scholarly journals Kaposi's Sarcoma-Associated Herpesvirus Inhibitor of cGAS (KicGAS), Encoded by ORF52, Is an Abundant Tegument Protein and Is Required for Production of Infectious Progeny Viruses

2016 ◽  
Vol 90 (11) ◽  
pp. 5329-5342 ◽  
Author(s):  
Wenwei Li ◽  
Denis Avey ◽  
Bishi Fu ◽  
Jian-jun Wu ◽  
Siming Ma ◽  
...  
Keyword(s):  
Life Cycle ◽  
Immune Evasion ◽  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Tegument Protein ◽  
Tegument Proteins ◽  
Viral Particles ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACTAlthough Kaposi's sarcoma-associated herpesvirus (KSHV) ORF52 (also known as KSHV inhibitor of cGAS [KicGAS]) has been detected in purified virions, the roles of this protein during KSHV replication have not been characterized. Using specific monoclonal antibodies, we revealed that ORF52 displays true late gene expression kinetics and confirmed its cytoplasmic localization in both transfected and KSHV-infected cells. We demonstrated that ORF52 comigrates with other known virion proteins following sucrose gradient centrifugation. We also determined that ORF52 resides inside the viral envelope and remains partially associated with capsid when extracellular virions are treated with various detergents and/or salts. There results indicate that ORF52 is a tegument protein abundantly present in extracellular virions. To characterize the roles of ORF52 in the KSHV life cycle, we engineered a recombinant KSHV ORF52-null mutant virus and found that loss of ORF52 results in reduced virion production and a further defect in infectivity. Upon analysis of the virion composition of ORF52-null viral particles, we observed a decrease in the incorporation of ORF45, as well as other tegument proteins, suggesting that ORF52 is important for the packaging of other virion proteins. In summary, our results indicate that, in addition to its immune evasion function, KSHV ORF52 is required for the optimal production of infectious virions, likely due to its roles in virion assembly as a tegument protein.IMPORTANCEThe tegument proteins of herpesviruses, including Kaposi's sarcoma-associated herpesvirus (KSHV), play key roles in the viral life cycle. Each of the three subfamilies of herpesviruses (alpha, beta, and gamma) encode unique tegument proteins with specialized functions. We recently found that one such gammaherpesvirus-specific protein, ORF52, has an important role in immune evasion during KSHV primary infection, through inhibition of the host cytosolic DNA sensing pathway. In this report, we further characterize ORF52 as a tegument protein with vital roles during KSHV lytic replication. We found that ORF52 is important for the production of infectious viral particles, likely through its role in virus assembly, a critical process for KSHV replication and pathogenesis. More comprehensive investigation of the functions of tegument proteins and their roles in viral replication may reveal novel targets for therapeutic interventions against KSHV-associated diseases.

scholarly journals The Kaposi’s Sarcoma-Associated Herpesvirus Protein ORF42 Is Required for Efficient Virion Production and Expression of Viral Proteins

Viruses ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 711 ◽  
Author(s):  
Matthew Butnaru ◽  
Marta Maria Gaglia
Keyword(s):  
Gene Expression ◽  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Viral Proteins ◽  
Lytic Replication ◽  
Replication Cycle ◽  
Viral Particles ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

Kaposi’s sarcoma-associated herpesvirus (KSHV), the etiologic agent of Kaposi’s sarcoma and other aggressive AIDS-associated malignancies, encodes over 90 genes, most of which are expressed only during the lytic replication cycle. The role of many of the KSHV lytic proteins in the KSHV replication cycle remains unknown, and many proteins are annotated based on known functions of homologs in other herpesviruses. Here we investigate the role of the previously uncharacterized KSHV lytic protein ORF42, a presumed tegument protein. We find that ORF42 is dispensable for reactivation from latency but is required for efficient production of viral particles. Like its alpha- and beta-herpesviral homologs, ORF42 is a late protein that accumulates in the viral particles. However, unlike its homologs, ORF42 appears to be required for efficient expression of at least some viral proteins and may potentiate post-transcriptional stages of gene expression. These results demonstrate that ORF42 has an important role in KSHV replication and may contribute to shaping viral gene expression.

scholarly journals The K1 Protein of Kaposi's Sarcoma-Associated Herpesvirus Augments Viral Lytic Replication

2016 ◽  
Vol 90 (17) ◽  
pp. 7657-7666 ◽  
Author(s):  
Zhigang Zhang ◽  
Wuguo Chen ◽  
Marcia K. Sanders ◽  
Kevin F. Brulois ◽  
Dirk P. Dittmer ◽  
...  
Keyword(s):  
Life Cycle ◽  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Akt Kinase ◽  
Recombinant Viruses ◽  
Infected Cells ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACTThe K1 gene product of Kaposi's sarcoma-associated herpesvirus (KSHV) is encoded by the first open reading frame (ORF) of the viral genome. To investigate the role of the K1 gene during the KSHV life cycle, we constructed a set of recombinant viruses that contained either wild-type (WT) K1, a deleted K1 ORF (KSHVΔK1), stop codons within the K1 ORF (KSHV-K15×STOP), or a revertant K1 virus (KSHV-K1REV). We report that the recombinant viruses KSHVΔK1 and KSHV-K15×STOPdisplayed significantly reduced lytic replication compared to WT KSHV and KSHV-K1REVupon reactivation from latency. Additionally, cells infected with the recombinant viruses KSHVΔK1 and KSHV-K15×STOPalso yielded smaller amounts of infectious progeny upon reactivation than did WT KSHV- and KSHV-K1REV-infected cells. Upon reactivation from latency, WT KSHV- and KSHV-K1REV-infected cells displayed activated Akt kinase, as evidenced by its phosphorylation, while cells infected with viruses deleted for K1 showed reduced phosphorylation and activation of Akt kinase. Overall, our results suggest that K1 plays an important role during the KSHV life cycle.IMPORTANCEKaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of three human malignancies, and KSHV K1 is a signaling protein that has been shown to be involved in cellular transformation and to activate the phosphatidylinositol 3-kinase (PI3K)/Akt/mTOR pathway. In order to investigate the role of the K1 protein in the life cycle of KSHV, we constructed recombinant viruses that were deficient for K1. We found that K1 deletion viruses displayed reduced lytic replication compared to the WT virus and also yielded smaller numbers of infectious progeny. We report that K1 plays an important role in the life cycle of KSHV.

scholarly journals HIV-1 Vpr Inhibits Kaposi's Sarcoma-Associated Herpesvirus Lytic Replication by Inducing MicroRNA miR-942-5p and Activating NF-κB Signaling

2016 ◽  
Vol 90 (19) ◽  
pp. 8739-8753 ◽  
Author(s):  
Qin Yan ◽  
Chenyou Shen ◽  
Jie Qin ◽  
Wan Li ◽  
Minmin Hu ◽  
...  
Keyword(s):  
Life Cycle ◽  
Kaposi's Sarcoma ◽  
Primary Effusion Lymphoma ◽  
Expression Profiles ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Luciferase Reporter ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus ◽  
Hiv 1

ABSTRACTKaposi's sarcoma-associated herpesvirus (KSHV) infection is required for the development of several AIDS-related malignancies, including Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL). The high incidence of AIDS-KS has been ascribed to the interaction of KSHV and HIV-1. We have previously shown that HIV-1-secreted proteins Tat and Nef regulate the KSHV life cycle and synergize with KSHV oncogenes to promote angiogenesis and tumorigenesis. Here, we examined the regulation of KSHV latency by HIV-1 viral protein R (Vpr). We found that soluble Vpr inhibits the expression of KSHV lytic transcripts and proteins, as well as viral particle production by activating NF-κB signaling following internalization into PEL cells. By analyzing the expression profiles of microRNAs combined with target search by bioinformatics and luciferase reporter analyses, we identified a Vpr-upregulated cellular microRNA (miRNA), miR-942-5p, that directly targeted IκBα. Suppression of miR-942-5p relieved the expression of IκBα and reduced Vpr inhibition of KSHV lytic replication, while overexpression of miR-942-5p enhanced Vpr inhibition of KSHV lytic replication. Our findings collectively illustrate that, by activating NF-κB signaling through upregulating a cellular miRNA to target IκBα, internalized HIV-1 Vpr inhibits KSHV lytic replication. These results have demonstrated an essential role of Vpr in the life cycle of KSHV.IMPORTANCECoinfection by HIV-1 promotes the aggressive growth of Kaposi's sarcoma-associated herpesvirus (KSHV)-related malignancies, including Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL). In this study, we have shown that soluble HIV-1 Vpr inhibits KSHV lytic replication by activating NF-κB signaling following internalization into PEL cells. Mechanistic studies revealed that a cellular microRNA upregulated by Vpr, miR-942-5p, directly targeted IκBα. Suppression of miR-942-5p relieved IκBα expression and reduced Vpr inhibition of KSHV replication, while overexpression of miR-942-5p enhanced Vpr inhibition of KSHV replication. These results indicate that by activating NF-κB signaling through upregulating a cellular miRNA to target IκBα, internalized Vpr inhibits KSHV lytic replication. This work illustrates a molecular mechanism by which HIV-1-secreted regulatory protein Vpr regulates KSHV latency and the pathogenesis of AIDS-related malignancies.

scholarly journals ORF45-Mediated Prolonged c-Fos Accumulation Accelerates Viral Transcription during the Late Stage of Lytic Replication of Kaposi's Sarcoma-Associated Herpesvirus

2015 ◽  
Vol 89 (13) ◽  
pp. 6895-6906 ◽  
Author(s):  
Xiaojuan Li ◽  
Shumin Du ◽  
Denis Avey ◽  
Yuqing Li ◽  
Fanxiu Zhu ◽  
...  
Keyword(s):  
Gene Expression ◽  
Life Cycle ◽  
Late Stage ◽  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Viral Proteins ◽  
Lytic Replication ◽  
Viral Transcription ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACTKaposi's sarcoma-associated herpesvirus (KSHV) encodes multiple viral proteins that activate extracellular signal-regulated kinase (ERK)–mitogen-activated protein kinase (MAPK) cascades. One of these viral proteins, ORF45, mediates sustained ERK-p90 ribosomal S6 kinase (RSK) activation during KSHV lytic replication and facilitates viral translation through the phosphorylation of a eukaryotic translation initiation factor, eIF4B. The importance of ERK-RSK activation for KSHV viral transcription has been shown; however, which transcription factor senses the sustained MAPK signaling and leads to viral transcription remains poorly understood. Here we show that the presence of ORF45 leads to the prolonged accumulation of c-Fos during the late stage of KSHV lytic replication through ERK-RSK-dependent phosphorylation and stabilization and that the depletion of c-Fos disrupts viral lytic transcription. Genome-wide screening revealed that c-Fos directly binds to multiple viral gene promoters and enhances viral transcription. Mutation of the ERK-RSK phosphorylation sites of c-Fos restrains KSHV lytic gene expression and virion production. These results indicate that the prolonged accumulation of c-Fos promotes the progression of viral transcription from early to late stages and accelerates viral lytic replication upon sustained ORF45-ERK-RSK activation during the KSHV lytic life cycle.IMPORTANCEDuring KSHV lytic replication, transient activation and sustained activation of ERK-RSK induce viral immediate early (IE) transcription and late transcription, respectively. Studies have revealed that ERK-RSK activates several transcription factors involved in IE gene expression, including Ets, AP-1, CREB, and C/EBP, which lead to the transient ERK-RSK activation-dependent IE transcription. Whereas c-Fos acts as a sensor of sustained ERK-RSK activation, ORF45-ERK-RSK signaling mediates c-Fos phosphorylation and accumulation during late KSHV lytic replication, consequently promoting viral transcription through the direct binding of c-Fos to multiple KSHV promoters. This finding indicates that c-Fos mediates distinct viral transcriptional progression following sustained ERK-RSK signaling during the KSHV lytic life cycle.

scholarly journals Upregulation of MicroRNA 711 Mediates HIV-1 Vpr Promotion of Kaposi's Sarcoma-Associated Herpesvirus Latency and Induction of Pro-proliferation and Pro-survival Cytokines by Targeting the Notch/NF-κB-Signaling Axis

2018 ◽  
Vol 92 (18) ◽  
Author(s):  
Qin Yan ◽  
Runran Zhao ◽  
Chenyou Shen ◽  
Fei Wang ◽  
Wan Li ◽  
...  
Keyword(s):  
Life Cycle ◽  
Notch Signaling ◽  
Kaposi's Sarcoma ◽  
Promoter Activity ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Alternative Mechanism ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus ◽  
Hiv 1

ABSTRACTCoinfection with HIV-1 and Kaposi's sarcoma-associated herpesvirus (KSHV) often leads to AIDS-related malignancies, including Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL). The interaction between HIV and KSHV plays a pivotal role in the progression of these malignancies. We have previously demonstrated that, by upregulating miR-942-5p, HIV-1 viral protein R (Vpr) inhibits KSHV lytic replication by targeting IκBα to activate the NF-κB signaling (Q. Yan, C. Shen, J. Qin, W. Li, M. Hu, H. Lu, D. Qin, J. Zhu, S. J. Gao, C. Lu, J Virol 90:8739–8753, 2016). Here, we show that Vpr inactivates Notch signaling, resulting in inhibition of KSHV lytic replication and induction of pro-proliferative and -survival cytokines, including interleukin-2 (IL-2), TIMP-1, IGF-1, and NT-4. Mechanistically, Vpr upregulates miR-711, which directly targets the Notch1 3′ untranslated region. Suppression of miR-711 relieved Notch1 and reduced Vpr inhibition of KSHV lytic replication and Vpr induction of pro-proliferation and -survival cytokines, while overexpression of miR-711 exhibited the opposite effect. Finally, overexpression of Notch1 reduced Vpr induction of NF-κB activity by promoting IκBα promoter activity. Our novel findings reveal that by upregulating miR-711 to target Notch1, Vpr silences Notch signaling to activate the NF-κB pathway by reducing IκBα expression, leading to inhibition of KSHV lytic replication and induction of pro-proliferation and -survival cytokines. Therefore, the miR-711/Notch/NF-κB axis is important in the pathogenesis of AIDS-related malignancies and could be an attractive therapeutic target.IMPORTANCEHIV-1 infection significantly increases the risk of KS and PEL in KSHV-infected individuals. Our previous study has shown that HIV-1 Vpr regulates the KSHV life cycle by targeting IκBα to activate NF-κB signaling through upregulating cellular miR-942-5p. In this study, we have further found that Vpr inactivates Notch signaling to promote KSHV latency and production of pro-proliferation and -survival cytokines. Another Vpr-upregulated cellular microRNA, miR-711, participates in this process by directly targeting Notch1. As a result, Notch1 upregulation of the IκBα promoter activity is attenuated, resulting in reduced levels of IκBα transcript and protein. Overall, these results illustrate an alternative mechanism of HIV-1 Vpr regulation of KSHV latency and aberrant cytokines through the miR-711/Notch/NF-κB axis. Our novel findings further demonstrate the role of an HIV-1-secreted regulatory protein in the KSHV life cycle and KSHV-related malignancies.

scholarly journals A Kaposi's Sarcoma-Associated Herpesvirus Protein That Forms Inhibitory Complexes with Type I Interferon Receptor Subunits, Jak and STAT Proteins, and Blocks Interferon-Mediated Signal Transduction

2009 ◽  
Vol 83 (10) ◽  
pp. 5056-5066 ◽  
Author(s):  
Sabine A. Bisson ◽  
Anne-Laure Page ◽  
Don Ganem
Keyword(s):  
Kaposi's Sarcoma ◽  
Human Tumor ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Type I Interferons ◽  
Type I ◽  
Type I Ifn ◽  
Reading Frame ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACT Type I interferons (IFNs) are important mediators of innate antiviral defense and function by activating a signaling pathway through their cognate type I receptor (IFNAR). Here we report that lytic replication of Kaposi's sarcoma-associated herpesvirus (KSHV) efficiently blocks type I IFN signaling and that an important effector of this blockade is the viral protein RIF, the product of open reading frame 10. RIF blocks IFN signaling by formation of inhibitory complexes that contain IFNAR subunits, the Janus kinases Jak1 and Tyk2, and the STAT2 transcription factor. Activation of both Tyk2 and Jak1 is inhibited, and abnormal recruitment of STAT2 to IFNAR1 occurs despite the decrement in Tyk2 activity. As a result of these actions, phosphorylation of both STAT2 and STAT1 is impaired, with subsequent failure of ISGF3 accumulation in the nucleus. The presence in the viral genome of potent inhibitors of type I IFN signaling, along with several viral genes that block IFN induction, highlights the importance of the IFN pathway in the control of this human tumor virus infection.

scholarly journals Kaposi's Sarcoma-Associated Herpesvirus ori-Lyt-Dependent DNA Replication: DualRole of Replication and Transcription Activator

2006 ◽  
Vol 80 (24) ◽  
pp. 12171-12186 ◽  
Author(s):  
Yan Wang ◽  
Qiyi Tang ◽  
Gerd G. Maul ◽  
Yan Yuan
Keyword(s):  
Dna Replication ◽  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Transcription Activator ◽  
Binding Motifs ◽  
Viral Propagation ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus ◽  
Lytic Dna Replication

ABSTRACT Lytic replication of Kaposi's sarcoma-associated herpesvirus (KSHV) is essential for viral propagation and pathogenicity. In Kaposi's sarcoma lesions, constant lytic replication plays a role in sustaining the population of latently infected cells that otherwise are quickly lost by segregation of latent viral episomes as spindle cells divide. Lytic DNA replication initiates from an origin (ori-Lyt) and requires trans-acting elements. Two functional ori-Lyts have been identified in the KSHV genome. Some cis-acting and trans-acting elements for ori-Lyt-dependent DNA replication have been found. Among these, K8 binding sites, a cluster of C/EBP binding motifs, and a replication and transcription activator (RTA) responsive element (RRE) are crucial cis-acting elements. Binding of K8 and RTA proteins to these motifs in ori-Lyt DNA was demonstrated to be absolutely essential for DNA replication. In the present study, functional roles of RTA in ori-Lyt-dependent DNA replication have been investigated. Two distinct functions of RTA were revealed. First, RTA activates an ori-Lyt promoter and initiates transcription across GC-rich tandem repeats. This RTA-mediated transcription is indispensable for DNA replication. Second, RTA is a component of the replication compartment, where RTA interacts with prereplication complexes composed of at least six core machinery proteins and K8. The prereplication complexes are recruited to ori-Lyt DNA through RTA, which interacts with the RRE, as well as K8, which binds to a cluster of C/EBP binding motifs with the aid of C/EBP α. The revelation of these two functions of RTA, together with its role in initiation of a transcriptional cascade that leads to transcription of all viral lytic genes, shows that RTA is a critical initiator and regulator of KSHV lytic DNA replication and viral propagation.

Kaposi’s sarcoma-associated herpesvirus ubiquitin ligases downregulate cell surface expression of l-selectin

2021 ◽  
Vol 102 (11) ◽  
Author(s):  
Mizuho Kajikawa ◽  
Nanae Imaizumi ◽  
Shiho Machii ◽  
Tomoka Nakamura ◽  
Nana Harigane ◽  
...  
Keyword(s):  
Cell Surface ◽  
Nk Cells ◽  
Immune Evasion ◽  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Ubiquitin Ligases ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

Kaposi’s sarcoma-associated herpesvirus (KSHV) is an oncogenic etiological factor for Kaposi’s sarcoma and primary effusion lymphoma in immunocompromised patients. KSHV utilizes two immune evasion E3 ubiquitin ligases, namely K3 and K5, to downregulate the expression of antigen-presenting molecules and ligands of natural killer (NK) cells in the host cells through an ubiquitin-dependent endocytic mechanism. This allows the infected cells to evade surveillance and elimination by cytotoxic lymphocytes and NK cells. The number of host cell molecular substrates reported for these ubiquitin ligases is limited. The identification of novel substrates for these ligases will aid in elucidating the mechanism underlying immune evasion of KSHV. This study demonstrated that K5 downregulated the cell surface expression of l-selectin, a C-type lectin-like adhesion receptor expressed in the lymphocytes. Tryptophan residue located at the centre of the E2-binding site in the K5 RINGv domain was essential to downregulate l-selectin expression. Additionally, the lysine residues located at the cytoplasmic tail of l-selectin were required for the K5-mediated downregulation of l-selectin. K5 promoted the degradation of l-selectin through polyubiquitination. These results suggest that K5 downregulates l-selectin expression on the cell surface by promoting polyubiquitination and ubiquitin-dependent endocytosis, which indicated that l-selectin is a novel substrate for K5. Additionally, K3 downregulated l-selectin expression. The findings of this study will aid in the elucidation of a novel immune evasion mechanism in KSHV.

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