Hippo Pathway Effector Yap Is an Ovarian Cancer Oncogene

The Hippo pathway regulates organ size and tumorigenesis in Drosophila and mammals and is altered in a variety of human cancers, yet it remains unclear if the Hippo pathway is of prognostic significance to cancer patients. Here we show that the key targets of Hippo signaling, transcriptional coactivators Yki and Yap, play a conserved role in promoting ovarian cancer in flies and humans, respectively. Whereas studies linking Yap to cancer in other tissues have focused on overall Yap levels, we show for the first time that subcellular levels of Yap show an exceptionally strong association with poor patient survival. Specifically, high levels of nuclear Yap (nYap), or low levels of cytoplasmic phosphorylated Yap (cpYap), associated with poor survival from ovarian cancer. Patients with both high nYap and low cpYap had ∼50% lower 5-year survival, and this combination is an independent prognostic marker for survival, with an exceptionally high hazard ratio of 7.8. We find that Yap2 is the predominantly expressed Yap isoform in both the ovarian surface epithelium (OSE) and epithelial ovarian cancers. Overexpression of Yap2 and phosphorylation-defective Yap2-5SA in immortalized OSE cells resulted in increased cell proliferation, resistance to cisplatin-induced apoptosis, faster cell migration, and anchorage-independent growth, whereas Yap knockdown resulted in increased sensitivity to cisplatin-induced apoptosis. Findings argue that the Hippo signaling pathway defines an important pathway in progression of ovarian cancer.