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)

Unlike the normal liver, numerous transplantable rodent and human hepatomas are unable to alter their rate of sterol synthesis and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-GoA) reductase [mevalonate: NADP+ oxidoreductase (CoA-acylating), EC 1.1.1.34] activity in response to a dietary cholesterol challenge. It has been suggested that this metabolic defect is linked to the process of malignant transformation. Hepatoma 7288C "lacks" feedback regulation of cholesterol synthesis when grown in vivo but expresses this regulatory property when grown in vitro (then called HTC). Therefore, it was used as a model system to answer whether an established hepatoma cell line that modulates its rate of cholesterol synthesis in vitro can express this property when grown in vivo, and whether cells reisolated from the tumor mass have the same regulatory phenotype as before transplantation. Our results show that long-term growth of hepatoma 7288C in tissue culture has not caused a biotransformation that permits feedback regulation of HMG-CoA reductase when the cells are transplanted back into host animals. In addition, HTC cells reisolated from the tumor mass and established in tissue culture continue to have the ability to regulate HMG-CoA reductase activity. Therefore, malignant transformation is not categorically linked to the loss of the cellular components necessary to regulate sterol synthesis and HMG-CoA reductase activity.
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PMID:Comparison of regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase in hepatoma cells grown in vivo and in vitro. 18 7

In mouse hepatoma Hepa-1c1c7 cultures, polycyclic aromatic compounds such as benzol[a]pyrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin) activate the Cyp1a-1 (cytochrome P(1)450) and Nmo-1[NAD(P)H:menadione-oxidoreductase] genes, two members of the aromatic hydrocarbon (Ah)-responsive gene battery. Mevinolin is known to inhibit 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase (EC 1.1.1.34), the rate-limiting step in cholesterol biosynthesis. We show here that in the absence of TCDD, mevinolin markedly increases Cyp1a-1 transcription, CYP1A1 mRNA and protein levels and enzyme activity, and NMO1 mRNA concentrations. Addition of mevalonate, the product of HMG-CoA reductase activity, fails to reverse the effects of mevinolin. In fact, when used at high concentrations, mevalonate activates Cyp1a-1 transcription. Mevinolin-induced Cyp1a-1 gene activation: (1) occurs independently of the lipid content of the growth medium, (2) is not suppressed by adding 25-hydroxycholesterol, which blocks MHG-CoA reductase activity, and (3) requires a functional Ah receptor and unimpaired nuclear translocation of the receptor. It is possible that an unknown metabolite (or metabolites) of mevinolin activates Cyp1a-1 expression and that high concentrations of mevalonate act via the same mechanism. Using chimaeric plasmids that contain different lengths of Cyp1a-1 5' flanking regions fused to the bacterial neomycin (neo) gene, we find that the mevinolin effect on Cyp1a-1 induction requires the 5' flanking sequences between -1647 and -824, which are also needed for TCDD induction. Mevinolin, however, is not a ligand for the Ah receptor. Gel mobility shift assays revealed that Cyp1a-1 activation caused by mevinolin does not involve the ligand-dependent formation of a functional Ah receptor-dependent DNA-binding complex, but instead appears to be correlated with release of a putative repressor from its cognate DNA site. Our results suggest that the basel level of Cyp1a-1 transcription is maintained by an unknown negative regulatory factor. We propose that Cyp1a-1 transcriptional activation can result not only from induction by polycyclic aromatic compounds but also from derepression by mevinolin, independent of HMG-CoA reductase inhibition.
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PMID:Transcriptional derepression of the murine Cyp1a-1 gene by mevinolin. 131 Dec 72

The relationship between the serum factor(s)-mediated induction of low-density lipoprotein (LDL) receptor activity and changes in cellular cholesterol metabolism was examined in the human hepatoma cell line Hep-G2. Relative to incubation with serum-free media [Eagle's minimal essential medium (MEM) control], short-term (less than 8 h) incubation with medium containing 15% of either calf serum (MEM + serum) or the d greater than 1.25 fraction of calf serum (MEM + d greater than 1.25) produced a time- and concentration-dependent increase in the uptake of 125I-LDL. Immunoblotting with anti-(LDL receptor) antibodies demonstrated that this was correlated with a 2-fold increase in the amount of the mature 136,000 Da LDL receptor protein in detergent-solubilized Hep-G2 cell membranes. Incubation with MEM + serum, but not MEM + d greater than 1.25, increased the efflux of radiolabelled cholesterol from Hep-G2 cells. However, the induction of 125I-LDL uptake by MEM + d greater than 1.25 (2.3-fold) and MEM + serum (2.2-fold) was virtually identical. Addition of the d less than 1.063 lipoproteins of calf serum to MEM + d greater than 1.25 at their original or three times their serum concentration decreased the induction of 125I-LDL uptake by MEM + d greater than 1.25 by only 20-30%. Together, these results suggest that the stimulation of 125I-LDL uptake was not due to the presence of high-density lipoprotein, the absence of LDL or the stimulation of cholesterol efflux. MEM + serum stimulated 125I-LDL uptake in cells cholesterol-loaded by incubation with rat very-low-density lipoprotein with beta electrophoretic mobility (beta-VLDL). Compared to incubation with the MEM control, either MEM + serum or MEM + d greater than 1.25 produced time-dependent increases in the activity of 3-hydroxy-3-methylglutaryl-CoA reductase which also occurred in cholesterol-loaded cells. However, cholesterol biosynthesis, whether measured from 3H2O, [14C]acetate or [3H]mevalonic acid, was not increased. Incubation with MEM + serum or MEM + d greater than 1.25 did not affect [3H]oleate incorporation into cellular cholesteryl esters, hydrolysis of intracellular [3H]cholesteryl esters or the cellular mass of unesterified or esterified cholesterol. Incubation with MEM + serum or MEM + d greater than 1.25 produced a transient increase in the level of LDL receptor mRNA, reaching a maximum of 5-10-fold by 2 h and decreasing to near baseline levels by 4 h. Actinomycin D blocked the serum-factor-mediated induction of LDL receptor mRNA.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Evidence for sterol-independent regulation of low-density lipoprotein receptor activity in Hep-G2 cells. 193 Jan 37

Cholesterol biosynthesis was characterized in cell-free post-mitochondrial supernatant systems prepared from both normal rat liver and Morris hepatoma 3924A. The rate of cholesterol synthesis per cell was 9-fold greater in the tumour system than in that from normal liver, and the tumour systems showed the loss of rate-limiting control at the hydroxymethylglutaryl-CoA reductase (HMGR)-catalysed step. The apparent absence of rate-limiting control over cell-free tumour cholesterogenesis was traced primarily to a discoordinate and dramatic increase in the amount of HMGR in the tumour relative to the liver system. Preliminary evidence for an altered control of the post-lanosterol portion of the pathway was also obtained with the tumour system.
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PMID:A discoordinate increase in the cellular amount of 3-hydroxy-3-methylglutaryl-CoA reductase results in the loss of rate-limiting control over cholesterogenesis in a tumour cell-free system. 270 93

THE FEEDBACK RESPONSE OF MEVALONATE: NADP oxidoreductase (acylating CoA; EC 1.1.1.34) in two varieties of hepatoma has been examined. In marked contrast to the feedback inhibition of this enzyme that is regularly observed in normal liver, the feedback control is completely lost in minimal-deviation hepatomas 9121 and 3924A. This finding provides the first specific biochemical localization of the defect in cholesterol feedback control, which has been shown previously to be a characteristic of all hepatomas.
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PMID:Loss of feedback control of hydroxymethylglutaryl coenzyme A reductase in hepatomas. 527 77

The reversible phosphorylation of microsomal 3-hydroxy-3-methylglutaryl CoA reductase in host liver and hepatoma 5123C has been investigated. The percentage of the total enzyme activity in vivo was similar in the normal liver, host liver and hepatoma 5123C. The inclusion of 30 mM EDTA and 10 mM mevalonic acid in assays of 3-hydroxy-3-methylglutaryl CoA reductase inactivation in vitro eliminated artifacts generated by the presence of mevalonate kinase. Inactivation of 3-hydroxy-3-methylglutaryl CoA reductase from normal liver, host liver and hepatoma occurred at a similar rate with similar half-times. We conclude that phosphorylation/dephosphorylation of 3-hydroxy-3-methylglutaryl CoA reductase occurs in hepatomas and that the lack of dietary cholesterol feedback inhibition in the hepatomas is not a result of a defect in this particular aspect of the reversible phosphorylation system.
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PMID:Reversible phosphorylation of 3-hydroxy-3-methylglutaryl CoA reductase in Morris hepatomas. 660 42

beta-(2-Hydroxyethoxy)-5 alpha-cholest-8(14)-en-15-one, a synthetic inhibitor of cholesterol biosynthesis, was shown to exhibit a high affinity to oxysterol binding protein. This was proved by ultracentrifugation of the protein fraction from rabbit liver in the presence of the 3H-labeled inhibitor, 3 beta-(2-hydroxy-2-[3H]ethoxy)-5 alpha-cholest-8(14)-en-15-one, or by the substitution of the [3H]-25-hydroxycholesterol in its complex with the oxysterol binding protein. In human hepatoma Hep G2 cells, the inhibitor decreased activity of 3-hydroxy-3-methylglutaryl CoA reductase [ID50 (2.7 +/- 0.7) x 10(-5) M] and was transformed into 3 beta-[2-(9-Z-octadecenoyloxy)ethoxy]-5 alpha-cholest-8(14)-en-15-one.
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PMID:[Affinity of 3-beta-(2-hydroxyethoxy)-5-alpha-cholest-8(14)-ene-15-one to oxysterol binding protein and its metabolism in HepG2 hepatoma cells]. 922 31

To determine whether differentiation therapy is useful in treating patients with hepatoma, we assayed the effects of 25-hydroxycholesterol (25-OH) and/or all-trans retinoic acid (ATRA) on rat AH136B ascites hepatoma cells. Flow cytometric DNA analysis showed that treatment of cells with 25-OH alone induced entry into the sub-G1 phase in a dose-dependent manner. While ATRA alone was ineffective, it enhanced the activity of 25-OH. Condensed and fragmented nuclei occurred mainly in cells treated with 25-OH (4 microg/ml). When cells treated with 25-OH (4 microg/ml), or 25-OH (4 microg/ml) + ATRA (1 microM) were transplanted into Donryu rats, we found that tumor development was completely inhibited; in contrast, rats administered the methanol-treated AH136B cells developed tumors. These findings suggest that AH136B cells in the sub-G1 phase can not recover tumorigenicity, and that the administration of a 3-hydroxy-3-methylglutaryl CoA reductase inhibitor, such as 25-OH, and ATRA may be effective in treating patients with hepatoma.
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PMID:Suppression of rat liver tumorigenesis by 25-hydroxycholesterol and all-trans retinoic acid: differentiation therapy for hepatocellular carcinoma. 1042 41

Farnesyl diphosphate synthase (FPPS: EC2.5.1.10), a key enzyme in isoprenoid metabolic pathways, catalyzes the synthesis of farnesyl diphosphate (FPP) an intermediate in the biosynthesis of both sterol and non-sterol isoprenoid end products. The localization of FPPS to peroxisomes has been reported (Krisans, S. K., J. Ericsson, P. A. Edwards, and G. A. Keller. 1994. J. Biol. Chem. 269: 14165;-14169). Using indirect immunofluorescence and immunoelectron microscopic techniques we show here that FPPS is localized predominantly in the peroxisomes of rat hepatoma H35 cells. However, the partial release of 60;-70% of cellular FPPS activity is observed by selective permeabilization of these cells with digitonin. Under these conditions, lactate dehydrogenase, a cytosolic enzyme, is completely released whereas catalase, a known peroxisomal enzyme, is fully retained. Digitonin treatment of H35 cells differentially affects the release of other peroxisomal enzymes involved in isoprenoid metabolism. For instance, mevalonate kinase and phosphomevalonate kinase are almost totally released (95% and 91%, respectively), whereas 3-hydroxy-3-methylglutaryl-CoA reductase is fully retained. Indirect immunoflourescence studies indicate that FPPS is localized in peroxisomes of Chinese hamster ovary (CHO)-K1 cells but is dispersed in the cytosol of ZR-82 cells, a mutant that lacks peroxisomes. Unlike in H35 cells, FPPS is completely released upon digitonin permeabilization of CHO-K1 and ZR-82 cells. In contrast, under the same permeabilization conditions, catalase is fully retained in CHO-K1 cells but completely released from ZR-82 cells. These studies indicate that FPPS and other enzymes in the isoprenoid biosynthetic pathways, involved in the formation of FPP, are differentially associated with peroxisomes and may easily diffuse to the cytosol. Based on these observations, the significance and a possible regulatory model in the formation of isoprenoid end-products are discussed.
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PMID:Differential binding of proteins to peroxisomes in rat hepatoma cells: unique association of enzymes involved in isoprenoid metabolism. 1048 4

The finding that expression of a cholesterol 7alpha-hydroxylase (CYP7A1) transgene in cultured rat hepatoma cells caused a coordinate increase in lipogenesis and secretion of apoB-containing lipoproteins led to the hypothesis that hepatic production of apoB-containing lipoproteins may be linked to the expression of CYP7A1 (Wang, S.-L., Du, E., Martin, T. D., and Davis, R. A. (1997) J. Biol. Chem. 272, 19351-19358). To examine this hypothesis in vivo, a transgene encoding CYP7A1 driven by the constitutive liver-specific enhancer of the human apoE gene was expressed in C56BL/6 mice. The expression of CYP7A1 mRNA (20-fold), protein ( approximately 10-fold), and enzyme activity (5-fold) was markedly increased in transgenic mice compared with non-transgenic littermates. The bile acid pool of CYP7A1 transgenic mice was doubled mainly due to increased hydrophobic dihydroxy bile acids. In CYP7A1 transgenic mice, livers contained approximately 3-fold more sterol response element-binding protein-2 mRNA. Hepatic expression of mRNAs encoding lipogenic enzymes (i.e. fatty-acid synthase, acetyl-CoA carboxylase, stearoyl-CoA desaturase, squalene synthase, farnesyl-pyrophosphate synthase, 3-hydroxy-3-methylglutaryl-CoA reductase, and low density lipoprotein receptor) as well as microsomal triglyceride transfer protein were elevated approximately 3-5-fold in transgenic mice. CYP7A1 transgenic mice also displayed a >2-fold increase in hepatic production and secretion of triglyceride-rich apoB-containing lipoproteins. Despite the increased hepatic secretion of apoB-containing lipoproteins in CYP7A1 mice, plasma levels of triglycerides and cholesterol were not significantly increased. These data suggest that the 5-fold increased expression of the low density lipoprotein receptor displayed by the livers of CYP7A1 transgenic mice was sufficient to compensate for the 2-fold increase production of apoB-containing lipoproteins. These findings emphasize the important homeostatic role that CYP7A1 plays in balancing the anabolic lipoprotein assembly/secretion pathway with the cholesterol catabolic bile acid synthetic pathway.
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PMID:Increased production of apolipoprotein B-containing lipoproteins in the absence of hyperlipidemia in transgenic mice expressing cholesterol 7alpha-hydroxylase. 1132 27


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