NRF2 inhibition causes repression of ATM and ATR expression leading to aberrant DNA Damage Response

Abstract

Nuclear factor (erythroid-derived 2)-like 2 (NRF2) is a master regulator of the antioxidant response (AR) pathway and functions as a transcription factor for basal and oxidative stress-induced expression of a battery of detoxification enzymes and cytoprotective genes. Recent evidence has also demonstrated a role of NRF2 in driving resistance of numerous cancers to chemotherapeutic agents. ATM and ATR are serine/threonine kinases that are activated following DNA damage and function as central components of DNA Damage Response (DDR) pathway. Activities of these kinases cause cell cycle arrest and activate DNA repair signals leading to cytoprotection against genotoxic agents. In this study, we elucidated the roles of ATM-and ATR-dependent DDR and NRF2-mediated AR pathways in promoting cytoprotection following cisplatin challenge in ovarian cancer cell line models. We also determined whether these pathways were inter-dependent for full activation following genotoxic insults and as such demonstrated crosstalk in their signaling mechanism to elicit cytoprotective pathways. Treatment with cisplatin caused NRF2 induction and generation of reactive oxygen species (ROS) that caused cytotoxicity in ovarian cancer cells. This was attenuated by the ROS scavenger N-Acetyl cysteine, implicating NRF2 function in cytoprotection against cisplatin. Treatment with retinoic acid (RA) caused down regulation of NRF2, disruption of AR pathway, significant accumulation of ROS and enhanced cisplatin cytotoxicity. Interestingly, RA treatment also led to repression of total ATM and ATR proteins and aberrant DDR activation following cisplatin challenge. In order to determine whether the RA induced ATM and ATR repression was dependent on NRF2 inhibition, we silenced NRF2 using SiRNA. This caused transcriptional repression of both ATM and ATR expression as determined by their promoter driven luciferase assays. Thus, NRF2 inhibition led to DDR suppression by down-regulating ATM and ATR that led to enhanced cytotoxicity. These findings demonstrate mechanism of crosstalk between the AR and the DDR pathways and extend the scope of NRF2 in promoting cancer therapeutic resistance.

Mechanics of PAK1—A new molecular player in the arena of skin cancer

“…Hence, we checked the response of NRF2 upon UV‐B treatment by western blot and confocal imaging (Figure a,b) and observed that NRF2 is a UV‐B responsive gene that localizes from the nucleus to the cytoplasm. Further, another study showed NRF2 is required for ATR expression, which coincides with our study (Khalil & Deeni, ).…”

“…Hence, we checked the response of NRF2 upon UV-B treatment by western blot and confocal imaging (Figure 3a,b) and observed that NRF2 is a UV-B responsive gene that localizes from the nucleus to the cytoplasm. Further, another study showed NRF2 is required for ATR expression, which coincides with our study (Khalil & Deeni, 2015). -------------------------------- The decisive fate of the cells exposed to UV is the sum of all the events that may lead to repair, recovery, mutation and cancer or cell death by apoptosis.…”

Emerging role of nuclear factor erythroid 2-related factor 2 in the mechanism of action and resistance to anticancer therapies

“…In turn, this suggests that Heme oxygenase inhibitors could represent a potential therapeutic strategy. Following the findings of the role of NRF2 in chemoresistance, researchers have focussed on identifying NRF2 inhibitors to modulate NRF2 to overcome chemoresistance [51,55,[80][81][82][83][84][85][86][87][88][89][90][91][92][93][94] .…”

“…Regulation of these genes by NRF2 is therefore likely to influence resistance. Expression of both Ataxia telangiectasia mutated (ATM) and Ataxia telangiectasia and Rad3 related (ATR) are under NRF2 control [ 212 ] . The repression of total ATM and ATR protein levels following NRF2 inhibition suggests transcriptional regulation of these kinases by NRF2.…”

Regulation of ATM and ATR by SMARCAL1 and BRG1

“…However, very few reports exist for transcriptional regulation of ATM and ATR. Inhibition of Nuclear factor like-2 (NRF2), a transcription factor, has been reported to cause transcriptional repression of ATM and ATR[55]. Peng et al have reported that downregulation of DNA-PKcs causes transcriptional repression of ATM[56].…”