Loss of E2F7 confers resistance to poly-ADP-ribose polymerase (PARP) inhibitors in BRCA2-deficient cells

Upon genotoxic stress, PCNA ubiquitination allows for replication of damaged DNA by recruiting lesion-bypass DNA polymerases. However, PCNA is also ubiquitinated during normal S-phase progression. By employing 293T and RPE1 cells deficient in PCNA ubiquitination, generated through CRISPR/Cas9 gene editing, here, we show that this modification promotes cellular proliferation and suppression of genomic instability under normal growth conditions. Loss of PCNA-ubiquitination results in DNA2-dependent but MRE11-independent nucleolytic degradation of nascent DNA at stalled replication forks. This degradation is linked to defective gap-filling in the wake of the replication fork and incomplete Okazaki fragment maturation, which interferes with efficient PCNA unloading by ATAD5 and subsequent nucleosome deposition by CAF-1. Moreover, concomitant loss of PCNA-ubiquitination and the BRCA pathway results in increased nascent DNA degradation and PARP inhibitor sensitivity. In conclusion, we show that by ensuring efficient Okazaki fragment maturation, PCNA-ubiquitination protects fork integrity and promotes the resistance of BRCA-deficient cells to PARP-inhibitors.

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“…Resulting colonies were screened by western blot. The BRCA2-knockout HeLa cells were previously published 72 .…”

Section: Methodsmentioning

confidence: 99%

Ubiquitinated-PCNA protects replication forks from DNA2-mediated degradation by regulating Okazaki fragment maturation and chromatin assembly

et al. 2020

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“…Together with these insights, our data suggest that low levels of E2F-dependent transcription sensitize cancer cells to replication stress. In further support of this notion, recent work showed that high levels of E2F-dependent transcription, via loss of E2F7, promotes resistance of cancer cells towards Poly (ADP-ribose) polymerase (PARP) inhibitors and interstrand-crosslinking drugs such as cisplatin or mitomycin C (33,34).…”

Section: Accepted Articlementioning

confidence: 95%

E2F7 Is a Potent Inhibitor of Liver Tumor Growth in Adult Mice

et al. 2021

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Upregulation of the E2F-dependent transcriptional network has been identified in nearly every human malignancy and is an important driver of tumorigenesis. Two members of the E2F family, E2F7 and E2F8, are potent repressors of E2F-dependent transcription. They are atypical in that they do not bind to dimerization partner (DP) proteins and are not controlled by pRb. The physiological relevance of E2F7 and E2F8 remains incompletely understood, largely because tools to manipulate their activity in vivo have been lacking. Here, we generated transgenic mice with doxycycline-controlled transcriptional activation of E2f7 and E2f8 and induce their expression during postnatal development, in adulthood, and in the context of cancer. Systemic induction of E2f7 and to lesser extendE2f8 transgenes in juvenile mice impaired cell proliferation, caused replication stress, DNA damage and apoptosis, and inhibited animal growth. In adult mice, however, E2F7 and E2F8 induction was well tolerated, yet profoundly interfered with DNA replication, DNA integrity and cell proliferation in DEN-induced liver tumors. Conclusion: Collectively, our findings demonstrate that atypical E2Fs can override cellcycle entry and progression governed by other E2F-family members, and suggest that this property can be exploited to inhibit proliferation of neoplastic hepatocytes when growth and development have subsided during adulthood.

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“…One study observed that BRCA2‐deficient cells treated with PARPi overcome therapeutic pressure by down‐regulating expression of the transcription repressor E2F7. One of the genes under the control of E2F7 is RAD51, and loss of E2F7 expression increases expression of RAD51, enhancing HR activity even in the absence of BRCA2 (Clements et al ., ).…”

Section: Targeting Dna Repair In Colorectal Cancermentioning

confidence: 97%

Exploiting DNA repair defects in colorectal cancer

et al. 2019

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Colorectal cancer ( CRC ) is the third leading cause of cancer‐related deaths worldwide. Therapies that take advantage of defects in DNA repair pathways have been explored in the context of breast, ovarian, and other tumor types, but not yet systematically in CRC . At present, only immune checkpoint blockade therapies have been FDA approved for use in mismatch repair‐deficient colorectal tumors. Here, we discuss how systematic identification of alterations in DNA repair genes could provide new therapeutic opportunities for CRC s. Analysis of The Cancer Genome Atlas Colon Adenocarcinoma ( TCGA ‐ COAD ) and Rectal Adenocarcinoma ( TCGA ‐ READ ) PanCancer Atlas datasets identified 141 (out of 528) cases with putative driver mutations in 29 genes associated with DNA damage response and repair, including the mismatch repair and homologous recombination pathways. Genetic defects in these pathways might confer repair‐deficient characteristics, such as genomic instability in the absence of homologous recombination, which can be exploited. For example, inhibitors of poly( ADP )‐ribose polymerase are effectively used to treat cancers that carry mutations in BRCA 1 and/or BRCA 2 and have shown promising results in CRC preclinical studies. HR deficiency can also occur in cells with no detectable BRCA 1/ BRCA 2 mutations but exhibiting BRCA ‐ like phenotypes. DNA repair‐targeting therapies, such as ATR and CHK 1 inhibitors (which are most effective against cancers carrying ATM mutations), can be used in combination with current genotoxic chemotherapies in CRC s to further improve therapy response. Finally, therapies that target alternative DNA repair mechanisms, such as thiopurines, also have the potential to confer increased sensitivity to current chemotherapy regimens, thus expanding the spectrum of therapy options and potentially improving clinical outcomes for CRC patients.

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Loss of E2F7 confers resistance to poly-ADP-ribose polymerase (PARP) inhibitors in BRCA2-deficient cells

Cited by 10 publications

References 41 publications

Ubiquitinated-PCNA protects replication forks from DNA2-mediated degradation by regulating Okazaki fragment maturation and chromatin assembly

Ubiquitinated-PCNA protects replication forks from DNA2-mediated degradation by regulating Okazaki fragment maturation and chromatin assembly

E2F7 Is a Potent Inhibitor of Liver Tumor Growth in Adult Mice

Exploiting DNA repair defects in colorectal cancer

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