title: 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.
abstract: 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.
authors.affiliation: University of Southern California, Keck School of Medicine, Department of Biochemistry and Molecular Biology, Los Angeles, California, United States of America.
authors.forename: Hui
authors.initials: H
authors.lastname: Peng
authors.affiliation: University of Southern California, Keck School of Medicine, Department of Biochemistry and Molecular Biology, Los Angeles, California, United States of America.
authors.forename: Qin-shi
authors.initials: QS
authors.lastname: Zhu
authors.affiliation: University of Southern California, Keck School of Medicine, Department of Biochemistry and Molecular Biology, Los Angeles, California, United States of America.
authors.forename: Shuping
authors.initials: S
authors.lastname: Zhong
authors.affiliation: University of Southern California, Keck School of Medicine, Department of Biochemistry and Molecular Biology, Los Angeles, California, United States of America.
authors.forename: Daniel
authors.initials: D
authors.lastname: Levy
mesh_terms: D001483:Base Sequence; D001647:Bile Acids and Salts / Q000378:metabolism*; D001692:Biological Transport / Q000235:genetics*; D045744:Cell Line, Tumor; D004851:Epoxide Hydrolases / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000378:metabolism; D006657:Histones / Q000378:metabolism*; D006801:Humans; D007438:Introns / Q000235:genetics; D008969:Molecular Sequence Data; D009707:Nucleosomes / Q000235:genetics; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases / Q000235:genetics* / Q000378:metabolism; D011110:Polymorphism, Genetic / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D012964:Sodium / Q000378:metabolism*; D014158:Transcription, Genetic / Q000235:genetics*
chemical_list: D001647:Bile Acids and Salts; D006657:Histones; D009707:Nucleosomes; D012964:Sodium; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; D004851:Epoxide Hydrolases; C522330:EPHX1 protein, human