JNK/c‐Jun pathway activation is essential for HBx‐induced IL‐35 elevation to promote persistent HBV infection

BACKGROUND: Immunoregulation plays pivotal roles during chronic hepatitis B virus (HBV) infection. Studies have shown that Interleukin (IL)‐35 is an important molecule associated with inadequate immune response against HBV. However, the mechanisms involved in the up‐regulation of IL‐35 expression during persistent HBV infection remain unknown. METHODS: In this study, we constructed a plasmid expressing the HBV X protein (pCMV‐HBx) to evaluate the relationship between HBx and IL‐35. Activation of the JNK/c‐Jun pathway was analyzed and chromatin immunoprecipitation followed by sequencing and luciferase reporter assays were performed to determine whether c‐Jun could regulate IL‐35 transcription. RESULTS: HBx can significantly activate IL‐35 promoter in both LO2 and HepG2 cells compared to the control plasmid (pCMV‐Tag2) using the dual‐luciferase assay. Whereas other viral proteins, such as S, preS1, the core protein, had no significant effect on IL‐35 expression. Similarly, WB and qRT‐PCR also showed that HBx can significantly promote IL‐35 expression at protein and mRNA levels in the aforementioned cells. The relevant pathway mechanism showed that the expression of JNK and c‐Jun genes was significantly higher in transfected cells carrying pCMV‐HBx than in the pCMV‐Tag2‐transfected and ‐untransfected cells. WB analysis revealed that phosphorylated JNK and c‐Jun were overexpressed after HBx action. Conversely, the addition of the JNK/c‐Jun signaling pathway inhibitor could significantly suppress HBx‐induced IL‐35 expression in a dose‐dependent manner. CONCLUSIONS: A novel molecular mechanism of HBV‐induced IL‐35 expression was revealed, which involves JNK/c‐Jun signaling in up‐regulating IL‐35 expression via HBx, resulting in transactivation of the IL‐35 subunit EBI3 and p35 promoter.