PHF6 cooperates with SWI/SNF complexes to facilitate transcriptional progression[CUT&RUN]

Genes encoding subunits of SWI/SNF chromatin remodeling complexes are mutated in nearly 25% of cancers. The SWI/SNF subunit SMARCB1 is the driving mutation in nearly all cases of rhabdoid tumor (RT), highly malignant cancers of childhood. While loss of SMARCB1 drives cancer, its absence also creates unique dependencies, which can illuminate mechanism and reveal potential therapeutic vulnerabilities. To identify such dependencies we undertook a genome-scale CRISPR screen comparing RT cell lines to 800 other cancer lines. We identified PHF6 as specifically essential for RT cell survival. Germline mutations in both SMARCB1 and PHF6 cause Coffin-Siris syndrome, and somatic mutations in PHF6 or SWI/SNF occur in T-ALL, suggesting a mechanistic link. We establish that PHF6 co-localizes with residual SWI/SNF complexes at active promoters and enhancers. We find that PHF6 is specifically required for H3K14ac accumulation immediately downstream of active promoters and for release of paused Pol II. Collectively, our work identifies novel integrated roles for PHF6 in chromatin and Pol II regulation, establishes a mechanistic basis for dependence upon PHF6 in RT, and reveals a novel potential therapeutic vulnerability in RT.