title: 4-Phenylbutyrate modulates ubiquitination of hepatocanalicular MRP2 and reduces serum total bilirubin concentration.
abstract: OBJECTIVE
  Multidrug resistance-associated protein 2 (in humans, MRP2; in rodents, Mrp2) mediates biliary excretion of bilirubin glucuronides. Therefore, upregulation of MRP2/Mrp2 expression may improve hyperbilirubinemia. We investigated the effects of 4-phenylbutyrate (4PBA), a drug used to treat ornithine transcarbamylase deficiency (OTCD), on the cell surface expression and transport function of MRP2/Mrp2 and serum T-Bil concentration.
  
  
  METHODS
  MRP2-expressing MDCKII (MRP2-MDCKII) cells and rats were studied to explore the change induced by 4PBA treatment in the cell surface expression and transport function of MRP2/Mrp2 and its underlying mechanism. Serum and liver specimens from OTCD patients were analyzed to examine the effect of 4PBA on hepatic MRP2 expression and serum T-Bil concentration in humans.
  
  
  RESULTS
  In MRP2-MDCKII cells and the rat liver, 4PBA increased the cell surface expression and transport function of MRP2/Mrp2. In patients with OTCD, hepatic MRP2 expression increased and serum T-Bil concentration decreased significantly after 4PBA treatment. In vitro studies designed to explore the mechanism underlying this drug action suggested that cell surface-resident MRP2/Mrp2 is degraded via ubiquitination-mediated targeting to the endosomal/lysosomal degradation pathway and that 4PBA inhibits the degradation of cell surface-resident MRP2/Mrp2 by reducing its susceptibility to ubiquitination.
  
  
  CONCLUSIONS
  4PBA activates MRP2/Mrp2 function through increased expression of MRP2/Mrp2 at the hepatocanalicular membrane by modulating its ubiquitination, and thereby decreases serum T-Bil concentration. 4PBA has thus therapeutic potential for improving hyperbilirubinemia.
authors.affiliation: Laboratory of Molecular Pharmacokinetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. Electronic address: hayapi@mol.f.u-tokyo.ac.jp.
authors.forename: Hisamitsu
authors.initials: H
authors.lastname: Hayashi
authors.affiliation: Laboratory of Molecular Pharmacokinetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Tadahaya
authors.initials: T
authors.lastname: Mizuno
authors.affiliation: Division of Endocrinology and Metabolism, National Center for Child Health and Development, 2-10-1 Okura, Setagaya-ku, Tokyo 157-8535, Japan.
authors.forename: Reiko
authors.initials: R
authors.lastname: Horikawa
authors.affiliation: Division of Metabolism, Chiba Children's Hospital, 579-1 Heta Cho, Midori-ku, Chiba 266-0007, Japan.
authors.forename: Hironori
authors.initials: H
authors.lastname: Nagasaka
authors.affiliation: Laboratory of Molecular Pharmacokinetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Yabuki
authors.affiliation: Department of Medicine, Teikyo University School of Medicine, Kaga 2-11-1, Itabashi-ku, Tokyo173-8605, Japan.
authors.forename: Hajime
authors.initials: H
authors.lastname: Takikawa
authors.affiliation: Laboratory of Molecular Pharmacokinetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. Electronic address: sugiyama@mol.f.u-tokyo.ac.jp.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Sugiyama
mesh_terms: D000328:Adult; D000818:Animals; D001663:Bilirubin / Q000097:blood*; D006528:Carcinoma, Hepatocellular / Q000378:metabolism / Q000473:pathology; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002675:Child, Preschool; D004285:Dogs; D005260:Female; D006801:Humans; D007223:Infant; D007668:Kidney / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D008099:Liver / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D008113:Liver Neoplasms / Q000378:metabolism / Q000473:pathology; D008297:Male; D023421:Models, Animal; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism*; D020163:Ornithine Carbamoyltransferase Deficiency Disease / Q000188:drug therapy / Q000378:metabolism*; D010654:Phenylbutyrates / Q000494:pharmacology* / Q000627:therapeutic use; D051381:Rats; D017207:Rats, Sprague-Dawley; D054875:Ubiquitination / Q000187:drug effects*; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D001663:Bilirubin; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D010654:Phenylbutyrates; C000715087:ABCC2 protein, human; C075773:4-phenylbutyric acid