PGRMC1 (progesterone receptor membrane component 1): a targetable protein with multiple functions in steroid signaling, P450 activation and drug binding

Spectroscopic and mutagenesis studies of human PGRMC1

Progesterone receptor membrane component 1 (PGRMC1) is a 25 kDa protein with an N-terminal transmembrane domain and a putative C-terminal cytochrome b5 domain. Heme-binding activity of PGRMC1 has been shown in various homologues of PGRMC1. Although the general definition of PGRMC1 is as a progesterone receptor, progesterone-binding activity has not been directly demonstrated in any of the purified PGRMC1 proteins fully loaded with heme. Here, we show that the human homologue of PGRMC1 (hPGRMC1) binds heme in a five-coordinate (5C) high-spin (HS) configuration, with an axial tyrosinate ligand, likely Y95. The negatively charged tyrosinate ligand leads to a relatively low redox potential of approximately -331 mV. The Y95C or Y95F mutation dramatically reduces the ability of the protein to bind heme, supporting the assignment of the axial heme ligand to Y95. On the other hand, the Y95H mutation retains ∼90% of the heme-binding activity. The heme in Y95H is also 5CHS, but it has a hydroxide axial ligand, conceivably stabilized by the engineered-in H95 via an H-bond; CO binding to the distal ligand-binding site leads to an exchange of the axial ligand to a histidine, possibly H95. We show that progesterone binds to hPGRMC1 and introduces spectral changes that manifest conformational changes to the heme. Our data offer the first direct evidence supporting progesterone-binding activity of PGRMC1.

Hyaluronic acid prevents immunosuppressive drug-induced ovarian damage via up-regulating PGRMC1 expression

Chemotherapy treatment in women can frequently cause damage to the ovaries, which may lead to primary ovarian insufficiency (POI). In this study, we assessed the preventative effects of hyaluronic acid (HA) in immunosuppressive drug-induced POI-like rat models and investigated the possible mechanisms. We found that HA, which was reduced in primary and immunosuppressant-induced POI patients, could protect the immunosuppressant-induced damage to granulosa cells (GCs) in vitro. Then we found that HA blocked the tripterygium glycosides (TG) induced POI-like presentations in rats, including delayed or irregular estrous cycles, reduced 17 beta-estradiol(E2) concentration, decreased number of follicles, destruction of follicle structure, and damage of reproductive ability. Furthermore, we investigated the mechanisms of HA prevention effects on POI, which was associated with promotion of GC proliferation and PGRMC1 expression. In conclusion, HA prevents chemotherapy-induced ovarian damage by promoting PGRMC1 in GCs. This study may provide a new strategy for prevention and treatment of POI.

Alzheimer's therapeutics targeting amyloid beta 1-42 oligomers II: Sigma-2/PGRMC1 receptors mediate Abeta 42 oligomer binding and synaptotoxicity

Amyloid beta (Abeta) 1-42 oligomers accumulate in brains of patients with Mild Cognitive Impairment (MCI) and disrupt synaptic plasticity processes that underlie memory formation. Synaptic binding of Abeta oligomers to several putative receptor proteins is reported to inhibit long-term potentiation, affect membrane trafficking and induce reversible spine loss in neurons, leading to impaired cognitive performance and ultimately to anterograde amnesia in the early stages of Alzheimer's disease (AD). We have identified a receptor not previously associated with AD that mediates the binding of Abeta oligomers to neurons, and describe novel therapeutic antagonists of this receptor capable of blocking Abeta toxic effects on synapses in vitro and cognitive deficits in vivo. Knockdown of sigma-2/PGRMC1 (progesterone receptor membrane component 1) protein expression in vitro using siRNA results in a highly correlated reduction in binding of exogenous Abeta oligomers to neurons of more than 90%. Expression of sigma-2/PGRMC1 is upregulated in vitro by treatment with Abeta oligomers, and is dysregulated in Alzheimer's disease patients' brain compared to age-matched, normal individuals. Specific, high affinity small molecule receptor antagonists and antibodies raised against specific regions on this receptor can displace synthetic Abeta oligomer binding to synaptic puncta in vitro and displace endogenous human AD patient oligomers from brain tissue sections in a dose-dependent manner. These receptor antagonists prevent and reverse the effects of Abeta oligomers on membrane trafficking and synapse loss in vitro and cognitive deficits in AD mouse models. These findings suggest sigma-2/PGRMC1 receptors mediate saturable oligomer binding to synaptic puncta on neurons and that brain penetrant, small molecules can displace endogenous and synthetic oligomers and improve cognitive deficits in AD models. We propose that sigma-2/PGRMC1 is a key mediator of the pathological effects of Abeta oligomers in AD and is a tractable target for small molecule disease-modifying therapeutics.

Progesterone receptor membrane component 1 deficiency attenuates growth while promoting chemosensitivity of human endometrial xenograft tumors

Endometrial cancer is the leading gynecologic cancer in women in the United States with 52,630 women predicted to be diagnosed with the disease in 2014. The objective of this study was to determine if progesterone (P4) receptor membrane component 1 (PGRMC1) influenced endometrial cancer cell viability in response to chemotherapy in vitro and in vivo. A lentiviral-based shRNA knockdown approach was used to generate stable PGRMC1-intact and PGRMC1-deplete Ishikawa endometrial cancer cell lines that also lacked expression of the classical progesterone receptor (PGR). Progesterone treatment inhibited mitosis of PGRMC1-intact, but not PGRMC1-deplete cells, suggesting that PGRMC1 mediates the anti-mitotic actions of P4. To test the hypothesis that PGRMC1 attenuates chemotherapy-induced apoptosis, PGRMC1-intact and PGRMC1-deplete cells were treated in vitro with vehicle, P4 (1 µM), doxorubicin (Dox, 2 µg/ml), or P4 + Dox for 48 h. Doxorubicin treatment of PGRMC1-intact cells resulted in a significant increase in cell death; however, co-treatment with P4 significantly attenuated Dox-induced cell death. This response to P4 was lost in PGRMC1-deplete cells. To extend these observations in vivo, a xenograft model was employed where PGRMC1-intact and PGRMC1-deplete endometrial tumors were generated following subcutaneous and intraperitoneal inoculation of immunocompromised NOD/SCID and nude mice, respectively. Tumors derived from PGRMC1-deplete cells grew slower than tumors from PGRMC1-intact cells. Mice harboring endometrial tumors were then given three treatments of vehicle (1:1 cremophor EL: ethanol + 0.9% saline) or chemotherapy [Paclitaxel (15 mg/kg, i.p.) followed after an interval of 30 minutes by CARBOplatin (50 mg/kg)] at five day intervals. In response to chemotherapy, tumor volume decreased approximately four-fold more in PGRMC1-deplete tumors when compared with PGRMC1-intact control tumors, suggesting that PGRMC1 promotes tumor cell viability during chemotherapeutic stress. In sum, these in vitro and in vivo findings demonstrate that PGRMC1 plays a prominent role in the growth and chemoresistance of human endometrial tumors.

Hyaluronic acid promotes the expression of progesterone receptor membrane component 1 via epigenetic silencing of miR-139-5p in human and rat granulosa cells

Primary ovarian insufficiency (POI) is a serious reproductive dysfunction in which the follicle pool is reduced and depleted. Abnormal apoptosis of ovarian granulosa cells (GCs) is believed to result in follicle loss. Progesterone receptor membrane component 1 (PGRMC1), which is critical for GC survival, was reported to be reduced in POI patients, but the mechanism is unknown. In the present study, we found that PGRMC1 expression was correlated with the level of hyaluronic acid (HA) in POI patients. HA up-regulated PGRMC1 expression in GCs via suppression of miR-139-5p, which was proven by Western blotting and luciferase reporter assays to target PGRMC1. Consistent with these findings, levels of miR-139-5p were significantly increased and presented an inverse correlation with PGRMC1 in POI patients. Noticeably, HA inhibited CD44-mediated miR-139-5p expression but had no effect on luciferase activity after insertion of miR-139 promoter into luciferase plasmid. Interestingly, miR-139-5p was significantly up-regulated in KGN cells (GC tumor cell line) by the histone deacetylase inhibitor trichostatin A, indicating that HA down-regulated miR-139-5p expression via histone deacetylation. Taken together, we report an unrecognized mechanism of HA in the promotion of PGRMC1 expression, suggesting that HA may be a potential molecule for the prevention and treatment of POI.

G protein-coupled receptors: extranuclear mediators for the non-genomic actions of steroids

Steroids hormones possess two distinct actions, a delayed genomic effect and a rapid non-genomic effect. Rapid steroid-triggered signaling is mediated by specific receptors localized most often to the plasma membrane. The nature of these receptors is of great interest and accumulated data suggest that G protein-coupled receptors (GPCRs) are appealing candidates. Increasing evidence regarding the interaction between steroids and specific membrane proteins, as well as the involvement of G protein and corresponding downstream signaling, have led to identification of physiologically relevant GPCRs as steroid extranuclear receptors. Examples include G protein-coupled receptor 30 (GPR30) for estrogen, membrane progestin receptor for progesterone, G protein-coupled receptor family C group 6 member A (GPRC6A) and zinc transporter member 9 (ZIP9) for androgen, and trace amine associated receptor 1 (TAAR1) for thyroid hormone. These receptor-mediated biological effects have been extended to reproductive development, cardiovascular function, neuroendocrinology and cancer pathophysiology. However, although great progress have been achieved, there are still important questions that need to be answered, including the identities of GPCRs responsible for the remaining steroids (e.g., glucocorticoid), the structural basis of steroids and GPCRs' interaction and the integration of extranuclear and nuclear signaling to the final physiological function. Here, we reviewed the several significant developments in this field and highlighted a hypothesis that attempts to explain the general interaction between steroids and GPCRs.

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.

New aspects of progesterone interactions with the actin cytoskeleton and neurosteroidogenesis in the cerebellum and the neuronal growth cone

The impact of progesterone on neuronal tissues in the central (CNS) and peripheral (PNS) nervous system is of significant scientific and therapeutic interest. Glial and neuronal cells of vertebrates express steroidogenic enzymes, and are able to synthesize progesterone de novo from cholesterol. Progesterone is described to have neuroprotective, neuroreparative, anti-degenerative, and anti-apoptotic effects in the CNS and the PNS. Thus, the first clinical studies promise new therapeutic options using progesterone in the treatment of patients with traumatic brain injury. Additionally, experimental data from different animal models suggest further positive effects of progesterone on neurological diseases such as cerebral ischemia, peripheral nerve injury and amyothropic lateral sclerosis. In regard to this future clinical use of progesterone, we discuss in this review the underlying physiological principles of progesterone effects in neuronal tissues. Mechanisms leading to morphological reorganizations of neurons in the CNS and PNS affected by progesterone are addressed, with special focus on the actin cytoskeleton. Furthermore, new aspects of a progesterone-dependent regulation of neurosteroidogenesis mediated by the recently described progesterone binding protein PGRMC1 in the nervous system are discussed.

Pathways driving the endocytosis of mutant and wild-type EGFR in cancer

EGFR (epidermal growth factor receptor) is activated through changes in expression or mutations in a number of tumors and is a driving force in cancer progression. EGFR is targeted by numerous inhibitors, including chimeric antibodies targeting the extracellular domain and small molecule kinase domain inhibitors. The kinase domain inhibitors are particularly active against mutant forms of the receptor, and subsequent mutations drive resistance to the inhibitors. Here, we review recent developments on the trafficking of wild-type and mutant EGFR, focusing on the roles of MIG6, SPRY2, ITSN, SHP2, S2R^PGRMC1 and RAK. Some classes of EGFR regulators affect wild-type and mutant EGFR equally, while others are specific for either the wild-type or mutant form of the receptor. Below we summarize multiple signaling-associated pathways that are important in trafficking wild-type and mutant EGFR with the goal being stimulation of new approaches for targeting the distinct forms of the receptor.

Genomic and non-genomic actions of progestogens in the breast

Evidence is growing that progestogens may enhance breast cancer risk under hormone therapy in the postmenopause or hormonal contraception. However, differences may exist within the progestogen class and certain progestogens may have a higher potency in terms of breast cancer risk. The mechanism(s) by which these progestogens might influence breast cancer risk appear to be mediated via genomic and/or non-genomic effects triggered by activated progestogen receptors. In general, regulation of gene expression by progestogen receptors seems to be a multifactorial process involving both actions which often converge. In the present review, we describe the known genomic and non-genomic effects in the breast, especially focusing on the progestins. This article is part of a Special Issue entitled 'Menopause'.

Long-term incubation with mifepristone (MLTI) increases the spine density in developing Purkinje cells: new insights into progesterone receptor mechanisms

Cerebellar Purkinje cells (PC) physiologically reveal an age-dependent expression of progesterone with high endogenous concentrations during the neonatal period. Even if progesterone has been previously shown to induce spinogenesis, dendritogenesis and synaptogenesis in immature PC, data about the effects of progesterone on mature PC are missing, even though they could be of significant therapeutic interest. The current study demonstrates for the first time a progesterone effect, depending on the developmental age of PC. Comparable with the physiological course of the progesterone concentration, experimental treatment with progesterone for 24 h achieves the highest effects on the dendritic tree during the early neonate, inducing an highly significant increase in dendritic length, spine number and spine area, while spine density in mature PC could not be further stimulated by progesterone incubation. Observed progesterone effects are certainly mediated by classical progesterone receptors, as spine area and number were comparable to controls when progesterone incubation was combined with mifepristone (incubation for 24 h), an antagonist of progesterone receptors A and B (PR-A/PR-B). In contrast, an increase in the spine number and area of both immature and mature PC was detected when slice cultures were incubated with mifepristone for more than 72 h (mifepristone long-time incubation, MLTI). By including time-lapse microscopy, electron microscopic techniques, PCR, western blot, and MALDI IMS receptor analysis, as well as specific antagonists like trilostane and AG 205, we were able to detect the underlying mechanism of this diverging mifepristone effect. Thus, our results provide new insights into the function and signaling mechanisms of the recently described progesterone receptor membrane component 1 (PGRMC1) in PC. It is highly suitable that progesterone does not just induce effects by the well-known genomic mechanisms of the classical progesterone receptors but also acts through PGRMC1 mediated non-genomic mechanisms. Thus, our results provide first proofs for a previously discussed progesterone-dependent induction of neurosteroidogenesis in PC by interaction with PGRMC1. But while genomic progesterone effects mediated through classical PR-A and PR-B seem to be restricted to the neonatal period of PC, PGRMC1 also transmits signals by non-genomic mechanisms like regulation of the neurosteroidogenesis in mature PC. Thus, PGRMC1 might be an interesting target for future clinical studies and therapeutic interventions.

Enhancement of cell surface expression and receptor functions of membrane progestin receptor α (mPRα) by progesterone receptor membrane component 1 (PGRMC1): evidence for a role of PGRMC1 as an adaptor protein for steroid receptors

A variety of functions have been proposed for progesterone receptor membrane component 1 (PGRMC1), including acting as a component of a membrane progestin receptor and as an adaptor protein. Here we show that stable overexpression of human PGRMC1 in nuclear progesterone receptor (PR)-negative breast cancer cell lines causes increased expression of PGRMC1 and membrane progesterone receptor α (mPRα) on cell membranes that is associated with increased specific [(3)H]progesterone binding. The membrane progestin binding affinity and specificity were characteristic of mPRα, with a Kd of 4.7 nM and high affinity for the mPR-specific agonist, Org OD 02-0, and low affinity for corticosteroids. Progestin treatment caused activation of G proteins, further evidence for increased expression of functional mPRs on PGRMC1-transfected cell membranes. Immunocytochemical and coimmunoprecipitation studies showed a close association of PGRMC1 with mPRα in cell membranes. Transfection of PGRMC1 into spontaneously immortalized rat granulosa cells was associated with membrane expression of PGRMC1 and mPRα as well as antiapoptotic effects of progestins that were abolished after cotransfection with small interfering RNA for mPRα. These data demonstrate that PGRMC1 can act as an adaptor protein, transporting mPRα to the cell surface, and that the progestin binding and apoptotic functions previously ascribed to PGRMC1 are dependent on cell surface expression of mPRα. Collectively, the results suggest PGRMC1 and mPRα are components of a membrane progesterone receptor protein complex. Increased expression of estrogen receptor β was also observed in the membranes of PGRMC1-transfected cells, suggesting that PGRMC1 can act as an adaptor protein for multiple classes of steroid receptors.

CYB5D2 requires heme-binding to regulate HeLa cell growth and confer survival from chemotherapeutic agents

The cytochrome b5 domain containing 2 (CYB5D2; Neuferricin) protein has been reported to bind heme, however, the critical residues responsible for heme-binding are undefined. Furthermore, the relationship between heme-binding and CYB5D2-mediated intracellular functions remains unknown. Previous studies examining heme-binding in two cytochrome b5 heme-binding domain-containing proteins, damage-associated protein 1 (Dap1; Saccharomyces cerevisiae) and human progesterone receptor membrane component 1 (PGRMC1), have revealed that conserved tyrosine (Y) 73, Y79, aspartic acid (D) 86, and Y127 residues present in human CYB5D2 may be involved in heme-binding. CYB5D2 binds to type b heme, however, only the substitution of glycine (G) at D86 (D86G) within its cytochrome b5 heme-binding (cyt-b5) domain abolished its heme-binding ability. Both CYB5D2 and CYB5D2(D86G) localize to the endoplasmic reticulum. Ectopic CYB5D2 expression inhibited cell proliferation and anchorage-independent colony growth of HeLa cells. Conversely, CYB5D2 knockdown and ectopic CYB5D2(D86G) expression increased cell proliferation and colony growth. As PGRMC1 has been reported to regulate the expression and activities of cytochrome P450 proteins (CYPs), we examined the role of CYB5D2 in regulating the activities of CYPs involved in sterol synthesis (CYP51A1) and drug metabolism (CYP3A4). CYB5D2 co-localizes with cytochrome P450 reductase (CYPOR), while CYB5D2 knockdown reduced lanosterol demethylase (CYP51A1) levels and rendered HeLa cells sensitive to mevalonate. Additionally, knockdown of CYB5D2 reduced CYP3A4 activity. Lastly, CYB5D2 expression conferred HeLa cell survival from chemotherapeutic agents (paclitaxel, cisplatin and doxorubicin), with its ability to promote survival being dependent on its heme-binding ability. Taken together, this study provides evidence that heme-binding is critical for CYB5D2 in regulating HeLa cell growth and survival, with endogenous CYB5D2 being required to modulate CYP activities.

A computational analysis of non-genomic plasma membrane progestin binding proteins: signaling through ion channel-linked cell surface receptors

A number of plasma membrane progestin receptors linked to non-genomic events have been identified. These include: (1) α1-subunit of the Na(+)/K(+)-ATPase (ATP1A1), (2) progestin binding PAQR proteins, (3) membrane progestin receptor alpha (mPRα), (4) progesterone receptor MAPR proteins and (5) the association of nuclear receptor (PRB) with the plasma membrane. This study compares: the pore-lining regions (ion channels), transmembrane (TM) helices, caveolin binding (CB) motifs and leucine-rich repeats (LRRs) of putative progesterone receptors. ATP1A1 contains 10 TM helices (TM-2, 4, 5, 6 and 8 are pores) and 4 CB motifs; whereas PAQR5, PAQR6, PAQR7, PAQRB8 and fish mPRα each contain 8 TM helices (TM-3 is a pore) and 2-4 CB motifs. MAPR proteins contain a single TM helix but lack pore-lining regions and CB motifs. PRB contains one or more TM helices in the steroid binding region, one of which is a pore. ATP1A1, PAQR5/7/8, mPRα, and MAPR-1 contain highly conserved leucine-rich repeats (LRR, common to plant membrane proteins) that are ligand binding sites for ouabain-like steroids associated with LRR kinases. LRR domains are within or overlap TM helices predicted to be ion channels (pore-lining regions), with the variable LRR sequence either at the C-terminus (PAQR and MAPR-1) or within an external loop (ATP1A1). Since ouabain-like steroids are produced by animal cells, our findings suggest that ATP1A1, PAQR5/7/8 and mPRα represent ion channel-linked receptors that respond physiologically to ouabain-like steroids (not progestin) similar to those known to regulate developmental and defense-related processes in plants.

Nonclassical progesterone signalling molecules in the nervous system

Progesterone (P4) regulates a wide range of cognitive, neuroendocrine, neuroimmune and neuroprotective functions. Therefore, it is not surprising that this ovarian hormone acts through multiple receptors. Ever since the 1980s, studies investigating the neural effects of P4 have focused mainly on genomic and nongenomic actions of the classical progestin receptor (PGR). More recently, two groups of nonclassical P4 signalling molecules have been identified: (i) the class II progestin and adipoQ receptor (PAQR) family, which includes PAQR 5, 6, 7, 8 and 9, also called membrane progestin receptor α (mPRα; PAQR7), mPRβ (PAQR8), mPRγ (PAQR5), mPRδ (PAQR6) and mPRε (PAQR9), and (ii) the b5-like haeme/steroid-binding protein family, which includes progesterone receptor membrane component 1 (Pgrmc1), Pgrmc2, neudesin and neuferricin. In this review, we describe the structures, neuroanatomical localisation and signalling mechanisms of these molecules. We also discuss gonadotrophin-releasing hormone regulation as an example of a physiological function regulated by multiple progesterone receptors but through different mechanisms.

Novel progesterone receptors: neural localization and possible functions

Progesterone (P₄) regulates a wide range of neural functions and likely acts through multiple receptors. Over the past 30 years, most studies investigating neural effects of P₄ focused on genomic and non-genomic actions of the classical progestin receptor (PGR). More recently the focus has widened to include two groups of non-classical P₄ signaling molecules. Members of the Class II progestin and adipoQ receptor (PAQR) family are called membrane progestin receptors (mPRs) and include: mPRα (PAQR7), mPRβ (PAQR8), mPRγ (PAQR5), mPRδ (PAQR6), and mPRε (PAQR9). Members of the b5-like heme/steroid-binding protein family include progesterone receptor membrane component 1 (PGRMC1), PGRMC2, neudesin, and neuferricin. Results of our recent mapping studies show that members of the PGRMC1/S2R family, but not mPRs, are quite abundant in forebrain structures important for neuroendocrine regulation and other non-genomic effects of P₄. Herein we describe the structures, neuroanatomical localization, and signaling mechanisms of these molecules. We also discuss possible roles for Pgrmc1/S2R in gonadotropin release, feminine sexual behaviors, fluid balance and neuroprotection, as well as catamenial epilepsy.

Sigma 1 receptor: a new therapeutic target for pain

Sigma 1 receptor (σ₁ receptor) is a unique ligand-regulated molecular chaperone located mainly in the endoplasmic reticulum and the plasma membrane. σ₁ receptor is activated under stress or pathological conditions and interacts with several neurotransmitter receptors and ion channels to modulate their function. The effects reported preclinically with σ₁ receptor ligands are consistent with a role for σ₁ receptor in central sensitization and pain hypersensitivity and suggest a potential therapeutic use of σ₁ receptor antagonists for the management of neuropathic pain as monotherapy. Moreover, data support their use in opioid adjuvant therapy: combination of σ₁ receptor antagonists and opioids results in potentiation of opioid analgesia, without significant increases in opioid-related unwanted effects. Results from clinical trials using selective σ₁ receptor antagonists in several pain conditions are eagerly awaited to ascertain the potential of σ₁ receptor modulation in pain therapy.

The putative roles of nuclear and membrane-bound progesterone receptors in the female reproductive tract

Progesterone produced by the corpus luteum (CL) is a key regulator of normal cyclical reproductive functions in the females of mammalian species. The physiological effects of progesterone are mediated by the canonical genomic pathway after binding of progesterone to its specific nuclear progesterone receptor (PGR), which acts as a ligand-activated transcription factor and has two main isoforms, PGRA and PGRB. These PGR isoforms play different roles in the cell; PGRB acts as an activator of progesterone-responsive genes, while PGRA can inhibit the activity of PGRB. The ratio of these isoforms changes during the estrous cycle and pregnancy, and it corresponds to the different levels of progesterone signaling occurring in the reproductive tract. Progesterone exerts its effects on cells also by a non-genomic mechanism by the interaction with the progesterone-binding membrane proteins including the progesterone membrane component (PGRMC) 1 and 2, and the membrane progestin receptors (mPRs). These receptors rapidly activate the appropriate intracellular signal transduction pathways, and subsequently they can initiate specific cell responses or modulate genomic cell responses. The diversity of progesterone receptors and their cellular actions enhances the role of progesterone as a factor regulating the function of the reproductive system and other organs. This paper deals with the possible involvement of nuclear and membrane-bound progesterone receptors in the function of target cells within the female reproductive tract.

Sigma-2 receptor ligands and their perspectives in cancer diagnosis and therapy

The sigma-2 receptor is highly expressed in various rapidly proliferating cancer cells and regarded as a cancer cell biomarker. Selective sigma-2 ligands have been shown to specifically label the tumor sites, induce cancer cells to undergo apoptosis, and inhibit tumor growth. Sigma-2 ligands are potentially useful as cancer diagnostics, anticancer therapeutics, or adjuvant anticancer treatment agents. However, both the cloning of this receptor and the identification of its endogenous ligand have not been successful, and the lack of structural information has severely hindered the understanding of its physiological roles, its signaling pathways, and the development of more selective sigma-2 ligands. Recent data have implicated that sigma-2 binding sites are within the lipid rafts and that PGRMC1 (progesterone receptor membrane component 1) complex and sigma-2 receptor may be coupled with EGFR (epidermal growth factor receptor), mTOR (mammalian target of rapamycin), caspases, and ion channels. Due to its promising applications in cancer management, there are rapidly increasing research efforts that are being directed into this field. This review article updates the current understanding of sigma-2 receptor and its potential physiological roles, applications, interaction with other effectors, with special focuses on the development of sigma-2 ligands, their chemical structures, pharmacological profiles, applications in imaging and anticancer therapy.

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.

The σ2 receptor: a novel protein for the imaging and treatment of cancer

The σ2 receptor is an important target for the development of molecular probes in oncology because of its 10-fold higher density in proliferating tumor cells compared with that in quiescent tumor cells and because of the observation that σ2 receptor agonists are able to kill tumor cells via apoptotic and nonapoptotic mechanisms. Although recent evidence indicates that the σ2 receptor binding site is localized within the progesterone receptor membrane component 1 (PGRMC1), most information regarding this protein has been obtained using either radiolabeled or fluorescent receptor-based probes and from biochemical analysis of the effect of σ2 selective ligands on cells grown in culture. This article reviews the development of σ2 receptor ligands and presents an overview of how they have been used in vitro and in vivo to increase our understanding of the role of the σ2 receptor in cancer and proliferation.

PGRMC2, a yet uncharacterized protein with potential as tumor suppressor, migration inhibitor, and regulator of cytochrome P450 enzyme activity

PGRMC2 (progesterone receptor membrane component 2) is highly homologous if compared with PGRMC1, a cytochrome-related protein, which is induced in several cancers and linked to cell growth in these cancers. Further it seems to be involved in progesterone signalling and cytochrome P450 binding. For PGRMC2 only sparse information is available. Recent data show that PGRMC1 and 2 share several similar characteristics, but there are also important differences in expression and function of the both proteins. Several findings point to the fact that PGRMC2 might play a role in cancer as well. The protein influences the migration rate of ovarian cancer cells and a loss of PGRMC2 might result in higher metastasis rates. In contrast to PGRMC1 it seems more likely to act as a tumor suppressor than a promoter. Altered PGRMC2 expression was further detected in the context of term and preterm labour, though the implications of this finding are currently unknown and need further examination. PGRMC2 further might play a role in gynaecologic diseases like preterm labour and endometriosis. PGRMC2 shares the cellular localisation and the ability to bind cytochrome enzymes with PGRMC1. Further the protein was shown to influence the activity of CYP3A4. In conclusion, though not much is known about PGRMC2 so far, it deserves further examination as data point to a role of PGRMC2 as tumor suppressor, migration inhibitor and regulator of cytochrome P450 proteins.

Progesterone and related compounds in hepatocellular carcinoma: basic and clinical aspects

Primary liver cancer is the fifth most common cancer worldwide and the third most common cause of cancer mortality. Hepatocellular carcinoma (HCC) accounts for 85% to 90% of primary liver cancers. Major risk factors for HCC include infection with HBV or HCV, alcoholic liver disease, and most probably nonalcoholic fatty liver disease. In general, men are two to four times more often associated with HCC than women. It can be suggested that sex hormones including progesterone may play some roles in HCC. Rather, very limited information discusses its potential involvement in HCC. This paper thus collects some recent studies of the potential involvement of progesterone and related compounds in HCC from basic and clinical aspects. In addition, two synthetic progestins, megestrol acetate (MA) and medroxyprogesterone acetate (MPA), will be discussed thoroughly. It is noted that progesterone can also serve as the precursor for androgens and estrogens produced by the gonadal and adrenal cortical tissues, while men have a higher incidence of HCC than women might be due to the stimulatory effects of androgen and the protective effects of estrogen. Eventually, this paper suggests a new insight on the associations of progesterone and related compounds with HCC development and treatment.

In vitro inhibition of SKOV-3 cell migration as a distinctive feature of progesterone receptor membrane component type 2 versus type 1

Progesterone receptor membrane component type 2 (PGRMC2) is strongly homologous to PGRMC1 which is highly expressed in ovarian cancer and other cancer cells and was claimed to play an important role in chemotherapy resistance. Whereas PGRMC1 has been extensively characterized in in vitro studies, comparably little is known about PGRMC2. To determine PGRMC2's role in ovarian cancer cell proliferation and mobility PGRMC1- and 2-depleted and -overexpressing SKOV-3 cells were generated. In electric cell-substrate impedance sensing studies, PGRMC2 negatively affects SKOV-3 migration rate if overexpressed; oppositely, depletion was associated with an increased migration rate. PGRMC1 had no effect in this assay. These effects were not associated with f-actin regulation or actin cytoskeleton reorganization. Yet, these highly homologous proteins share many properties. Both PGRMC1 and 2 are localized to the endoplasmic reticulum. As PGRMC1 was reported to interact with cytochrome P450 proteins (CYP) binding of two different CYPs to PGRMC2 was tested; a stable interaction of PGRMC2 with CYP3A4 and CYP21A2 was found in human embryonic kidney cells. For both PGRMC types, cell viability assays revealed no significant differences of SKOV-3 survival in overexpressing and depleted cells. PGRMC2 also does not seem to have any influence on the apoptotic effect of cisplatin or the antiapoptotic effect of progesterone which had been reported for PGRMC1. In contrast to PGRMC1, protein levels of PGRMC2 in SKOV-3 cells are reduced by treatment with cisplatin (30-60μM). In conclusion, we show for the first time that PGRMC2 inhibits migration of SKOV-3 ovarian cancer cells in vitro.

Progesterone increases the release of brain-derived neurotrophic factor from glia via progesterone receptor membrane component 1 (Pgrmc1)-dependent ERK5 signaling

Progesterone (P4) is cytoprotective in various experimental models, but our understanding of the mechanisms involved is still incomplete. Our laboratory has implicated brain-derived neurotrophic factor (BDNF) signaling as an important mediator of P4's protective actions. We have shown that P4 increases the expression of BDNF, an effect mediated by the classical P4 receptor (PR), and that the protective effects of P4 were abolished using inhibitors of Trk receptor signaling. In an effort to extend our understanding of the interrelationship between P4 and BDNF signaling, we determined whether P4 influenced BDNF release and examined the role of the classical PR and a putative membrane PR, progesterone receptor membrane component-1 (Pgrmc1), as mediators of this response. Given recent data from our laboratory that supported the role of ERK5 in BDNF release, we also tested whether P4-induced BDNF release was mediated by ERK5. In this study, we found that P4 and the membrane-impermeable P4 (P4-BSA) both induced BDNF release from cultured C6 glial cells and primary astrocytes. Both these cells lack the classical nuclear/intracellular PR but express high levels of membrane-associated PR, including Pgrmc1. Using RNA interference-mediated knockdown of Pgrmc1 expression, we determined that P4-induced BDNF release was dependent on the expression of Pgrmc1, although pharmacological inhibition of the PR failed to alter the effects of P4. Furthermore, the BDNF release elicited by P4 was mediated by ERK5, and not ERK1/2. Collectively, our data describe that P4 elicits an increase in BDNF release from glia via a Pgrmc1-induced ERK5 signaling mechanism and identify Pgrmc1 as a potential therapeutic target for future hormone-based drug development for the treatment of such degenerative diseases as Alzheimer's disease as well as other diseases wherein neurotrophin dysregulation is noted.

Progesterone suppresses the mTOR pathway and promotes generation of induced regulatory T cells with increased stability

While induced FoxP3(+) T cells (iTreg cells) are promising cellular therapeutics to treat inflammatory diseases, a limitation in utilizing iTreg cells prepared in vitro is their low stability in inflammatory conditions. Progesterone (P4) is an immune regulatory nuclear hormone with a potent Treg induction activity. We reasoned that this function of progesterone would be utilized to generate iTreg cells with highly suppressive activity and improved stability in vivo. Here we generated iTreg cells with progesterone in vitro and found that progesterone generates iTreg cells that are highly stable in inflammatory conditions. Moreover, P4-induced iTreg cells highly express latency-associated peptide TGF-β1 and are efficient in regulating inflammation in multiple tissues, whereas control iTreg cells induced with TGF-β1 alone are less stable and ineffective in suppressing inflammation. The function of progesterone in inducing iTreg cells with improved regulatory activity is associated with the function of P4 in suppressing the mTOR pathway. Moreover, the function of progesterone in inducing FoxP3(+) T cells is decreased but not completely abolished on nuclear progesterone receptor-deficient T cells, suggesting that both nuclear and nonnuclear progesterone receptors are involved in mediating the function. We conclude that P4 can be utilized to generate iTreg cells with a high therapeutic potential in treatment of tissue inflammation.

Nongenomic actions of aldosterone and progesterone revisited

After almost 30 years of research, the existence of nongenomic steroid actions is no longer disputed. Yet, there is still a debate on the nature of receptors involved, and answers to the inherent questions are important for translational activities. In the case of aldosterone, the existence of receptors different from the classic mineralocorticoid receptors (MR) had been postulated 25 years ago as the pharmacology of about 50% of rapid actions of aldosterone reported so far is incompatible with MR involvement (insensitivity to classic MR antagonists). Candidates proposed as alternatives to MR were protein kinase C, sodium-potassium ATPase or aberrant forms of MR, none of which supported convincing evidence to represent 'the aldosterone membrane receptor'. Early in 2011, data on GPR30 showed its involvement in rapid aldosterone action, and major pharmacological aspects of this action are compatible with the landmark deviations from MR pharmacology mentioned above. GPR30, therefore, may be a receptor candidate for nongenomic aldosterone action. Similarly, a variety of promising candidates mediating rapid progesterone action has been described, including progesterone receptor membrane component 1 (PGRMC1) which seems to be associated with tumor proliferation, and membrane progesterone receptor (mPR) originally identified in fish with potential linkage to reproductive processes. So far, no candidate was unanimously convincing. In 2010, two independent groups reported that CatSper, a calcium channel, is a strong receptor candidate for the rapid action of progesterone on sperm fertilization. With these novel receptors cloned, translational activities ultimately leading to new drugs for cardiovascular protection (in the case of aldosterone) or fertilization benefits (for progesterone) are much more promising.

Therapeutic targeting of pancreatic cancer utilizing sigma-2 ligands

One major barrier in the development of pancreas cancer therapeutics is the selective delivery of the drugs to their cellular targets. We have previously developed several sigma-2 ligands and reported the discovery of a component of the receptor for these ligands. Several sigma-2 ligands have been shown to trigger apoptosis in pancreas cancer cells. More importantly, sigma-2 ligands are internalized rapidly by the cancer cells and are capable of delivering other small-molecule therapeutics. Here we review sigma-2 ligands and conjugates as a potential novel therapy suitable for investigation in patients with pancreatic cancer.

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.

Continuous versus cyclic progesterone exposure differentially regulates hippocampal gene expression and functional profiles

This study investigated the impact of chronic exposure to continuous (CoP4) versus cyclic progesterone (CyP4) alone or in combination with 17β-estradiol (E2) on gene expression profiles targeting bioenergetics, metabolism and inflammation in the adult female rat hippocampus. High-throughput qRT-PCR analyses revealed that ovarian hormonal depletion induced by ovariectomy (OVX) led to multiple significant gene expression alterations, which were to a great extent reversed by co-administration of E2 and CyP4. In contrast, co-administration of E2 and CoP4 induced a pattern highly resembling OVX. Bioinformatics analyses further revealed clear disparities in functional profiles associated with E2+CoP4 and E2+CyP4. Genes involved in mitochondrial energy (ATP synthase α subunit; Atp5a1), redox homeostasis (peroxiredoxin 5; Prdx5), insulin signaling (insulin-like growth factor I; Igf1), and cholesterol trafficking (liver X receptor α subtype; Nr1h3), differed in direction of regulation by E2+CoP4 (down-regulation relative to OVX) and E2+CyP4 (up-regulation relative to OVX). In contrast, genes involved in amyloid metabolism (β-secretase; Bace1) differed only in degree of regulation, as both E2+CoP4 and E2+CyP4 induced down-regulation at different efficacy. E2+CyP4-induced changes could be associated with regulation of progesterone receptor membrane component 1(Pgrmc1). In summary, results from this study provide evidence at the molecular level that differing regimens of hormone therapy (HT) can induce disparate gene expression profiles in brain. From a translational perspective, confirmation of these results in a model of natural menopause, would imply that the common regimen of continuous combined HT may have adverse consequences whereas a cyclic combined regimen, which is more physiological, could be an effective strategy to maintain neurological health and function throughout menopausal aging.

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.

Differential responses of progesterone receptor membrane component-1 (Pgrmc1) and the classical progesterone receptor (Pgr) to 17β-estradiol and progesterone in hippocampal subregions that support synaptic remodeling and neurogenesis

Progesterone (P4) and estradiol (E2) modulate neurogenesis and synaptic remodeling in the hippocampus during the rat estrous cycle and in response to deafferenting lesions, but little is known about the steroidal regulation of hippocampal progesterone receptors associated with these processes. We examined the neuronal expression of progesterone receptor membrane component-1 (Pgrmc1) and the classical progesterone receptor (Pgr), by in situ hybridization and immunohistochemistry. Pgr, a transcription factor, has been associated with synaptic remodeling and other major actions of P4, whereas Pgrmc1 is implicated in P4-dependent proliferation of adult neuroprogenitor cells and with rapid P4 effects on membranes. Ovariectomized adult rats were given E2, P4, or E2+P4 on two schedules: a 4-d model of the rodent estrous cycle and a 30-d model of postmenopausal hormone therapy. Pgr was hormonally responsive only in CA1 pyramidal neurons, and the induction of Pgr by E2 was partly antagonized by P4 only on the 30-d schedule. In CA3 pyramidal and dentate gyrus (DG) neurons, Pgr was largely unresponsive to all hormone treatments. In contrast to Pgr, Pgrmc1 was generally induced by E2 and/or P4 throughout the hippocampus in CA1, CA3, and DG neurons. In neuroprogenitor cells of the DG (immunopositive for bromodeoxyuridine and doublecortin), both Pgrmc1 and Pgr were detected. The differential regulation of hippocampal Pgrmc1 and Pgr by E2 and P4 may guide drug development in hormonal therapy for support of neurogenesis and synaptic regeneration.

Expression of progesterone receptor membrane component 1, serpine mRNA binding protein 1 and nuclear progesterone receptor isoforms A and B in the bovine myometrium during the estrous cycle and early pregnancy

The aim of this study was to investigate the (1) expression of progesterone membrane component 1 (PGRMC1), serpine mRNA binding protein 1 (SERBP1) and progesterone receptor (PR) mRNA and (2) protein expression levels of PGRMC1, SERBP1 and PR isoforms A and B in the bovine myometrium during the estrous cycle and early pregnancy. Uteri from cows on days 1-5, 6-10, 11-16 and 17-21 of the estrous cycle and weeks 3-5, 6-8 and 9-12 of pregnancy were used (n=5-6 per period). There were no changes (P>0.05) in PGRMC1 mRNA expression during the estrous cycle, while expression of SERBP1 and PR mRNA was the lowest (P<0.05) on days 11-16 relative to other days of the cycle. The highest mRNA expression of PGRMC1, SERBP1 and PR was found during pregnancy. There were no changes (P>0.05) in SERBP1 protein expression in cycling and pregnant cows, while the highest (P<0.05) PGRMC1 protein expression was found during weeks 3-5 of pregnancy. Similar protein expression profiles for PRA and PRB were found, and protein levels were highest on days 1-5 of the estrous cycle. From day 6 of the cycle, PRA and PRB protein expression decreased and were maintained at this lower level during pregnancy. In conclusion, our study assessed mRNA and protein expression levels of PGRMC1, SERBP1 and PR in the bovine myometrium during the estrous cycle and the first trimester of pregnancy. It is possible that progesterone (P4) affects myometrial function in a genomic and nongenomic manner.

Membrane progesterone receptors: evidence for neuroprotective, neurosteroid signaling and neuroendocrine functions in neuronal cells

Membrane progesterone receptors (mPRs) are novel G protein-coupled receptors belonging to the progestin and adipoQ receptor family (PAQR) that mediate a variety of rapid cell surface-initiated progesterone actions in the reproductive system involving activation of intracellular signaling pathways (i.e. nonclassical actions). The mPRs are highly expressed in the brain, but research on their neural functions has only been conducted in a single neuronal cell line, GT1-7 cells, which have negligible nuclear progesterone receptor (PR) expression. GT1-7 cells express mPRα and mPRβ on their plasma membranes which is associated with the presence of high-affinity, specific [(3)H]-progesterone receptor binding. The neurosteroid, allopregnanolone, is an effective ligand for recombinant mPRα with a relative binding affinity of 7.6% that of progesterone. Allopregnanolone acts as a potent mPR agonist on GT1-7 cells, mimicking the progesterone-induced decrease in cAMP accumulation and its antiapoptotic actions at low nanomolar concentrations. The decrease in cAMP levels is associated with rapid progesterone-induced downregulation of GnRH pulsatile secretion from perifused GT1-7 cells. The recent suggestion that mPRs are alkaline ceramidases and mediate sphingolipid signaling is not supported by empirical evidence that TNFα does not bind to mPRs overexpressed in human cells and that exogenous sphingomyelinase is ineffective in mimicking progestin actions through mPRs to induce meiotic maturation of fish oocytes. Taken together, these recent studies indicate that mPRs mediate neuroprotective effects of progesterone and allopregnanolone and are also the likely intermediaries in progesterone-induced inhibition of pulsatile GnRH secretion in GT1-7 cells.

Progesterone receptor membrane component 1 modulates human cytochrome p450 activities in an isoform-dependent manner

Cytochromes P450 (P450s) catalyze the metabolism of a wide spectrum of compounds. Recently, progesterone receptor membrane component 1 (PGRMC1), which shares a key structural motif with cytochrome b(5), has been reported to bind to sterol- or steroid-synthesizing P450s, enhancing their activities. In this study, we investigated whether PGRMC1 affects human drug-metabolizing P450 activities. Using coexpression systems for PGRMC1 and P450s (CYP3A4, CYP2C9, or CYP2E1) in HepG2 cells, we found that PGRMC1 decreased the V(max) values and increased the K(m) values of the CYP3A4 activities, and it decreased the V(max) values but did not affect the K(m) values of the CYP2C9 activities. In contrast, PGRMC1 hardly affected the CYP2E1 activities. These results suggest that PGRMC1 negatively modulates the drug-metabolizing activities of P450, although it was isoform but not substrate dependent. It is worth noting that coimmunoprecipitation analysis using coexpression systems for FLAG-PGRMC1 and Myc-P450s in human embryonic kidney 293 cells revealed that PGRMC1 interacts with all three P450s, although the affinity seemed to vary. In 29 human liver microsomes (HLMs), there was a 5-fold variability in the PGRMC1 protein levels. By the correlation analyses using the P450 activities and the PGRMC1 levels, we could neither observe the contribution of PGRMC1 to the P450 activities in HLMs nor that of the NADPH-cytochrome P450 reductase or cytochrome b(5). In conclusion, in contrast to sterol- or steroid-synthesizing P450s, we found that PGRMC1 negatively modulates the human drug-metabolizing activities of P450 through direct interaction. Further studies are needed to determine the clinical significance of PGRMC1 in the pharmacokinetics of drugs.

Progesterone promotes differentiation of human cord blood fetal T cells into T regulatory cells but suppresses their differentiation into Th17 cells

Progesterone, a key female sex hormone with pleiotropic functions in maintenance of pregnancy, has profound effects on regulation of immune responses. We report in this work a novel function of progesterone in regulation of naive cord blood (CB) fetal T cell differentiation into key T regulatory cell (Treg) subsets. Progesterone drives allogeneic activation-induced differentiation of CB naive, but not adult peripheral blood, T cells into immune-suppressive Tregs, many of which express FoxP3. Compared with those induced in the absence of progesterone, the FoxP3(+) T cells induced in the presence of progesterone highly expressed memory T cell markers. In this regard, the Treg compartment in progesterone-rich CB is enriched with memory-type FoxP3(+) T cells. Moreover, CB APCs were more efficient than their peripheral blood counterparts in inducing FoxP3(+) T cells. Another related function of progesterone that we discovered was to suppress the differentiation of CB CD4(+) T cells into inflammation-associated Th17 cells. Progesterone enhanced activation of STAT5 in response to IL-2, whereas it decreased STAT3 activation in response to IL-6, which is in line with the selective activity of progesterone in generation of Tregs versus Th17 cells. Additionally, progesterone has a suppressive function on the expression of the IL-6 receptor by T cells. The results identified a novel role of progesterone in regulation of fetal T cell differentiation for promotion of immune tolerance.

Identification of the PGRMC1 protein complex as the putative sigma-2 receptor binding site

The sigma-2 receptor, whose gene remains to be cloned, has been validated as a biomarker for tumor cell proliferation. Here we report the use of a novel photoaffinity probe, WC-21, to identify the sigma-2 receptor binding site. WC-21, a sigma-2 ligand containing both a photoactive moiety azide and a fluorescein isothiocyanate group, irreversibly labels sigma-2 receptors in rat liver; the membrane-bound protein was then identified as PGRMC1 (progesterone receptor membrane component-1). Immunocytochemistry reveals that both PGRMC1 and SW120, a fluorescent sigma-2 receptor ligand, colocalizes with molecular markers of the endoplasmic reticulum and mitochondria in HeLa cells. Overexpression and knockdown of the PGRMC1 protein results in an increase and a decrease in binding of a sigma-2 selective radioligand, respectively. The identification of the putative sigma-2 receptor binding site as PGRMC1 should stimulate the development of unique imaging agents and cancer therapeutics that target the sigma-2 receptor/PGRMC1 complex.

CYB5D2 enhances HeLa cells survival of etoposide-induced cytotoxicity

Cytochrome b5 domain containing 2 (CYB5D2) (neuferricin) belongs to the family of membrane-associated progesterone receptors (MAPRs). MAPRs affect multiple cellular processes, including proliferation, differentiation, and survival. Consistent with these observations, we report here that CYB5D2 enhances HeLa cells survival of etoposide (ETOP)-mediated cytotoxicity. Overexpression of CYB5D2 enhanced the survival of HeLa cells compared with HeLa cells transfected with empty vector (EV) upon ETOP treatment. As ETOP initiates ATM-dependent DNA damage response (DDR), we were able to show that CYB5D2 did not affect ETOP-induced DDR. In line with these observations, CYB5D2 did not protect HeLa cells from UV-induced cytotoxicity. Additionally, CYB5D2 had no effects on TNFα-induced apoptosis. Collectively, CYB5D2 enhances HeLa cell survival of ETOP-induced cytotoxicity with some specificity. CYB5D2 contains a cytochrome b5 (cyt-b5) domain and a transmembrane (TM) motif. Both domains are required for CYB5D2-mediated protection of HeLa cells from ETOP-induced cytotoxicity. In an effort to search for the underlying mechanisms, we have profiled gene expression between HeLa-CYB5D2 and HeLa-EV cells. Although ectopic CYB5D2 does not massively alter gene expression, the expression of several transcripts was affected more than 2-fold, suggesting that they may contribute to CYB5D2-mediated HeLa cell survival of ETOP treatment.