Statin suppresses Hippo pathway-inactivated malignant mesothelioma cells and blocks the YAP/CD44 growth stimulatory axis

Cancer Letters 2016 October [Epub ahead of print] [Link]

Tanaka K, Osada H, Murakami-Tonami Y, Horio Y, Hida T, Sekido Y


Malignant mesothelioma (MM) frequently exhibits Hippo signaling pathway inactivation (HPI) mainly due to NF2 and/or LATS2 mutations, which leads to the activation of YAP transcriptional co-activator. Here, we show antitumor effects of statin on MM cells with HPI, through the interplay of the mevalonate and Hippo signaling pathways. Statin attenuated proliferation and migration of MM cells harboring NF2 mutation by accelerating YAP phosphorylation/inactivation. CD44 expression was decreased by statin, in parallel with YAP phosphorylation/inactivation. Importantly, we discovered that YAP/TEAD activated CD44 transcription by binding to the CD44 promoter at TEAD-binding sites. On the other hand, CD44 regulated Merlin phosphorylation according to cell density and sequentially promoted YAP transcriptional co-activator, suggesting that CD44 plays two pivotal functional roles as an upstream suppressor of the Hippo pathway and one of downstream targets regulated by YAP/TEAD. Moreover, the YAP/CD44 axis conferred cancer stem cell (CSC)-like properties in MM cells leading to chemoresistance, which was blocked by statin. Together, our findings suggest that YAP mediates CD44 up-regulation at the transcriptional level, conferring CSC-like properties in MM cells, and statin represents a potential therapeutic option against MM by inactivating YAP.