A helping hand for cytochrome p450 enzymes

Translocation of Adenosine A2B Receptor to Mitochondria Influences Cytochrome P450 2E1 Activity after Acetaminophen Overdose

The adenosine A2B receptor (A2BAR) is a member of a family of G-protein coupled receptors (GPCRs), which has a low affinity for adenosine and is now implicated in several pathophysiological conditions. We have demonstrated the beneficial effects of A2BAR activation in enhancing recovery after acute liver injury induced by an acetaminophen (APAP) overdose. While receptor trafficking within the cell is recognized to play a role in GPCR signaling, its role in the mediation of A2BAR effects in the context of APAP-induced liver injury is not well understood. This was investigated here, where C57BL/6J mice were subjected to an APAP overdose (300 mg/kg), and the temporal course of A2BAR intracellular localization was examined. The impact of A2BAR activation or inhibition on trafficking was examined by utilizing the A2BAR agonist BAY 60-6583 or antagonist PSB 603. The modulation of A2BAR trafficking via APAP-induced cell signaling was explored by using 4-methylpyrazole (4MP), an inhibitor of Cyp2E1 and JNK activation. Our results indicate that APAP overdose induced the translocation of A2BAR to mitochondria, which was prevented via 4MP treatment. Furthermore, we demonstrated that A2BAR is localized on the mitochondrial outer membrane and interacts with progesterone receptor membrane component 1 (PGRMC1). While the activation of A2BAR enhanced mitochondrial localization, its inhibition decreased PGRMC1 mitochondria levels and blunted mitochondrial Cyp2E1 activity. Thus, our data reveal a hitherto unrecognized consequence of A2BAR trafficking to mitochondria and its interaction with PGRMC1, which regulates mitochondrial Cyp2E1 activity and modulates APAP-induced liver injury.

Long-term and daily use of molecular hydrogen induces reprogramming of liver metabolism in rats by modulating NADP/NADPH redox pathways

Molecular hydrogen (H2) has emerged as a new therapeutic option in several diseases and is widely adopted by healthy people. However, molecular data to support therapeutic functions attributed to the biological activities of H2 remain elusive. Here, using transcriptomic and metabolomic approaches coupled with biochemistry and micro-CT technics, we evaluated the effect of long-term (6 months) and daily use of H2 on liver function. Rats exposed 2 h daily to H2 either by drinking HRW (H2 dissolved in H2O) or by breathing 4% H2 gas showed reduced lipogenesis and enhanced lipolysis in the liver, which was associated with apparent loss of visceral fat and brown adipose tissue together with a reduced level of serum lipids. Both transcripts and metabolites enriched in H2-treated rats revealed alteration of amino acid metabolism pathways and activation of purine nucleotides and carbohydrate biosynthesis pathways. Analysis of the interaction network of genes and metabolites and correlation tests revealed that NADP is the central regulator of H2 induced metabolic alterations in the liver, which was further confirmed by an increase in the level of components of metabolic pathways that require NADP as substrate. Evidence of immune response regulation activity was also observed in response to exposure to H2. This work is the first to provide metabolomic and transcriptomic data to uncover molecular targets for the effect of prolonged molecular hydrogen treatment on liver metabolism.

Quality Control of Protein Complex Assembly by a Transmembrane Recognition Factor

The inner nuclear membrane (INM) is continuous with the endoplasmic reticulum (ER) but harbors a distinctive proteome essential for nuclear functions. In yeast, the Asi1/Asi2/Asi3 ubiquitin ligase complex safeguards the INM proteome through the clearance of mislocalized ER membrane proteins. How the Asi complex selectively targets mislocalized proteins and coordinates its activity with other ER functions, such as protein biogenesis, is unclear. Here, we uncover a link between INM proteome identity and membrane protein complex assembly in the remaining ER. We show that lone proteins and complex subunits failing to assemble in the ER access the INM for Asi-mediated degradation. Substrates are recognized by direct binding of Asi2 to their transmembrane domains for subsequent ubiquitination by Asi1/Asi3 and membrane extraction. Our data suggest a model in which spatial segregation of membrane protein complex assembly and quality control improves assembly efficiency and reduces the levels of orphan subunits.

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Quality control of unassembled subunits of membrane complexes is restricted to the INM

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The Asi complex promotes degradation of folded but unassembled membrane proteins

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Binding of Asi2 to membrane domain of unassembled subunits mediates their recognition

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INM quality control maintains complex subunits within near-stoichiometric levels

Subfertility and reduced progestin synthesis in Pgrmc2 knockout zebrafish

Progestin receptor membrane component (Pgrmc1 & 2) is a heme-binding protein. Studies on Pgrmc1 have suggested possible roles in heme binding, activation of steroid-synthesizing P450s, along with binding and transferring of membrane proteins. However, the studies of Pgrmc1's paralog, Pgrmc2 are still lacking. In order to determine the physiologic function(s) of Pgrmc2, we generated a zebrafish mutant line (pgrmc2^-/-). We found a reduction in both spawning frequency and the number of embryos produced in female pgrmc2^-/-. This subfertility is caused by reduced oocyte maturation (germinal vesicle breakdown, GVBD) in pgrmc2^-/- in vivo. Nonetheless, oocytes from pgrmc2^-/- had similar sensitivity to 17α,20β-dihydroxy-4-pregnen-3-one (DHP, a maturation induced progestin in zebrafish) compared with wildtype (wt) in vitro. Therefore, we hypothesized that oocyte maturation tardiness found in vivo, could be due to lack of progestin in pgrmc2^-/-. Interestingly, we found significant reduced expression of hormones, receptors, and steroid synthesizing enzymes including lhcgr, egfra, ar, and esr2, cyp11a1 and hsd3b1. In addition, DHP levels in pgrmc2^-/- ovaries showed a significant decrease compared to those in wt. In summary, we have provided a plausible molecular mechanism for the physiological functions of Pgrmc2 in the regulation of female fertility, likely via regulation of receptors and steroids in the ovary, which in turn regulates oocyte maturation in zebrafish.

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 (PGRMC1) expression in fetal membranes among women with preterm premature rupture of the membranes (PPROM)

PGRMC1 function is implicated in maintaining fetal membrane (FM) integrity. PGRMC1 was detectable primarily in the cytoplasm of FM cells and was actively regulated in FMs and relevant for PGRMC1-mediated progesterone action. By cell type, PGRMC1 expression was higher in amnion and chorion compared with decidua. By clinical phenotype, PGRMC1 expression was higher among preterm-no-labor and term-no-labor subjects compared to PPROM. PGRMC1 expression appears to be diminished in PPROM subjects.

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.

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.

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

Progesterone receptor membrane component 1 (PGRMC1) has been shown to interact with several cytochromes P450 (P450s) and to activate enzymatic activity of P450s involved in sterol biosynthesis. We analyzed the interactions of PGRMC1 with the drug-metabolizing P450s, CYP2C2, CYP2C8, and CYP3A4, in transfected cells. Based on coimmunoprecipitation assays, PGRMC1 bound efficiently to all three P450s, and binding to the catalytic cytoplasmic domain of CYP2C2 was much more efficient than to a chimera containing only the N-terminal transmembrane domain. Down-regulation of PGRMC1 expression levels in human embryonic kidney 293 and HepG2 cell lines stably expressing PGRMC1-specific small interfering RNA had no effect on the endoplasmic reticulum localization and expression levels of P450s, whereas enzymatic activities of CYP2C2, CYP2C8, and CYP3A4 were slightly higher in PGRMC1-deficient cells. Cotransfection of cells with P450s and PGRMC1 resulted in PGRMC1 concentration-dependent inhibition of the P450 activities, and this inhibition was partially reversed by increased expression of the P450 reductase (CPR). In contrast, CYP51 activity was decreased by down-regulation of PGRMC1 and expression of PGRMC1 in the PGRMC1-deficient cells increased CYP51 activity. In cells cotransfected with CPR and PGRMC1, strong binding of CPR to PGRMC1 was observed; however, in the presence of CYP2C2, interaction of PGRMC1 with CPR was significantly reduced, suggesting that CYP2C2 competes with CPR for binding to PGRMC1. These data show that in contrast to sterol synthesizing P450, PGRMC1 is not required for the activities of several drug-metabolizing P450s, and its overexpression inhibits those P450 activities. Furthermore, PGRMC1 binds to CPR, which may influence P450 activity.

Systematic genetic and genomic analysis of cytochrome P450 enzyme activities in human liver

Liver cytochrome P450s (P450s) play critical roles in drug metabolism, toxicology, and metabolic processes. Despite rapid progress in the understanding of these enzymes, a systematic investigation of the full spectrum of functionality of individual P450s, the interrelationship or networks connecting them, and the genetic control of each gene/enzyme is lacking. To this end, we genotyped, expression-profiled, and measured P450 activities of 466 human liver samples and applied a systems biology approach via the integration of genetics, gene expression, and enzyme activity measurements. We found that most P450s were positively correlated among themselves and were highly correlated with known regulators as well as thousands of other genes enriched for pathways relevant to the metabolism of drugs, fatty acids, amino acids, and steroids. Genome-wide association analyses between genetic polymorphisms and P450 expression or enzyme activities revealed sets of SNPs associated with P450 traits, and suggested the existence of both cis-regulation of P450 expression (especially for CYP2D6) and more complex trans-regulation of P450 activity. Several novel SNPs associated with CYP2D6 expression and enzyme activity were validated in an independent human cohort. By constructing a weighted coexpression network and a Bayesian regulatory network, we defined the human liver transcriptional network structure, uncovered subnetworks representative of the P450 regulatory system, and identified novel candidate regulatory genes, namely, EHHADH, SLC10A1, and AKR1D1. The P450 subnetworks were then validated using gene signatures responsive to ligands of known P450 regulators in mouse and rat. This systematic survey provides a comprehensive view of the functionality, genetic control, and interactions of P450s.

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

Hormone signaling is important in a number of disease states, and hormone receptors are effective therapeutic targets. PGRMC1 (progesterone receptor membrane component 1) is a member of a multi-protein complex that binds to progesterone and other steroids, as well as pharmaceutical compounds. In spite of its name, PGRMC1 shares homology with cytochrome b5-related proteins rather than hormone receptors, and heme binding is the sole biochemical activity of PGRMC1. PGRMC1 and its homologues regulate cholesterol synthesis by activating the P450 protein Cyp51/lanosterol demethylase, and the cholesterol synthetic pathway is an important target in cardiovascular disease and in treating infections. PGRMC1 binding partners include multiple P450 proteins, PAIR-BP1, Insig, and an uncharacterized hormone/drug-binding protein. PGRMC1 is induced in a spectrum of cancers, where it promotes cell survival and damage resistance, and PGRMC1 is also expressed in the nervous system and tissues involved in drug metabolism, cholesterol synthesis and hormone synthesis and turnover. One of the appealing features of PGRMC1 and its associated protein complex is its affinity for steroids and drugs. Together with its biological role in promoting tumor survival, PGRMC1 is an attractive target for therapeutic intervention in cancer and related malignancies.

Non-genomic progesterone actions in female reproduction

BACKGROUND

The steroid hormone progesterone is indispensable for mammalian procreation by controlling key female reproductive events that range from ovulation to implantation, maintenance of pregnancy and breast development. In addition to activating the progesterone receptors (PRs)-B and -A, members of the superfamily of ligand-dependent transcription factors, progesterone also elicits a variety of rapid signalling events independently of transcriptional or genomic regulation. This review covers our current knowledge on the mechanisms and relevance of non-genomic progesterone signalling in female reproduction.

METHODS

PubMed was searched up to August 2008 for papers on progesterone actions in ovary/breast/endometrium/myometrium/brain, focusing primarily on non-genomic signalling mechanisms.

RESULTS

Convergence and intertwining of rapid non-genomic events and the slower transcriptional actions critically determine the functional response to progesterone in the female reproductive system in a cell-type- and environment-specific manner. Several putative progesterone-binding moieties have been implicated in rapid signalling events, including the 'classical' PR and its variants, progesterone receptor membrane component 1, and the novel family of membrane progestin receptors. Progesterone and its metabolites have also been implicated in the allosteric regulation of several unrelated receptors, such as gamma-aminobutyric acid type A, oxytocin and sigma(1) receptors.

CONCLUSIONS

Identification of the mechanisms and receptors that relay rapid progesterone signalling is an area of research fraught with difficulties and controversy. More in-depth characterization of the putative receptors is required before the non-genomic progesterone pathway in normal and pathological reproductive function can be targeted for pharmacological intervention.

Regulation of sterol synthesis in eukaryotes

Cholesterol is an essential component of mammalian cell membranes and is required for proper membrane permeability, fluidity, organelle identity, and protein function. Cells maintain sterol homeostasis by multiple feedback controls that act through transcriptional and posttranscriptional mechanisms. The membrane-bound transcription factor sterol regulatory element binding protein (SREBP) is the principal regulator of both sterol synthesis and uptake. In mammalian cells, the ER membrane protein Insig has emerged as a key component of homeostatic regulation by controlling both the activity of SREBP and the sterol-dependent degradation of the biosynthetic enzyme HMG-CoA reductase. In this review, we focus on recent advances in our understanding of the molecular mechanisms of the regulation of sterol synthesis. A comparative analysis of SREBP and HMG-CoA reductase regulation in mammals, yeast, and flies points toward an equilibrium model for how lipid signals regulate the activity of sterol-sensing proteins and their downstream effectors.

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

Progesterone (P4) receptor membrane component-1 (PGRMC1) and its binding partner, plasminogen activator inhibitor 1 RNA binding protein (PAIRBP1) are thought to form a complex that functions as membrane receptor for P4. The present investigations confirm PGRMC1's role in this membrane receptor complex by demonstrating that depleting PGMRC1 with PGRMC1 small interfering RNA results in a 60% decline in [(3)H]P4 binding and the loss of P4's antiapoptotic action. Studies conducted on partially purified GFP-PGRMC1 fusion protein indicate that [(3)H]P4 specifically binds to PGRMC1 at a single site with an apparent K(d) of about 35 nm. In addition, experiments using various deletion mutations reveal that the entire PGRMC1 molecule is required for maximal [(3)H]P4 binding and P4 responsiveness. Analysis of the binding data also suggests that the P4 binding site is within a segment of PGRMC1 that is composed of the transmembrane domain and the initial segment of the C terminus. Interestingly, PAIRBP1 appears to bind to the C terminus between amino acids 70-130, which is distal to the putative P4 binding site. Taken together, these data provide compelling evidence that PGRMC1 is the P4 binding protein that mediates P4's antiapoptotic action. Moreover, the deletion mutation studies indicate that each domain of PGRMC1 plays an essential role in modulating PGRMC1's capacity to both bind and respond to P4. Additional studies are required to more precisely delineate the role of each PGRMC1 domain in transducing P4's antiapoptotic action.

Extranuclear steroid receptors: nature and actions

Rapid effects of steroid hormones result from the actions of specific receptors localized most often to the plasma membrane. Fast-acting membrane-initiated steroid signaling (MISS) leads to the modification of existing proteins and cell behaviors. Rapid steroid-triggered signaling through calcium, amine release, and kinase activation also impacts the regulation of gene expression by steroids, sometimes requiring integration with nuclear steroid receptor function. In this and other ways, the integration of all steroid actions in the cell coordinates outcomes such as cell fate, proliferation, differentiation, and migration. The nature of the receptors is of intense interest, and significant data suggest that extranuclear and nuclear steroid receptor pools are the same proteins. Insights regarding the structural determinants for membrane localization and function, as well as the nature of interactions with G proteins and other signaling molecules in confined areas of the membrane, have led to a fuller understanding of how steroid receptors effect rapid actions. Increasingly, the relevance of rapid signaling for the in vivo functions of steroid hormones has been established. Examples include steroid effects on reproductive organ development and function, cardiovascular responsiveness, and cancer biology. However, although great strides have been made, much remains to be understood concerning the integration of extranuclear and nuclear receptor functions to organ biology. In this review, we highlight the significant progress that has been made in these areas.