Abstract
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.
Highlights
The highly condensed chromatin packaged with genomic DNA forms a repressive structure that tends to restrict the access of transcription factors and co-factors to DNA, and relief from this repression by chromatin remodeling is critical for gene transcription [1,2,3]
We provided evidence that Brahma-related gene 1 (Brg1) is preferentially recruited by p53 for inducing a subset of target genes through chromatin remodeling
To rule out the possibility that this was due to clonal variation, we examined the effect of Brg1 knockdown on p53 transcriptional activity in another cell line, MCF7-Brg1-KD-35, and found that DNA damage-mediated induction of p21 was inhibited by Brg1 knockdown (Fig. 2B, compare lanes 3 and 4)
Summary
Brahma; Brg, Brahma-related gene 1; siRNA, small interfering RNA; ChIP, chromatin immunoprecipitation; HA, hemagglutinin. We analyzed p53-mediated induction of p21 and MDM2 using cell lines in which Brm or Brg can be inducibly knocked down. We found that p21 induction is impaired by Brg but not Brm knockdown in MCF7 cells. In Brg1deficient H1299 cells, p21 induction is decreased by Brm knockdown. Brm is necessary for induction of p21 in MCF7 cell in which Brg is stably knocked down. Brm and Brg have little, if any, role in p53-mediated induction of MDM2. We demonstrated that the impaired induction of p21 upon Brg knockdown is at least in part due to decreased p53 binding to the p21 promoter. We provided evidence that Brm and Brg differentially regulate a subset of p53 target genes through chromatin remodeling
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