Dose-dependent spatiotemporal responses of mammalian cells to an alkylating agent

Cultured cell populations are composed of heterogeneous cells, and previous single-cell lineage tracking analysis of individual HeLa cells provided empirical evidence for significant heterogeneity of cell fates. Nevertheless, such cell lines have been used for investigations of cellular responses to various substances, resulting in incomplete characterizations. This problem caused by heterogeneity within cell lines could be overcome by analyzing the spatiotemporal responses of individual cells to a substance. However, no approach to investigate the responses using spatiotemporal data is currently available. Thus, the current study aimed to analyze the spatiotemporal responses of individual HeLa cells to cytotoxic, sub-cytotoxic, and non-cytotoxic doses of the well-characterized carcinogen, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Although cytotoxic doses of MNNG are known to induce cell death, the single-cell tracking approach revealed that cell death occurred following at least four different cellular events, suggesting that cell death is induced via multiple processes. We also found that HeLa cells exposed to sub-cytotoxic doses of MNNG were in a state of equilibrium between cell proliferation and cell death, with cell death again induced through different processes. However, exposure of cells to non-cytotoxic doses of MNNG promoted growth by reducing the cell doubling time, thus promoting the growth of a sub-population of cells previously recognized as putative cancer stem cells. These results demonstrate that the responses of cells to MNNG can be analyzed precisely using spatiotemporal data, regardless of the presence of heterogeneity among cultured cells, suggesting that single-cell lineage tracking analysis can be used as a novel and accurate analytical method to investigate cellular responses to various substances.