Ovarian cancers are the most lethal gynecological cancers. Mechanisms underlying their initiation and progression are unclear. The Hippo signaling pathway plays a critical role in tissue homeostasis and organ size control by regulating cell proliferation. Recent studies have indicated that dysregulation of the Hippo pathway is associated with cancer in various tissues and organs. However, the exact role and mechanisms used by the Hippo pathway in the initiation and progression of ovarian cancer are unclear. The aim of this study is to determine the role and the regulatory mechanism of the Hippo pathway in the initiation and progression of ovarian cancer. Immunohistochemistry was used to analyze the expression of YAP, a major downstream effector of the Hippo signaling pathway, in paraffin-embedded human normal and cancerous ovarian tissues. HOSE (an immortalized normal human ovarian surface epithelial cell line), TOV21G (an epithelial ovarian cancer cell line) and KGN (an ovarian granulosa cell tumor cell line) cells were used as cellular models to analyze cell proliferation and tumorigenesis. Cell proliferation and viability were examined by cell number counting and MTT assays, respectively. Cell cycle was monitored by flow cytometry. Key molecules associated with cell proliferation were detected with RT-PCR, Western blot, or fluorescent immunohistochemistry. Cell transformation was determined by soft agar assay. Tumorigenesis and tumor growth were determined using human tumor xenografts in an athymic nude mouse model. Immunohistochemistry using large cohort of patient samples (384 samples) indicate that YAP expression is associated with poor clinical outcomes in patients. Overexpression of YAP or a constitutively active YAP mutant lead to transformation and tumorigenesis in immortalized, non-tumorigenic human ovarian surface epithelial cells, and promoted growth of cancer cells in vivo and in vitro. Expression of YAP also induced expression of ERBB receptors (EGFR, ERBB3) and ligands (HBEGF, NRG1 and NRG2). Treatment of cancer cells with HBEGF or NRG1, in turn, activated YAP and stimulated anchorage-dependent and -independent cell growth and increased ERBB3 mRNA expression. Knockdown of ERBB3 or HBEGF eliminated the stimulatory effects of YAP on cell growth and transformation, while knockdown of YAP abrogated NRG1- and HBEGF-stimulated cell proliferation. Our results demonstrate that YAP has the potential to transform ovarian surface epithelial cells, leading to initiation, early expansion, and progression of ovarian cancer. Our study identified an autocrine loop (NRG1/ERBB3/YAP/NRG1) in ovarian cells, which may control tumorigenesis and promote cancer progression. Combined targeting of the Hippo/YAP and ERBB pathways, especially the NRG1/ERBB3 pathway, has potential to provide a novel strategy for ovarian cancer therapy.
Citation Format: Chunbo He, Xiangmin Lv, Guohua Hua, John S Davis, Cheng Wang. The hippo signaling pathway regulates ovarian cancer initiation and progression via an autocrine loop [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr POSTER-BIOL-1315.
- ©2015 American Association for Cancer Research.