Activation of NF-κB-Dependent Gene Expression by Accelerated Light and Heavy Ions

Kurzfassung

During space missions, astronauts are exposed to not only greater amounts of natural radiation than they receive on earth but also to a differing radiation quality, which can result in immediate and long-term risks. To estimate the cancer risk, the molecular and the cellular mechanisms of the response to cosmic radiation have to be uncovered. As the transcription factor Nuclear Factor κB (NF-κB) is involved in cell regulation of apoptosis (programmed cell death), it could influence the cellular outcome (survival, mutation, apoptosis) after radiation exposure and therefore the cancer risk. Human Embryonic Kidney (HEK/293) cells stably transfected with a receptor-reporter-construct carrying the destabilized variant of Enhanced Green Fluorescent Protein (d2EGFP) under the control of the NF-κB response element were used in this work to analyse the NF-κB-dependent gene expression in response to accelerated light and heavy ions. Irradiation was performed either with X-rays (150 kV), with 75 MeV/nucleon carbon or 29 MeV/nucleon lead ions at GANIL (LET ~30 or 8800 keV/μm, respectively), Caen, or with 2.1 MeV α particles (LET ~160 keV/μm) at PTB, Braunschweig. After irradiation the following biological endpoints were determined (i) cell survival via the colony forming ability test, (ii) time-dependent activation of NF-κB dependent d2EGFP gene expression using flow cytometry, (iii) quantitative Reverse Transcription Polymerase Chain Reaction (qRT-PCR) of selected NF-κB target genes. High X-ray doses induce the expression of IκBα and GADD45β. After exposure with 1 nuclear hit of 2.1 MeV α particles, d2EGFP fluorescence can already be seen. After exposure of HEK cells with 5 nuclear hits, maximal NF-κB activation is achieved. The NF-κB target genes IκBα and GADD45β are upregulated shortly after α-particle exposure. Exposure to carbon ions results in a slight activation of the NF-κB pathway. Lead ions induced the expression of the IκBα gene. The NF-κB pathway is activated by particle radiation, and the extent of activation seems to correlate with the LET of the applied radiation. As activation of the NF-κB pathway is supposed to play a role in the negative regulation of apoptosis, survival of cells with DNA damage might be favoured especially after low doses of densely ionising radiation.