Fig. 2: TRIM21 deficiency promotes cytosolic mtDNA release to activate STING signalling.

a–c WT and TRIM21-KO NPC cells were treated with or without IR. a After 48 h, the levels of total and phosphorylated STING, TBK1 and IRF3 were measured by western blot analysis. b Cytosolic DNA accumulation was assessed by IF staining with a dsDNA-specific antibody 24 h after IR. Representative images (scale bar, 10 μm) and quantitative results are shown (n = 30 cells per group). c The abundance of MTATP8 DNA sequence in the cytosolic fraction was measured by qPCR 24 h after IR. d Representative images showing cytosolic mtDNA accumulation in irradiated WT and TRIM21-KO NPC cells 24 h after IR treatment (scale bar, 10 μm). TFAM (mitochondrial transcription factor A, green) not associated with mitochondria (MitoTracker Red CMXRos) was considered as cytosolic mtDNA (as indicated by the white arrows). Quantitative results from 30 cells per group are reported. e The amounts of gDNA (GAPDH) and mtDNA (MTATP8) in control and rho⁰ NPC cells were estimated by qPCR. Rho⁰/control ratios are reported. f MTATP8 abundance in the cytosolic fraction of control and rho⁰ NPC cells 24 h after IR treatment. g, h Control and rho⁰ NPC cells were treated with IR. After 48 h, the levels of phosphorylated STING, TBK1, IRF3, and STAT1 (g) and the relative expression levels of IFNB1, CCL5 and CXCL10 were measured. The results are representative of three independent experiments (a–h). The data are presented as the mean ± SEM; one-way ANOVA with Tukey’s test for multiple comparisons (b–d, f, and h).