The Hippo pathway is an evolutionarily conserved signaling pathway that regulates proliferation and apoptosis to control organ size during developmental growth. Yes-associated
protein 1 (YAP1), the terminal effector of the Hippo pathway, is a transcriptional co-activator and a potent growth promoter that has emerged as a critical oncogene. Overexpression of YAP1 has been implicated in promoting resistance to chemo-, radiation and targeted
therapy in various
cancers. However, the role of YAP1 in radioresistance in
triple-negative breast cancer (TNBC) is currently unknown. We evaluated the role of YAP1 in radioresistance in TNBC in vitro, using two approaches to inhibit YAP1: 1) genetic inhibition by YAP1 specific
shRNA or
siRNA, and 2) pharmacological inhibition by using the small molecule inhibitor,
verteporfin that prevents YAP1 transcriptional activity. Our findings demonstrate that both genetic and pharmacological inhibition of YAP1 sensitizes TNBC cells to radiation by inhibiting the EGFR/PI3K/AKT signaling axis and causing an increased accumulation of DNA damage. Our results reveal that YAP1 activation exerts a protective role for TNBC cells in
radiotherapy and represents a pharmacological target to enhance the anti-
tumor effects of
DNA damaging modalities in the treatment of TNBC.