Activation of the unfolded protein response and autophagy after hepatitis C virus infection suppresses innate antiviral immunity in vitro
Po-Yuan Ke, Steve S.-L. Chen
Po-Yuan Ke, Steve S.-L. Chen
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Research Article Virology

Activation of the unfolded protein response and autophagy after hepatitis C virus infection suppresses innate antiviral immunity in vitro

Abstract

Autophagy, a process for catabolizing cytoplasmic components, has been implicated in the modulation of interactions between RNA viruses and their host. However, the mechanism underlying the functional role of autophagy in the viral life cycle still remains unclear. Hepatitis C virus (HCV) is a single-stranded, positive-sense, membrane-enveloped RNA virus that can cause chronic liver disease. Here we report that HCV induces the unfolded protein response (UPR), which in turn activates the autophagic pathway to promote HCV RNA replication in human hepatoma cells. Further analysis revealed that the entire autophagic process through to complete autolysosome maturation was required to promote HCV RNA replication and that it did so by suppressing innate antiviral immunity. Gene silencing or activation of the UPR-autophagy pathway activated or repressed, respectively, IFN-β activation mediated by an HCV-derived pathogen-associated molecular pattern (PAMP). Similar results were achieved with a PAMP derived from Dengue virus (DEV), indicating that HCV and DEV may both exploit the UPR-autophagy pathway to escape the innate immune response. Taken together, these results not only define the physiological significance of HCV-induced autophagy, but also shed light on the knowledge of host cellular responses upon HCV infection as well as on exploration of therapeutic targets for controlling HCV infection.

Authors

Po-Yuan Ke, Steve S.-L. Chen

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Figure 3

Activation of RIG-I–mediated IFN-β induction by knockdown of signaling molecules in UPR-autophagy.

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Activation of RIG-I–mediated IFN-β induction by knockdown of signaling m...
(A) VEC, ATG5KD, and CHOPKD cells were infected with HCV at an MOI of 10. Three days after infection, infected cells along with uninfected VEC cells were cotransfected with pIFN-β/Fluc reporter and pCMV22-Rluc plasmids together with an empty vector (–) or a RIG-I N expression construct (+). Twenty-four hours after DNA transfection, cells were harvested for the dual luciferase assay. The Renilla luciferase unit was used to normalize the transfection efficiency. The results are expressed as fold increase in IFNB promoter activity in the presence of RIGI-N relative to the basal level of the empty vector. (B) HCV infection and reporter transfection were performed as described in A, except that the ISRE promoter luciferase reporter was used instead of pIFN-β/Fluc and RIG-I N expression constructs. Twenty-four hours after transfection, cells were treated with or without 100 U/ml IFN-α for 16 hours before the dual luciferase assay. The results represent the fold induction of ISRE promoter activity in the presence of IFN-α relative to the basal level of cells without IFN-α treatment. (C) The indicated cells were analyzed for RIGI-N–mediated IFNB promoter activation as described in B. (D) The indicated cells were assessed for IFN-α–stimulated ISRE promoter activity as described in B. (E and F) Cell samples obtained from A and C and from B and D were analyzed by Western blotting, and the results are shown in E and F, respectively. Data represent mean ± SEM (n = 3) (A–D).