Abstract B43: Disruption of the YAP-LATS2 feedback loop switches ovarian cells from YAP-induced senescence to malignant transformation

Abstract

Abstract Introduction: Dysregulation of the Hippo signaling pathway leads to tumorigenesis in many organs and tissues. Our previous studies show that Yes-associated protein (YAP) induces tumorigenesis in immortalized ovarian surface epithelial cells and fallopian tube secretory epithelial cells. However, the role of Hippo/YAP signaling pathway in primary human ovarian cells is unknown. Aims: The present study seeks to: 1) determine the role of the Hippo/YAP pathway in primary human ovarian cells and 2) investigate the molecular mechanism by which interruption of the Hippo pathway regulates ovarian cell malignant transformation. Methods: Primary human ovarian surface epithelial (hOSE) cells and granulosa cells (hGCs) were employed as cellular models to determine potential roles of the core components of the Hippo/YAP pathway in ovarian cells. CRISPR/Cas9-based gene knockout system, lentiviral-based gene expression system, and siRNAs were utilized to manipulate the expression and activities of the major components of the Hippo/YAP pathway. Soft agar assays and xenograft mouse models were used to examine the role of the Hippo/YAP pathway in tumorigenesis. Results: Ectopic expression of YAP, the major oncogenic effector of the Hippo pathway, induced cell cycle arrest and cellular senescence in cultured primary hOSE cells and hGCs. Importantly, we found that LATS2, a major upstream suppressor of YAP, was elevated in both natural replicative and YAP-induced senescence. Knockout of LATS2 in primary hOSE cells not only diminished natural replicative senescence, but also prevented YAP-induced cellular senescence. Overexpression of LATS2 in primary hOSE cells sped the progression of natural replicative and YAP-induced senescence. Further studies showed that constitutive activation of YAP stimulated the expression of LATS2 in hOSE cells, indicating that YAP and LATS2 formed a negative feedback loop to regulate cellular senescence. Intriguingly, we found that constitutive activation of YAP in LATS2-deficient hOSE cells induced malignant transformation and tumor formation in a xenograft mouse model. Finally, our mechanistic studies showed that the ectopic expression of LATS2 in primary hOSE cells significantly increased expression of several major components of the DREAM (dimerization partner, RB-Like, E2F, and multi-vulval class B) complex, which represses gene expression during cellular quiescence, suggesting that the Hippo/YAP pathway may control cell fate via regulating assembly of DREAM complex. Conclusion: Our results suggest that LATS2 and YAP, two major components of the Hippo/YAP pathway, form a negative feedback loop to control cellular senescence and prevent ovarian cells from malignant transformation. Disruption of the Hippo pathway and the subsequent loss of the YAP-LATS2 negative feedback system may switch ovarian cells from YAP-induced senescence to tumorigenesis. Citation Format: Chunbo He, Xiangmin Lv, Huang Cong, Guohua Hua, Bowen Ma, Xingcheng Chen, Peter C. Angeletti, Jixin Dong, Jin Zhou, Bo Rueda, John S. Davis, Cheng Wang. Disruption of the YAP-LATS2 feedback loop switches ovarian cells from YAP-induced senescence to malignant transformation. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr B43.