RESUMO
MYC can be considered to be one of the most pressing and important targets for the development of novel anti-cancer therapies. This is due to its frequent dysregulation in tumors and due to the wide-ranging impact this dysregulation has on gene expression and cellular behavior. As a result, there have been numerous attempts to target MYC over the last few decades, both directly and indirectly, with mixed results. This article reviews the biology of MYC in the context of cancers and drug development. It discusses strategies aimed at targeting MYC directly, including those aimed at reducing its expression and blocking its function. In addition, the impact of MYC dysregulation on cellular biology is outlined, and how understanding this can underpin the development of approaches aimed at molecules and pathways regulated by MYC. In particular, the review focuses on the role that MYC plays in the regulation of metabolism, and the therapeutic avenues offered by inhibiting the metabolic pathways that are essential for the survival of MYC-transformed cells.
RESUMO
Patients with myelodysplastic syndrome and ring sideroblasts (MDS-RS) present with symptomatic anemia due to ineffective erythropoiesis that impedes their quality of life and increases morbidity. More than 80% of patients with MDS-RS harbor splicing factor 3B subunit 1 (SF3B1) mutations, the founder aberration driving MDS-RS disease. Here, we report how mis-splicing of coenzyme A synthase (COASY), induced by mutations in SF3B1, affects heme biosynthesis and erythropoiesis. Our data revealed that COASY was up-regulated during normal erythroid differentiation, and its silencing prevented the formation of erythroid colonies, impeded erythroid differentiation, and precluded heme accumulation. In patients with MDS-RS, loss of protein due to COASY mis-splicing led to depletion of both CoA and succinyl-CoA. Supplementation with COASY substrate (vitamin B5) rescued CoA and succinyl-CoA concentrations in SF3B1mut cells and mended erythropoiesis differentiation defects in MDS-RS primary patient cells. Our findings reveal a key role of the COASY pathway in erythroid maturation and identify upstream and downstream metabolites of COASY as a potential treatment for anemia in patients with MDS-RS.
Assuntos
Anemia , Síndromes Mielodisplásicas , Humanos , Eritropoese , Ácido Pantotênico , Qualidade de Vida , Fatores de Transcrição , Heme , Fatores de Processamento de RNA , FosfoproteínasRESUMO
Inhibition of the electron transport chain (ETC) prevents the regeneration of mitochondrial NAD+, resulting in cessation of the oxidative tricarboxylic acid (TCA) cycle and a consequent dependence upon reductive carboxylation for aspartate synthesis. NAD+ regeneration alone in the cytosol can rescue the viability of ETC-deficient cells. Yet, how this occurs and whether transfer of oxidative equivalents to the mitochondrion is required remain unknown. Here, we show that inhibition of the ETC drives reversal of the mitochondrial aspartate transaminase (GOT2) as well as malate and succinate dehydrogenases (MDH2 and SDH) to transfer oxidative NAD+ equivalents into the mitochondrion. This supports the NAD+-dependent activity of the mitochondrial glutamate dehydrogenase (GDH) and thereby enables anaplerosis-the entry of glutamine-derived carbon into the TCA cycle and connected biosynthetic pathways. Thus, under impaired ETC function, the cytosolic redox state is communicated into the mitochondrion and acts as a rheostat to support GDH activity and cell viability.
Assuntos
Malato Desidrogenase , NAD , NAD/metabolismo , Malato Desidrogenase/genética , Malato Desidrogenase/metabolismo , Oxirredução , Ciclo do Ácido Cítrico/fisiologia , RespiraçãoRESUMO
The MYC oncogene is a potent driver of growth and proliferation but also sensitises cells to apoptosis, which limits its oncogenic potential. MYC induces several biosynthetic programmes and primary cells overexpressing MYC are highly sensitive to glutamine withdrawal suggesting that MYC-induced sensitisation to apoptosis may be due to imbalance of metabolic/energetic supply and demand. Here we show that MYC elevates global transcription and translation, even in the absence of glutamine, revealing metabolic demand without corresponding supply. Glutamine withdrawal from MRC-5 fibroblasts depletes key tricarboxylic acid (TCA) cycle metabolites and, in combination with MYC activation, leads to AMP accumulation and nucleotide catabolism indicative of energetic stress. Further analyses reveal that glutamine supports viability through TCA cycle energetics rather than asparagine biosynthesis and that TCA cycle inhibition confers tumour suppression on MYC-driven lymphoma in vivo. In summary, glutamine supports the viability of MYC-overexpressing cells through an energetic rather than a biosynthetic mechanism.
Assuntos
Apoptose , Glutamina , Apoptose/genética , Linhagem Celular Tumoral , Ciclo do Ácido Cítrico , Fibroblastos/metabolismo , Glutamina/metabolismo , Proteínas Proto-Oncogênicas c-myc/genética , Proteínas Proto-Oncogênicas c-myc/metabolismoRESUMO
Infant MLL-AF4-driven acute lymphoblastic leukemia (ALL) is a devastating disease with dismal prognosis. A lack of understanding of the unique biology of this disease, particularly its prenatal origin, has hindered improvement of survival. We perform multiple RNA sequencing experiments on fetal, neonatal, and adult hematopoietic stem and progenitor cells from human and mouse. This allows definition of a conserved fetal transcriptional signature characterized by a prominent proliferative and oncogenic nature that persists in infant ALL blasts. From this signature, we identify a number of genes in functional validation studies that are critical for survival of MLL-AF4+ ALL cells. Of particular interest are PLK1 because of the readily available inhibitor and ELOVL1, which highlights altered fatty acid metabolism as a feature of infant ALL. We identify which aspects of the disease are residues of its fetal origin and potential disease vulnerabilities.
Assuntos
Ácidos Graxos/metabolismo , Feto/metabolismo , Células-Tronco Hematopoéticas/metabolismo , Leucemia-Linfoma Linfoblástico de Células Precursoras/metabolismo , Adulto , Animais , Linhagem Celular Tumoral , Feminino , Feto/embriologia , Humanos , Recém-Nascido , Masculino , Camundongos , Camundongos Transgênicos , Leucemia-Linfoma Linfoblástico de Células Precursoras/embriologiaRESUMO
A novel role of NKX3.1 in the mitochondria regulating the transcription of the electron transport chain components is reported. Mechanistically, HSPA9 chaperones NKX3.1 into the mitochondria in response to oxidative stress to regulate reactive oxygen species and suppress tumor initiation.See related article by Papachristodoulou et al., p. 2316.
Assuntos
Próstata , Neoplasias da Próstata , Proteínas de Homeodomínio/genética , Humanos , Masculino , Espécies Reativas de Oxigênio , Fatores de Transcrição/genéticaRESUMO
The aberrant gain of DNA methylation at CpG islands is frequently observed in colorectal tumours and may silence the expression of tumour suppressors such as MLH1. Current models propose that these CpG islands are targeted by de novo DNA methyltransferases in a sequence-specific manner, but this has not been tested. Using ectopically integrated CpG islands, here we find that aberrantly methylated CpG islands are subject to low levels of de novo DNA methylation activity in colorectal cancer cells. By delineating DNA methyltransferase targets, we find that instead de novo DNA methylation activity is targeted primarily to CpG islands marked by the histone modification H3K36me3, a mark associated with transcriptional elongation. These H3K36me3 marked CpG islands are heavily methylated in colorectal tumours and the normal colon suggesting that de novo DNA methyltransferase activity at CpG islands in colorectal cancer is focused on similar targets to normal tissues and not greatly remodelled by tumourigenesis.
Assuntos
Neoplasias Colorretais/genética , DNA (Citosina-5-)-Metiltransferases/metabolismo , Metilação de DNA , Regulação Neoplásica da Expressão Gênica , Código das Histonas/genética , Carcinogênese/genética , Linhagem Celular Tumoral , Sequenciamento de Cromatina por Imunoprecipitação , Colo/patologia , Neoplasias Colorretais/patologia , Ilhas de CpG/genética , DNA (Citosina-5-)-Metiltransferases/genética , Conjuntos de Dados como Assunto , Epigênese Genética , Técnicas de Inativação de Genes , Histonas/genética , Humanos , Regiões Promotoras Genéticas/genética , Transcrição GênicaRESUMO
Cellular senescence is triggered by diverse stimuli and is characterized by long-term growth arrest and secretion of cytokines and chemokines (termed the SASP-senescence-associated secretory phenotype). Senescence can be organismally beneficial as it can prevent the propagation of damaged or mutated clones and stimulate their clearance by immune cells. However, it has recently become clear that senescence also contributes to the pathophysiology of aging through the accumulation of damaged cells within tissues. Here, we describe that inhibition of the reaction catalysed by LSG1, a GTPase involved in the biogenesis of the 60S ribosomal subunit, leads to a robust induction of cellular senescence. Perhaps surprisingly, this was not due to ribosome depletion or translational insufficiency, but rather through perturbation of endoplasmic reticulum homeostasis and a dramatic upregulation of the cholesterol biosynthesis pathway. The underlying transcriptomic signature is shared with several other forms of senescence, and the cholesterol biosynthesis genes contribute to the cell cycle arrest in oncogene-induced senescence. Furthermore, targeting of LSG1 resulted in amplification of the cholesterol/ER signature and restoration of a robust cellular senescence response in transformed cells, suggesting potential therapeutic uses of LSG1 inhibition.
Assuntos
Senescência Celular/genética , Estresse do Retículo Endoplasmático/genética , GTP Fosfo-Hidrolases/genética , GTP Fosfo-Hidrolases/metabolismo , Subunidades Ribossômicas Maiores de Eucariotos/metabolismo , Pontos de Checagem do Ciclo Celular/genética , Colesterol/biossíntese , Retículo Endoplasmático/metabolismo , Fibroblastos/metabolismo , Técnicas de Silenciamento de Genes , Células HEK293 , Homeostase/genética , Humanos , Biossíntese de Proteínas/genética , RNA Interferente Pequeno/genética , Proteínas de Ligação a RNA/antagonistas & inibidores , Proteínas de Ligação a RNA/metabolismo , Transcriptoma , Transfecção , Proteína Supressora de Tumor p53/metabolismoRESUMO
Cellular senescence is a stress response program characterized by a robust cell cycle arrest and the induction of a proinflammatory senescence-associated secretory phenotype (SASP) that is triggered through an unknown mechanism. Here, we show that, during oncogene-induced senescence (OIS), the Toll-like receptor 2 (TLR2) and its partner TLR10 are key mediators of senescence in vitro and in murine models. TLR2 promotes cell cycle arrest by regulating the tumor suppressors p53-p21CIP1, p16INK4a, and p15INK4b and regulates the SASP through the induction of the acute-phase serum amyloids A1 and A2 (A-SAAs) that, in turn, function as the damage-associated molecular patterns (DAMPs) signaling through TLR2 in OIS. Last, we found evidence that the cGAS-STING cytosolic DNA sensing pathway primes TLR2 and A-SAAs expression in OIS. In summary, we report that innate immune sensing of senescence-associated DAMPs by TLR2 controls the SASP and reinforces the cell cycle arrest program in OIS.
Assuntos
Senescência Celular , Imunidade Inata , Receptor 2 Toll-Like/metabolismo , Alarminas/metabolismo , Animais , Senescência Celular/efeitos dos fármacos , Fibroblastos/citologia , Fibroblastos/metabolismo , Humanos , Proteínas de Membrana/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , NF-kappa B/metabolismo , Nucleotidiltransferases/metabolismo , Interferência de RNA , RNA Interferente Pequeno/metabolismo , Proteína Amiloide A Sérica/genética , Proteína Amiloide A Sérica/metabolismo , Transdução de Sinais , Tamoxifeno/análogos & derivados , Tamoxifeno/farmacologia , Receptor 10 Toll-Like/antagonistas & inibidores , Receptor 10 Toll-Like/genética , Receptor 10 Toll-Like/metabolismo , Receptor 2 Toll-Like/antagonistas & inibidores , Receptor 2 Toll-Like/genética , Proteínas Quinases p38 Ativadas por Mitógeno/metabolismo , Proteínas ras/genética , Proteínas ras/metabolismoRESUMO
In this issue of JEM, Umemoto et al. (https://doi.org/10.1084/jem.20180421) demonstrate that calcium influx stimulates mitochondrial metabolism and initiates proliferation in hematopoietic stem cells (HSCs). Extracellular adenosine, sourced from surrounding hematopoietic progenitors, inhibits this calcium influx, thereby suppressing mitochondrial metabolism and promoting HSC quiescence. This is the first demonstration that a calcium-mitochondria pathway regulates HSC division.
Assuntos
Cálcio , Células-Tronco Hematopoéticas , Divisão Celular , MitocôndriasRESUMO
Hypoxic cancer cells exhibit resistance to many therapies. This study compared the therapeutic effect of targeting the pH regulatory proteins (CAIX, NHE1 and V-ATPase) that permit cancer cells to adapt to hypoxic conditions, using both 2D and 3D culture models. Drugs targeting CAIX, NHE1 and V-ATPase exhibited anti-proliferative effects in MCF-7, MDA-MB-231 and HBL-100 breast cancer cell lines in 2D. Protein and gene expression analysis in 2D showed that CAIX was the most hypoxia-inducible protein of the 3 targets. However, the expression of CAIX differed between the 3 cell lines. This difference in CAIX expression in hypoxia was consistent with a varying activity of FIH-1 between the cell lines. 3D expression analysis demonstrated that both CAIX and NHE1 were up-regulated in the hypoxic areas of multicellular tumor spheroids. However, the induction of CAIX expression in hypoxia was again cell line dependent. 3D invasion assays conducted with spheroids showed that CAIX inhibition significantly reduced the invasion of cells. Finally, the capability of both NHE1 and CAIX inhibitors to combine effectively with irradiation was exhibited in clonogenic assays. Proteomic-mass-spectrometric analysis indicated that CAIX inhibition might be combining with irradiation through stimulating apoptotic cell death. Of the three proteins, CAIX represents the target with the most promise for the treatment of breast cancer.
Assuntos
Neoplasias da Mama/metabolismo , Concentração de Íons de Hidrogênio , Hipóxia/metabolismo , Neoplasias da Mama/genética , Anidrase Carbônica IX/antagonistas & inibidores , Anidrase Carbônica IX/metabolismo , Hipóxia Celular , Linhagem Celular Tumoral , Proliferação de Células , Feminino , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Humanos , Hipóxia/genética , Fator 1 Induzível por Hipóxia/metabolismo , Espectrometria de Massas , Oxigênio/metabolismo , Proteômica/métodos , Trocador 1 de Sódio-Hidrogênio/metabolismo , ATPases Vacuolares Próton-Translocadoras/metabolismoRESUMO
The function of macroautophagy/autophagy during tumor initiation or in established tumors can be highly distinct and context-dependent. To investigate the role of autophagy in gliomagenesis, we utilized a KRAS-driven glioblastoma mouse model in which autophagy is specifically disrupted via RNAi against Atg7, Atg13 or Ulk1. Inhibition of autophagy strongly reduced glioblastoma development, demonstrating its critical role in promoting tumor formation. Further supporting this finding is the observation that tumors originating from Atg7-shRNA injections escaped the knockdown effect and thereby still underwent functional autophagy. In vitro, autophagy inhibition suppressed the capacity of KRAS-expressing glial cells to form oncogenic colonies or to survive low serum conditions. Molecular analyses revealed that autophagy-inhibited glial cells were unable to maintain active growth signaling under growth-restrictive conditions and were prone to undergo senescence. Overall, these results demonstrate that autophagy is crucial for glioma initiation and growth, and is a promising therapeutic target for glioblastoma treatment.
Assuntos
Proteína 7 Relacionada à Autofagia/genética , Autofagia , Neoplasias Encefálicas/patologia , Glioblastoma/patologia , Animais , Proteínas Reguladoras de Apoptose/metabolismo , Proteína 7 Relacionada à Autofagia/metabolismo , Proteína Homóloga à Proteína-1 Relacionada à Autofagia/metabolismo , Neoplasias Encefálicas/metabolismo , Linhagem Celular Tumoral , Transformação Celular Neoplásica/genética , Senescência Celular , Galinhas , Fibroblastos/metabolismo , Glioblastoma/metabolismo , Hipóxia , Camundongos , Neuroglia/metabolismo , Proteínas Proto-Oncogênicas p21(ras)/metabolismo , Interferência de RNA , RNA Interferente Pequeno/farmacologia , Transdução de SinaisRESUMO
Dynamic interactions between RhoA and Rac1, members of the Rho small GTPase family, play a vital role in the control of cell migration. Using predictive mathematical modeling, mass spectrometry-based quantitation of network components, and experimental validation in MDA-MB-231 mesenchymal breast cancer cells, we show that a network containing Rac1, RhoA, and PAK family kinases can produce bistable, switch-like responses to a graded PAK inhibition. Using a small chemical inhibitor of PAK, we demonstrate that cellular RhoA and Rac1 activation levels respond in a history-dependent, bistable manner to PAK inhibition. Consequently, we show that downstream signaling, actin dynamics, and cell migration also behave in a bistable fashion, displaying switches and hysteresis in response to PAK inhibition. Our results demonstrate that PAK is a critical component in the Rac1-RhoA inhibitory crosstalk that governs bistable GTPase activity, cell morphology, and cell migration switches.
Assuntos
Citoesqueleto de Actina , Actinas , Linhagem Celular Tumoral , Movimento Celular , Citoesqueleto , Humanos , Proteínas Serina-Treonina Quinases , Transdução de Sinais , Proteínas rac1 de Ligação ao GTP , Proteína rhoA de Ligação ao GTPRESUMO
Tumor cell survival critically depends on heterotypic communication with benign cells in the microenvironment. Here, we describe a survival signaling pathway activated in stromal cells by contact to B cells from patients with chronic lymphocytic leukemia (CLL). The expression of protein kinase C (PKC)-ßII and the subsequent activation of NF-κB in bone marrow stromal cells are prerequisites to support the survival of malignant B cells. PKC-ß knockout mice are insusceptible to CLL transplantations, underscoring the in vivo significance of the PKC-ßII-NF-κB signaling pathway in the tumor microenvironment. Upregulated stromal PKC-ßII in biopsies from patients with CLL, acute lymphoblastic leukemia, and mantle cell lymphoma suggests that this pathway may commonly be activated in a variety of hematological malignancies.
Assuntos
Linfócitos B/patologia , Leucemia Linfocítica Crônica de Células B/patologia , NF-kappa B/genética , Proteína Quinase C/fisiologia , Animais , Linfócitos B/metabolismo , Citocinas/metabolismo , Regulação Neoplásica da Expressão Gênica , Humanos , Leucemia Linfocítica Crônica de Células B/metabolismo , Camundongos , Camundongos Knockout , Camundongos Transgênicos , NF-kappa B/metabolismo , Proteína Quinase C/genética , Proteína Quinase C/metabolismo , Proteína Quinase C beta , Transdução de Sinais , Células Estromais/metabolismo , Microambiente TumoralRESUMO
The recessive disorder poikiloderma with neutropenia (PN) is caused by mutations in the C16orf57 gene that encodes the highly conserved USB1 protein. Here, we present the 1.1 Å resolution crystal structure of human USB1, defining it as a member of the LigT-like superfamily of 2H phosphoesterases. We show that human USB1 is a distributive 3'-5' exoribonuclease that posttranscriptionally removes uridine and adenosine nucleosides from the 3' end of spliceosomal U6 small nuclear RNA (snRNA), directly catalyzing terminal 2', 3' cyclic phosphate formation. USB1 measures the appropriate length of the U6 oligo(U) tail by reading the position of a key adenine nucleotide (A102) and pausing 5 uridine residues downstream.We show that the 3' ends of U6 snRNA in PN patient lymphoblasts are elongated and unexpectedly carry nontemplated 3' oligo(A) tails that are characteristic of nuclear RNA surveillance targets. Thus, our study reveals a novel quality control pathway in which posttranscriptional 3'-end processing by USB1 protects U6 snRNA from targeting and destruction by the nuclear exosome. Our data implicate aberrant oligoadenylation of U6 snRNA in the pathogenesis of the leukemia predisposition disorder PN.
Assuntos
Mutação , Neutropenia/genética , Diester Fosfórico Hidrolases/genética , RNA Nuclear Pequeno/genética , Anormalidades da Pele/genética , Regiões 3' não Traduzidas/genética , Nucleotídeos de Adenina/genética , Nucleotídeos de Adenina/metabolismo , Sequência de Aminoácidos , Sequência de Bases , Domínio Catalítico , Linhagem Celular , Cristalografia por Raios X , Teste de Complementação Genética , Humanos , Modelos Genéticos , Modelos Moleculares , Dados de Sequência Molecular , Neutropenia/metabolismo , Oligorribonucleotídeos/genética , Oligorribonucleotídeos/metabolismo , Diester Fosfórico Hidrolases/química , Diester Fosfórico Hidrolases/metabolismo , Processamento Pós-Transcricional do RNA , RNA Nuclear Pequeno/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/crescimento & desenvolvimento , Homologia de Sequência de Aminoácidos , Anormalidades da Pele/metabolismo , Spliceossomos/genética , Spliceossomos/metabolismo , Uridina/genética , Uridina/metabolismoRESUMO
Removal of the assembly factor eukaryotic initiation factor 6 (eIF6) is critical for late cytoplasmic maturation of 60S ribosomal subunits. In mammalian cells, the current model posits that eIF6 release is triggered following phosphorylation of Ser 235 by activated protein kinase C. In contrast, genetic studies in yeast indicate a requirement for the ortholog of the SBDS (Shwachman-Bodian-Diamond syndrome) gene that is mutated in the inherited leukemia predisposition disorder Shwachman-Diamond syndrome (SDS). Here, by isolating late cytoplasmic 60S ribosomal subunits from Sbds-deleted mice, we show that SBDS and the GTPase elongation factor-like 1 (EFL1) directly catalyze eIF6 removal in mammalian cells by a mechanism that requires GTP binding and hydrolysis by EFL1 but not phosphorylation of eIF6 Ser 235. Functional analysis of disease-associated missense variants reveals that the essential role of SBDS is to tightly couple GTP hydrolysis by EFL1 on the ribosome to eIF6 release. Furthermore, complementary NMR spectroscopic studies suggest unanticipated mechanistic parallels between this late step in 60S maturation and aspects of bacterial ribosome disassembly. Our findings establish a direct role for SBDS and EFL1 in catalyzing the translational activation of ribosomes in all eukaryotes, and define SDS as a ribosomopathy caused by uncoupling GTP hydrolysis from eIF6 release.
Assuntos
Fatores de Iniciação em Eucariotos/metabolismo , Guanosina Trifosfato/metabolismo , Ribossomos/patologia , Animais , Doenças da Medula Óssea/genética , Doenças da Medula Óssea/fisiopatologia , Catálise , Células Cultivadas , Modelos Animais de Doenças , Fatores de Iniciação em Eucariotos/genética , Insuficiência Pancreática Exócrina/genética , Insuficiência Pancreática Exócrina/fisiopatologia , Humanos , Hidrólise , Lipomatose , Fígado/patologia , Camundongos , Camundongos Endogâmicos C57BL , Modelos Moleculares , Mutação , Fatores de Iniciação de Peptídeos/genética , Fatores de Iniciação de Peptídeos/metabolismo , Fosforilação , Ligação Proteica , Estrutura Terciária de Proteína , Proteínas/química , Proteínas/genética , Proteínas/metabolismo , Subunidades Ribossômicas Maiores de Eucariotos , Síndrome de Shwachman-DiamondRESUMO
The Myc transcription factor is a potent inducer of proliferation and is required for Wnt/beta-catenin signaling in intestinal epithelium. Since deregulation of the Wnt/beta-catenin pathway is a prerequisite for nonhereditary intestinal tumorigenesis, we asked whether activation of Myc recapitulates the tumorigenic changes that are driven by constitutive Wnt/beta-catenin pathway signaling following adenomatous polyposis coli (APC) inactivation. Using mice in which expression of MycER(TAM), a reversibly switchable form of Myc, is expressed transgenically in intestinal epithelium, we define the acute changes that follow Myc activation as well as subsequent deactivation. Myc activation reversibly recapitulates many, but not all, aspects of APC inactivation, including increased proliferation and apoptosis and loss of goblet cells. However, whereas APC inactivation induces redistribution of Paneth cells, direct Myc activation triggers their rapid attrition. Moreover, direct Myc activation engages the ARF/p53/p21(cip1) tumor suppressor pathway, whereas deregulation of Wnt/beta-catenin signaling does not. These observations illustrate key differences in oncogenic impact in intestinal epithelium of direct Myc activation and indirect Myc activation via the Wnt/beta-catenin pathway. Furthermore, the in situ dedifferentiation of mature goblet cells that Myc induces indicates a novel cross talk between the Wnt/beta-catenin and Notch signaling pathways.
Assuntos
Mucosa Intestinal/metabolismo , Proteínas Proto-Oncogênicas c-myc/metabolismo , Transdução de Sinais , Proteínas Wnt/metabolismo , beta Catenina/metabolismo , Animais , Apoptose , Proliferação de Células , Expressão Gênica , Mucosa Intestinal/citologia , Mucosa Intestinal/efeitos dos fármacos , Masculino , Camundongos , Camundongos Transgênicos , Proteínas Proto-Oncogênicas c-myc/genética , Tamoxifeno/farmacologiaRESUMO
Somatic activating mutations of BRAF are the earliest and most common genetic abnormality detected in the genesis of human melanoma. However, the mechanism(s) by which activated BRAF promotes melanoma cell cycle progression and/or survival remain unclear. Here we demonstrate that expression of BIM, a pro-apoptotic member of the BCL-2 family, is inhibited by BRAF-->MEK-->ERK signaling in mouse and human melanocytes and in human melanoma cells. Trophic factor deprivation of melanocytes leads to elevated BIM expression. However, re-addition of trophic factors or activation of a conditional form of BRAF(V600E) leads to rapid inhibition of BIM expression. In both cases, inhibition of BIM expression was dependent on the activity of MEK1/2 and the proteasome. Consistent with these observations, pharmacological inhibition of BRAF(V600E) or MEK1/2 in human melanoma cells (using PLX4720 and CI-1040 respectively) led to a striking elevation of BIM expression. Re-activation of BRAF-->MEK-->ERK signaling led to phosphorylation of BIM-EL on serine 69 and its subsequent degradation. Interestingly, endogenous expression of BIM in melanoma cells was insufficient to induce apoptosis unless combined with serum deprivation. Under these circumstances, inhibition of BIM expression by RNA interference provided partial protection from apoptosis. These data suggest that regulation of BIM expression by BRAF-->MEK-->ERK signaling is one mechanism by which oncogenic BRAF(V600E) can influence the aberrant physiology of melanoma cells.
Assuntos
Proteínas Reguladoras de Apoptose/metabolismo , Melanoma/metabolismo , Melanoma/patologia , Proteínas de Membrana/metabolismo , Proteínas Proto-Oncogênicas B-raf/metabolismo , Proteínas Proto-Oncogênicas/metabolismo , Neoplasias Cutâneas/metabolismo , Neoplasias Cutâneas/patologia , Animais , Apoptose/fisiologia , Proteínas Reguladoras de Apoptose/genética , Proteína 11 Semelhante a Bcl-2 , Linhagem Celular Tumoral , Sobrevivência Celular , Meios de Cultura Livres de Soro , Humanos , Peptídeos e Proteínas de Sinalização Intercelular/metabolismo , MAP Quinase Quinase 1/antagonistas & inibidores , MAP Quinase Quinase 1/metabolismo , MAP Quinase Quinase 2/antagonistas & inibidores , MAP Quinase Quinase 2/metabolismo , Melanócitos/citologia , Melanócitos/metabolismo , Proteínas de Membrana/genética , Camundongos , Mitocôndrias/metabolismo , Mutação Puntual , Proteínas Proto-Oncogênicas/genética , Proteínas Proto-Oncogênicas B-raf/genética , Proteínas Proto-Oncogênicas c-bcl-2/genética , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Interferência de RNA , Transdução de Sinais/fisiologiaRESUMO
Myc is a pleiotropic basic helix-loop-helix leucine zipper transcription factor that coordinates expression of the diverse intracellular and extracellular programs that together are necessary for growth and expansion of somatic cells. In principle, this makes inhibition of Myc an attractive pharmacological approach for treating diverse types of cancer. However, enthusiasm has been muted by lack of direct evidence that Myc inhibition would be therapeutically efficacious, concerns that it would induce serious side effects by inhibiting proliferation of normal tissues, and practical difficulties in designing Myc inhibitory drugs. We have modelled genetically both the therapeutic impact and the side effects of systemic Myc inhibition in a preclinical mouse model of Ras-induced lung adenocarcinoma by reversible, systemic expression of a dominant-interfering Myc mutant. We show that Myc inhibition triggers rapid regression of incipient and established lung tumours, defining an unexpected role for endogenous Myc function in the maintenance of Ras-dependent tumours in vivo. Systemic Myc inhibition also exerts profound effects on normal regenerating tissues. However, these effects are well tolerated over extended periods and rapidly and completely reversible. Our data demonstrate the feasibility of targeting Myc, a common downstream conduit for many oncogenic signals, as an effective, efficient and tumour-specific cancer therapy.
Assuntos
Terapia Genética , Neoplasias Pulmonares/terapia , Modelos Biológicos , Proteínas Proto-Oncogênicas c-myc/antagonistas & inibidores , Proteínas Proto-Oncogênicas c-myc/genética , Adenocarcinoma/genética , Adenocarcinoma/metabolismo , Adenocarcinoma/patologia , Adenocarcinoma/terapia , Animais , Trato Gastrointestinal/citologia , Trato Gastrointestinal/metabolismo , Trato Gastrointestinal/patologia , Genes Dominantes/genética , Genes ras , Neoplasias Pulmonares/genética , Neoplasias Pulmonares/metabolismo , Neoplasias Pulmonares/patologia , Masculino , Camundongos , Mutação/genética , Proteína Oncogênica p21(ras)/metabolismo , Proteínas Proto-Oncogênicas c-myc/metabolismo , Pele/citologia , Pele/metabolismo , Pele/patologia , Testículo/citologia , Testículo/metabolismo , Testículo/patologia , Transgenes/genéticaRESUMO
There is currently much interest in the idea of restoring p53 activity in tumor cells by inhibiting Hdm2/Mdm2. However, it has remained unclear whether this would also activate p53 in normal cells. Using a switchable endogenous p53 mouse model, which allows rapid and reversible toggling of p53 status between wild-type and null states, we show that p53 is spontaneously active in all tested tissues of mdm2-deficient mice, triggering fatal pathologies that include ablation of classically radiosensitive tissues. In apoptosis-resistant tissues, spontaneous unbuffered p53 activity triggers profound inhibition of cell proliferation. Such acute spontaneous p53 activity occurs in the absence of any detectable p53 posttranslational modification, DNA damage, or p19ARF signaling and triggers rapid p53 degradation.