Regulation of basolateral organic anion transporters in ethinylestradiol-induced cholestasis in the rat.
OBJECTIVE
Estrogen-mediated cholestasis is an important clinical entity, but its molecular pathophysiology is still not fully understood. Impaired sodium-dependent uptake of bile acids has been associated with diminished expression of a basolateral Na(+)/bile acid cotransporter (Ntcp), whereas sodium-independent uptake is maintained despite a down-regulation of the organic anion transporter Oatp1. Thus, expression of the two other rat Oatps (Oatps2 and -4) was determined in estrogen-induced cholestasis. In addition, known transactivators of Oatp2 and Ntcp were studied to further characterize transcriptional regulation of these transporter genes.


METHODS
Hepatic protein and mRNA expression of various Oatps (1, 2, 4) in comparison to Ntcp were analyzed after 0.5, 1, 3 and 5 days of ethinylestradiol (EE) treatment (5 mg/kg) in rats. Binding activities of Oatp2 and Ntcp transactivators were assessed by electrophoretic mobility shift assays.


RESULTS
All basolateral Oatps (1, 2 and 4) were specifically down-regulated at the protein level by 30-40% of controls, but less pronounced than Ntcp (minus 70-80%). In contrast to unaltered Oatp4 mRNA levels, Oatp1 and Oatp2 mRNAs were reduced to various extents (minus 40-90% of controls). Binding activity of known transactivators of Ntcp and Oatp2 such as hepatocyte nuclear factor 1 (HNF1), CAAT enhancer binding protein alpha (C/EBPalpha) and pregnane X receptor (PXR) were also diminished during the time of cholestasis.


CONCLUSIONS
Estrogen-induced cholestasis results in a down-regulation of all basolateral organic anion transporters. The moderate decline in expression of Oatp1, -2 and -4 may explain the unchanged sodium-independent transport of bile acids due to overlapping substrate specificity. Reduction in transporter gene expression seems to be mediated by a diminished nuclear binding activity of transactivators such as HNF1, C/EBP and PXR by estrogens.
Geier
Andreas
A
Department of Internal Medicine III, University of Technology Aachen, Pauwelsstrasse 30, 52074 Aachen, Germany.
Dietrich
Christoph G
CG
Gerloff
Thomas
T
Haendly
Jenny
J
Kullak-Ublick
Gerd A
GA
Stieger
Bruno
B
Meier
Peter J
PJ
Matern
Siegfried
S
Gartung
Carsten
C
D000818:Animals; D001483:Base Sequence; D001485:Basement Membrane / Q000187:drug effects / Q000378:metabolism; D015152:Blotting, Northern; D015153:Blotting, Western; D002779:Cholestasis / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers; D004997:Ethinyl Estradiol / Q000009:adverse effects*; D008297:Male; D027361:Organic Anion Transporters / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D014157:Transcription Factors / Q000378:metabolism
D017931:DNA Primers; D027361:Organic Anion Transporters; D012333:RNA, Messenger; D014157:Transcription Factors; D004997:Ethinyl Estradiol