Showing papers in "Science Signaling in 2009"
TL;DR: It is shown that endothelial cell–derived apoptotic bodies are generated during atherosclerosis and convey paracrine alarm signals to recipient vascular cells that trigger the production of CXCL12.
Abstract: Apoptosis is a pivotal process in embryogenesis and postnatal cell homeostasis and involves the shedding of membranous microvesicles termed apoptotic bodies. In response to tissue damage, the CXC chemokine CXCL12 and its receptor CXCR4 counteract apoptosis and recruit progenitor cells. Here, we show that endothelial cell-derived apoptotic bodies are generated during atherosclerosis and convey paracrine alarm signals to recipient vascular cells that trigger the production of CXCL12. CXCL12 production was mediated by microRNA-126 (miR-126), which was enriched in apoptotic bodies and repressed the function of regulator of G protein (heterotrimeric guanosine triphosphate-binding protein) signaling 16, an inhibitor of G protein-coupled receptor (GPCR) signaling. This enabled CXCR4, a GPCR, to trigger an autoregulatory feedback loop that increased the production of CXCL12. Administration of apoptotic bodies or miR-126 limited atherosclerosis, promoted the incorporation of Sca-1+ progenitor cells, and conferred features of plaque stability on different mouse models of atherosclerosis. This study highlights functions of microRNAs in health and disease that may extend to the recruitment of progenitor cells during other forms of tissue repair or homeostasis.
1,234 citations
TL;DR: Ex vivo endogenous H2S physiologically modifies cysteine residues in many proteins, including glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and actin, converting Cysteine -SH groups to -SSH groups in a process the authors call S-sulfhydration.
Abstract: Hydrogen sulfide (H2S), a messenger molecule generated by cystathionine gamma-lyase, acts as a physiologic vasorelaxant. Mechanisms whereby H2S signals have been elusive. We now show that H2S physiologically modifies cysteines in a large number of proteins by S-sulfhydration. About 10 to 25% of many liver proteins, including actin, tubulin, and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), are sulfhydrated under physiological conditions. Sulfhydration augments GAPDH activity and enhances actin polymerization. Sulfhydration thus appears to be a physiologic posttranslational modification for proteins.
1,027 citations
TL;DR: A rapid systemic signal in Arabidopsis thaliana was reported that traveled at a rate of 8.4 centimeters per minute and was dependent on the respiratory burst oxidase homolog D (RbohD) gene, which encodes a plant NADPH oxidase that generates reactive oxygen species.
Abstract: Cell-to-cell communication and long-distance signaling play a key role in the response of plants to pests, mechanical wounding, and extreme environmental conditions Here, we report on a rapid systemic signal in Arabidopsis thaliana that traveled at a rate of 84 centimeters per minute and was dependent on the respiratory burst oxidase homolog D (RbohD) gene Signal propagation was accompanied by the accumulation of reactive oxygen species (ROS) in the extracellular spaces between cells and was inhibited by the suppression of ROS accumulation at locations distant from the initiation site The rapid systemic signal was triggered by wounding, heat, cold, high-intensity light, and salinity stresses Our results reveal the profound role that ROS play in mediating rapid, long-distance, cell-to-cell propagating signals in plants
923 citations
TL;DR: CD36 binds to several major classes of ligands, including the matrix protein thrombospondin, long-chain fatty acids, and oxidized phospholipids and lipoproteins; in different contexts, it serves to regulate angiogenesis, innate immune responses, fatty acid metabolism, and sensory responses to fatty acids.
Abstract: CD36 is a multifunctional cell-surface receptor present on many cell types, including platelets, mononuclear phagocytes, and muscle, fat, and gut cells. It is conserved in mammals, and there are many invertebrate orthologs. CD36 binds to several major classes of ligands, including the matrix protein thrombospondin, long-chain fatty acids, and oxidized phospholipids and lipoproteins; in different contexts, it serves to regulate angiogenesis, innate immune responses, fatty acid metabolism, and sensory responses to fatty acids. CD36 signaling is mediated by activation of specific intracellular pathways that may include kinases of the Src family and mitogen-activated protein kinases. Because of the importance of CD36 signaling in human diseases, including atherosclerosis, thrombosis, Alzheimer’s disease, obesity, diabetes, and cancer, these signaling pathways are under intense scrutiny. This Review includes two figures and 123 citations.
903 citations
TL;DR: The findings suggest that tyrosine phosphorylation regulates PKM2 to provide a metabolic advantage to tumor cells, thereby promoting tumor growth.
Abstract: The Warburg effect describes a pro-oncogenic metabolism switch such that cancer cells take up more glucose than normal tissue and favor incomplete oxidation of glucose even in the presence of oxygen. To better understand how tyrosine kinase signaling, which is commonly increased in tumors, regulates the Warburg effect, we performed phosphoproteomic studies. We found that oncogenic forms of fibroblast growth factor receptor type 1 inhibit the pyruvate kinase M2 (PKM2) isoform by direct phosphorylation of PKM2 tyrosine residue 105 (Y(105)). This inhibits the formation of active, tetrameric PKM2 by disrupting binding of the PKM2 cofactor fructose-1,6-bisphosphate. Furthermore, we found that phosphorylation of PKM2 Y(105) is common in human cancers. The presence of a PKM2 mutant in which phenylalanine is substituted for Y(105) (Y105F) in cancer cells leads to decreased cell proliferation under hypoxic conditions, increased oxidative phosphorylation with reduced lactate production, and reduced tumor growth in xenografts in nude mice. Our findings suggest that tyrosine phosphorylation regulates PKM2 to provide a metabolic advantage to tumor cells, thereby promoting tumor growth.
690 citations
TL;DR: In old mice, rapamycin increased life span, restored the self-renewal and hematopoiesis of HSCs, and enabled effective vaccination against a lethal challenge with influenza virus.
Abstract: Age-related declines in hematopoietic stem cell (HSC) function may contribute to anemia, poor response to vaccination, and tumorigenesis. Here, we show that mammalian target of rapamycin (mTOR) activity is increased in HSCs from old mice compared to those from young mice. mTOR activation through conditional deletion of Tsc1 in the HSCs of young mice mimicked the phenotype of HSCs from aged mice in various ways. These included increased abundance of the messenger RNA encoding the CDK inhibitors p16(Ink4a), p19(Arf), and p21(Cip1); a relative decrease in lymphopoiesis; and impaired capacity to reconstitute the hematopoietic system. In old mice, rapamycin increased life span, restored the self-renewal and hematopoiesis of HSCs, and enabled effective vaccination against a lethal challenge with influenza virus. Together, our data implicate mTOR signaling in HSC aging and show the potential of mTOR inhibitors for restoring hematopoiesis in the elderly.
589 citations
TL;DR: A flurry of reports indicates that we are entering a new phase in the development of mammalian target of rapamycin (mTOR)-based therapies for oncology as mentioned in this paper, and the outlook for mTOR inhibitors as tools to study the mTOR pathway and as drugs in the clinic.
Abstract: A flurry of reports indicates that we are entering a new phase in the development of mammalian target of rapamycin (mTOR)-based therapies for oncology. Here, we summarize exciting findings regarding mTOR signaling and the outlook for mTOR inhibitors as tools to study the mTOR pathway and as drugs in the clinic.
558 citations
TL;DR: The results provide a basis for translating odorants into receptor neuron responses and for unraveling mammalian odor coding, and a model for predicting interactions between ORs and their ligands is developed.
Abstract: Deciphering olfactory encoding requires a thorough description of the ligands that activate each odorant receptor (OR). In mammalian systems, however, ligands are known for fewer than 50 of more than 1400 human and mouse ORs, greatly limiting our understanding of olfactory coding. We performed high-throughput screening of 93 odorants against 464 ORs expressed in heterologous cells and identified agonists for 52 mouse and 10 human ORs. We used the resulting interaction profiles to develop a predictive model relating physicochemical odorant properties, OR sequences, and their interactions. Our results provide a basis for translating odorants into receptor neuron responses and for unraveling mammalian odor coding.
518 citations
TL;DR: This comprehensive proteomic analysis of the substrates of a ubiquitin-like modifier (Ubl) identifies a pervasive role for SUMO proteins in the biologic response to hyperthermic stress.
Abstract: Covalent conjugation of the small ubiquitin-like modifier (SUMO) proteins to target proteins regulates many important eukaryotic cellular mechanisms. Although the molecular consequences of the conjugation of SUMO proteins are relatively well understood, little is known about the cellular signals that regulate the modification of their substrates. Here, we show that SUMO-2 and SUMO-3 are required for cells to survive heat shock. Through quantitative labeling techniques, stringent purification of SUMOylated proteins, advanced mass spectrometric technology, and novel techniques of data analysis, we quantified heat shock-induced changes in the SUMOylation state of 766 putative substrates. In response to heat shock, SUMO was polymerized into polySUMO chains and redistributed among a wide range of proteins involved in cell cycle regulation; apoptosis; the trafficking, folding, and degradation of proteins; transcription; translation; and DNA replication, recombination, and repair. This comprehensive proteomic analysis of the substrates of a ubiquitin-like modifier (Ubl) identifies a pervasive role for SUMO proteins in the biologic response to hyperthermic stress.
474 citations
TL;DR: This Review focuses on mechanisms whereby nitric oxide, carbon monoxide, and hydrogen sulfide signal by binding to metal centers in metalloproteins, such as in guanylyl cyclase, or modifying sulfhydryl groups in protein targets.
Abstract: Nitric oxide is well established as a major signaling molecule. Evidence is accumulating that carbon monoxide and hydrogen sulfide also are physiologic mediators in the cardiovascular, immune, and nervous systems. This Review focuses on mechanisms whereby they signal by binding to metal centers in metalloproteins, such as in guanylyl cyclase, or modifying sulfhydryl groups in protein targets.
411 citations
TL;DR: A methodology to isolate complexes associated with integrin adhesion receptors, which, like other receptor-associated signaling complexes, have been refractory to proteomic analysis is reported, to investigate the composition and function of adhesion complexes under different physiological conditions.
Abstract: The binding of integrin adhesion receptors to their extracellular matrix ligands controls cell morphology, movement, survival, and differentiation in various developmental, homeostatic, and disease processes. Here, we report a methodology to isolate complexes associated with integrin adhesion receptors, which, like other receptor-associated signaling complexes, have been refractory to proteomic analysis. Quantitative, comparative analyses of the proteomes of two receptor-ligand pairs, alpha(4)beta(1)-vascular cell adhesion molecule-1 and alpha(5)beta(1)-fibronectin, defined both core and receptor-specific components. Regulator of chromosome condensation-2 (RCC2) was detected in the alpha(5)beta(1)-fibronectin signaling network at an intersection between the Rac1 and adenosine 5'-diphosphate ribosylation factor 6 (Arf6) subnetworks. RCC2 knockdown enhanced fibronectin-induced activation of both Rac1 and Arf6 and accelerated cell spreading, suggesting that RCC2 limits the signaling required for membrane protrusion and delivery. Dysregulation of Rac1 and Arf6 function by RCC2 knockdown also abolished persistent migration along fibronectin fibers, indicating a functional role for RCC2 in directional cell movement. This proteomics workflow now opens the way to further dissection and systems-level analyses of adhesion signaling.
TL;DR: MM-121, a previously unidentified anticancer therapeutic designed using a systems approach, promises to benefit patients with combinatorial, ligand-induced activation of the ErbB signaling network that are not effectively treated by current therapies targeting overexpressed or mutated oncogenes.
Abstract: The signaling network downstream of the ErbB family of receptors has been extensively targeted by cancer therapeutics; however, understanding the relative importance of the different components of the ErbB network is nontrivial. To explore the optimal way to therapeutically inhibit combinatorial, ligand-induced activation of the ErbB–phosphatidylinositol 3-kinase (PI3K) axis, we built a computational model of the ErbB signaling network that describes the most effective ErbB ligands, as well as known and previously unidentified ErbB inhibitors. Sensitivity analysis identified ErbB3 as the key node in response to ligands that can bind either ErbB3 or EGFR (epidermal growth factor receptor). We describe MM-121, a human monoclonal antibody that halts the growth of tumor xenografts in mice and, consistent with model-simulated inhibitor data, potently inhibits ErbB3 phosphorylation in a manner distinct from that of other ErbB-targeted therapies. MM-121, a previously unidentified anticancer therapeutic designed using a systems approach, promises to benefit patients with combinatorial, ligand-induced activation of the ErbB signaling network that are not effectively treated by current therapies targeting overexpressed or mutated oncogenes.
TL;DR: This analysis suggests a role for phosphorylated serine and threonine residues in modulating protein-protein interactions between many proteins involved in T cell responses and proposes that modulation of PPIs by stimulus-dependent changes in S-T phosphorylation state is a widespread phenomenon applicable to many other signaling systems.
Abstract: Protein phosphorylation events during T cell receptor (TCR) signaling control the formation of complexes among proteins proximal to the TCR, the activation of kinase cascades, and the activation of transcription factors; however, the mode and extent of the influence of phosphorylation in coordinating the diverse phenomena associated with T cell activation are unclear. Therefore, we used the human Jurkat T cell leukemia cell line as a model system and performed large-scale quantitative phosphoproteomic analyses of TCR signaling. We identified 10,665 unique phosphorylation sites, of which 696 showed TCR-responsive changes. In addition, we analyzed broad trends in phosphorylation data sets to uncover underlying mechanisms associated with T cell activation. We found that, upon stimulation of the TCR, phosphorylation events extensively targeted protein modules involved in all of the salient phenomena associated with T cell activation: patterning of surface proteins, endocytosis of the TCR, formation of the F-actin cup, inside-out activation of integrins, polarization of microtubules, production of cytokines, and alternative splicing of messenger RNA. Further, case-by-case analysis of TCR-responsive phosphorylation sites on proteins belonging to relevant functional modules together with network analysis allowed us to deduce that serine-threonine (S-T) phosphorylation modulated protein-protein interactions (PPIs) in a system-wide fashion. We also provide experimental support for this inference by showing that phosphorylation of tubulin on six distinct serine residues abrogated PPIs during the assembly of microtubules. We propose that modulation of PPIs by stimulus-dependent changes in S-T phosphorylation state is a widespread phenomenon applicable to many other signaling systems.
TL;DR: Two studies now point to roles for ATP in the immune system: providing a costimulatory signal to T cells and driving the differentiation of intestinal T helper 17 (TH17) cells.
Abstract: Extracellular adenosine 5′-triphosphate (eATP) is ubiquitously used for cell-to-cell communication. The low concentration of eATP ([eATP]) that exists in a “halo” surrounding resting cells signals the presence of neighboring living cells. Transient increases in [eATP] are used for basic physiological signaling, namely, in the nervous and vascular systems. Larger increases in [eATP] that are associated with cell death serve as a key “danger” signal in inflammatory processes. Two studies now point to roles for ATP in the immune system: providing a costimulatory signal to T cells and driving the differentiation of intestinal T helper 17 (T H 17) cells.
TL;DR: This Review examines the mechanisms by which EGFR contributes to oncogenic transformation in an aggressive form of brain tumor (glioblastoma) and discusses the limitations of current treatment strategies and offers an outlook on how these therapies may be improved through the use of systems biology.
Abstract: The epidermal growth factor receptor (EGFR) is a primary contributor to glioblastoma (GBM) initiation and progression. Here, we examine how EGFR and key downstream signaling networks contribute to the hallmark characteristics of GBM such as rapid cancer cell proliferation and diffused invasion. Additionally, we discuss current therapeutic options for GBM patients and elaborate on the mechanisms through which EGFR promotes chemoresistance. We conclude by offering a perspective on how the potential of integrative systems biology may be harnessed to develop safe and effective treatment strategies for this disease.
TL;DR: Results identify a previously undescribed EGFR-mediated prosurvival metabolic pathway and suggest new therapeutic approaches to treating EG FR-activated glioblastomas.
Abstract: Glioblastoma, the most common malignant brain tumor, is among the most lethal and difficult cancers to treat. Although epidermal growth factor receptor (EGFR) mutations are frequent in glioblastoma, their clinical relevance is poorly understood. Studies of tumors from patients treated with the EGFR inhibitor lapatinib revealed that EGFR induces the cleavage and nuclear translocation of the master transcriptional regulator of fatty acid synthesis, sterol regulatory element–binding protein 1 (SREBP-1). This response was mediated by Akt; however, clinical data from rapamycin-treated patients showed that SREBP-1 activation was independent of the mammalian target of rapamycin complex 1, possibly explaining rapamycin’s poor efficacy in the treatment of such tumors. Glioblastomas without constitutively active EGFR signaling were resistant to inhibition of fatty acid synthesis, whereas introduction of a constitutively active mutant form of EGFR, EGFRvIII, sensitized tumor xenografts in mice to cell death, which was augmented by the hydroxymethylglutaryl coenzyme A reductase inhibitor atorvastatin. These results identify a previously undescribed EGFR-mediated prosurvival metabolic pathway and suggest new therapeutic approaches to treating EGFR-activated glioblastomas.
TL;DR: It is reported that TRPM2, in addition to its role as a plasma membrane channel, also functions as a Ca2+-release channel activated by intracellular ADPR in a lysosomal compartment, which is critically linked to hydrogen peroxide–induced β cell death.
Abstract: TRPM2 is a Ca 2+ -permeable cation channel that is specifically activated by adenosine diphosphoribose (ADPR). Channel activation in the plasma membrane leads to Ca 2+ influx and has been linked to apoptotic mechanisms. The primary agonist, ADPR, is produced both extra- and intracellularly and causes increases in intracellular calcium concentration ([Ca 2+ ] i ), but the mechanisms involved are not understood. Using short interfering RNA and a knockout mouse, we report that TRPM2, in addition to its role as a plasma membrane channel, also functions as a Ca 2+ -release channel activated by intracellular ADPR in a lysosomal compartment. We show that both functions of TRPM2 are critically linked to hydrogen peroxide–induced β cell death. Additionally, extracellular ADPR production by the ectoenzyme CD38 from its substrates NAD + (nicotinamide adenine dinucleotide) or cADPR causes IP 3 -dependent Ca 2+ release via P2Y and adenosine receptors. Thus, ADPR and TRPM2 represent multimodal signaling elements regulating Ca 2+ mobilization in β cells through membrane depolarization, Ca 2+ influx, and release of Ca 2+ from intracellular stores.
TL;DR: The possibility that concurrent targeting of VEGF-A and PlGF might improve the clinical effectiveness of antiangiogenic therapy in the treatment of malignant and nonmalignant diseases is examined.
Abstract: Vascular endothelial growth factor-A (VEGF-A) is a key target for new antiangiogenic drugs for the treatment of both malignant and nonmalignant human diseases. Vascular effects of VEGF family members are mainly mediated by VEGF receptor 2 (VEGFR2). Conversely, the function and signaling of VEGFR1, which is present on endothelial and nonendothelial cells, are poorly understood. Intriguingly, two of five members in the VEGF family--VEGF-B and placental growth factor (PlGF)--are exclusive ligands for VEGFR1 and do not interact with the other VEGFRs, VEGFR2 and VEGFR3. These VEGFR1-specific ligands may be important therapeutic targets for the treatment of cancer. This Review discusses the distinctive roles of VEGFR1 and its ligands PlGF and VEGF-B in the mediation of angiogenic signaling and considers the therapeutic potential of targeting these particular vascular factors.
TL;DR: It is shown that administration of l-DOPA in a mouse model of Parkinsonism led to dopamine D1 receptor–mediated activation of the mammalian target of rapamycin-sensitive mTOR complex 1 (mTORC1), which is implicated in several forms of synaptic plasticity.
Abstract: Parkinson’s disease (PD), a disorder caused by degeneration of the dopaminergic input to the basal ganglia, is commonly treated with L-DOPA. Use of this drug, however, is severely limited by motor side effects, or dyskinesia. We show that administration of L-DOPA in a mouse model of Parkinsonism led to dopamine D1 receptor–mediated activation of the mammalian target of rapamycin (mTOR) complex 1 (mTORC1), which is implicated in several forms of synaptic plasticity. This response occurred selectively in the GABAergic medium spiny neurons that project directly from the striatum to the output structures of the basal ganglia. The L-DOPA–mediated activation of mTORC1 persisted in mice that developed dyskinesia. Moreover, the mTORC1 inhibitor rapamycin prevented the development of dyskinesia without affecting the therapeutic efficacy of L-DOPA. Thus, the mTORC1 signaling cascade represents a promising target for the design of anti-Parkinsonian therapies.
TL;DR: It is shown that STIM2, but not STIM1, is essential for CCE and ischemia-induced cytosolic Ca2+ accumulation in neurons, which implicate CCE in ischemic neuronal cell death and establishSTIM2 as a critical mediator of this process.
Abstract: Excessive cytosolic calcium ion (Ca 2+ ) accumulation during cerebral ischemia triggers neuronal cell death, but the underlying mechanisms are poorly understood. Capacitive Ca 2+ entry (CCE) is a process whereby depletion of intracellular Ca 2+ stores causes the activation of plasma membrane Ca 2+ channels. In nonexcitable cells, CCE is controlled by the endoplasmic reticulum (ER)–resident Ca 2+ sensor STIM1, whereas the closely related protein STIM2 has been proposed to regulate basal cytosolic and ER Ca 2+ concentrations and make only a minor contribution to CCE. Here, we show that STIM2, but not STIM1, is essential for CCE and ischemia-induced cytosolic Ca 2+ accumulation in neurons. Neurons from Stim2 −/− mice showed significantly increased survival under hypoxic conditions compared to neurons from wild-type controls both in culture and in acute hippocampal slice preparations. In vivo, Stim2 −/− mice were markedly protected from neurological damage in a model of focal cerebral ischemia. These results implicate CCE in ischemic neuronal cell death and establish STIM2 as a critical mediator of this process.
TL;DR: It is shown that the kinesin protein Kif7 is a critical regulator of Hh signaling in mice, implying a greater commonality between the Drosophila and mammalian system than the prevailing view suggests.
Abstract: From insects to humans, the Hedgehog (Hh) signaling pathway has conserved roles in embryonic development and tissue homeostasis. However, it has been suggested that the lack of mammalian equivalents of Costal2 (Cos2) contributes to a divergence between the mechanism of Drosophila and mammalian Hh signal transduction. Here, we challenge this view by showing that the kinesin protein Kif7 is a critical regulator of Hh signaling in mice. Similar to Cos2, Kif7 physically interacted with Gli transcription factors and controlled their proteolysis and stability, and acted both positively and negatively in Hh signaling. Thus, Kif7 is a missing component of the mammalian Hh signaling machinery, implying a greater commonality between the Drosophila and mammalian system than the prevailing view suggests.
TL;DR: It is shown that protein kinase CIPK15 plays a key role in O2-deficiency tolerance in rice, which regulates the plant global energy and stress sensor SnRK1A (Snf1-relatedprotein kinase 1) and links O2 to sugar signaling to regulate sugar and energy production and to enable rice growth under floodwater.
Abstract: Flooding is a widespread natural disaster that leads to oxygen (O(2)) and energy deficiency in terrestrial plants, thereby reducing their productivity. Rice is unusually tolerant to flooding, but the underlying mechanism for this tolerance has remained elusive. Here, we show that protein kinase CIPK15 [calcineurin B-like (CBL)-interacting protein kinase] plays a key role in O(2)-deficiency tolerance in rice. CIPK15 regulates the plant global energy and stress sensor SnRK1A (Snf1-related protein kinase 1) and links O(2)-deficiency signals to the SnRK1-dependent sugar-sensing cascade to regulate sugar and energy production and to enable rice growth under floodwater. Our studies contribute to understanding how rice grows under the conditions of O(2) deficiency necessary for growing rice in irrigated lowlands.
TL;DR: It is proposed that the mechanical tissue deformation that occurs during the Snail-dependent stochastic phase is necessary for the Fog-dependent signaling that mediates the second collective constriction wave.
Abstract: During Drosophila gastrulation, two waves of constriction occur in the apical ventral cells, leading to mesoderm invagination. The first constriction wave is a stochastic process mediated by the constriction of 40% of randomly positioned mesodermal cells and is controlled by the transcription factor Snail. The second constriction wave immediately follows and involves the other 60% of the mesodermal cells. The second wave is controlled by the transcription factor Twist and requires the secreted protein Fog. Complete mesoderm invagination requires redistribution of the motor protein Myosin II to the apical side of the constricting cells. We show that apical redistribution of Myosin II and mesoderm invagination, both of which are impaired in snail homozygous mutants that are defective in both constriction waves, are rescued by local mechanical deformation of the mesoderm with a micromanipulated needle. Mechanical deformation appears to promote Fog-dependent signaling by inhibiting Fog endocytosis. We propose that the mechanical tissue deformation that occurs during the Snail-dependent stochastic phase is necessary for the Fog-dependent signaling that mediates the second collective constriction wave.
TL;DR: It is shown that reactive oxygen species (ROS) generated by the NADPH (reduced form of nicotinamide adenine dinucleotide phosphate) oxidase (Nox) system are necessary for invadopodia formation and function and proposed that Tks5 facilitates the production of ROS necessary for invaders formation, and that in turn ROS modulate Tk5 tyrosine phosphorylation in a positive feedback loop.
Abstract: Invadopodia are actin-rich membrane protrusions of cancer cells that facilitate pericellular proteolysis and invasive behavior. We show here that reactive oxygen species (ROS) generated by the NADPH (reduced form of nicotinamide adenine dinucleotide phosphate) oxidase (Nox) system are necessary for invadopodia formation and function. Knockdown of the invadopodia protein Tks5 [tyrosine kinase substrate with five Src homology 3 (SH3) domains], which is structurally related to the Nox component p47 phox , reduces total ROS abundance in cancer cells. Furthermore, Tks5 and p22 phox can associate with each other, suggesting that Tks5 is part of the Nox complex. Tyrosine phosphorylation of Tks5 and Tks4, but not other Src substrates, is reduced by Nox inhibition. We propose that Tks5 facilitates the production of ROS necessary for invadopodia formation, and that in turn ROS modulate Tks5 tyrosine phosphorylation in a positive feedback loop.
TL;DR: Mitofusin 2 (Mfn2), a mediator of mitochondrial fusion, interacts with MAVS to modulate antiviral immunity and suggests that Mfn2 acts as an inhibitor of antiviral signaling, a function that may be distinct from its role in mitochondrial dynamics.
Abstract: The innate immune response to viral infection involves the activation of multiple signaling steps that culminate in the production of type I interferons (IFNs). Mitochondrial antiviral signaling (MAVS), a mitochondrial outer membrane adaptor protein, plays an important role in this process. Here, we report that mitofusin 2 (Mfn2), a mediator of mitochondrial fusion, interacts with MAVS to modulate antiviral immunity. Overexpression of Mfn2 resulted in the inhibition of retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA-5), two cytosolic sensors of viral RNA, as well as of MAVS-mediated activation of the transcription factors interferon regulatory factor 3 (IRF-3) and nuclear factor kappaB (NF-kappaB). In contrast, loss of endogenous Mfn2 enhanced virus-induced production of IFN-beta and thereby decreased viral replication. Structure-function analysis revealed that Mfn2 interacted with the carboxyl-terminal region of MAVS through a heptad repeat region, providing a structural perspective on the regulation of the mitochondrial antiviral response. Our results suggest that Mfn2 acts as an inhibitor of antiviral signaling, a function that may be distinct from its role in mitochondrial dynamics.
TL;DR: The complementary inhibitory mechanism in which mTORC1 phosphorylates the autophagy regulatory complex containing unc-51-like kinase 1 (ULK1), the mammalian Atg13 protein, and focal adhesion kinase interacting protein of 200 kD (FIP200) has been elucidated.
Abstract: High nutrient availability stimulates the mammalian target of rapamycin complex 1 (mTORC1) to coordinately activate anabolic processes, such as protein synthesis, while inhibiting the cellular catabolism of autophagy. Positive regulation of protein synthesis through the mTORC1 substrates p70 ribosomal S6 kinase (p70S6K) and eukaryotic initiation factor 4E binding protein 1 (4E-BP1) has been well characterized. The complementary inhibitory mechanism in which mTORC1 phosphorylates the autophagy regulatory complex containing unc-51-like kinase 1 (ULK1), the mammalian Atg13 protein, and focal adhesion kinase interacting protein of 200 kD (FIP200) has also been elucidated.
TL;DR: Induction of EMT is controlled by microRNAs whose abundance depends on the balance between Akt1 and Akt2 rather than on overall Akt signaling per se, which is consistent with the hypothesis that in many cases breast cancer metastasis may be under the control of the Akt–miR-200–E-cadherin axis.
Abstract: Although Akt is known to play a role in human cancer, the relative contribution of its three isoforms to oncogenesis remains to be determined. We expressed each isoform individually in an Akt1(-/-)/Akt2(-/-)/Akt3(-/-) cell line. MicroRNA profiling of growth factor-stimulated cells revealed unique microRNA signatures for cells with each isoform. Among the differentially regulated microRNAs, the abundance of the miR-200 family was decreased in cells bearing Akt2. Knockdown of Akt1 in transforming growth factor-beta (TGFbeta)-treated MCF10A cells also decreased the abundance of miR-200; however, knockdown of Akt2, or of both Akt1 and Akt2, did not. Furthermore, Akt1 knockdown in MCF10A cells promoted TGFbeta-induced epithelial-mesenchymal transition (EMT) and a stem cell-like phenotype. Carcinomas developing in MMTV-cErbB2/Akt1(-/-) mice showed increased invasiveness because of miR-200 down-regulation. Finally, the ratio of Akt1 to Akt2 and the abundance of miR-200 and of the messenger RNA encoding E-cadherin in a set of primary and metastatic human breast cancers were consistent with the hypothesis that in many cases breast cancer metastasis may be under the control of the Akt-miR-200-E-cadherin axis. We conclude that induction of EMT is controlled by microRNAs whose abundance depends on the balance between Akt1 and Akt2 rather than on the overall activity of Akt.
TL;DR: A technique is presented, based on the Steiner tree problem, that uses previously reported protein-protein and protein-DNA interactions to determine how these hits are organized into functionally coherent pathways, revealing many components of the cellular response that are not readily apparent in the original data.
Abstract: Cellular signaling and regulatory networks underlie fundamental biological processes such as growth, differentiation, and response to the environment. Although there are now various high-throughput methods for studying these processes, knowledge of them remains fragmentary. Typically, the majority of hits identified by transcriptional, proteomic, and genetic assays lie outside of the expected pathways. These unexpected components of the cellular response are often the most interesting, because they can provide new insights into biological processes and potentially reveal new therapeutic approaches. However, they are also the most difficult to interpret. We present a technique, based on the Steiner tree problem, that uses previously reported protein-protein and protein-DNA interactions to determine how these hits are organized into functionally coherent pathways, revealing many components of the cellular response that are not readily apparent in the original data. Applied simultaneously to phosphoproteomic and transcriptional data for the yeast pheromone response, it identifies changes in diverse cellular processes that extend far beyond the expected pathways.
TL;DR: Advances in mass spectrometry and affinity-chemistry strategies have improved the detection of electrophile-induced protein modifications both in vitro and in vivo and have revealed a high degree of amino acid and protein selectivity of Electrophilic PTM.
Abstract: Chemically reactive by-products of cellular redox reactions are frequently thought to induce deleterious actions. However, not all redox-mediated modifications are harmful; some have important physiological consequences. Some posttranslational protein modifications that are induced by electrophilic products of redox reactions may modulate physiological signaling pathways that have evolved to act as sensors of oxidative conditions. Additional insight into specific biological targets of electrophiles and the regulation of their reactions can reveal new therapeutic strategies for treating pain, acute and chronic inflammatory injury, and metabolic diseases. This Review with 4 figures, 2 tables, and 148 references describes biologically important electrophiles, methods for detecting proteins modified by these electrophilic compounds and the cellular consequences of this type of posttranslational modification.
TL;DR: It is proposed that Act1 mediates IL- 17–induced signaling pathways through its E3 ubiquitin ligase activity and that TRAF6 is a critical substrate of Act1, which indicates the importance of protein ubiquitination in the IL-17–dependent inflammatory response.
Abstract: Interleukin-17 (IL-17), a proinflammatory cytokine mainly produced by cells of the T helper 17 (T(H)17) lineage, is required for host defense against bacterial and fungal infections and plays a critical role in the pathogenesis of inflammatory and autoimmune diseases. Act1 is an essential adaptor molecule in IL-17-mediated signaling and is recruited to the IL-17 receptor (IL-17R) upon IL-17 stimulation through an interaction between its SEFIR domain and that of the IL-17R. Here, we report that Act1 is a U-box E3 ubiquitin ligase and that its activity is essential for IL-17-mediated signaling pathways. Through the use of the Ubc13-Uev1A E2 complex, Act1 mediated the lysine-63-linked ubiquitination of tumor necrosis factor receptor-associated factor 6 (TRAF6), a component of IL-17-mediated signaling. Deletion and point mutations of the Act1 U-box abolished Act1-mediated ubiquitination of TRAF6 and impaired the ability of Act1 to restore IL-17-dependent signaling and expression of target genes in Act1(-/-) mouse embryonic fibroblasts. We also showed that the lysine-124 residue of TRAF6 was critical for efficient Act1-mediated ubiquitination of TRAF6 and for the ability of TRAF6 to mediate IL-17-induced activation of nuclear factor kappaB. Thus, we propose that Act1 mediates IL-17-induced signaling pathways through its E3 ubiquitin ligase activity and that TRAF6 is a critical substrate of Act1, which indicates the importance of protein ubiquitination in the IL-17-dependent inflammatory response.