DNA damage foci: Meaning and significance

Abstract

The discovery of DNA damage response proteins such as γH2AX, ATM, 53BP1, RAD51, and the MRE11/RAD50/NBS1 complex, that accumulate and/or are modified in the vicinity of a chromosomal DNA double-strand break to form microscopically visible, subnuclear foci, has revolutionized the detection of these lesions and has enabled studies of the cellular machinery that contributes to their repair. Double-strand breaks are induced directly by a number of physical and chemical agents, including ionizing radiation and radiomimetic drugs, but can also arise as secondary lesions during replication and DNA repair following exposure to a wide range of genotoxins. Here we aim to review the biological meaning and significance of DNA damage foci, looking specifically at a range of different settings in which such markers of DNA damage and repair are being studied and interpreted.

The second gamma-H2AX assay inter-comparison exercise carried out in the framework of the European biodosimetry network (RENEB)

“…the dicentric assay (Romm et al 2014). However, this is much less of an issue for the gamma-H2AX assay where, in comparison, there are many events (foci) per cell and many other factors contributing to dose uncertainty (Rothkamm & Horn 2009;Rothkamm et al 2015). In addition, no significant effect of post-exposure time on the dose estimate was seen, as found in the first inter-comparison.…”

“…To improve dose estimates, however, there are a number of additional points that will need to be addressed going forward, before all the influencing factors are fully understood and the assay can be categorized as fully operational for routine dose estimation. This includes the variability between individual slides (staining reproducibility) and variability between images (image/microscope setting reproducibility) (Rothkamm & Horn 2009;Rothkamm et al 2015).…”

“…The gamma-H2AX foci assay is a sensitive surrogate marker of radiation induced DNA double strand breaks (Ivashkevich et al 2012;Rothkamm et al 2015) and may be a useful early biodosimetry tool from hours to about three days post-exposure (Roch-Lef evre et al 2010;Mandina et al 2011). Several studies have shown that rapid processing time of the gamma-H2AX assay can produce dose estimates within a few hours of receiving a blood sample (Rothkamm et al 2013a;Ainsbury et al 2014).…”

Perturbation of PALB2 function by the T413S mutation found in small cell lung cancer

“…This observation is somewhat puzzling since most studies report a robust correlation between RAD51 and γH2A.X nuclear foci formation. Nonetheless, the exact nature, meaning and significance of DNA repair proteins nuclear foci remain unclear 45 , and the RAD51 nuclear foci observed in PALB2 T413S expressing cells do not necessarily reflect regular HDR events. It is conceivable that, through its interaction with BRCA1, PALB2 T413S can initiate RAD51 recruitment, but for as-yet-unknown reasons, fail to promote HDR.…”

Association between p53-binding protein 1 expression and genomic instability in oncocytic follicular adenoma of the thyroid

“…53BP1 is a nuclear protein that rapidly localizes to sites of DNA double-strand breaks and activates p53 along with other kinases, which plays critical roles in DDRs including cell cycle arrest, DNA repair, and apoptosis [18][19][20]. It has been well documented in vitro by immunofluorescence studies that 53BP1 exhibits faint diffuse nuclear staining in untreated primary cells, whereas after exposure to radiation, 53BP1 is localized at the sites of DNA double-strand breaks and forms discrete nuclear foci [20,21]. We have recently demonstrated that the presence of 53BP1 nuclear foci as detected by immunofluorescence might serve as a valuable molecular marker of genomic instability during carcinogenesis, which seems to be induced at the precancerous stage during thyroid, skin and cervical carcinogenesis, as follicular adenoma and actinic keratosis [22,23].…”