Multinucleation Associated DNA Damage causes quiescence despite compromised p53

Nuclear atypia is one of the earliest hallmarks of cancer progression. How distinct forms of nuclear atypia differently impact cell fate is not understood at the molecular level. Here, we perform single-cell tracking studies to determine the immediate and long-term impact of multinucleation or misshapen nuclei and reveal a significant difference between multinucleation and micronucleation, a catastrophic nuclear atypia known to promote genomic rearrangements and tumour heterogeneity. Tracking the fate of newborn cells exhibiting various nuclear atypia shows that multinucleation, unlike other forms of nuclear atypia, blocks proliferation in p53-compromised cells. Because compromised p53 is seen in over 50% of cancers, we explored how multinucleation blocks proliferation and promotes quiescence. Multinucleation increases 53BP1-decorated nuclear bodies (DNA damage repair platforms), along with a heterogeneous reduction in transcription and protein accumulation across the multi-nucleated compartments. Importantly, Multinucleation Associated DNA Damage (MADD) associated 53BP1-bodies remain unresolved for days, despite an intact NHEJ machinery that repairs laser-induced DNA damage within minutes. This persistent MADD signalling blocks the onset of DNA replication and is associated with driving proliferative G1 cells into quiescence, revealing a novel replication stress independent cell cycle arrest caused by mitotic lesions. These findings call for segregating protective and prohibitive nuclear atypia to inform therapeutic approaches aimed at limiting tumour heterogeneity. ### Competing Interest Statement The authors have declared no competing interest.