The oncogenic fusion protein EWS-FLI1 promotes premature ageing of biomolecular condensates by catalyzing fibril formation

Selig, Emily; Romero-Moreno, Alma K; Akula, Shivani; Xu, Xiaoping; Libich, David S.

doi:10.1101/2022.06.04.494830

Cited by 1 publication

(1 citation statement)

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“…The N-terminal low complexity domains of EWSR1::FLI1 are thought to mediate critical functions of EWSR1::FLI1 including recruitment of the SWI/SNF complex to GGAA microsatellite and the formation of phase separated condensates implicated in enhancing protein-protein interactions and regulating the expression of EWSR1::FLI1 target genes ( 7 , 63 – 65 ). Perturbing these EWSR1::FLI1-containing condensates through overexpression of the low complexity domains of EWSR1 or TAF15 decreases the expression of EWSR1::FLI1-regulated genes without displacing EWSR1::FLI1 from chromatin ( 66 , 67 ). Additionally, altering the ability of EWSR1::FLI1 to participate in phase separation by mutating the critical tyrosine residues in the N-terminus decreases SWI/SNF recruitment, chromatin accessibility, and deposition of enhancer-associated histone PTMs at EWSR1::FLI1-bound GGAA loci, and inhibits the expression of EWSR1::FLI1-regulated genes ( 7 ).…”

Section: Discussionmentioning

confidence: 99%

MS0621, a novel small-molecule modulator of Ewing sarcoma chromatin accessibility, interacts with an RNA-associated macromolecular complex and influences RNA splicing

et al. 2023

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Ewing sarcoma is a cancer of children and young adults characterized by the critical translocation-associated fusion oncoprotein EWSR1::FLI1. EWSR1::FLI1 targets characteristic genetic loci where it mediates aberrant chromatin and the establishment of de novo enhancers. Ewing sarcoma thus provides a model to interrogate mechanisms underlying chromatin dysregulation in tumorigenesis. Previously, we developed a high-throughput chromatin-based screening platform based on the de novo enhancers and demonstrated its utility in identifying small molecules capable of altering chromatin accessibility. Here, we report the identification of MS0621, a molecule with previously uncharacterized mechanism of action, as a small molecule modulator of chromatin state at sites of aberrant chromatin accessibility at EWSR1::FLI1-bound loci. MS0621 suppresses cellular proliferation of Ewing sarcoma cell lines by cell cycle arrest. Proteomic studies demonstrate that MS0621 associates with EWSR1::FLI1, RNA binding and splicing proteins, as well as chromatin regulatory proteins. Surprisingly, interactions with chromatin and many RNA-binding proteins, including EWSR1::FLI1 and its known interactors, were RNA-independent. Our findings suggest that MS0621 affects EWSR1::FLI1-mediated chromatin activity by interacting with and altering the activity of RNA splicing machinery and chromatin modulating factors. Genetic modulation of these proteins similarly inhibits proliferation and alters chromatin in Ewing sarcoma cells. The use of an oncogene-associated chromatin signature as a target allows for a direct approach to screen for unrecognized modulators of epigenetic machinery and provides a framework for using chromatin-based assays for future therapeutic discovery efforts.

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