DNA glycosylase activity and cell proliferation are key factors in modulating homologous recombination in vivo

Abstract

Cancer susceptibility varies between people, affected by genotoxic exposures, genetic makeup and physiological state. Yet, how these factors interact among each other to define cancer risk is largely unknown. Here, we uncover the interactive effects of genetical, environmental and physiological factors on genome rearrangements driven by homologous recombination (HR). Using FYDR mice to quantify HR-driven rearrangements in pancreas tissue, we show that DNA methylation damage (induced by methylnitrosourea) and cell proliferation (induced by thyroid hormone) each induce HR and together act synergistically to induce HR-driven rearrangements in vivo. These results imply that developmental or regenerative proliferation as well as mitogenic exposures may sensitize tissues to DNA damaging exposures. We exploited mice genetically deficient in alkyl-adenine DNA glycosylase (Aag) to analyse the relative contributions of unrepaired DNA base lesions versus intermediates formed during base excision repair (BER). Remarkably, results show that, in the pancreas, Aag is a major driver of spontaneous HR, indicating that BER intermediates (including abasic sites and single strand breaks) are more recombinogenic than the spontaneous base lesions removed by Aag. Given that mammals have about a dozen DNA glycosylases, these results point to BER as a major source of pressure on the HR pathway in vivo. Taken together, methylation damage, cell proliferation and Aag interact to define the risk of HR-driven sequence rearrangements in vivo. These data identify important sources of sequence changes in a cancer-relevant organ, and advance the effort to identify populations at high-risk for cancer.

ALKBH7 drives a tissue and sex-specific necrotic cell death response following alkylation-induced damage

“…Four independent studies were performed and analysis of the approximate LD 50 was assessed as we have previously described. 75 At four doses per experiment, the lowest dose at which a mouse was moribund or dies within 30 days was determined as the approximate LD 50 .…”

Contributions of DNA repair and damage response pathways to the non-linear genotoxic responses of alkylating agents

“…This paradigm is evident in the interactions between BER that promote HR events (Figure 5). The Engelward laboratory has shown that conditions inhibiting the initiation of BER actually suppress HR in vivo , presumably because the BER intermediates (including SSB or abasic sites) are more recombinogenic than some of the original adducted base substrates of BER [95]. These results show that changes in the balance of activity and protein products in one pathway (BER) can affect processing via another pathway (HR) and may put cells at increased risk of mutation.…”

BERing the burden of damage: Pathway crosstalk and posttranslational modification of base excision repair proteins regulate DNA damage management

“…To avoid the accumulation of deleterious damage intermediates, BER must therefore be efficiently and precisely regulated to initiate and complete repair. In fact, the BER intermediates generated by the alkyladenine glycosylase induce more robust HR than the initial alkylation damage in vivo 58 . The impact of BER and DSB repair pathway cross regulation and how the cell cycle phase contributes to pathway crosstalk to maintain genome stability are areas that require further study.…”