5　低線量γ線照射細胞からのATP 放出とその後のプリン受容体活性化を介した細胞内抗酸化物チオレドキシン-1（Trx-1）の誘導

Summary 　We previously reported that low doses（0.25-0.5 Gy）of γ-rays elevated Trx-1 in various organs of mice after whole-body irradiation. Meanwhile, it is reported that extracellular ATP, which is released in response to various stresses, regulates the expression of intracellular antioxidants through activation of P2 receptors. We have recently reported that ATP is released from the cells exposed to low-dose γ-rays. 　Here, we investigated whether or notγ-radiation-induced release of extracellular ATP contributes to the induction of cellular antioxidant thioredoxin（Trx-1）, using RAW264.7 cells. Irradiation withγ-rays or exogenously added ATP increased expression of Trx-1, and the increases were blocked by pretreatment with an ecto-nucleotidase in both cases. Moreover, ATP stimulation promoted generation of intracellular ROS and also increased Trx-1 expression. The increase of Trx-1 expression was significantly suppressed by pre-treatment of the cells with antioxidants. 　To sum up, theγ-radiation-induced release of extracellular ATP may, at least in part, contribute to production of ROS via purinergic signaling, leading to promotion of intracellular antioxidants to an oxidative stress.