Smarca4 (Brg1) is a haploinsufficient B-cell tumor suppressor that fine-tunes centrocyte cell fate decisions [rajiAUD_rna]

SMARCA4 encodes one of two mutually-exclusive ATPase subunits in the Brg/Brm associated factor (BAF) complex that is recruited by transcription factors to drive chromatin accessibility and transcriptional activation. SMARCA4 is among the most recurrently mutated genes in human cancer, including ~30% of germinal center (GC)-derived Burkitt lymphomas. In mice, GC-specific Smarca4 haploinsufficiency cooperates with Myc over-expression to drive lymphomagenesis. Furthermore, monoallelic Smarca4 deletion drove GC hyperplasia with centroblast polarization via significantly increased rates of centrocyte recycling to the dark zone. Mechanistically, Smarca4 loss reduced the activity of transcription factors that are activated in centrocytes to drive GC-exit, including SPI1 (PU.1), IRF family and NFκB. Loss of activity for these factors phenocopied aberrant Bcl6 activity within murine centrocytes and human BL cells. Smarca4 therefore facilitates chromatin accessibility for transcription factors that shape centrocyte trajectories, and loss of fine-control of these programs biases towards centroblast cell-fate and GC hyperplasia. Gene expression analysis of SMARCA4 protein degradation in an established auxin-inducible degron system