Japan. 8 These authors contributed equally to this work. Correspondence should be addressed to A.T. (takaoka@igm.hokudai.ac.jp). At least three DExD/H-box RNA helicases 4,5 , RIG-I, MDA5 and LGP2 are included in the RLR family. RIG-I is a key PRR for the detection of positive-and negative-stranded RNA viruses in the cytoplasm of cells 6,7 , and plays an important role in triggering responses against many viruses, such as orthomyxovirus (influenza A virus) and paramyxovirus (measles, mumps, and Sendai virus (SeV)) families, hepatitis C virus (HCV), and Japanese encephalitis virus (JEV) 8 . 5'-triphosphate modifications of RNA (3pRNA) are essential for RIG-I recognition and activation 9,10 . Ligand-binding activates the ATPase activity of RIG-I to change its structural conformation 6 , which in turn enables RIG-I to interact through its N-terminal tandem caspase recruitment domain (CARD) with the adaptor protein MAVS (for mitochondrial antiviral signaling protein, also known as IPS-1, VISA, or Cardif) [11][12][13][14] . MAVS then initiates the activation of interferon (IFN)-regulatory factor (IRF) 3, IRF7 and NF-κB transcriptional pathways for the subsequent production of type I IFNs and inflammatory cytokines, which are crucial for activating innate immune responses to viral infection 6,15 . Given the important role of the RIG-I pathway in the antiviral innate response, the mechanisms regulating RIG-I activation represent a topic of intense research [16][17][18] .Poly(ADP-ribose) polymerases (PARPs), a superfamily with least 17 members, are known to regulate not only cell survival and cell death programs triggered by DNA 3 damage, but also other biological functions as well as pathological processes, such as inflammatory and degenerative diseases, in a manner dependent or independent of their PARP activity [19][20][21][22] . Several PARP-superfamily members have a direct regulatory effect on replication of certain viruses 19,20,22,23 RESULTS 4PARPs contribute to the IFN response To investigate the role of the PARP-superfamily members in nucleic acid induced innate immune responses, we selected some of the PARP-superfamily members known to be involved in microbial infection, inflammation and immunity: PARP-1, PARP-2, PARP-7, PARP-9, 23,[31][32][33][34]. We then examined whether they have the ability to enhance the induction of IFNB mRNA in HEK293T cells in response to stimulation with three different types of nucleic acids-3pRNA, poly(rI:rC) and poly(dA-dT)•poly(dA-dT) (named poly(dA:dT) hereafter).Among the protein tested, PARP-13 uniquely showed a marked enhancing effect on IFNB mRNA expression induced by stimulation with 3pRNA, poly(rI:rC) and poly(dA:dT) ( Fig. 1a), all of which are known to activate the RIG-I-mediated pathway in HEK293T cells 9,10,[35][36][37] . A weak increase in IFNB mRNA expression was also detected in cells expressing PARP-1, PARP-2 and PARP-9. PARP-13 exists in at least two isoforms 22,26,38 . The amino-terminal 254-amino acid fragment of the rat homologue, which corresponds to the N...

Multiple host molecules are known to be involved in the cellular entry of filoviruses, including Ebola virus (EBOV); T-cell immunoglobulin and mucin domain 1 (TIM-1) and Niemann-Pick C1 (NPC1) have been identified as attachment and fusion receptors, respectively. However, the molecular mechanisms underlying the entry process have not been fully understood. We found that TIM-1 and NPC1 colocalized and interacted in the intracellular vesicles where EBOV glycoprotein (GP)-mediated membrane fusion occurred. Interestingly, a TIM-1-specific monoclonal antibody (MAb), M224/1, prevented GP-mediated membrane fusion and also interfered with the binding of TIM-1 to NPC1, suggesting that the interaction between TIM-1 and NPC1 is important for filovirus membrane fusion. Moreover, MAb M224/1 efficiently inhibited the cellular entry of viruses from all known filovirus species. These data suggest a novel mechanism underlying filovirus membrane fusion and provide a potential cellular target for antiviral compounds that can be universally used against filovirus infections. IMPORTANCE Filoviruses, including Ebola and Marburg viruses, cause rapidly fatal diseases in humans and nonhuman primates.There are currently no approved vaccines or therapeutics for filovirus diseases. In general, the cellular entry step of viruses is one of the key mechanisms to develop antiviral strategies. However, the molecular mechanisms underlying the entry process of filoviruses have not been fully understood. In this study, we demonstrate that TIM-1 and NPC1, which serve as attachment and fusion receptors for filovirus entry, interact in the intracellular vesicles where Ebola virus GP-mediated membrane fusion occurs and that this interaction is important for filovirus infection. We found that filovirus infection and GP-mediated membrane fusion in cultured cells were remarkably suppressed by treatment with a TIM-1-specific monoclonal antibody that interfered with the interaction between TIM-1 and NPC1. Our data provide new insights for the development of antiviral compounds that can be universally used against filovirus infections.

Background:It has been shown that heat shock protein 70 (Hsp70) plays a role in influenza A virus replication. Results: A correlation between viral replication/transcription activities and nuclear/cytoplasmic shuttling of Hsp70 was observed. Conclusion: Hsp70 modulates the influenza A virus polymerase activity. Significance: This study, for the first time, suggests that Hsp70 may actually assist in influenza A virus replication.

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Influenza is a respiratory disease induced by infection by the influenza virus, which is a member of Orthomyxoviridae family. This infectious disease has serious impacts on public health systems and results in considerable mortality and economic costs throughout the world. Based on several experimental studies, massive host immune reaction is associated with the disease severity of influenza. Programmed cell death is typically induced during virus infection as a consequence of host immune reaction to limit virus spread by eliminating niches for virus propagation without causing inflammation. However, in some viral infectious diseases, such as influenza, in the process of immune reaction, aberrant induction of programmed cell death disturbs the maintenance of organ function. Current reports show that there are different types of programmed cell death that vary in terms of molecular mechanisms and/or associations with inflammation. In addition, these novel types of programmed cell death are associated with pathogenesis rather than suppressing virus propagation in the disease course. Here, we review our current understanding of mechanisms of programmed cell death in the pathogenesis of influenza.