IFN-λ4 potently blocks IFN-α signalling by ISG15 and USP18 in hepatitis C virus infection

Abstract

Genetic polymorphisms in IFNL4 have been shown to predict responses to IFN-α-based therapy in hepatitis C virus (HCV)-infected patients. The IFNL4-ΔG genotype, which encodes functional IFN-λ4 protein, is associated with a poor treatment response. In the present study, we investigated the induction and biological effects of IFN-λ4 in HCV-infected hepatocytes and their association with responsiveness to IFN-α. We also studied the effects of direct-acting antiviral (DAA) treatment on IFN-λ4 expression and IFN-α responsiveness. HCV infection induced IFN-λ4 expression at mRNA and protein levels in primary human hepatocytes (PHHs). In hepatoma cells, IFNL4 gene transfection or recombinant IFN-λ4 protein treatment robustly increased the protein levels of ISG15 and USP18 in an IFNLR1-dependent manner and potently blocked IFN-α signalling. The ISG15/USP18-mediated IFN-α unresponsiveness was demonstrated by transfection of siRNAs targeting ISG15 and/or USP18. This potent IFN-λ4 effect was related to prolonged ISG expression after IFNL4 gene transfection. DAA treatment of HCV-infected PHHs reduced the expression of IFN-λs, including IFN-λ4, and restored IFN-α responsiveness. These results demonstrate that virus-induced IFN-λ4 potently blocks IFN-α signalling by inducing high protein levels of ISG15 and USP18. Moreover, the data clearly demonstrate that DAA therapy restores IFN-α responsiveness in HCV-infected cells.

Structure-based glycoengineering of interferon lambda 4 enhances its productivity and anti-viral potency

“…5A). IFNλ4 stimulation reportedly leads to the assembly of the ISGF3 transcription factor complex, which consists of phospho-STAT1, phospho-STAT2, and IRF9 and induces the expression of ISG15 [27], which is critical for anti-viral activity [28]. We showed that the M1, M3, and M7 IFNλ4 variants also induced the expression of ISG15 and inhibited HCV replication in HCVinfected Huh-7.5 cells ( Fig.…”

“…In this regard, a recent study demonstrated that IFNλs can suppress influenza virus without the inflammatory side effects of IFNα [44]. However, it was previously shown that the expression of functional IFNλ4 is associated with unresponsiveness to IFNα treatment among HCV-infected patients [9], and a subsequent study showed that long-term exposure to IFNλ4 leads to cellular unresponsiveness to IFNα treatment by upregulation of USP18 or SOCS1 [27,29], indicating that IFNλ4 treatment may be detrimental to virus-infected patients. On the other hand, our result shown in Fig.…”

“…Previously, eIFNλ4 is shown to induce the expression of negative regulators of IFN signaling [27,29] such as SOCS1 and USP18. To assess the effect of glycosylation on this functionality, we examined the expression level of SOCS1 and USP18 upon the treatment of M1, M3 and M7 variants on Huh7 cell line.…”

Revisiting the Paradox of Interferon‐Stimulated Gene Expression as a Predictor of Hepatitis C Virus Treatment Response, a Decade Later

“…Subsequent studies confirmed the inverse correlation with hepatic ISG set‐point levels and outcome of IFN therapy and showed cell‐type–specific differences in ISG expression . Induction of type III IFNs is the predominant antiviral pathway and driver of ISG induction, which render hepatocytes refractory to further type I IFN action, conceptually supported by the observation that blocking type III IFN enhances the antiviral activity of exogenous IFN‐α …”

“…Once sufficient viral proteins have accumulated in the cytosol, HCV uses its multifunctional NS3/4A protease, essential for HCV replication, to cleave MAVS and ablate RIG‐I–mediated innate immune signaling . Moreover, not all ISGs benefit the host, and several ISGs (including ISG15 and ubiquitin‐specific peptidase 18 [USP‐18]) have been reported to have proviral properties …”