proliferation

OBJECTIVE

This study aimed to find evidence that progesterone receptor membrane component 1 (PGRMC1) promotes estradiol (E2) + norethisterone (NET)-induced breast cancer proliferation through activation of the phosphatidylinositol-3-kinase (PI3K)-AKT pathway.

METHODS

PGRMC1-mediated breast cancer cellular proliferation and phosphorylation of PGRMC1 were studied using wild-type (hemagglutinin [HA]-tagged) MCF-7 cells, which were stably transfected with expression vector containing HA (MCF-7-HA cells), PGRMC1 (MCF-7-PGRMC1 cells) and Ser181 point mutated PGRMC1 (MCF-7-PGRMC1-S181A cells). Bioinformatics, cell proliferation, western blot, isobaric tags for relative and absolute quantitation (iTRAQ)-based RNA sequencing, real-time quantitative polymerase chain reaction (RT-qPCR) and cell cycle in vitro assays were performed to indicate the function of PGRMC1 and its possible mechanisms in breast cancer.

RESULTS

NET + E2 elicited a significant proliferation in MCF-7-Vec at 10^-6 M and 10^-10 M, respectively. MCF-7-PGRMC1 did increase the phosphorylation of AKT or ERK, which can be blocked by treatment with casein kinase 2 (CK2) inhibitor quinalizarin or in MCF-7-PGRMC1-S181A cells. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that the PI3K-AKT pathway is upregulated in MCF-7-PGRMC1 cells. Importantly, upregulation of the PI3K-AKT pathway mainly through promotion of cell cycle regulation strongly promoted cell proliferation in MCF-7-PGRMC1 cells.

CONCLUSIONS

CK2 is involved in phosphorylation of PGRMC1 at S181. The mechanism for the action of PGRMC1 for mediating proliferative progestogen effects obviously starts with promotion cell cycle regulation, and then activation of the PI3K-AKT pathway.

Progesterone Receptor Membrane Component 1 and Its Accomplice: Emerging Therapeutic Targets in Lung Cancer

Progesterone receptor membrane component 1 (PGRMC1) is a trans-membrane evolutionarily conserved protein with a cytochrome b5 like heme/steroid binding domain. PGRMC1 clinical levels are strongly suggested to correlate with poor patient survival and lung cancer prognosis. PGRMC1 has been reported to possess pleiotropic functions, such as participating in cellular and membrane trafficking, steroid hormone signaling, cholesterol metabolism and steroidogenesis, glycolysis and mitochondrial energy metabolism, heme transport and homeostasis, neuronal movement and synaptic function, autophagy, anti-apoptosis, stem cell survival and the list is still expanding. PGRMC1 mediates its pleiotropic functions through its ability to interact with multiple binding partners, such as epidermal growth factor receptor (EGFR), sterol regulatory element binding protein cleavage activating protein (SCAP), insulin induced gene-1 protein (Insig-1), heme binding proteins (hepcidin, ferrochelatase and cyp450 members), plasminogen activator inhibitor 1 RNA binding protein (PAIR-BP1). In this review, we provide a comprehensive overview of PGRMC1 and its associated pleiotropic functions that are indispensable for lung cancer promotion and progression, suggesting it as a prospective therapeutic target for intervention. Notably, we have compiled and reported various preclinical studies wherein prospective agonists and antagonists had been tested against PGRMC1 expressing cancer cell lines, suggesting it as a prospective therapeutic target for cancer intervention.

What Do We Know about Classical and Non-Classical Progesterone Receptors in the Human Female Reproductive Tract? A Review

The progesterone hormone regulates the human menstrual cycle, pregnancy, and parturition by its action via the different progesterone receptors and signaling pathways in the female reproductive tract. Progesterone actions can be exerted through classical and non-classical receptors, or even a combination of both. The former are nuclear receptors whose activation leads to transcriptional activity regulation and thus in turn leads to slower but long-lasting responses. The latter are composed of progesterone receptors membrane components (PGRMC) and membrane progestin receptors (mPRs). These receptors rapidly activate the appropriate intracellular signal transduction pathways, and they can subsequently initiate specific cell responses or even modulate genomic cell responses. This review covers our current knowledge on the mechanisms of action and the relevance of classical and non-classical progesterone receptors in female reproductive tissues ranging from the ovary and uterus to the cervix, and it exposes their crucial role in female infertility.

Estrogen- and Progesterone (P4)-Mediated Epigenetic Modifications of Endometrial Stromal Cells (EnSCs) and/or Mesenchymal Stem/Stromal Cells (MSCs) in the Etiopathogenesis of Endometriosis

Endometriosis is a common chronic inflammatory condition in which endometrial tissue appears outside the uterine cavity. Because ectopic endometriosis cells express both estrogen and progesterone (P4) receptors, they grow and undergo cyclic proliferation and breakdown similar to the endometrium. This debilitating gynecological disease affects up to 15% of reproductive aged women. Despite many years of research, the etiopathogenesis of endometrial lesions remains unclear. Retrograde transport of the viable menstrual endometrial cells with retained ability for attachment within the pelvic cavity, proliferation, differentiation and subsequent invasion into the surrounding tissue constitutes the rationale for widely accepted implantation theory. Accordingly, the most abundant cells in the endometrium are endometrial stromal cells (EnSCs). These cells constitute a particular population with clonogenic activity that resembles properties of mesenchymal stem/stromal cells (MSCs). Thus, a significant role of stem cell-based dysfunction in formation of the initial endometrial lesions is suspected. There is increasing evidence that the role of epigenetic mechanisms and processes in endometriosis have been underestimated. The importance of excess estrogen exposure and P4 resistance in epigenetic homeostasis failure in the endometrial/endometriotic tissue are crucial. Epigenetic alterations regarding transcription factors of estrogen and P4 signaling pathways in MSCs are robust in endometriotic tissue. Thus, perspectives for the future may include MSCs and EnSCs as the targets of epigenetic therapies in the prevention and treatment of endometriosis. Here, we reviewed the current known changes in the epigenetic background of EnSCs and MSCs due to estrogen/P4 imbalances in the context of etiopathogenesis of endometriosis. Graphical Abstract.

The Interface of Nuclear and Membrane Steroid Signaling

Steroid hormones bind receptors in the cell nucleus and in the cell membrane. The most widely studied class of steroid hormone receptors are the nuclear receptors, named for their function as ligand-dependent transcription factors in the cell nucleus. Nuclear receptors, such as estrogen receptor alpha, can also be anchored to the plasma membrane, where they respond to steroids by activating signaling pathways independent of their function as transcription factors. Steroids can also bind integral membrane proteins, such as the G protein-coupled estrogen receptor. Membrane estrogen and progestin receptors have been cloned and characterized in vitro and influence the development and function of many organ systems. Membrane androgen receptors were cloned and characterized in vitro, but their function as androgen receptors in vivo is unresolved. We review the identity and function of membrane proteins that bind estrogens, progestins, and androgens. We discuss evidence that membrane glucocorticoid and mineralocorticoid receptors exist, and whether glucocorticoid and mineralocorticoid nuclear receptors act at the cell membrane. In many cases, integral membrane steroid receptors act independently of nuclear steroid receptors, even though they may share a ligand.

Glycyrrhizin Derivatives Suppress Cancer Chemoresistance by Inhibiting Progesterone Receptor Membrane Component 1

Progesterone receptor membrane component 1 (PGRMC1) is highly expressed in various cancer cells and contributes to tumor progression. We have previously shown that PGRMC1 forms a unique heme-stacking functional dimer to enhance EGF receptor (EGFR) activity required for cancer proliferation and chemoresistance, and the dimer dissociates by carbon monoxide to attenuate its biological actions. Here, we determined that glycyrrhizin (GL), which is conventionally used to ameliorate inflammation, specifically binds to heme-dimerized PGRMC1. Binding analyses using isothermal titration calorimetry revealed that some GL derivatives, including its glucoside-derivative (GlucoGL), bind to PGRMC1 potently, whereas its aglycone, glycyrrhetinic acid (GA), does not bind. GL and GlucoGL inhibit the interaction between PGRMC1 and EGFR, thereby suppressing EGFR-mediated signaling required for cancer progression. GL and GlucoGL significantly enhanced EGFR inhibitor erlotinib- or cisplatin (CDDP)-induced cell death in human colon cancer HCT116 cells. In addition, GL derivatives suppressed the intracellular uptake of low-density lipoprotein (LDL) by inhibiting the interaction between PGRMC1 and the LDL receptor (LDLR). Effects on other pathways cannot be excluded. Treatment with GlucoGL and CDDP significantly suppressed tumor growth following xenograft transplantation in mice. Collectively, this study indicates that GL derivatives are novel inhibitors of PGRMC1 that suppress cancer progression, and our findings provide new insights for cancer treatment.

Classical and Non-Classical Progesterone Signaling in Breast Cancers

Much emphasis is placed on estrogen (E2) and estrogen receptor (ER) signaling as most research is focused on understanding E2 and ER’s ability to enhance proliferative signals in breast cancers. Progesterone (P4) is important for normal mammary gland development, function and menstrual control. However, P4 and its receptors (PRs) in breast cancer etiology continue to be understudied and its role in breast cancer remains controversial. The Women’s Health Initiative (WHI) clinical trial clearly demonstrated the importance of progestogens in breast cancer development. P4 has historically been associated with classical-signaling through nuclear receptors, however non-classical P4 signaling via membrane receptors has been described. Progestogens have the ability to bind to nuclear and membrane receptors and studies have demonstrated that both can promote breast cancer cell proliferation and breast tumor growth. In this review, we attempt to understand the classical and non-classical signaling role of P4 in breast cancers because both nuclear and membrane receptors could become viable therapeutic options for breast cancer patients.

Progesterone receptor ligands for the treatment of endometriosis: the mechanisms behind therapeutic success and failure

BACKGROUND

Despite intense research, it remains intriguing why hormonal therapies in general and progestins in particular sometimes fail in endometriosis.

OBJECTIVE AND RATIONALE

We review here the action mechanisms of progesterone receptor ligands in endometriosis, identify critical differences between the effects of progestins on normal endometrium and endometriosis and envisage pathways to escape drug resistance and improve the therapeutic response of endometriotic lesions to such treatments.

SEARCH METHODS

We performed a systematic Pubmed search covering articles published since 1958 about the use of progestins, estro-progestins and selective progesterone receptor modulators, to treat endometriosis and its related symptoms. Two reviewers screened the titles and abstracts to select articles for full-text assessment.

OUTCOMES

Progesterone receptor signalling leads to down-regulation of estrogen receptors and restrains local estradiol production through interference with aromatase and 17 beta-hydroxysteroid dehydrogenase type 1. Progestins inhibit cell proliferation, inflammation, neovascularisation and neurogenesis in endometriosis. However, progesterone receptor expression is reduced and disrupted in endometriotic lesions, with predominance of the less active isoform (PRA) over the full-length, active isoform (PRB), due to epigenetic abnormalities affecting the PGR gene transcription. Oxidative stress is another mechanism involved in progesterone resistance in endometriosis. Among the molecular targets of progesterone in the normal endometrium that resist progestin action in endometriotic cells are the nuclear transcription factor FOXO1, matrix metalloproteinases, the transmembrane gap junction protein connexin 43 and paracrine regulators of estradiol metabolism. Compared to other phenotypes, deep endometriosis appears to be more resistant to size regression upon medical treatments. Individual genetic characteristics can affect the bioavailability and pharmacodynamics of hormonal drugs used to treat endometriosis and, hence, explain part of the variability in the therapeutic response.

WIDER IMPLICATIONS

Medical treatment of endometriosis needs urgent innovation, which should start by deeper understanding of the disease core features and diverse phenotypes and idiosyncrasies, while moving from pure hormonal treatments to drug combinations or novel molecules capable of restoring the various homeostatic mechanisms disrupted by endometriotic lesions.

PGRMC2 is an intracellular haem chaperone critical for adipocyte function

Heme is an essential prosthetic group of numerous proteins and a central signaling molecule in many physiologic processes^1,2. The chemical reactivity of heme requires that a network of intracellular chaperone proteins exist to avert the cytotoxic effects of free heme, but the constituents of such trafficking pathways are unknown^3,4. Heme synthesis is completed in mitochondria, with ferrochelatase (FECH) adding iron to protoporphyrin IX. How this vital but highly reactive metabolite is delivered from mitochondria to hemoproteins throughout the cell remains poorly defined^3,4. Here, we show that PGRMC2 is required for delivery of labile, or signaling heme, to the nucleus. Deletion of PGMRC2 in brown fat, which has a high demand for heme, reduced labile heme in the nucleus and increased stability of the heme-responsive transcriptional repressors Rev-Erbα and BACH1. Ensuing alterations in gene expression spawn severe mitochondrial defects that rendered adipose-specific PGRMC2-null mice unable to activate adaptive thermogenesis and prone to greater metabolic deterioration when fed a high-fat diet. In contrast, obese-diabetic mice treated with a small-molecule PGRMC2 activator showed substantial improvement of diabetic features. These studies uncover a role for PGRMC2 in intracellular heme transport, reveal the impact of adipose tissue heme dynamics on physiology, and suggest that modulation of PGRMC2 may revert obesity-linked defects in adipocytes.

Genomic sequence analyses of classical and non-classical lamprey progesterone receptor genes and the inference of homologous gene evolution in metazoans

BACKGROUND

Nuclear progesterone receptor (nPR) is an evolutionary innovation in vertebrates that mediates genomic responses to progesterone. Vertebrates also respond to progesterone via membrane progesterone receptors (mPRs) or membrane associated progesterone receptors (MAPRs) through rapid nongenomic mechanisms. Lampreys are extant agnathan vertebrates, residing at the evolutionary juncture where vertebrates diverged from invertebrates. A survey of the progesterone receptor (PR) gene sequences in lamprey genomes would inform PR gene evolutionary events during the transition from invertebrates to vertebrates.

RESULTS

In this study, we annotated sequences of one nPR, four mPR (β, γ, δ and ε) and four MAPR genes from genomes of two lamprey species (Petromyzon marinus and Lethenteron japonicum). To infer the origin and evolutionary history of PR genes, we constructed phylogenetic trees of PR homologous sequences across representative species of metazoans. Phylogenetic analyses revealed that the mPRγ gene first appeared in non-bilaterians, and the mPRβ gene likely arose from a duplication of mPRγ. On the other hand, the mPRγ gene gave rise to the mPRδ and ε genes much later in the vertebrate lineage. In addition, the mPRα gene first appeared in cartilaginous fishes, likely derived from duplication of mPRβ after the agnathan-gnathostome divergence. All known MAPR genes were present in the lamprey genomes. Progesterone receptor membrane component 1 (PGRMC1), neudesin and neuferricin genes probably evolved in parallel in non-bilaterians, whereas two copies of PGRMC genes probably derived from duplication of ancestral PGRMC1 sequence and appeared before the speciation of lampreys.

CONCLUSIONS

Non-classical mPR and MAPR genes first evolved in non-bilaterians and classical nPR genes evolved later in basal vertebrates. Sequence repertoires for membrane progesterone receptor genes in vertebrates likely originated from an ancestral metazoan sequence and expanded via several duplication events.

Progesterone receptor membrane component 1 inhibits tumor necrosis factor alpha induction of gene expression in neural cells

Progesterone membrane receptor component 1 (Pgrmc1) is a cytochrome b5-related protein with wide-ranging functions studied most extensively in non-neural tissues. We previously demonstrated that Pgrmc1 is widely distributed in the brain with highest expression in the limbic system. To determine Pgrmc1 functions in cells of these regions, we compared transcriptomes of control siRNA-treated and Pgrmc1 siRNA-treated N42 hypothalamic cells using whole genome microarrays. Our bioinformatics analyses suggested that Pgrmc1 plays a role in immune functions and likely regulates proinflammatory cytokine signaling. In follow-up studies, we showed that one of these cytokines, TNFα, increased expression of rtp4, ifit3 and gbp4, genes found on microarrays to be among the most highly upregulated by Pgrmc1 depletion. Moreover, either Pgrmc1 depletion or treatment with the Pgrmc1 antagonist, AG-205, increased both basal and TNFα-induced expression of these genes in N42 cells. TNFα had no effect on levels of Rtp4, Ifit3 or Gbp4 mRNAs in mHippoE-18 hippocampal control cells, but Pgrmc1 knock-down dramatically increased basal and TNFα-stimulated expression of these genes. P4 had no effect on gbp4, ifit3 or rtp4 expression or on the ability of Pgrmc1 to inhibit TNFα induction of these genes. However, a majority of the top upstream regulators of Pgrmc1 target genes were related to synthesis or activity of steroids, including P4, that exert neuroprotective effects. In addition, one of the identified Pgrmc1 targets was Nr4a1, an orphan receptor important for the synthesis of most steroidogenic molecules. Our findings indicate that Pgrmc1 may exert neuroprotective effects by suppressing TNFα-induced neuroinflammation and by regulating neurosteroid synthesis.

Progestin therapy to prevent preterm birth: History and effectiveness of current strategies and development of novel approaches

In the 1930s the "progestin" hormone produced by the corpus luteum was isolated and found to be a Δ4-keto-steroid. It was aptly named progesterone (P4) and in the following 30 years the capacity of P4 and derivatives to prevent preterm birth (PTB) was examined. Outcomes of multiple small studies suggested that progestin prophylaxis beginning at mid-gestation decreases the risk for PTB. Subsequent larger trials found that prophylaxis with weekly intramuscular injections of 17α-hydroxyprogesterone caproate (17HPC) beginning at mid-gestation decreased PTB risk in women with a history of PTB. Other trials found that daily vaginal P4 prophylaxis, also beginning at mid-gestation decreased PTB risk in women with a short cervix. Currently, prophylaxis with 17HPC (in women with a history of PTB) or vaginal P4 (in women with a short cervix) are used to prevent PTB. Recent advances in understanding the molecular biology of P4 signaling in uterine cells is revealing novel progestin-based targets for PTB prevention. One possibility is to use selective P4 receptor (PR) modulators (SPRMs) to boost PR anti-inflammatory activity that blocks labor, while simultaneously preventing PR phosphorylation that causes loss of P4/PR anti-inflammatory activity. This may be achieved by SPRMs that induce a specific PR conformation that prevents site-specific serine phosphorylation that inhibits anti-inflammatory activity. Further advances in understanding how P4 promotes uterine quiescence and how its labor blocking actions are withdrawn to trigger parturition will reveal novel therapeutic targets to more effectively prevent PTB.

Function and structural regulation of the carbon monoxide (CO)-responsive membrane protein PGRMC1

Progesterone receptor membrane associated component 1 is a multifunctional heme-binding protein that plays a role in several biological processes such as tumor progression, metabolic regulation, and viability control of nerve cells. Notably, progesterone receptor membrane associated component 1 is highly expressed in various types of cancer cells, and facilitates cancer proliferation and chemoresistance. Recently, progesterone receptor membrane associated component 1 structure has been explored by X-ray crystallographic analysis. Interestingly, whereas apo- progesterone receptor membrane associated component 1 exists as a monomer, the heme-bound progesterone receptor membrane associated component 1 converts into a stable dimer by forming a unique heme-heme stacking structure, leading to activation of epidermal growth factor receptor signaling and chemoresistance in cancer cells. Furthermore, the gas mediator carbon monoxide inhibits progesterone receptor membrane associated component 1-mediated activation in cancer cells by dissociating the heme-stacking dimer of progesterone receptor membrane associated component 1. The dynamic structural regulation of progesterone receptor membrane associated component 1 will provide new insights for understanding the mechanisms underlying its various functions.

A novel progesterone receptor membrane component (PGRMC) in the human and swine parasite Taenia solium: implications to the host-parasite relationship

Background

We have previously reported that progesterone (P₄) has a direct in vitro effect on the scolex evagination and growth of Taenia solium cysticerci. Here, we explored the hypothesis that the P₄ direct effect on T. solium might be mediated by a novel steroid-binding parasite protein.

Methods

By way of using immunofluorescent confocal microscopy, flow cytometry analysis, double-dimension electrophoresis analysis, and sequencing the corresponding protein spot, we detected a novel PGRMC in T. solium. Molecular modeling studies accompanied by computer docking using the sequenced protein, together with phylogenetic analysis and sequence alignment clearly demonstrated that T. solium PGRMC is from parasite origin.

Results

Our results show that P₄ in vitro increases parasite evagination and scolex size. Using immunofluorescent confocal microscopy, we detected that parasite cells showed expression of a P₄-binding like protein exclusively located at the cysticercus subtegumental tissue. Presence of the P₄-binding protein in cyst cells was also confirmed by flow cytometry. Double-dimension electrophoresis analysis, followed by sequencing the corresponding protein spot, revealed a protein that was previously reported in the T. solium genome belonging to a membrane-associated progesterone receptor component (PGRMC). Molecular modeling studies accompanied by computer docking using the sequenced protein showed that PGRMC is potentially able to bind steroid hormones such as progesterone, estradiol, testosterone and dihydrodrotestosterone with different affinities. Phylogenetic analysis and sequence alignment clearly demonstrated that T. solium PGRMC is related to a steroid-binding protein of Echinoccocus granulosus, both of them being nested within a cluster including similar proteins present in platyhelminths such as Schistocephalus solidus and Schistosoma haematobium.

Conclusion

Progesterone may directly act upon T. solium cysticerci probably by binding to PGRMC. This research has implications in the field of host-parasite co-evolution as well as the sex-associated susceptibility to this infection. In a more practical matter, present results may contribute to the molecular design of new drugs with anti-parasite actions.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2703-1) contains supplementary material, which is available to authorized users.

Changes in the Width of the Tibiofibular Syndesmosis Related to Lower Extremity Joint Dynamics and Neuromuscular Coordination on Drop Landing During the Menstrual Cycle

Background:

Many injuries of the lower extremities, especially the knee and ankle, occur during sports activity, and the incidence rate is higher in women than in men.

Hypothesis:

The hypothesis was that phases of the menstrual cycle affect the width of the tibiofibular syndesmosis during drop landing in healthy young women and that such changes at the tibiofibular joint also affect the dynamics and neuromuscular coordination of the lower extremities.

Study Design:

Descriptive laboratory study.

Methods:

Participants included 28 healthy young women (mean age, 21.0 ± 0.8 years). Blood samples were collected to determine plasma levels of estradiol and progesterone immediately before the performance of the task: drop landing on a single leg from a 30-cm platform. Using ultrasonography, the distance between the tibia and the distal end of the fibula, regarded as the width of the tibiofibular syndesmosis, was measured in an upright position without flexion of the ankle. The peak ground-reaction force (GRF) on landing was measured using a force platform. The time to peak GRF (Tp-GRF) was measured as the time from initial ground contact to the peak GRF. Hip, knee, and ankle joint angles during the single-leg landing were calculated using a 3-dimensional motion analysis system. Muscle activities of the lower extremities were measured using surface electromyography.

Results:

The width of the tibiofibular syndesmosis was significantly greater in the luteal phase when compared with the menstrual, follicular, and ovulation phases (by 5%-8% of control). Also, during the luteal phase, the Tp-GRF was significantly shorter than in the follicular phase (by 6%); hip internal rotation and knee valgus were significantly greater than in the menstrual phase (by 43% and 34%, respectively); knee flexion was significantly less than in the menstrual and follicular phases (by 7%-9%); ankle dorsiflection was significantly less than in the follicular phase (by 11%); ankle adduction and eversion were significantly greater than in the menstrual and follicular phases (by 26%-46%, and 27%-33%, respectively); and activation of the gluteus maximus before landing was significantly lower than in the menstrual and follicular phases (by 20%-22%).

Conclusion:

The luteal phase appears to be associated with decreased strength and laxity of the ankle as well as lower extremity muscle activity in women. The changes presumably represent a greater risk for sports injuries.

Clinical Relevance:

The results of this study suggest that the luteal phase may be related to the greater incidence of lower extremity injuries in women.

Membrane Associated Progesterone Receptors: Promiscuous Proteins with Pleiotropic Functions - Focus on Interactions with Cytochromes P450

Membrane-associated progesterone receptors (MAPR) are a group of four rather small, partially homologous proteins, which share a similar non-covalent heme-binding domain that is related to cytochrome b5, a well-known functional interaction partner of microsomal cytochrome P450 (CYP) monooxygenase systems. Apart from their structural similarities the four proteins progesterone membrane component 1 (PGRMC1, also referred to as IZA, sigma-2 receptor, Dap1), PGRMC2, neudesin (NENF) and neuferricin (CYB5D2) display surprisingly divergent and multifunctional physiological properties related to cholesterol/steroid biosynthesis, drug metabolism and response, iron homeostasis, heme trafficking, energy metabolism, autophagy, apoptosis, cell cycle regulation, cell migration, neural functions, and tumorigenesis and cancer progression. The purpose of this mini-review is to briefly summarize the structural and functional properties of MAPRs with particular focus on their interactions with the CYP system. For PGRMC1, originally identified as a non-canonical progesterone-binding protein that mediates some immediate non-genomic actions of progesterone, available evidence indicates mainly activating interactions with steroidogenic CYPs including CYP11A1, CYP21A2, CYP17, CYP19, CYP51A1, and CYP61A1, while interactions with drug metabolizing CYPs including CYP2C2, CYP2C8, CYP2C9, CYP2E1, and CYP3A4 were either ineffective or slightly inhibitory. For the other MAPRs the evidence is so far less conclusive. We also point out that experimental limitations question some of the previous conclusions. Use of appropriate model systems should help to further clarify the true impact of these proteins on CYP-mediated metabolic pathways.

Conditional Ablation of Progesterone Receptor Membrane Component 2 Causes Female Premature Reproductive Senescence

The nonclassical progesterone receptors progesterone receptor membrane component (PGRMC) 1 and PGRMC2 have been implicated in regulating cell survival of endometrial and ovarian cells in vitro and are abundantly expressed in these cell types. The objective of this study was to determine if Pgrmc1 and Pgrmc2 are essential for normal female reproduction. To accomplish this objective, Pgrmc1 and/or Pgrmc2 floxed mice (Pgrmc2fl/fl and Pgrmc1/2fl/fl) were crossed with Pgr-cre mice, which resulted in the conditional ablation of Pgrmc1 and/or Pgrmc2 from female reproductive tissues (i.e.,Pgrmc2d/d and Pgrmc1/2d/d mice). A breeding trial revealed that conditional ablation of Pgrmc2 initially led to subfertility, with Pgrmc2d/d female mice producing 47% fewer pups/litter than Pgrmc2fl/fl mice (P = 0.001). Pgrmc2d/d mice subsequently underwent premature reproductive senescence by parities 2 to 5, producing 37.8% fewer litters overall during the trial compared with Pgrmc2fl/fl mice (P = 0.020). Similar results were observed with Pgrmc1/2d/d mice. Based on ovarian morphology and serum P4, the subfertility/infertility was not due to faulty ovulation or luteal insufficiency. Rather an analysis of midgestation implantation sites revealed that postimplantation embryonic death was the major cause of the subfertility/infertility. As with our previous report of Pgrmc1d/d mice, Pgrmc2d/d and Pgrmc1/2d/d mice developed endometrial cysts consistent with accelerated aging of this tissue. Given the timing of postimplantation embryonic demise, uterine decidualization may be disrupted in mice deficient in PGRMC2 or PGRMC1/2. Overall, this study revealed that Pgrmc1 and/or Pgrmc2 are required for the maintenance of uterine histoarchitecture and normal female reproductive lifespan.

Ligand and Target Discovery by Fragment-Based Screening in Human Cells

Advances in the synthesis and screening of small-molecule libraries have accelerated the discovery of chemical probes for studying biological processes. Still, only a small fraction of the human proteome has chemical ligands. Here, we describe a platform that marries fragment-based ligand discovery with quantitative chemical proteomics to map thousands of reversible small molecule-protein interactions directly in human cells, many of which can be site-specifically determined. We show that fragment hits can be advanced to furnish selective ligands that affect the activity of proteins heretofore lacking chemical probes. We further combine fragment-based chemical proteomics with phenotypic screening to identify small molecules that promote adipocyte differentiation by engaging the poorly characterized membrane protein PGRMC2. Fragment-based screening in human cells thus provides an extensive proteome-wide map of protein ligandability and facilitates the coordinated discovery of bioactive small molecules and their molecular targets.

Progesterone Receptor Membrane Component 1 Mediates Progesterone-Induced Suppression of Oocyte Meiotic Prophase I and Primordial Folliculogenesis

Well-timed progression of primordial folliculogenesis is essential for mammalian female fertility. Progesterone (P4) inhibits primordial follicle formation under physiological conditions; however, P4 receptor that mediates this effect and its underlying mechanisms are unclear. In this study, we used an in vitro organ culture system to show that progesterone receptor membrane component 1 (PGRMC1) mediated P4-induced inhibition of oocyte meiotic prophase I and primordial follicle formation. We found that membrane-impermeable BSA-conjugated P4 inhibited primordial follicle formation similar to that by P4. Interestingly, PGRMC1 and its partner serpine1 mRNA-binding protein 1 were highly expressed in oocytes in perinatal ovaries. Inhibition or RNA interference of PGRMC1 abolished the suppressive effect of P4 on follicle formation. Furthermore, P4-PGRMC1 interaction blocked oocyte meiotic progression and decreased intra-oocyte cyclic AMP (cAMP) levels in perinatal ovaries. cAMP analog dibutyryl cAMP reversed P4–PGRMC1 interaction-induced inhibition of meiotic progression and follicle formation. Thus, our results indicated that PGRMC1 mediated P4-induced suppression of oocyte meiotic progression and primordial folliculogenesis by decreasing intra-oocyte cAMP levels.

Proteomic Profiling for Identification of Novel Biomarkers Differentially Expressed in Human Ovaries from Polycystic Ovary Syndrome Patients

Objectives

To identify differential protein expression pattern associated with polycystic ovary syndrome (PCOS).

Methods

Twenty women were recruited for the study, ten with PCOS as a test group and ten without PCOS as a control group. Differential in-gel electrophoresis (DIGE) analysis and mass spectroscopy were employed to identify proteins that were differentially expressed between the PCOS and normal ovaries. The differentially expressed proteins were further validated by western blot (WB) and immunohistochemistry (IHC).

Results

DIGE analysis revealed eighteen differentially expressed proteins in the PCOS ovaries of which thirteen were upregulated, and five downregulated. WB and IHC confirmed the differential expression of membrane-associated progesterone receptor component 1 (PGRMC1), retinol-binding protein 1 (RBP1), heat shock protein 90B1, calmodulin 1, annexin A6, and tropomyosin 2. Also, WB analysis revealed significantly (P<0.05) higher expression of PGRMC1 and RBP1 in PCOS ovaries as compared to the normal ovaries. The differential expression of the proteins was also validated by IHC.

Conclusions

The present study identified novel differentially expressed proteins in the ovarian tissues of women with PCOS that can serve as potential biomarkers for the diagnosis and development of novel therapeutics for the treatment of PCOS using molecular interventions.

Conditional Ablation of Progesterone Receptor Membrane Component 1 Results in Subfertility in the Female and Development of Endometrial Cysts

Progesterone (P4) is essential for female fertility. The objective of this study was to evaluate the functional requirement of the nonclassical P4 receptor (PGR), PGR membrane component 1, in regulating female fertility. To achieve this goal, the Pgrmc1 gene was floxed by insertion of loxP sites on each side of exon 2. Pgrmc1 floxed (Pgrmc1(fl/fl)) mice were crossed with Pgr(cre) or Amhr2(cre) mice to delete Pgrmc1 (Pgrmc1(d/d)) from the female reproductive tract. A 6-month breeding trial revealed that conditional ablation of Pgrmc1 with Pgr(cre/+) mice resulted in a 40% reduction (P = .0002) in the number of pups/litter. Neither the capacity to ovulate in response to gonadotropin treatment nor the expression of PGR and the estrogen receptor was altered in the uteri of Pgrmc1(d/d) mice compared with Pgrmc1(fl/fl) control mice. Although conditional ablation of Pgrmc1 from mesenchymal tissue using Amhr2(cre/+) mice did not reduce the number of pups/litter, the total number of litters born in the 6-month breeding trial was significantly decreased (P = .041). In addition to subfertility, conditional ablation of Pgrmc1 using either Amhr2(cre/+) or Pgr(cre/+) mice resulted in the development of endometrial cysts starting around 4 months of age. Interestingly, pregnancy attenuated the formation of these uterine cysts. These new findings demonstrate that PGR membrane component 1 plays an important role in female fertility and uterine tissue homeostasis.

PGRMC1 Elevation in Multiple Cancers and Essential Role in Stem Cell Survival

Cancer is one of the leading causes of death in America, and there is an urgent need for new therapeutic approaches. The progesterone receptor membrane component 1 (PGRMC1) is a cytoch-rome b₅ related protein that binds heme and is associated with signaling, apoptotic suppression and autophagy. PGRMC1 is essential for tumor formation, invasion and metastasis, and is upregulated in breast, colon, lung and thyroid tumors. In the present study, we have analyzed PGRMC1 levels in over 600 tumor sections, including a larger cohort of lung tumors than in previous studies, and report the first clinical analysis of PGRMC1 levels in human oral cavity and ovarian tumors compared to corresponding nonmalignant tissues. PGRMC1 was highly expressed in lung and ovarian cancers and correlated with patient survival. PGRMC1 has been previously associated with drug resistance, a characteristic of cancer stem cells. The stem cell theory proposes that a subset of cancerous stem cells contribute to drug resistance and tumor maintenance, and PGRMC1 was detected in lung-tumor derived stem cells. Drug treatment with a PGRMC1 inhibitor, AG-205, triggered stem cell death whereas treatment with erlotinib and the ERK inhibitor, PD98059, did not, suggesting a specific role for PGRMC1 in cancer stem cell viability. Together, our data demonstrate PGRMC1 as a potential tumor biomarker across a variety of tumors, as well as a therapeutic target for cancer stem cells.

Progesterone receptor membrane component 1 promotes survival of human breast cancer cells and the growth of xenograft tumors

Triple negative breast cancers (TNBCs) are highly aggressive and grow in response to sex steroid hormones despite lacking expression of the classical estrogen (E2) and progesterone (P4) receptors. Since P4 receptor membrane component 1 (PGRMC1) is expressed in breast cancer tumors and is known to mediate P4-induced cell survival, this study was designed to determine the expression of PGRMC1 in TNBC tumors and the involvement of PGRMC1 in regulating proliferation and survival of TNBC cells in vitro and the growth of TNBC tumors in vivo. For the latter studies, the MDA-MB-231 (MDA) cell line derived from TNBC was used. These cells express PGRMC1 but lack expression of the classical P4 receptor. A lentiviral-based shRNA approach was used to generate a stably transfected PGRMC1-deplete MDA line for comparison to the PGRMC1-intact MDA line. The present studies demonstrate that PGRMC1: 1) is expressed in TNBC cells; 2) mediates the ability of P4 to suppress TNBC cell mitosis in vitro; 3) is required for P4 to reduce the apoptotic effects of doxorubicin in vitro; and 4) facilitates TNBC tumor formation and growth in vivo. Taken together, these findings indicate that PGRMC1 plays an important role in regulating the growth and survival of TNBC cells in vitro and ultimately in the formation and development of these tumors in vivo. Thus, PGRMC1 may be a therapeutic target for TNBCs.

Neudesin as a unique secreted protein with multi-functional roles in neural functions, energy metabolism, and tumorigenesis

Neudesin was originally identified as a secreted protein with neurotrophic activity, and, thereafter, was also termed neuron-derived neurotrophic factor (NENF) or the candidate oncogene GIG47. Neudesin with a conserved cytochrome 5-like heme/steroid-binding domain activates intracellular signaling pathways possibly through the activation of G protein-coupled receptors. In the brain, hypothalamic Neudesin decreases food intake. Neudesin knockout (KO) mice also exhibit anxiety-like behavior, indicating its roles in the hippocampal anxiety circuitry. Neudesin is also expressed in various peripheral tissues. Neudesin KO mice are strongly resistant to high-fat diet (HFD)-induced obesity due to elevated systemic sympathetic activity, heat production, and adipocytic lipolysis. Neudesin, which is over-expressed or induced by DNA hypomethylation in multiple human cancers, also stimulates tumorigenesis. These findings indicate that Neudesin plays roles in neural functions, energy metabolism, and tumorigenesis and is expected to be a novel target for obesity and anti-cancer treatments.

Genomic and non-genomic effects of progesterone on prostaglandin (PG) F2? and PGE2 production in the bovine endometrium

Progesterone (P4) acts through different actuating pathways called genomic and non-genomic pathways. Here we investigated whether P4 regulates prostaglandin (PG) F2? (PGF) and PGE2 production in bovine endometrium through different pathways. Cultured endometrial cells were exposed to P4 for a short time (5-20min) or bovine serum albumin (BSA)-conjugated P4 (P4-BSA) for 24h. Progesterone treatment for 24h stimulated PGE2 production in epithelial cells, but suppressed both PGF and PGE2 production and the expression of PG-metabolising enzymes including phospholipase A2 (PLA2) and cyclooxygenase-2 (COX2) in stromal cells. Short-term (5-20min) P4 treatment did not affect PLA2 or COX2 transcript levels in either cell type. P4-BSA increased PGF and PGE2 production only in epithelial cells. Nuclear P4 receptor mRNA expression in endometrium was higher at the follicular phase than at the early- to mid-luteal stages, whereas membrane P4 receptor mRNA expression did not change throughout the oestrous cycle. The overall results suggest that P4 controls PG production by inhibiting enzymes via a genomic pathway and by stimulating signal transduction via a non-genomic pathway. Consequently, P4 may protect the corpus luteum by attenuating PGF production in stromal cells and by increasing PGE2 secretion from epithelial cells.

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 receptor membrane component-1 (PGRMC1) and PGRMC-2 interact to suppress entry into the cell cycle in spontaneously immortalized rat granulosa cells

Progesterone receptor membrane component 1 (PGRMC1) and PGRMC2 are expressed in rat granulosa cells and spontaneously immortalized granulosa cells (SIGCs) but their biological roles are not well defined. The present studies demonstrate that depleting either Pgrmc1 or Pgrmc2 in SIGCs increases entry into the cell cycle but does not increase cell proliferation. Rather, PGRMC1 and/or PGRMC2-deplete cells accumulate in metaphase and undergo apoptosis. Because both PGRMC1 and PGRMC2 localize to the mitotic spindle, their absence likely accounts for cells arresting in metaphase. Moreover, pull-down assays, colocalization studies and in situ proximity ligation assays (PLA) indicate that PGRMC1 binds PGRMC2. Disrupting the PGRMC1:PGRMC2 complex through the use of siRNA or the cytoplasmic delivery of a PGRMC2 antibody increases entry into the cell cycle. Conversely, overexpressing either PGRMC1-GFP or GFP-PGRMC2 fusion protein inhibits entry into the cell cycle. Subsequent studies reveal that depleting PGRMC1 and/or PGRMC2 reduces the percentage of cells in G0 and increases the percentage of cells in G1. These observations indicate that in addition to their role at metaphase, PGRMC1 and PGRMC2 are involved in regulating entry into the G1 stage of the cell cycle. Interestingly, both PGRMC1 and PGRMC2 bind GTPase-activating protein-binding protein 2 (G3BP2) as demonstrated by pull-down assays, colocalization assays, and PLAs. G3bp2 siRNA treatment also promotes entry into the G1 stage. This implies that dynamic changes in the interaction among PGRMC1, PGRMC2, and G3BP2 play an important protein regulating the rate at which SIGCs enter into the cell cycle.

Role of protein-protein interactions in cytochrome P450-mediated drug metabolism and toxicity

Through their unique oxidative chemistry, cytochrome P450 monooxygenases (CYPs) catalyze the elimination of most drugs and toxins from the human body. Protein–protein interactions play a critical role in this process. Historically, the study of CYP–protein interactions has focused on their electron transfer partners and allosteric mediators, cytochrome P450 reductase and cytochrome b5. However, CYPs can bind other proteins that also affect CYP function. Some examples include the progesterone receptor membrane component 1, damage resistance protein 1, human and bovine serum albumin, and intestinal fatty acid binding protein, in addition to other CYP isoforms. Furthermore, disruption of these interactions can lead to altered paths of metabolism and the production of toxic metabolites. In this review, we summarize the available evidence for CYP protein–protein interactions from the literature and offer a discussion of the potential impact of future studies aimed at characterizing noncanonical protein–protein interactions with CYP enzymes.

Expression of progesterone receptor membrane component-2 within the immature rat ovary and its role in regulating mitosis and apoptosis of spontaneously immortalized granulosa cells

Progesterone receptor membrane component 2 (Pgrmc2) mRNA was detected in the immature rat ovary. By 48 h after eCG, Pgrmc2 mRNA levels decreased by 40% and were maintained at 48 h post-hCG. Immunohistochemical studies detected PGRMC2 in oocytes and ovarian surface epithelial, interstitial, thecal, granulosa, and luteal cells. PGRMC2 was also present in spontaneously immortalized granulosa cells, localizing to the cytoplasm of interphase cells and apparently to the mitotic spindle of cells in metaphase. Interestingly, PGRMC2 levels appeared to decrease during the G1 stage of the cell cycle. Moreover, overexpression of PGRMC2 suppressed entry into the cell cycle, possibly by binding the p58 form of cyclin dependent kinase 11b. Conversely, Pgrmc2 small interfering RNA (siRNA) treatment increased the percentage of cells in G1 and M stage but did not increase the number of cells, which was likely due to an increase in apoptosis. Depleting PGRMC2 did not inhibit cellular (3)H-progesterone binding, but attenuated the ability of progesterone to suppress mitosis and apoptosis. Taken together these studies suggest that PGRMC2 affects granulosa cell mitosis by acting at two specific stages of the cell cycle. First, PGRMC2 regulates the progression from the G0 into the G1 stage of the cell cycle. Second, PGRMC2 appears to localize to the mitotic spindle, where it likely promotes the final stages of mitosis. Finally, siRNA knockdown studies indicate that PGRMC2 is required for progesterone to slow the rate of granulosa cell mitosis and apoptosis. These findings support a role for PGRMC2 in ovarian follicle development.

Inhibition of 17α-hydroxylase/C17,20 lyase reduces gating deficits consequent to dopaminergic activation

Cogent evidence points to the involvement of neurosteroids in the regulation of dopamine (DA) neurotransmission and signaling, yet the neurobiological bases of this link remain poorly understood. We previously showed that inhibition of 5α-reductase (5αR), a key neurosteroidogenic enzyme, attenuates the sensorimotor gating deficits induced by DA receptor activation, as measured by the prepulse inhibition (PPI) of the acoustic startle reflex. To extend these findings, the present study was aimed at the assessment of the role of other key neurosteroidogenic enzymes in PPI, such as 17α-hydroxylase/C17,20 lyase (CYP17A1), 3α- and 3β-hydroxysteroid dehydrogenase (HSD), in Sprague-Dawley rats. The PPI deficits induced by the DAergic non-selective agonist apomorphine (APO, 0.25mg/kg, SC) were dose-dependently attenuated by the selective CYP17A1 inhibitor abiraterone (ABI, 10-50mg/kg, IP) in a fashion akin to that of the 5αR inhibitor finasteride (FIN, 100mg/kg, IP). These systemic effects were reproduced by intracerebroventricular injection of ABI (1 μg/1 μl), suggesting the involvement of brain CYP17A1 in PPI regulation. Conversely, the PPI disruption induced by APO was not significantly affected by the 3α- and 3β-HSD inhibitors indomethacin and trilostane. Given that CYP17A1 catalyzes androgen synthesis, we also tested the impact on PPI of the androgen receptor (AR) antagonist flutamide (10mg/kg, IP). However, this agent failed to reverse APO-induced PPI deficits; furthermore, AR endogenous ligands testosterone and dihydrotestosterone failed to disrupt PPI. Collectively, these data highlight CYP17A1 as a novel target for antipsychotic-like action, and suggest that the DAergic regulation of PPI is modulated by androgenic neurosteroids, through AR-unrelated mechanisms.

PGRMC1 and PGRMC2 in uterine physiology and disease

It is clear from studies using progesterone receptor (PGR) mutant mice that not all of the actions of progesterone (P4) are mediated by this receptor. Indeed, many rapid, non-classical P4 actions have been reported throughout the female reproductive tract. Progesterone treatment of Pgr null mice results in behavioral changes and in differential regulation of genes in the endometrium. Progesterone receptor membrane component (PGRMC) 1 and PGRMC2 belong to the heme-binding protein family and may serve as P4 receptors. Evidence to support this derives chiefly from in vitro culture work using primary or transformed cell lines that lack the classical PGR. Endometrial expression of PGRMC1 in menstrual cycling mammals is most abundant during the proliferative phase of the cycle. Because PGRMC2 expression shows the most consistent cross-species expression, with highest levels during the secretory phase, PGRMC2 may serve as a universal non-classical P4 receptor in the uterus. While the functional importance of PGRMC1/2 in the uterus remains to be fully explored, accumulating evidence suggests that disruption in PGRMC1/2 expression correlates with uterine disease. In this review we will summarize what is known about PGRMC1/2 in uterine physiology and we will provide examples of disrupted expression of these genes in uterine disease states.

Progesterone antagonism of neurite outgrowth depends on microglial activation via Pgrmc1/S2R

Neuronal plasticity is regulated by the ovarian steroids estradiol (E2) and progesterone (P4) in many normal brain functions, as well as in acute response to injury and chronic neurodegenerative disease. In a female rat model of axotomy, the E2-dependent compensatory neuronal sprouting is antagonized by P4. To resolve complex glial-neuronal cell interactions, we used the "wounding-in-a-dish" model of neurons cocultured with astrocytes or mixed glia (microglia to astrocytes, 1:3). Although both astrocytes and mixed glia supported E2-enhanced neurite outgrowth, P4 antagonized E2-induced neurite outgrowth only with mixed glia, but not astrocytes alone. We now show that P4-E2 antagonism of neurite outgrowth is mediated by microglial expression of progesterone receptor (Pgr) membrane component 1 (Pgrmc1)/S2R, a putative nonclassical Pgr mediator with multiple functions. The P4-E2 antagonism of neurite outgrowth was restored by add-back of microglia to astrocyte-neuron cocultures. Because microglia do not express the classical Pgr, we examined the role of Pgrmc1, which is expressed in microglia in vitro and in vivo. Knockdown by siRNA-Pgrmc1 in microglia before add-back to astrocyte-neuron cocultures suppressed the P4-E2 antagonism of neurite outgrowth. Conditioned media from microglia restored the P4-E2 activity, but only if microglia were activated by lipopolysaccharide or by wounding. Moreover, the microglial activation was blocked by Pgmrc1-siRNA knockdown. These findings explain why nonwounded cultures without microglial activation lack P4 antagonism of E2-induced neurite outgrowth. We suggest that microglial activation may influence brain responses to exogenous P4, which is a prospective therapy in traumatic brain injury.

Expression patterns of progesterone receptor membrane components 1 and 2 in endometria from women with and without endometriosis

Endometriosis is a hormone-dependent inflammatory condition associated with pain and infertility. A growing body of evidence supports attenuated secretory-phase progesterone responsiveness in women with this disease. Herein, we compare the expression of progesterone receptor membrane components (PGRMC) 1 and 2 in eutopic endometrium from 11 women with laparoscopically and/or histologically proven stage III/IV endometriosis and 23 disease-free women. Menstrual cycle phase was determined using a combination of reported cycle day, serum hormone profile, and endometrial histologic dating. The PGRMC-1 (fold change -3.3; P < .05) and PGRMC-2 (fold-change -8.8; P < .05) gene expression were significantly downregulated in secretory phase, eutopic endometrium from women with endometriosis. Immunohistochemistry demonstrated decreased PGRMC-1 and PGRMC-2 protein expression in the secretory phase endometrial stroma cells of women with endometriosis. Consistent with the preclinical work of others, our results reflect downregulation of endometrial PGRMC-1 and PGRMC-2 expression in secretory phase endometrium from women with advanced stage endometriosis. Understanding the molecular mechanisms of attenuated progesterone action in endometriosis has important diagnostic and therapeutic implications.

A truncated progesterone receptor (PR-M) localizes to the mitochondrion and controls cellular respiration

The cDNA for a novel truncated progesterone receptor (PR-M) was previously cloned from human adipose and aortic cDNA libraries. The predicted protein sequence contains 16 unique N-terminal amino acids, encoded by a sequence in the distal third intron of the progesterone receptor PR gene, followed by the same amino acid sequence encoded by exons 4 through 8 of the nuclear PR. Thus, PR-M lacks the N terminus A/B domains and the C domain for DNA binding, whereas containing the hinge and hormone-binding domains. In this report, we have localized PR-M to mitochondria using immunofluorescent localization of a PR-M-green fluorescent protein (GFP) fusion protein and in Western blot analyses of purified human heart mitochondrial protein. Removal of the putative N-terminal mitochondrial localization signal obviated association of PR-M with mitochondria, whereas addition of the mitochondrial localization signal to green fluorescent protein resulted in mitochondrial localization. Immunoelectron microscopy and Western blot analysis after mitochondrial fractionation identified PR-M in the outer mitochondrial membrane. Antibody specificity was shown by mass spectrometry identification of a PR peptide in a mitochondrial membrane protein isolation. Cell models of overexpression and gene silencing of PR-M demonstrated a progestin-induced increase in mitochondrial membrane potential and an increase in oxygen consumption consistent with an increase in cellular respiration. This is the first example of a truncated steroid receptor, lacking a DNA-binding domain that localizes to the mitochondrion and initiates direct non-nuclear progesterone action. We hypothesize that progesterone may directly affect cellular energy production to meet the increased metabolic demands of pregnancy.

Progesterone directly and rapidly inhibits GnRH neuronal activity via progesterone receptor membrane component 1

GnRH neurons are essential for reproduction, being an integral component of the hypothalamic-pituitary-gonadal axis. Progesterone (P4), a steroid hormone, modulates reproductive behavior and is associated with rapid changes in GnRH secretion. However, a direct action of P4 on GnRH neurons has not been previously described. Receptors in the progestin/adipoQ receptor family (PAQR), as well as progesterone receptor membrane component 1 (PgRMC1) and its partner serpin peptidase inhibitor, clade E (nexin, plasminogen activator inhibitor type 1) mRNA binding protein 1 (SERBP1), have been shown to mediate rapid progestin actions in various tissues, including the brain. This study shows that PgRMC1 and SERBP1, but not PAQR, are expressed in prenatal GnRH neurons. Expression of PgRMC1 and SERBP1 was verified in adult mouse GnRH neurons. To investigate the effect of P4 on GnRH neuronal activity, calcium imaging was used on primary GnRH neurons maintained in explants. Application of P4 significantly decreased the activity of GnRH neurons, independent of secretion of gamma-aminobutyric acidergic and glutamatergic input, suggesting a direct action of P4 on GnRH neurons. Inhibition was not blocked by RU486, an antagonist of the classic nuclear P4 receptor. Inhibition was also maintained after uncoupling of the inhibitory regulative G protein (G(i/o)), the signal transduction pathway used by PAQR. However, AG-205, a PgRMC1 ligand and inhibitor, blocked the rapid P4-mediated inhibition, and inhibition of protein kinase G, thought to be activated downstream of PgRMC1, also blocked the inhibitory activity of P4. These data show for the first time that P4 can act directly on GnRH neurons through PgRMC1 to inhibit neuronal activity.

Neutrophil gelatinase-associated lipocalin (NGAL) expression is dependent on the tumor-associated sigma-2 receptor S2RPgrmc1

Tumor invasion is a critical step in the spread of cancer. S2R (sigma-2 receptor)/Pgrmc1 (progesterone receptor membrane component 1) is a cytochrome b(5)-related drug-binding orphan receptor essential for tumor formation and invasion. Secretory proteins drive these processes, so we screened for S2R(Pgrmc1)-dependent secreted proteins using antibody arrays. S2R(Pgrmc1) markedly regulated the expression of NGAL/LCN2 (neutrophil gelatinase-associated lipocalin/lipocalin 2), a secreted glycoprotein that binds to MMP-9 (matrix metalloproteinase 9) and protects it from degradation. S2R(Pgrmc1) knock-down blocked NGAL/LCN2 expression at the protein and RNA levels and decreased MMP9 activity. NGAL expression was required for MMP-9 activity and tumor formation. S2R(Pgrmc1) associates with EGFR and increases EGFR levels at the plasma membrane, and the EGFR inhibitors erlotinib and AG1478, as well as Akt and ERK inhibitors, suppressed the NGAL/LCN2 RNA and protein levels. NGAL is transcriptionally regulated by NFκB, and S2R(Pgrmc1) knock-down decreased the NFκB subunit p65/RelA acetylation, phosphorylation, and activation. In S2R(Pgrmc1) knock-down cells, p65 acetylation was reversed by inhibitors of histone deacetylase 1, and the inhibitors partially restored NGAL levels. Our results are consistent with a model in which S2R(Pgrmc1) increases NGAL/LCN2 levels by activating NFκB via EGFR.

Alterations in progesterone receptor membrane component 2 (PGRMC2) in the endometrium of macaques afflicted with advanced endometriosis

The hormonally driven expression and cell-specific localization patterns of the progesterone receptor membrane components (PGRMC1 and PGRMC2) in the macaque endometrium during the menstrual cycle are unknown. Additionally, the expression and localization patterns of PGRMC1 and PGRMC2 in the secretory eutopic endometrium of primates afflicted with endometriosis are also unknown. Therefore, we used real-time PCR to quantify transcript expression levels of the PGRMCs in well-defined samples of endometrium collected from artificially cycled macaques during the menstrual cycle, and in the secretory phase endometrium of naturally cycling macaques afflicted with endometriosis. In situ hybridization and immunocytochemistry were used to localize PGRMC1 and PGRMC2 mRNA and protein, respectively. We compared the patterns of expression and localization of the PGRMCs with the expression and localization patterns of nuclear progesterone receptor (PGR). PGRMC1 and PGR were elevated during the proliferative phases of the cycle, and then declined to nearly undetectable levels during the late secretory phase of the cycle. Levels of PGRMC2 were lowest during the proliferative phases of the cycle and then increased markedly during the secretory phases. Strong staining for PGRMC2 was localized to the luminal and glandular epithelia during the secretory phases. When compared with artificially cycled disease-free animals, macaques with endometriosis exhibited no changes in the expression or localization patterns for PGR and PGRMC1 but exhibited strikingly reduced levels of PGRMC2 transcript and altered intracellular staining patterns for the PGRMC2 protein. Collectively, these results suggest that membrane-bound PGRMC2 may provide a pathway of action that could potentially mediate the non-genomic effects of progesterone on the glandular epithelia during the secretory phase of the cycle. Further, reduced levels of membrane-bound PGRMC2 may be associated with the progesterone insensitivity often observed in the endometrium of primates afflicted with endometriosis.

Cell Models for the Study of Sex Steroid Hormone Neurobiology

To date many aspects of neurons and glia biology remain elusive, due in part to the cellular and molecular complexity of the brain. In recent decades, cell models from different brain areas have been established and proven invaluable toward understanding this complexity. In the field of steroid hormone neurobiology, an important question is: what is the profile of steroid hormone receptor expression in these specific cell lines? Currently, a clear summary of such receptor profiling is lacking. For this reason, we summarized in this review the expression of estrogen, progesterone, and androgen receptors in several widely used cell lines (glial and neuronal) derived from the forebrain and midbrain, based on our own data and that from the literature. Such information will aid in the selection of specific cell lines used to test hypotheses related to the biology of estrogens, progestins, and/or androgens.

Progesterone signaling mechanisms in brain and behavior

Steroid hormone, progesterone, modulates neuroendocrine functions in the central nervous system resulting in alterations in physiology and behavior. These neuronal effects are mediated primarily by intracellular progestin receptors (PRs) in the steroid-sensitive neurons, resulting in transcription-dependent genomic actions (classical mechanism). In addition to progesterone, intracellular PRs can also be activated in a "ligand-independent" manner by neurotransmitters, peptide growth factors, cyclic nucleotides, and neurosteroids. Recent studies indicate that rapid, non-classical progesterone actions involving cytoplasmic kinase signaling and/or extranuclear PRs can result in both transcription-independent and transcription-dependent actions. Cross-talk between extranuclear and classical intracellular signaling pathways promotes progesterone-dependent behavior in mammals. This review focuses on the mechanisms by which progesterone-initiated signaling mechanisms converge with PRs in the brain to modulate reproductive behavior in female rodents.

Structure-function studies of FMRP RGG peptide recognition of an RNA duplex-quadruplex junction

We have determined the solution structure of the complex between an arginine-glycine-rich RGG peptide from the fragile X mental retardation protein (FMRP) and an in vitro-selected guanine-rich sc1 RNA. The bound RNA forms a novel G-quadruplex separated from the flanking duplex stem by a mixed junctional tetrad. The RGG peptide is positioned along the major groove of the RNA duplex, with the G-quadruplex forcing a sharp turn of R₁₀GGGGR₁₅ at the duplex-quadruplex junction. Arginines R10 and R15 form cross-strand specificity-determining intermolecular hydrogen-bonds with the major-groove edges of guanines of adjacent Watson-Crick G•C pairs. Filter binding assays on RNA and peptide mutations identify and validate contributions of peptide-RNA intermolecular contacts and shape complementarity to molecular recognition. These findings on FMRP RGG domain recognition by a combination of G-quadruplex and surrounding RNA sequences have implications for recognition of other genomic G-rich RNAs.

Progesterone receptor activation of extranuclear signaling pathways in regulating p53 expression in vascular endothelial cells

We previously showed that progesterone (P4) inhibited the proliferation of human umbilical vein endothelial cells (HUVECs) through a p53-dependent pathway. Now we investigated further the molecular mechanism underlying the hormone activity. In cultured HUVECs, P4 increased the protein levels of phosphorylated Src (p-Src), Raf-1, and ERK. The levels of p-Src and p-Src-progesterone receptor complex in HUVECs were increased by P4 treatment. These effects were blocked by pretreatment with a progesterone receptor antagonist, RU486. The P4-induced increase in p53 transactivity was abolished by pretreatment with Src kinase inhibitors. Moreover, administration with cSrc antisense oligonucleotide prevented the P4-induced increases of the levels of p53 mRNA and protein. These data suggest that P4-induced up-regulation of p53 might be mediated through activation of cSrc. Pretreatment with Src kinase inhibitors also prevented P4-induced membrane translocation of Kras and increases of the protein levels of phosphorylated Raf and phosphorylated ERK. Transfection with dominant-negative ERK2 prevented the P4-induced increases of protein level and promoter activity of p53 and a decrease of thymidine incorporation. P4 also increased nuclear factor-κB (NF-κB) nuclear translocation and NF-κB binding onto the p53 promoter. These effects were abolished by pretreatment with ERK inhibitors. The P4-induced up-regulation of the p53 promoter activity was prevented by preadministration with dominant-negative ERK2 or NF-κB inhibitors. Taken together, our data suggest that the cSrc/Kras/Raf-1/ERK2/NF-κB signaling pathway contributes to the P4-induced up-regulation of p53 in HUVECs. These findings highlight progesterone receptor activation of extranuclear signaling pathways in regulating p53 and cell cycle progression in HUVECs.

GPRC6A mediates the non-genomic effects of steroids

The identity of the putative G-protein coupled receptor (GPCR) that mediates the non-genomic effects of androgens is unknown. We present in vitro and in vivo evidence that the orphan GPRC6A receptor, a widely expressed calcium and amino acid sensing GPCR, transduces the non-genomic effects of testosterone and other steroids. Overexpression of GPRC6A imparts the ability of extracellular testosterone to illicit a rapid, non-genomic signaling response in HEK-293 cells lacking the androgen receptor. Conversely, testosterone-stimulated rapid signaling and phosphorylation of ERK is attenuated in bone marrow stromal cells derived from GPRC6A(-/-) mice and in 22Rv1 prostate cancer cells after siRNA-mediated knockdown of GPRC6A. Compared with wild-type controls, GPRC6A(-/-) null mice exhibit significantly less ERK activation and Egr-1 expression in both bone marrow and testis in response to pharmacological doses of testosterone in vivo. In addition, testosterone administration results in suppression of luteinizing hormone in wild-type male mice, but paradoxically stimulates serum luteinizing hormone levels in GPRC6A(-/-) null mice. These results suggest that GPRC6A is functionally important in regulating non-genomic effects of androgens in multiple tissues.

Cloning, mapping and molecular characterization of porcine progesterone receptor membrane component 2 (PGRMC2) gene

Progesterone plays an important role in sow reproduction by stimulating classic genomic pathways via nuclear receptors and non-genomic pathways via membrane receptors such a progesterone receptor membrane component 2 (PGRMC2). In this work, we used radiation hybrid mapping to assign PGRMC2 to pig chromosome 8 and observed that this receptor has two transcripts in pigs. The full-length cDNA of the large transcript is 1858 bp long and contains a 669-bp open reading frame (ORF) encoding a protein of 223 amino acids. The shorter transcript encodes a protein of 170 amino acids. The porcine PGRMC2 gene consists of three exons 446 bp, 156 bp and 1259 bp in length. The promoter sequence is GC-rich and lacks a typical TATA box. Several putative cis-regulatory DNA motifs were identified in the 208-bp upstream genomic region. Five single nucleotide polymorphisms (SNPs) were detected in introns* and the 3' UTR. RT-PCR indicated that the PGRMC2 gene is expressed ubiquitously in all pig tissues examined.

Pgrmc1 (progesterone receptor membrane component 1) associates with epidermal growth factor receptor and regulates erlotinib sensitivity

Tumorigenesis requires the concerted action of multiple pathways, including pathways that stimulate proliferation and metabolism. Epidermal growth factor receptor (EGFR) is a transmembrane receptor-tyrosine kinase that is associated with cancer progression, and the EGFR inhibitors erlotinib/tarceva and tyrphostin/AG-1478 are potent anti-cancer therapeutics. Pgrmc1 (progesterone receptor membrane component 1) is a cytochrome b(5)-related protein that is up-regulated in tumors and promotes cancer growth. Pgrmc1 and its homologues have been implicated in cell signaling, and we show here that Pgrmc1 increases susceptibility to AG-1478 and erlotinib, increases plasma membrane EGFR levels, and co-precipitates with EGFR. Pgrmc1 co-localizes with EGFR in cytoplasmic vesicles and co-fractionates with EGFR in high density microsomes. The findings have therapeutic potential because a Pgrmc1 small molecule ligand, which inhibits growth in a variety of cancer cell types, de-stabilized EGFR in multiple tumor cell lines. EGFR is one of the most potent receptor-tyrosine kinases driving tumorigenesis, and our data support a role for Pgrmc1 in promoting several cancer phenotypes at least in part by binding EGFR and stabilizing plasma membrane pools of the receptor.

Down-regulation of progesterone receptor membrane component 1 (PGRMC1) in peripheral nucleated blood cells associated with premature ovarian failure (POF) and polycystic ovary syndrome (PCOS)

BACKGROUND

Progesterone receptor membrane component 1 (PGRMC1) is a member of a progesterone-binding complex implicated in female reproduction. We aimed i) to determine the natural expression of PGRMC1 in peripheral nucleated blood cells throughout the menstrual cycle and ii) to investigate any association between PGRMC1 levels in leukocytes and conditions characterized by reduced fertility.

METHODS

We analyzed PGRMC1 expression in peripheral leukocytes from 15 healthy cycling women over four weeks. Additionally, we determined PGRMC1 levels in samples from patients with premature ovarian failure (POF) and polycystic ovary syndrome (PCOS) as well as in healthy postmenopausal women and male controls. The levels of PGRMC1 protein in nucleated peripheral blood cells were quantified by Western blot analysis.

RESULTS

PGRMC1 levels did not vary significantly throughout the menstrual cycle. We observed a significant down-regulation of PGRMC1 in postmenopausal women and in patients with premature ovarian failure (POF) and polycystic ovary syndrome (PCOS) when compared to early follicular phase of healthy women.

CONCLUSION

This study suggests that reduced levels of PGRMC1 in peripheral leukocytes are associated with perturbed ovulatory function.

Progesterone inhibits apoptosis in part by PGRMC1-regulated gene expression

Progesterone receptor membrane component-1 (PGRMC1) is present in both the cytoplasm and nucleus of spontaneously immortalized granulosa cells (SIGCs). PGRMC1 is detected as a monomer in the cytoplasm and a DTT-resistant PGRMC1 dimer in the nucleus. Transfected PGRMC1-GFP localizes mainly to the cytoplasm and does not form a DTT-resistant dimer. Moreover, forced expression of PGRMC1-GFP increases the sensitivity of the SIGCs to progesterone (P4)'s anti-apoptotic action, indicating that the PGRMC1 monomer is functional. However, when endogenous PGRMC1 is depleted by siRNA treatment and replaced with PGRMC1-GFP, P4 responsiveness is not enhanced, although overall levels of PGRMC1 are increased. P4's anti-apoptotic action is also attenuated by actinomycin D, an inhibitor of RNA synthesis, and P4 activation of PGRMC1 suppresses Bad and increases Bcl2a1d expression. Taken together, the present studies suggest a genomic component to PGRMC1's anti-apoptotic mechanism of action, which requires the presence of the PGRMC1 dimer.