ATP-dependent chromatin remodellers are actively recruited to chromatin to position nucleosomes and regulate chromatin structure. Chromatin remodelling plays a central role in transcriptional control, but emerging data indicates it also contributes to other aspects of chromatin biology including cell cycle control, DNA repair and DNA replication.
A whole genome CRISPR screen conducted in our laboratory identified that the chromatin remodeller BRG1 putatively functioned in the cellular response to replication stress. We depleted BRG1 from both WT and E6E7 IMR90 fibroblasts and treated them with aphidicolin to induce replication stress. We found a reduced response to replication stress, measured by CHK1-S345 in both cell lines. Correspondingly, BRG1 depletion in IMR90 fibroblasts increased in inter-origin distance measured in molecular combing assays, consistent with reduced origin firing. Interrogating public ChIP-seq data of K562 and HeLa cells identified a significant overlay in BRG1 binding sites with replication of origin proteins ORC1 and ORC2, and components of the MCM2-7 replicative helicase, consistent with BRG1 localization directly to replication origins.
As BRG1 functions in promoting active transcription, we examined the expression of replication initiation factors in BRG1 depleted IMR90 cultures. We found there was reduced expression of ORC6, MCM5 and CHK1 in WT but not E6E7 cells.
Together the data suggest a direct role for BRG1 at replication origins and an impact on replication firing in BRG1 depleted cells. We are currently expanding this research to investigate the underlying mechanism of BRG1 in DNA replication and genome stability.