Abstract LB-096: SMARCB1-mediated SWI/SNF complex function is essential for enhancer regulation

The gene encoding SMARCB1 (SNF5/INI1/BAF47), a core subunit of the SWI/SNF (BAF) chromatin remodeling complex, is biallelically inactivated in nearly all rhabdoid tumors (RTs), highly aggressive and lethal cancers of early childhood. RTs are among the most genomically stable cancers, suggesting an epigenetic mechanism by which SMARCB1 loss drives cancer. Here, we show that despite having indistinguishable mutational landscapes, human RTs show distinct H3K27ac signatures at enhancers that reveal remnants of differentiation programs. In elucidating the mechanism underlying RTs, we find that SMARCB1 is not only essential for the integrity and abundance of SWI/SNF complexes, but also facilitates their targeting to appropriate enhancers. Loss of SMARCB1 alters enhancer targeting—markedly impairing SWI/SNF binding to typical enhancers, particularly those required for differentiation, while maintaining SWI/SNF binding at super-enhancers (SEs). We show that these retained SEs are essential for RT survival, including some that are shared across all RT types, such as SPRY1, and other lineage-specific SEs like SOX2 in brain-derived RTs. Taken together, our findings reveal a novel chromatin-based epigenetic mechanism underlying the tumor suppressive activity of SMARCB1. Citation Format: Xiaofeng Wang, Ryan Lee, Burak Alver, Jeffrey Haswell, Su Wang, Emma Troisi, Bradley Bernstein, Peter Park, Charles Roberts. SMARCB1-mediated SWI/SNF complex function is essential for enhancer regulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-096. doi:10.1158/1538-7445.AM2017-LB-096