Modulation of Nuclear factor E2 related factor-2 (Nrf2) activation by the stress response gene Immediate Early Response-3 (IER3) in colonic epithelial cells - a novel mechanism of cellular adaption to inflammatory stress.

Imke Stachel, Claudia Geismann, Konrad Aden, Florian Deisinger, Philip Rosenstiel, Stefan Schreiber, Susanne Sebens, Alexander Arlt, Heiner Schaefer
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JBC papers in press
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Although Nuclear factor E2-related factor-2 (Nrf2) protects from carcinogen-induced tumorigenesis, underlying the rationale for using Nrf2-inducers in chemoprevention, this antioxidative transcription factor may also act as a protooncogene. Thus, an enhanced Nrf2 activity promotes formation and chemoresistance of colon cancer. One mechanism causing persistent Nrf2 activation is the adaptation of epithelial cells to oxidative stress during chronic inflammation, e.g. colonocytes in Inflammatory Bowel Diseases (IBD), and the multifunctional stress response gene Immediate Early Response-3 (IER3) has a crucial role under these conditions. We now demonstrate that colonic tissue from Ier3-/- mice subject of DSS colitis exhibit greater Nrf2 activity than Ier3+/+ mice manifesting as increased nuclear Nrf2 protein level and Nrf2 target gene expression. Likewise, human NCM460 colonocytes subject of shRNA mediated IER3 knock-down exhibit greater Nrf2 activity compared with control cells, whereas IER3 overexpression attenuated Nrf2 activation. IER3 deficient NCM460 cells exhibited reduced ROS level, indicating increased antioxidative protection, as well as lower sensitivity to TRAIL or anti-cancer drug induced apoptosis and greater clonogenicity. Knock-down of Nrf2 expression reversed these IER3 dependent effects. Further, the enhancing effect of IER3 deficiency on Nrf2 activity relates to the control of the inhibitory tyrosine kinase Fyn by the PI3K/Akt pathway. Thus, the PI3K inhibitor LY294002 or knock-down of Akt or Fyn expression abrogated the impact of IER3 deficiency on Nrf2 activity. In conclusion, the interference of IER3 with the PI3K/Akt-Fyn pathway represents a novel mechanism of Nrf2 regulation that may get lost in tumors and by which IER3 exerts its stress-adaptive and tumor suppressive activity.