IRF1 regulates IFN-λ1 expression in MDA5-mediated suppression of the HBV replication

Abstract

MDA5, a member of the RIG-I like receptor family, has been shown to sense HBV DNA and trigger the production of anti-viral molecules to clear the virus. However, the mechanism underlying the suppression of HBV replication mediated by MDA5 signaling remains to be investigated. Our transcriptome analysis using RNA-seq revealed that IFN-λ1, a member of type III interferons, was the most upregulated molecule in Huh7 cells co-transfected with HBV DNA and MDA5 expression plasmid compared to with HBV DNA and RIG-I expression plasmid. Here we aim to investigate the IFN-λ1 expression in MDA5-mediated suppression of HBV replication. Huh7 cells co-transfected with HBV DNA and MDA5 expression plasmid led to increased IFN-λ1 expression associated with decreased HBsAg and HBV RNA. On the other hand, knockdown of MDA5 dramatically impaired IFN-λ1 expression. We next investigated the transcription factors involved in regulating IFN-λ1 expression. IRF1, but not IRF3 and IRF7, was upregulated in Huh7 cells co-transfected with HBV DNA and MDA5 expression plasmid. Knockdown of IRF1 led to reduced IFN-λ1 expression along with reduced inhibitory effect on HBV replication. The promoter region of IFN-λ1 contains ISREs, potential sites for IRF binding. However, ChIP and luciferase reporter assays showed no evidence of direct binding of IRF1 to the ISRE sites of IFN-λ1 promoter. Therefore, it is likely that IRF1 regulates MDA5-mediated IFN-λ1 expression through other mechanism. Mechanism(s) on IRF1 regulating IFN-λ1 expression in MDA5-mediated suppression of HBV replication is currently under investigation.