Phase-separated nucleocapsid protein of SARS-CoV-2 suppresses cGAS-DNA recognition by disrupting cGAS-G3BP1 complex

Abstract

Currently, the incidence and fatality rate of SARS-CoV-2 remain continually high worldwide. COVID-19 patients infected with SARS-CoV-2 exhibited decreased type I interferon (IFN-I) signal, along with limited activation of antiviral immune responses as well as enhanced viral infectivity. Dramatic progresses have been made in revealing the multiple strategies employed by SARS-CoV-2 in impairing canonical RNA sensing pathways. However, it remains to be determined about the SARS-CoV-2 antagonism of cGAS-mediated activation of IFN responses during infection. In the current study, we figure out that SARS-CoV-2 infection leads to the accumulation of released mitochondria DNA (mtDNA), which in turn triggers cGAS to activate IFN-I signaling. As countermeasures, SARS-CoV-2 nucleocapsid (N) protein restricts the DNA recognition capacity of cGAS to impair cGAS-induced IFN-I signaling. Mechanically, N protein disrupts the assembly of cGAS with its co-factor G3BP1 by undergoing DNA-induced liquid-liquid phase separation (LLPS), subsequently impairs the double-strand DNA (dsDNA) detection ability of cGAS. Taken together, our findings unravel a novel antagonistic strategy by which SARS-CoV-2 reduces DNA-triggered IFN-I pathway through interfering with cGAS-DNA phase separation.

SARS-CoV-2 and innate immunity: the good, the bad, and the “goldilocks”

“…This IFN induction is dependent on spike cleavage and is increased in cells that overexpress host proteases, such as TMPRSS2, that are drug targets; furthermore, mutating the cleavage site completely abrogates IFN stimulation in fused cells [ 94 ]. Interestingly, damaged DNA released from the ruptured nucleus is not the only source for cGAS sensing, as SARS-CoV-2 infection also causes direct mtDNA damage [ 102 ]. However, as cGAS signaling requires cGAS-G3BP1 coassembly on dsDNA to form stress granules, the viral nucleocapsid restricts cGAS signaling by competitively binding G3BP1 to divert dsDNA into alternative liquid‒liquid phase-separation condensates (Fig.…”

“…However, as cGAS signaling requires cGAS-G3BP1 coassembly on dsDNA to form stress granules, the viral nucleocapsid restricts cGAS signaling by competitively binding G3BP1 to divert dsDNA into alternative liquid‒liquid phase-separation condensates (Fig. 1 ) [ 102 ].

Fig.

…”

SFTSV nucleoprotein mediates DNA sensor cGAS degradation to evade cGAS-dependent antiviral responses.

“…Therefore, it is worth to explore whether SFTSV has evolved capability to escape cGAS recognition. According to current reports, the strategies employed by RNA virus to evade the cGAS recognition included degradation, cleavage, or competitive inhibition 29,30,31,32 . Considering SFTSV NP interacting with cGAS, we then investigated whether NP could antagonize cGAS-STING-mediated antiviral innate immune responses.…”

“…Besides, Zika virus NS1 promoted the cleave of cGAS by caspase-1 31 . In addition, SARS-CoV-2 protein N competed with cGAS to bind to G3BP1, a co-factor of cGAS, to damage the function of cGAS to recognize DNA 32 . However, it remains unclear whether cGAS involves in the recognition of SFTSV, and the mechanism of the interaction between cGAS and SFTSV.…”