IFN-\u03bb4 potently blocks IFN-\u03b1 signalling by ISG15 and USP18 in hepatitis C virus infection

Pil Soo Sung,Jae-Hee Chung,Ho Min Kim,Seung Kew Yoon,Seon-Hui Hong,Eui-Cheol Shin,Sojeong Kim,Su-Hyung Park

doi:10.1038/s41598-017-04186-7

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.

Highlights

The global prevalence of hepatitis C virus (HCV) infection is approximately 3%1
We show that HCV infection induces IFN-λ4 expression and that IFN-λ4 potently attenuates the response to exogenous IFN-α treatment by the action of ISG15 and USP18
It was demonstrated previously that IFN-λ4 expression is induced by poly(I:C) transfection into PHHs14, 21, but it has not been known whether IFN-λ4 expression is induced by HCV infection in primary human hepatocytes (PHHs)

Summary

Introduction

The global prevalence of hepatitis C virus (HCV) infection is approximately 3%1. The majority of patients with HCV infection fail to clear the virus and develop chronic persistent infections[2]. Chronic hepatitis C patients with the rs368234815-∆G allele (∆G/TT or ∆G/∆G), which encodes the functional IFN-λ4 protein, respond poorly to peg-IFN-α-based therapy[14, 15]. The hepatic levels of ISGs in HCV-infected livers are associated with functional IFN-λ4 expression[18], and a functionally impaired variant of IFN-λ4 is associated with weaker induction of ISGs in HCV-infected livers[19]. These genotype-phenotype correlation studies demonstrate that functional IFN-λ4 protein is the driver of high hepatic ISG expression as well as the cause of poor treatment response. There have been no mechanistic studies that could explain why the rs368234815-∆G allele encoding the IFN-λ4 protein is associated with a poor response to peg-IFN-α-based treatment

Methods

Results

Conclusion