Metabolic alterations accompanying oncogene-induced senescence.
Ontology highlight
ABSTRACT:
SUBMITTER: Aird KM
PROVIDER: S-EPMC4904889 | biostudies-other | 2014 Jul-Sep
REPOSITORIES: biostudies-other
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Project description:Oncogene-induced senescence (OIS) is characterized by permanent growth arrest and the acquisition of a secretory, pro-inflammatory state. Increasingly, OIS is viewed as an important barrier to tumorgenesis. Surprisingly, relatively little is known about the metabolic changes that accompany and therefore may contribute to OIS. Here, we have performed a metabolomic and bioenergetic analysis of Ras-induced senescence. Profiling approximately 300 different intracellular metabolites reveals that cells that have undergone OIS develop a unique metabolic signature that differs markedly from cells undergoing replicative senescence. A number of lipid metabolites appear uniquely increased in OIS cells, including a marked increase in the level of certain intracellular long chain fatty acids. Functional studies reveal that this alteration in the metabolome reflects substantial changes in overall lipid metabolism. In particular, Ras-induced senescent cells manifest a decline in lipid synthesis and a significant increase in fatty acid oxidation. Increased fatty acid oxidation results in an unexpectedly high rate of basal oxygen consumption in cells that have undergone OIS. Pharmacological or genetic inhibition of carnitine palmitoyltransferase 1, the rate-limiting step in mitochondrial fatty acid oxidation, restores a pre-senescent metabolic rate and, surprisingly, selectively inhibits the secretory, pro-inflammatory state that accompanies OIS. Thus, Ras-induced senescent cells demonstrate profound alterations in their metabolic and bioenergetic profiles, particularly with regards to the levels, synthesis and oxidation of free fatty acids. Furthermore, the inflammatory phenotype that accompanies OIS appears to be related to these underlying changes in cellular metabolism.
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Project description:Biological aging profoundly impairs muscle function, performance, and metabolism. Because the progression of metabolic alterations associated with aging muscle has not been chronicled, we tracked the metabolic profiles of flight muscle from middle to advanced age in Manduca sexta to identify key molecules during the progression of muscle aging, as well as to evaluate the utility of the M. sexta system for molecular dissection of muscle aging. We identified a number of differences between Diel Time, Sexes, and Muscle Ages, including changes in metabolites related to energetics, extracellular matrix turnover, and glutathione metabolism. Increased abundances of glycolytic metabolites suggest a shift toward increased glycolysis with advancing age, whereas decreased abundances in lysolipids and acylcarnitines reflect decreasing beta-oxidation. We also observed a shift towards decreased polyamine metabolism with age, which might result in an age-related decline in lipid metabolism possibly due to regulation of energy metabolism by polyamines. Collectively, our findings demonstrate the feasibility of our system and approach and provide a deeper understanding of lepidopteran aging. More importantly, the results identify the key altered metabolic pathways that collectively contribute to the muscle aging phenotype and thereby improve our understanding of muscle senescence.
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Project description:Cellular senescence is an irreversible state of terminal growth arrest that requires functional p53. Acting to block tumor formation, induction of senescence has also been demonstrated to contribute to tumor clearance via the immune system following p53 reactivation. The Hdm2-antagonist, Nutlin-3a, has been shown to reactivate p53 and induce a quiescent state in various cancer cell lines, similar to the G(1) arrest observed upon RNAi targeting of Hdm2 in MCF7 breast cancer. In the present study we show that HdmX, a negative regulator of p53, impacts the senescence pathway. Specifically, overexpression of HdmX blocks Ras mediated senescence in primary human fibroblasts. The interaction of HdmX with p53 and the re-localization of HdmX to the nucleus through Hdm2 association appear to be required for this activity. Furthermore, inhibiting HdmX in prostate adenocarcinoma cells expressing wild-type p53, mutant Ras and high levels of HdmX induced cellular senescence as measured by an increase in irreversible b-galactosidase staining. Together these results suggest that HdmX overexpression may contribute to tumor formation by blocking senescence and that targeting HdmX may represent an attractive anti-cancer therapeutic approach.
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Project description:The expression of oncogenic ras in normal human cells quickly induces an aberrant proliferation response that later is curtailed by a cell cycle arrest known as cellular senescence. Here, we show that cells expressing oncogenic ras display an increase in the mitochondrial mass, the mitochondrial DNA, and the mitochondrial production of reactive oxygen species (ROS) prior to the senescent cell cycle arrest. By the time the cells entered senescence, dysfunctional mitochondria accumulated around the nucleus. The mitochondrial dysfunction was accompanied by oxidative DNA damage, a drop in ATP levels, and the activation of AMPK. The increase in mitochondrial mass and ROS in response to oncogenic ras depended on intact p53 and Rb tumor suppression pathways. In addition, direct interference with mitochondrial functions by inhibiting the expression of the Rieske iron sulfur protein of complex III or the use of pharmacological inhibitors of the electron transport chain and oxidative phosphorylation was sufficient to trigger senescence. Taking these results together, this work suggests that mitochondrial dysfunction is an effector pathway of oncogene-induced senescence.
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Project description:This experiment was designed to study oncogene-induced senescence (OIS). To this end we generated a series of cell lines derived from normal human diploid fibroblasts IMR90 forced to express the catalytic subunit of telomerase (hTERT). This cells were then subjected to further manipulation by orderly introducing defined genetic elements by retroviral transduction. The first cell line generated was ITV, which was obtained from the original cell line (IMR90 with hTERT) after introducing an empty vector. Subsequently, we introduced Mek:ER, which is a switchable version of the Mek kinase, a relevant downstream effector of Ras signaling during Ras-induced senescence, to generate ITM cells. We further modified this cell line by introducing SV40 small-t antigen (ST), papillomavirus oncoproteins E6 and E7 (E6/E7) or the combination of both (E6/E7 and ST). In this manner, we obtained ITMST, ITME6E7 and ITME6E7ST respectively. This cellular system allow us to have a representation of the different steps into neoplastic transformation. ITM and ITMST cells respond to Mek activation by inducing OIS. ITME6E7 and ITME6E7ST cells do not enter OIS after Mek activation. Mek activation is achieved by treating all cell cultures with 4-hydroxytamoxifen (4OHT) at 100 nM, in the absence of serum, and for 3 days. The gene expression profile of ITV cells served as a reference for all the expression values obtained with the rest of the cell lines. Thus, we ended up with the expression profiles of two cell lines representing oncogene-induced senescence (ITM and ITMST), and two cell lines representing bypass of oncogene-induced senescence, plus a reference profile provided by ITV, the cell line from which all the other cell lines were derived. Our final goal was to identify markers of the oncogene-induced senescence response by comparing the expression profiles of the cell lines entering OIS after Mek activation (that is, after 4OHT treatment) with the ones bypassing this response. Keywords: other
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Project description:Aging is a major risk factor for many neurodegenerative disorders. A key feature of aging biology that may underlie these diseases is cellular senescence. Senescent cells accumulate in tissues with age, undergo widespread changes in gene expression, and typically demonstrate altered, pro-inflammatory profiles. Astrocyte senescence has been implicated in neurodegenerative disease, and to better understand senescence-associated changes in astrocytes, we investigated changes in their transcriptome using RNA sequencing. Senescence was induced in human fetal astrocytes by transient oxidative stress. Brain-expressed genes, including those involved in neuronal development and differentiation, were downregulated in senescent astrocytes. Remarkably, several genes indicative of astrocytic responses to injury were also downregulated, including glial fibrillary acidic protein and genes involved in the processing and presentation of antigens by major histocompatibility complex class II proteins, while pro-inflammatory genes were upregulated. Overall, our findings suggest that senescence-related changes in the function of astrocytes may impact the pathogenesis of age-related brain disorders.
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Project description:Cellular senescence, an irreversible cell cycle arrest induced by a diversity of stimuli, has been considered as an innate tumor suppressing mechanism with implications and applications in cancer therapy. Using a targeted proteomics approach, we show that fibroblasts induced into senescence by expression of oncogenic Ras exhibit a decrease of global acetylation on all core histones, consistent with formation of senescence-associated heterochromatic foci. We also detected clear increases in repressive markers (e.g. >50% elevation of H3K27me2/3) along with decreases in histone marks associated with increased transcriptional expression/elongation (e.g. H3K36me2/3). Despite the increases in repressive marks of chromatin, 179 loci (of 2206 total) were found to be upregulated by global quantitative proteomics. The changes in the cytosolic proteome indicated an upregulation of mitochondrial proteins and downregulation of proteins involved in glycolysis. These alterations in primary metabolism are opposite to the well-known Warburg effect observed in cancer cells. This study significantly improves our understanding of stress-induced senescence and provides a potential application for triggering it in antiproliferative strategies that target the primary metabolism in cancer cells.
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Project description:To understand the role of the extensive senescence-associated 3D genome reorganization, we generated genome-wide chromatin interaction maps, epigenome, replication-timing, whole-genome bisulfite sequencing, and gene expression profiles from cells entering replicative senescence (RS) or upon oncogene-induced senescence (OIS). We identify senescence-associated heterochromatin domains (SAHDs). Differential intra- versus inter-SAHD interactions lead to the formation of senescence-associated heterochromatin foci (SAHFs) in OIS but not in RS. This OIS-specific configuration brings active genes located in genomic regions adjacent to SAHDs in close spatial proximity and favors their expression. We also identify DNMT1 as a factor that induces SAHFs by promoting HMGA2 expression. Upon DNMT1 depletion, OIS cells transition to a 3D genome conformation akin to that of cells in replicative senescence. These data show how multi-omics and imaging can identify critical features of RS and OIS and discover determinants of acute senescence and SAHF formation.
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Project description:Oncogenic stress-induced senescence (OIS) prevents the ability of oncogenic signals to induce tumorigenesis. It is now largely admitted that the mitogenic effect of oncogenes requires metabolic adaptations to respond to new energetic and bio constituent needs. Yet, whether glucose metabolism affects OIS response is largely unknown. This is largely because of the fact that most of the OIS cellular models are cultivated in glucose excess. In this study, we used human epithelial cells, cultivated without glucose excess, to study alteration and functional role of glucose metabolism during OIS. We report a slowdown of glucose uptake and metabolism during OIS. Increasing glucose metabolism by expressing hexokinase2 (HK2), which converts glucose to glucose-6-phosphate (G6P), favors escape from OIS. Inversely, expressing a glucose-6-phosphatase, [corrected] pharmacological inhibition of HK2, or adding nonmetabolizable glucose induced a premature senescence. Manipulations of various metabolites covering G6P downstream pathways (hexosamine, glycolysis, and pentose phosphate pathways) suggest an unexpected role of the hexosamine pathway in controlling OIS. Altogether, our results show that decreased glucose metabolism occurs during and participates to OIS.
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Project description:Oncogene-induced senescence functions to limit tumor development. However, a complete understanding of the signals that trigger this type of senescence is currently lacking. We found that mutations affecting NF1, Raf, and Ras induce a global negative feedback response that potently suppresses Ras and/or its effectors. Moreover, these signals promote senescence by inhibiting the Ras/PI3K pathway, which can impact the senescence machinery through HDM2 and FOXO. This negative feedback program is regulated in part by RasGEFs, Sprouty proteins, RasGAPs, and MKPs. Moreover, these signals function in vivo in benign human tumors. Thus, the ultimate response to the aberrant activation of the Ras pathway is a multifaceted negative feedback signaling network that terminates the oncogenic signal and participates in the senescence response.
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