The Dengue virus protease NS2B3 cleaves cyclic GMP-AMP synthase to suppress cGAS activation

Abstract

Dengue virus (DENV) is one of the most prevalent mosquito-transmitted human viruses that causes significant morbidity and mortality worldwide. To persist in the cell and consequently cause disease, DENV is evolved with mechanisms to suppress the induction of type I interferons by antagonizing cGAS-STING signaling. Using recombinant proteins and invitro cleavage assays, we have shown that the DENV protease NS2B3 is capable of cleaving cGAS in the N-terminal region without disrupting the C-terminal catalytic center. This generates two major cleavage products: cleavage product N-terminal (CP-N) and cleavage product C-terminal (CP-C). We observed reduction in DNA-binding affinity of CP-C as compared to full-length cGAS. Reduction in DNA-binding affinity is also correlated with the decrease in enzymatic activity of CP-C. CP-N, on the other hand, has almost comparable DNA-binding ability as that of the full-length cGAS. In fact, CP-N competitively inhibits cyclic GMP-AMP production by both full-length cGAS and CP-C. We hypothesize that high DNA-binding affinity of CP-N enables it to sequester the DNA from CP-C and noncleaved full-length cGAS and thus reduces the rate of enzyme activation and cyclic GMP-AMP synthesis. Furthermore, we found that NS2B3 physically interacts with full-length cGAS and CP-C, laying the basis for their shuttling to and eventual degradation in the autophagosome. Overall, our study highlights a multifaceted and effective strategy by which an RNA virus antagonizes cGAS-STING signaling which may be useful for the design of antivirals targeting viral proteases.