NF-κB has been well documented to play a critical role in signaling cell stress reactions. The extracellular signal-regulated kinase (ERK) regulates cell proliferation and survival. GADD45β is a primary cell cycle element responsive to NF-κB activation in anti-apoptotic responses. The present study provides evidence demonstrating that NK-κB, ERK and GADD45β are co-activated by ionizing radiation (IR) in a pattern of mutually dependence to increase cell survival. Stress conditions generated in human breast cancer MCF-7 cells by the administration of a single exposure of 5 Gy IR resulted in the activation of ERK but not p38 or JNK, along with an enhancement of the NF-κB transactivation and GADD45β expression. Overexpression of dominant negative Erk (DN-Erk) or pre-exposure to ERK inhibitor PD98059 inhibited NF-κB. Transfection of dominant negative mutant IκB that blocks NF-κB nuclear translocation, inhibited ERK activity and GADD45β expression and increased cell radiosensitivity. Interaction of p65 and ERK was visualized in living MCF-7 cells by bimolecular fluorescence complementation analysis. Anti-sense inhibition of GADD45β strikingly blocked IR-induced NF-κB and ERK but not p38 and JNK. Overall, these results demonstrate a possibility that NF-κB, ERK, and GADD45β are able to coordinate in a loop-like signaling network to defend cells against the cytotoxicity induced by ionizing radiation.
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