Chikungunya virus antagonizes cGAS-STING mediated type-I interferon responses by degrading cGAS

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus known to cause epidemics resulting in predominantly symptomatic infections, which in rare cases cause long term debilitating arthritis and arthralgia. Significant progress has been made in understanding the roles of canonical RNA sensing pathways in the host recognition of CHIKV; however, less is known regarding antagonism of CHIKV by cytosolic DNA sensing pathways like that of cyclic GMP-AMP synthase (cGAS) and Stimulator of Interferon Genes (STING). With the use of cGAS or STING null cells we demonstrate that the pathway restricts CHIKV replication in fibroblasts and immune cells. We show that DNA accumulates in the cytoplasm of infected cells and that CHIKV blocks DNA dependent IFN-β transcription. This antagonism of DNA sensing is via an early autophagy-mediated degradation of cGAS and expression of the CHIKV capsid protein is sufficient to induce cGAS degradation. Furthermore, we identify an interaction of CHIKV nsP1 with STING and map the interaction to 23 residues in the cytosolic loop of the adaptor protein. This interaction stabilizes the viral protein and increases the level of palmitoylated nsP1 in cells. Together, this work supports previous publications highlighting the relevance of the cGAS-STING pathway in the early detection of (+)ssRNA viruses and provides direct evidence that CHIKV interacts with and antagonizes cGAS-STING signaling.
Author summary Chikungunya virus (CHIKV) is an emerging vector-borne virus which causes outbreaks that spread within populations quickly. The virus has been shown to be highly susceptible to type-I interferon signaling and can block this antiviral pathway. No work has identified if CHIKV is able to block the induction of type-I IFN by antagonizing cytosolic DNA sensing. Here we show that CHIKV induces the accumulation of DNA in the cytoplasm of infected cells and that the virus blocks cGAS-STING dependent innate immune sensing via degradation of cGAS. This work provides the first description of CHIKV mediated inhibition of DNA dependent innate immune sensing and expands upon our previous works by identifying and characterizing another RNA virus family able to counteract cGAS-STING mediated DNA sensing.