Effects of compactin, mevalonate and low-density lipoprotein on 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity and low-density-lipoprotein-receptor activity in the human hepatoma cell line Hep G2.
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ABSTRACT:
SUBMITTER: Cohen LH
PROVIDER: S-EPMC1144140 | biostudies-other | 1984 Aug
REPOSITORIES: biostudies-other
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Project description:The human hepatoma cell line Hep G2 was studied with respect to metabolism of human low-density lipoprotein (LDL). The Hep G2 cells bind, take up and degrade human LDL with a high-affinity saturable and with a low-affinity non-saturable component. The high-affinity binding possesses a KD of 25 nM-LDL and a maximal amount of binding of about 70 ng of LDL-apoprotein/mg of cell protein. The high-affinity binding, uptake and degradation of LDL by Hep G2 cells is dependent on the extracellular Ca2+ concentration and is down-regulated by the presence of fairly high concentrations of extracellular LDL. Incubation of the Hep G2 cells with LDL results in suppression of the intracellular cholesterol synthesis. It is concluded that the human hepatoma cell line Hep G2 possesses specific LDL receptors similar to the LDL receptors demonstrated on extrahepatic tissue cells.
| S-EPMC1152337 | biostudies-other
Project description:(-)-Hydroxycitrate, a potent inhibitor of ATP citrate-lyase, was tested in Hep G2 cells for effects on cholesterol homoeostasis. After 2.5 h and 18 h incubations with (-)-hydroxycitrate at concentrations of 0.5 mM or higher, incorporation of [1,5-14C]citrate into fatty acids and cholesterol was strongly inhibited. This most likely reflects an effective inhibition of ATP citrate-lyase. Cholesterol biosynthesis was decreased to 27% of the control value as measured by incorporations from 3H2O, indicating a decreased flux of carbon units through the cholesterol-synthetic pathway. After 18 h preincubation with 2 mM-(-)-hydroxycitrate, the cellular low-density-lipoprotein (LDL) receptor activity was increased by 50%, as determined by the receptor-mediated association and degradation. Measurements of receptor-mediated binding versus LDL concentration suggests that this increase was due to an increase in the numbers of LDL receptors. Simultaneously, enzyme levels of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase as determined by activity measurements increased 30-fold. Our results suggest that the increases in HMG-CoA reductase and the LDL receptor are initiated by the decreased flux of carbon units in the cholesterol-synthetic pathway, owing to inhibition of ATP citratelyase. A similar induction of HMG-CoA reductase and LDL receptor was also found after preincubations of cells with 0.3 microM-mevinolin, suggesting that the underlying mechanism for this induction is identical for both drugs.
| S-EPMC1149674 | biostudies-other
Project description: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)
| S-EPMC1151564 | biostudies-other
Project description:Incubating Hep G2 cells for 18 h with triparanol, buthiobate and low concentrations (less than 0.5 microM) of U18666A, inhibitors of desmosterol delta 24-reductase, of lanosterol 14 alpha-demethylase and of squalene-2,3-epoxide cyclase (EC 5.4.99.7) respectively, resulted in a decrease of the HMG-CoA (3-hydroxy-3-methylglutaryl-coenzyme A) reductase activity. However, U18666A at concentrations higher than 3 microM increased the HMG-CoA reductase activity in a concentration-dependent manner. None of these inhibitors influenced directly the reductase activity in Hep G2 cell homogenates. Analysis by t.l.c. of 14C-labelled non-saponifiable lipids formed from either [14C]acetate or [14C]mevalonate during the cell incubations confirmed the sites of action of the drugs used. Beside the 14C-labelled substrates of the blocked enzymes and 14C-labelled cholesterol, another non-saponifiable lipid fraction was observed, which behaves as polar sterols on t.l.c. This was the case with triparanol and at those concentrations of U18666A that decreased the reductase activity, suggesting that polar sterols may play a role in suppressing the reductase activity. In the presence of 30 microM-U18666A (sterol formation blocked) the increase produced by simultaneously added compactin could be prevented by addition of mevalonate. This indicates the existence of a non-sterol mevalonate-derived effector in addition to a sterol-dependent regulation. LDL (low-density lipoprotein), which was shown to be able to decrease the compactin-induced increase in reductase activity, could not prevent the U18666A-induced increase. On the contrary, LDL enhanced the U18666A effect, showing that the LDL regulation is not merely the result of introducing cholesterol to the cells.
| S-EPMC1147567 | biostudies-other
Project description:Hep G2 cells were incubated under conditions known to influence the HMG-CoA (3-hydroxy-3-methylglutaryl-CoA) reductase activity, e.g. in the presence of compactin (a competitive inhibitor of HMG-CoA reductase itself) and U18666A (a squalene-2,3-epoxide cyclase inhibitor). We studied the effects of these conditions both on the HMG-CoA reductase activity and on the reductase mRNA content. In the presence of compactin the mRNA content increased, but less than the enzyme activity, as determined after removal of the inhibitor. The increase in mRNA could be prevented by addition of mevalonate or by a combination of low-density lipoprotein (LDL) plus a low concentration of mevalonate. LDL alone prevented the compactin-induced increases in mRNA and activity only partially. The effect of U18666A on reductase mRNA content and activity was biphasic, i.e. a slight decrease at low (0.3-0.5 microM) concentrations, with a concomitant formation of polar sterols [Boogaard, Griffioen & Cohen (1987) Biochem. J. 241, 345-351], and an increase at high (20-30 microM) concentrations, with complete blockage of sterol formation. At these high concentrations of U18666A, additional compactin (2 microM) increased the reductase activity, but not the mRNA content. We conclude that non-sterol metabolites of mevalonate regulate exclusively at the enzyme level, whereas sterol metabolites regulate at the reductase mRNA level. In the latter group of regulators we distinguish mevalonate metabolites which can, and metabolites which cannot, be replaced by exogenous LDL.
| S-EPMC1135190 | biostudies-other
Project description:We have previously shown that in Hep G2 cells and human hepatocytes, as compared with fibroblasts, the low-density lipoprotein (LDL) receptor activity is only weakly down-regulated after incubation of the cells with LDL, whereas incubation with high-density lipoproteins (HDL) of density 1.16-1.20 g/ml (heavy HDL) strongly increased the LDL-receptor activity. To elucidate this difference between hepatocytes and fibroblasts, we studied the cellular cholesterol homoeostasis in relation to the LDL-receptor activity in Hep G2 cells. (1) Interrupting the cholesteryl ester cycle by inhibiting acyl-CoA: cholesterol acyltransferase (ACAT) activity with compound 58-035 (Sandoz) resulted in an enhanced LDL-mediated down-regulation of the receptor activity. (2) The stimulation of the receptor activity by incubation of the cells with cholesterol acceptors such as heavy HDL was not affected by ACAT inhibition. (3) Incubation of the Hep G2 cells with LDL, heavy HDL or a combination of both grossly affected LDL-receptor activity, but did not significantly change the intracellular content of free cholesterol, suggesting that in Hep G2 cells the regulatory free cholesterol pool is small as compared with the total free cholesterol mass. (4) We used changes in ACAT activity as a sensitive (indirect) measure for changes in the regulatory free cholesterol pool. (5) Incubation of the cells with compactin (2 microM) without lipoproteins resulted in a 4-fold decrease in ACAT activity, indicating that endogenously synthesized cholesterol is directed to the ACAT-substrate pool. (6) Incubation of the cells with LDL or a combination of LDL and heavy HDL stimulated ACAT activity 3-5 fold, whereas incubation with heavy HDL alone decreased ACAT activity more than 20-fold. Our results suggest that in Hep G2 cells exogenously delivered (LDL)-cholesterol and endogenously synthesized cholesterol are primarily directed to the cholesteryl ester (ACAT-substrate) pool or, if present, to extracellular cholesterol acceptors (heavy HDL) rather than to the free cholesterol pool involved in LDL-receptor regulation.
| S-EPMC1148474 | biostudies-other
Project description:BackgroundHMGCR(3-Hydroxy-3-methylglutaryl coenzyme A reductase), the direct target of statin inhibition, undergoes alternative splicing of exon 13, which encodes part of the statin-binding domain of the enzyme. We hypothesized that HMGCR alternative splicing might be related to the interindividual variation in plasma low-density lipoprotein cholesterol response to statin treatment.Methods and resultsWe measured mRNA expression of both the full-length and the alternatively spliced HMGCR transcript lacking exon 13 (HMGCRv_1) in 170 simvastatin-incubated immortalized lymphocyte cell lines derived from participants in the Cholesterol and Pharmacogenetics (CAP) study who were treated with simvastatin 40 mg/d for 6 weeks. Greater upregulation of HMGCRv_1 in vitro was significantly correlated (P<or=0.0001) with smaller in vivo reductions of plasma total cholesterol, low-density lipoprotein cholesterol, apoprotein B, and triglycerides and explained 6% to 15% of the variation in their response to treatment. In contrast, no significant relationship was found between expression of the full-length HMGCR transcript and in vivo response. By siRNA knockdown of the full-length transcript, we found that HMGCR enzyme activity measured in cells enriched in HMGCRv_1 was relatively resistant to statin inhibition, consistent with the association of increased alternative splicing with reduced statin response in the CAP study. In addition, we found that a common HMGCR single-nucleotide polymorphism (rs3846662) located within intron 13 was associated with variation in the proportion of HMGCR mRNA that is alternatively spliced.ConclusionsVariation in the production of an HMGCR isoform with reduced statin sensitivity is a determinant of interindividual differences in low-density lipoprotein cholesterol, apolipoprotein B, and triglyceride response to statin treatment.
| S-EPMC2720070 | biostudies-literature
Project description:Background and objectivesHuman papillomaviruses have been linked causally to some human cancers such as cervical carcinoma, but there is very little research addressing the effect of HPV infection on human liver cells. We chose the human hepatoma derived cell line Hep G2 to investigate whether HPV gene integration took place in liver cells as well.MethodsWe applied PCR to detect the possible integration of HPV genes in Hep G2 cells. We also investigated the expression of the integrated E6 and E7 genes by using RT-PCR and Western blotting. Then, we silenced E6 and E7 expression and checked the cell proliferation and apoptosis in Hep G2 cells. Furthermore, we analyzed the potential genes involved in cell cycle and apoptosis regulatory pathways. Finally, we used in situ hybridization to detect HPV 16/18 in hepatocellular carcinoma samples.ResultsHep G2 cell line contains integrated HPV 18 DNA, leading to the expression of the E6 and E7 oncogenic proteins. Knockdown of the E7 and E6 genes expression reduced cell proliferation, caused the cell cycle arrest at the S phase, and increased apoptosis. The human cell cycle and apoptosis real-time PCR arrays analysis demonstrated E6 and E7-mediated regulation of some genes such as Cyclin H, UBA1, E2F4, p53, p107, FASLG, NOL3 and CASP14. HPV16/18 was found in only 9% (9/100) of patients with hepatocellular carcinoma.ConclusionOur investigations showed that HPV 18 E6 and E7 genes can be integrated into the Hep G2, and we observed a low prevalence of HPV 16/18 in hepatocellular carcinoma samples. However, the precise risk of HPV as causative agent of hepatocellular carcinoma needs further study.
| S-EPMC3360009 | biostudies-literature
Project description:Isoprenoids are a large and diverse group of metabolites with interesting properties such as flavour, fragrance and therapeutic properties. They are produced via two pathways, the mevalonate pathway or the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway. While plants are the richest source of isoprenoids, they are not the most efficient producers. Escherichia coli and yeasts have been extensively studied as heterologous hosts for plant isoprenoids production. In the current study, we describe the usage of the food grade Lactococcus lactis as a potential heterologous host for the production of sesquiterpenes from a local herbaceous Malaysian plant, Persicaria minor (synonym Polygonum minus). A sesquiterpene synthase gene from P. minor was successfully cloned and expressed in L. lactis. The expressed protein was identified to be a ?-sesquiphellandrene synthase as it was demonstrated to be functional in producing ?-sesquiphellandrene at 85.4% of the total sesquiterpenes produced based on in vitro enzymatic assays. The recombinant L. lactis strain developed in this study was also capable of producing ?-sesquiphellandrene in vivo without exogenous substrates supplementation. In addition, overexpression of the strain's endogenous 3-hydroxy-3-methylglutaryl coenzyme-A reductase (HMGR), an established rate-limiting enzyme in the eukaryotic mevalonate pathway, increased the production level of ?-sesquiphellandrene by 1.25-1.60 fold. The highest amount achieved was 33 nM at 2 h post-induction.
| S-EPMC3530464 | biostudies-literature
Project description:We have observed recently that high-density lipoproteins (HDL) are the predominant carriers of cholesteryl ester hydroperoxides (CEOOH), the major class of lipid hydroperoxides detectable at nanomolar concentrations in the plasma of healthy fasting humans. The present study investigates the effect of such very low levels of CEOOH in apolipoprotein E-free HDL3 on lipoprotein particle metabolism and 'selective uptake' of its CE by human Hep G2 cells. Minimal oxidation with aqueous peroxyl radicals had a negligible effect on the binding, internalization and degradation of 125I-labelled HDL3. In contrast, with an increasing degree of radical-mediated oxidation of labelled HDL3, [3H]cholesteryl linoleate ([3H]Ch18:2) was taken up at an increasingly greater rate than were 125I-apoproteins. When [3H]cholesteryl linoleate hydroperoxide ([3H]Ch18:2-OOH was incorporated into unoxidized HDL3 by exchange from donor liposomes, it was taken up at a more than 8-fold higher rate than was incorporated [3H]Ch18:2. The same degree of preferential uptake of oxidized CE was observed when HDL3 was used that was doubly labelled with [3H]Ch18:2-OOH and cholesteryl [14C]oleate ([14C]Ch18:1). In both situations, uptake of [3H]Ch18:2-OOH exceeded that of 125I-apolipoprotein A-I some 40-fold. This increased selective uptake of [3H]Ch18:2-OOH from very mildly oxidized HDL3 was accompanied by a parallel increase in the intracellular levels of labelled free cholesterol. In contrast, lipid hydroperoxides were not detectable within Hep G2 cells, suggesting efficient detoxification of CEOOH by these cells. Neither the increased selective uptake of Ch18:2-OOHs nor the levels of intracellular free cholesterol were influenced by the presence of 50 microM chloroquine, suggesting extralysosomal hydrolysis of oxidized CEs. These results show that the selective uptake of HDL CEOOH by Hep G2 cells is more efficient than that of unoxidized CE, and support a protective role for rapid selective uptake in the removal of circulating HDL CEOOH.
| S-EPMC1134528 | biostudies-other