Platinum compounds are the foundation of chemotherapy regimens for non-small cell lung cancer despite poor response rates and limited response duration. In order to identify novel target genes the modulation of which could influence drug sensitivity of lung cancer cells in response to cisplatin, we performed a high-throughput RNAi screen targeting the majority of genes in the human genome. We first transfected PC9 lung cancer cells with an shRNA library containing ∼60,000 individual shRNAs, then identified depleted versus enriched shRNAs following two weeks of cisplatin treatment versus vehicle in surviving cells. Standard quality control studies suggested good correlation among triplicates. After using strict selection criteria, we selected a narrow list of highly depleted genes- genes the activity of which is expected to be required for cell survival in the face of cisplatin therapy, including YAP (Yes associated protein). YAP shRNAs were depleted 80 fold in the cisplatin screen. YAP was initially identified as a protein interacting with the non-receptor tyrosine kinase c-Yes and is considered a nuclear effector of the Hippo pathway that promotes cell growth as a transcription co-activator. To validate this promising target identified in our screen, we first confirmed that an siRNA pool targeting YAP can efficiently knockdown YAP protein expression in multiple lung cancer cell lines, then next examined the effects of YAP knockdown on drug responses. YAP knockdown indeed quite prominently improved sensitivities not only to cisplatin, but also to ionizing radiation in several cell lines. Furthermore, YAP knockdown also induces prominent apoptosis as measured by induction of PARP cleavage concurrent with platinum therapy. Our findings indicate the YAP inhibition is potentially relevant to improve sensitivities to platinum-based chemotherapy and chemoradiation in lung cancer.

Citation Format: Haiying Cheng, Zhenfeng Zhang, Ruth Rodriguez-Barrueco, Jiyang Yu, Jose M. Silva, Simon Cheng, Roman Perez-Soler, Balazs Halmos. Down-regulation of YAP sensitizes lung cancer cells to platinum and ionizing radiation. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2044. doi:10.1158/1538-7445.AM2013-2044