Polymerase iota plays a key role during translesion synthesis of UV-induced lesions in the absence of polymerase eta.

Xeroderma pigmentosum (XP) variant cells are deficient in the translesion synthesis (TLS) DNA polymerase Polη (eta). This protein contributes to DNA damage tolerance, bypassing unrepaired UV photoproducts and allowing S-phase progression with minimal delay. In the absence of Polη, backup polymerases perform TLS of UV lesions. However, which polymerase plays this role in human cells remains an open question. Here, we investigated the potential role of Polι (iota) in bypassing ultraviolet (UV) induced photoproducts in the absence of Polη, using NER-deficient (XP-C) cells knocked down for Polι and/or Polη genes. Our results indicate that cells lacking either Polι or Polη have increased sensitivity to UVC radiation. The lack of both TLS polymerases led to increased cell death and defects in proliferation and migration. Loss of both polymerases induces a significant replication fork arrest and G1/S-phase blockage, compared to the lack of Polη alone. In conclusion, we propose that Polι acts as a bona fide backup for Polη in the TLS of UV-photoproducts.

The BRCA2 R2645G variant increases DNA binding and induces hyper-recombination.

BRCA2 tumor suppressor protein ensures genome integrity by mediating DNA repair via homologous recombination (HR). This function is executed in part by its canonical DNA binding domain located at the C-terminus (BRCA2CTD), the only folded domain of the protein. Most germline pathogenic missense variants are located in this highly conserved region which binds to single-stranded DNA (ssDNA) and to the acidic protein DSS1. These interactions are essential for the HR function of BRCA2. Here, we report that the variant R2645G, identified in breast cancer and located at the DSS1 interface, unexpectedly increases the ssDNA binding activity of BRCA2CTDin vitro. Human cells expressing this variant display a hyper-recombination phenotype, chromosomal instability in the form of chromatid gaps when exposed to DNA damage, and increased PARP inhibitor sensitivity. In mouse embryonic stem cells (mES), this variant alters viability and confers sensitivity to cisplatin and Mitomycin C. These results suggest that BRCA2 interaction with ssDNA needs to be tightly regulated to limit HR and prevent chromosomal instability and we propose that this control mechanism involves DSS1. Given that several missense variants located within this region have been identified in breast cancer patients, these findings might have clinical implications for carriers.

At the crossroads of RNA biology, genome integrity and cancer.

This article is the synthesis of the scientific presentations that took place during two international courses at Institute Curie, one on post-transcriptional gene regulation and the other on genome instability and human disease, that were joined together in their 2021 edition. This joined course brought together the knowledge on RNA metabolism and the maintenance of genome stability.

Zinc finger protein ZNF384 is an adaptor of Ku to DNA during classical non-homologous end-joining.

DNA double-strand breaks (DSBs) are among the most deleterious types of DNA damage as they can lead to mutations and chromosomal rearrangements, which underlie cancer development. Classical non-homologous end-joining (cNHEJ) is the dominant pathway for DSB repair in human cells, involving the DNA-binding proteins XRCC6 (Ku70) and XRCC5 (Ku80). Other DNA-binding proteins such as Zinc Finger (ZnF) domain-containing proteins have also been implicated in DNA repair, but their role in cNHEJ remained elusive. Here we show that ZNF384, a member of the C2H2 family of ZnF proteins, binds DNA ends in vitro and is recruited to DSBs in vivo. ZNF384 recruitment requires the poly(ADP-ribosyl) polymerase 1 (PARP1)-dependent expansion of damaged chromatin, followed by binding of its C2H2 motifs to the exposed DNA. Moreover, ZNF384 interacts with Ku70/Ku80 via its N-terminus, thereby promoting Ku70/Ku80 assembly and the accrual of downstream cNHEJ factors, including APLF and XRCC4/LIG4, for efficient repair at DSBs. Altogether, our data suggest that ZNF384 acts as a 'Ku-adaptor' that binds damaged DNA and Ku70/Ku80 to facilitate the build-up of a cNHEJ repairosome, highlighting a role for ZNF384 in DSB repair and genome maintenance.

DNA double-strand break repair: Putting zinc fingers on the sore spot.

Zinc-Finger (ZnF) proteins represent one of the most abundant group of proteins in the human genome. At first characterized as DNA binding proteins, it has become increasingly clear that ZnF-proteins have the ability to bind a large variety of substrates such as RNAs, proteins and post-translational modifications, suggesting potential roles in a variety of biological processes. Indeed, several studies have implicated ZnF-proteins for instance in transcription regulation, signal transduction and cell migration. Intriguingly, more recently these proteins have emerged as important protectors of the genome, particularly by orchestrating the repair of highly deleterious DNA double-strand breaks. Here we provide a comprehensive summary of the roles of ZnF domain-containing proteins in DNA double-strand break repair and discuss how their dysfunction impacts genome stability and human disease.