Background: The Hippo signaling pathway is associated with regulation of cell growth and apoptosis. Downstream effectors of this pathway, YAP and its paralog, TAZ, interact with TEA domain (TEAD) transcription factors leading to cell proliferation and anti-apoptosis. As a result, YAP and TAZ have emerged as attractive anti-cancer therapeutic targets. Several studies, including our previous report, have noted the individual effects of YAP or TAZ ablation; however, consequences of dual inhibition have not yet been investigated in lung cancer. We hypothesize that dual inhibition of YAP and TAZ will lead to more pronounced cytotoxicity than each knockdown alone as a result of diminished compensatory mechanism by the remaining family member.

Methods: NSCLC cell lines, such as PC9 and A549, were transfected with individual YAP1, TAZ siRNA or a combination of both siRNAs. Western blotting was performed to determine the levels of YAP1 and TAZ proteins following knockdown. Quantitative RT-PCR was also performed to confirm effective YAP1 and TAZ knockdown. In addition, gene and protein expression of downstream targets, such as CTGF and Cyr61, were assessed. Clonogenic assays were performed to determine cell survival.

Results: Successful siRNA-mediated YAP and TAZ ablation were confirmed with Western blot and qRT-PCR. The expression of the Hippo-YAP/TAZ downstream targets, CTGF, Cyr61 and AXL, were also reduced accordingly. Moreover, dual knockdown of YAP and TAZ led to a more pronounced inhibition of cell survival/proliferation than ablation of individual genes alone. In addition, dual inhibition of YAP/TAZ exhibited significantly diminished levels of the mesenchymal markers, vimentin and N-cadherin, and increased levels of the epithelial marker, E-cadherin. EMT has been recognized as an essential process during lung cancer tumor migration and metastasis.

Conclusion: Our findings show that dual inhibition of YAP1 and TAZ are synergistic in blocking NSCLC cell survival signaling. Thus, dual inhibition may serve as a better therapeutic strategy in targeting the Hippo pathway than sole YAP1 blockade in the management of NSCLC.

Citation Format: Elaine Shum, Huijie Liu, Liang Zhu, Roman Perez-Soler, Balazs Halmos, Haiying Cheng. Synergistic effects of dual inhibition of YAP1 and TAZ in non-small cell lung cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 518. doi:10.1158/1538-7445.AM2017-518