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)

In this study the effect of lipoprotein lipase (LPL) on the selective uptake of high density lipoprotein (HDL) cholesteryl esters (CE) by hepatic cells was investigated. Human HDL3 (d 1.125-1.21 g/ml) was radiolabeled with 125I in the protein moiety and with 3H in the CE moiety. LPL was prepared from bovine milk. Human hepatocytes in primary culture and human Hep3B hepatoma cells were incubated in medium containing doubly radiolabeled HDL3 with or without LPL. Without LPL, apparent HDL3 particle uptake according to the lipid tracer (3H) was in excess of that due to the protein label (125I) indicating selective CE uptake from HDL3. Addition of LPL increased selective CE uptake up to 7-fold. This stimulation of HDL3 selective CE uptake was independent of the lipolytic activity of LPL as suggested by several experimental approaches. Cell surface heparan sulfate proteoglycan deficiency decreased the LPL-mediated increase in selective CE uptake suggesting an important role for these molecules. In low density lipoprotein (LDL) receptor- or LDL receptor-related protein-(LRP)-deficient cells, LPL increased selective CE uptake as it did in normal cells yielding no evidence that these receptors play a role in the LPL effect on selective CE uptake. In summary, lipoprotein lipase increases the selective uptake of high density lipoprotein-associated cholesteryl ester by hepatic cells in culture. This effect is dependent on cell surface heparan sulfate proteoglycans but independent of lipolysis and of endocytosis mediated by low density lipoprotein receptor-related or low density lipoprotein receptors.
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PMID:Lipoprotein lipase mediates an increase in the selective uptake of high density lipoprotein-associated cholesteryl esters by hepatic cells in culture. 968 36

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

We have recently described a novel recycling pathway of triglyceride-rich lipoprotein (TRL)-associated apolipoprotein (apo) E in human hepatoma cells. We now demonstrate that not only TRL-derived apoE but also lipoprotein lipase (LPL) is efficiently recycled in vitro and in vivo. Similar recycling kinetics of apoE and LPL in normal and low density lipoprotein receptor-negative human fibroblasts also indicate that the low density lipoprotein receptor-related protein seems to be involved. Intracellular sorting mechanisms are responsible for reduced lysosomal degradation of both ligands after receptor-mediated internalization. Immediately after internalization in rat liver, TRLs are disintegrated, and apoE and LPL are found in endosomal compartments, whereas TRL-derived phospholipids accumulate in the perinuclear region of hepatocytes. Subsequently, substantial amounts of both proteins can be found in purified recycling endosomes, indicating a potential resecretion of these TRL components. Pulse-chase experiments of perfused rat livers with radiolabeled TRLs demonstrated a serum-induced release of internalized apoE and LPL into the perfusate. Analysis of the secreted proteins identified approximately 80% of the recycled TRL-derived proteins in the high density lipoprotein fractions. These results provide the first evidence that recycling of TRL-derived apoE and LPL could play an important role in the modulation of lipoproteins in vivo.
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PMID:Recycling of apolipoprotein E and lipoprotein lipase through endosomal compartments in vivo. 1154 20

To obtain the expression of human low density lipoprotein receptor ligand binding domain in methylotropic yeast, firstly the DNA fragment encoding for human low density lipoprotein receptor ligand binding domain was amplified by RT-PCR with human hepatoma Bel-7402 total RNA as template. The nucleotide sequencing analysis indicated that the sequence of the cloned DNA fragment was as same as the reported human LDLR cDNA sequence. Then the expression vector pPIC9K-sLDLr was constructed, linearized and introduced into Pichia pastoris GS115 by electroporation. The recombinant sLDLR was identified by SDS-PAGE, Western blot and Ligand binding blot in supernatant of GS115/pPIC9K-sLDLr. The SDS-PAGE and Western blot analysis showed that the apparent molecular weight of expressed sLDLR was about 36 kD. And the ligand binding blot analysis indicated the expressed sLDLR has the biological activity. The sLDLR, which had the biological activity, was successfully secretorily expressed in the Pichia pastoris (GS115).
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PMID:[Expression of the human soluble low density lipoprotein receptor in methylotropic yeast]. 1197 97

Mutations in Proprotein Convertase Subtilisin Kexin 9 (PCSK9) have been associated with autosomal dominant hypercholesterolemia. In vivo kinetic studies indicate that LDL catabolism was impaired and apolipoprotein B (apoB)-containing lipoprotein synthesis was enhanced in two patients presenting with the S127R mutation on PCSK9. To understand the physiological role of PCSK9, we overexpressed human PCSK9 in mouse and cellular models as well as attenuated the endogenous expression of PCSK9 in HuH7 hepatoma cells using RNA interference. Here, we show that PCSK9 dramatically impairs the expression of the low density lipoprotein receptor (LDLr) and, in turn, LDL cellular binding as well as LDL clearance from the plasma compartment in C57BL6/J mice but not in LDLr-deficient mice, establishing a definitive role for PCSK9 in the modulation of the LDLr metabolic pathway. In contrast to data obtained in S127R-PCSK9 patients presenting with increased apoB production, our study indicates that wild-type PCSK9 does not significantly alter the production and/or secretion of VLDL apoB in either cultured cells or mice. Finally, we show that unlike PCSK9 overexpression in mice, the S127R mutation in patients led to increased VLDL apoB levels, suggesting a potential gain of function for S127R-PCSK9 in humans.
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PMID:Wild-type PCSK9 inhibits LDL clearance but does not affect apoB-containing lipoprotein production in mouse and cultured cells. 1574 54

Dysregulation of mitogen-activated protein kinase (MAPK) signaling pathways by various viruses has been shown to be responsible for viral pathogenicity. The molecular mechanism by which hepatitis C virus (HCV) infection caused human liver diseases has been investigated on the basis of abnormal intracellular signal events. Current data are very limited involved in transmembrane signal transduction triggered by HCV E2 protein. Here we explored regulation of the MAPK/extracellular signal-regulated kinase (MAPK/ERK) signaling pathway by E2 expressed in Chinese hamster oval cells. In human hepatoma Huh-7 cells, E2 specifically activated the MAPK/ERK pathway including downstream transcription factor ATF-2 and greatly promoted cell proliferation. CD81 and low density lipoprotein receptor (LDLR) on the cell surface mediated binding of E2 to Huh-7 cells. The MAPK/ERK activation and cell proliferation driven by E2 were suppressed by blockage of CD81 as well as LDLR. Furthermore, pretreatment with an upstream kinase MEK1/2 inhibitor U0126 also impaired the MAPK/ERK activation and cell proliferation induced by E2. Our results suggest that the MAPK/ERK signaling pathway triggered by HCV E2 via its receptors maintains survival and growth of target cells.
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PMID:Hepatitis C virus E2 protein promotes human hepatoma cell proliferation through the MAPK/ERK signaling pathway via cellular receptors. 1577 84

The alkaloid drug berberine (BBR) was recently described to decrease plasma cholesterol and triglycerides (TGs) in hypercholesterolemic patients by increasing expression of the hepatic low density lipoprotein receptor (LDLR). Using HepG2 human hepatoma cells, we found that BBR inhibits cholesterol and TG synthesis in a similar manner to the AMP-activated protein kinase (AMPK) activator 5-aminoimidazole-4-carboxamide 1-beta-ribofuranoside (AICAR). Significant increases in AMPK phosphorylation and AMPK activity were observed when the cells were incubated with BBR. Activation of AMPK was also demonstrated by measuring the phosphorylation of acetyl-CoA carboxylase, a substrate of AMPK, correlated with a subsequent increase in fatty acid oxidation. All of these effects were abolished by the mitogen-activated protein kinase kinase inhibitor PD98059. Treatment of hyperlipidemic hamsters with BBR decreased plasma LDL cholesterol and strongly reduced fat storage in the liver. These findings indicate that BBR, in addition to upregulating the LDLR, inhibits lipid synthesis in human hepatocytes through the activation of AMPK. These effects could account for the strong reduction of plasma TGs observed with this drug in clinical trials.
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PMID:Inhibition of lipid synthesis through activation of AMP kinase: an additional mechanism for the hypolipidemic effects of berberine. 1650 37

Proprotein convertase subtilisin/kexin type 9 (PCSK9), a member of the proteinase K subfamily of subtilases, promotes internalization and degradation of low density lipoprotein receptors (LDLRs) after binding the receptor on the surface of hepatocytes. PCSK9 has autocatalytic activity that releases the prodomain at the N terminus of the protein. The prodomain remains tightly associated with the catalytic domain as the complex transits the secretory pathway. It is not known whether enzymatic activity is required for the LDLR-reducing effects of PCSK9. Here we expressed the prodomain together with a catalytically inactive protease domain in cells and purified the protein from the medium. The ability of the catalytically inactive PCSK9 to bind and degrade LDLRs when added to culture medium of human hepatoma HepG2 cells at physiological concentrations was similar to that seen using wild-type protein. Similarly, a catalytic-dead version of a gain-of-function mutant, PCSK9(D374Y), showed no loss of activity compared with a catalytically active counterpart; both proteins displayed approximately 10-fold increased activity in degradation of cell surface LDLRs compared with wild-type PCSK9. We conclude that the ability of PCSK9 to degrade LDLRs is independent of catalytic activity and suggest that PCSK9 functions as a chaperone to prevent LDLR recycling and/or to target LDLRs for lysosomal degradation.
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PMID:Catalytic activity is not required for secreted PCSK9 to reduce low density lipoprotein receptors in HepG2 cells. 1753 35

HCV recovered from low density fractions of infected blood is associated with lipid and host apo-lipoproteins in lipo-viro-particles (LVP). It has been proposed that these particles are capable of binding and entering hepatocytes by viral glycoprotein independent mechanisms utilizing uptake pathways of normal host lipoproteins after binding to cell surface glycosaminoglycans (GAG), the low density lipoprotein receptor (LDL-r) or scavenger receptor B1 (SR-B1). In this study binding to human hepatoma cells of HCV low density RNA containing particles, semi-purified from macerates of infected human liver, is compared with that of normal host low density lipoprotein (LDL). Binding of both LDL and HCV low density RNA containing particles paralleled LDL-r but not SR-B1 expression on the recipient cells. Binding of both particle types was sensitive to suramin at 0 degrees C but less so at 37 degrees C suggesting that they both bind initially to GAG but, at 37 degrees C, are internalized or transferred to a suramin resistant receptor. Suramin resistant uptake of both particles was blocked in the presence of excess LDL or oxidized LDL. However, whilst LDL uptake was blocked by anti-apoB-100, HCV low density RNA uptake was enhanced by anti-apoB100 and further enhanced by a cocktail of anti-apo-B100 and anti-apoE. Pre-incubation of HCV low density RNA containing particles with antibodies to the E2 glycoprotein had little or no effect on uptake. These data indicate that whilst liver derived HCV RNA containing particles are taken up by HepG2 cells by a virus glycoprotein independent mechanism, the mechanism differs from that of LDL uptake.
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PMID:Binding of liver derived, low density hepatitis C virus to human hepatoma cells. 1836 Aug 95

Very low density lipoprotein receptor (VLDLR) belongs to the low density lipoprotein receptor family, it is divided into two subtypes according to forms with an absence (type II) or a presence (type I) of the O-linked sugar domain. VLDLR have been detected in kinds of cancers so far; however, the subtype of VLDLR in hepatocellular carcinoma (HCC) tissues and hepatoma cell lines has yet to be reported. We detected the VLDLR expression in 39 cases of hepatocellular carcinoma and in three kinds of hepatoma cell lines: HepG2, HBV transfected HepG2.2.15, SMMC-7721 and normal human fetal liver cell line LO2 using RT-PCR and western blotting. The results showed that both type I and type II VLDLR were detected in HCC tissues and hepatoma cell lines, and the type II VLDLR expression was significantly higher than that of type I in cell lines. We inhibited the type II VLDLR expression by shRNA-mediated RNA interference in HepG2, SMMC-7721 cell and then subsequently found the cell proliferation slowed down. The cyclinD1 expression confirmed the cell cycle was arrested at the G0/G1 phase, suggesting that inhibiting the type II VLDLR expression may have a positive impact on carcinogenesis of HCC.
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PMID:Very low density lipoprotein receptor subtype II silencing by RNA interference inhibits cell proliferation in hepatoma cell lines. 2103 46


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