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)

Transgenic mouse lines were established bearing tandem arrays of a fusion construct comprising the promoter region of a housekeeping gene, HMGCR, encoding 3-hydroxy 3-methylglutaryl CoA reductase, linked to a bacterial cat reporter gene encoding chloramphenicol acetyltransferase (CAT). CAT activity was observed in all transgenic mouse tissues examined. The methylation state of the fusion transgene was determined. In non-transgenic mice the endogenous HMGCR promoter is devoid of methylation while flanking regions are extensively modified. In HMGCR-cat transgenic mice the fusion gene promoter was found to be similarly hypomethylated. However, the extent of hypomethylation varied with copy number: methylation-free status was progressively lost with increasing transgene copy number. Further transgenic mouse lines were constructed carrying a truncated HMGCR regulatory region linked to cat. Transgene expression and hypomethylation were observed in testis but not in any other tissue, and testis-specific methylation-free status was also lost at high copy number. Loss of hypomethylation at high copy number may indicate that saturable DNA-binding factors normally protect the HMGCR promoter from methylation.
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PMID:The methylation-free status of a housekeeping transgene is lost at high copy number. 221 Mar 79

Regulation of the expression of 3-hydroxy-3-methyglutaryl coenzyme A (HMG-CoA) reductase is a critical step in controlling cholesterol synthesis. Previous studies in cultured Chinese hamster ovary cells have shown that HMG-CoA reductase is transcribed from a cholesterol-regulated promoter to yield a heterogeneous collection of mRNAs with 5' untranslated regions of 68 to 670 nucleotides in length. Synthesis of these molecules is initiated at multiple sites, and multiple donor sites are used to excise an intron in the 5' untranslated region. In the current paper, I report that human HMG-CoA reductase gene resembles the Chinese hamster gene in having multiple sites of transcription initiation that are subject to suppression by cholesterol. The human gene differs from the hamster gene in that a single donor splice site is used to excise the intron in the 5' untranslated region. All of the resulting RNAs have short 5' untranslated regions of 68 to 100 nucleotides. This difference in the splicing pattern of the first intron is species specific and not a peculiarity of cultured cells in that HMG-CoA reductase mRNAs from Syrian hamster livers resemble those of the cultured Chinese hamster ovary cells. Comparison of the DNA sequences of the HMG-CoA reductase promoters from three different species--humans, Syrian hamsters, and Chinese hamsters--shows a highly conserved region of 179 nucleotides that extends from 220 to 42 nucleotides upstream of the transcription initiation sites. This region is 88% identical between the human and Chinese hamster promoter. When fused to the coding region of the Escherichia coli chloramphenicol acetyltransferase gene, this highly conserved region of the reductase gene directs the cholesterol-regulated expression of chloramphenicol acetyltransferase in transfected hamster cells, further indicating the interspecies conservation of the regulatory elements.
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PMID:Conservation of promoter sequence but not complex intron splicing pattern in human and hamster genes for 3-hydroxy-3-methylglutaryl coenzyme A reductase. 303 37

Cholesterol homeostasis is maintained by feedback inhibition of transcription of the gene encoding HMG CoA reductase. To study this mechanism, we joined the 5' end of the hamster reductase gene to the coding region for chloramphenicol acetyltransferase (CAT). The chimeric gene produced high levels of CAT activity in mouse L cells; sterols suppressed expression by 70% to 90%. Sequences responsible for both promotion and inhibition of transcription were distributed over 500 bp extending 300 bp upstream of the reductase transcription initiation sites. Any sizable deletion within this region decreased CAT expression in vivo and CAT mRNA transcription in vitro. This region contains five hexanucleotide repeats (CCGCCC or GGGCGG) that occur in promoters of viral and cellular housekeeping genes. Every reductase-CAT plasmid that showed transcriptional activity also showed inhibition by sterols, indicating that the sites for promotion and inhibition of transcription are closely associated.
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PMID:5' end of HMG CoA reductase gene contains sequences responsible for cholesterol-mediated inhibition of transcription. 386 Mar 1

We studied the effect of the coffee diterpene alcohols, cafestol and kahweol, on cholesterol metabolism in HepG2 cells. Uptake of 125I-tyramine cellobiose-labeled LDL was decreased by 15% to 20% (P < .05) after 18 hours of preincubation with cafestol (20 micrograms/mL), whereas 25-hydroxycholesterol reduced uptake by 55% to 65% (P < .05). Degradation of LDL in the presence of cafestol was decreased by 20% to 30% (P < .05) under the same conditions. The effect of cafestol (20 micrograms/mL) on uptake and degradation of LDL was greatest (35% to 40%, P < .05) after 6 and 10 hours of preincubation, respectively. Furthermore, the effect of cafestol was also dependent on its concentration, and a significant decrease in the LDL uptake (19%) was observed at 10 micrograms/mL (P < .05). Specific binding of LDL was reduced by 17% (P < .05) and 60% (P < .05) after preincubation with cafestol (20 micrograms/mL) and 25-hydroxycholesterol (5 micrograms/mL) for 6 hours, respectively, compared with control cells. Analysis of LDL binding showed that cafestol reduced the number of binding sites for LDL on the cell surface (capacity) by 35% (P < .05). In contrast, no significant effect on the level of mRNA for the LDL receptor was observed after incubation with cafestol, whereas 25-hydroxycholesterol reduced the mRNA level for the LDL receptor by 40% to 50% (P < .05). A fusion gene construct consisting of a synthetic sterol regulatory element-1 (SRE-1) promoter for the human LDL receptor coupled to the reporter gene for chloramphenicol acetyltransferase (CAT) was transfected into HepG2 cells. No change was observed in CAT activity in SRE-1-transfected cells after incubation with cafestol, whereas 25-hydroxycholesterol reduced CAT activity by 30% to 40% (P < .05). Incorporation of [14C]acetate into unesterified cholesterol and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity were unaffected in cells incubated with cafestol as well as the cafestol-kahweol mixture compared with control cells. Moreover, cafestol and the cafestol-kahweol mixture did not promote increased incorporation of radiolabeled [14C]oleic acid into cholesteryl esters after short-term incubation compared with control cells. On the other hand, 25-hydroxycholesterol caused a 70% to 90% reduction of cholesterol synthesis (P < .05) and HMG-CoA reductase activity (P < .05), decreased HMG-CoA reductase mRNA level by 70% to 80% (P < .05), and promoted a twofold increase in cholesterol esterification (P < .05). Finally, no effect of the coffee diterpenes on bile acid formation was observed. These results suggest that cafestol (and kahweol) may reduce the activity of hepatic LDL receptors and thereby cause extracellular accumulation of LDL.
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PMID:Effect of coffee lipids (cafestol and kahweol) on regulation of cholesterol metabolism in HepG2 cells. 935 83