Objective: We previously reported that gene expression profiling of primary hepatocytes treated with IFNα, IL28B, or both in combination revealed specific induction of leukocyte cell-derived chemotaxin 2 (LECT2), a secretory protein preferentially expressed in the liver, by IL28B. However, the molecular mechanisms of LECT2 in the liver are not completely understood. We aimed to determine the functional relevance of LECT2 in the innate antiviral system and HCV replication.
Methods: The innate immune response of LECT2-treated HepG2 cells was confirmed by the induction of IFNβ, ISGs, and IRF3, and IRF7 and STAT1 phosphorylation. We also generated LECT2 transgenic (Tg) and knockout (KO) mice and examined the effects of LECT2 on the innate immune response during IFN or poly (I:C) treatment.
Results: Overexpression of LECT2 increased expression of ISGs 2.5-fold, accelerated induction of ISGs by IL28B, and suppressed HCV replication to 50% of that of control. Interestingly, LECT2 recombinant protein-treated HepG2 cells enhanced the innate immune response following poly (I:C) and HCV-RNA transfection. LECT2 enhanced IFNβ induction 5–10 fold and increased induction of ISGs through the activation of IRF3, IRF7, and JAK/STAT pathway. siRNA-mediated knockdown of RIG-I, MDA5, and TLR3 revealed that LECT2 prominently enhanced RIG-I-mediated antiviral responses. To confirm the biologic significance of these results, we generated LECT2 transgenic (Tg) and knockout (KO) mice. LECT2-Tg mice showed increased induction of IFNβ and ISGs following poly (I:C) treatment in the liver via RIG-I-mediated IRF3 activation. Conversely, LECT2-KO mice showed induction of IFNβ and ISGs following IFN or poly (I:C) treatment that was reduced to 30–50% that of WT mice.
Conclusion: LECT2 strongly enhanced the innate immune response and antiviral activities via RIG-I signaling pathway. Our data suggest that LECT2 plays a potentially important role in the innate immune system in hepatocytes and might be a therapeutic target for chronic hepatitis C.