ABSTRACT
Proliferating mammalian cells use glutamine as a source of nitrogen and as a key anaplerotic source to provide metabolites to the tricarboxylic acid cycle (TCA) for biosynthesis. Recently, mammalian target of rapamycin complex 1 (mTORC1) activation has been correlated with increased nutrient uptake and metabolism, but no molecular connection to glutaminolysis has been reported. Here, we show that mTORC1 promotes glutamine anaplerosis by activating glutamate dehydrogenase (GDH). This regulation requires transcriptional repression of SIRT4, the mitochondrial-localized sirtuin that inhibits GDH. Mechanistically, mTORC1 represses SIRT4 by promoting the proteasome-mediated destabilization of cAMP-responsive element binding 2 (CREB2). Thus, a relationship between mTORC1, SIRT4, and cancer is suggested by our findings. Indeed, SIRT4 expression is reduced in human cancer, and its overexpression reduces cell proliferation, transformation, and tumor development. Finally, our data indicate that targeting nutrient metabolism in energy-addicted cancers with high mTORC1 signaling may be an effective therapeutic approach.
Subject(s)
Glutamine/metabolism , Mitochondrial Proteins/metabolism , Neoplasms/metabolism , Sirtuins/metabolism , Activating Transcription Factors/metabolism , Animals , Cell Proliferation , Embryo, Mammalian/cytology , Energy Metabolism , Glutamate Dehydrogenase/metabolism , Humans , Mechanistic Target of Rapamycin Complex 1 , Mice , Multiprotein Complexes , Neoplasm Transplantation , Neoplasms/pathology , TOR Serine-Threonine Kinases/metabolism , Transcription, Genetic , Transplantation, Heterologous , Tuberous Sclerosis Complex 2 Protein , Tumor Suppressor Proteins/genetics , Tumor Suppressor Proteins/metabolism , UbiquitinationABSTRACT
Loss of metabolic homeostasis is a hallmark of aging and is characterized by dramatic metabolic reprogramming. To analyze how the fate of labeled methionine is altered during aging, we applied 13C5-Methionine labeling to Drosophila and demonstrated significant changes in the activity of different branches of the methionine metabolism as flies age. We further tested whether targeted degradation of methionine metabolism components would "reset" methionine metabolism flux and extend the fly lifespan. Specifically, we created transgenic flies with inducible expression of Methioninase, a bacterial enzyme capable of degrading methionine and revealed methionine requirements for normal maintenance of lifespan. We also demonstrated that microbiota-derived methionine is an alternative and important source in addition to food-derived methionine. In this genetic model of methionine restriction (MetR), we also demonstrate that either whole-body or tissue-specific Methioninase expression can dramatically extend Drosophila health- and lifespan and exerts physiological effects associated with MetR. Interestingly, while previous dietary MetR extended lifespan in flies only in low amino acid conditions, MetR from Methioninase expression extends lifespan independently of amino acid levels in the food. Finally, because impairment of the methionine metabolism has been previously associated with the development of Alzheimer's disease, we compared methionine metabolism reprogramming between aging flies and a Drosophila model relevant to Alzheimer's disease, and found that overexpression of human Tau caused methionine metabolism flux reprogramming similar to the changes found in aged flies. Altogether, our study highlights Methioninase as a potential agent for health- and lifespan extension.
Subject(s)
Drosophila/genetics , Longevity/genetics , Methionine/genetics , Aging/genetics , Alzheimer Disease/genetics , Amino Acids/genetics , Animals , Animals, Genetically Modified/genetics , Carbon-Sulfur Lyases/genetics , Food , Humans , Models, GeneticABSTRACT
The RB1 tumor suppressor is recurrently mutated in a variety of cancers including retinoblastomas, small cell lung cancers, triple-negative breast cancers, prostate cancers, and osteosarcomas. Finding new synthetic lethal (SL) interactions with RB1 could lead to new approaches to treating cancers with inactivated RB1. We identified 95 SL partners of RB1 based on a Drosophila screen for genetic modifiers of the eye phenotype caused by defects in the RB1 ortholog, Rbf1. We validated 38 mammalian orthologs of Rbf1 modifiers as RB1 SL partners in human cancer cell lines with defective RB1 alleles. We further show that for many of the RB1 SL genes validated in human cancer cell lines, low activity of the SL gene in human tumors, when concurrent with low levels of RB1 was associated with improved patient survival. We investigated higher order combinatorial gene interactions by creating a novel Drosophila cancer model with co-occurring Rbf1, Pten and Ras mutations, and found that targeting RB1 SL genes in this background suppressed the dramatic tumor growth and rescued fly survival whilst having minimal effects on wild-type cells. Finally, we found that drugs targeting the identified RB1 interacting genes/pathways, such as UNC3230, PYR-41, TAK-243, isoginkgetin, madrasin, and celastrol also elicit SL in human cancer cell lines. In summary, we identified several high confidence, evolutionarily conserved, novel targets for RB1-deficient cells that may be further adapted for the treatment of human cancer.
Subject(s)
Neoplasms/genetics , Phosphotransferases (Alcohol Group Acceptor)/genetics , RNA Splicing , Retinoblastoma Protein/genetics , Signal Transduction , Ubiquitin/metabolism , Animals , Animals, Genetically Modified , Cell Line, Tumor , Drosophila Proteins/genetics , Drosophila Proteins/metabolism , Drosophila melanogaster/genetics , Drosophila melanogaster/metabolism , Eye Abnormalities/genetics , Eye Abnormalities/metabolism , Humans , Neoplasms/metabolism , Neoplasms/pathology , PTEN Phosphohydrolase/genetics , PTEN Phosphohydrolase/metabolism , Phosphotransferases (Alcohol Group Acceptor)/metabolism , RNA Interference , Retinoblastoma Protein/deficiency , Retinoblastoma Protein/metabolism , Species Specificity , Survival Analysis , Synthetic Lethal Mutations/genetics , Transcription Factors/genetics , Transcription Factors/metabolism , ras Proteins/genetics , ras Proteins/metabolismABSTRACT
Aging is a risk factor for many human pathologies and is characterized by extensive metabolic changes. Using targeted high-throughput metabolite profiling in Drosophila melanogaster at different ages, we demonstrate that methionine metabolism changes strikingly during aging. Methionine generates the methyl donor S-adenosyl-methionine (SAM), which is converted via methylation to S-adenosyl-homocysteine (SAH), which accumulates during aging. A targeted RNAi screen against methionine pathway components revealed significant life span extension in response to down-regulation of two noncanonical Drosophila homologs of the SAH hydrolase Ahcy (S-adenosyl-L-homocysteine hydrolase [SAHH[), CG9977/dAhcyL1 and Ahcy89E/CG8956/dAhcyL2, which act as dominant-negative regulators of canonical AHCY. Importantly, tissue-specific down-regulation of dAhcyL1/L2 in the brain and intestine extends health and life span. Furthermore, metabolomic analysis of dAhcyL1-deficient flies revealed its effect on age-dependent metabolic reprogramming and H3K4 methylation. Altogether, reprogramming of methionine metabolism in young flies and suppression of age-dependent SAH accumulation lead to increased life span. These studies highlight the role of noncanonical Ahcy enzymes as determinants of healthy aging and longevity.
Subject(s)
Aging/metabolism , Down-Regulation , Drosophila Proteins/genetics , Drosophila melanogaster/physiology , Intracellular Signaling Peptides and Proteins/genetics , Longevity/genetics , Animals , Brain/enzymology , Drosophila Proteins/metabolism , Drosophila melanogaster/enzymology , Drosophila melanogaster/genetics , Female , Heterochromatin/genetics , Intestines/enzymology , Intracellular Signaling Peptides and Proteins/metabolism , Male , Methionine/metabolism , Methylation , S-AdenosylhomocysteineABSTRACT
Activating mutations in the Kirsten rat sarcoma viral oncogene homolog (KRAS) underlie the pathogenesis and chemoresistance of â¼ 30% of all human tumors, yet the development of high-affinity inhibitors that target the broad range of KRAS mutants remains a formidable challenge. Here, we report the development and validation of stabilized alpha helices of son of sevenless 1 (SAH-SOS1) as prototype therapeutics that directly inhibit wild-type and mutant forms of KRAS. SAH-SOS1 peptides bound in a sequence-specific manner to KRAS and its mutants, and dose-responsively blocked nucleotide association. Importantly, this functional binding activity correlated with SAH-SOS1 cytotoxicity in cancer cells expressing wild-type or mutant forms of KRAS. The mechanism of action of SAH-SOS1 peptides was demonstrated by sequence-specific down-regulation of the ERK-MAP kinase phosphosignaling cascade in KRAS-driven cancer cells and in a Drosophila melanogaster model of Ras85D(V12) activation. These studies provide evidence for the potential utility of SAH-SOS1 peptides in neutralizing oncogenic KRAS in human cancer.
Subject(s)
Drosophila Proteins/metabolism , Gene Expression Regulation, Enzymologic/physiology , MAP Kinase Signaling System/physiology , Peptides/pharmacology , Proto-Oncogene Proteins/antagonists & inhibitors , SOS1 Protein/metabolism , ras Proteins/antagonists & inhibitors , ras Proteins/metabolism , Animals , Blotting, Western , Cell Line, Tumor , Chromatography, Gel , Drosophila melanogaster , Escherichia coli , Fluorescence , Humans , MAP Kinase Signaling System/genetics , Magnetic Resonance Spectroscopy , Microfluidics , Mutation/genetics , Peptides/genetics , Peptides/metabolism , Protein Binding , Protein Structure, Secondary/genetics , Proto-Oncogene Proteins/genetics , Proto-Oncogene Proteins p21(ras) , SOS1 Protein/genetics , ras Proteins/geneticsABSTRACT
Tuberous sclerosis complex (TSC) is a tumor suppressor syndrome characterized by benign tumors in multiple organs, including the brain and kidney. TSC-associated tumors exhibit hyperactivation of mammalian target of rapamycin complex 1 (mTORC1), a direct inhibitor of autophagy. Autophagy can either promote or inhibit tumorigenesis, depending on the cellular context. The role of autophagy in the pathogenesis and treatment of the multisystem manifestations of TSC is unknown. We found that the combination of mTORC1 and autophagy inhibition was more effective than either treatment alone in inhibiting the survival of tuberin (TSC2)-null cells, growth of TSC2-null xenograft tumors, and development of spontaneous renal tumors in Tsc2(+/-) mice. Down-regulation of Atg5 induced extensive central necrosis in TSC2-null xenograft tumors, and loss of one allele of Beclin1 almost completely blocked macroscopic renal tumor formation in Tsc2(+/-) mice. Surprisingly, given the finding that lowering autophagy blocks TSC tumorigenesis, genetic down-regulation of p62/sequestosome 1 (SQSTM1), the autophagy substrate that accumulates in TSC tumors as a consequence of low autophagy levels, strongly inhibited the growth of TSC2-null xenograft tumors. These data demonstrate that autophagy is a critical component of TSC tumorigenesis, suggest that mTORC1 inhibitors may have autophagy-dependent prosurvival effects in TSC, and reveal two distinct therapeutic targets for TSC: autophagy and the autophagy target p62/SQSTM1.
Subject(s)
Adaptor Proteins, Signal Transducing/metabolism , Heat-Shock Proteins/metabolism , Tuberous Sclerosis/metabolism , Tuberous Sclerosis/pathology , Adaptor Proteins, Signal Transducing/genetics , Animals , Apoptosis Regulatory Proteins/deficiency , Apoptosis Regulatory Proteins/genetics , Autophagy/genetics , Autophagy/physiology , Autophagy-Related Protein 5 , Beclin-1 , Cell Survival/genetics , Cell Survival/physiology , Genes, p53 , Heat-Shock Proteins/genetics , Mechanistic Target of Rapamycin Complex 1 , Mice , Mice, Inbred C57BL , Mice, Knockout , Mice, Nude , Mice, SCID , Microtubule-Associated Proteins/deficiency , Microtubule-Associated Proteins/genetics , Multiprotein Complexes , Proteins/genetics , Proteins/metabolism , Sequestosome-1 Protein , TOR Serine-Threonine Kinases , Tuberous Sclerosis/genetics , Tuberous Sclerosis Complex 2 Protein , Tumor Suppressor Proteins/deficiency , Tumor Suppressor Proteins/geneticsABSTRACT
Neuronal cells are highly specialized cells and have a specific metabolic profile to support their function. It has been demonstrated that the metabolic profiles of different cells/tissues undergo significant reprogramming with advancing age, which has often been considered a contributing factor towards aging-related diseases including Alzheimer's (AD) and Parkinson's (PD) diseases. However, it is unclear if the metabolic changes associated with normal aging predispose neurons to disease conditions or a distinct set of metabolic alterations happen in neurons in AD or PD which might contribute to disease pathologies. To decipher the changes in neuronal metabolism with age, in AD, or in PD, we performed high-throughput steady-state metabolite profiling on heads in wildtype Drosophila and in Drosophila models relevant to AD and PD. Intriguingly, we found that the spectrum of affected metabolic pathways is dramatically different between normal aging, Tau, or Synuclein overexpressing neurons. Genetic targeting of the purine and glutamate metabolism pathways, which were dysregulated in both old age and disease conditions partially rescued the neurodegenerative phenotype associated with the overexpression of wildtype and mutant tau. Our findings support a "two-hit model" to explain the pathological manifestations associated with AD where both aging- and Tau/Synuclein- driven metabolic reprogramming events cooperate with each other, and targeting both could be a potent therapeutic strategy.
ABSTRACT
Caloric restriction improves metabolic health but is often complicated by bone loss. We studied bone parameters in humans during a 10-day fast and identified candidate metabolic regulators of bone turnover. Pro-collagen 1 intact N-terminal pro-peptide (P1NP), a bone formation marker, decreased within 3 days of fasting. Whereas dual-energy x-ray absorptiometry measures of bone mineral density were unchanged after 10 days of fasting, high-resolution peripheral quantitative CT demonstrated remodeling of bone microarchitecture. Pathway analysis of longitudinal metabolomics data identified one-carbon metabolism as fasting dependent. In cultured osteoblasts, we tested the functional significance of one-carbon metabolites modulated by fasting, finding that methionine - which surged after 3 days of fasting - affected markers of osteoblast cell state in a concentration-dependent manner, in some instances exhibiting a U-shaped response with both low and high concentrations driving putative antibone responses. Administration of methionine to mice for 5 days recapitulated some fasting effects on bone, including a reduction in serum P1NP. In conclusion, a 10-day fast in humans led to remodeling of bone microarchitecture, potentially mediated by a surge in circulating methionine. These data support an emerging model that points to a window of optimal methionine exposure for bone health.
Subject(s)
Bone Density , Bone Remodeling , Fasting , Methionine , Methionine/metabolism , Methionine/administration & dosage , Animals , Humans , Bone Remodeling/drug effects , Bone Remodeling/physiology , Mice , Male , Female , Bone Density/drug effects , Osteoblasts/metabolism , Procollagen/metabolism , Procollagen/blood , Middle Aged , Adult , Absorptiometry, Photon , Peptide Fragments/metabolism , Peptide Fragments/blood , Caloric RestrictionABSTRACT
Lymphangioleiomyomatosis (LAM) is a destructive lung disease primarily affecting women. Genetic studies indicate that LAM cells carry inactivating tuberous sclerosis complex (TSC)-2 mutations, and metastasize to the lung. We previously discovered that estradiol increases the metastasis of TSC2-deficient cells in mice carrying xenograft tumors. Here, we investigate the molecular basis underlying the estradiol-induced lung metastasis of TSC2-deficient cells, and test the efficacy of Faslodex (an estrogen receptor antagonist) in a preclinical model of LAM. We used a xenograft tumor model in which estradiol induces the lung metastasis of TSC2-deficient cells. We analyzed the impact of Faslodex on tumor size, the extracellular matrix organization, the expression of matrix metalloproteinase (MMP)-2, and lung metastasis. We also examined the effects of estradiol and Faslodex on MMP2 expression and activity in tuberin-deficient cells in vitro. Estradiol resulted in a marked reduction of Type IV collagen deposition in xenograft tumors, associated with 2-fold greater MMP2 concentrations compared with placebo-treated mice. Faslodex normalized the Type IV collagen changes in xenograft tumors, enhanced the survival of the mice, and completely blocked lung metastases. In vitro, estradiol enhanced MMP2 transcripts, protein accumulation, and activity. These estradiol-induced changes in MMP2 were blocked by Faslodex. In TSC2-deficient cells, estradiol increased MMP2 concentrations in vitro and in vivo, and induced extracellular matrix remodeling. Faslodex inhibits the estradiol-induced lung metastasis of TSC2-deficient cells. Targeting estrogen receptors with Faslodex may be of efficacy in the treatment of LAM.
Subject(s)
Estradiol/analogs & derivatives , Estradiol/adverse effects , Extracellular Matrix/drug effects , Lung Neoplasms/secondary , Lymphangioleiomyomatosis/pathology , Airway Remodeling , Animals , Antineoplastic Agents/pharmacology , Collagen Type IV/metabolism , Drug Evaluation, Preclinical , Estradiol/pharmacology , Extracellular Matrix/metabolism , Female , Fulvestrant , Lung/drug effects , Lung/metabolism , Lung/pathology , Lymphangioleiomyomatosis/metabolism , Male , Matrix Metalloproteinase 2/metabolism , Mice , Mice, SCID , Rats , Receptors, Estradiol/antagonists & inhibitors , Survival Analysis , Tuberous Sclerosis Complex 2 Protein , Tumor Suppressor Proteins/genetics , Tumor Suppressor Proteins/metabolism , Xenograft Model Antitumor AssaysABSTRACT
Insight on the underlying mechanisms of aging will advance our ability to extend healthspan, treat age-related pathology and improve quality of life. Multiple genetic and pharmacological manipulations extend longevity in different species, yet monotherapy may be relatively inefficient, and we have limited data on the effect of combined interventions. Here we summarize interactions between age-related pathways and discuss strategies to simultaneously retard these in different organisms. In some cases, combined manipulations additively increase their impact on common hallmarks of aging and lifespan, suggesting they quantitatively participate within the same pathway. In other cases, interactions affect different hallmarks, suggesting their joint manipulation may independently maximize their effects on lifespan and healthy aging. While most interaction studies have been conducted with invertebrates and show varying levels of translatability, the conservation of pro-longevity pathways offers an opportunity to identify 'druggable' targets relevant to multiple human age-associated pathologies.
Subject(s)
Healthy Aging , Quality of Life , Humans , Aging/genetics , Longevity/genetics , Healthy Aging/geneticsABSTRACT
Insulin signaling promotes anabolic metabolism to regulate cell growth through multi-omic interactions. To obtain a comprehensive view of the cellular responses to insulin, we constructed a trans-omic network of insulin action in Drosophila cells that involves the integration of multi-omic data sets. In this network, 14 transcription factors, including Myc, coordinately upregulate the gene expression of anabolic processes such as nucleotide synthesis, transcription, and translation, consistent with decreases in metabolites such as nucleotide triphosphates and proteinogenic amino acids required for transcription and translation. Next, as cell growth is required for cell proliferation and insulin can stimulate proliferation in a context-dependent manner, we integrated the trans-omic network with results from a CRISPR functional screen for cell proliferation. This analysis validates the role of a Myc-mediated subnetwork that coordinates the activation of genes involved in anabolic processes required for cell growth.
ABSTRACT
Adaptation to nutrient scarcity involves an orchestrated response of metabolic and signaling pathways to maintain homeostasis. We find that in the fat body of fasting Drosophila, lysosomal export of cystine coordinates remobilization of internal nutrient stores with reactivation of the growth regulator target of rapamycin complex 1 (TORC1). Mechanistically, cystine was reduced to cysteine and metabolized to acetyl-coenzyme A (acetyl-CoA) by promoting CoA metabolism. In turn, acetyl-CoA retained carbons from alternative amino acids in the form of tricarboxylic acid cycle intermediates and restricted the availability of building blocks required for growth. This process limited TORC1 reactivation to maintain autophagy and allowed animals to cope with starvation periods. We propose that cysteine metabolism mediates a communication between lysosomes and mitochondria, highlighting how changes in diet divert the fate of an amino acid into a growth suppressive program.
Subject(s)
Cystine/metabolism , Drosophila Proteins/metabolism , Drosophila melanogaster/metabolism , Fasting , Lysosomes/metabolism , Mechanistic Target of Rapamycin Complex 1/metabolism , Transcription Factors/metabolism , Acetyl Coenzyme A/metabolism , Amino Acid Transport Systems, Neutral/metabolism , Amino Acids/metabolism , Animals , Autophagy , Citric Acid Cycle , Cysteine/metabolism , Cysteine/pharmacology , Cytosol/metabolism , Diet, Protein-Restricted , Drosophila melanogaster/growth & development , Fat Body/physiology , Models, Animal , Signal TransductionABSTRACT
Metabolism plays a significant role in the regulation of aging at different levels, and metabolic reprogramming represents a major driving force in aging. Metabolic reprogramming leads to impaired organismal fitness, an age-dependent increase in susceptibility to diseases, decreased ability to mount a stress response, and increased frailty. The complexity of age-dependent metabolic reprogramming comes from the multitude of levels on which metabolic changes can be connected to aging and regulation of lifespan. This is further complicated by the different metabolic requirements of various tissues, cross-organ communication via metabolite secretion, and direct effects of metabolites on epigenetic state and redox regulation; however, not all of these changes are causative to aging. Studies in yeast, flies, worms, and mice have played a crucial role in identifying mechanistic links between observed changes in various metabolic traits and their effects on lifespan. Here, we review how changes in the organismal and organ-specific metabolome are associated with aging and how targeting of any one of over a hundred different targets in specific metabolic pathways can extend lifespan. An important corollary is that restriction or supplementation of different metabolites can change activity of these metabolic pathways in ways that improve healthspan and extend lifespan in different organisms. Due to the high levels of conservation of metabolism in general, translating findings from model systems to human beings will allow for the development of effective strategies for human health- and lifespan extension.
Subject(s)
Aging , Longevity , Animals , Metabolic Networks and Pathways , Mice , Models, Biological , MutationABSTRACT
Aging is characterized by extensive metabolic reprogramming. To identify metabolic pathways associated with aging, we analyzed age-dependent changes in the metabolomes of long-lived Drosophila melanogaster. Among the metabolites that changed, levels of tyrosine were increased with age in long-lived flies. We demonstrate that the levels of enzymes in the tyrosine degradation pathway increase with age in wild-type flies. Whole-body and neuronal-specific downregulation of enzymes in the tyrosine degradation pathway significantly extends Drosophila lifespan, causes alterations of metabolites associated with increased lifespan, and upregulates the levels of tyrosine-derived neuromediators. Moreover, feeding wild-type flies with tyrosine increased their lifespan. Mechanistically, we show that suppression of ETC complex I drives the upregulation of enzymes in the tyrosine degradation pathway, an effect that can be rescued by tigecycline, an FDA-approved drug that specifically suppresses mitochondrial translation. In addition, tyrosine supplementation partially rescued lifespan of flies with ETC complex I suppression. Altogether, our study highlights the tyrosine degradation pathway as a regulator of longevity.
Subject(s)
Aging/drug effects , Longevity/physiology , Tyrosine Transaminase/metabolism , Tyrosine/metabolism , Tyrosine/pharmacology , Animals , Drosophila melanogaster/metabolism , Electron Transport Chain Complex Proteins/drug effects , Longevity/drug effects , Mitochondria/metabolism , Tigecycline/pharmacology , Tyrosine/analysisABSTRACT
Aging is emerging as a druggable target with growing interest from academia, industry and investors. New technologies such as artificial intelligence and advanced screening techniques, as well as a strong influence from the industry sector may lead to novel discoveries to treat age-related diseases. The present review summarizes presentations from the 7th Annual Aging Research and Drug Discovery (ARDD) meeting, held online on the 1st to 4th of September 2020. The meeting covered topics related to new methodologies to study aging, knowledge about basic mechanisms of longevity, latest interventional strategies to target the aging process as well as discussions about the impact of aging research on society and economy. More than 2000 participants and 65 speakers joined the meeting and we already look forward to an even larger meeting next year. Please mark your calendars for the 8th ARDD meeting that is scheduled for the 31st of August to 3rd of September, 2021, at Columbia University, USA.
Subject(s)
Aging , Artificial Intelligence , Biomedical Research , Longevity , Cellular Senescence , Congresses as Topic , Drug Discovery , Humans , Life Style , Pharmaceutical PreparationsABSTRACT
Methionine restriction (MetR) extends lifespan across different species and exerts beneficial effects on metabolic health and inflammatory responses. In contrast, certain cancer cells exhibit methionine auxotrophy that can be exploited for therapeutic treatment, as decreasing dietary methionine selectively suppresses tumor growth. Thus, MetR represents an intervention that can extend lifespan with a complementary effect of delaying tumor growth. Beyond its function in protein synthesis, methionine feeds into complex metabolic pathways including the methionine cycle, the transsulfuration pathway, and polyamine biosynthesis. Manipulation of each of these branches extends lifespan; however, the interplay between MetR and these branches during regulation of lifespan is not well understood. In addition, a potential mechanism linking the activity of methionine metabolism and lifespan is regulation of production of the methyl donor S-adenosylmethionine, which, after transferring its methyl group, is converted to S-adenosylhomocysteine. Methylation regulates a wide range of processes, including those thought to be responsible for lifespan extension by MetR. Although the exact mechanisms of lifespan extension by MetR or methionine metabolism reprogramming are unknown, it may act via reducing the rate of translation, modifying gene expression, inducing a hormetic response, modulating autophagy, or inducing mitochondrial function, antioxidant defense, or other metabolic processes. Here, we review the mechanisms of lifespan extension by MetR and different branches of methionine metabolism in different species and the potential for exploiting the regulation of methyltransferases to delay aging.
Subject(s)
Aging/metabolism , Longevity , Methionine/metabolism , Methyltransferases/metabolism , Animals , Humans , Species SpecificityABSTRACT
Spinal muscular atrophy (SMA), a degenerative motor neuron (MN) disease, caused by loss of functional survival of motor neuron (SMN) protein due to SMN1 gene mutations, is a leading cause of infant mortality. Increasing SMN levels ameliorates the disease phenotype and is unanimously accepted as a therapeutic approach for patients with SMA. The ubiquitin/proteasome system is known to regulate SMN protein levels; however, whether autophagy controls SMN levels remains poorly explored. Here, we show that SMN protein is degraded by autophagy. Pharmacological and genetic inhibition of autophagy increases SMN levels, while induction of autophagy decreases these levels. SMN degradation occurs via its interaction with the autophagy adapter p62 (also known as SQSTM1). We also show that SMA neurons display reduced autophagosome clearance, increased p62 and ubiquitinated proteins levels, and hyperactivated mTORC1 signaling. Importantly, reducing p62 levels markedly increases SMN and its binding partner gemin2, promotes MN survival, and extends lifespan in fly and mouse SMA models, revealing p62 as a potential new therapeutic target for the treatment of SMA.
Subject(s)
Muscular Atrophy, Spinal/drug therapy , Muscular Atrophy, Spinal/metabolism , SMN Complex Proteins/metabolism , Sequestosome-1 Protein/antagonists & inhibitors , Animals , Autophagy , Cells, Cultured , Disease Models, Animal , Gene Knockdown Techniques , HEK293 Cells , Humans , Mice , Mice, Inbred C57BL , Mice, Knockout , Motor Neurons/metabolism , Muscular Atrophy, Spinal/pathology , Mutation , Phenotype , Proteolysis , RNA, Small Interfering/genetics , SMN Complex Proteins/deficiency , SMN Complex Proteins/genetics , Sequestosome-1 Protein/genetics , Sequestosome-1 Protein/metabolism , Survival of Motor Neuron 1 Protein/antagonists & inhibitors , Survival of Motor Neuron 1 Protein/genetics , Survival of Motor Neuron 1 Protein/metabolism , TOR Serine-Threonine Kinases/metabolismABSTRACT
p62/sequestosome-1 (SQSTM1) is a multifunctional adaptor protein and autophagic substrate that accumulates in cells with hyperactive mTORC1, such as kidney cells with mutations in the tumor suppressor genes tuberous sclerosis complex (TSC)1 or TSC2. Here we report that p62 is a critical mediator of TSC2-driven tumorigenesis, as Tsc2+/- and Tsc2f/f Ksp-CreERT2+ mice crossed to p62-/- mice were protected from renal tumor development. Metabolic profiling revealed that depletion of p62 in Tsc2-null cells decreased intracellular glutamine, glutamate, and glutathione (GSH). p62 positively regulated the glutamine transporter Slc1a5 and increased glutamine uptake in Tsc2-null cells. We also observed p62-dependent changes in Gcl, Gsr, Nqo1, and Srxn1, which were decreased by p62 attenuation and implicated in GSH production and utilization. p62 attenuation altered mitochondrial morphology, reduced mitochondrial membrane polarization and maximal respiration, and increased mitochondrial reactive oxygen species and mitophagy marker PINK1. These mitochondrial phenotypes were rescued by addition of exogenous GSH and overexpression of Sod2, which suppressed indices of mitochondrial damage and promoted growth of Tsc2-null cells. Finally, p62 depletion sensitized Tsc2-null cells to both oxidative stress and direct inhibition of GSH biosynthesis by buthionine sulfoximine. Our findings show how p62 helps maintain intracellular pools of GSH needed to limit mitochondrial dysfunction in tumor cells with elevated mTORC1, highlighting p62 and redox homeostasis as nodal vulnerabilities for therapeutic targeting in these tumors. Cancer Res; 77(12); 3255-67. ©2017 AACR.
Subject(s)
Carcinogenesis/metabolism , Mitochondria/pathology , Multiprotein Complexes/metabolism , Sequestosome-1 Protein/metabolism , TOR Serine-Threonine Kinases/metabolism , Tuberous Sclerosis/metabolism , Animals , Carcinogenesis/pathology , Disease Models, Animal , Fluorescent Antibody Technique , Glutathione/biosynthesis , Immunohistochemistry , Kidney Neoplasms/metabolism , Kidney Neoplasms/pathology , Mechanistic Target of Rapamycin Complex 1 , Mice , Mice, Knockout , Tuberous Sclerosis/pathology , Tuberous Sclerosis Complex 2 Protein , Tumor Suppressor Proteins/metabolismABSTRACT
UNLABELLED: Tuberous sclerosis complex (TSC) is an autosomal dominant syndrome associated with tumors of the brain, heart, kidney, and lung. The TSC protein complex inhibits the mammalian or mechanistic target of rapamycin complex 1 (mTORC1). Inhibitors of mTORC1, including rapamycin, induce a cytostatic response in TSC tumors, resulting in temporary disease stabilization and prompt regrowth when treatment is stopped. The lack of TSC-specific cytotoxic therapies represents an important unmet clinical need. Using a high-throughput chemical screen in TSC2-deficient, patient-derived cells, we identified a series of molecules antagonized by rapamycin and therefore selective for cells with mTORC1 hyperactivity. In particular, the cell-permeable alkaloid chelerythrine induced reactive oxygen species (ROS) and depleted glutathione (GSH) selectively in TSC2-null cells based on metabolic profiling. N-acetylcysteine or GSH cotreatment protected TSC2-null cells from chelerythrine's effects, indicating that chelerythrine-induced cell death is ROS dependent. Induction of heme-oxygenase-1 (HMOX1/HO-1) with hemin also blocked chelerythrine-induced cell death. In vivo, chelerythrine inhibited the growth of TSC2-null xenograft tumors with no evidence of systemic toxicity with daily treatment over an extended period of time. This study reports the results of a bioactive compound screen and the identification of a potential lead candidate that acts via a novel oxidative stress-dependent mechanism to selectively induce necroptosis in TSC2-deficient tumors. IMPLICATIONS: This study demonstrates that TSC2-deficient tumor cells are hypersensitive to oxidative stress-dependent cell death, and provide critical proof of concept that TSC2-deficient cells can be therapeutically targeted without the use of a rapalog to induce a cell death response.