Transcriptional regulation of basal and phenobarbital-mediated expression of rat cytochrome 2B genes
Park, Youngkyu
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Permalink
https://hdl.handle.net/2142/20367
Description
Title
Transcriptional regulation of basal and phenobarbital-mediated expression of rat cytochrome 2B genes
Author(s)
Park, Youngkyu
Issue Date
1996
Doctoral Committee Chair(s)
Kemper, Byron W.
Department of Study
Molecular and Integrative Physiology
Discipline
Molecular and Integrative Physiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Molecular
Language
eng
Abstract
Cytochromes P450 2B1 and 2B2 (CYP2B1 and CYP2B2) are well known phenobarbital inducible genes in rat liver. Potential transcriptional regulatory elements in the proximal promoter regions of rat CYP2B genes were analyzed by transfection in HepG2 cells and by binding of nuclear proteins. Deletion of sequences from $-$110 to $-$57 markedly decreased the transcriptional activity, suggesting the presence of strong cis-acting elements in this region. Sequences similar to a basal transcription element (BTE), and a Barbie box are present from $-$89 to $-$67. However, no protection was detected in these regions by DNase I footprinting assay. Instead, a region (FP1) from $-$64 to $-$45 was protected by liver nuclear extracts. Mutation of either the BTE or FP1 sequences of CYP2B1 reduced transcriptional activity in HepG2 cells. FP1 was identified as a functional CCAAT/enhancer binding proteins (C/EBP) site by cotransfection of C/EBP expression vectors and supershift assays with C/EBP antisera.
"In order to study the phenobarbital induction, the promoter activities of the CYP2B1 and the rabbit CYP2C1 genes were assayed by direct DNA injection into rat liver. Activity of promoters, $-$3500 to +1 for CYP2C1, and $-$177 to +1, and $-$1400 to +1 for CYP2B1 were not increased by treatment of animals with phenobarbital. Insertion of the CYP2B2 sequence (PBRE) from $-$2318 to $-$2155 to the 5$\sp\prime$ side of the proximal promoters conferred phenobarbital responsiveness to both promoters. Phenobarbital treatment induced the activity of the CYP2C1 promoter by 5-fold and 15-fold when one and three copies of this sequence, respectively, were inserted to the 5$\sp\prime$ side of the promoter, and insertion of one to three copies resulted in 2.5- to 5-fold phenobarbital responses for the CYP2B1 promoter. Mutation of a BTE, a C/EBP element, and a ""Barbie box"", in the CYP2B1 proximal promoter did not reduce the relative response to phenobarbital mediated by triple copies of the PBRE. These results demonstrate that direct injection of DNA into rat liver may be used to assay phenobarbital responsiveness of cytochrome P450 genes and that the distal CYP2B2 element, and not proximal promoter elements, primarily mediate the response to phenobarbital in this system."
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