Multidrug resistance-associated protein 4 is up-regulated in liver but down-regulated in kidney in obstructive cholestasis in the rat.
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.
Denk
Gerald U
GU
Liver Center, Yale University School of Medicine, New Haven, CT 06520, USA.
Soroka
Carol J
CJ
Takeyama
Yasuaki
Y
Chen
Wen-Sheng
WS
Schuetz
John D
JD
Boyer
James L
JL
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
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