Mitochondrial DNA Repair through OGG1 Activity Attenuates Breast Cancer Progression and Metastasis

Mitochondria act as a key regulatory factor in cancer progression: Current concepts on mutations, mitochondrial dynamics, and therapeutic approach

The diversified impacts of mitochondrial function vs. dysfunction have been observed in almost all disease conditions including cancers. Mitochondria play crucial roles in cellular homeostasis and integrity, however, mitochondrial dysfunctions influenced by alterations in the mtDNA can disrupt cellular balance. Many external stimuli or cellular defects that cause cellular integrity abnormalities, also impact mitochondrial functions. Imbalances in mitochondrial activity can initiate and lead to accumulations of genetic mutations and can promote the processes of tumorigenesis, progression, and survival. This comprehensive review summarizes epigenetic and genetic alterations that affect the functionality of the mitochondria, with considerations of cellular metabolism, and as influenced by ethnicity. We have also reviewed recent insights regarding mitochondrial dynamics, miRNAs, exosomes that play pivotal roles in cancer promotion, and the impact of mitochondrial dynamics on immune cell mechanisms. The review also summarizes recent therapeutic approaches targeting mitochondria in anti-cancer treatment strategies.

CRISPR/Cas12a trans-cleavage triggered by cleavage ligation of dumbbell DNA for specific detection of human 8-oxoguanine DNA glycosylase activity

Human 8-oxoguanine DNA glycosylase (hOGG1) is an essential enzyme that recognizes and removes 8-oxoguanine (8-oxoG), a common DNA oxidative damage caused by reactive oxygen species, to maintain genomic integrity of living organisms. Abnormal expression of hOGG1 has been proved to be associated with different diseases such as cancer and neurogenerative disorders, making it a potential biomarker and therapeutic target. In this study, we report the development of  a novel strategy for detecting hOGG1 activity based on CRISPR/Cas12a trans-cleavage triggered by cleavage ligation of a dumbbell DNA probe (DBP) designed with a 3' overhang and an 8-oxoG modification. When hOGG1 is present, it cleaves the DBP at the 8-oxoG site, forming a 5' phosphate termini and exposing a single-strand region allowing complementary to the 3' overhang. After hybridization, the 3' and 5' termini in the juxtaposition are ligated by T4 DNA ligase, leading to a closed DBP for CRISPR/Cas12a-crRNA to recognize and initiate the trans-cleavage of the surrounding ssDNAs with fluorophore and quencher. The method achieves a limit of detection (LOD) with 370 μU/mL and high selectivity. Furthermore, it demonstrates a good compatibility for detecting hOGG1 activity in cell lysates, suggesting a good performance for further application in disease diagnosis and scientific research.

Low-Background CRISPR/Cas12a Sensors for Versatile Live-Cell Biosensing

The trans-cleavage activity of CRISPR/Cas12a has been widely used in biosensing. However, many CRISPR/Cas12a-based biosensors, especially those that work in "on-off-on" mode, usually suffer from high background and thus impossible intracellular application. Herein, this problem is efficiently overcome by elaborately designing the activator strand (AS) of CRISPR/Cas12a using the "RESET" effect found by our group. The activation ability of the as-designed AS to CRISPR/Cas12a can be easily inhibited, thus assuring a low background for subsequent biosensing applications, which not only benefits the detection sensitivity improvement of CRISPR/Cas12a-based biosensors but also promotes their applications in live cells as well as makes it possible to design high-performance biosensors with greatly improved flexibility, thus achieving the analysis of a wide range of targets. As examples, by using different strategies such as strand displacement, strand cleavage, and aptamer-substrate interaction to reactivate the inhibited enzyme activity, several CRISPR/Cas12a-based biosensing systems are developed for the sensitive and specific detection of different targets, including nucleic acid (miR-21), biological small molecules (ATP), and enzymes (hOGG1), giving the detection limits of 0.96 pM, 8.6 μM, and 8.3 × 10-5 U/mL, respectively. Thanks to the low background, these biosensors are demonstrated to work well for the accurate imaging analysis of different biomolecules in live cells. Moreover, we also demonstrate that these sensing systems can be easily combined with lateral flow assay (LFA), thus holding great potential in point-of-care testing, especially in poorly equipped or nonlaboratory environments.

Oxidative stress genes define two subtypes of triple-negative breast cancer with prognostic and therapeutic implications

Introduction: Oxidative stress (OS)-related genes have been confirmed to be closely related to the prognosis of triple-negative breast cancer (TNBC) patients; despite this fact, there is still a lack of TNBC subtype strategies based on this gene guidance. Here, we aimed to explore OS-related subtypes and their prognostic value in TNBC. Methods: Data from The Cancer Genome Atlas (TCGA)-TNBC and Sequence Read Archive (SRA) (SRR8518252) databases were collected, removing batch effects using a combat method before analysis. Consensus clustering analysis identified two OS subtypes (clusters A and B), with cluster A showing a better prognosis. Immune infiltration characteristics were analyzed using ESTIMATE and single-sample gene set enrichment analysis (ssGSEA) algorithms, revealing higher ImmuneScore and ESTIMATEscore in cluster A. Tumor-suppressive immune cells, human leukocyte antigen (HLA) genes, and three immune inhibitors were more prevalent in cluster A. Results: An eight-gene signature, derived from differentially expressed genes, was developed and validated as an independent risk factor for TNBC. A nomogram combining the risk score and clinical variables accurately predicted patient outcomes. Finally, we also validated the classification effect of subtypes using hub markers of each subtype in the test dataset. Conclusion: Our study reveals distinct molecular clusters based on OS-related genes to better clarify the reactive oxygen species (ROS)-mediated progression and the crosstalk between the ROS and tumor microenvironment (TME) in this heterogenetic disease, and construct a risk prognostic model which could provide more support for clinical treatment decisions.

A ratiometric SERS aptasensor array for human DNA glycosylaseat single-cell sensitivity/resolution

Human 8-oxoguanine DNA glycosylase (hOGG1) is involved in the cellular genomic 8-oxoguanine (8-oxoG) excision repair to maintain genome stability. Accurate detection of hOGG1 activity is essential for clinical diagnosis and treatment of various human pathology. Yet, the quantitative detection of hOGG1 remains challenging for existing methods due to poor reproducibility and portability. Herein, we propose a ratiometric array-based SERS point-of-care testing method for hOGG1 activity. A kind of reproducible, uniform and stable plasmonic multi-microarray reaction cells was constructed by assembling AuNPs on the substrate modified by aminosilane and segmented by silica gel gasket, which greatly improved the sensitivity, portability and repeatability of SERS measurement. Based on this, the ratiometric method is further used to effectively overcome the instability of single SERS signal intensity, which allows signal rationing and provides built-in correction for environment effects. In specific, we designed two different Raman-labeled probes for the detection of hOGG1, a thiol- and Cy3-labeled aptamer as an internal standard and a Rox-labeled 8-oxoG-modified complementary aptamer as a signal probe. The ratio value between Cy3 and Rox SERS intensity is well linear with the hOGG1 activity on logarithmic scales in the range from 5 × 10^-5 to 5 × 10^-3 U/mL, and the limit of detection reaches 3.3 × 10^-5 U/mL. Moreover, this strategy can be applied for the screening of inhibitors and the monitoring of cellular hOGG1 activity fluctuation at single-cell levels, providing a flexible and adaptive tool for clinical diagnosis, biochemical processes and drug discovery.

Assessment of hOGG1 Genetic Polymorphism (rs1052133) and DNA Damage in Radiation-Exposed Workers

OBJECTIVE

The aim of this study was to assess the effect of radiation exposure, human 8-oxoguanine DNA N-glycosylase-1 (hOGG1) exon 7 genetic polymorphism and confounding factors on DNA damage response.

METHODS

Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) and alkaline Comet assay method were applied to determine the hOGG1 genetic polymorphisms and DNA damage response. A total of 80 participants were enrolled in this study, consisting of 40 radiation-exposed workers as a case group and 40 non-radiation workers as a control group.

RESULT

The genotypes frequencies for controls were Ser/Ser (35%), Ser/Cys (32.5%), and Cys/Cys (32.5%), with frequencies of alleles being 326Ser (0.52) and 326Cys (0.48), whereas the genotypes frequencies for radiation-exposed workers (cases group) were Ser/Ser (17.5%), Ser/Cys (57.5%), and Cys/Cys (25%), with frequencies of alleles being 326Ser (0.46) and 326Cys (0.54). The results indicated that DNA damage response were not significantly higher in the exposed workers than in controls (22.55 ± 6.02 versus 21.72 ± 7.14; P=0.58). The time of exposure has a significantly negative correlation with comet tail length value among radiation workers. In addition, it was found that the DNA damage response was strongly associated with age and time of exposure with a decrease of 0.6 percent (P-value: 0.008) and 0.58 percent (P-value: 0.009), respectively. Whereas gender, smoking habit, and equivalent dose were not correlated with DNA damage.

CONCLUSION

The single-nucleotide polymorphism of hOGG1 exon 7 (rs1052133) demonstrated no association with the extent of DNA damage in radiation-exposed workers.

The Role of 8-oxoG Repair Systems in Tumorigenesis and Cancer Therapy

Tumorigenesis is highly correlated with the accumulation of mutations. The abundant and extensive DNA oxidation product, 8-Oxoguanine (8-oxoG), can cause mutations if it is not repaired by 8-oxoG repair systems. Therefore, the accumulation of 8-oxoG plays an essential role in tumorigenesis. To avoid the accumulation of 8-oxoG in the genome, base excision repair (BER), initiated by 8-oxoguanine DNA glycosylase1 (OGG1), is responsible for the removal of genomic 8-oxoG. It has been proven that 8-oxoG levels are significantly elevated in cancer cells compared with cells of normal tissues, and the induction of DNA damage by some antitumor drugs involves direct or indirect interference with BER, especially through inducing the production and accumulation of reactive oxygen species (ROS), which can lead to tumor cell death. In addition, the absence of the core components of BER can result in embryonic or early post-natal lethality in mice. Therefore, targeting 8-oxoG repair systems with inhibitors is a promising avenue for tumor therapy. In this study, we summarize the impact of 8-oxoG accumulation on tumorigenesis and the current status of cancer therapy approaches exploiting 8-oxoG repair enzyme targeting, as well as possible synergistic lethality strategies involving exogenous ROS-inducing agents.

Development of a CRISPR-Cas-Based Biosensor for Rapid and Sensitive Detection of 8-Oxoguanine DNA Glycosylase

8-Oxoguanine DNA glycosylase is essential for maintaining genomic integrity and stability, while its abnormal activity may lead to the disturbance in the normal DNA damage repair and the occurrence of carcinogenicity and teratogenicity. Herein, we construct a CRISPR-Cas-based biosensor for rapid and sensitive measurement of 8-oxoguanine DNA glycosylases. This biosensor involves a hairpin probe and integrates quadratic strand displacement amplification (SDA) with a CRISPR/Cas12a effector with the characteristics of rapidity (within 40 min) and isothermal assay. The presence of 8-oxoguanine DNA glycosylase can initiate the quadratic SDA to produce large amounts of activators with the assistance of polynucleotide kinase (PNK). Subsequently, the activators can bind with crRNA to activate Cas12a, cleaving signal probes and recovering Cy5 fluorescence, which can be accurately quantified by single-molecule imaging. Notably, the designed hairpin probes can effectively block the hybridization of the generated activators with free hairpin probes, endowing this biosensor with high sensitivity. In addition, the utilization of PNK instead of apurinic/apyrimidinic endonuclease (APE1) greatly simplifies the experimental procedure to only a one-step reaction. The introduction of a single-molecule detection further reduces the sample consumption and improves the sensitivity. This biosensor displays a detection limit of 4.24 × 10^-9 U μL^-1, and it can accurately quantify cellular human 8-oxoguanine DNA glycosylase at a single-cell level. Furthermore, this biosensor can be applied for the screening of inhibitors, the analysis of kinetic parameters, and the discrimination of cancer cells from normal cells, with potential applications in molecular diagnostic and point-of-care testing.

Chlorine, chromium, proteins of oxidative stress and DNA repair pathways are related to prognosis in oral cancer

The comparison of chemical and histopathological data obtained from the analysis of excised tumor fragments oral squamous cell carcinoma (OSCC) with the demographic and clinical evolution data is an effective strategy scarcely explored in OSCC studies. The aim was to analyze OSCC tissues for protein expression of enzymes related to oxidative stress and DNA repair and trace elements as candidates as markers of tumor aggressiveness and prognosis. Tumor fragments from 78 OSCC patients that had undergone ablative surgery were qualitatively analyzed by synchrotron micro-X-ray fluorescence for trace elements. Protein expression of SOD-1, Trx, Ref-1 and OGG1/2 was performed by immunohistochemistry. Sociodemographic, clinical, and histopathological data were obtained from 4-year follow-up records. Disease relapse was highest in patients with the presence of chlorine and chromium and lowest in those with tumors with high OGG1/2 expression. High expression of SOD-1, Trx, and Ref-1 was determinant of the larger tumor. Presence of trace elements can be markers of disease prognosis. High expression of enzymes related to oxidative stress or to DNA repair can be either harmful by stimulating tumor growth or beneficial by diminishing relapse rates. Interference on these players may bring novel strategies for the therapeutic management of OSCC patients.

Current Progress and Perspectives on Using Gold Compounds for the Modulation of Tumor Cell Metabolism

Altered cellular metabolism, which is essential for the growth and survival of tumor cells in a specific microenvironment, is one of the hallmarks of cancer. Among the most significant changes in the metabolic pattern of tumor cells is the shift from oxidative phosphorylation to aerobic glycolysis for glucose utilization. Tumor cells also exhibit changes in patterns of protein and nucleic acid metabolism. Recently, gold compounds have been shown to target several metabolic pathways and a number of metabolites in tumor cells. In this review, we summarize how gold compounds modulate glucose, protein, and nucleic acid metabolism in tumor cells, resulting in anti-tumor effects. We also discuss the rationale underlying the anti-tumor effects of these gold compounds and highlight how to effectively utilize against various types of tumors.

PD-1 derived CA-170 is an oral immune checkpoint inhibitor that exhibits preclinical anti-tumor efficacy

Small molecule immune checkpoint inhibitors targeting PD-1 and other pathways may offer advantages including ease of dosing, ability to manage immune-related adverse events (irAEs) due to their shorter pharmacokinetic exposure and opportunity to target more than one pathway for improving efficacy. Here we describe the identification and characterization of CA-170, an amino acid inspired small molecule inhibitor of PD-L1 and VISTA derived from the interface of PD-1 and PD-L1. CA-170 exhibited potent rescue of proliferation and effector functions of T cells inhibited by PD-L1/L2 and VISTA with selectivity over other immune checkpoint proteins as well as a broad panel of receptors and enzymes. Observed blocking of PD-L1 signaling and binding to PD-L1 in the cellular context without preventing the assembly of PD-1:PD-L1 complex support the formation of a defective ternary complex as the mechanism of action of CA-170. Oral administration of CA-170 resulted in increased proliferation and activation of T cells in the tumor, and significant anti-tumor efficacy in a number of immunocompetent mouse tumor models either as a single agent or in combination with approved therapeutics. These results prompted the advancement of CA-170 to human clinical trials.

Simple Mix-and-Read Assay with Multiple Cyclic Enzymatic Repairing Amplification for Rapid and Sensitive Detection of DNA Glycosylase

Human 8-oxoguanine DNA glycosylase (hOGG1) can initiate base excision repair of genomic 8-oxoguanine (8-oxoG), and it can locate and remove damaged 8-oxoG through extrusion and excision. Sensitive detection of hOGG1 is critical for clinical diagnosis. Herein, we develop a simple mix-and-read assay for the sensitive detection of DNA glycosylase using multiple cyclic enzymatic repairing amplification. The hOGG1 can excise the 8-oxoG base of the DNA substrate to produce an apurinic/apyrimidinic (AP) site, and then, the AP site can be cleaved by apurinic/apyrimidic endonuclease 1 (APE1), producing the substrate fragment with a free 3'-OH terminus. Subsequently, the substrate fragment can initiate cyclic enzymatic repairing amplification, generating two triggers. The resultant two triggers can function as the primers to induce three cyclic enzymatic repairing amplification, respectively, producing more and more triggers. We experimentally verify the occurrence of each cyclic enzymatic repairing amplification and uracil DNA glycosylase (UDG)-mediated exponential amplification. The amplification products can be simply detected using SYBR Green II as the fluorescent dye. This mix-and-read assay is very simple and rapid (within 40 min) without the requirement of any extra primers and modification/separation steps. This method can sensitively measure hOGG1 with a detection limit of 2.97 × 10^-8 U/μL, and it can be applied for the screening of inhibitors and the monitoring of cellular hOGG1 activity at the single-cell level, providing an adaptive and flexible tool for clinical diagnosis and drug discovery.

DNA Repair Pathways in Cancer Therapy and Resistance

DNA repair pathways are triggered to maintain genetic stability and integrity when mammalian cells are exposed to endogenous or exogenous DNA-damaging agents. The deregulation of DNA repair pathways is associated with the initiation and progression of cancer. As the primary anti-cancer therapies, ionizing radiation and chemotherapeutic agents induce cell death by directly or indirectly causing DNA damage, dysregulation of the DNA damage response may contribute to hypersensitivity or resistance of cancer cells to genotoxic agents and targeting DNA repair pathway can increase the tumor sensitivity to cancer therapies. Therefore, targeting DNA repair pathways may be a potential therapeutic approach for cancer treatment. A better understanding of the biology and the regulatory mechanisms of DNA repair pathways has the potential to facilitate the development of inhibitors of nuclear and mitochondria DNA repair pathways for enhancing anticancer effect of DNA damage-based therapy.

Genetic variations in base excision repair pathway genes and risk of hepatoblastoma: a seven-center case-control study

Hepatoblastoma is a rare childhood liver cancer without known explicit etiology. Base excision repair (BER) pathway genes have been implicated in the pathophysiology of cancer, yet the role of BER pathway gene single nucleotide polymorphisms (SNPs) on hepatoblastoma risk still awaits to be explored. This study aims to determine whether hepatoblastoma risk be modulated by polymorphisms in the BER pathway genes based on genotyped data from 313 cases and 1446 controls. We applied TaqMan assay to genotype these included samples. We comprehensively genotyped 20 SNPs across six genes of BER, and estimated odds ratio (ORs), 95% confidence intervals (CIs), and P-values of the selected SNPs' contribution to the risk of hepatoblastoma using logistic regression models. Only SNP rs293795 in the hOGG1 gene could significantly enhance hepatoblastoma risk under recessive model (adjusted OR=3.78, 95% CI=1.01-14.17, P=0.047). Stratified analysis revealed that rs159153 TC/CC genotype decreased hepatoblastoma risk in male subgroup. Moreover, rs293795 GG and 1-3 risk genotypes could increase hepatoblastoma risk in clinical stages I+II and male subgroups, respectively. False-positive report probability validated the reliability of the significant results. Our findings provide some clues of a potential risk effect of BER pathway gene hOGG1 SNPs on hepatoblastoma. Further investigation is warranted to confirm these findings and to better elucidate the biological pathways involved.

Acetylation and Deacetylation of DNA Repair Proteins in Cancers

Hundreds of DNA repair proteins coordinate together to remove the diverse damages for ensuring the genomic integrity and stability. The repair system is an extensive network mainly encompassing cell cycle arrest, chromatin remodeling, various repair pathways, and new DNA fragment synthesis. Acetylation on DNA repair proteins is a dynamic epigenetic modification orchestrated by lysine acetyltransferases (HATs) and lysine deacetylases (HDACs), which dramatically affects the protein functions through multiple mechanisms, such as regulation of DNA binding ability, protein activity, post-translational modification (PTM) crosstalk, and protein–protein interaction. Accumulating evidence has indicated that the aberrant acetylation of DNA repair proteins contributes to the dysfunction of DNA repair ability, the pathogenesis and progress of cancer, as well as the chemosensitivity of cancer cells. In the present scenario, targeting epigenetic therapy is being considered as a promising method at par with the conventional cancer therapeutic strategies. This present article provides an overview of the recent progress in the functions and mechanisms of acetylation on DNA repair proteins involved in five major repair pathways, which warrants the possibility of regulating acetylation on repair proteins as a therapeutic target in cancers.

Mitochondrial expression of the DNA repair enzyme OGG1 improves the prognosis of pancreatic ductal adenocarcinoma

BACKGROUND/OBJECTIVES

8-Hydroxydeoxyguanosine (8-OHdG) is an indicator of oxidative stress and causes transversion mutations and carcinogenesis. 8-OHdG is excision repaired by 8-OHdG DNA glycosylase 1 (OGG1), which is classified as nuclear and mitochondrial subtypes. We aimed to clarify the role of OGG1 in pancreatic ductal adenocarcinoma (PDAC).

METHODS

Ninety-two patients with PDAC who had undergone surgical resection at multiple institutions were immunohistochemically analyzed. The OGG1 and 8-OHdG expression levels were scored using the Germann Immunoreactive Score. The cutoff values of OGG1, as well as that of 8-OHdG, were determined.

RESULTS

The low nuclear OGG1 expression group (n = 41) showed significantly higher carbohydrate antigen (CA)19-9 (p = 0.026), and higher s-pancreas antigen (SPAN)-1 (p = 0.017) than the high expression group (n = 51). Nuclear OGG1 expression has no effect on the prognosis. The low mitochondrial OGG1 expression group (n = 40) showed higher CA19-9 (p = 0.041), higher SPAN-1 (p = 0.032), and more histological perineural invasion (p = 0.037) than the high expression group (n = 52). The low mitochondrial OGG1 expression group had a significantly shorter recurrence-free survival (p = 0.0080) and overall survival (p = 0.0073) rates. The Cox proportional hazards model revealed that low mitochondrial OGG1 expression is an independent risk factor of the PDAC prognosis. OGG1 expression was negatively correlated with 8-OHdG expression (p = 0.0004), and high 8-OHdG expression shortened the recurrence-free survival of patients with PDAC.

CONCLUSIONS

Low mitochondrial OGG1 expression might aggravate the PDAC prognosis.

Mitochondrial 8-oxoguanine DNA glycosylase mitigates alveolar epithelial cell PINK1 deficiency, mitochondrial DNA damage, apoptosis, and lung fibrosis

Alveolar epithelial cell (AEC) apoptosis, arising from mitochondrial dysfunction and mitophagy defects, is important in mediating idiopathic pulmonary fibrosis (IPF). Our group established a role for the mitochondrial (mt) DNA base excision repair enzyme, 8-oxoguanine-DNA glycosylase 1 (mtOGG1), in preventing oxidant-induced AEC mtDNA damage and apoptosis and showed that OGG1-deficient mice have increased lung fibrosis. Herein, we determined whether mice overexpressing the mtOGG1 transgene (mtOgg1^tg) are protected against lung fibrosis and whether AEC mtOGG1 preservation of mtDNA integrity mitigates phosphatase and tensin homolog-induced putative kinase 1 (PINK1) deficiency and apoptosis. Compared with wild type (WT), mtOgg1^tg mice have diminished asbestos- and bleomycin-induced pulmonary fibrosis that was accompanied by reduced lung and AEC mtDNA damage and apoptosis. Asbestos and H₂O₂ promote the MLE-12 cell PINK1 deficiency, as assessed by reductions in the expression of PINK1 mRNA and mitochondrial protein expression. Compared with WT, Pink1-knockout (Pink1-KO) mice are more susceptible to asbestos-induced lung fibrosis and have increased lung and alveolar type II (AT2) cell mtDNA damage and apoptosis. AT2 cells from Pink1-KO mice and PINK1-silenced (siRNA) MLE-12 cells have increased mtDNA damage that is augmented by oxidative stress. Interestingly, mtOGG1 overexpression attenuates oxidant-induced MLE-12 cell mtDNA damage and apoptosis despite PINK1 silencing. mtDNA damage is increased in the lungs of patients with IPF as compared with controls. Collectively, these findings suggest that mtOGG1 maintenance of AEC mtDNA is crucial for preventing PINK1 deficiency that promotes apoptosis and lung fibrosis. Given the key role of AEC apoptosis in pulmonary fibrosis, strategies aimed at preserving AT2 cell mtDNA integrity may be an innovative target.

Deregulated Mitochondrial DNA in Diseases

Mitochondria play various important roles in energy production, metabolism, and apoptosis. Mitochondrial dysfunction caused by alterations in mitochondrial DNA (mtDNA) can lead to the initiation and progression of cancers and other diseases. These alterations include mutations and copy number variations. Especially, the mutations in D-loop, MT-ND1, and MT-ND5 affect mitochondrial functions and are widely detected in various cancers. Meanwhile, several other mutations have been correlated with muscular and neuronal diseases, especially MT-TL1 is deeply related. These pieces of evidence indicated mtDNA alterations in diseases show potential as a novel therapeutic target. mtDNA repair enzymes are the target for delaying or stalling the mtDNA damage-induced cancer progression and metastasis. Moreover, some mutations reveal a prognosis ability of the drug resistance. Current efforts aim to develop mitochondrial transplantation technique as a direct cure for deregulated mitochondria-associated diseases. This review summarizes the implications of mitochondrial dysfunction in cancers and other pathologies; and discusses the relevance of mitochondria-targeted therapies, along with their contribution as potential biomarkers.

Roles of OGG1 in transcriptional regulation and maintenance of metabolic homeostasis

Cellular damage produced by conditions generating oxidative stress have far-reaching implications in human disease that encompass, but are not restricted to aging, cardiovascular disease, type 2 diabetes, airway inflammation/asthma, cancer, and metabolic syndrome including visceral obesity, insulin resistance, fatty liver disease, and dyslipidemia. Although there are numerous sources and cellular targets of oxidative stress, this review will highlight literature that has investigated downstream consequences of oxidatively-induced DNA damage in both nuclear and mitochondrial genomes. The presence of such damage can in turn, directly and indirectly modulate cellular transcriptional and repair responses to such stressors. As such, the persistence of base damage can serve as a key regulator in coordinated gene-response cascades. Conversely, repair of these DNA lesions serves as both a suppressor of mutagenesis and by inference carcinogenesis, and as a signal for the cessation of ongoing oxidative stress. A key enzyme in all these processes is 8-oxoguanine DNA glycosylase (OGG1), which, via non-catalytic binding to oxidatively-induced DNA damage in promoter regions, serves as a nucleation site around which changes in large-scale regulation of inflammation-associated gene expression can occur. Further, the catalytic function of OGG1 can alter the three-dimensional structure of specialized DNA sequences, leading to changes in transcriptional profiles. This review will concentrate on adverse deleterious health effects that are associated with both the diminution of OGG1 activity via population-specific polymorphic variants and the complete loss of OGG1 in murine models. This mouse model displays diet- and age-related induction of metabolic syndrome, highlighting a key role for OGG1 in protecting against these phenotypes. Conversely, recent investigations using murine models having enhanced global expression of a mitochondrial-targeted OGG1 demonstrate that they are highly resistant to diet-induced disease. These data suggest strategies through which therapeutic interventions could be designed for reducing or limiting adverse human health consequences to these ubiquitous stressors.

The interplay of circulating tumor DNA and chromatin modification, therapeutic resistance, and metastasis

Peripheral circulating free DNA (cfDNA) is DNA that is detected in plasma or serum fluid with a cell-free status. For cancer patients, cfDNA not only originates from apoptotic cells but also from necrotic tumor cells and disseminated tumor cells that have escaped into the blood during epithelial-mesenchymal transition. Additionally, cfDNA derived from tumors, also known as circulating tumor DNA (ctDNA), carries tumor-associated genetic and epigenetic changes in cancer patients, which makes ctDNA a potential biomarker for the early diagnosis of tumors, monitory and therapeutic evaluations, and prognostic assessments, among others, for various kinds of cancer. Moreover, analyses of cfDNA chromatin modifications can reflect the heterogeneity of tumors and have potential for predicting tumor drug resistance.

Pharmacologic Protection of Mitochondrial DNA Integrity May Afford a New Strategy for Suppressing Lung Ischemia-Reperfusion Injury

Lung ischemia-reperfusion (IR) injury contributes to post-transplant complications, including primary graft dysfunction. Decades of reports show that reactive oxygen species generated during lung IR contribute to pulmonary vascular endothelial barrier disruption and edema formation, but the specific target molecule(s) that "sense" injury-inducing oxidant stress to activate signaling pathways culminating in pathophysiologic changes have not been established. This review discusses evidence that mitochondrial DNA (mtDNA) may serve as a molecular sentinel wherein oxidative mtDNA damage functions as an upstream trigger for lung IR injury. First, the mitochondrial genome is considerably more sensitive than nuclear DNA to oxidant stress. Multiple studies suggest that oxidative mtDNA damage could be transduced to physiologic dysfunction by pathways that are either a direct consequence of mtDNA damage per se or involve formation of proinflammatory mtDNA damage-associated molecular patterns. Second, transgenic animals or cells overexpressing components of the base excision DNA repair pathway in mitochondria are resistant to oxidant stress-mediated pathophysiologic effects. Finally, published and preliminary studies show that pharmacologic enhancement of mtDNA repair or mtDNA damage-associated molecular pattern degradation suppresses reactive oxygen species-induced or IR injury in multiple organs, including preclinical models of lung procurement for transplant. Collectively, these findings point to the interesting prospect that pharmacologic enhancement of DNA repair during procurement or ex vivo lung perfusion may increase the availability of lungs for transplant and reduce the IR injury contributing to primary graft dysfunction.

Effects of the Ser326Cys Polymorphism in the DNA Repair OGG1 Gene on Cancer, Cardiovascular, and All-Cause Mortality in the PREDIMED Study: Modulation by Diet

BACKGROUND

Oxidatively induced DNA damage, an important factor in cancer etiology, is repaired by oxyguanine glycosylase 1 (OGG1). The lower repair capacity genotype (homozygote Cys326Cys) in the OGG1-rs1052133 (Ser326Cys) polymorphism has been associated with cancer risk. However, no information is available in relation to cancer mortality, other causes of death, and modulation by diet.

OBJECTIVE

Our aim was to evaluate the association of the OGG1-rs1052133 with total, cancer, and cardiovascular disease (CVD) mortality and to analyze its modulation by the Mediterranean diet, focusing especially on total vegetable intake as one of the main characteristics of this diet.

DESIGN

Secondary analysis in the PREDIMED (Prevención con Dieta Mediterránea) trial is a randomized, controlled trial conducted in Spain from 2003 to 2010.

PARTICIPANTS/SETTING

Study participants (n=7,170) were at high risk for CVD and were aged 55 to 80 years.

INTERVENTION

Participants were randomly allocated to two groups with a Mediterranean diet intervention or a control diet. Vegetable intake was measured at baseline.

MAIN OUTCOME MEASURES

Main outcomes were all-cause, cancer, and CVD mortality after a median follow-up of 4.8 years.

STATISTICAL ANALYSES

Multivariable-adjusted Cox regression models were fitted.

RESULTS

Three hundred eighteen deaths were detected (cancer, n=127; CVD, n=81; and other, n=110). Cys326Cys individuals (prevalence 4.2%) presented higher total mortality rates than Ser326-carriers (P=0.009). The multivariable-adjusted hazard ratio for Cys326Cys vs Ser326-carriers was 1.69 (95% CI 1.09 to 2.62; P=0.018). This association was greater for CVD mortality (P=0.001). No relationship was detected for cancer mortality in the whole population (hazard ratio 1.07; 95% CI 0.47 to 2.45; P=0.867), but a significant age interaction (P=0.048) was observed, as Cys326Cys was associated with cancer mortality in participants <66.5 years (P=0.029). Recessive effects limited our ability to investigate Cys326Cys×diet interactions for cancer mortality. No statistically significant interactions for total or CVD mortality were found for the Mediterranean diet intervention. However, significant protective interactions for CVD mortality were found for vegetable intake (hazard ratio interaction per standard deviation 0.42; 95% CI 0.18 to 0.98; P=0.046).

CONCLUSIONS

In this population, the Cys326Cys-OGG1 genotype was associated with all-cause mortality, mainly CVD instead of cancer mortality. Additional studies are needed to provide further evidence on its dietary modulation.

Understanding Mitochondrial Polymorphisms in Cancer

Alterations in mitochondrial DNA (mtDNA) were once thought to be predominantly innocuous to cell growth. Recent evidence suggests that mtDNA undergo naturally occurring alterations, including mutations and polymorphisms, which profoundly affect the cells in which they appear and contribute to a variety of diseases, including cardiovascular disease, diabetes, and cancer. Furthermore, interplay between mtDNA and nuclear DNA has been found in cancer cells, necessitating consideration of these complex interactions for future studies of cancer mutations and polymorphisms. In this issue of Cancer Research, Vivian and colleagues utilize a unique mouse model, called Mitochondrial Nuclear eXchange mice, that contain the nuclear DNA from one inbred mouse strain, and the mtDNA from a different inbred mouse strain to examine the genome-wide nuclear DNA methylation and gene expression patterns of brain tissue. Results demonstrated there were alterations in nuclear DNA expression and DNA methylation driven by mtDNA. These alterations may impact disease pathogenesis. In light of these results, in this review, we highlight alterations in mtDNA, with a specific focus on polymorphisms associated with cancer susceptibility and/or prognosis, mtDNA as cancer biomarkers, and considerations for investigating the role of mtDNA in cancer progression for future studies. Cancer Res; 77(22); 6051-9. ©2017 AACR.

Effects of airborne toxicants on pulmonary function and mitochondrial DNA damage in rodent lungs

Inhalation of airborne toxicants such as cigarette smoke and ozone is a shared health risk among the world's populations. The use of toxic herbicides like paraquat (PQ) is restricted by many countries, yet in the developing world PQ has demonstrable ill effects. The present study examined changes in pulmonary function, mitochondrial DNA (mtDNA) integrity and markers of DNA repair induced by acute or repeated exposure of PQ to rats. Similar to cigarette smoke and ozone, PQ promotes oxidative stress, and the impact of PQ on mtDNA was compared with that obtained with these agents. Tracheal instillation (i.t.) of PQ (0.01-0.075 mg/kg) dose dependently increased Penh (dyspnoea) by 48 h while body weight and temperature declined. Lung wet weight and the wet/dry weight ratio rose; for the latter, by as much as 52%. At low doses (0.02 and 0.03 mg/kg), PQ increased Penh by about 7.5-fold at 72 h. It quickly waned to near baseline levels. The lung wet/dry weight ratio remained elevated 7 days after administration coincident with marked inflammatory cell infiltrate. Repeated administration of PQ (1 per week for 8 weeks) resulted in a similar rise in Penh on the first instillation, but the magnitude of this response was markedly attenuated upon subsequent exposures. Pulmonary [lactate] and catalase activity, [8-oxodG] and histone fragmentation (cell death) were significantly increased. Repeated PQ instillation downregulated the expression of the mitochondrial-encoded genes, mtATP8, mtNd2 and mtcyB and nuclear ones for the DNA glycosylases, Ogg1, Neil1, Neil2 and Neil3. Ogg1 protein content decreased after acute and repeated PQ administration. mtDNA damage or changes in mtDNA copy number were evident in lungs of PQ-, cigarette smoke- and ozone-exposed animals. Taken together, these data indicate that loss of pulmonary function and inflammation are coupled to the loss of mtDNA integrity and DNA repair capability following exposure to airborne toxicants.

Mitochondrial DNA variants in colorectal carcinogenesis: Drivers or passengers?

INTRODUCTION

Mitochondrial DNA alterations have widely been reported in many age-related degenerative diseases and tumors, including colorectal cancer. In the past few years, the discovery of inter-genomic crosstalk between nucleus and mitochondria has reinforced the role of mitochondrial DNA variants in perturbing this essential signaling pathway and thus indirectly targeting nuclear genes involved in tumorigenic and invasive phenotype.

FINDINGS

Mitochondrial dysfunction is currently considered a crucial hallmark of carcinogenesis as well as a promising target for anticancer therapy. Mitochondrial DNA alterations include point mutations, deletions, inversions, and copy number variations, but numerous studies investigating their pathogenic role in cancer have provided inconsistent evidence. Furthermore, the biological impact of mitochondrial DNA variants may vary tremendously, depending on the proportion of mutant DNA molecules carried by the neoplastic cells (heteroplasmy).

CONCLUSIONS

In this review, we discuss the role of different type of mitochondrial DNA alterations in colorectal carcinogenesis and, in particular, we revisit the issue of whether they may be considered as causative driver or simply genuine passenger events. The advent of high-throughput techniques as well as the development of genetic and pharmaceutical interventions for the treatment of mitochondrial dysfunction in colorectal cancer are also explored.

Selected mitochondrial DNA landscapes activate the SIRT3 axis of the UPRmt to promote metastasis

By causing mitochondrial DNA (mtDNA) mutations and oxidation of mitochondrial proteins, reactive oxygen species (ROS) leads to perturbations in mitochondrial proteostasis. Several studies have linked mtDNA mutations to metastasis of cancer cells but the nature of the mtDNA species involved remains unclear. Our data suggests that no common mtDNA mutation identifies metastatic cells; rather the metastatic potential of several ROS-generating mutations is largely determined by their mtDNA genomic landscapes, which can act either as an enhancer or repressor of metastasis. However, mtDNA landscapes of all metastatic cells are characterized by activation of the SIRT/FOXO/SOD2 axis of the mitochondrial unfolded protein response (UPR^mt). The UPR^mt promotes a complex transcription program ultimately increasing mitochondrial integrity and fitness in response to oxidative proteotoxic stress. Using SOD2 as a surrogate marker of the UPR^mt, we found that in primary breast cancers, SOD2 is significantly increased in metastatic lesions. We propose that the ability of selected mtDNA species to activate the UPR^mt is a process that is exploited by cancer cells to maintain mitochondrial fitness and facilitate metastasis.

The Role of DNA Repair in Maintaining Mitochondrial DNA Stability

Mitochondria are vital double-membrane organelles that act as a "powerhouse" inside the cell and have essential roles to maintain cellular functions, e.g., ATP production, iron-sulfur synthesis metabolism, and steroid synthesis. An important difference with other organelles is that they contain their own mitochondrial DNA (mtDNA). Such powerful organelles are also sensitive to both endogenous and exogenous factors that can cause lesions to their structural components and their mtDNA, resulting in gene mutations and eventually leading to diseases. In this review, we will mainly focus on mammalian mitochondrial DNA repair pathways that safeguard mitochondrial DNA integrity and several important factors involved in the repair process, especially on an essential pathway, base excision repair. We eagerly anticipate to explore more methods to treat related diseases by constantly groping for these complexes and precise repair mechanisms.

Suppression of human 8-oxoguanine DNA glycosylase (OGG1) augments ultrasound-induced apoptosis in cervical cancer cells

PURPOSE

Human 8-oxoguanine DNA glycosylase (OGG1) is a major base excision repair enzyme, and it was reported to suppress the activation of intrinsic apoptotic signaling pathway in response to oxidative stress. In this study, our aim was to investigate the effects of OGG1 downregulation on ultrasound-induced apoptosis in cervical cancer cells.

METHODS

OGG1 expression was silenced by shRNA in the cervical cancer SW756 and CaSki cells. Cell viability was evaluated by MTT assay after OGG1 knockdown following ultrasound treatment. Ultrasound-induced apoptosis was measured by Annexin V-FITC/propidium iodide. Intracellular reactive oxygen species (ROS) production and Ca(2+) concentration were detected using a fluorescent probe, 2',7'-dichlorofluorescin diacetate (DCFH-DA) and a green fluorescent dye fluo-4AM, respectively. Western blotting was used to analyze the expression of Bcl-2, Bax, cleaved caspase-3, and nuclear factor-κB p65 (NF-κB p65).

RESULTS

The results indicated that OGG1 knockdown did not suppress cell proliferation, but significantly augmented ultrasound-induced inhibitory effects on the cell viability, and increased ultrasound-induced early apoptosis and late apoptosis and necrosis in the SW756 and CaSki cells when exposure to ultrasound (1MHz) at 1.5W/cm(2) for 30 and 60s. OGG1 knockdown significantly increased intracellular ROS production and Ca(2+) concentration after incubation of 6, 24, and 48h post-ultrasound treatment. The downregulation of Bcl-2 protein and the upregulation of Bax, cleaved caspase-3, and NF-κB p65 protein levels were observed in the shRNA-OGG1 cells and mock-shRNA cells, but no significant change of these protein levels was found between of them.

CONCLUSIONS

These results indicate that downregulation of OGG1 expression can augment ultrasound-induced apoptosis in cervical cancer cells, which suggests that OGG1 suppression might provide a new insight for ultrasound-induced therapeutic effects on cervical cancer treatment.

Association between polymorphisms of OGG1, EPHA2 and age-related cataract risk: a meta-analysis

Background

Evidences have identified the correlation of 8-oxoguanine DNA glycosylase-1 (OGG1) and eph-receptor tyrosine kinase-type A2 (EPHA2) polymorphisms in age-related cataract (ARC) risk. However, the results were not consistent. The objective of this study was to examine the role of these two gene polymorphisms in ARC susceptibility.

Methods

Eligible case–control studies published between January 2000 and 2015 were searched and retrieved in the electronic databases. The odds ratio with 95 % confidence interval (CI) was employed to calculate the strength of the relationship.

Results

We totally screened out six articles, including 5971 cataract patients and 4189 matched controls. Three variants were contained (OGG1 rs1052133; EPHA2 rs7543472 and rs11260867). For OGG1 rs1052133, we detected a significant correlation between OGG1 polymorphism and ARC risk under the heterogenous model (CG vs. CC: OR = 1.34, 95 % CI = 1.06–1.70, P = 0.01) and dominant model (GG+CG vs. CC: OR = 1.45, 95 % CI = 1.16–1.81, P = 0.001), especially in patients with cortical cataract of subgroup analysis by phenotypes (P < 0.05). For EPHA2 rs7543472 and rs11260867, we did not find a positive association between these two mutations and ARC susceptibility in total cases. Subgroup analysis by phenotypes of cataract showed that only in cortical cataract, genotypes of rs7543472 under the allele model, homogenous model and recessive model; genotypes of rs11260867 under the heterogenous model and dominant model were associated with ARC risk.

Conclusions

OGG1 rs1052133 (CG and CG+GG genotypes) might be risk factor for ARC, particularly in cortical cataract risk. EPHA2 rs7543472 (T allele and TT genotype) and rs11260867 (CG and GG+CG genotypes) might be associated with cortical cataract.

Molecular insights into the OGG1 gene, a cancer risk modifier in BRCA1 and BRCA2 mutations carriers

We have recently shown that rs2304277 variant in the OGG1 glycosidase gene of the Base Excision Repair pathway can increase ovarian cancer risk in BRCA1 mutation carriers. In the present study, we aimed to explore the role of this genetic variant on different genome instability hallmarks to explain its association with cancer risk.We have evaluated the effect of this polymorphism on OGG1 transcriptional regulation and its contribution to telomere shortening and DNA damage accumulation. For that, we have used a series of 89 BRCA1 and BRCA2 mutation carriers, 74 BRCAX cases, 60 non-carrier controls and 23 lymphoblastoid cell lines (LCL) derived from BRCA1 mutation carriers and non-carriers.We have identified that this SNP is associated to a significant OGG1 transcriptional down regulation independently of the BRCA mutational status and that the variant may exert a synergistic effect together with BRCA1 or BRCA2 mutations on DNA damage and telomere shortening.These results suggest that this variant, could be associated to a higher cancer risk in BRCA1 mutation carriers, due to an OGG1 transcriptional down regulation and its effect on genome instability.

The role of oxidative stress on breast cancer development and therapy

Reactive oxygen species (ROS) are produced by both enzymatic and non-enzymatic systems within eukaryotic cells and play important roles in cellular physiology and pathophysiology. Although physiological concentrations are crucial for ensuring cell survival, ROS overproduction is detrimental to cells, and considered key-factors for the development of several diseases, such as neurodegenerative diseases, cardiovascular disorders, and cancer. Cancer cells are usually submitted to higher ROS levels that further stimulate malignant phenotype through stimulus to sustained proliferation, death evasion, angiogenesis, invasiveness, and metastasis. The role of ROS on breast cancer etiology and progression is being progressively elucidated. However, less attention has been given to the development of redox system-targeted strategies for breast cancer therapy. In this review, we address the basic mechanisms of ROS production and scavenging in breast tumor cells, and the emerging possibilities of breast cancer therapies targeting ROS homeostasis.