Protein phosphatase 1 subunit Ppp1r15a/GADD34 regulates cytokine production in polyinosinic:polycytidylic acid-stimulated dendritic cells.

In response to inflammatory stimulation, dendritic cells (DCs) have a remarkable pattern of differentiation that exhibits specific mechanisms to control the immune response. Here we show that in response to polyriboinosinic:polyribocytidylic acid (pI:C), DCs mount a specific integrated stress response during which the transcription factor ATF4 and the growth arrest and DNA damage-inducible protein 34 (GADD34/Ppp1r15a), a phosphatase 1 (PP1) cofactor, are expressed. In agreement with increased GADD34 levels, an extensive dephosphorylation of the translation initiation factor eIF2α was observed during DC activation. Unexpectedly, although DCs display an unusual resistance to protein synthesis inhibition induced in response to cytosolic dsRNA, GADD34 expression did not have a major impact on protein synthesis. GADD34, however, was shown to be required for normal cytokine production both in vitro and in vivo. These observations have important implications in linking further pathogen detection with the integrated stress response pathways.

Inhibition of tau aggregation in a novel Caenorhabditis elegans model of tauopathy mitigates proteotoxicity.

Increased Tau protein amyloidogenicity has been causatively implicated in several neurodegenerative diseases, collectively called tauopathies. In pathological conditions, Tau becomes hyperphosphorylated and forms intracellular aggregates. The deletion of K280, which is a mutation that commonly appears in patients with frontotemporal dementia with Parkinsonism linked to chromosome 17, enhances Tau aggregation propensity (pro-aggregation). In contrast, introduction of the I277P and I308P mutations prevents ß-sheet formation and subsequent aggregation (anti-aggregation). In this study, we created a tauopathy model by expressing pro- or anti-aggregant Tau species in the nervous system of Caenorhabditis elegans. Animals expressing the highly amyloidogenic Tau species showed accelerated Tau aggregation and pathology manifested by severely impaired motility and evident neuronal dysfunction. In addition, we observed that the axonal transport of mitochondria was perturbed in these animals. Control animals expressing the anti-aggregant combination had rather mild phenotype. We subsequently tested several Tau aggregation inhibitor compounds and observed a mitigation of Tau proteotoxicity. In particular, a novel compound that crosses the blood-brain barrier of mammals proved effective in ameliorating the motility as well as delaying the accumulation of neuronal defects. Our study establishes a new C. elegans model of Tau aggregation-mediated toxicity and supports the emerging notion that inhibiting the nucleation of Tau aggregation can be neuroprotective.

Induction of GADD34 is necessary for dsRNA-dependent interferon-ß production and participates in the control of Chikungunya virus infection.

Nucleic acid sensing by cells is a key feature of antiviral responses, which generally result in type-I Interferon production and tissue protection. However, detection of double-stranded RNAs in virus-infected cells promotes two concomitant and apparently conflicting events. The dsRNA-dependent protein kinase (PKR) phosphorylates translation initiation factor 2-alpha (eIF2α) and inhibits protein synthesis, whereas cytosolic DExD/H box RNA helicases induce expression of type I-IFN and other cytokines. We demonstrate that the phosphatase-1 cofactor, growth arrest and DNA damage-inducible protein 34 (GADD34/Ppp1r15a), an important component of the unfolded protein response (UPR), is absolutely required for type I-IFN and IL-6 production by mouse embryonic fibroblasts (MEFs) in response to dsRNA. GADD34 expression in MEFs is dependent on PKR activation, linking cytosolic microbial sensing with the ATF4 branch of the UPR. The importance of this link for anti-viral immunity is underlined by the extreme susceptibility of GADD34-deficient fibroblasts and neonate mice to Chikungunya virus infection.

Inhibition of the interactions between eukaryotic initiation factors 4E and 4G impairs long-term associative memory consolidation but not reconsolidation.

Considerable evidence indicates that the general blockade of protein synthesis prevents both the initial consolidation and the postretrieval reconsolidation of long-term memories. These findings come largely from studies of drugs that block ribosomal function, so as to globally interfere with both cap-dependent and -independent forms of translation. Here we show that intra-amygdala microinfusions of 4EGI-1, a small molecule inhibitor of cap-dependent translation that selectively disrupts the interaction between eukaryotic initiation factors (eIF) 4E and 4G, attenuates fear memory consolidation but not reconsolidation. Using a combination of behavioral and biochemical techniques, we provide both in vitro and in vivo evidence that the eIF4E-eIF4G complex is more stringently required for plasticity induced by initial learning than for that triggered by reactivation of an existing memory.

SUnSET, a nonradioactive method to monitor protein synthesis.

We developed a nonradioactive fluorescence-activated cell sorting-based assay, called surface sensing of translation (SUnSET), which allows the monitoring and quantification of global protein synthesis in individual mammalian cells and in heterogeneous cell populations. We demonstrate here, using mouse dendritic and T cells as a model, that SUnSET offers a technical alternative to classical radioactive labeling methods for the study of mRNA translation and cellular activation.

Novel insights into the regulation of skeletal muscle protein synthesis as revealed by a new nonradioactive in vivo technique.

In this study, the principles of surface sensing of translation (SUnSET) were used to develop a nonradioactive method for ex vivo and in vivo measurements of protein synthesis (PS). Compared with controls, we first demonstrate excellent agreement between SUnSET and a [(3)H]phenylalanine method when detecting synergist ablation-induced increases in skeletal muscle PS ex vivo. We then show that SUnSET can detect the same synergist ablation-induced increase in PS when used in vivo (IV-SUnSET). In addition, IV-SUnSET detected food deprivation-induced decreases in PS in the heart, kidney, and skeletal muscles, with similar changes being visualized with an immunohistochemical version of IV-SUnSET (IV-IHC-SUnSET). By combining IV-IHC-SUnSET with in vivo transfection, we demonstrate that constitutively active PKB induces a robust increase in skeletal muscle PS. Furthermore, transfection with Ras homolog enriched in brain (Rheb) revealed that a PKB-independent activation of mammalian target of rapamycin is also sufficient to induce an increase in skeletal muscle PS. Finally, IV-IHC-SUnSET exposed the existence of fiber type-dependent differences in skeletal muscle PS, with PS in type 2B and 2X fibers being significantly lower than that in type 2A fibers within the same muscle. Thus, our nonradioactive method allowed us to accurately visualize and quantify PS under various ex vivo and in vivo conditions and revealed novel insights into the regulation of PS in skeletal muscle.

Genetic modification of murine dendritic cells by RNA transfection.

The ability to manipulate in vitro cultured dendritic cells (DCs) by transfection represents an attractive strategy to load these antigen-presenting cells with genetic material encoding various immunogenic epitopes. The gene transfer approach can also be applied to DCs with the aim of expressing immunologically active molecules such as cytokines, costimulatory molecules, or simply to transiently express proteins to perform cell biology studies. Available gene transfer technologies for DCs include both viral and non-viral vector-based approaches. In this chapter, we describe non-viral strategies of RNA transfection. Special emphasis is given to murine bone-marrow-derived DCs, since gene transfer to human DCs has been extensively described in the literature, especially in the context of cancer immunotherapy and other clinical applications. Methods to deliver small interfering RNA (siRNA) to DCs are described as well. Finally, the potential of exogenously delivered RNA to activate DCs is discussed and some practical advice to avoid DC activation is described.

Isotope pattern evaluation for the reduction of elemental compositions assigned to high-resolution mass spectral data from electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry.

The number of possible chemical formulae assigned to an accurate determined mass was significantly reduced by comparing spectral and theoretical isotope patterns based on mass measurement obtained with an ultrahigh-resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer (ESI-FTICR-MS) at high field intensity (7 T). Reduction is performed by rating congruency between experimental and theoretical pattern intensity and mass, and filtering out compositions with insufficient user-definable results. The methods used for isotope pattern simulation, peak searching, and comparison will be briefly described and evaluated on molecule ion signals of 25 compounds (300-1000 Da) applying a mass accuracy of +/-5 ppm, a set of eight elements with constant constraints (C0-200H0-1000N0-15O0-15S0-2Cl0-2Br0-2Ru0-1), natural isotope abundances and experimental resolution (full width at half maximum).

Phospho-proteomic analyses of B-Raf protein complexes reveal new regulatory principles.

B-Raf represents a critical physiological regulator of the Ras/RAF/MEK/ERK-pathway and a pharmacological target of growing clinical relevance, in particular in oncology. To understand how B-Raf itself is regulated, we combined mass spectrometry with genetic approaches to map its interactome in MCF-10A cells as well as in B-Raf deficient murine embryonic fibroblasts (MEFs) and B-Raf/Raf-1 double deficient DT40 lymphoma cells complemented with wildtype or mutant B-Raf expression vectors. Using a multi-protease digestion approach, we identified a novel ubiquitination site and provide a detailed B-Raf phospho-map. Importantly, we identify two evolutionary conserved phosphorylation clusters around T401 and S419 in the B-Raf hinge region. SILAC labelling and genetic/biochemical follow-up revealed that these clusters are phosphorylated in the contexts of oncogenic Ras, sorafenib induced Raf dimerization and in the background of the V600E mutation. We further show that the vemurafenib sensitive phosphorylation of the T401 cluster occurs in trans within a Raf dimer. Substitution of the Ser/Thr-residues of this cluster by alanine residues enhances the transforming potential of B-Raf, indicating that these phosphorylation sites suppress its signaling output. Moreover, several B-Raf phosphorylation sites, including T401 and S419, are somatically mutated in tumors, further illustrating the importance of phosphorylation for the regulation of this kinase.

PI3 kinase is important for Ras, MEK and Erk activation of Epo-stimulated human erythroid progenitors.

BACKGROUND: Erythropoietin is a multifunctional cytokine which regulates the number of erythrocytes circulating in mammalian blood. This is crucial in order to maintain an appropriate oxygen supply throughout the body. Stimulation of primary human erythroid progenitors (PEPs) with erythropoietin (Epo) leads to the activation of the mitogenic kinases (MEKs and Erks). How this is accomplished mechanistically remained unclear. RESULTS: Biochemical studies with human cord blood-derived PEPs now show that Ras and the class Ib enzyme of the phosphatidylinositol-3 kinase (PI3K) family, PI3K gamma, are activated in response to minimal Epo concentrations. Surprisingly, three structurally different PI3K inhibitors block Ras, MEK and Erk activation in PEPs by Epo. Furthermore, Erk activation in PEPs is insensitive to the inhibition of Raf kinases but suppressed upon PKC inhibition. In contrast, Erk activation induced by stem cell factor, which activates c-Kit in the same cells, is sensitive to Raf inhibition and insensitive to PI3K and PKC inhibitors. CONCLUSIONS: These unexpected findings contrast with previous results in human primary cells using Epo at supraphysiological concentrations and open new doors to eventually understanding how low Epo concentrations mediate the moderate proliferation of erythroid progenitors under homeostatic blood oxygen levels. They indicate that the basal activation of MEKs and Erks in PEPs by minimal concentrations of Epo does not occur through the classical cascade Shc/Grb2/Sos/Ras/Raf/MEK/Erk. Instead, MEKs and Erks are signal mediators of PI3K, probably the recently described PI3K gamma, through a Raf-independent signaling pathway which requires PKC activity. It is likely that higher concentrations of Epo that are induced by hypoxia, for example, following blood loss, lead to additional mitogenic signals which greatly accelerate erythroid progenitor proliferation.

Expression pattern and first functional characterization of riok-1 in Caenorhabditis elegans.

Rio kinases are atypical serine/threonine kinases that emerge as potential cooperation partners in Ras-driven tumors. In the current study, we performed an RNAi screen in Caenorhabditis elegans to identify suppressors of oncogenic Ras signaling. Aberrant Ras/Raf signaling in C. elegans leads to the formation of a multi-vulva (Muv) phenotype. We found that depletion of riok-1, the C. elegans orthologue of the mammalian RioK1, suppressed the Muv phenotype. By using a promoter GFP construct, we could show that riok-1 is expressed in neuronal cells, the somatic gonad, the vulva, the uterus and the spermatheca. Furthermore, we observed developmental defects in the gonad upon riok-1 knockdown in a wildtype background. Our data suggest that riok-1 is a modulator of the Ras signaling pathway, suggesting implications for novel interventions in the context of Ras-driven tumors.

Caenorhabditits elegans LRK-1 and PINK-1 act antagonistically in stress response and neurite outgrowth.

Mutations in two genes encoding the putative kinases LRRK2 and PINK1 have been associated with inherited variants of Parkinson disease. The physiological role of both proteins is not known at present, but studies in model organisms have linked their mutants to distinct aspects of mitochondrial dysfunction, increased vulnerability to oxidative and endoplasmic reticulum stress, and intracellular protein sorting. Here, we show that a mutation in the Caenorhabditits elegans homologue of the PTEN-induced kinase pink-1 gene resulted in reduced mitochondrial cristae length and increased paraquat sensitivity of the nematode. Moreover, the mutants also displayed defects in axonal outgrowth of a pair of canal-associated neurons. We demonstrate that in the absence of lrk-1, the C. elegans homologue of human LRRK2, all phenotypic aspects of pink-1 loss-of-function mutants were suppressed. Conversely, the hypersensitivity of lrk-1 mutant animals to the endoplasmic reticulum stressor tunicamycin was reduced in a pink-1 mutant background. These results provide the first evidence of an antagonistic role of PINK-1 and LRK-1. Due to the similarity of the C. elegans proteins to human LRRK2 and PINK1, we suggest a common role of both factors in cellular functions including stress response and regulation of neurite outgrowth. This study might help to link pink-1/PINK1 and lrk-1/LRRK2 function to the pathological processes resulting from Parkinson disease-related mutants in both genes, the first manifestations of which are cytoskeletal defects in affected neurons.

Ribosomal protein mRNAs are translationally-regulated during human dendritic cells activation by LPS.

BACKGROUND: Dendritic cells (DCs) are the sentinels of the mammalian immune system, characterized by a complex maturation process driven by pathogen detection. Although multiple studies have described the analysis of activated DCs by transcriptional profiling, recent findings indicate that mRNAs are also regulated at the translational level. A systematic analysis of the mRNAs being translationally regulated at various stages of DC activation was performed using translational profiling, which combines sucrose gradient fractionation of polysomal-bound mRNAs with DNA microarray analysis. RESULTS: Total and polysomal-bound mRNA populations purified from immature, 4 h and 16 h LPS-stimulated human monocyte-derived DCs were analyzed on Affymetrix microarrays U133 2.0. A group of 375 transcripts was identified as translationally regulated during DC-activation. In addition to several biochemical pathways related to immunity, the most statistically relevant biological function identified among the translationally regulated mRNAs was protein biosynthesis itself. We singled-out a cluster of 11 large ribosome proteins mRNAs, which are disengaged from polysomes at late time of maturation, suggesting the existence of a negative feedback loop regulating translation in DCs and linking ribosomal proteins to immuno-modulatory function. CONCLUSION: Our observations highlight the importance of translation regulation during the immune response, and may favor the identification of novel protein networks relevant for immunity. Our study also provides information on the potential absence of correlation between gene expression and protein production for specific mRNA molecules present in DCs.

Synthesis of new N-analogous corollosporine derivatives with antibacterial activity by laccase-catalyzed amination.

Corollosporine isolated from the marine fungus Corollospora maritima and N-analogous corollosporines are antimicrobial substances. Owing to the basic structure of the N-analogous corollosporines, they have become an attractive target for laccase-catalyzed derivatisation. In this regard we report on the straightforward laccase-catalyzed amination of dihydroxylated arenes with N-analogous corollosporines. In biological assays the obtained amination products are more active than the parent compounds.

Caenorhabditis elegans as a model system for Parkinson's disease.

Parkinson's disease (PD) is one of the most common age-related neurodegenerative diseases that is characterized by selective loss of dopaminergic neurons. Despite recent findings from mammalian model systems, molecular mechanisms of the pathophysiology are poorly understood. Given the high conservation of molecular pathways from invertebrates to mammalians, combined with technical advantages, such as high-throughput approaches, Caenorhabditis elegans represents a powerful system for the identification of factors involved in neurodegeneration. In this review we describe that C. elegans can be used to advance our understanding of the genetic mechanisms implicated in these disorders.

Components of the translational machinery are associated with juvenile glycine receptors and are redistributed to the cytoskeleton upon aging and synaptic activity.

The translation eukaryotic elongation factor 1alpha (eEF1A) is a monomeric GTPase involved in protein synthesis. In addition, this protein is thought to participate in other cellular functions such as actin bundling, cell cycle regulation, and apoptosis. Here we show that eEF1A is associated with the alpha2 subunit of the inhibitory glycine receptor in pulldown experiments with rat brain extracts. Moreover, additional proteins involved in translation like ribosomal S6 protein and p70 ribosomal S6 protein kinase as well as ERK1/2 and calcineurin were identified in the same pulldown approaches. Glycine receptor activation in spinal cord neurons cultured for 1 week resulted in an increased phosphorylation of ribosomal S6 protein. Immunocytochemistry showed that eEF1A and ribosomal S6 protein are localized in the soma, dendrites, and at synapses of cultured hippocampal and spinal cord neurons. Consistent with our biochemical data, immunoreactivities of both proteins were partially overlapping with glycine receptor immunoreactivity in cultured spinal cord and hippocampal neurons. After 5 weeks in culture, eEF1A immunoreactivity was redistributed to the cytoskeleton in about 45% of neurons. Interestingly, the degree of redistribution could be increased at earlier stages of in vitro differentiation by inhibition of either the ERK1/2 pathway or glycine receptors and simultaneous N-methyl-D-aspartate receptor activation. Our findings suggest a functional coupling of eEF1A with both inhibitory and excitatory receptors, possibly involving the ERK-signaling pathway.

Regulation of translation is required for dendritic cell function and survival during activation.

In response to inflammatory stimulation, dendritic cells (DCs) have a remarkable pattern of differentiation (maturation) that exhibits specific mechanisms to control antigen processing and presentation. Here, we show that in response to lipopolysaccharides, protein synthesis is rapidly enhanced in DCs. This enhancement occurs via a PI3K-dependent signaling pathway and is key for DC activation. In addition, we show that later on, in a manner similar to viral or apoptotic stress, DC activation leads to the phosphorylation and proteolysis of important translation initiation factors, thus inhibiting cap-dependent translation. This inhibition correlates with major changes in the origin of the peptides presented by MHC class I and the ability of mature DCs to prevent cell death. Our observations have important implications in linking translation regulation with DC function and survival during the immune response.

Carbon-oxygen bond formation by fungal laccases: cross-coupling of 2,5-dihydroxy-N-(2-hydroxyethyl)-benzamide with the solvents water, methanol, and other alcohols.

Laccase-catalyzed reactions lead to oxidation of the substrate via a cation radical, which has been described to undergo proton addition to form a quinonoid derivative or nucleophilic attack by itself producing homomolecular dimers. In this study, for the substrate 2,5-dihydroxy-N-(2-hydroxyethyl)-benzamide, we show that, besides the quinonoid form of substrate, all products formed are nonhomomolecular ones. Indeed, without addition of a reaction partner, heteromolecular products are formed from the quinonoid form of the laccase-substrate and the solvents water or methanol present in the incubation assay. Consequently, in laccase catalyzed syntheses performed in aqueous solutions or in the presence of methanol or other alcohols, undesirable heteromolecular coupling reactions between the laccase substrate and solvents must be taken into account. Additionally, it could be shown at the example of methanol and other alcohols that C-O-bound cross-coupling of dihydroxylated aromatic substances with the hydroxyl group of aliphatic alcohols can be catalyzed by fungal laccases.

The genetics of synapse formation and function in Caenorhabditis elegans.

The aim of this review is to introduce the reader to Caenorhabditis elegans as a model system, especially with respect to studies of synapse formation and function. We begin by giving a short description of the structure of the nervous system of C. elegans. As most of the findings that are reviewed here have emerged from studies of neuromuscular junctions (NMJs), two prominent NMJs of C. elegans will be outlined briefly. In addition, we summarize new findings that have added to our understanding of NMJs during the last few years.