Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019158 (hepatitis)
 30,205 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

B cells from nonimmune mice mediate the cytolysis of fibroblasts infected with the coronavirus, mouse hepatitis virus (MHV), strain A59. In this investigation, we report that splenic B cells and a B cell hybridoma induced the fragmentation of MHV-infected target cell DNA into a nucleosomal ladder pattern, characteristic of apoptosis. To determine the mechanism by which B cells mediated this killing event, we used criteria previously established for the killing of target cells by cytotoxic T lymphocytes (CTLs) and compared this B-cell-mediated killing to lymphocytic choriomeningitis virus (LCMV)-specific CTL killing of LCMV-infected target cells. Unlike CTL-mediated cytotoxicity, B cells efficiently lysed and induced the fragmentation of the DNA in their target cells in the presence of EGTA, arguing against a Ca(2+)-dependent granule exocytosis model for killing. In addition, paraformaldehyde-fixed B cells were able to kill MHV-infected targets. We were unable to detect TNF-alpha-associated cytotoxicity via bioassay with nonimmune effector B cells against the TNF-sensitive cell line, LM, or the TNF-alpha-resistant subline, L929.w, infected with MHV. Serine esterase inhibitors (benzamidine hydrochloride and N alpha-p-tosyl-L-arginine methyl ester) blocked CTL-induced 51Cr release and DNA fragmentation. In contrast, the inhibitors did not block the B-cell-induced 51Cr release, but did cause an inhibition in the fragmentation of the DNA of the target cell. These data indicate that B cells are capable of inducing the lysis and DNA fragmentation of MHV-infected target cells similar to CTL-induced apoptosis. However, we show that the mechanism(s) by which these processes are induced by B cells is distinct from CTL-mediated cytotoxicity.
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PMID:B cells induce apoptosis via a novel mechanism in fibroblasts infected with mouse hepatitis virus. 839 6

Gene products of hepatitis C virus (HCV), a possible major causative agent of posttransfusion non-A, non-B hepatitis, are considered to be produced from a precursor polyprotein via proteolytic processing mediated by either host cell or viral proteinases. The presence of HCV serine proteinase has been proposed from analyses of amino acid sequence homology. To examine the processing mechanism of the HCV precursor polyprotein, the amino-terminal region of the putative nonstructural protein region of the HCV genome, containing the serine proteinase motif, was expressed and analyzed by using an in vitro transcription/translation system and a transient expression system in cultured cells. Two distinct proteinase activities which function in the production of a 70-kDa protein (p70) from the precursor polyprotein were detected. One of these proteinase activities, which cleaved the carboxyl (C)-terminal side of p70, required the presence of the serine proteinase motif, which is located in the amino (N)-terminal region of p70. That suggested that the predicted HCV serine proteinase was functional. The other activity, which was responsible for the cleavage of the N-terminal side of p70, required the expression of the region upstream and downstream of that cleavage site, including the p70 serine proteinase domain. From the results of pulse-chase analysis, using proteinase inhibitors coupled with a point mutation analysis, the latter activity was proposed to be a novel zinc-dependent metalloproteinase.
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PMID:Two distinct proteinase activities required for the processing of a putative nonstructural precursor protein of hepatitis C virus. 839 6

The coronavirus mouse hepatitis virus-A59 (MHV-A59) encodes a serine-like proteinase (3C-like proteinase or 3CLpro) in ORF 1a of gene 1 between nucleotides 10,209 and 11,114. We previously have demonstrated that proteins expressed in vitro from a cDNA clone of the 3CLpro region possess proteinase activity, and that the proteinase is able to cleave substrate in trans. We sought to determine if the 27-kDa in vitro cleavage product (p27) was an active form of the 3CLpro and whether this was consistent with the 3CLpro expressed in virus-infected cells. Antibodies directed against the 3CLpro domain detected 27-kDa MHV proteins in vitro and in MHV-A59-infected cells. The 27-kDa proteins were able to cleave substrate in trans without other protein cofactors or supplemental membranes, and the p27 proteinase activity was retained after purification by immunoprecipitation and gel electrophoresis. When p27 was expressed in vitro with portions of the amino-and carboxy-terminal flanking domains (MP1 and MP2), p27 was not liberated by cls cleavage. The proteolytic activity of the 27-kDa proteins was inhibited by a variety of cysteine and serine proteinase inhibitors, and was eliminated by the cysteine proteinase inhibitor E64d. These results indicate that the 27-kDa protein is a mature proteinase in MHV-A59-infected cells, and that appropriate processing of this molecule occurs in vitro.
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PMID:Intracellular and in vitro-translated 27-kDa proteins contain the 3C-like proteinase activity of the coronavirus MHV-A59. 880 21

Hepatitis C virus (HCV) is the major etiological agent of posttransfusion and community-acquired non-A, non-B hepatitis. It is an enveloped virus, grouped as a separate genus in the Flaviviridae family. The plus-stranded RNA genome encodes a polyprotein of about 3000 amino acids with the structural proteins core, E1 and E2 residing in the amino terminal quarter of the polyprotein and the nonstructural proteins NS2, NS3, NS4A, NS4B, NS5A and NS5B in the remainder. Maturation of the structural proteins is mediated by host cell signalases located in the lumen of the endoplasmic reticulum and cleaving behind stretches of hydrophobic amino acids. At least two virally encoded proteinases are responsible for processing of the NS proteins: a zinc-dependent metallo-proteinase encompassing the NS2 domain and the amino terminal portion of NS3, which is essential for cleavage at the NS2/3 junction; a serine-type proteinase located in the amino terminal domain of NS3 is required for cleavage at all sites downstream of the NS3 carboxy terminus. However, although the NS3 domain contains proteolytic activity, with the exception of the NS5A/5B junction cleavage only occurs in the presence of NS4A. This 54 amino acid long peptide can modulate the proteolytic activity of the enzyme in cis and in trans, probably by the formation of a stable NS3/NS4A complex. Modulation of the proteinase activity may be a way to regulate the expression and replication of the HCV genome.
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PMID:Processing pathways of the hepatitis C virus proteins. 883 84

The coronavirus spike glycoprotein (S) mediates both the attachment of virus to the host cell receptor and membrane fusion. We describe here the characterization of a temperature-sensitive mutant of the coronavirus mouse hepatitis virus A59 (MHV-A59) having multiple S protein-related defects. The most remarkable of these was that the mutant, designated Albany 18 (Alb18), assembled virions devoid of the S glycoprotein at the nonpermissive temperature. Alb18 also failed to bring about syncytia formation in cells infected at the nonpermissive temperature. Virions of the mutant assembled at the permissive temperature were much more thermolabile than wild type. Moreover, mutant S protein that was incorporated into virions at the permissive temperature showed enhanced pH-dependent thermolability in its ability to bind to the MHV receptor. Alb18 was found to have a single point mutation in S resulting in a change of serine 287 to isoleucine, and it was shown by revertant analysis that this was the lesion responsible for the phenotype of the mutant.
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PMID:A conditional-lethal murine coronavirus mutant that fails to incorporate the spike glycoprotein into assembled virions. 883 89

The NS3 protein of hepatitis C virus contains a chymotrypsin-like serine proteinase domain. We built a homology model of this domain which predicts the presence of a tetradentate metal binding site formed by three cysteines and one histidine. These residues are strictly conserved in all known hepatitis C viral genotypes as well as in other recently discovered related hepatitis viruses. We show that the hepatitis C virus enzyme does indeed contain a Zn2+ ion with S3N ligation and that the metal is required for structural integrity and activity of the enzyme. Strikingly, the residues forming the metal binding site are also conserved in the chymotrypsin-like 2A cysteine proteinases of picornaviruses. Remarkably, in these highly variable viral genomes the metal binding site is more conserved than the catalytic residues and thus allows us to define a novel class of zinc binding chymotrypsin-like proteinases and to identify a new attractive target for antiviral therapy.
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PMID:A zinc binding site in viral serine proteinases. 887 93

Fas (Apo1/CD95) is a member of the tumour necrosis factor/nerve growth factor receptor superfamily and mediates apoptosis in various cell types (for review sec [1]). Although this apoptotic activity has been clearly related to homeostasis in the immune system and pathological situations in non-lymphoid organs, the Fas signaling pathway remains mostly elusive. We and others previously showed that Fas-induced apoptosis of primary culture hepatocytes requires either an inhibitor of translation or a protein kinase inhibitor, suggesting that two distinct pathways of Fas signaling exist in hepatocytes. We report here that activation of ICE-like and CPP32-like cysteine proteases are required for Fas-mediated apoptosis, but that these pathways involve different subclasses of serine proteases and are selectively modulated by inhibitors of protein tyrosine kinases. These results confirm that distinct pathways can lead to Fas-induced apoptosis in hepatocytes. Further understanding of these pathways could facilitate the rational design of anti-apoptotic drugs in liver diseases associated with massive Fas-mediated hepatocyte apoptosis, including fulminant hepatitis.
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PMID:Multiple pathways of Fas-induced apoptosis in primary culture of hepatocytes. 895 79

Hepatitis delta virus (HDV) encodes two isoforms of its principal gene product, hepatitis delta antigen (HDAg). These two forms play distinctive and complementary roles in viral replication. Here we report that the large (LHDAg), but not the small (SHDAg), isoform of HDAg has the capacity to activate the expression of cotransfected genes driven by a variety of promoters, including the pre-S, S, and C promoters of hepatitis B virus. Mutational analysis of the C-terminal 19 amino acids unique to LHDAg shows that changing prolines to alanines in the two PXXP motifs in this region specifically ablates the activation function without abolishing another activity of LHDAg, namely, its ability to inhibit HDV RNA synthesis. However, C-terminal truncations that also disrupt these PXXP motifs only slightly diminished the activation function, indicating that the proline mutations were not acting by inactivating potential SH3 interactions that could be mediated by these motifs. Mutation of the isoprenylated cysteine to serine decreases but does not abolish the activation activity, and overexpression of SHDAg does not interfere with the transactivation function of LHDAg. Although the mechanism and biological significance of this activity of LHDAg remain unknown, the presence of this activity serves as yet another marker that functionally distinguishes this protein from the closely related isoform SHDAg.
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PMID:Activation of heterologous gene expression by the large isoform of hepatitis delta antigen. 949 64

The pre-S envelope protein of duck hepatitis B virus (DHBV) contains a region, Asp-Asp-Pro-Leu-Leu (DDPLL), that is specifically required for virus assembly and secretion (Lenhoff and Summers, J Virol 1994;68:4565-4571). We found that amino acids 201 to 205 of the pre-S envelope protein of woodchuck hepatitis virus (WHV) form a conserved amino acid cluster, Gly-Asp-Pro-Ala-Leu (GDPAL), which resembles the DDPLL sequence of DHBV. To determine whether the GDPAL region was functionally equivalent to the DDPLL region, we deleted this region from the pre-S protein of WHV or mutated individual amino acids within the region. The mutant DNA was transfected into human hepatoma cell line Huh7, and the medium was assayed for virion production by immunoprecipitation and Southern blot analysis. We found that an in-frame deletion of this small region inhibited virion formation, suggesting that the GDPAL region of the pre-S envelope protein was required for virus assembly and/or secretion of WHV. Individual replacement of alanine 204, leucine 205, or serine 206 with other amino acid residues did not affect virus production. However, substitution of either aspartic acid 202 with valine or proline 203 with leucine dramatically inhibited WHV production. Furthermore, the GDPAL mutants were individually tested for their abilities to complement a pre-S1 defective genome. The results showed that the GDPAL region functioned as part of the pre-S1 protein but was not required to function as part of the pre-S2 protein.
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PMID:The GDPAL region of the pre-S1 envelope protein is important for morphogenesis of woodchuck hepatitis virus. 958 99

The hepatitis C virus (HCV) was identified as the major causative agent of posttransfusion and community-acquired non-A, non-B hepatitis throughout the world. It is an enveloped virus with a plus-strand RNA genome encoding a polyprotein of about 3,010 amino acids. This polyprotein is cleaved co- and posttranslationally into mature viral proteins by host cell signal peptidases and 2 viral enzymes designated the NS2-3 proteinase and the NS3/4A proteinase complex. It is assumed that virus replication takes place in a membrane-associated complex containing at least 2 viral enzymatic activities: the NS3 nucleoside triphosphatase (NTPase)/helicase and the NS5B RNA-dependent RNA polymerase (RdRp). Based on their important role for the viral life cycle and the wealth of information available for related cellular and viral proteins, the NS3/4A serine-type proteinase complex, the NS3 NTPase/helicase and the NS5B RdRp are the most attractive targets for development of HCV-specific antiviral therapies. This review will summarize our current knowledge about structure and function of these proteins and describe approaches pursued to identify effective antiviral compounds.
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PMID:Candidate targets for hepatitis C virus-specific antiviral therapy. 967 42


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