Surface‐Associated Proteins on Extracellular Vesicles Remodel the Tumor Microenvironment by Potentiating TGF‐β Signaling in a Contact‐Dependent Manner

Cancer-associated fibroblasts (CAFs) are a major stromal cell type within the tumor microenvironment (TME), where they drive extracellular matrix remodeling and influence tumor progression through the secretion of bioactive molecules. Transforming growth factor-β (TGF-β) is a key regulator of CAF activation, yet its impact on the composition and function of extracellular vesicles (EVs) secreted by CAFs remains largely unexplored. Here, it is shown that TGF-β activation alters the protein cargo and function of CAF-derived EVs (TGF-β-EVs), leading to a distinct enrichment of surface-associated proteins. One such protein is tumor necrosis factor-stimulated gene-6 protein (TSG6), which interacts with receptor CD44 and its ligand hyaluronan on EVs. The EV surface-associated proteins facilitate EV docking to cell membranes by binding to transmembrane receptors. Elevated TSG6 on CAF-derived EV surface promotes the clustering of the co-receptor CD44 and TGF-β type I receptor (TGFBR1) on recipient cells, enhancing TGF-β signaling. Functionally, TGF-β-EVs further activate CAFs and contribute to CD8⁺ T cell immunosuppression, thereby promoting cancer progression. Overall, the findings reveal a contact-dependent mechanism by which CAF-derived EVs influence cellular signaling in the TME, suggesting a broader paradigm in which EV surface-associated proteins regulate receptor clustering and downstream signaling, particularly in cells with low EV uptake.