Ionizing radiation induces autophagy in human oral squamous cell carcinoma

Purpose: Irradiation-induced autophagy has been reported in several types of cancers, however, the relationship between irradiation and autophagy in human oral squamous cell carcinoma (OSCC) has not yet been described. In this study we investigated the induction of autophagy in cell lines by exposing them to ionizing irradiation. Methods: Human OSCC OC3 and SAS cell lines were used in this study. Cell viability and induction of autophagy were determined under irradiation treatment. The GFP-LC3 puncta formation and the levels of LC3-II as indicators of autophagy were detected by fluorescence microscopy and Western blot method. The signaling pathways involved in irradiation-mediated autophagy were also determined by Western blot method. Results: Irradiation decreased cell viability only in OC3 cells, while autophagic machinery and related signaling pathways were found to be elevated after irradiation in OC3 and SAS cells. However, autophagic degradation determined by the reduction of 1962 levels was only found in OC3 cells, suggesting auto phagosome accumulation took place in SAS cells. In addition, irradiation accompanied with rapamycin treatment elevated autophagy formation and induced death of OC3 cells. Conclusions: These results suggested that induction of autophagy might provide an advantageous strategy to increase the anticancer effects of radiotherapy in patients with OSCCs.