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)

The influence of extracellular fatty acids on the uptake and esterification of [3H]retinol bound to human retinol-binding protein (RBP), to RBP-transthyretin (TTR), or in dispersed form by the human hepatoma, HepG2, and human mammary epithelial carcinoma, MCF-7, cell lines was studied. The esterification of [3H]retinol was significantly increased in cells incubated with myristic, palmitic, stearic oleic, or linoleic acid-albumin complexes and was observed for all forms of [3H]retinol. Enhancement of [3H]retinol uptake was also observed in cells incubated with these fatty acids, but this increase was relatively small for the dispersed form as compared to that observed for [3H]retinol bound to RBP or RBP-TTR. Comparing equal concentrations of the [3H]retinol donors, cell uptake and esterification was greatest from the dispersed form and least from that bound to RBP-TTR. After preincubation of cells with oleate, uptake and esterification of [3H]retinol was increased but not to the extent observed when oleate and [3H]retinol donor were co-incubated. Incubation of cells with oleate resulted in rapid and correlated increases in the rates of [3H]retinol uptake and esterification which persisted until the steady state for [3H]retinol uptake was achieved. Beyond this time, net esterification of [3H]retinol continued in the presence of oleate. This kinetic pattern was observed for all [3H]retinol donors. These effects on [3H]retinol uptake and esterification were dose-dependent as the oleate to albumin ratio was varied from 0.5 to 3.0 and were observed across a physiological concentration range of RBP-3H-retinol. The data indicate that: 1) the fatty acid status of cells is a determinant of retinol uptake and esterification; and 2) the form of retinol presentation to cells is not qualitatively important for these processes.
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PMID:Regulation of retinol uptake and esterification in MCF-7 and HepG2 cells by exogenous fatty acids. 164 43

Transthyretin (TTR) is a circulatory protein which plays an important role in the transport of both thyroid hormone and retinol. Hep G2 cells, a human hepatoma-derived cell line, have been used extensively in studies of protein secretion by liver cells. The original description of this cell line indicated that this line, unlike primary hepatocytes, does not secrete TTR. We now report studies which reexamine the ability of Hep G2 cells to synthesize and secrete TTR. For this purpose, total RNA was isolated from Hep G2 cells grown on both uncoated and collagen-coated plastic plates and was examined for TTR expression by Northern blot analysis. TTR mRNA was found to be present in nearly equal amounts in Hep G2 cells cultured in either condition. When Hep G2 cells were cultured in [35S]methionine-containing medium, the cells were found both to synthesize and to secrete immunoprecipitable [35S]TTR. Hep G2 cells were found, by sensitive and specific radioimmunoassay, to contain 142 +/- 91 ng TTR/10(6) cells and to secrete TTR into the medium at a nearly constant rate for at least 24 h after medium change. Our data demonstrate that Hep G2 cells do synthesize and secrete TTR and suggest that this cell line might be useful for studies of the secretion of TTR.
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PMID:Studies on the synthesis and secretion of transthyretin by the human hepatoma cell line Hep G2. 165 60

The transthyretin (TTR) gene is regulated by two DNA regions which elicit hepatocyte-specific expression: a proximal promoter and distal enhancer. The TTR promoter and enhancer are composed of at least eight DNA binding sites for three different hepatocyte nuclear factors (HNF), CCAAT/enhancer binding protein (C/EBP), and AP-1/cJun. Site directed mutations within each of the HNF binding sites in the TTR promoter were introduced to evaluate their contribution to transcriptional activity in hepatoma cells. The data indicate that the strong affinity HNF-3-S binding site (-106 to -94) is absolutely required for TTR promoter activity since several mutations in this site eliminate TTR expression in the context of its enhancer. Conversion of a second weak affinity HNF3-W site (-140 to -131) in the TTR promoter to a high affinity site resulted in higher levels of expression. TTR mutations that disrupted several weak affinity sites (HNF1, HNF3-W, and HNF4) only slightly diminished expression levels in the presence of the TTR enhancer. In contrast, when we deleted the TTR enhancer from these HNF mutant constructs, TTR expression decreased to undetectable levels. This result suggests cooperation between the factors binding to the TTR promoter and enhancer regions. These results also demonstrate that the HNF3-S site alone is not sufficient to activate TTR transcription, but rather requires the participation of three cell-specific factors to elicit minimal promoter activity. The complexity of this promoter design and the requirement for a minimal number of cell-specific factors to achieve transcription allows us to propose a model which may explain the maintenance of tissue-specific expression of TTR.
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PMID:Site-directed mutagenesis of hepatocyte nuclear factor (HNF) binding sites in the mouse transthyretin (TTR) promoter reveal synergistic interactions with its enhancer region. 187 Sep 69

To investigate the regulation of genes whose expression is enriched in liver we studied expression of the albumin and transthyretin (TTR) genes in a series of rat hepatoma cell lines (FaO, C2, C2rev7, and H5) that express these genes at different rates. The level of expression of albumin and TTR was compared to the expression and DNA-binding activity of four transcription factors, HNF1/LFB1, C/EBP, HNF3, and HNF4, that are found at high concentrations in liver. We conclude that the levels of these factors are controlled both transcriptionally (HNF-3, HNF-4, and C/EBP) and post-transcriptionally (HNF-1/LFB1), and that the cellular concentration of these DNA-binding proteins helps explain the level of transcriptional activity observed for the genes they regulate.
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PMID:Differential regulation of hepatocyte-enriched transcription factors explains changes in albumin and transthyretin gene expression among hepatoma cells. 187 51

In vivo examination of the occupancy of DNA elements that can regulate transcription is critical to reveal which proteins actually take part in establishing and maintaining gene expression. We describe a new genomic sequencing method involving the rapid purification of relevant DNA segments from the bulk of the genomic DNA using a biotinylated riboprobe. The purified sequences are revealed by a single primer extension using Taq DNA polymerase. We used this technique to study the promoter and the enhancer of mouse transthyretin (TTR), a gene highly expressed in the liver. Footprints showed high liver-specific occupancy of some, but not all, of the DNA sites that had been identified as important for expression by transfection studies in hepatoma cells. In addition, several previously undetected sites were observed that bound proteins specifically in liver. These results suggest that not all demonstrable binding sites are involved in ongoing transcription and that in vivo studies may reveal additional and probably more relevant sites.
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PMID:Rapid in vivo footprinting technique identifies proteins bound to the TTR gene in the mouse liver. 198 8

Evidence of cellular transthyretin (TTR) binding was sought because of the observation that transthyretin can increase the uptake of its hormonal ligand. Transthyretin was bound by human hepatoma (Hep G2) cells in a time- and temperature-dependent manner, reaching equilibrium within 2 h. Scatchard analysis was consistent with a single class of high affinity binding sites with a Kd of approximately 5 nM at 0 and 4 degrees C and 14 nM at 37 degrees C. These dissociation constants are more than 2 orders of magnitude lower than the concentration of transthyretin in human serum. The apparent capacity at 0 degrees C, corrected for internalized TTR, was approximately 20,000 sites/cell. Saturable, high affinity binding of human transthyretin was also demonstrable with rat primary hepatocytes and human renal adenocarcinoma, neuroblastoma, and transformed lung cells. Rat and human transthyretin were equipotent in displacing isotopically labeled, species-specific transthyretin from human hepatoma cells and rat primary hepatocytes, a finding that is consistent with the strong homology between rat and human transthyretin. Eighty-eight percent of the saturable uptake was internalized as determined by proteolytic removal of surface transthyretin. Internalization was dependent on receptor binding and was more markedly inhibited than surface binding at 0 degrees C. Concentrations of thyroxine within a range that saturated a significant proportion of the primary and secondary TTR iodothyronine binding sites increased the uptake and internalization of transthyretin in a dose-dependent manner. By analogy to the function of receptors for other transport proteins, the interaction between transthyretin and its receptor is likely to affect ligand delivery and may have additional metabolic effects.
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PMID:Receptor-mediated uptake and internalization of transthyretin. 215 33

In order to determine if iron was able to stimulate specifically ferritin synthesis and secretion in transformed human hepatocytes in culture, human hepatoma cell (HepG2) cultures were submitted to increasing doses of ferric nitrilotriacetate. Iron uptake by the cells was demonstrated by incorporation of 59 Fe and the staining method of Perls. The following results were obtained: 1. iron incorporation within the hepatocytes increased as a function of culture time; 2. during the first 24 h of treatment, ferritin synthesis increased progressively, in parallel to the iron uptake; 3. a dose-dependent significant stimulation of ferritin synthesis and secretion were observed when the medium iron concentration increased from 5 to 20 mumol/l; 4. albumin, transthyretin and transferrin secretions were unaffected. These data demonstrated that, in our hepatocyte culture model, iron load increased the expression of ferritin in a highly specific manner.
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PMID:Iron induction of ferritin synthesis and secretion in human hepatoma cell (Hep G2) cultures. 254 99

Retinol-binding protein (RBP) that is synthesized and secreted by the human hepatoma cell HepG2 has been measured using a sensitive radioimmunoassay in which RBP in media and hepatoma cell sonicates reacts identically to human serum RBP. RBP was synthesized and secreted when cells were grown in retinol-depleted as well as retinol-containing media. However, immunoreactive transthyretin (prealbumin) could not be detected in concentrated HepG2 medium. RBP secretion and accumulation per mg of cell protein could be modulated by the concentration of fetal calf serum in the growth medium: secreted RBP equaled 782 +/- 123 ng/mg of cell protein per 8 hr after preincubation with 10% fetal calf serum versus 555 +/- 86 ng/mg per 8 hr in the absence of serum, whereas RBP in cell sonicates decreased only slightly. When HepG2 cells were cultured for two or more passages in medium containing fetal calf serum depleted of retinol by ultraviolet irradiation, the amounts of RBP in the cells and released to the medium were both significantly increased. When vitamin A (90% as retinyl esters) in the form of chylomicron remnants was presented to cells, there was a significant, dose-dependent redistribution of RBP from cells to medium, both in cells grown in normal fetal calf serum and in retinol-depleted serum. These data indicate that the secretion of RBP by HepG2 can occur constitutively in the absence of retinol, but that secretion can be enhanced and regulated by retinol delivered by the chylomicron remnant.
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PMID:Production and secretion of retinol-binding protein by a human hepatoma cell line, HepG2. 282 27

The mouse genomic clone for the prealbumin (transthyretin) gene was cloned, and its upstream regulatory regions were analyzed. The 200 nucleotides 5' to the cap site when placed within a recombinant plasmid were sufficient to direct transient expression in HepG2 (human hepatoma) cells, but this DNA region did not support expression in HeLa cells. The sequence of the 200-nucleotide region is highly conserved between mouse and human DNA and can be considered a cell-specific promoter. Deletions of this promoter region identified a crucial element for cell-specific expression between 151 and 110 nucleotides 5' to the RNA start site. A region situated at about 1.6 to 2.15 kilobases upstream of the RNA start site was found to stimulate expression 10-fold in HepG2 cells but not in HeLa cells. This far upstream element was invertible and increased expression from the beta-globin promoter in HepG2 cells. Unlike the simian virus 40 enhancer, the prealbumin enhancer would not stimulate beta-globin synthesis in HeLa cells, and even the simian virus 40 enhancer did not stimulate the prealbumin promoter in HeLa cells. Thus, we identified in the prealbumin gene two DNA elements that respond in a cell-specific manner: a proximal promoter including a crucial sequence between -108 and -151 nucleotides and a distant enhancer element located between 1.6 and 2.15 kilobases upstream.
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PMID:Transcriptional control of the mouse prealbumin (transthyretin) gene: both promoter sequences and a distinct enhancer are cell specific. 302 66

We previously defined two distinct cell-specific DNA elements controlling the transient expression of the transthyretin gene in Hep G2 (human hepatoma) cells: a proximal promoter region (-202 base pairs [bp] to the cap site), and a far-upstream cell-specific enhancer located between 1.6 and 2.15 kilobases (kb) 5' of the cap site (R. H. Costa, E. Lai, and J. E. Darnell, Jr., Mol. Cell. Biol. 6:4697-4708, 1986). In this report, we located the effective transthyretin enhancer element within a 100-bp region between 1.96 and 1.86 kb 5' to the mRNA cap site. In Hep G2 nuclear extracts, three protein-binding sites within this minimal enhancer element were identified by gel mobility and methylation protection experiments. Each binding site was required for full enhancer activity in Hep G2 transient expression assays. Competition experiments in protein-binding assays suggested that two of the three sites were recognized by a similar factor and that the protein interaction with the third site was different. The nuclear protein(s) which bound to the two homologous sites was found mainly or only in cells of hepatic origin, suggesting an involvement of this region in the cell-specific function of this enhancer. The nuclear protein(s) recognizing the third enhancer region was also found in HeLa and spleen cells.
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PMID:The cell-specific enhancer of the mouse transthyretin (prealbumin) gene binds a common factor at one site and a liver-specific factor(s) at two other sites. 333 68


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