Theranostics 2020; 10(10):4422-4436. doi:10.7150/thno.42795

Research Paper

The WW domains dictate isoform-specific regulation of YAP1 stability and pancreatic cancer cell malignancy

Qiang Guo1*, Meiyu Quan1*, Jinglai Dong2, Jing Bai1, Jie Wang1, Rui Han1, Wei Wang2, Yaxin Cai2, Yu-Qing Lv2, Qianjie Chen1, Huijing Xu1, Han-Deng Lyu1, Liancheng Deng2, Depu Zhou1, Xueyuan Xiao3, Stijn De Langhe4, Daniel D. Billadeau5, Zhenkun Lou5, Jin-San Zhang1,2,5,6✉

1. School of Pharmaceutical Sciences, Wenzhou Medical University, Wenzhou, Zhejiang 325035, China
2. Center for Precision Medicine, the First Affiliated Hospital of Wenzhou Medical University, Wenzhou, Zhejiang 325000, China
3. Key Laboratory of Cell Proliferation and Regulation Biology, Ministry of Education, Beijing Normal University, Beijing 100875, China
4. Department of Medicine, Division of Pulmonary, Allergy and Critical Care Medicine, University of Alabama at Birmingham, Birmingham, 35294-2182 AL, USA
5. Division of Oncology Research, and Schulze Center for Novel Therapeutics, Mayo Clinic, Rochester, MN 55905, USA
6. Institute of Life Sciences, Wenzhou University, Wenzhou, Zhejiang 325035, China
*Equal contribution

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Citation:
Guo Q, Quan M, Dong J, Bai J, Wang J, Han R, Wang W, Cai Y, Lv YQ, Chen Q, Xu H, Lyu HD, Deng L, Zhou D, Xiao X, De Langhe S, Billadeau DD, Lou Z, Zhang JS. The WW domains dictate isoform-specific regulation of YAP1 stability and pancreatic cancer cell malignancy. Theranostics 2020; 10(10):4422-4436. doi:10.7150/thno.42795. Available from http://www.thno.org/v10p4422.htm

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Abstract

YAP1 is a key mediator of the Hippo pathway capable of exerting a profound effect on organ size as well as tumorigenesis. Alternative mRNA splicing of human YAP1 results in at least 8 protein isoforms that differ within the 2nd WW motif and the transcriptional activation domain.

Methods: To investigate the isoform-specific differences in their mRNA expression, transcriptional activity and tumor-promoting function, we cloned cDNA encoding all of the eight YAP1 protein isoforms. Then, we examined their mRNA expression, subcellular localization, transcriptional regulation properties, interactions with key regulatory partners, and protein stability in response to changes in cell density, as well as their effects on pancreatic cancer cell malignancy both in vitro and in vivo.

Results: Multiple YAP1 mRNA isoforms are expressed in commonly used pancreatic cancer lines as well as human pancreatic cancer PDX lines. Based on the analysis of heterologous reporter and endogenous target genes, all YAP1 isoforms are capable of activating transcription, albeit to a different extent. Importantly, we unveiled a marked discrepancy between the mRNA and protein expression levels of the YAP1-1 and YAP1-2 isoforms. We further discovered that the YAP1-2 isoform, which contains two tandem WW motifs, is less stable at the protein level, particularly at high cell densities. Mechanistically, we found that the presence of the 2nd WW motif in YAP1-2 facilitates the de novo formation of the YAP1-2/AMOT/LATS1 complex and contributes to a stronger binding of YAP1-2 to LATS1 and subsequently increased YAP1-2 ubiquitination and degradation by β-TRCP.

Conclusion: Our data reveals a potent effect of YAP1-1 on pancreatic cancer malignancy in vitro and in vivo and provides novel mechanistic insight into isoform-specific and cell density-dependent regulation of YAP1 stability, as well as its impact on cancer malignancy.

Keywords: YAP1, isoform, pancreatic cancer, WW domain, LATS1, protein stability