ETV5 functionally connects ALK and CXCR4 signaling in neuroblastoma

Activating ALK mutations occur in 10% of neuroblastomas (NB) and represent an important druggable target for more effective treatment of high-risk patients. In order to design effective novel targeted therapeutic approaches, gaining detailed insights into downstream ALK signaling is crucial. We and others identified PI3K/AKT and RAS/MAPK as major downstream signaling axes. Also, we connected FOXO3a controlled RET expression to the PI3K/AKT axis. Here, using multiple ALK activating and inhibiting cell models, we firmly establish ETV5 as a major RAS/MAPK downstream target upregulated through mutant ALK. ETV5 is known to act as regulator of epithelial-mesenchymal transition (EMT) and controls stem cell properties and neuronal cell fate decisions. Knockdown of ETV5 reduced the clonogenic potential and growth of NB cells in vitro and in vivo. RNAseq transcriptome profiling following ETV5 knock down provided an ETV5 signature score which identifies patients with poor overall survival and was enriched in gene sets controlling EMT in keeping with observed reduced invasive properties in ETV5 depleted NB cell lines. Finally, the chemokine receptor CXCR4 emerged as a crucial ETV5 target gene thus opening unexpected novel opportunities for drugging, as CXCR4 inhibitors are available. Our data highlight ETV5 as an intrinsic component of ALK downstream and RAS/MAPK signaling in NB. The presence of RAS/MAPK and acquired ALK mutations in relapsed NB tumors highlights the significance of the ETV5 signaling pathway in NB pathogenesis. Moreover, ETV5 provides a functional link between the ALK and chemotaxis pathways involved in cancer metastasis and identifies CXCR4 as novel drug target