Transcription of the human microsomal epoxide hydrolase gene (EPHX1) is regulated by an HNF-4α/CAR/RXR/PSF complex

EPHX1 mutations cause a lipoatrophic diabetes syndrome due to impaired epoxide hydrolysis and increased cellular senescence

Epoxide hydrolases (EHs) regulate cellular homeostasis through hydrolysis of epoxides to less-reactive diols. The first discovered EH was EPHX1, also known as mEH. EH functions remain partly unknown, and no pathogenic variants have been reported in humans. We identified two de novo variants located in EPHX1 catalytic site in patients with a lipoatrophic diabetes characterized by loss of adipose tissue, insulin resistance, and multiple organ dysfunction. Functional analyses revealed that these variants led to the protein aggregation within the endoplasmic reticulum and to a loss of its hydrolysis activity. CRISPR-Cas9-mediated EPHX1 knockout (KO) abolished adipocyte differentiation and decreased insulin response. This KO also promoted oxidative stress and cellular senescence, an observation confirmed in patient-derived fibroblasts. Metreleptin therapy had a beneficial effect in one patient. This translational study highlights the importance of epoxide regulation for adipocyte function and provides new insights into the physiological roles of EHs in humans.

Protein-DNA/RNA Interactions: An Overview of Investigation Methods in the -Omics Era

The fields of application of functional proteomics are not limited to the study of protein–protein interactions; they also extend to those involving protein complexes that bind DNA or RNA. These interactions affect fundamental processes such as replication, transcription, and repair in the case of DNA, as well as transport, translation, splicing, and silencing in the case of RNA. Analytical or preparative experimental approaches, both in vivo and in vitro, have been developed to isolate and identify DNA/RNA binding proteins by exploiting the advantage of the affinity shown by these proteins toward a specific oligonucleotide sequence. The present review proposes an overview of the approaches most commonly employed in proteomics applications for the identification of nucleic acid-binding proteins, such as affinity purification (AP) protocols, EMSA, chromatin purification methods, and CRISPR-based chromatin affinity purification, which are generally associated with mass spectrometry methodologies for the unbiased protein identification.

HNF-4 participates in the hibernation-associated transcriptional regulation of the chipmunk hibernation-related protein gene

The chipmunk hibernation-related protein 25 (HP-25) is involved in the circannual control of hibernation in the brain. The liver-specific expression of the HP-25 gene is repressed in hibernating chipmunks under the control of endogenous circannual rhythms. However, the molecular mechanisms that differentially regulate the HP-25 gene during the nonhibernation and hibernation seasons are unknown. Here, we show that the hibernation-associated HP-25 expression is regulated epigenetically. Chromatin immunoprecipitation analyses revealed that significantly less hepatocyte nuclear receptor HNF-4 bound to the HP-25 gene promoter in the liver of hibernating chipmunks compared to nonhibernating chipmunks. Concurrently in the hibernating chipmunks, coactivators were dissociated from the promoter, and active transcription histone marks on the HP-25 gene promoter were lost. On the other hand, small heterodimer partner (SHP) expression was upregulated in the liver of hibernating chipmunks. Overexpressing SHP in primary hepatocytes prepared from nonhibernating chipmunks caused HNF-4 to dissociate from the HP-25 gene promoter, and reduced the HP-25 mRNA level. These results suggest that hibernation-related HP-25 expression is epigenetically regulated by the binding of HNF-4 to the HP-25 promoter, and that this binding might be modulated by SHP in hibernating chipmunks.

The significance of Brf1 overexpression in human hepatocellular carcinoma

Brf1 (TFIIB-related factor 1) plays a crucial role in cell transformation and tumorigenesis. However, the significance of Brf1 expression in human HCC (hepatocellular carcinoma) cases remains to be addressed. In this study, biopsies of human HCC, liver tumor samples of mice and cell lines of normal and tumor liver were utilized to determine the alteration of Brf1 expression using cytological and molecular biological approaches. Brf1 expression is increased in human HCC cases, which is correlated with shorter survival times. Levels of Brf1 and Pol III (RNA polymerase III-dependent) gene transcription in HCC patients with alcohol consumption are higher than the cases of non-HCC with or without alcohol intake. Induction of Brf1 and Pol III genes by ethanol in hepatoma cells is higher than in non-tumor cells. Ethanol increases the rate of cell transformation. Repression of Brf1 inhibits alcohol-promoted cell transformation. Alcohol consumption enhances Brf1 expression to promote cell transformation. These studies demonstrate that Brf1 is a new biomarker of HCC.

Microsomal epoxide hydrolase 1 (EPHX1): Gene, structure, function, and role in human disease

Microsomal epoxide hydrolase (EPHX1) is an evolutionarily highly conserved biotransformation enzyme for converting epoxides to diols. Notably, the enzyme is able to either detoxify or bioactivate a wide range of substrates. Mutations and polymorphic variants in the EPHX1 gene have been associated with susceptibility to several human diseases including cancer. This review summarizes the key knowledge concerning EPHX1 gene and protein structure, expression pattern and regulation, and substrate specificity. The relevance of EPHX1 for human pathology is especially discussed.

Stem cells in reproductive medicine: ready for the patient?

STUDY QUESTION

Are there effective and clinically validated stem cell-based therapies for reproductive diseases?

SUMMARY ANSWER

At the moment, clinically validated stem cell treatments for reproductive diseases and alterations are not available.

WHAT IS KNOWN ALREADY

Research in stem cells and regenerative medicine is growing in scope, and its translation to the clinic is heralded by the recent initiation of controlled clinical trials with pluripotent derived cells. Unfortunately, stem cell 'treatments' are currently offered to patients outside of the controlled framework of scientifically sound research and regulated clinical trials. Both physicians and patients in reproductive medicine are often unsure about stem cells therapeutic options.

STUDY DESIGN, SIZE, DURATION

An international working group was assembled to review critically the available scientific literature in both the human species and animal models.

PARTICIPANTS/MATERIALS, SETTING, METHODS

This review includes work published in English until December 2014, and available through Pubmed.

MAIN RESULTS AND THE ROLE OF CHANCE

A few areas of research in stem cell and reproductive medicine were identified: in vitro gamete production, endometrial regeneration, erectile dysfunction amelioration, vaginal reconstruction. The stem cells studied range from pluripotent (embryonic stem cells and induced pluripotent stem cells) to monopotent stem cells, such as spermatogonial stem cells or mesenchymal stem cells. The vast majority of studies have been carried out in animal models, with data that are preliminary at best.

LIMITATIONS, REASONS FOR CAUTION

This review was not conducted in a systematic fashion, and reports in publications not indexed in Pubmed were not analyzed.

WIDER IMPLICATIONS OF THE FINDINGS

A much broader clinical knowledge will have to be acquired before translation to the clinic of stem cell therapies in reproductive medicine; patients and physicians should be wary of unfounded claims of improvement of existing medical conditions; at the moment, effective stem cell treatment for reproductive diseases and alterations is not available.

STUDY FUNDING/COMPETING INTERESTS

None.

TRIAL REGISTRATION NUMBER

NA.

Transcription of the Human Microsomal Epoxide Hydrolase Gene (EPHX1) Is Regulated by PARP-1 and Histone H1.2. Association with Sodium-Dependent Bile Acid Transport

Microsomal epoxide hydrolase (mEH) is a bifunctional protein that plays a central role in the metabolism of numerous xenobiotics as well as mediating the sodium-dependent transport of bile acids into hepatocytes. These compounds are involved in cholesterol homeostasis, lipid digestion, excretion of xenobiotics and the regulation of several nuclear receptors and signaling transduction pathways. Previous studies have demonstrated the critical role of GATA-4, a C/EBPα-NF/Y complex and an HNF-4α/CAR/RXR/PSF complex in the transcriptional regulation of the mEH gene (EPHX1). Studies also identified heterozygous mutations in human EPHX1 that resulted in a 95% decrease in mEH expression levels which was associated with a decrease in bile acid transport and severe hypercholanemia. In the present investigation we demonstrate that EPHX1 transcription is significantly inhibited by two heterozygous mutations observed in the Old Order Amish population that present numerous hypercholanemic subjects in the absence of liver damage suggesting a defect in bile acid transport into the hepatocyte. The identity of the regulatory proteins binding to these sites, established using biotinylated oligonucleotides in conjunction with mass spectrometry was shown to be poly(ADP-ribose)polymerase-1 (PARP-1) bound to the EPHX1 proximal promoter and a linker histone complex, H1.2/Aly, bound to a regulatory intron 1 site. These sites exhibited 71% homology and may represent potential nucleosome positioning domains. The high frequency of the H1.2 site polymorphism in the Amish population results in a potential genetic predisposition to hypercholanemia and in conjunction with our previous studies, further supports the critical role of mEH in mediating bile acid transport into hepatocytes.

Deciphering the roles of the constitutive androstane receptor in energy metabolism

The constitutive androstane receptor (CAR) is initially defined as a xenobiotic nuclear receptor that protects the liver from injury. Detoxification of damaging chemicals is achieved by CAR-mediated induction of drug-metabolizing enzymes and transporters. More recent research has implicated CAR in energy metabolism, suggesting a therapeutic potential for CAR in metabolic diseases, such as type 2 diabetes and obesity. A better understanding of the mechanisms by which CAR regulates energy metabolism will allow us to take advantage of its effectiveness while avoiding its side effects. This review summarizes the current progress on the regulation of CAR nuclear translocation, upstream modulators of CAR activity, and the crosstalk between CAR and other transcriptional factors, with the aim of elucidating how CAR regulates glucose and lipid metabolism.