scholarly journals Biology before the SOS Response—DNA Damage Mechanisms at Chromosome Fragile Sites

Cells ◽  
2021 ◽  
Vol 10 (9) ◽  
pp. 2275
Author(s):  
Devon M. Fitzgerald ◽  
Susan M Rosenberg
Keyword(s):  
Dna Damage ◽  
Genome Instability ◽  
Human Cancer ◽  
Sos Response ◽  
Fragile Sites ◽  
Holliday Junctions ◽  
Cancer Evolution ◽  
Dna Damage Tolerance ◽  
Chromosome Fragility ◽  
Species Evolution

The Escherichia coli SOS response to DNA damage, discovered and conceptualized by Evelyn Witkin and Miroslav Radman, is the prototypic DNA-damage stress response that upregulates proteins of DNA protection and repair, a radical idea when formulated in the late 1960s and early 1970s. SOS-like responses are now described across the tree of life, and similar mechanisms of DNA-damage tolerance and repair underlie the genome instability that drives human cancer and aging. The DNA damage that precedes damage responses constitutes upstream threats to genome integrity and arises mostly from endogenous biology. Radman’s vision and work on SOS, mismatch repair, and their regulation of genome and species evolution, were extrapolated directly from bacteria to humans, at a conceptual level, by Radman, then many others. We follow his lead in exploring bacterial molecular genomic mechanisms to illuminate universal biology, including in human disease, and focus here on some events upstream of SOS: the origins of DNA damage, specifically at chromosome fragile sites, and the engineered proteins that allow us to identify mechanisms. Two fragility mechanisms dominate: one at replication barriers and another associated with the decatenation of sister chromosomes following replication. DNA structures in E. coli, additionally, suggest new interpretations of pathways in cancer evolution, and that Holliday junctions may be universal molecular markers of chromosome fragility.

scholarly journals Two mechanisms of chromosome fragility at replication-termination sites in bacteria

2021 ◽  
Vol 7 (25) ◽  
pp. eabe2846
Author(s):  
Qian Mei ◽  
Devon M. Fitzgerald ◽  
Jingjing Liu ◽  
Jun Xia ◽  
John P. Pribis ◽  
...  
Keyword(s):  
Replication Fork ◽  
Genome Instability ◽  
Neurological Diseases ◽  
Strand Break ◽  
Fragile Sites ◽  
Holliday Junctions ◽  
Dna Breaks ◽  
Dna Damage And Repair ◽  
Chromosome Fragility ◽  
Chromosomal Fragile Sites

Chromosomal fragile sites are implicated in promoting genome instability, which drives cancers and neurological diseases. Yet, the causes and mechanisms of chromosome fragility remain speculative. Here, we identify three spontaneous fragile sites in the Escherichia coli genome and define their DNA damage and repair intermediates at high resolution. We find that all three sites, all in the region of replication termination, display recurrent four-way DNA or Holliday junctions (HJs) and recurrent DNA breaks. Homology-directed double-strand break repair generates the recurrent HJs at all of these sites; however, distinct mechanisms of DNA breakage are implicated: replication fork collapse at natural replication barriers and, unexpectedly, frequent shearing of unsegregated sister chromosomes at cell division. We propose that mechanisms such as both of these may occur ubiquitously, including in humans, and may constitute some of the earliest events that underlie somatic cell mosaicism, cancers, and other diseases of genome instability.

scholarly journals Holliday junction trap shows how cells use recombination and a junction-guardian role of RecQ helicase

2016 ◽  
Vol 2 (11) ◽  
pp. e1601605 ◽  
Author(s):  
Jun Xia ◽  
Li-Tzu Chen ◽  
Qian Mei ◽  
Chien-Hui Ma ◽  
Jennifer A. Halliday ◽  
...  
Keyword(s):  
Dna Damage ◽  
Genome Instability ◽  
Human Cancer ◽  
Single Cells ◽  
Strand Break ◽  
Holliday Junctions ◽  
Dna Breaks ◽  
E Coli ◽  
Dna Replication And Repair ◽  
The Many

DNA repair by homologous recombination (HR) underpins cell survival and fuels genome instability, cancer, and evolution. However, the main kinds and sources of DNA damage repaired by HR in somatic cells and the roles of important HR proteins remain elusive. We present engineered proteins that trap, map, and quantify Holliday junctions (HJs), a central DNA intermediate in HR, based on catalytically deficient mutant RuvC protein ofEscherichia coli. We use RuvCDefGFP (RDG) to map genomic footprints of HR at defined DNA breaks inE. coliand demonstrate genome-scale directionality of double-strand break (DSB) repair along the chromosome. Unexpectedly, most spontaneous HR-HJ foci are instigated, not by DSBs, but rather by single-stranded DNA damage generated by replication. We show that RecQ, theE. coliortholog of five human cancer proteins, nonredundantly promotes HR-HJ formation in single cells and, in a novel junction-guardian role, also prevents apparent non-HR–HJs promoted by RecA overproduction. We propose that one or more human RecQ orthologs may act similarly in human cancers overexpressing the RecA orthologRAD51and find that cancer genome expression data implicate the orthologs BLM and RECQL4 in conjunction with EME1 and GEN1 as probable HJ reducers in such cancers. Our results support RecA-overproducingE. colias a model of the many human tumors with up-regulatedRAD51and provide the first glimpses of important, previously elusive reaction intermediates in DNA replication and repair in single living cells.

scholarly journals Regulation of Cell Division in Bacteria by Monitoring Genome Integrity and DNA Replication Status

2019 ◽  
Vol 202 (2) ◽  
Author(s):  
Peter E. Burby ◽  
Lyle A. Simmons
Keyword(s):  
Cell Cycle ◽  
Dna Damage ◽  
Cell Division ◽  
Dna Replication ◽  
Cell Cycle Progression ◽  
Genome Instability ◽  
Sos Response ◽  
Bacterial Cells ◽  
Cycle Progression ◽  
Content Type

ABSTRACT All organisms regulate cell cycle progression by coordinating cell division with DNA replication status. In eukaryotes, DNA damage or problems with replication fork progression induce the DNA damage response (DDR), causing cyclin-dependent kinases to remain active, preventing further cell cycle progression until replication and repair are complete. In bacteria, cell division is coordinated with chromosome segregation, preventing cell division ring formation over the nucleoid in a process termed nucleoid occlusion. In addition to nucleoid occlusion, bacteria induce the SOS response after replication forks encounter DNA damage or impediments that slow or block their progression. During SOS induction, Escherichia coli expresses a cytoplasmic protein, SulA, that inhibits cell division by directly binding FtsZ. After the SOS response is turned off, SulA is degraded by Lon protease, allowing for cell division to resume. Recently, it has become clear that SulA is restricted to bacteria closely related to E. coli and that most bacteria enforce the DNA damage checkpoint by expressing a small integral membrane protein. Resumption of cell division is then mediated by membrane-bound proteases that cleave the cell division inhibitor. Further, many bacterial cells have mechanisms to inhibit cell division that are regulated independently from the canonical LexA-mediated SOS response. In this review, we discuss several pathways used by bacteria to prevent cell division from occurring when genome instability is detected or before the chromosome has been fully replicated and segregated.

scholarly journals Monohydrazone Based G-Quadruplex Selective Ligands Induce DNA Damage and Genome Instability in Human Cancer Cells

2020 ◽  
Vol 63 (6) ◽  
pp. 3090-3103 ◽  
Author(s):  
Jussara Amato ◽  
Giulia Miglietta ◽  
Rita Morigi ◽  
Nunzia Iaccarino ◽  
Alessandra Locatelli ◽  
...  
Keyword(s):  
Dna Damage ◽  
Cancer Cells ◽  
Genome Instability ◽  
Human Cancer ◽  
Human Cancer Cells ◽  
G Quadruplex ◽  
Selective Ligands

scholarly journals Helicase-Like Transcription Factor HLTF and E3 Ubiquitin Ligase SHPRH Confer DNA Damage Tolerance through Direct Interactions with Proliferating Cell Nuclear Antigen (PCNA)

2020 ◽  
Vol 21 (3) ◽  
pp. 693 ◽  
Author(s):  
Mareike Seelinger ◽  
Marit Otterlei
Keyword(s):  
Dna Damage ◽  
Transcription Factor ◽  
Damage Tolerance ◽  
Genome Instability ◽  
Ring Finger ◽  
Nuclear Antigen ◽  
Common Mutation ◽  
Dna Damage Tolerance ◽  
Replicative Stress ◽  
Template Switch

To prevent replication fork collapse and genome instability under replicative stress, DNA damage tolerance (DDT) mechanisms have evolved. The RAD5 homologs, HLTF (helicase-like transcription factor) and SHPRH (SNF2, histone-linker, PHD and RING finger domain-containing helicase), both ubiquitin ligases, are involved in several DDT mechanisms; DNA translesion synthesis (TLS), fork reversal/remodeling and template switch (TS). Here we show that these two human RAD5 homologs contain functional APIM PCNA interacting motifs. Our results show that both the role of HLTF in TLS in HLTF overexpressing cells, and nuclear localization of SHPRH, are dependent on interaction of HLTF and SHPRH with PCNA. Additionally, we detected multiple changes in the mutation spectra when APIM in overexpressed HLTF or SHPRH were mutated compared to overexpressed wild type proteins. In plasmids from cells overexpressing the APIM mutant version of HLTF, we observed a decrease in C to T transitions, the most common mutation caused by UV irradiation, and an increase in mutations on the transcribed strand. These results strongly suggest that direct binding of HLTF and SHPRH to PCNA is vital for their function in DDT.

DNA damage tolerance, mismatch repair and genome instability

BioEssays ◽  
1994 ◽  
Vol 16 (11) ◽  
pp. 833-839 ◽  
Author(s):  
P. Karran ◽  
M. Bignami
Keyword(s):  
Dna Damage ◽  
Mismatch Repair ◽  
Damage Tolerance ◽  
Genome Instability ◽  
Dna Damage Tolerance

scholarly journals Functional and Physical Interaction of Yeast Mgs1 with PCNA: Impact on RAD6-Dependent DNA Damage Tolerance

2006 ◽  
Vol 26 (14) ◽  
pp. 5509-5517 ◽  
Author(s):  
Takashi Hishida ◽  
Tomoko Ohya ◽  
Yoshino Kubota ◽  
Yusuke Kamada ◽  
Hideo Shinagawa
Keyword(s):  
Dna Damage ◽  
Posttranslational Modifications ◽  
Cell Cycle Progression ◽  
Damage Tolerance ◽  
Genome Instability ◽  
Dna Helicase ◽  
Nuclear Antigen ◽  
Physical Interaction ◽  
Dna Damage Tolerance ◽  
Exogenous Dna

ABSTRACT Proliferating cell nuclear antigen (PCNA), a sliding clamp required for processive DNA synthesis, provides attachment sites for various other proteins that function in DNA replication, DNA repair, cell cycle progression and chromatin assembly. It has been shown that differential posttranslational modifications of PCNA by ubiquitin or SUMO play a pivotal role in controlling the choice of pathway for rescuing stalled replication forks. Here, we explored the roles of Mgs1 and PCNA in replication fork rescue. We provide evidence that Mgs1 physically associates with PCNA and that Mgs1 helps suppress the RAD6 DNA damage tolerance pathway in the absence of exogenous DNA damage. We also show that PCNA sumoylation inhibits the growth of mgs1 rad18 double mutants, in which PCNA sumoylation and the Srs2 DNA helicase coordinately prevent RAD52-dependent homologous recombination. The proposed roles for Mgs1, Srs2, and modified PCNA during replication arrest highlight the importance of modulating the RAD6 and RAD52 pathways to avoid genome instability.

The Sos Response: Recent Insights intoumuDC-Dependent Mutagenesis and DNA Damage Tolerance

2000 ◽  
Vol 34 (1) ◽  
pp. 479-497 ◽  
Author(s):  
Mark D Sutton ◽  
Bradley T Smith ◽  
Veronica G Godoy ◽  
Graham C Walker
Keyword(s):  
Dna Damage ◽  
Damage Tolerance ◽  
Sos Response ◽  
Dna Damage Tolerance

scholarly journals DNA damage and genome instability by G-quadruplex ligands are mediated by R loops in human cancer cells

2018 ◽  
Vol 116 (3) ◽  
pp. 816-825 ◽  
Author(s):  
Alessio De Magis ◽  
Stefano G. Manzo ◽  
Marco Russo ◽  
Jessica Marinello ◽  
Rita Morigi ◽  
...  
Keyword(s):  
Dna Damage ◽  
Cancer Cells ◽  
Genome Instability ◽  
Human Cancer ◽  
Cell Killing ◽  
Dna Structures ◽  
Human Cancer Cells ◽  
Cellular Effects ◽  
Genome Wide ◽  
G Quadruplex

G quadruplexes (G4s) and R loops are noncanonical DNA structures that can regulate basic nuclear processes and trigger DNA damage, genome instability, and cell killing. By different technical approaches, we here establish that specific G4 ligands stabilize G4s and simultaneously increase R-loop levels within minutes in human cancer cells. Genome-wide mapping of R loops showed that the studied G4 ligands likely cause the spreading of R loops to adjacent regions containing G4 structures, preferentially at 3′-end regions of expressed genes, which are partially ligand-specific. Overexpression of an exogenous human RNaseH1 rescued DNA damage induced by G4 ligands in BRCA2-proficient and BRCA2-silenced cancer cells. Moreover, even if the studied G4 ligands increased noncanonical DNA structures at similar levels in nuclear chromatin, their cellular effects were different in relation to cell-killing activity and stimulation of micronuclei, a hallmark of genome instability. Our findings therefore establish that G4 ligands can induce DNA damage by an R loop-dependent mechanism that can eventually lead to different cellular consequences depending on the chemical nature of the ligands.

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