Project description:Children are considered more sensitive to radiation-induced cancer than adults, yet any differences in genomic alterations associated with age at exposure and their underlying mechanisms remain unclear. We analyzed the mutation of key tumor suppressor genes in T-cell lymphomas arising after weekly irradiation of female B6C3F1 mice with 1.2 Gy X-rays for 4 consecutive weeks starting during infancy (1 week old), adolescence (4 weeks old) or as young adults (8 weeks old). T-cell lymphoma incidence did not show any statistical differences among three irradiated groups; however, the frequency of loss of heterozygosity on chromosomes 11 and 19 showed opposing correlations with age at exposure. Ikaros on chromosome 11 was mutated frequently in the young adult–irradiation group (63%; 5/8), frequently incurring multiple independent hits (including deletions and mutations) or suffering a single hit predicted to result in a dominant negative protein (such as those lacking exon 4, an isoform we have designated Ik11, which lacks two of the four zinc–finger domains important for DNA binding). Pten on chromosome 19 was mutated more frequently in tumors from infant- (67%; 10/15) compared with young adult-irradiated mice (13%; 1/8, P = 0.041). Despite the presence of homozygous Pten mutations, DNA copy number was unchanged in the infant-irradiation group, suggesting duplication of the mutated allele by chromosome mis-segregation or mitotic recombination. Taken together, our findings demonstrate that while deletions on chromosome 11 affecting the Ikaros locus are a prominent feature of young adult irradiation-induced T-cell lymphoma, tumors arising after infant irradiation suffer a second hit in the Pten gene by chromosome mis-segregation or recombination. This is the first report showing age-at-exposure associated radiation-induced genomic alterations in two key tumor suppressor genes linked to T-cell lymphomagenesis. These data are important for considering the risks associated with childhood exposure to radiation.

Project description:While modern radiotherapy technologies can precisely deliver higher doses of radiation to tumors; thus, reducing overall radiation exposure to normal tissues, moderate dose and normal tissue toxicity still remains a significant limitation. The present study profiled the global effects on transcript and miR expression in Human Coronary Artery Endothelial Cells (HCAECs) using single-dose irradiation (SD, 10Gy) or multi-fractionated irradiation (MF, 2Gy x 5) regimens. Longitudinal timepoints were collected after a SD or final dose of MF irradiation for analysis using Agilent Human Gene Expression and miRNA microarray platforms. Compared to SD, the exposure to MF resulted in robust transcript and miR expression changes in terms of the number and magnitude. For data analysis, statistically significant mRNAs (2-fold) and miRs (1.5-fold) were processed by Ingenuity Pathway Analysis (IPA) to uncover miRs associated with target transcripts from several cellular pathways post-irradiation. Interestingly, MF radiation induced a cohort of mRNAs and miRs that coordinate the induction of immune response pathway under tight regulation. Additionally, mRNAs and miRs associated with DNA replication, recombination and repair, apoptosis, cardiovascular events and angiogenesis were revealed. Human Coronary Artery Endothelial Cells (HCAECs) were irradiated in a PANTAK high frequency X-ray generator (Precision X-ray Inc., N. Bedford, CT), operated at 300kV and 10MA. The dose rate was 1.6 Gy per min. Cells were plated into T75cm2 flasks (1-1.5 x 10^6 for single dose radiation and 0.6-0.8 x 10^6 for fractionated radiation). After 24h, cells were exposed to a total of 10 Gy radiation administered either as a single-dose radiation (SD), or as multi-fractionated radiation of 2 Gy x 5 (MF). These non-isoeffective doses were selected to simulate clinical hypofractionated and conventionally fractionated radiotherapy regimens. For the MF protocol, cells were exposed to 2 Gy radiation twice a day, at 6h interval. The cells were approximately 90% confluent at the time of harvesting. For both protocols, radiation-induced changes were analyzed at 6h and 24h after a SD and 6h and 24h after the final dose of fractionated irradiation. Separate controls were maintained for SD and MF radiation protocols.

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Mouse T-cell lymphomas induced by irradiation at different ages

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