Study On The Interaction Between H5N1-NS1 And NOLC1 Leading To Nucleolar Stress-induced Apoptosis

Nonstructural protein 1(NS1)is a key virulence factor of avian influenza virus,which plays an important role in virus replication and virulence enhancement.NS1 can interact with various types of RNAs and proteins to promote viral replication and inhibit host antiviral response.Our previous studies have shown that NS1 can interact with nucleolar and coiled-body phosphoprotein 1(NOLC1).NOLC1 mainly plays an important role in participating in the occurrence of nucleoli and regulating the transcription of nucleolar proteins and r DNA.During viral infection,the interaction between NS1 and NOLC1 is important for promoting host cell apoptosis and reducing viral replication.It is reported that telomeric repeat-binding factor 2(TRF2),a member of the complex responsible for telomere DNA protection,interacts with NOLC1.TRF2 is localized in the nucleoli of some cells in a cycle-dependent manner and participates in r RNA synthesis regulated by NOLC1.This study aimed to investigate the effects of NS1 and NOLC1 protein interaction on nucleolar TRF2 and r RNA synthesis under nucleolar stress.In this study,NOLC1 protein was down-regulated by exogenous NS1 gene expression in A549 cells.It has been reported that ribosomal proteins translocate from nucleolus to nucleoplasm and activate p53 pathway under nucleolar stress.We detected the interaction between ribosomal protein 11 and MDM2 protein in NS1-expressing cells by co-immunoprecipitation,which reduced the degradation of P53 protein and increased the expression of p21 gene.A series of experiments showed that NS1 protein induced nucleolar stress.Immunofluorescence showed that TRF2 protein was transferred from nucleolus to nucleoplasm under the conditions of down-regulation of NOLC1 expression and nucleolus stress.Under the conditions of TRF2 nucleoli metastasis and nucleoli stress caused by NS1 protein,the synthesis of host r RNA was inhibited.Cell cycle arrest usually occurs in the cells inhibited by r RNA synthesis.The cells expressing NS1 were detected by flow cytometry,and the cell cycle arrest was in the G1-G1 / S phase.The study on the effect of the interaction between NS1 and NOLC1 on nucleolar stress and TRF2 protein is helpful for us to further study how virulence factor NS1 interferes with r RNA transcription in the process of virus infection,which affects the host cell cycle process and virus infection process.The molecular mechanism of NS1 in the process of virus infection was expanded.