Search

NLP7 (NIN-LIKE-PROTEIN 7) is the major transcriptional factor responsible for the primary nitrate response (PNR), but the role of its homolog, NLP6, in nitrogen signaling and the interplay between NLP6 and NLP7 remain to be elucidated. In this study, we show that, like NLP7, nuclear localization of NLP6 via a nuclear retention mechanism is nitrate dependent, but nucleocytosolic shuttling of both NLP6 and NLP7 is independent of each other. Compared with single mutants, the nlp6nlp7 double mutant displays a synergistic growth retardation phenotype in response to nitrate. The transcriptome analysis of the PNR showed that NLP6 and NLP7 govern ∼50% of nitrate-induced genes, with cluster analysis highlighting 2 distinct patterns. In the A1 cluster, NLP7 plays the major role, whereas in the A2 cluster, NLP6 and NLP7 are partially functionally redundant. Interestingly, comparing the growth phenotype and PNR under high- and low-nitrate conditions demonstrated that NLP6 and NLP7 exert a more dominant role in the response to high nitrate. Apart from nitrate signaling, NLP6 and NLP7 also participated in high ammonium conditions. Growth phenotypes and transcriptome data revealed that NLP6 and NLP7 are completely functionally redundant and may act as repressors in response to ammonium. Other NLP family members also participated in the PNR, with NLP2 and NLP7 acting as broader regulators and NLP4, -5, -6, and -8 regulating PNR in a gene-dependent manner. Thus, our findings indicate that multiple modes of interplay exist between NLP6 and NLP7 that differ depending on nitrogen sources and gene clusters.

The cilium is an essential organelle at the surface of mammalian cells whose dysfunction causes a wide range of genetic diseases collectively called ciliopathies. The current rate at which new ciliopathy genes are identified suggests that many ciliary components remain undiscovered. We generated and rigorously analyzed genomic, proteomic, transcriptomic and evolutionary data and systematically integrated these using Bayesian statistics into a predictive score for ciliary function. This resulted in 285 candidate ciliary genes. We generated independent experimental evidence of ciliary associations for 24 out of 36 analyzed candidate proteins using multiple cell and animal model systems (mouse, zebrafish and nematode) and techniques. For example, we show that OSCP1, which has previously been implicated in two distinct non-ciliary processes, causes ciliogenic and ciliopathy-associated tissue phenotypes when depleted in zebrafish. The candidate list forms the basis of CiliaCarta, a comprehensive ciliary compendium covering 956 genes. The resource can be used to objectively prioritize candidate genes in whole exome or genome sequencing of ciliopathy patients and can be accessed at http://bioinformatics.bio.uu.nl/john/syscilia/ciliacarta/. This work was supported by the European Community’s Seventh Framework Programme [241955, 278568 to MU and KB, 602273 to RS]; the Virgo consortium, funded by the Dutch government [FES0908 to TvD, RvdL and MAH]; the Netherlands Genomics Initiative [050-060-452 to TvD, RvdL and MAH]; the Canadian Institutes of Health Research [MOP-142243, MOP-82870 and PJT-156042 to MRL]; Michael Smith Foundation for Health Research to MRL and VLJ; Kidney Research Scientist Core Education and National Training fellowship to VLJ; The Foundation Fighting Blindness [PPA-0717-0719-RAD to UW, RR, and MU]; the Dutch Kidney Foundation “KOUNCIL” consortium [CP11.18 to RHG, PLB and RR]; The Deutsche Forschungsgemeinschaft [Excellence grant CellNetworks to RBR and QL, CRC1140 “Kidney Disease – From Genes to Mechanisms” to MS, collaborative research center grant SFB-1411 KIDGEM to MS]; Metakids Foundation to RS; the National Institute for Health Research to PLB and VH-H. PLB is an NIHR Senior Investigator; Radboudumc Hypatia Tenure Track Fellowship, Radboud Universiteit excellence fellowship, ERC starting grant TREATCilia, grant agreement no. 716344 to MS; and the Netherlands Organization for Scientific Research [NWO Vici-865.12.005 to RR].

The BRAF proto-oncogene serine/threonine-protein kinase, known as BRAF, belongs to the RAF kinase family. It regulates the MAPK/ERK signalling pathway affecting several cellular processes such as growth, survival, differentiation, and cellular transformation. BRAF is mutated in ~8% of all human cancers with the V600E mutation constituting ~90% of mutations. Here, we have used quantitative mass spectrometry to map and compare phosphorylation site patterns between BRAF and BRAF V600E. We identified sites that are shared as well as several quantitative differences in phosphorylation abundance. The highest difference is phosphorylation of S614 in the activation loop which is ~5fold enhanced in BRAF V600E. Mutation of S614 increases the kinase activity of both BRAF and BRAF V600E and the transforming ability of BRAF V600E. The phosphorylation of S614 is mitogen inducible and the result of autophosphorylation. These data suggest that phosphorylation at this site is inhibitory, and part of the physiological shut-down mechanism of BRAF signalling. European Commission - Seventh Framework Programme (FP7) Science Foundation Ireland

The carboxy-terminal domain (CTD) of RNA polymerase II (Pol II) consists of heptad repeats with the consensus motif Y1-S2-P3-T4-S5-P6-S7. Dynamic phosphorylation of the CTD coordinates Pol II progression through the transcription cycle. Here, we use genetic and mass spectrometric approaches to directly detect and map phosphosites along the entire CTD. We confirm phosphorylation of CTD residues Y1, S2, T4, S5, and S7 in mammalian and yeast cells. Although specific phosphorylation signatures dominate, adjacent CTD repeats can be differently phosphorylated, leading to a high variation of coexisting phosphosites in mono- and di-heptad CTD repeats. Inhibition of CDK9 kinase specifically reduces S2 phosphorylation levels within the CTD.

Ciliopathies are Mendelian disorders caused by dysfunction of cilia, ubiquitous organelles involved in fluid propulsion (motile cilia) or signal transduction (primary cilia). Retinal dystrophy is a common phenotypic characteristic of ciliopathies since photoreceptor outer segments are specialized primary cilia. These ciliary structures heavily rely on intracellular minus-end directed transport of cargo, mediated at least in part by the cytoplasmic dynein 1 motor complex, for their formation, maintenance and function. Ninein-like protein (NINL) is known to associate with this motor complex and is an important interaction partner of the ciliopathy-associated proteins lebercilin, USH2A and CC2D2A. Here, we scrutinize the function of NINL with combined proteomic and zebrafish in vivo approaches. We identify Double Zinc Ribbon and Ankyrin Repeat domains 1 (DZANK1) as a novel interaction partner of NINL and show that loss of Ninl, Dzank1 or both synergistically leads to dysmorphic photoreceptor outer segments, accumulation of trans-Golgi-derived vesicles and mislocalization of Rhodopsin and Ush2a in zebrafish. In addition, retrograde melanosome transport is severely impaired in zebrafish lacking Ninl or Dzank1. We further demonstrate that NINL and DZANK1 are essential for intracellular dynein-based transport by associating with complementary subunits of the cytoplasmic dynein 1 motor complex, thus shedding light on the structure and stoichiometry of this important motor complex. Altogether, our results support a model in which the NINL-DZANK1 protein module is involved in the proper assembly and folding of the cytoplasmic dynein 1 motor complex in photoreceptor cells, a process essential for outer segment formation and function., Author Summary The cytoplasmic dynein 1 motor complex is known to be essential for photoreceptor outer segment formation and function. NINL, an important interaction partner of three ciliopathy-associated proteins (lebercilin, USH2A and CC2D2A), was previously shown to associate with this motor complex. In this work, we scrutinize the role of NINL using a combination of affinity proteomics and zebrafish studies, in order to gain insight into the pathogenic mechanisms underlying these three associated hereditary disorders. We identify DZANK1 as an important interaction partner of NINL and show that loss of Ninl, Dzank1, or a combination of both synergistically results in impaired transport of trans Golgi-derived vesicles and, as a consequence, defective photoreceptor outer segment formation. Using affinity proteomics, we demonstrate that NINL and DZANK1 associate with complementary subunits of the cytoplasmic dynein 1 complex. Our results support a model in which the NINL-DZANK1 protein module is essential for the proper assembly and folding of the cytoplasmic dynein 1 motor complex, shedding light on the structure and stoichiometry of this important motor complex.

Pull-downs based on tag fusion proteins as well as immunoprecipitations (IP) are widely used methods to analyze protein interactions. Selectivity and specificity of both methods are compromised by nonspecific binding to the capture agent or carrier beads thereby generating false positives. Here, we provide a method combining stable isotope labeling of amino acids in cell culture (SILAC) with affinity purification, coupled to quantitative tandem mass spectrometry. It permits the analysis of protein interactions with high sensitivity, while being able to discriminate contaminants and nonspecific binders. Besides pruning out contaminants, high-resolution MS data combined with quantitative proteomics software allow the comparative analysis of protein interaction patterns of different protein variants, for example mutated versus normal protein variant or of regulatory changes in a given protein complex due to different states of activity.

Pull-downs based on tag fusion proteins as well as immunoprecipitations (IP) are widely used methods to analyze protein interactions. Selectivity and specificity of both methods are compromised by nonspecific binding to the capture agent or carrier beads thereby generating false positives. Here, we provide a method combining stable isotope labeling of amino acids in cell culture (SILAC) with affinity purification, coupled to quantitative tandem mass spectrometry. It permits the analysis of protein interactions with high sensitivity, while being able to discriminate contaminants and nonspecific binders. Besides pruning out contaminants, high-resolution MS data combined with quantitative proteomics software allow the comparative analysis of protein interaction patterns of different protein variants, for example mutated versus normal protein variant or of regulatory changes in a given protein complex due to different states of activity.

Item does not contain fulltext Analyzing the molecular architecture of native multiprotein complexes via biochemical methods has so far been difficult and error prone. Protein complex isolation by affinity purification can define the protein repertoire of a given complex, yet, it remains difficult to gain knowledge of its substructure or modular composition. Here, we introduce SDS concentration gradient induced decomposition of protein complexes coupled to quantitative mass spectrometry and in silico elution profile distance analysis. By applying this new method to a cellular transport module, the IFT/lebercilin complex, we demonstrate its ability to determine modular composition as well as sensitively detect known and novel complex components. We show that the IFT/lebercilin complex can be separated into at least five submodules, the IFT complex A, the IFT complex B, the 14-3-3 protein complex and the CTLH complex, as well as the dynein light chain complex. Furthermore, we identify the protein TULP3 as a potential new member of the IFT complex A and showed that several proteins, classified as IFT complex B-associated, are integral parts of this complex. To further demonstrate EPASIS general applicability, we analyzed the modular substructure of two additional complexes, that of B-RAF and of 14-3-3-epsilon. The results show, that EPASIS provides a robust as well as sensitive strategy to dissect the substructure of large multiprotein complexes in a highly time- as well as cost-effective manner.

The intraflagellar transport (IFT) machinery is composed of mainly of two major components, IFT complex A and B as well as of motor proteins (kinesins and dyneins). The aim of this study was to identify comprehensively the composition of the IFT complex B as well as the structure of its functional sub-modules. We applied Strep/FLAG-tandem affinity purification (SF-TAP) and yeast-two-hybrid to identify protein complexes and protein-protein interactions within IFT complex B. By combining these methods with the biochemical separation and destabilization of the protein complex B into sub-complexes and mass spectrometric analysis, we further determined its structure. As a first step, we comprehensively identified the composition of the IFT complex B by SF-TAP using several IFT complex B proteins as baits. The sub-complex analysis by SDS-destabilization and sucrose-density gradient centrifugation revealed that this complex is composed of at least two stable sub-complexes. The analysis further revealed that these two sub-complexes are likely to be connected by two IFT complex B proteins that either are present in both sub-complexes, or are excluded from both but act as a linker. These data suggest, that the IFT complex B is not, as previously described, acting as a single stable complex with proteins associated to the core structure. The biochemical analysis of the sub-complex structure shows, that there are two sub-modules that are closely linked. It remains unclear, if these sub-complexes exert one function as a tandem, or if they can act as separated modules within cilia or possibly within other microtubular structures.

Leber Congenital Amaurosis (LCA) is one of the most common forms of congenital blindness in young children. It is the most severe retinal dystrophy, characterized by strong visual impairment or blindness within the first months after birth. Despite its genetic heterogeneity, the clinical phenotype is highly overlapping, pointing towards a common disease mechanism. To gain insights into the mechanism, we compared the interactomes of wild type and LCA causing mutants of lebercilin by quantitative mass spectrometry using SILAC followed by MaxQuant based analysis. This revealed that the link of lebercilin to the IFT complex is disrupted due to LCA-associated mutations. The interaction of the IFT proteins with lebercilin was confirmed by GST pull-down from retina, the loss of IFT proteins from the complex of mutants by western blot. While the disruption of the lebercilin-IFT interaction does not lead to disturbed ciliogenesis in both, hTERT-RPE1 cell and in the generated lebercilin knockout mice, the light dependent translocation of arrestin and transducing is clearly impaired, as well as the transport of opsins to the outer segments of photoreceptors. As a consequence this results in improper outer segment formation and finally photoreceptor degeneration. These data suggest that the interaction of lebercilin with the IFT complexes is important for ciliary transport in photoreceptors and thereby for formation and/or maintenance of outer segments. Further, our findings demonstrate that the disruption of ciliary transport to the outer segment is a cause for LCA. http://www.eye.uni-tuebingen.de/medical-proteome-center

Interest in the field of cilia biology and cilia-associated diseases – ciliopathies – has strongly increased over the last few years. Proteomic technologies, especially protein complex analysis by affinity purification-based methods, have been used to decipher various basic but also disease-associated mechanisms. This review focusses on some selected recent studies using affinity purification-based protein complex analysis, thereby exemplifying the great possibilities this technology offers.

Contains fulltext : 95818.pdf (Publisher’s version ) (Open Access) The mutations that cause Leber congenital amaurosis (LCA) lead to photoreceptor cell death at an early age, causing childhood blindness. To unravel the molecular basis of LCA, we analyzed how mutations in LCA5 affect the connectivity of the encoded protein lebercilin at the interactome level. In photoreceptors, lebercilin is uniquely localized at the cilium that bridges the inner and outer segments. Using a generally applicable affinity proteomics approach, we showed that lebercilin specifically interacted with the intraflagellar transport (IFT) machinery in HEK293T cells. This interaction disappeared when 2 human LCA-associated lebercilin mutations were introduced, implicating a specific disruption of IFT-dependent protein transport, an evolutionarily conserved basic mechanism found in all cilia. Lca5 inactivation in mice led to partial displacement of opsins and light-induced translocation of arrestin from photoreceptor outer segments. This was consistent with a defect in IFT at the connecting cilium, leading to failure of proper outer segment formation and subsequent photoreceptor degeneration. These data suggest that lebercilin functions as an integral element of selective protein transport through photoreceptor cilia and provide a molecular demonstration that disrupted IFT can lead to LCA.

Nitrate is an essential nutrient, and is involved in many adaptive responses of plants, such as localized proliferation of roots, flowering or stomatal movements. How such nitrate-specific mechanisms are regulated at the molecular level is poorly understood. Although the Arabidopsis ANR1 transcription factor appears to control stimulation of lateral root elongation in response to nitrate, no regulators of nitrate assimilation have so far been identified in higher plants. Legume-specific symbiotic nitrogen fixation is under the control of the putative transcription factor, NIN, in Lotus japonicus. Recently, the algal homologue NIT2 was found to regulate nitrate assimilation. Here we report that Arabidopsis thaliana NIN-like protein 7 (NLP7) knockout mutants constitutively show several features of nitrogen-starved plants, and that they are tolerant to drought stress. We show that nlp7 mutants are impaired in transduction of the nitrate signal, and that the NLP7 expression pattern is consistent with a function of NLP7 in the sensing of nitrogen. Translational fusions with GFP showed a nuclear localization for the NLP7 putative transcription factor. We propose NLP7 as an important element of the nitrate signal transduction pathway and as a new regulatory protein specific for nitrogen assimilation in non-nodulating plants.

Objective Mutations in different ciliopathy-associated genes often result in overlapping clinical phenotypes, which can in part be explained by disruption of overlapping functional protein modules. In this study we conducted large-scale affinity proteomics in a systems biologybased approach to boost insights into the assembly of these ciliary modules, and their connectivity in larger functional protein networks: the ciliary protein interaction landscape. This provides an important framework to deconvolute the pathways and processes that drive ciliopathies, and to understand the general importance of ciliary function for cellular homeostasis.

Recent (affinity) proteomics studies have focused on the composition and dynamics of ciliary protein interaction networks. This has unveiled important knowledge about the highly ordered, interconnected but very dynamic nature of the cilium as a molecular machine in the cell. Disruption of members of functional modules of this machine leads to overlapping phenotypes. Detailed analyses of the binding repertoire, the biochemical properties and the biological functions of such modules have yielded the identification of new ciliopathy genes as well as new insights into the pathogenic mechanisms underlying ciliopathies. To gain better insights into the molecular disease mechanisms that underlie ciliopathies and to acquire knowledge about the general importance of the cilium for cellular homeostasis, we are conducting ciliary interactome studies and will combine this information with subcellular localization data, and functional data derived from gene knockdown in ciliated cells or knockout/mutant vertebrate models. This integrated dataset enables us to generate models of interacting functional modules associated with cell signalling cascades, developmental events or specific ciliary functions such as intraflagellar transport. To date, we have performed affinity proteomics for the majority of known ciliopathy-associated proteins and many other ciliary proteins. In addition, yeast two-hybrid experiments have been performed to study the physical interaction between ciliary proteins in more detail. Our current dataset shows high interconnectivity between many of the ciliopathy-associated proteins. These may be part of functional ciliary modules as many are associated with clinically overlapping phenotypes. In addition, new members of these modules are excellent novel candidate ciliopathy proteins.

This essay was supported by a research grant from the DATAR (the French national agency for regional development) who fixed its main aim as that of feeding discussion of the future of motorway and road systems with particular reference to the innovations which are expected in the telecommunications field. The first part is devoted to a panoramic view of professional thinking about the motor car and its infrastructure between the years 2000 and 2020. The second part provides a brief "state of the art" of current telecommunications oriented road research. The third part presents three opposable scenarios based upon options for road pricing and traffic information. In the fourth, final part, we sketch some consequences of long range probable change in road supply for urban and regional "master" planning., Cette étude a été financée par la DATAR, laquelle avait pour objectif d'alimenter un débat sur l'avenir des réseaux routier et autoroutier, en mettant un accent particulier sur l'impact des innovations attendues dans le domaine des télécommunications. Le premier volet consiste en une vision panoramique des points de vue des professionnels sur l'automobile et son infrastructure à l'horizon 2000-2020. La seconde partie fournit un "état de l'art" des recherches sur les télécommunications appliquées à la route. La troisième partie détaille trois scénarios alternatifs fondés sur des options différentes de facturation de l'usage de la route et d'information sur l'état de la circulation. Dans le quatrième et dernier volet, sont abordées quelques conséquences des changements probables à long terme dans les volets routiers des documents d'urbanisme et de planification régionale., Bieber Alain, Texier Pierre-Yves, Ferry Benoît. Innovations in road systems and their anticipated impact on urban development in the years 2000-2020. In: Flux, n°17, 1994. pp. 41-53.