Abstract
In order to investigate function of NBS1, the protein responsible for Nijmegene breakage syndrome (NBS), we established Nbs1 knockout DT40 cell lines. The Nbs1-knockout cells showed not only the defect in homologous recombination repair of DNA double strand breaks, but also marked suppression of apoptosis induction following irradiation. Because DT40 cells lack p53, Nbs1 mediating apoptosis seemed to be independent of p53 pathway. The suppression of apoptosis was also observed in lymphoblastoid cells derived from NBS patients with functional p53. Because NBS lymphoblastoid showed further reduction of apoptosis compared to ATM deficient cells, NBS1 might function in ATM-p53 independent pathway. To determine the apoptotic pathway mediated by NBS1, expression of pro-apoptotic factors in NBS fibroblast immortalized with SV40 or in its NBS1 complemented cells was analyzed. Although Chk2 activation after irradiation was impaired in NBS cells, any differences in E2F-1 stabilization between NBS and the complemented cells were not observed. In contrast, Bax activation was obviously decreased in NBS cells, and it was well correlated to complementation of apoptosis induction, suggesting the involvement of NBS1 in Bax activation process. In this presentation, the role of NBS1 in Bax activation and critical domains of NBS1 for apoptosis regulation will be discussed.
