scholarly journals The FAT10 Posttranslational Modification Is Involved in Lytic Replication of Kaposi’s Sarcoma-Associated Herpesvirus

2021 ◽  
Vol 95 (10) ◽  
Author(s):  
Atsuko Sugimoto ◽  
Yuichi Abe ◽  
Tadashi Watanabe ◽  
Kohei Hosokawa ◽  
Jun Adachi ◽  
...  
Keyword(s):  
Protein Expression ◽  
Posttranslational Modifications ◽  
Posttranslational Modification ◽  
Kaposi's Sarcoma ◽  
Virus Production ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Lytic Cycle ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACT During Kaposi’s sarcoma-associated herpesvirus (KSHV) lytic replication, host cell functions, including protein expression and posttranslational modification pathways, are dysregulated by KSHV to promote virus production. Here, we attempted to identify key proteins for KSHV lytic replication by profiling protein expression in the latent and lytic phases using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Proteomic analysis, immunoblotting, and quantitative PCR demonstrated that antigen F (HLA-F) adjacent transcript 10 (FAT10) and UBE1L2 (also known as ubiquitin-like modifier-activating enzyme 6 [UBA6]) were upregulated during lytic replication. FAT10 is a ubiquitin-like protein (UBL). UBE1L2 is the FAT10-activating enzyme (E1), which is essential for FAT10 modification (FAT10ylation). FAT10ylated proteins were immediately expressed after lytic induction and increased over time during lytic replication. Knockout of UBE1L2 suppressed KSHV production but not KSHV DNA synthesis. In order to isolate FAT10ylated proteins during KSHV lytic replication, we conducted immunoprecipitation using anti-FAT10 antibody and nickel-nitrilotriacetic acid (Ni-NTA) chromatography of exogenously expressed His-tagged FAT10 from cells undergoing latent or lytic replication. LC-MS/MS was performed to identify FAT10ylated proteins. We identified KSHV ORF59 and ORF61 as FAT10ylation substrates. Our study revealed that the UBE1L2-FAT10 system is upregulated during KSHV lytic replication, and it contributes to viral propagation. IMPORTANCE Ubiquitin and UBL posttranslational modifications, including FAT10, are utilized and dysregulated by viruses for achievement of effective infection and virion production. The UBE1L2-FAT10 system catalyzes FAT10ylation, where one or more FAT10 molecules are covalently linked to a substrate. FAT10ylation is catalyzed by the sequential actions of E1 (activation enzyme), E2 (conjugation enzyme), and E3 (ligase) enzymes. The E1 enzyme for FAT10ylation is UBE1L2, which activates FAT10 and transfers it to E2/USE1. FAT10ylation regulates the cell cycle, interferon (IFN) signaling, and protein degradation; however, its primary biological function remains unknown. Here, we revealed that KSHV lytic replication induces UBE1L2 expression and production of FAT10ylated proteins, including KSHV lytic proteins. Moreover, UBE1L2 knockout suppressed virus production during the lytic cycle. This is the first report demonstrating the contribution of the UBE1L2-FAT10 system to KSHV lytic replication. Our findings provide insight into the physiological function(s) of novel posttranslational modifications in KSHV lytic replication.

scholarly journals Activation of Kaposi's Sarcoma-Associated Herpesvirus (Human Herpesvirus 8) Lytic Replication by Human Cytomegalovirus

2001 ◽  
Vol 75 (3) ◽  
pp. 1378-1386 ◽  
Author(s):  
Jeffrey Vieira ◽  
Patricia O'Hearn ◽  
Louise Kimball ◽  
Bala Chandran ◽  
Lawrence Corey
Keyword(s):  
Human Cytomegalovirus ◽  
Kaposi's Sarcoma ◽  
Human Fibroblasts ◽  
Human Herpesvirus ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Lytic Cycle ◽  
Nuclear Antigen ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACT The majority of Kaposi's sarcoma-associated herpesvirus (KSHV)-infected cells identified in vivo contain latent KSHV, with lytic replication in only a few percent of cells, as is the case for the cells of Kaposi's sarcoma (KS) lesions. Factors that influence KSHV latent or lytic replication are not well defined. Because persons with KS are often immunosuppressed and susceptible to many infectious agents, including human cytomegalovirus (HCMV), we have investigated the potential for HCMV to influence the replication of KSHV. Important to this work was the construction of a recombinant KSHV, rKSHV.152, expressing the green fluorescent protein (GFP) andneo (conferring resistance to G418). The expression of GFP was a marker of KSHV infection in cells of both epithelial and endothelial origin. The rKSHV.152 virus was used to establish cells, including human fibroblasts (HF), containing only latent KSHV, as demonstrated by latency-associated nuclear antigen expression and Gardella gel analysis. HCMV infection of KSHV latently infected HF activated KSHV lytic replication with the production of infectious KSHV. Dual-color immunofluorescence detected both the KSHV lytic open reading frame 59 protein and the HCMV glycoprotein B in coinfected cells, and UV-inactivated HCMV did not activate the production of infectious KSHV-GFP. In addition, HCMV coinfection increased the production of KSHV from endothelial cells and activated lytic cycle gene expression in keratinocytes. These data demonstrate that HCMV can activate KSHV lytic replication and suggest that HCMV could influence KSHV pathogenesis.

scholarly journals ORF33 and ORF38 of Kaposi's Sarcoma-Associated Herpesvirus Interact and Are Required for Optimal Production of Infectious Progeny Viruses

2015 ◽  
Vol 90 (4) ◽  
pp. 1741-1756 ◽  
Author(s):  
Jian-jun Wu ◽  
Denis Avey ◽  
Wenwei Li ◽  
Joseph Gillen ◽  
Bishi Fu ◽  
...  
Keyword(s):  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Lytic Cycle ◽  
Viral Gene ◽  
Virus Propagation ◽  
Progeny Virion ◽  
Cytoplasmic Vesicles ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACTWe recently showed that the interaction between Kaposi's sarcoma-associated herpesvirus (KSHV) tegument proteins ORF33 and ORF45 is crucial for progeny virion production, but the exact functions of KSHV ORF33 during lytic replication were unknown (J. Gillen, W. Li, Q. Liang, D. Avey, J. Wu, F. Wu, J. Myoung, and F. Zhu, J Virol89:4918–4931, 2015,http://dx.doi.org/10.1128/JVI.02925-14). Therefore, here we investigated the relationship between ORF33 and ORF38, whose counterparts in both alpha- and betaherpesviruses interact with each other. Using specific monoclonal antibodies, we found that both proteins are expressed during the late lytic cycle with similar kinetics and that both are present in mature virions as components of the tegument. Furthermore, we confirmed that ORF33 interacts with ORF38. Interestingly, we observed that ORF33 tightly associates with the capsid, whereas ORF38 associates with the envelope. We generated ORF33-null, ORF38-null, and double-null mutants and found that these mutants apparently have identical phenotypes: the mutations caused no apparent effect on viral gene expression but reduced the yield of progeny virion by about 10-fold. The progeny virions also lack certain virion component proteins, including ORF45. During viral lytic replication, the virions associate with cytoplasmic vesicles. We also observed that ORF38 associates with the membranes of vesicles and colocalizes with the Golgi membrane or early endosome membrane. Further analyses of ORF33/ORF38 mutants revealed the reduced production of virion-containing vesicles, suggesting that ORF33 and ORF38 are involved in the transport of newly assembled viral particles into cytoplasmic vesicles, a process important for viral maturation and egress.IMPORTANCEHerpesvirus assembly is an essential step in virus propagation that leads to the generation of progeny virions. It is a complicated process that depends on the delicate regulation of interactions among virion proteins. We previously revealed an essential role of ORF45-ORF33 binding for virus assembly. Here, we report that ORF33 and its binding partner, ORF38, are required for infectious virus production due to their important role in the tegumentation process. Moreover, we found that both ORF33 and ORF38 are involved in the transportation of virions through vesicles during maturation and egress. Our results provide new insights into the important roles of ORF33 and ORF38 during viral assembly, a process critical for virus propagation that is intimately linked to KSHV pathobiology.

scholarly journals Binding of Cellular Export Factor REF/Aly by Kaposi's Sarcoma-Associated Herpesvirus (KSHV) ORF57 Protein Is Not Required for Efficient KSHV Lytic Replication

2012 ◽  
Vol 86 (18) ◽  
pp. 9866-9874 ◽  
Author(s):  
Da-Jiang Li ◽  
Dinesh Verma ◽  
Sankar Swaminathan
Keyword(s):  
Gene Expression ◽  
Nuclear Export ◽  
Kaposi's Sarcoma ◽  
Rna Binding ◽  
Virus Production ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Viral Mrnas ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

Kaposi's sarcoma-associated herpesvirus (KSHV) ORF57 protein is expressed early during lytic KSHV replication, enhances expression of many KSHV genes, and is essential for virus production. ORF57 is a member of a family of proteins conserved among all human and many animal herpesviruses that are multifunctional regulators of gene expression and act posttranscriptionally to increase accumulation of their target mRNAs. The mechanism of ORF57 action is complex and may involve effects on mRNA transcription, stability, and export. ORF57 directly binds to REF/Aly, a cellular RNA-binding protein component of the TREX complex that mediates RNA transcription and export. We analyzed the effects of an ORF57 mutation known to abrogate REF/Aly binding and demonstrate that the REF-binding mutant is impaired in activation of viral mRNAs and noncoding RNAs confined to the nucleus. Although the inability to bind REF leads to decreased ORF57 activity in enhancing gene expression, there is no demonstrable effect on nuclear export of viral mRNA or the ability of ORF57 to support KSHV replication and virus production. These data indicate that REF/Aly-ORF57 interaction is not essential for KSHV lytic replication but may contribute to target RNA stability independent of effects on RNA export, suggesting a novel role for REF/Aly in viral RNA metabolism.

scholarly journals The Human Cytomegalovirus UL112-113 Locus Can Activate the Full Kaposi's Sarcoma-Associated Herpesvirus Lytic Replication Cycle

2009 ◽  
Vol 83 (9) ◽  
pp. 4695-4699 ◽  
Author(s):  
Richard Wells ◽  
Laurence Stensland ◽  
Jeffrey Vieira
Keyword(s):  
Human Cytomegalovirus ◽  
Kaposi's Sarcoma ◽  
Hcmv Infection ◽  
Infectious Virus ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Lytic Cycle ◽  
A Cell ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACT Human cytomegalovirus (HCMV) infection of a cell containing latent Kaposi's sarcoma-associated herpesvirus (KSHV) results in the activation of KSHV lytic replication and the production of infectious virus. In this study, we examined the HCMV genes identified as having a role in the activation of HCMV early genes for their ability to activate KSHV lytic replication. It was found that the UL112-113 locus was able to activate the complete KSHV lytic cycle, while the UL122-123 locus, encoding the IE1 and IE2 proteins, known to be strong transactivators, did not.

scholarly journals Kaposi’s Sarcoma-Associated Herpesvirus ORF7 Is Essential for Virus Production

2021 ◽  
Vol 9 (6) ◽  
pp. 1169
Author(s):  
Yuki Iwaisako ◽  
Tadashi Watanabe ◽  
Mizuki Hanajiri ◽  
Yuichi Sekine ◽  
Masahiro Fujimuro
Keyword(s):  
Dna Cleavage ◽  
Kaposi's Sarcoma ◽  
Stop Codon ◽  
Primary Effusion Lymphoma ◽  
Virus Production ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Capsid Formation ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

Kaposi’s sarcoma-associated herpesvirus (KSHV) causes Kaposi’s sarcoma, primary effusion lymphoma (PEL), and multicentric Castleman disease. Although capsid formation and maturation in the alpha-herpesvirus herpes simplex virus 1 are well understood, these processes in KSHV remain unknown. The KSHV ORF7, encoding the viral terminase (DNA cleavage and packaging protein), is thought to contribute to capsid formation; however, functional information is lacking. Here, we investigated the role of ORF7 during KSHV lytic replication by generating two types of ORF7 knock-out (KO) mutants (frameshift-induced and stop codon-induced ORF7 deficiency), KSHV BAC16, and its revertants. The results revealed that both ORF7-KO KSHVs showed significantly reduced viral production but there was no effect on lytic gene expression and viral genome replication. Complementation assays showed virus production from cells harboring ORF7-KO KSHV could be recovered by ORF7 overexpression. Additionally, exogenously expressed ORF7 partially induced nuclear relocalization of the other terminase components, ORF29 and ORF67.5. ORF7 interacted with both ORF29 and ORF67.5, whereas ORF29 and ORF67.5 failed to interact with each other, suggesting that ORF7 functions as a hub molecule in the KSHV terminase complex for interactions between ORF29 and ORF67.5. These findings indicate that ORF7 plays a key role in viral replication, as a component of terminase.

scholarly journals Nuclear Innate Immune DNA Sensor IFI16 Is Degraded during Lytic Reactivation of Kaposi's Sarcoma-Associated Herpesvirus (KSHV): Role of IFI16 in Maintenance of KSHV Latency

2016 ◽  
Vol 90 (19) ◽  
pp. 8822-8841 ◽  
Author(s):  
Arunava Roy ◽  
Dipanjan Dutta ◽  
Jawed Iqbal ◽  
Gina Pisano ◽  
Olsi Gjyshi ◽  
...  
Keyword(s):  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Innate Immune ◽  
Lytic Cycle ◽  
Lytic Gene ◽  
Lytic Reactivation ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACTIFI16 (interferon gamma-inducible protein 16) recognizes nuclear episomal herpesvirus (Kaposi's sarcoma-associated herpesvirus [KSHV], Epstein-Barr virus [EBV], and herpes simplex virus 1 [HSV-1]) genomes and induces the inflammasome and interferon beta responses. It also acts as a lytic replication restriction factor and inhibits viral DNA replication (human cytomegalovirus [HCMV] and human papillomavirus [HPV]) and transcription (HSV-1, HCMV, and HPV) through epigenetic modifications of the viral genomes. To date, the role of IFI16 in the biology of latent viruses is not known. Here, we demonstrate that knockdown of IFI16 in the latently KSHV-infected B-lymphoma BCBL-1 and BC-3 cell lines results in lytic reactivation and increases in levels of KSHV lytic transcripts, proteins, and viral genome replication. Similar results were also observed during KSHV lytic cycle induction in TREX-BCBL-1 cells with the doxycycline-inducible lytic cycle switch replication and transcription activator (RTA) gene. Overexpression of IFI16 reduced lytic gene induction by the chemical agent 12-O-tetradecoylphorbol-13-acetate (TPA). IFI16 protein levels were significantly reduced or absent in TPA- or doxycycline-induced cells expressing lytic KSHV proteins. IFI16 is polyubiquitinated and degraded via the proteasomal pathway. The degradation of IFI16 was absent in phosphonoacetic acid-treated cells, which blocks KSHV DNA replication and, consequently, late lytic gene expression. Chromatin immunoprecipitation assays of BCBL-1 and BC-3 cells demonstrated that IFI16 binds to KSHV gene promoters. Uninfected epithelial SLK and osteosarcoma U2OS cells transfected with KSHV luciferase promoter constructs confirmed that IFI16 functions as a transcriptional repressor. These results reveal that KSHV utilizes the innate immune nuclear DNA sensor IFI16 to maintain its latency and repression of lytic transcripts, and a late lytic KSHV gene product(s) targets IFI16 for degradation during lytic reactivation.IMPORTANCELike all herpesviruses, latency is an integral part of the life cycle of Kaposi's sarcoma-associated herpesvirus (KSHV), an etiological agent for many human cancers. Herpesviruses utilize viral and host factors to successfully evade the host immune system to maintain latency. Reactivation is a complex event where the latent episomal viral genome springs back to active transcription of lytic cycle genes. Our studies reveal that KSHV has evolved to utilize the innate immune sensor IFI16 to keep lytic cycle transcription in dormancy. We demonstrate that IFI16 binds to the lytic gene promoter, acts as a transcriptional repressor, and thereby helps to maintain latency. We also discovered that during the late stage of lytic replication, KSHV selectively degrades IFI16, thus relieving transcriptional repression. This is the first report to demonstrate the role of IFI16 in latency maintenance of a herpesvirus, and further understanding will lead to the development of strategies to eliminate latent infection.

scholarly journals Differential Regulation of the Overlapping Kaposi's Sarcoma-Associated Herpesvirus vGCR (orf74) and LANA (orf73) Promoters

2001 ◽  
Vol 75 (4) ◽  
pp. 1798-1807 ◽  
Author(s):  
Joseph Jeong ◽  
James Papin ◽  
Dirk Dittmer
Keyword(s):  
Kaposi's Sarcoma ◽  
Regulatory Region ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Lytic Cycle ◽  
Nuclear Antigen ◽  
Barr Virus ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
High Level ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACT Similar to that of other herpesviruses, Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8) lytic replication destroys the host cell, while the virus can persist in a latent state in synchrony with the host. During latency only a few genes are transcribed, and the question becomes one of what determines latent versus lytic gene expression. Here we undertake a detailed analysis of the latency-associated nuclear antigen (LANA [orf73]) promoter (LANAp). We characterized a minimal region that is necessary and sufficient to maintain high-level transcription in all tissues tested, including primary endothelial cells and B cells, which are the suspected natural host for KSHV. We show that in transient-transfection assays LANAp mimics the expression pattern observed for the authentic promoter in the context of the KSHV episome. Unlike other KSHV promoters tested thus far, LANAp is not affected by tetradecanoyl phorbol acetate or viral lytic cycle functions. It is, however, subject to control by LANA itself and cellular regulatory factors, such as p53. This is in contrast to the K14/vGCR (orf74) promoter, which overlaps LANAp and directs transcription on the opposite strand. We isolated a minimal cis-regulatory region sufficient for K14/vGCR promoter activity and show that it, too, mimics the regulation observed for the authentic viral promoter. In particular, we demonstrate that its activity is absolutely dependent on the immediate-early transactivator orf50, the KSHV homolog of the Epstein-Barr virus Rta transactivator.

scholarly journals Overexpression of the Kaposi's Sarcoma-Associated Herpesvirus Transactivator K-Rta Can Complement a K-bZIP Deletion BACmid and Yields an Enhanced Growth Phenotype

2007 ◽  
Vol 81 (24) ◽  
pp. 13519-13532 ◽  
Author(s):  
Taeko Kato-Noah ◽  
Yiyang Xu ◽  
Cyprian C. Rossetto ◽  
Kelly Colletti ◽  
Iva Papousková ◽  
...  
Keyword(s):  
Subcellular Localization ◽  
Kaposi's Sarcoma ◽  
Gene Expression Pattern ◽  
Human Herpesvirus ◽  
Virus Production ◽  
Kaposi’S Sarcoma ◽  
Lytic Cycle ◽  
Growth Phenotype ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACT Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8 (HHV8) ORF50 encodes a transactivator, K-Rta, which functions as the switch from latent to lytic virus replication. K-bZIP interacts with K-Rta and can repress its transactivation activity for some viral promoters. Both K-Rta and K-bZIP are required for origin-dependent DNA replication. To determine the role of K-bZIP in the context of the viral genome, we generated a recombinant HHV8 bacterial artificial chromosome (BAC) with a deletion in the K-bZIP open reading frame. This BACmid, BAC36ΔK8, displayed an enhanced growth phenotype with respect to virus production and accumulation of virus-encoded mRNAs measured by real-time PCR when K-Rta was used to induce the virus lytic cycle. Conversely, induction of the virus lytic cycle using tetradecanoyl phorbol acetate/n-butyrate resulted in no virus production and an aberrant gene expression pattern from BAC36ΔK8-containing cells compared to wild-type (wt) BAC. This null virus phenotype was efficiently complemented by the expression of K-bZIP in trans, restoring virus production to wt BAC levels. Immunofluorescence staining revealed that subcellular localization of K-Rta was unchanged; however, a disruption of LANA subcellular localization was observed in cells harboring BAC36ΔK8, suggesting that K-bZIP influences LANA localization. Coimmunoprecipitation experiments confirmed that K-bZIP interacts with LANA in BCBL-1 cells and in cotransfection assays. Lastly, the chromatin immunoprecipitation assay revealed that, in an environment where K-Rta is overexpressed and in the absence of K-bZIP, K-Rta binds to CAAT enhancer binding protein α sites within oriLyt, suggesting that it is K-Rta that supplies an essential replication function and that K-bZIP may serve to augment or facilitate the interaction of K-Rta with oriLyt.

scholarly journals Kaposi’s Sarcoma-Associated Herpesvirus Lytic Replication Interferes with mTORC1 Regulation of Autophagy and Viral Protein Synthesis

2019 ◽  
Vol 93 (21) ◽  
Author(s):  
Eric S. Pringle ◽  
Carolyn-Ann Robinson ◽  
Craig McCormick
Keyword(s):  
Protein Synthesis ◽  
Viral Protein ◽  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Lytic Cycle ◽  
Viral Protein Synthesis ◽  
Global Protein Synthesis ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACT Mechanistic target of rapamycin complex 1 (mTORC1) is a master regulator of cellular metabolism. In nutrient-rich environments, mTORC1 kinase activity stimulates protein synthesis to meet cellular anabolic demands. Under nutrient-poor conditions or under stress, mTORC1 is rapidly inhibited, global protein synthesis is arrested, and a cellular catabolic process known as autophagy is activated. Kaposi’s sarcoma-associated herpesvirus (KSHV) encodes multiple proteins that stimulate mTORC1 activity or subvert autophagy, but precise roles for mTORC1 in different stages of KSHV infection remain incompletely understood. Here, we report that during latent and lytic stages of KSHV infection, chemical inhibition of mTORC1 caused eukaryotic initiation factor 4F (eIF4F) disassembly and diminished global protein synthesis, which indicated that mTORC1-mediated control of translation initiation was largely intact. We observed that mTORC1 was required for synthesis of the replication and transcription activator (RTA) lytic switch protein and reactivation from latency, but once early lytic gene expression had begun, mTORC1 was not required for genome replication, late gene expression, or the release of infectious progeny. Moreover, mTORC1 control of autophagy was dysregulated during lytic replication, whereby chemical inhibition of mTORC1 prevented ULK1 phosphorylation but did not affect autophagosome formation or rates of autophagic flux. Together, these findings suggest that mTORC1 is dispensable for viral protein synthesis and viral control of autophagy during lytic infection and that KSHV undermines mTORC1-dependent cellular processes during the lytic cycle to ensure efficient viral replication. IMPORTANCE All viruses require host cell machinery to synthesize viral proteins. A host cell protein complex known as mechanistic target of rapamycin complex 1 (mTORC1) is a master regulator of protein synthesis. Under nutrient-rich conditions, mTORC1 is active and promotes protein synthesis to meet cellular anabolic demands. Under nutrient-poor conditions or under stress, mTORC1 is rapidly inhibited, global protein synthesis is arrested, and a cellular catabolic process known as autophagy is activated. Kaposi’s sarcoma-associated herpesvirus (KSHV) stimulates mTORC1 activity and utilizes host machinery to synthesize viral proteins. However, we discovered that mTORC1 activity was largely dispensable for viral protein synthesis, genome replication, and the release of infectious progeny. Likewise, during lytic replication, mTORC1 was no longer able to control autophagy. These findings suggest that KSHV undermines mTORC1-dependent cellular processes during the lytic cycle to ensure efficient viral replication.

scholarly journals Immunoreceptor Tyrosine-Based Activation Motif-Dependent Signaling by Kaposi's Sarcoma-Associated Herpesvirus K1 Protein: Effects on Lytic Viral Replication

2001 ◽  
Vol 75 (13) ◽  
pp. 5891-5898 ◽  
Author(s):  
Michael Lagunoff ◽  
David M. Lukac ◽  
Don Ganem
Keyword(s):  
Signal Transduction ◽  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
B Cell Lymphoma ◽  
Lytic Replication ◽  
Lytic Cycle ◽  
Luciferase Reporter ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus ◽  
Activation Motif

ABSTRACT The Kaposi's sarcoma-associated herpesvirus (KSHV) K1 gene encodes a polypeptide bearing an immunoreceptor tyrosine-based activation motif (ITAM) that is constitutively active for ITAM-based signal transduction. Although ectopic overexpression of K1 in cultured fibroblasts can lead to growth transformation, in vivo this gene is primarily expressed in lymphoid cells undergoing lytic infection. Here we have examined function of K1 in the setting of lytic replication, through the study of K1 mutants lacking functional ITAMs. Expression of such mutants in BJAB cells cotransfected with wild-type K1 results in dramatic inhibition of K1 signal transduction, as judged by impaired activation of Syk kinase and phospholipase C-γ2 as well as by diminished expression of a luciferase reporter gene dependent upon K1-induced calcium and Ras signaling. Thus, the mutants behave as dominantly acting inhibitors of K1 function. To assess the role of K1 in lytic replication, we introduced these K1 mutants into BCBL-1 cells, a B-cell lymphoma line latently infected with KSHV, and induced lytic replication by ectopic expression of the KSHV ORF50 transactivator. Expression of lytic cycle genes was diminished up to 80% in the presence of a K1 dominant negative mutant. These inhibitory effects could be overridden by tetradecanoyl phorbol acetate treatment, indicating that inhibition was not due to irreversible cell injury and suggesting that other signaling events could bypass the block. We conclude that ITAM-dependent signaling by K1 is not absolutely required for lytic reactivation but functions to modestly augment lytic replication in B cells, the natural reservoir of KSHV.

Sign in / Sign up

Export Citation Format

Share Document