- 157- TP53 Foci Formation at Sites of Radiation-Induced DNA-Damage


The tumour suppressor protein TP53 plays an essential role in the cellular radiation response and in the maintenance of genomic integrity, being involved in cell cycle regulation and DNA repair. TP53 is a sequence specific transcription activator, yet it can also bind to DNA in an unspecific way. In connection with the prolonged cell cycle arrest and repair times observed after complex DNA damage, we were interested in studying the interrelation between these endpoints. We examined the subnuclear localisation of TP53 after ionising radiation by means of immuncytochemical staining and confocal laser scanning microscopy. The TP53 protein was found to accumulate into foci in the cell nuclei after X-ray and ion irradiation (Fig. 1). The response was observed in primary (AG1522) and TP53 wild type tumour cells. We could detect the development of TP53 foci 2 h after X-ray irradiation and even earlier (0.5 h) after ion irradiation. However, TP53 foci were not detected immediately after irradiation. U a) TP53 b) γH2AX TP53 merged Figure1: a)TP53fociformation2hafterirradiationwithUions2×10 6 p/cm 2 b) Colocalization of TP53 and DSB-Marker γH2AX 5 h after irradiation with 2 Gy X-rays; both a) and b) nuclei of human fibroblasts. We showed the correlation between TP53 foci and the sites of particle traversals by the retrospective etching method [1]. After immuncytochemical staining of TP53, the pattern of foci was found to coincide extremely well with the pattern of particle traversals at the corresponding irradiated positions (Fig. 2). TP53 and PI Next we compared the number of residual TP53 foci per nucleus for different doses (5 to 20 Gy) 17 h after irradiation with X-rays. The increase of the mean values with increasing doses shows a dose dependency in the persistence of TP53 foci after irradiation (Fig. 3)

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