High-LET Carbon and Iron Ions Elicit a Prolonged and Amplified p53 Signaling and Inflammatory Response Compared to low-LET X-Rays in Human Peripheral Blood Mononuclear Cells

Abstract

Understanding the differences in biological response to photon and particle radiation is important for optimal exploitation of particle therapy for cancer patients, as well as for the adequate application of radiation protection measures for astronauts. To address this need, we compared the transcriptional profiles of isolated peripheral blood mononuclear cells 8 h after exposure to 1 Gy of X-rays, carbon ions or iron ions with those of non-irradiated cells using microarray technology. All genes that were found differentially expressed in response to either radiation type were up-regulated and predominantly controlled by p53. Quantitative PCR of selected genes revealed a significantly higher up-regulation 24 h after exposure to heavy ions as compared to X-rays, indicating their prolonged activation. This coincided with increased residual DNA damage as evidenced by quantitative γH2AX foci analysis. Furthermore, despite the converging p53 signature between radiation types, specific gene sets related to the immune response were significantly enriched in up-regulated genes following irradiation with heavy ions. In addition, irradiation, and in particular exposure to carbon ions, promoted transcript variation. Differences in basal and iron ion exposure-induced expression of DNA repair genes allowed the identification of a donor with distinct DNA repair profile. This suggests that gene signatures may serve as a sensitive indicator of individual DNA damage repair capacity. In conclusion, we have shown that photon and particle irradiation induce similar transcriptional pathways, albeit with variable amplitude and timing, but also elicit radiation type-specific responses that may have implications for cancer progression and treatment

Comparison of the Medical Uses and Cellular Effects of High and Low Linear Energy Transfer Radiation

“…Following exposure to 0.5 Gy of either gamma rays, protons, carbon ions or alpha particles, it was observed that DSB-protein complexes persisted longer in the cell nucleus following higher LET irradiation [ 153 ]. In a similar study of 1 Gy X-ray, or carbon or iron ions, DSB foci in peripheral blood mononuclear cells were slower to resolve from high- LET radiations [ 154 ]. The dependence of high LET on HRR for DNA repair and the reduced rate of DNA repair in general suggested that high-LET radiation may reduce the efficiency of NHEJ [ 153 , 155 ].…”

“…p53 protein is recruited to DSB lesions containing ATM, ATR, and phosphorylated histone H2AX (γH2AX) [ 131 ]. The specific rearrangements of phosphorylation on p53 at 18 amino acids are critical for the modulation of its downstream activity [ 148 , 154 , 161 ]. Following DDR activation by radiation, p53 is rapidly dephosphorylated (dephosphosphorylated-S37, -S46, and -T55—apoptosis), while other sites are phosphorylated (phospho-S15—cell cycle arrest) [ 148 , 161 , 162 ].…”

“…Following DDR activation by radiation, p53 is rapidly dephosphorylated (dephosphosphorylated-S37, -S46, and -T55—apoptosis), while other sites are phosphorylated (phospho-S15—cell cycle arrest) [ 148 , 161 , 162 ]. p53 has been shown to have at least 350 confirmed gene targets and over 3500 potential targets [ 148 , 154 , 161 ]. A lack of p53 protein activation was shown to result in the loss of cell cycle inhibition (at either G1/S or G2/M) and the loss of cell checkpoint protein regulation [ 163 ].…”

“…A transcriptomic study of normal peripheral blood mononuclear cells showed that p53 was the primary transcription factor activated at 8 h following exposure to 1 Gy carbon or iron ion radiation or 1 Gy of X-ray irradiation, albeit with different kinetics [ 154 ]. Similar results were also found using normal fibroblasts, human mesenchymal stem cells, and human bronchial epithelial cells exposed to gamma radiation and high-LET radiation ( 125 I radiation, iron, or silicon ions), where genes regulating cell cycle and DNA damage were regulated comparably, likely downstream of p53 activation [ 228 , 229 , 230 ].…”

“…In contrast, studies suggest that the activation of NF-κB is more dependent upon the total dose and LET of radiation exposure, as well as on the cell type examined [ 154 , 231 , 232 ]. A study of HEK cells showed that NF-κB was activated at 4 h by ~1 Gy of high-LET radiation, but required 16 Gy of X-rays for activation at this time point [ 226 ].…”