The role of AP-1 in the transcriptional regulation of the rat apical sodium-dependent bile acid transporter.
Ileal reclamation of bile salts, a critical determinant of their enterohepatic circulation, is mediated primarily by the apical sodium-dependent bile acid transporter (ASBT=SLC10A2). We have defined mechanisms involved in the transcriptional regulation of ASBT. The ASBT gene extends over 17 kilobases and contains five introns. Primer extension analysis localized two transcription initiation sites 323 and 255 base pairs upstream of the initiator methionine. Strong promoter activity is imparted by both a 2.7- and 0.2-kilobase 5'-flanking region of ASBT. The promoter activity is cell line specific (Caco-2, not Hep-G2, HeLa-S3, or Madin-Darby canine kidney cells). Four distinct specific binding proteins were identified by gel shift and cross-linking studies using Caco-2 or rat ileal nuclear extracts. Two AP-1 consensus sites were identified in the proximal promoter. DNA binding and promoter activity could be abrogated by mutation of the proximal AP-1 site. Supershift analysis revealed binding of c-Jun and c-Fos to this AP-1 element. Co-expression of c-Jun enhanced promoter activity in Caco-2 cells and activated the promoter in Madin-Darby canine kidney cells. Region and developmental stage-specific expression of ASBT in the rat intestine correlated with the presence of one of these DNA-protein complexes and both c-Fos and c-Jun proteins. A specific AP-1 element regulates transcription of the rat ASBT gene.
Chen
F
F
Department of Pediatrics, Division of Pediatric Gastroenterology, Nutrition and Liver Diseases, Mount Sinai School of Medicine, New York, New York 10029, USA.
Ma
L
L
Al-Ansari
N
N
Shneider
B
B
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D015153:Blotting, Western; D018938:Caco-2 Cells; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003001:Cloning, Molecular; D005091:Exons; D005786:Gene Expression Regulation; D015723:Gene Library; D006801:Humans; D007421:Intestine, Small / Q000378:metabolism; D008156:Luciferases / Q000378:metabolism; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D029363:Organic Anion Transporters, Sodium-Dependent; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D012689:Sequence Homology, Nucleic Acid; D027981:Symporters; D018808:Transcription Factor AP-1 / Q000378:metabolism* / Q000502:physiology*; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D027981:Symporters; D018808:Transcription Factor AP-1; C071908:sodium-bile acid cotransporter; D008156:Luciferases