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)

Peroxisome proliferators (PPs) are potent tumor promoters in rodents. The mechanism of hepatocarcinogenesis requires the nuclear receptor peroxisome proliferator activated receptor-alpha (PPARalpha), but might also involve the PPARalpha independent alteration of signaling pathways that regulate cell growth. Here, we studied the effects of PPs on the mevalonate pathway, a critical pathway that controls cell proliferation. Liver X receptors (LXRs) are nuclear receptors that act as sterol sensors in the mevalonate pathway. In gene reporter assays in COS-7 cells, the basal activity of the LXR responsive reporter gene (LXRE-luc) was suppressed by 10 microM lovastatin and zaragozic acid A, suggesting that this activity was attributed to the activation of native LXRs, by endogenously produced mevalonate products. The potent PP and rodent tumor promoter, pirinixic acid (WY-14643) also inhibited LXR-mediated transcription in a dose related manner (approximate IC(50) of 100 microM). As did several other PPs including ciprofibric acid and mono-ethylhexylphthalate. Polyunsaturated and medium to long chain fatty acids at 100 microM were also potent inhibitors; the arachidonic acid analogue eicosatetraynoic acid being the most active (approximate IC(50) of 10 microM). Of the PPs and fatty acids tested, there was a strong correlation between the ability of these agents to suppress de novo sterol synthesis in a rat hepatoma cell line, H4IIEC3, and inhibit LXR-mediated transcription in COS-7 cells, but a discordance between these endpoints and PPARalpha activation and fatty acid acyl-CoA oxidase induction. Taken together, these results suggest that PPs and fatty acids negatively regulate the mevalonate pathway through a mechanism that is not entirely dependent on PPARalpha activation. Because of the importance of the mevalonate pathway in regulating cell proliferation, the modulation of this pathway by PPs and fatty acids might contribute to their actions on cell growth/differentiation.
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PMID:Peroxisome proliferators and fatty acids negatively regulate liver X receptor-mediated activity and sterol biosynthesis. 1135 75

A non-radioactive in situ hybridization (ISH) protocol for localization of mRNAs encoding peroxisomal proteins in hepatoma cell lines from humans (HepG2) and rats (MH1C1) is presented. In comparison to a similar procedure reported for tissue sections, the cell culture preparations require only brief fixation in 4% paraformaldehyde and their permeabilization is achieved by a very low concentration (1 microg/ml) of proteinase K. The exclusive localization of transcripts in the cytoplasm of hepatoma cells with the absence of nuclear staining and the completely negative sense controls confirm the specificity of the method. The marked differences in signal intensity between the results of albumin and beta-actin mRNAs which are of high abundance in contrast to moderate to low abundance of peroxisomal mRNAs show the high sensitivity and the wide range of applicability of our protocol. This is also confirmed by divergent results of treatment of hepatoma cell lines with clofibrate and cetaben on mRNA levels of catalase and acyl-CoA oxidase. The ISH results of drug treatment of cell lines are confirmed also by slot blot analysis of total RNA extracts using 32P-labeled probes. Thus the protocol presented here provides a sensitive tool for ISH localization of mRNAs encoding peroxisomal proteins. In combination with immunocytochemistry it may be useful to monitor intercellular differences in expression levels of specific mRNAs in correlation with the abundance of structurally divergent forms of peroxisomes (tubular versus spherical) and their importance in the biogenesis of peroxisomes.
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PMID:Localization of mRNAs encoding peroxisomal proteins in cell culture by non-radioactive in situ hybridization. Comparison of rat and human hepatoma cells and their responses to two divergent hypolipidemic drugs. 1145 50

Human HepG2 and rat MH1C1 hepatoma cell lines were examined for their response to cetaben, an exceptional type of peroxisome proliferator. Shape change and proliferation of peroxisomes as well as induction of selected peroxisomal enzymes catalase, acyl-CoA oxidase, and peroxisomal bifunctional enzyme, were assessed in response to cetaben. In MH1C1 cells, peroxisomes were seen in clusters displaying typical features of microperoxisomes. Cetaben caused little but reversible proliferation and morphological heterogeneity with the occurrence of dumbbell-shaped and cup-shaped peroxisomal profiles. Peroxisomes in HepG2 cells showed marked variation in size and shape. Cetaben treatment of HepG2 cells caused disintegration of Golgi regions and augmented mitochondrial matrix. Interestingly, MH1C1 cells showed different subunit composition of acyl-CoA oxidase in immunoblot analysis: only subunit A at 72 kDa was detected but not the cleavage products. In situ hybridization underlined the marked morphological heterogeneity observed, and both cell lines revealed different stages of gene expression. Our results indicate that cetaben represents an extraordinary type of peroxisomal proliferator with pleiotropic effects on human and rat hepatoma cells, and, at least in the human hepatoma cell line HepG2, these effects are not restricted to peroxisome proliferation.
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PMID:Cetaben-induced changes on the morphology and peroxisomal enzymes in MH1C1 rat hepatoma cells and HepG2 human hepatoblastoma cells. 1145 51

Hepatic steatosis and hepatocellular carcinoma (HCC) are common and serious features of hepatitis C virus (HCV) infection, and the core protein has been shown to play distinct roles in the pathogenesis. Here we report the direct interaction of HCV core protein with retinoid X receptor alpha (RXRalpha), a transcriptional regulator that controls many aspects of cell proliferation, differentiation, and lipid metabolism. The core protein binds to the DNA-binding domain of RXRalpha, leading to increase the DNA binding of RXRalpha to its responsive element. In addition, RXRalpha is activated in cells expressing the core protein as well as in the livers of the core-transgenic mice that would develop hepatic steatosis and HCC later in their lives. Using promoter genes of cellular retinol binding protein II (CRBPII) and acyl-CoA oxidase as reporters, we also show that the expression of the core protein enhances the transcriptional activity regulated by the RXRalpha homodimer as well as by the heterodimer with peroxisome proliferator activated receptor alpha. Furthermore, expression of the CRBPII gene is also up-regulated in the livers of HCV core-transgenic mice. In conclusion, these results suggest that modulation of RXRalpha-controlled gene expression via interaction with the core protein contributes to the pathogenesis of HCV infection.
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PMID:Interaction of hepatitis C virus core protein with retinoid X receptor alpha modulates its transcriptional activity. 1191 42

We examined the effect of dietary conjugated linoleic acid (CLA) on the growth of injected hepatoma dRLh-84 in Donryu rats. After experimental diets containing 0% or 2% CLA were given to male Donryu rats for 3 wk, dRLh-84 cells were injected into the left lobe of the hepatic capsule, and the experimental diet was continued. The cells formed a solid tumor > or = 1 wk after the injection, and thereafter the tumor grew with feeding duration. In a morphological study, this tumor appeared to be a low-differentiated hepatoma, and there was no remarkable difference in the morphology of the tumor between 0% and 2% CLA groups. Tumor weight was significantly higher in the 2% CLA group than in the 0% CLA group throughout the feeding period after the injection. Serum glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase activities were significantly higher in 2% CLA-injected rats than in 0% CLA-injected rats at 3 wk after the injection. CLA upregulated acyl-CoA oxidase activity, especially 1 wk after the injection. However, dietary CLA did not activate carnitine palmitoyl transferase II, which is a rate-limiting enzyme in the mitochondrial beta-oxidation pathway. Natural killer cell activity in the spleen tended to be higher in injected rats, but a significant effect of dietary CLA was not recognized. Serum interferon-gamma and tumor necrosis factor-alpha levels were higher in injected than in sham rats. Moreover, these levels were higher in 2% CLA groups than in the respective 0% CLA groups.
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PMID:Effect of dietary conjugated linoleic acid on the in vivo growth of rat hepatoma dRLh-84. 1196 49

Fatty acyl-CoA oxidase null mice (AOX-/-) develop hepatocellular carcinomas in 100% of animals between 10 and 15 months. We evaluated spontaneously developed HCC in AOX-/- mice for PPARalpha, PPARalpha regulated genes and peroxisome volume density and compared with adjacent non-neoplastic liver and liver in wild-type (AOX+/+) and heterozygous (AOX+/-) mice. The level of PPARalpha mRNA was 2.5-fold higher in HCC compared to the adjacent liver. mRNAs of PPARalpha regulated genes such as peroxisomal bifunctional enzyme, thiolase, cytochrome P450 CYP4A1 and CYP4A3 were similar in HCC and adjacent liver and increased by 7- to 22-fold compared with wild-type and heterozygous mice. Immunoblot analysis of HCC showed high amounts of PPARalpha, peroxisomal bifunctional enzyme and thiolase. Electron microscopic examination revealed 3.8 and 8.3-fold increase in the volume density of peroxisomes in HCC and adjacent liver, respectively, compared to the volume density in wild-type mice. These results demonstrate that spontaneously developed HCC in AOX-/- mice display a similar type of pleiotropic responses to high levels of PPARalpha ligands as the non-neoplastic liver. The changes observed in HCC and adjacent liver in AOX-/- mice were identical to those observed in rats and mice exposed to peroxisome proliferators.
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PMID:Expression of peroxisome proliferator-activated receptor alpha, and PPARalpha regulated genes in spontaneously developed hepatocellular carcinomas in fatty acyl-CoA oxidase null mice. 1242 65

Chemicals known as peroxisome proliferators (PPs) are the subject of intense study because of their ability to cause hepatocellular carcinoma in laboratory rodents. These chemicals act through a family of proteins termed the peroxisome proliferator-activated receptors (PPARs), in particular PPARalpha. It has become increasingly apparent that the role of the PPs in the development of cancer encompasses many different aspects of cell growth regulation. Immortalized hepatocytes from wild-type (PPARalpha(+/+)) and PPARalpha(-/-) mice were generated using a temperature-sensitive SV40 virus. Characterization of the murine SV40 hepatocytes (MuSH) generated from both genotypes (MuSHalpha(+/+), MuSHalpha(-/-)) show markers of differentiation such as albumin expression, but is devoid of Kupffer cell contamination. Hallmark PPARalpha-mediated responses such as induction of acyl-CoA oxidase mRNA by PPs are present in the MuSHalpha(+/+) but are absent in MuSHalpha(-/-) cells. In contrast to most cell culture systems, the wild-type MuSH hepatocytes retain the mitogenic activity of PPs, whereas the MuSHalpha(-/-) does not respond in this manner, thus making this cell culture system an ideal tool to examine growth regulatory gene expression affected by PPs. Microarray experiments performed on both cell types identified many genes in which regulation is dependent on the presence of PPARalpha, and these changes were verified with reverse transcriptase-PCR. Genes involved in carcinogenesis and control of the cell cycle that are regulated by PPs in a PPARalpha-dependent manner include ubiquitin COOH-terminal hydrolase 37 (also known as UCT-L5) and cyclin T1. These results show that MuSH cells reflect the biological properties of both the wild-type and PPARalpha-null animals and can be used to identify novel PPARalpha-regulated genes that could be involved in regulation of the cell cycle and carcinogenesis.
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PMID:Comprehensive gene expression analysis of peroxisome proliferator-treated immortalized hepatocytes: identification of peroxisome proliferator-activated receptor alpha-dependent growth regulatory genes. 1452 98

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

Peroxisome proliferator-activated receptor alpha (PPARalpha) is a member of the nuclear receptor family of transcription factors and is recognized as the molecular target of the hypolipidemic fibrate drugs. Fibrates promote lipid catabolism by inducing genes involved in fatty acid beta-oxidation. In rodents this is accompanied by peroxisome proliferation, and after chronic dosing hepatocarcinoma, whereas epidemiological studies suggest these adverse events are lacking in humans. Rodents such as rats and mice appear particularly sensitive to PPARalpha-induced peroxisome proliferation while humans are resistant. These findings question the utility of rodent models for safety monitoring of experimental PPARalpha agonists and highlight the need for additional preclinical models that display greater physiological relevance for human response. Thus we have focused on elucidating the molecular mechanism of species-dependent peroxisome proliferation by understanding the PPARalpha-dependent regulation of the acyl-CoA oxidase (AOX) promoter, the rate-limiting step of peroxisomal beta-oxidation. We have chosen the cynomolgus monkey as a model that is modestly responsive to peroxisome proliferation and functionally characterized it against the highly responsive rat and non-responsive human species. We report the identification of a putative peroxisome proliferator response element (PPRE) within the 2.3 kb proximal promoter of the cynomolgus monkey AOX gene. Characterization of these promoters using a series of constitutively active, PPARalpha constructs demonstrate that the PPREs within the proximal cynomolgus and human AOX promoters are non-responsive to PPARalpha whereas the rat PPRE is highly responsive. These findings were verified in vivo using a small molecule PPARalpha agonist. Taken together, we demonstrate concordant regulation of the AOX promoter by PPARalpha in cynomolgus monkeys and humans and suggest that this model is superior to rodent models with respect to preclinical evaluation of PPARalpha agonists.
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PMID:Differential regulation of the cynomolgus, human, and rat acyl-CoA oxidase promoters by PPARalpha. 1682 88


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