RT Journal Article SR Electronic T1 TP53 loss initiates chromosomal instability in high-grade serous ovarian cancer JF bioRxiv FD Cold Spring Harbor Laboratory SP 2021.03.12.435079 DO 10.1101/2021.03.12.435079 A1 Daniel Bronder A1 Darawalee Wangsa A1 Dali Zong A1 Thomas J. Meyer A1 René Wardenaar A1 Paul Minshall A1 Anthony Tighe A1 Daniela Hirsch A1 Kerstin Heselmeyer-Haddad A1 Louisa Nelson A1 Diana Spierings A1 Joanne C. McGrail A1 Maggie Cam A1 André Nussenzweig A1 Floris Foijer A1 Thomas Ried A1 Stephen S. Taylor YR 2021 UL http://biorxiv.org/content/early/2021/03/12/2021.03.12.435079.abstract AB High-grade serous ovarian cancer (HGSOC) originates in the fallopian tube epithelium and is characterized by ubiquitous TP53 mutation and extensive chromosomal instability (CIN). While the direct causes of CIN are errors during DNA replication and/or chromosome segregation, mutations in genes encoding DNA replication and mitotic factors are rare in HGSOC. Thus, the drivers of CIN remain undefined. We therefore asked whether the oncogenic lesions that are frequently observed in HGSOC are capable of driving CIN via indirect mechanisms. To address this question, we genetically manipulated non-transformed hTERT-immortalized human fallopian tube epithelial cells to model homologous recombination deficiency (HRD) and oncogenic signalling in HGSOC. Using CRISPR/Cas9-mediated gene editing, we sequentially mutagenized the tumour suppressors TP53 and BRCA1, followed by overexpression of the MYC oncogene. Single-cell shallow-depth whole-genome sequencing revealed that loss of p53 function was sufficient to lead to the emergence of heterogenous karyotypes harbouring whole chromosome and chromosome arm aneuploidies, a phenomenon exacerbated by subsequent loss of BRCA1 function. In addition, whole-genome doubling events were observed in independent p53/BRCA1-deficient subclones. Global transcriptomics showed that TP53 mutation was also sufficient to deregulate gene expression modules involved in cell cycle commitment, DNA replication, G2/M checkpoint control and mitotic spindle function, suggesting that p53-deficiency induces cell cycle distortions that could precipitate CIN. Again, loss of BRCA1 function and MYC overexpression exacerbated these patterns of transcriptional deregulation. Thus, our observations support a model whereby the initial loss of the key tumour suppressor TP53 is sufficient to deregulate gene expression networks governing multiple cell cycle controls, and that this in turn is sufficient to drive CIN in pre-malignant fallopian tube epithelial cells.SUMMARY STATEMENT High-grade serous ovarian cancer is defined by TP53 mutation and chromosomal instability, the cause of which remains poorly understood. We developed a novel model system that implicates cell cycle deregulation upon p53-loss as cause of CIN.Competing Interest StatementThe authors have declared no competing interest.