YAP1 inhibition radiosensitizes triple negative breast cancer cells by targeting the DNA damage response and cell survival pathways

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// Daniel Andrade 1 , Meghna Mehta 1 , James Griffith 1 , Janani Panneerselvam 2 , Akhil Srivastava 2 , Tae-Dong Kim 3 , Ralf Janknecht 3, 4 , Terence Herman 1, 4 , Rajagopal Ramesh 2, 4 and Anupama Munshi 1, 4 1 Department of Radiation Oncology, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA 2 Department of Pathology, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA 3 Department of Cell Biology, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA 4 Stephenson Cancer Center, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA Correspondence to: Anupama Munshi, email: anupama-munshi@ouhsc.edu Keywords: yes associated protein 1, triple negative breast cancer, DNA damage, radiotherapy, verteporfin Received: June 14, 2017      Accepted: September 29, 2017      Published: October 20, 2017 ABSTRACT 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.