The Protective Role And Mechanism Of Nrf2 In Radiation Induced Damage

Radiotherapy is one of the major method in eradicating of malignant tumor. The radio resistance and recurrence has become the biggest obstacle in cancer therapy. Numerous studies has been focused on increasing the sensitivity of tumor cells to radiation so as to improve the cure rate. The Nrf2/ARE is one of the most important endogeneous anti-oxidant pathway. The protein NF-E2-related factor 2(Nrf2) transcript numerous antioxidase, non-antioxidase as well as proteins related to DNA damage repair through binding with antioxidant response element (ARE). Moreover, Nrf2 also functioned in regulating of cell cycle arrest, cell inflammation and cell apoptosis. Nrf2 is closely related to cell DNA damage. Evidences began to accumulate that Nrf2 play an important role in radio and multidrug resistence during cancer therapy. It is now widely accepted that Nrf2 would be a promising target for radio sensitivity. Two experiments were conducted to explain the protective roles and mechanisms of Nrf2 radiation induced DNA damage in this research.Part 1. The mechanisms of Nrf2 in Low dose a particle induced resistence to high doseMedical radiation is the major artifical radiation received by mankind. For example, The localization of solid tumor depended on CT and PET-CT is an essential step in radio therapy. Recently, the low dose radiation received in this process has attracted broad attention. In our research, We conducted our study on highly radiation resistance lung cancer A549 cell and explored the role of Nrf2 in low dose radiation. We found that 5cGy a particle pre-irradiation reduced the damage of 75cGy, The pre-irradiation reduced the cell apoptosis as well as increased the cell clony formation rate. In our research, we found that the ROS, particularly the superoxide anion had a moderate increase under low dose radiation. The moderate increase of ROS acted as an intracellular signaling induced Nrf2 activation in autophagy dependant way. ROS scavenger or autophagy inhibitor were able to inhibit the expression of Nrf2, which ultimately affected the radiation tolerance occurred in radiation. In our study, we also found that in the low dose induced radiation resistance, Nrf2 played its protective function through protein expression of HO-1. ZnPP inhibition of HO-1 or hemoglobin clearance of CO, one of metabolites of HO-1 can eliminate the low dose induced cell radiation tolerance effectively. It follows that under action of low dose, the antioxidant Nrf2/HO-1 activated by ROS endowed A549 cells tolerance to high dose radiation.Part 2. The protective effect and mechanism of Nrf2 in radiation induced DNA damageBased on the study above, we realized that the antioxidant pathway Nrf2/ARE activation act as a protection role in ionizing radiation. DNA is the primary target within cells undergoing radiation. Therefore, we try to explore the role of Nrf2 in radiation induced DNA damage.In our experiment, we find that 50 cGy a particle effectively damage U-2OS cells, as shown by y-H2AX foci detection and micronuclear formation. The stimulation of Nrf2 expression reduced radiation induced DNA damage while the knockdown of Nrf2 by shRNA significantly increased DNA damage as well as reduced cell viability compared with the scramble cells. The results revealed that Nrf2 played an important role in a-particle lethality. Furtherly, our study revealed that the activation of Nrf2 is via autophagy dependant ERK1/2 kinase. For autophagy prevention and ERK1/2 kinase inhibition both inhibit Nrf2 activation by a particles radiation.These studies revealed the mechanism of Nrf2 and its protective role in radiation injury. Taken together, this findings will provide usefull clues for cancer radiotherapy.