title: Regulation of basal promoter activity of the human thiamine pyrophosphate transporter SLC44A4 in human intestinal epithelial cells.
abstract: Microbiota of the large intestine synthesize considerable amount of vitamin B1 in the form of thiamine pyrophosphate (TPP). There is a specific high-affinity regulated carrier-mediated uptake system for TPP in human colonocytes (product of the SLC44A4 gene). The mechanisms of regulation of SLC44A4 gene expression are currently unknown. In this study, we characterized the SLC44A4 minimal promoter region and identified transcription factors important for basal promoter activity in colonic epithelial cells. The 5'-regulatory region of the SLC44A4 gene (1,022 bp) was cloned and showed promoter activity upon transient transfection into human colonic epithelial NCM460 cells. With the use of a series of 5'- and 3'-deletion luciferase reporter constructs, the minimal genomic region that required basal transcription of the SLC44A4 gene expression was mapped between nucleotides -178 and +88 (using the distal transcriptional start site as +1). Mutational analysis performed on putative cis-regulatory elements established the involvement of ETS/ELF3 [E26 transformation-specific sequence (ETS) proteins], cAMP-responsive element (CRE), and SP1/GC-box sequence motifs in basal SLC44A4 promoter activity. By means of EMSA, binding of ELF3 and CRE-binding protein-1 (CREB-1) transcription factors to the SLC44A4 minimal promoter was shown. Contribution of CREB into SLC44A4 promoter activity was confirmed using NCM460 cells overexpressing CREB. We also found high expression of ELF3 and CREB-1 in colonic (NCM460) compared with noncolonic (ARPE19) cells, suggesting their possible contribution to colon-specific pattern of SLC44A4 expression. This study represents the first characterization of the SLC44A4 promoter and reports the importance of both ELF3 and CREB-1 transcription factors in the maintenance of basal promoter activity in colonic epithelial cells.
authors.affiliation: Departments of Medicine and Physiology/Biophysics, University of California, Irvine, California; and Department of Veterans Affairs Medical Center, Long Beach, California.
authors.forename: Svetlana M
authors.initials: SM
authors.lastname: Nabokina
authors.affiliation: Departments of Medicine and Physiology/Biophysics, University of California, Irvine, California; and Department of Veterans Affairs Medical Center, Long Beach, California.
authors.forename: Mel Brendan
authors.initials: MB
authors.lastname: Ramos
authors.affiliation: Departments of Medicine and Physiology/Biophysics, University of California, Irvine, California; and Department of Veterans Affairs Medical Center, Long Beach, California.
authors.forename: Judith E
authors.initials: JE
authors.lastname: Valle
authors.affiliation: Departments of Medicine and Physiology/Biophysics, University of California, Irvine, California; and Department of Veterans Affairs Medical Center, Long Beach, California hmsaid@uci.edu.
authors.forename: Hamid M
authors.initials: HM
authors.lastname: Said
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D001692:Biological Transport; D002460:Cell Line; D003001:Cloning, Molecular; D003106:Colon / Q000166:cytology / Q000378:metabolism*; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism*; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006801:Humans; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D011401:Promoter Regions, Genetic; D050783:Proto-Oncogene Proteins c-ets / Q000235:genetics / Q000378:metabolism; D013835:Thiamine Pyrophosphate / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: C115163:CREB1 protein, human; D017362:Cyclic AMP Response Element-Binding Protein; D004268:DNA-Binding Proteins; C105529:ELF3 protein, human; D026901:Membrane Transport Proteins; D050783:Proto-Oncogene Proteins c-ets; C583905:SLC44A4 protein, human; D014157:Transcription Factors; D013835:Thiamine Pyrophosphate
keywords: SLC44A4; colonocytes; promoter; thiamine pyrophosphate; transcription regulation