PBRM1-dependent PBAF targeting is required for EMT and metastasis in breast cancer.

SWI/SNF chromatin remodelers are represented by three biochemically distinct subcomplexes, the abundant cBAF and the less abundant PBAF and GBAF. Genetics have identified important roles for PBAF in development and disease; however, relating PBAF-mediated phenotypes to biochemical function in chromatin regulation and gene activation has been challenging. Here, we show that the PBRM1 subunit of PBAF is critical for the completion of TGFβ1-mediated epithelial-mesenchymal transition (EMT) of mammary cells in vitro as well as the metastasis of murine breast cancers in vivo. Using epigenomics to profile different stages of EMT, we find that PBRM1 is necessary for targeting PBAF to inducible promoters marked by H3K14ac. We further find that PBRM1 facilitates DNA accessibility at sites bound by TGFβ1-inducible transcription factors, such as Atf3, for the induction of genes involved in migration, cell survival, and inflammation, providing evidence that PBAF is a vulnerability in late-stage metastatic cancers.