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Birt-Hogg-Dubé (BHD) syndrome patients are uniquely susceptible to all renal tumour subtypes. The underlying mechanism of carcinogenesis is unclear. To study cancer development in BHD, we used human proximal kidney (HK2) cells and found that long-term folliculin (FLCN) knockdown was required to increase their tumorigenic potential, forming larger spheroids in non-adherent conditions. Transcriptomic and proteomic analysis uncovered links between FLCN, cell cycle control and the DNA damage response (DDR) machinery. HK2 cells lacking FLCN had an altered transcriptome profile with cell cycle control gene enrichment. G1/S cell cycle checkpoint signaling was compromised with heightened protein levels of cyclin D1 (CCND1) and hyperphosphorylation of retinoblastoma 1 (RB1). A FLCN interactome screen uncovered FLCN binding to DNA-dependent protein kinase (DNA-PK). This novel interaction was reversed in an irradiation-responsive manner. Knockdown of FLCN in HK2 cells caused a marked elevation of γH2AX and RB1 phosphorylation. Both CCND1 and RB1 phosphorylation remained raised during DNA damage, showing an association with defective cell cycle control with FLCN knockdown. Furthermore, Flcn-knockdown C. elegans were defective in cell cycle arrest by DNA damage. This work implicates that long-term FLCN loss and associated cell cycle defects in BHD patients could contribute to their increased risk of cancer.
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Hyperactivation of mechanistic target of rapamycin complex 1 (mTORC1) is a feature of many solid tumours and is a key pathogenic driver in the inherited condition Tuberous Sclerosis Complex (TSC). Modulation of the tumour microenvironment by extracellular vesicles (EVs) is known to facilitate the development of various cancers. The role of EVs in modulating the tumour microenvironment and their impact on the development of TSC tumours, however, remains unclear. This study, therefore, focuses on the poorly defined contribution of EVs to tumour growth in TSC. We characterised EVs secreted from TSC2-deficient and TSC2-expressing cells and identified a distinct protein cargo in TSC2-deficient EVs, containing an enrichment of proteins thought to be involved in tumour-supporting signalling pathways. We show EVs from TSC2-deficient cells promote cell viability, proliferation and growth factor secretion from recipient fibroblasts within the tumour microenvironment. Rapalogs (mTORC1 inhibitors) are the current therapy for TSC tumours. Here, we demonstrate a previously unknown intercellular therapeutic effect of rapamycin in altering EV cargo and reducing capacity to promote cell proliferation in the tumour microenvironment. Furthermore, EV cargo proteins have the potential for clinical applications as TSC biomarkers, and we reveal three EV-associated proteins that are elevated in plasma from TSC patients compared to healthy donor plasma.
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Vesículas Extracelulares , Esclerose Tuberosa , Humanos , Proteínas Supressoras de Tumor , Esclerose Tuberosa/metabolismo , Esclerose Tuberosa/patologia , Proteína 2 do Complexo Esclerose Tuberosa , Vesículas Extracelulares/metabolismo , Alvo Mecanístico do Complexo 1 de Rapamicina/metabolismo , Microambiente TumoralRESUMO
This article was originally published under standard licence, but has now been made available under a CC BY 4.0 license. The PDF and HTML versions of the paper have been modified accordingly.
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Delineating the contributions of specific cell signalling cascades to the development and maintenance of tumours has greatly informed our understanding of tumorigenesis and has advanced the modern era of targeted cancer therapy. It has been revealed that one of the key pathways regulating cell growth, the phosphatidylinositol 3-kinase/mechanistic target of rapamycin (PI3K/mTOR) signalling axis, is commonly dysregulated in cancer. With a specific, well-tolerated inhibitor of mTOR available, the impact of inhibiting this pathway at the level of mTOR has been tested clinically. This review highlights some of the promising results seen with mTOR inhibitors in the clinic and assesses some of the challenges that remain in predicting patient outcome following mTOR-targeted therapy.
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To find new anti-cancer drug therapies, we wanted to exploit homeostatic vulnerabilities within Tuberous Sclerosis Complex 2 (TSC2)-deficient cells with mechanistic target of rapamycin complex 1 (mTORC1) hyperactivity. We show that nelfinavir and mefloquine synergize to selectively evoke a cytotoxic response in TSC2-deficient cell lines with mTORC1 hyperactivity. We optimize the concentrations of nelfinavir and mefloquine to a clinically viable range that kill cells that lack TSC2, while wild-type cells tolerate treatment. This new clinically viable drug combination causes a significant level of cell death in TSC2-deficient tumor spheroids. Furthermore, no cell recovery was apparent after drug withdrawal, revealing potent cytotoxicity. Transcriptional profiling by RNA sequencing of drug treated TSC2-deficient cells compared to wild-type cells suggested the cytotoxic mechanism of action, involving initial ER stress and an imbalance in energy homeostatic pathways. Further characterization revealed that supplementation with methyl pyruvate alleviated energy stress and reduced the cytotoxic effect, implicating energy deprivation as the trigger of cell death. This work underpins a critical vulnerability with cancer cells with aberrant signaling through the TSC2-mTORC1 pathway that lack flexibility in homeostatic pathways, which could be exploited with combined nelfinavir and mefloquine treatment.
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Cancer cells lose homeostatic flexibility because of mutations and dysregulated signaling pathways involved in maintaining homeostasis. Tuberous Sclerosis Complex 1 (TSC1) and TSC2 play a fundamental role in cell homeostasis, where signal transduction through TSC1/TSC2 is often compromised in cancer, leading to aberrant activation of mechanistic target of rapamycin complex 1 (mTORC1). mTORC1 hyperactivation increases the basal level of endoplasmic reticulum (ER) stress via an accumulation of unfolded protein, due to heightened de novo protein translation and repression of autophagy. We exploit this intrinsic vulnerability of tumor cells lacking TSC2, by treating with nelvinavir to further enhance ER stress while inhibiting the proteasome with bortezomib to prevent effective protein removal. We show that TSC2-deficient cells are highly dependent on the proteosomal degradation pathway for survival. Combined treatment with nelfinavir and bortezomib at clinically relevant drug concentrations show synergy in selectively killing TSC2-deficient cells with limited toxicity in control cells. This drug combination inhibited tumor formation in xenograft mouse models and patient-derived cell models of TSC and caused tumor spheroid death in 3D culture. Importantly, 3D culture assays differentiated between the cytostatic effects of the mTORC1 inhibitor, rapamycin, and the cytotoxic effects of the nelfinavir/bortezomib combination. Through RNA sequencing, we determined that nelfinavir and bortezomib tip the balance of ER protein homeostasis of the already ER-stressed TSC2-deficient cells in favor of cell death. These findings have clinical relevance in stratified medicine to treat tumors that have compromised signaling through TSC and are inflexible in their capacity to restore ER homeostasis.
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Protocolos de Quimioterapia Combinada Antineoplásica/farmacologia , Estresse do Retículo Endoplasmático/efeitos dos fármacos , Neoplasias/patologia , Proteína 2 do Complexo Esclerose Tuberosa/metabolismo , Animais , Bortezomib/farmacologia , Linhagem Celular Tumoral , Estresse do Retículo Endoplasmático/fisiologia , Humanos , Camundongos , Camundongos Endogâmicos NOD , Camundongos SCID , Nelfinavir/farmacologia , Neoplasias/metabolismo , Ensaios Antitumorais Modelo de XenoenxertoRESUMO
Uncontrolled cell growth in Tuberous Sclerosis Complex occurs due to inappropriate activation of mechanistic (mammalian) target of rapamycin complex 1 (mTORC1). The current therapy, rapamycin, produced promising clinical trial results, but patient tumours regrow if treatment is discontinued, revealing rapamycin has cytostatic properties rather than a cytotoxic effect. Taking advantage of the enhanced levels of endoplasmic reticulum (ER) stress present in TSC2-null cells, we investigated drug combinations producing a cytotoxic response. We found a nelfinavir and salinomycin combination specifically killed TSC2-deficient, mTORC1 hyperactive cells. Cytotoxicity was rescued by reducing protein synthesis, either through mTORC1 inhibition or cycloheximide treatment. This indicates that the drug combination targets the cells by tipping the protein homeostasis balance of the already metabolically stressed TSC2-deficient cells in favour of cell death. Furthermore, this drug combination also inhibited tumour formation in TSC2-deficient cell models and caused tumour spheroid death in 3D culture. Importantly, the 3D assay could differentiate the cytostatic agent, rapamycin, from the cytotoxic nelfinavir/salinomycin combination. Sporadic cancer cell lines with hyperactive mTORC1 signalling were also susceptible to this nelfinavir/salinomycin drug combination. This work indicates that the protein homeostasis pathway is an attractive therapeutic target in both Tuberous Sclerosis Complex and mTORC1-driven sporadic cancers.
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Homeostase/efeitos dos fármacos , Alvo Mecanístico do Complexo 1 de Rapamicina/metabolismo , Nelfinavir/farmacologia , Biossíntese de Proteínas/efeitos dos fármacos , Piranos/farmacologia , Animais , Morte Celular/efeitos dos fármacos , Quimioterapia Combinada , Estresse do Retículo Endoplasmático/efeitos dos fármacos , Fibroblastos/efeitos dos fármacos , Fibroblastos/metabolismo , Técnicas de Inativação de Genes , Humanos , Camundongos , Proteína 2 do Complexo Esclerose Tuberosa , Proteínas Supressoras de Tumor/genética , Proteínas Supressoras de Tumor/metabolismoRESUMO
Tuberous sclerosis complex (TSC) is a rare genetic disorder where patients develop benign tumours in several organ systems. Central to TSC pathology is hyper-activation of the mammalian target of rapamycin complex 1 (mTORC1) signalling pathway, which is a key controller of cell growth. As a result, TSC model systems are a valuable tool for examining mTORC1-driven cellular processes. The immunosuppressant, rapamycin, is a specific inhibitor of mTORC1 and has shown promise as a therapeutic agent in TSC as well as in malignancy. This review will focus on the cellular processes controlled by mTORC1 and how TSC-deficient cell lines and mouse models have broadened our understanding of the mTORC1 signalling network. It will also discuss how our knowledge of TSC signalling can help us understand sporadic conditions where mTORC1 activity is implicated in disease onset or progression, and the possibility of using rapamycin to treat sporadic disease.
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Esclerose Tuberosa/patologia , Animais , Autofagia , Proliferação de Células/fisiologia , Humanos , Alvo Mecanístico do Complexo 1 de Rapamicina , Complexos Multiproteicos/metabolismo , Neoplasias/genética , Neoplasias/patologia , Transdução de Sinais , Serina-Treonina Quinases TOR/metabolismo , Esclerose Tuberosa/genética , Esclerose Tuberosa/metabolismoRESUMO
The mammalian target of rapamycin complex 1 (mTORC1) is the key signaling hub that regulates cellular protein homeostasis, growth, and proliferation in health and disease. As a prerequisite for activation of mTORC1 by hormones and mitogens, there first has to be an available pool of intracellular amino acids. Arginine, an amino acid essential during mammalian embryogenesis and early development is one of the key activators of mTORC1. Herein, we demonstrate that arginine acts independently of its metabolism to allow maximal activation of mTORC1 by growth factors via a mechanism that does not involve regulation of mTORC1 localization to lysosomes. Instead, arginine specifically suppresses lysosomal localization of the TSC complex and interaction with its target small GTPase protein, Rheb. By interfering with TSC-Rheb complex, arginine relieves allosteric inhibition of Rheb by TSC. Arginine cooperates with growth factor signaling which further promotes dissociation of TSC2 from lysosomes and activation of mTORC1. Arginine is the main amino acid sensed by the mTORC1 pathway in several cell types including human embryonic stem cells (hESCs). Dependence on arginine is maintained once hESCs are differentiated to fibroblasts, neurons, and hepatocytes, highlighting the fundamental importance of arginine-sensing to mTORC1 signaling. Together, our data provide evidence that different growth promoting cues cooperate to a greater extent than previously recognized to achieve tight spatial and temporal regulation of mTORC1 signaling.
Cells need to be able to sense and respond to signals from their environment. A group (or complex) of conserved proteins called mTORC1 acts a key signaling hub that regulates cell growth and many other processes. This complex can be activated by many different signals from outside the cell. However, mTORC1 can only be activated by these signals if there is also a good supply of amino acids which are needed to make new proteins within the cell. The amino acids are thought to be presented to mTORC1 on the outer surface of cellular compartments known as lysosomes. A protein called Rheb on the surface of the lysosomes activates mTORC1, while a protein complex called TSC inhibits the activity of Rheb to regulate mTORC1 activity. Previous studies have shown that some amino acids influence whether mTORC1 can be activated by affecting whether it is localized to the lysosomes or not. Here, Carroll et al. explored how an amino acid called arginine regulates mTORC1. The experiments show that arginine is the major amino acid that influences whether mTORC1 can be activated in several different types of human cell. When cells were deprived of arginine, the activity of the complex was strongly suppressed. However, microscopy showed that arginine had no effect on whether mTORC1 was found at the lysosomes or not, which suggests that arginine might be acting in a different way to other amino acids. Further experiments found that a lack of arginine led to an increase in the number of TSC complexes at the lysosomes. This led to the inhibition of Rheb and therefore prevented mTORC1 from being activated. Together, Carroll et al.'s findings provide evidence that the different signals that regulate mTORC1 signaling cooperate to a greater extent than previously thought. A future challenge will be to understand the molecular details of how the arginine is detected.
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Arginina/metabolismo , Proteínas Monoméricas de Ligação ao GTP/metabolismo , Complexos Multiproteicos/metabolismo , Neuropeptídeos/metabolismo , Transdução de Sinais , Serina-Treonina Quinases TOR/metabolismo , Proteínas Supressoras de Tumor/metabolismo , Diferenciação Celular , Células-Tronco Embrionárias/fisiologia , Humanos , Alvo Mecanístico do Complexo 1 de Rapamicina , Proteína Enriquecida em Homólogo de Ras do Encéfalo , Proteína 2 do Complexo Esclerose TuberosaRESUMO
Birt-Hogg-Dubé (BHD) syndrome is a rare autosomal dominant condition caused by mutations in the FLCN gene and characterized by benign hair follicle tumors, pneumothorax, and renal cancer. Folliculin (FLCN), the protein product of the FLCN gene, is a poorly characterized tumor suppressor protein, currently linked to multiple cellular pathways. Autophagy maintains cellular homeostasis by removing damaged organelles and macromolecules. Although the autophagy kinase ULK1 drives autophagy, the underlying mechanisms are still being unraveled and few ULK1 substrates have been identified to date. Here, we identify that loss of FLCN moderately impairs basal autophagic flux, while re-expression of FLCN rescues autophagy. We reveal that the FLCN complex is regulated by ULK1 and elucidate 3 novel phosphorylation sites (Ser406, Ser537, and Ser542) within FLCN, which are induced by ULK1 overexpression. In addition, our findings demonstrate that FLCN interacts with a second integral component of the autophagy machinery, GABA(A) receptor-associated protein (GABARAP). The FLCN-GABARAP association is modulated by the presence of either folliculin-interacting protein (FNIP)-1 or FNIP2 and further regulated by ULK1. As observed by elevation of GABARAP, sequestome 1 (SQSTM1) and microtubule-associated protein 1 light chain 3 (MAP1LC3B) in chromophobe and clear cell tumors from a BHD patient, we found that autophagy is impaired in BHD-associated renal tumors. Consequently, this work reveals a novel facet of autophagy regulation by ULK1 and substantially contributes to our understanding of FLCN function by linking it directly to autophagy through GABARAP and ULK1.
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Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Autofagia , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Proteínas Associadas aos Microtúbulos/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas Proto-Oncogênicas/metabolismo , Proteínas Supressoras de Tumor/metabolismo , Sequência de Aminoácidos , Animais , Proteínas Reguladoras de Apoptose , Proteína Homóloga à Proteína-1 Relacionada à Autofagia , Síndrome de Birt-Hogg-Dubé/metabolismo , Síndrome de Birt-Hogg-Dubé/patologia , Proteínas de Transporte/metabolismo , Humanos , Camundongos , Dados de Sequência Molecular , Fosforilação , Ligação Proteica , Proteínas Proto-Oncogênicas/química , Proteínas Proto-Oncogênicas/deficiência , Proteína Sequestossoma-1 , Proteínas Supressoras de Tumor/química , Proteínas Supressoras de Tumor/deficiênciaRESUMO
The Warburg effect is a tumorigenic metabolic adaptation process characterized by augmented aerobic glycolysis, which enhances cellular bioenergetics. In normal cells, energy homeostasis is controlled by AMPK; however, its role in cancer is not understood, as both AMPK-dependent tumor-promoting and -inhibiting functions were reported. Upon stress, energy levels are maintained by increased mitochondrial biogenesis and glycolysis, controlled by transcriptional coactivator PGC-1α and HIF, respectively. In normoxia, AMPK induces PGC-1α, but how HIF is activated is unclear. Germline mutations in the gene encoding the tumor suppressor folliculin (FLCN) lead to Birt-Hogg-Dubé (BHD) syndrome, which is associated with an increased cancer risk. FLCN was identified as an AMPK binding partner, and we evaluated its role with respect to AMPK-dependent energy functions. We revealed that loss of FLCN constitutively activates AMPK, resulting in PGC-1α-mediated mitochondrial biogenesis and increased ROS production. ROS induced HIF transcriptional activity and drove Warburg metabolic reprogramming, coupling AMPK-dependent mitochondrial biogenesis to HIF-dependent metabolic changes. This reprogramming stimulated cellular bioenergetics and conferred a HIF-dependent tumorigenic advantage in FLCN-negative cancer cells. Moreover, this pathway is conserved in a BHD-derived tumor. These results indicate that FLCN inhibits tumorigenesis by preventing AMPK-dependent HIF activation and the subsequent Warburg metabolic transformation.
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Proteínas Quinases Ativadas por AMP/metabolismo , Proteínas Proto-Oncogênicas/metabolismo , Proteínas Supressoras de Tumor/metabolismo , Trifosfato de Adenosina/metabolismo , Animais , Síndrome de Birt-Hogg-Dubé/etiologia , Síndrome de Birt-Hogg-Dubé/genética , Síndrome de Birt-Hogg-Dubé/metabolismo , Linhagem Celular , Transformação Celular Neoplásica , Metabolismo Energético , Fator 1 Induzível por Hipóxia/metabolismo , Camundongos , Camundongos Knockout , Mitocôndrias/metabolismo , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo , Proteínas Proto-Oncogênicas/deficiência , Proteínas Proto-Oncogênicas/genética , Espécies Reativas de Oxigênio/metabolismo , Fatores de Transcrição/metabolismo , Proteínas Supressoras de Tumor/deficiência , Proteínas Supressoras de Tumor/genéticaRESUMO
Subcellular localization is emerging as an important mechanism for mTORC1 regulation. We report that the tuberous sclerosis complex (TSC) signalling node, TSC1, TSC2 and Rheb, localizes to peroxisomes, where it regulates mTORC1 in response to reactive oxygen species (ROS). TSC1 and TSC2 were bound by peroxisomal biogenesis factors 19 and 5 (PEX19 and PEX5), respectively, and peroxisome-localized TSC functioned as a Rheb GTPase-activating protein (GAP) to suppress mTORC1 and induce autophagy. Naturally occurring pathogenic mutations in TSC2 decreased PEX5 binding, and abrogated peroxisome localization, Rheb GAP activity and suppression of mTORC1 by ROS. Cells lacking peroxisomes were deficient in mTORC1 repression by ROS, and peroxisome-localization-deficient TSC2 mutants caused polarity defects and formation of multiple axons in neurons. These data identify a role for the TSC in responding to ROS at the peroxisome, and identify the peroxisome as a signalling organelle involved in regulation of mTORC1.
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Autofagia , Regulação Enzimológica da Expressão Gênica , Complexos Multiproteicos/genética , Peroxissomos/metabolismo , Espécies Reativas de Oxigênio , Transdução de Sinais , Serina-Treonina Quinases TOR/genética , Animais , Linhagem Celular , Células HEK293 , Humanos , Células MCF-7 , Alvo Mecanístico do Complexo 1 de Rapamicina , Proteínas de Membrana/metabolismo , Camundongos , Complexos Multiproteicos/metabolismo , Ligação Proteica , Ratos , Serina-Treonina Quinases TOR/metabolismo , Proteína 1 do Complexo Esclerose Tuberosa , Proteína 2 do Complexo Esclerose Tuberosa , Proteínas Supressoras de Tumor/metabolismoRESUMO
Protein synthesis and autophagy work as two opposing processes to control cell growth in response to nutrient supply. The mammalian/mechanistic target of rapamycin complex 1 (mTORC1) pathway, which acts as a master regulator to control protein synthesis, has recently been shown to inhibit autophagy by phosphorylating and inactivating ULK1, an autophagy regulatory protein. ULK1 also inhibits phosphorylation of a mTORC1 substrate, S6K1, indicating that a complex signaling interplay exists between mTORC1 and ULK1. Here, we demonstrate that ULK1 induces multisite phosphorylation of Raptor in vivo and in vitro. Using phospho-specific antibodies we identify Ser855 and Ser859 as being strongly phosphorylated by ULK1, with moderate phosphorylation of Ser792 also observed. Interestingly, ULK1 overexpression also increases phosphorylation of Raptor Ser863 and the mTOR autophosphorylation site, Ser2481 in a mTORC1-dependent manner. Despite this evidence for heightened mTORC1 kinase activity following ULK1 overexpresssion, mTORC1-mediated phosphorylation of S6K1 and 4E-BP1 is significantly inhibited. ULK1 expression has no effect on protein-protein interactions between the components of mTORC1, but does reduce the ability of Raptor to bind to the substrate 4E-BP1. Furthermore, shRNA knockdown of ULK1 leads to increased phosphorylation of mTORC1 substrates and decreased phosphorylation of Raptor at Ser859 and Ser792. We propose a new mechanism whereby ULK1 contributes to mTORC1 inhibition through hindrance of substrate docking to Raptor. This is a novel negative feedback loop that occurs upon activation of autophagy to maintain mTORC1 inhibition when nutrient supplies are limiting.
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Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas/metabolismo , Transdução de Sinais , Proteína Homóloga à Proteína-1 Relacionada à Autofagia , Proteínas de Ciclo Celular , Técnicas de Silenciamento de Genes , Células HEK293 , Humanos , Alvo Mecanístico do Complexo 1 de Rapamicina , Complexos Multiproteicos , Fosfoproteínas/metabolismo , Fosforilação , Proteína Regulatória Associada a mTOR , Proteínas Quinases S6 Ribossômicas 70-kDa/metabolismo , Especificidade por Substrato , Serina-Treonina Quinases TORRESUMO
Tuberous sclerosis complex (TSC) is a genetic condition characterized by the growth of benign tumours in multiple organs, including the brain and kidneys, alongside intellectual disability and seizures. Identification of a causative mutation in TSC1 or TSC2 is important for accurate genetic counselling in affected families, but it is not always clear from genetic data whether a sequence variant is pathogenic or not. In vitro functional analysis could provide support for determining whether an unclassified TSC1 or TSC2 variant is disease-causing. We have performed a detailed functional analysis of four patient-derived TSC2 mutations, E92V, R505Q, H597R and L1624P. One mutant, E92V, functioned similarly to wild-type TSC2, whereas H597R and L1624P had abnormal function in all assays, consistent with available clinical and segregation information. One TSC2 mutation, R505Q, was identified in a patient with intellectual disability, seizures and autistic spectrum disorder but who did not fulfil the diagnostic criteria for TSC. The R505Q mutation was also found in two relatives, one with mild learning difficulties and one without apparent phenotypic abnormality. R505Q TSC2 exhibited partially disrupted function in our assays. These data highlight the difficulties of assessing pathogenicity of a mutation and suggest that multiple lines of evidence, both genetic and functional, are required to assess the pathogenicity of some mutations.
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Mutação/genética , Proteínas Supressoras de Tumor/genética , Proteínas Supressoras de Tumor/metabolismo , Adolescente , Animais , Células Cultivadas , Criança , Pré-Escolar , Doenças Genéticas Inatas/genética , Doenças Genéticas Inatas/fisiopatologia , Genótipo , Células HEK293 , Humanos , Lactente , Alvo Mecanístico do Complexo 1 de Rapamicina , Camundongos , Complexos Multiproteicos , Fenótipo , Fosforilação/genética , Multimerização Proteica/genética , Estabilidade Proteica , Proteínas/metabolismo , Serina-Treonina Quinases TOR , Proteína 1 do Complexo Esclerose Tuberosa , Proteína 2 do Complexo Esclerose TuberosaRESUMO
Erythropoietin (Epo), the major regulator of erythropoiesis, and its cognate receptor (EpoR) are also expressed in nonerythroid tissues, including tumors. Clinical studies have highlighted the potential adverse effects of erythropoiesis-stimulating agents when used to treat cancer-related anemia. We assessed the ability of EpoR to enhance tumor growth and invasiveness following Epo stimulation. A benign noninvasive rat mammary cell line, Rama 37, was used as a model system. Cell signaling and malignant cell behavior were compared between parental Rama 37 cells, which express few or no endogenous EpoRs, and a modified cell line stably transfected with human EpoR (Rama 37-28). The incubation of Rama 37-28 cells with pharmacologic levels of Epo led to the rapid and sustained increases in phosphorylation of signal transducers and activators of transcription 5, Akt, and extracellular signal-regulated kinase. The activation of these signaling pathways significantly increased invasion, migration, adhesion, and colony formation. The Epo-induced invasion capacity of Rama 37-28 cells was reduced by the small interfering RNA-mediated knockdown of EpoR mRNA levels and by inhibitors of the phosphoinositide 3-kinase/Akt and Ras/extracellular signal-regulated kinase signaling pathways with adhesion also reduced by Janus-activated kinase 2/signal transducers and activators of transcription 5 inhibition. These data show that Epo induces phenotypic changes in the behavior of breast cancer cell lines and establishes links between individual cell signaling pathways and the potential for cancer spread.
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Neoplasias da Mama/metabolismo , Carcinoma/metabolismo , Eritropoetina/metabolismo , Transdução de Sinais/fisiologia , Ativação Transcricional/fisiologia , Animais , Neoplasias da Mama/genética , Carcinoma/genética , Linhagem Celular Tumoral , Movimento Celular/efeitos dos fármacos , Movimento Celular/fisiologia , Proliferação de Células , Transformação Celular Neoplásica/genética , Transformação Celular Neoplásica/metabolismo , Inibidores Enzimáticos/farmacologia , Eritropoetina/farmacologia , MAP Quinases Reguladas por Sinal Extracelular/efeitos dos fármacos , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Feminino , Humanos , Janus Quinase 2/efeitos dos fármacos , Janus Quinase 2/metabolismo , Invasividade Neoplásica/genética , Invasividade Neoplásica/fisiopatologia , Fosfatidilinositol 3-Quinases/efeitos dos fármacos , Fosfatidilinositol 3-Quinases/metabolismo , Fosforilação/fisiologia , Proteínas Proto-Oncogênicas c-akt/efeitos dos fármacos , Proteínas Proto-Oncogênicas c-akt/metabolismo , Interferência de RNA , Ratos , Receptores da Eritropoetina/genética , Fator de Transcrição STAT5/efeitos dos fármacos , Fator de Transcrição STAT5/metabolismo , Transdução de Sinais/efeitos dos fármacos , Ativação Transcricional/efeitos dos fármacos , Regulação para Cima/efeitos dos fármacos , Regulação para Cima/fisiologia , Proteínas ras/efeitos dos fármacos , Proteínas ras/metabolismoRESUMO
The mammalian target of rapamycin (mTOR) Ser/Thr kinase signals in at least two multiprotein complexes distinguished by their different partners and sensitivities to rapamycin. Acute rapamycin inhibits signaling by mTOR complex 1 (mTORC1) but not mTOR complex 2 (mTORC2), which both promote cell growth, proliferation, and survival. Although mTORC2 regulation remains poorly defined, diverse cellular mitogens activate mTORC1 signaling in a manner that requires sufficient levels of amino acids and cellular energy. Before the identification of distinct mTOR complexes, mTOR was reported to autophosphorylate on Ser-2481 in vivo in a rapamycin- and amino acid-insensitive manner. These results suggested that modulation of mTOR intrinsic catalytic activity does not universally underlie mTOR regulation. Here we re-examine the regulation of mTOR Ser-2481 autophosphorylation (Ser(P)-2481) in vivo by studying mTORC-specific Ser(P)-2481 in mTORC1 and mTORC2, with a primary focus on mTORC1. In contrast to previous work, we find that acute rapamycin and amino acid withdrawal markedly attenuate mTORC1-associated mTOR Ser(P)-2481 in cycling cells. Although insulin stimulates both mTORC1- and mTORC2-associated mTOR Ser(P)-2481 in a phosphatidylinositol 3-kinase-dependent manner, rapamycin acutely inhibits insulin-stimulated mTOR Ser(P)-2481 in mTORC1 but not mTORC2. By interrogating diverse mTORC1 regulatory input, we find that without exception mTORC1-activating signals promote, whereas mTORC1-inhibitory signals decrease mTORC1-associated mTOR Ser(P)-2481. These data suggest that mTORC1- and likely mTORC2-associated mTOR Ser-2481 autophosphorylation directly monitors intrinsic mTORC-specific catalytic activity and reveal that rapamycin inhibits mTORC1 signaling in vivo by reducing mTORC1 catalytic activity.
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Antibióticos Antineoplásicos/farmacologia , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Transdução de Sinais/fisiologia , Sirolimo/farmacologia , Células 3T3-L1 , Animais , Anticorpos/farmacologia , Catálise , Linhagem Celular Transformada , Fibroblastos/citologia , Humanos , Peptídeos e Proteínas de Sinalização Intracelular/imunologia , Rim/citologia , Alvo Mecanístico do Complexo 1 de Rapamicina , Camundongos , Complexos Multiproteicos , Fosforilação , Proteínas Serina-Treonina Quinases/imunologia , Proteínas , Coelhos , Serina/metabolismo , Serina-Treonina Quinases TOR , Fatores de Transcrição/metabolismoRESUMO
Immunohistochemical studies on formalin-fixed, paraffin-embedded (FFPE) tissue utilizing polyclonal antibodies form the cornerstone of many reports claiming to demonstrate erythropoietin receptor (EPOR) expression in malignant tissue. Recently, Elliott et al. (Blood 2006;107:1892-1895) reported that the antibodies commonly used to detect EPOR expression also detect non-EPOR proteins, and that their binding to EPOR was severely abrogated by two synthetic peptides based on the sequence of heat shock protein (HSP) 70, HSP70-2, and HSP70-5. We have investigated the specificity of the C20 antibody for detecting EPOR expression in non-small cell lung carcinoma (NSCLC) utilizing tissue microarrays. A total of 34 cases were available for study. Antibody absorbed with peptide resulted in marked suppression of cytoplasmic staining compared with nonabsorbed antibody. Four tumors that initially showed a membranous pattern of staining retained this pattern with absorbed antibody. Positive membranous immunoreactivity was also observed in 6 of 30 tumors that originally showed a predominantly cytoplasmic pattern of staining. Using the C20 antibody for Western blots, we detected three main bands, at 100, 66, and 59 kDa. Preincubation with either peptide caused abolition of the 66-kDa band, which contains non-EPOR sequences including heat shock peptides. These results call into question the significance of previous immunohistochemical studies of EPOR expression in malignancy and emphasize the need for more specific anti-EPOR antibodies to define the true extent of EPOR expression in neoplastic tissue.
Assuntos
Carcinoma Pulmonar de Células não Pequenas/genética , Neoplasias Pulmonares/genética , Receptores da Eritropoetina/genética , Sequência de Aminoácidos , Especificidade de Anticorpos , Carcinoma Pulmonar de Células não Pequenas/imunologia , Linhagem Celular Tumoral , Proteínas de Choque Térmico HSP70/genética , Proteínas de Choque Térmico/genética , Humanos , Neoplasias Pulmonares/imunologia , Dados de Sequência Molecular , Fragmentos de Peptídeos/química , Receptores da Eritropoetina/imunologiaRESUMO
Recent evidence confirms the presence of erythropoietin receptors on a variety of cancer cells. This has raised concerns about the use of erythropoiesis-stimulating agents in the treatment of cancer-related anemia. Having previously identified expression of functional erythropoietin receptors in a non-small cell lung carcinoma cell line, H838, which activated key signaling pathways in response to erythropoietin stimulation, we now demonstrate impaired downregulation of the erythropoietin receptor in these tumor cells. The erythropoietin receptor is not ubiquitinated following erythropoietin stimulation in this cancer cell line, and there is no turnover of the receptor in either unstimulated or stimulated cells. Compounding this blunted response is impaired SOCS3 induction downstream of erythropoietin stimulation and an extremely delayed SOCS1 response. If this finding in non-small cell lung carcinoma is a widespread phenomenon, then impaired erythropoietin receptor downregulation and degradation in tumor cells has clinical implications for those patients receiving erythropoiesis-stimulating agents for cancer-related anemia.