SFTSV NSs interacts with AGO2 to regulate the RNAi pathway for viral replication

Area of Science:

• Molecular Virology
• RNA Interference (RNAi)
• Host-Pathogen Interactions

Background:

• RNA interference (RNAi) is a crucial antiviral defense mechanism in eukaryotes, involving DICER and AGO2 in processing viral RNAs and cleaving viral genomes.
• Viruses have evolved strategies to evade or suppress host RNAi pathways, posing a significant challenge to host defense.
• Severe fever with thrombocytopenia syndrome virus (SFTSV) is a highly pathogenic virus with a high mortality rate, and its interaction with host antiviral mechanisms remains incompletely understood.

Purpose of the Study:

• To investigate the mechanism by which SFTSV suppresses the host RNA interference (RNAi) pathway.
• To identify the specific viral protein responsible for RNAi suppression and its molecular target within the RNAi machinery.
• To elucidate the functional consequences of this interaction on viral replication and pathogenesis.

Main Methods:

• Co-immunoprecipitation assays to detect interactions between SFTSV NSs protein and host RNAi factors (DICER, AGO2).
• Functional assays using shRNA and siRNA to assess RNAi activity in the presence of SFTSV NSs.
• Mutational analysis of NSs to identify critical domains for AGO2 interaction and RNAi suppression.
• Viral infection studies in wild-type and AGO2-deficient cells to evaluate the role of RNAi in antiviral defense.

Main Results:

• The SFTSV nonstructural protein (NSs) directly interacts with AGO2, a key component of the RNA-induced silencing complex (RISC).
• NSs forms a ternary complex with DICER and AGO2, competing with siRNA for AGO2 binding and thereby inhibiting RNAi-mediated gene silencing.
• A specific NSs mutant (NSs-A26) lacking AGO2-binding capability failed to suppress RNAi, confirming NSs's role as a viral suppressor of RNAi (VSR).
• SFTSV exhibited higher replication in AGO2-deficient cells compared to wild-type cells, underscoring the antiviral role of RNAi against SFTSV.

Conclusions:

• SFTSV NSs acts as a potent viral suppressor of RNAi (VSR) by directly targeting AGO2, a critical host antiviral factor.
• The NSs-AGO2 interaction effectively neutralizes the RNAi pathway, facilitating SFTSV replication and contributing to its pathogenesis.
• Understanding this viral evasion strategy opens potential avenues for therapeutic interventions against SFTSV infection.