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

As an initial step toward understanding the transcriptional regulation of cholesterol 7 alpha-hydroxylase (CYP7) in man, we isolated and functionally characterized the 5'-flanking region of the human CYP7 gene. The nucleotide sequences of the first exon and 1.6 kb preceding the exon were determined and found to contain a TATA box at position -30, a modified CAAT box at position -92, three potential hepatocyte nuclear factor 3 (HNF-3) recognition sites at nucleotides -316, -288, and -255, respectively, and a modified sterol response element at position -271. DNA sequences containing 1.3 kb of the 5'-flanking region and 29 nucleotides of the first exon were linked to the chloramphenicol acetyltransferase gene and transiently transfected into several cell lines. Promoter activity was very strong in the human hepatoma cell line HepG2 but absent in cells of nonhepatic origin. Mutational analysis of the promoter identified several regions that function in the transcriptional regulation of CYP7. Introduction of a fragment containing the region from -432 to -220 upstream of a heterologous promoter, in either orientation, resulted in a tremendous stimulation of activity in HepG2 cells. DNase I footprint analysis identified three regions within this fragment which were protected from digestion. The overexpression of HNF-3 in HepG2 cells resulted in a 4-fold stimulation of CYP7 transcriptional activity. We suggest that the region between -432 and -220 functions as a cell-specific enhancer whose activity is controlled, in part, by HNF-3.
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PMID:Transcriptional regulation of the human cholesterol 7 alpha-hydroxylase gene. 131 51

To investigate the importance of the 3'-untranslated region (UTR) of the mouse cholesterol 7alpha-hydroxylase (cyp7) mRNA in post-transcriptional regulation of expression of the cyp7 gene, chimaeric genes encoding mRNA containing the structural sequence of chloramphenicol acetyltransferase (CAT) linked to either the 3'-UTR of the mouse cyp7 mRNA or the SV40 early gene mRNA were constructed. The human cytomegalovirus (CMV) promoter was used to drive the expression of all the chimaeric genes. Thus the transgenes had identical sequences in the promoter, the regions encoding the 5'-UTR and translated sequence but differed in the region encoding the 3'-UTR of their respective mRNA species. The transgene containing the entire cyp7 3'-UTR (designated CMV.CAT.CYP7) gave rise to CAT activity in transfected hepatoma cells that was one-quarter of that obtained in cells transfected with the transgene containing the SV40 3'-UTR (designated CMV.CAT.SV40). The 3'-UTR of the cyp7 mRNA contains sequences resembling AU-rich elements (AREs). Deleting eight of nine putative AREs from the CYP7 3'-UTR sequence increased the CAT activity to a level greater than that observed for CMV.CAT. SV40, whereas deletion of the intron region had no effect. These results show that the AREs of the 3'-UTR of the cyp7 mRNA decrease transgene expression. Bile acids are known to repress the expression of the cyp7 gene. To test whether the 3'-UTR of the cyp7 mRNA has a role in this process, the expression of the chimaeric genes was evaluated in hepatoma cells competent for bile acid uptake. Conjugated bile acids, but not unconjugated bile acids, further decreased the expression of the CMV.CAT.CYP7 transgene. The same bile acids had no effect on the expression of the CMV.CAT.SV40 transgene. Deletion of the intron from the cyp7 sequence did not alter the CAT activity compared with the parental plasmid, and also did not alter the sensitivity of the transgene to the conjugated bile acids. Deletion of the AREs from the cyp7 3'-UTR, which increased the expression of the transgene, did not abolish the sensitivity of the transgene to repression by conjugated bile acids. Thus the 3'-UTR of the mouse cyp7 mRNA also contains elements that facilitate the further repression of transgene expression in the presence of conjugated bile acids. The results indicate that the 3'-UTR of the mouse cyp7 mRNA contains information specifying regulation at the post-transcriptional level.
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PMID:The 3'-untranslated region of the mouse cholesterol 7alpha-hydroxylase mRNA contains elements responsive to post-transcriptional regulation by bile acids. 937 93

We examined the molecular basis by which T3 regulates the human cholesterol 7alpha-hydroxylase gene (CYP7A1) promoter. L-T3 decreased chloramphenicol acetyltransferase activity in hepatoma cells cotransfected with a plasmid encoding the T3 receptor (TR) alpha [NR1a1] and a chimeric gene containing nucleotides -372 to +61 of the human CYP7A1 gene fused to the chloramphenicol acetyltransferase structural gene. Deoxyribonuclease I footprinting revealed that recombinant TRalpha protected two regions in this segment of the human CYP7A1 gene promoter. In EMSAs, TRalpha bound to both regions. The binding was competed by oligonucleotides bearing an idealized TRalpha binding motif and abolished by mutation of these elements. In assays of promoter function, mutation of only one of the TRalpha binding sites blocked repression by T3. The results indicate that T3-dependent repression of human CYP7A1 gene expression is mediated via a novel site in the human CYP7A1 gene promoter.
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PMID:A distinct thyroid hormone response element mediates repression of the human cholesterol 7alpha-hydroxylase (CYP7A1) gene promoter. 1177 35