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Platinum agents are cornerstone therapies for many cancers but often cause neurotoxicity in post-mitotic tissues, for which effective interventions are lacking. This limitation reflects an incomplete understanding of neuronal responses to DNA damage. We show that nucleotide excision repair (NER) mediates cisplatin lesion removal in neurons; however, unlike its protective role in dividing cells, NER promotes neuronal death in response to cisplatin. This vulnerability arises because neurons possess low deoxynucleoside triphosphate (dNTP) pools. dNTPs are initially consumed during transcription-coupled NER to resolve transcription-blocking lesions. As dNTP levels become depleted, repair fails to complete, leading to accumulation of double-strand breaks, particularly during global-genome NER. Supplementation with deoxynucleosides or genetic upregulation of dNTP synthesis restores nucleotide pools, protects neurons from cell death, and reduces cisplatin-induced neuropathic pain. These findings identify limited dNTP availability as a key vulnerability in post-mitotic cells and suggest nucleoside supplementation as a potential strategy to mitigate chemotherapy-induced neurotoxicity.

DNA replication and transcription must be intricately coordinated as both machineries navigate the same chromatin landscape to ensure genome stability and proper cell function. Here, we show that altering their elongation rates-specifically, slowed transcriptional elongation alongside rapid replication fork progression-does not elicit replicative stress. Instead, this independent kinetic variation accelerates the acquisition of naive pluripotency during in vitro dedifferentiation, revealing an unexpected link between transcription kinetics and cell plasticity. Mechanistically, we show that the transition to naive pluripotency is accompanied by a distinctive alternative splicing program indicative of reduced RNA polymerase II (RNAPII) elongation. These findings redefine the functional relationship between replication and transcription dynamics and uncover transcriptional velocity as a tunable layer of control over cellular identity transitions.

Cytarabine (ara-C) and fludarabine (F-ara-A) are key drugs in leukaemia treatment. SAMHD1 is known to confer resistance to ara-C and F-ara-A, and we previously identified ribonucleotide reductase inhibitors as indirect SAMHD1 inhibitors in a phenotypic screen. The inosine monophosphate dehydrogenase (IMPDH) inhibitor mycophenolic acid (MPA) was also a hit in this screen. IMPDH inhibitors (IMPDHi) have previously shown efficacy against KMT2A-rearranged (KMT2Ar) acute myeloid leukaemia (AML). We investigated whether IMPDH inhibition could enhance the effect of ara-C and F-ara-A in AML cell lines and primary AML samples, and whether this effect was linked to KMT2A status. We found that sensitivity to IMPDHi was independent of KMT2A status. IMPDHi synergized with ara-C and F-ara-A in a SAMHD1-dependent manner in a subset of AML cells, but not in acute lymphoblastic leukaemia cell lines. Mechanistically, IMPDHi depleted allosteric SAMHD1 activators GTP and dGTP, thereby increasing active triphosphate metabolites in SAMHD1-proficient, but not SAMHD1-deficient, cells. Our findings suggest that the addition of IMPDHi to ara-C and F-ara-A may have therapeutic benefits in some AML cases.

Molnupiravir is a nucleoside analogue antiviral drug against RNA viruses, including its clinical indication SARSCoV2. Whilst its mechanismofaction is well defined, host factors that regulate its therapeutic responses have not been thoroughly deci phered and characterized. Here we show that uridine cytidine kinases (UCKs), key enzymes in pyrimidine salvage, effectively phosphorylate and thereby bioactivate N4hydroxycytidine (NHC) – the active compound of molnupiravir, thus dictating its antiSARSCoV2 efficacy and furthermore selectivity. In vitro, both isoforms of UCKs (UCK1 and UCK2) effectively phosphorylated NHC, where the structural basis of the catalysis was further deciphered via the first complete substrate bound cocrystal structure of UCK, i.e., UCK1NHCAMPPNP. In SARSCoV2infected cells, UCK2 knockdown via siRNA hampered the intracellular accumulation of the triphosphorylated antiviral metabolite of NHC, resulting in a 10fold reduction of the antiviral efficacy, and surprisingly, 2fold reduction of its selectivity, which were critically recapitulated in a dosedependent manner using a panUCK inhibitor. Altogether, this work underscores UCKs as pivotal players in upholding molnupiravir efficacy and therapeutic window of molnupiravir, and furthermore as pharmacologi cally tractable targets for tailoring the drug response.

Disruptions in deoxynucleoside triphosphate (dNTP) supply impair DNA replication and lead to genomic instability. While exogenous ribonucleosides (rNuc) have been suggested to alleviate replication stress by increasing dNTP levels, their precise metabolic effects remain unclear. Here, we show that rNuc supplementation primarily elevates CTP and UTP levels, with only modest increases in dCTP, and has minimal impact on replication fork speed across multiple mammalian cell lines. In contrast, thymidine (dThd), either alone or in combination with rNuc-as in EmbryoMax Nucleosides-significantly increases dTTP and dGTP levels, leading to accelerated replication fork progression. Notably, dThd, rather than rNuc, drives fork acceleration and counteracts fork slowdown caused by elevated dUTP, consistent with primer extension assays showing that dUTP transiently inhibits Pol ϵ-mediated DNA synthesis at template adenines. These results clarify the distinct roles of nucleosides in nucleotide metabolism, providing a mechanistic basis for how dThd promotes fork progression and preserves genomic stability.

In Saccharomyces cerevisiae, glucose depletion induces metabolic reprogramming through widespread transcriptional and translational reorganization. We report that initial, very rapid translational silencing is driven by a specialized metabolic mechanism. Following glucose withdrawal, intracellular NTP levels drop drastically over 30 s before stabilizing at a regulated, post-stress set point. Programmed translational control results from the differential NTP affinities of key enzymes; ATP falls below the (high) binding constants for DEAD-box helicase initiation factors, including eIF4A, driving mRNA release and blocking 80S assembly. Contrastingly, guanosine triphosphate (GTP) levels always greatly exceed the (low) binding constants for elongation factors, allowing ribosome run-off and orderly translation shutdown. Translation initiation is immediately lost on all pre-existing mRNAs before being preferentially re-established on newly synthesized, upregulated stress-response transcripts. We conclude that enzymatic constants are tuned for metabolic remodeling. This response counters energy depletion rather than being glucose specific, allowing hierarchical inhibition of energy-consuming processes on very rapid timescales.

Perturbation of DNA replication, for instance by hydroxyurea-dependent dNTP exhaustion, often leads to stalling or collapse of replication forks. This triggers a replication stress response that stabilizes these forks, activates cell cycle checkpoints, and induces expression of DNA damage response genes. While several factors are known to act in this response, the full repertoire of proteins involved remains largely elusive. Here, we develop Replication-IDentifier (Repli-ID), which allows for genome-wide identification of regulators of DNA replication in Saccharomyces cerevisiae. During Repli-ID, the replicative polymerase epsilon (Pol ε) is tracked at a barcoded origin of replication by chromatin immunoprecipitation (ChIP) coupled to next-generation sequencing of the barcode in thousands of hydroxyurea-treated yeast mutants. Using this approach, 423 genes that promote Pol ε binding at replication forks were uncovered, including LGE1 and ROX1. Mechanistically, we show that Lge1 affects replication initiation and/or fork stability by promoting Bre1-dependent H2B mono-ubiquitylation. Rox1 affects replication fork progression by regulating S-phase entry and checkpoint activation, hinging on cellular ceramide levels via transcriptional repression of SUR2. Thus, Repli-ID provides a unique resource for the identification and further characterization of factors and pathways involved in the cellular response to DNA replication perturbation.

Mitochondrial DNA (mtDNA) replication requires a steady supply of deoxyribonucleotides (dNTPs), synthesized de novo by ribonucleotide reductase (RNR). In nondividing cells, RNR consists of RRM1 and RRM2B subunits. Mutations in RRM2B cause mtDNA depletion syndrome, linked to muscle weakness, neurological decline, and early mortality. The impact of RRM2B deficiency on dNTP pools in nondividing tissues remains unclear. Using a mouse knockout model, we demonstrate that RRM2B deficiency selectively depletes dATP and dGTP, while dCTP and dTTP levels remain stable or increase. This depletion pattern resembles the effects of hydroxyurea, an inhibitor that reduces overall RNR activity. Mechanistically, we propose that the depletion of dATP and dGTP arises from their preferred degradation by the dNTPase SAMHD1 and the lower production rate of dATP by RNR. Identifying dATP and dGTP depletion as a hallmark of RRM2B deficiency provides insights for developing nucleoside bypass therapies to alleviate the effects of RRM2B mutations.

Alterations in deoxyribonucleoside triphosphate (dNTP) pools have been linked to increased mutation rates and genome instability in unicellular organisms and cell cultures. However, the role of dNTP pool changes in tumor development in mammals remains unclear. In this study, we present a mouse model with a point mutation at the allosteric specificity site of ribonucleotide reductase, RRM1-Y285A. This mutation reduced ribonucleotide reductase activity, impairing the synthesis of deoxyadenosine triphosphate (dATP) and deoxyguanosine triphosphate (dGTP). Heterozygous Rrm1^+/Y285A mice exhibited distinct alterations in dNTP pools across various organs, shorter lifespans and earlier tumor onset compared with wild-type controls. Mutational spectrum analysis of tumors revealed two distinct signatures, one resembling a signature extracted from a human cancer harboring a mutation of the same amino acid residue in ribonucleotide reductase, RRM1^Y285C. Our findings suggest that mutations in enzymes involved in dNTP metabolism can serve as drivers of cancer development.

Human development relies on the correct replication, maintenance and segregation of our genetic blueprints. How these processes are monitored across embryonic lineages, and why genomic mosaicism varies during development remain unknown. Using pluripotent stem cells, we identify that several patterning signals—including WNT, BMP, and FGF—converge into the modulation of DNA replication stress and damage during S-phase, which in turn controls chromosome segregation fidelity in mitosis. We show that the WNT and BMP signals protect from excessive origin firing, DNA damage and chromosome missegregation derived from stalled forks in pluripotency. Cell signalling control of chromosome segregation declines during lineage specification into the three germ layers, but re-emerges in neural progenitors. In particular, we find that the neurogenic factor FGF2 induces DNA replication stress-mediated chromosome missegregation during the onset of neurogenesis, which could provide a rationale for the elevated chromosomal mosaicism of the developing brain. Our results highlight roles for morphogens and cellular identity in genome maintenance that contribute to somatic mosaicism during mammalian development.