Showing papers on "Signal transduction published in 2012"

Inflammation in Atherosclerosis

Abstract: Experimental work has elucidated molecular and cellular pathways of inflammation that promote atherosclerosis. Unraveling the roles of cytokines as inflammatory messengers provided a mechanism whereby risk factors for atherosclerosis can alter arterial biology, and produce a systemic milieu that favors atherothrombotic events. The discovery of the immune basis of allograft arteriosclerosis demonstrated that inflammation per se can drive arterial hyperplasia, even in the absence of traditional risk factors. Inflammation regulates aspects of plaque biology that trigger the thrombotic complications of atherosclerosis. Translation of these discoveries to humans has enabled both novel mechanistic insights and practical clinical advances.

Short-Chain Fatty Acids Stimulate Glucagon-Like Peptide-1 Secretion via the G-Protein–Coupled Receptor FFAR2

Abstract: Interest in how the gut microbiome can influence the metabolic state of the host has recently heightened. One postulated link is bacterial fermentation of “indigestible” prebiotics to short-chain fatty acids (SCFAs), which in turn modulate the release of gut hormones controlling insulin release and appetite. We show here that SCFAs trigger secretion of the incretin hormone glucagon-like peptide (GLP)-1 from mixed colonic cultures in vitro. Quantitative PCR revealed enriched expression of the SCFA receptors ffar2 (grp43) and ffar3 (gpr41) in GLP-1–secreting L cells, and consistent with the reported coupling of GPR43 to Gq signaling pathways, SCFAs raised cytosolic Ca2+ in L cells in primary culture. Mice lacking ffar2 or ffar3 exhibited reduced SCFA-triggered GLP-1 secretion in vitro and in vivo and a parallel impairment of glucose tolerance. These results highlight SCFAs and their receptors as potential targets for the treatment of diabetes.

Tumour micro-environment elicits innate resistance to RAF inhibitors through HGF secretion

Abstract: Drug resistance presents a challenge to the treatment of cancer patients. Many studies have focused on cell-autonomous mechanisms of drug resistance. By contrast, we proposed that the tumour micro-environment confers innate resistance to therapy. Here we developed a co-culture system to systematically assay the ability of 23 stromal cell types to influence the innate resistance of 45 cancer cell lines to 35 anticancer drugs. We found that stroma-mediated resistance is common, particularly to targeted agents. We characterized further the stroma-mediated resistance of BRAF-mutant melanoma to RAF inhibitors because most patients with this type of cancer show some degree of innate resistance. Proteomic analysis showed that stromal cell secretion of hepatocyte growth factor (HGF) resulted in activation of the HGF receptor MET, reactivation of the mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3-OH kinase (PI(3)K)-AKT signalling pathways, and immediate resistance to RAF inhibition. Immunohistochemistry experiments confirmed stromal cell expression of HGF in patients with BRAF-mutant melanoma and showed a significant correlation between HGF expression by stromal cells and innate resistance to RAF inhibitor treatment. Dual inhibition of RAF and either HGF or MET resulted in reversal of drug resistance, suggesting RAF plus HGF or MET inhibitory combination therapy as a potential therapeutic strategy for BRAF-mutant melanoma. A similar resistance mechanism was uncovered in a subset of BRAF-mutant colorectal and glioblastoma cell lines. More generally, this study indicates that the systematic dissection of interactions between tumours and their micro-environment can uncover important mechanisms underlying drug resistance.

Autophagy modulation as a potential therapeutic target for diverse diseases

Abstract: The lysosomal degradation pathway known as autophagy has an essential homeostatic role in controlling the quality of the cytoplasm. However, this pathway has also been implicated in the pathology of an array of human disorders. Here, Rubinsztein and colleagues provide an overview of the mechanisms and regulation of autophagy, discuss the role of this pathway in disease and highlight potential strategies for therapeutic modulation.

Signaling in Innate Immunity and Inflammation

Abstract: Inflammation is triggered when innate immune cells detect infection or tissue injury. Surveillance mechanisms involve pattern recognition receptors (PRRs) on the cell surface and in the cytoplasm. Most PRRs respond to pathogen-associated molecular patterns (PAMPs) or host-derived damage-associated molecular patterns (DAMPs) by triggering activation of NF-κB, AP1, CREB, c/EBP, and IRF transcription factors. Induction of genes encoding enzymes, chemokines, cytokines, adhesion molecules, and regulators of the extracellular matrix promotes the recruitment and activation of leukocytes, which are critical for eliminating foreign particles and host debris. A subset of PRRs activates the protease caspase-1, which causes maturation of the cytokines IL1β and IL18. Cell adhesion molecules and chemokines facilitate leukocyte extravasation from the circulation to the affected site, the chemokines stimulating G-protein-coupled receptors (GPCRs). Binding initiates signals that regulate leukocyte motility and effector functions. Other triggers of inflammation include allergens, which form antibody complexes that stimulate Fc receptors on mast cells. Although the role of inflammation is to resolve infection and injury, increasing evidence indicates that chronic inflammation is a risk factor for cancer.

The complex world of WNT receptor signalling

Abstract: 30 years after the identification of WNTs, their signal transduction has become increasingly complex, with the discovery of more than 15 receptors and co-receptors in seven protein families. The recent discovery of three receptor classes for the R-spondin family of WNT agonists further adds to this complexity. What emerges is an intricate network of receptors that form higher-order ligand-receptor complexes routing downstream signalling. These are regulated both extracellularly by agonists such as R-spondin and intracellularly by post-translational modifications such as phosphorylation, proteolytic processing and endocytosis.

Functions of S100 Proteins

Abstract: The S100 protein family consists of 24 members functionally distributed into three main subgroups: those that only exert intracellular regulatory effects, those with intracellular and extracellular functions and those which mainly exert extracellular regulatory effects. S100 proteins are only expressed in vertebrates and show cell-specific expression patterns. In some instances, a particular S100 protein can be induced in pathological circumstances in a cell type that does not express it in normal physiological conditions. Within cells, S100 proteins are involved in aspects of regulation of proliferation, differentiation, apoptosis, Ca2+ homeostasis, energy metabolism, inflammation and migration/invasion through interactions with a variety of target proteins including enzymes, cytoskeletal subunits, receptors, transcription factors and nucleic acids. Some S100 proteins are secreted or released and regulate cell functions in an autocrine and paracrine manner via activation of surface receptors (e.g. the receptor for advanced glycation end-products and toll-like receptor 4), G-protein-coupled receptors, scavenger receptors, or heparan sulfate proteoglycans and N-glycans. Extracellular S100A4 and S100B also interact with epidermal growth factor and basic fibroblast growth factor, respectively, thereby enhancing the activity of the corresponding receptors. Thus, extracellular S100 proteins exert regulatory activities on monocytes/macrophages/microglia, neutrophils, lymphocytes, mast cells, articular chondrocytes, endothelial and vascular smooth muscle cells, neurons, astrocytes, Schwann cells, epithelial cells, myoblasts and cardiomyocytes, thereby participating in innate and adaptive immune responses, cell migration and chemotaxis, tissue development and repair, and leukocyte and tumor cell invasion.

Signal Transduction by Vascular Endothelial Growth Factor Receptors

Abstract: Vascular endothelial growth factors (VEGFs) are master regulators of vascular development and of blood and lymphatic vessel function during health and disease in the adult. It is therefore important to understand the mechanism of action of this family of five mammalian ligands, which act through three receptor tyrosine kinases (RTKs). In addition, coreceptors like neuropilins (NRPs) and integrins associate with the ligand/receptor signaling complex and modulate the output. Therapeutics to block several of the VEGF signaling components have been developed with the aim to halt blood vessel formation, angiogenesis, in diseases that involve tissue growth and inflammation, such as cancer. In this review, we outline the current information on VEGF signal transduction in relation to blood and lymphatic vessel biology.

PAMPs and DAMPs: Signal 0s that Spur Autophagy and Immunity

Abstract: Pathogen-associated molecular pattern molecules (PAMPs) are derived from microorganisms and recognized by pattern recognition receptor (PRR)-bearing cells of the innate immune system as well as many epithelial cells. In contrast, damage-associated molecular pattern molecules (DAMPs) are cell-derived and initiate and perpetuate immunity in response to trauma, ischemia, and tissue damage, either in the absence or presence of pathogenic infection. Most PAMPs and DAMPs serve as so-called 'Signal 0s' that bind specific receptors [Toll-like receptors, NOD-like receptors, RIG-I-like receptors, AIM2-like receptors, and the receptor for advanced glycation end products (RAGE)] to promote autophagy. Autophagy, a conserved lysosomal degradation pathway, is a cell survival mechanism invoked in response to environmental and cellular stress. Autophagy is inferred to have been present in the last common eukaryotic ancestor and only to have been lost by some obligatory intracellular parasites. As such, autophagy represents a unifying biology, subserving survival and the earliest host defense strategies, predating apoptosis, within eukaryotes. Here, we review recent advances in our understanding of autophagic molecular mechanisms and functions in emergent immunity.

STING specifies IRF3 phosphorylation by TBK1 in the cytosolic DNA signaling pathway.

Abstract: As part of the innate immune response, various pattern recognition receptors, such as Toll-like receptor 3 (TLR3) and TLR4, activate the kinase TBK1, which phosphorylates the transcription factor IRF3, leading to the production of type I interferons (IFNs). Tanaka and Chen used an in vitro reconstitution system to investigate the mechanism by which TBK1-mediated IRF3 activation occurs in response to the presence of cytosolic DNA from viruses or bacteria, a response that depends on the adaptor protein STING (see the Perspective by Bowie). Cytosolic DNA triggered the sequential recruitment of TBK1 and IRF3 to STING, which acted as a scaffold upon which TBK1 phosphorylated both STING and IRF3. Given that not all pattern recognition receptors that stimulate TBK1 lead to IRF3 activation, the authors suggest that STING specifies the activation of IRF3 by a subset of receptors that activate both TBK1 and STING—and that other adaptor proteins may fulfill similar roles in other innate immune pathways.

The impact of the unfolded protein response on human disease

Abstract: A central function of the endoplasmic reticulum (ER) is to coordinate protein biosynthetic and secretory activities in the cell. Alterations in ER homeostasis cause accumulation of misfolded/unfolded proteins in the ER. To maintain ER homeostasis, eukaryotic cells have evolved the unfolded protein response (UPR), an essential adaptive intracellular signaling pathway that responds to metabolic, oxidative stress, and inflammatory response pathways. The UPR has been implicated in a variety of diseases including metabolic disease, neurodegenerative disease, inflammatory disease, and cancer. Signaling components of the UPR are emerging as potential targets for intervention and treatment of human disease.

Programmed cell death 1 forms negative costimulatory microclusters that directly inhibit T cell receptor signaling by recruiting phosphatase SHP2.

Abstract: Programmed cell death 1 (PD-1) is a negative costimulatory receptor critical for the suppression of T cell activation in vitro and in vivo. Single cell imaging elucidated a molecular mechanism of PD-1–mediated suppression. PD-1 becomes clustered with T cell receptors (TCRs) upon binding to its ligand PD-L1 and is transiently associated with the phosphatase SHP2 (Src homology 2 domain–containing tyrosine phosphatase 2). These negative costimulatory microclusters induce the dephosphorylation of the proximal TCR signaling molecules. This results in the suppression of T cell activation and blockade of the TCR-induced stop signal. In addition to PD-1 clustering, PD-1–TCR colocalization within microclusters is required for efficient PD-1–mediated suppression. This inhibitory mechanism also functions in PD-1hi T cells generated in vivo and can be overridden by a neutralizing anti–PD-L1 antibody. Therefore, PD-1 microcluster formation is important for regulation of T cell activation.

Cellular function and molecular structure of ecto-nucleotidases

Abstract: Ecto-nucleotidases play a pivotal role in purinergic signal transmission. They hydrolyze extracellular nucleotides and thus can control their availability at purinergic P2 receptors. They generate extracellular nucleosides for cellular reuptake and salvage via nucleoside transporters of the plasma membrane. The extracellular adenosine formed acts as an agonist of purinergic P1 receptors. They also can produce and hydrolyze extracellular inorganic pyrophosphate that is of major relevance in the control of bone mineralization. This review discusses and compares four major groups of ecto-nucleotidases: the ecto-nucleoside triphosphate diphosphohydrolases, ecto-5′-nucleotidase, ecto-nucleotide pyrophosphatase/phosphodiesterases, and alkaline phosphatases. Only recently and based on crystal structures, detailed information regarding the spatial structures and catalytic mechanisms has become available for members of these four ecto-nucleotidase families. This permits detailed predictions of their catalytic mechanisms and a comparison between the individual enzyme groups. The review focuses on the principal biochemical, cell biological, catalytic, and structural properties of the enzymes and provides brief reference to tissue distribution, and physiological and pathophysiological functions.

PI3K-PKB/Akt Pathway

Abstract: Protein kinase B (PKB, or Akt) plays a role in cell metabolism, growth, proliferation, and survival. Its activation is controlled by a multi-step process that involves phosphoinositide-3-kinase (PI3K).

MAP Kinase Pathways

Abstract: MAP kinases are activated within protein kinase cascades that regulate cell proliferation, differentiation, and death. In mammals, MAP kinases are grouped into three families: ERKs, JNKs, and p38/SAPKs.

NPR3 and NPR4 are receptors for the immune signal salicylic acid in plants

Abstract: Salicylic acid (SA) is a plant immune signal produced after pathogen challenge to induce systemic acquired resistance. It is the only major plant hormone for which the receptor has not been firmly identified. Systemic acquired resistance in Arabidopsis requires the transcription cofactor nonexpresser of PR genes 1 (NPR1), the degradation of which acts as a molecular switch. Here we show that the NPR1 paralogues NPR3 and NPR4 are SA receptors that bind SA with different affinities. NPR3 and NPR4 function as adaptors of the Cullin 3 ubiquitin E3 ligase to mediate NPR1 degradation in an SA-regulated manner. Accordingly, the Arabidopsis npr3 npr4 double mutant accumulates higher levels of NPR1, and is insensitive to induction of systemic acquired resistance. Moreover, this mutant is defective in pathogen effector-triggered programmed cell death and immunity. Our study reveals the mechanism of SA perception in determining cell death and survival in response to pathogen challenge. Plant resistance to pathogen challenge is thought to be mediated through salicylic acid (SA) signalling; here NPR3 and NPR4, paralogues of the transcription cofactor NPR1, are identified as receptors of SA. Salicylic acid is the only major plant hormone for which a receptor has not been firmly identified. It is produced in plants in response to pathogen challenge, and induces systemic acquired resistance against secondary infection. This process requires the transcription cofactor NPR1, which indicated that NPR1 might be a salicylic acid receptor, but NPR1 alone does not bind to the hormone. Here, Xinnian Dong and colleagues identify the NPR1 paralogues NPR3 and NPR4 as salicylic acid receptors with different binding affinities. The authors propose a model for the regulation of NPR1 by NPR3 and NPR4 in response to different levels of salicylic acid.

Cancer Cell Metabolism: One Hallmark, Many Faces

Abstract: Cancer cells must rewire cellular metabolism to satisfy the demands of growth and proliferation. Although many of the metabolic alterations are largely similar to those in normal proliferating cells, they are aberrantly driven in cancer by a combination of genetic lesions and nongenetic factors such as the tumor microenvironment. However, a single model of altered tumor metabolism does not describe the sum of metabolic changes that can support cell growth. Instead, the diversity of such changes within the metabolic program of a cancer cell can dictate by what means proliferative rewiring is driven, and can also impart heterogeneity in the metabolic dependencies of the cell. A better understanding of this heterogeneity may enable the development and optimization of therapeutic strategies that target tumor metabolism. Significance: Altered tumor metabolism is now a generally regarded hallmark of cancer. Nevertheless, the recognition of metabolic heterogeneity in cancer is becoming clearer as a result of advancements in several tools used to interrogate metabolic rewiring and dependencies. Deciphering this context-dependent heterogeneity will supplement our current understanding of tumor metabolism and may yield promising therapeutic and diagnostic utilities. Cancer Discov; 2(10); 881–98. ©2012 AACR .

Regulation and function of mTOR signalling in T cell fate decisions

Abstract: In T cells, the kinase mTOR (mammalian target of rapamycin) integrates immune signals and metabolic cues to control T cell maintenance and activation. This Review describes the role of mTOR in determining T cell fate decisions and the implications of targeting mTOR in the treatment of disease.

Targeting the MAPK–RAS–RAF signaling pathway in cancer therapy

Abstract: Introduction: The MAPK pathway comprises several key signaling components and phosphorylation events that play a role in tumorigenesis. These activated kinases transmit extracellular signals that regulate cell growth, differentiation, proliferation, apoptosis and migration functions. Alteration of the RAS–RAF–MEK–ERK–MAPK (RAS–MAPK) pathway has been reported in human cancer as a result of abnormal activation of receptor tyrosine kinases or gain-of-function mutations mainly in the RAS or RAF genes. These pathways are considered potential therapeutic targets for cancer treatment. Recently, several small-molecule inhibitors targeting this pathway have been developed and are currently being tested in clinical trials. Areas covered: The biological role of the RAS–MAPK pathway, the consequence of its disregulation and the development of small-molecule inhibitors. The rationale for targeting the RAS–MAPK pathway and the application and the results of various inhibitory molecules as anticancer agents in clinical ...

The H19 lincRNA is a developmental reservoir of miR-675 that suppresses growth and Igf1r

Abstract: The H19 large intergenic non-coding RNA (lincRNA) is one of the most highly abundant and conserved transcripts in mammalian development, being expressed in both embryonic and extra-embryonic cell lineages, yet its physiological function is unknown. Here we show that miR-675, a microRNA (miRNA) embedded in H19's first exon, is expressed exclusively in the placenta from the gestational time point when placental growth normally ceases, and placentas that lack H19 continue to grow. Overexpression of miR-675 in a range of embryonic and extra-embryonic cell lines results in their reduced proliferation; targets of the miRNA are upregulated in the H19 null placenta, including the growth-promoting insulin-like growth factor 1 receptor (Igf1r) gene. Moreover, the excision of miR-675 from H19 is dynamically regulated by the stress-response RNA-binding protein HuR. These results suggest that H19's main physiological role is in limiting growth of the placenta before birth, by regulated processing of miR-675. The controlled release of miR-675 from H19 may also allow rapid inhibition of cell proliferation in response to cellular stress or oncogenic signals.

H2S signalling through protein sulfhydration and beyond

Abstract: Hydrogen sulfide (H(2)S) has recently emerged as a mammalian gaseous messenger molecule, akin to nitric oxide and carbon monoxide. H(2)S is predominantly formed from Cys or its derivatives by the enzymes cystathionine β-synthase and cystathionine γ-lyase. One of the mechanisms by which H(2)S signals is by sulfhydration of reactive Cys residues in target proteins. Although analogous to protein nitrosylation, sulfhydration is substantially more prevalent and usually increases the catalytic activity of targeted proteins. Physiological actions of sulfhydration include the regulation of inflammation and endoplasmic reticulum stress signalling as well as of vascular tension.

Lamin B1 loss is a senescence-associated biomarker

Abstract: Cellular senescence is a potent tumor-suppressive mechanism that arrests cell proliferation and has been linked to aging However, studies of senescence have been impeded by the lack of simple, exclusive biomarkers of the senescent state Senescent cells develop characteristic morphological changes, which include enlarged and often irregular nuclei and chromatin reorganization Because alterations to the nuclear lamina can affect both nuclear morphology and gene expression, we examined the nuclear lamina of senescent cells We show here than lamin B1 is lost from primary human and murine cell strains when they are induced to senesce by DNA damage, replicative exhaustion, or oncogene expression Lamin B1 loss did not depend on the p38 mitogen-activated protein kinase, nuclear factor-κB, ataxia telangiectasia-mutated kinase, or reactive oxygen species signaling pathways, which are positive regulators of senescent phenotypes However, activation of either the p53 or pRB tumor suppressor pathway was sufficient to induce lamin B1 loss Lamin B1 declined at the mRNA level via a decrease in mRNA stability rather than by the caspase-mediated degradation seen during apoptosis Last, lamin B1 protein and mRNA declined in mouse tissue after senescence was induced by irradiation Our findings suggest that lamin B1 loss can serve as biomarker of senescence both in culture and in vivo