Project description:Historically, ribosomes have been viewed as unchanged homogeneous macromolecular machines with no intrinsic regulatory capacity for mRNA translation. However, an emerging concept is that heterogeneity of ribosomal composition exists, which can exert a regulatory function or specificity in translational control. This is supported by recent discoveries identifying compositionally distinct ‘specialised ribosomes’ that actively regulate mRNA translation. Viruses lack their own translational machinery and impose a high translational demand on the host cell during replication. Here we explore the possibility that Kaposi’s sarcoma-associated herpesvirus (KSHV) can manipulate host ribosome biogenesis during infection to produce specialised ribosomes which preferentially translate viral transcripts. Quantitative proteomic analysis has identified changes in the stoichiometry and composition of precursor ribosomal complexes during the switch from latent to lytic KSHV replication. Intriguingly, we demonstrate the enhanced association of ribosomal biogenesis factors BUD23 and NOC4L, and a previously uncharacterised KSHV lytic protein, ORF11, with small ribosomal subunit precursor complexes during lytic KSHV infection. Notably, BUD23 depletion resulted in significantly reduced viral gene expression and progression through the lytic cascade, culminating in a dramatic reduction of infectious virion production. Importantly, ribosome profiling demonstrated that BUD23 is essential for the reduced association of ribosomes with KSHV uORFs in late lytic genes, required for the efficient translation of the main open reading frame. Together our results provide new mechanistic insights into KSHV-mediated manipulation of cellular ribosome composition inducing a population of specialised ribosomes to facilitate efficient translation of viral mRNAs.
Project description:Historically, ribosomes have been viewed as unchanged homogeneous macromolecular machines with no intrinsic regulatory capacity for mRNA translation. However, an emerging concept is that heterogeneity of ribosomal composition exists, which can exert a regulatory function or specificity in translational control. This is supported by recent discoveries identifying compositionally distinct ‘specialised ribosomes’ that actively regulate mRNA translation. Viruses lack their own translational machinery and impose a high translational demand on the host cell during replication. Here we explore the possibility that Kaposi’s sarcoma-associated herpesvirus (KSHV) can manipulate host ribosome biogenesis during infection to produce specialised ribosomes which preferentially translate viral transcripts. Quantitative proteomic analysis has identified changes in the stoichiometry and composition of precursor ribosomal complexes during the switch from latent to lytic KSHV replication. Intriguingly, we demonstrate the enhanced association of ribosomal biogenesis factors BUD23 and NOC4L, and a previously uncharacterised KSHV lytic protein, ORF11, with small ribosomal subunit precursor complexes during lytic KSHV infection. Notably, BUD23 depletion resulted in significantly reduced viral gene expression and progression through the lytic cascade, culminating in a dramatic reduction of infectious virion production. Importantly, ribosome profiling demonstrated that BUD23 is essential for the reduced association of ribosomes with KSHV uORFs in late lytic genes, required for the efficient translation of the main open reading frame. Together our results provide new mechanistic insights into KSHV-mediated manipulation of cellular ribosome composition inducing a population of specialised ribosomes to facilitate efficient translation of viral mRNAs.
Project description:The epitranscriptomic modification m6A is a ubiquitous feature of the mammalian transcriptome. It modulates mRNA fate and dynamics to exert regulatory control over numerous cellular processes and disease pathways, including viral infection. Kaposi’s sarcoma-associated herpesvirus (KSHV) reactivation from the latent phase leads to redistribution of m6A topology upon both viral and cellular mRNAs within infected cells. Here we investigate the role of m6A in cellular transcripts upregulated during KSHV lytic replication. Results show that m6A is crucial for the stability of the GPRC5A mRNA, whose expression is induced by the KSHV latent-lytic switch master regulator, the replication and transcription activator (RTA) protein. Moreover, we demonstrate that GPRC5A is essential for efficient KSHV lytic replication by directly regulating NFκB signalling. Overall, this work highlights the central importance of m6A in modulating cellular gene expression to influence viral infection.
Project description:During lytic replication of Kaposi’s sarcoma-associated herpesvirus (KSHV), a nuclear viral long noncoding RNA known as PAN RNA becomes the most abundant polyadenylated transcript in the cell. Knockout or knockdown of KSHV PAN RNA results in loss of late lytic viral gene expression and, consequently, reduction of progeny virion release from the cell. We studied KSHV and RRV PAN RNA homologs using capture hybridization analysis of RNA targets (CHART) and observed their reproducible associations with host chromatin, but the loci differ between PAN RNA homologs.
Project description:Kaposi’s Sarcoma (KS) is a heterogenous, multifocal vascular malignancy caused by the human herpesvirus 8 (HHV8), also known as Kaposi’s Sarcoma-Associated Herpesvirus (KSHV). Here, we show that KS lesions express iNOS/NOS2 broadly throughout KS lesions, with enrichment in LANA positive spindle cells. The iNOS byproduct 3-nitrotyrosine is also enriched in LANA positive tumor cells and colocalizes with a fraction of LANA-nuclear bodies. We show that iNOS is highly expressed in the L1T3 tumor model of KS. iNOS expression correlated with KSHV lytic cycle gene expression, which was elevated in late-stage tumors (>4 weeks) but to a lesser degree in early stage (1 week) xenografts. Further, we show that L1T3 tumor growth is sensitive to an inhibitor of nitric oxide, L-NMMA. These finding suggest that iNOS is expressed in KSHV infected endothelial-transformed tumor cells in KS, that iNOS expression depends on tumor microenvironment stress conditions, and that iNOS enzymatic activity contributes to KS tumor growth.
Project description:Kaposi’s sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi’s sarcoma (KS) and multiple types of B cellmalignancies. Emerging evidence demonstrates that KSHV reprograms host-cell central carbon metabolic pathways, which contributesto viral persistence and tumorigenesis. However, the mechanisms underlying KSHV-mediated metabolic reprogramming remain poorlyunderstood. Carbamoyl-phosphate synthetase 2, aspartate transcarbamoylase, and dihydroorotase (CAD) is a key enzyme of the denovo pyrimidine synthesis, and was recently identified to deamidate the NF-κB subunit RelA to promote aerobic glycolysis and cellproliferation. Here we report that KSHV infection exploits CAD for nucleotide synthesis and glycolysis. Mechanistically, KSHV vCyclin binds to and hijacks cyclin-dependent kinase CDK6 to phosphorylate Ser-1900 on CAD, thereby activating CAD-mediatedpyrimidine synthesis and RelA-deamidation-mediated glycolytic reprogramming. Correspondingly, genetic depletion orpharmacological inhibition of CDK6 and CAD potently impeded KSHV lytic replication and thwarted tumorigenesis of primaryeffusion lymphoma (PEL) cells in vitro and in vivo. Altogether, our work defines a viral metabolic reprogramming mechanismunderpinning KSHV oncogenesis, which may spur the development of new strategies to treat KSHV-associated malignancies and otherdiseases.
Project description:Methylation at the N6 position of adenosine (m6A) is a highly prevalent reversible modification within eukaryotic mRNAs that has been linked to many stages of RNA processing and fate. Recent studies suggest that m6A deposition and proteins involved in the m6A pathway play a diverse set of roles in either restricting or modulating the lifecycles of select viruses. Here, we report that m6A levels are significantly increased in cells infected with the oncogenic human DNA virus Kaposi’s sarcoma-associated herpesvirus (KSHV). Transcriptome-wide m6A-sequencing of the KSHV-positive renal carcinoma cell line iSLK.219 during lytic reactivation revealed the presence of m6A across multiple kinetic classes of viral transcripts, and a concomitant decrease in m6A levels across much of the host transcriptome.
Project description:Kaposi’s Sarcoma associated herpesvirus (KSHV) is an oncogenic human virus and leading cause of mortality in HIV infection. Reactivation of KSHV from latent to lytic stage infection initiates a cascade of viral gene expression, and here we show how these changes remodel the host cell proteome to enable viral replication. By undertaking a systematic and unbiased analysis of changes to the endothelial cell proteome following lytic KSHV reactivation, we quantify >7000 cellular and 71 viral proteins. Lytic KSHV infection resulted in >2-fold downregulation of 291 cellular proteins, including PKR, the key cellular sensor of double-stranded RNA. A complementary KSHV genome-wide CRISPR genetic screen identified K5 as the viral gene responsible for the downregulation of two novel KSHV targets, Nectin-2 and CD155, both ligands of the NK cell DNAM-1 receptor. Despite the high episome copy number, we show that CRISPR Cas9 provides a remarkably efficient way to target KSHV genomes.
Project description:Kaposi’s Sarcoma associated herpesvirus (KSHV) is an oncogenic human virus and leading cause of mortality in HIV infection. Reactivation of KSHV from latent to lytic stage infection initiates a cascade of viral gene expression, and here we show how these changes remodel the host cell proteome to enable viral replication. By undertaking a systematic and unbiased analysis of changes to the endothelial cell proteome following lytic KSHV reactivation, we quantify >7000 cellular and 71 viral proteins. Lytic KSHV infection resulted in >2-fold downregulation of 291 cellular proteins, including PKR, the key cellular sensor of double-stranded RNA. A complementary KSHV genome-wide CRISPR genetic screen identified K5 as the viral gene responsible for the downregulation of two novel KSHV targets, Nectin-2 and CD155, both ligands of the NK cell DNAM-1 receptor. Despite the high episome copy number, we show that CRISPR Cas9 provides a remarkably efficient way to target KSHV genomes.