Inhibition of autophagy enhances the radiosensitivity of nasopharyngeal carcinoma by reducing Rad51 expression

Radiotherapy has long been considered as the mainstay of treatment for nasopharyngeal carcinoma (NPC). However, locoregional recurrence or distant metastasis may occur in some patients due to the radiation resistance of cancer cells. Autophagy plays a vital role in protecting cells against radiation. However, the mechanism of autophagy in radiation therapy remains obscure. In the present study, we demonstrated that suppression of autophagy related 5 (Atg5) aggravated ionizing radiation (IR)-induced DNA damage and apoptosis in human NPC cells without accelerating the cell cycle, whereas regulation of the cell cycle has been widely regarded as the most important determinant of IR sensitivity. Further study showed that inhibition of autophagy suppressed the mRNA expression of Rad51, a key protein of homologous recombination that has been demonstrated to play a critical role in the repair of DNA double-strand breaks induced by radiation. Moreover, suppression of Atg5 had no impact on the radiosensitivity when cells were pre-treated by the Rad51 inhibitor, and the enhanced radiosensitivity by Atg5 suppression was reversed by overexpression of Rad51 in human NPC cells. Our results suggest that inhibition of autophagy enhances the susceptibility of NPC cells to radiation by reducing Rad51 expression. Therefore, Rad51 targeted therapy may be investigated as a potential novel agent for the adjuvant treatment of traditional radiation of NPC.