RESUMEN
An enhanced capacity for de novo lipid synthesis is a metabolic feature of most cancer cells that distinguishes them from their cells of origin. However, the mechanisms through which oncogenes alter lipid metabolism are poorly understood. We find that expression of oncogenic PI3K (H1047R) or K-Ras (G12V) in breast epithelial cells is sufficient to induce de novo lipogenesis, and this occurs through the convergent activation of the mechanistic target of rapamycin complex 1 (mTORC1) downstream of these common oncogenes. Oncogenic stimulation of mTORC1 signaling in this isogenic setting or a panel of eight breast cancer cell lines leads to activation of the sterol regulatory element-binding proteins (SREBP1 and SREBP2) that are required for oncogene-induced lipid synthesis. The SREBPs are also required for the growth factor-independent growth and proliferation of oncogene-expressing cells. Finally, we find that elevated mTORC1 signaling is associated with increased mRNA and protein levels of canonical SREBP targets in primary human breast cancer samples. These data suggest that the mTORC1/SREBP pathway is a major mechanism through which common oncogenic signaling events induce de novo lipid synthesis to promote aberrant growth and proliferation of cancer cells.
Asunto(s)
Lipogénesis , Complejos Multiproteicos/metabolismo , Fosfatidilinositol 3-Quinasas/metabolismo , Proteínas Proto-Oncogénicas p21(ras)/metabolismo , Proteína 1 de Unión a los Elementos Reguladores de Esteroles/metabolismo , Proteína 2 de Unión a Elementos Reguladores de Esteroles/metabolismo , Serina-Treonina Quinasas TOR/metabolismo , Animales , Línea Celular Tumoral , Proliferación Celular , Regulación Neoplásica de la Expresión Génica , Humanos , Diana Mecanicista del Complejo 1 de la Rapamicina , Ratones , Transducción de SeñalRESUMEN
Because of insufficient understanding of the molecular effects of low levels of radiation exposure, there is a great uncertainty regarding its health risks. We report here that treatment of normal human cells with low-dose radiation induces a metabolic shift from oxidative phosphorylation to aerobic glycolysis resulting in increased radiation resistance. This metabolic change is highlighted by upregulation of genes encoding glucose transporters and enzymes of glycolysis and the oxidative pentose phosphate pathway, concomitant with downregulation of mitochondrial genes, with corresponding changes in metabolic flux through these pathways. Mechanistically, the metabolic reprogramming depends on HIF1α, which is induced specifically by low-dose irradiation linking the metabolic pathway with cellular radiation dose response. Increased glucose flux and radiation resistance from low-dose irradiation are also observed systemically in mice. This highly sensitive metabolic response to low-dose radiation has important implications in understanding and assessing the health risks of radiation exposure.
Asunto(s)
Subunidad alfa del Factor 1 Inducible por Hipoxia/efectos de la radiación , Mitocondrias/efectos de la radiación , Adaptación Fisiológica , Animales , Linfocitos B/efectos de la radiación , Línea Celular Tumoral , Relación Dosis-Respuesta en la Radiación , Fibroblastos/efectos de la radiación , Glucólisis/efectos de la radiación , Humanos , Ratones , Ratones Endogámicos BALB C , Fosforilación Oxidativa/efectos de la radiaciónRESUMEN
The mammalian target of rapamycin (mTOR) is responsive to numerous extracellular and intracellular cues and, through the formation of two physically and functionally distinct complexes, has a central role in the homeostatic control of cell growth, proliferation and survival. Through the aberrant activation of mTOR signaling, the perception of cellular growth signals becomes disconnected from the processes promoting cell growth, and this underlies the pathophysiology of a number of genetic tumor syndromes and cancers. Here, we review the oncogenes and tumor suppressors comprising the regulatory network upstream of mTOR, highlight the human cancers in which mTOR is activated and discuss how dysregulated mTOR signaling provides tumors a selective growth advantage. In addition, we discuss why activation of mTOR, as a consequence of distinct oncogenic events, results in diverse clinical outcomes, and how the complexity of the mTOR signaling network might dictate therapeutic approaches.
Asunto(s)
Péptidos y Proteínas de Señalización Intracelular/metabolismo , Neoplasias/fisiopatología , Proteínas Serina-Treonina Quinasas/metabolismo , Transducción de Señal/fisiología , Proteínas Supresoras de Tumor/fisiología , Animales , Antibióticos Antineoplásicos/uso terapéutico , Humanos , Modelos Biológicos , Neoplasias/tratamiento farmacológico , Neoplasias/metabolismo , Transducción de Señal/efectos de los fármacos , Sirolimus/uso terapéutico , Serina-Treonina Quinasas TOR , Proteínas Supresoras de Tumor/metabolismoRESUMEN
The molecular interplay between the phosphoinositide 3-kinase (PI3K) pathway and mammalian target of rapamycin (mTOR) signalling in the control of cell growth and proliferation has been the subject of much interest and debate amongst cell biologists. A recent escalation of research in this area has come from the discovery of the tuberous sclerosis complex gene products, tuberin and hamartin, as central regulators of mTOR activation. The PI3K effector Akt/protein kinase B has been found to directly phosphorylate tuberin and is thereby thought to activate mTOR through inhibition of the tuberin-hamartin complex. The many recent studies aimed at defining the molecular nature of this revamped PI3K/Akt/mTOR pathway are reviewed here. The collective data discussed have laid the groundwork for important new insights into the many cancers caused by aberrant PI3K activation and the clinically challenging tuberous sclerosis complex disease and have suggested a possible means of treatment for both.
Asunto(s)
Fosfatidilinositol 3-Quinasas/genética , Proteínas Quinasas/genética , Proteínas Serina-Treonina Quinasas , Esclerosis Tuberosa/genética , Genes Supresores de Tumor , Humanos , Proteínas Quinasas/fisiología , Proteínas Tirosina Quinasas/genética , Proteínas/genética , Proteínas Proto-Oncogénicas/genética , Proteínas Proto-Oncogénicas c-akt , Proteínas Represoras/genética , Transducción de Señal/genética , Serina-Treonina Quinasas TOR , Esclerosis Tuberosa/enzimología , Proteína 1 del Complejo de la Esclerosis Tuberosa , Proteína 2 del Complejo de la Esclerosis Tuberosa , Proteínas Supresoras de TumorRESUMEN
Proteins that physically associate with members of the kinesin superfamily are critical for the functional diversity observed for these microtubule motor proteins. However, quaternary structures of complexes between kinesins and kinesin-associated proteins are poorly defined. We have analyzed the nature of the interaction between the Kar3 motor protein, a minus-end-directed kinesin from yeast, and its associated protein Cik1. Extraction experiments demonstrate that Kar3p and Cik1p are tightly associated. Mapping of the interaction domains of the two proteins by two-hybrid analyses indicates that Kar3p and Cik1p associate in a highly specific manner along the lengths of their respective coiled-coil domains. Sucrose gradient velocity centrifugation and gel filtration experiments were used to determine the size of the Kar3-Cik1 complex from both mating pheromone-treated cells and vegetatively growing cells. These experiments predict a size for this complex that is consistent with that of a heterodimer containing one Kar3p subunit and one Cik1p subunit. Finally, immunoprecipitation of epitope-tagged and untagged proteins confirms that only one subunit of Kar3p and Cik1p are present in the Kar3-Cik1 complex. These findings demonstrate that the Kar3-Cik1 complex has a novel heterodimeric structure not observed previously for kinesin complexes.
Asunto(s)
Proteínas Fúngicas/metabolismo , Cinesinas/metabolismo , Proteínas de Microtúbulos , Proteínas Asociadas a Microtúbulos , Proteínas de Saccharomyces cerevisiae , Secuencia de Aminoácidos , Centrifugación por Gradiente de Densidad , Fraccionamiento Químico , Dimerización , Proteínas Fúngicas/genética , Cinesinas/genética , Datos de Secuencia Molecular , Peso Molecular , Feromonas/farmacología , Estructura Terciaria de Proteína , Saccharomyces cerevisiae/efectos de los fármacos , Saccharomyces cerevisiae/metabolismo , Análisis de Secuencia , SacarosaRESUMEN
Members of the kinesin superfamily of proteins participate in a wide variety of cellular processes. Although much attention has been devoted to the structural and biophysical properties of the force-generating motor domain of kinesins, the factors controlling the functional specificity of each kinesin have only recently been examined. Genetic and biochemical approaches have identified two classes of proteins that associate physically with the diverse non-motor domains of kinesins. These proteins can be divided into two general classes: first, those that form tight complexes with the kinesin and are instrumental in directing the distinct function of the motor (i.e. drivers) and, second, those proteins that might transiently interact with the motor or be an integral part of the motor's cargo (i.e. passengers). Here, we discuss known kinesin-binding proteins, and how they might participate in the activity of their motor partners.
Asunto(s)
Proteínas Adaptadoras Transductoras de Señales , Proteínas Portadoras/fisiología , Proteínas del Citoesqueleto , Cinesinas/fisiología , Proteínas de Microtúbulos , Proteínas Asociadas a Microtúbulos , Proteínas Motoras Moleculares/fisiología , Proteínas de Saccharomyces cerevisiae , Proteínas Fúngicas/fisiología , Saccharomyces cerevisiae/fisiologíaRESUMEN
The mechanisms by which kinesin-related proteins interact with other proteins to carry out specific cellular processes is poorly understood. The kinesin-related protein, Kar3p, has been implicated in many microtubule functions in yeast. Some of these functions require interaction with the Cik1 protein (Page, B.D., L.L. Satterwhite, M.D. Rose, and M. Snyder. 1994. J. Cell Biol. 124:507-519). We have identified a Saccharomyces cerevisiae gene, named VIK1, encoding a protein with sequence and structural similarity to Cik1p. The Vik1 protein is detected in vegetatively growing cells but not in mating pheromone-treated cells. Vik1p physically associates with Kar3p in a complex separate from that of the Kar3p-Cik1p complex. Vik1p localizes to the spindle-pole body region in a Kar3p-dependent manner. Reciprocally, concentration of Kar3p at the spindle poles during vegetative growth requires the presence of Vik1p, but not Cik1p. Phenotypic analysis suggests that Cik1p and Vik1p are involved in different Kar3p functions. Disruption of VIK1 causes increased resistance to the microtubule depolymerizing drug benomyl and partially suppresses growth defects of cik1Delta mutants. The vik1Delta and kar3Delta mutations, but not cik1Delta, partially suppresses the temperature-sensitive growth defect of strains lacking the function of two other yeast kinesin-related proteins, Cin8p and Kip1p. Our results indicate that Kar3p forms functionally distinct complexes with Cik1p and Vik1p to participate in different microtubule-mediated events within the same cell.
Asunto(s)
Proteínas Fúngicas/metabolismo , Cinesinas/metabolismo , Proteínas de Microtúbulos , Proteínas de Saccharomyces cerevisiae , Secuencia de Aminoácidos , Secuencia de Bases , Cartilla de ADN/genética , Proteínas Fúngicas/genética , Genes Fúngicos , Factor de Apareamiento , Proteínas Asociadas a Microtúbulos/genética , Proteínas Asociadas a Microtúbulos/metabolismo , Datos de Secuencia Molecular , Mutación , Péptidos/farmacología , Fenotipo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/crecimiento & desarrollo , Saccharomyces cerevisiae/metabolismo , Homología de Secuencia de Aminoácido , Huso Acromático/metabolismoRESUMEN
Rom2p is a GDP/GTP exchange factor for Rho1p and Rho2p GTPases; Rho proteins have been implicated in control of actin cytoskeletal rearrangements. ROM2 and RHO2 were identified in a screen for high-copy number suppressors of cik1 delta, a mutant defective in microtubule-based processes in Saccharomyces cerevisiae. A Rom2p::3XHA fusion protein localizes to sites of polarized cell growth, including incipient bud sites, tips of small buds, and tips of mating projections. Disruption of ROM2 results in temperature-sensitive growth defects at 11 degrees C and 37 degrees C. rom2 delta cells exhibit morphological defects. At permissive temperatures, rom2 delta cells often form elongated buds and fail to form normal mating projections after exposure to pheromone; at the restrictive temperature, small budded cells accumulate. High-copy number plasmids containing either ROM2 or RHO2 suppress the temperature-sensitive growth defects of cik1 delta and kar3 delta strains. KAR3 encodes a kinesin-related protein that interacts with Cik1p. Furthermore, rom2 delta strains exhibit increased sensitivity to the microtubule depolymerizing drug benomyl. These results suggest a role for Rom2p in both polarized morphogenesis and functions of the microtubule cytoskeleton.
Asunto(s)
División Celular/fisiología , Citoesqueleto/fisiología , Proteínas de Unión al GTP/análisis , Proteínas de Unión al GTP/fisiología , Saccharomyces cerevisiae/química , Saccharomyces cerevisiae/fisiología , Proteínas de Unión al GTP rho , Sitios de Unión , Polaridad Celular , Microtúbulos/metabolismo , Feromonas/farmacología , Proteínas de Saccharomyces cerevisiaeRESUMEN
Burkholderia cepacia has attracted attention because of its extraordinary degradative abilities and its potential as a pathogen for plants and for humans. This bacterium was formerly considered to belong to the genus Pseudomonas in the gamma-subclass of the Proteobacteria, but recently has been assigned to the beta-subclass is based on rrn gene sequence analyses and other key phenotypic characteristics. The B. cepacia genome is comprised of multiple chromosomes and is rich in insertion sequences. These two features may have played a key role in the evolution of novel degradative functions and the unusual adaptability of this bacterium.