EWS/FLI utilizes NKX2-2 to repress mesenchymal features of Ewing sarcoma
John Fadul1,2, Russell Bell1,2, Laura M. Hoffman1,3, Mary C. Beckerle1,2,3, Michael E. Engel1,2,4,5 and Stephen L. Lessnick1,2,4,5
1 Huntsman Cancer Institute, School of Medicine, University of Utah, Salt Lake City, Utah, USA
2 Department of Oncological Sciences, School of Medicine, University of Utah, Salt Lake City, Utah, USA
3 Department of Biology, School of Medicine, University of Utah, Salt Lake City, Utah, USA
4 Center for Children’s Cancer Research, School of Medicine, University of Utah, Salt Lake City, Utah, USA
5 Division of Pediatric Hematology and Oncology, School of Medicine, University of Utah, Salt Lake City, Utah, USA
Correspondence:
Stephen L. Lessnick, email:
Keywords: Ewing sarcoma, NKX2-2, EWS/FLI, mesenchymal, adhesion
Received: February 25, 2015 Accepted: April 16, 2015 Published: April 17, 2015
Abstract
In Ewing sarcoma, NKX2-2 is a critical activated target of the oncogenic transcription factor EWS/FLI that is required for transformation. However, its biological function in this malignancy is unknown. Here we provide evidence that NKX2-2 mediates the EWS/FLI-controlled block of mesenchymal features. Transcriptome-wide RNA sequencing revealed that NKX2-2 represses cell adhesion and extracellular matrix organization genes. NKX2-2-depleted cells form more focal adhesions and organized actin stress fibers, and spread over a wider area—hallmarks of mesenchymally derived cells. Furthermore, NKX2-2 represses the actin-stabilizing protein zyxin, suggesting that these morphological changes are attributable to zyxin de-repression. In addition, NKX2-2-knockdown cells display marked increases in migration and substrate adhesion. However, only part of the EWS/FLI phenotype is NKX2-2-dependent; consequently, NKX2-2 is insufficient to rescue EWS/FLI repression of mesenchymalization. Strikingly, we found that EWS/FLI- and NKX2-2-repressed genes are activated by ZEB2, which was previously shown to block Ewing sarcoma epithelialization. Together, these data support an emerging theme wherein Ewing sarcoma cells highly express transcription factors that maintain an undifferentiated state. Importantly, co-opting epithelial and mesenchymal traits by Ewing sarcoma cells may explain how the primary tumor grows rapidly while also “passively” metastasizing, without the need for transitions toward differentiated states, as in carcinomas.
