ARID1A loss impairs enhancer-mediated gene regulation and drives colon cancer in mice

Charles Roberts and colleagues show that deletion of Arid1a from mouse intestinal epithelium results in invasive adenocarcinomas resembling human colorectal cancer. They further show that ARID1A loss impairs SWI/SNF targeting and enhancer-mediated gene regulation. Genes encoding subunits of SWI/SNF (BAF) chromatin-remodeling complexes are collectively mutated in ∼20% of all human cancers1,2. Although ARID1A is the most frequent target of mutations, the mechanism by which its inactivation promotes tumorigenesis is unclear. Here we demonstrate that Arid1a functions as a tumor suppressor in the mouse colon, but not the small intestine, and that invasive ARID1A-deficient adenocarcinomas resemble human colorectal cancer (CRC). These tumors lack deregulation of APC/β-catenin signaling components, which are crucial gatekeepers in common forms of intestinal cancer. We find that ARID1A normally targets SWI/SNF complexes to enhancers, where they function in coordination with transcription factors to facilitate gene activation. ARID1B preserves SWI/SNF function in ARID1A-deficient cells, but defects in SWI/SNF targeting and control of enhancer activity cause extensive dysregulation of gene expression. These findings represent an advance in colon cancer modeling and implicate enhancer-mediated gene regulation as a principal tumor-suppressor function of ARID1A.