Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 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

We report the isolation and nucleotide sequence of the human farnesyl pyrophosphate synthetase cDNA, an enzyme in the cholesterogenic pathway. Partial cDNAs for the human farnesyl pyrophosphate synthetase were isolated by screening human hepatoma (HepG2) and placental cDNA libraries with the rat liver cDNA for farnesyl pyrophosphate synthetase as a probe. Anchored polymerase chain reaction was used to isolate the 5'-end of the cDNA. The nucleotide sequence of the human farnesyl pyrophosphate synthetase cDNA has high identity (86%) to the rat liver cDNA. Treatment of the human monocytic leukemia cell line THP-1 with phorbol esters led to 2--7-fold increases in mRNA concentrations for the three cholesterogenic enzymes, farnesyl pyrophosphate synthetase, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, and HMG-CoA synthase within 5 h. Immunoprecipitation of radiolabeled cells demonstrated that there was a corresponding increase in the rate of synthesis of all three proteins. The addition of cycloheximide to cells also led to increases in the mRNA concentrations of the three enzymes. Treatment of cells with phorbol esters and cycloheximide resulted in superinduction of all three mRNAs; HMG-CoA synthase mRNA levels increased 35-fold, farnesyl pyrophosphate synthetase 17-fold, and HMG-CoA reductase 16-fold 5 h after treatment. The mRNA levels returned to pretreatment levels by 20 h. Cells were also preincubated in the presence of a lipoprotein-deficient fraction of serum plus mevinolin to induce the levels of the three mRNAs. Addition of phorbol esters and cycloheximide to these derepressed cells led to further increases in the mRNA levels for all three enzymes. These results are consistent with the hypothesis that THP-1 cells contain a short-lived negative transcription factor which regulates transcription of the FPP synthetase, HMG-CoA reductase, and HMG-CoA synthase genes. Phorbol esters also regulate these same genes, presumably by modifying a common negative transcription factor and/or by inducing a positive transcription factor(s).
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PMID:Isolation and sequence of the human farnesyl pyrophosphate synthetase cDNA. Coordinate regulation of the mRNAs for farnesyl pyrophosphate synthetase, 3-hydroxy-3-methylglutaryl coenzyme A reductase, and 3-hydroxy-3-methylglutaryl coenzyme A synthase by phorbol ester. 196 62

Human hepatoma HepG2 cells were used to demonstrate coordinate regulation of three enzymes of cholesterol synthesis under a variety of conditions. Addition of either delipidized serum and mevinolin or low density lipoprotein, 25-hydroxycholesterol, or mevalonic acid to HepG2 cells resulted in rapid changes both in the levels of the mRNAs and in the rates of synthesis of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) synthase, HMG-CoA reductase, and farnesyl pyrophosphate synthetase (prenyltranferase). In all cases, the changes in mRNA levels were paralleled by changes in the rates of specific protein synthesis. Pulse-chase techniques were used to determine the half-lives of all three proteins. Addition of low density lipoprotein to the media during the chase increased the rate of degradation of HMG-CoA reductase 4.6-fold but had no affect on the half-lives of HMG-CoA synthase or prenyltransferase. Therefore, we conclude that the coordinate regulation of these three enzymes under a variety of conditions occurs at the level of enzyme synthesis and not at the level of protein stability.
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PMID:Coordinate regulation of 3-hydroxy-3-methylglutaryl-coenzyme A synthase, 3-hydroxy-3-methylglutaryl-coenzyme A reductase, and prenyltransferase synthesis but not degradation in HepG2 cells. 256 58

Cellular processes responsible for maintaining cholesterol homoeostasis are highly regulated. To determine whether two of these processes, cholesterol biosynthesis and receptor-mediated uptake of low-density lipoprotein (LDL), are co-ordinately regulated in human liver, we employed a human hepatoma cell line (HepG2) and measured the accumulation of mRNA for LDL receptor, 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase and HMG-CoA synthase under a variety of conditions. Genomic Southern-blot analysis demonstrated that the integrity of these genes is maintained in the transformed cell. Treatment of HepG2 cells with mevalonate, 25-hydroxycholesterol, LDL, lovastatin or miconazole resulted in a similar effect on the accumulation of all three mRNAs at the concentrations tested. The onset of the response to drug, whether repression or induction of mRNA accumulation, occurred after approximately the same period of exposure for each mRNA. We conclude that the expression of the LDL receptor, HMG-CoA reductase and HMG-CoA synthase is co-ordinately regulated in HepG2 cells.
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PMID:Co-ordinate regulation of low-density-lipoprotein receptor and 3-hydroxy-3-methylglutaryl-CoA reductase and synthase gene expression in HepG2 cells. 256 63

The mitochondrial 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase gene is expressed in a limited set of tissues in the adult rat. Methylation of the 5' flanking region of the gene in vitro leads to its transcriptional inactivation when transfected in hepatoma-derived cell lines. In liver and kidney, expression of the gene correlates inversely with its degree of methylation, indicating that the methylation of the 5' flanking region and the first exon of the gene may be one of the factors responsible for the repression of its transcription. During the fetal/neonatal transition, a process of selective undermethylation of specific sites takes place in the 5' flanking region of the mitochondrial HMG-CoA synthase gene. Moreover, treatment with the hypomethylating agent 5-azacytidine of a hepatoma-derived cell line that presents barely detectable levels of mitochondrial HMG-CoA synthase mRNA leads to a significant increase in the mRNA levels. These results point to methylation as one of the regulatory mechanisms that operate on the mitochondrial HMG-CoA synthase gene.
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PMID:Methylation of the regulatory region of the mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase gene leads to its transcriptional inactivation. 769 71

Mitochondrial 3-hydroxy-3-methylglutaryl-coenzyme-A (HMG-CoA) synthase, a liver-specific enzyme, is a constituent of the HMG-CoA cycle responsible for ketone-body synthesis. We report the isolation and characterization of genomic clones that encompass the gene for rat mitochondrial HMG-CoA synthase. The gene spans at least 24 kbp and contains ten exons and nine introns. The 5' flanking region of the gene has also been cloned and characterized. Exon 1 contains the untranslated sequence of the transcript, extending downstream to enclose the coding region for the putative mitochondrial-targeting signal (35 amino acids). The 1149-bp proximal region of the transcription start point permits transcription of a reporter gene in transfected hepatoma cells but not in an extrahepatic cell line, confirming the function of the promoter. A truncated construct of 142 bp is still able to promote transcription in hepatoma cells, suggesting the presence of liver-specific enhancer elements in the proximal promoter region. The 5' flanking region contains typical promoter elements, including a TATA box and several putative recognition sequences for transcription factors involved in controlling both basal-level and hormone-modulated transcription rates. Furthermore, the presence in the mitochondrial HMG-CoA-synthase promoter of cis-elements, responsible for the multihormonal regulation of transcription, is supported by transient transfection experiments.
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PMID:The rat mitochondrial 3-hydroxy-3-methylglutaryl-coenzyme-A-synthase gene contains elements that mediate its multihormonal regulation and tissue specificity. 809 64

The chicken ovalbumin upstream-promoter transcription factor (COUP-TF) has a dual effect on the regulation of the mitochondrial 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase gene. COUP-TF could act as a transcriptional activator or repressor of this gene through different DNA sequences. COUP-TF induces expression of a reporter gene linked to the mitochondrial HMG-CoA synthase gene promoter in human hepatoma HepG2 cells, but represses it in a Leydig tumour cell line (R2C); in both these cell lines the expression of the mitochondrial HMG-CoA synthase gene mimics that of liver and testis. The activation is promoted by a fragment of the gene from coordinates -62 to +28, which contains a GC box and a TATA box, and where no COUP-TF binding site was observed by in vitro DNA binding studies. On the other hand, the COUP-TF inhibitory effect is mainly due to repression of peroxisome-proliferator-activated receptor-dependent activation of the gene, interacting with the region from -104 to -92. To our knowledge this work represents the second example of a target gene for COUP-TF I that could be either activated or repressed by the action of this receptor through different DNA sequences of the same gene.
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PMID:Chicken ovalbumin upstream-promoter transcription factor (COUP-TF) could act as a transcriptional activator or repressor of the mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase gene. 929 Nov 36

Lifibrol (4-(4'-tert. butylphenyl)-1-(4'-carboxyphenoxy)-2-butanol) is a new hypocholesterolemic compound; it effectively lowers low density lipoprotein (LDL) cholesterol. We studied the effects of lifibrol on the cholesterol metabolism of cultured cells. In the hepatoma cell line HepG2, Lifibrol decreased the formation of sterols from [14C]-acetic acid by approximately 25%. Similar to lovastatin, lifibrol had no effect on the synthesis of sterols from [14C]-mevalonic acid. Lifibrol did not inhibit 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase. Instead, cholesterol synthesis inhibition by lifibrol was entirely accounted for by competitive inhibition of HMG-CoA synthase. Lifibrol enhanced the cellular binding, uptake, and degradation of LDL in cultured cells in a dose dependent fashion. The stimulation of LDL receptors was significantly stronger than expected from the effect of lifibrol on sterol synthesis. In parallel, lifibrol increased the amount of immunologically detectable receptor protein. Stimulation of LDL receptor mediated endocytosis was observed both in the presence and in the absence of cholesterol-containing lipoproteins. In the absence of an extracellular source of cholesterol, both lifibrol and lovastatin induced microsomal HMG-CoA reductase. Co-incubation with LDL was sufficient to suppress the lifibrol mediated increase in reductase activity, indicating that lifibrol does not affect the production of the non-sterol derivative(s) which are thought to regulate HMG-CoA reductase activity at the post-transcriptional level. Considered together, the data suggest that the hypolipidemic action of lifibrol may, at least in part, be mediated by sterol-independent stimulation of the LDL receptor pathway. A potential advantage of lifibrol is that therapeutic concentrations do not interfere with the production of mevalonate which is required not only to synthesize sterols but also as a precursor of electron transport moieties, glycoproteins and farnesylated proteins.
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PMID:The effects of lifibrol (K12.148) on the cholesterol metabolism of cultured cells: evidence for sterol independent stimulation of the LDL receptor pathway. 1105 1

Peroxisome proliferation is a well-defined pleiotropic effect that is mediated by the ligand inducible transcription factor peroxisome proliferator-activated receptor (PPAR) alpha. Because marked peroxisome proliferation occurs in rodents but not in humans, we aimed to elucidate the molecular and cellular determinants of this species-specificity in hepatocytes. Analysis of peroxisomal marker enzyme activities confirmed that peroxisome proliferators induced acyl-CoA oxidase (ACOX) and to a lesser extent catalase in rat hepatocytes, but not in human hepatoma HepG2 cells. Transient transfection assays revealed that ciprofibrate and Wy 14,643 induced rat but not human PPARalpha-mediated reporter gene activity in rat FAO and primary hepatocytes on rat but not on human PPARalpha response elements (PPREs). In contrast, in human HepG2 and primary human hepatocytes, peroxisome proliferators did not induce either human or rat PPARalpha activity regardless of rat or human PPRE sequences. In addition, no induction of ACOX gene expression was observed in human hepatocytes independent of the expression level of human PPARalpha. Remarkably, no distinct peroxisome proliferation related responses were observed in human hepatocytes when rat PPARalpha was transfected, although human hepatocytes were responsive to PPARalpha-mediated induction of carnitine palmitoyl transferase-1A and 3-hydroxy-3-methylglutaryl-CoA synthase. These results confirmed that PPARalpha and PPREs are important determinants for the species-specificity of peroxisome proliferation. Nevertheless, our results showed that human hepatocytes limit the extent of peroxisome proliferation regardless of PPARalpha expression.
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PMID:Characterization of the species-specificity of peroxisome proliferators in rat and human hepatocytes. 1497 57

In rats, oxidized fats activate the peroxisome proliferator-activated receptor alpha (PPARalpha), leading to reduced triglyceride concentrations in liver, plasma and very low density lipoproteins. Oxidation products of linoleic acid constitute an important portion of oxidized dietary fats. This study was conducted to check whether the primary lipid peroxidation product of linoleic acid, 13-hydroperoxy-9,11-octadecadienoic acid (13-HPODE), might be involved in the PPARalpha-activating effect of oxidized fats. Therefore, we examined the effect of 13-HPODE on the expression of PPARalpha target genes in the rat Fao and the human HepG2 hepatoma cell lines. In Fao cells, 13-HPODE increased the mRNA concentration of the PPARalpha target genes acyl-CoA oxidase (ACO), cytochrome P450 4A1 and carnitine-palmitoyltransferase 1A (CPT1A). Furthermore, the concentration of cellular and secreted triglycerides was reduced in Fao cells treated with 13-HPODE. Because PPARalpha mRNA was not influenced, we conclude that these effects are due to an activation of PPARalpha by 13-HPODE. In contrast, HepG2 cells seemed to be resistant to PPARalpha activation by 13-HPODE because no remarkable induction of the PPARalpha target genes ACO, CPT1A, mitochondrial HMG-CoA synthase and delta9-desaturase was observed. Consequently, cellular and secreted triglyceride levels were not changed after incubation of HepG2 cells with 13-HPODE. In conclusion, this study shows that 13-HPODE activates PPARalpha in rat Fao but not in human HepG2 hepatoma cells.
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PMID:Differential action of 13-HPODE on PPARalpha downstream genes in rat Fao and human HepG2 hepatoma cell lines. 1621 87


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