Abstract IA019: Ectopic levels of low-complexity domain interactions repress endogenous oncogenic transcription

Abstract Mammalian transcription factors (TFs) ubiquitously contain intrinsically disordered low-complexity domains (LCDs) that perform transactivation functions. Recent studies have shown that dynamic, multivalent, and selective interactions between TF LCDs play an essential role in transactivation, but how such interactions mediate gene transcription remains unclear. It has been proposed that liquid-liquid phase separation (LLPS) of TFs driven by extensive LCD-LCD interactions is the mechanism underlying transactivation. Here, we investigate how tuning the level and localization of LCD-LCD interactions in vivo affects transcription of endogenous human genes. By quantitative single-cell imaging, we reveal that efficient gene activation by the oncogenic TF EWS/FLI1 requires narrow optimum of LCD-LCD interactions at its target genes associated with GGAA microsatellites. Increasing LCD-LCD interactions toward putative LLPS represses transcription of these genes in Ewing sarcoma cells. Likewise, ectopically creating LCD-LCD interactions to sequester EWS/FLI1 into a well-documented LLPS compartment, the nucleolus, represses EWS/FLI1 -driven transcription and inhibits malignant transformation of Ewing sarcoma. In addition, using live-cell single-molecule imaging, we show that a TF diffuses significantly more slowly in the nucleolus than in the nucleoplasm, demonstrating an important impact of LLPS on TF dynamic behaviors and single-molecule diffusion measurement as an effective approach to diagnose LLPS in vivo. Our findings show how altering the balance of LCD-LCD interactions can influence transcriptional regulation and suggest a potential therapeutic strategy for targeting disease-causing TFs. Citation Format: Shasha Chong. Ectopic levels of low-complexity domain interactions repress endogenous oncogenic transcription. [abstract]. In: Proceedings of the AACR Special Conference: Cancer Epigenomics; 2022 Oct 6-8; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2022;82(23 Suppl_2):Abstract nr IA019.