Non-structural Proteins of Severe Fever With Thrombocytopenia Syndrome Virus Suppress RNA Synthesis in a Transcriptionally Active cDNA-Derived Viral RNA Synthesis System

Abstract

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by the tick-borne SFTS bunyavirus (SFTSV) resulting in a high fatality rate up to 30%. SFTSV is a negative-strand RNA virus containing three single-stranded RNA genome segments designated as L, M, and S, which respectively, encode the RNA-dependent RNA polymerase (RdRp), glycoproteins Gn and Gc, and nucleoprotein (N) and non-structural proteins (NSs). NSs can form inclusion bodies (IBs) in infected and transfected cells. A previous study has provided a clue that SFTSV NSs may be involved in virus-like or viral RNA synthesis; however, the details remain unclear. Our work described here reveals that SFTSV NSs can downregulate virus-like RNA synthesis in a dose-dependent manner within a cDNA-derived viral RNA synthesis system, i.e., minigenome (−) and minigenome (+) systems based on transfection, superinfection, and luciferase reporter activity determination; meanwhile, NSs also show a weak inhibitory effect on virus replication. By using co-immunoprecipitation (Co-IP) and RT-PCR combined with site-directed mutagenesis, we found that NSs suppress virus-like RNA or virus replication through interacting with N but not with RdRp, and the negative regulatory effect correlates closely with the IB structure it formed but is not associated with its role of antagonizing host innate immune responses. When the cytoplasmic structure of IB formed by SFTSV NSs was deprived, the inhibitory effect of NSs on virus-like RNA synthesis would weaken and even disappear. Similarly, we also evaluated other bandavirus NSs that cannot form IB in neither infected nor transfected cells, and the results showed that the NSs of Heartland bandavirus (HRTV) did not show a significant inhibitory effect on virus-like RNA synthesis within a minigenome system. Our findings provide experimental evidence that SFTSV NSs participate in regulating virus-like or viral RNA synthesis and the negative effect may be due to the NSs–N interaction.

Association of low HDL-c levels with severe symptoms and poor clinical prognosis in patients with severe fever and thrombocytopenia syndrome

“…This disease is most prevalent during the summer, and the population is generally susceptible. SFTS virus (SFTSV) is an RNA virus with a single-stranded genome, primarily transmitted through tick bites ( Ren et al, 2021 ). Ticks serve as the main vectors responsible for infecting hosts, including humans, livestock, and wild animals, thereby facilitating the transmission of SFTSV ( Luo et al, 2015 ).…”

Non-Structural Protein-W61 as a Novel Target in Severe Fever with Thrombocytopenia Syndrome Virus (SFTSV): An In-Vitro and In-Silico Study on Protein-Protein Interactions with Nucleoprotein and Viral Replication

“…Furthermore, the NSs-TRIM21 interaction-mediated activation of Nrf2 may have a specific role in viral pathogenesis. Moreover, NSs were sufficient to inhibit IFN-β induction by interfering with LSm14A as an activator of IFN regulatory factor3 (IRF3) [ 11 ]. Extracellular IFNs activate Janus kinase–signal transducer and activator of transcription and the phosphoinositide 3-kinase–AKT–mechanistic target of rapamycin pathway, which regulates the expression of autophagy-related genes.…”

“…NSs are associated with viral NP and RNA and may be involved in viral RNA replication [ 9 ]. Furthermore, it has been reported that NSs can act as a skeletal protein supporting SFTSV RNA replication, as replication intermediates of viral RNA in the form of NP and dsRNA have been found in VLS [ 10 , 11 ]. The role of NS proteins and their significance in SFTSV RNA replication are unknown.…”

Advancements in the Worldwide Detection of Severe Fever with Thrombocytopenia Syndrome Virus Infection from 2009 to 2023

“…The S segment, containing 1,744 nucleotides, codes for the nucleocapsid protein (N) (29)(30). The M segment, made up of 3,378 nucleotides, is responsible for coding the glycoprotein precursor (GPC) (31). Lastly, the L segment, with 6,368 nucleotides, codes for the RNA-dependent RNA polymerase (RdRp) (32).…”

“…The glycoprotein precursor of SFTSV undergoes post-translational cleavage, forming spikes on the surface of the virus. The Gn protein plays a critical role in attaching to the receptors of the host cell, while the Gc protein facilitates fusion with the membranes of the host cell (31).…”