Reduced cell death, invasive and angiogenic features conferred by BRCAI-deficiency in mammary epithelial cells transformed with H-Ras

摘要

To investigate the role of tumor suppressors BRCAI and p53 proteins in human breast tumorigenesis, we transformed immortalized human mammary epithelial cells, MCFIOA, with or without BRCAI/p53 gene-specific knockdowns. Stable knockdown of BRCAI alone in MCFIOA cells led to centrosome amplification, impaired p53 protein stability, increased sensitivity towards DNA-damaging agents, defective chromosomal condensation at mitosis and elevated protein levels of cyclin Dl and c-myc. While over-expression of mutant H-Ras transformed MCFIOA cells, depletion of BRCAI dramatically enhanced the in vivo tumorigenesis that was associated with higher levels of VEGF, enhanced vascularization and less apoptosis in the BRCAI-deficient Ras-transformed tumors. The Ras-transformed BRCAI-deficient tumors exhibited features of the epithelial-to-mesenchymal transition, appeared to secrete matrix metalloproteases as visualized by in vivo bio-imaging of tumors using fluorescent probe MMP680, and were locally metastatic to lymph nodes. Our results suggest that loss of BRCAI function may contribute to the aggressiveness of Ras-MAPK driven human breast cancer with associated increase in levels of cyclin Dl and c-myc, enhanced MAPK activity, angiogenic potential & invasiveness. This mammary xenograft tumor model may be useful as a tool to understand human breast tumor angiogenesis and metastasis, as well as to test candidate therapeutics.