Role of Immunoproteasome Catalytic Subunits in the Immune Response to Hepatitis B Virus

Robek, Michael D.; Garcia, Mayra L.; Boyd, Bryan; Chisari, Francis V.

doi:10.1128/jvi.01779-06

Cited by 42 publications

(46 citation statements)

References 49 publications

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“…Previous studies have demonstrated that HBV replication is inhibited by the IFN-␣/␤-mediated antiviral response and that IFN sensitivity by HBV requires proteasome activity but not the IFN- induced proteasome catalytic subunits (35,36). Furthermore, IFN-␣/␤ disrupts the formation of RNA-containing capsids at a posttranslational step, although the precise mechanism is not defined (50,51).…”

Section: Resultsmentioning

confidence: 94%

Hepatitis B Virus Replication and Release Are Independent of Core Lysine Ubiquitination

Garcia

Byfield

Robek

2009

J Virol

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Ubiquitin conjugation to lysine residues regulates a variety of protein functions, including endosomal trafficking and degradation. While ubiquitin plays an important role in the release of many viruses, the requirement for direct ubiquitin conjugation to viral structural proteins is less well understood. Some viral structural proteins require ubiquitin ligase activity, but not ubiquitin conjugation, for efficient release. Recent evidence has shown that, like other viruses, hepatitis B virus (HBV) requires a ubiquitin ligase for release from the infected cell. The HBV core protein contains two lysine residues (K7 and K96), and K96 has been suggested to function as a potential ubiquitin acceptor site based on the fact that previous studies have shown that mutation of this amino acid to alanine blocks HBV release. We therefore reexamined the potential connection between core lysine ubiquitination and HBV replication, protein trafficking, and virion release. In contrast to alanine substitution, we found that mutation of K96 to arginine, which compared to alanine is more conserved but also cannot mediate ubiquitin conjugation, does not affect either virus replication or virion release. We also found that the core lysine mutants display wild-type sensitivity to the antiviral activity of interferon, which demonstrates that ubiquitination of core lysines does not mediate the interferon-induced disruption of HBV capsids. However, mutation of K96 to arginine alters the nuclear-cytoplasmic distribution of core, leading to an accumulation in the nucleolus. In summary, these studies demonstrate that although ubiquitin may regulate the HBV replication cycle, these mechanisms function independently of direct lysine ubiquitination of core protein.The hepatitis B virus (HBV) particle consists of an enveloped nucleocapsid that contains the viral polymerase (Pol) and an incomplete 3.2-kb double-stranded DNA genome (9). In the cytoplasm, the viral core structural proteins interact to form homodimers, which further self-assemble into capsid particles that package Pol and the viral pregenomic RNA. Encapsidated Pol subsequently reverse transcribes pregenomic RNA to give rise to mature double-stranded relaxed circular DNAcontaining capsids. HBV DNA-containing capsids are released from the cell as mature virions after acquiring an envelope consisting of cellular membrane lipids and the viral small, middle, and large envelope proteins (4, 9, 41). Due to the directed insertion of the envelope proteins in the endoplasmic reticulum and Golgi membrane, and the requirement of the large envelope protein for virion release, nucleocapsids are hypothesized to bud at intracellular membranes for release through the constitutive secretory pathway (5). Although the mechanism and site of HBV nucleocapsid envelopment and release remain poorly understood, emerging evidence indicates that the cellular ubiquitin pathway may play a role in this process.Structural proteins of some enveloped RNA viruses contain highly conserved sequences [PPXY, P(T/S)AP, an...

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Section: Resultsmentioning

confidence: 94%

Hepatitis B Virus Replication and Release Are Independent of Core Lysine Ubiquitination

Garcia

Byfield

Robek

2009

J Virol

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“…We noted that the LANA binding site upstream of the TAP1 and PSMB9 (LMP2) genes are located in a bidirectional promoter regulatory element known to be IFN-␥-inducible (16,34,45). Since IFN-␥ signals mainly through the JAK-STAT pathway to achieve transcriptional activation of IFN-␥-inducible genes (23,55,62), we compared our LANA ChIP-Seq analysis data with IFN-␥-inducible STAT1 DNA binding ChIP-Seq data from a previously published study (http://www.nature.com/nmeth/journal/v4/n8 /suppinfo/nmeth1068_S1.html) (46).…”

Section: Resultsmentioning

confidence: 99%

Identification of Host-Chromosome Binding Sites and Candidate Gene Targets for Kaposi's Sarcoma-Associated Herpesvirus LANA

Lü

Tsai

Chen

et al. 2012

J Virol

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LANA is essential for tethering the Kaposi's sarcoma-associated herpesvirus (KSHV) genome to metaphase chromosomes and for modulating host-cell gene expression, but the binding sites in the host-chromosome remain unknown. Here, we use LANA-specific chromatin immunoprecipitation coupled with high-throughput sequencing (ChIP-Seq) to identify LANA binding sites in the viral and host-cell genomes of a latently infected pleural effusion lymphoma cell line BCBL1. LANA bound with high occupancy to the KSHV genome terminal repeats (TR) and to a few minor binding sites in the KSHV genome, including the LANA promoter region. We identified 256 putative LANA binding site peaks with P < 0.01 and overlap in two independent ChIP-Seq experiments. We validated several of the high-occupancy binding sites by conventional ChIP assays and quantitative PCR. Candidate cellular LANA binding motifs were identified and assayed for binding to purified recombinant LANA protein in vitro but bound with low affinity compared to the viral TR binding site. More than half of the LANA binding sites (170/256) could be mapped to within 2.5 kb of a cellular gene transcript. Pathways and Gene Ontogeny (GO) analysis revealed that LANA binds to genes within the p53 and tumor necrosis factor (TNF) regulatory network. Further analysis revealed partial overlap of LANA and STAT1 binding sites in several gamma interferon (IFN-γ)-regulated genes. We show that ectopic expression of LANA can downmodulate IFN-γ-mediated activation of a subset of genes, including the TAP1 peptide transporter and proteasome subunit beta type 9 (PSMB9), both of which are required for class I antigen presentation. Our data provide a potential mechanism through which LANA may regulate several host cell pathways by direct binding to gene regulatory elements.

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“…In the mouse model, it was shown that incorporation of LMP7 into the proteasome enhances the production of the immunodominant HBV-pol(803-811) epitope and alters the magnitude and specificity of the CD8 T-cell response to HBV envelope protein (37). Based on this result, it can be speculated that the reduced immunoproteasome activity even after interferon stimulation in HBV-replicating hepatocytes reduces the capability of antigen processing, finally conferring to an impaired elimination of HBV-positive hepatocytes.…”

Section: Discussionmentioning

confidence: 99%

“…The error bars represent the standard deviations. Analysis of Proteasome Activity-Proteasomes were isolated by differential centrifugation based on the protocol of Robek et al (37). Analysis of constitutive proteasome function was performed using a commercial assay system (20 S proteasome activity assay kit, Millipore, Germany) measuring release of the fluorophor 7-amino-4-methylcoumarin (AMC) after cleavage from the labeled substrate peptide LLVY-AMC.…”

Section: Methodsmentioning

confidence: 99%

“…It was found that LMP7 and LMP2 subunits affect the magnitude of CD8 T-cell response in HLA-A2 transgenic mice (37). Because of the relevance of the interferon-inducible subunits for the HBV-specific CD8 T-cell response and thereby for the progression of the infection, we analyzed whether stimulation of HBV-replicating cells with IFN␣ or IFN␥ overcomes the inhibitory effect of HBV on the activity of the immunoproteasome.…”

Section: Hbv-positive Cells Are More Protected Against Oxidative Damamentioning

confidence: 99%

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Hepatitis B Virus Induces Expression of Antioxidant Response Element-regulated Genes by Activation of Nrf2

Schaedler

Krause

Himmelsbach

et al. 2010

Journal of Biological Chemistry

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Role of Immunoproteasome Catalytic Subunits in the Immune Response to Hepatitis B Virus

Cited by 42 publications

References 49 publications

Hepatitis B Virus Replication and Release Are Independent of Core Lysine Ubiquitination

Hepatitis B Virus Replication and Release Are Independent of Core Lysine Ubiquitination

Identification of Host-Chromosome Binding Sites and Candidate Gene Targets for Kaposi's Sarcoma-Associated Herpesvirus LANA

Hepatitis B Virus Induces Expression of Antioxidant Response Element-regulated Genes by Activation of Nrf2

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