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
Published December 6, 2010
Citation Information: J Clin Invest. 2011;121(1):37-56. https://doi.org/10.1172/JCI41474.
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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 5

Enhancement of HCV PAMP–mediated IFN response by disruption of UPR-autophagy activation.

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Enhancement of HCV PAMP–mediated IFN response by disruption of UPR-autop...
(A) Huh7 cells were first transfected with 400 pmol each of control, LC3B, ATG5, or CHOP siRNA duplexes for 72 hours and then harvested for analysis of LC3B, ATG5, CHOP, and β-actin expression (top left panel). The asterisks indicate nonspecific background signals. An uncropped image of A is shown in Supplemental Figure 9, left panel. A portion of siRNA-transfected cells was then transfected with the control HCV 5′-UTR RNA or HCV 3′-UTR PAMP RNA 36 hours after siRNA transfection. Twenty-four hours after PAMP RNA transfection, the cells were harvested for analyses of the IFNB mRNA level (top right) and ISG56 expression (bottom). The fold increase in IFNB mRNA level was determined by normalization to the basal level of control RNA transfection. (B) WT and Atg5–/– MEFs were transfected with pIFN-β/Fluc promoter reporter and pCMV22-Rluc plasmids. Twenty-four hours later, cells were transfected with control HCV 5′-UTR RNA (Control), HCV 3′-UTR PAMP RNA, or DEV PAMP RNA. An additional 24 hours after PAMP RNA transfection, cells were harvested and dual luciferase activity determined (left panel). The fold increase was calculated by normalization to the basal level of control RNA transfection. In parallel, the cells were also analyzed for ISG56, ATG5-ATG12, and β-actin expression by Western blotting (right panel). Data represent mean ± SEM (n = 3) (A, middle panel, and B).