Role of TopBP1 during breast tumorigenesis

Abstract

DNA topoisomerase IIβ -binding protein 1 (TopBP1) is a mediator protein that regulates cell cycle checkpoint signaling pathway. A plethora of studies suggest that TopBP1 protein levels are high and positively associated with various hallmark properties of cancers. Although TopBP1 transcript as well as protein expression levels are high in breast cancers, its role in breast tumorigenesis is yet to be explored. In our studies, we observed that TopBP1 levels are high in premalignant and malignant cells of the MCF10A cancer progression series compared to the non-tumorigenic MCF10A cells. In order to establish the role of TopBP1 in tumorigenesis and other hallmarks of cancers, TopBP1-MCF10A, and shTopBP1-MCF10CA1a cells were cultured in Matrigel. Overexpression of TopBP1 in MCF10A 3D cultures induced hyper proliferation, disruption of polarity and cell-cell junctions. Moreover, TopBP1 overexpressing dissociated cells from acinar cultures exhibited EMT-like phenotype and cancer properties such as increased cell migration, invasion, colony formation capabilities and anchorage-independent growth, indicating acquisition of cellular transformation. Finally, we observed that TopBP1 overexpressing cells formed tumours in athymic mice thereby confirming their tumorigenic potential. Mechanistically it was confirmed that overexpression of TopBP1 led to the mutations in TP53 and other genomic insults. To summarise, we observed that ectopic expression of TopBP1 transforms MCF10A breast epithelial cells into cancer cells. These transformed cells harbour phenotypic and genotypic characters of cancerous cells.