Pulsed low dose-rate irradiation response in isogenic HNSCC cell lines with different radiosensitivity

Todorovic, Vesna; Prevc, Ajda; Zakelj, Martina Niksic; Savarin, Monika; Bucek, Simon; Groselj, Blaz; Strojan, Primoz; Cemazar, Maja; Sersa, Gregor

doi:10.2478/raon-2020-0015

Figure 1

Schematic diagram of irradiation schedule.

Figure 2

$Surviving fraction of parental FaDu and radioresistant FaDu-RR cells after exposure to low doses of ionizing radiation. Symbols are mean ± standard error of the mean from four independent experiments. * - significantly different from FaDu cells.$

Surviving fraction of parental FaDu and radioresistant FaDu-RR cells after exposure to low doses of ionizing radiation. Symbols are mean ± standard error of the mean from four independent experiments. * - significantly different from FaDu cells.

Figure 3

$Surviving fraction of parental FaDu and radioresistant FaDu-RR after exposure to different PLDR irradiation regimes. (A) Surviving fraction of parental FaDu cells after 7x0.3 Gy PLDR and (B) after 10x0.2 Gy PLDR irradiation. (C) Surviving fraction of radioresistant FaDu-RR cells after 7x0.3 Gy PLDR and (D) after 10x0.2 Gy PLDR irradiation. Bars present mean ± SEM from four independent experiments. ** = significantly different from 0 Gy and low dose IR (0.3 Gy or 0.2 Gy); * = significant difference between the groups; n. s. = non-significant difference.$

Surviving fraction of parental FaDu and radioresistant FaDu-RR after exposure to different PLDR irradiation regimes. (A) Surviving fraction of parental FaDu cells after 7x0.3 Gy PLDR and (B) after 10x0.2 Gy PLDR irradiation. (C) Surviving fraction of radioresistant FaDu-RR cells after 7x0.3 Gy PLDR and (D) after 10x0.2 Gy PLDR irradiation. Bars present mean ± SEM from four independent experiments. ** = significantly different from 0 Gy and low dose IR (0.3 Gy or 0.2 Gy); * = significant difference between the groups; n. s. = non-significant difference.

Figure 4

Cell cycle distribution in parental FaDu and radioresistant FaDu-RR cells after exposure to different PLDR irradiation regimes. (A) Cell cycle distribution in FaDu cells 5 h and (B) 24 h after irradiation. (C) Cell cycle distribution in FaDu-RR cells 5 h and (D) 24 h after irradiation. Bars present mean ± SEM from four independent experiments. * = significantly different from 0 Gy; ** = significantly different from 0 Gy and 0.3 Gy; # = significantly different from 0 Gy, 0.3 Gy and 2.1 Gy; n. s. = non-significant difference.

Figure 5

Heat maps of DNA damage signalling gene expression in parental FaDu (A) and radioresistant FaDu-RR cells (B) in 0.3 Gy, 2.1 Gy and 7x0.3 Gy irradiated cells relative to the gene expression in control non-irradiated cells. The magnitude of the fold change in gene expression of each gene from three independent experiments is represented by the colour. Green indicates under-expressed genes, and red indicates over-expressed genes.

Figure 6

DNA damage signalling gene expression in parental FaDu and radioresistant FaDu-RR cells in response to different irradiation protocols. (A) Gene expression of FaDu cells in response to 0.3 Gy, 2.1 Gy, and 7x0.3 Gy irradiation relative to the control non-irradiated FaDu cells. (B) Gene expression in FaDu-RR cells in response to 0.3 Gy, 2.1 Gy, and 7x0.3 Gy irradiation relative to the control non-irradiated FaDu-RR cells. Volcano plots show the fold change in gene expression and statistical significance (p value). The horizontal line shows the statistical significance threshold (p value < 0.05). Two vertical dashed lines show the threshold of over-expressed (right) and under-expressed genes (left), while the solid vertical line shows no change in gene expression. Symbols represent the mean gene expression of each tested gene in irradiated cells relative to control non-irradiated cells from three independent experiments.

Figure 7

Venn diagrams of DNA damage signalling gene expression in parental FaDu and radioresistant FaDu-RR cells showing overlapping and differential gene expression. Only genes significantly over-expressed or under-expressed relative to control non-irradiated cells are shown. Genes in bold red are over-expressed, genes in bold green are under-expressed.

Figure 8

Heat maps of DNA damage signalling gene expression in radioresistant FaDu-RR cells relative to the gene expression in parental FaDu cells. The magnitude of the fold change in gene expression of each gene from three independent experiments is represented by colour. Green indicates under-expressed genes, and red indicates over-expressed genes.

Figure 9

DNA damage signalling gene expression in radioresistant FaDu-RR cells relative to parental FaDu. (A) Gene expression in control non-irradiated cells. (B) Gene expression in 0.3 Gy irradiated cells. (C) Gene expression in 2.1 Gy irradiated cells. (D) Gene expression in 7x0.3 Gy irradiated cells. Volcano plots show the fold change in gene expression in radioresistant FaDu-RR relative to parental FaDu cells and statistical significance (p value). The horizontal line shows the statistical significance threshold (p value < 0.05). Two vertical dashed lines show the threshold of over-expressed (right) and under-expressed genes (left), while the solid vertical line shows no change in gene expression. Symbols represent the mean gene expression of each tested gene in radioresistant FaDu-RR cells relative to parental FaDu cells from three independent experiments.

Figure 10

Venn diagrams of DNA damage signalling gene expression in radioresistant FaDu-RR cells showing overlapping and different gene expression after different irradiation protocols relative to parental FaDu cells. Only genes significantly over-expressed or under-expressed relative to parental FaDu cells are shown. Gene in bold red is over-expressed, genes in bold green are under-expressed.