Chronic low-dose radiation inhibits the cells death by cytotoxic high-dose radiation increasing the level of AKT and acinus proteins via NF-kappa B activation

Purpose : This study explored the effects of low-dose and low-dose-rate irradiation in human lung fibroblast CCD-18Lu cells and examined the role of AKT (protein kinase B, PKB) in cellular responses. Materials and methods : We examined cell survival after chronic low-dose irradiation (0.01 Gy or 0.05 Gy) with challenging high-dose (2 or 10 Gy) irradiation. We examined the effect of AKT activation on cell survival after chronic low-dose radiation using transduced cells with retroviral vector expressing constitutively active AKT (CA-AKT). Results : Chronic low-dose priming irradiation increased cells viability against the challenging high-dose irradiation. Irradiation at 0.05 Gy increased cellular levels of AKT and acinus long form (L) and short form (S). The chronic low-dose radiation promoted cells proliferation in the exogenously expressed CA-AKT cells. It also increased nuclear factor-kappa B (NF-kappa B) activity in a biphasic induction pattern. Suppression of NF-kappa B activation by mutant form of inhibitor of kappa B alpha (I kappa B alpha M) antagonized the radiation-induced expression of AKT and acinus L and S. Conclusions : Chronic low-dose radiation increases the levels of AKT and acinus proteins via NF-kappa B activation, and the NF-kappa B/AKT pathway responding to chronic low-dose irradiation plays an important role in the radiation adaptive response.