Localization of targets for regulation of gene expression after ionising radiation

Ionising radiation induces different and diverse effects in cells. Early and late response genes are induced by the radiation stress. The signal transduction for genes regulated by ionising radiation involves the activation of different kinases. However, the localisation of the triggering elements for the regulation of genes after ionising radiation has not been characterised. The aim of this thesis was to localise and identify elements responsible for the regulation of genes after low level ionising radiation. Different radiolabelled chemicals were employed to target different cellular compartments. Tritiated thymidine, 125I-concanavalin A and tritiated water were employed to irradiate the nucleus, membrane and whole cell, respectively. Compared to whole cell irradiation, nuclear irradiation at low doses (0.5 h at 0.075, 0.4 Gy/h) resulted in preferential regulation of c-fos and c-myc proteins over their encoding mRNA. On the other hand, membrane irradiation at much higher doses (0.5 h at 6.8 Gy/h) only resulted in the induction of c-fos transcripts. The results in this thesis propose a distinctive role for the different cellular compartments in the regulation of genes at different levels after ionising radiation. Triggering of the regulatory mechanisms for the regulation of different genes could be controlled by elements in different cellular compartments. Furthermore, the sensitivity and effectiveness of the nucleus in regulating genes and inducing cell death after ionising radiation is unequivocally evident. Nonetheless, the transcriptional regulation of NF-κB (1.9 fold) after low membrane doses (0.5 h at 0.25 Gy/h) suggests the presence of some sensitive elements in the cellular membrane. Damage to membrane elements is also implicated in the apoptotic processes responsible for cell lethality after membrane irradiation (LD50 = 80.19). These results have implications for radiation induced carcinogenesis and mutation after low level ionising radiation. (author)