Ceramide-induced cleavage of GPR64 intracellular domain drives Ewing sarcoma.

Ewing sarcoma is a cancer of bone and soft tissue in children and young adults primarily driven by the EWS-FLI1 fusion oncoprotein, which has been undruggable. Here, we report that Ewing sarcoma depends on secreted sphingomyelin phosphodiesterase 1 (SMPD1), a ceramide-generating enzyme, and ceramide. We find that G-protein-coupled receptor 64 (GPR64)/adhesion G-protein-coupled receptor G2 (ADGRG2) responds to ceramide and mediates critical growth signaling in Ewing sarcoma. We show that ceramide induces the cleavage of the C-terminal intracellular domain of GPR64, which translocates to the nucleus and restrains the protein levels of RIF1 in a manner dependent on SPOP, a substrate adaptor of the Cullin3-RING E3 ubiquitin ligase. We demonstrate that both SMPD1 and GPR64 are transcriptional targets of EWS-FLI1, indicating that SMPD1 and GPR64 are EWS-FLI1-induced cytokine-receptor dependencies. These results reveal the SMPD1-ceramide-GPR64 pathway, which drives Ewing sarcoma growth and is amenable to therapeutic intervention.

MYOD-SKP2 axis boosts tumorigenesis in fusion negative rhabdomyosarcoma by preventing differentiation through p57Kip2 targeting.

Rhabdomyosarcomas (RMS) are pediatric mesenchymal-derived malignancies encompassing PAX3/7-FOXO1 Fusion Positive (FP)-RMS, and Fusion Negative (FN)-RMS with frequent RAS pathway mutations. RMS express the master myogenic transcription factor MYOD that, whilst essential for survival, cannot support differentiation. Here we discover SKP2, an oncogenic E3-ubiquitin ligase, as a critical pro-tumorigenic driver in FN-RMS. We show that SKP2 is overexpressed in RMS through the binding of MYOD to an intronic enhancer. SKP2 in FN-RMS promotes cell cycle progression and prevents differentiation by directly targeting p27Kip1 and p57Kip2, respectively. SKP2 depletion unlocks a partly MYOD-dependent myogenic transcriptional program and strongly affects stemness and tumorigenic features and prevents in vivo tumor growth. These effects are mirrored by the investigational NEDDylation inhibitor MLN4924. Results demonstrate a crucial crosstalk between transcriptional and post-translational mechanisms through the MYOD-SKP2 axis that contributes to tumorigenesis in FN-RMS. Finally, NEDDylation inhibition is identified as a potential therapeutic vulnerability in FN-RMS.