Yi, M-J., Park, S-H., Cho, H-N., Chung, H. Y., Kim, J-I., Cho, C-K., Lee, S-J. and Lee, Y-S. Heat-Shock Protein 25 (Hspb1) Regulates Manganese Superoxide Dismutase through Activation of Nfkb (NF-κB). Radiat. Res. 158, 641–649 (2002).

We previously demonstrated that overexpression of HSP25 (now known as Hspb1) conferred increased resistance to ionizing radiation (Radiat Res. 154, 421–428, 2000). In the present study, L929 cells overexpressing Hspb1 were shown to have increased expression of the manganese superoxide dismutase gene (now known as SOD2) and its enzyme activity. To elucidate Hspb1-induced pathways leading to activation of these antioxidant enzymes, the production of the tumor necrosis factor alpha (Tnf) and interleukin 1 beta (Il1b) genes was examined. Increased expression of Tnf and Il1b resulting from Hspb1 overexpression was detected by RT-PCR. Increased activation of Nfkb (degradation of Ikb, a member of the Nfkb family) was also found in Hspb1-overexpressing cells. When treated with Tnf, Nfkb activation and SOD2 gene expression were increased more by Hspb1 overexpression. Moreover, transfection with the Hspb1 antisense gene abrogated all of the Hspb1-mediated phenomena. To further elucidate the exact relationship between induction of SOD2 and Nfkb activation, a dominant negative I-kBα (now known as Nfkb1a) construct was transfected into Hspb1-overexpressing cells. The dominant negative Nfkb1a inhibited Hspb1-mediated SOD2 gene expression. In addition, Hspb1-mediated radioresistance was blocked by dominant negative Nfkb1a transfection. When the SOD2 gene was transfected into L929 cells, a somewhat increased radioresistance was detected by a clonogenic survival assay compared to control cells. Hspb1 produced Tnf and Il1b and facilitated SOD2 gene expression through Nfkb activation, possibly resulting in Hspb1-mediated radioresistance.