Human cytomegalovirus protein pUL36: a dual cell death pathway inhibitor
ABSTRACT: Human cytomegalovirus (HCMV) is an important human pathogen and a paradigm of intrinsic, innate and adaptive viral immune evasion. Here, we employ multiplexed tandem mass tag-based proteomics to characterise host proteins targeted for degradation late during HCMV infection. This approach revealed that mixed lineage kinase domain-like protein (MLKL), a key terminal mediator of cellular necroptosis, was rapidly and persistently degraded by the minimally passaged HCMV strain Merlin but not the extensively passaged strain AD169. The strain Merlin viral inhibitor of apoptosis pUL36 was necessary and sufficient both to degrade MLKL and to inhibit necroptosis. Furthermore, mutation of pUL36 Cys131 abrogated MLKL degradation and restored necroptosis. As the same residue is also required for pUL36-mediated inhibition of apoptosis by preventing proteolytic activation of pro-caspase 8, we define pUL36 as a multifunctional inhibitor of both apoptotic and necroptotic cell death.
Project description:Human cytomegalovirus (HCMV) is an important pathogen and a paradigm of viral immune evasion. Here, we describe a multiplexed approach to discover proteins with novel innate immune functions on the basis of their active proteasomal or lysosomal degradation during the early phase of HCMV infection. Using three orthogonal proteomic/transcriptomic screens to quantify protein degradation, we identified 35 proteins with high confidence that were enriched in known antiviral restriction factors. A final screen facilitated global analysis of the mechanism of viral immune-modulation by predicting which viral genes target >250 human proteins. Helicase-like Transcription Factor (HLTF), a DNA helicase important in error-free post-replication DNA repair, was rapidly degraded during infection and potently inhibited early viral gene expression. HCMV UL145, a protein of previously unknown function, recruits the Cullin 4 E3 ligase complex to degrade HLTF. Our approach and data will enable further identifications of innate pathways targeted by HCMV and other viruses.
Project description:Human cytomegalovirus is an important pathogen in immunocompromised individuals and neonates, and a paradigm for viral immune evasion. We previously developed a quantitative proteomic approach that identified 133 proteins degraded during the early phase of HCMV infection, including known and novel antiviral factors. The majority were rescued from degradation by MG132, which is known to inhibit lysosomal cathepsins in addition to the proteasome. Global definition of the precise mechanisms of host protein degradation is important both to improve our understanding of viral biology, and to inform novel antiviral therapeutic strategies. We therefore developed and optimised a multiplexed comparative proteomic analysis using the selective proteasome inhibitor bortezomib in addition to MG132, to provide a global mechanistic view of protein degradation. Of proteins rescued from degradation by MG132, 62-85% were also rescued by bortezomib, suggesting both that the predominant mechanism of protein degradation employed by HCMV is via the proteasome, and that alternative pathways for degradation are nevertheless important. Our approach and data will enable improved mechanistic understanding of HCMV and other viruses, and provide a shortlist of candidate restriction factors for further analysis.
Project description:BK polyomavirus (BKPyV) is a small DNA virus that establishes a life-long persistent infection in the urinary tract of most people. BKPyV is known to cause severe morbidity in renal transplant recipients and can lead to graft rejection. The simple 5.2 kilobase pair dsDNA genome expresses just seven known proteins, thus it relies heavily on host machinery to replicate. How the host proteome changes over the course of infection is key to understanding this host:virus interplay. Here for the first time quantitative temporal viromics has been used to quantify global changes in >9,000 host proteins in two types of primary human epithelial cell throughout 72 hours of BKPyV infection. These data demonstrate the importance both of cell cycle progression and pseudo-G2 arrest in effective BKPyV replication, along with a surprising lack of innate immune response throughout the whole virus replication cycle. BKPyV thus evades pathogen recognition to prevent activation of innate immune responses in a sophisticated manner.
Project description:Human cytomegalovirus (HCMV) is an important pathogen that extensively modulates host cells, downregulating >900 human proteins over the course of viral replication and degrading ≥133 proteins shortly after infection. The mechanism of degradation of most host proteins remains unresolved, and the functions of many viral proteins are incompletely characterised. We performed a systematic interactome analysis of 169 canonical HCMV proteins, and a subset of non-canonical HCMV proteins, in infected cells. This identified an extensive network of >3,400 virus-host and >150 virus-virus protein interactions, providing insights into novel functions for multiple viral genes. Domain analysis predicted binding of the viral UL25 protein to the SH3 domains of NCK Adaptor Protein 1. Viral interacting proteins were identified for 31/133 degraded host targets. Finally, the uncharacterised, non-canonical ORFL147C protein was found to interact with elements of the mRNA splicing machinery, and a mutational study suggested its importance in viral replication. The interactome data will be important for future studies of herpesvirus infection.
Project description:Human cytomegalovirus (HCMV) is an important human pathogen and a paradigm of intrinsic, innate, and adaptive viral immune evasion. Here, we employed multiplexed tandem mass tag-based proteomics to characterize host proteins targeted for degradation late during HCMV infection. This approach revealed that mixed lineage kinase domain-like protein (MLKL), a key terminal mediator of cellular necroptosis, was rapidly and persistently degraded by the minimally passaged HCMV strain Merlin but not the extensively passaged strain AD169. The strain Merlin viral inhibitor of apoptosis pUL36 was necessary and sufficient both to degrade MLKL and to inhibit necroptosis. Furthermore, mutation of pUL36 Cys131 abrogated MLKL degradation and restored necroptosis. As the same residue is also required for pUL36-mediated inhibition of apoptosis by preventing proteolytic activation of procaspase-8, we define pUL36 as a multifunctional inhibitor of both apoptotic and necroptotic cell death.
Project description:Herpesviruses are ubiquitous in the human population and they extensively remodel the cellular environment during infection. Multiplexed quantitative proteomic analysis over the time-course of herpes simplex virus (HSV)-1 infection was used to characterize changes in the host-cell proteome and the kinetics of viral protein production. Several host-cell proteins are targeted for rapid degradation by HSV-1, including the cellular trafficking factor GOPC. We show that the poorly-characterized HSV-1 pUL56 directly binds GOPC, stimulating its ubiquitination and proteasomal degradation. Plasma membrane profiling revealed that pUL56 mediates specific changes to the cell surface proteome of infected cells, including loss of IL18 receptor and Toll-like receptor 2, and that cell surface expression of Toll-like receptor 2 is GOPC-dependent. Our study provides significant resources for future investigation of HSV-host interactions and highlights an unanticipated and efficient mechanism whereby a single virus protein targets a cellular trafficking factor to modify the surface of infected cells.
Project description:Vaccinia virus (VACV) has numerous immune evasion strategies, including multiple mechanisms of inhibition of IRF-3, NF-κB and type I interferon (IFN) signaling. Here, we used highly multiplexed proteomics to quantify >8,000 cellular proteins and ~80% of viral proteins over seven time points spanning the whole course of VACV infection. This identified multiple novel viral targets, including putative natural killer cell ligands and IFN-stimulated genes. The class II histone deacetylase HDAC5 was selectively degraded early during VACV infection. Use of cell lines in which HDAC5 was overexpressed or knocked out showed that HDAC5 restricted replication of both VACV and herpes simplex virus type 1 (HSV-1). By generating a protein-based temporal classification of VACV gene expression, we identified the early protein C6, a multifunctional IFN antagonist, as the factor that targets HDAC5 for proteasomal degradation. Our approach thus identifies both a novel restriction factor and a viral mechanism of innate immune evasion.
Project description:Monocytes are a critical component of the cellular innate immune system, and can be subdivided into classical, intermediate and non-classical subsets on the basis of surface CD14 and CD16 expression. Classical monocytes play the canonical role of phagocytosis, and account for the majority of circulating cells. Intermediate and non-classical cells are known to exhibit varying levels of phagocytosis and cytokine secretion, and are differentially expanded in certain pathological states. Characterisation of cell surface proteins expressed by each subset is informative not only to improve understanding of phenotype, but also to provide biological insight into function. Here we use highly multiplexed Tandem-Mass-Tag (TMT)-based mass spectrometry with selective cell surface biotinylation to characterise the classical monocyte surface proteome, then interrogate the phenotypic differences between each monocyte subset to identify novel protein markers.
Project description:The human cytomegalovirus (HCMV) US12 family consists of ten sequentially arranged genes (US12-21) with poorly characterized function. We now identify novel NK cell evasion functions for four members: US12, US14, US18 and US20. Using a systematic multiplexed proteomics approach to quantify ~1,300 cell surface and ~7,200 whole cell proteins, we demonstrate that the US12 family selectively targets plasma membrane proteins and plays key roles in regulating NK ligands, adhesion molecules and cytokine receptors. US18 and US20 work in concert to suppress cell surface expression of the critical NKp30 ligand B7-H6 thus inhibiting NK cell activation. The US12 family is therefore identified as a major new hub of immune regulation.
Project description:The human cytomegalovirus (HCMV) genome was sequenced 20 years ago. However, like other complex viruses, our understanding of its protein coding potential is far from complete. Here, we use ribosome profiling and transcript analysis to experimentally define the HCMV translation products and follow their temporal expression. We identified several hundred previously unidentified open reading frames and confirmed a fraction by mass spectrometry. We found that regulated use of alternative transcript start sites plays a broad role in enabling tight temporal control of HCMV protein expression and allowing multiple distinct polypeptides to be generated from a single genomic locus. Our results reveal an unanticipated complexity to the HCMV coding capacity and illustrate the role of regulated changes in transcript start sites in generating this complexity. Ribosome profiling and mRNA-seq from 3 time points (5hr, 24hr, 72hr) along HCMV infection. The supplementary file 'GSE41605_merlin_final_orfs.bed.gz' includes the 751 ORFs of HCMV that were identified in this study.