Depletion of USP6 was also able to specifically radiosensitive head and neck squamous cell carcinoma cells (UMSCC74A) to high-LET protons, but not low-LET protons (Fig. E3A-E3D; available online at https://doi.org/10.1016/j.ijrobp.2019.02.053). Here, USP6 is linked to head and neck squamous cell carcinoma.