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 CIII (apoCIII), a lipid-binding protein involved in the transport of triglycerides and cholesterol in the plasma, is synthesized primarily in the liver and the intestine. A cis-acting regulatory element, C3P, located at -90 to -66 upstream from the apoCIII gene transcriptional start site (+1), is necessary for maximal expression of the apoCIII gene in human hepatoma (HepG2) and intestinal carcinoma (Caco2) cells. This report shows that three members of the steroid receptor superfamily of transcription factors, hepatocyte nuclear factor 4 (HNF-4), apolipoprotein AI regulatory protein 1 (ARP-1), and Ear3/COUP-TF, act at the C3P site. HNF-4 activates apoCIII gene expression in HepG2 and Caco2 cells, while ARP-1 and Ear3/COUP-TF repress its expression in the same cells. HNF-4 activation is abolished by increasing amounts of ARP-1 or Ear3/COUP-TF, and repression by ARP-1 or Ear3/COUP-TF is alleviated by increasing amounts of HNF-4. HNF-4 and ARP-1 bind with similar affinities to the C3P site, suggesting that their opposing transcriptional effects may be mediated by direct competition for DNA binding. HNF-4 and ARP-1 mRNAs are present within the same cells in the liver and intestine, and protein extracts from hepatic tissue, HepG2, and Caco2 cells contain significantly more HNF-4 than ARP-1 or Ear3/COUP-TF binding activities. These findings suggest that the transcription of the apoCIII gene in vivo is dependent, at least in part, upon the intracellular balance of these positive and negative regulatory factors.
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PMID:Antagonism between apolipoprotein AI regulatory protein 1, Ear3/COUP-TF, and hepatocyte nuclear factor 4 modulates apolipoprotein CIII gene expression in liver and intestinal cells. 131 68

We have used apolipoprotein genes to investigate the signal transduction mechanisms involved in the control of intestinal specific gene expression. The human apoAI, apoCIII, and apoAIV genes are tandemly organized within a 15-kb DNA segment and are expressed predominantly in the liver and intestine. Transient transfection of various human apoAI gene plasmid constructs into human hepatoma (HepG2) and colon carcinoma (Caco-2) cells showed that apoAI gene transcription is under the control of two separate and distinct cell-specific promoters. The region between nucleotides -192 and -41 is essential for expression in HepG2 cells, whereas the region from -595 to -192 is essential for expression in Caco-2 cells. A third 0.6 kb DNA fragment in the apoCIII gene promoter region, approximately 5 kb down-stream from the human apoAI gene, enhances transcription mediated by either of these two tissue-specific apoAI promoters. In Caco-2 cells, expression of the apoAI gene and activation by the distal enhancer required the presence of a nuclear hormone receptor response element (NHRRE) located in the -214 to -192 apoAI promoter region. Overexpression of the orphan receptor hepatocyte nuclear factor 4 (HNF-4), which binds to the NHRRE, dramatically stimulates apoAI gene expression in Caco-2 cells but not in HepG2 cells. Maximal stimulation of transcription by HNF-4 in Caco-2 cells required the presence of both the intestinal specific promoter, the NHRRE, and distal enhancer elements. Transactivation by HNF-4 thus appears to result from functional synergy between the NHRRE binding HNF-4 and distal DNA elements containing intestinal-specific DNA binding activities. The apoAI gene provides a model system to define the mechanism(s) governing intestinal cell specific gene regulation and the role of nuclear hormone receptors in the establishment and regulation of enterocytic gene transcription.
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PMID:Intestinal apolipoprotein AI gene transcription is regulated by multiple distinct DNA elements and is synergistically activated by the orphan nuclear receptor, hepatocyte nuclear factor 4. 761 25

A hierarchy of liver-enriched transcription factors plays an important role in activating expression of many hepatic genes. In particular, hepatocyte nuclear factor 4 (HNF-4) is a major activator of the gene encoding HNF-1, and HNF-1 itself activates expression of more than 20 liver genes. To dissect this activation pathway genetically, we prepared somatic cell variants that were deficient in expression of the liver-specific alpha 1-antitrypsin (alpha 1AT) gene, which requires both HNF-1 and HNF-4 for high-level gene activity. This was accomplished in two steps. First, hepatoma transfectants that stably expressed two selectable markers under alpha 1AT promoter control were prepared; second, variant sublines that could no longer express either transgene were isolated by direct selection. In this report, we demonstrate that the variants contain defects in the HNF-4/HNF-1 activation pathway. These defects functioned in trans, as expression of many liver genes was affected, but the variant phenotypes were recessive to wild type in somatic cell hybrids. Three different variant classes could be discriminated by their phenotypic responses to ectopic expression of either HNF-4 or HNF-1. Two variant clones appeared specifically deficient in HNF-4 expression, as transfection with an HNF-4 expression cassette fully restored their hepatic phenotypes. Another line activated HNF-1 in response to forced HNF-4 expression, but activation of downstream genes failed to occur. One clone was unresponsive to either HNF-1 or HNF-4. Using the variants, we demonstrate further that the chromosomal genes encoding alpha 1AT, aldolase B, and alpha-fibrinogen display strict requirements for HNF-1 activation in vivo, while other liver genes were unaffected by the presence or absence of HNF-1 or HNF-4. We also provide evidence for the existence of an autoregulatory loop in which HNF-1 regulates its own expression through activation of HNF-4.
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PMID:Genetic analysis of a transcriptional activation pathway by using hepatoma cell variants. 793 24

Blood coagulation Factor X and its activated form Factor Xa play an essential role in the midphase of the clotting cascade. To delineate the mechanisms governing the liver-specific expression of Factor X, we have previously characterized the complete 2.8 kilobase pairs of the 5'-flanking region of Factor X and demonstrated that the first 209 base pairs is sufficient to confer maximal promoter activity in HepG2 cells, a hepatoma cell line that expresses Factor X. We have also shown that mutations at ACTTTG and CCAAT elements located at -56 to -51 and -120 to -116, respectively, significantly reduce the promoter activity. In this report, we demonstrate that Factor X mRNA is primarily but not exclusively expressed in the liver. Using DNase I footprinting analysis, we determine four protein binding sites within the 209-base pair fragment, designated site 1 (-73) to -44), site 2 (-128 to -94), site 3 (-165 to -132), and site 4(-195 to -169). Using gel mobility shift assays in combination with competition and supershift experiments, we demonstrate that hepatocyte nuclear factor 4 and Sp1 bind at site 1, the site which contains the ACTTTG element. Methylation interference assays reveal that HNF-4 and Sp1 contact adjacent sites with minor overlap. HNF-4 and Sp1 appear to bind site 1 in a mutually exclusive fashion. We also demonstrate that HNF-4 can transactivate the Factor X promoter in HeLa cells; mutation at the adjacent Sp1 site further increases the transactivation. Heteromeric transcription factor NF-Y was identified as the protein that binds the CCAAT box at site 2. We conclude that HNF-4 and NF-Y play crucial roles in modulating the activity of the proximal promoter of Factor X.
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PMID:Liver-enriched transcription factor HNF-4 and ubiquitous factor NF-Y are critical for expression of blood coagulation factor X. 856 96

Characterization of the rat PRL receptor (PRLR) gene has revealed three separate untranslated exon 1 sequences, each associated with a different transcription start site and 5'-flanking sequence. We show by RT-PCR that exon 1A is expressed primarily in liver but is also detectable in ovary and mammary gland. Exon 1B expression is observed exclusively in the ovary, whereas exon 1C is expressed in all three tissues. Transient transfection of luciferase reporter constructs containing parts of the 5'-flanking regions (0.3-1.1 kb) of exon 1A, 1B, and 1C, respectively, showed activity of the 1A promoter in Chinese hamster ovary (CHO) cells, the human hepatoma cell line, HepG2, and the rat hepatoma cell line, H4II, which was 10- to 14-fold increased compared with the activity of the promoter-less luciferase vector. No activity of the 1A promoter was detected in the human mammary cell line, T-47D. Relative to a vector containing the Simian virus 40 (SV40) promoter, the 1A promoter had 20% activity in H4II cells and 1-3% activity in CHO and HepG2 cells. The 1B promoter produced a 6.1-fold increase of luciferase activity in CHO cells (approximately 2% of the SV40 promoter), whereas no significant activity was detected in HepG2, H4II, and T-47D cells. The 1C promoter was strongly active in T-47D cells (approximately 64-fold over control) and moderately active in the other cell lines tested (9- to 13-fold over control). 5'-Deletion analysis of the 1A promoter revealed that a fragment containing -83/ +81 bp, relative to the transcription start site, was sufficient to drive transcription in hepatoma cells, whereas this construct was inactive in CHO cells. Cotransfection of CHO cells with the -83/+81 construct and an expression vector encoding the liver-enriched transcription factor, hepatocyte nuclear factor 4 (HNF4), revealed a dose-dependent transactivation of the proximal 1A promoter with a maximal stimulation of approximately 10-fold. Electrophoretic mobility shift assays showed binding of HNF4 to the sequence -14/+24 of the 1A promoter, and mutational analysis revealed that the sequence GGGCAAAGTCA at position +11/+21 is required for this binding. We conclude that the 1A, 1B, and 1C promoters of the PRLR gene are used in a cell type- dependent way that may play a role in differential hormonal regulation of the gene. In particular, we have shown that HNF4 operates on the proximal 1A promoter and may be responsible, in combination with other factors, for the increased activity of this promoter in adult female liver.
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PMID:Differential promoter usage in prolactin receptor gene expression: hepatocyte nuclear factor 4 binds to and activates the promoter preferentially active in the liver. 877 26

Two similar, yet functionally distinct genomic RNAs are transcribed from the DNA genome of the human hepatitis B virus. The pre-C RNAs encode the precore protein which is proteolytically processed to yield e antigen. The pregenomic RNAs encode both the nucleocapsid protein and reverse transcriptase and serve as the templates for viral DNA replication. To determine whether synthesis of these two RNAs is directed from a single or a closely spaced pair of promoters, we introduced point and insertion mutations into the basal elements of the promoter that directs their synthesis. Transcription from these mutants was examined both in cell-free transcription systems derived from hepatoma (HepG2) and nonliver (HeLa) cell lines and by transient transfection of hepatoma cell lines (Huh7 and HepG2). The data from these experiments indicated that synthesis of the pre-C and pregenomic RNAs is directed by two distinct promoters and that the basal elements of these two promoters partially overlap, yet are genetically separable, with each consisting of its own transcriptional initiator and a TATA box-like sequence situated approximately 25 to 30 bp upstream of its sites of initiation. A 15-bp insertion was found to be sufficient to physically separate these two promoters. Furthermore, these two promoters can be differentially regulated, with the transcriptional activator Sp1 specifically activating transcription from the pregenomic promoter and the hepatocyte nuclear factor 4 specifically repressing transcription from the pre-C promoter. Thus, we conclude that the promoters used in synthesis of the pre-C and pregenomic mRNAs are genetically distinct and separately regulated.
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PMID:Promoters for synthesis of the pre-C and pregenomic mRNAs of human hepatitis B virus are genetically distinct and differentially regulated. 897 Sep 99

We have further characterized the most distal of the three alpha-fetoprotein (AFP) enhancers required for expression of the AFP gene in fetal hepatocytes and yolk sac endodermal cells. Almost total rat AFP enhancer 3 (E3) activity is driven by a 160-bp fragment at -6 kb containing three target regions for nuclear proteins that cooperate to stimulate transcription from the AFP and the thymidine kinase promoters in HepG2 hepatoma cells. Region 1, recently shown to be crucial for correct function of the enhancer in liver of transgenic mice, is recognized by two sets of transcription factors that bind to partly overlapping sites, 1a and 1b, in a noncooperative and nonexclusive manner. Site 1a contains a motif, AGGTCA, which is recognized by chicken ovalbumin upstream promoter transcription factors (COUP-TFs), but not by hepatocyte nuclear factor 4. Hepatocyte nuclear factor 3 (HNF3) and CCAAT/enhancer binding protein (C/EBP), which bind to regions 2 and 3, respectively, are likely responsible for the liver-specific E3 action. They play a key role by acting in synergy. The participation of nuclear receptors such as COUP-TFs, with C/EBP and HNF3, in the tight control of the distal AFP enhancer is a new, and perhaps key, step toward understanding the regulation and function of this enhancer, which may remain active throughout development.
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PMID:Chicken ovalbumin upstream promoter-transcription factor, hepatocyte nuclear factor 3, and CCAAT/enhancer binding protein control the far-upstream enhancer of the rat alpha-fetoprotein gene. 898 20

The capacity of the liver-enriched transcription factor hepatocyte nuclear factor 4 (HNF4) to direct redifferentiation of dedifferentiated rat hepatoma cells was investigated by stable transfection of epitope-tagged HNF4 cDNA into H5 variant cells. HNF4-producing cells expressed the previously silent HNF1 gene and showed activation of some hepatic functions, including alpha1-antitrypsin, beta-fibrinogen, and transthyretin, but not of the endogenous HNF4 gene. Expression of the other hepatocyte-enriched transcription factors was not modified. Treatment of the HNF4tag-expressing cells with dexamethasone induced expression of the transgene by 10-fold, resulting in enhanced expression of target genes of both glucocorticoid hormones and HNF4. The set of activated hepatic genes was extended by treatment of cells with the demethylating agent 5-azacytidine followed by selection in dexamethasone-containing glucose-free medium. Some of the colonies that developed reexpressed the entire set of hepatic functions tested. Fusion of HNF4tag-producing H5 cells with well-differentiated Fao cells showed that only those hybrids which maintained expression of HNF4tag were protected from complete extinction, including that of the Fao HNF4 gene. Thus, H5 cells must produce an extinguisher of the HNF4 gene. In addition, this result implies that HNF4 itself, or its target HNF1, is a positive regulator of HNF4. In conclusion, HNF4tag expression overcomes repression of the hepatic phenotype of the H5 cell without abolishing its potential to extinguish an active genome. Taken together, these results predict that expression of HNF4 should be sufficient to establish heritable expression of many parameters of the hepatic differentiated state.
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PMID:Hepatocyte nuclear factor 4 expression overcomes repression of the hepatic phenotype in dedifferentiated hepatoma cells. 912 39

Using recombinant adenoviral vectors and a dominant negative mutant of HNF-4, we have examined the contribution of hepatocyte nuclear factor 4 (HNF-4) to endogenous apolipoprotein AI and CIII mRNA expression. Overexpression of HNF-4 leads to a 7.4-fold increase in apolipoprotein CIII expression, while infection with the dominant negative mutant of HNF-4 reduces the level of apolipoprotein CIII mRNA by 80%, demonstrating that endogenous HNF-4 is necessary for apolipoprotein CIII expression. Experiments using the hepatoma cell lines, HepG2 and Hep3B, indicate that HNF-4 is also involved in the regulation of apolipoprotein AI expression in these lines. However, the effect of HNF-4 on apolipoprotein AI expression is much more dramatic in cell lines derived from intestinal epithelium. Infection of the intestinal-derived cell line IEC-6 with the HNF-4 adenovirus resulted in a greater than 20-fold increase in the level of apolipoprotein AI mRNA. These results indicate that HNF-4 does regulate apolipoprotein AI and CIII mRNA expression and suggest that HNF-4 is critical for intestinal apolipoprotein AI expression.
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PMID:Utilization of recombinant adenovirus and dominant negative mutants to characterize hepatocyte nuclear factor 4-regulated apolipoprotein AI and CIII expression. 915 49

Among the liver-enriched transcription factors identified to date, only expression of hepatocyte nuclear factor 4 (HNF4) and hepatocyte nuclear factor 1 (HNF1) is in strict correlation with hepatic differentiation in cultured rat hepatoma cells. Indeed, differentiated hepatoma cells that stably express an extensive set of adult hepatic functions express liver-enriched transcription factors, while dedifferentiated cells that have lost expression of all these hepatic functions no longer express HNF4 and HNF1. We describe a new heritable phenotype, designated as uncoupled, in which there is a spontaneous dissociation between the expression of these transcription factors and that of the hepatic functions. Cells presenting this phenotype, isolated from differentiated hepatoma cells, cease to accumulate all transcripts coding for hepatic functions but nevertheless maintain expression of HNF4 and HNF1. Transitory transfection experiments indicate that these two factors present in these cells have transcriptional activity similar to that of differentiated hepatoma cells. Characterization of the appropriate intertypic cell hybrids demonstrates that this new phenotype is recessive to the dedifferentiated state and fails to be complemented by differentiated cells. These results indicate the existence of mechanisms that inhibit transcription of genes coding for hepatocyte functions in spite of the presence of functional HNF4 and HNF1. Cells of the uncoupled phenotype present certain properties of oval cells described for pathological states of the liver.
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PMID:Liver-enriched transcription factors uncoupled from expression of hepatic functions in hepatoma cell lines. 934 92


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