Clustered DNA lesion repair in eukaryotes: Relevance to mutagenesis and cell survival

Abstract

A clustered DNA lesion, also known as a multiply damaged site, is defined as ≥ 2 damages in the DNA within 1-2 helical turns. Only ionizing radiation and certain chemicals introduce DNA damage in the genome in this non-random way. What is now clear is that the lethality of a damaging agent is not just related to the types of DNA lesions introduced, but also to how the damage is distributed in the DNA. Clustered DNA lesions were first hypothesized to exist in the 1990's, and work has progressed where these complex lesions have been characterized and measured in irradiated as well as in non-irradiated cells. A clustered lesion can consist of single as well as double strand breaks, base damage and abasic sites, and the damages can be situated on the same strand or opposing strands. They include tandem lesions, double strand break (DSB) clusters and non-DSB clusters, and base excision repair as well as the DSB repair pathways can be required to remove these complex lesions. Due to the plethora of oxidative damage induced by ionizing radiation, and the repair proteins involved in their removal from the DNA, it has been necessary to study how repair systems handle these lesions using synthetic DNA damage. This review focuses on the repair process and mutagenic consequences of clustered lesions in yeast and mammalian cells. By examining the studies on synthetic clustered lesions, and the effects of low vs high LET radiation on mammalian cells or tissues, it is possible to extrapolate the potential biological relevance of these clustered lesions to the killing of tumor cells by radiotherapy and chemotherapy, and to the risk of cancer in non-tumor cells, and this will be discussed.

Limited Repair of Critical DNA Damage in Cells Exposed to Low Dose Radiation

“…Many of IR-induced lesions are not randomly distributed but form, to a large extent, clusters, that is, they can be located in close proximity to each other. Typically, cluster DNA damage results from local matches of two or more single lesions within 1-2 turns of the DNA helix (Hada and Georgakilas, 2008;Sage and Harrison, 2011). A clustered DNA damage may represent damaged bases, AP sites located next to DSB or SSB.…”

“…It is well established that the level of clustering of DNA damage and their complexity increase with increasing LET of radiation (Terato and Ide, 2004;Sage and Harrison, 2011). For low-LET IR, this clustering occurs mainly on small sites of DNA and nucleosomes in the chromatin.…”

“…High-LET radiation can produce in DNA several DSB close to each other (Radulescu et al, 2004). The relationship between various DNA lesions in cells exposed to radiation with high-LET is changing in favor of more complex DNA damage (Sutherland et al, 2002;Sage and Harrison, 2011). Low-LET radiation, γ-rays in particular, causes in DNA DSB, 30% of which represent cluster formations.…”

“…This is due, exclusively, to the complexity of these breaks (Heilmann et al, 1993;Dianov et al, 2001). Tandems of different single lesions with DSB may further complicate the repair of both types of injury and increase their biological significance (Sutherland et al, 2000;Sage and Harrison, 2011). Thus, it is believed that the complexity and clustering are the most important specific characteristics of radiation-induced DNA lesions, which distinguishes them from the endogenous damage.…”

Papel das proteínas XPD e DNA polimerase eta nas respostas de células humanas a danos no genoma

“…Pode ocorrer também a formação de lesões em cluster, definidas pela presença de duas ou mais lesões (do tipo bases oxidadas, sítios AP ou quebras) dentro de uma ou duas voltas da hélice do DNA (Sage e Harrison, 2011 Charlet-Berguerand et al, 2006), enquanto polimerases ligadas a processos de reparo como a DNA polimerase beta (pol ) tendem a inserir a base correta, no caso C (Shibutani et al, 1991). Acredita-se que os efeitos deletérios dessa lesão estejam ligados principalmente à mutagênese, uma vez que por não ser uma lesão distorsiva, 8-OHdG causa uma parada apenas transiente da RNA polimerase II (Tornaletti et al, 2004;Kathe et al, 2004;Larsen et al, 2004); essa parada, entretanto, pode ser influenciada por outras variáveis como a concentração de ATP ou a sequência na qual a lesão está inserida (Allgayer et al, 2013).…”