RADIATION RESPONSE OF MOUSE LYMPHOID AND MYELOID CELL-LINES .3. DIFFERENT SIGNALS CAN LEAD TO APOPTOSIS AND MAY INFLUENCE SENSITIVITY TO KILLING BY DNA DOUBLE-STRAND BREAKAGE

We have examined the timing of gamma-irradiation-induced death in rela tion to cell cycle progression using a panel of mouse lymphoid or myel oid cell lines. Death was found to occur immediately after irradiation ('rapid interphase' death), or after arrest in G(2) phase ('delayed i nterphase' death), or following one or more mitoses ('mitotic/delayed mitotic' death). In part II of this series of papers we demonstrated t he occurrence of radiation-induced apoptosis in all these cell lines. This suggests that different signals can lead to apoptosis in these ce ll lints. DNA double-strand breakage appeared to directly stimulate th e destruction of cell lines susceptible to rapid interphase death, whi lst the signal for delayed interphase and mitotic death appeared to be chromosomal aberrations. Several of the cell lines showed different t iming of death dependent upon the radiation dose used. These differenc es in the timing of radiation-induced death are shown to be useful ind icators of the relative radiosensitivity of haematopoietic cell lines.