DNA Damage Recognition Research Articles

SIRT1 siRNA-loaded lipid nanoparticles enhanced doxorubicin-induced cell death in prostate cancer cell lines

Most chemotherapeutics induce apoptosis by creating DNA damage in tumor cells. However, high expression of Sirtuin 1 (SIRT1), which is a histone deacetylase activates DNA repair mechanisms leading to the repair of chemotherapeutic-induced DNA damage and subsequently prevention of apoptosis. Therefore, inhibition of SIRT1 is a useful strategy in cancer therapy to achieve a more efficient eradication of tumor cells.In this study, novel lipoplexes composed of 1,2-di-O-octadecenyl-3-trimethylammonium propane (DOTMA) containing lipid nanoparticles and SIRT1 siRNA have been formulated by the freeze-drying method. SIRT1 silencing effect has been demonstrated by a 2.5- to 4- fold decrease in mRNA and protein expression levels. The efficiency of the lipoplexes to enhance the activity of doxorubicin, a DNA damage-inducing chemotherapeutic agent, has been studied on prostate cancer cell lines with different p53 expression patterns, namely LNCaP, DU145, and PC3. SIRT1 silencing by lipoplexes enhanced DNA damage recognition and increased the activity of doxorubicin on cancer cell death. These results have shown that SIRT1 siRNA-loaded lipid nanoparticles can enhance the efficiency of doxorubicin on prostate cancer cell lines.

Pharmacological Activation of Autophagy Restores Cellular Homeostasis in Ultraviolet-(B)-Induced Skin Photodamage.

Ultraviolet (UV) exposure to the skin causes photo-damage and acts as the primary etiological agent in photo-carcinogenesis. UV-B exposure induces cellular damage and is the major factor challenging skin homeostasis. Autophagy allows the fundamental adaptation of cells to metabolic and oxidative stress. Cellular dysfunction has been observed in aged tissues and in toxic insults to cells undergoing stress. Conversely, promising anti-aging strategies aimed at inhibiting the mTOR pathway have been found to significantly improve the aging-related disorders. Recently, autophagy has been found to positively regulate skin homeostasis by enhancing DNA damage recognition. Here, we investigated the geno-protective roles of autophagy in UV-B-exposed primary human dermal fibroblasts (HDFs). We found that UV-B irradiation to HDFs impairs the autophagy response in a time- and intensity-independent manner. However, improving autophagy levels in HDFs with pharmacological activators regulates the UV-B-induced cellular stress by decreasing the induction of DNA photo-adducts, promoting the DNA repair process, alleviating oxidative and ER stress responses, and regulating the expression levels of key cell cycle regulatory proteins. Autophagy also prevents HDFs from UV-B-induced nuclear damage as is evident in TUNEL assay and Acridine Orange/Ethidium Bromide co-staining. Salubrinal (an eIF2α phosphatase inhibitor) relieves ER stress response in cells and also significantly alleviates DNA damage and promotes the repair process in UV-B-exposed HDFs. P62-silenced HDFs show enhanced DNA damage response and also disturb the tumor suppressor PTEN/pAKT signaling axis in UV-B-exposed HDFs whereas Atg7-silenced HDFs reveal an unexpected consequence by decreasing the UV-B-induced DNA damage. Taken together, these results suggest that interventional autophagy offers significant protection against UV-B radiation-induced photo-damage and holds great promise in devising it as a suitable therapeutic strategy against skin pathological disorders.

Hsa_circ_0069244 acts as the sponge of miR-346 to inhibit non-small cell lung cancer progression by regulating XPC expression

Circular RNAs (circRNAs) play a significant role in the progression of diverse malignancies. Here, we aimed to probe the function and mechanism of circ_0069244 in non-small cell lung cancer (NSCLC). In the present study, circ_0069244 was selected from the circRNA microarray datasets (GSE112214). Quantitative real-time polymerase chain reaction (qRT-PCR) was applied to examine circ_0069244, miR-346 and XPC complex subunit, DNA damage recognition and repair factor (XPC) expression levels. Kaplan-Meier curve was employed to analyze the association between circ_0069244 expression and overall survival of NSCLC patients. Cell counting kit-8 (CCK-8) and 5-Bromo-2'-deoxyuridine (BrdU) experiments were utilized to examine the proliferation of NSCLC cells. Scratch healing and Transwell experiments were executed to examine the migration of NSCLC cells. Western blot was conducted to detect XPC expression at protein level in NSCLC cells. Bioinformatics analysis, dual-luciferase reporter gene and RNA immunoprecipitation (RIP) experiments predicted and validated the targeting relationships of circ_0069244 and miR-346, as well as miR-346 and 3'untranslated region (UTR) of XPC mRNA, respectively. We reported that circ_0069244 was remarkably down modulated in NSCLC and was linked to shorter survival and poor tumor histological grade in NSCLC patients. Functionally, circ_0069244 repressed NSCLC cell proliferation and migration. Furthermore, miR-346-5p was unveiled to be a downstream target of circ_0069244, and miR-346-5p specifically modulated XPC expression. Rescue experiments indicated that the inhibitory effect of circ_0069244 was abolished by co-expression of miR-346-5p mimics. Taken together, circ_0069244 restrained NSCLC progression by modulating the miR-346-5p/XPC axis.

Human Radiosensitivity and Radiosusceptibility: What Are the Differences?

The individual response to ionizing radiation (IR) raises a number of medical, scientific, and societal issues. While the term “radiosensitivity” was used by the pioneers at the beginning of the 20st century to describe only the radiation-induced adverse tissue reactions related to cell death, a confusion emerged in the literature from the 1930s, as “radiosensitivity” was indifferently used to describe the toxic, cancerous, or aging effect of IR. In parallel, the predisposition to radiation-induced adverse tissue reactions (radiosensitivity), notably observed after radiotherapy appears to be caused by different mechanisms than those linked to predisposition to radiation-induced cancer (radiosusceptibility). This review aims to document these differences in order to better estimate the different radiation-induced risks. It reveals that there are very few syndromes associated with the loss of biological functions involved directly in DNA damage recognition and repair as their role is absolutely necessary for cell viability. By contrast, some cytoplasmic proteins whose functions are independent of genome surveillance may also act as phosphorylation substrates of the ATM protein to regulate the molecular response to IR. The role of the ATM protein may help classify the genetic syndromes associated with radiosensitivity and/or radiosusceptibility.

Abstract 3064: Investigation of ionizing radiation response in new resistance models of glioblastoma

Abstract Glioblastoma is one of the most aggressive central nervous system tumors, which constitutes 50% of all primary brain tumors. Glioblastomas have a very poor prognosis, approximately 12-15 months even with standard therapy. Current treatment protocols include surgery, chemotherapy, and radiotherapy. High rates of recurrence after treatment, genetic heterogeneity, and developing resistance to chemotherapy and radiotherapy are challenges to overcome in glioblastoma treatment. Therefore, developing models of chemo- or radio-resistance is of priority to understand the molecular mechanisms that operate during the transition of cells to therapy-refractory state, and to develop new therapeutic approaches. In this study, we generated ionizing radiation (IR)-exposed glioblastoma cell populations to investigate molecular alterations associated with acquired radiotherapy resistance. To generate a clinically relevant radioresistance model, we have exposed glioblastoma cells to a total dose of 60 Gy IR over a 6-week period and cultured age-matched parental cells. We successfully generated sustainable radioresistant cells, as demonstrated by cell viability and colony formation assays. RNA sequencing, performed on these matched cell lines revealed major alterations in the expression of genes of the cell cycle, DNA damage recognition, and repair machinery in the radioresistant cells. Specifically, elements of the DNA double strand break (DSB) recognition and repair, such as ATM, ATR, and CHK1 were markedly upregulated in the radioresistant cell populations. In line with these findings, DNA repair capacity of the radioresistant cell populations was increased, as revealed by the faster clearance of H2AX and 53BP1 in the radioresistant populations. Complementing this approach, pharmacological inhibition of major DNA damage response elements, such as ATM, ATR, as well as CHK1 markedly sensitized the radioresistant cells. Our results prepare a groundwork for studying the molecular mechanisms of radiotherapy resistance and developing novel combination therapy strategies for glioblastomas. Citation Format: Nareg Pinarbasi, Tugba Bagci-Onder, Ilknur Sur Erdem, Ugur Selek. Investigation of ionizing radiation response in new resistance models of glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3064.

The correlation between polymorphisms in the XPC gene and glioma susceptibility in a Chinese pediatric population

BackgroundA previous study revealed that single nucleotide polymorphisms (SNPs) in coding genes play a key role in tumorigenesis, genetic disorders, and drug resistance. Xeroderma pigmentosum group C (XPC) protein is a key DNA damage recognition factor that is required for maintaining the genomic stability. However, the correlation between XPC polymorphisms and glioma susceptibility is still unclear. Hence, this study aimed to investigate the correlation between XPC polymorphisms and pediatric glioma susceptibility.MethodsA total of 399 participants (171 glioma patients and 228 controls) were enrolled to evaluate the correlation between XPC polymorphism and pediatric glioma susceptibility. The count data of two groups was analyzed by chi-squared (χ2) test. Moreover, logistic regression was used to assess the strength of XPC polymorphisms associated with glioma susceptibility.ResultsWe identified that XPC rs1870134 G>C reduced pediatric glioma susceptibility. Compared to participants with rs1870134 GG/GC genotypes, those with rs1870134 CC genotype had a significantly lower risk for glioma [adjusted odds ratio (AOR) =0.10, 95% confidence interval (CI): 0.01 to 0.78, P=0.028]. Patients with 4–5 genotypes have higher risk of glioma than those with 0–3 genotypes (AOR =1.59, 95% CI: 1.04 to 2.43, P=0.031). The stratified analysis showed that the risky effects of rs2228000 CT/TT genotypes and rs2229090 GC/CC genotypes were more predominant among children aged ≥60 months, astrocytic tumors, and clinical stage I.ConclusionsWe found for the first time that XPC polymorphisms had a statistically significant correlation with pediatric glioma susceptibility in a Chinese population. The XPC rs2228000 CT/TT and rs2229090 GC/CC genotypes could both increase the risk of pediatric glioma in subgroups with females, astrocytic tumors, and clinical stage I. The XPC polymorphism has potential to be a useful adjunct method to screen pediatric glioma.

Integrated Analyses Reveal the Multi-Omics and Prognostic Characteristics of ATP5B in Breast Cancer.

The beta subunit of F1Fo-ATP synthase (ATP5B) has been demonstrated to play an essential role in tumor progression and metastasis. However, there has been no comprehensive pan-cancer multi-omics analysis of ATP5B, while the clinical relevance of ATP5B and its potential mechanism in regulating breast cancer are still poorly understood. In this study, we demonstrated that ATP5B has a higher frequency of amplification than deletion in most cancer types, and the copy number variation (CNV) of ATP5B was significantly positively correlated with its mRNA expression level. DNA methylation analysis across pan-cancer also revealed a strong correlation between ATP5B expression and epigenetic changes. We identified 6 significant methylation sites involved in the regulation of ATP5B expression. Tissue microarrays (TMA) from 129 breast cancer samples, integrated with multiple additional breast cancer dataset, were used to evaluate the ATP5B expression and its correlation with prognosis. Higher levels of ATP5B expression were consistently associated with a worse OS in all datasets, and Cox regression analysis suggested that ATP5B expression was an independent prognostic factor. Gene enrichment analysis indicated that the gene signatures of DNA damage recognition, the E-cadherin nascent pathway and the PLK1 pathway were enriched in ATP5B-high patients. Moreover, somatic mutation analysis showed that a significant different mutation frequency of CDH1 and ADAMTSL3 could be observed between the ATP5B-high and ATP5B-low groups. In conclusion, this study reveals novel significance regarding the genetic characteristics and clinical value of ATP5B highlighted in predicting the outcome of breast cancer patients.

Phosphorylation of histone H2A.X as a DNA‑associated biomarker (Review)

The complex genomic structure of eukaryotic cells is primarily achieved by the binding of DNA to histones. Different members of the histone families form a complex with genomic DNA and, as a nucleosome, constitute the functional unit of chromatin. In addition to their structural functionality, histones are also involved in other molecular mechanisms, such as DNA damage recognition and repair. A very important factor of DNA damage management is the histone H2A.X. The phosphorylation of H2A.X initiates various processes of the DNA repair systems and plays significant roles in cellular regulation. The H2A.X phosphorylation status represents a central sum parameter for genome integrity and allows conclusions to be drawn about DNA‑associated processes in cells and tissues. As a biomarker for DNA damage and genotoxicity, as well as a clinical marker for radiotherapy outcome, drug efficacy and tissue regeneration, the H2A.X phosphorylation status represents an effective biomarker for current and future biomedical applications. The present brief review article provides an overview of the various molecular functions and cellular events in which the phosphorylation of histone H2A.X can occur.

515 p63 regulates XPC binding dynamics and global nucleotide excision repair in keratinocytes

The p63 transcription factor, critical for epidermal development, also regulates the response to DNA damage, including global nucleotide excision repair (NER) efficiency. We have reported that vitamin D receptor (VDR) is also required for efficient global NER of ultraviolet radiation (UV)-induced 6-4 pyrimidine-pyrimidone photoproducts and for releasing XPC—the initial ultraviolet radiation (UV)-induced DNA damage recognition sensor—from DNA damage. Since p63 and VDR have been reported to regulate each other, we assessed p63’s effect on XPC binding and dissociation. TERT-immortalized keratinocytes expressing shRNA targeting all isoforms of p63 exhibited reduced levels of VDR relative to non-targeting controls. Upon UV irradiation through 3 μm pores in otherwise opaque filters to create sub-nuclear focal spots of DNA damage, keratinocytes depleted of p63 exhibited slower removal of 6-4 photoproducts than control cells over 90 minutes. Co-staining with antibodies to XPC revealed that XPC rapidly accumulated at DNA damage foci, peaking within 15 minutes and gradually fading over 90 minutes as NER proceeded in control keratinocytes. In p63-depleted keratinocytes, XPC associated with DNA damage with comparable efficiency, but the dissociation of XPC was delayed so that substantially more XPC was retained at 30 minutes than in control cells. These results support a model where XPC dissociation is necessary for normal completion of subsequent NER steps and confirm our previous observations that p63 is important for efficient removal of UV-induced DNA damage. The results recapitulate those in keratinocytes depleted of VDR and are consistent with crosstalk between p63 and VDR in promoting normal dissociation of XPC from damaged DNA such that absence of either p63 or VDR can lead to non-productive binding of XPC and reduced NER. These results further link two important regulators of epidermal growth and differentiation to DNA repair.

USP44 Stabilizes DDB2 to Facilitate Nucleotide Excision Repair and Prevent Tumors.

Nucleotide excision repair (NER) is a pathway involved in the repair of a variety of potentially mutagenic lesions that distort the DNA double helix. The ubiquitin E3-ligase complex UV-DDB is required for the recognition and repair of UV-induced cyclobutane pyrimidine dimers (CPDs) lesions through NER. DDB2 directly binds CPDs and subsequently undergoes ubiquitination and proteasomal degradation. DDB2 must remain on damaged chromatin, however, for sufficient time to recruit and hand-off lesions to XPC, a factor essential in the assembly of downstream repair components. Here we show that the tumor suppressor USP44 directly deubiquitinates DDB2 to prevent its premature degradation and is selectively required for CPD repair. Cells lacking USP44 have impaired DDB2 accumulation on DNA lesions with subsequent defects in XPC retention. The physiological importance of this mechanism is evident in that mice lacking Usp44 are prone to tumors induced by NER lesions introduced by DMBA or UV light. These data reveal the requirement for highly regulated ubiquitin addition and removal in the recognition and repair of helix-distorting DNA damage and identify another mechanism by which USP44 protects genomic integrity and prevents tumors.

P53 long noncoding RNA regulatory network in cancer development.

The protein p53 as a transcription factor with strong tumor-suppressive activities is known to trigger apoptosis via multiple pathways and is directly involved in the recognition of DNA damage and DNA repair processes. P53 alteration is now recognized as a common event in the pathogenesis of many types of human malignancies. Deregulation of tumor suppressor p53 pathways plays an important role in the activation of cell proliferation or inactivation of apoptotic cell death during carcinogenesis and tumor progression. Mounting evidence indicates that the p53 status of tumors and also the regulatory functions of p53 may be relevant to the long noncoding RNAs (lncRNA)-dependent gene regulation programs. Besides coding genes, lncRNAs that do not encode for proteins are induced or suppressed by p53 transcriptional response and thus control cancer progression. LncRNAs also have emerged as key regulators that impinge on the p53 signaling network orchestrating global gene-expression profile. Studies have suggested that aberrant expression of lncRNAs as a molecular-genomic signature may play important roles in cancer biology. Accordingly, it is important to elucidate the mechanisms by which the crosstalk between lncRNAs and p53 occurs in the development of numerous cancers. Here, we review how several classes of lncRNAs and p53 pathways are linked together in controlling the cell cycle and apoptosis in various cancer cells in both human and mouse model systems.

Assessing the sequence dependence of pyrimidine–pyrimidone (6–4) photoproduct in a duplex double-stranded DNA: A pitfall for microsecond range simulation

Sequence dependence of the (6-4) photoproduct conformational landscape when embedded in six 25-bp duplexes is evaluated along extensive unbiased and enhanced (replica exchange with solute tempering, REST2) molecular dynamics simulations. The structural reorganization as the central pyrimidines become covalently tethered is traced back in terms of non-covalent interactions, DNA bending, and extrusion of adenines of the opposite strands. The close sequence pattern impacts the conformational landscape around the lesion, inducing different upstream and downstream flexibilities. Moreover, REST2 simulations allow us to probe structures possibly important for damaged DNA recognition.

Genetic deletion of Nox4 enhances cancerogen-induced formation of solid tumors

Reactive oxygen species (ROS) can cause cellular damage and promote cancer development. Besides such harmful consequences of overproduction of ROS, all cells utilize ROS for signaling purposes and stabilization of cell homeostasis. In particular, the latter is supported by the NADPH oxidase 4 (Nox4) that constitutively produces low amounts of H2O2 By that mechanism, Nox4 forces differentiation of cells and prevents inflammation. We hypothesize a constitutive low level of H2O2 maintains basal activity of cellular surveillance systems and is unlikely to be cancerogenic. Utilizing two different murine models of cancerogen-induced solid tumors, we found that deletion of Nox4 promotes tumor formation and lowers recognition of DNA damage. Nox4 supports phosphorylation of H2AX (γH2AX), a prerequisite of DNA damage recognition, by retaining a sufficiently low abundance of the phosphatase PP2A in the nucleus. The underlying mechanism is continuous oxidation of AKT by Nox4. Interaction of oxidized AKT and PP2A captures the phosphatase in the cytosol. Absence of Nox4 facilitates nuclear PP2A translocation and dephosphorylation of γH2AX. Simultaneously AKT is left phosphorylated. Thus, in the absence of Nox4, DNA damage is not recognized and the increased activity of AKT supports proliferation. The combination of both events results in genomic instability and promotes tumor formation. By identifying Nox4 as a protective source of ROS in cancerogen-induced cancer, we provide a piece of knowledge for understanding the role of moderate production of ROS in preventing the initiation of malignancies.

Genome-wide landscape of mRNAs, microRNAs, lncRNAs, and circRNAs in hemorrhagic shock-induced ALI/ARDS in rats.

Hemorrhagic shock (HS) can develop into multiple organ dysfunction syndrome, among which acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) usually lead to poor outcomes. The underlying molecular mechanisms of HS-induced ALI/ARDS remain unclear. This study sought to investigate gene expression profiles and predict competing endogenous RNA (ceRNA) regulatory networks in an HS-induced ALI/ARDS preclinical model. Sprague Dawley rats were subjected to a fixed volume of hemorrhage (HS, 40% estimated total blood volume) or not (sham) randomly. After 8 hours of observation, left lung tissue was harvested to evaluate lung injury. Right lung was collected for RNA sequencing. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses were performed and the long noncoding RNA (lncRNA)/circular RNA (circRNA)-microRNA (miRNA)-messenger RNA (mRNA) linkages were predicted using the ceRNA theory. Quantitative real-time polymerase chain reaction was used to validate the RNA sequencing findings. Hemorrhagic shock lungs showed noticeable ALI/ARDS features, and 437 mRNAs, 31 miRNAs, 734 lncRNAs, and 29 circRNAs were differentially expressed. In Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses, the differentially expressed transcripts were enriched in the following terms: the metabolic pathways, signal transduction pathways, necroptosis, DNA damage recognition and repair, inflammatory cell migration and chemotaxis, the NOD-like receptor signaling pathway, the Janus kinase/signal transducer and activator of transcription signaling pathway, the mitogen-activated protein kinase signaling pathway, the phosphatidylinositol-3-kinase/protein kinase B signaling pathway, and so on. Also, this study identified lncRNA-miRNA-mRNA linkages with 12 lncRNAs, 5 miRNAs, 15 mRNAs, and circRNA-miRNA-mRNA linkages with 10 circRNAs, 16 miRNAs, 39 mRNAs. These networks might play important regulatory roles. This is the first high-throughput analysis of gene expression profiles in HS-induced ALI/ARDS. It shows that metabolism, cell signaling, DNA damage and repair, and necroptosis-related RNAs altered, and inflammatory response-associated RNAs and pathways have pivotal roles in HS-induced ALI/ARDS progression. It also prompts some important RNAs and regulatory networks for future research. Basic science article.

A Targeted and Tuneable DNA Damage Tool Using CRISPR/Cas9.

Mammalian cells are constantly subjected to a variety of DNA damaging events that lead to the activation of DNA repair pathways. Understanding the molecular mechanisms of the DNA damage response allows the development of therapeutics which target elements of these pathways. Double-strand breaks (DSB) are particularly deleterious to cell viability and genome stability. Typically, DSB repair is studied using DNA damaging agents such as ionising irradiation or genotoxic drugs. These induce random lesions at non-predictive genome sites, where damage dosage is difficult to control. Such interventions are unsuitable for studying how different DNA damage recognition and repair pathways are invoked at specific DSB sites in relation to the local chromatin state. The RNA-guided Cas9 (CRISPR-associated protein 9) endonuclease enzyme is a powerful tool to mediate targeted genome alterations. Cas9-based genomic intervention is attained through DSB formation in the genomic area of interest. Here, we have harnessed the power to induce DSBs at defined quantities and locations across the human genome, using custom-designed promiscuous guide RNAs, based on in silico predictions. This was achieved using electroporation of recombinant Cas9-guide complex, which provides a generic, low-cost and rapid methodology for inducing controlled DNA damage in cell culture models.

Vitamin D Receptor Promotes Global Nucleotide Excision Repair by Facilitating XPC Dissociation from Damaged DNA

Vitamin D receptor (VDR) is important for normal DNA repair, although the mechanism by which it acts is unclear. After focal UV irradiation to create subnuclear spots of DNA damage, epidermal keratinocytes from VDR-null mice as well as human epidermal keratinocytes depleted of VDR with small interfering RNA removed pyrimidine-pyrimidone (6-4) photoproducts more slowly than control cells. Costaining with antibodies to XPC, the DNA damage recognition sensor that initiates nucleotide excision repair, showed that XPC rapidly accumulated at spots of damage and gradually faded in control human keratinocytes. In VDR-depleted keratinocytes, XPC associated with DNA damage with comparable efficiency; however, XPC's dissociation dynamics were altered so that significantly more XPC was bound and retained over time than in control cells. The XPF endonuclease, which acts subsequently in nucleotide excision repair, bound and dissociated with comparable kinetics in control and VDR-depleted cells, but the extent of binding was reduced in the latter. These results as well as kinetic modeling of the data suggest that VDR's importance in the repair of UV-induced DNA damage is mediated in part by its ability to facilitate the dissociation of XPC from damaged DNA for the normal recruitment and assembly of other repair proteins to proceed.

Evaluation of the geroprotective effects of withaferin A in Drosophila melanogaster.

Withanolides are a class of compounds usually found in plant extracts which are an attractive geroprotective drug design starting point. We evaluated the geroprotective properties of Withaferin A (WA) in vivo using the Drosophila model. Flies were supplemented by nutrient medium with WA (at a concentration of 1, 10, or 100 μM dissolved in ethanol) for the experiment group and 30 μM of ethanol for the control group. WA treatment at 10 and 100 μM concentrations prolong the median life span of D. melanogaster’s male by 7.7, 9.6% (respectively) and the maximum life span (the age of death 90% of individuals) by 11.1% both. Also WA treatment at 1, 10 and 100 μM improved the intestinal barrier permeability in older flies and affected an expression of genes involved in antioxidant defense (PrxV), recognition of DNA damage (Gadd45), heat shock proteins (Hsp68, Hsp83), and repair of double-strand breaks (Ku80). WA was also shown to have a multidirectional effect on the resistance of flies to the prooxidant paraquat (oxidative stress) and 33° C hyperthermia (heat shock). WA treatment increased the resistance to oxidative stress in males at 4 and 7 week old and decreased it at 6 weeks old. It increased the male’s resistance to hyperthermia at 2, 4 and 7 weeks old and decreased it at 3, 5 and 8 weeks old. WA treatment decreased the resistance to hyperthermia in females at 1, 2 and 3 weeks old and not affected on their resistance to oxidative stress.

MRN complex is an essential effector of DNA damage repair.

Genome stability can be threatened by both endogenous and exogenous agents. Organisms have evolved numerous mechanisms to repair DNA damage, including homologous recombination (HR) and non-homologous end joining (NHEJ). Among the factors associated with DNA repair, the MRE11-RAD50-NBS1 (MRN) complex (MRE11-RAD50-XRS2 in Saccharomyces cerevisiae) plays important roles not only in DNA damage recognition and signaling but also in subsequent HR or NHEJ repair. Upon detecting DNA damage, the MRN complex activates signaling molecules, such as the protein kinase ataxia-telangiectasia mutated (ATM), to trigger a broad DNA damage response, including cell cycle arrest. The nuclease activity of the MRN complex is responsible for DNA end resection, which guides DNA repair to HR in the presence of sister chromatids. The MRN complex is also involved in NHEJ, and has a species-specific role in hairpin repair. This review focuses on the structure of the MRN complex and its function in DNA damage repair.

A DNA Damage-Repair Dynamic Model for HRS/IRR Effects of C.elegans Induced by Neutron Irradiation.

Neutron irradiation which could trigger severe biological effects, is being applied in nuclear plants, radiotherapy, and aerospace gradually. Low dose hyper-radiosensitivity response of low Linear Energy Transfer (LET) irradiation on the cell survival has become a matter of great interest since its discovery, but a few research have been done on this response induced by neutron irradiation. To investigate this response induced by neutron irradiation, Caenorhabditis elegans (C. elegans) was irradiated by neutron irradiation. The surviving fraction of C. elegans on the 12th day after irradiation was analyzed, which showed a hyper-radiosensitive response at low doses and followed by an increase in survival fraction at slightly higher doses. The finding of this work that neutron irradiation decreased the surviving fraction in a non-dose-dependent manner was different from previous low-LET irradiation studies. To understand the experimental results, a DNA damage-repair model was introduced. By comparing experimental results with theoretical analyses, we suggest that the low dose hyper-radiosensitivity response of neutron irradiation may possible related to different radiation types and DNA damage recognition proteins and immune system of C. elegans.

The shaping of a molecular linguist: How a career studying DNA energetics revealed the language of molecular communication

My personal and professional journeys have been far from predictable based on my early childhood. Owing to a range of serendipitous influences, I miraculously transitioned from a rebellious, apathetic teenage street urchin who did poorly in school to a highly motivated, disciplined, and ambitious academic honors student. I was the proverbial “late bloomer.” Ultimately, I earned my PhD in biophysical chemistry at Yale, followed by a postdoc fellowship at Berkeley. These two meccas of thermodynamics, coupled with my deep fascination with biology, instilled in me a passion to pursue an academic career focused on mapping the energy landscapes of biological systems. I viewed differential energetics as the language of molecular communication that would dictate and control biological structures, as well as modulate the modes of action associated with biological functions. I wanted to be a “molecular linguist.” For the next 50 years, my group and I used a combination of spectroscopic and calorimetric techniques to characterize the energy profiles of the polymorphic conformational space of DNA molecules, their differential ligand-binding properties, and the energy landscapes associated with mutagenic DNA damage recognition, repair, and replication. As elaborated below, the resultant energy databases have enabled the development of quantitative molecular biology through the rational design of primers, probes, and arrays for diagnostic, therapeutic, and molecular-profiling protocols, which collectively have contributed to a myriad of biomedical assays. Such profiling is further justified by yielding unique energy-based insights that complement and expand elegant, structure-based understandings of biological processes.