Molecular cloning of a human DNA repair gene

Characterization and Comparative Genomic Analysis of a Deep-Sea Bacillus Phage Reveal a Novel Genus

As the most abundant biological entities, viruses are the major players in marine ecosystems. However, our knowledge on virus diversity and virus-host interactions in the deep sea remains very limited. In this study, vB_BteM-A9Y, a novel bacteriophage infecting Bacillus tequilensis, was isolated from deep-sea sediments in the South China Sea. vB_BteM-A9Y has a hexametric head and a long, complex contractile tail, which are typical features of myophages. vB_BteM-A9Y initiated host lysis at 60 min post infection with a burst size of 75 PFU/cell. The phage genome comprises 38,634 base pairs and encodes 54 predicted open reading frames (ORFs), of which 27 ORFs can be functionally annotated by homology analysis. Interestingly, abundant ORFs involved in DNA damage repair were identified in the phage genome, suggesting that vB_BteM-A9Y encodes multiple pathways for DNA damage repair, which may help to maintain the stability of the host/phage genome. A BLASTn search of the whole genome sequence of vB_BteM-A9Y against the GenBank revealed no existing homolog. Consistently, a phylogenomic tree and proteome-based phylogenetic tree analysis showed that vB_BteM-A9Y formed a unique branch. Further comparative analysis of genomic nucleotide similarity and ORF homology of vB_BteM-A9Y with its mostly related phages showed that the intergenomic similarity between vB_BteM-A9Y and these phages was 0-33.2%. Collectively, based on the comprehensive morphological, phylogenetic, and comparative genomic analysis, we propose that vB_BteM-A9Y belongs to a novel genus under Caudoviricetes. Therefore, our study will increase our knowledge on deep-sea virus diversity and virus-host interactions, as well as expanding our knowledge on phage taxonomy.

The Spectrum of MORC2-Related Disorders: A Potential Link to Cockayne Syndrome

BACKGROUND

Cockayne syndrome (CS) is a DNA repair disorder primarily associated with pathogenic variants in ERCC6 and ERCC8. As in other Mendelian disorders, there are a number of genetically unsolved CS cases.

METHODS

We ascertained five individuals with monoallelic pathogenic variants in MORC2, previously associated with three dominantly inherited phenotypes: an axonal form of Charcot-Marie-Tooth disease type 2Z; a syndrome of developmental delay, impaired growth, dysmorphic facies, and axonal neuropathy; and a rare form of spinal muscular atrophy.

RESULTS

One of these individuals bore a strong phenotypic resemblance to CS. We then identified monoallelic pathogenic MORC2 variants in three of five genetically unsolved individuals with a clinical diagnosis of CS. In total, we identified eight individuals with MORC2-related disorder, four of whom had clinical features strongly suggestive of CS.

CONCLUSIONS

Our findings indicate that some forms of MORC2-related disorder have phenotypic similarities to CS, including features of accelerated aging. Unlike classic DNA repair disorders, MORC2-related disorder does not appear to be associated with a defect in transcription-coupled nucleotide excision repair and follows a dominant pattern of inheritance with variants typically arising de novo. Such de novo pathogenic variants present particular challenges with regard to both initial gene discovery and diagnostic evaluations. MORC2 should be included in diagnostic genetic test panels targeting the evaluation of microcephaly and/or suspected DNA repair disorders. Future studies of MORC2 and its protein product, coupled with further phenotypic characterization, will help to optimize the diagnosis, understanding, and therapy of the associated disorders.

Mapping of the regions implicated in nuclear localization of multi-functional DNA repair endonuclease XPF-ERCC1

The structure-specific endonuclease XPF-ERCC1 is a multi-functional heterodimer that participates in a variety of DNA repair mechanisms for maintaining genome integrity. Both subunits contain C-terminal tandem helix-hairpin-helix (HhH₂ ) domains, which are necessary for not only their dimerization but also enzymatic activity as well as protein stability. However, the interdependency of both subunits in their nuclear localization remains poorly understood. In this study, we have analyzed the region(s) that affects the subcellular localization of XPF and ERCC1 using various deletion mutants. We first identified the nuclear localization signal (NLS) in XPF, which was essential for its nuclear localization under the ERCC1-free condition, but dispensable in the presence of ERCC1 (probably as XPF-ERCC1 heterodimer). Interestingly, in the NLS-independent and ERCC1-dependent XPF nuclear localization, the physical interaction between XPF and ERCC1 via C-terminal HhH₂ domains was not needed. Instead, the amino acid regions 311-469 of XPF and 216-260 of ERCC1 are required for the nuclear localization. Furthermore, we found that the 311-469 region of XPF interacts with ERCC1 in a co-immunoprecipitation assay. These results suggest that the nuclear localization of XPF-ERCC1 heterodimer is regulated at multiple levels in an interdependent manner.

Mechanism of action of nucleotide excision repair machinery

Nucleotide excision repair (NER) is a versatile DNA repair pathway essential for the removal of a broad spectrum of structurally diverse DNA lesions arising from a variety of sources, including UV irradiation and environmental toxins. Although the core factors and basic stages involved in NER have been identified, the mechanisms of the NER machinery are not well understood. This review summarizes our current understanding of the mechanisms and order of assembly in the core global genome (GG-NER) pathway.

Impairment Mechanisms and Intervention Approaches for Aged Human Neuromuscular Junctions

The neuromuscular junction (NMJ) is a chemical synapse formed between a presynaptic motor neuron and a postsynaptic muscle cell. NMJs in most vertebrate species share many essential features; however, some differences distinguish human NMJs from others. This review will describe the pre- and postsynaptic structures of human NMJs and compare them to NMJs of laboratory animals. We will focus on age-dependent declines in function and changes in the structure of human NMJs. Furthermore, we will describe insights into the aging process revealed from mouse models of accelerated aging. In addition, we will compare aging phenotypes to other human pathologies that cause impairments of pre- and postsynaptic structures at NMJs. Finally, we will discuss potential intervention approaches for attenuating age-related NMJ dysfunction and sarcopenia in humans.

Oncological role of HMGA2 (Review)

The high mobility group A2 (HMGA2) protein is a non‑histone architectural transcription factor that modulates the transcription of several genes by binding to AT‑rich sequences in the minor groove of B‑form DNA and alters the chromatin structure. As a result, HMGA2 influences a variety of biological processes, including the cell cycle process, DNA damage repair process, apoptosis, senescence, epithelial‑mesenchymal transition and telomere restoration. In addition, the overexpression of HMGA2 is a feature of malignancy, and its elevated expression in human cancer predicts the efficacy of certain chemotherapeutic agents. Accumulating evidence has suggested that the detection of HMGA2 can be used as a routine procedure in clinical tumour analysis.

AC138128.1 an Intronic lncRNA originating from ERCC1 Implies a Potential Application in Lung Cancer Treatment

Lung cancer is one of the most devastating tumors with a high incidence and mortality worldwide. Polymorphisms and expression of ERCC1 commonly predicted the occurrence and prognosis of lung cancer. However, few studies have focused on long non-coding RNAs related to ERCC1 though some studies reminded the importance of its post-transcriptional regulation. In the present study, an intronic lncRNA AC138128.1 originated from ERCC1 was firstly identified in microarray chip and database, and its possibility as a novel biomarker to predict lung cancer treatment was further discussed. Firstly, the qRT-PCR data showed that AC138128.1 expression was much lower in lung cancer comparing with its para-cancer tissues, which further analyzed by ROC curve. Similarly, the difference was also verified in 16HBE, A549 and LK₂ cells. Then AC138128.1 expression was found to have an increasing trend in a dose or time-dependent manner after cisplatin treatment. Finally, the subcellular distribution of AC138128.1 reminded that AC138128.1 was mainly expressed in the nucleus. Interestingly a positive relationship between AC138128.1 and ERCC1 expression was only found in cancer tissues, which reminded AC138128.1 may be involved in the regulation of ERCC1. Therefore, as a preliminary exploration of the lncRNA originated from ERCC1, the present study suggested AC138128.1 is of potential value in predicting platinum analogue benefit in lung cancer.

Promoter methylation of DNA damage repair (DDR) genes in human tumor entities: RBBP8/CtIP is almost exclusively methylated in bladder cancer

Background

Genome-wide studies identified pan-cancer genes and shared biological networks affected by epigenetic dysregulation among diverse tumor entities. Here, we systematically screened for hypermethylation of DNA damage repair (DDR) genes in a comprehensive candidate-approach and exemplarily identify and validate candidate DDR genes as targets of epigenetic inactivation unique to bladder cancer (BLCA), which may serve as non-invasive biomarkers.

Methods

Genome-wide DNA methylation datasets (2755 CpG probes of n = 7819 tumor and n = 659 normal samples) of the TCGA network covering 32 tumor entities were analyzed in silico for 177 DDR genes. Genes of interest were defined as differentially methylated between normal and cancerous tissues proximal to transcription start sites. The lead candidate gene was validated by methylation-specific PCR (MSP) and/or bisulfite-pyrosequencing in different human cell lines (n = 36), in primary BLCA tissues (n = 43), and in voided urine samples (n = 74) of BLCA patients. Urines from healthy donors and patients with urological benign and malignant diseases were included as controls (n = 78). mRNA expression was determined using qRT-PCR in vitro before (n = 5) and after decitabine treatment (n = 2). Protein expression was assessed by immunohistochemistry (n = 42). R 3.2.0. was used for statistical data acquisition and SPSS 21.0 for statistical analysis.

Results

Overall, 39 DDR genes were hypermethylated in human cancers. Most exclusively and frequently methylated (37%) in primary BLCA was RBBP8, encoding endonuclease CtIP. RBBP8 hypermethylation predicted longer overall survival (OS) and was found in 2/4 bladder cancer cell lines but not in any of 33 cancer cell lines from entities with another origin like prostate. RBBP8 methylation was inversely correlated with RBBP8 mRNA and nuclear protein expression while RBBP8 was re-expressed after in vitro demethylation. RBBP8 methylation was associated with histological grade in primary BLCA and urine samples. RBBP8 methylation was detectable in urine samples of bladder cancer patients achieving a sensitivity of 52%, at 91% specificity.

Conclusions

RBBP8 was identified as almost exclusively hypermethylated in BLCA. RBBP8/CtIP has a proven role in homologous recombination-mediated DNA double-strand break repair known to sensitize cancer cells for PARP1 inhibitors. Since RBBP8 methylation was detectable in urines, it may be a complementary marker of high specificity in urine for BLCA detection.

Comparative Genomics of Chrysochromulina Ericina Virus and Other Microalga-Infecting Large DNA Viruses Highlights Their Intricate Evolutionary Relationship with the Established Mimiviridae Family

Chrysochromulina ericina virus CeV-01B (CeV) was isolated from Norwegian coastal waters in 1998. Its icosahedral particle is 160 nm in diameter and encloses a 474-kb double-stranded DNA (dsDNA) genome. This virus, although infecting a microalga (the haptophyceae Haptolina ericina, formerly Chrysochromulina ericina), is phylogenetically related to members of the Mimiviridae family, initially established with the acanthamoeba-infecting mimivirus and megavirus as prototypes. This family was later split into two genera (Mimivirus and Cafeteriavirus) following the characterization of a virus infecting the heterotrophic stramenopile Cafeteria roenbergensis (CroV). CeV, as well as two of its close relatives, which infect the unicellular photosynthetic eukaryotes Phaeocystis globosa (Phaeocystis globosa virus [PgV]) and Aureococcus anophagefferens (Aureococcus anophagefferens virus [AaV]), are currently unclassified by the International Committee on Viral Taxonomy (ICTV). The detailed comparative analysis of the CeV genome presented here confirms the phylogenetic affinity of this emerging group of microalga-infecting viruses with the Mimiviridae but argues in favor of their classification inside a distinct clade within the family. Although CeV, PgV, and AaV share more common features among them than with the larger Mimiviridae, they also exhibit a large complement of unique genes, attesting to their complex evolutionary history. We identified several gene fusion events and cases of convergent evolution involving independent lateral gene acquisitions. Finally, CeV possesses an unusual number of inteins, some of which are closely related despite being inserted in nonhomologous genes. This appears to contradict the paradigm of allele-specific inteins and suggests that the Mimiviridae are especially efficient in spreading inteins while enlarging their repertoire of homing genes.IMPORTANCE Although it infects the microalga Chrysochromulina ericina, CeV is more closely related to acanthamoeba-infecting viruses of the Mimiviridae family than to any member of the Phycodnaviridae, the ICTV-approved family historically including all alga-infecting large dsDNA viruses. CeV, as well as its relatives that infect the microalgae Phaeocystic globosa (PgV) and Aureococcus anophagefferens (AaV), remains officially unclassified and a source of confusion in the literature. Our comparative analysis of the CeV genome in the context of this emerging group of alga-infecting viruses suggests that they belong to a distinct clade within the established Mimiviridae family. The presence of a large number of unique genes as well as specific gene fusion events, evolutionary convergences, and inteins integrated at unusual locations document the complex evolutionary history of the CeV lineage.

ERCC1-XPF cooperates with CTCF and cohesin to facilitate the developmental silencing of imprinted genes

Inborn defects in DNA repair are associated with complex developmental disorders whose causal mechanisms are poorly understood. Using an in vivo biotinylation tagging approach in mice, we show that the nucleotide excision repair (NER) structure-specific endonuclease ERCC1-XPF complex interacts with the insulator binding protein CTCF, the cohesin subunits SMC1A and SMC3 and with MBD2; the factors co-localize with ATRX at the promoters and control regions (ICRs) of imprinted genes during postnatal hepatic development. Loss of Ercc1 or exposure to MMC triggers the localization of CTCF to heterochromatin, the dissociation of the CTCF-cohesin complex and ATRX from promoters and ICRs, altered histone marks and the aberrant developmental expression of imprinted genes without altering DNA methylation. We propose that ERCC1-XPF cooperates with CTCF and cohesin to facilitate the developmental silencing of imprinted genes and that persistent DNA damage triggers chromatin changes that affect gene expression programs associated with NER disorders.

High mobility group (HMG) proteins: Modulators of chromatin structure and DNA repair in mammalian cells

It has been almost a decade since the last review appeared comparing and contrasting the influences that the different families of High Mobility Group proteins (HMGA, HMGB and HMGN) have on the various DNA repair pathways in mammalian cells. During that time considerable progress has been made in our understanding of how these non-histone proteins modulate the efficiency of DNA repair by all of the major cellular pathways: nucleotide excision repair, base excision repair, double-stand break repair and mismatch repair. Although there are often similar and over-lapping biological activities shared by all HMG proteins, members of each of the different families appear to have a somewhat 'individualistic' impact on various DNA repair pathways. This review will focus on what is currently known about the roles that different HMG proteins play in DNA repair processes and discuss possible future research areas in this rapidly evolving field.

The ERCC1 and ERCC4 (XPF) genes and gene products

The ERCC1 and ERCC4 genes encode the two subunits of the ERCC1-XPF nuclease. This enzyme plays an important role in repair of DNA damage and in maintaining genomic stability. ERCC1-XPF nuclease nicks DNA specifically at junctions between double-stranded and single-stranded DNA, when the single-strand is oriented 5' to 3' away from a junction. ERCC1-XPF is a core component of nucleotide excision repair and also plays a role in interstrand crosslink repair, some pathways of double-strand break repair by homologous recombination and end-joining, as a backup enzyme in base excision repair, and in telomere length regulation. In many of these activities, ERCC1-XPF complex cleaves the 3' tails of DNA intermediates in preparation for further processing. ERCC1-XPF interacts with other proteins including XPA, RPA, SLX4 and TRF2 to perform its functions. Disruption of these interactions or direct targeting of ERCC1-XPF to decrease its DNA repair function might be a useful strategy to increase the sensitivity of cancer cells to some DNA damaging agents. Complete deletion of either ERCC1 or ERCC4 is not compatible with viability in mice or humans. However, mutations in the ERCC1 or ERCC4 genes cause a remarkable array of rare inherited human disorders. These include specific forms of xeroderma pigmentosum, Cockayne syndrome, Fanconi anemia, XFE progeria and cerebro-oculo-facio-skeletal syndrome.

The bacterial alkyltransferase-like (eATL) protein protects mammalian cells against methylating agent-induced toxicity

In both pro- and eukaryotes, the mutagenic and toxic DNA adduct O(6)-methylguanine (O(6)MeG) is subject to repair by alkyltransferase proteins via methyl group transfer. In addition, in prokaryotes, there are proteins with sequence homology to alkyltransferases, collectively designated as alkyltransferase-like (ATL) proteins, which bind to O(6)-alkylguanine adducts and mediate resistance to alkylating agents. Whether such proteins might enable similar protection in higher eukaryotes is unknown. Here we expressed the ATL protein of Escherichia coli (eATL) in mammalian cells and addressed the question whether it is able to protect them against the cytotoxic effects of alkylating agents. The Chinese hamster cell line CHO-9, the nucleotide excision repair (NER) deficient derivative 43-3B and the DNA mismatch repair (MMR) impaired derivative Tk22-C1 were transfected with eATL cloned in an expression plasmid and the sensitivity to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was determined in reproductive survival, DNA double-strand break (DSB) and apoptosis assays. The results indicate that eATL expression is tolerated in mammalian cells and conferes protection against killing by MNNG in both wild-type and 43-3B cells, but not in the MMR-impaired cell line. The protection effect was dependent on the expression level of eATL and was completely ablated in cells co-expressing the human O(6)-methylguanine-DNA methyltransferase (MGMT). eATL did not protect against cytotoxicity induced by the chloroethylating agent lomustine, suggesting that O(6)-chloroethylguanine adducts are not target of eATL. To investigate the mechanism of protection, we determined O(6)MeG levels in DNA after MNNG treatment and found that eATL did not cause removal of the adduct. However, eATL expression resulted in a significantly lower level of DSBs in MNNG-treated cells, and this was concomitant with attenuation of G2 blockage and a lower level of apoptosis. The results suggest that eATL confers protection against methylating agents by masking O(6)MeG/thymine mispaired adducts, preventing them from becoming a substrate for mismatch repair-mediated DSB formation and cell death.

USP45 deubiquitylase controls ERCC1-XPF endonuclease-mediated DNA damage responses

Reversible protein ubiquitylation plays important roles in various processes including DNA repair. Here, we identify the deubiquitylase USP45 as a critical DNA repair regulator. USP45 associates with ERCC1, a subunit of the DNA repair endonuclease XPF-ERCC1, via a short acidic motif outside of the USP45 catalytic domain. Wild-type USP45, but not a USP45 mutant defective in ERCC1 binding, efficiently deubiquitylates ERCC1 in vitro, and the levels of ubiquitylated ERCC1 are markedly enhanced in USP45 knockout cells. Cells lacking USP45 are hypersensitive specifically to UV irradiation and DNA interstrand cross-links, similar to cells lacking ERCC1. Furthermore, the repair of UV-induced DNA damage is markedly reduced in USP45-deficient cells. ERCC1 translocation to DNA damage-induced subnuclear foci is markedly impaired in USP45 knockout cells, possibly accounting for defective DNA repair. Finally, USP45 localises to sites of DNA damage in a manner dependent on its deubiquitylase activity, but independent of its ability to bind ERCC1-XPF. Together, these results establish USP45 as a new regulator of XPF-ERCC1 crucial for efficient DNA repair.

DNA damage, NF-κB and accelerated aging

The aging process is the major risk factor for disease and disability yet the cellular mechanisms for aging are uncertain. By studying transgenic mice with altered expression of the DNA repair enzyme, ERCC1, it was concluded that DNA damage is an important, if not the primary mechanism for aging. Moreover it was established that altered activity of the transcription factor, NF-κB (nuclear factor kappa B) mediates the effects of DNA damage on aging. Therefore inhibition of NF-κB might have a role in delaying aging.

Fluorescence-based incision assay for human XPF-ERCC1 activity identifies important elements of DNA junction recognition

The structure-specific endonuclease activity of the human XPF–ERCC1 complex is essential for a number of DNA processing mechanisms that help to maintain genomic integrity. XPF–ERCC1 cleaves DNA structures such as stem–loops, bubbles or flaps in one strand of a duplex where there is at least one downstream single strand. Here, we define the minimal substrate requirements for cleavage of stem–loop substrates allowing us to develop a real-time fluorescence-based assay to measure endonuclease activity. Using this assay, we show that changes in the sequence of the duplex upstream of the incision site results in up to 100-fold variation in cleavage rate of a stem-loop substrate by XPF-ERCC1. XPF–ERCC1 has a preference for cleaving the phosphodiester bond positioned on the 3′-side of a T or a U, which is flanked by an upstream T or U suggesting that a T/U pocket may exist within the catalytic domain. In addition to an endonuclease domain and tandem helix–hairpin–helix domains, XPF has a divergent and inactive DEAH helicase-like domain (HLD). We show that deletion of HLD eliminates endonuclease activity and demonstrate that purified recombinant XPF–HLD shows a preference for binding stem–loop structures over single strand or duplex alone, suggesting a role for the HLD in initial structure recognition. Together our data describe features of XPF–ERCC1 and an accepted model substrate that are important for recognition and efficient incision activity.

Inhibition of Gli1 results in altered c-Jun activation, inhibition of cisplatin-induced upregulation of ERCC1, XPD and XRCC1, and inhibition of platinum-DNA adduct repair

The transcription of ERCC1 and other nucleotide excision repair (NER) genes is strongly influenced by c-jun. C-jun is transcriptionally regulated by Gli proteins of the Hedgehog pathway. We therefore studied the possible relationships between Gli1, c-jun, and the upregulation of ERCC1, XPD and XRCC1 in cisplatin-resistant human ovarian cancer cells. We studied the paired human ovarian cancer cell lines A2780 and A2780-CP70. We used a shRNA construct that specifically degrades Gli1 message. Genes we assessed for mRNA and/or protein levels included: c-jun, ERCC1, XPD, XRCC1, Gli1, Gli2, SHH, IHH, GAPDH and α-tubulin. Platinum-DNA adduct repair was assessed by atomic absorbance spectrometry with Zeeman background correction. Use of the anti-Gli1 shRNA in cisplatin-resistant cells resulted in a block of the cell's ability to upregulate genes in response to cisplatin treatment, including: c-jun, ERCC1, XPD and XRCC1. This block in upregulation of c-jun was concurrent with a change in the phosphorylation pattern of the c-jun protein, shifting that pattern from a Ser63/73 dominant pattern, to a Thr91/93 dominant pattern. A2780-CP70 cells were treated at their cisplatin IC50, and DNA repair was assessed after pretreatment with anti-Gli1 shRNA or scrambled shRNA control. Control cells repaired 78% of platinum-DNA adducts at 12 h, compared with 33% repair in cells pretreated with anti-Gli1 shRNA resulting in a 2.4-fold difference. Pretreatment of A2780-CP70 cells with anti-Gli1 shRNA resulted in supra-additive cell killing with cisplatin; shifting the cisplatin IC50 (half maximal inhibitory concentration) from 30 μM to 5 μM. Pretreatment of these cells with cyclopamine did not shift the cisplatin IC50. We conclude that the transcriptional protein Gli1 is important in the upregulation of these three DNA repair genes in human ovarian cancer cells, and that Gli1 strongly influences platinum-DNA adduct repair, and cellular sensitivity to cisplatin. This Gli1 role has c-jun as an intermediate in the pathway. In all, inhibition of Gli1 by a specific shRNA inhibits the upregulation of c-jun Ser63/73, and also inhibits the upregulation of three genes essential to NER (ERCC1, XPD) and base excision repair (XRCC1).

Regulation of nucleotide excision repair through ubiquitination

Nucleotide excision repair (NER) is the most versatile DNA-repair pathway in all organisms. While bacteria require only three proteins to complete the incision step of NER, eukaryotes employ about 30 proteins to complete the same step. Here we summarize recent studies demonstrating that ubiquitination, a post-translational modification, plays critical roles in regulating the NER activity either dependent on or independent of ubiquitin-proteolysis. Several NER components have been shown as targets of ubiquitination while others are actively involved in the ubiquitination process. We argue through this analysis that ubiquitination serves to coordinate various steps of NER and meanwhile connect NER with other related pathways to achieve the efficient global DNA-damage response.

Transcriptional modulation of a human monocytic cell line exposed to PM(10) from an urban area

Insight into the mechanisms by which ambient air particulate matter mediates adverse health effects is needed to provide biological plausibility to epidemiological studies demonstrating an association between PM(10) exposure and increased morbidity and mortality. In vitro studies of the effects of air pollution on human cells help to establish conditions for the analysis of cause-effect relationships. One of the major challenges is to test native atmosphere in its complexity, rather than the various components individually. We have developed an in vitro system in which human monocyte-macrophage U937 cells are directly exposed to filters containing different amounts of PM(10) collected in the city of Rome. Transcriptional profiling obtained after short exposure (1h) of cells to a filter containing 1666μg PM(10) (77.6μg/cm(2)) using a macroarray panel of 1176 genes reveals a significant change in the mRNA level (>2 fold) for 87 genes relative to cells exposed to a control filter. Overall, 9 out of 87 modulated genes were annotated as "lung cancer". qRT-PCR confirmed the induction of relevant genes involved in DNA repair and apoptosis, specifically: ERCC1, TDG, DAD1 and MCL1. In cells exposed for 10min, 1h and 3h to different amounts of PM(10), transcription of TNFα and TRAP1, which code for a key pro-inflammatory cytokine and a mitochondrial protein involved in cell protection from oxidative stress, respectively, was shown to be modulated in a time-dependent, but not a dose-dependent manner. Taken together, these data indicate that it is possible to analyze the effects of untreated particulate matter on human cells by the direct-exposure approach we have developed, possibly providing new clues to traffic-related health hazard.

Regulation of endonuclease activity in human nucleotide excision repair

Nucleotide excision repair (NER) is a DNA repair pathway that is responsible for removing a variety of lesions caused by harmful UV light, chemical carcinogens, and environmental mutagens from DNA. NER involves the concerted action of over 30 proteins that sequentially recognize a lesion, excise it in the form of an oligonucleotide, and fill in the resulting gap by repair synthesis. ERCC1-XPF and XPG are structure-specific endonucleases responsible for carrying out the incisions 5' and 3' to the damage respectively, culminating in the release of the damaged oligonucleotide. This review focuses on the recent work that led to a greater understanding of how the activities of ERCC1-XPF and XPG are regulated in NER to prevent unwanted cuts in DNA or the persistence of gaps after incision that could result in harmful, cytotoxic DNA structures.

Physiological consequences of defects in ERCC1-XPF DNA repair endonuclease

ERCC1-XPF is a structure-specific endonuclease required for nucleotide excision repair, interstrand crosslink repair, and the repair of some double-strand breaks. Mutations in ERCC1 or XPF cause xeroderma pigmentosum, XFE progeroid syndrome or cerebro-oculo-facio-skeletal syndrome, characterized by increased risk of cancer, accelerated aging and severe developmental abnormalities, respectively. This review provides a comprehensive overview of the health impact of ERCC1-XPF deficiency, based on these rare diseases and mouse models of them. This offers an understanding of the tremendous health impact of DNA damage derived from environmental and endogenous sources.

A microdosing approach for characterizing formation and repair of carboplatin-DNA monoadducts and chemoresistance

Formation and repair of platinum (Pt)-induced DNA adducts is a critical step in Pt drug-mediated cytotoxicity. Measurement of Pt-DNA adduct kinetics in tumors may be useful for better understanding chemoresistance and therapeutic response. However, this concept has yet to be rigorously tested because of technical challenges in measuring the adducts at low concentrations and consistent access to sufficient tumor biopsy material. Ultrasensitive accelerator mass spectrometry was used to detect [(14)C]carboplatin-DNA monoadducts at the attomole level, which are the precursors to Pt-DNA crosslink formation, in six cancer cell lines as a proof-of-concept. The most resistant cells had the lowest monoadduct levels at all time points over 24 hr. [(14)C]Carboplatin "microdoses" (1/100th the pharmacologically effective concentration) had nearly identical adduct formation and repair kinetics compared to therapeutically relevant doses, suggesting that the microdosing approach can potentially be used to determine the pharmacological effects of therapeutic treatment. Some of the possible chemoresistance mechanisms were also studied, such as drug uptake/efflux, intracellular inactivation and DNA repair in selected cell lines. Intracellular inactivation and efficient DNA repair each contributed significantly to the suppression of DNA monoadduct formation in the most resistant cell line compared to the most sensitive cell line studied (p < 0.001). Nucleotide excision repair (NER)-deficient and -proficient cells showed substantial differences in carboplatin monoadduct concentrations over 24 hr that likely contributed to chemoresistance. The data support the utility of carboplatin microdosing as a translatable approach for defining carboplatin-DNA monoadduct formation and repair, possibly by NER, which may be useful for characterizing chemoresistance in vivo.

DNA damage response

Structural changes to DNA severely affect its functions, such as replication and transcription, and play a major role in age-related diseases and cancer. A complicated and entangled network of DNA damage response (DDR) mechanisms, including multiple DNA repair pathways, damage tolerance processes, and cell-cycle checkpoints safeguard genomic integrity. Like transcription and replication, DDR is a chromatin-associated process that is generally tightly controlled in time and space. As DNA damage can occur at any time on any genomic location, a specialized spatio-temporal orchestration of this defense apparatus is required.

DNA damage and repair in translational oncology: an overview

Unknown to early investigators, DNA damage and repair has been a major focus of anticancer therapy from the beginning of clinical oncology. From the early days of using x-irradiation, to the development of nitrogen mustard analogs, to today's more sophisticated approaches, DNA damage and repair has strongly impacted our ability to successfully treat human malignancy. This area of basic, translational, and clinical science is very broad. The traditional focus of DNA damage and repair has been on diseases such as Xeroderma pigmentosum, and attempting to understand the basic molecular mechanisms of DNA repair processes. It is only recently that we have begun to appreciate how we might modulate these processes to improve our ability to advance cancer care. No fewer than 10 separate DNA repair processes are operative in higher organisms, and the total number of separable processes could be substantially higher. Some of our most useful clinical agents depend on causing DNA damage that is repaired by nucleotide excision repair. X-irradiation induces damage that is mostly repaired by base excision repair and double-strand break repair. We are now learning how to modulate select DNA repair pathways to benefit patients with breast cancer and other malignancies.

Trichothiodystrophy view from the molecular basis of DNA repair/transcription factor TFIIH

Trichothiodystrophy (TTD) is a rare autosomal recessive disorder characterized by brittle hair and also associated with various systemic symptoms. Approximately half of TTD patients exhibit photosensitivity, resulting from the defect in the nucleotide excision repair. Photosensitive TTD is due to mutations in three genes encoding XPB, XPD and p8/TTDA subunits of the DNA repair/transcription factor TFIIH. Mutations in these subunits disturb either the catalytic and/or the regulatory activity of the two XPB, XPD helicase/ATPases and consequently are defective in both, DNA repair and transcription. Moreover, mutations in any of these three TFIIH subunits also disturb the overall architecture of the TFIIH complex and its ability to transactivate certain nuclear receptor-responsive genes, explaining in part, some of the TTD phenotypes.

Specific targeted gene repair using single-stranded DNA oligonucleotides at an endogenous locus in mammalian cells uses homologous recombination

The feasibility of introducing point mutations in vivo using single-stranded DNA oligonucleotides (ssON) has been demonstrated but the efficiency and mechanism remain elusive and potential side effects have not been fully evaluated. Understanding the mechanism behind this potential therapy may help its development. Here, we demonstrate the specific repair of an endogenous non-functional hprt gene by a ssON in mammalian cells, and show that the frequency of such an event is enhanced when cells are in S-phase of the cell cycle. A potential barrier in using ssONs as gene therapy could be non-targeted mutations or gene rearrangements triggered by the ssON. Both the non-specific mutation frequencies and the frequency of gene rearrangements were largely unaffected by ssONs. Furthermore, we find that the introduction of a mutation causing the loss of a functional endogenous hprt gene by a ssON occurred at a similarly low but statistically significant frequency in wild type cells and in cells deficient in single strand break repair, nucleotide excision repair and mismatch repair. However, this mutation was not induced in XRCC3 mutant cells deficient in homologous recombination. Thus, our data suggest ssON-mediated targeted gene repair is more efficient in S-phase and involves homologous recombination.

XPF/ERCC4 and ERCC1: their products and biological roles

ERCC4 is the gene mutated in XPF cells and also in rodent cells representing the mutant complementation groups ERCC4 and ERCC 11. The protein functions principally as a complex with ERCC1 in a diversity of biological pathways that include NER, ICL repair, telomere maintenance and immunoglobulin switching. Sorting out these roles is an exciting and challenging problem and many important questions remain to be answered. The ERCC1/ERCC4 complex is conserved across most species presenting an opportunity to examine some functions in model organisms where mutants can be more readily generated and phenotypes more quickly assessed.

Kinetics of gamma-H2AX focus formation upon treatment of cells with UV light and alkylating agents

Histone H2AX is rapidly phosphorylated in response to DNA double-strand breaks (DSBs) induced by ionizing radiation (IR). Here we show that DNA damage induced by alkylating agents [methyl methanesulfonate (MMS) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)] and ultraviolet light (UV-C) leads to a dose and time dependent accumulation of phosphorylated H2AX (gamma-H2AX). Time course experiments revealed that the number of gamma-H2AX foci reached peak levels 8 hr after MMS or MNNG treatment and declined to almost control values within 24 hr after exposure. Upon UV-C treatment, a biphasic response was observed with a maximum 12 hr after treatment. In 43-3B cells deficient in nucleotide excision repair (NER) the number of gamma-H2AX foci increased steadily. gamma-H2AX foci were preferentially formed in BrdU labeled cells. In proliferation compromised cells, the gamma-H2AX level was significantly reduced, indicating that most of the gamma-H2AX foci induced by UV-C and alkylating agent treatments were replication dependent. The data are in line with the view that DNA damage induced by UV-C light and simple alkylating agents, leads to the formation of DSBs during DNA replication giving rise to H2AX phosphorylation. In replicating NER defective cells, DSBs accumulate due to nonrepaired primary DNA lesions that produce a high level of DSBs during replication. The data support that gamma-H2AX foci are a useful marker of DSBs that are induced by S-phase dependent genotoxins during replication.

Relationship between DNA lesions, DNA repair and chromosomal damage induced by acetaldehyde

Acetaldehyde (AA) was tested along with two other crosslinking agents: formaldehyde (FA), an inducer of DNA-protein crosslinks (DPCs) and mitomycin C (MMC), an inducer of interstrand crosslinks (ICLs), to find out whether the mechanism of action of AA resembles more MMC or FA. Using a modification of the standard protocol for comet assay we demonstrate that AA induces crosslinks. Using a combination of alkaline comet version and proteinase-K, a clear abrogation of AA-induced reduction in DNA migration, like after FA treatment, was observed demonstrating that both agents induce DPCs, whereas MMC induces predominantly ICLs. A possible correlation between the types of induced crosslink and the induction chromosome damage in different repair deficient mutant Chinese hamster ovary cell lines treated with AA, MMC and FA was investigated. TCR/NER pathways are involved in repairing FA induced DPCs, but less in AA-induced DPCs. Our preliminary data suggest that DPCs are weaker inducers of SCEs in comparison with ICLs.

Structural and functional relationships of the XPF/MUS81 family of proteins

Proteins belonging to the XPF/MUS81 family play important roles in the repair of DNA lesions caused by UV-light or DNA cross-linking agents. Most eukaryotes have four family members that assemble into two distinct heterodimeric complexes, XPF-ERCC1 and MUS81-EME1. Each complex contains one catalytic and one noncatalytic subunit and exhibits endonuclease activity with a variety of 3'-flap or fork DNA structures. The catalytic subunits share a characteristic core containing an excision repair cross complementation group 4 (ERCC4) nuclease domain and a tandem helix-hairpin-helix (HhH)(2) domain. Diverged domains are present in the noncatalytic subunits and may be required for substrate targeting. Vertebrates possess two additional family members, FANCM and Fanconi anemia-associated protein 24 kDa (FAAP24), which possess inactive nuclease domains. Instead, FANCM contains a functional Superfamily 2 (SF2) helicase domain that is required for DNA translocation. Determining how these enzymes recognize specific DNA substrates and promote key repair reactions is an important challenge for the future.

Characterization of CHO XPF mutant UV41: influence of XPF heterozygosity on double-strand break-induced intrachromosomal recombination

The UV hypersensitive CHO cell mutant UV41 is the archetypal XPF mammalian cell mutant, and was essential for cloning the human nucleotide excision repair (NER) gene XPF by DNA transfection and rescue. The ERCC1 and XPF genes encode proteins that form the heterodimer responsible for making incisions required in NER and the processing of certain types of recombination intermediates. In this study, we cloned and sequenced the CHO cell XPF cDNA, determining that the XPF mutation in UV41 is a +1 insertion in exon 8 generating a premature stop codon at amino acid position 499; however, the second allele of XPF is apparently unaltered in UV41, resulting in XPF heterozygosity. XPF expression was found to be several-fold lower in UV41 compared to its parental cell line, AA8. Using approaches we previously developed to study intrachromosomal recombination in CHO cells, we modified UV41 and its parental cell line AA8 to allow site-specific gene targeting at a Flp recombination target (FRT) in intron 3 of the endogenous adenine phosphoribosyltransferase (APRT) locus. Using FLP/FRT targeting, we integrated a plasmid containing an I-SceI endonuclease sequence into this site in the paired cell lines to generate a heteroallelic APRT duplication. Frequencies of intrachromosomal recombination between APRT heteroalleles and the structures of resulting recombinants were analyzed after I-SceI induction of site-specific double-strand breaks (DSBs) in a non-homologous insertion contained within APRT homology. Our results show that I-SceI induced a small proportion of aberrant recombinants reflecting DSB-induced deletions/rearrangements in parental, repair-proficient AA8 cells. However, in XPF mutant UV41, XPF heterozygosity is responsible for a similar, but much more pronounced genomic instability phenotype, manifested independently of DSB induction. In addition, gene conversions were suppressed in UV41 cells compared to wild-type cells. These observations suggest that UV41 exhibits a genomic instability phenotype of aberrant recombinational repair, confirming a critical role for XPF in mammalian cell recombination.

ERCC1/XPF limits L1 retrotransposition

Retrotransposons are currently active in the human and mouse genomes contributing to novel disease mutations and genomic variation via de novo insertions. However, little is known about the interactions of non-long terminal repeat (non-LTR) retrotransposons with the host DNA repair machinery. Based on the model of retrotransposition for the human and mouse LINE-1 element, one likely intermediate is an extension of cDNA that is heterologous to the genomic target, a flap intermediate. To determine whether a human flap endonuclease could recognize and process this potential intermediate, the genetic requirement for the ERCC1/XPF heterodimer during LINE-1 retrotransposition was characterized. Reduction of XPF in human cells increased retrotransposition whereas complementation of ERCC1-deficiency in hamster cells reduced retrotransposition. These results demonstrate for the first time that DNA repair enzymes act to limit non-LTR retrotransposition and may provide insight into the genetic instability phenotypes of ercc1 and xpf individuals.

DNA repair deficiency and BPDE-induced chromosomal alterations in CHO cells

The induction of chromosomal aberrations and sister chromatid exchanges by BPDE was evaluated in parental and different DNA repair deficient Chinese hamster ovary cell lines in order to elucidate the mechanisms involved in their induction. These included the parental line (AA8), nucleotide excision repair (UV4, UV5, UV61), base excision repair (EM9), homologous recombination repair (Irs1SF) and non-homologous end joining (V3-3) deficient ones. The ranking of different cell lines for BPDE-induced chromosome aberrations was: UV4, Irs1SF, UV5, UV 61, EM9, V3-3, and AA8 in a descending order. Cells deficient in NER and HRR were found to be very sensitive, indicating the importance of these pathways in the repair of lesions induced by BPDE. For induction of SCEs, HRR and BER deficient cells were refractory, whereas the other cell lines responded with a dose-dependent increase. The possible mechanisms involved in BPDE-induced chromosomal alterations are discussed.

Nucleotide excision repair pathway review I: Implications in ovarian cancer and platinum sensitivity

Platinum-based chemotherapy has been the mainstay of treatment for advanced gynecological cancers following cytoreductive surgery and in radiation sensitization of cervical cancer. Despite its initial high overall clinical response rate, a significant number of patients develop resistance to platinum combination therapies. The precise mechanism of platinum-resistance is multifactorial and accumulation of multiple genetic changes may lead to the drug-resistant phenotype. Platinum chemotherapy exerts its cytotoxic effect by forming DNA adducts and subsequently inhibiting DNA replication. It is now clear that the nucleotide excision repair (NER) pathway repairs platinum-DNA adducts in cellular DNA. Evaluation of genetic polymorphisms in cancer susceptibility as one etiology for platinum resistance may help us to understand the significance of these factors in the identification of individuals at higher risk of developing resistance to anti-cancer drug therapies. In this review, we summarized the relevant studies, both in vitro and in vivo, that pertain to NER in ovarian cancer and platinum resistance. It is evident also that there are a few limited studies in genetic polymorphisms of NER and ovarian cancer. These studies reviewed suggest that concurrent up-regulation of genes involved in NER may be important in clinical resistance to platinum-based chemotherapy in ovarian cancer. In the future, larger and well-designed population-based studies will be needed for a more complete understanding of relevant genetic factors that may result in improved strategies for determining both chemotherapy choice and efficacy in patients with advanced ovarian and cervical cancer. Review II will focus on the NER pathway in cervical cancer and platinum sensitivity.

Tagging single nucleotide polymorphisms in excision repair cross-complementing group 1 (ERCC1) and risk of primary lung cancer in a Chinese population

BACKGROUND AND OBJECTIVE

Low nucleotide excision repair (NER) capacity has been associated with increased risk of lung cancer. Excision repair cross-complementing group 1 (ERCC1) is one of the NER core enzymes, and polymorphisms in ERCC1 may lead to altered repair function of the enzyme and therefore confer predisposition to cancer. The goal of this study was to test the hypothesis that common variants in ERCC1 were associated with lung cancer risk.

METHODS

The genotyping analyses for 7 selected single nucleotide polymorphisms in ERCC1 using the TaqMan assay was conducted in a case-control study of 1010 patients with incident lung cancer and 1011 cancer-free controls in a Chinese population.

RESULTS

We found that the variant genotypes of the rs3212948 C allele were associated with significantly decreased risk of lung cancer [adjusted odds ratio (OR)=0.73 (95% CI=0.60-0.88) for CG; 0.96 (95% CI=0.65-1.41) for CC and 0.76 (95% CI=0.63-0.91) for CG/CC, compared with the GG genotype]. Similarly, a significant protective effect was also evident for the variant genotypes of rs1007616 C/T [adjusted OR=0.72 (95% CI=0.59-0.89) for CT; 0.90 (95% CI=0.61-1.35) for TT and 0.75 (95% CI=0.62-0.91) for CT/TT, compared with the CC genotype]. Stratified analysis revealed that the protective effects of these 2 single nucleotide polymorphisms were both more evident among young patients and patients without family history of cancer. Consistently, when assessing each unique haplotype compared with the most common haplotype 'TAGCACG', lung cancer risk was significantly decreased among patients who carried the haplotype 'TCCCATT' with the variant rs3212948C and rs1007616T alleles (P value=0.0340, P-sim=0.0325, adjusted OR=0.78; 95% CI=0.63-0.97).

CONCLUSION

These findings indicate that ERCC1 polymorphisms may contribute to the etiology of lung cancer. Further functional studies were warranted to elucidate the mechanism of the associations.

First reported patient with human ERCC1 deficiency has cerebro-oculo-facio-skeletal syndrome with a mild defect in nucleotide excision repair and severe developmental failure

Nucleotide excision repair (NER) is a genome caretaker mechanism responsible for removing helix-distorting DNA lesions, most notably ultraviolet photodimers. Inherited defects in NER result in profound photosensitivity and the cancer-prone syndrome xeroderma pigmentosum (XP) or two progeroid syndromes: Cockayne and trichothiodystrophy syndromes. The heterodimer ERCC1-XPF is one of two endonucleases required for NER. Mutations in XPF are associated with mild XP and rarely with progeria. Mutations in ERCC1 have not been reported. Here, we describe the first case of human inherited ERCC1 deficiency. Patient cells showed moderate hypersensitivity to ultraviolet rays and mitomycin C, yet the clinical features were very severe and, unexpectedly, were compatible with a diagnosis of cerebro-oculo-facio-skeletal syndrome. This discovery represents a novel complementation group of patients with defective NER. Further, the clinical severity, coupled with a relatively mild repair defect, suggests novel functions for ERCC1.

Molecular mechanisms of sister-chromatid exchange

Sister-chromatid exchange (SCE) is the process whereby, during DNA replication, two sister chromatids break and rejoin with one another, physically exchanging regions of the parental strands in the duplicated chromosomes. This process is considered to be conservative and error-free, since no information is generally altered during reciprocal interchange by homologous recombination. Upon the advent of non-radiolabel detection methods for SCE, such events were used as genetic indicators for potential genotoxins/mutagens in laboratory toxicology tests, since, as we now know, most forms of DNA damage induce chromatid exchange upon replication fork collapse. Much of our present understanding of the mechanisms of SCE stems from studies involving nonhuman vertebrate cell lines that are defective in processes of DNA repair and/or recombination. In this article, we present a historical perspective of studies spearheaded by Dr. Anthony V. Carrano and colleagues focusing on SCE as a genetic outcome, and the role of the single-strand break DNA repair protein XRCC1 in suppressing SCE. A more general overview of the cellular processes and key protein "effectors" that regulate the manifestation of SCE is also presented.

Dominant-negative histone H3 lysine 27 mutant derepresses silenced tumor suppressor genes and reverses the drug-resistant phenotype in cancer cells

Histone modifications and DNA methylation are epigenetic phenomena that play a critical role in many neoplastic processes, including silencing of tumor suppressor genes. One such histone modification, particularly at H3 and H4, is methylation at specific lysine (K) residues. Whereas histone methylation of H3-K9 has been linked to DNA methylation and aberrant gene silencing in cancer cells, no such studies of H3-K27 have been reported. Here, we generated a stable cell line overexpressing a dominant-negative point mutant, H3-K27R, to examine the role of that specific lysine in ovarian cancer. Expression of this construct resulted in loss of methylation at H3-K27, global reduction of DNA methylation, and increased expression of tumor suppressor genes. One of the affected genes, RASSF1, was shown to be a direct target of H3-K27 methylation-mediated silencing. By increasing DNA-platinum adduct formation, indicating increased access of the drug to target DNA sequences, removal of H3-K27 methylation resensitized drug-resistant ovarian cancer cells to the chemotherapeutic agent cisplatin. This increased platinum-DNA access was likely due to relaxation of condensed chromatin. Our results show that overexpression of mutant H3-K27 in mammalian cells represents a novel tool for studying epigenetic mechanisms and the Histone Code Hypothesis in human cancer. Such findings show the significance of H3-K27 methylation as a promising target for epigenetic-based cancer therapies.

Homologous recombination is involved in repair of chromium-induced DNA damage in mammalian cells

Chromium is a potent human carcinogen, probably because of its well-documented genotoxic effects. Chromate (Cr[VI]) causes a wide range of DNA lesions, including DNA crosslinks and strand breaks, presumably due to the direct and indirect effects of DNA oxidation. Homologous recombination repair (HRR) is important for error-free repair of lesions occurring at replication forks. Here, we show that HR deficient cell lines irs1SF and V-C8, deficient in XRCC3 and BRCA2, respectively, are hypersensitive to Cr[VI], implicating this repair pathway in repair of Cr[VI] damage. Furthermore, we find that Cr[VI] causes DNA double-strand breaks and triggers both Rad51 foci formation and induction of HRR. Collectively, these data suggest that HRR is important in repair of Cr[VI]-induced DNA damage. In addition, we find that ERCC1, XRCC1 and DNA-PKcs defective cells are hypersensitive to Cr[VI], indicating that several repair pathways cooperate in repairing Cr[VI]-induced DNA damage.

Gene-smoking interaction associations for the ERCC1 polymorphisms in the risk of lung cancer

Cigarette smoking may induce DNA damage. Lower DNA repair capacities have been associated with higher risk of lung cancer. Excision repair cross-complementing group 1 (ERCC1) is the lead enzyme in the nucleotide excision repair process, and low expression of ERCC1 mRNA levels has been associated with higher risk of cancers. We examined the association between two polymorphisms of ERCC1, 8092C > A (rs3212986) and 19007T > C (codon 118, rs11615), which are associated with altered ERCC1 mRNA stability and mRNA levels, in 1,752 Caucasian lung cancer patients and 1,358 controls. The results were analyzed using logistic regression models, adjusting for relevant covariates. The two polymorphisms were in Hardy-Weinberg disequilibrium and in linkage disequilibrium. There was no overall association between ERCC1 polymorphisms and lung cancer risk, with the adjusted odds ratios (AOR) of 1.26 [95% confidence interval (95% CI), 0.81-1.96] for the 8092C > A polymorphism (A/A versus C/C) and 0.93 (95% CI, 0.67-1.30) for the 19007T > C polymorphism (C/C versus T/T). Stratified analyses revealed that the AORs for the 8092C > A polymorphism (A/A versus C/C) decreased significantly as pack-years increased, with the AOR of 2.11 (95% CI, 1.03-4.31) in never smokers and 0.50 (95% CI, 0.25-1.01) in heavy smokers (>/=56 pack-years), respectively. Consistent results were found when gene-smoking interaction was incorporated by joint effects and interactions models that considered both discrete and continuous variables for cumulative smoking exposure. The same direction for the gene-smoking interaction was found for the 19007T > C polymorphism, although the interaction was not statistically significant. In conclusion, ERCC1 8092C > A polymorphism may modify the associations between cumulative cigarette smoking and lung cancer risk.