BRCA1 ensures genome integrity by eliminating estrogen-induced pathological topoisomerase II–DNA complexes

Abstract

Women having BRCA1 germ-line mutations develop cancer in breast and ovary, estrogen-regulated tissues, with high penetrance. Binding of estrogens to the estrogen receptor (ER) transiently induces DNA double-strand breaks (DSBs) by topoisomerase II (TOP2) and controls gene transcription. TOP2 resolves catenated DNA by transiently generating DSBs, TOP2-cleavage complexes (TOP2ccs), where TOP2 covalently binds to 5′ ends of DSBs. TOP2 frequently fails to complete its catalysis, leading to formation of pathological TOP2ccs. We have previously shown that the endonucleolytic activity of MRE11 plays a key role in removing 5′ TOP2 adducts in G1phase. We show here that BRCA1 promotes MRE11-mediated removal of TOP2 adducts in G1phase. We disrupted theBRCA1gene in53BP1-deficient ER-positive breast cancer and B cells. The loss of BRCA1 caused marked increases of pathological TOP2ccs in G1phase following exposure to etoposide, which generates pathological TOP2ccs. We conclude that BRCA1 promotes the removal of TOP2 adducts from DSB ends for subsequent nonhomologous end joining.BRCA1-deficient cells showed a decrease in etoposide-induced MRE11 foci in G1phase, suggesting that BRCA1 repairs pathological TOP2ccs by promoting the recruitment of MRE11 to TOP2cc sites. BRCA1 depletion also leads to the increase of unrepaired DSBs upon estrogen treatment both in vitro in G1-arrested breast cancer cells and in vivo in epithelial cells of mouse mammary glands. BRCA1 thus plays a critical role in removing pathological TOP2ccs induced by estrogens as well as etoposide. We propose that BRCA1 suppresses tumorigenesis by removing estrogen-induced pathological TOP2ccs throughout the cell cycle.

SMC5/6 acts jointly with Fanconi anemia factors to support DNA repair and genome stability

“…[52]. As we experienced low IP efficiency with commercial SMC5 antibodies, we tagged endogenous SMC5 alleles C-terminally with the mAID-EGFP tag in human TK6 cells using CRISPR-Cas9, using the strategy reported in Ref.…”

A conserved SUMO-Ubiquitin pathway directed by RNF4/SLX5-SLX8 and PIAS4/SIZ1 drives proteasomal degradation of topoisomerase DNA-protein crosslinks

“…phosphodiesterases (TDPs) that hydrolyze the covalent tyrosine-DNA bond, with TDP1 excising TOP1-DPCs (Pouliot et al, 1999) and TDP2 excising TOP2-DPCs in higher eukaryotes (Cortes Ledesma et al, 2009). In additions to TDPs, endonucleases such as Mre11 and XPF have been reported to play a key role in removing both TOP-DPCs presumably by incising the DNA adjacent to the TOP-DPC (Aparicio et al, 2016;Pommier et al, 2016;Sasanuma et al, 2018). Proteolytic degradation is required for TDP activities and earlier work showed that the ubiquitin (Ub)proteasome pathway (UPP) plays an important role in proteolyzing TOP-DPCs (Desai et al, 1997;Mao et al, 2001).…”

DNA Double Strand Breaks and Chromosomal Translocations Induced by DNA Topoisomerase II

“…If HR is not available, in contrast to the "clean" end processing mediated by TDP2, endonucleases would potentially generate the loss of information at DNA ends (Figure 1). However, it has been shown that MRE11, the nuclease activity of the MRN complex, can process abortive TOP2 DSBs regulated by a HR-independent role of BRCA1 (Hoa et al, 2016;Sasanuma et al, 2018). Notably, MRE11 H129N (nuclease deficient) mutants exhibit increased instability and translocations when treated with TOP2 poisons (Sasanuma et al, 2018;Gothe et al, 2019).…”

“…However, it has been shown that MRE11, the nuclease activity of the MRN complex, can process abortive TOP2 DSBs regulated by a HR-independent role of BRCA1 (Hoa et al, 2016;Sasanuma et al, 2018). Notably, MRE11 H129N (nuclease deficient) mutants exhibit increased instability and translocations when treated with TOP2 poisons (Sasanuma et al, 2018;Gothe et al, 2019). The contribution of MRE11 and other nucleases such as ARTEMIS in the repair of physiological levels of TOP2 breaks, their relevance in TOP2 poison-based chemotherapy and their implication in TOP2-induced genome instability is under discussion.…”