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

doi:10.1016/j.steroids.2012.12.002

Steroids

Volume 78, Issue 6, June 2013, Pages 555-558

https://doi.org/10.1016/j.steroids.2012.12.002 Get rights and content

Abstract

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.

Highlights

► PGRMC2 is highly homologous to PGRMC1. ► In contrast to PGRMC1, PGRMC2 is rather a tumor suppressor, than a promoter. ► PGRMC2 inhibits cancer cell migration. ► PGRMC2 might be involved in gynaecologic diseases (endometriosis and preterm labour). ► PGRCMC2 binds cytochrome P450 proteins and seems to influence their activity.

Introduction

In the nineties, Gerdes et al. cloned two human membrane proteins and identified them as putative progesterone receptors HPR6.6 (PGRMC1) and Dg6 (PGRMC2)[1].

PGRMC1 was characterized in several cell types and has been shown to be overexpressed in several cancer cell lines and tissues [2]. The protein seems to play a role in chemotherapy resistance and was shown to promote the antiapoptotic effect of progesterone [3], [4], [5]. Further it was shown to bind several cytochrome P450 enzymes [6], [7].

PGRMC2 is highly homologous to PGRMC1. Sequence alignment and phylogenetic analysis indicate that PGRMC1 and 2 may have diverged from a common gene. It is therefore tempting to speculate that the proteins have similar functions. Both proteins consist of an N-terminal extracellular domain, followed by a transmembrane domain and a larger cytoplasmic domain. The cytoplasmic domain contains a cytochrome b5 similar heme-binding domain [8]. This cytochrome b5 similar heme binding domain is highly conserved, including the region for ERK binding and Lck/Abl tyrosine kinase binding, and the putative SH2 target sequence [9]. Further a C-terminal putative SH2 target sequence is also present in both proteins [9]. Sequences of the both proteins are quite different at the N-terminal end and the transmembrane domain pointing to the possibility of distinct interacting proteins. PGRMC2 is located on chromosome 4 while PGRMC1 is located on the X chromosome.

While PGRMC1 has been examined in several cells, tissues and contexts, PGRMC2 was not thoroughly characterized until now. Those limited but interesting facts for PGRMC2 will be summarised in the following.

Section snippets

Localisation of PGRMC2

In SKOV-3 ovarian cancer cells PGRMC2 was shown to be mainly localised in the endoplasmatic reticulum (ER) [10]. Further a localisation in the cytoplasm and in the nucleus was detected, but most of the protein was localised at the ER. For PGRMC1 the localisation was the same [10].

In the endometrium of macaques PGRMC2 was localised in the cytoplasm of the epithelial cells of both functionalis and basalis glands. In macaques with endometriosis the localisation of PGRMC2 changed to the nuclear

Expression of PGRMC2

PGRMC2 is expressed in several tissues, with especially high expression in the placenta [1]. Expression of PGRMC2 was found to be influenced by several different conditions in different cell types. For example, estrogen receptor α has no effect on the expression of PGRMC1 but correlates with the expression of PGRMC2 in breast cancer tissue. Further PGRMC2 is increased in stage III cancer tissue compared to stage II, while in the same study no effect is visible for PGRMC1 in breast cancer tissue

Regulation of PGRMC2

Virtually nothing is known about the regulation of PGRMC2, but a recent study demonstrates that PGRMC2 contains an ubiquitylation site [16]. The most studied function of ubiquitylation is the role of substrate linked ubiquitin as a proteasomal degradation signal for target proteins in the ubiquitin proteasome system (UPS). Post translational modification of proteins by ubiquitin is a reversible regulatory mechanism, which plays an important role in several cellular processes like DNA damage

PGRMC2 in other organisms

The porcine PGRMC2 was cloned in 2010 and molecular characterisation was performed [23]. In this study, two transcripts were found. The sequence has 96% similarity to the human PGRMC2. The authors showed that the genomic organization of PGRMC2 from several mammals is similar. All consist of two introns and three exons. The exon/intron boundaries are absolutely conserved among all tested mammals [23]. This indicates that PGRMC2 is well conserved in evolution.

PGRMC2 in pig was expressed in all

PGRMC2 in cancer

PGRMC1 seems to play a role in tumor promotion and chemotherapy resistance of cancer cells [3], [4], [5]. The role of PGRMC2 in cancer has not yet been studied in detail, but there are hints that PGRMC2 plays a role in tumor suppression and not, as PGRMC1, in tumor promotion.

For example, in nodal metastasis of endocervical adenocarcinomas in the uterus a high rate of loss of PGRMC2 was detected suggesting that PGRMC2 might act as a tumor suppressor in metastasis of endocervical adenocarcinoma

PGRMC2 in preterm/term labour

In the choriodecidua, PGRMC2 is upregulated in term and preterm labour and seems to be regulated by the labour specific hormonal environment [29], but the function of this protein in pregnancy and labour has not been analysed yet. For PGRMC1 it was already shown that PGRMC1 is upregulated in pregnancy and downregulated in term and preterm labour [30]. Therefore PGRMC1 may contribute to the onset of labour by withdrawal of the PGRMC1 receptors. It was further speculated that PGRMC1 is involved

Potential involvements of PGRMC2 in further diseases

A slight upregulation of PGRMC2 in patients with diminished ovarian reserve was detected [32], but this result needs confirmation. For PGRMC1 it was shown that women with premature ovarian failure often show mutant or reduced levels of PGRMC1 [11], [33]. Analogous data for PGRMC2 are scarce, and further studies need to clarify the involvement of both receptors in these diseases.

Alterations in PGRMC1 expression and localisation were also found in the endometrium of macaques with endometriosis

Binding partners of PGRMC2

PGRMC1 has been shown to form big protein complexes. Binding partners for PGRMC1 are Insig (insulin induced gene), SCAP (SREBP cleavage activation protein), PAIR-BP (plasminogen activator inhibitor RNA binding protein-1) (Fig. 1) and an unknown steroid binding protein [34]. Whether these proteins are also binding partners of PGRMC2 or not, remains to be elucidated.

Further it has been shown that PGRMC1 binds cytochrome P450 (CYP) proteins like CYP51, CYP21A2, CYP21, CYP7A1 and CYP3A4 (Fig. 1)

Outlook

PGRMC2 has not been thoroughly characterized until now, but it shares several characteristics with PGRMC1, like overall sequence homology, localisation, and binding of CYPs. Nevertheless PGRMC2 has interesting characteristics which clearly differ from those of PGRMC1. In contrast to PGRMC1, PGRMC2 negatively influences migration velocity in ovarian cancer cells and a high rate of loss of PGRMC2 was detected in nodal metastasis in endocervical adenocarcinomas. Therefore PGRMC2 might play an

Conflict of interest statement

AW has nothing to declare. MW was employed by AstraZeneca R&D, Mölndal, as director of discovery medicine (= translational medicine) from 2004–2006, while on sabbatical leave from his professorship at the University of Heidelberg. After return to this position in January 2007, he received lecturing and consulting fees from Sanofi-Aventis, Novartis, Takeda, Roche, Pfizer, Bristol-Myers, Daichii-Sankyo, Lilly and Novo-Nordisk.

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Molecular identification of a PGRMC-2 receptor in maturing oocytes of the zoonotic nematode parasite Trichinella spiralis
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We previously reported that the Trichinella nematode showed higher parasite loads in one gender than another, but also the parasite molting rate decreased when it was cultivated in the presence of progesterone. In this study we explored the hypothesis that the direct effect of progesterone on Trichinella spiralis could be mediated by a steroid-binding parasite protein.
We sequenced, cloned and amplified the Cyt-domain of the progesterone receptor membrane component-2 of Trichinella spiralis (PGRMC2-Ts). Furthermore, we expressed the protein and developed an antibody to perform confocal microscopy and flow cytometry. The expression of the PGRMC2-Ts protein was exclusively detected at the oocyte and the parasite’s cuticle in cross-sections of the parasite, and this expression was confirmed by western blot and flow cytometry. Molecular modeling studies and computer docking for the PGRMC2-Ts protein showed that it is potentially able to bind to progesterone, estradiol, testosterone, and dihydrotestosterone with different affinities. Furthermore, phylogenetic analysis demonstrated that T. spiralis PGRMC2 is related to a steroid-binding protein of another platyhelminth. Progesterone probably acts upon Trichinella spiralis oocytes by binding to PGRMC2-Ts. Our data showed that the PGRMC2-Ts protein is present in the parasite’s oocytes, a development step that is crucial for the life cycle of the parasite. Indeed, this research might have implications in the field of host-parasite co-evolution and the sex-associated susceptibility to this infection. In a more practical matter, these results may contribute to the design of new drugs with anti-parasite effects.
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Citation Excerpt :
From the pBirA complementation screen, PGRMC2 was also identified as a STIM1-Orai1 interactor (Figure S1). PGRMC1 and PGRMC2 perform similar functions by binding each other (Wendler and Wehling, 2013). However, PGRMC2 expression did not show a dramatic difference among breast cell lines compared with PGRMC1 (Figures S6A–S6C).
Progesterone receptor membrane component 1 (PGRMC1), the overexpression of which reduces survivability of cancer patients, is essential for cell migration and metastasis. However, the intracellular signaling pathways involved are largely unknown. Here, we report that PGRMC1 promotes store-operated Ca²⁺ entry (SOCE) as a functional interactor of stromal interaction molecule 1 (STIM1). PGRMC1 was repeatedly detected as an interactor of STIM1-Orai1 complex via complementation-dependent in situ labeling. Genetic depletion of PGRMC1 decreased SOCE and impaired activation of the nuclear factor of the activated T cell (NFAT) pathway. Mechanistically, PGRMC1 directly bound to the coiled-coil domain of STIM1, promoting STIM1 conformational switch. In breast cancer cells, PGRMC1 depletion reduced epidermal growth factor (EGF)-induced SOCE and disrupted focal adhesion turnover and actomyosin formation. These findings identify PGRMC1 as an essential regulator of Ca²⁺ signaling in breast cancer cells, providing a target for treating cancer metastasis and an insight for dissecting various PGRMC1/SOCE-induced biological processes.
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Consistent with a non-genomic mode of action of P5, none of the nuclear-localized proteins are annotated as putative steroid receptors, but we did retrieve the progesterone receptor membrane component 2 (PGRMC2) in the P5 interactome from both cell types. The PGRMC2 family belongs to the unconventional membrane receptor family of the hormone progesterone (P4) (Wendler and Wehling, 2013), a direct product of pregnenolone. De novo synthesis of P5 in CD8+ T cells indicated P5's role in modulating immune cell plasticity and differentiation (Jia et al., 2013).
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Fifty-two normal responders and 15 poor responders according to the Bologna criteria were enrolled for IVF and intracytoplasmic sperm injection and stimulated with 200 IU of follitrophin alpha and gonadotrophin-releasing hormone antagonist. HCG was administered for final oocyte maturation. On days 1, 6 and 10 of stimulation, blood samples were obtained, serum hormone levels were measured, RNA was extracted from PBMC and real-time polymerase chain reaction was carried out to identify the mRNA levels. Relative mRNA expression of each gene was calculated by the comparative 2^−DDCt method.
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PGRMC2, a yet uncharacterized protein with potential as tumor suppressor, migration inhibitor, and regulator of cytochrome P450 enzyme activity

Abstract

Highlights

Introduction

Section snippets

Localisation of PGRMC2

Expression of PGRMC2

Regulation of PGRMC2

PGRMC2 in other organisms

PGRMC2 in cancer

PGRMC2 in preterm/term labour

Potential involvements of PGRMC2 in further diseases

Binding partners of PGRMC2

Outlook

Conflict of interest statement

Cell Metab

J Steroid Biochem Mol Biol

Steroids

J Surg Res

Neuroscience

Neuroscience

Mol Cell

Neuron

Mol Cell Neurosci

Am J Obstet Gynecol

Pharmacol Ther

Cloning and tissue expression of two putative steroid membrane receptors

Biol Chem

Overexpression of the cytochrome p450 activator hpr6 (heme-1 domain protein/human progesterone receptor) in tumors

Tumour Biol

Hpr6 (heme-1 domain protein) regulates the susceptibility of cancer cells to chemotherapeutic drugs

J Pharmacol Exp Ther

Progesterone membrane receptor component 1 expression in the immature rat ovary and its role in mediating progesterone’s antiapoptotic action

Endocrinology

Progesterone receptor membrane component-1 (PGRMC1) is the mediator of progesterone’s antiapoptotic action in spontaneously immortalized granulosa cells as revealed by PGRMC1 small interfering ribonucleic acid treatment and functional analysis of PGRMC1 mutations

Endocrinology

Progesterone receptor membrane component 1 inhibits the activity of drug-metabolizing cytochromes P450 and binds to cytochrome P450 reductase

Mol Pharmacol