title: Nrf2 facilitates repair of radiation induced DNA damage through homologous recombination repair pathway in a ROS independent manner in cancer cells.
abstract: Nrf2 is a redox sensitive transcription factor that is involved in the co-ordinated transcription of genes involved in redox homeostasis. But the role of Nrf2 in DNA repair is not investigated in detail. We have employed A549 and MCF7 cells to study the role of Nrf2 on DNA repair by inhibiting Nrf2 using all-trans retinoic acid (ATRA) or by knock down approach prior to radiation exposure (4 Gy). DNA damage and repair analysis was studied by γH2AX foci formation and comet assay. Results suggested that the inhibition of Nrf2 in A549 or MCF7 cells led to significant slowdown in DNA repair as compared to respective radiation controls. The persistence of residual DNA damage even in the presence of free radical scavenger N-acetyl cysteine, suggested that the influence of Nrf2 on DNA repair was not linked to its antioxidant functions. Further, its influence on non-homologous end joining repair pathway was studied by inhibiting both Nrf2 and DNA-PK together. This led to synergistic reduction of survival fraction, indicating that Nrf2 may not be influencing the NHEJ pathway. To investigate the role of homologous recombination repair (HR) pathway, RAD51 foci formation was monitored. There was a significant reduction in the foci formation in cells treated with ATRA or shRNA against Nrf2 as compared to their respective radiation controls. Further, Nrf2 inhibition led to significant reduction in mRNA levels of RAD51. BLAST analysis was also performed on upstream regions of DNA repair genes to identify antioxidant response element and found that many repair genes that are involved in HR pathway may be regulated by Nrf2. Together, these results suggest the involvement of Nrf2 in DNA repair, a hitherto unknown function of Nrf2, putatively through its influence on HR pathway.
authors.affiliation: Radiation Biology and Health Sciences Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
authors.forename: Sundarraj
authors.initials: S
authors.lastname: Jayakumar
authors.affiliation: Radiation Biology and Health Sciences Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
authors.forename: Debojyoti
authors.initials: D
authors.lastname: Pal
authors.affiliation: Radiation Biology and Health Sciences Division, Bhabha Atomic Research Centre, Mumbai 400085, India. Electronic address: sskumar@barc.gov.in.
authors.forename: Santosh K
authors.initials: SK
authors.lastname: Sandur
mesh_terms: D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects; D004249:DNA Damage / Q000528:radiation effects; D059766:DNA End-Joining Repair / Q000235:genetics / Q000528:radiation effects*; D016166:Free Radical Scavengers / Q000378:metabolism; D006657:Histones / Q000235:genetics / Q000378:metabolism; D006801:Humans; D061986:MCF-7 Cells; D051267:NF-E2-Related Factor 2 / Q000037:antagonists & inhibitors / Q000235:genetics*; D051135:Rad51 Recombinase / Q000235:genetics* / Q000378:metabolism; D011836:Radiation Tolerance / Q000235:genetics / Q000528:radiation effects; D011839:Radiation, Ionizing; D017382:Reactive Oxygen Species / Q000378:metabolism; D059767:Recombinational DNA Repair / Q000235:genetics / Q000528:radiation effects*; D014212:Tretinoin / Q000008:administration & dosage
chemical_list: D016166:Free Radical Scavengers; C468783:H2AX protein, human; D006657:Histones; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D017382:Reactive Oxygen Species; D014212:Tretinoin; D051135:Rad51 Recombinase
keywords: DNA damage; DNA repair; Ionizing radiation; Nrf2; RAD51; Radiosensitivity