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KMID : 0617219970080010081
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Duksung Bulletin Phamaceutical Sciences
1997 Volume.8 No. 1 p.81 ~ p.88
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Regulation of the Constitutive Expression of the Human CYP1A2 Gene
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CHUNG INJAE
Edward Bresnick
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Abstract
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Cytochorome P4501A2(CYP1A2) is a member of the cytochrome P450 family that is involved in phase I drug metabolism in vertebrates. To understand how the constitutive expression of the human CYP1A2 gene is regulated, its 5´flanking region was analyzed. The promother activity of a human CYP1A2 gene sequence[base pairs(bp)-3203 to + 58bp] was measured in transiently transfected HepG2 cells using fusion constructs containing the luciferase reporter gene. Using 5´-end deletion analysis, two functionally important cis elements, i.e., a proximal 42-bp DNA from bp -72 to bp -31 and a distal 259-bp DNA from bp -2352 to bp -2094, were identified. The proximal sequence (bp -72 to -31) contained CCAAT and GC boxes, with which well characterized transcription factors such as nuclear factor-1/CCAAT transcription factor and simian virus 40 promoter factor-1 could interact. With regard to the 259-bp fragment (bp -2352 to bp -2094), gel mobility shift analyses with HepG2 nuclear lysates indicated high affinity, specific interactions of several trans-acting factors. Three protein binding sites within the 259-bp fragment were identified by DNasel footprinting analysis; these sites contained activator protein-1, nuclear factor-E1.7, and one-half hepatic nuclear factor-1(HNF-1)binding consensus sequences. Only the region from bp -2124 to bp -2098, in which the HNF-1 binding site was located, was markedly protected by a HepG2 nuclear extract, compared with a MCF7 human breast cancer nuclear extract. These results suggested that the 259-bp DNA fragment contained positive regulator binding sites and HNF-1 could contribute to the liver-specific expression of human CYP1A2.
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KEYWORD
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