RESUMEN
Telomere length maintenance is crucial to cancer cell immortality. Up to 15% of cancers utilize a telomerase-independent, recombination-based mechanism termed alternative lengthening of telomeres (ALT). Currently, the primary ALT biomarker is the C-circle, a type of circular DNA with extrachromosomal telomere repeats (cECTRs). How C-circles form is not well characterized. We investigated C-circle formation in the human cen3tel cell line, a long-telomere, telomerase+ (LTT+) cell line with progressively hyper-elongated telomeres (up to â¼100 kb). cECTR signal was observed in 2D gels and C-circle assays but not t-circle assays, which also detect circular DNA with extrachromosomal telomere repeats. Telomerase activity and C-circle signal were not separable in the analysis of clonal populations, consistent with C-circle production occurring within telomerase+ cells. We observed similar cECTR results in two other LTT+ cell lines, HeLa1.3 (â¼23 kb telomeres) and HeLaE1 (â¼50 kb telomeres). In LTT+ cells, telomerase activity did not directly impact C-circle signal; instead, C-circle signal correlated with telomere length. LTT+ cell lines were less sensitive to hydroxyurea than ALT+ cell lines, suggesting that ALT status is a stronger contributor to replication stress levels than telomere length. Additionally, the DNA repair-associated protein FANCM did not suppress C-circles in LTT+ cells as it does in ALT+ cells. Thus, C-circle formation may be driven by telomere length, independently of telomerase and replication stress, highlighting limitations of C-circles as a stand-alone ALT biomarker.
Asunto(s)
ADN Circular , Telomerasa , Telómero , Humanos , ADN Helicasas/metabolismo , Telomerasa/metabolismo , Telómero/genética , Telómero/metabolismo , Homeostasis del Telómero , Línea Celular , Células HeLa , Replicación del ADN , Hidroxiurea , Reparación del ADNRESUMEN
Here, with the aim of obtaining insight into the intriguing selectivity of G-quadruplex (G4) ligands toward cancer compared to normal cells, a genetically controlled system of progressive transformation in human BJ fibroblasts was analyzed. Among the different comparative evaluations, we found a progressive increase of DNA damage response (DDR) markers throughout the genome from normal toward immortalized and transformed cells. More interestingly, sensitivity to G4 ligands strongly correlated with the presence of a basal level of DNA damage, including at the telomeres, where the chromosome ends were exposed to the DDR without concurrent induction of DNA repair activity, as revealed by the lack of 53BP1 recruitment and telomere aberrations. The link between telomere uncapping and the response to G4 stabilization was directly assessed by showing that a partial TRF2 depletion, causing a basal level of telomere localized DDR, rendered telomerized fibroblasts prone to G4-induced telomere damage and anti-proliferative defects. Taken together these data strongly indicate that the presence of a basal level of telomere-associated DDR is a determinant of susceptibility to G4 stabilization.
Asunto(s)
Daño del ADN , G-Cuádruplex/efectos de los fármacos , Neoplasias/genética , Telómero , Western Blotting , Inmunoprecipitación de Cromatina , Humanos , Hibridación Fluorescente in Situ , Células Tumorales CultivadasRESUMEN
An increasing number of studies suggest an important role of host immunity as a barrier to tumor formation and progression. Complex mechanisms and multiple pathways are involved in evading innate and adaptive immune responses, with a broad spectrum of chemicals displaying the potential to adversely influence immunosurveillance. The evaluation of the cumulative effects of low-dose exposures from the occupational and natural environment, especially if multiple chemicals target the same gene(s) or pathway(s), is a challenge. We reviewed common environmental chemicals and discussed their potential effects on immunosurveillance. Our overarching objective was to review related signaling pathways influencing immune surveillance such as the pathways involving PI3K/Akt, chemokines, TGF-ß, FAK, IGF-1, HIF-1α, IL-6, IL-1α, CTLA-4 and PD-1/PDL-1 could individually or collectively impact immunosurveillance. A number of chemicals that are common in the anthropogenic environment such as fungicides (maneb, fluoxastrobin and pyroclostrobin), herbicides (atrazine), insecticides (pyridaben and azamethiphos), the components of personal care products (triclosan and bisphenol A) and diethylhexylphthalate with pathways critical to tumor immunosurveillance. At this time, these chemicals are not recognized as human carcinogens; however, it is known that they these chemicalscan simultaneously persist in the environment and appear to have some potential interfere with the host immune response, therefore potentially contributing to promotion interacting with of immune evasion mechanisms, and promoting subsequent tumor growth and progression.
Asunto(s)
Sustancias Peligrosas/efectos adversos , Sustancias Peligrosas/inmunología , Evasión Inmune/efectos de los fármacos , Vigilancia Inmunológica/efectos de los fármacos , Neoplasias/inducido químicamente , Neoplasias/inmunología , Animales , Ambiente , Humanos , Evasión Inmune/inmunología , Vigilancia Inmunológica/inmunología , Neoplasias/etiologíaRESUMEN
Carcinogenesis is thought to be a multistep process, with clonal evolution playing a central role in the process. Clonal evolution involves the repeated 'selection and succession' of rare variant cells that acquire a growth advantage over the remaining cell population through the acquisition of 'driver mutations' enabling a selective advantage in a particular micro-environment. Clonal selection is the driving force behind tumorigenesis and possesses three basic requirements: (i) effective competitive proliferation of the variant clone when compared with its neighboring cells, (ii) acquisition of an indefinite capacity for self-renewal, and (iii) establishment of sufficiently high levels of genetic and epigenetic variability to permit the emergence of rare variants. However, several questions regarding the process of clonal evolution remain. Which cellular processes initiate carcinogenesis in the first place? To what extent are environmental carcinogens responsible for the initiation of clonal evolution? What are the roles of genotoxic and non-genotoxic carcinogens in carcinogenesis? What are the underlying mechanisms responsible for chemical carcinogen-induced cellular immortality? Here, we explore the possible mechanisms of cellular immortalization, the contribution of immortalization to tumorigenesis and the mechanisms by which chemical carcinogens may contribute to these processes.
Asunto(s)
Carcinogénesis/inducido químicamente , Carcinógenos/administración & dosificación , Senescencia Celular/efectos de los fármacos , Sustancias Peligrosas/efectos adversos , Animales , Exposición a Riesgos Ambientales/efectos adversos , HumanosRESUMEN
Environmental contributions to cancer development are widely accepted, but only a fraction of all pertinent exposures have probably been identified. Traditional toxicological approaches to the problem have largely focused on the effects of individual agents at singular endpoints. As such, they have incompletely addressed both the pro-carcinogenic contributions of environmentally relevant low-dose chemical mixtures and the fact that exposures can influence multiple cancer-associated endpoints over varying timescales. Of these endpoints, dysregulated metabolism is one of the most common and recognizable features of cancer, but its specific roles in exposure-associated cancer development remain poorly understood. Most studies have focused on discrete aspects of cancer metabolism and have incompletely considered both its dynamic integrated nature and the complex controlling influences of substrate availability, external trophic signals and environmental conditions. Emerging high throughput approaches to environmental risk assessment also do not directly address the metabolic causes or consequences of changes in gene expression. As such, there is a compelling need to establish common or complementary frameworks for further exploration that experimentally and conceptually consider the gestalt of cancer metabolism and its causal relationships to both carcinogenesis and the development of other cancer hallmarks. A literature review to identify environmentally relevant exposures unambiguously linked to both cancer development and dysregulated metabolism suggests major gaps in our understanding of exposure-associated carcinogenesis and metabolic reprogramming. Although limited evidence exists to support primary causal roles for metabolism in carcinogenesis, the universality of altered cancer metabolism underscores its fundamental biological importance, and multiple pleiomorphic, even dichotomous, roles for metabolism in promoting, antagonizing or otherwise enabling the development and selection of cancer are suggested.
Asunto(s)
Carcinogénesis/inducido químicamente , Carcinogénesis/metabolismo , Carcinógenos Ambientales/efectos adversos , Exposición a Riesgos Ambientales/efectos adversos , Neoplasias/inducido químicamente , Neoplasias/metabolismo , Animales , Humanos , Neoplasias/etiologíaRESUMEN
An emerging area in environmental toxicology is the role that chemicals and chemical mixtures have on the cells of the human immune system. This is an important area of research that has been most widely pursued in relation to autoimmune diseases and allergy/asthma as opposed to cancer causation. This is despite the well-recognized role that innate and adaptive immunity play as essential factors in tumorigenesis. Here, we review the role that the innate immune cells of inflammatory responses play in tumorigenesis. Focus is placed on the molecules and pathways that have been mechanistically linked with tumor-associated inflammation. Within the context of chemically induced disturbances in immune function as co-factors in carcinogenesis, the evidence linking environmental toxicant exposures with perturbation in the balance between pro- and anti-inflammatory responses is reviewed. Reported effects of bisphenol A, atrazine, phthalates and other common toxicants on molecular and cellular targets involved in tumor-associated inflammation (e.g. cyclooxygenase/prostaglandin E2, nuclear factor kappa B, nitric oxide synthesis, cytokines and chemokines) are presented as example chemically mediated target molecule perturbations relevant to cancer. Commentary on areas of additional research including the need for innovation and integration of systems biology approaches to the study of environmental exposures and cancer causation are presented.
Asunto(s)
Carcinógenos Ambientales/efectos adversos , Exposición a Riesgos Ambientales/efectos adversos , Inflamación/inducido químicamente , Inflamación/inmunología , Neoplasias/inducido químicamente , Neoplasias/inmunología , Animales , Carcinogénesis/inducido químicamente , Carcinogénesis/inmunología , Humanos , Inmunidad Innata/efectos de los fármacos , Inmunidad Innata/inmunología , Neoplasias/etiología , RiesgoRESUMEN
Potentially carcinogenic compounds may cause cancer through direct DNA damage or through indirect cellular or physiological effects. To study possible carcinogens, the fields of endocrinology, genetics, epigenetics, medicine, environmental health, toxicology, pharmacology and oncology must be considered. Disruptive chemicals may also contribute to multiple stages of tumor development through effects on the tumor microenvironment. In turn, the tumor microenvironment consists of a complex interaction among blood vessels that feed the tumor, the extracellular matrix that provides structural and biochemical support, signaling molecules that send messages and soluble factors such as cytokines. The tumor microenvironment also consists of many host cellular effectors including multipotent stromal cells/mesenchymal stem cells, fibroblasts, endothelial cell precursors, antigen-presenting cells, lymphocytes and innate immune cells. Carcinogens can influence the tumor microenvironment through effects on epithelial cells, the most common origin of cancer, as well as on stromal cells, extracellular matrix components and immune cells. Here, we review how environmental exposures can perturb the tumor microenvironment. We suggest a role for disrupting chemicals such as nickel chloride, Bisphenol A, butyltins, methylmercury and paraquat as well as more traditional carcinogens, such as radiation, and pharmaceuticals, such as diabetes medications, in the disruption of the tumor microenvironment. Further studies interrogating the role of chemicals and their mixtures in dose-dependent effects on the tumor microenvironment could have important general mechanistic implications for the etiology and prevention of tumorigenesis.
Asunto(s)
Exposición a Riesgos Ambientales/efectos adversos , Sustancias Peligrosas/efectos adversos , Microambiente Tumoral/efectos de los fármacos , Animales , Carcinogénesis/inducido químicamente , Humanos , Neoplasias/inducido químicamenteRESUMEN
As part of the Halifax Project, this review brings attention to the potential effects of environmental chemicals on important molecular and cellular regulators of the cancer hallmark of evading growth suppression. Specifically, we review the mechanisms by which cancer cells escape the growth-inhibitory signals of p53, retinoblastoma protein, transforming growth factor-beta, gap junctions and contact inhibition. We discuss the effects of selected environmental chemicals on these mechanisms of growth inhibition and cross-reference the effects of these chemicals in other classical cancer hallmarks.
Asunto(s)
Exposición a Riesgos Ambientales/efectos adversos , Sustancias Peligrosas/efectos adversos , Neoplasias/inducido químicamente , Neoplasias/etiología , Animales , Humanos , Transducción de Señal/efectos de los fármacosRESUMEN
One of the important 'hallmarks' of cancer is angiogenesis, which is the process of formation of new blood vessels that are necessary for tumor expansion, invasion and metastasis. Under normal physiological conditions, angiogenesis is well balanced and controlled by endogenous proangiogenic factors and antiangiogenic factors. However, factors produced by cancer cells, cancer stem cells and other cell types in the tumor stroma can disrupt the balance so that the tumor microenvironment favors tumor angiogenesis. These factors include vascular endothelial growth factor, endothelial tissue factor and other membrane bound receptors that mediate multiple intracellular signaling pathways that contribute to tumor angiogenesis. Though environmental exposures to certain chemicals have been found to initiate and promote tumor development, the role of these exposures (particularly to low doses of multiple substances), is largely unknown in relation to tumor angiogenesis. This review summarizes the evidence of the role of environmental chemical bioactivity and exposure in tumor angiogenesis and carcinogenesis. We identify a number of ubiquitous (prototypical) chemicals with disruptive potential that may warrant further investigation given their selectivity for high-throughput screening assay targets associated with proangiogenic pathways. We also consider the cross-hallmark relationships of a number of important angiogenic pathway targets with other cancer hallmarks and we make recommendations for future research. Understanding of the role of low-dose exposure of chemicals with disruptive potential could help us refine our approach to cancer risk assessment, and may ultimately aid in preventing cancer by reducing or eliminating exposures to synergistic mixtures of chemicals with carcinogenic potential.
Asunto(s)
Carcinogénesis/inducido químicamente , Carcinógenos Ambientales/efectos adversos , Exposición a Riesgos Ambientales/efectos adversos , Sustancias Peligrosas/efectos adversos , Neoplasias/inducido químicamente , Neoplasias/etiología , Neovascularización Patológica/inducido químicamente , Animales , HumanosRESUMEN
The purpose of this review is to stimulate new ideas regarding low-dose environmental mixtures and carcinogens and their potential to promote invasion and metastasis. Whereas a number of chapters in this review are devoted to the role of low-dose environmental mixtures and carcinogens in the promotion of invasion and metastasis in specific tumors such as breast and prostate, the overarching theme is the role of low-dose carcinogens in the progression of cancer stem cells. It is becoming clearer that cancer stem cells in a tumor are the ones that assume invasive properties and colonize distant organs. Therefore, low-dose contaminants that trigger epithelial-mesenchymal transition, for example, in these cells are of particular interest in this review. This we hope will lead to the collaboration between scientists who have dedicated their professional life to the study of carcinogens and those whose interests are exclusively in the arena of tissue invasion and metastasis.
Asunto(s)
Carcinógenos Ambientales/efectos adversos , Invasividad Neoplásica/patología , Metástasis de la Neoplasia/patología , Animales , Progresión de la Enfermedad , Exposición a Riesgos Ambientales/efectos adversos , Transición Epitelial-Mesenquimal/efectos de los fármacos , HumanosRESUMEN
The aim of this work is to review current knowledge relating the established cancer hallmark, sustained cell proliferation to the existence of chemicals present as low dose mixtures in the environment. Normal cell proliferation is under tight control, i.e. cells respond to a signal to proliferate, and although most cells continue to proliferate into adult life, the multiplication ceases once the stimulatory signal disappears or if the cells are exposed to growth inhibitory signals. Under such circumstances, normal cells remain quiescent until they are stimulated to resume further proliferation. In contrast, tumour cells are unable to halt proliferation, either when subjected to growth inhibitory signals or in the absence of growth stimulatory signals. Environmental chemicals with carcinogenic potential may cause sustained cell proliferation by interfering with some cell proliferation control mechanisms committing cells to an indefinite proliferative span.
Asunto(s)
Carcinógenos Ambientales/efectos adversos , Proliferación Celular/efectos de los fármacos , Exposición a Riesgos Ambientales/efectos adversos , Sustancias Peligrosas/efectos adversos , Neoplasias/inducido químicamente , Neoplasias/etiología , Transducción de Señal/efectos de los fármacos , Animales , HumanosRESUMEN
Genome instability is a prerequisite for the development of cancer. It occurs when genome maintenance systems fail to safeguard the genome's integrity, whether as a consequence of inherited defects or induced via exposure to environmental agents (chemicals, biological agents and radiation). Thus, genome instability can be defined as an enhanced tendency for the genome to acquire mutations; ranging from changes to the nucleotide sequence to chromosomal gain, rearrangements or loss. This review raises the hypothesis that in addition to known human carcinogens, exposure to low dose of other chemicals present in our modern society could contribute to carcinogenesis by indirectly affecting genome stability. The selected chemicals with their mechanisms of action proposed to indirectly contribute to genome instability are: heavy metals (DNA repair, epigenetic modification, DNA damage signaling, telomere length), acrylamide (DNA repair, chromosome segregation), bisphenol A (epigenetic modification, DNA damage signaling, mitochondrial function, chromosome segregation), benomyl (chromosome segregation), quinones (epigenetic modification) and nano-sized particles (epigenetic pathways, mitochondrial function, chromosome segregation, telomere length). The purpose of this review is to describe the crucial aspects of genome instability, to outline the ways in which environmental chemicals can affect this cancer hallmark and to identify candidate chemicals for further study. The overall aim is to make scientists aware of the increasing need to unravel the underlying mechanisms via which chemicals at low doses can induce genome instability and thus promote carcinogenesis.
Asunto(s)
Carcinogénesis/inducido químicamente , Carcinógenos Ambientales/efectos adversos , Exposición a Riesgos Ambientales/efectos adversos , Inestabilidad Genómica/efectos de los fármacos , Sustancias Peligrosas/efectos adversos , Neoplasias/inducido químicamente , Neoplasias/etiología , Animales , HumanosRESUMEN
Cell death is a process of dying within biological cells that are ceasing to function. This process is essential in regulating organism development, tissue homeostasis, and to eliminate cells in the body that are irreparably damaged. In general, dysfunction in normal cellular death is tightly linked to cancer progression. Specifically, the up-regulation of pro-survival factors, including oncogenic factors and antiapoptotic signaling pathways, and the down-regulation of pro-apoptotic factors, including tumor suppressive factors, confers resistance to cell death in tumor cells, which supports the emergence of a fully immortalized cellular phenotype. This review considers the potential relevance of ubiquitous environmental chemical exposures that have been shown to disrupt key pathways and mechanisms associated with this sort of dysfunction. Specifically, bisphenol A, chlorothalonil, dibutyl phthalate, dichlorvos, lindane, linuron, methoxychlor and oxyfluorfen are discussed as prototypical chemical disruptors; as their effects relate to resistance to cell death, as constituents within environmental mixtures and as potential contributors to environmental carcinogenesis.
Asunto(s)
Carcinogénesis/inducido químicamente , Carcinógenos Ambientales/efectos adversos , Muerte Celular/efectos de los fármacos , Exposición a Riesgos Ambientales/efectos adversos , Sustancias Peligrosas/efectos adversos , Neoplasias/inducido químicamente , Neoplasias/etiología , Animales , Homeostasis/efectos de los fármacos , HumanosRESUMEN
Lifestyle factors are responsible for a considerable portion of cancer incidence worldwide, but credible estimates from the World Health Organization and the International Agency for Research on Cancer (IARC) suggest that the fraction of cancers attributable to toxic environmental exposures is between 7% and 19%. To explore the hypothesis that low-dose exposures to mixtures of chemicals in the environment may be combining to contribute to environmental carcinogenesis, we reviewed 11 hallmark phenotypes of cancer, multiple priority target sites for disruption in each area and prototypical chemical disruptors for all targets, this included dose-response characterizations, evidence of low-dose effects and cross-hallmark effects for all targets and chemicals. In total, 85 examples of chemicals were reviewed for actions on key pathways/mechanisms related to carcinogenesis. Only 15% (13/85) were found to have evidence of a dose-response threshold, whereas 59% (50/85) exerted low-dose effects. No dose-response information was found for the remaining 26% (22/85). Our analysis suggests that the cumulative effects of individual (non-carcinogenic) chemicals acting on different pathways, and a variety of related systems, organs, tissues and cells could plausibly conspire to produce carcinogenic synergies. Additional basic research on carcinogenesis and research focused on low-dose effects of chemical mixtures needs to be rigorously pursued before the merits of this hypothesis can be further advanced. However, the structure of the World Health Organization International Programme on Chemical Safety 'Mode of Action' framework should be revisited as it has inherent weaknesses that are not fully aligned with our current understanding of cancer biology.
Asunto(s)
Carcinogénesis/inducido químicamente , Carcinógenos Ambientales/efectos adversos , Exposición a Riesgos Ambientales/efectos adversos , Sustancias Peligrosas/efectos adversos , Neoplasias/inducido químicamente , Neoplasias/etiología , Animales , HumanosRESUMEN
Telomere length maintenance is critical for organisms' long-term survival and cancer cell proliferation. Telomeres are kept within species-specific length ranges by the interplay between telomerase activity and telomeric chromatin organization. In this paper, we exploited telomerase immortalized human fibroblasts (cen3tel) that gradually underwent neoplastic transformation during culture propagation to study telomere composition and length regulation during the transformation process. Just after telomerase catalytic subunit (hTERT) expression, cen3tel telomeres shortened despite the presence of telomerase activity. At a later stage and concomitantly with transformation, cells started elongating telomeres, which reached a mean length greater than 100kb in about 900 population doublings. Super-telomeres were stable and compatible with cell growth and tumorigenesis. Telomere extension was associated with increasing levels of telomerase activity that were linked to the deregulation of endogenous telomerase RNA (hTERC) and exogenous telomerase reverse transcriptase (hTERT) expression. Notably, the increase in hTERC levels paralleled the increase in telomerase activity, suggesting that this subunit plays a role in regulating enzyme activity. Telomeres ranging in length between 10 and more than 100kb were maintained in an extendible state although TRF1 and TRF2 binding increased with telomere length. Super-telomeres neither influenced subtelomeric region global methylation nor the expression of the subtelomeric gene FRG1, attesting the lack of a clear-cut relationship between telomere length, subtelomeric DNA methylation and expression in human cells. The cellular levels of the telomeric proteins hTERT, TRF1, TRF2 and Hsp90 rose with transformation and were independent of telomere length, pointing to a role of these proteins in tumorigenesis.
Asunto(s)
Transformación Celular Neoplásica/genética , Fibroblastos/fisiología , Homeostasis del Telómero/genética , Telómero/genética , Telómero/metabolismo , Línea Celular Transformada , Transformación Celular Neoplásica/metabolismo , Metilación de ADN , Fibroblastos/metabolismo , Humanos , Proteínas de Microfilamentos , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , ARN/genética , Proteínas de Unión al ARN , Telomerasa/genética , Proteína 1 de Unión a Repeticiones Teloméricas/genética , Proteína 1 de Unión a Repeticiones Teloméricas/metabolismo , Proteína 2 de Unión a Repeticiones Teloméricas/genética , Proteína 2 de Unión a Repeticiones Teloméricas/metabolismoRESUMEN
Many human primary somatic cells can be immortalized by inducing telomerase activity through the exogenous expression of the human telomerase catalytic subunit (hTERT). This approach has been extended to the immortalization of cell lines from several mammals. Here, we show that hTERT expression is not sufficient to immortalize primary fibroblasts from three equid species, namely donkey, Burchelli's zebra and Grevy's zebra. In vitro analysis of a reconstituted telomerase composed by hTERT and an equid RNA component of telomerase (TERC) revealed a low activity of this enzyme compared to human telomerase, suggesting a low compatibility of equid and human telomerase subunits. This conclusion was also strengthened by comparison of human and equid TERC sequences, which revealed nucleotide differences in key regions for TERC and TERT interaction. We then succeeded in immortalizing equid fibroblasts by expressing hTERT and hTERC concomitantly. Expression of both human telomerase subunits led to telomerase activity and telomere elongation, indicating that human telomerase is compatible with the other equid telomerase subunits and proteins involved in telomere metabolism. The immortalization procedure described herein could be extended to primary cells from other mammals. The availability of immortal cells from endangered species could be particularly useful for obtaining new information on the organization and function of their genomes, which is relevant for their preservation.
Asunto(s)
Fibroblastos/citología , ARN/metabolismo , Telomerasa/metabolismo , Animales , Secuencia de Bases , Dominio Catalítico , Células Cultivadas , Equidae , Fibroblastos/metabolismo , Caballos , Humanos , Ratones , Datos de Secuencia Molecular , Subunidades de Proteína/química , Subunidades de Proteína/genética , Subunidades de Proteína/metabolismo , ARN/química , ARN/genética , Telomerasa/química , Telomerasa/genética , Telómero/genética , Telómero/metabolismo , TransfecciónRESUMEN
Telomere length maintenance is crucial to cancer cell immortality. Up to 15% of cancers utilize a telomerase-independent, recombination-based mechanism termed alternative lengthening of telomeres (ALT). The primary ALT biomarker is the C-circle, a type of circular DNA with extrachromosomal telomere repeats (cECTRs). How C-circles form is not well characterized. To investigate C-circle formation in telomerase+ cells, we studied the human cen3tel cell line, in which telomeres progressively hyper-elongated post TERT -immortalization. cECTR signal was observed in 2D gels and C-circle assays but not t-circle assays, which also detect cECTRs. Telomerase activity and C-circle signal were not separable in the analysis of clonal populations, consistent with C-circle production occurring within telomerase+ cells. Two other long telomere, telomerase+ (LTT+) cell lines, HeLa1.3 (~23 kb telomeres) and HeLaE1 (~50 kb telomeres), had similar cECTR properties. Telomerase activity did not directly impact C-circle signal in LTT+ cells; instead, C-circle signal correlated with telomere length. LTT+ lines were less sensitive to hydroxyurea than an ALT+ cell line, suggesting that ALT status is a stronger contributor to replication stress levels than telomere length. Additionally, FANCM did not suppress C-circles in LTT+ cells as it does in ALT+ cells. Thus, C-circle formation may be driven by telomere length, independently of telomerase and replication stress, highlighting limitations of C-circles as a stand-alone ALT biomarker.
RESUMEN
Apoptosis, the best known form of programmed cell death, is tightly regulated by a number of sensors, signal transducers and effectors. Apoptosis is mainly active during embryonic development, when deletion of redundant cellular material is required for the correct morphogenesis of tissues and organs; moreover, it is essential for the maintenance of tissue homeostasis during cell life. Cells also activate apoptosis when they suffer from various insults, such as damage to DNA or to other cellular components, or impairment of basic processes, such as DNA replication and DNA repair. Removal of damaged cells is fundamental in maintaining the health of organisms. In addition, apoptosis induction following DNA damage is exploited to kill cancer cells. In this chapter we will review the main features of developmental and induced apoptosis.
Asunto(s)
Apoptosis , Reparación del ADN , Replicación del ADN , Desarrollo Embrionario , HumanosRESUMEN
The adenine misincorporated by replicative DNA polymerases (pols) opposite 7,8-dihydro-8-oxoguanine (8-oxo-G) is removed by a specific glycosylase, leaving the lesion on the DNA. Subsequent incorporation of C opposite 8-oxo-G on the resulting 1-nt gapped DNA is essential for the removal of the 8-oxo-G to prevent G-C to T-A transversion mutations. By using model DNA templates, purified DNA pols beta and lambda and knockout cell extracts, we show here that the auxiliary proteins replication protein A and proliferating cell nuclear antigen act as molecular switches to activate the DNA pol lambda- dependent highly efficient and faithful repair of A:8-oxo-G mismatches in human cells and to repress DNA pol beta activity. By using an immortalized human fibroblast cell line that has the potential to induce cancer in mice, we show that the development of a tumoral phenotype in these cells correlated with a differential expression of DNA pols lambda and beta.
Asunto(s)
ADN Polimerasa beta/metabolismo , Reparación del ADN , Guanina/análogos & derivados , Antígeno Nuclear de Célula en Proliferación/metabolismo , Proteína de Replicación A/metabolismo , Animales , Línea Celular Transformada , Transformación Celular Neoplásica/genética , Transformación Celular Neoplásica/metabolismo , Sistema Libre de Células/metabolismo , Inhibidor p16 de la Quinasa Dependiente de Ciclina/genética , Inhibidor p16 de la Quinasa Dependiente de Ciclina/metabolismo , ADN/genética , ADN/metabolismo , ADN Glicosilasas/genética , ADN Glicosilasas/metabolismo , ADN Polimerasa beta/genética , Reparación del ADN/genética , Replicación del ADN/genética , Guanina/metabolismo , Humanos , Ratones , Mutación , Proteínas Proto-Oncogénicas c-myc/genética , Proteínas Proto-Oncogénicas c-myc/metabolismo , Especies Reactivas de Oxígeno/metabolismo , Proteína de Replicación A/genética , Proteína p14ARF Supresora de Tumor/genética , Proteína p14ARF Supresora de Tumor/metabolismo , Proteína p53 Supresora de Tumor/genética , Proteína p53 Supresora de Tumor/metabolismoRESUMEN
During tumorigenesis, oncogene activation and metabolism rewiring are interconnected. Activated cMyc upregulates several genes involved in glutamine metabolism, making cancer cells dependent on high levels of this amino acid to survive and proliferate. After studying the response to glutamine deprivation in cancer cells, it was found that glutamine starvation not only blocked cellular proliferation, but also altered cMyc protein expression, leading to a reduction in the levels of the canonical cMyc isoform and an increase in the expression of cMyc 1, a cMyc isoform translated from an inframe 5' CUG codon. In an attempt to identify nutrients able to counteract glutamine deprivation effects, it was shown that, in the absence of glutamine, asparagine permitted cell survival and proliferation, and maintained cMyc expression as in glutaminefed cells, with high levels of canonical cMyc and cMyc 1 almost undetectable. In asparaginefed cells, global protein translation was higher than in glutaminestarved cells, and there was an increase in the levels of glutamine synthetase (GS), whose activity was essential for cellular viability and proliferation. In glutaminestarved asparaginefed cells, the inhibition of cMyc activity led to a decrease in global protein translation and GS synthesis, suggesting an association between cMyc expression, GS levels and cellular proliferation, mediated by asparagine when exogenous glutamine is absent.