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DExD/H-box helicases play essential roles in RNA metabolism, and emerging data suggests that they have additional functions in antiviral immunity across species. However, little is known about this evolutionarily conserved family in antiviral responses in lower species. Here, through isolation of poly(I:C)-binding proteins in amphioxus, an extant basal chordate, we found that DExD/H-box helicases DHX9, DHX15, and DDX23 are responsible for cytoplasmic dsRNA detection in amphioxus. Since the antiviral roles of DDX23 have not been characterized in mammals, we performed further poly(I:C) pull-down assays and found that human DDX23 binds to LMW poly(I:C) through its N-terminal region, suggesting that DDX23 is an evolutionarily conserved dsRNA sensor. Knockdown of human DDX23 enhanced the replication of VSV and reduced the activation of the NF-κB and IRF3. Moreover, when stimulated with poly(I:C) or VSV, human DDX23 translocated from the nucleus to the cytoplasm and formed complexes with TRIF or MAVS to initiate downstream signaling. Collectively, this comparative immunological study not only defined DDX23 as an emerging nuclear pattern recognition receptor (PRR) for the innate sensing of an RNA virus, but also extended the essential role of the DExD/H helicase family in viral RNA sensing from mammals to basal chordates.

DExD/H-box helicases play essential roles in RNA metabolism, and emerging data suggests that they have additional functions in antiviral immunity across species. However, little is known about this evolutionarily conserved family in antiviral responses in lower species. Here, through isolation of poly(I:C)-binding proteins in amphioxus, an extant basal chordate, we found that DExD/H-box helicases DHX9, DHX15, and DDX23 are responsible for cytoplasmic dsRNA detection in amphioxus. Since the antiviral roles of DDX23 have not been characterized in mammals, we performed further poly(I:C) pull-down assays and found that human DDX23 binds to LMW poly(I:C) through its N-terminal region, suggesting that DDX23 is an evolutionarily conserved dsRNA sensor. Knockdown of human DDX23 enhanced the replication of VSV and reduced the activation of the NF-κB and IRF3. Moreover, when stimulated with poly(I:C) or VSV, human DDX23 translocated from the nucleus to the cytoplasm and formed complexes with TRIF or MAVS to initiate downstream signaling. Collectively, this comparative immunological study not only defined DDX23 as an emerging nuclear pattern recognition receptor (PRR) for the innate sensing of an RNA virus, but also extended the essential role of the DExD/H helicase family in viral RNA sensing from mammals to basal chordates. [ABSTRACT FROM AUTHOR]

Viral infection is an environmental trigger that has been suggested to initiate pancreatic β-cell damage, leading to the development of autoimmune diabetes. Viruses potently activate the immune system and can damage β cells by either directly infecting them or stimulating the production of secondary effector molecules (such as proinflammatory cytokines) during bystander activation. However, how and where β cells recognize viruses is unclear, and the antiviral responses that are initiated following virus recognition are incompletely understood. In this study, we show that the β-cell response to dsRNA, a viral replication intermediate known to activate antiviral responses, is determined by the cellular location of sensing (intracellular versus extracellular) and differs from the cellular response to cytokine treatment. Using biochemical and immunological methods, we show that β cells selectively respond to intracellular dsRNA by expressing type I interferons (IFNs) and inducing apoptosis, but that they do not respond to extracellular dsRNA. These responses differ from the activities of cytokines on β cells, which are mediated by inducible nitric oxide synthase expression and β-cell production of nitric oxide. These findings provide evidence that the antiviral activities of type I IFN production and apoptosis are elicited in β cells via the recognition of intracellular viral replication intermediates and that β cells lack the capacity to respond to extracellular viral intermediates known to activate innate immune responses., (© 2020 Shaheen et al.)