The Function And Molecular Mechanism Of STAT1 In Innate Immunity Independent Of JAK/STAT Pathway

As an indispensable part of the immune system,innate immunity is mediated by the recognition of pathogen-related molecular patterns by pattern recognition receptors expressed on cell surfaces.This interaction triggers the activation of downstream signaling pathways,ultimately inducing the release of type Ⅰ interferons and various cytokines[1,2]Innate immunity plays an essential role in clearing the invading pathogens to protect human beings and animals.After the viral entry into the cell,the viral nucleic acid in the cytoplasm can be sensed by PRRs such as RIG-Ⅰ like receptors(RLRs)or intracellular DNA receptors such as cGAS.Those associations between PRRs and PAMPS further activate the downstream signals to induce the expression of type Ⅰ interferons through signaling transduction.Secreted type Ⅰ interferons initiate the transcription and expression of IFN stimulated genes(ISGs)via JAK/STAT cascade reactions,resulting in antiviral effects[3-5].Previous studies have shown that STAT1,as an important transcriptional regulator in the JAK/STAT pathway,participates in the regulation of the expression of ISGs genes[6,7].But it is not clear whether STAT1 can also contribute to typeⅠ interferons production independent of the JAK/STAT pathway and directly modulates the upstream signalings.Therefore,our study aims to explore the function and mechanism of STAT1 independent of the JAK/STAT pathway in innate immunity.In this study,we construct the STAT1 knockout cell line by CRISPR/Cas9 technology and observe that knockout of STAT1 can significantly inhibit the type Ⅰ interferons expression stimulated by Sendai Virus(SeV),Vesicular Stomatitis Virus(VSV),and herpes simplex virus 1(HSV-1).Besides,STAT1 deficiency attenuates the phosphorylation of TBK1 and IRF3,the upstream event of interferon expression.Further study shows that STAT1 still positively modulates the production of type Ⅰ interferons and the phosphorylation of TBK1 and IRF3 with the condition of Ifnarl knockout or IFNAR1 blockade.We also demonstrate that the positive effect of STAT1 does not depend on its DNA binding activity but may be achieved through its interaction with RIG-Ⅰ,TBK1,IRF3,and STING.In summary,our study indicates that STAT1 plays a positive role in RLRs and cGAS-STING signaling pathways independent of the JAK/STAT cascade response,which implies a novel mechanism of STAT1 in antiviral innate immune regulation.