Modulate DNA Repair Research Articles

Autophagy Roles in the Modulation of DNA Repair Pathways.

Autophagy and DNA repair are biological processes vital for cellular homeostasis maintenance and when dysfunctional, they lead to several human disorders including premature aging, neurodegenerative diseases, and cancer. The interchange between these pathways is complex and it may occur in both directions. Autophagy is activated in response to several DNA lesions types and it can regulate different mechanisms and molecules involved in DNA damage response (DDR), such as cell cycle checkpoints, cell death, and DNA repair. Thus, autophagy may modulate DNA repair pathways, the main focus of this review. In addition to the already well-documented autophagy positive effects on homologous recombination (HR), autophagy has also been implicated with other DNA repair mechanisms, such as base excision repair (BER), nucleotide excision repair (NER), and mismatch repair (MMR). Given the relevance of these cellular processes, the clinical applications of drugs targeting this autophagy-DNA repair interface emerge as potential therapeutic strategies for many diseases, especially cancer.

Ticking time bombs: connections between circadian clocks and cancer.

Connections between mammalian circadian and cell division cycles have been postulated since the early 20th century, and epidemiological and genetic studies have linked disruption of circadian clock function to increased risk of several types of cancer. In the past decade, it has become clear that circadian clock components influence cell growth and transformation in a cell-autonomous manner. Furthermore, several molecular mechanistic connections have been described in which clock proteins participate in sensing DNA damage, modulating DNA repair, and influencing the ubiquitination and degradation of key players in oncogenesis (c-MYC) and tumor suppression (p53).

Inhibiting polo-like kinase 1 enhances radiosensitization via modulating DNA repair proteins in non-small-cell lung cancer.

To assure faithful chromosome segregation, cells make use of the spindle assembly checkpoint, which can be activated in aneuploid cancer cells. In this study, the efficacies of inhibiting polo-like kinase 1 (PLK1) on the radiosensitization of non-small-cell lung cancer (NSCLC) cells were studied. Clonogenic survival assay was performed to identify the effects of the PLK1 inhibitor on radiosensitivity within NSCLC cells. Mitotic catastrophe assessment was used to measure the cell death and histone H2AX protein (γH2AX) foci were utilized to assess the DNA double-strand breaks (DSB). The transcriptome was analyzed via unbiased profiling of microarray expression. The results showed that the postradiation mitotic catastrophe induction and the DSB repair were induced by PLK1 inhibitor BI-6727, leading to an increase in the radiosensitivity of NSCLC cells. BI-6727 in combination with radiation significantly induced the delayed tumor growth. PLK1-silenced NSCLC cells showed an altered mRNA and protein expression related to DNA damaging, replication, and repairing, including the DNA-dependent protein kinase (DNAPK) and topoisomerase II alpha (TOPO2A). Furthermore, inhibition of PLK1 blocked 2 important DNA repair pathways. To summarize, our study showed PLK1 kinase as an option in the therapy of NSCLC.

Olaparib modulates DNA repair efficiency, sensitizes cervical cancer cells to cisplatin and exhibits anti-metastatic property

PARP1 trapping at DNA lesion by pharmacological inhibitors has been exploited in several cancers exhibiting defects in DNA repair mechanisms. PARP1 hyperactivation is involved in therapeutic resistance in multiple cancers. The role of PARP1 in cervical cancer (CC) resistance and implication of PARP inhibitor is yet to be elucidated. Our data demonstrates significantly higher expression of PARP1 in primary cervical tumors and CC cell lines SiHa and ME180. Upon cisplatin treatment CC cells display significant overexpression of PARP1 and its hyperactivation. PARP inhibitor olaparib shows significant anti-proliferative effect on CC cells and drive loss of clonogenic survival and enhanced cell death in combination with cisplatin. PARP inhibited cells show delay in resolution of γH2A.X foci and prolonged late S and G2-M phase arrest resulting in apoptosis. Further, PARP inhibition disrupts the localization of base excision repair (BER) effector XRCC1 and non-homologous end joining (NHEJ) proteins Ku80 and XRCC4. Due to disrupted relocation of repair factors, cisplatin induced stalled replication forks collapse and convert into double strand breaks (DSBs). Interestingly, PARP inhibition also shows anti-migratory and anti-invasive properties in CC cells, increases anchorage independent cell death and induces anoikis. Collectively, our data demonstrates therapeutic potential of PARP inhibitor in cervical cancer.

Bacterial infection increases risk of carcinogenesis by targeting mitochondria.

As up to a fifth of all cancers worldwide, have now been linked to microbial infections, it is essential to understand the carcinogenic nature of the bacterial/host interaction. This paper reviews the bacterial targeting of mediators of mitochondrial genomic fidelity and of mitochondrial apoptotic pathways, and compares the impact of the bacterial alteration of mitochondrial function to that of cancer. Bacterial virulence factors have been demonstrated to induce mutations of mitochondrial DNA (mtDNA) and to modulate DNA repair pathways of the mitochondria. Furthermore, virulence factors can induce or impair the intrinsic apoptotic pathway. The effect of bacterial targeting of mitochondria is analogous to behavior of mitochondria in a wide array of tumours, and this strongly suggests that mitochondrial targeting of bacteria is a risk factor for carcinogenesis.

A Strong Relationship Between Oral Squamous Cell Carcinoma and DNA Repair Genes.

Single nucleotide polymorphisms of DNA repair genes alter protein function and modulate DNA repair efficiency in various cancers. The X-ray repair cross-complementing group (XRCC) is responsible for the repair of DNA base damage and single-strand breaks. The aim of our study was to investigate the association of XRCC1 Arg399Gln and XRCC3 Thr241Met polymorphisms with the susceptibility to develop oral squamous cell carcinoma (OSCC) in Turkish subjects. One hundred eleven patients with OSCC and 148 healthy controls were recruited for the study. Genetic analysis was performed using polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP). We found that the XRCC1 Arg399Gln Gln/Gln genotype and Gln allele were risk factors for OSCC. Also, Arg/Arg genotype and Arg allele had protective effects against OSCC. Relative to XRCC3 Thr241Met polymorphism, carrying homozygote variants (Thr/Thr and Met/Met) was related with elevated OSCC risk. However, the heterozygote genotype and Thr allele variants were shown to be protective against OSCC. We suggest that XRCC1 Arg399Gln Gln/Gln genotype, Gln allele, and homozygote variants of XRCC3 Thr241Met polymorphism may be a risk factor for predisposition of OSCC in Turkish. In addition, XRCC3 Thr241Met genotype could be associated with tumor size and level of daily smoking.

Effect of Watermelon Powder Supplementation on Azoxymethane‐Induced Colon Carcinogenesis in Rats

Colorectal cancer (CRC) is a public health concern and one of the most common cancers in men and women globally. Given the substantial morbidity and mortality associated with this disease, methods for prevention, in part through a diet high in fruits and vegetables, are under investigation. Specifically, watermelon may be a practical method for reducing CRC risk factors due to its high concentration of L‐citrulline, a precursor to L‐arginine, which plays a crucial role in endothelial nitric oxide (NO) production. Evidence suggests that increased levels of NO have tumoricidal effects; therefore, the purpose of this study was to determine the effects of watermelon powder supplementation on aberrant crypt foci (ACF) formation, precancerous lesions, and biomarkers that are associated with colon carcinogenesis in rats. Thirty‐two male Sprague‐Dawley rats, at 21 days old, were divided into three groups: control, 0.36% L‐arginine, or 0.5% watermelon powder. The 0.5% watermelon powder diet provided 0.36% of L‐arginine+L‐citrulline. Rats were injected subcutaneously with azoxymethane (dose of 15 mg/kg body weight), a carcinogenic agent, at the beginning of weeks 3 and 4. The watermelon group exhibited higher blood NO levels compared to the control group (P < 0.05). Both the L‐arginine and watermelon powder groups exhibited lower total numbers of ACF and high multiplicity aberrant crypt foci (HMACF, > 4 aberrant crypts/focus) (P < 0.01). The watermelon powder group exhibited lower 8‐hydroxyguanosine DNA damage in the blood (P < 0.05) compared to controls. Watermelon powder and L‐arginine downregulated 8‐oxoguanine DNA glycosylase (OGG1) gene expression (P < 0.05) and upregulated O6‐methylguanine DNA methyltransferase (MGMT) gene expression (P < 0.01). Cyclooxgenase‐2 (COX‐2) gene expression in the colon mucosa of the watermelon group was lower compared to the control group (P < 0.05). These results suggest that watermelon powder or L‐arginine consumption may reduce the risk of colon cancer by suppressing ACF formation through lowering oxidative DNA damage and inflammation, modulating DNA repair enzyme expression, and enhancing NO production.Support or Funding InformationThe study was funded by The US National Watermelon Promotion Board.

Radiosensitizing effect of 5-aza-2'-deoxycytidin in human glioblastoma cells

Glioblastoma multiforme represents the most aggressive brain tumor. Its high infiltration rate and resistance to current treatment protocols results in a median survival of only 15 months following surgical removal and standard therapy. Epigenetic modulators have been shown to inhibit the growth of IDH-mutant glioma cells and may modulate DNA repair. Here, we analyzed the combined effect of the methyltransferase inhibitor 5-aza-2'-deoxycytidine (5-aza-dC) and ionizing radiation (IR) on the clonogenic survival of human glioblastoma cells.

Abstract 3670: Matrix metalloproteinase 9 has a novel tumor suppressive role in inflammation associated colorectal cancer by modulating intrinsic tumor microenvironment

Abstract Colitis associated cancer (CAC) is a deadly complication of inflammatory bowel disease, and a subtype of colon cancer. CAC malignancy progresses through enhanced DNA damage. Observance of microsatellite instability and chromosomal instability in non-cancer related inflammatory conditions, supports the fact that inflammation could contribute to genomic destabilization by generating reactive oxygen nitrogen species, producing double strand breaks leading to DNA damage. Thus chronic colitis can induce DNA damage and modulate DNA repair systems- components of the intrinsic pathway to modulate tumor microenvironment. Matrix metalloproteinases (MMPs) are the most prominent family of proteinases associated with almost all the junctures of inflammation and tumorigenesis. They mediate inflammation, tissue remodeling, invasion, metastasis and tumor growth. Among the 24 known human MMPs, MMP9 is very unique as it is undetectable in normal tissues but highly expressed in inflamed or ulcerated tissues. We have observed that MMP9 has a protective role in CAC, which is exclusive and contrary to its traditional role of a facilitator in acute inflammation and sporadic colon cancer. In this study we explore the molecular mechanism by which MMP9 prevents DNA damage by activating tumor suppressors and DNA repair pathways in CAC. We generated transgenic mice overexpressing MMP9 in intestinal epithelium (TgM9) and to mimic human CAC, 3 cycles of 3% DSS (dextran sodium sulfate, a colonic inflammation inducer) for 5 days, followed by two weeks of recovery was used for in vivo model. Stably-transfected HCT116 cells with/without p-EGFP-MMP9 plasmid were used for in vitro experiments. We have observed that in CAC, TgM9 mice had significantly decreased tumor incidence and dysplastic lesions and a lower histological score compared to their WT littermates. TgM9 mice exhibited increased apoptosis, protein expressions of active-Notch1, p19ARF, p53, p21WAF1/Cip1, caspase-3 and cyclinE in CAC compared to WTs. HCT116-cells overexpressing MMP9 indicated decreased cell proliferation. FACS analysis indicated S-phase cell-cycle arrest and WB analysis of phosphorylated gamma-H2AX expressions indicated less DSBs compared to vector. HCT116 cells overexpressing MMP9 indicated increased expression of MDC1 and mis-match repair proteins MLH1. Our study highlights two novel findings i) MMP9 being a secretory protein activates transcellular protein Notch1 which translocates to nucleus and activates wildtype p53 via ARF and ii) MMP9 suppresses DNA double strand breaks by activating MMR gene- MLH1 and removing the damaged cells by apoptosis and or cell cycle arrest. Our study highlights the paradox of using MMP9 inhibitors in current therapies to treat CAC patients, implying that MMP9 expression might be a natural/ biological way to suppress inflammation associated ulceration. Citation Format: Lewins Walter, Adani Pujada, Sayeed Mohammadian, Agnieszka Bialkowska, Vincent Yang, Pallavi Garg. Matrix metalloproteinase 9 has a novel tumor suppressive role in inflammation associated colorectal cancer by modulating intrinsic tumor microenvironment. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3670.

MiR146a-mediated targeting of FANCM during inflammation compromises genome integrity.

Inflammation is a potent inducer of tumorigenesis. Increased DNA damage or loss of genome integrity is thought to be one of the mechanisms linking inflammation and cancer development. It has been suggested that NF-κB-induced microRNA-146 (miR146a) may be a mediator of the inflammatory response. Based on our initial observation that miR146a overexpression strongly increases DNA damage, we investigated its potential role as a modulator of DNA repair. Here, we demonstrate that FANCM, a component in the Fanconi Anemia pathway, is a novel target of miR146a. miR146a suppressed FANCM expression by directly binding to the 3′ untranslated region of the gene. miR146a-induced downregulation of FANCM was associated with inhibition of FANCD2 monoubiquitination, reduced DNA homologous recombination repair and checkpoint response, failed recovery from replication stress, and increased cellular sensitivity to cisplatin. These phenotypes were recapitulated when miR146a expression was induced by overexpressing the NF-κB subunit p65/RelA or Helicobacter pylori infection in a human gastric cell line; the phenotypes were effectively reversed with an anti-miR146a antagomir. These results suggest that undesired inflammation events caused by a pathogen or over-induction of miR146a can impair genome integrity via suppression of FANCM.

Alleviation of Aflatoxin B1-Induced Genomic Damage by Proanthocyanidins via Modulation of DNA Repair.

In order to study the mechanisms underlying the alleviation of aflatoxin B1-induced genomic damage by proanthocyanidins (PAs), we examined the modulation of oxidative DNA damage induced by aflatoxin B1 in PAs-pretreated animals. The effects of PAs on changes in the expression of DNA damage and repair genes induced by aflatoxin B1 were also evaluated in rat marrow cells. Administration of PAs before aflatoxin B1 significantly mitigated aflatoxin B1-induced oxidative DNA damage in a dose-dependent manner. Aflatoxin B1 treatment induced significant alterations in the expression of specific DNA repair genes, and the pre-treatment of rats with PAs ameliorated the altered expression of these genes. Conclusively, PAs protect against aflatoxin B1-induced oxidative DNA damage in rats. These protective effects are attributed to the antioxidant effects of PA and enhanced DNA repair through modulation of DNA repair gene expression. Therefore, PAs are a promising chemoprotective agent for averting genotoxic risks associated with aflatoxin B1 exposure.

All-Trans Retinoic Acid Modulates DNA Damage Response and the Expression of the VEGF-A and MKI67 Genes in ARPE-19 Cells Subjected to Oxidative Stress.

Age-related macular degeneration (AMD) is characterized by the progressive degradation of photoreceptors and retinal pigment epithelium (RPE) cells. ARPE-19 is an RPE cell line established as an in vitro model for the study of AMD pathogenesis. Oxidative stress is an AMD pathogenesis factor that induces DNA damage. Thus, the oxidative stress-mediated DNA damage response (DDR) of ARPE-19 cells can be important in AMD pathogenesis. The metabolism of retinoids—which regulates cell proliferation, differentiation, and the visual cycle in the retina—was reported to be disturbed in AMD patients. In the present work, we studied the effect of all-trans retinoic acid (ATRA, a retinoid) on DDR in ARPE-19 cells subjected to oxidative stress. We observed that ATRA increased the level of reactive oxygen species (ROS), alkali-labile sites in DNA, DNA single-strand breaks, and cell death evoked by oxidative stress. ATRA did not modulate DNA repair or the distribution of cells in cell cycle in the response of ARPE-19 cells to oxidative stress. ATRA induced autophagy in the absence of oxidative stress, but had no effect on this process in the stress. ATRA induced over-expression of proliferation marker MKI67 and neovascularization marker VEGF-A. In conclusion, ATRA increased oxidative stress in ARPE-19 cells, resulting in more lesions to their DNA and cell death. Moreover, ATRA can modulate some properties of these cells, including neovascularization, which is associated with the exudative form of AMD. Therefore, ATRA can be important in the prevention, diagnosis, and therapy of AMD.

Altered Secretory Activity of APE1/Ref-1 D148E Variants Identified in Human Patients With Bladder Cancer.

Purpose:Apurinic/apyrimidinic endonuclease 1/redox factor-1 (APE1/Ref-1) is a multifunctional protein involved in DNA repair and redox modulation. Recently, serum and urinary APE1/Ref-1 levels were reported to be increased in patients with bladder cancer. Genetic variations of APE/Ref-1 are associated with the risk of cancer. However, the effect of APE1/Ref-1 variants on its secretory activity is yet unknown.Methods:APE1/Ref-1 variants were evaluated by DNA sequencing analysis of reverse transcription polymerase chain reaction products in coding DNA sequences (CDS) of APE1/Ref-1 in bladder tissue samples from patients with bladder cancer (n=10). Secretory activity of APE1/Ref-1 variants was evaluated with immunoblot and enzyme-linked immunosorbent assay of the culture medium supernatants.Results:Four different substitution mutants (D148E, I64V/D148E, W67R/D148E, and E86G/D148E) of APE1/Ref-1 were identified in bladder cancer specimens. However, deletion mutants of APE1/Ref-1 CDS were not found. The secretory activity of the APE1/Ref-1 variants (D148E, I64V/D148E, and E86G/D148E) was increased compared to that of wild type APE1/Ref-1. Furthermore, the secretory activity in basal or hyperacetylated conditions was much higher than that in APE1/Ref-1 D148E-transfected HEK293 cells.Conclusions:Taken together, our data suggest that the increased secretory activity of D148E might contribute to increased serum levels of APE1/Ref-1 in patients with bladder cancer.

Combined Effects of High-Dose Bisphenol A and Oxidizing Agent (KBrO3) on Cellular Microenvironment, Gene Expression, and Chromatin Structure of Ku70-deficient Mouse Embryonic Fibroblasts.

Background:Exposure to bisphenol A (BPA) has been reported to alter global gene expression, induce epigenetic modifications, and interfere with complex regulatory networks of cells. In addition to these reprogramming events, we have demonstrated that BPA exposure generates reactive oxygen species and promotes cellular survival when co-exposed with the oxidizing agent potassium bromate (KBrO3).Objectives:We determined the cellular microenvironment changes induced by co-exposure of BPA and KBrO3 versus either agent alone.Methods:Ku70-deficient cells were exposed to 150 μM BPA, 20 mM KBrO3, or co-exposed to both agents. Four and 24 hr post-damage initiation by KBrO3, with BPA-only samples timed to coincide with these designated time points, we performed whole-genome microarray analysis and evaluated chromatin structure, DNA lesion load, glutathione content, and intracellular pH.Results:We found that 4 hr post-damage initiation, BPA exposure and co-exposure transiently condensed chromatin compared with untreated and KBrO3-only treated cells; the transcription of DNA repair proteins was also reduced. At this time point, BPA exposure and co-exposure also reduced the change in intracellular pH observed after treatment with KBrO3 alone. Twenty-four hours post-damage initiation, BPA-exposed cells showed less condensed chromatin than cells treated with KBrO3 alone; the intracellular pH of the co-exposed cells was significantly reduced compared with untreated and KBrO3-treated cells; and significant up-regulation of DNA repair proteins was observed after co-exposure.Conclusion:These results support the induction of an adaptive response by BPA co-exposure that alters the microcellular environment and modulates DNA repair. Further work is required to determine whether BPA induces similar DNA lesions in vivo at environmentally relevant doses; however, in the Ku70-deficient mouse embryonic fibroblasts, exposure to a high dose of BPA was associated with changes in the cellular microenvironment that may promote survival.Citation:Gassman NR, Coskun E, Jaruga P, Dizdaroglu M, Wilson SH. 2016. Combined effects of high-dose bisphenol A and oxidizing agent (KBrO3) on cellular microenvironment, gene expression, and chromatin structure of Ku70-deficient mouse embryonic fibroblasts. Environ Health Perspect 124:1241–1252; http://dx.doi.org/10.1289/EHP237

Combined metformin and resveratrol confers protection against UVC-induced DNA damage in A549 lung cancer cells via modulation of cell cycle checkpoints and DNA repair.

Aging in humans is a multi-factorial cellular process that is associated with an increase in the risk of numerous diseases including diabetes, coronary heart disease and cancer. Aging is linked to DNA damage, and a persistent source of DNA damage is exposure to ultraviolet (UV) radiation. As such, identifying agents that confer protection against DNA damage is an approach that could reduce the public health burden of age-related disorders. Metformin and resveratrol have both shown effectiveness in preventing several age-related diseases; using human A549 cells, we investigated whether metformin or resveratrol, alone or combined, prevent UVC-induced DNA damage. We found that metformin inhibited UVC-induced upregulation of p53, as well as downregulated the expression of two DNA damage markers: γH2AX and p-chk2. Metformin also upregulated DNA repair as evidenced by the increase in expression of p53R2. Treatment with metformin also induced cell cycle arrest in UVC-induced cells, in correlation with a reduction in the levels of cyclinE/cdk2/Rb and cyclinB1/cdk1. Compared to metformin, resveratrol as a single agent showed less effectiveness in counteracting UVC-elicited cellular responses. However, resveratrol displayed synergism when combined with metformin as shown by the downregulation of p53/γH2AX/p-chk2. In conclusion, the results of the present study validate the effectiveness of metformin, alone or with the addition of resveratrol, in reducing the risk of aging by conferring protection against UV-induced DNA damage.

Long noncoding RNA POU6F2-AS2 is associated with oesophageal squamous cell carcinoma.

Oesophageal carcinoma is one of the most lethal cancer types in the world, especially in some part of China. Oesophageal squamous cell carcinoma (OSCC) is a major subtype, which has been shown to be associated with unhealthy diet habit, smoking, environmental carcinogens etc. The OSCC often progress slowly, however, it is often diagnosed at an advanced stage. Thus it is imperative to elucidate the molecular mechanisms involved in the initiation and progression of OSCC. Long noncoding RNAs (lncRNA) has emerged as a novel functional player transcribed from the genome. Here, we describe a novel lncRNA POU6F2-AS2 specifically expressed in OSCC. POU6F2-AS2 is involved in the DNA damage response and regulates cells survival after ionizing radiation. POU6F2-AS2 interacts with Ybx1 protein and regulates its chromatin localization. Our current study represents the first description of an OSCC associated lncRNA that modulates DNA repair.

New and emerging developments in extensive-stage small cell lung cancer therapeutics.

Extensive-stage small cell lung cancer (ES-SCLC) remains a disease with a dismal prognosis, with median survival of approximately 8-10 months. Despite many attempts to develop effective systemic therapies, very little progress has been made in the last several decades. Platinum-based combination chemotherapy remains the standard of care in the first-line setting and is associated with high response rates albeit short-lived. However, there have been recent advances in the use of radiation therapy, as well as new insights into the biology of SCLC. Some of the most appreciable advances in the last decade have involved the use of local radiation therapy. With the use of new laboratory techniques such as genomic sequencing, there remains promise of rationally targeted drug development. Circulating tumor cell research may also provide insights to SCLC biology and further refine treatment. Systemic therapy for SCLC has changed little over the past 30 years with the most significant advances in ES-SCLC relating to radiotherapy rather than systemic therapy. The effectiveness of prophylactic cranial irradiation and thoracic radiotherapy has renewed interest in therapeutics focused on the modulation of DNA damage or repair. Recent developments in genomic sequencing and immunotherapy may translate to new treatment paradigms for SCLC.

The acetyltransferase Tip60 contributes to mammary tumorigenesis by modulating DNA repair.

The acetyltransferase Tip60/Kat5 acetylates both histone and non-histone proteins, and is involved in a variety of biological processes. By acetylating p53, Tip60 controls p53-dependent transcriptional activity and so is implicated as a tumor suppressor. However, many breast cancers with low Tip60 also show p53 mutation, implying that Tip60 has a tumor suppressor function independent of its acetylation of p53. Here, we show in a p53-null mouse model of sporadic invasive breast adenocarcinoma that heterozygosity for Tip60 deletion promotes mammary tumorigenesis. Low Tip60 reduces DNA repair in normal and tumor mammary epithelial cells, both under resting conditions and following genotoxic stress. We demonstrate that Tip60 controls homologous recombination (HR)-directed DNA repair, and that Tip60 levels correlate inversely with a gene expression signature associated with defective HR-directed DNA repair. In human breast cancer data sets, Tip60 mRNA is downregulated, with low Tip60 levels correlating with p53 mutations in basal-like breast cancers. Our findings indicate that Tip60 is a novel breast tumor suppressor gene whose loss results in genomic instability leading to cancer formation.

Role of Deubiquitinating Enzymes in DNA Repair.

Both proteolytic and nonproteolytic functions of ubiquitination are essential regulatory mechanisms for promoting DNA repair and the DNA damage response in mammalian cells. Deubiquitinating enzymes (DUBs) have emerged as key players in the maintenance of genome stability. In this minireview, we discuss the recent findings on human DUBs that participate in genome maintenance, with a focus on the role of DUBs in the modulation of DNA repair and DNA damage signaling.

Sirtuins and their interactions with transcription factors and poly(ADP-ribose) polymerases.

Sirtuins (SIRT1 to -7) are unique histone deacetylases (HDACs) whose activity depends on NAD+, thus making them capable of sensing the cellular metabolic status. Sirtuins orchestrate the stress response and damage repair, and are able to modulate the course of ageing and neurodegenerative diseases. Despite their classification as HDACs, sirtuins deacetylate a vast number of targets in many cellular compartments, and some display additional enzymatic activities including mono(ADP-ribosyl)ation. SIRTs interact with multiple signalling proteins, transcription factors and enzymes including p53, FOXOs (forkhead box subgroup O), PPARs (peroxisome proliferator-activated receptors), NF-B, and DNA-PK (DNA-dependent protein kinase). Sirtuins also interact extensively with the family of poly(ADP- ribose) polymerases (PARPs), a crucial and widespread class of NAD+-consuming post-translational protein modifiers. PARPs share a significant number of roles with sirtuins: these enzymes modulate DNA repair, gene expression, and the activities of signalling pathways. We focus on the expanding cross-talk between sirtuins, transcription factors and PARPs, which is a highly promising therapeutic target in a number of age-related neurodegenerative disorders, including the most devastating: Alzheimer's and Parkinson's diseases.