A RAD18-UBC13-PALB2-RNF168 axis mediates replication fork recovery in BRCA1-deficient cancer cells.

BRCA1/2 proteins function in genome stability by promoting repair of double-stranded DNA breaks through homologous recombination and by protecting stalled replication forks from nucleolytic degradation. In BRCA1/2-deficient cancer cells, extensively degraded replication forks can be rescued through distinct fork recovery mechanisms that also promote cell survival. Here, we identified a novel pathway mediated by the E3 ubiquitin ligase RAD18, the E2-conjugating enzyme UBC13, the recombination factor PALB2, the E3 ubiquitin ligase RNF168 and PCNA ubiquitination that promotes fork recovery in BRCA1- but not BRCA2-deficient cells. We show that this pathway does not promote fork recovery by preventing replication fork reversal and degradation in BRCA1-deficient cells. We propose a mechanism whereby the RAD18-UBC13-PALB2-RNF168 axis facilitates resumption of DNA synthesis by promoting re-annealing of the complementary single-stranded template strands of the extensively degraded forks, thereby allowing re-establishment of a functional replication fork. We also provide preliminary evidence for the potential clinical relevance of this novel fork recovery pathway in BRCA1-mutated cancers, as RAD18 is over-expressed in BRCA1-deficient cancers, and RAD18 loss compromises cell viability in BRCA1-deficient cancer cells.

Cybulla E ，Wallace S ，Meroni A ，Jackson J ，Agashe S ，Tennakoon M ，Limbu M ，Quinet A ，Lomonosova E ，Noia H ，Tirman S ，Wood M ，Lemacon D ，Fuh K ，Zou L ，Vindigni A ... -  《-》

The E3 ligase RAD18-mediated ubiquitination of henipavirus matrix protein promotes its nuclear-cytoplasmic trafficking and viral egress.

Jin D ，Zhang L ，Peng C ，He M ，Wang W ，Li Z ，Liu C ，Du J ，Zhou J ，Yin L ，Shan C ，Qin Y ，Chen M ... -  《Emerging Microbes & Infections》

PCNA-binding activity separates RNF168 functions in DNA replication and DNA double-stranded break signaling.

RNF168 orchestrates a ubiquitin-dependent DNA damage response to regulate the recruitment of repair factors, such as 53BP1 to DNA double-strand breaks (DSBs). In addition to its canonical functions in DSB signaling, RNF168 may facilitate DNA replication fork progression. However, the precise role of RNF168 in DNA replication remains unclear. Here, we demonstrate that RNF168 is recruited to DNA replication factories in a manner that is independent of the canonical DSB response pathway regulated by Ataxia-Telangiectasia Mutated (ATM) and RNF8. We identify a degenerate Proliferating Cell Nuclear Antigen (PCNA)-interacting peptide (DPIP) motif in the C-terminus of RNF168, which together with its Motif Interacting with Ubiquitin (MIU) domain mediates binding to mono-ubiquitylated PCNA at replication factories. An RNF168 mutant harboring inactivating substitutions in its DPIP box and MIU1 domain (termed RNF168 ΔDPIP/ΔMIU1) is not recruited to sites of DNA synthesis and fails to support ongoing DNA replication. Notably, the PCNA interaction-deficient RNF168 ΔDPIP/ΔMIU1 mutant fully rescues the ability of RNF168-/- cells to form 53BP1 foci in response to DNA DSBs. Therefore, RNF168 functions in DNA replication and DSB signaling are fully separable. Our results define a new mechanism by which RNF168 promotes DNA replication independently of its canonical functions in DSB signaling.

Yang Y ，Jayaprakash D ，Jhujh SS ，Reynolds JJ ，Chen S ，Gao Y ，Anand JR ，Mutter-Rottmayer E ，Ariel P ，An J ，Cheng X ，Pearce KH ，Blanchet SA ，Nandakumar N ，Zhou P ，Fradet-Turcotte A ，Stewart GS ，Vaziri C ... -  《-》

PALB2 chromatin recruitment restores homologous recombination in BRCA1-deficient cells depleted of 53BP1.

Belotserkovskaya R ，Raga Gil E ，Lawrence N ，Butler R ，Clifford G ，Wilson MD ，Jackson SP ... -  《Nature Communications》

Orchestration of the DNA-damage response by the RNF8 ubiquitin ligase.

Kolas NK ，Chapman JR ，Nakada S ，Ylanko J ，Chahwan R ，Sweeney FD ，Panier S ，Mendez M ，Wildenhain J ，Thomson TM ，Pelletier L ，Jackson SP ，Durocher D ... -  《-》