Syntenin Controls Extracellular Vesicle-Induced Tumour Migration by Regulating the Expression of Adhesion Proteins on Small Extracellular Vesicles.

Despite extensive proof for the tumour-supporting function of cancer-derived small extracellular vesicles (sEVs), attributions of pathological effects to specific sEV subpopulations are poorly described. In this study, we aimed to characterise a distinct sEV species under the control of Syntenin, a key regulator of endosomal sEV biogenesis, regarding its proteomic cargo and pro-tumourigenic functions. Using mass spectrometry (MS), we detected 178 down- and 236 up-regulated proteins on sEVs from breast cancer cells upon Syntenin knockout (KO). Pathway enrichment analysis suggested that Syntenin depletion was particularly associated with adhesion-related processes. Accordingly, sEVs from Syntenin-deficient 4T1 and MCF-7 breast cancer cells showed a reduced expression of several focal adhesion and cell-cell junction proteins. Syntenin silencing reduced the Fibronectin-binding capacity of sEVs from both cell lines, which was mediated by sEV-associated Integrin alpha-V/beta-3 (α(V)β(3)). Compared to sEVs from wildtype cells, Syntenin KO sEVs showed decreased tropism towards the Fibronectin-rich liver microenvironment in vivo, provided less adhesive support for 4T1 cells and thereby failed to induce cancer cell migration, which appeared to be independent of EV uptake. In summary, this study revealed that Syntenin has a large-scale effect on the proteomic cargo of sEVs and regulates their adhesive, organotropic and pro-migratory properties in breast cancer.