Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.7.49 (reverse transcriptase)
 31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The double-stranded DNA genome of hepatitis B virus (HBV) is reverse transcribed from the viral pregenome RNA template by a virally encoded reverse transcriptase enzyme (RT) that possesses both priming and elongation activities. Prior efforts have failed to express an active form of HBV RT outside the nucleocapsid in animal cells or to release it from viral nucleocapsids, thus restricting the characterization of this important enzyme. Here, we have engineered epitope-tagged HBV RT proteins and expressed them in Xenopus oocytes via a synthetic RT mRNA which does not include the viral capsid protein or the known initiation site for viral DNA synthesis, DR1. We demonstrate the production of an immunoprecipitable 96-kDa HBV RT protein and show, using a simple in vitro RT assay, that oocyte lysates containing this protein possess an activity that (i) catalyzes an RNA-dependent deoxynucleotide triphosphate polymerization reaction by using an as-yet-unidentified RNA template and (ii) is sensitive to the RT inhibitors actinomycin D and phosphonoformate. Experiments with the chain terminator ddATP suggest that a significant amount of chain elongation occurs in our in vitro reaction. Electrophoretic analysis reveals a heterogeneous array of RT reaction products with sizes ranging from about 100 bases to far larger than that of the input RT mRNA. These products appear to contain covalently bound protein, consistent with the notion that the RT protein may have primed their synthesis. We conclude that HBV RT activity can be uncoupled from both the nucleocapsid and the replication origin, DR1. Our results raise the possibility that unless HBV employs novel mechanisms to regulate its constitutively active RT, cellular RNAs may be reverse transcribed during HBV infection, with potential implications for the development of HBV-related liver cancer. The use of the oocyte system should facilitate studies of HBV RT, including the development of HBV RT inhibitors for antiviral therapy.
 ...
PMID:Recombinant human hepatitis B virus reverse transcriptase is active in the absence of the nucleocapsid or the viral replication origin, DR1. 768 99

Pathological changes arising in altered cell biology and diseases such as cancer are driven by changes in gene expression. In the inherited disease haemochromatotis (HC) progressive iron loading of the parenchymal cells (hepatocytes) of the liver leads to cellular toxicity. If left untreated, fibrosis, cirrhosis and ultimately liver cancer occur. By using differential display reverse transcriptase polymerase chain reaction (DDRT-PCR) techniques, we have identified and isolated several differentially displayed mRNAs that are excessively expressed or repressed in HC liver compared to normal human liver. One of these mRNAs was found to be strongly expressed in the liver of a patient with HC and in tumour tissue from a subject with hepatocellular carcinoma complicating HC (HC/HCC). The message of this gene was detected at a very low level in normal human liver. Northern analysis showed that this gene is also expressed in lymphocytes of HC patients and in MOLT-4 human T-lymphoid cells irrespective of iron status. The partial 1.0 kb cDNA sequence of the 9.5 kb transcript of this gene is unique and we propose that this gene may be related to cell proliferation and HC/HCC human liver.
 ...
PMID:Molecular cloning of a novel mRNA highly expressed in haemochromatotic human liver and proliferating cells. 880 57

Hepatitis B viruses establish a chronic, productive, and noncytopathic infection of hepatocytes. Viral products are produced by transcription from multiple copies (5-50) of covalently closed circular (ccc) viral DNA. This cccDNA does not replicate, but can be replaced by DNA precursors that are synthesized in the cytoplasm. The present study was carried out to determine if long-term treatment with an inhibitor of viral DNA synthesis would lead to loss of virus products, including cccDNA, from the liver of woodchucks chronically infected with woodchuck hepatitis virus. Viral DNA synthesis was inhibited with the nucleoside analog, lamivudine (2'-deoxy-3'-thiacytidine). Lamivudine treatment produced a slow but progressive decline in viral titers in serum, to about 0.3% or less of the initial level. However, even after maintenance of drug therapy for 3-12 months, > 95% of the hepatocytes in most animals were still infected. Significant declines in the percentage of infected hepatocytes and of intrahepatic cccDNA levels were observed in only three woodchucks, two in the group receiving lamivudine and one in the placebo control group. Moreover, virus titers eventually rose in woodchucks receiving lamivudine, suggesting that drug-resistant viruses began to spread through the liver starting at least as early as 9-12 months of treatment. Three types of mutation that may be associated with drug resistance were found at this time, in a region upstream of the YMDD motif in the active site of the viral reverse transcriptase. The YMDD motif itself remained unchanged. Not unexpectedly, the lamivudine therapy did not have a impact on development of liver cancer.
 ...
PMID:Lamivudine therapy of WHV-infected woodchucks. 961 64

Hepatitis G virus (HGV) is a flavivirus that can cause acute hepatitis and persistent infection but its role in chronic liver disease or primary liver cancer is unproven. In this study we have examined the prevalence of HGV RNA in the serum of patients with hepatitis C virus (HCV) infection and in patients with cryptogenic chronic liver disease, including non-alcoholic steatohepatitis (NASH), and in patients with HCV-related hepatocellular carcinoma (HCC) and HCC arising in patients with cryptogenic liver disease. One-hundred and thirty patients who were positive for antibody to HCV (anti-HCV), 54 patients with cryptogenic chronic liver disease (including 17 patients with NASH) and 46 patients with hepatitis C-related (n = 27) or cryptogenic liver disease-related HCC (n = 19) were studied. HGV RNA was detected using nested reverse transcriptase-polymerase chain reaction (RT-PCR) and was found in 16.1% of patients with HCV infection. HGV RNA was not detected in any patient with cryptogenic liver disease. In patients with HCC, 7/34 samples were positive for HGV RNA and six out of seven HGV-positive subjects also had HCV infection. Only one patient with HCC in cryptogenic liver disease was positive for HGV RNA. Hence, cryptogenic liver disease in the UK is not caused by HGV/GBVc infection. It seems unlikely that HGV plays a significant role in hepatocarcinogenesis.
 ...
PMID:Hepatitis G infection: role in cryptogenic chronic liver disease and primary liver cell cancer in the UK. Trent Hepatitis C virus Study Group. 965 69

Molecular epidemiological studies of populations at high risk for liver cancer have shown that hepatitis B virus (HBV) and aflatoxin B1 exposures are two major risk factors for this disease. Oltipraz is currently being considered for clinical trial to protect against aflatoxin B1-induced hepatocarcinogenesis based on its proven protective effect in many different animal models. In addition, oltipraz inhibits human immunodeficiency virus (HIV) replication. The inactivation of reverse transcriptase of HIV appears to be the antiviral mechanism. It has been demonstrated that a number of compounds that inhibit HIV replication also inhibit HBV replication in vitro. Therefore, we tested the possibility of oltipraz blocking HBV replication in 2.2.15 cells (clonal cells derived from HepG2 cells that were transfected with a plasmid containing HBV DNA) in vitro. Results of the experiments indicate that oltipraz has a dose-dependent inhibitory effect on HBV replication and specifically blocks HBV transcription in 2.2.15 cells. In addition, oltipraz induces endogenous wild-type p53 protein in a dose- and time-course-dependent manner. Taken together, we speculate that the effects of oltipraz against replication of HBV and specific blocking of HBV transcription may be through the induction of p53-mediated pathway in 2.2.15 cells. In addition to its known chemopreventive action on aflatoxin B1 hepatocarcinogenesis, oltipraz was shown here to inhibit HBV replication. These dual effects put oltipraz as the excellent candidate for the chemopreventive agent of human hepatocellular carcinoma.
 ...
PMID:Oltipraz, a novel inhibitor of hepatitis B virus transcription through elevation of p53 protein. 988 68

Currently seven viruses, A, B, C, D, E, G and transfusion transmitted virus (TTV), are recognised in the hepatitis virus alphabet. Hepatitis G virus and TTV probably do not cause liver disease in humans. Hepatitis A and E usually cause a self-limiting hepatitis followed by complete recovery but occasionally cause fulminant hepatic failure. Hepatitis B and C are major public health problems worldwide due to their sequelae of chronic hepatitis, cirrhosis and primary liver cancer. Chronic hepatitis C is a particular health issue for Western Europe already, accounting for 40% of end-stage cirrhosis and 30% of liver transplants. The contribution of hepatitis C to chronic liver disease is predicted to rise in the future. Vaccines can prevent hepatitis A and B. Interferon alpha is effective treatment in 25-30% of patients with chronic hepatitis B or C. The prospects for treating chronic hepatitis B have been improved by the introduction of reverse transcriptase inhibitors. Lamivudine is the first drug of this class to be licensed. The optimal use of these new drugs is currently being studied. The success rate for treating chronic hepatitis C can be raised to about 40% with combination therapy of interferon alpha and ribavirin. A large research effort to discover new antiviral agents against hepatitis C is already giving the prospect of more effective therapies in the next few years.
 ...
PMID:Virus hepatitis update. 1119 85

A rat cell line-nominated CC-62 derived from a combined hepatocellular and cholangiocellular carcinoma obtained by administration of 2-acetylaminofluorene to male Wistar rats, has been established. Using light and electron microscopy it was determined that morphologically the tumor consisted of a mixed population of hepatocytes and cholangiolar neoplastic cells, intermingled with small, undifferentiated oval-like cells. The CC-62 line has been maintained through 90 passages in culture adopting a paving stone arrangement. Doubling time at the 12th passage was 23 h. Immunostaining with a panel of antisera was performed to identify the cytological profiles of the cell line. There was no k-ras or p53 expression by immunohistochemistry, and molecular biology failed to detect mutations. Molecular analysis by reverse transcriptase-polymerase chain reaction revealed transcripts for c-met but no expression of HGF messenger ribonucleic acid. Three cell lines cloned from CC-62 showed the same immunohistochemical and molecular pattern as the parental line. Cytogenetic analysis revealed a chromosome number ranging from 74 to 82 with a modal number of 79 but no clonal structural abnormalities were found. Deoxyribonucleic acid ploidy analysis showed an aneuploid peak. CC-62 caused tumors 1 mo after subcutaneous transplantation into nude mice, with morphological patterns of mucosecretory solid and spindle-shaped carcinoma. This cell line is the first established from a primary rat combined hepatocellular and cholangiocellular neoplasm. The resulting cells expressed biological and morphological markers of hepatocytes and cholangiolar cells. Therefore this cell line may contribute to a better understanding of the histogenesis of liver cancer.
 ...
PMID:Characterization of a new rat cell line established from 2'AAF-induced combined hepatocellular cholangiocellular carcinoma. 1124 1

The presence of telomerase has been demonstrated recently in many different malignancies. Several reports documented that in human hepatocellular carcinoma, the level of telomerase activity parallels its differentiation stage. In the present study, the effect of the differentiation-inducing agent sodium butyrate on telomerase activity in four human liver cancer cell lines was investigated using the telomeric repeat amplification protocol. We assayed telomerase activity before and after butyrate treatment and in cell cycle synchronized non-dividing quiescent cells. In addition, telomerase reverse transcriptase levels were measured at the mRNA level. All four cell lines possessed high but not identical levels of telomerase activity. Telomerase activity was significantly reduced by treatment with sodium butyrate as well as trichostatin A in a dose- and time-dependent fashion, paralleling the reduction of cell proliferation. Although methotrexate, hydroxyurea, and colchicine synchronized the cell cycle at G1, S, and G2/M, respectively, and thereby also caused proliferating cells to cease dividing and become quiescent, in this case telomerase activity remained essentially unaltered compared to the control cultures. Moreover, levels of mRNA encoding telomerase reverse transcriptase were not always significantly altered by either sodium butyrate treatment or cell cycle synchronization. These results suggest that sodium butyrate, as a histone deacetylase inhibitor, effectively reduces telomerase activity without affecting transcription levels of the reverse transcriptase component.
 ...
PMID:Reduction of telomerase activity in human liver cancer cells by a histone deacetylase inhibitor. 1131 63

We have previously isolated and characterized a novel human gene HUEL (C4orf1) that is ubiquitously expressed in a wide range of human fetal, adult tissues and cancer cell lines. HUEL maps to region 4p12-p13 within the short arm of chromosome 4 whose deletion is frequently associated with bladder and other carcinomas. Here we present the genomic organization, sizes and boundaries of exons and introns of HUEL. The GC-rich upstream genomic region and 5' untranslated region (UTR) together constitute a CpG island, a hallmark of housekeeping genes. The 3250 bp HUEL cDNA incorporates a 1704 bp ORF that translates into a hydrophilic protein of 568-amino acids (aa), detected as a band of approximately 70 kDa by Western blotting. We have isolated the murine homolog of HUEL which exhibits 89% nucleotide and 94% amino acid identity to its human counterpart. The HUEL protein shares significant homology with the minimal DNA-binding domain (DNA-BD) of the DNA repair protein encoded by the xeroderma pigmentosum group A (XPA) gene. Other notable features within HUEL include the putative nuclear receptor interaction motif, nuclear localization and export signals, zinc finger, leucine zipper and acidic domains. Mimosine-mediated cell cycle synchronization of PLC/PRF/5 liver cancer cells clearly portrayed translocation of HUEL into the nucleus specifically during the S phase of the cell cycle. Yeast two-hybrid experiments revealed interactions of HUEL with two partner proteins (designated HIPC and HIPB) bearing similarity to a mitotically phosphorylated protein and to reverse transcriptase. Co-immunoprecipitation assays validated the interaction between HUEL and HIPC proteins in mammalian cells. HUEL is likely to be an evolutionarily conserved, housekeeping gene that plays a role intimately linked with cellular replication, DNA synthesis and/or transcriptional regulation.
 ...
PMID:The novel human HUEL (C4orf1) protein shares homology with the DNA-binding domain of the XPA DNA repair protein and displays nuclear translocation in a cell cycle-dependent manner. 1190 20

Diisononyl phthalate (DINP) is a compound widely used as a plasticizer in the production of polyvinyl chloride products. Chronic exposure to DINP leads to liver cancer in rats and mice. Many phthalates are considered to be relatively weak peroxisome proliferators (PP), a group of rodent hepatocarcinogens that cause a variety of adaptive responses in liver through the PP-activated receptor alpha (PPARalpha). The objectives of this study were to determine whether DINP-induced effects in the liver associated with carcinogenesis are mediated by PPARalpha and to identify novel gene targets of DINP. Male and female SV129 wild-type, SV129 PPARalpha-null, and B6C3F1 mice were administered DINP by gavage or in the feed. Transcript profile technology and reverse transcriptase (RT)-polymerase chain reaction (PCR) were used to identify gene targets. Dose-dependent increases in relative liver weights were dependent on PPARalpha in 10- or 12-week-old male and female mice and 30-week-old male mice. Female 30-week-old mice exhibited PPARalpha-independent increases in relative liver weights. Increases in hepatocyte proliferation, palmitoyl-CoA oxidase (PCO) activity, and levels of enzymes involved in beta- and omega-oxidation of fatty acids were shown to be dependent on PPARalpha. Five novel genes were shown to be altered in the livers of female wild-type mice after a 3-week exposure, but not in PPARalpha-null, mice. These genes included those involved in DNA repair and recombination (ATP-dependent helicase and Endonuclease III homolog), drug metabolism (Cyp2a4) and protein trafficking (FKBP-1, FKBP-13). An additional gene (Cyp2d9) was shown to be down-regulated in wild-type mice but up-regulated in PPARalpha-null mice indicating more complex regulation by PPARalpha and additional factors. These data support the hypothesis that PPARalpha plays a dominant role in mediating the effects associated with hepatocarcinogenesis after DINP exposure.
 ...
PMID:Role of the peroxisome proliferator-activated receptor alpha in responses to diisononyl phthalate. 1296 24


1 2 3 Next >>