Inactive Parp2 causes Tp53-dependent lethal anemia by blocking replication-associated nick ligation in erythroblasts.

Unlabelled: PARP1&2 enzymatic inhibitors (PARPi) are promising cancer treatments. But recently, their use has been hindered by unexplained severe anemia and treatment-related leukemia. In addition to enzymatic inhibition, PARPi also trap PARP1&2 at DNA lesions.

Inactive PARP1 causes embryonic lethality and genome instability in a dominant-negative manner.

PARP1 (poly-ADP ribose polymerase 1) is recruited and activated by DNA strand breaks, catalyzing the generation of poly-ADP-ribose (PAR) chains from NAD+. PAR relaxes chromatin and recruits other DNA repair factors, including XRCC1 and DNA Ligase 3, to maintain genomic stability. Here we show that, in contrast to the normal development of Parp1-null mice, heterozygous expression of catalytically inactive Parp1 (E988A, ) acts in a dominant-negative manner to disrupt murine embryogenesis.

ATR kinase supports normal proliferation in the early S phase by preventing replication resource exhaustion.

The ATR kinase, which coordinates cellular responses to DNA replication stress, is also essential for the proliferation of normal unstressed cells. Although its role in the replication stress response is well defined, the mechanisms by which ATR supports normal cell proliferation remain elusive. Here, we show that ATR is dispensable for the viability of G0-arrested naïve B cells.

Oncogenic IDH mutations increase heterochromatin-related replication stress without impacting homologous recombination.

Oncogenic mutations in isocitrate dehydrogenases 1 and 2 (IDH1/2) produce 2-hydroxyglutarate (2HG), which inhibits dioxygenases that modulate chromatin dynamics. The effects of 2HG have been reported to sensitize IDH tumors to poly-(ADP-ribose) polymerase (PARP) inhibitors. However, unlike PARP-inhibitor-sensitive BRCA1/2 tumors, which exhibit impaired homologous recombination, IDH-mutant tumors have a silent mutational profile and lack signatures associated with impaired homologous recombination.

Phosphorylation of DNA-PKcs at the S2056 cluster ensures efficient and productive lymphocyte development in XLF-deficient mice.

The nonhomologous end-joining (NHEJ) pathway is a major DNA double-strand break repair pathway in mammals and is essential for lymphocyte development. Ku70 and Ku80 heterodimer (KU) initiates NHEJ, thereby recruiting and activating the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs). While DNA-PKcs deletion only moderately impairs end-ligation, the expression of kinase-dead DNA-PKcs completely abrogates NHEJ.

ATR kinase supports normal proliferation in the early S phase by preventing replication resource exhaustion.

The ATR kinase, which coordinates cellular responses to DNA replication stress, is also essential for the proliferation of normal unstressed cells. Although its role in the replication stress response is well defined, the mechanisms by which ATR supports normal cell proliferation remain elusive. Here, we show that ATR is dispensable for the viability of G0-arrested naïve B cells.