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)

Apolipoprotein A-I is a major secretory product of the human hepatoma cell line, Hep G2; approx. 70% of apolipoprotein A-I was separated from the medium as lipid-poor apolipoprotein A-I in the d greater than 1.21 g/ml fraction while 30% was associated with high-density lipoproteins (HDL) of d 1.063-1.21 g/ml. The lipid-poor apolipoprotein A-I contains 50% proapolipoprotein A-I which is similar to the isoform distribution in Hep G2 preformed HDL. We tested the ability of lipid-poor apolipoprotein A-I from Hep G2 to form complexes with dimyristoylphosphatidylcholine (DMPC) vesicles at DMPC/apolipoprotein A-I molar ratios of 100:1 and 300:1. Lipid-poor apolipoprotein A-I was recovered in complex form while at a 300:1 ratio, 68.8 +/- 6.3% was recovered. On electron microscopy, the former complexes were small discs 16.9 nm +/- 4.5 S.D. in diameter while the latter were larger discs 21.4 +/- 4.4 nm diameter. Non-denaturing gradient gel electrophoresis of complexes formed at a 100:1 ratio had a peak in the region corresponding to 9.64 +/- 0.08 nm; these particles possessed two apolipoprotein A-I molecules. At the higher ratio, 300:1, two distinct complexes were identifiable, one which banded in the 9.7 nm region and the other in the 16.9-18.7 nm region. The former particles contained two molecules of apolipoprotein A-I and the latter, three molecules. This study demonstrates that lipid-poor apolipoprotein A-I which is rich in more basic isoforms forms discrete lipoprotein complexes similar to those formed by mature apolipoprotein A-I. It is further suggested that, under the appropriate conditions, precursor or nascent HDL may be assembled extracellularly.
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PMID:Lipid-poor apolipoprotein A-I in Hep G2 cells: formation of lipid-rich particles by incubation with dimyristoylphosphatidylcholine. 303 92

Human hepatocarcinoma Hep G2 cells were grown in culture medium containing [45Ca2+]. The secreted lipoproteins of d less than 1.063 g/ml and d 1.063-1.21 g/ml were isolated from the culture media and analyzed by 3.3% and 7% SDS-polyacrylamide gel electrophoresis. Radioactivity profiles of [45Ca] from the gels showed that the peak of radioactivity corresponded to the apolipoprotein B band. The molar ratio of the incorporated [45Ca2+] and apolipoprotein B was close to unity. No radioactivity was found associated with any other secreted apolipoproteins. To confirm these findings, apolipoprotein B-containing lipoproteins were precipitated with anti-apolipoprotein B and high density lipoproteins were precipitated with anti-apolipoprotein A-I. Only the former precipitate was radioactive. These results suggest that apolipoprotein B is a calcium binding protein.
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PMID:Apolipoprotein B is a calcium binding protein. 308 60

Lipoprotein synthesis was demonstrated by double diffusion with low density lipoprotein antibody, and by 3H-labeled amino acid incorporation into proteins of the d less than 1.063 g/ml centrifugally isolated lipoprotein fraction. Radioactive label was incorporated predominantly into apolipoprotein B (60%), apolipoprotein A-I (20%) and apolipoprotein C (12%), as determined by Sepharose column chromatography and polyacrylamide gel electrophoresis. Incorporation of radioactive label into apolipoprotein B was inhibited by the presence of albumin in the medium, and was restored to control levels with the addition of 1 mM oleic acid, indicating that cell synthesis of apolipoproteins could be modified by culture conditions. The human hepatoma cell line, Hep G2, provides a potential in vitro model for the study of regulation of human hepatic lipoprotein and apolipoprotein synthesis.
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PMID:Lipoprotein apolipoprotein synthesis by human hepatoma cells in culture. 627 70

The primary translation product of human intestinal apolipoprotein A-I mRNA was isolated from wheat germ and ascites cell-free translation systems. Comparison of its NH2-terminal sequence with that of plasma high density lipoprotein-associated A-I showed that it is initially synthesized as a preproprotein. Like rat preproapolipoprotein A-I, it contains an 18-amino acid prepeptide and a 6-amino acid propeptide. The highly unusual COOH-terminal Gln-Gln dipeptide present in the rat pro-segment is also represented at the same position in the human sequence. The functional division of the 24-amino acid NH2-terminal extention into pro- and presegments was verified by finding that the stable intracellular form of A-I in a human hepatoma cell line was the proprotein. Edman degradation of radiolabeled intracellular and extracellular A-I indicated that this apolipoprotein was secreted without proteolytic cleavage of its hexapeptide prosegment. Therefore, it appears that apolipoprotein A-I undergoes an additional proteolytic processing step before it is fully integrated into plasma high density lipoprotein. Two-dimensional gel electrophoresis of purified proapolipoprotein A-I isolated from the hepatocyte cell culture media indicated that it corresponds to isoforms 2 and 3, the basic A-I isoproteins which are the precursors of plasma A-I and the predominant plasma A-I isoforms found in patients with Tangier's disease (Zannis, V. I., Lees, A. M., Lees, R. S., and Breslow, J. L. (1982) J. Biol. Chem., 257, 4978-4986). Therefore this pathologic state probably arises from a defect in the conversion of proapolipoprotein A-I to apolipoprotein A-I.
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PMID:Proteolytic processing of human preproapolipoprotein A-I. A proposed defect in the conversion of pro A-I to A-I in Tangier's disease. 630 70

Previous studies have established that human hepatocellular carcinoma cells (Hep G2) secrete into serum-free medium the pro form of apolipoprotein A-I (proapo-A-I) suggesting that its conversion to mature apo-A-I occurs after secretion. In order to assess the mode and site of proapo-A-I to apo-A-I conversion, we incubated the medium from [3H]proline-labeled Hep G2 cells with either human plasma, serum, lymph, or fractions thereof obtained by density gradient ultracentrifugation. The conversion was monitored by two-dimensional gel electrophoresis and by Edman degradation. Human plasma, serum, or mesenteric lymph all induced proapo-A-I to apo-A-I conversion; this was time dependent, unaffected by the serine protease inhibitor phenylmethylsulfonyl fluoride and inhibited by EDTA. Purified radiolabeled proapo-A-I bound to lymph chylomicrons and plasma high density lipoproteins. The converting enzyme was associated with both of these particles. Activity was also found in the d greater than 1.21-g/ml fraction and may have been derived from high density lipoprotein after displacement by high salts and/or ultracentrifugal force. We conclude that the conversion of proapo-A-I to apo-A-I occurs extracellularly and is probably effected by a metallo-enzyme which may act at the amphiphilic surface of either chylomicrons or high density lipoproteins.
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PMID:In vitro conversion of proapoprotein A-I to apoprotein A-I. Partial characterization of an extracellular enzyme activity. 631 11

We examined the ability of the plasma of a 52-yr-old male Tangier patient to effect the conversion of radiolabeled pro-apolipoprotein A-I (apo A-I), isolated from hepatoma cell culture media, into mature apo A-I. The conversion was assessed by amino-terminal sequence analysis, isoform patterns with two-dimensional gel electrophoresis, and a rapid assay based on the different solubilities of intact pro-apo A-I and its hexapeptide prosegment in 10% trichloroacetic acid. We found that the converting activity of Tangier plasma was comparable to that exhibited by control normolipidemic plasma and that in both cases pro-apo A-I was correctly processed at the Gln-Asp bond. After ultracentrifugal fractionation of Tangier plasma at d = 1.21 g/ml, the pro-apo A-I-to-mature apo A-I converting activity was mainly recovered in the middle fraction of d = 1.225 g/ml and was at least 10-fold more effective than the top and bottom fractions. In contrast, in normal plasma the activity was only present in the top and bottom fractions. It has been previously established that in Tangier plasma the pro-apo A-I/apo A-I ratio is significantly higher than normal (1 vs. 0.02). Our studies suggest that this abnormal ratio is not the result of a reduced converting enzyme activity and may relate to differences in turnover rates between Tangier and normal plasma apolipoproteins.
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PMID:Comparative in vitro study of the pro-apolipoprotein A-I to apolipoprotein A-I converting activity between normal and Tangier plasma. 643 45

The human hepatoma derived HepG2 cells were treated with transforming growth factor-beta (TGF-beta) or interleukin-6 (IL-6) +/- dexamethasone. The effects of treatment on lecithin:cholesterol acyltransferase (LCAT) catalytic activity and mRNA level as well as on the apolipoprotein A-I (apo A-I) mRNA level were determined. Both the LCAT activity in medium from treated HepG2 cells and the LCAT mRNA level were decreased by TGF-beta. There was no significant effect of IL-6 +/- dexamethasone, neither on the LCAT activity nor on LCAT mRNA levels. Treatment with dexamethasone alone resulted in a decreased LCAT activity in spite of a slight increase in LCAT mRNA level. The apo A-I mRNA level was reduced after treatment with TGF-beta and increased after treatment with IL-6 +/- dexamethasone and dexamethasone alone. To analyze if the effects on mRNA levels were caused by transcriptional or post-transcriptional mechanisms, run-on experiments on isolated nuclei from treated HepG2 cells and mRNA degradation experiments were performed. The transcription rate of the LCAT gene was not affected by TGF-beta, but was increased (50-100%) after treatment with IL-6 +/- dexamethasone and dexamethasone alone. The transcription rate of the apo A-I gene was reduced (20%) by TGF-beta and increased (30-60%) by IL-6 +/- dexamethasone and dexamethasone alone. Both dexamethasone and TGF-beta increased the rate of LCAT mRNA degradation. These results show that the reduced LCAT mRNA level after treatment with TGF-beta was caused by post-transcriptional mechanisms.
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PMID:Regulation of lecithin:cholesterol acyltransferase by TGF-beta and interleukin-6. 773 42

Previous studies have identified lipid-poor high density lipoproteins with electrophoretic pre-beta mobility as the initial acceptors of cell-derived cholesterol in human plasma. These lipoproteins contain apolipoprotein A-I (apo A-I) as their sole apolipoprotein. In the present study, incubation of human plasma with [3H]cholesterol-laden skin fibroblasts has led to the identification of another lipoprotein that serves as a potent initial acceptor of cell-derived cholesterol. This lipoprotein, which we term gamma-LpE, exhibits gamma mobility on agarose gel electrophoresis. As determined by nondenaturing PAGE and by electron microscopy, the size of the spherical particle ranges between 12 and 16 nm. SDS/PAGE and subsequent immunoblotting identified apoE as its sole apolipoprotein. Plasma from normal and apoA-I-deficient mice, but not from apoE-deficient mice, released [3H]cholesterol from fibroblasts into a gamma-migrating lipoprotein. Cell culture media from hepatoma cells or mouse peritoneal macrophages, both of which contain apoE of cellular origin, also promoted efflux of [3H]cholesterol from fibroblasts into a gamma-migrating fraction. This was not observed with cell culture medium from fibroblasts alone. In conclusion, our results strongly indicate the presence in human plasma of a lipoprotein containing only apoE, gamma-LpE, which is secreted by peripheral cells and is a potent acceptor of cell-derived cholesterol.
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PMID:A plasma lipoprotein containing only apolipoprotein E and with gamma mobility on electrophoresis releases cholesterol from cells. 812 90

Apolipoprotein (apo) A-I is the major protein component of high-density lipoproteins (HDLs), which are responsible for reverse cholesterol transport from peripheral tissues to the liver. A low level of plasma HDL is correlated with susceptibility to atherosclerosis and coronary heart disease. Mammalian apo A-I synthesis has been attributed mainly to liver and intestine. Recently, apo A-I expression has been shown in porcine brain capillaries, suggesting an independent lipid metabolism within the brain. In this study, protein synthesis and secretion were investigated in primary cultures of porcine brain microvascular endothelial cells and compared with those in large vessel endothelium. Active protein synthesis in vitro was demonstrated by metabolic labeling. Cerebral endothelial cells were shown to secrete apo A-I into the culture supernatant, whereas aortic endothelial cells were negative for apo A-I expression. Further studies of transcriptional regulation showed that cerebral endothelium was responsive to apo A-I-inducing agents, such as cholesterol, insulin, and retinoic acid, as previously shown in human hepatoma HepG2 cells. Thus, cultures of porcine cerebral endothelial cells may represent a suitable model for physiological studies of apo A-I-regulation with regard to brain lipid metabolism and blood-brain barrier function. To investigate the interspecies conservation of regulatory elements, 178 bp of the 5' flanking region of the porcine apo A-I gene was cloned using PCR techniques. Alignments of the cDNA, of the deduced apo A-I protein sequence, and of the 5' promoter region with the corresponding genomic sequences of different species show a high degree of similarity between the porcine and the primate apo A-I genes, thus indicating a similar function and possibly common regulatory mechanisms in those species. In contrast, the rodent and avian apolipoprotein A-I promoter sequences differed significantly.
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PMID:Expression of apolipoprotein A-I in porcine brain endothelium in vitro. 829 40

The regulation of apolipoprotein A-I (apo A-I) gene expression by 12-O-tetradecanoylphorbol 13-acetate (TPA) was investigated in the human hepatoma cell line Hep G2. TPA treatment decreased apo A-I mRNA levels in a time-dependent manner, by up to 50% versus control cells within 24 h. Nuclear run-on transcription assays demonstrated a transcriptional effect of TPA. Using transfection analysis with a plasmid construct containing the -1378/+11 apo A-I promoter fused to the secreted placental alkaline phosphatase (SPAP) reporter gene, we showed that the SPAP activity was decreased to 50% when Hep G2 cells were incubated in the presence of TPA. The inhibitory effect of TPA was still maintained when fragment -253 to -4 of apo A-I promoter was linked to the CAT reporter gene. These data indicate that transcriptional modulation of apolipoprotein A-I gene expression following phorbol ester treatment is transduced by gene elements located between -253 and -4 of the apo A-I promoter.
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PMID:Transcriptional regulation of apolipoprotein A-I expression in Hep G2 cells by phorbol ester. 852 77


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