Quand un corpus rencontre un adjectif du troisième type. Etude distributionnelle de prochain

L’adjectif prochain fait partie de ces adjectifs que Schnedecker (2002a) nomme « les adjectifs du troisième type ». Ni qualificatifs ni relationnels, souvent marginalisés, ces derniers possèdent des caractéristiques qui n’ont fait l’objet d’aucune étude systématique sur corpus. Nous nous proposons de combler cette lacune en réalisant une analyse distributionnelle de prochain dans différents genres textuels (oraux et écrits). Dans un premier temps, l’analyse portera sur les phénomènes de sélection lexicale qui apparaissent dans les emplois attestés et qui semblent fortement conditionnés par la position de l’adjectif par rapport à son nom recteur. Nous verrons également que le nombre du nom recteur impose des contraintes d’emploi qui ont été peu détaillées dans les travaux antérieurs. Dans un deuxième temps, nous nous intéresserons aux noms recteurs, tels fois, saison et siècle, dont le fonctionnement diffère. L’étude sera l’occasion de comparer la description sur corpus avec celle proposée par Berthonneau (2002), basée sur une analyse introspective. La comparaison permettra de mettre en évidence les spécificités et les limites des deux approches. Une démarche similaire sera développée à partir des entrées de quelques dictionnaires. Au-delà de l’analyse de détail, l’article a pour objectif de présenter les bases descriptives permettant de problématiser le statut catégoriel de prochain.When a corpus meets an adjective of the Third Kind. Distributional analysis of ‘prochain’ in FrenchProchain is one of those adjectives that Schnedecker (2002a) called « adjectifs du troisième type ». Neither qualifiers nor relational adjectives, often marginalized, they have characteristics that have been no systematic study on corpus. We propose to bridge this gap by an analysis of the prochain distribution in various genres (spoken and written French). Firstly, the analysis will focus on the lexical selection phenomena that appear in corpora. It seems strongly influenced by the position of the adjective from his head noun. We will also see that the grammatical number of head noun imposes constraints that were not detailed in previous work. Secondly, our study will focus on “special” head nouns like fois,saison and siècle. In addition, we will compare our description with Berthonneau (2002), mainly based on introspection, which allows us to highlight the features and limitations of both approaches. We will do the same with some dictionary entries. Beyond the precise analysis, the paper aims to present the descriptive bases that enable the problematization of the categorial status of prochain

The Ins and Outs of HIV-1 Tat

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HIV-1 Tat is unconventionally secreted through the plasma membrane.

International audienceThe Tat protein is required for efficient HIV-1 (human immunodeficiency virus type 1) transcription. Moreover, Tat is secreted by infected cells, and circulating Tat can affect several cell types, thereby contributing to HIV-1 pathogenesis. We monitored Tat secretion by transfected CD4+ T-cells. A Tat chimaera carrying an N-glycosylation site did not become glycosylated when expressed in cells, while the chimaera was glycosylated when mechanically introduced into purified microsomes. These data indicate that secreted Tat does not transit through the endoplasmic reticulum. The use of pharmacological inhibitors indicated that the Tat secretion pathway is unusual compared with previously identified unconventional secretion routes and does not involve intracellular organelles. Moreover, cell incubation at 16 degrees C inhibited Tat secretion and caused its accumulation at the plasma membrane, suggesting that secretion takes place at this level

Detecting HIV-1 Tat in Cell Culture Supernatants by ELISA or Western Blot

International audienceHIV-1 Tat is efficiently secreted by HIV-1-infected or Tat-transfected cells. Accordingly, Tat concentrations in the nanomolar range have been measured in the sera of HIV-1-infected patients, and this protein acts as a viral toxin on bystander cells. Nevertheless, assaying Tat concentration in media or sera is not that straightforward because extracellular Tat is unstable and particularly sensitive to oxidation. Moreover, most anti-Tat antibodies display limited affinity. Here, we describe methods to quantify extracellular Tat using a sandwich ELISA or Western blotting when Tat is secreted by suspension or adherent cells, respectively. In both cases it is important to capture exported Tat using antibodies before any Tat oxidation occurs; otherwise it will become denatured and unreactive toward antibodies

Neuronal retrograde transport of Borna disease virus occurs in signalling endosomes

International audienceLong-range axonal retrograde transport is a key mechanism for the cellular dissemination of neuroinvasive viruses, such as Borna disease virus (BDV), for which entry and egress sites are usually distant from the nucleus, where viral replication takes place. Although BDV is known to disseminate very efficiently in neurons, both in vivo and in primary cultures, the modalities of its axonal transport are still poorly characterized. In this work, we combined different methodological approaches, such as confocal microscopy and biochemical purification of endosomes, to study BDV retrograde transport. We demonstrate that BDV ribonucleoparticles (composed of the viral genomic RNA, nucleoprotein and phosphoprotein), as well as the matrix protein, are transported towards the nucleus into endocytic carriers. These specialized organelles, called signalling endosomes, are notably used for the retrograde transport of neurotrophins and activated growth factor receptors. Signalling endosomes have a neutral luminal pH and thereby offer protection against degradation during long-range transport. This particularity could allow the viral particles to be delivered intact to the cell body of neurons, avoiding their premature release in the cytoplasm

HIV-1 Tat inhibits phagocytosis by preventing the recruitment of Cdc42 to the phagocytic cup

International audienceMost macrophages remain uninfected in HIV-1-infected patients. Nevertheless, the phagocytic capacity of phagocytes from these patients is impaired, favouring the multiplication of opportunistic pathogens. The basis for this phagocytic defect is not known. HIV-1 Tat protein is efficiently secreted by infected cells. Secreted Tat can enter uninfected cells and reach their cytosol. Here we found that extracellular Tat, at the subnanomolar concentration present in the sera of HIV-1-infected patients, inhibits the phagocytosis of Mycobacterium avium or opsonized Toxoplasma gondii by human primary macrophages. This inhibition results from a defect in mannose- and Fcγ-receptor-mediated phagocytosis, respectively. Inhibition relies on the interaction of Tat with phosphatidylinositol (4,5)bisphosphate that interferes with the recruitment of Cdc42 to the phagocytic cup, thereby preventing Cdc42 activation and pseudopod elongation. Tat also inhibits FcγR-mediated phagocytosis in neutrophils and monocytes. This study provides a molecular basis for the phagocytic defects observed in uninfected phagocytes following HIV-1 infection

Densovirus Crosses the Insect Midgut by Transcytosis and Disturbs the Epithelial Barrier Function

Densoviruses are parvoviruses that can be lethal for insects of different orders at larval stages. Although the horizontal transmission mechanisms are poorly known, densoviral pathogenesis usually starts with the ingestion of contaminated food by the host. Depending on the virus, this leads to replication restricted to the midgut or excluding it. In both cases the success of infection depends on the virus capacity to enter the intestinal epithelium. Using the Junonia coenia densovirus (JcDNV) as the prototype virus and the lepidopteran host Spodoptera frugiperda as an interaction model, we focused on the early mechanisms of infection during which JcDNV crosses the intestinal epithelium to reach and replicate in underlying target tissues. We studied the kinetics of interaction of JcDNV with the midgut epithelium and the transport mechanisms involved. Using several approaches, in vivo, ex vivo, and in vitro, at molecular and cellular levels, we show that JcDNV is specifically internalized by endocytosis in absorptive cells and then crosses the epithelium by transcytosis. As a consequence, viral entry disturbs the midgut function. Finally, we showed that four mutations on the capsid of JcDNV affect specific recognition by the epithelial cells but not their binding

Phosphatidylinositol-(4,5)-bisphosphate enables efficient secretion of HIV-1 Tat by infected T-cells

International audienceHuman immunodeficiency virus type 1 (HIV-1) transcription relies on its transactivating Tat protein. Although devoid of a signal sequence, Tat is released by infected cells and secreted Tat can affect uninfected cells, thereby contributing to HIV-1 pathogenesis. The mechanism and the efficiency of Tat export remained to be documented. Here, we show that, in HIV-1-infected primary CD4(+) T-cells that are the main targets of the virus, Tat accumulates at the plasma membrane because of its specific binding to phosphatidylinositol-4,5-bisphosphate (PI(4,5)P(2)). This interaction is driven by a specific motif of the Tat basic domain that recognizes a single PI(4,5)P(2) molecule and is stabilized by membrane insertion of Tat tryptophan side chain. This original recognition mechanism enables binding to membrane-embedded PI(4,5)P(2) only, but with an unusually high affinity that allows Tat to perturb the PI(4,5)P(2)-mediated recruitment of cellular proteins. Tat-PI(4,5)P(2) interaction is strictly required for Tat secretion, a process that is very efficient, as approximately 2/3 of Tat are exported by HIV-1-infected cells during their lifespan. The function of extracellular Tat in HIV-1 infection might thus be more significant than earlier thought

Cyclophilin A enables specific HIV-1 Tat palmitoylation and accumulation in uninfected cells

International audienceMost HIV-1 Tat is unconventionally secreted by infected cells following Tat interaction with phosphatidylinositol (4,5) bisphosphate (PI(4,5)P2) at the plasma membrane. Extracellular Tat is endocytosed by uninfected cells before escaping from endosomes to reach the cytosol and bind PI(4,5)P2. It is not clear whether and how incoming Tat concentrates in uninfected cells. Here we show that, in uninfected cells, the S-acyl transferase DHHC-20 together with the prolylisomerases cyclophilin A (CypA) and FKBP12 palmitoylate Tat on Cys31 thereby increasing Tat affinity for PI(4,5)P2. In infected cells, CypA is bound by HIV-1 Gag, resulting in its encapsidation and CypA depletion from cells. Because of the lack of this essential cofactor, Tat is not palmitoylated in infected cells but strongly secreted. Hence, Tat palmitoylation specifically takes place in uninfected cells. Moreover, palmitoylation is required for Tat to accumulate at the plasma membrane and affect PI(4,5)P2-dependent membrane traffic such as phagocytosis and neurosecretion