Apoptosis induced by X-rays and chemical agents in murine fibroblastic cell lines with a defect in repair of DNA double-strand breaks

Purpose: To investigate apoptosis in murine fibroblasts that are deficient in DNA double-stand breaks (dsb) repair. Materials and methods: BALB/c 3T3 cells and cells from a severe combined immunodeficient (scid) mouse were exposed to X-rays, UV light, bleomycin, etoposide or cisplatin. After exposure, the rate of apoptosis was assayed by propidium iodide staining based on characteristic morphological change. Results: The scid cells, defective in dsb repair, were extremely sensitive to apoptosis induced by X-rays and bleomycin compared with BALB/c 3T3 cells. The scid cells were slightly sensitive to apoptosis induced by etoposide, an agent producing proteinassociated dsb, and to apoptosis induced by agents not causing dsb. Conclusions: These studies show that sensitivity of cells to apoptosis induced by X-rays or bleomycin is enhanced by the scid mutation and that apoptosis induced by etoposide, which causes proteinassociated dsb, is not greatly affected. There may be different processes involved in the induction of apoptosis by X-rays or bleomycin and etoposide.