1. HRTV and SFTSV NSs, but not UUKV NSs, inhibits JAK/STAT IFN signaling.
HRTV and SFTSV NSs, but not UUKV NSs, inhibits JAK/STAT IFN signaling. (A) ISRE reporter assay in the presence of tick-borne Phlebovirus NSs proteins. HEK293T cells were transfected with a Firefly luciferase reporter plasmid under the control of an ISRE promoter and a Renilla luciferase control plasmid in the presence of the indicated amounts of untagged or V5-tagged UUKV, HRTV, or SFTSV NSs proteins. The cells were stimulated with IFN-β (500 U/ml) 24 h posttransfection and lysed 18 h later for analysis. Induction was normalized against the induction control, whose results were assigned a value of 100%. The data represent results of three independent experiments performed in duplicate (n = 3), presented as fold induction means ± SEM. RLU, relative light units. (B) Western blots of transfected cell lysates. (C and D) Cell lysates from HEK293T cells transiently expressing V5-tagged UUKV, HRTV, or SFTSV NSs were immunoprecipitated with an anti-V5 antibody and analyzed by Western blotting with STAT1 and STAT2 antibodies (C) or with a STAT3 antibody (D). (E) Phosphorylation of STAT1 and STAT2 in HEK293T cells upon treatment with recombinant IFN-β. HEK293T cells transiently expressing untagged or V5-tagged UUKV, HRTV, or SFTSV NSs were treated with recombinant IFN-β 24 h posttransfection. Upon 30 min of IFN-β treatment, the cell lysates were harvested and utilized for Western blotting of STAT2, STAT2 phosphorylated at Tyr690, STAT1, STAT1 phosphorylated at Ser727 or Tyr701, actin, and V5 with the appropriate antibodies. (F and G) HeLa cells were transfected with plasmids encoding V5-tagged HRTV or SFTSV NSs. At 24 h posttransfection, the cells were treated with IFN-β (1,000 U/ml) for 30 min, fixed, permeabilized, and probed with (V5) STAT1 (F) and STAT2 (G) antibodies to visualize the subcellular localization of endogenous STATs (red), V5-tagged NSs (green), and DAPI-stained nuclei (blue) by confocal microscopy. Scale bars indicate 20 μm. (H) HEK293T cells transiently expressing untagged or V5-tagged UUKV, HRTV, or SFTSV NSs proteins were treated with 50 ng IFN-γ. At 24 h posttreatment, total cellular RNA was isolated and subjected to RT-qPCR to examine mRNA levels of IP-10 and CXCL10. Fold increase was derived by normalizing relative mRNA levels of the target to GAPDH mRNA levels using a ΔΔCT method.
Veronica V. Rezelj et al. mSphere 2017; doi: /mSphere