STIM1-regulated exosomal EBV-LMP1 empowers endothelial cells with aggressive phenotype by activating the Akt/ERK pathway in nasopharyngeal carcinoma

Background: Stromal interaction molecule 1 (STIM1)-mediated Ca 2+ signaling regulates tumor angiogenesis in nasopharyngeal carcinoma (NPC), an Epstein-Barr virus (EBV)-related human malignancy. However, the mechanism by which STIM1 modulates the endothelial functional phenotypes contributing to tumor angiogenesis remains elusive. Methods: We explored the intercellular communication via exosomal biomolecules released by EBV-infected NPC cells and delivered to endothelial cells (ECs). The NPC cell-derived exosomes were isolated via differential centrifugation and observed with transmission electron microscopy. Exosome particle size was assessed by nanoparticle tracking analysis (NTA). Uptake of exosomes by recipient ECs was detected by fluorescent labeling of the exosomes with PKH26. Tumor angiogenesis-associated profiles were characterized by determining cell proliferation, migration, tubulogenesis, and permeability in human umbilical vein endothelial cells (HUVECs). Activation of the Akt/ERK pathway was elucidated by detecting the phosphorylation level using western blotting. A chick embryo chorioallantoic membrane (CAM) xenograft model was employed to study tumor-associated neovascularization in vivo . Results: The NPC cell-derived exosomes harboring EBV-encoded latent membrane protein 1 (LMP1) promoted proliferation, migration, tubulogenesis, and permeability by activating the Akt/ERK pathway in ECs. STIM1 silencing reduced LMP1 enrichment in NPC cell-derived exosomes, thereby reversing its pro-oncogenic effects in an Akt/ERK pathway-dependent manner. Furthermore, STIM1 knockdown in NPC cells blunted tumor-induced vascular network formation and inhibited intra-tumor neovascularization in the chorioallantoic membrane (CAM) xenograft model. Conclusion: STIM1 regulates tumor angiogenesis by controlling exosomal EBV-LMP1 delivery to ECs in the NPC tumor microenvironment. Blocking exosome-mediated cell-to-cell horizontal transfer of EBV-associated oncogenic signaling molecules may be an effective therapeutic strategy for NPC.