Abstract
In mammals, the cGAS-cGAMP-STING pathway is crucial for sensing viral infection and initiating an anti-viral type I interferon response. cGAS and STING are highly conserved genes that originated in bacteria and are present in most animals. By contrast, interferons only emerged in vertebrates; thus, the function of STING in invertebrates is unclear. Here, we use the STING ligand 2’3’-cGAMP to activate immune responses in a model cnidarian invertebrate, the starlet sea anemone Nematostella vectensis. Using RNA-Seq, we found that 2’3’-cGAMP induces robust transcription of both anti-viral and anti-bacterial genes, including the conserved transcription factor NF-κB. Knockdown experiments identified a role for NF-κB in specifically inducing anti-bacterial genes downstream of 2’3’-cGAMP, and some of these genes were also found to be induced during Pseudomonas aeruginosa infection. Furthermore, we characterized the protein product of one of the putative anti-bacterial genes, the N. vectensis homolog of Dae4, and found that it has conserved anti-bacterial activity. This work describes an unexpected role of a cGAMP sensing pathway in anti-bacterial immunity and suggests that a broad transcriptional response is an evolutionarily ancestral output of 2’3’-cGAMP signaling in animals.
Significance statement Anti-viral immune responses are initiated via signaling pathways such as the STING pathway. In mammals, activation of this pathway results in the production of anti-viral molecules called interferons. Surprisingly, the STING pathway is present in organisms such as sea anemones that lack interferons; the function of this pathway in these organisms is thus unclear. Here we report that in the anemone Nematostella vectensis, a small molecule activator of the STING pathway, cGAMP, not only induces an anti-viral response, but also stimulates an anti-bacterial immune response. These results provide insights into the evolutionary origins of innate immunity, and suggest a broader ancestral role for cGAMP-STING signaling that evolved toward more specialized anti-viral functions in mammals.
Competing Interest Statement
R.E.V. consults for Ventus Therapeutics. The other authors declare no competing interests.
