UBQLN2 and esophageal squamous cell carcinoma: Therefore, in order to verify the critical role of the MAPK signaling pathway in the regulation of UBQLN2-mediated radiosensitization of ESCC cells, we used Western blotting to detect the key molecules of this pathway, including extracellularly regulated protein kinases (ERK), p38 MAPK, Jun-amino-terminal kinase (JNK), and ERK5.