Objective:Cancer cell radioresistance is a stumbling block in radiation therapy.The activity in the nuclear factor kappa B(NFκB)pathway correlates with anti-apoptotic mechanisms and increased radioresistance.The IKK complex plays a major role in NFκB activation upon numerous signals.In this study,we examined the interaction between ionizing radiation(IR)and different members of the IKK-NFκB pathway,as well as upstream activators,RAF1,ERK,and AKT1.Methods:The effect of 4 Gy of IR on the expression of the RAF1-ERK-IKK-NFκB pathway was examined in A549 and H1299 lung cancer cell lines using Western blot analysis and confocal microscopy.We examined changes in radiation sensitivity using gene silencing or pharmacological inhibitors of ERK and IKKβ.Results:IKKα,IKKγ,and IκBαincreased upon exposure to IR,thereby affecting nuclear levels of NFκB(phospho-p65).ERK inhibition or si RNA-mediated down-regulation of RAF1 suppressed the post-irradiation survival of the examined lung cancer cell lines.A similar effect was detected on survival upon silencing IKKα/IKKγor inhibiting IKKβ.Conclusions:Exposure of lung cancer cells to IR results in NFκB activation via IKK.The genetic or pharmacological blockage of the RAF1-ERK-IKK-NFκB pathway sensitizes cells to therapeutic doses of radiation.Therefore,the IKK pathway is a promising target for therapeutic intervention in combination with radiotherapy. Objective: Cancer cell radioresistance is a stumbling block in radiation therapy. The activity in the nuclear factor kappa B (NFκB) pathway correlates with anti-apoptotic mechanisms and increased radioresistance. IKK complex plays a major role in NFκB activation upon numerous signals. this study, we examined the interaction between ionizing radiation (IR) and different members of the IKK-NFκB pathway, as well as upstream activators, RAF1, ERK, and AKT1.Methods: The effect of 4 Gy of IR on the expression of the RAF1-ERK-IKK-NFκB pathway was examined in A549 and H1299 lung cancer cell lines using Western blot analysis and confocal microscopy. We examined changes in radiation sensitivity using gene silencing or pharmacological inhibitors of ERK and IKKβ. Results: IKKα, IKKγ, and IκBαincreased upon exposure to IR, thereby affecting nuclear levels of NFκB (phospho-p65) .ERK inhibition or si RNA-mediated down-regulation of RAF1 suppressed the post-irradiation survival of the examined lung cancer cell lines. A similar effect was detected on survival in silencing IKKα / IKKγor inhibiting IKKβ.Conclusions: Exposure of lung cancer cells to IR results in NFκB activation via IKK.The genetic or pharmacological blockage of the RAF1-ERK-IKK-NFκB pathway sensitizes cells to therapeutic doses of radiation. therefore, the IKK pathway is a promising target for therapeutic intervention in combination with radiotherapy.