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)

Oncostatin M is a growth regulatory protein secreted by macrophages and activated T lymphocytes. In a hepatoma cell line (HepG2) the polypeptide very potently increased low density lipoprotein (LDL) uptake with an EC50 of 0.1-0.2 nM. The stimulation of LDL uptake was detectable by 2 h, was maximal by 8 h, and remained elevated through 20 h of oncostatin M incubation. In a similar fashion, oncostatin M also increased the number of cell surface LDL receptors by a mechanism that was inhibited by cycloheximide or the protein kinase C inhibitor H-7. Oncostatin M stimulation of LDL uptake and receptor protein occurred regardless of the state of cholesterol-dependent regulation of HepG2 LDL receptor (i.e. cells incubated in medium containing lipoproteins responded to the same extent as did cells incubated in the absence of lipoproteins). No significant effects were observed on sterol synthesis over 8 h or on DNA synthesis over 24 h. Oncostatin M induced rapid alterations in HepG2 phospholipid metabolism. Within 5-15 min there was a 20-50% increase in incorporation of 32P into several classes of phospholipids, including the phosphoinositides. Radiolabeled diacylglycerol levels were elevated 20% by 2 min and nearly 50% by 15 min. In addition, the polypeptide induced rapid increased (within 1 min) in phosphorylation of HepG proteins on tyrosine residues. Stimulation of both phosphotyrosine and LDL receptor up-regulation by oncostatin M was decreased by the tyrosine kinase inhibitor genistein. We propose that oncostatin M up-regulates HepG2 LDL receptor expression by a mechanism that includes stimulation of a tyrosine kinase followed by generation of phospholipid-related second messengers.
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PMID:Oncostatin M up-regulates low density lipoprotein receptors in HepG2 cells by a novel mechanism. 165 40

For the determination of LDL receptor expression on living human cells two monoclonal antibodies specific for the extracellular domain of LDL receptor were established using affinity-purified LDL receptor and carrier-conjugated LDL receptor peptide 163-174 as immunizing antigens. The 125I-labeled antibodies were used to quantify increases in LDL receptor expression on human cells grown in the presence of increasing concentrations of various growth factors. Growth factor-mediated increase of LDL receptor expression was entirely different in various cell lines with respect to a distinct growth factor and for different growth factors when tested with one and the same cell line. An increased LDL receptor expression was observed on A431 epidermoid carcinoma cells of the vulva in the presence of epidermal growth factor (EGF) or insulin but not with platelet-derived growth factor (PDGF), on HUV-EC primary endothelial cells in the presence of insulin or PDGF but not with EGF, and on MRC-5 diploid fetal lung cells only in the presence of PDGF. HEP-3B hepatoma cells did not respond to any of the three growth factors essentially maintaining the original level of LDL receptor expression.
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PMID:Expression of LDL receptor on tumor cells induced by growth factors. 185 Feb 20

We showed previously that net secretory output of apolipoprotein B (apo B) from cultured human hepatoma cells (HepG2) is regulated by rapid reuptake of nascent lipoproteins before they have diffused away from the vicinity of the cells. We now sought to determine if the nascent lipoproteins could be remodeled to enhance or impede reuptake. We found that lipoprotein lipase (LpL), an enzyme that hydrolyzes lipoprotein triglyceride, reduced HepG2 output of apo B to one-quarter to one-half of control. The reduction was apparent during co-incubations as short as 2 h and as long as 24 h. Heparin, which blocks receptor-mediated binding of lipoproteins, abolished the effect of LpL on apo B output, without causing enzyme inhibition. To assess uptake directly, we prepared labeled nascent lipoproteins. LpL tripled the cellular uptake of labeled nascent lipoproteins, from 15.2% +/- 0.7% to 48.7% +/- 0.3% of the total applied to the cells. Cellular uptake of 125I-labeled anti-LDL receptor IgG was unaffected by LpL; thus, LpL enhanced reuptake by altering lipoproteins, not receptors. Because LpL is present in the space of Disse in the liver, we conclude that LpL may act on newly secreted lipoproteins to enhance reuptake in vivo. LpL deficiency would reduce local reuptake of apo B, which would appear as overproduction, thereby providing a mechanistic link between partial LpL deficiency and familial combined hyperlipidemia.
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PMID:Lipoprotein lipase modulates net secretory output of apolipoprotein B in vitro. A possible pathophysiologic explanation for familial combined hyperlipidemia. 191 80

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

Previous work has shown that low-density lipoproteins (LDL) secreted by hepatoma-derived cell lines have an unusual composition compared to plasma LDL; rather than cholesteryl ester, the hepatoma cell-secreted LDL have a triacylglycerol core. We have found that they also have an increased negative charge, as judged by agarose electrophoresis. Since apolipoprotein B is a glycoprotein containing carbohydrate chains terminated with negatively charged sialic acid residues, we examined whether increased glycosylation of the apolipoprotein B from three hepatoma cell lines (Hep G2, Hep 3B and Huh 7) might account for the differences in LDL charge. The weight percent carbohydrate for Hep G2, Hep 3B and Huh 7 LDL-protein (1.1 +/- 0.2; 1.7 +/- 0.8; 0.4 +/- 0.1) was found to be extremely low compared with the 2.8-9% range we found for plasma LDL-protein, while the amount of LDL-lipid associated carbohydrate from hepatoma LDL was similar to that we found in plasma LDL. Furthermore, desialation of hepatoma cell-secreted LDL with neuraminidase did not normalize the negative charge to that of neuraminidase-treated plasma LDL. Western blots of thrombin proteolytic fragments indicated that, in addition to the T1-T4 fragments seen in plasma apolipoprotein B, apolipoprotein B of hepatoma-derived LDL produced four to five new fragments (T5-T9), suggesting increased exposure of proteolytic sites. Western blotting of the new fragments with antibodies specific for known apolipoprotein B sequences suggests that many of the new cleavage sites cluster in or near the putative LDL receptor recognition site.
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PMID:Unique structural properties of apolipoprotein B in low-density lipoproteins produced by several human hepatoma-derived cell lines. 217 71

The effect of doxazosin on cholesterol synthesis was determined by measuring the content of deuterium-enriched cholesterol in rabbit fibroblasts with and without receptors for low-density lipoproteins (LDL) and in hepatoma (Hep G2 cells). Doxazosin, at concentrations of 5-20 mumol/L, increased LDL binding to hepatic cells in a dose-related manner. Also, in these hepatic cells, doxazosin produced dose-related decreases in both newly synthesized cholesterol and cholesterol ester. In rabbit fibroblasts that were LDL receptor negative, de novo cholesterol synthesis was markedly reduced by increasing concentrations of doxazosin. Taken together, these results suggest that doxazosin may have a direct inhibitory effect on cholesterol synthesis independent of the LDL receptor. The inhibition of cholesterol synthesis by doxazosin may cause cells to compensate by upregulating the LDL receptor, thereby increasing the importation of lipoprotein cholesterol and reducing LDL cholesterol in the medium. This hypothesis supports findings in the clinical setting whereby doxazosin has a beneficial effect on the lipid profile, and suggests a useful additional property for this antihypertensive agent.
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PMID:Effect of doxazosin on cholesterol synthesis in cell culture. 247 Oct 8

The low-density-lipoprotein (LDL)-receptor mRNA content of human hepatoma (Hep G2) cells has been estimated from densitometric scans of autoradiograms obtained following the hybridisation of Northern blots of a poly(A)-rich RNA fraction with a 32P-labelled cDNA probe for the LDL-receptor gene. The recovery of beta-actin mRNA was used to correct for losses occurring during the preparation of the poly(A)-rich RNA. The content of LDL-receptor mRNA was reduced when the cells were pre-incubated in medium containing foetal calf serum, 25-hydroxycholesterol, or LDL, compared to that measured in cells which had been pre-incubated in medium containing lipoprotein-deficient serum (LPDS). When insulin (100 mU/ml) was included in pre-incubation medium containing LPDS, the amount of LDL-receptor mRNA increased approximately twofold. The level of beta-actin mRNA was not significantly increased by insulin treatment. Addition of insulin to incubation medium containing LPDS also overcame the suppressive effect of exogenous LDL on the cellular content of mRNA for the LDL receptor. These findings suggest that one action of insulin in these cells may be to promote transcription of the LDL-receptor gene by a mechanism that can override the sterol regulatory pathway.
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PMID:Regulation of low-density-lipoprotein-receptor mRNA by insulin in human hepatoma Hep G2 cells. 247 39

Human hepatoma HepG2 cells were used to study the effects of cholesterol loading and depletion on apolipoprotein B (apoB) secretion and low-density lipoprotein (LDL) receptor activity. Exposure of HepG2 cells to cholesterol and oleic acid, which elevated intracellular cholesterol levels, stimulated apoB secretion and reduced receptor-mediated uptake of LDL, whereas recombinant complexes of apolipoprotein A-I with dimyristoylphosphatidylcholine, which depleted the cellular cholesterol pool, inhibited apoB secretion and up-regulated LDL receptors. Significant negative correlation (r = -0.92, P less than 0.001) between the levels of apoB secretion and LDL uptake was found. These data suggest that the cholesterol content of the cells may induce concomitant changes in apoB secretion and LDL receptor activity.
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PMID:Effect of cell cholesterol content on apolipoprotein B secretion and LDL receptor activity in the human hepatoma cell line, HepG2. 253 98

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

Administration of estrogens in pharmacologic doses to rats and rabbits induces hepatic low-density lipoprotein (LDL) receptor activity. To determine if estrogens can regulate LDL receptor activity in human cells, 125I-LDL binding and ligand blotting studies were performed with the cell line Hep G2, well-differentiated cells derived from a human hepatoma, and with normal human fibroblasts. Addition of estradiol to Hep G2 cells growing in lipoprotein-deficient medium increased cell surface receptor activity by 141%, whereas fibroblast receptors were slightly reduced. Measurement of LDL internalization and degradation showed that estradiol induced the entire LDL receptor pathway and not simply surface receptors for LDL. Scatchard analysis of specific binding data in Hep G2 cells revealed that increased LDL receptor activity was due to high-affinity binding. When Hep G2 cells were incubated with LDL as well as estradiol, estradiol induction of LDL receptor activity did not occur. Estrogen treatment reduced Hep G2 free cholesterol content by 24% as determined by gas-liquid chromatography but had no significant effect on fibroblast free cholesterol, suggesting that estrogens may induce Hep G2 LDL receptor activity indirectly by lowering intracellular cholesterol. LDL receptor activity in Hep G2 cells grown in the absence of estradiol was resistant to down-regulation by LDL; incubation of cells with LDL for 48 h reduced receptor activity by only 25.8% in Hep G2 cells compared to 80.3% in fibroblasts. The Hep G2 LDL receptor was shown to be biochemically similar to the fibroblast receptor by ligand blotting and immunoblotting with IgG-C7, a monoclonal antibody to the extrahepatic LDL receptor.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Estrogens induce low-density lipoprotein receptor activity and decrease intracellular cholesterol in human hepatoma cell line Hep G2. 282 2


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