The Expression of Yes-Associated Protein (YAP) Maintains Putative Cancer Stemness and Is Associated with Poor...

Intrahepatic cholangiocarcinoma (ICC) is resistant to most chemotherapeutic agents. Yes-associated protein (YAP) is related to tumor progression; however, its role in ICC remains unknown. We investigated the mechanism underlying YAP-mediated cancer progression by focusing on the property of cancer stem cells (CSCs) in ICC. Immunohistochemistry results revealed the positive YAP expression in 37 of 52 resected ICC cases. Those with positive YAP expression showed poor prognosis in Kaplan-Meier analysis (P = 0.023). YAP expression was associated with vimentin and the putative CSC marker, hepatic oval cell marker 6 (OV-6). The knockdown of YAP expression using specific siRNAs in ICC cells decreased octamer-binding transcription factor 4 (OCT4) expression in Western blot analyses and OV-6 and CD133 expression in flow cytometry analysis. Verteporfin, a YAP inhibitor, decreased N-cadherin and OCT4 expression in Western blot analyses. In vitro sphere formation and anoikis resistance assays revealed the impairment in CSC property and anoikis resistance in response to the decrease in YAP expression. Verteporfin treatment activated the protein kinase B/mechanistic target of rapamycin signaling pathway and dramatically impaired IL-6-stimulated STAT3 phosphorylation in ICC cells. The combination of verteporfin and rapamycin, an inhibitor of mechanistic target of rapamycin phosphorylation, inhibited cell proliferation and tumor growth. In conclusion, verteporfin regulates multiple signaling pathways and, in combination with rapamycin, might be a promising therapeutic strategy for ICC treatment.