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

Abstract 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.