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 6

Downregulation of HCV- and DEV-PAMP RNA–triggered IFN-β activation by autophagy inducers.

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Downregulation of HCV- and DEV-PAMP RNA–triggered IFN-β activation by au...
(A) Huh7/RFP-LC3 cells were treated with EBSS, HBSS, or with fresh medium containing 4 mM rapamycin for 6 hours. Cells were fixed and analyzed for the formation of RFP-LC3B–labeled autophagic vacuoles by confocal microscopy (scale bars: 10 μm). A set of confocal images is shown (left panel). The degree of cells forming autophagic vacuoles was also quantified (right panel). (B) Huh7/RFP-LC3 cells were starved or treated with rapamycin as described in A, and cells were fixed and subjected to TEM analysis. The ratio of autophagy (autophagic cells/total cells) was determined by counting the number of cells containing autophagic vacuoles among the total 30 randomly selected cells. (C) Huh7/RFP-LC3 cells were transfected with the pIFN-β/Fluc promoter reporter and cultured for 24 hours. Cells were then transfected with control HCV 5′-UTR RNA or 3′-UTR PAMP RNA, and maintained for an additional 12 hours. The transfected cells were then treated with chemicals as described in A prior to determination of IFNB promoter activation. The fold increase in IFNB promoter of the PAMP RNA–transfected cells was determined by normalization to the basal level of the control RNA–transfected cells. (D) The effects of EBSS, HBSS, and rapamycin on DEV PAMP RNA–induced IFNB promoter reporter activation were determined as described in C. Data represent mean ± SEM (n = 3) (A, C, and D).