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)

Hepatitis C virus (HCV), a major etiologic agent of transfusion associated hepatitis, is a positive, single-stranded RNA virus and is also known to be implicated in liver cirrhosis and hepatocellular carcinoma. Nonstructural protein 5A (NS5A) of HCV contains acidic and proline-rich amino acids in its carboxy-terminal half. These structural features resemble eukaryotic transcription activators. In this report, we show that NS5A functions as a potent transcriptional activator when fused to the yeast (Saccharomyces cerevisiae) GAL4 DNA-binding domain (1-147). The potential transcriptional activator maps to the C-terminal half of NS5A in the yeast cell. Therefore, our data provides the first evidence that NS5A may modulate host cell function at the transcriptional level.
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PMID:Hepatitis C virus nonstructural protein 5A contains potential transcriptional activator domains. 938 55

Amino acid (aa) mutations in the interferon-sensitivity determining region (ISDR) (aa position 237-276 of the nonstructural region 5A [NS5A] protein consisting of 447 amino acids) of hepatitis C virus (HCV) are related to increased interferon sensitivity and low viral load, but its mechanism has not been clarified. Recently, the NS5A protein has been reported to have a transcriptional activation function, like other viral transactivator proteins known to repress interferon-induced gene expression, and the ISDR overlaps one of the acidic amino acid regions, putative domains conferring this activity. In the present study, we investigated the transcriptional activation function of the ISDR itself and the effect of amino acid mutations in the ISDR on this activity. The full-length or truncated NS5A cDNA with different ISDR sequences was cloned into a yeast or mammalian expression vector to form a fusion protein consisting of the GAL4 DNA-binding domain (GAL4-DBD) and NS5A protein. Following transfection, the transcriptional activities of these constructs were determined using beta-galactosidase (yeast) or chloramphenicol acetyltransferase (CAT) (mammalian cell) reporter gene expression under the control of GAL4 binding sites. In yeast, both the full-length sequence of NS5A-R (a clone with one aa mutation in the ISDR) and NS5A-S (a derivative of NS5A-R with six aa mutations in the ISDR) had no distinguishable transcriptional activity, whereas an amino-terminal deletion construct of NS5A-R (aa position 228-447) lacking 227 aa, showed remarkable activity with the relative value of 117.0 over that of the backbone vector. The same deletion mutant of NS5A-S produced five times higher activity with the relative value of 575.0, indicating that aa mutations in the ISDR profoundly affect this transcriptional activity. In a hepatoma cell line, HuH-7, the transcriptional activity was more prominent with a construct consisting of only the ISDR and short flanking sequences (aa 228-284) than larger deletion constructs of NS5A-R. Analysis using six different ISDR clones revealed that different mutations enhanced this activity to various extent compared with the wild-type ISDR. In particular, site-directed mutagenesis targeted to the aa position 252 showed that this aa residue had profound influence on the activity. These results suggest that the ISDR has a transcriptional activity, and it is enhanced by aa mutations that are also related to decreased viral load and increased interferon sensitivity. The possible association between transcriptional activation and interferon sensitivity or viral replication should be studied further.
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PMID:Mutations in the interferon-sensitivity determining region of hepatitis C virus and transcriptional activity of the nonstructural region 5A protein. 975 55

The cyclic AMP response element (CRE) of the rat phosphoenolpyruvate carboxykinase (PEPCK) gene promoter is required for a complete glucocorticoid response. Proteins known to bind the PEPCK CRE include the CRE-binding protein (CREB) and members of the CCAAT/enhancer-binding protein (C/EBP) family. We took two different approaches to determine which of these proteins provides the accessory factor activity for the glucocorticoid response from the PEPCK CRE. The first strategy involved replacing the CRE of the PEPCK promoter/chloramphenicol acetyltransferase reporter plasmid (pPL32) with a consensus C/EBP-binding sequence. This construct, termed pDeltaCREC/EBP, binds C/EBPalpha and beta but not CREB, yet it confers a nearly complete glucocorticoid response when transiently transfected into H4IIE rat hepatoma cells. These results suggest that one of the C/EBP family members may be the accessory factor. The second strategy involved co-transfecting H4IIE cells with a pPL32 mutant, in which the CRE was replaced with a GAL4-binding sequence (pDeltaCREGAL4), and various GAL4 DNA-binding domain (DBD) fusion protein expression vectors. Although chimeric proteins consisting of the GAL4 DBD fused to either CREB or C/EBPalpha are able to confer an increase in basal transcription, they do not facilitate the glucocorticoid response. In contrast, a fusion protein consisting of the GAL4 DBD and amino acids 1-118 of C/EBPbeta provides a significant glucocorticoid response. Additional GAL4 fusion studies were done to map the minimal domain of C/EBPbeta needed for accessory factor activity to the glucocorticoid response. Chimeric proteins containing amino acid regions 1-84, 52-118, or 85-118 of C/EBPbeta fused to the GAL4 DBD do not mediate a glucocorticoid response. We conclude that the amino terminus of C/EBPbeta contains a multicomponent domain necessary to confer accessory factor activity to the glucocorticoid response from the CRE of the PEPCK gene promoter.
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PMID:CCAAT/enhancer-binding protein beta is an accessory factor for the glucocorticoid response from the cAMP response element in the rat phosphoenolpyruvate carboxykinase gene promoter. 1002 11

We isolated two cDNA clones of rat Hex, a homeobox protein, studied its expression in rat liver and various cells, and characterized the protein. The levels of Hex mRNA were only slightly increased in liver of rats refed with a high-carbohydrate diet or after partial hepatectomy. Whereas the expression of Hex mRNA was detected in hepatocytes isolated from adult rat liver and also in highly differentiated hepatoma cells, no Hex mRNA was detected in poorly differentiated hepatoma cells. Hex mRNA was also detected in liver from embryo aged 15 days. Expression of Hex was increased in F9 cells during differentiation into visceral endoderm cells by treatment with retinoic acid. This stimulation occurred prior to an increase in the level of alpha-fetoprotein mRNA. When fusion-protein expression vectors of GAL4 DNA-binding domain and Hex were co-transfected with luciferase reporter plasmid, with or without five copies of the GAL4-binding site, into HepG2 cells, the luciferase activities were decreased in concentration- and GAL4-binding site-dependent manners. This repression did not require the presence of the homeodomain, which is located between the amino acid residues 137 and 196. Its repression domain was mapped between the residues 45 and 136 in the proline-rich N-terminal region. In addition, the homeodomain was responsible for DNA-binding of Hex. These results indicate that Hex functions as a transcriptional repressor and may be involved in the differentiation and/or maintenance of the differentiated state in hepatocytes.
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PMID:cDNA cloning and expression of rat homeobox gene, Hex, and functional characterization of the protein. 1008 34

Hepatitis C virus NS5A protein transcriptionally modulates cellular genes and promotes cell growth. NS5A is likely to exert its activity in concert with cellular factor(s). Using a yeast two-hybrid screen, we have demonstrated that NS5A interacts with the C-terminal end of a newly identified cellular transcription factor, SRCAP. The authenticity of this interaction was verified by a mammalian two-hybrid assay, in vitro pull-down experiment, and an in vivo coimmunoprecipitation assay in human hepatoma (HepG2) cells. An in vitro transient transfection assay demonstrated that SRCAP can efficiently activate transcription when recruited by the Gal4 DNA-binding domain to the promoter. However, down-regulation of p21 promoter activity by NS5A was enhanced following ectopic expression of SRCAP. Together these results suggest that the interaction of NS5A and SRCAP may be one of the mechanisms by which NS5A exerts its effect on cell growth regulation contributing to hepatitis C virus-mediated pathogenesis.
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PMID:Hepatitis C virus NS5A protein modulates transcription through a novel cellular transcription factor SRCAP. 1070 87

Infection with hepadnaviruses and exposure to aflatoxin B1 (AFB1) are considered to be major risk factors in the development of hepatocellular carcinoma (HCC) in humans. A high rate of p53 mutations at codon 249 has been reported in these tumors. The tree shrew (Tupaia belangeri chinensis) is a useful animal model for the development of HCC after human hepatitis B virus (HBV) infection or AFB1 treatment. Therefore, it was of particular interest to determine whether the p53 gene in tree shrew HCCs associated with HBV infection and/or with exposure to AFB1 is affected in the same manner as in human HCCs. We determined the tree shrew p53 wild-type nucleotide sequences by RT-PCR and automatic DNA-sequencing. Tree shrew wild-type p53 sequence showed 91.7 and 93.4% homologies with human p53 nucleotide and amino acids sequences, respectively, while it showed 77.2 and 73.7% homologies in mice. One HCC and normal liver tissue from AFB1 treated and one HCC from AFB1- and HBV-treated tree shrew showed no change in p53 sequences, while three HCCs from AFB1- and HBV-treated tree shrews showed point mutations in p53 sequences. One HCC showed point mutations at codon 275, which is on the DNA-binding domain of p53 gene, which might be a cause of gain-of-function during the development of HCC. As a result, our finding indicates that tree shrews exposed to AFB1 and/or HBV had neither codon 249 mutations nor significant levels of other mutations in the p53 gene, as is the case with humans.
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PMID:Mutations in the p53 tumor suppressor gene in tree shrew hepatocellular carcinoma associated with hepatitis B virus infection and intake of aflatoxin B1. 1086 98

Transforming growth factor-beta (TGF-beta) inhibits cell cycle progression, in part through up-regulation of gene expression of the p21(WAF1/Cip1) (p21) cell cycle inhibitor. Previously we have reported that the intracellular effectors of TGF-beta, Smad3 and Smad4, functionally cooperate with Sp1 to activate the human p21 promoter in hepatoma HepG2 cells. In this study we show that Smad3 and Smad4 when overexpressed in HaCaT keratinocytes lead to activation of the p21 promoter. Activation requires the binding sites for the ubiquitous transcription factor Sp1 on the proximal promoter. Induction of the endogenous HaCaT p21 gene by TGF-beta1 is further enhanced after overexpression of Smad3 and Smad4, whereas dominant negative mutants of Smad3 and Smad4 and the inhibitory Smad7 all inhibit p21 induction by TGF-beta1 in a dose-dependent manner. We show that Sp1 expressed in the Sp1-deficient Drosophila SL-2 cells binds to the proximal p21 promoter sequences, whereas Smad proteins do not. In support of this finding, we show that DNA-binding domain mutants of Smad3 and Smad4 are capable of transactivating the p21 promoter as efficiently as wild type Smads. Co-expression of Smad3 with Smad4 and Sp1 in SL-2 cells or co-incubation of phosphorylated Smad3, Smad4, and Sp1 in vitro results in enhanced binding of Sp1 to the p21 proximal promoter sequences. We demonstrate that Sp1 physically and directly interacts with Smad2, Smad3, and weakly with Smad4 via their amino-terminal (Mad-Homology 1) domain. Finally, by using GAL4 fusion proteins we show that the glutamine-rich sequences in the transactivation domain of Sp1 contribute to the cooperativity with Smad proteins. In conclusion, Smad proteins play important roles in regulation of the p21 gene by TGF-beta, and the functional cooperation of Smad proteins with Sp1 involves the physical interaction of these two types of transcription factors.
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PMID:Role of Smad proteins and transcription factor Sp1 in p21(Waf1/Cip1) regulation by transforming growth factor-beta. 1087 24

p73, a structural homologue of the tumor suppressor gene, p53, has recently been identified and mapped to chromosome 1p36, where genomic loss of heterozygosity (LOH) often occurs in human hepatocellular carcinoma (HCC). To determine whether p73 is involved in the development of HCC and whether there is an inverse correlation between the mutations of p73 and p53, we examined 22 paired tumors/noncancerous liver tissues for allelic expression, LOH and mutation of p73 and for mutation of p53. p73 was biallelically expressed in noncancerous liver tissues and in 7 out of the 8 informative tumors. One tumor tissue expressed only a single allele. LOH of p73 was found in 2 out of the 11 (18%) informative cases. A tumor-specific five-nucleotide deletion mutation causing a reading frameshift/early truncation of p73 DNA-binding domain was found, in which case no concomitant mutation in the DNA-binding domain of p53 was identified. Nine out of the 22 cases (41%) contained tumor-specific mutations in the DNA-binding domain of p53. Two of the three cases with p73 genetic alternations had a tumor size of less than 2 centimeters. These results suggest that p73 is a biallelically expressed gene in the liver and that allelic loss and mutation of p73 is infrequent and may occur early in HCC. p73 is unlikely to be the putative tumor suppressor gene located at chromosome 1p36 in HCC.
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PMID:Genetic alternations of p73 are infrequent but may occur in early stage hepatocellular carcinoma. 1092 60

The forkhead box (Fox) family of transcription factors share homology in the winged helix/forkhead DNA-binding domain and play important roles in regulating cellular proliferation, differentiation, longevity, and cellular transformation. Forkhead box M1B (FoxM1B) is a ubiquitously expressed member of the Fox transcription factor family whose expression is restricted to proliferating cells and that mediates hepatocyte entry into DNA synthesis and mitosis during liver regeneration. Recent cDNA microarray studies indicated that age-related defects in cellular proliferation are associated with diminished expression of the FoxM1B transcription factor. Here, we show that increased levels of FoxM1B in regenerating liver of old transgenic mice restore the sharp peaks in hepatocyte DNA replication and mitosis that are the hallmarks of young regenerating mouse liver. Restoration of the young regenerating liver phenotype is associated with increased expression of numerous cell cycle regulatory genes that include cyclin D1, cyclin A2, cyclin F, cyclin B1, cyclin B2, Cdc25B, and p55cdc. Cotransfection assays in the human hepatoma HepG2 cell line demonstrated that FoxM1B protein stimulated expression of both the cyclin B1 and cyclin D1 promoters, suggesting that these cyclin genes are a direct FoxM1B transcriptional target. These results suggest that FoxM1B controls the transcriptional network of genes that are essential for cell division and exit from mitosis. Our results indicate that reduced expression of the FoxM1B transcription factor contributes to the decline in cellular proliferation observed in the aging process.
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PMID:Increased levels of forkhead box M1B transcription factor in transgenic mouse hepatocytes prevent age-related proliferation defects in regenerating liver. 1157 93

Hepatic steatosis and hepatocellular carcinoma (HCC) are common and serious features of hepatitis C virus (HCV) infection, and the core protein has been shown to play distinct roles in the pathogenesis. Here we report the direct interaction of HCV core protein with retinoid X receptor alpha (RXRalpha), a transcriptional regulator that controls many aspects of cell proliferation, differentiation, and lipid metabolism. The core protein binds to the DNA-binding domain of RXRalpha, leading to increase the DNA binding of RXRalpha to its responsive element. In addition, RXRalpha is activated in cells expressing the core protein as well as in the livers of the core-transgenic mice that would develop hepatic steatosis and HCC later in their lives. Using promoter genes of cellular retinol binding protein II (CRBPII) and acyl-CoA oxidase as reporters, we also show that the expression of the core protein enhances the transcriptional activity regulated by the RXRalpha homodimer as well as by the heterodimer with peroxisome proliferator activated receptor alpha. Furthermore, expression of the CRBPII gene is also up-regulated in the livers of HCV core-transgenic mice. In conclusion, these results suggest that modulation of RXRalpha-controlled gene expression via interaction with the core protein contributes to the pathogenesis of HCV infection.
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PMID:Interaction of hepatitis C virus core protein with retinoid X receptor alpha modulates its transcriptional activity. 1191 42


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