Mechanistic insights into the survival curve of HeLa cells with a short shoulder and their S phase-specific sensitivity†.

HeLa cells are a cell line with two unique cellular features: a short-shouldered survival curve and two peaks of radioresistance during the cell cycle phase, while their underlying mechanisms remain unclear. We herein proposed that these radiobiological features are due to a common mechanism by which radiation suppresses homologous recombination repair (HRR) in a dose-dependent manner. This radio-suppression of HRR is mediated by an intra-S checkpoint and reduces survivals of cells in S phase, especially early S phase, resulting in both short shoulder and radioresistance with two peaks in the cell cycle. This new explanation may not be limited to HeLa cells since a similar close association of these features is also observed in other type of cells.

Establishment and activity of the planning and acting network for low dose radiation research in Japan (PLANET): 2016-2023.

The Planning and Acting Network for Low Dose Radiation Research in Japan (PLANET) was established in 2017 in response to the need for an all-Japan network of experts. It serves as an academic platform to propose strategies and facilitate collaboration to improve quantitative estimation of health risks from ionizing radiation at low-doses and low-dose-rates. PLANET established Working Group 1 (Dose-Rate Effects in Animal Experiments) to consolidate findings from animal experiments on dose-rate effects in carcinogenesis. Considering international trends in this field as well as the situation in Japan, PLANET updated its priority research areas for Japanese low-dose radiation research in 2023 to include (i) characterization of low-dose and low-dose-rate radiation risk, (ii) factors to be considered for individualization of radiation risk, (iii) biological mechanisms of low-dose and low-dose-rate radiation effects and (iv) integration of epidemiology and biology. In this context, PLANET established Working Group 2 (Dose and Dose-Rate Mapping for Radiation Risk Studies) to identify the range of doses and dose rates at which observable effects on different endpoints have been reported; Working Group 3 (Species- and Organ-Specific Dose-Rate Effects) to consider the relevance of stem cell dynamics in radiation carcinogenesis of different species and organs; and Working Group 4 (Research Mapping for Radiation-Related Carcinogenesis) to sort out relevant studies, including those on non-mutagenic effects, and to identify priority research areas. These PLANET activities will be used to improve the risk assessment and to contribute to the revision of the next main recommendations of the International Commission on Radiological Protection.