Role of the dimerization domain of black carp STING during the antiviral innate immunity

Stimulator of interferon gene (STING) functions importantly as antiviral adaptor protein during the innate immune activation. The role of the dimerization domain (DD) of STING remains obscure although other domains of this molecule have been studied extensively. To clarify the mechanism of black carp STING (bcSTING) in the innate immunity, bcSTING-ΔDD (bcSTING without DD) and bcSTING-ΔCTT (bcSTING without CTT domain) were constructed and analyzed in this manuscript. The reporter assays revealed that the induced transcription of IFN promoters mediated by bcSTING-ΔDD were much higher than that of the wild type bcSTING; however, bcSTING-ΔCTT almost lost the activities to trigger the interferon (IFN) promoters transcription. The mRNA transcriptional levels of IFN and interferon stimulated genes (ISGs) in EPC cells expressing bcSTING-ΔDD were obviously higher than those of EPC cells expressing wild type bcSTING; however, the transcriptional levels of the above cytokines of EPC cells expressing bcSTING-ΔCTT were basically the same as those of control cells. EPC cells overexpressing bcSTING-DD showed stronger antiviral activity than those overexpressing wild-type bcSTING. Furthermore, the co-immunoprecipitation assay identified the self-interaction between bcSTING-ΔDD molecules. And it was interesting that the affinity between bcSTING-ΔDD and bcTBK1 was obviously stronger than that between bcTBK1 and wild-type bcSTING. Thus, our data suggests that DD of black carp STING plays a negative regulatory role in STING-mediated antiviral immunity, which provides a new perspective for further researching the function of fish STING in the innate immunity.