The activity of p53 is differentially regulated by Brm- and Brg1-containing SWI/SNF chromatin remodeling complexes

Brahma (Brm) and Brahma-related gene-1 (Brg1) ATPases share similarities in structure and function, but their presence in human SWI/SNF chromatin remodeling complexes is mutually exclusive. Although Brm and Brg1 can compensate for each other, it is possible that Brm and Brg1 have their unique properties to differentially regulate gene expression in vivo. To explore this, we examined the requirement of Brm and Brg1 for p53-dependent transcription, especially p53-mediated induction of p21 and MDM2, using cell lines in which Brm or Brg1 could be inducibly knocked down. We found that Brg1, but not Brm, is required for p21 induction in MCF7 cells. However, in Brg1-deficient H1299 cells, Brm is also required for p21 induction. Likewise, Brm is necessary for induction of p21 in MCF7 cells in which Brg1 is stably knocked down. In contrast, Brg1 has little, if any, effect on p53-mediated induction of MDM2 in cells that have Brm and vice versa. In addition, we demonstrated that the impaired induction of p21 upon Brg1 knockdown is at least in part due to decreased p53 binding to the p21 promoter. Taken together, we provided evidence that Brg1 is preferentially recruited by p53 for inducing a subset of target genes through chromatin remodeling. Thus, we hypothesize that the potential tumor suppressor function for Brg1 is mediated in part through the p53 pathway.