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 cytochrome P-450 3A gene family comprises the dominant forms of cytochrome P-450 found in human liver. We examined as a possible useful system for studying the regulation of cytochrome P-450 3A under controlled conditions in vitro, primary monolayer cultures of human hepatocytes and compared the results with those obtained from the study of cytochrome P-450 3A in the human hepatoblastoma cell line HepG2 or in the human hepatocellular carcinoma cell line TONG/HCC. Using 3A antibodies, 3A cDNAs and 3A3, 3A4, 3A5 and 3A7 isozyme-specific oligonucleotides as probes, we determined that primary human hepatocyte cultures routinely expressed a 3A3/4* immunoreactive protein and 3A mRNA. These gene products were well maintained for many days and were induced by treatment of the cultures with dexamethasone, phenobarbital, macrolide antibiotics, the HMG CoA reductase inhibitor lovastatin or an antifungal agent, clotrimazole. Of six donor livers examined, only two contained mRNA or protein for 3A5, a form found in only a few adult human subjects. In cultures prepared from one of these two livers, 3A5 mRNA was detectable for several days. In cultures of hepatocytes from the remaining four human livers that did not contain 3A5 mRNA or protein, we detected neither spontaneous nor inducible 3A5 proteins or mRNAs. HepG2 cells contained only 3A7 protein, a form found in human fetal liver, even after treatment with inducers. treatment of HepG2 cells with dexamethasone, macrolide antibiotics, phenobarbital and phenobarbital-like inducers or lovastatin produced dose-dependent induction of 3A7 mRNA and 3A7 immunoreactive protein. TONG/HCC cells contained 3A3, 3A4 and 3A5 mRNAs, but only 3A5 immunoreactive protein could be detected.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Regulation of human liver cytochromes P-450 in family 3A in primary and continuous culture of human hepatocytes. 822 33

Abnormalities of lipid composition and metabolism are frequently observed in patients with cholestatic liver disease. Both elevated low-density lipoprotein (LDL) levels and the appearance of lipoprotein-X (LP-X) in plasma underlie the high incidence of hypercholesterolemia in this population. We tested the hypothesis that the hypercholesterolemia of cholestasis may reflect a failure of normal feedback regulation of hepatic cholesterogenesis by determining the influence of LP-X on the rate-limiting enzyme of cholesterol synthesis, hydroxymethylglutaryl coenzyme A (HMG CoA) reductase. Cultured human hepatoma (HepG2) cells were incubated in purified lipoprotein for 24 hours, harvested, and then assayed for HMG CoA reductase activity and mass. LDL isolated from either normal controls or patients with cholestasis decreased reductase activity in a dose-dependent fashion (2 to 30 micrograms cholesterol/mL media) to a level approximately 50% of that measured in cells incubated in lipid-deficient serum. LP-X failed to downregulate enzyme activity compared with LDL, with little change in reductase activity at cholesterol concentrations (30 micrograms/mL media) that produced maximal reductase inhibition by LDL. Three distinct LP-X subspecies were purified from the plasma of a patient with primary biliary cirrhosis (PBC) and tested in an analogous manner. All LP-X subspecies were similar in their inability to decrease reductase activity as compared with LDL. HMG CoA reductase mass was increased approximately twofold in cells incubated with LP-X, as estimated by Western blot analysis. These results suggest that LP-X may contribute to hypercholesterolemia in the cholestatic patient by not effectively downregulating hepatic cholesterol synthesis.
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PMID:Lipoprotein-X fails to inhibit hydroxymethylglutaryl coenzyme A reductase in HepG2 cells. 834 91

25R)-26-Hydroxycholesterol, 25-hydroxycholesterol, and 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one, all extraordinarily potent suppressors of sterol synthesis and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity in mammalian cells, have been studied with respect to their effects on the metabolism of low density lipoproteins (LDL) by human hepatocarcinoma (HepG2) cells. The three oxysterols differed markedly in their effects on LDL metabolism, as measured by the combination of cell-associated plus degraded 125I-LDL. The 26-hydroxysterol, at concentrations from 0.1 microM to 75 microM, lowered LDL metabolism. In contrast, the 25-hydroxysterol and the 15-ketosterol, at concentrations from 0.05 microM to 2.5 microM, caused an increase in LDL metabolism. At higher concentrations of these oxysterols, LDL metabolism was suppressed. However, upon increasing the concentration of the 15-ketosterol further to 75 microM, an extraordinary 9-fold increase in LDL metabolism was observed. In contrast to their effects on LDL metabolism, the 25-hydroxysterol and the 15-ketosterol caused simple concentration-dependent decreases in the levels of HMG-CoA reductase activity under the same conditions.
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PMID:Differing effects of three oxysterols on low density lipoprotein metabolism in HepG2 cells. 839 99

The possible difference between lovastatin (mevinolin, MK-803), simvastatin (MK-733) and pravastatin (CS-514), all chemically-related competitive inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, were tested in the human hepatoma cell line Hep G2, which is often used as a model for the human hepatocyte. After an 18-hr incubation of the cells with the drugs, pravastatin (IC50 = 1900 nM) was less potent than simvastatin and lovastatin (IC50 = 34 and 24 nM, respectively) in inhibiting the sterol synthesis. As a consequence of this inhibition, the HMG-CoA reductase mRNA levels and squalene synthase activity, both negatively-regulated by sterols, were increased equally by simvastatin and lovastatin, whereas the induction by pravastatin was much less. In contrast, there were fewer differences between the compounds in inhibiting HMG-CoA reductase activity, when assayed directly in Hep G2 cell homogenates (IC50 values = 18, 61 and 95 nM for simvastatin, lovastatin and pravastatin, respectively). Moreover, in experiments with human hepatocytes in primary culture the IC50 values for inhibition of the cholesterol synthesis by simvastatin and pravastatin were of the same order of magnitude (23 and 105 nM, respectively). The results are therefore explained as follows: the three drugs act in the same way within the Hep G2 cell in terms of inhibiting HMG-CoA reductase and their subsequent effect on the feedback regulation of the cholesterol synthesis, i.e. increasing squalene synthase and HMG-CoA reductase mRNA. However, pravastatin seems to be less able to enter the cells compared with simvastatin and lovastatin, possibly because of the higher hydrophobicity of the latter compounds. The observation with human hepatocytes suggests that in Hep G2 cells a specific hepatic transporter is missing. On one hand the human hepatoma cell line Hep G2 has proved to be a good model for the study of the feedback regulation of enzymes of the cholesterol biosynthetic pathway such as HMG-CoA reductase and squalene synthase, but, on the other hand seems to be less suitable as a model for the study of specific uptake of drugs, e.g. the vastatins, in human hepatocytes.
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PMID:Pravastatin inhibited the cholesterol synthesis in human hepatoma cell line Hep G2 less than simvastatin and lovastatin, which is reflected in the upregulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase and squalene synthase. 851 61

So far, treatment with anti-cancer agents has failed to achieve satisfactory results in hepatocellular carcinoma. In the process of hepatocarcinogenesis, ras has been shown to play a role. ras requires a farnesyl moiety for activation. It has been found that UCFI-C (manumycin), an antibiotic, inhibits farnesyl protein transferase, an enzyme that catalyzes farnesylation. Therefore, we investigated the effects of UCFI-C on cell growth, prenylation of cellular proteins including ras and Rapl, MAP kinase activity, activities of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, and synthesis of cholesterol in a ras-activated human hepatoma cell line, Hep G2. Treatment with varying concentrations of UCF1-C(10-30 microM for 24 and 72 hr resulted in a time- and dose-dependent inhibition of cell numbers. 3H-Thymidine incorporation was also inhibited in a dose-dependent manner, with 50% inhibition after 44 hr being observed at a concentration of 17 microM. UCFI-C dose-dependently inhibited ras farnesylation and MAP kinase activity, but did not decrease Rap 1++ geranylgeranylation or prenylation of 21-to 26-kDa proteins. Neither the activities of 3-hydroxy-3-methylglutaryl-coenzyme A reductase nor cholesterol synthesis were inhibited. These results suggest that UCFI-C antagonizes the growth of Hep G2 via the suppression of ras farnesylation and could be a lead for the development of new anti-cancer agents blocking the function of oncogenic ras associated with human cancer, including hepatocellular carcinoma.
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PMID:Inhibition of cell growth of human hepatoma cell line (Hep G2) by a farnesyl protein transferase inhibitor: a preferential suppression of ras farnesylation. 859 13

Sterol biosynthesis requires the removal of the 14 alpha-methyl group from lanosterol in animals and fungi and from obtusifoliol in plants. This reaction is catalyzed by a microsomal cytochrome P450, the sterol 14 alpha-demethylase (P450(14DM), which is the only P450 described so far to be expressed in different phyla. A cDNA encoding human P450(14DM) was isolated from a liver cDNA library using a partial rat lanosterol 14 alpha-demethylase cDNA probe. The deduced amino acid sequence is 93% and 38--42% identical to rat and fungal P450(14DM), respectively. Expression of the human CYP51 cDNA in Escherichia coli showed that the cDNA encodes an enzyme having lanosterol 14 alpha-demethylase activity. Northern blot analysis showed that CYP51 mRNA is ubiquitously expressed with highest levels in testis, ovary, adrenal, prostate, liver, kidney, and lung. Many genes involved in cholesterol homeostasis are regulated by cholesterol or its metabolites. In the case of CYP51, cholesterol deprivation led to a 2.6- to 3.8-fold induction of mRNA levels in human adrenocortical H295R cells and this effect was suppressed by the addition of 25-hydroxycholesterol. In human hepatoma HepG2 cells, no effect of cholesterol deprivation was observed; however, the levels of CYP51 mRNA were reduced 4- to 6-fold by the addition of 25-hydroxycholesterol. Thus, like several other genes in the cholesterol biosynthetic pathway, including the 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) synthase, HMG CoA reductase, squalene synthase, and farnesyl diphosphate synthase, the expression of the human CYP51 is suppressed by oxysterols.
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PMID:The ubiquitously expressed human CYP51 encodes lanosterol 14 alpha-demethylase, a cytochrome P450 whose expression is regulated by oxysterols. 861 37

Oxysterols, a class of cholesterol oxidation products exhibit several important biological activities. Some of these natural compounds are potent inhibitors of the enzyme HMG-CoA reductase, a key enzyme in the cholesterol biosynthetic pathway. Many studies have been directed towards to the verification of the hypothesis that some oxysterols are endogenous intracellular regulators of cholesterol homeostasis. In adition to oxysterols derived directly from oxidation of cholesterol, several others are formed from squalene dioxide. It is presently well established that, in addition to the classical cholesterol biosynthetic pathway, there exists an alternate bifurcation from squalene oxide. The cyclisation of squalene dioxide leads to a series of new oxysterols. Thus, several types of oxysterols and several molecular targets are involved in the regulation of steroid biosynthesis. Many oxysterols, particularly those obtained from the oxidations of phytosterols and tetracyclic triterpenes are potent cytotoxic agents. They are selectively cytotoxic against tumorous cells. This cytotoxicity depends markedly on the specific structure of each oxysterol. Some structures are very cytotoxic, while their stereoisomers are inactive. The activity depends on the tumor cells which are used in the assay system: some compounds display inhibitory activity towards hepatoma cells but are inactive against lymphoma cells while others act in the opposite manner. Free oxysterols do not depress tumor growth in living animals. However, several water soluble prodrugs of oxysterols are able to depress different type of tumors in vivo. Clinical trial studies are presently conducted in order to learn the therapeutic values of these oxysterols.
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PMID:[From cholesterol to oxysterols. Current data]. 867 29

The conversion of 7-dehydrocholesterol to cholesterol is the last reaction in the cholesterol biosynthesis pathway catalyzed by the microsomal enzyme, 7-dehydrocholesterol-delta 7-reductase. We studied whether malignant tumor growth that depends on cholesterol could be slowed by inhibiting late cholesterol biosynthesis. The inhibitor 7-dehydrocholester-delta 7-reductase, BM 15.766 alone, or in combination with 2% cholesterol was fed to 20 male Buffalo rats for 2 weeks immediately after Morris hepatoma 7288CTC was implanted in both flanks. Tumor weights were compared and sterol composition, hepatic hydroxymethyl glutaryl coenzyme A (HMG-CoA) reductase activity, and low-density lipoprotein (LDL) receptor binding in the tumor were correlated with those in the liver. In the plasma of rats treated with BM 15.766, cholesterol levels dropped 75% and the precursor, 7-dehydrocholesterol rose substantially. Tumor weights were 43% less (P < .05) than controls (5.9 +/- 1.5 g vs. 10.4 +/- 2.2 g) with sterol concentrations reduced 25%, and the precursor, 7-dehydrocholesterol, increased to represent 71% of the tumor sterols. Feeding cholesterol with BM 15.766 normalized plasma but only partially restored tumor cholesterol concentrations, which still remained 49% below the hepatomas in the control group. With BM 15.766, hepatic cholesterol decreased 76% and was associated with a marked rise of 7-dehydrocholesterol that could be almost entirely prevented by feeding cholesterol. After the tumor was implanted, hepatic HMG-CoA reductase activity increased 56% and was 8.6 times higher than in the tumor. Enzyme activities were enhanced about 50% in the liver and the tumor after BM 15.766 was administered but decreased 38% below control when cholesterol was added to the diet. Hepatic receptor-mediated LDL binding rose 67% after tumor implantation, and declined to control levels with cholesterol feeding. These results suggest that de novo cholesterol synthesis in Morris hepatoma 7288CTC is much lower than the liver and tumor growth depends on circulating plasma cholesterol. Inhibiting the last step in cholesterol biosynthesis profoundly reduced tissue and plasma cholesterol concentrations and accumulated precursors substantially to slow hepatoma growth. Feeding cholesterol restored liver but not hepatoma cholesterol levels. Thus, inhibiting late cholesterol synthesis hinders growth of rapidly enlarging malignant tumors.
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PMID:Blocking late cholesterol biosynthesis inhibits the growth of transplanted Morris hepatomas (7288CTC) in rats. 869 Apr 17

The effect of recombinant human hepatocyte growth factor (HGF) on low density lipoprotein (LDL) receptor gene expression was studied in the human hepatoma cell line HepG2. HepG2 cells were incubated with serum-free media in the presence and absence of HGF for various times and 125I-labeled LDL specific binding at 4 degrees C, uptake at 37 degrees C, and the levels of LDL receptor mRNA were measured. Incubation with HGF produced time- and concentration-dependent increases in 125I-labeled LDL binding (2-fold), uptake (2.5-fold), and LDL receptor mRNA (6-fold). HGF increased the rate of LDL receptor gene transcription 4- to 5-fold relative to that of several "house-keeping" genes as measured by nuclear run-on transcription. The half-life of LDL receptor mRNA, measured with actinomycin D, was not increased in HGF-treated cells. The stimulation of LDL receptor expression occurred independently of changes in cellular cholesterol or DNA biosynthesis or total cell protein. HepG2 cells were transiently transfected with plasmids bearing either three copies of repeats 2 and 3 (pLDLR(23)3LUC) or one copy of the LDL receptor promoter from -556 to +53 (pLDLR600LUC) linked to firefly luciferase. Incubation of pLDLR(23)3LUC, or pLDLR600LUC-transfected cells with HGF for 4 or 24 h at 37 degrees C produced a concentration-dependent increase in luciferase activity. A maximal stimulation of 3 to 6-fold was achieved for each construct at an HGF concentration of 100 ng/ml. In contrast, HGF had little or no effect on reporter activity in HepG2 cells transfected with a luciferase reporter plasmid bearing the HMG-CoA reductase promoter extending from -325 to +22. Thus, when compared to the native LDL receptor promoter, multiple copies of repeats 2 and 3 of the LDL receptor promoter can fully support activation of the luciferase reporter gene by HGF, demonstrating that the effect of HGF is mediated through the SRE-1. The lack of HGF effects mediated through the HMG-CoA reductase sterol regulatory element suggests, however, that sterol depletion may not be responsible for the induction of the LDL receptor promoter by growth factors. The signalling pathways or effectors responsible for activation of the LDL receptor and HMG-CoA reductase genes thus differ in their response to HGF. These data suggest that the level of SREBP's reaching the nucleus may be determined by as yet unidentified second messengers as well as by sterols.
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PMID:Activation of LDL receptor gene expression in HepG2 cells by hepatocyte growth factor. 872 51

Stable plasmid-driven expression of the liver-specific gene product cholesterol 7alpha-hydroxylase (7alpha-hydroxylase) was used to alter the cellular content of transcriptionally active sterol response element binding protein 1 (SREBP1). As a result of stable expression of 7alpha-hydroxylase, individual single cell clones expressed varying amounts of mature SREBP1 protein. These single cell clones provided an opportunity to identify SREBP1-regulated genes that may influence the assembly and secretion of apoB-containing lipoproteins. Our results show that in McArdle rat hepatoma cells, which normally do not express 7alpha-hydroxylase, plasmid-driven expression of 7alpha-hydroxylase results in the following: 1) a linear relationship between (i) the cellular content of mature SREBP1 and 7alpha-hydroxylase protein, (ii) the relative expression of 7alpha-hydroxylase mRNA and the mRNA's encoding the enzymes regulating fatty acid, i.e. acetyl-CoA carboxylase and sterol synthesis, i.e. HMG-CoA reductase, (iii) the relative expression of 7alpha-hydroxylase mRNA and microsomal triglyceride transfer protein mRNA, a gene product that is essential for the assembly and secretion of apoB-containing lipoproteins; 2) increased synthesis of all lipoprotein lipids (cholesterol, cholesterol esters, triglycerides, and phospholipids); and 3) increased secretion of apoB100 without any change in apoB mRNA. Cells expressing 7alpha-hydroxylase contained significantly less cholesterol (both free and esterified). The increased cellular content of mature SREBP1 and increased secretion of apoB100 were concomitantly reversed by 25-hydroxycholesterol, suggesting that the content of mature SREBP1, known to be decreased by 25-hydroxycholesterol, mediates the changes in the lipoprotein assembly and secretion pathway that are caused by 7alpha-hydroxylase. These data suggest that several steps in the assembly and secretion of apoB-containing lipoproteins by McArdle hepatoma cells may be coordinately linked through the cellular content of mature SREBP1.
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PMID:Coordinate regulation of lipogenesis, the assembly and secretion of apolipoprotein B-containing lipoproteins by sterol response element binding protein 1. 923 33


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