Abstract
NBS1 is known to be involved in DNA damageβinduced cellular responses after exposure to ionizing radiation (IR). Phosphorylation of NBS1 contributes to cellβcycle checkpoints. The aim of this study was to determine whether heat exposure induces or stimulates cellular responses mediated by the phosphorylation of NBS1 in human skin fibroblast cell lines. The results of immunofluorescent staining and Western blot analysis showed that NBS1 proteins are phosphorylated after exposure to heat in the nucleus of a normal skin fibroblast cell line (82β6 cells). This suggests that the NBS1βmediated signal transduction could be induced by heat. We further examined whether a deficiency in the NBS1 protein modifies heat sensitivity in human skin fibroblast cell lines. A skin fibroblast cell line (Gmtert), derived from a Nijmegen breakage syndrome (NBS) patient containing mutant NBS1, showed higher sensitivity to heat than the same cell line transfected with the wildβtype copy of the NBS1 gene. We also showed that transfection of a DNA cassette expressing small interference RNA (siRNA) targeted to NBS1 into 82β6 cells enhanced cell sensitivity to heat. These results suggest that NBS1 is involved in cellular responses to DNA damage which is induced by heat exposure as well as by radiation exposure in human skin fibroblast cells. J. Cell. Biochem. 99: 1642β1650, 2006. Β© 2006 WileyβLiss, Inc.