Analysis of Drosophila STING Reveals an Evolutionarily Conserved Antimicrobial Function

Abstract

SUMMARY The vertebrate protein STING, an intracellular sensor of cyclic dinucleotides, is critical to the innate immune response and the induction of type I interferon during pathogenic infection. Here, we show that a STING ortholog (dmSTING) exists in Drosophila, which, similar to vertebrate STING, associates with cyclic dinucleotides to initiate an innate immune response. Following infection with Listeria monocytogenes, dmSTING activates an innate immune response via activation of the NF-κB transcription factor Relish, part of the immune deficiency (IMD) pathway. DmSTING-mediated activation of the immune response reduces the levels of Listeria-induced lethality and bacterial load in the host. Of significance, dmSTING triggers an innate immune response in the absence of a known functional cyclic guanosine monophosphate (GMP)-AMP synthase (cGAS) ortholog in the fly. Together, our results demonstrate that STING is an evolutionarily conserved antimicrobial effector between flies and mammals, and it comprises a key component of host defense against pathogenic infection in Drosophila.

The STING pathway does not contribute to Pink1/parkin phenotypes in Drosophila

“…Therefore, to further interrogate the potential contribution of this pathway to Pink1/parkin pathology, we also analyzed a downstream effector of the Sting-IMD pathway, the transcription factor Relish (Rel). While RNAi knockdown using two previously characterized transgenes 11,13 elicited modest effect on climbing, Rel mutants ( Rel E20 ) displayed a strong locomotor defect (Fig. 4A).…”

“…Drosophila Sting mutants have recently been generated and, consistent with Sting’s role in triggering an innate immune response, shown to be more susceptible to infection. As other organismal phenotypes were not reported 11–13 we first assessed whether loss of Sting may induce additional phenotypes associated with the neuromuscular system that might confound further genetic interaction analysis. To this end, we examined the motor behavior and muscle integrity in Sting loss of function conditions.…”

“…The question arises why loss of Sting does not suppress Pink1/parkin phenotypes in flies when it is capable of completely preventing pathology in mice? At this stage, the answer is unknown and rather puzzling given that innate immune signaling is dysregulated in parkin mutants 15 , and Sting performs an analogous function in flies as it does in vertebrates 11 . One possibility is that the aberrant innate immune activation observed in parkin mutant flies is not mediated by the presence of cytosolic DNA and activation of the Sting pathway.…”

“…The recently identified Drosophila Sting ortholog has been shown to bind to cyclic-dinucleotides and trigger an immune response to bacterial and viral infection 11–13 , mediated by the IMD pathway and the transcription factor Relish (homologous to NF-κB). Consequently, Drosophila mutant for Sting showed a reduced survival upon infection.…”

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].…”