title: Competitive regulation of human intestinal β-carotene 15,15'-monooxygenase 1 (BCMO1) gene expression by hepatocyte nuclear factor (HNF)-1α and HNF-4α.
abstract: OBJECTIVE
  Among the pro-vitamin A carotenoids, β-carotene is an excellent source of vitamin A. β-Carotene 15,15'-monooxygenase 1 (BCMO1) is a critical enzyme involved in the conversion of β-carotene into vitamin A (retinal) in the small intestine of many vertebrates. In the present study, we investigated the regulation of human BCMO1 gene expression using human intestinal Caco-2 BBe cells.
  
  
  METHODS
  We performed electrophoretic mobility shift assays and chromatin immunoprecipitation assays to investigate the binding properties of hepatocyte nuclear factor (HNF)-1α and HNF-4α to the proximal promoter of the human BCMO1 gene. Caco-2 BBe cells were also transfected with HNF-1α and HNF-4α siRNAs, and BCMO1 gene expression levels and promoter activity were analyzed by real-time reverse transcription-polymerase chain reaction and luciferase reporter assays, respectively.
  
  
  RESULTS
  We identified overlapping binding sites for HNF-1α and HNF-4α in the human BCMO1 gene proximal promoter. Endogenous nuclear HNF-1α and HNF-4α proteins competitively bound these sites in Caco-2 BBe cells. BCMO1 gene expression levels and promoter activity were significantly decreased in HNF-1α siRNA-transfected Caco-2 BBe cells. In contrast, HNF-4α siRNA-transfected cells exhibited a significant increase in BCMO1 gene expression and promoter activity. Mutation of these overlapping binding sites dramatically decreased BCMO1 promoter activity.
  
  
  CONCLUSIONS
  Our study indicates that the competitive actions of HNF-1α and HNF-4α on their overlapping binding sites in the human BCMO1 gene promoter oppositely regulate BCMO1 gene expression in the human small intestine.
authors.affiliation: Laboratory of Nutritional Physiology, Graduate School of Human Health Sciences, University of Nagasaki Siebold, Nagasaki 851-2195, Japan.
authors.forename: Noriaki
authors.initials: N
authors.lastname: Yamaguchi
authors.affiliation: Laboratory of Nutritional Physiology, Graduate School of Nutritional and Environmental Sciences and Global COE, University of Shizuoka, Shizuoka 422-8526, Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Sunto
authors.affiliation: Laboratory of Nutritional Physiology, Graduate School of Nutritional and Environmental Sciences and Global COE, University of Shizuoka, Shizuoka 422-8526, Japan.
authors.forename: Toshinao
authors.initials: T
authors.lastname: Goda
authors.affiliation: Laboratory of Nutritional Physiology, Graduate School of Human Health Sciences, University of Nagasaki Siebold, Nagasaki 851-2195, Japan. Electronic address: suruga@sun.ac.jp.
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Suruga
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D018938:Caco-2 Cells; D005786:Gene Expression Regulation; D051538:Hepatocyte Nuclear Factor 1-alpha / Q000378:metabolism*; D051557:Hepatocyte Nuclear Factor 4 / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D050559:beta-Carotene 15,15'-Monooxygenase / Q000235:genetics*
chemical_list: C496592:HNF4A protein, human; D051538:Hepatocyte Nuclear Factor 1-alpha; D051557:Hepatocyte Nuclear Factor 4; C493358:BCO1 protein, human; D050559:beta-Carotene 15,15'-Monooxygenase
keywords: BCMO1; Caco-2 BBe cell; HNF-1α; HNF-4α; Human small intestine; Vitamin A; β-Carotene