MSI-H tumors hijack TREX1 to suppress intrinsic cGAS–STING pathway. (A) The heatmap of genes in four groups from RNA-seq data. (B) The Venn diagram of upregulated genes from RNA-seq data of 4T1-Trex1^−/−Mlh1^−/− (day 90) vs. 4T1-Mlh1^−/− (day 90) and 4T1-Trex1^−/− vs. 4T1 WT. The figure indicates there are 182 overlap genes from two groups. (C) Dot plot shows the significantly enriched hallmark pathways for specific high-expression genes in 4T1-Trex1^−/−Mlh1^−/− (day 90) vs. 4T1-Mlh1^−/− (day 90) cells; the point color indicates the adjusted P value, and the point size indicates the upregulated gene count in each signal pathway. (D) 4T1 (Mlh1^−/− day 93) cells (n = 3/group) were collected for Isg15 mRNA detection by RT-qPCR. (E and F) MC38 cells (n = 3/group) were collected for Ifnb1 (E) and Cxcl10 (F) mRNA detection by RT-qPCR. (G) C57BL/6 mice (n = 5) were transplanted s.c. with 1 × 10⁷ MC38 WT or MC38-Trex1^−/− cells; 15 days later, tumors were removed, and the expression of MHC-I in tumor cells was validated by flow cytometry. MFI, mean fluorescence intensity. (H and I) MFC, MFC-Trex1^−/−, MFC-Mlh1^−/− (day 78), and MFC-Trex1^−/−Mlh1^−/− (day 78) cells (n = 3/group) were collected for Ifnb1 (H) and Cxcl10 (I) mRNA detection by RT-qPCR. (J and K) MC38, MC38-Trex1^−/−, 4T1, 4T1-Trex1^−/−, 4T1 Mlh1^−/− (day 108), and 4T1-Mlh1^−/−Trex1^−/− (day 105) cells were collected for analysis of MSI score (J) and TMB (K) through WES data. Data indicate mean ± SEM and are representative of three (D–I) independent experiments. The statistical analysis was performed by unpaired Student’s two-tailed t test in D–I. *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001.