Who's on first in the cellular response to DNA damage?

Endonucleosis mediates internalization of cytoplasm into the nucleus

Setd8 regulates transcription elongation, mitotic DNA condensation, DNA damage response and replication licensing. Here we show that, in mitogen-stimulated liver-specific Setd8-KO mice, most of the hepatocytes are eliminated by necrosis but a significant number of them survive via entering a stage exhibiting several senescence-related features. Setd8-deficient hepatocytes had enlarged nuclei, chromosomal hyperploidy and nuclear engulfments progressing to the formation of intranuclear vesicles surrounded by nuclear lamina. These vesicles contain glycogen, cytoplasmic proteins and even entire organelles. We term this process "endonucleosis". Intranuclear vesicles are absent in hepatocytes of Setd8/Atg5 knockout mice, suggesting that the process requires the function of the canonical autophagy machinery. Endonucleosis and hyperploidization are temporary, early events in the surviving Setd8-deficient cells. Larger vesicles break down into microvesicles over time and are eventually eliminated. The results reveal sequential events in cells with extensive DNA damage, which function as part of survival mechanisms to prevent necrotic death.

N-acetylcysteine as a novel methacrylate-based resin cement component: effect on cell apoptosis and genotoxicity in human gingival fibroblasts

BACKGROUND

N-acetylcysteine (NAC) reduces the cytotoxicity and genotoxicity induced by monomers leached from dental composite resins. Herein, we investigated the effects of methacrylate-based resin cement used in dental implant restoration on apoptosis and genotoxicity, as well as the antiapoptotic and antigenotoxic capabilities of its component, NAC.

METHODS

The antioxidant NAC (0.1 or 1 wt.%) was experimentally incorporated into the methacrylate-based dental resin cement Premier®. The Premier® + NAC (0.1 or 1 wt.%) mixture was subsequently immersed into Dulbecco's modified Eagle's medium for 72 h, and used to treat human gingival fibroblasts (HGFs). The viability of HGFs was determined using the XTT assay. The formation of deoxyribonucleic acid (DNA) double-strand breaks (DNA-DSBs) was determined using a γ-H2AX assay. Reactive oxygen species (ROS), apoptosis, necrosis, and cell cycles were detected and analyzed using flow cytometry.

RESULTS

The eluate of Premier® significantly inhibited HGF proliferation in vitro by promoting a G1-phase cell cycle arrest, resulting in cell apoptosis. Significant ROS production and DNA-DSB induction were also found in HGFs exposed to the eluate. Incorporating NAC (1 wt.%) into Premier® was found to reduce cell cytotoxicity, the percentage of G1-phase cells, cell apoptosis, ROS production, and DNA-DSB induction.

CONCLUSION

Incorporating NAC (1 wt.%) into methacrylate-based resin cement Premier® decreases the cell cytotoxicity, ROS production, and DNA-DSBs associated with resin use, and further offers protective effects against the early stages of cell apoptosis and G1-phase cell cycle arrest in HGFs. Overall, our in vitro results indicate that the addition of NAC into methacrylate-based resin cements may have clinically beneficial effects on the cytotoxicity and genotoxicity of these materials.

Generation and Repair of Postreplication Gaps in Escherichia coli

When replication forks encounter template lesions, one result is lesion skipping, where the stalled DNA polymerase transiently stalls, disengages, and then reinitiates downstream to leave the lesion behind in a postreplication gap. Despite considerable attention in the 6 decades since postreplication gaps were discovered, the mechanisms by which postreplication gaps are generated and repaired remain highly enigmatic. This review focuses on postreplication gap generation and repair in the bacterium Escherichia coli. New information to address the frequency and mechanism of gap generation and new mechanisms for their resolution are described. There are a few instances where the formation of postreplication gaps appears to be programmed into particular genomic locations, where they are triggered by novel genomic elements.

Effects of antimony exposure on DNA damage and genome-wide variation in zebrafish (Danio rerio) liver

Antimony (Sb) is a potentially toxic and carcinogenic cumulative contaminant that poses a serious threat to aquatic ecosystems. To better clarify the genotoxicity of Sb and its mechanism of action. In this study, we investigated DNA damage and genome-wide variation in the liver of a model organism, zebrafish (Danio rerio), under subacute Sb exposure and explored its potential toxicological mechanisms. The results showed that medium and high concentrations of Sb significantly reduced the total antioxidant capacity and increased the content of reactive oxygen species in zebrafish liver, and further studies revealed that it increased oxidative DNA damage and DNA-DNA cross-link (DDC), but had little effect on DNA-protein cross-link (DPC). The result of resequencing showed that the mutation sites of the genes with high concentrations of Sb were higher than those with medium concentrations, and the mutation was mainly a single nucleotide. The pathways significantly enriched for nonsynonymous single nucleotide polymorphisms (SNPs) and insertion/deletion mutations (InDels) variant genes in the coding regions of both the medium and high Sb-treated groups were ECM-receptor interactions, and the high Sb-treated group also included lysine degradation, hematopoietic cell lineage, and cytokine-cytokine receptor interactions. This suggests that ECM-receptor interactions play an important role in the mechanism of antimony toxicity to the liver of zebrafish.

miR-33b in human cancer: Mechanistic and clinical perspectives

The microRNAs (miRNAs), an extensive class of small noncoding RNAs (∼22 nucleotides), have been shown to have critical functions in various biological processes during development. miR-33b (or hsa-miR-33b) is down-regulated in cancer of multiple systems. Notably, at least 27 protein-coding genes can be targeted by miR-33b. miR-33b regulates the cell cycle, cell proliferation, various metabolism pathways, epithelial-mesenchymal transition (EMT), cancer cell invasion and migration, etc. In prostate cancer, Cullin 4B (CUL4B) can be recruited to the promoter to inhibit the expression of miR-33b. In gastric cancer, the hypermethylation of the CpG island regulated the expression of miR-33b. Besides, miR-33b could be negatively regulated by 7 competing-endogenous RNAs (ceRNAs), which are all long non-coding RNAs (lncRNAs). There are at least 4 signaling pathways, including NF-κB, MAP8, Notch1, and Wnt/β-catenin signaling pathways, which could be regulated partially by miR-33b. Additionally, low expression of miR-33b was associated with clinicopathology and prognosis in cancer patients. In addition, the aberrant expression of miR-33b was connected with the resistance of cancer cells to 5 anticancer drugs (cisplatin, docetaxel, bortezomib, paclitaxel, and daunorubicin). Importantly, our work systematically summarizes the aberrant expression of miR-33b in various neoplastic diseases and the effect of its downregulation on the biological behavior of cancer cells. Furthermore, this review focuses on recent advances in understanding the molecular regulation mechanisms of miR-33b. Moreso, the relationship between the miR-33b expression levels and the clinicopathological data and prognosis of tumor patients was summarized for the first time. Overall, we suggest that the current studies of miR-33b are insufficient but provide potential hints and direction for future miR-33b-related research.

RNA-sequencing analysis reveals the potential molecular mechanism of RAD54B in the proliferation of inflamed human dental pulp cells

AIM

To investigate the role of RAD54B in the proliferation of inflamed human dental pulp cells (hDPCs) induced by lipopolysaccharide (LPS).

METHODOLOGY

Normal, carious and pulpitic human dental pulp tissues were collected. Total RNA was subjected to RNA-sequencing (seq) and gene expression profiles were studied by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. Differentially expressed genes (DEGs) in homologous recombination repair (HRR) were validated with qRT-PCR. The expression of RAD54B and TNF-α in human dental pulp tissues was detected using immunohistochemistry. HDPCs were cultured and RAD54B level in hDPCs was detected after LPS stimulation using western blot. CCK-8 was used to investigate the proliferation of hDPCs transfected with negative control (Nc) small interfering RNA (siRNA), RAD54B siRNA, P53 siRNA or both siRNAs with or without LPS stimulation. Flow cytometry was used to detect the cell cycle distribution, and western blot and immunofluorescence were used to analyse the expression of RAD54B, P53 and P21 under the above treatments. One-way and two-way anova followed by least significant difference posttest were used for statistical analysis.

RESULTS

RNA-seq results identified DEGs amongst the three groups. KEGG pathway analysis revealed enrichment of DEGs in the replication and repair pathway. HRR and non-homologous end joining (NHEJ) components were further verified and qRT-PCR results were basically consistent with the sequencing data. RAD54B, an HRR accessory factor highly expressed in carious and pulpitic tissues as compared to that in normal pulps, was chosen as our gene of interest. High RAD54B expression was confirmed in inflamed human dental pulp tissues and LPS-stimulated hDPCs. Upon RAD54B knockdown, P53 and P21 expressions in hDPCs were upregulated whereas the proliferation was significantly downregulated, accompanied by increased G2/M phase arrest. After inhibiting P53 expression in RAD54B-knockdown hDPCs, P21 expression and cell proliferation were reversed.

CONCLUSIONS

Gene expression profiles of normal, carious and pulpitic human dental pulp tissues were revealed. HRR components were elucidated to function in dental pulp inflammation. Amongst the DEGs in HRR, RAD54B regulated the proliferation of inflamed hDPCs via P53/P21 signalling. This research deepens our understanding of dental pulp inflammation and provides new insight to clarify the underlying mechanisms.

High doses of nano-polystyrene aggravate the oxidative stress, DNA damage, and the cell death in onions

Plastic pollution has been reported to negatively impact global biodiversity and ecosystem health. However, the molecular mechanisms of nano-plastics in plants are unidentified, especially their negative impacts on genomic stability. This study for the first time showed that nano-polystyrene leads to cell death in plants by subjugating the cellular antioxidant defence mechanisms through the aggravated production of ROS, which in turn could induce the DNA damage impairing the genetic regulation of the corresponding DNA repair pathway. To validate the proposed hypothesis, the DNA damage potential of nano-polystyrene and the expression levels of key genetic regulators of the DNA damage repair pathway (such as - CYCA/B, CDKA, SOG1, MYB transcription factors, and RAD51) have been assessed in onion roots after 72 h exposure with three ecologically relevant concentrations (25, 50, and 100 μg ml^-1) of 100 nm nano-polystyrene. In addition, imbalance in redox homeostasis (oxidative stress), cell viability, and nuclear aberrations such as - the frequency of micronucleus and bi-nucleate cells that are directly linked to the DNA damages have been checked to point out the cause and effect of nano-polystyrene-induced DNA damage. Results showed a significant increase in oxidative stress in each treatment concentrations of nano-polystyrene. However, ROS generated at 100 μg ml^-1 nano-polystyrene dose subdues the antioxidant defence system and induces cell death. These observations may be ascribed to the accumulation damaged DNA and the down-regulation of repair pathway-associated genes, as observed in this treatment group. Conversely, the observed DNA damage and the reduced expressions of genes would be a mere consequence of reduced cellular viability.

Integration of DNA damage responses with dynamic spatial genome organization

The maintenance of genome stability and cellular homeostasis depends on the temporal and spatial coordination of successive events constituting the classical DNA damage response (DDR). Recent findings suggest close integration and coordination of DDR signaling with specific cellular processes. The mechanisms underlying such coordination remain unclear. We review emerging crosstalk between DNA repair factors, chromatin remodeling, replication, transcription, spatial genome organization, cytoskeletal forces, and liquid-liquid phase separation (LLPS) in mediating DNA repair. We present an overarching DNA repair framework within which these dynamic processes intersect in nuclear space over time. Collectively, this interplay ensures the efficient assembly of DNA repair proteins onto shifting genome structures to preserve genome stability and cell survival.

An Oligonucleotide-Distortion-Responsive Organic Transistor for Platinum-Drug-Induced DNA-Damage Detection

Organic transistor with DNA-damage evaluation ability can open up novel opportunities for bioelectronic devices. Even though trace amounts of drugs can cause cumulative gene damage in vivo, the extremely low occurrence proportion makes them hardly transduced into detectable electric signals. Here, an ultrasensitive DNA-damage sensor based on an oligonucleotide-distortion-responsive organic transistor (DROT) is reported by creating controllable conformation change of double-stranded DNA on the surface of organic semiconductors. In combination with interfacial charge redistribution and efficient signal amplification, the DROT provides an ultrasensitive single-site DNA-damage response with 20.5 s even upon 1 × 10-12 m cisplatin. The high generalizability of this DROT to three generations of classical platinum drugs and gene-relevant DNA damage is demonstrated. A biochip is further designed for intelligent damage analysis in complex environments, which holds the potential for high-throughput biotoxicity evaluation and drug screening in the future.

Peijingsu effectively improves sperm DNA integrity

Intact human sperm DNA is an essential prerequisite for successful fertilization and embryo development. Abnormal sperm DNA fragmentation is a independent factor for male infertility. The objective of this study was to investigate the effects of Peijingsu, a health product, on the DNA integrity of human sperm. Peijingsu was administered for 15 days to 22 patients who had an abnormal sperm DNA fragmentation index (DFI). The DFIs before and after treatment were compared and analyzed using paired t-test. DFIs decreased significantly (P = 0.0008) after treatment, therefore it was concluded that Peijingsu effectively improved sperm DNA integrity in infertile patients who had an abnormal sperm DFI.

Regulation of ddb2 expression in blind cavefish and zebrafish reveals plasticity in the control of sunlight-induced DNA damage repair

We have gained considerable insight into the mechanisms which recognize and repair DNA damage, but how they adapt to extreme environmental challenges remains poorly understood. Cavefish have proven to be fascinating models for exploring the evolution of DNA repair in the complete absence of UV-induced DNA damage and light. We have previously revealed that the Somalian cavefish Phreatichthys andruzzii, lacks photoreactivation repair via the loss of light, UV and ROS-induced photolyase gene transcription mediated by D-box enhancer elements. Here, we explore whether other systems repairing UV-induced DNA damage have been similarly affected in this cavefish model. By performing a comparative study using P. andruzzii and the surface-dwelling zebrafish, we provide evidence for a conservation of sunlight-regulated Nucleotide Excision Repair (NER). Specifically, the expression of the ddb2 gene which encodes a key NER recognition factor is robustly induced following exposure to light, UV and oxidative stress in both species. As in the case of the photolyase genes, D-boxes in the ddb2 promoter are sufficient to induce transcription in zebrafish. Interestingly, despite the loss of D-box-regulated photolyase gene expression in P. andruzzii, the D-box is required for ddb2 induction by visible light and oxidative stress in cavefish. However, in the cavefish ddb2 gene this D-box-mediated induction requires cooperation with an adjacent, highly conserved E2F element. Furthermore, while in zebrafish UV-induced ddb2 expression results from transcriptional activation accompanied by stabilization of the ddb2 mRNA, in P. andruzzii UV induces ddb2 expression exclusively via an increase in mRNA stability. Thus, we reveal plasticity in the transcriptional and post transcriptional mechanisms regulating the repair of sunlight-induced DNA damage under long-term environmental challenges.

A Review on the Biocompatibility of PMMA-Based Dental Materials for Interim Prosthetic Restorations with a Glimpse into their Modern Manufacturing Techniques

This paper's primary aim is to outline relevant aspects regarding the biocompatibility of PMMA (poly(methyl methacrylate))-based materials used for obtaining interim prosthetic restorations, such as the interaction with oral epithelial cells, fibroblasts or dental pulp cells, the salivary oxidative stress response, and monomer release. Additionally, the oral environment's biochemical response to modern interim dental materials containing PMMA (obtained via subtractive or additive methods) is highlighted in this review. The studies included in this paper confirmed that PMMA-based materials interact in a complex way with the oral environment, and therefore, different concerns about the possible adverse oral effects caused by these materials were analyzed. Adjacent to these aspects, the present work describes several advantages of PMMA-based dental materials. Moreover, the paper underlines that recent scientific studies ascertain that the modern techniques used for obtaining interim prosthetic materials, milled PMMA, and 3D (three-dimensional) printed resins, have distinctive advantages compared to the conventional ones. However, considering the limited number of studies focusing on the chemical composition and biocompatibility of these modern interim prosthetic materials, especially for the 3D printed ones, more aspects regarding their interaction with the oral environment need to be further investigated.

N-Acetyl Cysteine as a Novel Polymethyl Methacrylate Resin Component: Protection against Cell Apoptosis and Genotoxicity

The present study investigated the antiapoptotic and antigenotoxic capabilities of N-acetyl cysteine- (NAC-) containing polymethyl methacrylate (PMMA) resin. An in vitro Transwell insert model was used to mimic the clinical provisional restorations placed on vital teeth. Various parameters associated with cell apoptosis and genotoxicity were investigated to obtain a deeper insight into the underlying mechanisms. The exposure of human dental pulp cell (hDPC) cultures to the PMMA resin (Unifast Trad™) resulted in a rapid increase in reactive oxygen species (ROS) level beginning at 1 h, which was followed by time-dependent cell detachment and overt death. The formation of γ-H2AX and cell cycle G1 phase arrest indicated that oxidative DNA damage occurred as a result of the interactions between DNA bases and ROS, beyond the capacities of cellular redox regulation. Such oxidative DNA damage triggers the activation of p53 via the ataxia telangiectasia mutated (ATM) signaling pathway and the induction of intrinsic mitochondrial apoptosis. Oxidative stress, cell apoptosis, and DNA damage induced by the PMMA resin were recovered to almost the level of untreated controls by the incorporation of NAC. The results indicate that the PMMA resin induced the intrinsic mitochondrial apoptosis as a consequence of p53 activation via the ATM pathway in response to oxidative DNA damage. More importantly, the incorporation of NAC as a novel component into the Unifast Trad™ PMMA resin offers protective effects against cell apoptosis and genotoxicity. This procedure represents a beneficial strategy for developing more biocompatible PMMA-based resin materials.

Modulation of DNA Repair Systems in Blind Cavefish during Evolution in Constant Darkness

How the environment shapes the function and evolution of DNA repair systems is poorly understood. In a comparative study using zebrafish and the Somalian blind cavefish, Phreatichthys andruzzii, we reveal that during evolution for millions of years in continuous darkness, photoreactivation DNA repair function has been lost in P. andruzzii. We demonstrate that this loss results in part from loss-of-function mutations in pivotal DNA-repair genes. Specifically, C-terminal truncations in P. andruzzii DASH and 6-4 photolyase render these proteins predominantly cytoplasmic, with consequent loss in their functionality. In addition, we reveal a general absence of light-, UV-, and ROS-induced expression of P. andruzzii DNA-repair genes. This results from a loss of function of the D-box enhancer element, which coordinates and enhances DNA repair in response to sunlight. Our results point to P. andruzzii being the only species described, apart from placental mammals, that lacks the highly evolutionary conserved photoreactivation function. We predict that in the DNA repair systems of P. andruzzii, we may be witnessing the first stages in a process that previously occurred in the ancestors of placental mammals during the Mesozoic era.

The Base Pairing Partner Modulates Alkylguanine Alkyltransferase

O⁶-Alkylguanine DNA adducts are repaired by the suicide enzyme alkylguanine alkyltransferase (AGT). AGT facilitates repair by binding DNA in the minor groove, flipping out the damaged base, and transferring the O⁶-alkyl group to a cysteine residue in the enzyme's active site. Despite there being significant knowledge concerning the mechanism of AGT repair, there is limited insight regarding how altered interactions of the adduct with its complementary base in the DNA duplex influence its recognition and repair. In this study, the relationship of base pairing interactions and repair by human AGT (hAGT) was tested in the frequently mutated codon 12 of the KRAS gene with complementary sequences containing each canonical DNA base. The rate of O⁶-MeG repair decreased 2-fold when O⁶-MeG was paired with G, whereas all other canonical bases had no impact on the repair rate. We used a combination of biochemical studies, molecular modeling, and artificial nucleobases to elucidate the mechanism accounting for the 2-fold decrease. Our results suggest that the reduced rate of repair is due to O⁶-MeG adopting a syn conformation about the glycosidic bond precluding the formation of a repair-active complex. These data provide a novel chemical basis for how direct reversion repair may be impeded through modification of the base pair partner and support the use of artificial nucleobases as tools to probe the biochemistry of damage repair processes.

Astaxanthin in Skin Health, Repair, and Disease: A Comprehensive Review

Astaxanthin, a xanthophyll carotenoid, is a secondary metabolite naturally synthesized by a number of bacteria, microalgae, and yeasts. The commercial production of this pigment has traditionally been performed by chemical synthesis, but the microalga Haematococcus pluvialis appears to be the most promising source for its industrial biological production. Due to its collective diverse functions in skin biology, there is mounting evidence that astaxanthin possesses various health benefits and important nutraceutical applications in the field of dermatology. Although still debated, a range of potential mechanisms through which astaxanthin might exert its benefits on skin homeostasis have been proposed, including photoprotective, antioxidant, and anti-inflammatory effects. This review summarizes the available data on the functional role of astaxanthin in skin physiology, outlines potential mechanisms involved in the response to astaxanthin, and highlights the potential clinical implications associated with its consumption.

The protective role of DOT1L in UV-induced melanomagenesis

The DOT1L histone H3 lysine 79 (H3K79) methyltransferase plays an oncogenic role in MLL-rearranged leukemogenesis. Here, we demonstrate that, in contrast to MLL-rearranged leukemia, DOT1L plays a protective role in ultraviolet radiation (UVR)-induced melanoma development. Specifically, the DOT1L gene is located in a frequently deleted region and undergoes somatic mutation in human melanoma. Specific mutations functionally compromise DOT1L methyltransferase enzyme activity leading to reduced H3K79 methylation. Importantly, in the absence of DOT1L, UVR-induced DNA damage is inefficiently repaired, so that DOT1L loss promotes melanoma development in mice after exposure to UVR. Mechanistically, DOT1L facilitates DNA damage repair, with DOT1L-methylated H3K79 involvement in binding and recruiting XPC to the DNA damage site for nucleotide excision repair (NER). This study indicates that DOT1L plays a protective role in UVR-induced melanomagenesis.

Dietary proanthocyanidins prevent ultraviolet radiation-induced non-melanoma skin cancer through enhanced repair of damaged DNA-dependent activation of immune sensitivity

Numerous plant products have been used to prevent and manage a wide variety of diseases for centuries. These products are now considered as promising options for the development of more effective and less toxic alternatives to the systems of medicine developed primarily in developed countries in the modern era. Grape seed proanthocyanidins (GSPs) are of great interest due to their anti-carcinogenic effects that have been demonstrated using various tumor models including ultraviolet (UV) radiation-induced non-melanoma skin cancer. In a pre-clinical mouse model supplementation of a control diet (AIN76A) with GSPs at concentrations of 0.2% and 0.5% (w/w) significantly inhibits the growth and multiplicity of UVB radiation-induced skin tumors. In this review, we summarize the evidence that this inhibition of UVB-induced skin tumor development by dietary GSPs is mediated by a multiplicity of coordinated effects including: (i) Promotion of the repair of damaged DNA by nuclear excision repair mechanisms, and (ii) DNA repair-dependent stimulation of the immune system following the functional activation of dendritic cells and effector T cells. Dietary GSPs hold promise for the development of an effective alternative strategy for the prevention of excessive solar UVB radiation exposure-induced skin diseases including the risk of non-melanoma skin cancer in humans.

Cadmium(II) inhibition of human uracil-DNA glycosylase by catalytic water supplantation

Toxic metals are known to inhibit DNA repair but the underlying mechanisms of inhibition are still not fully understood. DNA repair enzymes such as human uracil-DNA glycosylase (hUNG) perform the initial step in the base excision repair (BER) pathway. In this work, we showed that cadmium [Cd(II)], a known human carcinogen, inhibited all activity of hUNG at 100 μM. Computational analyses based on 2 μs equilibrium, 1.6 μs steered molecular dynamics (SMD), and QM/MM MD determined that Cd(II) ions entered the enzyme active site and formed close contacts with both D145 and H148, effectively replacing the catalytic water normally found in this position. Geometry refinement by density functional theory (DFT) calculations showed that Cd(II) formed a tetrahedral structure with D145, P146, H148, and one water molecule. This work for the first time reports Cd(II) inhibition of hUNG which was due to replacement of the catalytic water by binding the active site D145 and H148 residues. Comparison of the proposed metal binding site to existing structural data showed that D145:H148 followed a general metal binding motif favored by Cd(II). The identified motif offered structural insights into metal inhibition of other DNA repair enzymes and glycosylases.

DNA damage responsive miR-33b-3p promoted lung cancer cells survival and cisplatin resistance by targeting p21WAF1/CIP1

Cisplatin is the most potent and widespread used chemotherapy drug for lung cancer treatment. However, the development of resistance to cisplatin is a major obstacle in clinical therapy. The principal mechanism of cisplatin is the induction of DNA damage, thus the capability of DNA damage response (DDR) is a key factor that influences the cisplatin sensitivity of cancer cells. Recent advances have demonstrated that miRNAs (microRNAs) exerted critical roles in DNA damage response; nonetheless, the association between DNA damage responsive miRNAs and cisplatin resistance and its underlying molecular mechanism still require further investigation. The present study has attempted to identify differentially expressed miRNAs in cisplatin induced DNA damage response in lung cancer cells, and probe into the effects of the misexpressed miRNAs on cisplatin sensitivity. Deep sequencing showed that miR-33b-3p was dramatically down-regulated in cisplatin-induced DNA damage response in A549 cells; and ectopic expression of miR-33b-3p endowed the lung cancer cells with enhanced survival and decreased γH2A.X expression level under cisplatin treatment. Consistently, silencing of miR-33b-3p in the cisplatin-resistant A549/DDP cells evidently sensitized the cells to cisplatin. Furthermore, we identified CDKN1A (p21) as a functional target of miR-33b-3p, a critical regulator of G1/S checkpoint, which potentially mediated the protection effects of miR-33b-3p against cisplatin. In aggregate, our results suggested that miR-33b-3p modulated the cisplatin sensitivity of cancer cells might probably through impairing the DNA damage response. And the knowledge of the drug resistance conferred by miR-33b-3p has great clinical implications for improving the efficacy of chemotherapies for treating lung cancers.

Mesenchymal stem cell therapy promotes the improvement and recovery of renal function in a preclinical model

Acute renal failure (ARF) is an extremely important public health issue in need of novel therapies. The present study aimed to evaluate the capacity of mesenchymal stem cell (MSC) therapy to promote the improvement and recovery of renal function in a preclinical model. Wistar rats were used as the experimental model, and our results show that cisplatin (5mg/kg) can efficiently induce ARF, as measured by changes in biochemical (urea and creatinine) and histological parameters. MSC therapy performed 24h after the administration of chemotherapy resulted in normalized plasma urea and creatinine levels 30 and 45d after the onset of kidney disease. Furthermore, MSC therapy significantly reduced histological changes (intratubular cast formation in protein overload nephropathy and tubular hydropic degeneration) in this ARF model. Thus, considering that current therapies for ARF are merely palliative and that MSC therapy can promote the improvement and recovery of renal function in this model system, we suggest that innovative/alternative therapies involving MSCs should be considered for clinical studies in humans to treat ARF.

Dietary proanthocyanidins inhibit UV radiation-induced skin tumor development through functional activation of the immune system

The incidence of skin cancer is equivalent to the incidence of malignancies in all other organs combined. The main risk factor for this disease is overexposure of the skin to solar ultraviolet (UV) radiation. UV irradiation induces inflammation, oxidative stress, DNA damage, and suppression of the immune system in the skin, which together contribute to carcinogenesis. The use of dietary phytochemicals shows great promise as a complementary and alternative strategy for skin cancer prevention. Grape seed proanthocyanidins (GSPs) have been tested extensively for their anti-skin cancer effect using in vivo animal models. Supplementation of an AIN76A control diet with GSPs (0.2 and 0.5%, w/w) significantly inhibits UV radiation-induced skin tumor development as well as malignant transformation of papillomas to carcinoma in mice. The inhibition of UVB-induced skin tumor development by GSPs is mediated through interrelated mechanisms of action including: (i) inhibition of inflammation, (ii) rapid repair of damaged DNA, and (iii) stimulation of immune system. Additionally, the chemopreventive effects of GSPs involve DNA repair-dependent functional activation of antigen-presenting cells and stimulation of CD8(+) effector T cells. These effects of GSPs could be useful in attenuation of the adverse effects of UV radiation and may have health benefits in humans.

Methacryloxylethyl Cetyl Ammonium Chloride Induces DNA Damage and Apoptosis in Human Dental Pulp Cells via Generation of Oxidative Stress

The polymerizable antibacterial monomer methacryloxylethyl cetyl ammonium chloride (DMAE-CB) has provided an effective strategy to combat dental caries. However, the application of such material raises the question about the biological safety and the question remains open. The mechanism of this toxic action, however, is not yet clearly understood. The present study aims at providing novel insight into the possible causal link between cellular oxidative stress and DNA damage, as well as apoptosis in human dental pulp cells exposed to DMAE-CB. The enhanced formation of reactive oxygen species and depletion of glutathione, as well as differential changes in activities of superoxide dismutase, glutathione peroxidase, and catalase in DMAE-CB-treated cells indicated oxidative stress. By using substances that can alter GSH synthesis, we found that GSH was the key component in the regulation of cell response towards oxidative stress induced by DMAE-CB. The increase in oxidative stress-sensitive 8-Oxo-2'-deoxyguanosine (8-OHdG) content, formation of γ-H2AX and cell cycle G1 phase arrest indicated that DNA damage occurred as a result of the interaction between DNA base and ROS beyond the capacities of antioxidant mechanisms in cells exposed to DMAE-CB. Such oxidative DNA damage thus triggers the activation of ataxia telangiectasia-mutated (ATM) signaling, the intrinsic apoptotic pathway, and destruction of mitochondrial morphology and function.

Historical perspective on the DNA damage response

The DNA damage response (DDR) has been broadly defined as a complex network of cellular pathways that cooperate to sense and repair lesions in DNA. Multiple types of DNA damage, some natural DNA sequences, nucleotide pool deficiencies and collisions with transcription complexes can cause replication arrest to elicit the DDR. However, in practice, the term DDR as applied to eukaryotic/mammalian cells often refers more specifically to pathways involving the activation of the ATM (ataxia-telangiectasia mutated) and ATR (ATM-Rad3-related) kinases in response to double-strand breaks or arrested replication forks, respectively. Nevertheless, there are distinct responses to particular types of DNA damage that do not involve ATM or ATR. In addition, some of the aberrations that cause replication arrest and elicit the DDR cannot be categorized as direct DNA damage. These include nucleotide pool deficiencies, nucleotide sequences that can adopt non-canonical DNA structures, and collisions between replication forks and transcription complexes. The response to these aberrations can be called the genomic stress response (GSR), a term that is meant to encompass the sensing of all types of DNA aberrations together with the mechanisms involved in coping with them. In addition to fully functional cells, the consequences of processing genomic aberrations may include mutagenesis, genomic rearrangements and lethality.

Photochemistry and Photobiology of the Spore Photoproduct: A 50-Year Journey

Fifty years ago, a new thymine dimer was discovered as the dominant DNA photolesion in UV-irradiated bacterial spores [Donnellan, J. E. & Setlow R. B. (1965) Science, 149, 308-310], which was later named the spore photoproduct (SP). Formation of SP is due to the unique environment in the spore core that features low hydration levels favoring an A-DNA conformation, high levels of calcium dipicolinate that acts as a photosensitizer, and DNA saturation with small, acid-soluble proteins that alters DNA structure and reduces side reactions. In vitro studies reveal that any of these factors alone can promote SP formation; however, SP formation is usually accompanied by the production of other DNA photolesions. Therefore, the nearly exclusive SP formation in spores is due to the combined effects of these three factors. Spore photoproduct photoreaction is proved to occur via a unique H-atom transfer mechanism between the two involved thymine residues. Successful incorporation of SP into an oligonucleotide has been achieved via organic synthesis, which enables structural studies that reveal minor conformational changes in the SP-containing DNA. Here, we review the progress on SP photochemistry and photobiology in the past 50 years, which indicates a very rich SP photobiology that may exist beyond endospores.

Ultraviolet radiation-induced non-melanoma skin cancer: Regulation of DNA damage repair and inflammation

Exposure to ultraviolet (UV) radiation is associated with approximately 65% of melanoma cases, and 90% of non-melanoma skin cancers (NMSC), including basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). While the incidence of most other malignancies has either stabilized or declined, that of NMSC has increased and is developing even in younger age groups. NMSCs account for nearly 15,000 deaths, 3.5 million new cases, and more than 3 billion dollars a year in medical costs in the United States alone, representing a major public health concern. As sun protection efforts have not been proven effective, targeted chemoprevention strategies are much needed. Skin carcinogenesis by DNA damage is considered a predominant paradigm for UV toxicity. Exposure to UV radiation can activate various oncogenes while inactivating tumor suppressor genes, resulting in inappropriate survival and proliferation of keratinocytes that harbor these damages. Moreover, increasing evidence demonstrate that inflammatory responses by the immune cells within the tumor microenvironment also contribute significantly to skin tumorigenesis. Initiation and progression of skin carcinogenesis mediated by UV radiation involve complex pathways, including those of apoptosis, proliferation, autophagy, DNA repair, checkpoint signaling, metabolism, and inflammation. In this review, we highlight the recent advances in two of these key molecular processes that result in UV-mediated skin carcinogenesis. In particular, we discuss 1) pathways that regulate DNA damage repair and 2) the regulation of the inflammatory process its crosstalk with DNA repair potentially leading to non-melanoma skin carcinogenesis.

Genome-scale transcriptome analysis of the alpine "glasshouse" plant Rheum nobile (Polygonaceae) with special translucent bracts

BACKGROUND

Rheum nobile is an alpine plant with translucent bracts concealing the inflorescence which produce a "glasshouse" effect promoting the development of fertile pollen grains in such conditions. The current understanding of the adaptation of such bracts to alpine environments mainly focuses on the phenotypic and physiological changes while the genetic basis is very limited. By sequencing the upper bract and the lower rosulate leaf from the same R. nobile stem, we identified candidate genes that may be involved in alpine adaption of the translucent bract in "glasshouse" plants and illustrated the changes in gene expression underlying the adaptive and complex evolution of the bracts phenotype.

RESULTS

A total of 174.2 million paired-end reads from each transcriptome were assembled into 25,249 unigenes. By comparing the gene expression profiles, we identified 1,063 and 786 genes up-regulated respectively in the upper bract and the lower leaf. Functional enrichment analyses of these genes recovered a number of differential important pathways, including flavonoid biosynthesis, mismatch repair and photosynthesis related pathways. These pathways are mainly involved in three types of functions: 9 genes in the UV protective process, 9 mismatch repair related genes and 88 genes associated with photosynthesis.

CONCLUSIONS

This study provides the first comprehensive dataset characterizing Rheum nobile gene expression at the transcriptomic scale, and provides novel insights into the gene expression profiles associated with the adaptation of the "glasshouse" plant bracts. The dataset will be served as a public genetic resources for further functional and evolutionary studies of "glasshouse" plants.

PTEN, Longevity and Age-Related Diseases

Since the discovery of PTEN, this protein has been shown to be an effective suppressor of cancer and a contributor to longevity. This report will review, in depth, the associations between PTEN and other molecules, its mutations and regulations in order to present how PTEN can be used to increase longevity. This report will collect recent research of PTEN and use this to discuss PTEN’s role in caloric restriction, antioxidative defense of DNA-damage and the role it plays in suppressing tumors. The report will also discuss that variety of ways that PTEN can be compromised, through mutations, complete loss of alleles and its main antagonist, the PI3K/AKT pathway.

Homologous Recombination Occurs in Entamoeba and Is Enhanced during Growth Stress and Stage Conversion

Homologous recombination (HR) has not been demonstrated in the parasitic protists Entamoeba histolytica or Entamoeba invadens, as no convenient method is available to measure it. However, HR must exist to ensure genome integrity, and possible genetic exchange, especially during stage conversion from trophozoite to cyst. Here we show the up regulation of mitotic and meiotic HR genes in Entamoeba during serum starvation, and encystation. To directly demonstrate HR we use a simple PCR-based method involving inverted repeats, which gives a reliable read out, as the recombination junctions can be determined by sequencing the amplicons. Using this read out, we demonstrate enhanced HR under growth stress in E. histolytica, and during encystation in E. invadens. We also demonstrate recombination between chromosomal inverted repeats. This is the first experimental demonstration of HR in Entamoeba and will help future investigations into this process, and to explore the possibility of meiosis in Entamoeba.

In vivo evaluation of the antimutagenic and antigenotoxic effects of β-glucan extracted from Saccharomyces cerevisiae in acute treatment with multiple doses

Ample evidence suggests that cancer is triggered by mutagenic damage and diets or supplements capable of reducing such incidences can be related to the prevention of neoplasy development or to an improvement in life quality of patients who undergo chemotherapy. This research aimed to evaluate the antimutagenic and antigenotoxic activity of β-glucan. We set up 8 experimental groups: control (Group 1), cyclophosphamide (Group 2), Groups 3–5 to assess the effect of β-glucan administration, and Groups 6–8 to evaluate the association between cyclophosphamide and β-glucan. The intraperitonial concentrations of β-glucan used were 100, 150 and 200 mg/kg. Micronucleus and comet assays showed that within the first week of treatment β-glucan presented a damage reduction rate between 100–62.04% and 94.34–59.52% for mutagenic and genotoxic damages, respectively. This activity decreased as the treatment was extended. During the sixth week of treatment antimutagenicity rates were reduced to 59.51–39.83% and antigenotoxicity was not effective. This leads to the conclusion that the efficacy of β-glucan in preventing DNA damage is limited when treatment is extended, and that its use as a chemotherapeutic adjuvant need to be better clarified.

An S/T-Q cluster domain census unveils new putative targets under Tel1/Mec1 control

Background

The cellular response to DNA damage is immediate and highly coordinated in order to maintain genome integrity and proper cell division. During the DNA damage response (DDR), the sensor kinases Tel1 and Mec1 in Saccharomyces cerevisiae and ATM and ATR in human, phosphorylate multiple mediators which activate effector proteins to initiate cell cycle checkpoints and DNA repair. A subset of kinase substrates are recognized by the S/T-Q cluster domain (SCD), which contains motifs of serine (S) or threonine (T) followed by a glutamine (Q). However, the full repertoire of proteins and pathways controlled by Tel1 and Mec1 is unknown.

Results

To identify all putative SCD-containing proteins, we analyzed the distribution of S/T-Q motifs within verified Tel1/Mec1 targets and arrived at a unifying SCD definition of at least 3 S/T-Q within a stretch of 50 residues. This new SCD definition was used in a custom bioinformatics pipeline to generate a census of SCD-containing proteins in both yeast and human. In yeast, 436 proteins were identified, a significantly larger number of hits than were expected by chance. These SCD-containing proteins did not distribute equally across GO-ontology terms, but were significantly enriched for those involved in processes related to the DDR. We also found a significant enrichment of proteins involved in telophase and cytokinesis, protein transport and endocytosis suggesting possible novel Tel1/Mec1 targets in these pathways. In the human proteome, a wide range of similar proteins were identified, including homologs of some SCD-containing proteins found in yeast. This list also included high concentrations of proteins in the Mediator, spindle pole body/centrosome and actin cytoskeleton complexes.

Conclusions

Using a bioinformatic approach, we have generated a census of SCD-containing proteins that are involved not only in known DDR pathways but several other pathways under Tel1/Mec1 control suggesting new putative targets for these kinases.

Enhanced UV resistance and improved killing of malaria mosquitoes by photolyase transgenic entomopathogenic fungi

The low survival of microbial pest control agents exposed to UV is the major environmental factor limiting their effectiveness. Using gene disruption we demonstrated that the insect pathogenic fungus Metarhizium robertsii uses photolyases to remove UV-induced cyclobutane pyrimidine dimers (CPD) and pyrimidine (6-4) photoproducts [(6-4)PPs] from its DNA. However, this photorepair is insufficient to fix CPD lesions and prevent the loss of viability caused by seven hours of solar radiation. Expression of a highly efficient archaeal (Halobacterium salinarum) CPD photolyase increased photorepair >30-fold in both M. robertsii and Beauveria bassiana. Consequently, transgenic strains were much more resistant to sunlight and retained virulence against the malaria vector Anopheles gambiae. In the field this will translate into much more efficient pest control over a longer time period. Conversely, our data shows that deleting native photolyase genes will strictly contain M. robertsii to areas protected from sunlight, alleviating safety concerns that transgenic hypervirulent Metarhizium spp will spread from mosquito traps or houses. The precision and malleability of the native and transgenic photolyases allows design of multiple pathogens with different strategies based on the environments in which they will be used.

PTEN in DNA damage repair

The ability of DNA repair in a cell is vital to its genomic integrity and thus to the normal functioning of an organism. Phosphatase and tensin homolog (PTEN) is a well-established tumor suppressor gene that induces apoptosis and controls cell growth by inhibiting the PI3K/AKT pathway. In various human cancers, PTEN is frequently found to be mutated, deleted, or epigenetically silenced. Recent new findings have demonstrated that PTEN also plays a critical role in DNA damage repair and DNA damage response. This review summarizes the recent progress in the function of PTEN in DNA damage repair, especially in double strand break repair and nucleotide excision repair. In addition, we will discuss the role of PTEN in DNA damage response through its interaction with the Chk1 and p53 pathways. We will focus on the newly discovered mechanisms and the potential implications in cancer prevention and therapeutic intervention.

p38γ regulates UV-induced checkpoint signaling and repair of UV-induced DNA damage

In eukaryotic cells, DNA damage triggers activation of checkpoint signaling pathways that coordinate cell cycle arrest and repair of damaged DNA. These DNA damage responses serve to maintain genome stability and prevent accumulation of genetic mutations and development of cancer. The p38 MAPK was previously implicated in cellular responses to several types of DNA damage. However, the role of each of the four p38 isoforms and the mechanism for their involvement in DNA damage responses remained poorly understood. In this study, we demonstrate that p38γ, but not the other p38 isoforms, contributes to the survival of UV-treated cells. Deletion of p38γ sensitizes cells to UV exposure, accompanied by prolonged S phase cell cycle arrest and increased rate of apoptosis. Further investigation reveal that p38γ is essential for the optimal activation of the checkpoint signaling caused by UV, and for the efficient repair of UV-induced DNA damage. These findings have established a novel role of p38γ in UV-induced DNA damage responses, and suggested that p38γ contributes to the ability of cells to cope with UV exposure by regulating the checkpoint signaling pathways and the repair of damaged DNA.

Evidence that herpes simplex virus DNA derived from quiescently infected cells in vitro, and latently infected cells in vivo, is physically damaged

Using polymerase chain reaction (PCR) and alkaline gel electrophoresis, the authors show that, compared with DNA derived from virions used to establish infection, herpes simplex virus DNA derived from quiescently infected rat pheochromocytoma (PC12) cells in culture accumulates alkaline-labile lesions. That is, compared with equivalent amounts of virion DNA, viral DNA from nerve growth factor-differentiated long-term infected cells in culture is consistently 3 to 10 times more refractory to amplification by PCR. Despite using equal mole amounts of DNA isolated from quiescently infected cells (determined by quantitative Southern blots), DNA from quiescently infected cells could not be detected by PCR under conditions in which the virion-derived DNA was easily detected. Refractoriness to PCR was confirmed by analysis with a ligation-mediated PCR technique. The refractoriness was not the result of genomic circularization. The refractoriness was, however, related to the time that the quiescently infected cells had been maintained in culture. The refractoriness to PCR was taken as an indication that the viral DNA was damaged. This hypothesis was confirmed by showing that viral DNA from quiescently infected PC12 cells accumulated alkaline-labile DNA lesions, as determined by alkaline gel electrophoresis. The phenomenon was not limited to tissue culture, because viral DNA derived from the ganglia of latently infected mice is also 3 to 10 times more refractory to amplification than are equivalent amounts of virion-derived genomes. Taken together, these results represent the first evidence that herpes simplex virus DNA is physically damaged as a function of long-term infection. Implications for viral reactivation and pathogenesis are discussed.

Proanthocyanidins inhibit photocarcinogenesis through enhancement of DNA repair and xeroderma pigmentosum group A-dependent mechanism

Dietary grape seed proanthocyanidins (GSP) inhibit photocarcinogenesis in mice; however, the molecular mechanisms underlying this effect have not been fully elucidated. As ultraviolet B (UVB)-induced DNA damage in the form of cyclobutane pyrimidine dimers (CPDs) has been implicated in skin cancer risk, we studied whether dietary GSPs enhance repair of UVB-induced DNA damage and, if so, what is the potential mechanism? Supplementation of GSPs (0.5%, w/w) with AIN76A control diet significantly reduced the levels of CPD(+) cells in UVB-exposed mouse skin; however, GSPs did not significantly reduce UVB-induced CPD(+) cells in the skin of interleukin-12p40 (IL-12) knockout (KO) mice, suggesting that IL-12 is required for the repair of CPDs by GSPs. Using IL-12 KO mice and their wild-type counterparts and standard photocarcinogenesis protocol, we found that supplementation of control diet with GSPs (0.5%, w/w) significantly reduced UVB-induced skin tumor development in wild-type mice, which was associated with the elevated mRNA levels of nucleotide excision repair genes, such as XPA, XPC, DDB2, and RPA1; however, this effect of GSPs was less pronounced in IL-12 KO mice. Cytostaining analysis revealed that GSPs repaired UV-induced CPD(+) cells in xeroderma pigmentosum complementation group A (XPA)-proficient fibroblasts from a healthy individual but did not repair in XPA-deficient fibroblasts from XPA patients. Furthermore, GSPs enhance nuclear translocation of XPA and enhanced its interactions with other DNA repair protein ERCC1. Together, our findings reveal that prevention of photocarcinogenesis by GSPs is mediated through enhanced DNA repair in epidermal cells by IL-12- and XPA-dependent mechanisms.

A positive role for c-Abl in Atm and Atr activation in DNA damage response

DNA damage triggers Atm- and/or Atr-dependent signaling pathways to control cell cycle progression, apoptosis, and DNA repair. However, how Atm and Atr are activated is not fully understood. One of the downstream targets of Atm is non-receptor tyrosine kinase c-Abl, which is phosphorylated and activated by Atm. The current view is that c-Abl relays pro-apoptotic signals from Atm to p73 and p53. Here we show that c-Abl deficiency resulted in a broad spectrum of defects in cell response to genotoxic stress, including activation of Chk1 and Chk2, activation of p53, nuclear foci formation, apoptosis, and DNA repair, suggesting that c-Abl might also act upstream of the DNA damage-activated signaling cascades in addition to its role in p73 and p53 regulation. Indeed, we found that c-Abl is required for proper activation of both Atm and Atr. c-Abl is bound to the chromatin and shows enhanced interaction with Atm and Atr in response to DNA damage. c-Abl can phosphorylate Atr on Y291 and Y310 and this phosphorylation appears to have a positive role in Atr activation under genotoxic stress. These findings suggest that Atm-mediated c-Abl activation in cell response to double-stranded DNA breaks might facilitate the activation of both Atm and Atr to regulate their downstream cellular events.

DNA damage and repair in human oocytes and embryos: a review

The genome of all cells is protected at all times by mechanisms collectively known as DNA repair activity (DRA). Such activity is particularly important at the beginning of human life, i.e. at fertilization, immediately after and at the very onset of embryonic development. DRA in early development is, by definition, of maternal origin: the transcripts stored during maturation, need to control the integrity of chromatin, at least until the maternal/zygotic transition at the 4- to 8-cell stage in the human embryo. Tolerance towards DNA damage must be low during this critical stage of development. The majority of DNA damage is due to either apoptosis or reactive oxygen species (ROS). Apoptosis, abortive or not, is a common feature in human sperm, especially in oligoasthenospermic patients and FAS ligand has been reported on the surface of human spermatozoa. The susceptibility of human sperm to DNA damage is well documented, particularly the negative effect of ROS (Kodama et al., 1997; Lopes et al., 1998a, b) and DNA modifying agents (Zenzes et al., 1999; Badouard et al., 2007). DNA damage in sperm is one of the major causes of male infertility and is of much concern in relation to the paternal transmission of mutations and cancer (Zenzes, 2000; Aitken et al., 2003; Fernández-Gonzalez, 2008). It is now clear that DNA damaged spermatozoa are able to reach the fertilization site in vivo (Zenzes et al., 1999), fertilize oocytes and generate early embryos both in vivo and in vitro. The effect of ROS on human oocytes is not as easy to study or quantify. It is a common consensus that the maternal genome is relatively well protected while in the maturing follicle; however damage may occur during the long quiescent period before meiotic re-activation (Zenzes et al., 1998). In fact, during the final stages of follicular growth, the oocyte may be susceptible to damage by ROS. With regards to the embryo there is active protection against ROS in the surrounding environment i.e. in follicular and tubal fluid (El Mouatassim et al., 2000; Guerin et al., 2001). DNA repair activity in the zygote is mandatory in order to avoid mutation in the germ line (Derijck et al., 2008). In this review we focus on the expression of mRNAs that regulate DNA repair capacity in the human oocyte and the mechanisms that protect the embryo against de novo damage.

Melanocyte-stimulating hormone directly enhances UV-Induced DNA repair in keratinocytes by a xeroderma pigmentosum group A-dependent mechanism

Melanocyte-stimulating hormone (MSH) reduces UV-induced DNA damage through the induction of pigmentation. In this study, we provide evidence that MSH also enhances DNA repair in skin keratinocytes by modulating the function of DNA repair molecules. Intracutaneous injection of MSH prevented UV-induced DNA damage in human and mouse skin independent of its effects on melanogenesis. In keratinocytes, MSH bound to the melanocyte melanocortin receptor type 1 and activated adenylate cyclase activity, which in turn activated Xeroderma pigmentosum group A (XPA)-binding protein 1 and induced nuclear translocation of XPA, a critical factor controlling nucleotide excision repair signaling pathways. Together, our findings reveal a novel pigmentation-independent mechanism that underlies MSH-mediated DNA repair following UVB irradiation.

Coordination of centrosome homeostasis and DNA repair is intact in MCF-7 and disrupted in MDA-MB 231 breast cancer cells

When cells encounter substantial DNA damage, critical cell cycle events are halted while DNA repair mechanisms are activated to restore genome integrity. Genomic integrity also depends on proper assembly and function of the bipolar mitotic spindle, which is required for equal chromosome segregation. Failure to execute either of these processes leads to genomic instability, aging, and cancer. Here, we show that following DNA damage in the breast cancer cell line MCF-7, the centrosome protein centrin2 moves from the cytoplasm and accumulates in the nucleus in a xeroderma pigmentosum complementation group C protein (XPC)-dependent manner, reducing the available cytoplasmic pool of this key centriole protein and preventing centrosome amplification. MDA-MB 231 cells do not express XPC and fail to move centrin into the nucleus following DNA damage. Reintroduction of XPC expression in MDA-MB 231 cells rescues nuclear centrin2 sequestration and reestablishes control against centrosome amplification, regardless of mutant p53 status. Importantly, the capacity to repair DNA damage was also dependent on the availability of centrin2 in the nucleus. These observations show that centrin and XPC cooperate in a reciprocal mechanism to coordinate centrosome homeostasis and DNA repair and suggest that this process may provide a tractable target to develop treatments to slow progression of cancer and aging.

Interaction of DNA topoisomerase 1 with DNA intermediates and proteins of base excision repair

The interaction of human recombinant DNA topoisomerase 1 (Top1) with linear and circular DNA structures containing a nick or short gap but lacking a specific Top1 recognition site was studied. The effect of key excision repair proteins on formation of the Top1 covalent adduct with the DNA repair intermediates was shown. Partial inhibition of the Top1-DNA-adduct formation upon addition of poly(ADP-ribose) polymerase 1 in the absence of NAD+ was shown, whereas in the presence of NAD+ formation of a high molecular weight product, most likely corresponding to poly(ADP)-ribosylated Top1-DNA adduct, was observed. The data show that the key base excision repair proteins can influence formation of suicide Top1-DNA adducts. Top1 was identified by immunoprecipitation in the bovine testis nuclear extract as the protein forming the main modification product with nick-containing DNA.

Flipping of alkylated DNA damage bridges base and nucleotide excision repair

Alkyltransferase-like proteins (ATLs) share functional motifs with the cancer chemotherapy target O(6)-alkylguanine-DNA alkyltransferase (AGT) and paradoxically protect cells from the biological effects of DNA alkylation damage, despite lacking the reactive cysteine and alkyltransferase activity of AGT. Here we determine Schizosaccharomyces pombe ATL structures without and with damaged DNA containing the endogenous lesion O(6)-methylguanine or cigarette-smoke-derived O(6)-4-(3-pyridyl)-4-oxobutylguanine. These results reveal non-enzymatic DNA nucleotide flipping plus increased DNA distortion and binding pocket size compared to AGT. Our analysis of lesion-binding site conservation identifies new ATLs in sea anemone and ancestral archaea, indicating that ATL interactions are ancestral to present-day repair pathways in all domains of life. Genetic connections to mammalian XPG (also known as ERCC5) and ERCC1 in S. pombe homologues Rad13 and Swi10 and biochemical interactions with Escherichia coli UvrA and UvrC combined with structural results reveal that ATLs sculpt alkylated DNA to create a genetic and structural intersection of base damage processing with nucleotide excision repair.

Understanding DNA damage response and DNA repair pathways: applications to more targeted cancer therapeutics

Radiation therapy and many of the commonly used cancer chemotherapeutic drugs target DNA for cytotoxicity. Indeed, the subsequent DNA damage response (DDR) to these cancer treatments in both malignant and normal cells/tissues determines the therapeutic index (TI) of the treatment. The DDR is a complex set of cell processes involving multiple DNA repair, cell cycle regulation, and cell death/survival pathways (or networks) with both damage specificity and coordination of the DDR to different types of DNA damage. Over the last decade, significant progress has been made in elucidating these complex cellular and molecular networks involved in the DDR in human tumor and normal tissues. Based on what has been learned about these processes using experimental in vitro and in vivo models, DDR and DNA pathways are now potential targets for cancer therapy. This article presents an overview of our current understanding of the DDR, including the key DNA repair pathways involved in determining the cytotoxicity to several classes of chemotherapy drugs (CT) as well as ionizing radiation (IR). Since many different types of human cancers can arise from genetic or epigenetic changes in the DDR and DNA repair pathways, this article also covers recent developments in cancer therapeutics that attempt to target these specific tumor-related DDR/DNA repair defects as monotherapy or, more commonly, when combined with conventional cancer treatments.

Von Hippel-Lindau-coupled and transcription-coupled nucleotide excision repair-dependent degradation of RNA polymerase II in response to trabectedin

PURPOSE

Ecteinascidin 743 (Et743; trabectedin, Yondelis) has recently been approved in Europe for the treatment of soft tissue sarcomas and is undergoing clinical trials for other solid tumors. Et743 selectively targets cells proficient for TC-NER, which sets it apart from other DNA alkylating agents. In the present study, we examined the effects of Et743 on RNA Pol II.

EXPERIMENTAL DESIGN AND RESULTS

We report that Et743 induces the rapid and massive degradation of transcribing Pol II in various cancer cell lines and normal fibroblasts. Pol II degradation was abrogated by the proteasome inhibitor MG132 and was dependent on TC-NER. Cockayne syndrome (CS) cells and xeroderma pigmentosum (XP) cells (XPD, XPA, XPG, and XPF) were defective in Pol II degradation, whereas XPC cells whose defect is limited to global genome NER in nontranscribing regions were proficient for Pol II degradation. Complementation of the CSB and XPD cells restored Pol II degradation. We also show that cells defective for the VHL complex were defective in Pol II degradation and that complementation of those cells restores Pol II degradation. Moreover, VHL deficiency rendered cells resistant to Et743-induced cell death, a similar effect to that of TC-NER deficiency.

CONCLUSION

These results suggest that both TC-NER-induced and VHL-mediated Pol II degradation play a role in cell killing by Et743.