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Chromatin-Directed Proteomics Identifies ZNF84 as a p53-Independent Regulator of p21 in Genotoxic Stress Response. Cancers (Basel) 2021; 13:cancers13092115. [PMID: 33925586 PMCID: PMC8123910 DOI: 10.3390/cancers13092115] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2021] [Revised: 04/18/2021] [Accepted: 04/22/2021] [Indexed: 12/12/2022] Open
Abstract
Simple Summary Chemotherapy is a commonly applied anticancer treatment, however therapy-induced senescent growth arrest has been associated with aggressive disease recurrence. The p21 protein, encoded by CDKN1A, plays a vital role in the induction of senescence. Its transcriptional control by p53 is well-established. However, in many cancers where TP53 is mutated, p21 expression must be triggered by p53-independent mechanisms. We here used a chromatin-directed proteomic approach and identified ZNF84 as a regulator of CDKN1A gene expression in various p53-deficient cell lines. Knock-down of ZNF84, an as-yet un-characterized protein, inhibited p21 gene and protein expression in response to doxorubicin and facilitated senescence bypass. Intriguingly, ZNF84 depletion diminished genotoxic burden evoked by doxorubicin. Clinical data association studies indicated the relevance of ZNF84 expression for patient survival. Collectively, we identified ZNF84 as a critical regulator of senescence-proliferation outcome of chemotherapy, opening possibilities for its targeting in novel anti-cancer therapies of p53-mutated tumours. Abstract The p21WAF1/Cip1 protein, encoded by CDKN1A, plays a vital role in senescence, and its transcriptional control by the tumour suppressor p53 is well-established. However, p21 can also be regulated in a p53-independent manner, by mechanisms that still remain less understood. We aimed to expand the knowledge about p53-independent senescence by looking for novel players involved in CDKN1A regulation. We used a chromatin-directed proteomic approach and identified ZNF84 as a novel regulator of p21 in various p53-deficient cell lines treated with cytostatic dose of doxorubicin. Knock-down of ZNF84, an as-yet un-characterized protein, inhibited p21 gene and protein expression in response to doxorubicin, it attenuated senescence and was associated with enhanced proliferation, indicating that ZNF84-deficiency can favor senescence bypass. ZNF84 deficiency was also associated with transcriptomic changes in genes governing various cancer-relevant processes e.g., mitosis. In cells with ZNF84 knock-down we discovered significantly lower level of H2AX Ser139 phosphorylation (γH2AX), which is triggered by DNA double strand breaks. Intriguingly, we observed a reverse correlation between the level of ZNF84 expression and survival rate of colon cancer patients. In conclusion, ZNF84, whose function was previously not recognized, was identified here as a critical p53-independent regulator of senescence, opening possibilities for its targeting in novel therapies of p53-null cancers.
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Latorre E, Birar VC, Sheerin AN, Jeynes JCC, Hooper A, Dawe HR, Melzer D, Cox LS, Faragher RGA, Ostler EL, Harries LW. Small molecule modulation of splicing factor expression is associated with rescue from cellular senescence. BMC Cell Biol 2017; 18:31. [PMID: 29041897 PMCID: PMC5645932 DOI: 10.1186/s12860-017-0147-7] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2017] [Accepted: 10/09/2017] [Indexed: 12/31/2022] Open
Abstract
Background Altered expression of mRNA splicing factors occurs with ageing in vivo and is thought to be an ageing mechanism. The accumulation of senescent cells also occurs in vivo with advancing age and causes much degenerative age-related pathology. However, the relationship between these two processes is opaque. Accordingly we developed a novel panel of small molecules based on resveratrol, previously suggested to alter mRNA splicing, to determine whether altered splicing factor expression had potential to influence features of replicative senescence. Results Treatment with resveralogues was associated with altered splicing factor expression and rescue of multiple features of senescence. This rescue was independent of cell cycle traverse and also independent of SIRT1, SASP modulation or senolysis. Under growth permissive conditions, cells demonstrating restored splicing factor expression also demonstrated increased telomere length, re-entered cell cycle and resumed proliferation. These phenomena were also influenced by ERK antagonists and agonists. Conclusions This is the first demonstration that moderation of splicing factor levels is associated with reversal of cellular senescence in human primary fibroblasts. Small molecule modulators of such targets may therefore represent promising novel anti-degenerative therapies. Electronic supplementary material The online version of this article (10.1186/s12860-017-0147-7) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Eva Latorre
- Institute of Biomedical and Clinical Sciences, University of Exeter Medical School, University of Exeter, Barrack Road, Exeter, Devon, EX2 5DW, UK
| | - Vishal C Birar
- School of Pharmacy and Biomolecular Sciences, University of Brighton, Cockcroft Building, Moulsecoomb, Brighton, BN2 4GJ, UK
| | - Angela N Sheerin
- School of Pharmacy and Biomolecular Sciences, University of Brighton, Cockcroft Building, Moulsecoomb, Brighton, BN2 4GJ, UK
| | - J Charles C Jeynes
- Centre for Biomedical Modelling and Analysis, University of Exeter, Exeter, Devon, EX2 5DW, UK
| | - Amy Hooper
- Institute of Biomedical and Clinical Sciences, University of Exeter Medical School, University of Exeter, Barrack Road, Exeter, Devon, EX2 5DW, UK
| | - Helen R Dawe
- College of Life and Environmental Sciences, University of Exeter, Exeter, Devon, EX4 4QD, UK
| | - David Melzer
- Institute of Biomedical and Clinical Sciences, University of Exeter Medical School, University of Exeter, Barrack Road, Exeter, Devon, EX2 5DW, UK
| | - Lynne S Cox
- Department of Biochemistry, University of Oxford, Oxford, OX1 3QU, UK
| | - Richard G A Faragher
- School of Pharmacy and Biomolecular Sciences, University of Brighton, Cockcroft Building, Moulsecoomb, Brighton, BN2 4GJ, UK
| | - Elizabeth L Ostler
- School of Pharmacy and Biomolecular Sciences, University of Brighton, Cockcroft Building, Moulsecoomb, Brighton, BN2 4GJ, UK.
| | - Lorna W Harries
- Institute of Biomedical and Clinical Sciences, University of Exeter Medical School, University of Exeter, Barrack Road, Exeter, Devon, EX2 5DW, UK.
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Davis T, Brook AJC, Rokicki MJ, Bagley MC, Kipling D. Evaluating the Role of p38 MAPK in the Accelerated Cell Senescence of Werner Syndrome Fibroblasts. Pharmaceuticals (Basel) 2016; 9:ph9020023. [PMID: 27136566 PMCID: PMC4932541 DOI: 10.3390/ph9020023] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2016] [Revised: 04/21/2016] [Accepted: 04/25/2016] [Indexed: 01/02/2023] Open
Abstract
Progeroid syndromes show features of accelerated ageing and are used as models for human ageing, of which Werner syndrome (WS) is one of the most widely studied. WS fibroblasts show accelerated senescence that may result from p38 MAP kinase activation since it is prevented by the p38 inhibitor SB203580. Thus, small molecule inhibition of p38-signalling may be a therapeutic strategy for WS. To develop this approach issues such as the in vivo toxicity and kinase selectivity of existing p38 inhibitors need to be addressed, so as to strengthen the evidence that p38 itself plays a critical role in mediating the effect of SB203580, and to find an inhibitor suitable for in vivo use. In this work we used a panel of different p38 inhibitors selected for: (1) having been used successfully in vivo in either animal models or human clinical trials; (2) different modes of binding to p38; and (3) different off-target kinase specificity profiles, in order to critically address the role of p38 in the premature senescence seen in WS cells. Our findings confirmed the involvement of p38 in accelerated cell senescence and identified p38 inhibitors suitable for in vivo use in WS, with BIRB 796 the most effective.
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Affiliation(s)
- Terence Davis
- Division of Cancer and Genetics, School of Medicine, Cardiff University, Heath Park, Cardiff, CF 14 4XN, UK.
| | - Amy J C Brook
- Division of Cancer and Genetics, School of Medicine, Cardiff University, Heath Park, Cardiff, CF 14 4XN, UK.
| | - Michal J Rokicki
- Division of Cancer and Genetics, School of Medicine, Cardiff University, Heath Park, Cardiff, CF 14 4XN, UK.
| | - Mark C Bagley
- Department of Chemistry, School of Life Sciences, University of Sussex, Falmer, Brighton, East Sussex BN1 9QJ, UK.
| | - David Kipling
- Division of Cancer and Genetics, School of Medicine, Cardiff University, Heath Park, Cardiff, CF 14 4XN, UK.
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Suppression of the senescence-associated secretory phenotype (SASP) in human fibroblasts using small molecule inhibitors of p38 MAP kinase and MK2. Biogerontology 2015; 17:305-15. [PMID: 26400758 PMCID: PMC4819486 DOI: 10.1007/s10522-015-9610-z] [Citation(s) in RCA: 103] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Accepted: 09/18/2015] [Indexed: 01/10/2023]
Abstract
Senescent cells show an altered secretome profile termed the senescence-associated secretory phenotype (SASP). There is an increasing body of evidence that suggests that the accumulation of SASP-positive senescent cells in humans is partially causal in the observed shift to a low-level pro-inflammatory state in aged individuals. This in turn suggests the SASP as a possible therapeutic target to ameliorate inflammatory conditions in the elderly, and thus a better understanding of the signalling pathways underlying the SASP are required. Prior studies using the early generation p38 MAPK inhibitor SB203580 indicated that p38 signalling was required for the SASP. In this study, we extend these observations using two next-generation p38 inhibitors (UR-13756 and BIRB 796) that have markedly improved selectivity and specificity compared to SB203580, to strengthen the evidence that the SASP is p38-dependent in human fibroblasts. BIRB 796 has an efficacy and toxicity profile that has allowed it to reach Phase III clinical trials, suggesting its possible use to suppress the SASP in vivo. We also demonstrate for the first time a requirement for signalling through the p38 downstream MK2 kinase in the regulation of the SASP using two MK2 inhibitors. Finally, we demonstrate that a commercially-available multiplex cytokine assay technology can be used to detect SASP components in the conditioned medium of cultured fibroblasts from both young and elderly donors. This assay is a high-throughput, multiplex microtitre-based assay system that is highly sensitive, with very low sample requirements, allowing it to be used for low-volume human biological fluids. Our initial studies using existing multiplex plates form the basis for a “SASP signature” assay that could be used as a high-throughput system in a clinical study setting. Our findings therefore provide important steps towards the study of, and intervention in, the SASP in human ageing and age-related disease.
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Abstract
The control of organism and organ size is a central question in biology. Despite the attention it has received, our understanding of how adult organ size is determined and maintained is still incomplete. Early work has shown that both autonomous and regulated mechanisms drive vertebrate organ growth, and both intrinsic and extrinsic cues contribute to organ size. The molecular nature of organ-size determinants has been the subject of intense study, and major pathways, which underlie cell interactions controlling cell compartment size, have been identified. In this work, we review these data as well as the future perspectives of research in this important area of study.
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Affiliation(s)
- Alfredo I Penzo-Méndez
- Departments of Medicine and Cell and Developmental Biology, Abramson Family Cancer Research Institute, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Ben Z Stanger
- Departments of Medicine and Cell and Developmental Biology, Abramson Family Cancer Research Institute, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania 19104
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Serum from calorie-restricted animals delays senescence and extends the lifespan of normal human fibroblasts in vitro. Aging (Albany NY) 2015; 7:152-66. [PMID: 25855056 PMCID: PMC4394727 DOI: 10.18632/aging.100719] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The cumulative effects of cellular senescence and cell loss over time in various tissues and organs are considered major contributing factors to the ageing process. In various organisms, caloric restriction (CR) slows ageing and increases lifespan, at least in part, by activating nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylases of the sirtuin family. Here, we use an in vitro model of CR to study the effects of this dietary regime on replicative senescence, cellular lifespan and modulation of the SIRT1 signaling pathway in normal human diploid fibroblasts. We found that serum from calorie-restricted animals was able to delay senescence and significantly increase replicative lifespan in these cells, when compared to serum from ad libitum fed animals. These effects correlated with CR-mediated increases in SIRT1 and decreases in p53 expression levels. In addition, we show that manipulation of SIRT1 levels by either over-expression or siRNA-mediated knockdown resulted in delayed and accelerated cellular senescence, respectively. Our results demonstrate that CR can delay senescence and increase replicative lifespan of normal human diploid fibroblasts in vitro and suggest that SIRT1 plays an important role in these processes. (185 words).
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Nijmegen breakage syndrome fibroblasts expressing the C-terminal truncated NBN(p70) protein undergo p38/MK2-dependent premature senescence. Biogerontology 2014; 16:43-51. [PMID: 25214013 PMCID: PMC4305097 DOI: 10.1007/s10522-014-9530-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Accepted: 09/03/2014] [Indexed: 01/23/2023]
Abstract
Fibroblasts from the progeroid Nijmegen breakage syndrome that express a truncated version of the nibrin protein (NBNp70) undergo premature senescence and have an enlarged morphology with high levels of senescence-associated β-galactosidase, although they do not have F-actin stress fibres. Growth of these fibroblasts in the continuous presence of p38 inhibitors resulted in a large increase in replicative capacity and changed the cellular morphology so that the cells resembled young normal fibroblasts. A similar effect was seen using an inhibitor of the p38 downstream effector kinase MK2. These data suggest that NBNp70 expressing cells undergo a degree of stress-induced replicative senescence via p38/MK2 activation, potentially due to increased telomere dysfunction, that may play a role in the progeroid features seen in this syndrome.
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Werner syndrome: association of premature aging and cancer predisposition. Mol Oncol 2013. [DOI: 10.1017/cbo9781139046947.036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
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Davis T, Tivey HSE, Brook AJC, Grimstead JW, Rokicki MJ, Kipling D. Activation of p38 MAP kinase and stress signalling in fibroblasts from the progeroid Rothmund-Thomson syndrome. AGE (DORDRECHT, NETHERLANDS) 2013; 35:1767-83. [PMID: 23001818 PMCID: PMC3776094 DOI: 10.1007/s11357-012-9476-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2012] [Accepted: 09/09/2012] [Indexed: 05/12/2023]
Abstract
Rothmund-Thomson fibroblasts had replicative lifespans and growth rates within the range for normal fibroblasts; however, they show elevated levels of the stress-associated p38 MAP kinase, suggestive of stress during growth. Treatment with the p38 MAP kinase inhibitor SB203580 increased both lifespan and growth rate, as did reduction of oxidative stress using low oxygen in some strains. At replicative senescence p53, p21(WAF1) and p16(INK4A) levels were elevated, and abrogation of p53 using shRNA knockdown allowed the cells to bypass senescence. Ectopic expression of human telomerase allowed Rothmund-Thomson fibroblasts to bypass senescence. However, activated p38 was still present, and continuous growth for some telomerised clones required either a reduction in oxidative stress or SB203580 treatment. Overall, the evidence suggests that replicative senescence in Rothmund-Thomson cells resembles normal senescence in that it is telomere driven and p53 dependent. However, the lack of RECQL4 leads to enhanced levels of stress during cell growth that may lead to moderate levels of stress-induced premature senescence. As replicative senescence is believed to underlie human ageing, a moderate level of stress-induced premature senescence and p38 activity may play a role in the relatively mild ageing phenotype seen in Rothmund-Thomson.
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Affiliation(s)
- Terence Davis
- Institute of Cancer and Genetics, School of Medicine, Cardiff University, Heath Park, Cardiff, CF14 4XN, UK,
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Tivey HSE, Rokicki MJ, Barnacle JR, Rogers MJ, Bagley MC, Kipling D, Davis T. Small molecule inhibition of p38 MAP kinase extends the replicative life span of human ATR-Seckel syndrome fibroblasts. J Gerontol A Biol Sci Med Sci 2013; 68:1001-9. [PMID: 23401567 PMCID: PMC3738025 DOI: 10.1093/gerona/gls336] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Ataxia-telangiectasia and rad3 (ATR)-related Seckel syndrome is associated with growth retardation and premature aging features. ATR-Seckel fibroblasts have a reduced replicative capacity in vitro and an aged morphology that is associated with activation of stress-associated p38 mitogen-activated protein kinase and phosphorylated HSP27. These phenotypes are prevented using p38 inhibitors, with replicative capacity restored to the normal range. However, this stressed phenotype is retained in telomerase-immortalized ATR-Seckel fibroblasts, indicating that it is independent of telomere erosion. As with normal fibroblasts, senescence in ATR-Seckel is bypassed by p53 abrogation. Young ATR-Seckel fibroblasts show elevated levels of p21WAF1, p16INK4A, phosphorylated actin-binding protein cofilin, and phosphorylated caveolin-1, with small molecule drug inhibition of p38 reducing p16INK4A and caveolin-1 phosphorylation. In conclusion, ATR-Seckel fibroblasts undergo accelerated aging via stress-induced premature senescence and p38 activation that may underlie certain clinical features of Seckel syndrome, and our data suggest a novel target for pharmacological intervention in this human syndrome.
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Affiliation(s)
- Hannah S E Tivey
- Institute of Cancer and Genetics, School of Medicine, Cardiff University, Heath Park, Cardiff, Wales, UK
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Li X, Xu H, Xu C, Lin M, Song X, Yi F, Feng Y, Coughlan KA, Cho WCS, Kim SS, Cao L. The yin-yang of DNA damage response: roles in tumorigenesis and cellular senescence. Int J Mol Sci 2013; 14:2431-48. [PMID: 23354477 PMCID: PMC3587995 DOI: 10.3390/ijms14022431] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2012] [Revised: 01/08/2013] [Accepted: 01/09/2013] [Indexed: 01/06/2023] Open
Abstract
Senescent cells are relatively stable, lacking proliferation capacity yet retaining metabolic activity. In contrast, cancer cells are rather invasive and devastating, with uncontrolled proliferative capacity and resistance to cell death signals. Although tumorigenesis and cellular senescence are seemingly opposite pathological events, they are actually driven by a unified mechanism: DNA damage. Integrity of the DNA damage response (DDR) network can impose a tumorigenesis barrier by navigating abnormal cells to cellular senescence. Compromise of DDR, possibly due to the inactivation of DDR components, may prevent cellular senescence but at the expense of tumor formation. Here we provide an overview of the fundamental role of DDR in tumorigenesis and cellular senescence, under the light of the Yin-Yang concept of Chinese philosophy. Emphasis is placed on discussing DDR outcome in the light of in vivo models. This information is critical as it can help make better decisions for clinical treatments of cancer patients.
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Affiliation(s)
- Xiaoman Li
- Key Laboratory of Medical Cell Biology, Ministry of Education, China Medical University, Shenyang 110001, China; E-Mails: (X.L.); (H.X.); (M.L.); (X.S.); (F.Y.); (Y.F.)
| | - Hongde Xu
- Key Laboratory of Medical Cell Biology, Ministry of Education, China Medical University, Shenyang 110001, China; E-Mails: (X.L.); (H.X.); (M.L.); (X.S.); (F.Y.); (Y.F.)
| | - Chongan Xu
- Department of Medical Oncology, The Fourth Affiliated Hospital, China Medical University, Shenyang 110032, China; E-Mail:
| | - Meina Lin
- Key Laboratory of Medical Cell Biology, Ministry of Education, China Medical University, Shenyang 110001, China; E-Mails: (X.L.); (H.X.); (M.L.); (X.S.); (F.Y.); (Y.F.)
| | - Xiaoyu Song
- Key Laboratory of Medical Cell Biology, Ministry of Education, China Medical University, Shenyang 110001, China; E-Mails: (X.L.); (H.X.); (M.L.); (X.S.); (F.Y.); (Y.F.)
| | - Fei Yi
- Key Laboratory of Medical Cell Biology, Ministry of Education, China Medical University, Shenyang 110001, China; E-Mails: (X.L.); (H.X.); (M.L.); (X.S.); (F.Y.); (Y.F.)
| | - Yanling Feng
- Key Laboratory of Medical Cell Biology, Ministry of Education, China Medical University, Shenyang 110001, China; E-Mails: (X.L.); (H.X.); (M.L.); (X.S.); (F.Y.); (Y.F.)
| | - Kathleen A. Coughlan
- Section of Molecular Medicine, Department of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA; E-Mail:
| | | | - Sang Soo Kim
- Radiation Medicine Branch, National Cancer Center, Goyang, Gyenggi 410-769, Korea
- Authors to whom correspondence should be addressed; E-Mails: (S.S.K.); (L.C.); Tel.: +82-31-920-2491 (S.S.K.); +86-24-23256666 (ext. 6014) (L.C.); Fax: +82-31-920-2494 (S.S.K.); +86-24-23264417 (L.C.)
| | - Liu Cao
- Key Laboratory of Medical Cell Biology, Ministry of Education, China Medical University, Shenyang 110001, China; E-Mails: (X.L.); (H.X.); (M.L.); (X.S.); (F.Y.); (Y.F.)
- Authors to whom correspondence should be addressed; E-Mails: (S.S.K.); (L.C.); Tel.: +82-31-920-2491 (S.S.K.); +86-24-23256666 (ext. 6014) (L.C.); Fax: +82-31-920-2494 (S.S.K.); +86-24-23264417 (L.C.)
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Tivey HSE, Brook AJC, Rokicki MJ, Kipling D, Davis T. p38 (MAPK) stress signalling in replicative senescence in fibroblasts from progeroid and genomic instability syndromes. Biogerontology 2012; 14:47-62. [PMID: 23112078 PMCID: PMC3627027 DOI: 10.1007/s10522-012-9407-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2011] [Accepted: 10/17/2012] [Indexed: 12/26/2022]
Abstract
Werner Syndrome (WS) is a human segmental progeria resulting from mutations in a DNA helicase. WS fibroblasts have a shortened replicative capacity, an aged appearance, and activated p38 MAPK, features that can be modulated by inhibition of the p38 pathway. Loss of the WRNp RecQ helicase has been shown to result in replicative stress, suggesting that a link between faulty DNA repair and stress-induced premature cellular senescence may lead to premature ageing in WS. Other progeroid syndromes that share overlapping pathophysiological features with WS also show defects in DNA processing, raising the possibility that faulty DNA repair, leading to replicative stress and premature cellular senescence, might be a more widespread feature of premature ageing syndromes. We therefore analysed replicative capacity, cellular morphology and p38 activation, and the effects of p38 inhibition, in fibroblasts from a range of progeroid syndromes. In general, populations of young fibroblasts from non-WS progeroid syndromes do not have a high level of cells with an enlarged morphology and F-actin stress fibres, unlike young WS cells, although this varies between strains. p38 activation and phosphorylated HSP27 levels generally correlate well with cellular morphology, and treatment with the p38 inhibitor SB203580 effects cellular morphology only in strains with enlarged cells and phosphorylated HSP27. For some syndromes fibroblast replicative capacity was within the normal range, whereas for others it was significantly shorter (e.g. HGPS and DKC). However, although in most cases SB203580 extended replicative capacity, with the exception of WS and DKC the magnitude of the effect was not significantly different from normal dermal fibroblasts. This suggests that stress-induced premature cellular senescence via p38 activation is restricted to a small subset of progeroid syndromes.
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Affiliation(s)
- Hannah S E Tivey
- Institute of Cancer and Genetics, School of Medicine, Cardiff University, Heath Park, Cardiff, CF14 4XN, UK
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Wu X, Jia S, Zhang X, Si X, Tang W, Luo Y. Two mechanisms underlying the loss of p16(Ink4a) function are associated with distinct tumorigenic consequences for WS MEFs escaping from senescence. Mech Ageing Dev 2012; 133:549-55. [PMID: 22813853 DOI: 10.1016/j.mad.2012.07.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Revised: 06/22/2012] [Accepted: 07/08/2012] [Indexed: 01/26/2023]
Abstract
Werner syndrome (WS) mouse embryonic fibroblasts (MEFs) can spontaneously escape from senescence and become immortalized, either tumorigenic or non-tumorigenic. Our data revealed a single p53(N236S) point mutation in the tumorigenic cell lines, which was correlated with the down-regulation of p21(Waf1/Cip1). p16(Ink4a) expression was significantly decreased in all immortalized cell lines. Bisulfate sequencing indicated that the p16(Ink4a) gene was methylated in the tumorigenic cells. Exogenous overexpression of p21(Waf1/Cip1) demethylated p16(Ink4a) and restored its expression, which induced cell growth arrest and senescence. While in non-tumorigenic immortalized cells, the Ink4a loci and adjacent genomic DNA were found to be deleted. These data suggest that the loss of p16(Ink4a) function by either genomic DNA deletion or methylation have been adopted by senescent WS MEFs escaping from senescence, with distinct tumorigenic consequences. The fact that cells that had escaped senescence via the spontaneous biallelic deletion of the Ink4a loci could not form tumors suggests that the functional loss of p16(Ink4a)per se might not be sufficient for tumorigenesis; most likely, it is a byproduct and passenger mutation. The mutations in factors regulating p16(Ink4a) methylation might be the driver mutation. These findings shed light on the strategy of anti-aging by regulating p16(Ink4a) expression.
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Affiliation(s)
- Xiaoming Wu
- Laboratory of Molecular Genetics of Aging & Tumor, Faculty of Medicine, Kunming University of Science & Technology, 727 Jing Ming Nan Road, Chenggong County, Kunming, 650500, Yunnan Province, China
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Sheerin AN, Smith SK, Jennert‐Burston K, Brook AJ, Allen MC, Ibrahim B, Jones D, Wallis C, Engelmann K, Rhys‐Williams W, Faragher RGA, Kipling D. Characterization of cellular senescence mechanisms in human corneal endothelial cells. Aging Cell 2012; 11:234-40. [PMID: 22128747 PMCID: PMC3440103 DOI: 10.1111/j.1474-9726.2011.00776.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The human cornea is a tri-laminar structure composed of several cell types with substantial mitotic potential. Age-related changes in the cornea are associated with declining visual acuity and the onset of overt age-related corneal diseases. Corneal transplantation is commonly used to restore vision in patients with damaged or diseased corneas. However, the supply of donor tissue is limited, and thus there is considerable interest in the development of tissue-engineered alternatives. A major obstacle to these approaches is the short replicative lifespan of primary human corneal endothelial cells (HCEC). Accordingly, a comprehensive investigation of the signalling pathways and mechanisms underpinning proliferative lifespan and senescence in HCEC was undertaken. The effects of exogenous human telomerase reverse transcriptase expression, p53 knockdown, disruption of the pRb pathway by over-expression of CDK4 and reduced oxygen concentration on the lifespan of primary HCEC were evaluated. We provide proof-of-principle that forced expression of telomerase, when combined with either p53 knockdown or CDK4 over-expression, is sufficient to produce immortalized HCEC lines. The resultant cell lines express an HCEC-specific transcriptional fingerprint, and retain expression of the corneal endothelial temperature-sensitive potassium channel, suggesting that significant dedifferentiation does not occur as a result of these modes of immortalization. Exploiting these insights into proliferative lifespan barriers in HCEC will underpin the development of novel strategies for cell-based therapies in the human cornea.
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Affiliation(s)
- Angela N. Sheerin
- School of Pharmacy and Biomolecular Sciences, University of Brighton, Huxley Building, Lewes Road, Brighton BN2 4GJ, UK
| | - S. Kaye Smith
- School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, UK
| | - Katrin Jennert‐Burston
- School of Pharmacy and Biomolecular Sciences, University of Brighton, Huxley Building, Lewes Road, Brighton BN2 4GJ, UK
| | - Amy J. Brook
- School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, UK
| | - Marcus C. Allen
- School of Pharmacy and Biomolecular Sciences, University of Brighton, Huxley Building, Lewes Road, Brighton BN2 4GJ, UK
| | - Badr Ibrahim
- School of Pharmacy and Biomolecular Sciences, University of Brighton, Huxley Building, Lewes Road, Brighton BN2 4GJ, UK
| | - Dawn Jones
- School of Pharmacy and Biomolecular Sciences, University of Brighton, Huxley Building, Lewes Road, Brighton BN2 4GJ, UK
| | - Corrin Wallis
- School of Pharmacy and Biomolecular Sciences, University of Brighton, Huxley Building, Lewes Road, Brighton BN2 4GJ, UK
| | - Katrin Engelmann
- Department of Ophthalmology, Klinikum Chemnitz GmbH, Klinik für Augenheilkunde, Flemmingstraße 2, 09116 Chemnitz, Dresden, Germany
- DFG‐Center for Regenerative Therapies Dresden, Tatzberg 47/49, D‐01307 Dresden, Germany
| | - William Rhys‐Williams
- Destiny Pharma Ltd., Sussex Innovation Centre, Science Park Square, Falmer, Brighton BN1 9SB, UK
| | - Richard G. A. Faragher
- School of Pharmacy and Biomolecular Sciences, University of Brighton, Huxley Building, Lewes Road, Brighton BN2 4GJ, UK
| | - David Kipling
- School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, UK
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15
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Lachapelle S, Oesterreich S, Lebel M. The Werner syndrome helicase protein is required for cell proliferation, immortalization, and tumorigenesis in Scaffold attachment factor B1 deficient mice. Aging (Albany NY) 2011; 3:277-90. [PMID: 21464516 PMCID: PMC3091521 DOI: 10.18632/aging.100300] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Werner syndrome (WS) is a rare disorder characterized by the premature onset of several pathologies associated with aging. The gene responsible for WS codes for a RecQ-type DNA helicase and is believed to be involved in different aspects of DNA repair, replication, and transcription. We recently identified the Scaffold attachment factor B1 (SAFB1) as a potential interactants in human cells. SAFB1 is a multifunctional protein that binds both nucleic acids and is involved in the attachment of chromatin to the nuclear matrix, transcription, and stress response. Mice lacking SAFB1 exhibit developmental abnormalities in their lungs, high incidence of perinatal lethality, and adults develop different types of tumors. Mouse embryonic fibroblasts from Safb1-null animals are immortalized in culture. In this study, mice with a mutation in the helicase domain of the Wrn gene were crossed to Safb1-null mice. Double homozygous mutant mice exhibited increased apoptosis, a lower cell proliferation rate in their lungs and a higher incidence of perinatal death compared to Safb1-null mice. Few double homozygous mutants survived weaning and died before the age of six months. Finally, mouse embryonic fibroblasts lacking a functional Wrn helicase inhibited the immortalization of Safb1-null cells. These results indicate that an intact Wrn protein is required for immortalization and tumorigenesis in Safb1-null mice.
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Affiliation(s)
- Sophie Lachapelle
- Centre de Recherche en Cancérologie de l'Université Laval, Hôpital Hôtel‐Dieu de Québec, Québec City, Canada
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16
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Jeppesen DK, Bohr VA, Stevnsner T. DNA repair deficiency in neurodegeneration. Prog Neurobiol 2011; 94:166-200. [PMID: 21550379 DOI: 10.1016/j.pneurobio.2011.04.013] [Citation(s) in RCA: 243] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2011] [Revised: 04/18/2011] [Accepted: 04/22/2011] [Indexed: 01/17/2023]
Abstract
Deficiency in repair of nuclear and mitochondrial DNA damage has been linked to several neurodegenerative disorders. Many recent experimental results indicate that the post-mitotic neurons are particularly prone to accumulation of unrepaired DNA lesions potentially leading to progressive neurodegeneration. Nucleotide excision repair is the cellular pathway responsible for removing helix-distorting DNA damage and deficiency in such repair is found in a number of diseases with neurodegenerative phenotypes, including Xeroderma Pigmentosum and Cockayne syndrome. The main pathway for repairing oxidative base lesions is base excision repair, and such repair is crucial for neurons given their high rates of oxygen metabolism. Mismatch repair corrects base mispairs generated during replication and evidence indicates that oxidative DNA damage can cause this pathway to expand trinucleotide repeats, thereby causing Huntington's disease. Single-strand breaks are common DNA lesions and are associated with the neurodegenerative diseases, ataxia-oculomotor apraxia-1 and spinocerebellar ataxia with axonal neuropathy-1. DNA double-strand breaks are toxic lesions and two main pathways exist for their repair: homologous recombination and non-homologous end-joining. Ataxia telangiectasia and related disorders with defects in these pathways illustrate that such defects can lead to early childhood neurodegeneration. Aging is a risk factor for neurodegeneration and accumulation of oxidative mitochondrial DNA damage may be linked with the age-associated neurodegenerative disorders Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis. Mutation in the WRN protein leads to the premature aging disease Werner syndrome, a disorder that features neurodegeneration. In this article we review the evidence linking deficiencies in the DNA repair pathways with neurodegeneration.
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Affiliation(s)
- Dennis Kjølhede Jeppesen
- Danish Centre for Molecular Gerontology and Danish Aging Research Center, University of Aarhus, Department of Molecular Biology, Aarhus, Denmark
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17
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Jung YS, Qian Y, Chen X. Examination of the expanding pathways for the regulation of p21 expression and activity. Cell Signal 2010; 22:1003-12. [PMID: 20100570 PMCID: PMC2860671 DOI: 10.1016/j.cellsig.2010.01.013] [Citation(s) in RCA: 324] [Impact Index Per Article: 23.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2010] [Accepted: 01/16/2010] [Indexed: 02/06/2023]
Abstract
p21(Waf1/Cip1/Sdi1) was originally identified as an inhibitor of cyclin-dependent kinases, a mediator of p53 in growth suppression and a marker of cellular senescence. p21 is required for proper cell cycle progression and plays a role in cell death, DNA repair, senescence and aging, and induced pluripotent stem cell reprogramming. Although transcriptional regulation is considered to be the initial control point for p21 expression, there is growing evidence that post-transcriptional and post-translational regulations play a critical role in p21 expression and activity. This review will briefly discuss the activity of p21 and focus on current knowledge of the determinants that control p21 transcription, mRNA stability and translation, and protein stability and activity.
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Affiliation(s)
- Yong-Sam Jung
- Center for Comparative Oncology, University of California, Davis, California 95616, USA
| | - Yingjuan Qian
- Center for Comparative Oncology, University of California, Davis, California 95616, USA
| | - Xinbin Chen
- Center for Comparative Oncology, University of California, Davis, California 95616, USA
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18
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Use of p38 MAPK Inhibitors for the Treatment of Werner Syndrome. Pharmaceuticals (Basel) 2010; 3:1842-1872. [PMID: 27713332 PMCID: PMC4033955 DOI: 10.3390/ph3061842] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2010] [Revised: 05/13/2010] [Accepted: 05/26/2010] [Indexed: 11/17/2022] Open
Abstract
Werner syndrome provides a convincing model for aspects of the normal ageing phenotype and may provide a suitable model for therapeutic interventions designed to combat the ageing process. Cultured primary fibroblast cells from Werner syndrome patients provide a powerful model system to study the link between replicative senescence in vitro and in vivo pathophysiology. Genome instability, together with an increased pro-oxidant state, and frequent replication fork stalling, all provide plausible triggers for intracellular stress in Werner syndrome cells, and implicates p38 MAPK signaling in their shortened replicative lifespan. A number of different p38 MAPK inhibitor chemotypes have been prepared rapidly and efficiently using microwave heating techniques for biological study in Werner syndrome cells, including SB203580, VX-745, RO3201195, UR-13756 and BIRB 796, and their selectivity and potency evaluated in this cellular context. Werner syndrome fibroblasts treated with a p38 MAPK inhibitor reveal an unexpected reversal of the accelerated ageing phenotype. Thus the study of p38 inhibition and its effect upon Werner pathophysiology is likely to provide new revelations into the biological mechanisms operating in cellular senescence and human ageing in the future.
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19
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Benson EK, Zhao B, Sassoon DA, Lee SW, Aaronson SA. Effects of p21 deletion in mouse models of premature aging. Cell Cycle 2009; 8:2002-4. [PMID: 19535900 DOI: 10.4161/cc.8.13.8997] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
An approach to investigate the role of cellular senescence in organismal aging has been to abrogate signaling pathways known to induce cellular senescence and to assess the effects in mouse models of premature aging. Recently, we reported the effect of loss of function of p21, a gene implicated in p53-induced cellular senescence, in the background of the Ku80(-/-) premature aging mouse (Zhao et al., EMBO Rep 2009). Here, we provide an overview of the effects of p21 deletion in different models of premature aging.
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Affiliation(s)
- Erica K Benson
- Department of Oncological Sciences, Mount Sinai School of Medicine, New York, NY 10029, USA
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20
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Davis T, Kipling D. Assessing the role of stress signalling via p38 MAP kinase in the premature senescence of ataxia telangiectasia and Werner syndrome fibroblasts. Biogerontology 2008; 10:253-66. [PMID: 18830681 DOI: 10.1007/s10522-008-9179-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2008] [Accepted: 09/18/2008] [Indexed: 10/21/2022]
Abstract
The premature ageing ataxia telangiectasia (AT) and Werner syndromes (WS) are associated with accelerated cellular ageing. Young WS fibroblasts have an aged appearance and activated p38 MAP kinase, and treatment with the p38 inhibitor SB230580 extends their lifespan to within the normal range. SB203580 also extends the replicative lifespan of normal adult dermal fibroblasts, however, the effect is much reduced when compared to WS cells, suggesting that WS fibroblasts undergo a form of stress-induced premature senescence (SIPS). A small lifespan extension is seen in AT cells, which is not significant compared to normal fibroblasts, and the majority of young AT cells do not have an aged appearance and lack p38 activation, suggesting that the premature ageing does not result from SIPS. The lack of p38 activation is supported by the clinical manifestation, since AT is not associated with inflammatory disease, whereas WS individuals are predisposed to atherosclerosis, type II diabetes and osteoporosis, conditions known to be associated with p38 activation.
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Affiliation(s)
- Terence Davis
- Department of Pathology, Cardiff University, Heath Park, Cardiff, CF14 4XN, UK.
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21
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Garcia SN, Pereira-Smith O. MRGing Chromatin Dynamics and Cellular Senescence. Cell Biochem Biophys 2008; 50:133-41. [DOI: 10.1007/s12013-008-9006-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2007] [Accepted: 12/15/2007] [Indexed: 11/28/2022]
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22
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Abstract
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.
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Affiliation(s)
- Robert M Brosh
- Laboratory of Molecular Gerontology, National Institute on Aging, NIH, 5600 Nathan Shock Drive, Baltimore, MD 21224, USA
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23
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Cox LS, Faragher RGA. From old organisms to new molecules: integrative biology and therapeutic targets in accelerated human ageing. Cell Mol Life Sci 2007; 64:2620-41. [PMID: 17660942 PMCID: PMC2773833 DOI: 10.1007/s00018-007-7123-x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Understanding the basic biology of human ageing is a key milestone in attempting to ameliorate the deleterious consequences of old age. This is an urgent research priority given the global demographic shift towards an ageing population. Although some molecular pathways that have been proposed to contribute to ageing have been discovered using classical biochemistry and genetics, the complex, polygenic and stochastic nature of ageing is such that the process as a whole is not immediately amenable to biochemical analysis. Thus, attempts have been made to elucidate the causes of monogenic progeroid disorders that recapitulate some, if not all, features of normal ageing in the hope that this may contribute to our understanding of normal human ageing. Two canonical progeroid disorders are Werner's syndrome and Hutchinson-Gilford progeroid syndrome (also known as progeria). Because such disorders are essentially phenocopies of ageing, rather than ageing itself, advances made in understanding their pathogenesis must always be contextualised within theories proposed to help explain how the normal process operates. One such possible ageing mechanism is described by the cell senescence hypothesis of ageing. Here, we discuss this hypothesis and demonstrate that it provides a plausible explanation for many of the ageing phenotypes seen in Werner's syndrome and Hutchinson-Gilford progeriod syndrome. The recent exciting advances made in potential therapies for these two syndromes are also reviewed.
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Affiliation(s)
- L. S. Cox
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU UK
| | - R. G. A. Faragher
- School of Pharmacy and Biomolecular Science, University of Brighton, Cockcroft Building, Moulescoomb, Brighton, BN2 4GJ UK
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24
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Islam MQ, Islam K, Sharp CA. Epigenetic reprogramming of nonreplicating somatic cells for long-term proliferation by temporary cell-cell contact. Stem Cells Dev 2007; 16:253-68. [PMID: 17521237 DOI: 10.1089/scd.2006.0094] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Embryonic stem (ES) cells are potential sources of tissue regeneration; however, transplanted ES cells produce tumors in the host tissues. In addition, transplantation between genetically unrelated individuals often results in graft rejection. Although the development of patient specific stem cell lines by somatic cell nuclear transfer (SCNT) represents a means of overcoming the problem of rejection, its human application has ethical dilemmas. Adult stem (AS) cells can also differentiate into specialized cells and may provide an alternative source of cells for human applications. In common with other somatic cells, AS cells have limited capacity for proliferation and cannot be produced in large quantities without genetic manipulation. We demonstrate here that nonreplicating mammalian cells can be reprogrammed for long-term proliferation by temporary cell-cell contact through coculture of AS cells with the GM05267-derived F7 mouse cell line. Subsequent elimination of F7 cells from the co-culture allows proliferation of previously nonreplicating cells, colonies of which can be isolated to produce cell lines. We also demonstrate that the epigenetically reprogrammed AS cells, without the physical transfer of either nuclear or cytoplasmic material from other cells, are capable of long-term proliferation and able to relay signals to other nonreplicating cells to reinitiate proliferation with no addition of recombinant factors. The reported cell amplification procedure is methodologically simple and can be easily reproduced. This procedure allows the production of an unlimited number of cells from a limited number of AS cells, making them an ideal source of cells for applications involving autologous cell transplantation.
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Affiliation(s)
- M Q Islam
- Laboratory of Cancer Genetics, Laboratory Medicine Center (LMC), University Hospital Linköping, 58216 Linköping, Sweden.
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25
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Davis T, Wyllie FS, Rokicki MJ, Bagley MC, Kipling D. The role of cellular senescence in Werner syndrome: toward therapeutic intervention in human premature aging. Ann N Y Acad Sci 2007; 1100:455-69. [PMID: 17460211 DOI: 10.1196/annals.1395.051] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Werner syndrome (WS) is a premature aging disorder used as a model of normal human aging. WS individuals have several characteristics of normal aging, such as cataracts, hair graying, and skin aging, but manifest these at an early age. Additionally, WS individuals have high levels of inflammatory diseases, such as atherosclerosis and type 2 diabetes. The in vivo aging in WS is associated with accelerated aging of fibroblasts in culture. The cause of the accelerated senescence is not understood, but may be due to the genomic instability that is a hallmark of WS. Genome instability results in activation of stress kinases, such as p38, and the p38-specific inhibitor SB203580, prevents the accelerated senescence seen in WS fibroblasts. However, oxidative damage plays a role, as low oxygen conditions and antioxidant treatment revert some of the accelerated senescence phenotype. The effects of oxidative stress appear to be suppressible by SB203580; however, it does not appear to be transduced by p38. As SB203580 is known to inhibit other kinases in addition to p38, this suggests that more than one kinase pathway is involved. The recent development of p38 inhibitors with different binding properties, specificities, and oral bioavailability, and of new potent and selective inhibitors of JNK and MK2, will make it possible to dissect the roles of various kinase pathways in the accelerated senescence of WS cells. If this accelerated senescence is reflective of WS aging in vivo, these kinase inhibitors may well form the basis of antiaging therapies for individuals with WS.
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Affiliation(s)
- Terence Davis
- Department of Pathology, School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, UK.
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26
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Islam MQ, Panduri V, Islam K. Generation of somatic cell hybrids for the production of biologically active factors that stimulate proliferation of other cells. Cell Prolif 2007; 40:91-105. [PMID: 17227298 PMCID: PMC6496579 DOI: 10.1111/j.1365-2184.2007.00422.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
OBJECTIVE Some normal somatic cells in culture divide a limited number of times before entering a non-dividing state called replicative senescence and fusion of normal cells with immortal cells claimed to produce hybrid cells of limited proliferation. We reinvestigated the proliferative capacity of hybrid cells between normal cell and immortal cell. MATERIALS AND METHODS Normal pig fibroblast cells and cells of immortal mouse fibroblast cell line F7, a derivative of GM05267, were fused by polyethylene glycol treatment and subsequently the fused cells were cultured in a selective medium containing hypoxanthine-aminopterin-thymidine in order to enrich the hybrid cells. The hybrid cells were then monitored for chromosome content and proliferation. RESULTS Cytogenetic analysis revealed that the hybrid cells contained polyploidy chromosomes derived from normal pig fibroblasts. These hybrid cells exhibit no sign of replicative senescence after more than 190 population doublings in vitro. Instead, these hybrid cells have an accelerated growth and proliferate even in the complete absence of glutamine. In addition, these hybrids produce biologically active factors in the conditioned media, which not only can accelerate their own proliferation but also can reinitiate mitotic activity in the senescent-like normal fibroblast cells. CONCLUSIONS Our results question the validity of cellular senescence as a dominant trait. Additionally, the generation of hybrid cells using the specific mouse cell line can be applied to the generation of hybrids with other normal cell types and can be used to produce tissue-specific growth-factor(s) to extend the lifespan and/or improve the proliferation of various normal cells, including adult stem cells.
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Affiliation(s)
- M Q Islam
- Laboratory of Cancer Genetics, Laboratory Medicine Center (LMC), University Hospital Linköping, Linköping, Sweden.
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27
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Sharma S, Stumpo DJ, Balajee AS, Bock CB, Lansdorp PM, Brosh RM, Blackshear PJ. RECQL, a member of the RecQ family of DNA helicases, suppresses chromosomal instability. Mol Cell Biol 2006; 27:1784-94. [PMID: 17158923 PMCID: PMC1820448 DOI: 10.1128/mcb.01620-06] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The mouse gene Recql is a member of the RecQ subfamily of DEx-H-containing DNA helicases. Five members of this family have been identified in both humans and mice, and mutations in three of these, BLM, WRN, and RECQL4, are associated with human diseases and a cellular phenotype that includes genomic instability. To date, no human disease has been associated with mutations in RECQL and no cellular phenotype has been associated with its deficiency. To gain insight into the physiological function of RECQL, we disrupted Recql in mice. RECQL-deficient mice did not exhibit any apparent phenotypic differences compared to wild-type mice. Cytogenetic analyses of embryonic fibroblasts from the RECQL-deficient mice revealed aneuploidy, spontaneous chromosomal breakage, and frequent translocation events. In addition, the RECQL-deficient cells were hypersensitive to ionizing radiation, exhibited an increased load of DNA damage, and displayed elevated spontaneous sister chromatid exchanges. These results provide evidence that RECQL has a unique cellular role in the DNA repair processes required for genomic integrity. Genetic background, functional redundancy, and perhaps other factors may protect the unstressed mouse from the types of abnormalities that might be expected from the severe chromosomal aberrations detected at the cellular level.
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Affiliation(s)
- Sudha Sharma
- NIEHS MD A2-05, 111 Alexander Drive, Research Triangle Park, NC 27709, USA
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28
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Eller MS, Liao X, Liu S, Hanna K, Bäckvall H, Opresko PL, Bohr VA, Gilchrest BA. A role for WRN in telomere-based DNA damage responses. Proc Natl Acad Sci U S A 2006; 103:15073-8. [PMID: 17015833 PMCID: PMC1586178 DOI: 10.1073/pnas.0607332103] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2006] [Indexed: 12/26/2022] Open
Abstract
Telomeres cap the ends of eukaryotic chromosomes and prevent them from being recognized as DNA breaks. We have shown that certain DNA damage responses induced during senescence and, at times of telomere uncapping, also can be induced by treatment of cells with small DNA oligonucleotides homologous to the telomere 3' single-strand overhang (T-oligos), implicating this overhang in generation of these telomere-based damage responses. Here, we show that T-oligo-treated fibroblasts contain gammaH2AX foci and that these foci colocalize with telomeres. T-oligos with nuclease-resistant 3' ends are inactive, suggesting that a nuclease initiates T-oligo responses. We therefore examined WRN, a 3'-->5' exonuclease and helicase mutated in Werner syndrome, a disorder characterized by aberrant telomere maintenance, premature aging, chromosomal rearrangements, and predisposition to malignancy. Normal fibroblasts and U20S osteosarcoma cells rendered deficient in WRN showed reduced phosphorylation of p53 and histone H2AX in response to T-oligo treatment. Together, these data demonstrate a role for WRN in processing of telomeric DNA and subsequent activation of DNA damage responses. The T-oligo model helps define the role of WRN in telomere maintenance and initiation of DNA damage responses after telomere disruption.
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Affiliation(s)
- Mark S. Eller
- *Department of Dermatology, Boston University School of Medicine, 609 Albany Street, Boston, MA 02118
| | - Xiaodong Liao
- *Department of Dermatology, Boston University School of Medicine, 609 Albany Street, Boston, MA 02118
| | - SuiYang Liu
- *Department of Dermatology, Boston University School of Medicine, 609 Albany Street, Boston, MA 02118
| | - Kendra Hanna
- *Department of Dermatology, Boston University School of Medicine, 609 Albany Street, Boston, MA 02118
| | - Helena Bäckvall
- *Department of Dermatology, Boston University School of Medicine, 609 Albany Street, Boston, MA 02118
| | - Patricia L. Opresko
- Department of Environmental and Occupational Health, University of Pittsburgh, 100 Technology Drive, Cellomics Building, Suite 350, Pittsburgh, PA 15219; and
| | - Vilhelm A. Bohr
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, 5600 Nathan Shock Drive, Baltimore, MD 21224-6825
| | - Barbara A. Gilchrest
- *Department of Dermatology, Boston University School of Medicine, 609 Albany Street, Boston, MA 02118
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29
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Sharma S, Doherty K, Brosh R. Mechanisms of RecQ helicases in pathways of DNA metabolism and maintenance of genomic stability. Biochem J 2006; 398:319-37. [PMID: 16925525 PMCID: PMC1559444 DOI: 10.1042/bj20060450] [Citation(s) in RCA: 193] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Helicases are molecular motor proteins that couple the hydrolysis of NTP to nucleic acid unwinding. The growing number of DNA helicases implicated in human disease suggests that their vital specialized roles in cellular pathways are important for the maintenance of genome stability. In particular, mutations in genes of the RecQ family of DNA helicases result in chromosomal instability diseases of premature aging and/or cancer predisposition. We will discuss the mechanisms of RecQ helicases in pathways of DNA metabolism. A review of RecQ helicases from bacteria to human reveals their importance in genomic stability by their participation with other proteins to resolve DNA replication and recombination intermediates. In the light of their known catalytic activities and protein interactions, proposed models for RecQ function will be summarized with an emphasis on how this distinct class of enzymes functions in chromosomal stability maintenance and prevention of human disease and cancer.
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Affiliation(s)
- Sudha Sharma
- Laboratory of Molecular Gerontology, National Institute on Aging, NIH, 5600 Nathan Shock Drive, Baltimore, MD 21224, U.S.A
| | - Kevin M. Doherty
- Laboratory of Molecular Gerontology, National Institute on Aging, NIH, 5600 Nathan Shock Drive, Baltimore, MD 21224, U.S.A
| | - Robert M. Brosh
- Laboratory of Molecular Gerontology, National Institute on Aging, NIH, 5600 Nathan Shock Drive, Baltimore, MD 21224, U.S.A
- To whom correspondence should be addressed (email )
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30
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Davis T, Haughton MF, Jones CJ, Kipling D. Prevention of Accelerated Cell Aging in the Werner Syndrome. Ann N Y Acad Sci 2006; 1067:243-7. [PMID: 16803993 DOI: 10.1196/annals.1354.031] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
In the Werner syndrome (WS) fibroblasts have an increased life span and growth rate when treated with the p38 inhibitor SB203580. Additionally, the cellular morphology reverts to that seen in young normal fibroblasts. The p38 pathway is activated in young WS cells, associated with high levels of p21(WAF1) leading to cell cycle arrest, and is suppressed by SB203580. As these changes are also seen in telomerized WS cells, these data show that the growth problems seen in WS cells, and perhaps the accelerated in vivo aging, are due to a telomere-independent premature senescence mechanism. The suppression of this mechanism by SB203580 treatment suggests a route whereby WS may be amenable to therapeutic intervention.
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Affiliation(s)
- Terence Davis
- Department of Pathology, Henry Wellcome Building, School of Medicine, Cardiff University, Heath Park, Wales, UK.
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31
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Davis T, Baird DM, Haughton MF, Jones CJ, Kipling D. Prevention of Accelerated Cell Aging in Werner Syndrome Using a p38 Mitogen-Activated Protein Kinase Inhibitor. J Gerontol A Biol Sci Med Sci 2005; 60:1386-93. [PMID: 16339323 DOI: 10.1093/gerona/60.11.1386] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
We investigated the role of p38 mitogen-activated protein kinase (MAPK) signalling in the accelerated aging of Werner Syndrome (WS) fibroblasts by use of SB203580, a cytokine-suppressive anti-inflammatory drug that targets p38 activity. SB203580 treatment reverts the aged morphology of young WS fibroblasts to that seen in young normal fibroblasts. In addition, SB203580 increases the life span and growth rate of WS fibroblasts to within the normal range. In young WS cells, p38 is activated coincident with an up-regulation of p21(WAF1), and a reduction in the levels of both activated p38 and p21(WAF1) are seen following treatment with SB203580. As these effects are not seen in young normal cells, our data suggest that the abbreviated replicative life span of WS cells is due to a stress-induced, p38-mediated growth arrest that is independent of telomere erosion. With some p38 inhibitors already in clinical trials, our data suggest a potential route to drug intervention in a premature aging syndrome.
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Affiliation(s)
- Terence Davis
- D.Phil, Department of Pathology, School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, United Kingdom
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Kyng KJ, May A, Stevnsner T, Becker KG, Kølvrå S, Bohr VA. Gene expression responses to DNA damage are altered in human aging and in Werner Syndrome. Oncogene 2005; 24:5026-42. [PMID: 15897889 DOI: 10.1038/sj.onc.1208692] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The accumulation of DNA damage and mutations is considered a major cause of cancer and aging. While it is known that DNA damage can affect changes in gene expression, transcriptional regulation after DNA damage is poorly understood. We characterized the expression of 6912 genes in human primary fibroblasts after exposure to three different kinds of cellular stress that introduces DNA damage: 4-nitroquinoline-1-oxide (4NQO), gamma-irradiation, or UV-irradiation. Each type of stress elicited damage specific gene expression changes of up to 10-fold. A total of 85 genes had similar changes in expression of 3-40-fold after all three kinds of stress. We examined transcription in cells from young and old individuals and from patients with Werner syndrome (WS), a segmental progeroid condition with a high incidence of cancer, and found various age-associated transcriptional changes depending upon the type of cellular stress. Compared to young individuals, both WS and old individuals had similarly aberrant transcriptional responses to gamma- and UV-irradiation, suggesting a role for Werner protein in stress-induced gene expression. Our results suggest that aberrant DNA damage-induced gene regulation may contribute to the aging process and the premature aging in WS.
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Affiliation(s)
- Kasper J Kyng
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, 5600 Nathan Shock Drive, Baltimore, MD 21224, USA
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Pagano G, Zatterale A, Degan P, d'Ischia M, Kelly FJ, Pallardó FV, Kodama S. Multiple Involvement of Oxidative Stress in Werner Syndrome Phenotype. Biogerontology 2005; 6:233-43. [PMID: 16333757 DOI: 10.1007/s10522-005-2624-1] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2005] [Accepted: 06/23/2005] [Indexed: 01/12/2023]
Abstract
Werner syndrome is a genetic disease characterized by early ageing, excess cancer risk, high incidence of type II diabetes mellitus, early atherosclerosis, ocular cataracts, and osteoporosis. The protein encoded by the defective gene, WRN (WRNp) associates with three activities, that is, a RecQ DNA helicase, 3'-5'-exonuclease and ATPase activities. By highlighting the DNA helicase activity, a widespread consensus in WS-associated defect(s) has been established, pointing toward a deficiency in maintaining DNA integrity. However, a possible involvement of redox pathways in WS may be suggested by several lines of evidence that include: (i) the multiple functions and interactions of WRNp with oxidative stress-related activities and factors; (ii) the pleiotropic WS clinical phenotype encompassing a number of oxidative stress-related pathologies; (iii) redox-related toxicity mechanisms of several xenobiotics exerting excess toxicity in WS cells; (iv) recent in vivo and in vitro findings of redox abnormalities in WS patients and in WS cells. The working hypothesis is raised that a deficiency in WRNp, and the pleiotropic clinical phenotype in WS patients may provide the basis to envision an underlying in vivo prooxidant state, which causes oxidative damage to biomolecules, with multiple oxidative stress-related alterations, resulting in multi-faceted clinical consequences.
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Affiliation(s)
- Giovanni Pagano
- Italian National Cancer Institute, G. Pascale Foundation, I-80131 Naples, Italy.
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Davis T, Skinner JW, Faragher RGA, Jones CJ, Kipling D. Replicative senescence in sheep fibroblasts is a p53 dependent process. Exp Gerontol 2005; 40:17-26. [PMID: 15664728 DOI: 10.1016/j.exger.2004.09.004] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2004] [Revised: 09/06/2004] [Accepted: 09/13/2004] [Indexed: 11/26/2022]
Abstract
Studies on telomere and telomerase biology are fundamental to the understanding of human ageing, and age-related diseases such as cancer. However, human studies are hampered by the lack of fully reflective animal model systems. Here we describe basic studies of telomere length and telomerase activity in sheep tissues and cells. Terminal restriction fragment lengths from sheep tissues ranged from 9 to 23 kb, with telomerase activity present in testis but suppressed in somatic tissues. Sheep fibroblasts had a finite lifespan in culture, after which the cells entered senescence. During in vitro growth the mean terminal restriction fragment lengths decreased in size at a rate of 210 and 350 bp per population doubling (PD). Senescent skin fibroblasts had increased levels of p53 and p21WAF1 compared to young cells. Incubation of senescent cells with siRNA duplexes specific for p53 suppressed p53 expression and allowed the cells to re-enter the cell cycle. Five PDs beyond senescence the siRNA-treated cells reached a second proliferative barrier. This study shows that telomere biology in sheep is similar to that in humans, with senescence in sheep GM03550 fibroblasts being a telomere-driven, p53-(p21WAF1)-dependent process. Therefore sheep may represent an alternative model system for studying telomere biology, replicative senescence, and by implication human ageing.
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Affiliation(s)
- Terence Davis
- Department of Pathology, School of Medicine, University of Cardiff, Heath Park, Cardiff CF14 4XN, Wales, UK
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Lombard DB, Chua KF, Mostoslavsky R, Franco S, Gostissa M, Alt FW. DNA repair, genome stability, and aging. Cell 2005; 120:497-512. [PMID: 15734682 DOI: 10.1016/j.cell.2005.01.028] [Citation(s) in RCA: 648] [Impact Index Per Article: 34.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Aging can be defined as progressive functional decline and increasing mortality over time. Here, we review evidence linking aging to nuclear DNA lesions: DNA damage accumulates with age, and DNA repair defects can cause phenotypes resembling premature aging. We discuss how cellular DNA damage responses may contribute to manifestations of aging. We review Sir2, a factor linking genomic stability, metabolism, and aging. We conclude with a general discussion of the role of mutant mice in aging research and avenues for future investigation.
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Affiliation(s)
- David B Lombard
- Howard Hughes Medical Institute, The Children's Hospital, Department of Genetics, Harvard Medical School and, The CBR Institute for Biomedical Research, Boston, Massachusetts 02115, USA
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Hardy K, Mansfield L, Mackay A, Benvenuti S, Ismail S, Arora P, O'Hare MJ, Jat PS. Transcriptional networks and cellular senescence in human mammary fibroblasts. Mol Biol Cell 2004; 16:943-53. [PMID: 15574883 PMCID: PMC545924 DOI: 10.1091/mbc.e04-05-0392] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Senescence, the molecular program that limits the finite proliferative potential of a cell, acts as an important barrier to protect the body from cancer. Techniques for measuring transcriptome changes and for modulating their expression suggest that it may be possible to dissect the transcriptional networks underlying complex cellular processes. HMF3A cells are conditionally immortalized human mammary fibroblasts that can be induced to undergo coordinated senescence. Here, we used these cells in conjunction with microarrays, RNA interference, and in silico promoter analysis to promote the dissection of the transcriptional networks responsible for regulating cellular senescence. We first identified changes in the transcriptome when HMF3A cells undergo senescence and then compared them with those observed upon replicative senescence in primary human mammary fibroblasts. In addition to DUSP1 and known p53 and E2F targets, a number of genes such as PHLDA1, NR4A3, and a novel splice variant of STAC were implicated in senescence. Their role in senescence was then analyzed by RNA silencing followed by microarray analysis. In silico promoter analysis of all differential genes predicted that nuclear factor-kappaB and C/EBP transcription factors are activated upon senescence, and we confirmed this by electrophoretic mobility shift assay. The results suggest a putative signaling network for cellular senescence.
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Affiliation(s)
- K Hardy
- Ludwig Institute for Cancer Research, University College School of Medicine, London W1W 7BS, United Kingdom
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Kipling D, Davis T, Ostler EL, Faragher RGA. What can progeroid syndromes tell us about human aging? Science 2004; 305:1426-31. [PMID: 15353794 DOI: 10.1126/science.1102587] [Citation(s) in RCA: 126] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Human genetic diseases that resemble accelerated aging provide useful models for gerontologists. They combine known single-gene mutations with deficits in selected tissues that are reminiscent of changes seen during normal aging. Here, we describe recent progress toward linking molecular and cellular changes with the phenotype seen in two of these disorders. One in particular, Werner syndrome, provides evidence to support the hypothesis that the senescence of somatic cells may be a causal agent of normal aging.
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Affiliation(s)
- David Kipling
- Department of Pathology, School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, UK
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de Magalhães JP, Migeot V, Mainfroid V, de Longueville F, Remacle J, Toussaint O. No Increase in Senescence-Associated β-Galactosidase Activity in Werner Syndrome Fibroblasts after Exposure to H2O2. Ann N Y Acad Sci 2004; 1019:375-8. [PMID: 15247048 DOI: 10.1196/annals.1297.066] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Normal human diploid fibroblasts (HDFs) exposed to a single H(2)O(2) subcytotoxic stress display features of premature senescence, termed stress-induced premature senescence (SIPS). In this work, our aim was to study SIPS in Werner syndrome (WS) fibroblasts, derived from a patient with WS, a disease resembling accelerated aging. The subcytotoxic dose for WS fibroblasts was found to be inferior to that of normal HDFs, indicating WS fibroblasts are more sensitive to hydrogen peroxide than normal HDFs. SA beta-gal activity has been shown to occur both in vitro and in vivo, and we studied the proportion of WS cells positive for SA beta-gal. Intriguingly, the percentage of positive cells did not increase with the dose of H(2)O(2) used. Contrary to other HDFs, the DNA-binding activity of p53 in WS fibroblasts did not increase in SIPS. We found, based on our results, that WS fibroblasts feature an altered stress response and do not reach SIPS from H(2)O(2). We suggest that the proportion of cells that in normal HDFs would enter SIPS instead die in WS fibroblasts. Last, we propose that aging derives from a loss of integrity of the chromatin structure, which occurs faster in WS patients.
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Opresko PL, Otterlei M, Graakjaer J, Bruheim P, Dawut L, Kølvraa S, May A, Seidman MM, Bohr VA. The Werner Syndrome Helicase and Exonuclease Cooperate to Resolve Telomeric D Loops in a Manner Regulated by TRF1 and TRF2. Mol Cell 2004; 14:763-74. [PMID: 15200954 DOI: 10.1016/j.molcel.2004.05.023] [Citation(s) in RCA: 232] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2003] [Revised: 04/27/2004] [Accepted: 04/27/2004] [Indexed: 11/25/2022]
Abstract
Werner syndrome (WS) is characterized by features of premature aging and is caused by loss of the RecQ helicase protein WRN. WS fibroblasts display defects associated with telomere dysfunction, including accelerated telomere erosion and premature senescence. In yeast, RecQ helicases act in an alternative pathway for telomere lengthening (ALT) via homologous recombination. We found that WRN associates with telomeres when dissociation of telomeric D loops is likely during replication and recombination. In human ALT cells, WRN associates directly with telomeric DNA. The majority of TRF1/PCNA colocalizing foci contained WRN in live S phase ALT cells but not in telomerase-positive HeLa cells. Biochemically, the WRN helicase and 3' to 5' exonuclease act simultaneously and cooperate to release the 3' invading tail from a telomeric D loop in vitro. The telomere binding proteins TRF1 and TRF2 limit digestion by WRN. We propose roles for WRN in dissociating telomeric structures in telomerase-deficient cells.
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Affiliation(s)
- Patricia L Opresko
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
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Davis T, Faragher RGA, Jones CJ, Kipling D. Investigation of the Signaling Pathways Involved in the Proliferative Life Span Barriers in Werner Syndrome Fibroblasts. Ann N Y Acad Sci 2004; 1019:274-7. [PMID: 15247028 DOI: 10.1196/annals.1297.046] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Werner syndrome (WS) fibroblasts enter replicative senescence after a reduced in vitro life span. Although this has been postulated as causal in the accelerated aging seen in this disease, controversy remains as to whether WS is showing the acceleration of a normal cellular aging mechanism or, instead, the occurrence of a novel WS-specific process. To address this, we analyzed the signaling pathways involved in senescence in WS fibroblasts. Cultured WS fibroblasts underwent senescence after approximately 20 population doublings, with the majority of the cells having a 2N DNA content. This was associated with high levels of the CdkIs p16 and p21. Senescent WS cells reentered the cell cycle after microinjection of a p53-neutralizing antibody. Similarly, presenescent WS fibroblasts expressing the E6 and/or E7 oncoproteins bypassed M1 and ultimately reached a second proliferative life span barrier, which strongly resembled the second life span barriers found in normal cells for growth dynamics, cellular morphology, and expression of p16 and p21. The strong similarity between the signaling pathways triggering cell cycle arrest in WS and normal fibroblasts provides support for the defect in WS causing the acceleration of a normal aging mechanism and validates the use of WS as a model for some aspects of human aging.
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Affiliation(s)
- Terence Davis
- Department of Pathology, University of Wales College of Medicine, Heath Park, Cardiff CF14 4XN, Wales.
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Preto A, Singhrao SK, Haughton MF, Kipling D, Wynford-Thomas D, Jones CJ. Telomere erosion triggers growth arrest but not cell death in human cancer cells retaining wild-type p53: implications for antitelomerase therapy. Oncogene 2004; 23:4136-45. [PMID: 15064743 DOI: 10.1038/sj.onc.1207564] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Telomerase activity in tumours is often associated with p53 mutation. Many antitelomerase therapies take advantage of the inability of cells expressing mutant p53 to undergo replicative senescence, since this allows telomere erosion to continue until 'crisis', hence providing the desired cytotoxic effect. However, some tumour types, including breast, melanomas and thyroid, retain wild-type p53 function and the effectiveness of antitelomerase therapies in such tumour cells have not been adequately addressed. To explore this, we made use of two thyroid cancer cell lines K1 and K2, which retain wt p53. Telomere erosion induced by the expression of a dominant-negative (DN) hTERT resulted in delayed onset of growth arrest in K1 and K2 cells, reminiscent of replicative senescence, with low levels of BrdU labelling and apoptosis, associated with high p21(WAF1) and senescence-associated beta galactosidase expression. In contrast, abrogation of p53 function by the expression of HPV16 E6 in K1 and K2 cells either at the same time as DNhTERT or just prior to the onset of senescence allowed cells to continue growing until 'crisis'. Likewise, microinjection of a p53 neutralizing antibody into 'senescent' K1 DNhTERT cells permitted re-entry into the cell cycle. We conclude that thyroid tumour cells with wild-type p53 retain an intact p53-mediated growth arrest response to telomere erosion. This raises the intriguing question of why, therefore, p53 mutation is not selected for in such cancers, and also calls into question the therapeutic value of telomerase inhibitors in such cases.
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Affiliation(s)
- Ana Preto
- Institute of Molecular Pathology and Immunology of the University of Porto, (IPATIMUP), Rua Dr Roberto Frias, s/n, 4200-465 Porto, Portugal
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Kyng KJ, May A, Kølvraa S, Bohr VA. Gene expression profiling in Werner syndrome closely resembles that of normal aging. Proc Natl Acad Sci U S A 2003; 100:12259-64. [PMID: 14527998 PMCID: PMC218746 DOI: 10.1073/pnas.2130723100] [Citation(s) in RCA: 123] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2003] [Indexed: 01/29/2023] Open
Abstract
Werner syndrome (WS) is a premature aging disorder, displaying defects in DNA replication, recombination, repair, and transcription. It has been hypothesized that several WS phenotypes are secondary consequences of aberrant gene expression and that a transcription defect may be crucial to the development of the syndrome. We used cDNA microarrays to characterize the expression of 6,912 genes and ESTs across a panel of 15 primary human fibroblast cell lines derived from young donors, old donors, and WS patients. Of the analyzed genes, 6.3% displayed significant differences in expression when either WS or old donor cells were compared with young donor cells. This result demonstrates that the WS transcription defect is specific to certain genes. Transcription alterations in WS were strikingly similar to those in normal aging: 91% of annotated genes displayed similar expression changes in WS and in normal aging, 3% were unique to WS, and 6% were unique to normal aging. We propose that a defect in the transcription of the genes as identified in this study could produce many of the complex clinical features of WS. The remarkable similarity between WS and normal aging suggests that WS causes the acceleration of a normal aging mechanism. This finding supports the use of WS as an aging model and implies that the transcription alterations common to WS and normal aging represent general events in the aging process.
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Affiliation(s)
- Kasper J Kyng
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
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