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

PLOS ONE, Dec 2019

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.

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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

May 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 Hui Peng 0 1 2 Qin-shi Zhu 0 1 2 Shuping Zhong 0 1 2 Daniel Levy 0 1 2 0 University of Southern California, Keck School of Medicine, Department of Biochemistry and Molecular Biology , Los Angeles, California , United States of America 1 Funding: R01 DK025836 National Institutes of Health. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript 2 Academic Editor: Makoto Makishima, Nihon University School of Medicine , JAPAN 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/EBP-NF/Y complex and an HNF-4/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. - Competing Interests: The authors have declared that no competing interests exist. Microsomal epoxide hydrolase (mEH) is a 48-kDa bifunctional protein that is expressed on the hepatocyte endoplasmic reticulum membrane in two distinct topological orientations [1] where the type I form plays a central role in the metabolism of numerous xenobiotics [2]. The type II form is targeted to the plasma membrane where it can mediate the sodium-dependent transport of bile acids [310] in parallel with the sodium-taurocholate cotransporting protein (Ntcp) [11]. The bile acids play a critical role in the digestion of dietary lipids, excretion of xenobiotics, and in the regulation of cholesterol homeostasis, nuclear receptors such as FXR and signal transduction such as the AKT and ERK1/2 pathways [1214]. The regulation of bile acid transporter capacity/function is of critical importance in order to maintain the proper concentration and cellular distribution of the bile acids. Defects in bile salt transporters thus are involved in the etiology of numerous hepatobiliary disorders [15]. Previous studies from this laboratory have demonstrated that GATA-4 [16], a C/EBP-NF/Y complex [17] and an HNF-4/CAR/RXR/PSF complex [18] play critical roles in regulating the transcription of the mEH gene (EPHX1). Studies have also identified mutations in human EPHX1 that resulted in a 95% decrease in mEH expression that was associated with a significant decrease in bile acid uptake across the sinusoidal plasma membrane resulting in a 100-fold increase in serum bile salt levels (hypercholanemia) in the absence of liver damage [19]. In contrast, the Ntcp mRNA and protein expression levels in this subject were normal with no mutations in the amino acid sequence [20]. In order to further explore the role of mEH in sodium-dependent hepatocyte bile acid transport we investigated the occurrence of EPHX1 mutations in the Lancaster County Old Order Amish population that exhibit numerous cases of hypercholanemia [21] in the absence of hepatocellular injury suggesting a defect in bile acid uptake [22]. Linkage analysis identified several candidate genes [21] as well as a heterozygous region that contains the EPHX1 locus at 1q42.1 (L. Bull, personal communication). Sequencing and genotyping studies of EPHX1 have identified 2 functional mutations; one at a poly(ADP-ribose)polymerase-1 (PARP-1) binding site in the proximal promoter region (-17) and a second at a linker histone (H1.2) binding site in intron 1 (+2557), the latter mutation originally ob (...truncated)


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Hui Peng, Qin-shi Zhu, Shuping Zhong, Daniel Levy. 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, PLOS ONE, 2015, 5, DOI: 10.1371/journal.pone.0125318