Evidence for a lack of DNA double-strand break repair in human cells exposed to very low x-ray doses

TY - JOUR

T1 - Evidence for a lack of DNA double-strand break repair in human cells exposed to very low x-ray doses

AU - Rothkamm, Kai

AU - Löbrich, Markus

PY - 2003/4/29

Y1 - 2003/4/29

N2 - DNA double-strand breaks (DSBs) are generally accepted to be the most biologically significant lesion by which ionizing radiation causes cancer and hereditary disease. However, no information on the induction and processing of DSBs after physiologically relevant radiation doses is available. Many of the methods used to measure DSB repair inadvertently introduce this form of damage as part of the methodology, and hence are limited in their sensitivity. Here we present evidence that foci of gamma-H2AX (a phosphorylated histone), detected by immunofluorescence, are quantitatively the same as DSBs and are capable of quantifying the repair of individual DSBs. This finding allows the investigation of DSB repair after radiation doses as low as 1 mGy, an improvement by several orders of magnitude over current methods. Surprisingly, DSBs induced in cultures of nondividing primary human fibroblasts by very low radiation doses (approximately 1 mGy) remain unrepaired for many days, in strong contrast to efficient DSB repair that is observed at higher doses. However, the level of DSBs in irradiated cultures decreases to that of unirradiated cell cultures if the cells are allowed to proliferate after irradiation, and we present evidence that this effect may be caused by an elimination of the cells carrying unrepaired DSBs. The results presented are in contrast to current models of risk assessment that assume that cellular responses are equally efficient at low and high doses, and provide the opportunity to employ gamma-H2AX foci formation as a direct biomarker for human exposure to low quantities of ionizing radiation.

AB - DNA double-strand breaks (DSBs) are generally accepted to be the most biologically significant lesion by which ionizing radiation causes cancer and hereditary disease. However, no information on the induction and processing of DSBs after physiologically relevant radiation doses is available. Many of the methods used to measure DSB repair inadvertently introduce this form of damage as part of the methodology, and hence are limited in their sensitivity. Here we present evidence that foci of gamma-H2AX (a phosphorylated histone), detected by immunofluorescence, are quantitatively the same as DSBs and are capable of quantifying the repair of individual DSBs. This finding allows the investigation of DSB repair after radiation doses as low as 1 mGy, an improvement by several orders of magnitude over current methods. Surprisingly, DSBs induced in cultures of nondividing primary human fibroblasts by very low radiation doses (approximately 1 mGy) remain unrepaired for many days, in strong contrast to efficient DSB repair that is observed at higher doses. However, the level of DSBs in irradiated cultures decreases to that of unirradiated cell cultures if the cells are allowed to proliferate after irradiation, and we present evidence that this effect may be caused by an elimination of the cells carrying unrepaired DSBs. The results presented are in contrast to current models of risk assessment that assume that cellular responses are equally efficient at low and high doses, and provide the opportunity to employ gamma-H2AX foci formation as a direct biomarker for human exposure to low quantities of ionizing radiation.

KW - Cell Line

KW - DNA/radiation effects

KW - DNA Damage

KW - DNA Repair

KW - Dose-Response Relationship, Radiation

KW - Electrophoresis, Gel, Pulsed-Field

KW - Fluorescent Antibody Technique

KW - Histones/metabolism

KW - Humans

KW - Phosphorylation

U2 - 10.1073/pnas.0830918100

DO - 10.1073/pnas.0830918100

M3 - SCORING: Journal article

C2 - 12679524

VL - 100

SP - 5057

EP - 5062

JO - P NATL ACAD SCI USA

JF - P NATL ACAD SCI USA

SN - 0027-8424

IS - 9

ER -