ENG and osteosarcoma: Furthermore, tumor-derived S1P activated autocrine signaling in osteosarcoma cells, enhancing the secretion of soluble and extracellular vesicle-associated pro-angiogenic mediators, including bFGF and the TGF-β co-receptor Endoglin (CD105).<h4>Discussion</h4>These findings identify a previously unrecognized acidosis-S1P axis that contributes to angiogenic remodeling in osteosarcoma.