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Mecanismos moleculares e celulares de citotoxicidade de FGF2 parácrino em células tumorais dependentes de Ras; Molecular and cellular mechanisms of paracrine FGF2 cytotoxicity in Ras-driven tumor cells

Salotti, Jacqueline
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 30/06/2009 Português
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Descrevemos, recentemente, que FGF2 parácrino dispara senescência nas linhagens celulares murinas Y1 e 3T3-B61, transformadas malignamente por Ras, mas sem ativação das vias apoptóticas (Costa et al., 2008). Nesta tese, estudamos os mecanismos celulares e moleculares desta resposta de estresse irreversível, disparada por FGF2. Focalizamos, principalmente, a linhagem Y1, que carrega uma amplificação do oncogene Kras, mas apresenta um controle parcial da transição G0/G1 → S do ciclo celular. Por estas características fenotípicas, as células Y1 foram utilizadas no estudo dos mecanismos das ações antagônicas de FGF2, isto é, a atividade mitogênica clássica e a nova ação citotóxica que causa senescência. Análises de citometria de fluxo e marcação com BrdU mostraram que FGF2 promove a transição G0/G1 → S (atividade mitogênica), mas bloqueia a progressão através de S e G2/M (atividade antimitogênica). Ensaios de viabilidade celular (MTS e Cyto-Tox) demonstraram que, durante o bloqueio do ciclo celular por FGF2, as células permanecem íntegras e metabolicamente ativas, embora exibam alterações morfológicas, que sugerem estresse celular. Além disso, experimentos de tomada de 3H-timidina em DNA evidenciaram que...

Lack of telomere shortening during senescence in Paramecium.

Gilley, D; Blackburn, E H
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/03/1994 Português
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Paramecium tetraurelia cells have a limited clonal life span and die after approximately 200 fissions if they do not undergo the process of autogamy or conjugation. To test the possibility that cellular senescence of this species is caused by telomere shortening, we analyzed the genomic DNA of the macronucleus during the clonal life span of P. tetraurelia. We found that telomeric DNA sequences were not shortened during the interval of decreased fission rate and cellular death, defined as senescence in these cells. However, the mean size of the macronuclear DNA was markedly decreased during the clonal life span. We present a model that expands upon previous proposals that accumulated DNA damage causes cellular senescence in P. tetraurelia.

Premature senescence of highly proliferative endothelial progenitor cells is induced by tumor necrosis factor-α via the p38 mitogen-activated protein kinase pathway

Zhang, Yanmin; Herbert, Brittney-Shea; Rajashekhar, Gangaraju; Ingram, David A.; Yoder, Mervin C.; Clauss, Matthias; Rehman, Jalees
Fonte: The Federation of American Societies for Experimental Biology Publicador: The Federation of American Societies for Experimental Biology
Tipo: Artigo de Revista Científica
Publicado em /05/2009 Português
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Senescence of endothelial cells increases with systemic aging and is thought to contribute to the development of atherosclerosis. Cell therapy with highly proliferative endothelial progenitor cells (EPCs) is an emerging therapeutic option to promote endothelial regeneration, but little is known about their senescence and their vulnerability to inflammatory stressors. We therefore studied the senescence of proliferative human EPCs and investigated the effects of the proinflammatory cytokine tumor necrosis factor-α (TNF-α) on their senescence. Human EPCs had a significantly lower rate of senescence at baseline, compared with that of mature endothelial cells. However, EPCs up-regulated the expression of the senescence-associated cell cycle arrest protein p16INK4a and markedly increased measured senescence levels when exposed to chronic TNF-α treatment. Analysis of telomere length showed that the increases in senescence were not related to changes in telomere length. Inhibition of the p38 mitogen-activated protein kinase pathway blocked the induction of p16INK4a and cellular senescence. In conclusion, highly proliferative EPCs have a low rate of intrinsic senescence but are vulnerable to premature senescence induction by chronic proinflammatory stimulation. These findings will lead to a better understanding of physiological endothelial regeneration as well as to targeted therapies with the aim of promoting endothelial regeneration through endothelial progenitor cells.—Zhang...

Re-expression of ABI3BP Suppresses Thyroid Tumor Growth by Promoting Senescence and Inhibiting Invasion

Latini, Flavia R. M.; Hemerly, Jefferson P.; Oler, Gisele; Riggins, Gregory J.; Cerutti, Janete M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
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Loss of ABI gene family member 3 binding protein (ABI3BP) expression may be functionally involved in the pathogenesis of cancer. Previous reports have indicated a loss of expression in lung cancer and a presumed role in inducing cellular senescence. We show here that ABI3BP expression is significantly decreased in most malignant thyroid tumors of all types. To better understand ABI3BP’s role we created a model by re-expressing ABI3BP in two thyroid cancer cell lines. Re-expression of ABI3BP in thyroid cells resulted in a decrease in transforming activity, cell growth, cell viability, migration, invasion and tumor growth in nude mice. ABI3BP re-expression appears to trigger cellular senescence through the p21 pathway. Additionally, ABI3BP induced formation of HP1γ-positive senescence-associated heterochromatin foci (SAHF) and accumulation of senescence-associated β-galactosidase. The combination of a decrease in cell growth, invasion and other effects upon ABI3BP re-expression in vitro helps explain the large reduction in tumor growth we observed in nude mice. Together, our data provides evidence that the loss of ABI3BP expression could play a functional role in thyroid tumorigenesis. Activation of ABI3BP or its pathway may represent a possible basis for targeted therapy of certain cancers.

p16INK4a Suppression by Glucose Restriction Contributes to Human Cellular Lifespan Extension through SIRT1-Mediated Epigenetic and Genetic Mechanisms

Li, Yuanyuan; Tollefsbol, Trygve O.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 24/02/2011 Português
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Although caloric restriction (CR) has been shown to increase lifespan in various animal models, the mechanisms underlying this phenomenon have not yet been revealed. We developed an in vitro system to mimic CR by reducing glucose concentration in cell growth medium which excludes metabolic factors and allows assessment of the effects of CR at the cellular and molecular level. We monitored cellular proliferation of normal WI-38, IMR-90 and MRC-5 human lung fibroblasts and found that glucose restriction (GR) can inhibit cellular senescence and significantly extend cellular lifespan compared with cells receiving normal glucose (NG) in the culture medium. Moreover, GR decreased expression of p16INK4a (p16), a well-known senescence-related gene, in all of the tested cell lines. Over-expressed p16 resulted in early replicative senescence in glucose-restricted cells suggesting a crucial role of p16 regulation in GR-induced cellular lifespan extension. The decreased expression of p16 was partly due to GR-induced chromatin remodeling through effects on histone acetylation and methylation of the p16 promoter. GR resulted in an increased expression of SIRT1, a NAD-dependent histone deacetylase, which has positive correlation with CR-induced longevity. The elevated SIRT1 was accompanied by enhanced activation of the Akt/p70S6K1 signaling pathway in response to GR. Furthermore...

Roles of FGF signaling in stem cell self-renewal, senescence and aging

Coutu, Daniel L.; Galipeau, Jacques
Fonte: Impact Journals LLC Publicador: Impact Journals LLC
Tipo: Artigo de Revista Científica
Publicado em 09/10/2011 Português
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The aging process decreases tissue function and regenerative capacity, which has been associated with cellular senescence and a decline in adult or somatic stem cell numbers and self-renewal within multiple tissues. The potential therapeutic application of stem cells to reduce the burden of aging and stimulate tissue regeneration after trauma is very promising. Much research is currently ongoing to identify the factors and molecular mediators of stem cell self-renewal to reach these goals. Over the last two decades, fibroblast growth factors (FGFs) and their receptors (FGFRs) have stood up as major players in both embryonic development and tissue repair. Moreover, many studies point to somatic stem cells as major targets of FGF signaling in both tissue homeostasis and repair. FGFs appear to promote self-renewing proliferation and inhibit cellular senescence in nearly all tissues tested to date. Here we review the role of FGFs and FGFRs in stem cell self-renewal, cellular senescence, and aging.

Senescence of chondrocytes in aging articular cartilage: GADD45β mediates p21 expression in association with C/EBPβ in senescence-accelerated mice

Shimada, Hirofumi; Sakakima, Harutoshi; Tsuchimochi, Kaneyuki; Matsuda, Fumiyo; Komiya, Setsuro; Goldring, Mary B.; Ijiri, Kosei
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
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Growth arrest and DNA damage-inducible protein 45 β (GADD45β) is expressed in normal and early osteoarthritic articular cartilage. We recently reported that GADD45β enhances CCAAT/enhancer binding protein β (C/EBPβ) activation in vitro. This study was undertaken in order to determine whether GADD45β is expressed with C/EBPβ in aging articular cartilage. We also investigated whether the synergistic expression of GADD45β and C/EBPβ may be involved in the mechanism of chondrocyte senescence. Senescence-accelerated mice (SAMP1) were used as a model of aging. GADD45β, C/EBPβ, and p21 were analyzed by immunohistochemistry. A luciferase reporter assay using ATDC5 cells was performed in order to examine p21 as a target gene of the GADD45β/C/EBPβ cascade. GADD45β exhibited increased expression in the aging articular cartilage of SAMP1 mice compared to that in control mice. The co-localization of GADD45β and C/EBPβ was confirmed by double immunostaining. The synergistic mechanisms of GADD45β and C/EBPβ on the gene regulation of p21, a molecule related to cellular senescence, were verified by a p21-luciferase reporter assay. Co-expression of C/EBPβ and p21 was confirmed. These observations suggest that the synergism between GADD45β and C/EBPβ may play an important role in cellular senescence in the aging articular cartilage.

Perspectives on translational and therapeutic aspects of SIRT1 in inflammaging and senescence

Yao, Hongwei; Rahman, Irfan
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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SIRT1, a type III protein deacetylase, is considered as a novel anti-aging protein involved in regulation of cellular senescence/aging and inflammation. SIRT1 level and activity are decreased during lung inflammaging caused by oxidative stress. The mechanism of SIRT1-mediated protection against inflammaging is associated with the regulation of inflammation, premature senescence, telomere attrition, senescence associated secretory phenotype, and DNA damage response. A variety of dietary polyphenols and pharmacological activators are shown to regulate SIRT1 so as to intervene the progression of type 2 diabetes, cancer, cardiovascular diseases, and chronic obstructive pulmonary disease associated with inflammaging. However, recent studies have shown the non-specific regulation of SIRT1 by the aforementioned pharmacological activators and polyphenols. In this perspective, we have briefly discussed the role of SIRT1 in regulation of cellular senescence and its associated secretory phenotype, DNA damage response, particularly in lung inflammaging and during the development of chronic obstructive pulmonary diseases. We have also discussed the potential directions for future translational therapeutic avenues for SIRT1 in modulating lung inflammaging associated with senescence in chronic lung diseases associated with increased oxidative stress.

Protein Oxidative Damage at the Crossroads of Cellular Senescence, Aging, and Age-Related Diseases

Baraibar, Martin A.; Liu, Liang; Ahmed, Emad K.; Friguet, Bertrand
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
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Protein damage mediated by oxidation, protein adducts formation with advanced glycated end products and with products of lipid peroxidation, has been implicated during aging and age-related diseases, such as neurodegenerative diseases. Increased protein modification has also been described upon replicative senescence of human fibroblasts, a valid model for studying aging in vitro. However, the mechanisms by which these modified proteins could impact on the development of the senescent phenotype and the pathogenesis of age-related diseases remain elusive. In this study, we performed in silico approaches to evidence molecular actors and cellular pathways affected by these damaged proteins. A database of proteins modified by carbonylation, glycation, and lipid peroxidation products during aging and age-related diseases was built and compared to those proteins identified during cellular replicative senescence in vitro. Common cellular pathways evidenced by enzymes involved in intermediate metabolism were found to be targeted by these modifications, although different tissues have been examined. These results underscore the potential effect of protein modification in the impairment of cellular metabolism during aging and age-related diseases.

Sensitive Detection and Monitoring of Senescence-Associated Secretory Phenotype by SASP-RAP Assay

Gu, Liubao; Kitamura, Masanori
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 18/12/2012 Português
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Senescence-associated secretory phenotype (SASP) is characterized by abundant secretion of various proteins in senescent cells and implicated in tumor progression and inflammatory responses. However, the profile of secreted proteins in SASP is different from cell type to cell type, and currently, universal markers for SASP have not been reported. In the present investigation, we show that SASP-responsive alkaline phosphatase (SASP-RAP) serves as a sensitive, general and convenient marker for SASP. Etoposide-treated cells exhibited a senescent phenotype characterized by senile morphology, positive staining for senescence-associated β-galactosidase, growth arrest and induction of p53 and p21WAF1/CIP1. In SASP-RAP-transfected cells, exposure to etoposide increased secretion of SASP-RAP time-dependently. The kinetics of secretion was closely correlated with that of activation of the p21WAF1/CIP1 promoter and the p16INK4a promoter. The enhanced secretion of SASP-RAP by senescence was also observed in cells treated with other senescence inducers such as trichostatin A, doxorubicin and 4-phenylbutylic acid. The induction of SASP-RAP by senescence was similarly observed in natural replicative senescence. To confirm selectivity of the SASP-RAP response...

Mediterranean diet reduces senescence-associated stress in endothelial cells

Marin, Carmen; Delgado-Lista, Javier; Ramirez, Rafael; Carracedo, Julia; Caballero, Javier; Perez-Martinez, Pablo; Gutierrez-Mariscal, Francisco Miguel; Garcia-Rios, Antonio; Delgado-Casado, Nieves; Cruz-Teno, Cristina; Yubero-Serrano, Elena Maria; Tinaho
Fonte: Springer Netherlands Publicador: Springer Netherlands
Tipo: Artigo de Revista Científica
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This paper aims to study the effects of the oxidative stress induced by quality and quantity of dietary fat on cellular senescence. Twenty elderly subjects consumed three diets, each for 4 weeks: a saturated fatty acid diet (SFA), a low-fat and high-carbohydrate diet (CHO-ALA), and a Mediterranean diet (MedDiet) enriched in monounsaturated fatty acid following a randomized crossover design. For each diet, we investigated intracellular reactive oxidative species (ROS), cellular apoptosis and telomere length in human umbilical endothelial cells incubated with serum from each patient. MedDiet induced lower intracellular ROS production, cellular apoptosis, and percentage of cell with telomere shortening, compared with the baseline and with SFA and CHO-ALA diets. Dietary fat modulates the oxidative stress in human endothelial cells. MedDiet protects these cells from oxidative stress, prevents cellular senescence and reduces cellular apoptosis.

Environmental stress, ageing and glial cell senescence: a novel mechanistic link to Parkinson’s disease?

Chinta, Shankar J; Lieu, Christopher A; DeMaria, Marco; Laberge, Remi-Martin; Campisi, Judith; Andersen, Julie K
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/2013 Português
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Exposure to environmental toxins is associated with a variety of age-related diseases including cancer and neurodegeneration. For example, in Parkinson’s disease (PD), chronic environmental exposure to certain toxins has been linked to the age-related development of neuropathology. Neuronal damage is believed to involve the induction of neuroinflammatory events as a consequence of glial cell activation. Cellular senescence is a potent anti-cancer mechanism that occurs in a number of proliferative cell types and causes the arrest of proliferation of cells at risk of malignant transformation following exposure to potentially oncogenic stimuli. With age, senescent cells accumulate and express a senescence-associated secretory phenotype (SASP; i.e. the robust secretion of many inflammatory cytokines, growth factors and proteases). Whereas cell senescence in peripheral tissues has been causally linked to a number of age-related pathologies, little is known about the induction of cellular senescence and the SASP in the brain. Based on recently reported findings, we propose that environmental stressors associated with PD may act in part by eliciting senescence and the SASP within non-neuronal glial cells in the ageing brain, thus contributing to the characteristic decline in neuronal integrity that occurs in this disorder.

Histone Modifications in Senescence-Associated Resistance to Apoptosis by Oxidative Stress☆☆☆

Sanders, Yan Y.; Liu, Hui; Zhang, Xiangyu; Hecker, Louise; Bernard, Karen; Desai, Leena; Liu, Gang; Thannickal, Victor J.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em 31/01/2013 Português
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Aging and age-related diseases are associated with cellular senescence that results in variable apoptosis susceptibility to oxidative stress. Although fibroblast senescence has been associated with apoptosis resistance, mechanisms for this have not been well defined. In this report, we studied epigenetic mechanisms involving histone modifications that confer apoptosis resistance to senescent human diploid fibroblasts (HDFs). HDFs that undergo replicative senescence display typical morphological features, express senescence-associated β-galactosidase, and increased levels of the tumor suppressor genes, p16, p21, and caveolin-1. Senescent HDFs are more resistant to oxidative stress (exogenous H2O2)-induced apoptosis in comparison to non-senescent (control) HDFs; this is associated with constitutively high levels of the anti-apoptotic gene, Bcl-2, and low expression of the pro-apoptotic gene, Bax. Cellular senescence is characterized by global increases in H4K20 trimethylation and decreases in H4K16 acetylation in association with increased activity of Suv420h2 histone methyltransferase (which targets H4K20), decreased activity of the histone acetyltransferase, Mof (which targets H4K16), as well as decreased total histone acetyltransferase activity. In contrast to Bax gene...

The Tumor Suppressor PML Specifically Accumulates at RPA/Rad51-Containing DNA Damage Repair Foci but Is Nonessential for DNA Damage-Induced Fibroblast Senescence

Münch, Sandra; Weidtkamp-Peters, Stefanie; Klement, Karolin; Grigaravicius, Paulius; Monajembashi, Shamci; Salomoni, Paolo; Pandolfi, Pier Paolo; Weißhart, Klaus; Hemmerich, Peter
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /05/2014 Português
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The PML tumor suppressor has been functionally implicated in DNA damage response and cellular senescence. Direct evidence for such a role based on PML knockdown or knockout approaches is still lacking. We have therefore analyzed the irradiation-induced DNA damage response and cellular senescence in human and mouse fibroblasts lacking PML. Our data show that PML nuclear bodies (NBs) nonrandomly associate with persistent DNA damage foci in unperturbed human skin and in high-dose-irradiated cell culture systems. PML bodies do not associate with transient γH2AX foci after low-dose gamma irradiation. Superresolution microscopy reveals that all PML bodies within a nucleus are engaged at Rad51- and RPA-containing repair foci during ongoing DNA repair. The lack of PML (i) does not majorly affect the DNA damage response, (ii) does not alter the efficiency of senescence induction after DNA damage, and (iii) does not affect the proliferative potential of primary mouse embryonic fibroblasts during serial passaging. Thus, while PML NBs specifically accumulate at Rad51/RPA-containing lesions and senescence-derived persistent DNA damage foci, they are not essential for DNA damage-induced and replicative senescence of human and murine fibroblasts.

Cholangiocyte Senescence by Way of N-Ras Activation Is a Characteristic of Primary Sclerosing Cholangitis

Tabibian, James H.; O’Hara, Steven P.; Splinter, Patrick L.; Trussoni, Christy E.; LaRusso, Nicholas F.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
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Primary sclerosing cholangitis (PSC) is an incurable cholangiopathy of unknown etiopathogenesis. Here we tested the hypothesis that cholangiocyte senescence is a pathophysiologically important phenotype in PSC. We assessed markers of cellular senescence and senescence-associated secretory phenotype (SASP) in livers of patients with PSC, primary biliary cirrhosis, hepatitis C, and in normals by fluorescent in situ hybridization (FISH) and immunofluorescence microscopy (IFM). We tested whether endogenous and exogenous biliary constituents affect senescence and SASP in cultured human cholangiocytes. We determined in coculture whether senescent cholangiocytes induce senescence in bystander cholangiocytes. Finally, we explored signaling mechanisms involved in cholangiocyte senescence and SASP. In vivo, PSC cholangiocytes expressed significantly more senescence-associated p16INK4a and γH2A.x compared to the other three conditions; expression of profibroinflammatory SASP components (i.e., IL-6, IL-8, CCL2, PAI-1) was also highest in PSC cholangiocytes. In vitro, several biologically relevant endogenous (e.g., cholestane 3,5,6 oxysterol) and exogenous (e.g., lipopolysaccharide) molecules normally present in bile induced cholangiocyte senescence and SASP. Furthermore...

Global Characteristics of CSIG-Associated Gene Expression Changes in Human HEK293 Cells and the Implications for CSIG Regulating Cell Proliferation and Senescence

Ma, Liwei; Zhao, Wenting; Zhu, Feng; Yuan, Fuwen; Xie, Nan; Li, Tingting; Wang, Pingzhang; Tong, Tanjun
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 15/05/2015 Português
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Cellular senescence-inhibited gene (CSIG), also named as ribosomal_L1 domain-containing 1 (RSL1D1), is implicated in various processes including cell cycle regulation, cellular senescence, apoptosis, and tumor metastasis. However, little is known about the regulatory mechanism underlying its functions. To screen important targets and signaling pathways modulated by CSIG, we compared the gene expression profiles in CSIG-silencing and control HEK293 cells using Affymetrix microarray Human Genome U133 Plus 2.0 GeneChips. A total of 590 genes displayed statistically significant expression changes, with 279 genes up-regulated and 311 down-regulated, respectively. These genes are involved in a broad array of biological processes, mainly in transcriptional regulation, cell cycle, signal transduction, oxidation reduction, development, and cell adhesion. The differential expression of genes such as ZNF616, KPNA5, and MAP3K3 was further validated by real-time PCR and western blot analysis. Furthermore, we investigated the correlated expression patterns of Cdc14B, ESCO1, KPNA5, MAP3K3, and CSIG during cell cycle and senescence progression, which imply the important pathways CSIG regulating cell cycle and senescence. The mechanism study showed that CSIG modulated the mRNA half-life of Cdc14B...

The intrinsic stiffness of human trabecular meshwork cells increases with senescence

Morgan, Joshua T.; Raghunathan, Vijay Krishna; Chang, Yow-Ren; Murphy, Christopher J.; Russell, Paul
Fonte: Impact Journals LLC Publicador: Impact Journals LLC
Tipo: Artigo de Revista Científica
Publicado em 12/04/2015 Português
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Dysfunction of the human trabecular meshwork (HTM) plays a central role in the age-associated disease glaucoma, a leading cause of irreversible blindness. The etiology remains poorly understood but cellular senescence, increased stiffness of the tissue, and the expression of Wnt antagonists such as secreted frizzled related protein-1 (SFRP1) have been implicated. However, it is not known if senescence is causally linked to either stiffness or SFRP1 expression. In this study, we utilized in vitro HTM senescence to determine the effect on cellular stiffening and SFRP1 expression. Stiffness of cultured cells was measured using atomic force microscopy and the morphology of the cytoskeleton was determined using immunofluorescent analysis. SFRP1 expression was measured using qPCR and immunofluorescent analysis. Senescent cell stiffness increased 1.88±0.14 or 2.57±0.14 fold in the presence or absence of serum, respectively. This was accompanied by increased vimentin expression, stress fiber formation, and SFRP1 expression. In aggregate, these data demonstrate that senescence may be a causal factor in HTM stiffening and elevated SFRP1 expression, and contribute towards disease progression. These findings provide insight into the etiology of glaucoma and...

Genome-Wide Loss-of-Function Genetic Screens Identify Novel Senescence Genes and Putative Tumor Suppressors

Burrows, Anna
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation
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During every cell cycle and upon exogenous stress, tumor suppression programs are engaged to ensure genomic stability. In response to replicative aging and oncogenic stimuli, the p53 and Rb pathways are activated to prevent the proliferation of damaged cells. Several lines of evidence suggest that escape from senescence is a crucial early step in oncogenic progression. A major challenge in the cancer field is to combine genomic information regarding cancer-associated genetic changes with high-throughput functional studies, in order to confirm genetic requirements and pinpoint biological roles of these perturbed genes in oncogenesis. Furthermore, a complete genetic understanding of replicative senescence, and how it might be bypassed, is lacking. We describe here two genome scale loss-of-function genetic screens that interrogate these tumor suppressor programs. We utilized a unique sensitization approach to isolate senescence pathways and unmask compensatory mechanisms that may have been difficult to identify in previous studies. These genetic screens have generated comprehensive and validated datasets of putative senescence and p53 pathway genes. We present this dataset as a high-quality resource for further investigation into these biological pathways. We have uncovered several genes in distinct biological pathways which have not been demonstrated to have a functional role in senescence...

PKCη promotes senescence induced by oxidative stress and chemotherapy

Zurgil, U; Ben-Ari, A; Atias, K; Isakov, N; Apte, R; Livneh, E
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
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Senescence is characterized by permanent cell-cycle arrest despite continued viability and metabolic activity, in conjunction with the secretion of a complex mixture of extracellular proteins and soluble factors known as the senescence-associated secretory phenotype (SASP). Cellular senescence has been shown to prevent the proliferation of potentially tumorigenic cells, and is thus generally considered a tumor suppressive process. However, some SASP components may act as pro-tumorigenic mediators on premalignant cells in the microenvironment. A limited number of studies indicated that protein kinase C (PKC) has a role in senescence, with different isoforms having opposing effects. It is therefore important to elucidate the functional role of specific PKCs in senescence. Here we show that PKCη, an epithelial specific and anti-apoptotic kinase, promotes senescence induced by oxidative stress and DNA damage. We further demonstrate that PKCη promotes senescence through its ability to upregulate the expression of the cell cycle inhibitors p21Cip1 and p27Kip1 and enhance transcription and secretion of interleukin-6 (IL-6). Moreover, we demonstrate that PKCη creates a positive loop for reinforcing senescence by increasing the transcription of both IL-6 and IL-6 receptor...

BRG1 Is Required for Formation of Senescence-Associated Heterochromatin Foci Induced by Oncogenic RAS or BRCA1 Loss

Tu, Zhigang; Zhuang, Xinying; Yao, Yong-Gang; Zhang, Rugang
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /05/2013 Português
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Cellular senescence is an important tumor suppression mechanism. We have previously reported that both oncogene-induced dissociation of BRCA1 from chromatin and BRCA1 knockdown itself drive senescence by promoting formation of senescence-associated heterochromatin foci (SAHF). However, the molecular mechanism by which BRCA1 regulates SAHF formation and senescence is unclear. BRG1 is a chromatin-remodeling factor that interacts with BRCA1 and pRB. Here we show that BRG1 is required for SAHF formation and senescence induced by oncogenic RAS or BRCA1 loss. The interaction between BRG1 and BRCA1 is disrupted during senescence. This correlates with an increased level of chromatin-associated BRG1 in senescent cells. BRG1 knockdown suppresses the formation of SAHF and senescence, while it has no effect on BRCA1 chromatin dissociation induced by oncogenic RAS, indicating that BRG1 functions downstream of BRCA1 chromatin dissociation. Furthermore, BRG1 knockdown inhibits SAHF formation and senescence induced by BRCA1 knockdown. Conversely, BRG1 overexpression drives SAHF formation and senescence in a DNA damage-independent manner. This effect depends upon BRG1's chromatin-remodeling activity as well as the interaction between BRG1 and pRB. Indeed...