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Fig. 6 FTR42 facilitates IRF7 mRNA decay to downregulate IFN response in vitro (A–C) FTR42 attenuated IRF7 protein levels independently of protein degradation. CAB cells seeded in 3.5 cm2 dishes overnight were transfected with IRF7, together with FTR42 (1 μg ecah) for different time points (A) or with FTR42 at increasing amounts (B) for 30 h; or CAB cells seeded in 12-well plates were transfected for 24 h with FTR42 and IRF7 (0.5 μg each), followed by treatment with MG132, NH4Cl, or chloroquine for additional 6 h (C). (D–F) FTR42 downregulated IRF7-trigged IFN response by attenuating IRF7 transcription. CAB cells seeded in 3.5 cm2 dishes were transfected with IRF7 and FTR42 (1 μg each) for different time points (D and E), or CAB cells seeded in 6-well plates were transfected for 24 h with IRF7 (0.5 μg) and FTR42 at increasing amounts (F), followed by RT-qPCR detection of mRNA expression from the transfected FTR42 and IRF7 plasmid (D and F), or from cellular ifn, mx and viperin (E and F). (G) FTR42-mediated reduction of IRF7 protein was blocked by CHX. CAB cells seeded in 12-well plates overnight were transfected for 24 h with IRF7 (0.5 μg) and FTR42 at increasing doses (0, 0.2, 0.4, 0.8 μg), followed by addition of CHX or DMSO as control. Another 6 h later, the cells were collected for western blotting (left panel), followed by densitometric quantification of IRF7 protein expression normalized to β-actin (right panel). (H) FTR42-mediated reduction of IRF7 mRNA was not impaired by ActD. CAB cells seeded in 12-well plates overnight were transfected as (F). 24 h later, ActD (1 μg/mL) was added to the plates for 4 h or 7 h, followed by RT-qPCR detection of mRNA from the transfected IRF7 plasmid. Data were shown as mean ± SD (N = 3). p values were calculated using Student’s t test. ∗∗p < 0.01, ∗∗∗p < 0.001.