Cell death pathways in directly irradiated cells and cells exposed to medium from irradiated cells

Abstract

Purpose: The aim of this study was to compare levels of apoptosis, necrosis, mitotic cell death and senescence after treatment with both direct radiation and irradiated cell conditioned medium.

Materials and methods: Human keratinocytes (HaCaT cell line) were irradiated (0.005, 0.05 and 0.5 Gy) using a cobalt 60 teletherapy unit. For bystander experiments, the medium was harvested from donor HaCaT cells 1 hour after irradiation and transferred to recipient HaCaT cells. Clonogenic assay, apoptosis, necrosis, mitotic cell death, senescence and cell cycle analysis were measured in both directly irradiated cells and bystander cells

Results: A reduction in cell survival was observed for both directly irradiated cells and irradiated cell conditioned medium (ICCM)-treated cells. Early apoptosis and necrosis was observed predominantly after direct irradiation. An increase in the number of cells in G2/M phase was observed at 6 and 12 h which led to mitotic cell death after 72 h following direct irradiation and ICCM treatment. No senescence was observed in the HaCaT cell line following either direct irradiation or treatment with ICCM.

Conclusion: This study has shown that directly irradiated cells undergo apoptosis, necrosis and mitotic cell death whereas ICCM-treated cells predominantly undergo mitotic cell death.

Keywords::

• Radiation-induced bystander effects
• apoptosis
• necrosis
• mitotic cell death
• senescence

Acknowledgements

The authors are very grateful to St Luke's Hospital, Dublin, for continued access to the cobalt-60 radiotherapy source.

Declaration of interest The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

The authors acknowledge financial support from the European Sixth Framework Programme (FP6) Integrated Project, Non-targeted effects of ionising radiation (NOTE) FI6R 036465. The work was also conducted as part of the National Biophotonics and Imaging Platform of Ireland (NBIPI), funded by the Irish Government’s Programme for Research in Third Level Institutions, Cycle 4 (2007–2013).