Precise modulation of BRG1 levels reveals features of mSWI/SNF dosage sensitivity.

Mammalian switch/sucrose nonfermentable (mSWI/SNF) complex regulates chromatin accessibility and frequently shows alterations due to mutation in cancer and neurological diseases. Inadequate expression of mSWI/SNF in heterozygous mice can lead to developmental defects, indicating dosage-sensitive effects of mSWI/SNF. However, how its dosage affects function has remained unclear. Using a targeted protein degradation system, we investigated its dosage-sensitive effects by precisely controlling protein levels of BRG1, the ATPase subunit of the mSWI/SNF complex. We found that binding of BRG1 to chromatin exhibited a linear response to the BRG1 protein level. Although chromatin accessibility at most promoters and insulators was largely unaffected by BRG1 depletion, 44% of enhancers, including 84% of defined superenhancers, showed reduced accessibility. Notably, half of the BRG1-regulated enhancers, particularly superenhancers, exhibited a buffered response to BRG1 loss. Consistently, transcription exhibited a predominantly buffered response to changes in BRG1 levels. Collectively, our findings demonstrate a genomic feature-specific response to BRG1 dosage, shedding light on the dosage-sensitive effects of mSWI/SNF complex defects in cancer and other diseases.