Investigation of murine cytomegalovirus modulation of TLR/IL-1β signalling pathways

Cytomegaloviruses (CMV), the prototypical β-herpesviruses, have co-evolved with their hosts and thus acquired multiple strategies for modulation of the immune response. Viral engagement of pattern recognition receptors (PRR), such as toll-like receptors (TLRs) and cytosolic nucleic acids sensors, initiates the host immune response through activation of elaborate signalling programs. The ensuing inflammatory response is further sustained and amplified through cytokines, such as IL-1β, activating signalling pathways greatly overlapping those utilized by TLRs. The central hypothesis of this thesis is that a viral counter-measure by murine CMV (MCMV) involves specific targeting of TLR- and IL-1β-induced signalling along the MyD88 to NF-κB pathway. To test this hypothesis MCMV inhibition of IL-1β signalling was initially investigated in a fibroblast cell line. It was demonstrated that in MCMV infected cells IL-1β-induced IκBα degradation is largely inhibited. Comparison of productive and non-productive infection showed this modulation requires de-novo viral gene expression beyond the immediate early region. Further investigations utilising a ORF M45 deletion mutant identified viral gene M45 as necessary for mediating the observed modulation of IL-1β- induced IκBα degradation. To further test the hypothesis, studies were extended to include TLR stimulation in the context of bone marrow-derived macrophages (BMDM) infection. It was found that TLR7/9-induced NF-κB activation is inhibited in MCMV infected BMDM. Overall, data presented in this study demonstrate a previously unrecognised MCMV inhibition of IL-1β- and TLR7/9-induced NF-κB activation, and indicate a role for viral gene M45 in mediating this effect

TRAF2 facilitates Vaccinia virus replication by promoting rapid virus entry.

Tumor necrosis factor receptor (TNFR)-associated factor 2 (TRAF2) is a pivotal intracellular mediator of signaling pathways downstream of TNFR1 and -2 with known pro- and antiviral effects. We investigated its role in the replication of the prototype poxvirus vaccinia virus (VACV). Loss of TRAF2 expression, either through small interfering RNA treatment of HeLa cells or through genetic knockout in murine embryonic fibroblasts (MEFs), led to significant reductions in VACV growth following low-multiplicity infection. In single-cycle infections, there was delayed production of both early and late VACV proteins as well as accelerated virus-induced alterations to cell morphology, indicating that TRAF2 influences early stages of virus replication. Consistent with an early role, uncoating assays showed normal virus attachment but delayed virus entry in the absence of TRAF2. Although alterations to c-Jun N-terminal kinase (JNK) signaling were apparent in VACV-infected TRAF2(−/−) MEFs, treatment of wild-type cells with a JNK inhibitor did not affect virus entry. Instead, treatment with an inhibitor of endosomal acidification greatly reduced virus entry into TRAF2(−/−) MEFs, suggesting that VACV is reliant on the endosomal route of entry in the absence of TRAF2. Thus, TRAF2 is a proviral factor for VACV that plays a role in promoting efficient viral entry, most likely via the plasma membrane. IMPORTANCE Tumor necrosis factor receptor-associated factors (TRAFs) are key facilitators of intracellular signaling with roles in innate and adaptive immunity and stress responses. We have discovered that TRAF2 is a proviral factor in vaccinia virus replication in both HeLa cells and mouse embryonic fibroblasts and that its influence is exercised through promotion of efficient virus entry

A Loss of Function Analysis of Host Factors Influencing Vaccinia virus Replication by RNA Interference

Vaccinia virus (VACV) is a large, cytoplasmic, double-stranded DNA virus that requires complex interactions with host proteins in order to replicate. To explore these interactions a functional high throughput small interfering RNA (siRNA) screen targeting 6719 druggable cellular genes was undertaken to identify host factors (HF) influencing the replication and spread of an eGFP-tagged VACV. The experimental design incorporated a low multiplicity of infection, thereby enhancing detection of cellular proteins involved in cell-to-cell spread of VACV. The screen revealed 153 pro- and 149 anti-viral HFs that strongly influenced VACV replication. These HFs were investigated further by comparisons with transcriptional profiling data sets and HFs identified in RNAi screens of other viruses. In addition, functional and pathway analysis of the entire screen was carried out to highlight cellular mechanisms involved in VACV replication. This revealed, as anticipated, that many pro-viral HFs are involved in translation of mRNA and, unexpectedly, suggested that a range of proteins involved in cellular transcriptional processes and several DNA repair pathways possess anti-viral activity. Multiple components of the AMPK complex were found to act as pro-viral HFs, while several septins, a group of highly conserved GTP binding proteins with a role in sequestering intracellular bacteria, were identified as strong anti-viral VACV HFs. This screen has identified novel and previously unexplored roles for cellular factors in poxvirus replication. This advancement in our understanding of the VACV life cycle provides a reliable knowledge base for the improvement of poxvirus-based vaccine vectors and development of anti-viral theraputics

Viral Mediated Redirection of NEMO/IKKγ to Autophagosomes Curtails the Inflammatory Cascade

The early host response to viral infections involves transient activation of pattern recognition receptors leading to an induction of inflammatory cytokines such as interleukin-1β (IL-1β) and tumor necrosis factor α (TNFα). Subsequent activation of cytokine receptors in an autocrine and paracrine manner results in an inflammatory cascade. The precise mechanisms by which viruses avert an inflammatory cascade are incompletely understood. Nuclear factor (NF)-κB is a central regulator of the inflammatory signaling cascade that is controlled by inhibitor of NF-κB (IκB) proteins and the IκB kinase (IKK) complex. In this study we show that murine cytomegalovirus inhibits the inflammatory cascade by blocking Toll-like receptor (TLR) and IL-1 receptor-dependent NF-κB activation. Inhibition occurs through an interaction of the viral M45 protein with the NF-κB essential modulator (NEMO), the regulatory subunit of the IKK complex. M45 induces proteasome-independent degradation of NEMO by targeting NEMO to autophagosomes for subsequent degradation in lysosomes. We propose that the selective and irreversible degradation of a central regulatory protein by autophagy represents a new viral strategy to dampen the inflammatory response

Investigation of murine cytomegalovirus modulation of TLR/IL-1β signalling pathways

Cytomegaloviruses (CMV), the prototypical β-herpesviruses, have co-evolved with their hosts and thus acquired multiple strategies for modulation of the immune response. Viral engagement of pattern recognition receptors (PRR), such as toll-like receptors (TLRs) and cytosolic nucleic acids sensors, initiates the host immune response through activation of elaborate signalling programs. The ensuing inflammatory response is further sustained and amplified through cytokines, such as IL-1β, activating signalling pathways greatly overlapping those utilized by TLRs. The central hypothesis of this thesis is that a viral counter-measure by murine CMV (MCMV) involves specific targeting of TLR- and IL-1β-induced signalling along the MyD88 to NF-κB pathway. To test this hypothesis MCMV inhibition of IL-1β signalling was initially investigated in a fibroblast cell line. It was demonstrated that in MCMV infected cells IL-1β-induced IκBα degradation is largely inhibited. Comparison of productive and non-productive infection showed this modulation requires de-novo viral gene expression beyond the immediate early region. Further investigations utilising a ORF M45 deletion mutant identified viral gene M45 as necessary for mediating the observed modulation of IL-1β- induced IκBα degradation. To further test the hypothesis, studies were extended to include TLR stimulation in the context of bone marrow-derived macrophages (BMDM) infection. It was found that TLR7/9-induced NF-κB activation is inhibited in MCMV infected BMDM. Overall, data presented in this study demonstrate a previously unrecognised MCMV inhibition of IL-1β- and TLR7/9-induced NF-κB activation, and indicate a role for viral gene M45 in mediating this effect.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

M45 targets NEMO to autophagosomes.

<p>(A) NIH-3T3 cells stably expressing Flag-tagged NEMO were mock infected or infected with wt MCMV-GFP or MCMV-GFP-ΔM45 at an MOI of 6. Cells were fixed 6 hpi, and NEMO distribution was analyzed by immunofluorescence. The arrow indicates the region which is shown in higher magnification in the right corner of the picture. (B) NIH-3T3 cells were transfected with Flag-NEMO and M45-HA expressing plasmids as indicated. 24 h later, cells were fixed and double immunofluorescence staining was performed using antibodies against the HA and Flag tags. Regions shown in higher magnification in the left corner of the pictures are indicated by arrows. (C) NIH-3T3 cells stably expressing Flag-NEMO were mock infected or infected with MCMV-M45-HA or MCMV-ΔM45 at an MOI of 7. Seven hpi, cells were fixed and analyzed as described for panel B. (D) NIH-3T3 cells were transfected with expression plasmids for Flag-NEMO and M45-HA or empty vector as indicated. Plasmids encoding GFP-tagged LC3, Rab5, or Rab7 were cotransfected. 24 hours posttransfection cells were fixed and used for anti-Flag immunofluorescence staining.</p

M45 targets RIP1 and NEMO, two crucial components of the inflammatory cascade.

<p>M45 targets RIP1 and NEMO, two crucial components of the inflammatory cascade.</p

M45 inhibits TLR- and IL-1R-mediated NF-κB but not p38 activation.

<p>(A) NIH-3T3 cells were transduced with retroviral vectors expressing M45 or GFP. Two days after transduction cells were stimulated with the TLR4 agonist LPS (10 µg/ml), the TLR2 agonist LTA-SA (10 µg/ml), or IL-1β (20 ng/ml). IκBα levels were determined by immunoblotting. (B) NIH-3T3 cells were transduced with an M45-expressing or an empty retroviral vector. 30 min after stimulation with IL-1β (10 ng/ml) cells were fixed, and subcellular localization of the NF-κB p65 subunit was analyzed by immunofluorescence. (C) NIH-3T3 cells expressing an NF-κB-dependent secreted alkaline phosphatase (SEAP) reporter were transduced with retroviral vectors expressing M45 or GFP and stimulated 78 h later with the TLR2 agonist Pam₃CSK₄ (Pam.,1 µg/ml), the TLR4 agonist LPS (0.1 µg/ml), or IL-1β (5 ng/ml). SEAP activity in the supernatant was quantified 15 h after stimulation and is shown as fold induction of SEAP activity of stimulated cells compared to non-stimulated cells (mean ± SD) (D) NIH-3T3 cells transduced with retroviral vectors expressing M45 or GFP were stimulated with IL-1β (20 ng/ml, 15 min) or TNFα (10 ng/ml, 5 min). Phosphorylated and total p38 in cell lysates was detected by immunoblotting.</p