EphA2 receptor is a key player in the metastatic onset of Ewing sarcoma

Ewing sarcoma (ES) is the second most common bone malignancy affecting children and young adults with poor prognosis due to high metastasis incidence. Our group previously described that EphA2, a tyrosine kinase receptor, promotes angiogenesis in Ewing sarcoma (ES) cells via ligand-dependent signaling. Now we wanted to explore EphA2 ligand-independent activity, controlled upon phosphorylation at S897 (p-EphA2(S897)), as it has been linked to metastasis in several malignancies. By reverse genetic engineering we explored the phenotypic changes after EphA2 removal or reintroduction. Gene expression microarray was used to identify key players in EphA2 signaling. Mice were employed to reproduce metastatic processes from orthotopically implanted engineered cells. We established a correlation between ES cells aggressiveness and p-EphA2(S897). Moreover, stable overexpression of EphA2 in low EphA2 expression ES cells enhanced proliferation and migration, but not a non-phosphorylable mutant (S987A). Consistently, silencing of EphA2 reduced tumorigenicity, migration and invasion in vitro, and lung metastasis incidence in experimental and spontaneous metastasis assays in vivo. A gene expression microarray revealed the implication of EphA2 in cell signaling, cellular movement and survival. ADAM19 knockdown by siRNA technology strongly reproduced the negative effects on cell migration observed after EphA2 silencing. Altogether, our results suggest that p-EphA2(S897) correlates with aggressiveness in ES, so blocking its function may be a promising treatment. What's new? Ewing sarcoma (ES) tumors, the second most frequent bone tumors among children and adolescents, are very aggressive and tend to recur and metastasize. Lack of knowledge regarding the molecular mechanisms that regulate this metastatic process is the main reason for the lack of efficient therapeutics. Here, by using gain- and loss-of-function experiments and in vitro and in vivo assays, the authors established a correlation between ES aggressiveness and phosphorylation of the tyrosine kinase receptor EphA2. Altogether, the findings suggest that blocking EphA2 expression or its function with drugs or genetic tools may be of use for the treatment of ES.