RESUMO
Humans are frequently exposed to acrylamide, a probable human carcinogen found in commonplace sources such as most heated starchy foods or tobacco smoke. Prior evidence has shown that acrylamide causes cancer in rodents, yet epidemiological studies conducted to date are limited and, thus far, have yielded inconclusive data on association of human cancers with acrylamide exposure. In this study, we experimentally identify a novel and unique mutational signature imprinted by acrylamide through the effects of its reactive metabolite glycidamide. We next show that the glycidamide mutational signature is found in a full one-third of approximately 1600 tumor genomes corresponding to 19 human tumor types from 14 organs. The highest enrichment of the glycidamide signature was observed in the cancers of the lung (88% of the interrogated tumors), liver (73%), kidney (>70%), bile duct (57%), cervix (50%), and, to a lesser extent, additional cancer types. Overall, our study reveals an unexpectedly extensive contribution of acrylamide-associated mutagenesis to human cancers.
Assuntos
Acrilamidas/toxicidade , Carcinogênese/genética , Exposição Ambiental , Mutagênicos/toxicidade , Mutação , Neoplasias/genética , Animais , Carcinogênese/induzido quimicamente , Células Cultivadas , Compostos de Epóxi/toxicidade , Genoma Humano , Humanos , Camundongos , Neoplasias/induzido quimicamente , Proteína Supressora de Tumor p53/genéticaRESUMO
Inactivation of the retinoblastoma tumor suppressor (pRB) alters the expression of a myriad of genes. To understand the altered cellular environment that these changes create, we took advantage of the Drosophila model system and used targeted liquid chromatography tandem mass spectrometry (LC-MS/MS) to profile the metabolic changes that occur when RBF1, the fly ortholog of pRB, is removed. We show that RBF1-depleted tissues and larvae are sensitive to fasting. Depletion of RBF1 causes major changes in nucleotide synthesis and glutathione metabolism. Under fasting conditions, these changes interconnect, and the increased replication demand of RBF1-depleted larvae is associated with the depletion of glutathione pools. In vivo (13)C isotopic tracer analysis shows that RBF1-depleted larvae increase the flux of glutamine toward glutathione synthesis, presumably to minimize oxidative stress. Concordantly, H(2)O(2) preferentially promoted apoptosis in RBF1-depleted tissues, and the sensitivity of RBF1-depleted animals to fasting was specifically suppressed by either a glutamine supplement or the antioxidant N-acetyl-cysteine. Effects of pRB activation/inactivation on glutamine catabolism were also detected in human cell lines. These results show that the inactivation of RB proteins causes metabolic reprogramming and that these consequences of RBF/RB function are present in both flies and human cell lines.
Assuntos
Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/genética , Drosophila melanogaster/metabolismo , Glutamina/biossíntese , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Animais , Apoptose , Linhagem Celular Tumoral , Dano ao DNA , Jejum/metabolismo , Glutationa/biossíntese , Humanos , Larva , Mutação , Nucleotídeos/biossíntese , Estresse Oxidativo , Proteína do Retinoblastoma , Estresse FisiológicoRESUMO
In recent years, there has been an increasing interest in investigating the carcinogenicity of mycotoxins in humans. This systematic review aims to provide an overview of data linking exposure to different mycotoxins with human cancer risk. Publications (2019 and earlier) of case-control or longitudinal cohort studies were identified in PubMed and EMBASE. These articles were then screened by independent reviewers and their quality was assessed according to the Newcastle-Ottawa scale. Animal, cross-sectional, and molecular studies satisfied criteria for exclusion. In total, 14 articles were included: 13 case-control studies and 1 longitudinal cohort study. Included articles focused on associations of mycotoxin exposure with primary liver, breast, and cervical cancer. Overall, a positive association between the consumption of aflatoxin-contaminated foods and primary liver cancer risk was verified. Two case-control studies in Africa investigated the relationship between zearalenone and its metabolites and breast cancer risk, though conflicting results were reported. Two case-control studies investigated the association between hepatocellular carcinoma and fumonisin B1 exposure, but no significant associations were observed. This systematic review incorporates several clear observations of dose-dependent associations between aflatoxins and liver cancer risk, in keeping with IARC Monograph conclusions. Only few human epidemiological studies investigated the associations between mycotoxin exposures and cancer risk. To close this gap, more in-depth research is needed to unravel evidence for other common mycotoxins, such as deoxynivalenol and ochratoxin A. The link between mycotoxin exposures and cancer risk has mainly been established in experimental studies, and needs to be confirmed in human epidemiological studies to support the evidence-based public health strategies.
Assuntos
Micotoxinas/efeitos adversos , Neoplasias/induzido quimicamente , Neoplasias/epidemiologia , Animais , Exposição Ambiental/efeitos adversos , Contaminação de Alimentos , HumanosRESUMO
Rapidly accumulating data from large-scale cancer genomics studies have been generating important information about genes and their somatic alterations underlying cell transformation, cancer onset and tumor progression. However, these events are usually defined by using computational techniques, whereas the understanding of their actual functional roles and impact typically warrants validation by experimental means. Critical information has been obtained from targeted genetic perturbation (gene knockout) studies conducted in animals, yet these investigations are cost-prohibitive and time-consuming. In addition, the 3R principles (replacement, reduction, refinement) have been set in place to reduce animal use burden and are increasingly observed in many areas of biomedical research. Consequently, the focus has shifted to new designs of innovative cell-based experimental models of cell immortalization and transformation in which the critical cancer driver events can be introduced by mutagenic insult and studied functionally, at the level of critical phenotypic readouts. From these efforts, primary cell-based selective barrier-bypass models of cell immortalization have emerged as an attractive system that allows studies of the functional relevance of acquired mutations as well as their role as candidate cancer driver events. In this review, we provide an overview of various experimental systems linking carcinogen exposure-driven cell transformation with the study of cancer driver events. We further describe the advantages and disadvantages of the currently available cell-based models while outlining future directions for in vitro modeling and functional testing of cancer driver events.
Assuntos
Genômica , Neoplasias/genética , Transformação Celular Neoplásica , Cromatina/química , Humanos , MutaçãoRESUMO
Inactivation of the retinoblastoma tumor suppressor (pRb) is a common oncogenic event that alters the expression of genes important for cell cycle progression, senescence, and apoptosis. However, in many contexts, the properties of pRb-deficient cells are similar to wild-type cells suggesting there may be processes that counterbalance the transcriptional changes associated with pRb inactivation. Therefore, we have looked for sets of evolutionary conserved, functionally related genes that are direct targets of pRb/E2F proteins. We show that the expression of NANOS, a key facilitator of the Pumilio (PUM) post-transcriptional repressor complex, is directly repressed by pRb/E2F in flies and humans. In both species, NANOS expression increases following inactivation of pRb/RBF1 and becomes important for tissue homeostasis. By analyzing datasets from normal retinal tissue and pRb-null retinoblastomas, we find a strong enrichment for putative PUM substrates among genes de-regulated in tumors. These include pro-apoptotic genes that are transcriptionally down-regulated upon pRb loss, and we characterize two such candidates, MAP2K3 and MAP3K1, as direct PUM substrates. Our data suggest that NANOS increases in importance in pRb-deficient cells and helps to maintain homeostasis by repressing the translation of transcripts containing PUM Regulatory Elements (PRE).
Assuntos
Proteínas de Drosophila/metabolismo , Drosophila melanogaster/metabolismo , Regulação da Expressão Gênica , Processamento Pós-Transcricional do RNA , Proteínas de Ligação a RNA/metabolismo , Proteína do Retinoblastoma/fisiologia , Animais , Animais Geneticamente Modificados , Western Blotting , Proliferação de Células , Células Cultivadas , Imunoprecipitação da Cromatina , Proteínas de Drosophila/genética , Drosophila melanogaster/genética , Fatores de Transcrição E2F/genética , Fatores de Transcrição E2F/metabolismo , Humanos , MAP Quinase Quinase 3/genética , MAP Quinase Quinase 3/metabolismo , MAP Quinase Quinase Quinase 1/genética , MAP Quinase Quinase Quinase 1/metabolismo , Proteína MyoD/genética , Proteína MyoD/metabolismo , Interferência de RNA , RNA Mensageiro/genética , Proteínas de Ligação a RNA/genética , Reação em Cadeia da Polimerase em Tempo Real , Retinoblastoma/genética , Retinoblastoma/metabolismo , Retinoblastoma/patologia , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
dREAM complexes represent the predominant form of E2F/RBF repressor complexes in Drosophila. dREAM associates with thousands of sites in the fly genome but its mechanism of action is unknown. To understand the genomic context in which dREAM acts we examined the distribution and localization of Drosophila E2F and dREAM proteins. Here we report a striking and unexpected overlap between dE2F2/dREAM sites and binding sites for the insulator-binding proteins CP190 and Beaf-32. Genetic assays show that these components functionally co-operate and chromatin immunoprecipitation experiments on mutant animals demonstrate that dE2F2 is important for association of CP190 with chromatin. dE2F2/dREAM binding sites are enriched at divergently transcribed genes, and the majority of genes upregulated by dE2F2 depletion represent the repressed half of a differentially expressed, divergently transcribed pair of genes. Analysis of mutant animals confirms that dREAM and CP190 are similarly required for transcriptional integrity at these gene pairs and suggest that dREAM functions in concert with CP190 to establish boundaries between repressed/activated genes. Consistent with the idea that dREAM co-operates with insulator-binding proteins, genomic regions bound by dREAM possess enhancer-blocking activity that depends on multiple dREAM components. These findings suggest that dREAM functions in the organization of transcriptional domains.
Assuntos
Proteínas de Drosophila/metabolismo , Fator de Transcrição E2F2/metabolismo , Regulação da Expressão Gênica , Proteínas Associadas aos Microtúbulos/metabolismo , Proteínas Nucleares/metabolismo , Transcrição Gênica , Animais , Sítios de Ligação , DNA/metabolismo , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Drosophila/genética , Drosophila/metabolismo , Proteínas de Drosophila/genética , Fator de Transcrição E2F2/genética , Elementos Facilitadores Genéticos , Proteínas do Olho/genética , Proteínas do Olho/metabolismo , Proteínas Associadas aos Microtúbulos/genética , Mutação , Proteínas Nucleares/genética , Fatores de Transcrição/metabolismoRESUMO
Tobacco usage is linked to multiple cancer types and accounts for a quarter of all cancer-related deaths. Tobacco smoke contains various carcinogenic compounds, including polycyclic aromatic hydrocarbons (PAH), though the mutagenic potential of many tobacco-related chemicals remains largely unexplored. In particular, the highly carcinogenic tobacco-specific nitrosamines NNN and NNK form pre-mutagenic pyridyloxobutyl (POB) DNA adducts. In the study presented here, we identified genome-scale POB-induced mutational signatures in cell lines and rat tumors, while also investigating their role in human cancer. These signatures are characterized by T>N and C>T mutations forming from specific POB adducts damaging dT and dC residues. Analysis of 2,780 cancer genomes uncovered POB signatures in â¼180 tumors; from cancer types distinct from the ones linked to smoking-related signatures SBS4 and SBS92. This suggests that, unlike PAH compounds, the POB pathway may contribute uniquely to the mutational landscapes of certain hematological malignancies and cancers of the kidney, breast, prostate and pancreas.
RESUMO
Retinoblastoma tumor suppressor protein (pRb) regulates various biological processes during development and tumorigenesis. Although the molecular mechanism by which pRb controls cell cycle progression is well characterized, how pRb promotes cell-type specification and differentiation is less understood. Here, we report that Extra Macrochaetae (EMC), the Drosophila homolog of inhibitor of DNA binding/differentiation (ID), is an important protein contributing to the developmental defects caused by Rb deficiency. An emc allele was identified from a genetic screen designed to identify factors that, when overexpressed, cooperate with mutations in rbf1, which encodes one of the two Rb proteins found in Drosophila. EMC overexpression in an rbf1 hypomorphic mutant background induces cone cell and photoreceptor defects but has negligible effects in the wild-type background. Interestingly, a substantial fraction of the rbf1-null ommatidia normally exhibit similar cone cell and photoreceptor defects in the absence of ectopic EMC expression. Detailed EMC expression analyses revealed that RBF1 suppresses expression of both endogenous and ectopic EMC protein in photoreceptors, thus explaining the synergistic effect between EMC overexpression and rbf1 mutations, and the developmental defect observed in rbf1-null ommatidia. Our findings demonstrate that ID family proteins are an evolutionarily conserved determinant of Rb-deficient cells, and play an important role during development.
Assuntos
Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Drosophila/crescimento & desenvolvimento , Células Fotorreceptoras de Invertebrados/citologia , Proteínas Repressoras/metabolismo , Células Fotorreceptoras Retinianas Cones/citologia , Proteína do Retinoblastoma/genética , Fatores de Transcrição/genética , Animais , Drosophila/citologia , Drosophila/genética , Proteínas de Drosophila/deficiência , Olho/anatomia & histologia , Olho/crescimento & desenvolvimento , Olho/ultraestrutura , Mutação , Proteína do Retinoblastoma/deficiência , Fatores de Transcrição/deficiênciaRESUMO
BACKGROUND: Microarray studies have shown that the E2F transcription factor influences the expression of many genes but it is unclear how many of these targets are important for E2F-mediated control of cell proliferation. RESULTS: We assembled a collection of mutant alleles of 44 dE2F1-dependent genes and tested whether these could modify visible phenotypes caused by the tissue-specific depletion of dE2F1. More than half of the mutant alleles dominantly enhanced de2f1-dsRNA phenotypes suggesting that the in vivo functions of dE2F1 can be limited by the reduction in the level of expression of many different targets. Unexpectedly, several mutant alleles suppressed de2f1-dsRNA phenotypes. One of the strongest of these suppressors was Orc5. Depletion of ORC5 increased proliferation in cells with reduced dE2F1 and specifically elevated the expression of dE2F1-regulated genes. Importantly, these effects were independent of dE2F1 protein levels, suggesting that reducing the level of ORC5 did not interfere with the general targeting of dE2F1. CONCLUSIONS: We propose that the interaction between ORC5 and dE2F1 may reflect a feedback mechanism between replication initiation proteins and dE2F1 that ensures that proliferating cells maintain a robust level of replication proteins for the next cell cycle.
Assuntos
Proteínas de Drosophila/metabolismo , Fatores de Transcrição E2F/metabolismo , Fatores de Transcrição/metabolismo , Alelos , Animais , Proliferação de Células , Drosophila , Proteínas de Drosophila/genética , Fatores de Transcrição E2F/genética , Imuno-Histoquímica , Hibridização In Situ , Modelos Biológicos , Complexo de Reconhecimento de Origem/genética , Complexo de Reconhecimento de Origem/metabolismo , Fatores de Transcrição/genéticaRESUMO
Aristolochic acids (AAs) are a group of naturally occurring compounds present in many plant species of the Aristolochiaceae family. Exposure to AA is a significant risk factor for severe nephropathy, and urological and hepatobiliary cancers (among others) that are often recurrent and characterized by the prominent mutational fingerprint of AA. However, herbal medicinal products that contain AA continue to be manufactured and marketed worldwide with inadequate regulation, and possible environmental exposure routes receive little attention. As the trade of food and dietary supplements becomes increasingly globalized, we propose that further inaction on curtailing AA exposure will have far-reaching negative effects on the disease trends of AA-associated cancers. Our Review aims to systematically present the historical and current evidence for the mutagenicity and carcinogenicity of AA, and the effect of removing sources of AA exposure on cancer incidence trends. We discuss the persisting challenges of assessing the scale of AA-related carcinogenicity, and the obstacles that must be overcome in curbing AA exposure and preventing associated cancers. Overall, this Review aims to strengthen the case for the implementation of prevention measures against AA's multifaceted, detrimental and potentially fully preventable effects on human cancer development.
Assuntos
Ácidos Aristolóquicos , Neoplasias , Ácidos Aristolóquicos/toxicidade , Humanos , Mutagênese , Neoplasias/induzido quimicamente , Neoplasias/epidemiologia , Saúde PúblicaRESUMO
Smarca5, an ATPase of the ISWI class of chromatin remodelers, is a key regulator of chromatin structure, cell cycle and DNA repair. Smarca5 is deregulated in leukemia and breast, lung and gastric cancers. However, its role in oncogenesis is not well understood. Chromatin remodelers often play dosage-dependent roles in cancer. We therefore investigated the epigenomic and phenotypic impact of controlled stepwise attenuation of Smarca5 function in the context of primary cell transformation, a process relevant to tumor formation. Upon conditional single- or double-allele Smarca5 deletion, the cells underwent both accelerated growth arrest and senescence entry and displayed gradually increased sensitivity to genotoxic insults. These phenotypic characteristics were explained by specific remodeling of the chromatin structure and the transcriptome in primary cells prior to the immortalization onset. These molecular programs implicated Smarca5 requirement in DNA damage repair, telomere maintenance, cell cycle progression and in restricting apoptosis and cellular senescence. Consistent with the molecular programs, we demonstrate for the first time that Smarca5-deficient primary cells exhibit dramatically decreased capacity to bypass senescence and immortalize, an indispensable step during cell transformation and cancer development. Thus, Smarca5 plays a crucial role in key homeostatic processes and sustains cancer-promoting molecular programs and cellular phenotypes.
Assuntos
Cromatina , Neoplasias , Adenosina Trifosfatases/metabolismo , Montagem e Desmontagem da Cromatina , Dano ao DNA , Reparo do DNARESUMO
BACKGROUND: Mycotoxins have been suggested to contribute to a spectrum of adverse health effects in humans, including at low concentrations. The recognition of these food contaminants being carcinogenic, as co-occurring rather than as singularly present, has emerged from recent research. The aim of this study was to assess the potential associations of single and multiple mycotoxin exposures with renal cell carcinoma risk in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. METHODS: Food questionnaire data from the EPIC cohort were matched to mycotoxin food occurrence data compiled by the European Food Safety Authority (EFSA) from European Member States to assess long-term dietary mycotoxin exposures, and to associate these with the risk of renal cell carcinoma (RCC, n = 911 cases) in 450,112 EPIC participants. Potential confounding factors were taken into account. Analyses were conducted using Cox's proportional hazards regression models to compute hazard ratios (HRs) and 95% confidence intervals (95% CIs) with mycotoxin exposures expressed as µg/kg body weight/day. RESULTS: Demographic characteristics differed between the RCC cases and non-cases for body mass index, age, alcohol intake at recruitment, and other dietary factors. In addition, the mycotoxin exposure distributions showed that a large proportion of the EPIC population was exposed to some of the main mycotoxins present in European foods such as deoxynivalenol (DON) and derivatives, fumonisins, Fusarium toxins, Alternaria toxins, and total mycotoxins. Nevertheless, no statistically significant associations were observed between the studied mycotoxins and mycotoxin groups, and the risk of RCC development. CONCLUSIONS: These results show an absence of statistically significant associations between long-term dietary mycotoxin exposures and RCC risk. However, these results need to be validated in other cohorts and preferably using repeated dietary exposure measurements. In addition, more occurrence data of, e.g., citrinin and fumonisins in different food commodities and countries in the EFSA database are a prerequisite to establish a greater degree of certainty.
Assuntos
Carcinoma de Células Renais , Fumonisinas , Neoplasias Renais , Micotoxinas , Carcinoma de Células Renais/induzido quimicamente , Carcinoma de Células Renais/epidemiologia , Contaminação de Alimentos/análise , Fumonisinas/análise , Humanos , Neoplasias Renais/induzido quimicamente , Neoplasias Renais/epidemiologia , Micotoxinas/efeitos adversos , Micotoxinas/análise , Estudos ProspectivosRESUMO
BACKGROUND: Systematic evaluation of literature data on the cancer hazards of human exposures is an essential process underlying cancer prevention strategies. The scope and volume of evidence for suspected carcinogens can range from very few to thousands of publications, requiring a complex, systematically planned, and critical procedure to nominate, prioritize and evaluate carcinogenic agents. To aid in this process, database fusion, cheminformatics and text mining techniques can be combined into an integrated approach to inform agent prioritization, selection, and grouping. RESULTS: We have applied these techniques to agents recommended for the IARC Monographs evaluations during 2020-2024. An integration of PubMed filters to cover cancer epidemiology, key characteristics of carcinogens, chemical lists from 34 databases relevant for cancer research, chemical structure grouping and a literature data-based clustering was applied in an innovative approach to 119 agents recommended by an advisory group for future IARC Monographs evaluations. The approach also facilitated a rational grouping of these agents and aids in understanding the volume and complexity of relevant information, as well as important gaps in coverage of the available studies on cancer etiology and carcinogenesis. CONCLUSION: A new data-science approach has been applied to diverse agents recommended for cancer hazard assessments, and its applications for the IARC Monographs are demonstrated. The prioritization approach has been made available at www.cancer.idsl.me site for ranking cancer agents.
Assuntos
Neoplasias , Carcinogênese , Carcinógenos/toxicidade , Mineração de Dados , Bases de Dados Factuais , Humanos , Neoplasias/epidemiologiaRESUMO
Recent years have witnessed an expansion of mutagenesis research focusing on experimentally modeled genome-scale mutational signatures of carcinogens and of endogenous processes. Experimental mutational signatures can explain etiologic links to patterns found in human tumors that may be linked to same exposures, and can serve as biomarkers of exposure history and may even provide insights on causality. A number of innovative exposure models have been employed and reported, based on cells cultured in monolayers or in 3-D, on organoids, induced pluripotent stem cells, non-mammalian organisms, microorganisms and rodent bioassays. Here we discuss some of the latest developments and pros and cons of these experimental systems used in mutational signature analysis. Integrative designs that bring together multiple exposure systems (in vitro, in vivo and in silico pan-cancer data mining) started emerging as powerful tools to identify robust mutational signatures of the tested cancer risk agents. We further propose that devising a new generation of cell-based models is warranted to streamline systematic testing of carcinogen effects on the cell genomes, while seeking to increasingly supplant animal with non-animal systems to address relevant ethical issues and accentuate the 3R principles. We conclude that the knowledge accumulating from the growing body of signature modelling investigations has considerable power to advance cancer etiology studies and to support cancer prevention efforts through streamlined characterization of cancer-causing agents and the recognition of their specific effects.
Assuntos
Carcinógenos/toxicidade , Mutagênese/efeitos dos fármacos , Mutação/efeitos dos fármacos , Neoplasias/induzido quimicamente , Animais , Análise Mutacional de DNA/métodos , Genoma Humano/efeitos dos fármacos , Genoma Humano/genética , Humanos , Mutagênese/genética , Mutação/genéticaRESUMO
Inactivation of the retinoblastoma tumour suppressor protein (pRb) is a hallmark of most human cancers. Accordingly, pRb is serving as a paradigm in our quest to understand tumour suppressor function. The role played by pRb and the related 'pocket proteins', p107 and p130, in regulating cell cycle progression has been extensively studied over the past two decades. The function of pRb in regulating transcriptional programmes in differentiating cells is less well understood. Recently, the use of a variety of different cell, animal and plant model systems has allowed us a first glimpse at some of the molecular mechanisms underlying pRb-mediated transcriptional regulation during differentiation and development.
Assuntos
Diferenciação Celular/fisiologia , Fatores de Transcrição E2F/fisiologia , Regulação da Expressão Gênica/fisiologia , Proteína do Retinoblastoma/fisiologia , Transcrição Gênica/fisiologia , Animais , Ciclo Celular/fisiologia , Fatores de Transcrição E2F/metabolismo , Humanos , Ligação Proteica , Proteína do Retinoblastoma/metabolismoRESUMO
DNA in dividing cells is prone to mutagenesis, with mutations making key contributions to human disease including cancer. The tumour suppressor gene TP53 is the most frequently mutated gene in human tumours. Here, we present a robust protocol for studying TP53 mutagenesis utilising human TP53 knock-in (Hupki) mouse embryonic fibroblasts (HUFs). In the HUF immortalisation assay (HIMA), primary HUFs are treated with known or suspected carcinogens at 3% oxygen and then transferred to 20% atmospheric oxygen to induce senescence. Cells containing mutations (e.g., in TP53) that allow bypassing of senescence eventually emerge as immortalised clonal cell lines after 2-3 months of serial passaging. As not all immortalised HUF cells contain TP53 mutations, we developed a Nutlin-3a counter-screen to select for TP53-mutated clones prior to sequencing. TP53 mutation spectra generated can be compared with those of human tumours recorded in the International Agency for Research on Cancer TP53 mutation database. Environmental mutagens that have demonstrated and validated the utility of the HIMA include ultraviolet radiation, aristolochic acid, and benzo[a]pyrene. The TP53 mutation patterns induced by these mutagens in the HIMA corresponded to those found in human tumours from patients exposed to these mutagens. The approach presented helps to deepen our understanding of human cancer aetiology.
RESUMO
Many proteins have been proposed to be involved in retinoblastoma protein (pRB)-mediated repression, but it is largely uncertain which cofactors are essential for pRB to repress endogenous E2F-regulated promoters. Here we have taken advantage of the stream-lined Drosophila dE2F/RBF pathway, which has only two E2Fs (dE2F1 and dE2F2), and two pRB family members (RBF1 and RBF2). With RNA interference (RNAi), we depleted potential corepressors and looked for the elevated expression of groups of E2F target genes that are known to be directly regulated by RBF1 and RBF2. Previous studies have implicated histone deacetylase (HDAC) and SWI/SNF chromatin-modifying complexes in pRB-mediated repression. However, our results fail to support the idea that the SWI/SNF proteins are required for RBF-mediated repression and suggest that a requirement for HDAC activities is likely to be limited to a subset of targets. We found that the chromatin assembly factor p55/dCAF-1 is essential for the repression of dE2F2-regulated targets. The removal of p55 deregulated the expression of E2F targets that are normally repressed by dE2F2/RBF1 and dE2F2/RBF2 complexes in a cell cycle-independent manner but had no effect on the expression of E2F targets that are normally coupled with cell proliferation. The results indicate that the mechanisms of RBF regulation at these two types of E2F targets are different and suggest that p55, and perhaps p55's mammalian orthologs RbAp46 and RbAp48, have a conserved function in repression by pRB-related proteins.
Assuntos
Proteínas Cromossômicas não Histona/metabolismo , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/genética , Regulação da Expressão Gênica , Chaperonas Moleculares/metabolismo , Fatores de Transcrição/metabolismo , Animais , Proteínas de Transporte/metabolismo , Células Cultivadas , Proteínas Cromossômicas não Histona/genética , Proteínas de Drosophila/genética , Drosophila melanogaster/fisiologia , Fator de Transcrição E2F2 , Inibidores de Histona Desacetilases , Histona Desacetilases/metabolismo , Humanos , Chaperonas Moleculares/genética , Proteínas Nucleares/metabolismo , Regiões Promotoras Genéticas , Ligação Proteica , Interferência de RNA , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismo , Proteína do Retinoblastoma/genética , Proteína do Retinoblastoma/metabolismo , Proteína 4 de Ligação ao Retinoblastoma , Proteína 7 de Ligação ao Retinoblastoma , Fatores de Transcrição/genéticaRESUMO
All forms of life on Earth share a common ancestry. As a consequence, Homo sapiens shares a large number of genes essential for the development and maintenance of multicellular life with "simple" animals, such as the fruit fly Drosophila melanogaster and the nematode worm Caenorhabdites elegans. Indeed, Drosophila and C. elegans have successfully been used to unravel fundamental mechanisms underlying animal development. The sequencing of their genomes has revealed that a surprisingly large proportion of genes relevant for human disease have counterparts in the worm and in the fly. This includes many oncogenes and tumour suppressor genes and provides us with a unique opportunity to exploit the advantages of simple model organisms to further our understanding of the molecular basis of cancer. Recent work on the fly and worm homologs of the Retinoblastoma tumour suppressor (pRb) has uncovered some unexpected pRb functions: Evolutionary conserved pRb complexes participate in cell fate determination, repress germline-specific gene expression and interact with RNA interference pathways. Similar complexes appear to operate in human cells.
Assuntos
Caenorhabditis elegans/fisiologia , Drosophila melanogaster/fisiologia , Proteína do Retinoblastoma/fisiologia , Animais , Caenorhabditis elegans/citologia , Drosophila melanogaster/citologia , HumanosRESUMO
Mutation spectra in cancer genomes provide information on the disease aetiology and the causality underlying the evolution and progression of cancer. Genome-wide mutation patterns reflect the effects of mutagenic insults and can thus reveal past carcinogen-specific exposures and inform hypotheses on the causative factors for specific cancer types. To identify mutation profiles in human cancers, single-gene studies were first employed, focusing mainly on the tumour suppressor gene TP53. Furthermore, experimental studies had been developed in model organisms. They allowed the characterization of the mutation patterns specific to known human carcinogens, such as polycyclic aromatic hydrocarbons or ultraviolet light. With the advent of massively parallel sequencing, mutation landscapes become revealed on a large scale, in human primary tumours and in experimental models, enabling deeper investigations of the functional and structural impact of mutations on the genome, including exposure-specific base-change fingerprints known as mutational signatures. These studies can now accelerate the identification of aetiological factors, contribute to carcinogen evaluation and classification and ultimately inform cancer prevention measures.
Assuntos
Carcinógenos/toxicidade , Exposição Ambiental/efeitos adversos , Mutagênicos/toxicidade , Neoplasias/genética , Animais , Modelos Animais de Doenças , Genes Reporter/genética , Engenharia Genética/métodos , Sequenciamento de Nucleotídeos em Larga Escala , Humanos , Modelos Genéticos , Testes de Mutagenicidade/métodos , Mutação , Análise de Sequência de DNA/métodosRESUMO
To understand the consequences of the complete elimination of E2F regulation, we profiled the proteome of Drosophila dDP mutants that lack functional E2F/DP complexes. The results uncovered changes in the larval fat body, a differentiated tissue that grows via endocycles. We report an unexpected mechanism of E2F/DP action that promotes quiescence in this tissue. In the fat body, dE2F/dDP limits cell-cycle progression by suppressing DNA damage responses. Loss of dDP upregulates dATM, allowing cells to sense and repair DNA damage and increasing replication of loci that are normally under-replicated in wild-type tissues. Genetic experiments show that ectopic dATM is sufficient to promote DNA synthesis in wild-type fat body cells. Strikingly, reducing dATM levels in dDP-deficient fat bodies restores cell-cycle control, improves tissue morphology, and extends animal development. These results show that, in some cellular contexts, dE2F/dDP-dependent suppression of DNA damage signaling is key for cell-cycle control and needed for normal development.