BRG1 is the catalytic ATPase subunit of the chromatin remodeling SWI/SNF complex. Expression of the SWI/SNF complex is altered across multiple cancer types. Medulloblastoma is the most common malignant brain tumour affecting children, accounting for nearly 20% of cases. Four molecular subgroups of medulloblastoma can be categorised based on transcriptional and epigenetic profiles. In the Sonic Hedgehog (SHH) subgroup of medulloblastoma, BRG1 has been implicated in driving expression of oncogenes to promote cell proliferation. However, there is a lack of understanding about how BRG1 is working at an epigenetic level to influence chromatin dynamics and mitotic organisation that ultimately contribute to cancer pathway regulation and cell survival.
We performed live-cell imaging of SHH-medulloblastoma cell lines to explore BRG1-mediated chromatin dynamics. When ONS-76 and Daoy cells were treated with a BRG1 inhibitor (BRM014), they showed altered cell cycling and a decrease in normal mitotic outcomes. The FUCCI cell system, a protein-based three-colour cell cycle indicator, was used to classify cell division outcomes and record the duration of G1, S/G2 and M phases to observe if there were specific delays in the presence of the BRG1 inhibitor. We observed increases in the length of all cell cycle phases. Fluorescently labelled chromatin (H2B-mCherry) was tracked through mitosis, with chromatin defects such as lagging chromosomes, DNA bridges and micronuclei identified. These chromatin phenotypes have been associated with increased mitotic stress and genome instability in cancer cells. These insights expand upon the current understanding of the role BRG1 plays in SHH-medulloblastoma, with potential for findings to be applicable to other cancer types where BRG1 exhibits similar oncogenic activities.