The Kinase IKKβ Regulates a STING- and NF-κB-Dependent Antiviral Response Pathway in Drosophila

Abstract

Antiviral immunity in Drosophila involves RNA interference and poorly characterized inducible responses. Here, we showed that two components of the IMD pathway, the kinase dIKKβ and the transcription factor Relish, were required to control infection by two picorna-like viruses. We identified a set of genes induced by viral infection and regulated by dIKKβ and Relish, which included an ortholog of STING. We showed that dSTING participated in the control of infection by picorna-like viruses, acting upstream of dIKKβ to regulate expression of Nazo, an antiviral factor. Our data reveal an antiviral function for STING in an animal model devoid of interferons and suggest an evolutionarily ancient role for this molecule in antiviral immunity.

2’3’-cGAMP triggers a STING and NF-κB dependent broad antiviral response in Drosophila

“…Furthermore, the induction of AGO2 by CDNs suggest a crosstalk between the two pathways where activation of dSTING potentiates the siRNA response. Intriguingly, our previous results pointed to a specific contribution of the dSTING-IKKβ-Relish pathway in resistance to DCV and CrPV, although a significant but smaller effect was visible also for VSV 5 . This apparent discrepancy could be explained by differences between viruses in the induction of the pathway based on their tissue tropisms, the type of virus-associated molecular pattern produced or the existence of escape strategies, all of which may be bypassed by systemic injection of 2’3’-cGAMP.…”

“…Interestingly, one of the three canonical components of the siRNA pathway, AGO2 , was rapidly induced by 2’3’-cGAMP, together with pst and ref(2)P , which encode restriction factors against picorna-like viruses 22, 23 and rhabdoviruses 24 , respectively. Late induced genes were mainly unknown but included the JAK-STAT regulated gene vir-1 and the antiviral gene Nazo (Fig.2a’’) 5, 25 . Gene ontology analysis revealed that the early and sustained upregulated genes were significantly enriched for a single functional category, namely immunity (Fig.2b).…”

“…Since most invertebrates lack the IRF family of transcription factors (with the notable exception of mollusks) as well as interferons, the lack of a C-terminal tail (CTT) in invertebrate STING suggests that this recent addition co-evolved with the onset of IRF transcription factors and IFN cytokines 16 . In contrast, the ability of STING to regulate transcription factors of the NF-κB family 17 18 5 or autophagy 19 , seems conserved throughout metazoa. Importantly, these responses are triggered in a CTT-independent manner in mammals 13–15 .…”

“…Apart from RNAi, these mechanisms are still poorly characterized and appear to be largely virus-specific 2–4 . Combining genetics and transcriptomic analysis, we recently showed that the evolutionarily conserved factor dSTING participates together with the kinase IKKβ and the NF-κB transcription factor Relish in a novel pathway controlling infection by the picorna-like viruses Drosophila C virus (DCV) and Cricket Paralysis Virus (CrPV) in the model organism Drosophila melanogaster 5 .…”

Conserved strategies for pathogen evasion of cGAS–STING immunity

“…Functional poxin enzymes are also found in the genomes of insect viruses in the family Baculoviridae, and moths and butterflies, which serve as hosts to these viruses [33 ]. The emerging role for cGAS-STING signaling in insects is likely to enable discovery of additional insect pathogen inhibitors of pathway activation [40][41][42]. In mammals, no cytosolic enzymes have been discovered which degrade 2 0 3 0 -cGAMP, but instead the extracellular enzyme ectonucleotide pyrophosphatase/phosphodiesterase family member 1 (ENPP1) has been shown to be the major source of 2 0 3 0 -cGAMPdegrading activity in mammalian tissue and plasma [43].…”