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)

A plasmid containing the CCAAT/enhancer-binding protein (C/EBP alpha) gene transcriptionally controlled by the metallothionein promoter was constructed. The gene was transfected into the human hepatocellular carcinoma cell lines Hep3B and HepG2. When cultured in vitro in the presence of 100 microM ZnSO(4), C/EBP alpha expression caused reversible growth arrest. In soft agar clonogenic assays, C/EBP alpha expression decreased both the colony size and the total number of colonies compared with zinc-free controls. C/EBP alpha expressing cells s.c. implanted in CD-1 nu/nu mice were essentially nontumorigenic, whereas C/EBP alpha tumor cells implanted into immunodeficient SCID mice demonstrated a significantly delayed time of tumor appearance compared with cells transfected with a vector control plasmid. These studies suggest that the expression of endogenous genes normally associated with a quiescent, differentiated state, such as C/EBP alpha, can result in impaired proliferative activity and suppressed tumorigenicity of hepatoma cell lines.
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PMID:Impaired proliferation and tumorigenicity induced by CCAAT/enhancer-binding protein. 864 Jul 62

Expression of the albumin gene in the liver is controlled by several liver-enriched transcription factors. However, the mechanisms which contribute to its regulation during pathophysiological states, such as liver regeneration, are still little understood. In the present study we found that during liver regeneration down-regulation of albumin mRNA expression is transcriptionally controlled through a minimal element (nucleotide -170 to +22) of the albumin promoter and is observed mainly during the G1 phase of the cell cycle, while high levels of albumin expression are preserved at later time points. Decreased albumin mRNA levels correlate with a dramatic increase in nuclear expression of C/EBP-beta/LAP, a protein known to bind to the D site of the albumin promoter and also to be involved in cell cycle control. In contrast, nuclear expression of other factors such as HNF-1 or C/EBP-alpha, which also have been shown to transcriptionally control albumin expression, is either unchanged or slightly decreased. We show that pre- and post-translational mechanisms are involved in the higher nuclear expression of C/EBP-beta/LAP as early as 1 h after hepatectomy, which also leads to its increased binding toward the D site of the albumin promoter. Finally, in vitro transcription assays with liver nuclear extracts and recombinant C/EBP-beta/LAP demonstrate that C/EBP-beta/LAP can directly down-regulate transcription mediated by the minimal element of the albumin promoter. Additionally the inhibitory role of C/EBP-beta/LAP on the albumin minimal promoter could be confirmed by transfection experiments in hepatoma cells. These results indicate that C/EBP-beta/LAP, while enhancing transcription of cell cycle-related genes and controlling G1/S phase checkpoint, down-regulates a major liver function, i.e. albumin synthesis, to prepare the hepatocyte for entry into the cell cycle.
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PMID:C/EBP-beta/LAP controls down-regulation of albumin gene transcription during liver regeneration. 870 43

The sixth complement component (C6) is a late-acting complement protein that participates in the assembly of the membrane attack complex. C6 and most of the complement proteins are mainly synthesized in the liver. However, the human hepatoma-derived cell line Hep-G2, which produces the majority of complement proteins, synthesizes traces of C6. Here, we have isolated and characterized the human C6 promoter. Approximately 1 kb of C6 upstream sequence is shown to be sufficient to achieve tissue-specific expression of a luciferase reporter gene in two hepatic (Hep-G2 and Hep-3B) and two extrahepatic cell lines (fibroblast M1 and HeLa) in a manner similar to endogenous C6. There are wide differences in C6 mRNA expression among the four cell lines, whereas Hep-3B expresses high levels of C6, Hep-G2 and M1 poorly synthesize C6, and HeLa completely lacks C6 expression. Deletional and mutational analysis demonstrates that a C/EBP (CCAAT/enhancer binding protein) site located at -67 is required for C6 expression in Hep-3B cells, but it has little effect in M1 and Hep-G2 cells. Electrophoretic mobility shift assays show that this sequence binds to a C/EBP alpha using Hep-3B nuclear extract, but a negligible activity is detected using a Hep-G2 extract. To further investigate whether C/EBP alpha is the limiting factor for C6 expression, we have transfected a C/EBP alpha expression vector into Hep-G2 and Ml cells. C/EBP alpha expression vector dramatically trans-activates the luciferase reporter gene controlled by the C6 promoter, and it partially restores C6 mRNA expression in Hep-G2 cells.
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PMID:Characterization of the human C6 promoter: requirement of the CCAAT enhancer binding protein binding site for C6 gene promoter activity. 880 25

By genetic correlation with the growth-suppressible phenotype and direct functional tests, we demonstrate that the glucocorticoid-stimulated expression of the CCAAT/enhancer-binding protein alpha (C/EBP alpha) transcription factor is required for the steroid-mediated G1 cell cycle arrest of minimal-deviation rat hepatoma cells. Comparison of C/EBP alpha transcript and active protein levels induced by the synthetic glucocorticoid dexamethasone in glucocorticoid growth-suppressible (BDS1), nonsuppressible receptor-positive (EDR1) and nonsuppressible receptor-deficient (EDR3) hepatoma cell proliferative variants revealed that the stimulation of C/EBP alpha expression is a rapid, glucocorticoid receptor-mediated response associated with the G1 cell cycle arrest. Consistent with the role of C/EBP alpha as a critical intermediate in the growth suppression response, maximal induction of transcription factor mRNA occurred within 2 h of dexamethasone treatment whereas maximal inhibition of [3H] thymidine incorporation was observed 24 h after steroid treatment. As a direct functional approach, ablation of C/EBP alpha protein expression and DNA-binding activity by transfection of an antisense C/EBP alpha expression vector blocked the dexamethasone-induced G1 cell cycle arrest of hepatoma cells but did not alter general glucocorticoid responsiveness. Transforming growth factor beta induced a G1 cell cycle arrest in C/EBP alpha antisense transfected cells, demonstrating the specific involvement of C/EBP alpha in the glucocorticoid growth suppression response. Constitutive expression of a conditionally activated form of C/EBP alpha caused a G1 cell cycle arrest of BDS1 hepatoma cells in the absence of glucocorticoids. In contrast, overexpression of C/EBP beta or C/EBP delta had no effect on hepatoma cell growth. Taken together, these results demonstrate that the steroid-induced expression of C/EBP alpha is necessary to mediate the glucocorticoid G1 cell cycle arrest of rat hepatoma cells and implicates a role for this transcription factor in the growth control of liver-derived epithelial tumor cells.
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PMID:Glucocorticoid-stimulated CCAAT/enhancer-binding protein alpha expression is required for steroid-induced G1 cell cycle arrest of minimal-deviation rat hepatoma cells. 881 41

The rat CYP2D5 P-450 gene is activated in the liver during postnatal development. We previously showed that liver-specific transcription of the CYP2D5 gene is dictated by a proximal promoter element, termed 2D5, that is composed of a binding site for Sp1 or a related factor, and an adjacent cryptic C/EBP (CCAAT/enhancer-binding protein) site. Despite the fact that both C/EBP alpha and C/EBP beta are expressed abundantly in liver, only C/EBP beta is capable of stimulating the 2D5 promoter in HepG2 hepatocarcinoma cells. In addition, activation of the 2D5 promoter by C/EBP beta is completely dependent on the presence of the Sp1 site. Domain switch experiments reveal that C/EBP beta proteins containing either the leucine zipper or the activation domain of C/EBP alpha are unable to stimulate the 2D5 promoter yet are fully capable of transactivating an artificial promoter bearing a high-affinity C/EBP site. Thus, the leucine zipper and the activation domain of C/EBP beta are absolutely required to support transactivation of the 2D5 promoter. Using Drosophila cells that lack endogenous Sp1 activity, we show that the serine/threonine- and glutamine-rich activation domains A and B of Sp1 are required for efficient cooperatively with C/EBP beta. Furthermore, analysis of c/ebp beta-deficient mice shows that mutant animals are defective in expression of a murine CYP2D5 homolog in hepatic cells, confirming the selective ability of C/EBP beta to activate this liver-specific P-450 gene in vivo. Our findings illustrate that two members of a transcription factor family can achieve distinct target gene specificities through differential interactions with a cooperating Sp1 protein.
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PMID:The ability of C/EBP beta but not C/EBP alpha to synergize with an Sp1 protein is specified by the leucine zipper and activation domain. 912 52

There is a significant body of evidence which suggests that the alpha-isoform of the CCAAT/enhancer binding protein (C/EBP alpha) plays a central regulatory role in energy metabolism in the liver. However, there is little information available regarding regulation of its expression in this tissue. In this study, we examined the effect of hormones and diabetes on its expression in rat H4IIE hepatoma cells and in rat liver. Treatment of H4IIE cells with dexamethasone led to a threefold increase in C/EBP alpha mRNA within 4 h. Insulin treatment produced a bi-phasic response, initially reducing mRNA levels up to the 4 h time point, but after 8 h a twofold increase in C/EBP alpha mRNA was observed. Treatment with 8-chlorophenylthio-cAMP produced a twofold induction of C/EBP alpha mRNA after 8 h. Western analysis indicated that the changes in mRNA in response to hormonal treatment generally resulted in corresponding alterations in C/EBP alpha protein levels. Finally, we observed an inhibition of C/EBP alpha gene expression in streptozotocin-diabetic rat liver, reflected by a decrease in both mRNA and protein levels that were partially reversed by insulin treatment. These results indicate that the expression of C/EBP alpha in liver is under complex control by both hormonal and metabolic signals, which is consistent with its role as a trans -regulator of genes which play a role in energy metabolism.
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PMID:Hepatic expression of CCAAT/enhancer binding protein alpha: hormonal and metabolic regulation in rats. 934 91

The preceding paper (Cha, H. H., Cram, E. J., Wang, E. C., Huang, A. J., Kasler, H. G., and Firestone, G. L. (1998) J. Biol. Chem. 273, 0000-0000(478563) defined a glucocorticoid responsive region within teh promoter of the p21 CDK inhibitor gene that contains a putative DNA-binding site for the transcription factor CCAAT/ enhancer binding protein-alpha (C/EBP alpha). Wild type rat BDS1 hepatoma cells as well as as4 hepatoma cells, which express antisense sequences to C/EBP alpha and ablate its protein production, were utilized to investigate the role of this transcription factor in the glucocorticoid regulation of p21 gene expression. The stimulation of p21 protein levels and promoter activity, as well as inhibition of CDK2-mediated retinoblastoma protein phosphorylation, by the synthetic glucocorticoid, dexamethasone, required the expression of C/EBP alpha. Overexpression of C/EBP alpha in as4 cells rescued the dexamethasone responsiveness of the p21 promoter. Site-directed mutagenesis of the p21 promoter revealed that dexamethasone stimulation of p21 promoter activity required the C/EBP consensus DNA-binding site. Furthermore, in glucocorticoid receptor-defective EDR1 hepatoma cells, dexamethasone failed to stimulate C/EBP alpha and p21 protein expression and promoter activities. Our results have established a functional link between the glucocorticoid receptor signaling pathway that mediates a G1 cell cycle arrest of rat hepatoma cells and the transcriptional control of p21 by a cascade that requires the steroid induction of C/EBP alpha gene expression.
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PMID:Role of the CCAAT/enhancer binding protein-alpha transcription factor in the glucocorticoid stimulation of p21waf1/cip1 gene promoter activity in growth-arrested rat hepatoma cells. 944 37

The CCAAT/enhancer-binding protein alpha (C/EBP) is a transcription factor that trans-activates a number of metabolically important genes. Previous work has demonstrated that C/EBPalpha and C/EBPbeta have the potential to mediate the cAMP responsiveness of phosphoenolpyruvate carboxykinase (PEPCK) in liver cells. However, these studies used GAL4 fusion proteins and artificial promoter-reporter gene vectors in transfection experiments; as a result, these studies only indicated that both isoforms had the potential to mediate the hormonal response and not which isoform actually participated in vivo. To address this issue, we produced hepatoma cell lines that stably expressed either a dominant negative inhibitor or antisense RNA for these two main liver C/EBP isoforms. Inhibition of all C/EBP isoforms via expression of the dominant negative protein eliminated cAMP responsiveness, and reduced glucocorticoid responsiveness, of the endogenous PEPCK gene in hepatoma cells. Antisense directed against C/EBPalpha mRNA, which reduced C/EBPalpha protein levels by nearly 80%, also significantly reduced the cAMP responsiveness of the endogenous PEPCK promoter, whereas antisense directed against C/EBPbeta was without effect. There was no major alteration in cAMP signaling in the C/EBPalpha antisense cells, as cAMP induction of the C/EBPbeta gene was similar to that in wild-type H4IIE cells. These data suggest that the alpha-isoform of C/EBP is specifically utilized for mediating the cAMP responsiveness of the PEPCK gene.
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PMID:Hormonal regulation of the phosphoenolpyruvate carboxykinase gene. Role of specific CCAAT/enhancer-binding protein isoforms. 1068 69

The X gene product of the human hepatitis B virus (HBx), a major factor responsible for hepatitis and hepatocellular carcinoma, modulates transactivation by a variety of transcription factors. Herein, expression of the phosphoenolpyruvate carboxykinase (PEPCK) gene was found to be regulated transcriptionally by HBx through two distinct promoter regions. The cAMP response element (CRE)-1 site within the proximal promoter region mediated the HBx-induced transactivation of the PEPCK gene through C/EBP alpha and ATF-2. A retinoid X receptor (RXR) response element within the distal promoter region also contributed to the HBx-induced transactivation. Consistent with these results, HBx directly interacted with RXR, and the interaction interfaces were localized to the transactivation domain of HBx and the ligand binding domain of RXR.
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PMID:Direct binding of hepatitis B virus X protein and retinoid X receptor contributes to phosphoenolpyruvate carboxykinase gene transactivation. 1104 64

The BC2 cell line derived from the human hepatocarcinoma, HGB, undergoes a spontaneous sharp differentiation process in culture as it becomes confluent, remains stably differentiated for several weeks, and may return to proliferation thereafter under appropriate density conditions. The relevance of the line as an hepatic model has been evaluated. Cells synthesize a large number of plasma proteins, and rates of glycogen and urea synthesis increase with time of confluency and become sensitive to insulin, reflecting the process of differentiation. Differentiated BC2 cells express the most relevant cytochrome P-450 (CYP) isozyme activities (CYP1A1/2, 2A6, 2B6, 2C9, 2E1, and 3A4) and conjugating enzymes (glutathione S-transferase and UDP-glucuronyltransferase) and also respond to model inducers. Methylcholanthrene induced an increase in CYP1A1/2 enzyme activity (eightfold), phenobarbital induced CYP2B6 activity (1.7-fold), and dexamethasone induced CYP3A4 activity (fivefold). In parallel, expression of the most relevant liver-enriched transcription factors, HNF-4, HNF-1, C/EBP-alpha and C/EBP-beta mRNAs, was significantly increased in differentiated cultures. This increase was largest in HNF-1 and HNF-4, which supports the idea that a redifferentiation process towards the hepatic phenotype takes place. BC2 is an hepatic cell line that is able to express most hepatic functions, especially the drug-biotransformation function, far more efficiently than any previously described human hepatoma cell line.
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PMID:Expression and induction of a large set of drug-metabolizing enzymes by the highly differentiated human hepatoma cell line BC2. 1123 Dec 98


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