In vitro studies of the genotoxicity of ionizing radiation in human G0 T lymphocytes

Abstract

In an effort to mimic human in vivo exposures to ionizing irradiation, G(0) phase T lymphocytes from human peripheral blood samples were utilized for in vitro studies of the genotoxic effects of (137)Cs low-LET irradiation and (222)Rn high-LET irradiation. Both types of radiation induced mutations in the HPRT gene in a dose-dependent manner, with a mutant frequency (MF) = 4.28 + 1.34x + 7.51x(2) for (137)Cs (R(2) = 0.95) and MF = 4.81 + 0.67x for (222)Rn (R(2) = 0.51). Post (137)Cs irradiation incubation in the presence of cytosine arabinoside, a reversible inhibitor of DNA repair, caused an increase in the MF over irradiation alone, consistent with a misrepair mechanism being involved in the mutagenicity of low-LET irradiation. The spectrum of (137)Cs irradiation-induced mutation displayed an increase in macro-deletions (in particular total gene deletions) and rearrangement events, some of which were further defined by either chromosome painting or direct DNA sequencing. The spectrum of (222)Rn irradiation-induced mutation was characterized by an increase in small alterations, especially multiple single base deletions/substitutions and micro-deletions. These studies define the specific response of human peripheral blood T cells to ionizing irradiation in vitro and form a basis for evaluating the genotoxic effects of human in vivo exposure.

Numt-Mediated Double-Strand Break Repair Mitigates Deletions during Primate Genome Evolution

“…In contrast, complex breaks include fragmented sugar damaged or missing bases in the vicinity of the break [64],[65]. While simple DSBs generated by endonucleases mainly cause small deletions, it is clear that a subset of random breaks leads to large deletions and translocations [43], [66]–[68]. For example, ionizing radiation induced hprt mutants resulted in deletions up to 56 kb whereas improper IgH class switching and spontaneous DSBs can lead to translocations [43], [66]–[68].…”

“…While simple DSBs generated by endonucleases mainly cause small deletions, it is clear that a subset of random breaks leads to large deletions and translocations [43], [66]–[68]. For example, ionizing radiation induced hprt mutants resulted in deletions up to 56 kb whereas improper IgH class switching and spontaneous DSBs can lead to translocations [43], [66]–[68]. Molecular characterization of large deletions and translocations revealed that they are mainly caused by microhomology-mediated repair [8],[43],[67],[69].…”

The Cellular and Molecular Carcinogenic Effects of Radon Exposure: A Review

“…Further analysis of CHO-K1 cells, following up from the study conducted by Hsie et al [117], failed to detect a difference between Hprt mutation spectra [118] and again in a similar contrast to some previous studies, work in human T lymphocytes [119] demonstrated less than 2% total gene deletions at the HPRT locus after exposure to radon and its daughters, although partial deletions were still present. Furthermore, human T lymphocytes exposed to high-LET radon (using the same methodology as described by Jostes et al [111]) and low-LET Caesium-137 found that the main marker of low-LET exposed lymphocytes were large deletions of the entire HPRT gene and high-LET exposure predominantly resulted in partial deletions and multiple single base changes [120]. Although not comparing high and low-LET exposures, other work in CHO cells using varying doses of Caesium-137 gamma-radiation has observed dose-dependent changes in mutation spectra [121] and a difference in mutation type between exposures of low (resulting mainly in point mutations) and high-dose (resulting in multibase deletion mutations).…”