Zika virus infection triggers caspase cleavage of STAT1

Abstract

ABSTRACT Zika virus (ZIKV) is an important pathogen that causes Guillain-Barre syndrome in adults and congenital Zika syndrome in newborns. Interferon (IFN) triggers intracellular antiviral signaling through two essential mediators STAT1 and STAT2, which are critical for host innate antiviral immunity. ZIKV has been reported to antagonize host IFN signaling by diverse mechanisms, including NS5-dependent and -independent ablation of STAT2. Whether flaviviruses target STAT1 remains controversial. In this study, we used infectious clones of ZIKV MR766 as tools and found that ZIKV infection triggered caspase-dependent cleavage of STAT1 during late infection. Further studies identified that the cleavage site is the aspartic acid 694, and the D694A mutation rendered STAT1 resistant to ZIKV infection-induced cleavage. Murine STAT1 (mSTAT1) was resistant to cleavage in ZIKV-infected cells. Ectopically expressed STAT1.D694A and mSTAT1 exerted comparable anti-ZIKV activity upon IFN treatment, challenging the role of STAT1 cleavage in IFN antagonism. We further knocked out STAT1 in the mouse embryonic fibroblast NIH3T3 cells, and STAT1 knockout dramatically augmented ZIKV infection, suggesting a STAT1-mediated viral restriction. Intriguingly, in the STAT1-knockout NIH3T3 cells, complementation of mSTAT1.D695G, a cleavage-sensitive variant, and the wild-type mSTAT1 both restored comparable anti-viral activities. These data suggest that caspase-mediated STAT1 cleavage is dispensable for IFN antagonism in ZIKV-infected cells. IMPORTANCE Zika virus (ZIKV) is a re-emerging flavivirus. Similar to other flaviviruses, ZIKV antagonizes the host interferon (IFN) signaling pathway to establish infection. Understanding the molecular mechanism by which ZIKV antagonizes IFN-induced antiviral signaling may lead to a new antiviral strategy by cracking the IFN antagonism. Flaviviruses have been reported to employ NS5-dependent and -independent mechanisms to block STAT2-mediated signaling, whereas whether flaviviruses target STAT1 remains controversial. Herein, we found that ZIKV infection triggered caspase-dependent cleavage of STAT1 at the aspartic acid 694 during late infection, whereas murine STAT1 (mSTAT1) was resistant to cleavage. Intriguingly, ectopically expressed cleavage-resistant human STAT1.D694A or complementation of cleavable mSTAT1.D695G exerted comparable anti-ZIKV activity with their counterparts, challenging the role of caspase-mediated STAT1 cleavage in the IFN antagonism in ZIKV-infected cells. These data may also imply a dominant role of the antagonism of STAT2 but not STAT1 in ZIKV-infected cells.