Loss of sumoylation triggers a spontaneous IFN response in THP-1 cells. THP-1 monocytes were targeted by lentiCRISPR endoding the indicated gRNAs. (A) Western blot evaluation of the indicated proteins. (B and C) Evaluation of IFNB1, IFI27, and ISG15 mRNA expression is shown in PMA-differentiated THP-1s by quantitative RT-PCR. (D) THP-1 monocytes were transduced with lentiviruses encoding GFP, wild-type SAE2 (WT), and a catalytic mutant of SAE2 (C173S), and then transduced with a lentiCRISPR lentivirus encoding Cas9 and the indicated gRNA. Western blot evaluation of the indicated proteins. (E) Evaluation of IFNB1, IFI27, and ISG15 mRNA expression in PMA-differentiated THP-1s by quantitative RT-PCR. Statistical analysis in B was performed using a one-way ANOVA and comparing control cells to targeted cells. In D, a two-way ANOVA was used, comparing GFP expressing THP-1s to WT and C173S reconstituted cells. Both tests corrected for multiple comparisons using the Holm–Sidak method. n = 3–5 where n is the number of unique polyclonal cell lines. n.s., not significant; *P ≤ 0.05; **P ≤ 0.01; ****P ≤ 0.0001.