Host Factor SGTA Interacts With Influenza Virus M2 Protein And Promotes Virus Replication

Influenza virus is the pathogen that causes human influenza.In recent years,with the prevalence of influenza viruses,new mutant strains have emerged,together with enlarged host range and progressively increased pathogenicity and transmissibility,resulting in more severe threat to public health.Influenza virus is characterized with simple structure and a small genome,and can express more than ten viral proteins by frameshift and alternative splicing.However,it still needs to rely on the host machinery,such as the protein synthesis and transportation system,energy system and alternative splicing system,to complete its replication cycle.On the other hand,influenza virus is recognized by the immune system when it invades into the host,resulting in inhibition of virus replication by the host immune-related proteins.Therefore,the interaction between influenza virus and host is a very complicated process,and an in-depth study of the interaction between viral and host proteins is essential for understanding the replication mechanism and pathogenesis of influenza viruses,so as to achieve effective prevention and control of influenza.Influenza virus M2 protein is a multifunctional protein.Its ion channel activity can mediate virus uncoating in the early stage of virus replication,enabling the vRNP complex to enter the nucleus,and can also assist HA protein maturation in trans-Golgi apparatus.Moreover,M2 protein promotes budding and release of progeny virus particles at the late stage of virus replication.Given the important role of M2 protein in the replication cycle of influenza virus,the yeast two-hybrid system was used in our laboratory to screen for host proteins that interact with M2 protein,and one of them was identified to be small glutamine-rich tetratricopeptide repeat-containing protein ?(SGTA).In this study,we identified that SGTA and M2 protein can interact with each other in yeast and 293 T cells.Further studies revealed that amino acids 91-313 in the C-terminus of SGTA were the key region interacting with M2 protein.Confocal microscopy experiments showed that the exogenously transfected SGTA and M2 protein were co-localized in the cytoplasm.We found that overexpression of SGTA protein can promote influenza virus replication,whereas down-regulation of SGTA expression by siRNA or knockout of SGTA by CRISPR-Cas9 significantly inhibited virus replication,indicating that SGTA positively regulates influenza virus replication.Moreover,siRNA knockdown of SGTA expression did not affect the nuclear import of viral NP protein,suggesting that SGTA has no role in the early stage of influenza virus replication cycle.Instead,the expression of SGTA increased the stability of M2,which was evidenced by the progressively increased level of M2 as the exogenous expression of SGTA was gradually increasing.Our study partially elucidated the mechanism by which host protein SGTA positively regulates influenza virus replication through interaction with viral M2 protein,and enriched the interaction network between influenza virus and host.