Inflammatory-mediated repression of the rat ileal sodium-dependent bile acid transporter by c-fos nuclear translocation.
OBJECTIVE
Ileal malabsorption of bile salts is observed in Crohn's ileitis. We define the transcriptional mechanisms involved in cytokine-mediated repression of the rat apical sodium-dependent bile acid transporter (ASBT).


METHODS
ASBT regulation was studied in IL-1beta-treated IEC-6 and Caco-2 cells and in indomethacin-treated rats.


RESULTS
Indomethacin-induced ileitis in Lewis rats leads to specific reductions in ileal ASBT messenger RNA and protein levels, whereas c-jun and c-fos are induced. The proinflammatory cytokines interleukin-1beta and tumor necrosis factor repress the activity of the ASBT promoter in Caco-2 and intestinal epithelial cell-6 cells. This effect is blocked by the proteasome inhibitor, MG-132, or by the phosphatidyl inositol 3-kinase inhibitor, wortmannin. Indomethacin (in vivo) or proinflammatory cytokine (in vitro) treatment leads to serine phosphorylation and nuclear translocation of c-fos. Mutation of a 5' activated protein (AP)-1 site inactivates the ASBT promoter, whereas mutation of the 3' site abrogates the proinflammatory cytokine-mediated repression. The 5' site binds a c-jun homodimer, whereas the 3' site binds a c-jun/c-fos heterodimer. c-Jun overexpression enhances ASBT promoter activity, whereas a dominant negative c-jun construct inactivates the promoter. c-Fos overexpression represses promoter activity. A 27 base pair cis-element from the 3' site in the ASBT promoter imparts cytokine-mediated down-regulation to a heterologous SV40 promoter construct.


CONCLUSIONS
The ASBT promoter contains 2 distinct cis AP-1 elements; the 5' element binds homodimeric c-jun and mediates basal transcription. Inflammation is associated with up-regulation, phosphorylation, and nuclear translocation of c-fos, which then represses ASBT promoter activity via binding of the 3' AP-1 element by a c-fos/c-jun heterodimer.
Chen
Frank
F
Division of Pediatric Gastroenterology, Nutrition and Liver Diseases, Department of Pediatrics and the Immunobiology Center, Mount Sinai School of Medicine, New York, New York 10029, USA.
Ma
Lin
L
Sartor
R Balfour
RB
Li
Fengling
F
Xiong
Huabao
H
Sun
An-Qiang
AQ
Shneider
Benjamin
B
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D018938:Caco-2 Cells; D002352:Carrier Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D005260:Female; D006706:Homeostasis; D006801:Humans; D007079:Ileitis / Q000378:metabolism*; D007082:Ileum / Q000378:metabolism*; D007375:Interleukin-1 / Q000494:pharmacology; D007976:Leupeptins / Q000494:pharmacology; D029363:Organic Anion Transporters, Sodium-Dependent; D011401:Promoter Regions, Genetic / Q000187:drug effects; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D051381:Rats; D011917:Rats, Inbred Lew; D027981:Symporters; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D015854:Up-Regulation; D000077191:Wortmannin
D000730:Androstadienes; D002352:Carrier Proteins; D007375:Interleukin-1; D007976:Leupeptins; D029363:Organic Anion Transporters, Sodium-Dependent; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D027981:Symporters; D014409:Tumor Necrosis Factor-alpha; C071908:sodium-bile acid cotransporter; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; D000077191:Wortmannin