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)

The isolation and characterization of the rat genomic clone encoding the cholesterogenic enzyme farnesyl diphosphate (FPP) synthase is reported. The gene is localized on a 15-kilobase (kb) genomic fragment, spans approximately 12 kb and contains eight exons. Sequences containing from 3.9 kb to 132 base pairs (bp) of the putative promoter were joined to the coding region of the bacterial reporter gene chloramphenicol acetyltransferase (CAT). The CAT activities or CAT mRNA levels of the hybrid genes were determined following either transient transfections into human hepatoma HepG2 cells or stable transfections into Chinese hamster ovary cells. The transient transfections identified a 319-bp fragment that was required for a 4-fold induction in the absence of sterols. Sequence analysis of this region showed it contained five potential copies of the sterol regulatory element (SRE-1) (Smith, J.R., Osborne, T.F., Brown, M.S., Goldstein, J.L., and Gil, G. (1988) J. Biol. Chem. 263, 18480-18487) previously identified in the promoters of the 3-hydroxy-3-methyl-coenzyme A (HMG-CoA) reductase, HMG-CoA synthase, and low density lipoprotein receptor genes. Further mutational and deletion analysis of the FPP synthase promoter-CAT constructs followed by stable transfection and primer extension of the CAT mRNA levels indicated that these potential SRE-1 regulatory elements were not involved in the sterol-mediated transcriptional regulation of the gene. Our analyses have identified a 115-bp region that is required for the transcriptional induction of FPP synthase in the absence of sterols. These results suggest that the FPP synthase gene may be regulated at the transcriptional level by a different mechanism than other sterol regulated genes.
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PMID:Molecular cloning and promoter analysis of the rat liver farnesyl diphosphate synthase gene. 132 Nov 49

Through substitution mutagenesis we identified the promoter elements responsible for basal expression and sterol-mediated repression of transcription of the gene for 3-hydroxy-3-methylglutaryl coenzyme A reductase, a rate-controlling enzyme of cholesterol biosynthesis. Mutant promoters containing 277 base pairs (bp) of reductase 5' flanking sequence were inserted into recombinant plasmids upstream of the coding region for bacterial chloramphenicol acetyltransferase. The plasmids were transfected into hamster fibroblasts, and transcription was measured in the presence and absence of sterols. Mutations in three regions that are known to bind nuclear proteins markedly reduced transcription. Mutation of another protein-binding region of 20 bp in length did not reduce transcription, but it did abolish sterol-mediated repression, producing an operator constitutive phenotype. This mutation also abolished protein binding to the corresponding 20-bp region of DNA as determined by footprinting assays. When a DNA fragment containing these 20 bp was inserted into the herpes simplex virus thymidine kinase promoter, sterol-mediated repression was observed. This sequence contains an octanucleotide that shows a 7/8-bp match with a previously identified regulatory sequence in repeat 2 of the low density lipoprotein receptor promoter, another sterol-repressible gene. We hypothesize that this octanucleotide, GTGGCGGTG, is the core binding site for a sterol-dependent protein that represses transcription.
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PMID:Operator constitutive mutation of 3-hydroxy-3-methylglutaryl coenzyme A reductase promoter abolishes protein binding to sterol regulatory element. 334 49

The low density lipoprotein receptor is encoded by a "housekeeping" gene that is transcribed in most mammalian cells and is subject to negative feedback regulation by sterols. To determine the basis for this regulated expression, we performed a transfection analysis with hybrid genes containing up to 6500 base pairs of 5' flanking DNA from the low density lipoprotein receptor gene fused to the coding region of the bacterial chloramphenicol acetyltransferase gene. These studies identified a 177-base pair fragment of 5' flanking DNA that is sufficient for expression as well as negative regulation by sterols. The positive elements within this region were further defined by analysis of a series of 15 mutations in which overlapping 10-base pair segments were scrambled by site-specific mutagenesis. These studies identified the positive elements as three imperfect direct repeats of 16 base pairs and a TATA-like sequence. The three repeats contain a sequence that is homologous to the consensus DNA sequence recognized by transcription factor Sp1.
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PMID:Three direct repeats and a TATA-like sequence are required for regulated expression of the human low density lipoprotein receptor gene. 361 Oct 89

Oncostatin M (OM), a cytokine produced by macrophages and activated T cells, has been shown to be a potent inducer of liver low density lipoprotein receptor (LDLR) activity by increasing LDL uptake and cell surface LDLR number in HepG2 cells. To investigate whether OM regulates the transcription of the LDLR gene and if the effect is independent of the sterol pathway, we examined the effects of OM on the promoter activity of the LDLR gene and the expression of LDLR mRNA. HepG2 cells were transfected with hybrid genes containing three different lengths of DNA fragments from the 5' flanking region of the LDLR gene that were fused to the coding region of the chloramphenicol acetyltransferase (CAT) gene. OM induced an approximately 3-fold increase in CAT activities in pLDLR-CAT vector-transfected cells that were incubated in lipoprotein-depleted medium and a 6-fold increase in CAT activities when the transfected cells were treated with sterols. OM stimulated similar increases in CAT activities in HepG2 cells transfected with pLDLR-CAT 234, pLDLR-CAT 1563, and pLDLR-CAT 6500, suggesting that the essential cis-acting element that mediates the OM effect is located within the 177 base pairs upstream of the transcription start site of the LDLR gene. Examination of the regulation of the endogenous LDLR mRNA expression by OM gave results similar to those in transfected cells. OM increased the levels of mRNA of LDLR, regardless of the presence or absence of lipoprotein and sterols. These data suggest that the up-regulation of the LDLR by OM is at the transcriptional level through a nonsterol mediated mechanism.
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PMID:Oncostatin M activates low density lipoprotein receptor gene transcription in sterol-repressed liver cells. 769 81