BRG1 cooperates with PLK1 to regulate dormant origin activation during S phase.

The ATP-dependent chromatin remodeler BRG1 is well-established in the regulation of gene expression, DNA replication, homologous recombination, DNA damage repair, and apoptosis. While its genome-wide occupancy has primarily been linked to transcriptional regulation, its potential role in DNA replication control remains less well defined. In this study, we investigated BRG1s involvement in replication origin regulation by integrating BRG1 ChIP-seq data with replication origin mapping and chromatin state analyses. Our results revealed that BRG1 is preferentially enriched at genomic regions characterized by DNase I hypersensitivity, low GC content, and a capacity to form G-quadruplex structures hallmarks of dormant replication origins. Notably, BRG1-bound sites were also enriched in late-replicating, heterochromatic regions. These findings suggest a specific association of BRG1 with dormant replication origins. To validate this association, we performed functional assays in HeLa cells. BRG1 depletion via siRNA led to reduced replication fork progression and increased activation of dormant origins, consistent with replication stress. Mechanistically, we found that BRG1 physically interacts with the mitotic kinase PLK1. Loss of BRG1 reduced chromatin-bound levels of both BRG1 and PLK1, implicating BRG1 in PLK1 recruitment or stability. Importantly, overexpression of PLK1 in BRG1-depleted cells rescued replication fork progression, supporting a cooperative role for BRG1 and PLK1 in regulating replication through dormant origins. Together, these data uncover a previously unrecognized function for BRG1 in the selective regulation of dormant replication origin firing, acting in concert with PLK1.