Super enhancer dysregulation in rhabdoid tumor cells is regulated by the SWI/SNF ATPase BRG1
Mutations in the SWI/SNF chromatin remodeling complex occur in ~20% of cancers. In rhabdoid tumors defined by loss of the SWI/SNF subunit SMARCB1, dysregulation of enhancer-mediated gene expression is pivotal in driving oncogenesis. Enhancer dysregulation in this setting is tied to retention of the SWI/SNF ATPase BRG1—which becomes essential in the absence of SMARCB1—but precisely how BRG1 contributes to this process remains unknown. To characterize how BRG1 participates in chromatin remodeling and gene expression in SMARCB1-deficient cells, we performed a genome-wide characterization of the impact of BRG1 depletion in multiple rhabdoid tumor cell lines. We find that although BRG1-regulated open chromatin sites are distinct at the locus level, the biological characteristics of the loci are very similar, converging on a set of thematically related genes and pointing to involvement of the AP-1 transcription factor. The open chromatin sites regulated by BRG1 colocalize with histone-marked enhancers and intriguingly include almost all super-enhancers, revealing that BRG1 plays a critical role in maintaining super-enhancer function in this setting. These studies can explain the essentiality of BRG1 to rhabdoid tumor cell identity and survival and implicate the involvement of AP-1 as critical downstream effector of pro-tumorigenic transcriptional programs. Overall design: We used rhabdoid tumor cell lines derived from various tissues and interrogated the contribution of BRG1 to gene regulation using the well-characterized BRG1 chemical degrader called ACBI1. We performed chromatin binding assays, transcriptomic assays, and chromatin accessibility assays.