Cell-cell contact-dependent secretion of large-extracellular vesicles from EFNBhigh cancer cells accelerates peritoneal dissemination

Background Large non-apoptotic vesicles released from the plasma membrane protrusions are classified as large-EVs (LEVs). However, the triggers of LEV secretion and their functions in tumors remain unknown. Methods Coculture system of cancer cells, peritoneal mesothelial cells (PMCs), and macrophages (MΦs) was conducted to observe cell-cell contact-mediated LEV secretion. Lineage tracing of PMCs was performed using Wt1 CreERT2 -tdT nu mice to explore the effects of LEVs on PMCs in vivo, and lymphangiogenesis was assessed by qRT-PCR and flow-cytometry. Results In peritoneal dissemination, cancer cells expressing Ephrin-B (EFNB) secreted LEVs upon the contact with PMCs expressing ephrin type-B (EphB) receptors, which degraded mesothelial barrier by augmenting mesothelial-mesenchymal transition. LEVs were incorporated in subpleural MΦs, and these MΦs transdifferentiated into lymphatic endothelial cells (LEC) and integrated into the lymphatic vessels. LEC differentiation was also induced in PMCs by interacting with LEV-treated MΦs, which promoted lymphangiogenesis. Mechanistically, activation of RhoA-ROCK pathway through EFNB reverse signaling induced LEV secretion. EFNBs on LEVs activated EphB forward signaling in PMC and MΦs, activating Akt, ERK and TGF-β1 pathway, which were indispensable for causing MMT and LEC differentiation. LEVs accelerated peritoneal dissemination and lymphatic invasions by cancer cells. Blocking of EFNBs on LEVs using EphB-Fc-fusion protein attenuated these events. Conclusions EFNB high cancer cells scattered LEVs when they attached to PMCs, which augmented the local reactions of PMC and MΦ (MMT and lymphangiogenesis) and exaggerated peritoneal dissemination.