YAP/TAZ inhibition reduces metastatic potential of Ewing sarcoma cells

Lisa Bierbaumer,Gloria Pedot,Sandra Högler,Branka Radic-Sarikas,Anna M Katschnig,Elisabeth Gurnhofer,Jeffrey A Petro,Florian Kromp,Lukas Kenner,Raphaela Schwentner,Heinrich Kovar,Maximilian O Kauer,Aykut Uren,Dave N T Aryee,Karin Mühlbacher,Beat W Schäfer

doi:10.1038/s41389-020-00294-8

Abstract

Ewing sarcoma (EwS) is a highly metastatic bone cancer characterized by the ETS fusion oncoprotein EWS-FLI1. EwS cells are phenotypically highly plastic and switch between functionally distinct cell states dependent on EWS-FLI1 fluctuations. Whereas EWS-FLI1high cells proliferate, EWS-FLI1low cells are migratory and invasive. Recently, we reported activation of MRTFB and TEAD, effectors of RhoA and Hippo signalling, upon low EWS-FLI1, orchestrating key steps of the EwS migratory gene expression program. TEAD and its co-activators YAP and TAZ are commonly overexpressed in cancer, providing attractive therapeutic targets. We find TAZ levels to increase in the migratory EWS-FLI1low state and to associate with adverse prognosis in EwS patients. We tested the effects of the potent YAP/TAZ/TEAD complex inhibitor verteporfin on EwS cell migration in vitro and on metastasis in vivo. Verteporfin suppressed expression of EWS-FLI1 regulated cytoskeletal genes involved in actin signalling to the extracellular matrix, effectively blocked F-actin and focal-adhesion assembly and inhibited EwS cell migration at submicromolar concentrations. In a mouse EwS xenograft model, verteporfin treatment reduced relapses at the surgical site and delayed lung metastasis. These data suggest that YAP/TAZ pathway inhibition may prevent EwS cell dissemination and metastasis, justifying further preclinical development of YAP/TAZ inhibitors for EwS treatment.

Highlights

Ewing sarcoma (EwS), the second most common malignant bone tumour in children and adolescents, has a high propensity for early onset dissemination, and current treatment strategies are only poorly effective against metastatic disease[1]
As EWS-FLI1low expressing cells have been linked to an invasive phenotype recently, we asked whether EWS-FLI1 affects YAP and TAZ protein levels in three EwS cell lines carrying doxycycline - inducible sh-EWS-FLI1 constructs
Kaplan–Meier analysis of an independent series of 85 primary EwS with complete clinical annotation (GEO ID: gse6315733) indicated an association of high TAZ expression with adverse event-free and overall survival (Fig. 1d). These findings suggest that TAZ might play an important role in the onset of EwS metastasis

Summary

Introduction

Ewing sarcoma (EwS), the second most common malignant bone tumour in children and adolescents, has a high propensity for early onset dissemination, and current treatment strategies are only poorly effective against metastatic disease[1]. EwS is driven by a EWSR1-ETS fusion oncogene, most commonly EWSR1-FLI12,3, which results in the expression of the oncogenic transcription factor EWS-FLI1 that drives cell transformation and oncogenicity[4]. Recent studies suggest that EWS-FLI1 may oscillate between high and low expression states, thereby orchestrating distinct phenotypic programs[5]. We have recently identified a regulatory mechanism involving the myocardin related and TEA-domain transcription factors MRTFB and TEAD1–4 triggering cytoskeletal reorganization in EWS-FLI1low cells[10]. In EWS-FLI1high cells, EWS-FLI1 bound to and prohibited access of MRTFB to TEAD-regulated enhancers. TEADs require co-activation by the Yes-associated protein 1 (YAP-1, YAP) or its paralogue, the transcriptional co-activator with PDZ-binding motif (TAZ, WWTR1), which are typically controlled by Hippo signalling in organ development and tissue homoeostasis[11,12].

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