Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
 5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cytochrome P450 2C6 (CYP2C6) is a developmentally regulated, constitutively expressed form of rat liver microsomal cytochrome P450 that in the liver of adult male rats is induced to a limited extent by phenobarbital. The gene is not expressed at detectable levels in the lung, kidney, or brain. It is expressed and inducible by phenobarbital in differentiated Reuber hepatoma cells that express many hepatocyte-specific genes but not in dedifferentiated derivatives lacking the majority of hepatocyte-specific functions. A 505-base pair proximal segment of the CYP2C6 promoter is highly efficient in driving transcription of a linked chloramphenicol acetyltransferase reporter gene in the differentiated rat hepatoma cell line FGC4, is much less effective in a related dedifferentiated variant H5, and has no measurable activity in nonhepatic C33 human cervical carcinoma cells. The activity of the CYP2C6 promoter in the differentiated hepatoma cells is strongly dependent on hepatocyte nuclear factor (HNF)3, which acts at a complex site just upstream of the TATA motif. Transactivation experiments show that the D-site-binding protein (DBP) may also contribute to CYP2C6 promoter activity, via a site that is adjacent to the proximal HNF3 site. A substantial contribution to promoter activity by the base pair -505 to -316 segment is observed in FGC4 and H5 cells but not in HepG2 cells; deletion of this segment causes a marked diminution in promoter activity only in the former two cell lines. Although footprinting experiments have permitted the definition of three protein binding sites in this region (two HNF3 and one unidentified), mutation of these sites does not diminish promoter activity. The functionally important cis sequences in this region therefore remain to be defined. In HepG2 cells the distal region does not contribute to promoter activity. This most likely accounts for the low promoter activity in HepG2 and implies a deficiency in the relevant trans-acting factor(s).
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PMID:Hepatocyte nuclear factor 3 is a major determinant of CYP2C6 promoter activity in hepatoma cells. 805 60

Cytochrome P450 (CYP) 3A23 is transcriptionally regulated in rat liver by such glucocorticoids as dexamethasone (DEX) and by such antiglucocorticoids as pregnenolone 16 alpha-carbonitrile (PCN). Based on studies of CYP3A23 gene fragments expressed in primary cultures of adult rat hepatocytes and tested for DNA-protein interactions, we have proposed that the mechanism of CYP3A23 induction by these steroid hormones involves the glucocorticoid receptor or a protein induced by glucocorticoids indirectly interacting with proteins constitutively bound to an enhancer element consisting of a direct repeat of 7-bp separated by two nucleotides in the 5'-flanking region of the CYP3A23 gene (L. Quattrochi et al., J. Biol. Chem. 270, 28,917, 1995). In the present study, we prepared and transiently expressed in cultured rat hepatocytes 20-bp double-stranded (ds)-oligonucleotides containing this direct repeat or various mutations of this direct repeat inserted into a chloramphenicol acetyltransferase (CAT) reporter plasmid. We found that both repeats were necessary for induction of CAT by either DEX or PCN. Analysis of proteins bound to CYP3A23 enhancer through the use of uv cross-linking revealed two rat liver nuclear proteins with molecular masses of approximately 130 and 100 kDa, as well as several proteins of molecular masses between 45 and 60 kDa, that specifically bind to the 20-bp ds-oligonucleotide CYP3A23 enhancer. Methylation interference assays determined that all guanine residues within the direct repeats of this oligonucleotide are important for protein binding. Mutations of these guanine residues abolished binding of nuclear proteins and eliminated DEX or PCN inducibility of CAT. These data suggest that constitutively bound proteins, interacting with the CYP3A23 enhancer possibly as a heterodimeric complex, play a role in the glucocorticoid inducibility of CYP3A23.
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PMID:Characterization of DNA-binding proteins required for glucocorticoid induction of CYP3A23. 944 12