Study On Mechanism Of Fever With Thrombocytopenia Syndrome Virus Nonstructural Protein Inhibiting The Beta Interferon Responses

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a new member of the genus Phlebovirus, family Bunyaviridae, and is the cause of Severe fever with thrombocytopenia syndrome (SFTS), which is characterized with high fever, thrombocytopenia, multiple organ damage and even death, with an approximately10%case fatality rate (CFR). SFTSV is a negative-strand RNA virus containing three single-stranded RNA genome segments designated as large (L), medium (M), and small (S). The S segment encodes a nucleoprotein (NP) and a nonstructural protein (NSs) via an ambisense coding strategy. The NSs of SFTSV mainly exists in the infected host cell but is not the part of viral particles and its specific features and clinical significances are unclear. Virus evolve strategies to escape the innate immune system in order to produce effective infection. At the same time, the level of interferon is low in the patients, so SFTSV can escape/from the natural immune system. But the mechanisms that counter the innate immune responses is still poorly understood. The aim of this paper is to explore the mechanism of SFTSV for escaping the innate immune responses.Innate immunity system is the first line to defense virus invasion, and interferon is most important antiviral molecules. Interferon-β is produced by the fiber cells, which are invaded by various viruses.Therefore, using a duel-reporter system we firstly determine the influence of SFTSV on the expression of IFN-β, and then we need to find out specific proteins that can influence IFN-P expression, and on the basis, we explore viral protein that effects IFN-P expression and its function sites. Experimental results confirmed that the SFTSV could inhibit the expression of IFN-P and the nonstructural protein (NSs) of SFTSV existed strong inhibitory effect to the expression of IFN-β. Then specific mechanisms of SFTSV NSs suppressing the interferon-p (IFN-β) express were found through tests of immune co-precipitation, mass spectrum detection and Western blot. NSs strongly combined with TBKl in cells, but at the same time, there were no effects on TBK1expression and phosphorylation, but this specific combination could effectively inhibit the phosphorylation and dimerization of IRF3by TBK1stimulating, resulting in suppression the expression of IFN-P and ultimately SFTSV successfully escaped innate immune effect of the host cell. On this basis, we also tried to search functional sites of SFTSV NSs, and as a result, we found that the function site of suppressing IFN-β express mainly in the N terminal near25amino acids. The combination capacity with TBK1and the inhibitory effect to IFN-β would reduce after NSs was deleted. Above all, these data shows that activation the pathway of IFN-β expression is blocked since NSs specific bind with TBK1and disrupt the signal pathway which stimulate the expression of IFN-β. In addition, IFN-P is suppressed mainly by NSs in site at N terminal near25amino acids. This study provides theoretical guidance and technical support for the prevention and control of SFTSV, and make some contributions for the research of virus immune mechanisms.