DDX23, an Evolutionary Conserved dsRNA Sensor, Participates in Innate Antiviral Responses by Pairing With TRIF or MAVS.

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.