EWSR1::ATF1 Orchestrates the Clear Cell Sarcoma Transcriptome in Human Tumors and a Mouse Genetic Model

Clear cell sarcoma (CCS) is a rare, aggressive malignancy that most frequently arises in the soft tissues of the extremities. It is defined and driven by expression of one member of a family of related translocation-generated fusion oncogenes, the most common of which is EWSR1::ATF1. The EWSR1::ATF1 fusion oncoprotein reprograms transcription. However, the binding distribution of EWSR1::ATF1 across the genome and its target genes remain unclear. Here, we interrogated the genomic distribution of V5-tagged EWSR1::ATF1 in tumors it had induced upon expression in mice that also recapitulated the transcriptome of human CCS. ChIP-sequencing of V5-EWSR1::ATF1 identified previously unreported motifs including the AP1 motif and motif comprised of TGA repeats that resemble GGAA-repeating microsatellites bound by EWSR1::FLI1 in Ewing sarcoma. ChIP-sequencing of H3K27ac identified super enhancers in the mouse model and human contexts of CCS, which showed a shared super enhancer structure that associates with activated genes.