Role of TopBP1 in transformation of 3D breast acini cultures

Abstract

TopBP1 is an important mediator protein involved in the cell cycle checkpoint signaling pathway that is activated when there are single strand lesions on DNA. TopBP1 has structural and functional similarity to BRCA1 (a tumor suppressor gene). However, there are contradicting reports suggesting the role of TopBP1 either as an oncogene or a tumor suppressor gene. The primary objective of the study was to investigate the role of TopBP1 in cellular transformation of breast epithelial cells. 3D “on-top” culture of MCF10A cells was used as a model system because of its close similarity to the “in-vivo” glandular architecture. MCF10A cells over-expressing TopBP1 when grown on Matrigel® for 16 days formed acini with larger surface area than the control MCF10A cells. An increase in nuclear size was also observed. TopBP1 over-expressing cells showed disruption of basal polarity which is one the markers of transformation. An increase in collective cell migration was observed in TopBP1 over-expressing MCF10A cells. An increase in MMP activation, one of the key features of invading cells, was also observed, suggested the role of over-expressed TopBP1 in invasion. However, only slight difference was observed in the levels of the various EMT markers in TopBP1-MCF10A acini at protein level. There was no chemoresistance induced in TopBP1 over-expressing cells. Preliminary results suggest that TopBP1 can induce transformation of breast epithelial cells.