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)

We previously reported that polymyxin B (PMB) enhances cellular catabolism of low density lipoproteins (LDLs) through a non-LDL receptor-mediated endocytotic pathway. These data were obtained mainly by using Hep G2 cells, a well differentiated human hepatoma cell line. In the current study, we explore the mechanisms of PMB-mediated endocytotic catabolism of LDL. We found that PMB enhanced LDL catabolism also in homozygous familial hypercholesterolemia fibroblasts, thereby establishing that PMB-mediated cellular catabolism of LDL does not involve LDL receptors. By using [14C]sucrose, and ligands for the asialoglycoprotein (ASGP) receptors, possibilities were excluded that PMB enhances cellular endocytosis of LDL, by inducing a general increase of cellular pinocytic activity or by causing endocytosis of LDL via the ASGP receptors in Hep G2 cells. We further show, by using polymyxin B coupled Sepharose 4B (PMB-Sepharose 4B) beads, that PMB binds to LDL to form a complex. This binding was tight, and changes in pH and salt concentrations had no significant effect on the binding, but unlabelled LDL competed with 125I-LDL to bind to PMB-Sepharose 4B. Urea and endotoxins decreased this binding, suggesting that PMB binds to LDL at least partially through hydrophobic interactions. Agarose gel electrophoresis of PMB-LDL indicates that PMB cationizes LDL. In conclusion, PMB binds to LDL to form a PMB-LDL complex presumably through interactions between lipid groups. This endows LDL with positive charges, which enhances LDL binding to negatively charged cell membranes, and such bound LDL is rapidly internalized through absorptive endocytosis.
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PMID:Polymyxin B complexes with and cationizes low density lipoproteins. The cause of polymyxin B-induced enhancement of endocytotic catabolism of low density lipoproteins. 849 42

A neutral bile salt-dependent cholesteryl ester hydrolase (CEH) in rat liver has been shown to be indistinguishable from the pancreatic CEH by a number of criteria (Harrison, E. H. (1988) Biochim. Biophys. Acta 963, 28-34; Zolfaghari, R., Harrison, E. H., Ross, A. C., and Fisher, E. A. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 6913-6919; Camulli, E. D., Linke, M. J., Brockman, H. L., and Hui, D. Y. (1989) Biochim. Biophys. Acta 1005, 177-182). The rat hepatoma cell line Fu5AH, which lacks this particular CEH activity, was stably transfected with the cDNA of rat pancreatic CEH, and the effects on cholesterol and cholesteryl ester metabolism in clones with varying levels of CEH expression determined. In spite of significant amounts of intracellular enzyme protein demonstrated by Western blotting, in cell lysates there was a consistently low level of catalytic activity, and in cultured cells there was no evidence that CEH served as an effective intracellular cholesteryl ester hydrolase or synthase. In contrast, the catalytic activity of the secreted enzyme was relatively higher and there was a small, but significant, increase in the ability of high density lipoprotein (added to the medium) to promote the clearance of cholesteryl ester from cells secreting high levels of CEH. Overall, these results suggest that in the liver, intracellular CEH does not significantly affect the turnover of cholesteryl esters and warrant future studies focusing on the function of the secreted enzyme. For example, secreted CEH may modify lipoproteins and affect their interactions with cells.
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PMID:The effects of varying the expression of a neutral cholesteryl ester hydrolase on the turnover of cholesteryl ester in rat hepatoma cells. 851 86

The effect has been studied of various media, hormones and of amino acids on the membrane potential of rat hepatoma cells in culture measured by microelectrode impalement. Cells in Eagle's minimal essential medium plus 5% serum had a value which varied daily from about 5-8 mV, inside negative. The membrane potential of rat hepatocytes was measured to be 8.7 +/- 0.2 mV, inside negative. The membrane potential of the hepatoma cells was decreased by insulin and increased by glucagon. Membrane potential was unaffected by change of medium to Hanks' or Earle's balanced salt solutions or deprivation of serum. It was, however, reduced in cells in phosphate-buffered saline and by reduction of pH. The former effect was shown to be due to the higher [Na+] of phosphate-buffered saline as opposed to the other media. Addition of alanine, glycine, serine, proline and methylaminoisobutyrate all reduced membrane potential by 2-3 mV. Smaller decreases were seen with methionine, leucine and phenylalanine, but none with glutamine, threonine, BCH (2-aminonorborane-2-carboxylic acid) and D-alanine. The results are compared with the effects of similar conditions on aminoisobutyrate uptake. Whilst there was a correlation under some conditions there was not under others. It is concluded that for the hepatoma cells factors additional to the membrane potential must exert some influence on the capacity for amino acid transport.
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PMID:Membrane potential of rat hepatoma cells in culture: influence of factors affecting amino acid transport. 856 68

Both enantiomers of alpha-naphthyl 2-phenylpropanoate (PhPr(ONap)), N-acetylalaninate (AcAla(ONap)), N-methoxycarbonylalaninate (MocAla(ONap)), N-methoxycarbonylvalinate (MocVal(ONap)), N-acetylprolinate (AcPro(ONap)), and N-(trifluoroacetyl)prolinate (TfaPro(ONap)) were prepared and used with Fast Blue RR salt for activity staining of esterases separated by polyacrylamide gel electrophoresis. Comparison of the band thicknesses stained with each enantiomer indicates stereoselectivity of the major esterase in that band. Several esterases in normal rat liver, rat hepatoma-derived cells, and mouse B16 melanoma showed alteration or inversion of stereoselectivity by the substrate change from MocAla(ONap) to MocVal(ONap) or from AcPro(ONap) to TfaPro(ONap). The stereoselectivity of the major esterases for MocVal(ONap) was reversed between the murine liver and the B16 melanoma enzymes. The present staining with chiral naphthyl esters is very effective for surveying rapidly the stereoselectivity of animal tissue and cancer esterases.
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PMID:Direct evaluation of stereoselectivity of cancer esterases by polyacrylamide gel electrophoresis coupled with activity staining with chiral naphthyl esters. 859 76

Bile salt stimulated cholesterol esterase is predominantly synthesized in the pancreas. However, this enzyme is also synthesized by the liver and was found to be present in plasma. The physiologic role of the systemic cholesterol esterase has not been clearly defined. In the current study, the human hepatoma cell line HepG2 was used as a model to determine the role of cholesterol esterase on hepatic uptake of high density lipoprotein (HDL)-associated cholesteryl esters. The results showed that hepatic uptake of the cholesteryl esters analog [3H]cholesteryl ether on reconstituted HDL was inhibited by anti-cholesterol esterase antibodies. The HDL-associated cholesteryl ester transported to HepG2 cells was also increased 2-fold in the presence of taurocholate, an activator of the cholesterol esterase. These results suggest that liver-derived cholesterol esterase may play an important role in cellular uptake of cholesteryl esters from HDL. This hypothesis was supported by demonstrating the ability of exogenously added cholesterol esterase to further enhance hepatic uptake of HDL-associated cholesteryl esters. The results of the current study also showed that cholesterol esterase increased free-to-esterified cholesterol ratio in the lipoprotein. Thus, alteration of HDL structure and composition contributes to the cholesterol esterase-induced cellular uptake of HDL-associated cholesteryl esters. On the basis of these observations, we propose that liver-derived cholesterol esterase may play an important role in lipoprotein metabolism.
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PMID:Bile salt stimulated cholesterol esterase increases uptake of high density lipoprotein-associated cholesteryl esters by HepG2 cells. 863 15

The two steps of DNA digestion seen in apoptotic cells were recreated in nuclei isolated from 5123tc rat hepatoma cells. The initial DNA cleavage, into high molecular weight fragments (300-50 kb), was stimulated by magnesium ions alone, whereas the second step required both calcium and magnesium ions and produced the ladder of oligonucleosomes. Endonucleolytic activities involved in both steps of DNA cleavage could be separated under appropriate conditions since the magnesium-modulated activity was tightly bound to the chromatin whereas the calcium/magnesium-dependent internucleosomal cleaving activity was easily extractable with a low ionic strength buffer. This calcium/ magnesium-dependent activity was attributed to a novel 97 kDa endonuclease which was also activated by manganese and cobalt and inhibited by millimolar concentrations of zinc, consistent with the properties ascribed to the apoptotic endonuclease. Furthermore, this activity became resistant to extraction with a low salt buffer in nuclei of apoptotic cells. Isoelectrofocusing revealed that the p97 protein existed in multiple forms of different isoelectric points (pI range 4.6-5.0), indicative of its postranslational modification. The p97 enzyme was present constitutively in a variety of cultured cells and rat tissues. It was active over a broad range of pH (6-9), but it was inactivated by reducing agents. In vitro, it displayed both endo- and exonucleolytic activities, and it was capable of both single- and double-stranded DNA cleavage. Rabbit polyclonal anti-p97 antibodies were generated and used to further distinguish this protein from other known cellular nucleases, namely, DNases I and II.
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PMID:Identification of a novel 97 kDa endonuclease capable of internucleosomal DNA cleavage. 902 Jul 68

Rat liver d-3-phosphoglycerate dehydrogenase was purified to homogeneity and digested with trypsin, and the sequences of two peptides were determined. This sequence information was used to screen a rat hepatoma cDNA library. Among 11 positive clones, two covered the whole coding sequence. The deduced amino acid sequence (533 residues; Mr 56493) shared closer similarity with Bacillus subtilis 3-phosphoglycerate dehydrogenase than with the enzymes from Escherichia coli, Haemophilus influenzae and Saccharomyces cerevisiae. In all cases the similarity was most apparent in the substrate- and NAD+-binding domains, and low or insignificant in the C-terminal domain. A corresponding 2.1 kb mRNA was present in rat tissues including kidney, brain and testis, whatever the dietary status, and also in livers of animals fed a protein-free, carbohydrate-rich diet, but not in livers of control rats, suggesting transcriptional regulation. The full-length rat 3-phosphoglycerate dehydrogenase was expressed in E. coli and purified. The recombinant enzyme and the protein purified from liver displayed hyperbolic kinetics with respect to 3-phosphoglycerate, NAD+ and NADH, but substrate inhibition by 3-phosphohydroxypyruvate was observed; this inhibition was antagonized by salts. Similar properties were observed with a truncated form of 3-phosphoglycerate dehydrogenase lacking the C-terminal domain, indicating that the latter is not implicated in substrate inhibition or in salt effects. By contrast with the bacterial enzyme, rat 3-phosphoglycerate dehydrogenase did not catalyse the reduction of 2-oxoglutarate, indicating that this enzyme is not involved in human D- or L-hydroxyglutaric aciduria.
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PMID:Cloning, sequencing and expression of rat liver 3-phosphoglycerate dehydrogenase. 916 25

The Ah receptor (AhR) and the Ah receptor nuclear translocator (ARNT) are capable of forming a transcriptionally active heterodimeric complex. The biochemical events that are required for dimerization and transactivation are not fully understood. The purpose of this study was to determine whether covalent modifications of ARNT occur between ARNT existing in the monomeric form and after heterodimerization with the AhR and subsequent binding to DNA. Mouse hepatoma cell line 1c1c7 (Hepa 1) cytosol and ARNT immunoprecipitations were subjected to two-dimensional gel electrophoresis. ARNT was visualized with two antibodies, with distinct epitope specificity, and each detected a considerable level of charge heterogeneity. The pI range observed was 5.7-6.4, with the predominant form at a pI of 6.2. The AhR/ARNT heterodimer was immunoprecipitated from high-salt nuclear extract obtained from Hepa 1 cells treated with beta-naphthoflavone using an anti-AhR polyclonal antibody. This immunoprecipitate was subjected to two-dimensional gel electrophoresis, and coimmunoprecipitated ARNT was visualized. The results indicated that ARNT complexed with the AhR in the nucleus has an isoform pattern shifted toward the basic end, with the predominant isoform having a pI of 6.8. Thus, a significant shift in pI occurs during the dimerization and/or after binding to DNA. In vitro transformation of the AhR with 2,3,7,8-tetrachlorodibenzo-p-dioxin in cytosol leads to heterodimerization with ARNT. Two-dimensional gel electrophoresis of ARNT coimmunoprecipitated with the AhR revealed the same isoform pattern as seen in cytosol. This would indicate that each isoform of ARNT is capable of heterodimerizing with the AhRin vitro. ARNT is a phosphoprotein, and the more acidic isoforms appear to have a higher level of phosphorylation.
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PMID:Ah receptor nuclear translocator protein heterogeneity is altered after heterodimerization with the Ah receptor. 922 Sep 96

The pyridine derivative cerivastatin is a new entirely synthetic and enantiomerically pure inhibitor of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase. As a sodium salt cerivastatin is present in the active, open ring form. Cerivastatin inhibited the membrane-bound (non-solubilized) HMG-CoA reductase of the native microsomal fraction isolated from rat liver with a Ki value of 1.3 x 10(-9) M. The reference compound lovastatin was 100-fold less potent and exhibited a Ki value of 150 x 10(-9) M. Cerivastatin inhibited the cholesterol synthesis in the human hepatoma cell line HepG2 cells with a similar IC50 value of 1.0 x 10(-9) M. In vivo studies reflected its high in vitro activity. In both rats and dogs, cerivastatin inhibited the hepatic [14C]cholesterol synthesis from [14C]acetate with an oral ED50 value of 0.002 mg/kg body weight, while lovastatin exhibited an oral ED50 value of 0.3 mg/kg in rats, showing again the ratio of 100 or more between cerivastatin and lovastatin. In the small intestine and testes, cerivastatin was at least 50-fold less active with oral ED50 values higher than 0.1 mg/kg, which is indicative for a high liver selectivity of cerivastatin. In cholestyramine-primed dogs cerivastatin dose-dependently lowered the serum cholesterol concentrations by up to 59% with 0.1 mg/kg after 20 days. Interestingly, the serum triglycerides were markedly reduced by 53 and 76% with 0.03 and 0.1 mg/kg, respectively. In normal chow fed dogs the low density lipoprotein (LDL) concentrations were reduced by up to 75% after 0.1 mg cerivastatin/kg. The ratio of HDL/LDL increased by 81% compared with a change of only 14% in the placebo treated control group. The antiatherogenic effect of cerivastatin was shown in rabbits fed a diet enriched with 0.2% cholesterol. After 9 weeks on diet 0.1 mg cerivastatin/kg decreased the accumulation of cholesterol ester in the arterial tissue by 73%. In summary, these data as compared to published data on other HMG-CoA reductase inhibitors demonstrate cerivastatin to be the most active compound in this class. Vastatins used in therapy are effective in mg doses, while cerivastatin offers a new low dose therapy in the microg range.
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PMID:Cerivastatin: pharmacology of a novel synthetic and highly active HMG-CoA reductase inhibitor. 939 80

Efficient transport of bile acids, a typical characteristic of hepatocytes, is partially lost in most hepatoma cell lines and in normal hepatocytes after some days in culture. We have tested whether the polarized rat hepatoma-human fibroblast hybrid WIF (hybrids between W138 and Fao cells) cells previously obtained by our group were able to perform vectorial transport of the fluorescent bile acid derivative cholylglycylamidofluorescein (CGamF) towards the bile canaliculi (BC). Four different WIF clones were analyzed. All were well polarized, as shown by the formation of spherical and even tubular BC-like structures and by the restricted localization at the BC, visualized by immunofluorescence, of the apical membrane marker HA4, a possible bile acid carrier. WIF-B and its subclone WIF-B9 were found to accumulate CGamF in 65% to 75% of their BC. This transport was time, temperature, and partly sodium dependent and was inhibited by coincubation with the parental natural bile salt cholylglycine. Dinitrophenyl glutathione, a substrate of the canalicular multispecific organic anion transporter, did not inhibit CGamF canalicular secretion, whereas it greatly impaired the canalicular secretion of a non-bile acid organic anion, fluorescein, generated intracellularly from fluorescein diacetate. Confocal microscopy confirmed the presence of CGamF in the cytoplasm, supporting a transcellular route from medium to BC. In contrast, two other polarized clones exhibited a poor ability (WIF 12-6) or no ability (WIF12-1 TGdelta) to vectorially transport CGamE In conclusion, WIF-B and WIF-B9 exhibit not only structural but also functional polarity, at least as far as vectorial organic anion transport is concerned.
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PMID:Efficient in vitro vectorial transport of a fluorescent conjugated bile acid analogue by polarized hepatic hybrid WIF-B and WIF-B9 cells. 946 60


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