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Morreall J, Limpose K, Sheppard C, Kow YW, Werner E, Doetsch PW. Inactivation of a common OGG1 variant by TNF-alpha in mammalian cells. DNA Repair (Amst) 2014; 26:15-22. [PMID: 25534136 DOI: 10.1016/j.dnarep.2014.11.007] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2014] [Revised: 11/20/2014] [Accepted: 11/25/2014] [Indexed: 12/17/2022]
Abstract
Reactive oxygen species threaten genomic integrity by inducing oxidative DNA damage. One common form of oxidative DNA damage is the mutagenic lesion 8-oxoguanine (8-oxodG). One driver of oxidative stress that can induce 8-oxodG is inflammation, which can be initiated by the cytokine tumor necrosis factor alpha (TNF-α). Oxidative DNA damage is primarily repaired by the base excision repair pathway, initiated by glycosylases targeting specific DNA lesions. 8-oxodG is excised by 8-oxoguanine glycosylase 1 (OGG1). A common Ogg1 allelic variant is S326C-Ogg1, prevalent in Asian and Caucasian populations. S326C-Ogg1 is associated with various forms of cancer, and is inactivated by oxidation. However, whether oxidative stress caused by inflammatory cytokines compromises OGG1 variant repair activity remains unknown. We addressed whether TNF-α causes oxidative stress that both induces DNA damage and inactivates S326C-OGG1 via cysteine 326 oxidation. In mouse embryonic fibroblasts, we found that S326C-OGG1 was inactivated only after exposure to H2O2 or TNF-α. Treatment with the antioxidant N-acetylcysteine prior to oxidative stress rescued S326C-OGG1 activity, demonstrated by in vitro and cellular repair assays. In contrast, S326C-OGG1 activity was unaffected by potassium bromate, which induces oxidative DNA damage without causing oxidative stress, and presumably cysteine oxidation. This study reveals that Cys326 is vulnerable to oxidation that inactivates S326C-OGG1. Physiologically relevant levels of TNF-α simultaneously induce 8-oxodG and inactivate S326C-OGG1. These results suggest a mechanism that could contribute to increased risk of cancer among S326C-Ogg1 homozygous individuals.
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Werner E, Wang H, Doetsch PW. Opposite roles for p38MAPK-driven responses and reactive oxygen species in the persistence and resolution of radiation-induced genomic instability. PLoS One 2014; 9:e108234. [PMID: 25271419 PMCID: PMC4182705 DOI: 10.1371/journal.pone.0108234] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Accepted: 08/27/2014] [Indexed: 01/26/2023] Open
Abstract
We report the functional and temporal relationship between cellular phenotypes such as oxidative stress, p38MAPK-dependent responses and genomic instability persisting in the progeny of cells exposed to sparsely ionizing low-Linear Energy Transfer (LET) radiation such as X-rays or high-charge and high-energy (HZE) particle high-LET radiation such as 56Fe ions. We found that exposure to low and high-LET radiation increased reactive oxygen species (ROS) levels as a threshold-like response induced independently of radiation quality and dose. This response was sustained for two weeks, which is the period of time when genomic instability is evidenced by increased micronucleus formation frequency and DNA damage associated foci. Indicators for another persisting response sharing phenotypes with stress-induced senescence, including beta galactosidase induction, increased nuclear size, p38MAPK activation and IL-8 production, were induced in the absence of cell proliferation arrest during the first, but not the second week following exposure to high-LET radiation. This response was driven by a p38MAPK-dependent mechanism and was affected by radiation quality and dose. This stress response and elevation of ROS affected genomic instability by distinct pathways. Through interference with p38MAPK activity, we show that radiation-induced stress phenotypes promote genomic instability. In contrast, exposure to physiologically relevant doses of hydrogen peroxide or increasing endogenous ROS levels with a catalase inhibitor reduced the level of genomic instability. Our results implicate persistently elevated ROS following exposure to radiation as a factor contributing to genome stabilization.
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Wang H, Wang X, Chen G, Zhang X, Tang X, Park D, Cucinotta FA, Yu DS, Deng X, Dynan WS, Doetsch PW, Wang Y. Distinct roles of Ape1 protein, an enzyme involved in DNA repair, in high or low linear energy transfer ionizing radiation-induced cell killing. J Biol Chem 2014; 289:30635-30644. [PMID: 25210033 DOI: 10.1074/jbc.m114.604959] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
High linear energy transfer (LET) radiation from space heavy charged particles or a heavier ion radiotherapy machine kills more cells than low LET radiation, mainly because high LET radiation-induced DNA damage is more difficult to repair. Relative biological effectiveness (RBE) is the ratio of the effects generated by high LET radiation to low LET radiation. Previously, our group and others demonstrated that the cell-killing RBE is involved in the interference of high LET radiation with non-homologous end joining but not homologous recombination repair. This effect is attributable, in part, to the small DNA fragments (≤40 bp) directly produced by high LET radiation, the size of which prevents Ku protein from efficiently binding to the two ends of one fragment at the same time, thereby reducing non-homologous end joining efficiency. Here we demonstrate that Ape1, an enzyme required for processing apurinic/apyrimidinic (known as abasic) sites, is also involved in the generation of small DNA fragments during the repair of high LET radiation-induced base damage, which contributes to the higher RBE of high LET radiation-induced cell killing. This discovery opens a new direction to develop approaches for either protecting astronauts from exposure to space radiation or benefiting cancer patients by sensitizing tumor cells to high LET radiotherapy.
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Morreall JF, Petrova L, Doetsch PW. Transcriptional mutagenesis and its potential roles in the etiology of cancer and bacterial antibiotic resistance. J Cell Physiol 2014; 228:2257-61. [PMID: 23696333 PMCID: PMC3963475 DOI: 10.1002/jcp.24400] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Accepted: 05/07/2013] [Indexed: 02/04/2023]
Abstract
Most cells do not undergo continuous cell division and DNA replication, yet they can still acquire novel RNA mutations that can result in the production of mutant proteins and induce a phenotypic change. All cells are frequently subjected to genotoxic insults that give rise to damaged nucleotides which, similarly to DNA replication, can undergo base mispairing during transcription. This mutagenic lesion bypass by RNA polymerase, transcriptional mutagenesis (TM), has been studied in a variety of systems and organisms, and may be involved in diverse pathogenic processes, such as tumorigenesis and the acquisition of bacterial antibiotic resistance. Tumor cells and bacteria within the human body are subject to especially high levels of oxidative stress, which can damage DNA and consequently drive TM. Mutagenesis at the level of transcription may allow cells to escape growth arrest and undergo replication that could permanently establish mutations in DNA in a process called retromutagenesis (RM). Here, we review the broad range of DNA damages which may result in TM including a variety of non-bulky lesions and some bulky lesions, which recent studies indicate may not completely block transcription, and emerging evidence supporting the RM concept in the context of tumorigenesis and antibiotic resistance.
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Bauer NC, Corbett AH, Doetsch PW. Automated quantification of the subcellular localization of multicompartment proteins via Q-SCAn. Traffic 2013; 14:1200-8. [PMID: 24034606 PMCID: PMC3836439 DOI: 10.1111/tra.12118] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Revised: 09/06/2013] [Accepted: 09/11/2013] [Indexed: 01/19/2023]
Abstract
In eukaryotic cells, proteins can occupy multiple intracellular compartments and even move between compartments to fulfill critical biological functions or respond to cellular signals. Examples include transcription factors that reside in the cytoplasm but are mobilized to the nucleus as well as dual-purpose DNA repair proteins that are charged with simultaneously maintaining the integrity of both the nuclear and mitochondrial genomes. While numerous methods exist to study protein localization and dynamics, automated methods to quantify the relative amounts of proteins that occupy multiple subcellular compartments have not been extensively developed. To address this need, we present a rapid, automated method termed quantitative subcellular compartmentalization analysis (Q-SCAn). To develop this method, we exploited the facile molecular biology of the budding yeast, Saccharomyces cerevisiae. Individual subcellular compartments are defined by a fluorescent marker protein and the intensity of a target GFP-tagged protein is then quantified within each compartment. To validate Q-SCAn, we analyzed relocalization of the transcription factor Yap1 following oxidative stress and then extended the approach to multicompartment localization by examining two DNA repair proteins critical for the base excision repair pathway, Ntg1 and Ung1. Our findings demonstrate the utility of Q-SCAn for quantitative analysis of the subcellular distribution of multicompartment proteins.
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Marullo R, Werner E, Degtyareva N, Moore B, Altavilla G, Ramalingam SS, Doetsch PW. Cisplatin induces a mitochondrial-ROS response that contributes to cytotoxicity depending on mitochondrial redox status and bioenergetic functions. PLoS One 2013; 8:e81162. [PMID: 24260552 PMCID: PMC3834214 DOI: 10.1371/journal.pone.0081162] [Citation(s) in RCA: 523] [Impact Index Per Article: 47.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Accepted: 10/09/2013] [Indexed: 11/30/2022] Open
Abstract
Cisplatin is one of the most effective and widely used anticancer agents for the treatment of several types of tumors. The cytotoxic effect of cisplatin is thought to be mediated primarily by the generation of nuclear DNA adducts, which, if not repaired, cause cell death as a consequence of DNA replication and transcription blockage. However, the ability of cisplatin to induce nuclear DNA (nDNA) damage per se is not sufficient to explain its high degree of effectiveness nor the toxic effects exerted on normal, post-mitotic tissues. Oxidative damage has been observed in vivo following exposure to cisplatin in several tissues, suggesting a role for oxidative stress in the pathogenesis of cisplatin-induced dose-limiting toxicities. However, the mechanism of cisplatin-induced generation of ROS and their contribution to cisplatin cytotoxicity in normal and cancer cells is still poorly understood. By employing a panel of normal and cancer cell lines and the budding yeast Saccharomyces cerevisiae as model system, we show that exposure to cisplatin induces a mitochondrial-dependent ROS response that significantly enhances the cytotoxic effect caused by nDNA damage. ROS generation is independent of the amount of cisplatin-induced nDNA damage and occurs in mitochondria as a consequence of protein synthesis impairment. The contribution of cisplatin-induced mitochondrial dysfunction in determining its cytotoxic effect varies among cells and depends on mitochondrial redox status, mitochondrial DNA integrity and bioenergetic function. Thus, by manipulating these cellular parameters, we were able to enhance cisplatin cytotoxicity in cancer cells. This study provides a new mechanistic insight into cisplatin-induced cell killing and may lead to the design of novel therapeutic strategies to improve anticancer drug efficacy.
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Xie M, Yen Y, Owonikoko TK, Ramalingam SS, Khuri FR, Curran WJ, Doetsch PW, Deng X. Bcl2 induces DNA replication stress by inhibiting ribonucleotide reductase. Cancer Res 2013; 74:212-23. [PMID: 24197132 DOI: 10.1158/0008-5472.can-13-1536-t] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
DNA replication stress is an inefficient DNA synthesis process that leads replication forks to progress slowly or stall. Two main factors that cause replication stress are alterations in pools of deoxyribonucleotide (dNTP) precursors required for DNA synthesis and changes in the activity of proteins required for synthesis of dNTPs. Ribonucleotide reductase (RNR), containing regulatory hRRM1 and catalytic hRRM2 subunits, is the enzyme that catalyzes the conversion of ribonucleoside diphosphates (NDP) to deoxyribonucleoside diphosphates (dNDP) and thereby provides dNTP precursors needed for the synthesis of DNA. Here, we demonstrate that either endogenous or exogenous expression of Bcl2 results in decreases in RNR activity and intracellular dNTP, retardation of DNA replication fork progression, and increased rate of fork asymmetry leading to DNA replication stress. Bcl2 colocalizes with hRRM1 and hRRM2 in the cytoplasm and directly interacts via its BH4 domain with hRRM2 but not hRRM1. Removal of the BH4 domain of Bcl2 abrogates its inhibitory effects on RNR activity, dNTP pool level, and DNA replication. Intriguingly, Bcl2 directly inhibits RNR activity by disrupting the functional hRRM1/hRRM2 complex via its BH4 domain. Our findings argue that Bcl2 reduces intracellular dNTPs by inhibiting ribonucleotide reductase activity, thereby providing insight into how Bcl2 triggers DNA replication stress.
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Degtyareva NP, Heyburn L, Sterling J, Resnick MA, Gordenin DA, Doetsch PW. Oxidative stress-induced mutagenesis in single-strand DNA occurs primarily at cytosines and is DNA polymerase zeta-dependent only for adenines and guanines. Nucleic Acids Res 2013; 41:8995-9005. [PMID: 23925127 PMCID: PMC3799438 DOI: 10.1093/nar/gkt671] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Localized hyper-mutability caused by accumulation of lesions in persistent single-stranded (ss) DNA has been recently found in several types of cancers. An increase in endogenous levels of reactive oxygen species (ROS) is considered to be one of the hallmarks of cancers. Employing a yeast model system, we addressed the role of oxidative stress as a potential source of hyper-mutability in ssDNA by modulation of the endogenous ROS levels and by exposing cells to oxidative DNA-damaging agents. We report here that under oxidative stress conditions the majority of base substitution mutations in ssDNA are caused by erroneous, DNA polymerase (Pol) zeta-independent bypass of cytosines, resulting in C to T transitions. For all other DNA bases Pol zeta is essential for ROS-induced mutagenesis. The density of ROS-induced mutations in ssDNA is lower, compared to that caused by UV and MMS, which suggests that ssDNA could be actively protected from oxidative damage. These findings have important implications for understanding mechanisms of oxidative mutagenesis, and could be applied to development of anticancer therapies and cancer prevention.
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Zhang H, Hu Z, Jiang N, Marullo R, Doetsch PW, Hunt WD, Chen GZ, Shin DM. Abstract 1298: The role of nuclear factor kappa B in survival of human papillomavirus-positive head and neck cancer cell lines. Cancer Res 2013. [DOI: 10.1158/1538-7445.am2013-1298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Nuclear factor kappa B (NFκB) has been implicated in the development of head and neck squamous cell carcinoma (HNSCC) from premalignant changes to tumor progression, and in treatment resistance and recurrence. However, the roles of NFκB in the sensitivity to chemoradiation of human papillomavirus (HPV)-associated HNSCC have not been well defined. Previously we reported that high expression of NFκB detected by immunohistochemistry in pretreated HPV+ oropharyngeal cancer patients was significantly associated with poor progression free survival (AACR 2012 Abstract #4489). Therefore, we hypothesized that NFκB could play a role in pro-survival in HPV+ head and neck cancer cells. We first examined the sensitivity of five HPV+ head and neck cancer cell lines (HPV16: UDSCC2, 93-VU-147T, UM-SCC47, UPCI:SCC90, HPV18: SCC1483) to radiation and cisplatin, Consistent with current models, when we knocked down expression of the HPV16E6 oncogene, SCC47 and SCC1483 cells with restored expression of p53 displayed a significant reduction in S phase entry as revealed by cell cycle analysis (SCC47: scrambled control 14.08% ± 0.55% versus siRNA-E6 6.39% ± 2.40, p=0.004; SCC1483: scrambled control 13.39% ± 1.28% versus 7.49% ± 0.83, p=0.002). In addition, all five cell lines displayed reduced sensitivity to cisplatin compared with cells treated with scrambled control siRNA. The basal level of activated NFκB in HPV+ cell lines was correlated with the sensitivity to radiation and cisplatin as assessed by colony formation and cell growth assays. Suppression of NFκBp65 by siRNA resulted in marked increases in apoptosis associated with reduction of Bcl-2 in both SCC47 and SCC1483 cells. This pattern was more pronounced with increasing doses of the proteasome inhibitor bortezomib (32.5 to 130 nM for 48 to 72 hr). Furthermore, SCC47 and SCC1483 cells treated with siRNA NFκBp65 displayed a significantly greater level of apoptosis induced by radiation or cisplatin compared to cells treated with non-targeted control siRNA, indicating a pro-survival effect for NFκB. Further studies are warranted to delineate the effects of HPV oncogene interactions with NFκB signaling pathways on chemoradiation sensitivity. (This study was supported by the V Foundation).
Citation Format: Hongzheng Zhang, Zhongliang Hu, Ning Jiang, Rossella Marullo, Paul W. Doetsch, William D. Hunt, Georgia Z. Chen, Dong M. Shin. The role of nuclear factor kappa B in survival of human papillomavirus-positive head and neck cancer cell lines. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1298. doi:10.1158/1538-7445.AM2013-1298
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Morris LP, Degtyareva N, Sheppard C, Heyburn L, Ivanov AA, Kow YW, Doetsch PW. Saccharomyces cerevisiae Apn1 mutation affecting stable protein expression mimics catalytic activity impairment: implications for assessing DNA repair capacity in humans. DNA Repair (Amst) 2012; 11:753-65. [PMID: 22818187 DOI: 10.1016/j.dnarep.2012.06.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2012] [Revised: 06/18/2012] [Accepted: 06/25/2012] [Indexed: 11/18/2022]
Abstract
Apurinic/apyrimidinic (AP) endonucleases play a major role in the repair of AP sites, oxidative damage and alkylation damage in DNA. We employed Saccharomyces cerevisiae in an unbiased forward genetic screen to identify amino acid substitutions in the major yeast AP endonuclease, Apn1, that impair cellular DNA repair capacity by conferring sensitivity to the DNA alkylating agent methyl methanesulfonate. We report here the identification and characterization of the Apn1 V156E amino acid substitution mutant through biochemical and functional analysis. We found that steady state levels of Apn1 V156E were substantially decreased compared to wild type protein, and that this decrease was due to more rapid degradation of mutant protein compared to wild type. Based on homology to E. coli endonuclease IV and computational modeling, we predicted that V156E impairs catalytic ability. However, overexpression of mutant protein restored DNA repair activity in vitro and in vivo. Thus, the V156E substitution decreases DNA repair capacity by an unanticipated mechanism via increased degradation of mutant protein, leading to substantially reduced cellular levels. Our study provides evidence that the V156 residue plays a critical role in Apn1 structural integrity, but is not involved in catalytic activity. These results have important implications for elucidating structure-function relationships for the endonuclease IV family of proteins, and for employing simple eukaryotic model systems to understand how structural defects in the major human AP endonuclease APE1 may contribute to disease etiology.
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Rowe LA, Degtyareva N, Doetsch PW. Yap1: a DNA damage responder in Saccharomyces cerevisiae. Mech Ageing Dev 2012; 133:147-56. [PMID: 22433435 PMCID: PMC3351557 DOI: 10.1016/j.mad.2012.03.009] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2011] [Revised: 02/29/2012] [Accepted: 03/09/2012] [Indexed: 12/27/2022]
Abstract
Activation of signaling pathways in response to genotoxic stress is crucial for cells to properly repair DNA damage. In response to DNA damage, intracellular levels of reactive oxygen species increase. One important function of such a response could be to initiate signal transduction processes. We have employed the model eukaryote Saccharomyces cerevisiae to delineate DNA damage sensing mechanisms. We report a novel, unanticipated role for the transcription factor Yap1 as a DNA damage responder, providing direct evidence that reactive oxygen species are an important component of the DNA damage signaling process. Our findings reveal an epistatic link between Yap1 and the DNA base excision repair pathway. Corruption of the Yap1-mediated DNA damage response influences cell survival and genomic stability in response to exposure to genotoxic agents.
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Swartzlander DB, Bauer NC, Corbett AH, Doetsch PW. Regulation of base excision repair in eukaryotes by dynamic localization strategies. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2012; 110:93-121. [PMID: 22749144 DOI: 10.1016/b978-0-12-387665-2.00005-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
This chapter discusses base excision repair (BER) and the known mechanisms defined thus far regulating BER in eukaryotes. Unlike the situation with nucleotide excision repair and double-strand break repair, little is known about how BER is regulated to allow for efficient and accurate repair of many types of DNA base damage in both nuclear and mitochondrial genomes. Regulation of BER has been proposed to occur at multiple, different levels including transcription, posttranslational modification, protein-protein interactions, and protein localization; however, none of these regulatory mechanisms characterized thus far affect a large spectrum of BER proteins. This chapter discusses a recently discovered mode of BER regulation defined in budding yeast cells that involves mobilization of DNA repair proteins to DNA-containing organelles in response to genotoxic stress.
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Abstract
The majority of human cells do not multiply continuously but are quiescent or slow-replicating and devote a large part of their energy to transcription. When DNA damage in the transcribed strand of an active gene is bypassed by a RNA polymerase, they can miscode at the damaged site and produce mutant transcripts. This process is known as transcriptional mutagenesis and, as discussed in this Perspective, could lead to the production of mutant proteins and might therefore be important in tumour development.
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Clauson CL, Saxowsky TT, Doetsch PW. Dynamic flexibility of DNA repair pathways in growth arrested Escherichia coli. DNA Repair (Amst) 2010; 9:842-7. [PMID: 20462807 PMCID: PMC2893249 DOI: 10.1016/j.dnarep.2010.04.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2010] [Accepted: 04/06/2010] [Indexed: 01/17/2023]
Abstract
The DNA of all organisms is constantly damaged by exogenous and endogenous agents. Base excision repair (BER) is important for the removal of several non-bulky lesions from the DNA, however not much is known about the contributions of other DNA repair pathways to the processing of non-bulky lesions. Here we utilized a luciferase reporter system to assess the contributions of transcription-coupled repair (TCR), BER and nucleotide excision repair (NER) to the repair of two non-bulky lesions, 8-oxoguanine (8OG) and uracil (U), in vivo under non-growth conditions. We demonstrate that both TCR and NER are utilized by Escherichia coli to repair 8OG and U. Additionally, the relative level of recognition of these lesions by BER and NER suggests that TCR can utilize components of either pathway for lesion removal, depending upon their availability. These findings indicate a dynamic flexibility of DNA repair pathways in the removal of non-bulky DNA lesions in prokaryotes, and reveal their respective contributions to the repair of 8OG and U in vivo.
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Swartzlander DB, Griffiths LM, Lee J, Degtyareva NP, Doetsch PW, Corbett AH. Regulation of base excision repair: Ntg1 nuclear and mitochondrial dynamic localization in response to genotoxic stress. Nucleic Acids Res 2010; 38:3963-74. [PMID: 20194111 PMCID: PMC2896512 DOI: 10.1093/nar/gkq108] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Numerous human pathologies result from unrepaired oxidative DNA damage. Base excision repair (BER) is responsible for the repair of oxidative DNA damage that occurs in both nuclei and mitochondria. Despite the importance of BER in maintaining genomic stability, knowledge concerning the regulation of this evolutionarily conserved repair pathway is almost nonexistent. The Saccharomyces cerevisiae BER protein, Ntg1, relocalizes to organelles containing elevated oxidative DNA damage, indicating a novel mechanism of regulation for BER. We propose that dynamic localization of BER proteins is modulated by constituents of stress response pathways. In an effort to mechanistically define these regulatory components, the elements necessary for nuclear and mitochondrial localization of Ntg1 were identified, including a bipartite classical nuclear localization signal, a mitochondrial matrix targeting sequence and the classical nuclear protein import machinery. Our results define a major regulatory system for BER which when compromised, confers a mutator phenotype and sensitizes cells to the cytotoxic effects of DNA damage.
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Pawar V, Jingjing L, Patel N, Kaur N, Doetsch PW, Shadel GS, Zhang H, Siede W. Checkpoint kinase phosphorylation in response to endogenous oxidative DNA damage in repair-deficient stationary-phase Saccharomyces cerevisiae. Mech Ageing Dev 2009; 130:501-8. [PMID: 19540258 DOI: 10.1016/j.mad.2009.06.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2008] [Revised: 06/03/2009] [Accepted: 06/07/2009] [Indexed: 10/20/2022]
Abstract
Stationary-phase Saccharomyces cerevisiae can serve as a model for post-mitotic cells of higher eukaryotes. Phosphorylation and activation of the checkpoint kinase Rad53 was observed after more than 2 days of culture if two major pathways of oxidative DNA damage repair, base excision repair (BER) and nucleotide excision repair (NER), are inactive. The wild type showed a low degree of Rad53 phosphorylation when the incubation period was drastically increased. In the ber ner strain, Rad53 phosphorylation can be abolished by inclusion of antioxidants or exclusion of oxygen. Furthermore, this modification and enhanced mutagenesis in extended stationary phase were absent in rho degrees strains, lacking detectable mitochondrial DNA. This checkpoint response is therefore thought to be dependent on reactive oxygen species originating from mitochondrial respiration. There was no evidence for progressive overall telomere shortening during stationary-phase incubation. Since Rad50 (of the MRN complex) and Mec1 (the homolog of ATR) were absolutely required for the observed checkpoint response, we assume that resected random double-strand breaks are the critical lesion. Single-strand resection may be accelerated by unrepaired oxidative base damage in the vicinity of a double-strand break.
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Griffiths LM, Doudican NA, Shadel GS, Doetsch PW. Mitochondrial DNA oxidative damage and mutagenesis in Saccharomyces cerevisiae. Methods Mol Biol 2009; 554:267-86. [PMID: 19513680 DOI: 10.1007/978-1-59745-521-3_17] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Mutation of human mitochondrial DNA (mtDNA) has been linked to maternally inherited neuromuscular disorders and is implicated in more common diseases such as cancer, diabetes, and Parkinson's disease. Mutations in mtDNA also accumulate with age and are therefore believed to contribute to aging and age-related pathology. Housed within the mitochondrial matrix, mtDNA encodes several of the proteins involved in the production of ATP via the process of oxidative phosphorylation, which involves the flow of high-energy electrons through the electron transport chain (ETC). Because of its proximity to the ETC, mtDNA is highly vulnerable to oxidative damage mediated by reactive oxygen species (ROS) such as hydrogen peroxide, superoxide, and hydroxyl radicals that are constantly produced by this system. Therefore, it is important to be able to measure oxidative mtDNA damage under normal physiologic conditions and during environmental or disease-associated stress. The budding yeast, Saccharomyces cerevisiae, is a facile and informative model system in which to study such mtDNA oxidative damage because it is a unicellular eukaryotic facultative anaerobe that is conditionally dependent on mitochondrial oxidative phosphorylation for viability. Here, we describe methods for quantifying oxidative mtDNA damage and mutagenesis in S. cerevisiae, several of which could be applied to the development of similar assays in mammalian cells and tissues. These methods include measuring the number of point mutations that occur in mtDNA with the erythromycin resistance assay, quantifying the amount of oxidative DNA damage utilizing a modified Southern blot assay, and measuring mtDNA integrity with the "petite induction" assay.
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Rowe LA, Degtyareva N, Doetsch PW. DNA damage-induced reactive oxygen species (ROS) stress response in Saccharomyces cerevisiae. Free Radic Biol Med 2008; 45:1167-77. [PMID: 18708137 PMCID: PMC2643028 DOI: 10.1016/j.freeradbiomed.2008.07.018] [Citation(s) in RCA: 204] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/16/2008] [Revised: 07/02/2008] [Accepted: 07/11/2008] [Indexed: 01/13/2023]
Abstract
Cells are exposed to both endogenous and exogenous sources of reactive oxygen species (ROS). At high levels, ROS can lead to impaired physiological function through cellular damage of DNA, proteins, lipids, and other macromolecules, which can lead to certain human pathologies including cancers, neurodegenerative disorders, and cardiovascular disease, as well as aging. We have employed Saccharomyces cerevisiae as a model system to examine the levels and types of ROS that are produced in response to DNA damage in isogenic strains with different DNA repair capacities. We find that when DNA damage is introduced into cells from exogenous or endogenous sources there is an increase in the amount of intracellular ROS which is not directly related to cell death. We have examined the spectrum of ROS in order to elucidate its role in the cellular response to DNA damage. As an independent verification of the DNA damage-induced ROS response, we show that a major activator of the oxidative stress response, Yap1, relocalizes to the nucleus following exposure to the DNA-alkylating agent methyl methanesulfonate. Our results indicate that the DNA damage-induced increase in intracellular ROS levels is a generalized stress response that is likely to function in various signaling pathways.
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Suhadolnik RJ, Doetsch PW, Devash Y, Henderson EE, Charubala R, Pfleiderer W. 2′,5′-Adenylate and Cordycepin Trimer Cores: Metabolic Stability and Evidence for Antimitogenesis without 5′-Rephosphorylation. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/07328318308078869] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Abstract
Cells exposed to DNA-damaging agents in their natural environment do not undergo continuous cycles of replication but are more frequently engaged in gene transcription. Despite the relatively high efficiency of the different DNA repair pathways, some lesions remain in DNA. During transcription, RNA polymerase can bypass DNA damage on the transcribed strand of an active gene. This bypass can be at the origin of the production of "mutated" mRNA because of the transcriptional miscoding (transcriptional mutagenesis) due to the altered pairing specificities of the lesion. In vivo consequences of transcriptional mutagenesis on normal cell physiology have not well been documented because of the lack of a robust system allowing for its study. We describe here a procedure that we developed using a plasmid-based luciferase reporter assay to analyze the transcriptional mutagenesis events induced by different types of DNA lesions. Introduction of the DNA lesion to be studied at a specific site on the plasmid is based on the synthesis of a complementary strand of a circular, single-stranded DNA (ssDNA) from a DNA lesion-containing oligonucleotide. Once obtained, this construct can be transformed into different Escherichia coli strains that can express the luciferase gene under nongrowth conditions. Quantification of luciferase activity and sequencing of luciferase cDNAs allow for the characterization of transcriptional mutagenesis both quantitatively and qualitatively.
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Saxowsky TT, Doetsch PW. RNA polymerase encounters with DNA damage: transcription-coupled repair or transcriptional mutagenesis? Chem Rev 2006; 106:474-88. [PMID: 16464015 DOI: 10.1021/cr040466q] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
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Beljanski V, Villanueva JM, Doetsch PW, Natile G, Marzilli LG. Marked dependence on carrier-ligand bulk but not on carrier-ligand chirality of the duplex versus single-strand forms of a DNA oligonucleotide with a series of G-Pt(II)-G intrastrand cross-links modeling cisplatin-DNA adducts. J Am Chem Soc 2006; 127:15833-42. [PMID: 16277526 DOI: 10.1021/ja053089n] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The N7-Pt-N7 adjacent G,G intrastrand DNA cross-link responsible for cisplatin anticancer activity is dynamic, promotes local "melting" in long DNA, and converts many oligomer duplexes to single strands. For 5'-d(A1T2G3G4G5T6A7C8C9C10A11T12)-3' (G3), treatment of the (G3)2 duplex with five pairs of [LPt(H2O)2]2+ enantiomers (L = an asymmetric diamine) formed mixtures of LPt-G3 products (1 Pt per strand) cross-linked at G3,G4 or at G4,G5 in all cases. L chirality exerted little influence. For primary diamines L with bulk on chelate ring carbons (e.g., 1,2-diaminocyclohexane), the duplex was converted completely into single strands (G3,G4 coils and G4,G5 hairpins), exactly mirroring results for cisplatin, which lacks bulk. In sharp contrast, for secondary diamines L with bulk on chelate ring nitrogens (e.g., 2,2'-bipiperidine, Bip), unexpectedly stable duplexes having two platinated strands (even a unique G3,G4/G4,G5 heteroduplex) were formed. After enzymatic digestion of BipPt-G3 duplexes, the conformation of the relatively nondynamic G,G units was shown to be head-to-head (HH) by HPLC/mass spectrometric characterization. Because the HH conformation dominates at the G,G lesion in duplex DNA and in the BipPt-G3 duplexes, the stabilization of the duplex form only when the L nitrogen adducts possess bulk suggests that H-bonding interactions of the Pt-NH groups with the flanking DNA lead to local melting and to destabilization of oligomer duplexes. The marked dependence of adduct properties on L bulk and the minimal dependence on L chirality underscore the need for future exploration of the roles of the L periphery in affecting anticancer activity.
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O'Rourke TW, Doudican NA, Zhang H, Eaton JS, Doetsch PW, Shadel GS. Differential involvement of the related DNA helicases Pif1p and Rrm3p in mtDNA point mutagenesis and stability. Gene 2005; 354:86-92. [PMID: 15907372 DOI: 10.1016/j.gene.2005.03.031] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2004] [Revised: 12/21/2004] [Accepted: 03/23/2005] [Indexed: 10/25/2022]
Abstract
With the exception of base excision repair, conserved pathways and mechanisms that maintain mitochondrial genome stability have remained largely undelineated. In the budding yeast, Saccharomyces cerevisiae, Pif1p is a unique DNA helicase that is localized both to the nucleus and mitochondria, where it is involved in maintaining DNA integrity. We previously elucidated a role for Pif1p in oxidative mtDNA damage resistance that appears to be distinct from its postulated function in mtDNA recombination. Strains lacking Pif1p (pif1Delta) exhibit an increased rate of formation of petite mutants (an indicator of mtDNA instability) and elevated mtDNA point mutagenesis. Here we show that deletion of the RRM3 gene, which encodes a DNA helicase closely related to Pif1p, significantly rescues the petite-induction phenotype of a pif1Delta strain. However, suppression of this phenotype was not accompanied by a corresponding decrease in mtDNA point mutagenesis. Instead, deletion of RRM3 alone resulted in an increase in mtDNA point mutagenesis that was synergistic with that caused by a pif1Delta mutation. In addition, we found that over-expression of RNR1, encoding a large subunit of ribonucleotide reductase (RNR), rescued the petite-induction phenotype of a pif1Delta mutation to a similar extent as deletion of RRM3. This, coupled to our finding that the Rad53p protein kinase is phosphorylated in the rrm3Delta pif1Delta double-mutant strain, leads us to conclude that one mechanism whereby deletion of RRM3 influences mtDNA stability is by modulating mitochondrial deoxynucleoside triphosphate pools. We propose that this is accomplished by signaling through the conserved Mec1/Rad53, S-phase checkpoint pathway to induce the expression and activity of RNR. Altogether, our results define a novel role for Rrm3p in mitochondrial function and indicate that Pif1p and Rrm3p influence a common process (or processes) involved in mtDNA replication, repair, or stability.
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Doudican NA, Song B, Shadel GS, Doetsch PW. Oxidative DNA damage causes mitochondrial genomic instability in Saccharomyces cerevisiae. Mol Cell Biol 2005; 25:5196-204. [PMID: 15923634 PMCID: PMC1140570 DOI: 10.1128/mcb.25.12.5196-5204.2005] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mitochondria contain their own genome, the integrity of which is required for normal cellular energy metabolism. Reactive oxygen species (ROS) produced by normal mitochondrial respiration can damage cellular macromolecules, including mitochondrial DNA (mtDNA), and have been implicated in degenerative diseases, cancer, and aging. We developed strategies to elevate mitochondrial oxidative stress by exposure to antimycin and H(2)O(2) or utilizing mutants lacking mitochondrial superoxide dismutase (sod2Delta). Experiments were conducted with strains compromised in mitochondrial base excision repair (ntg1Delta) and oxidative damage resistance (pif1Delta) in order to delineate the relationship between these pathways. We observed enhanced ROS production, resulting in a direct increase in oxidative mtDNA damage and mutagenesis. Repair-deficient mutants exposed to oxidative stress conditions exhibited profound genomic instability. Elimination of Ntg1p and Pif1p resulted in a synergistic corruption of respiratory competency upon exposure to antimycin and H(2)O(2). Mitochondrial genomic integrity was substantially compromised in ntg1Delta pif1Delta sod2Delta strains, since these cells exhibit a total loss of mtDNA. A stable respiration-defective strain, possessing a normal complement of mtDNA damage resistance pathways, exhibited a complete loss of mtDNA upon exposure to antimycin and H(2)O(2). This loss was preventable by Sod2p overexpression. These results provide direct evidence that oxidative mtDNA damage can be a major contributor to mitochondrial genomic instability and demonstrate cooperation of Ntg1p and Pif1p to resist the introduction of lesions into the mitochondrial genome.
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Brégeon D, Doetsch PW. Reliable method for generating double-stranded DNA vectors containing site-specific base modifications. Biotechniques 2005; 37:760-2, 764, 766. [PMID: 15560132 DOI: 10.2144/04375st01] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Cells of all living organisms are continuously exposed to physical and chemical agents that damage DNA and alter the integrity of their genomes. Despite the relatively high efficiency of the different repair pathways, some lesions remain in DNA when it is replicated or transcribed. Lesion bypass by DNA and RNA polymerases has been the subject of numerous investigations. However, knowledge of the in vivo mechanism of transcription lesion bypass is very limited because no robust methodology is available. Here we describe a protocol based on the synthesis of a complementary strand of a circular, single-stranded DNA molecule, which allows for the production of large amounts of double-stranded DNA containing a lesion at a specific position in a transcribed sequence. Such constructs can subsequently be used for lesion bypass studies in vivo by RNA polymerase and to ascertain how these events can be affected by the genetic background of the cells.
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