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The Werner syndrome protein operates in base excision repair and cooperates with DNA polymerase
, 2005
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Increased chromosome instability and accumulation of DNA double‐strand breaks
- in Werner syndrome cells. J Radiat Res. 2007; www.impactaging.com
"... dative stress/Genomic instability. Werner syndrome (WS) is a premature aging syndrome caused by mutations of the WRN gene. Here, we demonstrate that a strain of WS fibroblast cells shows abnormal karyotypes characterized by several complex translocations and 50-fold more frequency of abnormal metaph ..."
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dative stress/Genomic instability. Werner syndrome (WS) is a premature aging syndrome caused by mutations of the WRN gene. Here, we demonstrate that a strain of WS fibroblast cells shows abnormal karyotypes characterized by several complex translocations and 50-fold more frequency of abnormal metaphases including dicentric chromo-somes without fragments than normal cells when examined at a similar culture stage. Further, telomere fluorescence in situ hybridization indicates that the abnormal signals, extra telomere signal and loss of telomere signal, emerge two- to three-fold more frequently in WS cells than in normal cells. Taken together, these results indicate that chromosome instability including dysfunction of telomere maintenance is more prominent in WS cells than in normal cells. In addition, the accumulation of DNA double-strand breaks (DSBs) at the G1 phase, including those at telomeres, detected by phosphorylated ATM (ataxia telangiectasia mutated) foci is accelerated in WS cells even at a low senescence level. The increased accu-mulation of DSBs in WS cells is reduced in the presence of anti-oxidative agents, suggesting that enhanced oxidative stress in WS cells is involved in accelerated accumulation of DSBs. These results indi-cate that WS cells are prone to accumulate DSBs spontaneously due to a defect of WRN, which leads to increased chromosome instability that could activate checkpoints, resulting in accelerated senescence.
Acetylation Regulates WRN Catalytic Activities and Affects Base Excision DNA Repair
, 2007
"... Background: The Werner protein (WRN), defective in the premature aging disorder Werner syndrome, participates in a number of DNA metabolic processes, and we have been interested in the possible regulation of its function in DNA repair by post-translational modifications. Acetylation mediated by hist ..."
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Background: The Werner protein (WRN), defective in the premature aging disorder Werner syndrome, participates in a number of DNA metabolic processes, and we have been interested in the possible regulation of its function in DNA repair by post-translational modifications. Acetylation mediated by histone acetyltransferases is of key interest because of its potential importance in aging, DNA repair and transcription. Methodology/Principal Findings: Here, we have investigated the p300 acetylation mediated changes on the function of WRN in base excision DNA repair (BER). We show that acetylation of WRN increases in cells treated with methyl methanesulfonate (MMS), suggesting that acetylation of WRN may play a role in response to DNA damage. This hypothesis is consistent with our findings that acetylation of WRN stimulates its catalytic activities in vitro and in vivo, and that acetylated WRN enhances pol b-mediated strand displacement DNA synthesis more than unacetylated WRN. Furthermore, we show that cellular exposure to the histone deacetylase inhibitor sodium butyrate stimulates long patch BER in wild type cells but not in WRN depleted cells, suggesting that acetylated WRN participates significantly in this process. Conclusion/Significance: Collectively, these results provide the first evidence for a specific role of p300 mediated WRN acetylation in regulating its function during BER.
Werner Syndrome Protein, WRN, Protects Cells from DNA Damage Induced by the Benzene Metabolite Hydroquinone
, 2008
"... Werner syndrome (WS) is a rare autosomal progeroid disorder caused by a mutation in the gene encoding the WRN (Werner syndrome protein), a member of the RecQ family of helicases with a role in maintaining genomic stability. Genetic association studies have previously suggested a link between WRN and ..."
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Werner syndrome (WS) is a rare autosomal progeroid disorder caused by a mutation in the gene encoding the WRN (Werner syndrome protein), a member of the RecQ family of helicases with a role in maintaining genomic stability. Genetic association studies have previously suggested a link between WRN and susceptibility to benzene-induced hematotoxicity. To further explore the role of WRN in benzene-induced hematotoxicity, we used short hairpin RNA to silence endogenous levels of WRN in the human HL60 acute promyelocytic cell line and subsequently exposed the cells to hydroquinone (HQ). Suppression of WRN led to an accelerated cell growth rate, increased susceptibility to hydroquinone-induced cytotoxicity and genotoxicity as measured by the single-cell gel electrophoresis assay, and an enhanced DNA damage response. More specifically, loss of WRN resulted in higher levels of early apoptosis, marked by increases in relative levels of cleaved
RECQL5 plays co-operative and complementary roles with WRN syndrome helicase
- Nucleic Acids Res
, 2013
"... Humans have five RecQ helicases, whereas simpler organisms have only one. Little is known about whether and how these RecQ helicases co-operate and/or complement each other in response to cellular stress. Here we show that RECQL5 associ-ates longer at laser-induced DNA double-strand breaks in the ab ..."
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Humans have five RecQ helicases, whereas simpler organisms have only one. Little is known about whether and how these RecQ helicases co-operate and/or complement each other in response to cellular stress. Here we show that RECQL5 associ-ates longer at laser-induced DNA double-strand breaks in the absence of Werner syndrome (WRN) protein, and that it interacts physically and function-ally with WRN both in vivo and in vitro. RECQL5 co-operates with WRN on synthetic stalled replica-tion fork-like structures and stimulates its helicase activity on DNA fork duplexes. Both RECQL5 and WRN re-localize from the nucleolus into the nucleus after replicative stress and significantly as-sociate with each other during S-phase. Further, we show that RECQL5 is essential for cell survival in the absence of WRN. Loss of both RECQL5 and WRN severely compromises DNA replication, accumu-lates genomic instability and ultimately leads to cell death. Collectively, our results indicate that RECQL5 plays both co-operative and complemen-tary roles with WRN. This is an early demonstration of a significant functional interplay and a novel synthetic lethal interaction among the human RecQ helicases.
The Werner syndrome gene product (WRN): a repressor of hypoxia-inducible factor-1 activity
"... Hypoxia-inducible factor-1 (HIF-1) is a decisive element for the transcriptional regulation of genes essential for adaptation to low oxygen conditions. HIF-1 is also implicated in the molecular mechanisms of ageing. Here, we show that the cellular depletion of WRN protein (by siRNA targeting) leads ..."
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Hypoxia-inducible factor-1 (HIF-1) is a decisive element for the transcriptional regulation of genes essential for adaptation to low oxygen conditions. HIF-1 is also implicated in the molecular mechanisms of ageing. Here, we show that the cellular depletion of WRN protein (by siRNA targeting) leads to increased HIF-1 complex stabilization and activation. HIF-1 activation in the absence of WRN involves the generation of mitochondrial reactive oxygen species (mtROS) since SkQ1, a mitochondrial-targeted antioxidant, and stigmatellin, an inhibitor of mitochondrial complex III, blocked increased HIF-1 levels. Ascorbate, an essential co-factor involved in HIF-1 stability, was decreased in WRN-depleted cells. Interestingly, expression levels of GLUT1, a known dehydroascorbic acid transporter, were also decreased in WRN-depleted cells. Ascorbate supplementation of WRN-depleted cells led to a dose-dependent inhibition of HIF-1 activation. These results indicate that WRN protein regulates HIF-1 activation by affecting mitochondrial ROS production and intracellular ascorbate levels. This work provides a novel mechanistic link between HIF-1 activity and different age-associated pathologies.
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"... Variceal hemorrhage is a major cause of death in patients with cirrhosis. Over the past two decades new treatment modalities have been introduced in the management of acute variceal bleeding (AVB) and several recent studies have suggested that the outcome of patients with cirrhosis and AVB has impr ..."
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Variceal hemorrhage is a major cause of death in patients with cirrhosis. Over the past two decades new treatment modalities have been introduced in the management of acute variceal bleeding (AVB) and several recent studies have suggested that the outcome of patients with cirrhosis and AVB has improved. Improved supportive measures, combination therapy which include early use of portal pressure reducing drugs with low rates of adverse effects (somatostatin, octerotide or terlipressin) and endoscopic variceal ligation has become the first line treatment in the management of AVB. Short-term antibiotic prophylaxis, early use of lactulose for prevention of hepatic encephalopathy, application of early transjugular intrahepatic portasystemic shunts (TIPS), fully covered self-expandable metallic stent in patients for AVB may be useful in those cases where balloon tamponade is considered. Early and wide availability of liver transplantation has changed the armamentarium of the clinician for patients with AVB. High hepatic venous pressure gradient (HVPG) >20 mmHg in AVB has become a useful predictor of outcomes and more aggressive therapies with early TIPS based on HVPG measurement may be the treatment of choice to reduce mortality further.
doi:10.1093/nar/gkm1008 SURVEY AND SUMMARY Human premature aging, DNA repair and
, 2007
"... Genomic instability leads to mutations, cellular dysfunction and aberrant phenotypes at the tissue and organism levels. A number of mechanisms have evolved to cope with endogenous or exogenous stress to prevent chromosomal instability and maintain cellular homeostasis. DNA helicases play important r ..."
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Genomic instability leads to mutations, cellular dysfunction and aberrant phenotypes at the tissue and organism levels. A number of mechanisms have evolved to cope with endogenous or exogenous stress to prevent chromosomal instability and maintain cellular homeostasis. DNA helicases play important roles in the DNA damage response. The RecQ family of DNA helicases is of particular interest since several human RecQ helicases are defective in diseases associated with premature aging and cancer. In this review, we will provide an update on our understanding of the specific roles of human RecQ helicases in the maintenance of genomic stability through their catalytic activities and protein interactions in various pathways of cellular nucleic acid metabolism with an emphasis on DNA replication and repair. We will also discuss the clinical features of the premature aging disorders associated with RecQ helicase deficiencies and how they relate to the molecular defects.
