Involving DNA Repair Research Articles

103 Metabolic Characterization of IDH1mutant and IDH Wildtype Gliomaspheres Uncovers Cell-type Specific Vulnerabilities

Abstract INTRODUCTION Large scale sequencing of tumor banks has revealed a subset of tumors that have a mutation in the isocitrate dehydrogenase (IDH1) enzyme, which bestows a novel function of reducing alpha-ketoglutarate into 2-hydroxyglutarate (2-HG). There has been considerable interest in defining metabolic differences of IDH1mutant tumors to exploit in therapy. However, most studies are limited by over-expressing the mutant IDH1 gene on an IDH1WT background. In this study we attempt to define metabolic differences between a cohort of patient-derived IDH1mutant and IDH1WT gliomaspheres to design patient-specific therapy. METHODS We propagated 59 patient-derived gliomasphere lines (7 bearing IDH1mutations) and performed microarray expression and KEGG analysis to define the pathways that were differentially enriched in IDH1mutant and IDH1WT cells. We used mass spectroscopy with labeled glucose and glutamine to determine differences in metabolite uptake and utilization. We then used inhibitors of de novo synthesis and Xray radiation treatment to test the predictions made by our expression analysis. RESULTS >Expression analysis showed IDH1WT cells to be enriched for pathways involving de novo DNA synthesis while IDH1mutant cells were enriched for pathways involving DNA repair after radiation. Using LC-MS we were able to define labeling patterns between IDH1WT and IDH1mutant cells particularly in regards to glucose utilization in nucleotide precursors. IDH1WT cells utilize more of the de novo pathway to synthesize nucleotides and consequently to be more sensitive to inhibitors of de novo synthesis. IDH1mutant cells were found to show less DNA damage after radiation and to more quickly repair that damage. They also showed better growth after radiation. CONCLUSION In this study we have identified key metabolic differences between IDH1mutant and IDH1wildtype tumors that suggest these two groups require different treatment modalities.

MP88-07 ANDROGEN RECEPTOR ACTIVITY MODULATES RADIOSENSITIVITY IN BLADDER CANCER CELLS

You have accessJournal of UrologyBladder Cancer: Basic Research & Pathophysiology IV1 Apr 2017MP88-07 ANDROGEN RECEPTOR ACTIVITY MODULATES RADIOSENSITIVITY IN BLADDER CANCER CELLS Hiroki Ide, Satoshi Inoue, Taichi Mizushima, Mototsugu Oya, and Hiroshi Miyamoto Hiroki IdeHiroki Ide More articles by this author , Satoshi InoueSatoshi Inoue More articles by this author , Taichi MizushimaTaichi Mizushima More articles by this author , Mototsugu OyaMototsugu Oya More articles by this author , and Hiroshi MiyamotoHiroshi Miyamoto More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2017.02.2732AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Although radiation therapy often with chemotherapy has been shown to offer survival rates comparable to radical cystectomy in select patients with bladder cancer, the development of radiosensitization may significantly enhance its application. Meanwhile, emerging preclinical evidence has indicated the involvement of androgen receptor (AR) signaling in urothelial cancer progression. In prostate cancer, AR has also been linked to radioresistance involving DNA repair pathways. We therefore assessed whether AR signals contribute to the sensitivity to radiotherapy in bladder cancer cells. METHODS We compared the inhibitory effects of irradiation (2 Gy) on bladder cancer cell viability or colony formation between AR-positive [e.g. UMUC3 expressing control-short hairpin RNA (shRNA), 5637 or 647V stably expressing wild-type AR] versus AR-negative lines (e.g. UMUC3 stably expressing AR-shRNA, 5637 or 647V expressing vector only) or between AR-positive lines with versus without treatment with dihydrotestosterone (DHT) or an anti-androgen hydroxyflutamide (HF). We also compared DNA double strand breaks (DSB) via γ-H2AX foci formation in these cells after irradiation. RESULTS Ionizing radiation reduced the numbers of viable cells or colonies of AR-negative lines more significantly than those of AR-positive lines. Similarly, in AR-positive cells cultured in androgen-depleted conditions, DHT treatment lowered the effects of irradiation. In AR-positive cells cultured in the presence of androgens, HF treatment then enhanced the effects of irradiation. Furthermore, the percentage of cells containing >10 γ-H2AX foci in AR-negative lines was significantly higher than that in AR-positive lines after irradiation (4, 8, 12, and 24h). DSB repair was also delayed by HF treatment in AR-positive cells after irradiation (4, 8, 12, and 24h). CONCLUSIONS These findings suggest that AR activity correlates with the sensitivity to radiotherapy in bladder cancer cells. Accordingly, anti-androgenic drugs may function as sensitizers of irradiation, especially in patients with AR-positive urothelial cancer. © 2017FiguresReferencesRelatedDetails Volume 197Issue 4SApril 2017Page: e1176 Advertisement Copyright & Permissions© 2017MetricsAuthor Information Hiroki Ide More articles by this author Satoshi Inoue More articles by this author Taichi Mizushima More articles by this author Mototsugu Oya More articles by this author Hiroshi Miyamoto More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Tumor-treating fields elicit a conditional vulnerability to ionizing radiation via the downregulation of BRCA1 signaling and reduced DNA double-strand break repair capacity in non-small cell lung cancer cell lines

The use of tumor-treating fields (TTFields) has revolutionized the treatment of recurrent and newly diagnosed glioblastoma (GBM). TTFields are low-intensity, intermediate frequency, alternating electric fields that are applied to tumor regions and cells using non-invasive arrays. The predominant mechanism by which TTFields are thought to kill tumor cells is the disruption of mitosis. Using five non-small cell lung cancer (NSCLC) cell lines we found that there is a variable response in cell proliferation and cell killing between these NSCLC cell lines that was independent of p53 status. TTFields treatment increased the G2/M population, with a concomitant reduction in S-phase cells followed by the appearance of a sub-G1 population indicative of apoptosis. Temporal changes in gene expression during TTFields exposure was evaluated to identify molecular signaling changes underlying the differential TTFields response. The most differentially expressed genes were associated with the cell cycle and cell proliferation pathways. However, the expression of genes found within the BRCA1 DNA-damage response were significantly downregulated (P<0.05) during TTFields treatment. DNA double-strand break (DSB) repair foci increased when cells were exposed to TTFields as did the appearance of chromatid-type aberrations, suggesting an interphase mechanism responsible for cell death involving DNA repair. Exposing cells to TTFields immediately following ionizing radiation resulted in increased chromatid aberrations and a reduced capacity to repair DNA DSBs, which were likely responsible for at least a portion of the enhanced cell killing seen with the combination. These findings suggest that TTFields induce a state of ‘BRCAness’ leading to a conditional susceptibility resulting in enhanced sensitivity to ionizing radiation and provides a strong rationale for the use of TTFields as a combined modality therapy with radiation or other DNA-damaging agents.

The efficacy of trabectedin in treating ovarian cancer

ABSTRACTIntroduction: The majority of women with epithelial ovarian cancer present with advanced stage disease and there is a critical need for novel drugs and treatment strategies to improve outcomes. Trabectedin is a unique cytotoxic agent with a complex mechanism of action. It binds to guanines in the N2 position in the minor groove of DNA and its cytotoxicity involves DNA repair pathways and transcription regulation. Trabectedin’s activity is also related to the drug-induced changes of the tumor microenvironment. It has been shown to improve progression-free survival in combination with pegylated liposomal doxorubicin in patients with platinum-sensitive relapsed ovarian cancer. The most common adverse events experienced with trabectedin are nausea, vomiting, fatigue, neutropenia and transaminitis. Studies of biomarkers that are predictors of trabectedin benefit are underway.Areas covered: This review covers trabectedin’s mechanism of action and pharmacology, the clinical development of the drug in ovarian cancer, ongoing trials, and the use of biomarkers to predict efficacy to trabectedin.Expert opinion: Ongoing phase III trials with biomarker studies will help to elucidate the patient population that will best benefit from trabectedin and pave the way for personalized treatment decisions and potential future approval of trabectedin in the United States.

A Zygotic Checkpoint for Unrepaired Lesions

DNA demethylation, a process involving DNA repair, is critical for reprogramming of the paternal genome during the oocyte-to-zygote transition. A new study by Ladstätter and Tachibana-Konwalski shows that a Chk1-mediated zygotic checkpoint monitors the cohesin-dependent repair of DNA lesions arising from DNA demethylation, which prevents zygotes carrying unrepaired lesions from entering mitosis.

Multiple and Variable NHEJ-Like Genes Are Involved in Resistance to DNA Damage in Streptomyces ambofaciens.

Non-homologous end-joining (NHEJ) is a double strand break (DSB) repair pathway which does not require any homologous template and can ligate two DNA ends together. The basic bacterial NHEJ machinery involves two partners: the Ku protein, a DNA end binding protein for DSB recognition and the multifunctional LigD protein composed a ligase, a nuclease and a polymerase domain, for end processing and ligation of the broken ends. In silico analyses performed in the 38 sequenced genomes of Streptomyces species revealed the existence of a large panel of NHEJ-like genes. Indeed, ku genes or ligD domain homologues are scattered throughout the genome in multiple copies and can be distinguished in two categories: the “core” NHEJ gene set constituted of conserved loci and the “variable” NHEJ gene set constituted of NHEJ-like genes present in only a part of the species. In Streptomyces ambofaciens ATCC23877, not only the deletion of “core” genes but also that of “variable” genes led to an increased sensitivity to DNA damage induced by electron beam irradiation. Multiple mutants of ku, ligase or polymerase encoding genes showed an aggravated phenotype compared to single mutants. Biochemical assays revealed the ability of Ku-like proteins to protect and to stimulate ligation of DNA ends. RT-qPCR and GFP fusion experiments suggested that ku-like genes show a growth phase dependent expression profile consistent with their involvement in DNA repair during spores formation and/or germination.

A Novel Role of Chromodomain Protein CBX8 in DNA Damage Response

Induction of DNA damage induces a dynamic repair process involving DNA repair factors and epigenetic regulators. Chromatin alterations must occur for DNA repair factors to gain access to DNA lesions and restore original chromatin configuration to preserve the gene expression profile. We characterize the novel role of CBX8, a chromodomain-containing protein with established roles in epigenetic regulation in DNA damage response. CBX8 protein rapidly accumulates at the sites of DNA damage within 30 s and progresses to accumulate until 4 min before gradually dispersing back to its predamage distribution by 15 min. CBX8 recruitment to the sites of DNA damage is dependent upon PARP1 activation and not dependent on ATM activation. CBX8 biochemically interacts with TRIM33, and its recruitment to DNA damage is also dependent on the presence of TRIM33. Knockdown of CBX8 using siRNA significantly reduces the efficiency of both homologous and the other non-homologous recombination, as well as increases sensitivity of cells to ionizing radiation. These findings demonstrate that CBX8 functions in the PARP-dependent DNA damage response partly through interaction with TRIM33 and is required for efficient DNA repair.

Association between XRCC3 Thr241Met polymorphism and nasopharyngeal carcinoma risk: evidence from a large-scale case-control study and a meta-analysis

The X-ray repair cross-complementing group 3 (XRCC3) Thr241Met polymorphism (rs861539, C>T) has drawn wide attentions as its association with cancer risk and its involvement in DNA repair. Several studies have attempted to link rs861539 to nasopharyngeal cancer (NPC) risk; however, the sample sizes of these studies are small and the results are controversial. To investigate the relationship of rs861539 and NPC susceptibility, we conducted a large-scale case-control study involving 4001 NPC cases and 2967 controls of southern Chinese. Logistic regression analysis revealed significant association for rs861539 and NPC risk under the recessive model (TT vs. CT+CC) with adjustment of age and gender (odds ratio, OR =2.72; 95% CI 1.10-6.72; P=0.03). Further, meta-analysis involving 4457 NPC cases and 4132 controls from four studies showed consistent association of TT carriers and NPC risk (OR=3.12; 95% CI 1.58-6.13; P=0.001). Taken together, our findings based on large-scale sample size suggested rs861539 at XRCC3 to be associated with NPC risk through recessive model.

PARG Inhibitors and Functional PARG Inhibition Models.

Poly(ADP-ribose) polymerases (PARPs) family proteins catalyze poly(ADP-ribosylation) (PARylation) by conjugating ADP-ribose residues repeatedly on amino acid residues using nicotinamide adenine dinucleotide as a substrate. The inhibitors of PARP widely block DNA repair processes and are currently examined in clinical trials of cancer therapy. Poly(ADP-ribose) glycohydrolase (PARG) is the main nuclear enzyme, which digests poly(ADP-ribose) into ADP-ribose. PARG inhibitor could also be considered as a chemotherapeutic agent for cancer, because of its involvement in DNA repair. Various PARG inhibitors with IC50 value of micromolar to submicromolar range have been reported. However, for most of these chemicals, the specificity of inhibition has not been fully evaluated. PARG functional inhibition models in various organisms have been developed. Here, inducible PARG knockdown system was developed in HeLa cells and the cell line will be useful for identifying the synthetic lethal genes or affecting genes for PARG inhibitor treatment and also for functional elucidation of PARP superfamily molecules.

Restricting retrotransposons: a review.

Retrotransposons have generated about 40 % of the human genome. This review examines the strategies the cell has evolved to coexist with these genomic “parasites”, focussing on the non-long terminal repeat retrotransposons of humans and mice. Some of the restriction factors for retrotransposition, including the APOBECs, MOV10, RNASEL, SAMHD1, TREX1, and ZAP, also limit replication of retroviruses, including HIV, and are part of the intrinsic immune system of the cell. Many of these proteins act in the cytoplasm to degrade retroelement RNA or inhibit its translation. Some factors act in the nucleus and involve DNA repair enzymes or epigenetic processes of DNA methylation and histone modification. RISC and piRNA pathway proteins protect the germline. Retrotransposon control is relaxed in some cell types, such as neurons in the brain, stem cells, and in certain types of disease and cancer, with implications for human health and disease. This review also considers potential pitfalls in interpreting retrotransposon-related data, as well as issues to consider for future research.

DNA damage to human genetic disorders with neurodevelopmental defects

Although some mutations are beneficial and are the driving force behind evolution, it is important to maintain DNA integrity and stability because it contains genetic information. However, in the oxygen-rich environment we live in, the DNA molecule is under constant threat from endogenous or exogenous insults. DNA damage could trigger the DNA damage response (DDR), which involves DNA repair, the regulation of cell cycle checkpoints, and the induction of programmed cell death or senescence. Dysregulation of these physiological responses to DNA damage causes developmental defects, neurological defects, premature aging, infertility, immune system defects, and tumors in humans. Some human syndromes are characterized by unique neurological phenotypes including microcephaly, mental retardation, ataxia, neurodegeneration, and neuropathy, suggesting a direct link between genomic instability resulting from defective DDR and neuropathology. In this review, rare human genetic disorders related to abnormal DDR and damage repair with neural defects will be discussed.

360. Genotype/Phenotype Correlation of Cellular Function and AAV-Mediated Gene Delivery to Treat Xeroderma Pigmentosum - Cockayne Syndrome (XP - CS)

Cockayne Syndrome (CS) is a rare, autosomal recessive, neurodegenerative disorder characterized by deficiencies which all contribute to an overall phenotype of premature aging. The underlying cause is a defect in genes involving DNA repair mechanisms. This includes CSA and CSB as well as several genes associated with Xeroderma Pigmentosum (XP). Specifically, Xeroderma Pigmentosum Group G (XPG) is a disorder with two distinct clinical presentations: photosensitivity alone (XP) and photosensitivity with neurodegeneration (XP-CS).XPG's role as an endonuclease in nucleotide excision repair following UV exposure is well-described and explains the photosensitivity phenotype, yet a separate function for XPG that explains the neurological/early aging deficit that occurs in some patients remains obscure. Other CS proteins known to be involved in nuclear DNA repair have been shown to also function as free radical scavengers in mitochondria. As growing bodies of data illustrate the importance of mitochondria in aging, neuronal cell development and maintenance, and tissue repair, we hypothesize that XPG is trafficked to mitochondria where it could play an important role in mitochondrial function via free radical regulation. Such a deficiency could explain the neurodegeneration and multi-system early aging phenotype observed in CS patients. Our preliminary data (expansion rates, oxygen consumption, ATP generation, free radical sensitivity, Metronidazole [a drug that causes liver failure in CS patients] sensitivity) support this hypothesis through demonstration of decreased viability and mitochondrial function in fibroblasts derived from XPG patients displaying the XP-CS phenotype but not in those from patients displaying the XP phenotype alone. Mitochondrial isolations are being performed to confirm the presence of XPG in these organelles, as well as to better evaluate mitochondrial function.These characterizations will be used as outcome measures to determine the efficacy of AAV mediated gene therapy for XP-CS. A functional CMV-XPG plasmid has been cloned, and is being packaged into Adeno-associated virus (AAV). Further analyses in XP and XP-CS patient induced pluripotent stem cells differentiated into neurons and an XPG mouse model which closely replicates the human phenotype will yield useful information regarding the dual roles of this protein and provide data to support translation of gene therapy for CS. If successful, this will be the first therapeutic measure to demonstrate correction of the debilitating effects of XP-CS.

DNA Damage in Major Psychiatric Diseases

Human cells are exposed to exogenous insults and continuous production of different metabolites. These insults and unwanted metabolic products might interfere with the stability of genomic DNA. Recently, many studies have demonstrated that different psychiatric disorders show substantially high levels of oxidative DNA damage in the brain accompanied with morphological and functional alterations. It reveals that damaged genomic DNA may contribute to the pathophysiology of these mental illnesses. In this article, we review the roles of oxidative damage and reduced antioxidant ability in some vastly studied psychiatric disorders and emphasize the inclusion of treatment options involving DNA repair. In addition, while most currently used antidepressants are based on the manipulation of the neurotransmitter regulation in managing different mental abnormalities, they are able to prevent or reverse neurotoxin-induced DNA damage. Therefore, it may be plausible to target on genomic DNA alterations for psychiatric therapies, which is of pivotal importance for future antipsychiatric drug development.

Immunochip analysis identifies association of the RAD50/IL13 region with human longevity.

SummaryHuman longevity is characterized by a remarkable lack of confirmed genetic associations. Here, we report on the identification of a novel locus for longevity in the RAD50/IL13 region on chromosome 5q31.1 using a combined European sample of 3208 long‐lived individuals (LLI) and 8919 younger controls. First, we performed a large‐scale association study on 1458 German LLI (mean age 99.0 years) and 6368 controls (mean age 57.2 years) by targeting known immune‐associated loci covered by the Immunochip. The analysis of 142 136 autosomal single nucleotide polymorphisms (SNPs) revealed an Immunochip‐wide significant signal (PI mmunochip = 7.01 × 10–9) for the SNP rs2075650 in the TOMM40/APOE region, which has been previously described in the context of human longevity. To identify novel susceptibility loci, we selected 15 markers with PI mmunochip < 5 × 10–4 for replication in two samples from France (1257 LLI, mean age 102.4 years; 1811 controls, mean age 49.1 years) and Denmark (493 LLI, mean age 96.2 years; 740 controls, mean age 63.1 years). The association at SNP rs2706372 replicated in the French study collection and showed a similar trend in the Danish participants and was also significant in a meta‐analysis of the combined French and Danish data after adjusting for multiple testing. In a meta‐analysis of all three samples, rs2706372 reached a P‐value of PI mmunochip+Repl = 5.42 × 10−7 (OR = 1.20; 95% CI = 1.12–1.28). SNP rs2706372 is located in the extended RAD50/IL13 region. RAD50 seems a plausible longevity candidate due to its involvement in DNA repair and inflammation. Further studies are needed to identify the functional variant(s) that predispose(s) to a long and healthy life.

PARP-1 inhibition influences the oxidative stress response of the human lens

Poly(ADP-ribose) polymerase-1 (PARP-1) is best characterised for its involvement in DNA repair. PARP-1 activity is also linked to cell fate, confounding its roles in maintaining genome integrity. The current study assessed the functional roles of PARP-1 within human lens cells in response to oxidative stress. The human lens epithelial cell line FHL124 and whole human lens cultures were used as experimental systems. Hydrogen peroxide (H2O2) was employed to induce oxidative stress and cell death was assessed by LDH release. The functional influence of PARP-1 was assessed using targeted siRNA and chemical inhibition (by AG14361). Immunocytochemistry and western blotting were used to assess PARP-1 expression and the alkaline comet assay determined the levels of DNA strand breaks. PARP-1 was generally observed in the cell nucleus in both the FHL124 cell line and whole human lenses. PARP-1 inhibition rendered FHL124 cells more susceptible to H2O2-induced DNA strand breaks. Interestingly, reduction of PARP-1 activity significantly inhibited H2O2-induced cell death relative to control cells. Inhibition of PARP-1 in whole human lenses resulted in a reduced level of lens opacity and cell death following exposure to H2O2 relative to matched pair controls. Thus, we show that PARP-1 could play a role in the fate of human lens cells, and these first observations in human lenses suggest that it could impact on lens opacity. Further studies are required to elucidate the regulatory processes that give rise to these effects.

Synergistic Actions of Ogg1 and Mutyh DNA Glycosylases Modulate Anxiety-like Behavior in Mice.

Ogg1 and Mutyh DNA glycosylases cooperate to prevent mutations caused by 8-oxoG, a major premutagenic DNA lesion associated with cognitive decline. We have examined behavior and cognitive function in mice deficient of these glycosylases. Ogg1(-/-)Mutyh(-/-) mice were more active and less anxious, with impaired learning ability. In contrast, Mutyh(-/-) mice showed moderately improved memory. We observed no apparent change in genomic 8-oxoG levels, suggesting that Ogg1 and Mutyh play minor roles in global repair in adult brain. Notably, transcriptome analysis of hippocampus revealed that differentially expressed genes in the mutants belong to pathways known to be involved in anxiety and cognition. Esr1 targets were upregulated, suggesting a role of Ogg1 and Mutyh in repression of Esr1 signaling. Thus, beyond their involvement in DNA repair, Ogg1 and Mutyh regulate hippocampal gene expression related to cognition and behavior, suggesting a role for the glycosylases in regulating adaptive behavior.

Novel genes associated with lymph node metastasis in triple negative breast cancer.

Triple negative breast cancer (TNBC) is the most aggressive breast cancer subtype with the worst prognosis and no targeted treatments. TNBC patients are more likely to develop metastases and relapse than patients with other breast cancer subtypes. We aimed to identify TNBC-specific genes and genes associated with lymph node metastasis, one of the first signs of metastatic spread. A total of 33 TNBCs were used; 17 of which had matched normal adjacent tissues available, and 15 with matched lymph node metastases. Gene expression microarray analysis was used to reveal genes that were differentially expressed between these groups. We identified and validated 66 genes that are significantly altered when comparing tumours to normal adjacent samples. Further, we identified 83 genes that are associated with lymph node metastasis and correlated these with miRNA-expression. Pathway analysis revealed their involvement in DNA repair, recombination and cell death, chromosomal instability and other known cancer-related pathways. Finally, four genes were identified that were specific for TNBC, of which one was associated with overall survival. This study has identified novel genes involved in LN metastases in TNBC and genes that are TNBC specific that may be used as treatment targets or prognostic indicators in the future.

14-3-3σ confers cisplatin resistance in esophageal squamous cell carcinoma cells via regulating DNA repair molecules.

Esophageal squamous cell carcinoma (ESCC) is the predominant type of esophageal cancer in Asia. Cisplatin is commonly used in chemoradiation for unresectable ESCC patients. However, the treatment efficacy is diminished in patients with established cisplatin resistance. To understand the mechanism leading to the development of cisplatin resistance in ESCC, we compared the proteomes from a cisplatin-resistant HKESC-2R cell line with its parental-sensitive counterpart HKESC-2 to identify key molecule involved in this process. Mass spectrometry analysis detected 14-3-3σ as the most abundant molecule expressed exclusively in HKESC-2R cells, while western blot result further validated it to be highly expressed in HKESC-2R cells when compared to HKESC-2 cells. Ectopic expression of 14-3-3σ increased cisplatin resistance in HKESC-2 cells, while its suppression sensitized SLMT-1 cells to cisplatin. Among the molecules involved in drug detoxification, drug transportation, and DNA repair, the examined DNA repair molecules HMGB1 and XPA were found to be highly expressed in HKESC-2R cells with high 14-3-3σ expression. Subsequent manipulation of 14-3-3σ by both overexpression and knockdown approaches concurrently altered the expression of HMGB1 and XPA. 14-3-3σ, HMGB1, and XPA were preferentially expressed in cisplatin-resistant SLMT-1 cells when compared to those more sensitive to cisplatin. In ESCC patients with poor response to cisplatin-based chemoradiation, their pre-treatment tumors expressed higher expression of HMGB1 than those with response to such treatment. In summary, our results demonstrate that 14-3-3σ induces cisplatin resistance in ESCC cells and that 14-3-3σ-mediated cisplatin resistance involves DNA repair molecules HMGB1 and XPA. Results from this study provide evidences for further work in researching the potential use of 14-3-3σ and DNA repair molecules HMGB1 and XPA as biomarkers and therapeutic targets for ESCC.

Benzimidazole derivatives as potential dual inhibitors for PARP-1 and DHODH

Poly (ADP-ribose) polymerases (PARPs) play diverse roles in various cellular processes that involve DNA repair and programmed cell death. Amongst these polymerases is PARP-1 which is the key DNA damage-sensing enzyme that acts as an initiator for the DNA repair mechanism. Dihydroorotate dehydrogenase (DHODH) is an enzyme in the pyrimidine biosynthetic pathway which is an important target for anti-hyperproliferative and anti-inflammatory drug design. Since these enzymes share a common role in the DNA replication and repair mechanisms, it may be beneficial to target both PARP-1 and DHODH in attempts to design new anti-cancer agents.Benzimidazole derivatives have shown a wide variety of pharmacological activities including PARP and DHODH inhibition. We hereby report the design, synthesis and bioactivities of a series of benzimidazole derivatives as inhibitors of both the PARP-1 and DHODH enzymes.

Evaluating the Role of Histone H2A Variants and Epigenetic Modification in the DNA Repair System of Bdelloid Rotifers

Bdelloid rotifers are microscopic invertebrates with an extraordinary ability to repair DNA double strand breaks (DSBs) induced by high doses of ionizing radiation. This DNA repair mechanism, although not well understood, likely evolved to allow bdelloids to recover from desiccation-induced DSBs. Interestingly, bdelloids possess histone H2A variants that are distinct from canonical H2A in that the proteins have longer C-terminal tails than those of other eukaryotes. Extended C-terminal tails are prospective targets for post-translational modifications (PTMs), which might facilitate DNA repair. The objective of this project was to use gene expression studies and high-resolution mass spectrometry (HR-MS) to investigate the role of bdelloid-specific H2A variants during DNA repair. To induce DSBs, the bdelloid Adineta vaga was exposed to 280 Gray of ionizing radiation. Following irradiation, RNA was extracted at time intervals and used for quantitative real-time PCR. Genes encoding H2Abd2 and putative H2AX were upregulated following irradiation, while other histone genes (H2B, H3, H4) were unaffected. This implies an involvement for H2A variants in DNA repair. Following irradiation, histones were also purified and subjected to HR-MS to identify relative protein quantities and PTMs in irradiated and non-irradiated bdelloids. Five H2A variants were identified and several PTMs appear to be novel to bdelloids and are candidates for involvement in DNA repair. Identifying PTM combinations and comparing those to patterns in other eukaryotes will establish the histone code for bdelloids and begin to elucidate the role for these proteins in DNA repair. This work was supported by grants from the NCRR (5P20RR016460) & NIGMS (8P20GM103429) from the NIH.