Chromatin Structure Following UV-Induced DNA Damage—Repair or Death?

In eukaryotes, DNA is compacted into a complex structure known as chromatin. The unravelling of DNA is a crucial step in DNA repair, replication, transcription and recombination as this allows access to DNA for these processes. Failure to package DNA into the nucleosome, the individual unit of chromatin, can lead to genomic instability, driving a cell into apoptosis, senescence, or cellular proliferation. Ultraviolet (UV) radiation damage causes destabilisation of chromatin integrity. UV irradiation induces DNA damage such as photolesions and subjects the chromatin to substantial rearrangements, causing the arrest of transcription forks and cell cycle arrest. Highly conserved processes known as nucleotide and base excision repair (NER and BER) then begin to repair these lesions. However, if DNA repair fails, the cell may be forced into apoptosis. The modification of various histones as well as nucleosome remodelling via ATP-dependent chromatin remodelling complexes are required not only to repair these UV-induced DNA lesions, but also for apoptosis signalling. Histone modifications and nucleosome remodelling in response to UV also lead to the recruitment of various repair and pro-apoptotic proteins. Thus, the way in which a cell responds to UV irradiation via these modifications is important in determining its fate. Failure of these DNA damage response steps can lead to cellular proliferation and oncogenic development, causing skin cancer, hence these chromatin changes are critical for a proper response to UV-induced injury

MC1R FUNCTIONS, EXPRESSION, AND IMPLICATIONS FOR TARGETED THERAPY

The G protein-coupled MC1R is expressed in melanocytes and has a pivotal role in human skin pigmentation, with reduced function in human genetic variants exhibiting a red hair phenotype and increased melanoma predisposition. Beyond its role in pigmentation, MC1R is increasingly recognized as promoting UV-induced DNA damage repair. Consequently, there is mounting interest in targeting MC1R for therapeutic benefit. However, whether MC1R expression is restricted to melanocytes or is more widely expressed remains a matter of debate. In this paper, we review MC1R function and highlight that unbiased analysis suggests that its expression is restricted to melanocytes, granulocytes, and the brain

ASF1 Proteins are Involved in UV-induced DNA Damage Repair and are Cell Cycle Regulated by E2F Transcription Factors in Arabidopsis thaliana

ASF1 is a key histone H3/H4 chaperone that participates in a variety of DNA and chromatin-related processes, including DNA repair, where chromatin assembly and disassembly is of primaryrelevance. Information concerning the role of ASF1 proteins in post-UV response in higher plants is currently limited. In Arabidopsis thaliana, an initial analysis of in vivo localization of ASF1A andASF1B indicates that both proteins are mainly expressed in proliferative tissues. In silico promoteranalysis identified ASF1A and ASF1B as potential targets of E2F transcription factors. Theseobservations were experimentally validated, both in vitro by electrophoretic mobility shift assays, and in vivo by chromatin immunoprecipitation assays and expression analysis using transgenic plants with altered levels of different E2F transcription factors. These data suggest that ASF1A and ASF1B are regulated during cell cycle progression through E2F transcription factors. In addition, we found that ASF1A and ASF1B are associated with the UV-B induced DNA damage response in A. thaliana. Transcript levels of ASF1A and ASF1B were increased following a UV-B-treatment. Consistent with a potential role in ultraviolet-B (UV-B) response, RNAi silenced plants of both genes showed increased sensitivity to UV-B compared to wild type plants. Finally, by coimmunoprecipitation analysis, we found that ASF1 physically interacts with N-terminal acetylated histones H3 and H4, and with acetyltransferases of the HAM subfamily, which are known to be involved in cell cycle control and DNA repair, among other functions. Together, here we provide evidence that ASF1A and ASF1B are regulated by cell cycle progression and are involved in DNA repair after UV-B irradiation.Fil: Lario, Luciana Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Centro de Estudios Fotosintéticos y Bioquímicos (i); ArgentinaFil: Gutierrez, Crisanto. Universidad Autónoma de Madrid; EspañaFil: Ramirez Parra, Elena. Universidad Politecnica de Madrid; EspañaFil: Spampinato, Claudia Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Centro de Estudios Fotosintéticos y Bioquímicos (i); ArgentinaFil: Casati, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Centro de Estudios Fotosintéticos y Bioquímicos (i); Argentin

Hydrogen peroxide induced genomic instability in nucleotide excision repair-deficient lymphoblastoid cells

Copyright @ 2010 Gopalakrishnan et al; licensee BioMed Central Ltd.Background The Nucleotide Excision Repair (NER) pathway specialises in UV-induced DNA damage repair. Inherited defects in the NER can predispose individuals to Xeroderma Pigmentosum (XP). UV-induced DNA damage cannot account for the manifestation of XP in organ systems not directly exposed to sunlight. While the NER has recently been implicated in the repair of oxidative DNA lesions, it is not well characterised. Therefore we sought to investigate the role of NER factors Xeroderma Pigmentosum A (XPA), XPB and XPD in oxidative DNA damage-repair by subjecting lymphoblastoid cells from patients suffering from XP-A, XP-D and XP-B with Cockayne Syndrome to hydrogen peroxide (H2O2). Results Loss of functional XPB or XPD but not XPA led to enhanced sensitivity towards H2O2-induced cell death. XP-deficient lymphoblastoid cells exhibited increased susceptibility to H2O2-induced DNA damage with XPD showing the highest susceptibility and lowest repair capacity. Furthermore, XPB- and XPD-deficient lymphoblastoid cells displayed enhanced DNA damage at the telomeres. XPA- and XPB-deficient lymphoblastoid cells also showed differential regulation of XPD following H2O2 treatment. Conclusions Taken together, our data implicate a role for the NER in H2O2-induced oxidative stress management and further corroborates that oxidative stress is a significant contributing factor in XP symptoms. Resistance of XPA-deficient lymphoblastoid cells to H2O2-induced cell death while harbouring DNA damage poses a potential cancer risk factor for XPA patients. Our data implicate XPB and XPD in the protection against oxidative stress-induced DNA damage and telomere shortening, and thus premature senescence.This research is supported by the Defence Innovative Research Programme, Defence Science and Technology Agency, Singapore (POD: 0613592) and the Academic Research Fund, Ministry of Education, Singapore (T206B3108). Supported in part by a grant from British Council, PMI2 Connect (Grant Number: RC134)

miR-183 Inhibits UV-Induced DNA Damage Repair in Human Trabecular Meshwork Cells by Targeting of KIAA0101

PURPOSE. The purpose of this study was to investigate the mechanisms by which miR-183 may contribute to the phenotypic alterations associated with stress-induced senescence of human trabecular meshwork (HTM) cells. METHODS. Changes in gene expression induced by miR-183 in HTM cells were evaluated by gene array analysis, confirmed by quantitative-PCR (Q-PCR), and analyzed by MetaCore pathway analysis. Effects of miR-183 on cell proliferation were assessed by incorporation of bromodeoxyuridine incorporation, and DNA damage by CometAssay after ultraviolet (UV) irradiation in primary HTM cells, and confirmed in human diploid fibroblasts (HDF) and HeLa cells. A plasmid expressing KIAA0101 without its 3 0 -untranslated region (3 0 -UTR) was cotransfected with miR-183 to evaluate the role of KIAA0101 on the effects induced by miR-183. RESULTS. miR-183 affected the expression of multiple genes involved in cell cycle regulation and DNA damage response in HTM cells. Forced expression of miR-183 in HTM and HDF resulted in a significant decrease in proliferation in primary HTM and HDF cells but not in HeLa cells. In all cell types tested, overexpression of miR-183 resulted in increased DNA damage under UV irradiation. Expression of KIAA0101 lacking the 3 0 -UTR region partially prevented the effects of miR-183 on cell proliferation and completely reversed the effects on UV-induced DNA damage. CONCLUSIONS. Our results suggest that the observed up-regulation of miR-183 after stressinduced senescence in HTM cells may contribute to reinforce cellular senescence by inhibiting cell cycle progression through multiple gene targets and limiting the DNA repair mechanisms through inhibition of KIAA0101

CC3/TIP30 affects DNA damage repair

<p>Abstract</p> <p>Background</p> <p>The pro-apoptotic protein CC3/TIP30 has an unusual cellular function as an inhibitor of nucleocytoplasmic transport. This function is likely to be activated under conditions of stress. A number of studies support the notion that CC3 acts as a tumor and metastasis suppressor in various types of cancer. The yeast homolog of CC3 is likely to be involved in responses to DNA damage. Here we examined the potential role of CC3 in regulation of cellular responses to genotoxic stress.</p> <p>Results</p> <p>We found that forced expression of CC3 in CC3-negative cells strongly delays the repair of UV-induced DNA damage. Exogenously introduced CC3 negatively affects expression levels of DDB2/XPE and p21CIP1, and inhibits induction of c-FOS after UV exposure. In addition, exogenous CC3 prevents the nuclear accumulation of P21CIP in response to UV. These changes in the levels/localization of relevant proteins resulting from the enforced expression of CC3 are likely to contribute to the observed delay in DNA damage repair. Silencing of CC3 in CC3-positive cells has a modest delaying effect on repair of the UV induced damage, but has a much more significant negative affect on the translesion DNA synthesis after UV exposure. This could be related to the higher expression levels and increased nuclear localization of p21CIP1 in cells where expression of CC3 is silenced. Expression of CC3 also inhibits repair of oxidative DNA damage and leads to a decrease in levels of nucleoredoxin, that could contribute to the reduced viability of CC3 expressing cells after oxidative insult.</p> <p>Conclusions</p> <p>Manipulation of the cellular levels of CC3 alters expression levels and/or subcellular localization of proteins that exhibit nucleocytoplasmic shuttling. This results in altered responses to genotoxic stress and adversely affects DNA damage repair by affecting the recruitment of adequate amounts of required proteins to proper cellular compartments. Excess of cellular CC3 has a significant negative effect on DNA repair after UV and oxidant exposure, while silencing of endogenous CC3 slightly delays repair of UV-induced damage.</p

Arsenite-Induced Alterations of DNA Photodamage Repair and Apoptosis After Solar-Simulation UVR in Mouse Keratinocytes in Vitro

Our laboratory has shown that arsenite markedly increased the cancer rate caused by solar-simulation ultraviolet radiation (UVR) in the hairless mouse skin model. In the present study, we investigated how arsenite affected DNA photodamage repair and apoptosis after solar-simulation UVR in the mouse keratinocyte cell line 291.03C. The keratinocytes were treated with different concentrations of sodium arsenite (0.0, 2.5, 5.0 μM) for 24 hr and then were immediately irradiated with a single dose of 0.30 kJ/m(2) UVR. At 24 hr after UVR, DNA photoproducts [cyclobutane pyrimidine dimers (CPDs) and 6–4 photoproducts (6-4PPs)] and apoptosis were measured using the enzyme-linked immunosorbent assay and the two-color TUNEL (terminal deoxynucleotide transferase dUTP nick end labeling) assay, respectively. The results showed that arsenite reduced the repair rate of 6-4PPs by about a factor of 2 at 5.0 μM and had no effect at 2.5 μM. UVR-induced apoptosis at 24 hr was decreased by 22.64% at 2.5 μM arsenite and by 61.90% at 5.0 μM arsenite. Arsenite decreased the UVR-induced caspase-3/7 activity in parallel with the inhibition of apoptosis. Colony survival assays of the 291.03C cells demonstrate a median lethal concentration (LC(50)) of arsenite of 0.9 μM and a median lethal dose (LD(50)) of UVR of 0.05 kJ/m(2). If the present results are applicable in vivo, inhibition of UVR-induced apoptosis may contribute to arsenite’s enhancement of UVR-induced skin carcinogenesis

The new era of autoimmune disease research

Recent genome-wide association studies have advanced our understanding of genetic factors that underlie systemic lupus erythematosus (SLE), a multifactorial autoimmune disease characterized by various clinical manifestations. SLE also has an environmental component, which can trigger or exacerbate the disease. Despite extensive efforts aimed at elucidating the cellular and biological abnormalities that arise in the immune system of patients with SLE, its pathology remains unclear. Lee and colleagues recently carried out gene expression profiling of patients with SLE followed by bioinformatics analysis and discovered the existence of abnormal regulatory networks and potential key molecules. The authors found that ATP synthesis and DNA repair pathways may be involved in the pathogenesis, providing a potential explanation for photosensitivity experienced by patients with SLE

Differential role of RB in response to UV and IR damage

The retinoblastoma tumor suppressor (RB) is functionally inactivated in the majority of cancers and is a critical mediator of DNA damage checkpoints. Despite the critical importance of RB function in tumor suppression, the coordinate impact of RB loss on the response to environmental and therapeutic sources of damage has remained largely unexplored. Here, we utilized a conditional knockout system to ablate RB in adult fibroblasts. This model system enabled us to investigate the temporal role of RB loss on cell cycle checkpoints and DNA damage repair following ultraviolet (UV) and ionizing radiation (IR) damage. We demonstrate that RB loss compromises rapid cell cycle arrest following UV and IR exposure in adult primary cells. Detailed kinetic analysis of the checkpoint response revealed that disruption of the checkpoint is concomitant with RB target gene deregulation, and is not simply a manifestation of chronic RB loss. RB loss had a differential effect upon repair of the major DNA lesions induced by IR and UV. Whereas RB did not affect resolution of DNA double-strand breaks, RB-deficient cells exhibited accelerated repair of pyrimidine pyrimidone photoproducts (6-4 PP). In parallel, this repair was coupled with enhanced expression of specific factors and the behavior of proliferating cell nuclear antigen (PCNA) recruitment to replication and repair foci. Thus, RB loss and target gene deregulation hastens the repair of specific lesions distinct from its ubiquitous role in checkpoint abrogation