PRKDC and esophageal squamous cell carcinoma: We found that the level of activated DNA-PKcs, an important protein involved in NHEJ repair [25], was substantially decreased in ESCC cell lines with UBQLN2 suppression, which further confirmed that downregulation of UBQLN2 impeded DNA damage NHEJ repair and increased the radiosensitivity of ESCC cells (Figure 8).