Mechanisms of Dealing with DNA Damage-Induced Replication Problems

ArticleinCell biochemistry and biophysics 53(1):17-31 · December 2008with10 Reads
DOI: 10.1007/s12013-008-9039-y · Source: PubMed
Abstract
During every S phase, cells need to duplicate their genomes so that both daughter cells inherit complete copies of genetic information. Given the large size of mammalian genomes and the required precision of DNA replication, genome duplication requires highly fine-tuned corrective and quality control processes. A major threat to the accuracy and efficiency of DNA synthesis is the presence of DNA lesions, caused by both endogenous and exogenous damaging agents. Replicative DNA polymerases, which carry out the bulk of DNA synthesis, evolved to do their job extremely precisely and efficiently. However, they are unable to use damaged DNA as a template and, consequently, are stopped at most DNA lesions. Failure to restart such stalled replication forks can result in major chromosomal aberrations and lead to cell dysfunction or death. Therefore, a well-coordinated response to replication perturbation is essential for cell survival and fitness. Here we review how this response involves activating checkpoint signaling and the use of specialized pathways promoting replication restart. Checkpoint signaling adjusts cell cycle progression to the emergency situation and thus gives cells more time to deal with the damage. Replication restart is mediated by two pathways. Homologous recombination uses homologous DNA sequence to repair or bypass the lesion and is therefore mainly error free. Error-prone translesion synthesis employs specialized, low fidelity polymerases to bypass the damage.
    • "The importance of processive DNA replication has been reinforced by studies over a number of years; however, this concept has largely developed from experiments in which cells are exposed to agents that induce DNA damage or interfere with the ability of DNA polymerase to incorporate nucleotides during nascent DNA synthesis (reviewed in [91][92][93]). A heightened awareness of the biological effects of naturally occurring structured DNA on replication-associated events is beginning to emerge. "
    [Show abstract] [Hide abstract] ABSTRACT: Mounting evidence indicates that alternate DNA structures, which deviate from normal double helical DNA, form in vivo and influence cellular processes such as replication and transcription. However, our understanding of how the cellular machinery deals with unusual DNA structures such as G-quadruplexes (G4), triplexes, or hairpins is only beginning to emerge. New advances in the field implicate a direct role of the Fanconi Anemia Group J (FANCJ) helicase, which is linked to a hereditary chromosomal instability disorder and important for cancer suppression, in replication past unusual DNA obstacles. This work sets the stage for significant progress in dissecting the molecular mechanisms whereby replication perturbation by abnormal DNA structures leads to genomic instability. In this review, we focus on FANCJ and its role to enable efficient DNA replication when the fork encounters vastly abundant naturally occurring DNA obstacles, which may have implications for targeting rapidly dividing cancer cells.
    Full-text · Article · Jul 2016
    • "This is a major cause for genomic instability in both normal and cancer cells, and it is believed to represent a major mechanism of carcinogenesis, by allowing cells to accumulate mutations and acquire cancer phenotypes (16–18). Two major mechanisms are available to cells for restarting stalled replication forks: HR and translesion synthesis (TLS) (1,4,12,13,19). HR can be initiated at stalled forks to re-establish replication following formation of a recombination structure called displacement (D) loop. Essential to HR is the protein RAD51, which is loaded by BRCA2 * To whom correspondence should be addressed. "
    [Show abstract] [Hide abstract] ABSTRACT: Genomic instability, a major hallmark of cancer cells, is caused by incorrect or ineffective DNA repair. Many DNA repair mechanisms cooperate in cells to fight DNA damage, and are generally regulated by post-translational modification of key factors. Poly-ADP-ribosylation, catalyzed by PARP1, is a post-translational modification playing a prominent role in DNA repair, but much less is known about mono-ADP-ribosylation. Here we report that mono-ADP-ribosylation plays an important role in homologous recombination DNA repair, a mechanism essential for replication fork stability and double strand break repair. We show that the mono-ADP-ribosyltransferase PARP14 interacts with the DNA replication machinery component PCNA and promotes replication of DNA lesions and common fragile sites. PARP14 depletion results in reduced homologous recombination, persistent RAD51 foci, hypersensitivity to DNA damaging agents and accumulation of DNA strand breaks. Our work uncovered PARP14 as a novel factor required for mitigating replication stress and promoting genomic stability. © The Author(s) 2015. Published by Oxford University Press on behalf of Nucleic Acids Research.
    Full-text · Article · Mar 2015
    • "Defects in DNA-PKcs – RPA32 signaling result in more persistent DSB damage (-H2AX) after release from replication stress [33] . Because HR is an important mechanism for restarting collapsed forks [8], one possibility is that persistent damage underlies the elevated HR in DNA-PKcs KD and S4A/S8A mutants. However, DNA-PKcs null cells (with low ATM) display persistent -H2AX, as do DNA-PKcs KD and S4A/S8A mutants [33,37] , yet HR is not elevated above WT in DNA- PKcs null mutants. "
    [Show abstract] [Hide abstract] ABSTRACT: Genotoxins and other factors cause replication stress that activate the DNA damage response (DDR), comprising checkpoint and repair systems. The DDR suppresses cancer by promoting genome stability, and it regulates tumor resistance to chemo- and radiotherapy. Three members of the phosphatidylinositol 3-kinase-related kinase (PIKK) family, ATM, ATR, and DNA-PK, are important DDR proteins. A key PIKK target is replication protein A (RPA), which binds single-stranded DNA and functions in DNA replication, DNA repair, and checkpoint signaling. An early response to replication stress is ATR activation, which occurs when RPA accumulates on ssDNA. Activated ATR phosphorylates many targets, including the RPA32 subunit of RPA, leading to Chk1 activation and replication arrest. DNA-PK also phosphorylates RPA32 in response to replication stress, and we demonstrate that cells with DNA-PK defects, or lacking RPA32 Ser4/Ser8 targeted by DNA-PK, confer similar phenotypes, including defective replication checkpoint arrest, hyper-recombination, premature replication fork restart, failure to block late origin firing, and increased mitotic catastrophe. We present evidence that hyper-recombination in these mutants is ATM-dependent, but the other defects are ATM-independent. These results indicate that DNA-PK and ATR signaling through RPA32 plays a critical role in promoting genome stability and cell survival in response to replication stress.
    Full-text · Article · May 2014
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