Exosomal Interferon‐Induced Transmembrane Protein 2 Transmitted to Dendritic Cells Inhibits Interferon Alpha Pathway Activation and Blocks Anti–Hepatitis B Virus Efficacy of Exogenous Interferon Alpha

Abstract

The negative regulators in the interferon (IFN) signaling pathway inhibit intrahepatic immune response, resulting in suboptimal therapeutic response to IFNα treatment in chronic hepatitis B (CHB) patients. Identifying the key negative factors and elucidating the regulating mechanism are essential for improving anti‐HBV (hepatitis B virus) efficacy of IFNα. From the Gene Expression Omnibus (GEO) database, we downloaded and analyzed gene expression profiles of CHB patients with different responses to IFNα (GSE54747), and found that innate immune status was associated with the IFNα‐based therapeutic response in CHB patients. Through PCR array, we found higher baseline level of IFN‐induced transmembrane protein 2 (IFITM2) mRNA and lower baseline level of IFNα mRNA in peripheral blood mononuclear cells (PBMCs) of CHB patients with suboptimal response to IFNα treatment. Increased IFITM2 protein was also found in the serum of IFNα nonresponsive patients. With further experiments, we found that overexpressing IFITM2 in Huh7 cells suppressed endogenous IFNα synthesis by inhibiting phosphorylation of extracellular signal–regulated kinase (ERK), TANK‐binding kinase 1 (TBK1), and interferon regulatory factor 3 (IRF3); knocking out IFITM2 enhanced activation of the endogenous IFNα synthesis pathway, exhibiting better inhibition on HBV replication. We also found that IFITM2 protein was shuttled by exosomes to dendritic cells (DCs), the main source of endogenous IFNα. Exosome‐mediated transport of IFITM2 inhibited synthesis of endogenous IFNα in DCs whereas the inhibitory effect was abolished when IFITM2 was knocked out. Furthermore, we demonstrated that both palmitoylation inhibitor and mutation on 70/71 sites of IFITM2 protein influenced its incorporation into exosomes. Mutated IFITM2 protein increased the effect of IFNα against HBV. Conclusion: Exosome‐mediated transport of IFITM2 to DCs inhibits IFNα pathway activation and blocks anti‐HBV efficacy of exogenous IFNα. The findings provide an explanation to the suboptimal response of CHB patients to IFNα treatment.

The Effects of RKI-1447 in a Mouse Model of Nonalcoholic Fatty Liver Disease Induced by a High-Fat Diet and in HepG2 Human Hepatocellular Carcinoma Cells Treated with Oleic Acid

“…As a downstream factor in TLR4 expression, TBK1 serves as the crucial regulator for IRF3 [36]. The phosphorylation of TBK1/IRF3 inhibits the inflammatory response in hepatitis [37]. IRF3 relieves hepatic steatosis and insulin resistance in high fat diet-induced metabolic dysfunction [38].…”

Exosomes in Hepatitis B Virus Transmission and Related Immune Response

“…NK cell, natural killer cell; DCs, dendritic cells; IFN, interferon; IL-6, interleukin-6; APOBEC3G, apolipoprotein B messenger RNA-editing enzyme catalytic polypeptide-like 3G; PD-1, programmed-death protein 1; PD-L1, programmed death-ligand 1; NKG2DL, NKG2D ligands; rc DNA, relaxed circular DNA. cells (DCs), thereby suppressing endogenous IFN-α synthesis and blocking the anti-HBV efficacy of exogenous IFN-α(Shi et al 2019)…”

Bmp8a Is a Novel Player in Regulation of Antiviral Immunity

“…In addition, Alk6a was found to be required to induce the phosphorylation of p38 MAPK, which is consistent with the findings in mouse that Alk6 knockdown suppresses p38 MAPK phosphorylation 51 . Previous studies have shown that MAPK signaling pathway is crucial in the phosphorylation of TBK1 and IRF3 upon viral infection 42 . Thus, we probably discover a new pathway of Bmp8a signaling in antiviral immune responses that Bmp8a acts as a positive regulator through the promotion of phosphorylation of Tbk1 via p38 MAPK pathway, i.e., Bmp8a binds to Alk6a, which induces p38 MAPK phosphorylation, and in turn enhances Tbk1 and Irf3 phosphorylation, eventually resulting in increased synthesis of type I IFN (Fig.…”