1. ¹Laboratory of Radiation Effect, Division of Radiation Biology, Korea Institute of Radiological and Medical Sciences, 215-4 Gongneung-Dong, Nowon-Ku, Seoul 139-706, Korea
2. ²Department of Microbiology, College of Medicine, Hanyang University, Seoul 133-791, Korea
3. ³Division of Molecular Life Science, Ewha Woman's University, Seoul 120-750, Korea
4. ⁴Laboratory of Signal Transduction, Department of Chemistry, Inha University, Incheon 402-751, Korea
5. ⁵Division of Life Sciences, Kangwon National University College of Natural Sciences, Chuncheon 200-701, Korea

Correspondence: Y-S Lee, E-mail: [email protected]

Received 19 October 2004; Revised 30 November 2004; Accepted 30 November 2004; Published online 04 April 2005.

Abstract

Since radiation-induced caspase-dependent apoptosis and ROS generation were partially prevented by HSP25 overexpression, similar to the treatment of control cells with antioxidant agents such as DPI and tiron, questions arise whether radiation-mediated ROS generation contributes to the apoptotic cell death, and also whether HSP25 overexpression can reduce ROS mediated apoptotic cell death. In the present study, radiation-induced cytochrome c release from mitochondria and activation of caspases accompanied by a decrease of mitochondrial membrane potential in Jurkat T cells were shown to be inhibited by mitochondrial complex I inhibitor rotenone, suggesting that mitochondrial ROS might be important in radiation-induced caspase-dependent apoptosis. When HSP25 was overexpressed, effects similar to the treatment of cells with the antioxidants were obtained, indicating that HSP25 suppressed radiation-induced mitochondrial alteration that resulted in apoptosis. Furthermore, activation of p38 MAP kinase by radiation was associated with radiation-induced cell death and ROS production and PKC was an upstream molecule for p38 MAP kinase activation, ROS generation and subsequent caspase-dependent apoptotic events. However, in the HSP25 overexpressed cells, the above-described effects were blocked. In fact, radiation-induced membrane translocation of PKC and tyrosine phosphorylation were inhibited by HSP25. Based on the above data, we suggest that HSP25 downregulates PKC, which is a key molecule for radiation-induced ROS generation and mitochondrial-mediated caspase-dependent apoptotic events.