USP8 promotes cancer progression and extracellular vesicle-mediated CD8+T cell exhaustion by deubiquitinating the TGF-beta receptor T beta RII

TGF-beta signaling is a key player in tumor progression and immune evasion, and is associated with poor response to cancer immunotherapies. Here, we identified ubiquitin-specific peptidase 8 (USP8) as a metastasis enhancer and a highly active deubiquitinase in aggressive breast tumors. USP8 acts both as a cancer stemness-promoting factor and an activator of the TGF-beta/SMAD signaling pathway. USP8 directly deubiquitinates and stabilizes the type II TGF-beta receptor T beta RII, leading to its increased expression in the plasma membrane and in tumor-derived extracellular vesicles (TEVs). Increased USP8 activity was observed in patients resistant to neoadjuvant chemotherapies. USP8 promotes TGF-beta/SMAD-induced epithelial-mesenchymal transition (EMT), invasion, and metastasis in tumor cells. USP8 expression also enables T beta RII+ circulating extracellular vesicles (crEVs) to induce T cell exhaustion and chemoimmunotherapy resistance. Pharmacological inhibition of USP8 antagonizes TGF-beta/SMAD signaling, and reduces T beta RII stability and the number of T beta RII+ crEVs to prevent CD8+ T cell exhaustion and to reactivate anti-tumor immunity. Our findings not only reveal a novel mechanism whereby USP8 regulates the cancer microenvironment but also demonstrate the therapeutic advantages of engineering USP8 inhibitors to simultaneously suppress metastasis and improve the efficacy of cancer immunotherapy.