フォークヘッド転写因子FOXO3aによるインターフェロン-β遺伝子の発現制御機構の検討

FOXO3a

北海道歯学会

北海道歯学雑誌

Interferon-β (IFN-β) plays a pivotal role in immune response induced by viral infection. Previous reports have shown that the forkhead transcription factor FOXO3a negatively regulates IFN-β expression. However, mechanisms underlying the FOXO3a-mediated regulation of IFN-β gene expression are largely unknown. In this study, we aimed to elucidate regulatory mechanisms of the IFN-β gene expression by FOXO3a. At first, we examined the effect of FOXO3a overexpression on polyIC-induced IFN-β gene expression. FOXO3a-transfected 293T or 293-TLR3 cells were stimulated with polyIC and a quantitative RT-PCR (qRT-PCR) analysis was performed. We found that overexpression of FOXO3a reduced IFN-β mRNA induced by polyIC treatment. Next, we performed IFN-β promoter reporter gene assay in 293T cells and found that FOXO3a reduced MAVS- and TBK1-induced IFN-β reporter activity. However, FOXO3a had no effect on the reporter activity induced by IRF3 5D, a constitutively active form of IRF3. Furthermore, we examined molecular interaction between FOXO3a and TBK1. Immunoprecipitation analysis showed that FOXO3a physically associated with TBK1. In addition, western blot analysis revealed that overexpression of FOXO3a reduced the TBK1- meditaed phosphorylation of IRF3. Finally, we examined the effect of the PI3K inhibitor LY294002 on FOXO3a subcellular localization and IFN-β gene expression. Using immune fluorescent staining, we found that LY294002 treatment induced nuclear translocation of FOXO3a. In addition, qRT-PCR analysis showed that LY294002 treatment promoted IFN-β mRNA levels stimulated with polydAdT treatment in 293T cells. Taken together, these results suggest that FOXO3a negatively regulates IFN-β gene expression by physically interacting with TBK1 and reducing the phosphorylation of IRF3.