Abstract 3308: SUMOylation-mediated enhancer activity regulates type I interferon pathway

Abstract

Abstract Type I interferon (IFN) pathway plays an important role in innate immunity and anti-tumor immune response. Previous study has reported that SUMOylation represses type I interferon production, and that deletion of the E2 enzyme Ubc9 or SUMO2 or 3 greatly enhanced type I interferon response. However, the detailed mechanism of how SUMOylation regulates type I interferon response in controversial in the literature. In this study, we found that inhibition of the SUMO E1 enzyme with ML-792 significant enhanced type I cytokine IFNβ expression in human monocytes THP1 cell line, up to 1,500 folds. Similar induction was observed in human peripheral blood mononuclear cells (PBMCs). However, ML-792 treatment showed no effect in IFNβ promoter reporter assay, indicating that ML-792 induced IFNβ expression is not through activation of the transcription factors, such as through the STING pathway, that act on the promoter region. Genome browser ENCODE analysis showed SET Domain Bifurcated Histone Lysine Methyltransferase 1 (SETDB1) binds at a ifnb1 enhancer region, known as L2, located ~9kb upstream of ifnb1 transcription start site (TSS). Knockdown of SETDB1 increased IFNβ level resulting in enhanced type I IFN downstream gene expression, indicating that SETDB1 is a transcriptional suppressor of ifnb1 gene. Chromatin immunoprecipitation (ChIP) assay determined that ML-792 treatment or knockdown of the catalytic subunit of the SUMO E1 greatly reduced SETDB1 SUMOylation and occupancy at ifnb1 gene enhancer region. Mutation of SETDB1 SUMOylation sites (4KR, with all 4 SUMOylation sites mutated: K355R, K1032R, K1050R, K1069R) also reduced SETDB1 binding at ifnb1 gene enhancer region shown by ChIP assay, demonstrating that SUMOylation is required for SETDB1 binding to ifnb1 gene enhancer region. In conclusion, our study identified SETDB1 as a novel transcriptional suppressor of ifnb1gene. In addition, we found that at least one mechanism of SUMOylation in preventing type I IFN production is through regulating SETDB1 binding to the enhancer of ifnb1 and consequently histone methylation. Citation Format: Li Du, Yuan Chen, Steven Rosen. SUMOylation-mediated enhancer activity regulates type I interferon pathway [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3308.