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Nature Nov 2021Extrachromosomal circular DNA elements (eccDNAs) have been described in the literature for several decades, and are known for their broad existence across different...
Extrachromosomal circular DNA elements (eccDNAs) have been described in the literature for several decades, and are known for their broad existence across different species. However, their biogenesis and functions are largely unknown. By developing a new circular DNA enrichment method, here we purified and sequenced full-length eccDNAs with Nanopore sequencing. We found that eccDNAs map across the entire genome in a close to random manner, suggesting a biogenesis mechanism of random ligation of genomic DNA fragments. Consistent with this idea, we found that apoptosis inducers can increase eccDNA generation, which is dependent on apoptotic DNA fragmentation followed by ligation by DNA ligase 3. Importantly, we demonstrated that eccDNAs can function as potent innate immunostimulants in a manner that is independent of eccDNA sequence but dependent on eccDNA circularity and the cytosolic DNA sensor Sting. Collectively, our study not only revealed the origin, biogenesis and immunostimulant function of eccDNAs but also uncovered their sensing pathway and potential clinical implications in immune response.
Topics: Animals; Apoptosis; Cells, Cultured; Chromosome Mapping; DNA Fragmentation; DNA Ligase ATP; DNA, Circular; Endodeoxyribonucleases; Gene Expression Regulation; Genome; Immunity, Innate; Male; Membrane Proteins; Mice; Poly-ADP-Ribose Binding Proteins
PubMed: 34671165
DOI: 10.1038/s41586-021-04009-w -
Molecular Cell Jul 2021Mammalian DNA base excision repair (BER) is accelerated by poly(ADP-ribose) polymerases (PARPs) and the scaffold protein XRCC1. PARPs are sensors that detect...
Mammalian DNA base excision repair (BER) is accelerated by poly(ADP-ribose) polymerases (PARPs) and the scaffold protein XRCC1. PARPs are sensors that detect single-strand break intermediates, but the critical role of XRCC1 during BER is unknown. Here, we show that protein complexes containing DNA polymerase β and DNA ligase III that are assembled by XRCC1 prevent excessive engagement and activity of PARP1 during BER. As a result, PARP1 becomes "trapped" on BER intermediates in XRCC1-deficient cells in a manner similar to that induced by PARP inhibitors, including in patient fibroblasts from XRCC1-mutated disease. This excessive PARP1 engagement and trapping renders BER intermediates inaccessible to enzymes such as DNA polymerase β and impedes their repair. Consequently, PARP1 deletion rescues BER and resistance to base damage in XRCC1 cells. These data reveal excessive PARP1 engagement during BER as a threat to genome integrity and identify XRCC1 as an "anti-trapper" that prevents toxic PARP1 activity.
Topics: Animals; Cell Line; DNA; DNA Breaks, Single-Stranded; DNA Damage; DNA Ligase ATP; DNA Polymerase beta; DNA Repair; DNA-Binding Proteins; Fibroblasts; Humans; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerase Inhibitors; Poly(ADP-ribose) Polymerases; Protein Binding; X-ray Repair Cross Complementing Protein 1
PubMed: 34102106
DOI: 10.1016/j.molcel.2021.05.009 -
Current Opinion in Structural Biology Dec 2018Bacterial replisomes are dynamic multiprotein DNA replication machines that are inherently difficult for structural studies. However, breakthroughs continue to come. The... (Review)
Review
Bacterial replisomes are dynamic multiprotein DNA replication machines that are inherently difficult for structural studies. However, breakthroughs continue to come. The structures of Escherichia coli DNA polymerase III (core)-clamp-DNA subcomplexes solved by single-particle cryo-electron microscopy in both polymerization and proofreading modes and the discovery of the stochastic nature of the bacterial replisomes represent notable progress. The structures reveal an intricate interaction network in the polymerase-clamp subassembly, providing insights on how replisomes may work. Meantime, ensemble and single-molecule functional assays and fluorescence microscopy show that the bacterial replisomes can work in a decoupled and uncoordinated way, with polymerases quickly exchanging and both leading-strand and lagging-strand polymerases and the helicase working independently, contradictory to the elegant textbook view of a highly coordinated machine.
Topics: Bacillus subtilis; Bacteriophage T7; DNA Helicases; DNA Ligases; DNA Polymerase I; DNA Polymerase III; DNA Replication; DNA-Directed DNA Polymerase; Escherichia coli; Helicobacter pylori; Multienzyme Complexes
PubMed: 30292863
DOI: 10.1016/j.sbi.2018.09.006 -
Nucleic Acids Research Jun 2017DNA library preparation for high-throughput sequencing of genomic DNA usually involves ligation of adapters to double-stranded DNA fragments. However, for highly...
DNA library preparation for high-throughput sequencing of genomic DNA usually involves ligation of adapters to double-stranded DNA fragments. However, for highly degraded DNA, especially ancient DNA, library preparation has been found to be more efficient if each of the two DNA strands are converted into library molecules separately. We present a new method for single-stranded library preparation, ssDNA2.0, which is based on single-stranded DNA ligation with T4 DNA ligase utilizing a splinter oligonucleotide with a stretch of random bases hybridized to a 3΄ biotinylated donor oligonucleotide. A thorough evaluation of this ligation scheme shows that single-stranded DNA can be ligated to adapter oligonucleotides in higher concentration than with CircLigase (an RNA ligase that was previously chosen for end-to-end ligation in single-stranded library preparation) and that biases in ligation can be minimized when choosing splinters with 7 or 8 random nucleotides. We show that ssDNA2.0 tolerates higher quantities of input DNA than CircLigase-based library preparation, is less costly and better compatible with automation. We also provide an in-depth comparison of library preparation methods on degraded DNA from various sources. Most strikingly, we find that single-stranded library preparation increases library yields from tissues stored in formalin for many years by several orders of magnitude.
Topics: Animals; Bone and Bones; DNA; DNA Ligases; DNA Primers; DNA, Single-Stranded; Fossils; Gene Library; High-Throughput Nucleotide Sequencing; Horses; Humans; Liver; Nucleic Acid Hybridization; Oligonucleotides; Polymerase Chain Reaction; Sequence Analysis, DNA; Swine
PubMed: 28119419
DOI: 10.1093/nar/gkx033 -
Nature Oct 2021Transcription-coupled DNA repair removes bulky DNA lesions from the genome and protects cells against ultraviolet (UV) irradiation. Transcription-coupled DNA repair...
Transcription-coupled DNA repair removes bulky DNA lesions from the genome and protects cells against ultraviolet (UV) irradiation. Transcription-coupled DNA repair begins when RNA polymerase II (Pol II) stalls at a DNA lesion and recruits the Cockayne syndrome protein CSB, the E3 ubiquitin ligase, CRL4 and UV-stimulated scaffold protein A (UVSSA). Here we provide five high-resolution structures of Pol II transcription complexes containing human transcription-coupled DNA repair factors and the elongation factors PAF1 complex (PAF) and SPT6. Together with biochemical and published data, the structures provide a model for transcription-repair coupling. Stalling of Pol II at a DNA lesion triggers replacement of the elongation factor DSIF by CSB, which binds to PAF and moves upstream DNA to SPT6. The resulting elongation complex, EC, uses the CSA-stimulated translocase activity of CSB to pull on upstream DNA and push Pol II forward. If the lesion cannot be bypassed, CRL4 spans over the Pol II clamp and ubiquitylates the RPB1 residue K1268, enabling recruitment of TFIIH to UVSSA and DNA repair. Conformational changes in CRL4 lead to ubiquitylation of CSB and to release of transcription-coupled DNA repair factors before transcription may continue over repaired DNA.
Topics: Carrier Proteins; Cryoelectron Microscopy; DNA Helicases; DNA Repair; DNA Repair Enzymes; DNA-Binding Proteins; Humans; Models, Molecular; Multiprotein Complexes; Poly-ADP-Ribose Binding Proteins; RNA Polymerase II; Transcription Elongation, Genetic; Transcription Factor TFIIH; Transcription Factors; Transcription, Genetic; Ubiquitin-Protein Ligases; Ubiquitination
PubMed: 34526721
DOI: 10.1038/s41586-021-03906-4 -
DNA Repair Sep 2020To ensure genome integrity, the joining of breaks in the phosphodiester backbone of duplex DNA is required during DNA replication and to complete the repair of almost... (Review)
Review
To ensure genome integrity, the joining of breaks in the phosphodiester backbone of duplex DNA is required during DNA replication and to complete the repair of almost all types of DNA damage. In human cells, this task is accomplished by DNA ligases encoded by three genes, LIG1, LIG3 and LIG4. Mutations in LIG1 and LIG4 have been identified as the causative factor in two inherited immunodeficiency syndromes. Moreover, there is emerging evidence that DNA ligases may be good targets for the development of novel anti-cancer agents. In this graphical review, we provide an overview of the roles of the DNA ligases encoded by the three human LIG genes in DNA replication and repair.
Topics: DNA; DNA Damage; DNA Ligase ATP; DNA Repair; DNA Replication; Humans; Poly-ADP-Ribose Binding Proteins
PubMed: 33087274
DOI: 10.1016/j.dnarep.2020.102908 -
Molecular Cell Nov 2021Inhibitors of poly(ADP-ribose) (PAR) polymerase (PARPi) have entered the clinic for the treatment of homologous recombination (HR)-deficient cancers. Despite the success...
Inhibitors of poly(ADP-ribose) (PAR) polymerase (PARPi) have entered the clinic for the treatment of homologous recombination (HR)-deficient cancers. Despite the success of this approach, preclinical and clinical research with PARPi has revealed multiple resistance mechanisms, highlighting the need for identification of novel functional biomarkers and combination treatment strategies. Functional genetic screens performed in cells and organoids that acquired resistance to PARPi by loss of 53BP1 identified loss of LIG3 as an enhancer of PARPi toxicity in BRCA1-deficient cells. Enhancement of PARPi toxicity by LIG3 depletion is dependent on BRCA1 deficiency but independent of the loss of 53BP1 pathway. Mechanistically, we show that LIG3 loss promotes formation of MRE11-mediated post-replicative ssDNA gaps in BRCA1-deficient and BRCA1/53BP1 double-deficient cells exposed to PARPi, leading to an accumulation of chromosomal abnormalities. LIG3 depletion also enhances efficacy of PARPi against BRCA1-deficient mammary tumors in mice, suggesting LIG3 as a potential therapeutic target.
Topics: Animals; BRCA1 Protein; Biopsy; CRISPR-Cas Systems; Cell Line; Cell Nucleus; Cell Proliferation; Chromosome Aberrations; DNA Damage; DNA Ligase ATP; DNA, Single-Stranded; Female; Humans; Lentivirus; MRE11 Homologue Protein; Mammary Neoplasms, Animal; Mice; Mutation; Ovarian Neoplasms; Poly(ADP-ribose) Polymerase Inhibitors; Poly-ADP-Ribose Binding Proteins; RNA, Small Interfering; Transgenes; Triple Negative Breast Neoplasms; Tumor Suppressor p53-Binding Protein 1
PubMed: 34555355
DOI: 10.1016/j.molcel.2021.09.005 -
Nature Mar 2024Cyclic GMP-AMP synthase (cGAS) senses aberrant DNA during infection, cancer and inflammatory disease, and initiates potent innate immune responses through the synthesis...
Cyclic GMP-AMP synthase (cGAS) senses aberrant DNA during infection, cancer and inflammatory disease, and initiates potent innate immune responses through the synthesis of 2'3'-cyclic GMP-AMP (cGAMP). The indiscriminate activity of cGAS towards DNA demands tight regulatory mechanisms that are necessary to maintain cell and tissue homeostasis under normal conditions. Inside the cell nucleus, anchoring to nucleosomes and competition with chromatin architectural proteins jointly prohibit cGAS activation by genomic DNA. However, the fate of nuclear cGAS and its role in cell physiology remains unclear. Here we show that the ubiquitin proteasomal system (UPS) degrades nuclear cGAS in cycling cells. We identify SPSB3 as the cGAS-targeting substrate receptor that associates with the cullin-RING ubiquitin ligase 5 (CRL5) complex to ligate ubiquitin onto nuclear cGAS. A cryo-electron microscopy structure of nucleosome-bound cGAS in a complex with SPSB3 reveals a highly conserved Asn-Asn (NN) minimal degron motif at the C terminus of cGAS that directs SPSB3 recruitment, ubiquitylation and cGAS protein stability. Interference with SPSB3-regulated nuclear cGAS degradation primes cells for type I interferon signalling, conferring heightened protection against infection by DNA viruses. Our research defines protein degradation as a determinant of cGAS regulation in the nucleus and provides structural insights into an element of cGAS that is amenable to therapeutic exploitation.
Topics: Animals; Humans; Mice; Cell Nucleus; Cryoelectron Microscopy; Degrons; DNA Virus Infections; DNA Viruses; DNA, Viral; Immunity, Innate; Innate Immunity Recognition; Interferon Type I; Nuclear Proteins; Nucleosomes; Nucleotidyltransferases; Proteasome Endopeptidase Complex; Protein Stability; Proteolysis; Substrate Specificity; Ubiquitin; Ubiquitin-Protein Ligases; Ubiquitination
PubMed: 38418882
DOI: 10.1038/s41586-024-07112-w -
Molecular Cell Feb 2021Lesions on DNA uncouple DNA synthesis from the replisome, generating stretches of unreplicated single-stranded DNA (ssDNA) behind the replication fork. These ssDNA gaps...
Lesions on DNA uncouple DNA synthesis from the replisome, generating stretches of unreplicated single-stranded DNA (ssDNA) behind the replication fork. These ssDNA gaps need to be filled in to complete DNA duplication. Gap-filling synthesis involves either translesion DNA synthesis (TLS) or template switching (TS). Controlling these processes, ubiquitylated PCNA recruits many proteins that dictate pathway choice, but the enzymes regulating PCNA ubiquitylation in vertebrates remain poorly defined. Here we report that the E3 ubiquitin ligase RFWD3 promotes ubiquitylation of proteins on ssDNA. The absence of RFWD3 leads to a profound defect in recruitment of key repair and signaling factors to damaged chromatin. As a result, PCNA ubiquitylation is inhibited without RFWD3, and TLS across different DNA lesions is drastically impaired. We propose that RFWD3 is an essential coordinator of the response to ssDNA gaps, where it promotes ubiquitylation to drive recruitment of effectors of PCNA ubiquitylation and DNA damage bypass.
Topics: Animals; Cell Line, Tumor; Chromatin; DNA Breaks, Single-Stranded; DNA Repair; DNA Replication; DNA-Directed DNA Polymerase; Female; Humans; Proliferating Cell Nuclear Antigen; Substrate Specificity; Ubiquitin-Protein Ligases; Ubiquitination; Xenopus laevis
PubMed: 33321094
DOI: 10.1016/j.molcel.2020.11.029 -
Frontiers in Plant Science 2021Protein modification by the small ubiquitin-like modifier (SUMO) plays an important role in multiple plant processes, including growth, development, and the response to... (Review)
Review
Protein modification by the small ubiquitin-like modifier (SUMO) plays an important role in multiple plant processes, including growth, development, and the response to abiotic stresses. Mechanistically, SUMOylation is a sequential multi-enzymatic process where SUMO E3 ligases accelerate SUMO conjugation while also influencing target identity and interactions. This review explores the biological functions of plant SUMO E3 ligases [SAP AND MIZ1 DOMAIN-CONTAINING LIGASE (SIZs), METHYL METHANESULFONATE-SENSITIVITY PROTEIN 21 (MMS21s), and PROTEIN INHIBITOR OF ACTIVATED STAT-LIKE (PIALs)] in relation to their molecular activities and domains. We also explore the sub-cellular localization of SUMO E3 ligases and review evidence suggesting a connection between certain SUMO E3 ligases and DNA that contributes to gene expression regulation.
PubMed: 33897743
DOI: 10.3389/fpls.2021.652170