DAI Senses Influenza A Virus Genomic RNA and Activates RIPK3-Dependent Cell Death

Abstract

Summary Influenza A virus (IAV) is an RNA virus that is cytotoxic to most cell types in which it replicates. IAV activates the host kinase RIPK3, which induces cell death via parallel pathways of necroptosis, driven by the pseudokinase MLKL, and apoptosis, dependent on the adaptor proteins RIPK1 and FADD. How IAV activates RIPK3 remains unknown. We report that DAI (ZBP-1/DLM-1), previously implicated as a cytoplasmic DNA sensor, is essential for RIPK3 activation by IAV. Upon infection, DAI recognizes IAV genomic RNA, associates with RIPK3, and is required for recruitment of MLKL and RIPK1 to RIPK3. Cells lacking DAI or containing DAI mutants deficient in nucleic acid binding are resistant to IAV-triggered necroptosis and apoptosis. DAI-deficient mice fail to control IAV replication and succumb to lethal respiratory infection. These results identify DAI as a link between IAV replication and RIPK3 activation, and implicate DAI as a sensor of RNA viruses.

Programmed cell death as a defence against infection

“…The RIPK3 pathway also defends against a mouse adapted influenza infection. Zbp1 −/− and Ripk3 −/− mice have increased mortality during infection influenza A PR8 54,64 . However, the susceptibility of Ripk3 −/− mice to influenza virus was not replicated in another study 70 and a third study shows the reverse, where Zbp1 −/− mice have higher viral titers but reduced tissue damage and mortality 53 , suggesting a simultaneously beneficial role in defense paired with a detrimental role in immunopathology.…”

“…ZBP1 binds either Z-DNA or Z-RNA via two Z-DNA binding motifs, and can respond to MCMV (a DNA virus) or Influenza (a RNA virus) 52–54 . Unlike the normal B-form of DNA, Z-form DNA results from tosional strain that may occur during rapid DNA synthesis that could occur during viral infection.…”

RIPK3 in cell death and inflammation: the good, the bad, and the ugly

“…DAI was initially described as a sensor of DNA in the unusual Z-form conformation (Z-DNA) (43), and has since been shown to elicit cell death and transcriptional responses to DNA viruses via its Z-DNA binding domain (44, 45). However, more recent data have shown that DAI can trigger necroptosis downstream of influenza A virus (IAV)(46, 47), a single-stranded negative-sense segmented RNA virus (discussed later in this review), as well as in sterile settings in which the ability of RIPK1’s scaffolding function to suppress RIPK3 is disrupted (48, 49). As neither of these functions is consistent with the sensing of Z-DNA, it remains unclear how DAI is activated in these settings.…”

“…Subsequently, multiple groups demonstrated that IAV activates RIPK3 and triggers necroptosis through DAI—a molecule that that was previously thought to directly sense DNA (46, 47). How DAI senses IAV infection is somewhat disputed, however; one initial report indicated that DAI senses the viral proteins NP and PB1 (46), while another indicated that DAI recognizes and binds nascent IAV RNA genomes (47).…”

“…How DAI senses IAV infection is somewhat disputed, however; one initial report indicated that DAI senses the viral proteins NP and PB1 (46), while another indicated that DAI recognizes and binds nascent IAV RNA genomes (47). The contribution of DAI— and indeed of necroptosis itself—in controlling IAV infection in vivo is also somewhat unclear.…”