title: Functional mapping of tissue-specific elements of the human alpha-fetoprotein gene enhancer.
abstract: Serum alpha-fetoprotein (AFP) levels in hepatocellular carcinoma (HCC) patients and expression of the protein in cultured HCC cell lines are highly variable. These observations may arise from features correlated with tissue-specific expression of the gene. Extremely strong and potent liver-specific enhancer activity is confined from -4.1 to -3.3 kb upstream to the human AFP gene in contrast with that of the rodent which exists in three widely separated regions. To understand the tissue-specific expression of AFP, we examined cis-acting elements in the enhancer. Results revealed binding sites for selected liver-enriched transcription factors (LETFs) in both domains A (-4120 to -3756 bp) and B (-3492 to -3300 bp) of the gene. These sites included: one hepatocyte nuclear factor (HNF)-1 and HNF-4, two HNF-3, and two C/EBP binding sites in domain A. An adjacent domain B contained one HNF-3 site and three C/EBP sites plus a previously identified HNF-1 site. Each of these elements alone has the ability to stimulate heterogeneous promoter activity in a dose-dependent manner when transfected into AFP producing cells. A comparative study showed that the presence of two HNF-1 and one HNF-4 site is a characteristic feature of human but not rodent AFP enhancer. The mRNA levels of the liver-enriched transcription factors (LETFs) were variable in individual HCC cell lines and together with silencer activities may underlie differential expression of the AFP gene.
authors.affiliation: Department of Biochemistry, Hokkaido University School of Medicine, Sapporo 060-8638, Japan. hnakabay@med.hokudai.ac.jp
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Nakabayashi
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Koyama
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Suzuki
authors.forename: Hong Mei
authors.initials: HM
authors.lastname: Li
authors.forename: Masaharu
authors.initials: M
authors.lastname: Sakai
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Miura
authors.forename: Norman C W
authors.initials: NC
authors.lastname: Wong
authors.forename: Shinzo
authors.initials: S
authors.lastname: Nishi
mesh_terms: D000418:Albumins / Q000096:biosynthesis / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D019556:COS Cells; D045744:Cell Line, Tumor; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D005333:Fetus / Q000378:metabolism; D040461:Gene Components / Q000235:genetics; D005786:Gene Expression Regulation / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D008099:Liver / Q000378:metabolism*; D008875:Middle Aged; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000096:biosynthesis; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D014162:Transfection; D000509:alpha-Fetoproteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism
chemical_list: D000418:Albumins; D022762:CCAAT-Enhancer-Binding Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D000509:alpha-Fetoproteins