The rat canalicular conjugate export pump (Mrp2) is down-regulated in intrahepatic and obstructive cholestasis.
OBJECTIVE
The excretion of various organic anions into bile is mediated by an adenosine triphosphate-dependent conjugate export pump, which has been identified as the canalicular isoform of the multidrug resistance protein (Mrp2). Mrp2 function is impaired in various experimental models of intrahepatic and obstructive cholestasis, but the underlying molecular mechanisms are unclear. The aim of this study was to investigate these molecular mechanisms.


METHODS
The effects of endotoxin, ethinylestradiol, and common bile duct ligation (CBDL) on Mrp2 protein, messenger RNA (mRNA) expression, and Mrp2 tissue localization were determined in rat livers by Northern blotting, Western analysis, and tissue immunofluorescence. To assess whether changes were specific for Mrp2, we also examined the expression of canalicular ecto-adenosine triphosphatase (ecto-ATPase) and mdr P-glycoproteins (P-gp).


RESULTS
All three cholestatic models resulted in a marked decrease in Mrp2 protein (P < 0.01) and its tissue localization at the canalicular membrane. Mrp2 mRNA levels diminished profoundly after endotoxin (P < 0.0005) and CBDL (P < 0.05), but did not change after ethinylestradiol. In contrast to Mrp2, protein expression of ecto-ATPase and P-gp remained unchanged in endotoxin- and ethinylestradiol-treated animals, whereas P-gp levels increased after CBDL (P < 0.05).


CONCLUSIONS
Down-regulation of Mrp2 expression may explain impaired biliary excretion of amphiphilic anionic conjugates in these models of cholestasis.
Trauner
M
M
Liver Center and Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520-8019, USA.
Arrese
M
M
Soroka
C J
CJ
Ananthanarayanan
M
M
Koeppel
T A
TA
Schlosser
S F
SF
Suchy
F J
FJ
Keppler
D
D
Boyer
J L
JL
D018528:ATP-Binding Cassette Transporters / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001648:Bile Canaliculi / Q000378:metabolism*; D015152:Blotting, Northern; D015153:Blotting, Western; D002779:Cholestasis / Q000209:etiology / Q000378:metabolism*; D002780:Cholestasis, Intrahepatic / Q000209:etiology / Q000378:metabolism*; D003135:Common Bile Duct / Q000601:surgery; D015536:Down-Regulation / Q000187:drug effects; D018432:Drug Resistance, Multiple; D004997:Ethinyl Estradiol; D019084:Fluorescent Antibody Technique, Indirect; D005786:Gene Expression Regulation; D008070:Lipopolysaccharides; D008297:Male; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley
D018528:ATP-Binding Cassette Transporters; D004997:Ethinyl Estradiol; D008070:Lipopolysaccharides; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012333:RNA, Messenger