The Role Of U1 Small Nuclear RNA In Regulating Antiviral Innate Immunity

Upon viral infection,the host immune system initiates a series of highly complex and delicate antiviral immune responses to combat invade viruses.Innate immunity plays a crucial role as the first line of defense against viral infection.However,excessive activation of the innate immune response leads to immune injuries and even autoimmune diseases.Therefore,precise regulation of the innate immune response is very important,which not only promotes resistance to viral infection but also avoids autoimmune damage during antiviral processes.Numerous non-coding RNAs(ncRNAs)including microRNA(miRNA),long non-coding RNA(lncRNA)and circular RNA(circRNA)have been shown to participate in the precise regulation of antiviral immunity.However,it is almost unknown that the role of small nuclear RNA(snRNA)in antiviral immunity.U1 snRNA,one of the most abundant ncRNAs,exists as a gene family with multiple copies of true genes,as well as many pseudogenes with the same or similar sequences as true genes.Our previous study has found that RNVU1-18,a pseudogene of U1 snRNA,is significantly upregulated during influenza virus infection,and U1 snRNA protects host against multiple RNA viruses at the cellular level.Based on our previous study,we further explored the role of U1 snRNA in the regulation of the antiviral innate immunity.First,we studied the biological characteristics of U1,including its evolutionary conservation and expression abundance.We found that U1 was highly conserved in more than 70 species and expressed abundantly in humans and mice.Meanwhile,we investigated the correlation between U1 and antiviral immunity and found that the expression of U1 was upregulated in the host cells infected with different viruses.Additionally,overexpression of U1 in A549 significantly induced the expression of antiviral genes,and U1 enhanced the immune response induced by viral RNA mimics and viral DNA mimics.These results indicate a positive correlation between U1 and antiviral immunity,suggesting that U1 plays an important role in both RNA virus and DNA virusinduced antiviral immune responses.Subsequently,we studied the role of U1 in RNA virus-induced antiviral innate immunity.U1 pseudogene RNVU1-18 was upregulated during influenza virus infection,and knockout of RNVU1-18 in A549 cells inhibited the antiviral innate immune response and promoted viral infection.In in vivo experiments,we effectively delivered the si-U1 to the lungs of mice using fluorinated α-helical polypeptide,followed by infection with influenza virus PR8,and found that silencing U1 in the lungs inhibited the antiviral immune response and thus promoted PR8 infection.In terms of a mechanism,we demonstrated that U1 interacted with TRIM25,promoting TRIM25-mediated RIG-I K63linked polyubiquitination and activation.Therefore,U1 enhances host antiviral innate immunity against RNA virus infection by promoting TRIM25-mediated RIG-I activation.Finally,we studied the role of U1 in DNA virus-induced antiviral innate immunity.Through the overexpression and knockdown of U1 in macrophages,we demonstrated that U1 positively regulated the antiviral innate immune response induced by HSV-1 infection.Then,we generated U1 myeloid-specific knock-in mice and found that knock-in of U1 enhanced the HSV-1-induced antiviral immune response in the primary mouse macrophages.In vivo experiments showed that knock-in of U1 protected mice against HSV-1 infection.Mechanistically,we found that U1 interacted with the nuclear DNA sensor hnRNPA2B1 and facilitated HSV-1-induced antiviral innate immune response by promoting the dimerization,nucleocytoplasmic translocation,and downstream TBK1IRF3 signaling activation of hnRNPA2B1.Therefore,our study has demonstrated that U1 promotes antiviral innate immune response against DNA virus such as HSV-1 by targeting hnRNPA2B1.In conclusion,this study has revealed the role of U1 snRNA in regulating antiviral innate immunity,providing new insights for the functional research of U1 snRNA and enriching our understanding of U1 snRNA.Additionally,this study provides a broader theoretical basis for understanding the regulatory role and mechanism of ncRNAs in antiviral innate immunity and offers novel targets and strategies for the prevention and treatment of viral infectious diseases.