Abstract 2016: Mst2 is required for tumor progression and Yap activity

The survival of patients with head and neck cancer has remained unchanged for decades [1]. Novel therapeutic approaches are needed. The transcription co-activator Yap is known to initiate proliferation and migration programs in response to cytoskeletal cues [2]. As evidence of the relevance of Yap in cancer increases, the lack of pharmacological strategies to inhibit it hinders the possibility of clinical testing. The main Yap regulatory signals in mammals are cytoskeletal integrity and cell shape [2]. Interestingly, Mst2 regulates microtubule coordination in parallel to kinesin Eg5 motor activity[3] and actin polymerization through Rac1 activation [4]. We set out to explore the role of Mst2 in cancer biology and the influence of its cytoskeletal effects in Yap activity using silencing and overexpression systems in early passage oral squamous cell cancer cell lines. In clinically annotated databases, high Mst2 expression correlated with poor prognosis in lung, breast and head and neck cancer. Standard in vitro experiments showed that Mst2 was required and promoted cell migration and invasion. Immunofluorescence staining quantification revealed that Mst2 was necessary for actin polymerization, microtubule targeting to the focal adhesions and microtubule distribution. These effects increased cell height and reduced cell spreading. In keeping with cytoskeletal and cell shape changes, in luciferase reporter assays Mst2 was required for Yap activation, and inhibition of kinesin Eg5 with Monastrol reduced Yap activity in an Mst2 dependent manner. Confocal imaging quantification of 3D organotypic tumors revealed that Mst2 was required for primary tumor invasion into human dermis. Consistently, in an orthotopic xenograft model, tumors with lower Mst2 expression showed a significant reduction in circulating tumor DNA and lung metastasis formation. Although further preclinical studies are warranted, our results support the hypothesis that kinesin Eg5 inhibitors may be used to target Yap activity in oral squamous cell cancers with high Mst2 expression. 1. CRUK. CRUK Oral Cancer Statistics. 2009 [cited 2013; Available from: http://www.cancerresearchuk.org/cancer-info/cancerstats/types/oral/]. 2. Pan, D., The hippo signaling pathway in development and cancer. Dev Cell, 2010. 19(4): p. 491-505. 3. Mardin, B.R., et al., Components of the Hippo pathway cooperate with Nek2 kinase to regulate centrosome disjunction. Nat Cell Biol, 2010. 12(12): p. 1166-76. 4. Mou, F., et al