Abstract 3017: Inhibition of YAP/TAZ-dependent transforming properties in LATS1/2 deleted RPE1 cells by MAPKAPK5 targeting
Authors: Kim Min Hwan , Kim Joon 
Published: July 2017

Abstract
Purpose: Recent evidence suggests the Hippo pathway effectors YAP/TAZ play important roles in tumor pathogenesis, including tumorigenesis, metastasis, and drug resistance. Loss of LATS1/2, the negative regulators of YAP/TAZ, has been reported in various human tumors, and suggested to activate YAP/TAZ in tumorigenic process. However, the molecular consequence of LATS1/2 genetic loss in benign human cells has not been addressed, and therapeutic targets for tumors with LATS1/2 loss have not been explored. We aimed to investigate the transforming potential of LATS1/2 loss in human RPE1 cells, and to find targetable kinases that support YAP/TAZ activation in tumors with LATS1/2 loss
Method: To examine the effect of LATS1/2 loss, both LATS1 and LATS2 alleles were deleted by CRISPR-Cas9 genome editing in RPE1-hTERT cells. YAP/TAZ activity of LATS1/2-null RPE1 cells was measured by immunofluorescence (IF) staining and qRT-PCR. Transforming properties of LATS1/2 loss were monitored on both 2-dimensional (2D) and 3D culture, and the centrosome number and DNA contents of cells were determined by IF and propidium iodide staining. LATS1/2-null RPE1 cells were subjected to an image-based kinome-wide siRNA library screening for identifying YAP/TAZ downregulating hits.
Results: The LATS1/2-null RPE1 cells showed persistent nuclear localization and transcriptional activation of YAP/TAZ. In contrast to wild-type RPE1 cells, the LATS1/2-null RPE1 cells showed high proliferation rate, loss of contact inhibition, and sphere formation capacity in matrigel 3D culture, demonstrating transforming activity of LATS1/2 loss. Moreover, LATS1/2 knockout caused genomic instability and centrosome overduplication in RPE1 cells that might be related to defects in mitotic checkpoint regulation. Next, we performed an image-based siRNA library screening to find potential therapeutic targets for tumors with LATS1/2 loss. We found that the inhibition of a p38 MAPK pathway component, MAPKAPK5, suppresses YAP/TAZ nuclear localization and activation in LATS1/2-null RPE1 cells. MAPKAPK5 physically interacted with YAP, and RNAi-mediated MAPKAPK5 inhibition decreased YAP/TAZ protein level and transcriptional activity. MAPKAPK5 depletion resulted in suppression of LATS1/2-null RPE1 cell proliferation on 2D culture as well as sphere formation capacity on 3D culture. Conversely, constitutively active MAPKAPK5 mutant expression in RPE1 cells induced YAP/TAZ nuclear enrichment.
Conclusion: These results suggest that LATS1/2 genetic loss drives transforming properties in human RPE1 cells, and MAPKAPK5 inhibition suppresses YAP/TAZ activation induced by LATS1/2 loss. We suggest that MAPKAPK5 is a novel positive regulator of YAP/TAZ and may serve as a therapeutic target for YAP/TAZ-driven tumors.
Citation Format: Min Hwan Kim, Joon Kim. Inhibition of YAP/TAZ-dependent transforming properties in LATS1/2 deleted RPE1 cells by MAPKAPK5 targeting [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 3017. doi:10.1158/1538-7445.AM2017-3017