title: Multidrug resistance-associated protein 4 is up-regulated in liver but down-regulated in kidney in obstructive cholestasis in the rat.
abstract: OBJECTIVE
  Multidrug resistance-associated protein 4 (Mrp4, ABCC4) transports cyclic nucleotides, anti-retroviral compounds, and sulfated bile acids. Mrp4 expression is increased in farnesyl/bile acid receptor knockout mice. Our aim was to investigate Mrp4 expression and function in rat liver and kidney in obstructive cholestasis.
  
  
  METHODS
  Male Sprague-Dawley rats were subjected to bile duct ligation (BDL) or sham-surgery. Animals were sacrificed after 3, 7, and 14 days and tissues were harvested for Western blot analysis, real-time reverse transcriptase-mediated polymerase chain reaction (RT-PCR), and immunohistochemistry.
  
  
  RESULTS
  Western blot analysis revealed a progressive, more than seven-fold increase (P < 0.05) of Mrp4 expression in cholestatic livers, 14 days after BDL. In contrast, Mrp4 in 14-day BDL kidneys decreased to 26+/-4% of controls (P < 0.005). Immunohistochemistry localized Mrp4 to the basolateral hepatocyte membrane and corroborated its hepatic up-regulation after BDL. Real-time RT-PCR demonstrated no major changes of Mrp4 mRNA levels in liver and kidney after BDL. Cyclic adenosine monophosphate, an MRP4 substrate, was increased in plasma and urine, consistent with these findings.
  
  
  CONCLUSIONS
  Obstructive cholestasis in rats results in progressive up-regulation of Mrp4 protein in liver but down-regulation in kidney. The absence of corresponding changes in Mrp4 mRNA suggests posttranscriptional mechanisms as predominant regulators of Mrp4 expression in BDL rats.
authors.affiliation: Liver Center, Yale University School of Medicine, New Haven, CT 06520, USA.
authors.forename: Gerald U
authors.initials: GU
authors.lastname: Denk
authors.forename: Carol J
authors.initials: CJ
authors.lastname: Soroka
authors.forename: Yasuaki
authors.initials: Y
authors.lastname: Takeyama
authors.forename: Wen-Sheng
authors.initials: WS
authors.lastname: Chen
authors.forename: John D
authors.initials: JD
authors.lastname: Schuetz
authors.forename: James L
authors.initials: JL
authors.lastname: Boyer
mesh_terms: D000818:Animals; D001483:Base Sequence; D001647:Bile Acids and Salts / Q000097:blood / Q000652:urine; D002779:Cholestasis / Q000235:genetics* / Q000378:metabolism*; D000242:Cyclic AMP / Q000097:blood / Q000652:urine; D004247:DNA / Q000235:genetics; D015536:Down-Regulation; D007150:Immunohistochemistry; D007668:Kidney / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics* / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015854:Up-Regulation
chemical_list: D001647:Bile Acids and Salts; D000242:Cyclic AMP; D004247:DNA; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012333:RNA, Messenger; C489542:Abcc4 protein, rat