title: Ursodeoxycholic acid stabilizes the bile salt export pump in the apical membrane in MDCK II cells.
abstract: BACKGROUND
  Ursodeoxycholic acid (UDCA) partly exerts choleretic effects by modifying the function of the bile salt export pump (Bsep, ABCB11). UDCA induces insertion of Bsep into the canalicular membrane of hepatocytes; however, underlying mechanisms remain unknown. We aimed to elucidate molecular mechanisms behind UDCA-induced Bsep activation.
  
  
  METHODS
  We established MDCK II cells stably expressing both Bsep and Na(+)-taurocholate cotransporting polypeptide, and investigated the effect of UDCA on activity and protein expression of Bsep using these cells. We performed inhibitor study to know the molecules involved in UDCA-induced Bsep activation, and also tested the influence of UDCA on Bsep having a disease-associated mutation.
  
  
  RESULTS
  UDCA activated Bsep in a dose-dependent manner. UDCA did not affect Bsep protein expression in whole cell lysates but increased its apical surface expression by extending the half-life from 2.4 to 5.0 h. This effect was specific to Bsep because UDCA did not affect other apical and basolateral proteins, and was independent of protein kinase A, adenylate cyclase, p38(MAPK), phosphatidylinositide 3-kinase, Ca(2+), and microtubules. NorUDCA activated Bsep similar to UDCA; however, cholic acid, taurocholic acid, and tauroUDCA had no effect. UDCA significantly increased the activity of Bsep with a benign recurrent intrahepatic cholestasis 2 mutation (A570T) but did not affect Bsep with a progressive familial intrahepatic cholestasis 2 mutation (G982R or D482G).
  
  
  CONCLUSIONS
  We demonstrated that UDCA stabilizes Bsep protein in the apical membrane and increases its activity in MDCK II cells, presumably by retarding the endocytotic process.
authors.affiliation: Division of Gastroenterology, Department of Internal Medicine, Tokai University School of Medicine, Shimokasuya 143, Isehara, Kanagawa, 259-1193, Japan, kagawa@tokai.ac.jp.
authors.forename: Tatehiro
authors.initials: T
authors.lastname: Kagawa
authors.forename: Reiko
authors.initials: R
authors.lastname: Orii
authors.forename: Shunji
authors.initials: S
authors.lastname: Hirose
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Arase
authors.forename: Koichi
authors.initials: K
authors.lastname: Shiraishi
authors.forename: Akiko
authors.initials: A
authors.lastname: Mizutani
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Tsukamoto
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Mine
mesh_terms: D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D002780:Cholestasis, Intrahepatic / Q000235:genetics; D004285:Dogs; D004705:Endocytosis / Q000502:physiology; D022781:Hepatocytes / Q000378:metabolism*; D061985:Madin Darby Canine Kidney Cells; D009154:Mutation; D051381:Rats; D013656:Taurocholic Acid / Q000378:metabolism; D014580:Ursodeoxycholic Acid / Q000008:administration & dosage / Q000378:metabolism*
chemical_list: D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters; C490548:Abcb11 protein, rat; D013656:Taurocholic Acid; D014580:Ursodeoxycholic Acid