Analysis of the relationship between the KRAS G12V oncogene and the Hippo effector YAP1 in embryonal rhabdomyosarcoma

Abdalla D Mohamed,Nupur Shah,Neil Vargesson,Simone Hettmer,Henning Wackerhage

doi:10.1038/s41598-018-33852-7

Abstract

Persistent hyperactivity of the Hippo effector YAP in activated satellite cells is sufficient to cause embryonal rhabdomyosarcoma (ERMS) in mice. In humans, YAP is abundant and nuclear in the majority of ERMS cases, and high YAP expression is associated with poor survival. However, YAP1 is rarely mutated in human ERMS. Instead, the most common mutations in ERMS are oncogenic RAS mutations. First, to compare YAP1S127A and KRASG12V-driven rhabdomyosarcomas, we re-analysed gene expression microarray datasets from mouse rhabdomyosarcomas caused by these genes. This revealed that only 20% of the up or downregulated genes are identical, suggesting substantial differences in gene expression between YAP and KRAS-driven rhabdomyosarcomas. As oncogenic RAS has been linked to YAP in other types of cancer, we also tested whether KRAS G12V alone or in combination with loss of p53 and p16 activates YAP in myoblasts. We found that neither KRAS G12V alone nor KRAS G12V combined with loss of p53 and p16 activated Yap or Yap/Taz-Tead1–4 transcriptional activity in C2C12 myoblasts or U57810 cells. In conclusion, whilst oncogenic KRAS mutation might activate Yap in other cell types, we could find no evidence for this in myoblasts because the expression of KRAS G12V expression did not change Yap/Taz activity in myoblasts and there was a limited overlap in gene expression between KRAS G12V and YAP1 S127A-driven tumours.

Highlights

Rhabdomyosarcoma is the most common soft tissue sarcoma in children
Genes induced by KRAS G12V-Cdkn2a null but not YAP1 S127A-driven embryonal rhabdomyosarcoma (ERMS) are enriched for genes associated with cell differentiation, cell projections and neuronal differentiation plus junctions and focal adhesions (Table S4)
A key dilemma in embryonal rhabdomyosarcoma is that YAP is expressed, nuclear and presumably active in the majority of human ERMS cases[7] but that YAP1 is not significantly mutated in human ERMS which has a high frequency of oncogenic RAS mutations[1] Given that interactions between mutated, oncogenic RAS and YAP have been reported for other cell and cancer types[13,14,15], we tested for evidence that mutated, oncogenic KRAS can activate YAP in myoblasts to regulate the expression of a shared set of genes

Summary

Introduction

Rhabdomyosarcoma is the most common soft tissue sarcoma in children. The two main subtypes are alveolar rhabdomyosarcoma (ARMS), which is associated with PAX3/7-FOXO1 fusion genes, and embryonal rhabdomyosarcoma (ERMS), which is associated with mutations in common cancer genes such as HRAS, KRAS, NRAS, CTNNB1, PIK3CA and TP531. The frequency of Hippo gene copy number aberrations and other mutations is too low to account for the common nuclear localization of YAP in human ERMS7, suggesting that mutated cancer genes cause the activation of YAP and TAZ. Supporting this notion are studies that link oncogenic RAS isoforms[13,14,15], WNT members[16], and mTOR mutants[17,18] to the Hippo pathway and especially YAP activity. In KRAS G12V expressing human myoblasts, YAP has been shown to promote cell proliferation and inhibit apoptosis and myogenic differentiation in vitro and in murine xenografts in vivo[20]

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