The role of mitophagy in radioresistance of cancers

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Human cancer cells (HCT8, A549, MCF7 and MDA-MB-453) were used in this study. The expression of DNA damage marker (γH2AX), cyclin-dependent kinase inhibitor (p21), and the level of mitochondrial superoxide were significantly increased in human cancer cells 8, 24, and 48 hours after 5 Gy X-rays exposure.Interestingly, radiation exposure significantly increased the expression of several mitophagy receptors 48 hours after 5 Gy X-rays exposure, but not 8 or 24 hours after 5 Gy X-rays exposure. It suggests that radiation exposure induces mitophagy activity. To verify the role of mitophagy in regulating the radioresistance of cancer cells, we used small interfering RNA to knockdown the expression of radiation-induced mitophagy receptors. Western blot analysis showed that the knockdown of some radiation-induced mitophagy receptors enhanced the expression of γH2AX and the level of mitochondrial superoxide in cancer cells 48 hours after 5 Gy X-rays exposure. We are still investigating how the overexpression of the key mitophagy receptors will affect the radioresistance of cancer cells.Our data suggests that mitophagy may regulate the acquired radioresistance of cancers following radiotherapy.