SUMMARY During anti-viral defense, interferon (IFN) signaling triggers nuclear transport of tyrosine phosphorylated STAT1 (PY-STAT1), which occurs via a subset of karyopherin alpha (KPNA) nuclear transporters. Many viruses, including Ebola virus, actively antagonize STAT1 signaling to counteract the antiviral effects of IFN. Ebola virus VP24 protein (eVP24) binds KPNA to inhibit PY-STAT1 nuclear transport and render cells refractory to IFNs. We describe the structure of human KPNA5 C-terminus in complex with eVP24. In the complex, eVP24 recognizes a unique non-classical nuclear localization signal (NLS) binding site on KPNA5 that is necessary for efficient PY-STAT1 nuclear transport. eVP24 binds KPNA5 with very high affinity to effectively compete with and inhibit PY-STAT1 nuclear transport. In contrast, eVP24 binding does not affect the transport of classical NLS cargo. Thus, eVP24 counters cell-intrinsic innate immunity by selectively targeting PY-STAT1 nuclear import while leaving the transport of other cargo that maybe required for viral replication unaffected.

Kelch-like ECH-associated protein 1 (Keap1) is an ubiquitin E3 ligase specificity factor that targets transcription factor Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) for ubiquitination and degradation. Disrupting Keap1-Nrf2 interaction stabilizes Nrf2; resulting in Nrf2 nuclear accumulation, binding to antioxidant response elements (AREs) and transcription of cytoprotective genes. Marburg virus (MARV) is a zoonotic pathogen that likely uses bats as reservoir hosts. We demonstrate that MARV protein VP24 (mVP24) binds the Kelch domain of either human or bat Keap1. This binding is of high affinity and 1:1 stoichiometry and activates Nrf2. Modeling based on the Zaire Ebola virus VP24 (eVP24) structure identified in mVP24 an acidic loop (K-loop) critical for Keap1 interaction. Transfer of K-loop to eVP24, which otherwise does not bind Keap1, confers Keap1 binding and Nrf2 activation; and infection by MARV but not EBOV activates ARE gene expression. Therefore, MARV targets Keap1 to activate Nrf2-induced cytoprotective responses during infection.

The host innate immune response is the first line of defense against pathogens and is orchestrated by the concerted expression of genes induced by microbial stimuli. Deregulated expression of these genes is linked to the initiation and progression of diseases associated with exacerbated inflammation. We identified topoisomerase 1 (Top1) as a positive regulator of RNA polymerase II transcriptional activity at pathogen-induced genes. Depletion or chemical inhibition of Top1 suppresses the host response against influenza and Ebola viruses as well as bacterial products. Therapeutic pharmacological inhibition of Top1 protected mice from death in experimental models of lethal inflammation. Our results indicate that Top1 inhibition could be used as therapy against life-threatening infections characterized by an acutely exacerbated immune response.

Filoviruses, marburgvirus (MARV) and ebolavirus (EBOV), are causative agents of highly lethal hemorrhagic fever in humans. MARV and EBOV share a common genome organization but show important differences in replication complex formation, cell entry, host tropism, transcriptional regulation, and immune evasion. Multifunctional filoviral viral protein (VP) 35 proteins inhibit innate immune responses. Recent studies suggest double-stranded (ds)RNA sequestration is a potential mechanism that allows EBOV VP35 to antagonize retinoic-acid inducible gene-I (RIG-I) like receptors (RLRs) that are activated by viral pathogen-associated molecular patterns (PAMPs), such as double-strandedness and dsRNA blunt ends. Here, we show that MARV VP35 can inhibit IFN production at multiple steps in the signaling pathways downstream of RLRs. The crystal structure of MARV VP35 IID in complex with 18-bp dsRNA reveals that despite the similar protein fold as EBOV VP35 IID, MARV VP35 IID interacts with the dsRNA backbone and not with blunt ends. Functional studies show that MARV VP35 can inhibit dsRNA-dependent RLR activation and interferon (IFN) regulatory factor 3 (IRF3) phosphorylation by IFN kinases TRAF family member-associated NFkb activator (TANK) binding kinase-1 (TBK-1) and IFN kB kinase e (IKKe) in cell-based studies. We also show that MARV VP35 can only inhibit RIG-I and melanoma differentiation associated gene 5 (MDA5) activation by double strandedness of RNA PAMPs (coating backbone) but is unable to inhibit activation of RLRs by dsRNA blunt ends (end capping). In contrast, EBOV VP35 can inhibit activation by both PAMPs. Insights on differential PAMP recognition and inhibition of IFN induction by a similar filoviral VP35 fold, as shown here, reveal the structural and functional plasticity of a highly conserved virulence factor.T he Filoviridae family of viruses, which includes marburgvirus (MARV) and ebolavirus (EBOV), can cause intermittent outbreaks that often result in high fatality rates (1). The family consists of five species of EBOV, Zaire, Reston, Sudan, Taï Forest, and Bundibugyo; one species of MARV; and a proposed genus Cuevavirus possessing a single species Lloviu cuevavirus (2). Despite overall similarities in genome size and organization, virion structure, and disease characteristics (3), EBOV and MARV exhibit important differences, including their strategies for immune evasion (4). For example, although EBOV viral protein (VP) 24 and MARV VP40 counter IFN signaling, neither MARV VP24 nor EBOV VP40 appears to function similarly to its corresponding counterparts with regard to immune evasion (5-10).Filoviruses also counteract innate immunity through the multifunctional VP35 proteins, which perform critical roles in viral RNA synthesis, virus assembly, and virus structure (reviewed in refs. 11 and 12). EBOV VP35 interacts with several components of innate antiviral defenses, including retinoic-acid inducible gene-I (RIG-I)-like receptor (RLR) pathways that lead to IFN production (13-24). These include inhibition of ...

SUMMARY Suppression of innate immune responses during filoviral infection contributes to disease severity. Ebola (EBOV) and Marburg (MARV) viruses each encode a VP35 protein that suppresses RIG-I-like receptor signaling and interferon-α/β (IFN-α/β) production by several mechanisms, including direct binding to double-stranded RNA (dsRNA). Here, we demonstrate that in cell culture MARV infection results in a greater upregulation of IFN responses as compared to EBOV infection. This correlates with differences in the efficiencies by which EBOV and MARV VP35s antagonize RIG-I signaling. Furthermore, structural and biochemical studies suggest that differential recognition of RNA elements by the respective VP35 C-terminal IFN inhibitory domain (IID) rather than affinity for RNA by the respective VP35s is critical for this observation. Our results reveal functional differences in EBOV versus MARV VP35 RNA binding result in unexpected differences in the host response to deadly viral pathogens.

Deep sequencing of RNAs produced by Zaire ebolavirus (EBOV) or the Angola strain of Marburgvirus (MARV-Ang) identified novel viral and cellular mechanisms that diversify the coding and noncoding sequences of viral mRNAs and genomic RNAs. We identified previously undescribed sites within the EBOV and MARV-Ang mRNAs where apparent cotranscriptional editing has resulted in the addition of non-template-encoded residues within the EBOV glycoprotein (GP) mRNA, the MARV-Ang nucleoprotein (NP) mRNA, and the MARV-Ang polymerase (L) mRNA, such that novel viral translation products could be produced. Further, we found that the well-characterized EBOV GP mRNA editing site is modified at a high frequency during viral genome RNA replication. Additionally, editing hot spots representing sites of apparent adenosine deaminase activity were found in the MARV-Ang NP 3′-untranslated region. These studies identify novel filovirus-host interactions and reveal production of a greater diversity of filoviral gene products than was previously appreciated.

S U M M A R Y A consecutive series of 75 patients with syringomyelia is presented, all of whom were treated by cranio-vertebral operations. Attention is drawn to the difficulty in assessing the results of treatment but 56 were stabilised or showed modest improvement after surgery. Occluding the central canal appeared to have no greater influence on the progression of the disease than did simple decompression and did have a higher incidence of complications. Upper motor neurone weakness, joint position sense and central neck pain are the features most likely to improve and it is concluded that relieving the medullary compression resulting from a Chiari type 1 malformation, rather than influencing the syrinx, is the means by which this may occur. Simple decompression with preservation of the arachnoid membrane, combined with syringostomy in certain cases, is recommended.The condition of syringomelia has been recognised as a nosological entity for over 150 years,' and operative treatment was carried out as early as 1891,' but even at the present time, the place of surgery in its management and the results that may be expected are still uncertain despite many publications on this subject. The factors responsible for this state of affairs are numerous and comprise the rarity of the disease, the lack of a uniform classification, the multiplicity of signs from random and asymmetric involvement of the tracts of the spinal cord and medulla oblongata and, in many patients, its long duration so that premature conclusions have tended to be drawn from too short a post-operative follow-up. Again, in many reports the results have been graded by such categories as "excellent," "good" or "poor" which, despite definition, has little meaning in a condition with so much variation in the response of individual neurological modalities to surgical treatment, some of which may show improvement and others deterioration. The occasional occurrence (although not in this series) of a patient, * Emeritus Professor of Neurosurgery. t Consultant Neurosurgeon.

Human respiratory syncytial virus (hRSV) is a major cause of morbidity and mortality in the pediatric, elderly, and immune compromised populations1,2. A gap in our understanding of hRSV disease pathology is the interplay between virally encoded immune antagonists and host components that limit hRSV replication. hRSV encodes for non-structural (NS) proteins that are important immune antagonists3–6; however, the role of these proteins in viral pathogenesis is incompletely understood. Here we report the crystal structure of hRSV NS1 protein, which suggests that NS1 is a structural paralog of hRSV matrix (M) protein. Comparative analysis of the shared structural fold with M revealed regions unique to NS1. Studies on NS1 WT or mutant alone or in recombinant RSVs demonstrate that structural regions unique to NS1 contribute to modulation of host responses, including inhibition of type I IFN responses, suppression of dendritic cell maturation, and promotion of inflammatory responses. Transcriptional profiles of A549 cells infected with recombinant RSVs show significant differences in multiple host pathways, suggesting that NS1 may have a greater role in regulating host responses than previously appreciated. These results provide a framework to target NS1 for therapeutic development to limit hRSV associated morbidity and mortality.