RESUMEN
The tumor suppressor p53 is activated upon genotoxic and oxidative stress and in turn inhibits cell proliferation and growth through induction of specific target genes. Cell growth is positively regulated by mTOR, whose activity is inhibited by the TSC1:TSC2 complex. Although genotoxic stress has been suggested to inhibit mTOR via p53-mediated activation of mTOR inhibitors, the precise mechanism of this link was unknown. We now demonstrate that the products of two p53 target genes, Sestrin1 and Sestrin2, activate the AMP-responsive protein kinase (AMPK) and target it to phosphorylate TSC2 and stimulate its GAP activity, thereby inhibiting mTOR. Correspondingly, Sestrin2-deficient mice fail to inhibit mTOR signaling upon genotoxic challenge. Sestrin1 and Sestrin2 therefore provide an important link between genotoxic stress, p53 and the mTOR signaling pathway.
Asunto(s)
Proteínas de Ciclo Celular/metabolismo , Proteínas/metabolismo , Transducción de Señal , Proteína p53 Supresora de Tumor/metabolismo , Proteínas Supresoras de Tumor/metabolismo , Proteínas Quinasas Activadas por AMP , Animales , Proteínas de Ciclo Celular/genética , Línea Celular , Línea Celular Tumoral , Daño del ADN , Humanos , Ratones , Ratones Endogámicos C57BL , Complejos Multienzimáticos/metabolismo , Proteínas Nucleares , Peroxidasas , Proteínas Serina-Treonina Quinasas/metabolismo , Proteínas/genética , Proteína 1 del Complejo de la Esclerosis Tuberosa , Proteína 2 del Complejo de la Esclerosis TuberosaRESUMEN
Skin cancer is the most common cancer in the United States and is mainly caused by environmental UV radiation. Reducing skin cancer incidence is becoming an urgent issue. The stress-inducible protein Sestrin2 (Sesn2) plays an important role in maintaining redox and metabolic homeostasis and their related pathologies. However, the role of Sesn2 in cancer remains unclear. Here we show that UVB radiation induces Sesn2 expression in normal human keratinocytes, mouse skin, normal human melanocytes, and melanoma cells. In addition, Sesn2 promotes AKT activation through a PTEN-dependent mechanism. Sesn2 deletion or knockdown sensitizes squamous cell carcinoma (SCC) cells to 5-fluorouracil-induced apoptosis and melanoma cells to UVB- and vemurafenib-induced apoptosis. In mice Sesn2 knockdown suppresses tumor growth from injected human SCC and melanoma cells. Last, as compared with normal skin, Sesn2 is up-regulated in both human skin SCC and melanoma. Our findings demonstrate that Sesn2 promotes AKT activation and survival in response to UVB stress and chemotherapeutics and suggest that Sesn2 is oncogenic in skin SCC and melanoma.
Asunto(s)
Carcinoma de Células Escamosas/patología , Melanoma Experimental/patología , Proteínas Nucleares/fisiología , Proteínas Proto-Oncogénicas c-akt/metabolismo , Neoplasias Cutáneas/patología , Animales , Antineoplásicos/farmacología , Apoptosis , Carcinoma de Células Escamosas/metabolismo , Supervivencia Celular , Femenino , Células HeLa , Humanos , Melanoma Experimental/metabolismo , Ratones , Ratones Desnudos , Trasplante de Neoplasias , Transducción de Señal , Neoplasias Cutáneas/metabolismo , Carga Tumoral , Regulación hacia ArribaRESUMEN
Tumor suppressor p53 is inactivated in most cancers and the critical role of p53 in the suppression of carcinogenesis has been confirmed in many mouse models. The protein product of the tumor suppressor p53 gene works as a transcriptional regulator, activating expression of numerous genes involved in cell death, cell cycle arrest, senescence, DNA-repair and many other processes. In spite of the multiple efforts to characterize the functions of p53, the mechanisms of tumor suppression by p53 are still elusive. Recently, new activities of p53 such as regulation of reactive oxygen species (ROS) and metabolism have been described and the p53-regulated genes responsible for these functions have been identified. Metabolic derangements and accumulation of ROS are features of carcinogenesis, supporting the idea that many tumor suppressive effects of p53 can be mediated by regulation of metabolism and/or ROS. Mutations in the p53 gene can not only inactivate wild type function of p53 but also endow p53 with new functions such as activation of new metabolic pathways contributing to carcinogenesis. Understanding the metabolic and antioxidant functions of p53 allows us to develop approaches to restore p53 function in cancers, where p53 is inactivated, in other to ensure the best outcome of anti-cancer treatment.
Asunto(s)
Antioxidantes/metabolismo , Genes p53 , Reparación del ADN , Humanos , Mutación , Estrés Oxidativo , Especies Reactivas de Oxígeno/metabolismoRESUMEN
It is widely accepted that the p53 tumor suppressor restricts abnormal cells by induction of growth arrest or by triggering apoptosis. Here we show that, in addition, p53 protects the genome from oxidation by reactive oxygen species (ROS), a major cause of DNA damage and genetic instability. In the absence of severe stresses, relatively low levels of p53 are sufficient for upregulation of several genes with antioxidant products, which is associated with a decrease in intracellular ROS. Downregulation of p53 results in excessive oxidation of DNA, increased mutation rate and karyotype instability, which are prevented by incubation with the antioxidant N-acetylcysteine (NAC). Dietary supplementation with NAC prevented frequent lymphomas characteristic of Trp53-knockout mice, and slowed the growth of lung cancer xenografts deficient in p53. Our results provide a new paradigm for a nonrestrictive tumor suppressor function of p53 and highlight the potential importance of antioxidants in the prophylaxis and treatment of cancer.
Asunto(s)
Apoptosis/fisiología , Daño del ADN , Regulación de la Expresión Génica/fisiología , Modelos Biológicos , Especies Reactivas de Oxígeno/metabolismo , Proteína p53 Supresora de Tumor/metabolismo , 8-Hidroxi-2'-Desoxicoguanosina , Acetilcisteína/farmacología , Animales , Northern Blotting , Western Blotting , Línea Celular Tumoral , Inhibidor p21 de las Quinasas Dependientes de la Ciclina/metabolismo , Cartilla de ADN , Desoxiguanosina/análogos & derivados , Desoxiguanosina/metabolismo , Vectores Genéticos , Inestabilidad Genómica/efectos de los fármacos , Humanos , Cariotipificación , Lentivirus , Ratones , Mutagénesis , ARN Interferente Pequeño/genética , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Bazo/metabolismo , Proteína p53 Supresora de Tumor/genéticaRESUMEN
Sestrins are a family of stress-responsive antioxidant proteins responsible for regulation of cell viability and metabolism. The best known Sestrin targets are mTORC1 and mTORC2 kinases that control different cellular processes including growth, viability, autophagy, and mitochondrial metabolism. Inactivation of the single Sestrin gene in invertebrates has an adverse impact on their healthspan and longevity, whereas each of the three Sestrin genes in mammals and other vertebrate organisms has a different impact on maintenance of a particular tissue, affecting its stress tolerance, function and regenerative capability. As a result, Sestrins attenuate ageing and suppress development of many age-related diseases including myocardial infarction, muscle atrophy, diabetes, and immune dysfunction, but exacerbate development of chronic obstructive pulmonary disease. Moreover, Sestrins play opposite roles in carcinogenesis in different tissues. Stem cells support tissue remodelling that influences ageing, and Sestrins might suppress ageing and age-related pathologies through control of stem cell biology. In this review, we will discuss the potential link between Sestrins, stem cells, and ageing.
Asunto(s)
Envejecimiento/fisiología , Estrés Oxidativo/fisiología , Sestrinas/metabolismo , Células Madre/fisiología , Animales , Antioxidantes/metabolismo , HumanosRESUMEN
SESN2 is a member of the evolutionarily conserved sestrin protein family found in most of the Metazoa species. The SESN2 gene is transcriptionally activated by many stress factors, including metabolic derangements, reactive oxygen species (ROS), and DNA-damage. As a result, SESN2 controls ROS accumulation, metabolism, and cell viability. The best-known function of SESN2 is the inhibition of the mechanistic target of rapamycin complex 1 kinase (mTORC1) that plays a central role in support of cell growth and suppression of autophagy. SESN2 inhibits mTORC1 activity through interaction with the GATOR2 protein complex preventing an inhibitory effect of GATOR2 on the GATOR1 protein complex. GATOR1 stimulates GTPase activity of the RagA/B small GTPase, the component of RagA/B:RagC/D complex, preventing mTORC1 translocation to the lysosomes and its activation by the small GTPase Rheb. Despite the well-established role of SESN2 in mTORC1 inhibition, other SESN2 activities are not well-characterized. We recently showed that SESN2 could control mitochondrial function and cell death via mTORC1-independent mechanisms, and these activities might be explained by direct effects of SESN2 on mitochondria. In this work, we examined mitochondrial localization of SESN2 and demonstrated that SESN2 is located on mitochondria and can be directly involved in the regulation of mitochondrial functions.
Asunto(s)
Mitocondrias/metabolismo , Proteínas Nucleares/metabolismo , Células A549 , Animales , Caenorhabditis elegans/citología , Caenorhabditis elegans/metabolismo , Fraccionamiento Celular , Respiración de la Célula , Citosol/metabolismo , Humanos , Especies Reactivas de OxígenoRESUMEN
A unique property of skeletal muscle is its ability to adapt its mass to changes in activity. Inactivity, as in disuse or aging, causes atrophy, the loss of muscle mass and strength, leading to physical incapacity and poor quality of life. Here, through a combination of transcriptomics and transgenesis, we identify sestrins, a family of stress-inducible metabolic regulators, as protective factors against muscle wasting. Sestrin expression decreases during inactivity and its genetic deficiency exacerbates muscle wasting; conversely, sestrin overexpression suffices to prevent atrophy. This protection occurs through mTORC1 inhibition, which upregulates autophagy, and AKT activation, which in turn inhibits FoxO-regulated ubiquitin-proteasome-mediated proteolysis. This study reveals sestrin as a central integrator of anabolic and degradative pathways preventing muscle wasting. Since sestrin also protected muscles against aging-induced atrophy, our findings have implications for sarcopenia.
Asunto(s)
Proteínas de Choque Térmico/metabolismo , Músculo Esquelético/patología , Atrofia Muscular/prevención & control , Proteínas Nucleares/metabolismo , Transducción de Señal , Envejecimiento , Animales , Autofagia , Modelos Animales de Enfermedad , Proteína Forkhead Box O1/genética , Proteína Forkhead Box O1/metabolismo , Proteína Forkhead Box O3/genética , Proteína Forkhead Box O3/metabolismo , Expresión Génica , Proteínas de Choque Térmico/genética , Humanos , Masculino , Diana Mecanicista del Complejo 1 de la Rapamicina/genética , Diana Mecanicista del Complejo 1 de la Rapamicina/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Proteínas Musculares/genética , Proteínas Musculares/metabolismo , Músculo Esquelético/metabolismo , Atrofia Muscular/genética , Atrofia Muscular/metabolismo , Atrofia Muscular/patología , Proteínas Nucleares/genética , Sarcopenia/genética , Sarcopenia/metabolismo , Sarcopenia/patología , Sarcopenia/prevención & controlRESUMEN
SESTRINs (SESN1-3) are proteins encoded by an evolutionarily conserved gene family that plays an important role in the regulation of cell viability and metabolism in response to stress. Many of the effects of SESTRINs are mediated by negative and positive regulation of mechanistic target of rapamycin kinase complexes 1 and 2 (mTORC1 and mTORC2), respectively, that are often deregulated in human cancers where they support cell growth, proliferation, and cell viability. Besides their effects on regulation of mTORC1/2, SESTRINs also control the accumulation of reactive oxygen species, cell death, and mitophagy. SESN1 and SESN2 are transcriptional targets of tumor suppressor protein p53 and may mediate tumor suppressor activities of p53. Therefore, we conducted studies based on a mouse lung cancer model and human lung adenocarcinoma A549 cells to evaluate the potential impact of SESN1 and SESN2 on lung carcinogenesis. While we observed that expression of SESN1 and SESN2 is often decreased in human tumors, inactivation of Sesn2 in mice positively regulates tumor growth through a mechanism associated with activation of AKT, while knockout of Sesn1 has no additional impact on carcinogenesis in Sesn2-deficient mice. However, inactivation of SESN1 and/or SESN2 in A549 cells accelerates cell proliferation and imparts resistance to cell death in response to glucose starvation. We propose that despite their contribution to early tumor growth, SESTRINs might suppress late stages of carcinogenesis through inhibition of cell proliferation or activation of cell death in conditions of nutrient deficiency.
RESUMEN
The ATF4 transcription factor is a key regulator of the adaptive integrated stress response (ISR) induced by various stresses and pathologies. Identification of novel transcription targets of ATF4 during ISR would contribute to the understanding of adaptive networks and help to identify novel therapeutic targets. We were previously searching for genes that display an inverse regulation mode by the transcription factors ATF4 and p53 in response to mitochondrial respiration chain complex III inhibition. Among the selected candidates the human genes for cytokeratine 16 (KRT16), anti-apoptotic protein Niban (FAM129A) and hexokinase HKDC1 have been found highly responsive to ATF4 overexpression. Here we explored potential roles of the induction of KRT16, FAM129A and HKDC1 genes in ISR. As verified by RT-qPCR, a dysfunction of mitochondrial respiration chain and ER stress resulted in a partially ATF4-dependent stimulation of KRT16, FAM129A and HKDC1 expression in the HCT116 colon carcinoma cell line. ISRIB, a specific inhibitor of ISR, was able to downregulate the ER stress-induced levels of KRT16, FAM129A and HKDC1 transcripts. An inhibition of ATF4 by RNAi attenuated the induction of KRT16, FAM129A and HKDC1 mRNAs in response to ER stress or to a dysfunctional mitochondrial respiration. The similar induction of the three genes was observed in another tumor-derived cervical carcinoma cell line HeLa. However, in HaCaT and HEK293T cells that display transformed phenotypes, but do not originate from patient-derived tumors, the ER stress-inducing treatments resulted in an upregulation of FAM129A and HKDC1, but not KRT16 transcripts, By a luciferase reporter approach we identified a highly active ATF4-responsive element within the upstream region of the KRT16 gene. The results suggest a conditional regulation of KRT16 gene by ATF4 that may be inhibited in normal cells, but engaged during cancer progression. Potential roles of KRT16, FAM129A and HKDC1 genes upregulation in adaptive stress responses and pathologies are discussed.
Asunto(s)
Factor de Transcripción Activador 4/fisiología , Biomarcadores de Tumor/genética , Hexoquinasa/genética , Queratina-16/genética , Proteínas de Neoplasias/genética , Estrés Fisiológico , Línea Celular , Estrés del Retículo Endoplásmico , Regulación de la Expresión Génica/genética , Humanos , Regiones Promotoras Genéticas , Interferencia de ARN , ARN Mensajero/genética , Reacción en Cadena en Tiempo Real de la Polimerasa , Regulación hacia ArribaRESUMEN
Follicular lymphoma (FL) is an incurable form of B cell lymphoma. Genomic studies have cataloged common genetic lesions in FL such as translocation t(14;18), frequent losses of chromosome 6q, and mutations in epigenetic regulators such as EZH2 Using a focused genetic screen, we identified SESTRIN1 as a relevant target of the 6q deletion and demonstrate tumor suppression by SESTRIN1 in vivo. Moreover, SESTRIN1 is a direct target of the lymphoma-specific EZH2 gain-of-function mutation (EZH2Y641X ). SESTRIN1 inactivation disrupts p53-mediated control of mammalian target of rapamycin complex 1 (mTORC1) and enables mRNA translation under genotoxic stress. SESTRIN1 loss represents an alternative to RRAGC mutations that maintain mTORC1 activity under nutrient starvation. The antitumor efficacy of pharmacological EZH2 inhibition depends on SESTRIN1, indicating that mTORC1 control is a critical function of EZH2 in lymphoma. Conversely, EZH2Y641X mutant lymphomas show increased sensitivity to RapaLink-1, a bifunctional mTOR inhibitor. Hence, SESTRIN1 contributes to the genetic and epigenetic control of mTORC1 in lymphoma and influences responses to targeted therapies.
Asunto(s)
Proteína Potenciadora del Homólogo Zeste 2/metabolismo , Epigénesis Genética , Proteínas de Choque Térmico/genética , Linfoma Folicular/genética , Diana Mecanicista del Complejo 1 de la Rapamicina/metabolismo , Animales , Deleción Cromosómica , Cromosomas Humanos Par 6/genética , Proteína Potenciadora del Homólogo Zeste 2/antagonistas & inhibidores , Silenciador del Gen , Pruebas Genéticas , Genoma Humano , Proteínas de Choque Térmico/deficiencia , Humanos , Ratones , Mutación/genética , Biosíntesis de Proteínas , ARN Mensajero/genética , ARN Mensajero/metabolismoRESUMEN
Both inactivation of p53 function and loss of sensitivity to Fas contribute to a malignant phenotype and frequently occur during tumor progression. Although in the majority of cases only one of the p53 alleles is mutated, some tumors acquire mutations in both alleles of the p53 gene. To determine the biological significance of this phenomenon, we analyzed p53 mutants, p53(223Leu) and p53(274Phe), from Fas-resistant prostate carcinoma cell line DU145. Both mutants differed from wild-type p53 in their conformation, transactivation ability, and effect on the growth of p53-deficient cells, with p53(223Leu) being more similar to wild-type p53 than was p53(274Phe). Interestingly, the biological effect of coexpression of the DU145-derived mutants was dramatically different from that of each mutant expressed alone. Whereas neither of the two mutants was found to be dominant-negative against wild-type p53, each neutralized the other's growth-suppressive effects and, in combination, were capable of down-regulating Fas expression and converting Fas-sensitive prostate carcinoma cells PC3 into Fas-resistant ones. These results indicate that two different p53 mutants that are separately rather weak can cooperate to generate p53 protein with anti-Fas function that is likely to provide additional selective advantages to the tumor.
Asunto(s)
Alelos , Genes p53/genética , Neoplasias de la Próstata/genética , Neoplasias de la Próstata/patología , Proteína p53 Supresora de Tumor/fisiología , Receptor fas/fisiología , Animales , Apoptosis/fisiología , División Celular/genética , División Celular/fisiología , Humanos , Masculino , Ratones , Mutación , Conformación Proteica , Activación Transcripcional , Transfección , Células Tumorales Cultivadas , Proteína p53 Supresora de Tumor/genéticaRESUMEN
Sestrin2 is a member of a family of stress responsive proteins, which controls cell viability via antioxidant activity and regulation of the mammalian target of rapamycin protein kinase (mTOR). Sestrin2 is induced by different stress insults, which diminish ATP production and induce energetic stress in the cells. Glucose is a critical substrate for ATP production utilized via glycolysis and mitochondrial respiration as well as for glycosylation of newly synthesized proteins in the endoplasmic reticulum (ER) and Golgi. Thus, glucose starvation causes both energy deficiency and activation of ER stress followed by the unfolding protein response (UPR). Here, we show that UPR induces Sestrin2 via ATF4 and NRF2 transcription factors and demonstrate that Sestrin2 protects cells from glucose starvation-induced cell death. Sestrin2 inactivation sensitizes cells to necroptotic cell death that is associated with a decline in ATP levels and can be suppressed by Necrostatin 7. We propose that Sestrin2 protects cells from glucose starvation-induced cell death via regulation of mitochondrial homeostasis.
Asunto(s)
Apoptosis/fisiología , Glucosa/metabolismo , Proteínas Nucleares/biosíntesis , Proteínas Nucleares/fisiología , Respuesta de Proteína Desplegada , Factor de Transcripción Activador 4/fisiología , Animales , Estrés del Retículo Endoplásmico/fisiología , Diana Mecanicista del Complejo 1 de la Rapamicina , Ratones , Ratones Noqueados , Complejos Multiproteicos/metabolismo , Factor 2 Relacionado con NF-E2/fisiología , Peroxidasas , Especies Reactivas de Oxígeno/metabolismo , Serina-Treonina Quinasas TOR/metabolismoRESUMEN
OBJECTIVES: Sestrin-2 (Sesn2) belongs to a family of highly conserved antioxidant proteins that were discovered as p53-inducible proteins and inhibits cell growth and proliferation. Our aim was to assess the levels of Sesn2 in malignant pleural effusions of lung cancer patients compared to benign pleural effusions. DESIGN AND METHODS: We enrolled 73 patients (55/males and 18/females) diagnosed with pleural effusion (PE). PEs were grouped as 44 malignant pleural effusions (MPEs; lung cancer) and 29 benign (BPE; 7 congestive heart failure, 9 tuberculosis, 13 parapneumonic). Pleural fluid (PF) Sesn2 levels were determined by enzyme-linked immunosorbent assay (ELISA) kit. Standard biochemical PF analysis was also performed and Sesn2 levels were correlated with PF lactate dehydrogenase (LDH), protein, cell counts and age. RESULTS: Sesn2 was detected in 24/44 patients with MPEs and in 3/29 patients with BPEs (p=0.0001). The mean value (mean±SEM) of Sesn2 in patients with MPEs was 0.54±0.22ng/mL while in BPEs it was 0.12±0.04ng/mL (p=0.0004). In MPEs Sesn2 pleural fluid levels did not correlate with PF LDH and cell counts (p=0.89 and p=0.64 respectively). CONCLUSIONS: Our study shows that Sesn2 is significantly increased in MPEs compared to BPEs. Moreover, the lack of correlation of Sesn2 levels with PF cell counts and PF LDH suggests that it is potentially secreted by pleural mesothelial cells.
Asunto(s)
Biomarcadores/metabolismo , Epitelio/metabolismo , Exudados y Transudados/metabolismo , Neoplasias Pulmonares/complicaciones , Proteínas Nucleares/metabolismo , Derrame Pleural Maligno/metabolismo , Ensayo de Inmunoadsorción Enzimática , Femenino , Estudios de Seguimiento , Humanos , Masculino , Persona de Mediana Edad , Derrame Pleural Maligno/etiología , Derrame Pleural Maligno/patología , PronósticoRESUMEN
cDNA microarray hybridization was used in an attempt to identify novel genes participating in cellular responses to prolonged hypoxia. One of the identified novel genes, designated Hi95 shared significant homology to a p53-regulated GADD family member PA26. In addition to its induction in response to prolonged hypoxia, the increased Hi95 transcription was observed following DNA damage or oxidative stress, but not following hyperthermia or serum starvation. Whereas induction of Hi95 by prolonged hypoxia or by oxidative stress is most likely p53-independent, its induction in response to DNA damaging treatments (gamma- or UV-irradiation, or doxorubicin) occurs in a p53-dependent manner. Overexpression of Hi95 full-length cDNA was found toxic for many types of cultured cells directly leading either to their apoptotic death or to sensitization to serum starvation and DNA damaging treatments. Unexpectedly, conditional overexpression of the Hi95 cDNA in MCF7-tet-off cells resulted in their protection against cell death induced by hypoxia/glucose deprivation or H(2)O(2). Thus, Hi95 gene seems to be involved in complex regulation of cell viability in response to different stress conditions.
Asunto(s)
Neoplasias Encefálicas/genética , Glioma/genética , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Secuencia de Aminoácidos , Animales , Antineoplásicos/farmacología , Secuencia de Bases , Northern Blotting , Western Blotting , Neoplasias Encefálicas/metabolismo , Neoplasias Encefálicas/patología , Neoplasias de la Mama/genética , Neoplasias de la Mama/metabolismo , Neoplasias de la Mama/patología , División Celular , Supervivencia Celular , Clonación Molecular , Cartilla de ADN/química , Doxorrubicina/farmacología , Glioma/metabolismo , Glioma/patología , Humanos , Peróxido de Hidrógeno/farmacología , Hipoxia/metabolismo , Etiquetado Corte-Fin in Situ , Ratones , Ratones Desnudos , Datos de Secuencia Molecular , Análisis de Secuencia por Matrices de Oligonucleótidos , ARN Mensajero/metabolismo , Ratas , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Homología de Secuencia de Aminoácido , Células Tumorales Cultivadas , Proteína p53 Supresora de Tumor/genética , Proteína p53 Supresora de Tumor/metabolismoRESUMEN
SESTRINs, proteins encoded by the SESN1-3 genes in mammals, are well-established suppressors of the mechanistic target of rapamycin complex 1 (mTORC1) kinase. Recently, we found that SESTRINs bind the GATOR2 protein complex, which is a regulator of RRAGA/B guanosine triphosphatase. Three independent studies support the RRAGA/B-dependence of mTORC1 regulation by SESTRINs; however, the role of GATOR2 in this process requires clarification.
RESUMEN
Apoptosis plays a critical physiological role in controlling cell number and eliminating damaged, non-functional and transformed cells. Cancerous cells as well as some types of normal cells are often resistant to cell death induced by pro-inflammatory cytokines through death receptors. This potentially allows cancer cells to evade the control from the immune system and to proceed toward a more malignant stage, although the mechanisms of this evasion are not well established. We have recently identified the stress-responsive Sestrin2 protein as a critical regulator of cell viability under stress conditions. Sestrin2 is a member of a small family of antioxidant proteins and inhibitors of mechanistic Target of Rapamycin Complex 1 (mTORC1) kinase. Down-regulation of Sestrin1/2 leads to genetic instability and accelerates the growth of lung adenocarcinoma xenografts. Here we addressed the potential role of Sestrin2 in regulation of cell death induced by TNFR1 and related Fas and TRAIL receptors in lung adenocarcinoma cells. We found that Sestrin2 silencing strongly inhibits cytokine-induced cell death through a mechanism independent of ROS and mTORC1 regulation. We determined that the X-linked inhibitor of apoptosis protein (XIAP) plays a critical role in the control of cytokine-induced cell death by Sestrin2. Thus our study defines a new, previously unrecognized role of Sestrin2 in the regulation of apoptosis.
Asunto(s)
Adenocarcinoma/metabolismo , Apoptosis/fisiología , Neoplasias Pulmonares/metabolismo , Proteínas Nucleares/fisiología , Receptores del Ligando Inductor de Apoptosis Relacionado con TNF/metabolismo , Proteína Inhibidora de la Apoptosis Ligada a X/metabolismo , Adenocarcinoma/patología , Adenocarcinoma del Pulmón , Apoptosis/efectos de los fármacos , Muerte Celular/efectos de los fármacos , Muerte Celular/fisiología , Línea Celular Tumoral , Células HEK293 , Humanos , Neoplasias Pulmonares/patología , Proteínas Nucleares/deficiencia , Factor de Necrosis Tumoral alfa/toxicidadRESUMEN
The mechanistic target of rapamycin complex 1 (mTORC1) kinase is a sensor of different environmental conditions and regulator of cell growth, metabolism, and autophagy. mTORC1 is activated by Rag GTPases, working as RagA:RagB and RagC:RagD heterodimers. Rags control mTORC1 activity by tethering mTORC1 to the lysosomes where it is activated by Rheb GTPase. RagA:RagB, active in its GTP-bound form, is inhibited by GATOR1 complex, a GTPase-activating protein, and GATOR1 is in turn negatively regulated by GATOR2 complex. Sestrins are stress-responsive proteins that inhibit mTORC1 via activation of AMP-activated protein kinase (AMPK) and tuberous sclerosis complex. Here we report an AMPK-independent mechanism of mTORC1 inhibition by Sestrins mediated by their interaction with GATOR2. As a result of this interaction, the Sestrins suppress mTOR lysosomal localization in a Rag-dependent manner. This mechanism is potentially involved in mTORC1 regulation by amino acids, rotenone, and tunicamycin, connecting stress response with mTORC1 inhibition.
Asunto(s)
Complejos Multiproteicos/metabolismo , Proteínas Nucleares/metabolismo , Serina-Treonina Quinasas TOR/metabolismo , Proteínas Quinasas Activadas por AMP/metabolismo , Aminoácidos/metabolismo , Animales , Activación Enzimática/efectos de los fármacos , GTP Fosfohidrolasas/metabolismo , Células HEK293 , Humanos , Lisosomas/efectos de los fármacos , Lisosomas/metabolismo , Diana Mecanicista del Complejo 1 de la Rapamicina , Ratones , Peroxidasas , Fosforilación/efectos de los fármacos , Unión Proteica/efectos de los fármacos , Transporte de Proteínas/efectos de los fármacos , Proteínas Quinasas S6 Ribosómicas 70-kDa/metabolismo , Rotenona/farmacología , Transducción de Señal/efectos de los fármacos , Tunicamicina/farmacologíaRESUMEN
The Sestrins constitute a family of evolutionarily conserved stress-inducible proteins that suppress oxidative stress and regulate AMP-dependent protein kinase (AMPK)-mammalian target of rapamycin (mTOR) signaling. By virtue of these activities, the Sestrins serve as important regulators of metabolic homeostasis. Accordingly, inactivation of Sestrin genes in invertebrates resulted in diverse metabolic pathologies, including oxidative damage, fat accumulation, mitochondrial dysfunction, and muscle degeneration, that resemble accelerated tissue aging. Likewise, Sestrin deficiencies in mice led to accelerated diabetic progression upon obesity. Further investigation of Sestrin function and regulation should provide new insights into age-associated metabolic diseases, such as diabetes, myopathies, and cancer.
Asunto(s)
Envejecimiento , Proteínas Nucleares/metabolismo , Proteínas Quinasas Activadas por AMP/metabolismo , Animales , Mitocondrias/metabolismo , Neoplasias/metabolismo , Neoplasias/patología , Proteínas Nucleares/genética , Obesidad/metabolismo , Obesidad/patología , Estrés Oxidativo , Transducción de Señal , Serina-Treonina Quinasas TOR/metabolismoRESUMEN
Chronic activation of mammalian target of rapamycin complex 1 (mTORC1) and p70 S6 kinase (S6K) in response to hypernutrition contributes to obesity-associated metabolic pathologies, including hepatosteatosis and insulin resistance. Sestrins are stress-inducible proteins that activate AMP-activated protein kinase (AMPK) and suppress mTORC1-S6K activity, but their role in mammalian physiology and metabolism has not been investigated. We show that Sestrin2--encoded by the Sesn2 locus, whose expression is induced upon hypernutrition--maintains metabolic homeostasis in liver of obese mice. Sesn2 ablation exacerbates obesity-induced mTORC1-S6K activation, glucose intolerance, insulin resistance, and hepatosteatosis, all of which are reversed by AMPK activation. Furthermore, concomitant ablation of Sesn2 and Sesn3 provokes hepatic mTORC1-S6K activation and insulin resistance even in the absence of nutritional overload and obesity. These results demonstrate an important homeostatic function for the stress-inducible Sestrin protein family in the control of mammalian lipid and glucose metabolism.
Asunto(s)
Metabolismo Energético/fisiología , Hígado Graso/metabolismo , Proteínas de Choque Térmico/metabolismo , Homeostasis/fisiología , Hígado/fisiología , Obesidad/metabolismo , Proteínas/metabolismo , Proteínas Quinasas Activadas por AMP/metabolismo , Tejido Adiposo/metabolismo , Animales , Hígado Graso/etiología , Resistencia a la Insulina/genética , Hígado/metabolismo , Diana Mecanicista del Complejo 1 de la Rapamicina , Ratones , Ratones Noqueados , Ratones Obesos , Complejos Multiproteicos , Proteínas Nucleares , Obesidad/complicaciones , Peroxidasas , Proteínas/genética , Proteínas Quinasas S6 Ribosómicas 70-kDa/metabolismo , Serina-Treonina Quinasas TORRESUMEN
The tumor suppressor p53 protects organisms from most types of cancer through multiple mechanisms. The p53 gene encodes a stress-activated transcriptional factor that transcriptionally regulates a large set of genes with versatile functions. These p53-activated genes mitigate consequences of stress regulating cell viability, growth, proliferation, repair, and metabolism. Recently, we described a novel antioxidant function of p53, which is important for its tumor suppressor activity. Among the many antioxidant genes activated by p53, Sestrins (Sesns) are critical for suppression of reactive oxygen species (ROS) and protection from oxidative stress, transformation, and genomic instability. Sestrins can regulate ROS through their direct effect on antioxidant peroxiredoxin proteins and through the AMP-activated protein kinase-target of rapamycin signaling pathway. The AMP-activated protein kinase-target of rapamycin axis is critical for regulation of metabolism and autophagy, two processes associated with ROS production, and deregulation of this pathway increases vulnerability of the organism to stress, aging, and age-related diseases, including cancer. Recently, we have shown that inactivation of Sestrin in fly causes accumulation of age-associated damage. Hence, Sestrins can link p53 with aging and age-related diseases.