Interleukin-1beta suppresses retinoid transactivation of two hepatic transporter genes involved in bile formation.
Cytokines have been implicated in the pathogenesis of inflammatory cholestasis. This is due to transcriptional down-regulation of hepatic transporters including the Na(+)/bile acid cotransporter, ntcp, and the multispecific organic anion exporter, mrp2. We have recently shown that ntcp suppression by lipopolysaccharide in vivo is caused by down-regulation of transactivators including the previously uncharacterized Footprint B-binding protein. Both the ntcp FpB element and the mrp2 promoter contain potential retinoid-response elements. We hypothesized that retinoic acid receptor (RAR) and retinoid X receptor (RXR) heterodimers would activate these two genes and that cytokines that reduce bile flow might do so by suppressing nuclear levels of these transactivators. Retinoid transactivation and interleukin-1beta down-regulation of the ntcp and mrp2 promoters were mapped to RXRalpha:RARalpha-response elements. Gel mobility shift assays demonstrated specific binding of RXRalpha:RARalpha heterodimers to the ntcp and mrp2 retinoid-response elements. The RXRalpha:RARalpha complex was down-regulated by IL-1beta in HepG2 cells. An unexpected finding was that an adjacent CAAT-enhancer-binding protein element was required for maximal transactivation of the ntcp promoter by RXRalpha:RARalpha. Taken together, these studies demonstrate regulation of two hepatobiliary transporter genes by RXRalpha:RARalpha and describe a mechanism which likely contributes to their down-regulation during inflammation.
Denson
L A
LA
Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
Auld
K L
KL
Schiek
D S
DS
McClure
M H
MH
Mangelsdorf
D J
DJ
Karpen
S J
SJ
D000418:Albumins / Q000235:genetics; D000818:Animals; D027321:Anion Transport Proteins; D001646:Bile / Q000378:metabolism*; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics*; D002779:Cholestasis / Q000209:etiology; D016207:Cytokines / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism; D019281:Dimerization; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology*; D015850:Interleukin-6 / Q000235:genetics; D008099:Liver / Q000378:metabolism*; D026901:Membrane Transport Proteins; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism; D029363:Organic Anion Transporters, Sodium-Dependent; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D020033:Protein Isoforms / Q000378:metabolism; D051381:Rats; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D020218:Response Elements; D047488:Retinoid X Receptors; D012176:Retinoids / Q000494:pharmacology*; D027981:Symporters; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation
D000418:Albumins; D027321:Anion Transport Proteins; D002352:Carrier Proteins; D016207:Cytokines; D004268:DNA-Binding Proteins; D007375:Interleukin-1; D015850:Interleukin-6; D026901:Membrane Transport Proteins; D009687:Nuclear Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D020033:Protein Isoforms; D018168:Receptors, Retinoic Acid; D011993:Recombinant Fusion Proteins; D047488:Retinoid X Receptors; D012176:Retinoids; D027981:Symporters; D014157:Transcription Factors; C071908:sodium-bile acid cotransporter