Functional mapping of tissue-specific elements of the human alpha-fetoprotein gene enhancer.
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.
Nakabayashi
Hidekazu
H
Department of Biochemistry, Hokkaido University School of Medicine, Sapporo 060-8638, Japan. hnakabay@med.hokudai.ac.jp
Koyama
Yoshikazu
Y
Suzuki
Hiroshi
H
Li
Hong Mei
HM
Sakai
Masaharu
M
Miura
Yutaka
Y
Wong
Norman C W
NC
Nishi
Shinzo
S
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
D000418:Albumins; D022762:CCAAT-Enhancer-Binding Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D000509:alpha-Fetoproteins