PubMed Health⌕ Search

Biomedical subjects

V Laurent

Publications and source records attributed to V Laurent.

At least 19 recordsLinked to original sources
PubMed2002

Mortality in 7B2 null mice can be rescued by adrenalectomy: involvement of dopamine in ACTH hypersecretion.

The serine protease prohormone convertase 2 (PC2), principally involved in the processing of polypeptide hormone precursors in neuroendocrine tissues, requires interaction with the neuroendocrine protein 7B2 to generate an enzymatically active form. 7B2 null mice express no PC2 activity and release large quantities of uncleaved ACTH, resulting in a lethal endocrine condition that resembles pituitary Cushing's (Westphal, C. H., Muller, L., Zhou, A., Bonner-Weir, S., Schambelan, M., Steiner, D. F., Lindberg, I. & Leder, P. (1999) Cell 96, 689). Here, we have compared the 7B2 and PC2 null mouse models to determine why the 7B2 null, but not the PC2 null, exhibits a lethal disease state. Both 7B2 and PC2 nulls contained highly elevated pituitary adrenocorticotropic hormone (ACTH); the neurointermediate lobe content of ACTH in 7B2 nulls was 13-fold higher than in WT mice; that of the PC2 null was 65-fold higher. However, circulating ACTH levels were much higher in the 7B2 null than in the PC2 null. Because hypothalamic inhibitory dopaminergic control represents the major influence on intermediate lobe proopiomelanocortin-derived peptide secretion, dopamine levels were measured, and they revealed that 7B2 null pituitaries contained only one-fourth of WT pituitary dopamine. Adrenalectomized 7B2 null animals survived past the usual time of death at 5 weeks; a month after adrenalectomy, they exhibited normal levels of pituitary dopamine, circulating ACTH, and corticosterone. Elevated corticosterone, therefore, seems to play a central role in the lethal phenotype of the 7B2 null, whereas a 7B2-mediated dopaminergic deficiency state may be involved in the actual ACTH hypersecretion phenomenon. Interestingly, adrenalectomized 7B2 nulls also developed unexpectedly severe obesity.

Adrenal Glands↗
PubMed2001

Functional expression and characterization of the cytoplasmic aminopeptidase P of Caenorhabditis elegans.

Aminopeptidase P (AP-P; X-Pro aminopeptidase; EC 3.4.11.9) cleaves the N-terminal X-Pro bond of peptides and occurs in mammals as both cytosolic and plasma membrane forms, encoded by separate genes. In mammals, the plasma membrane AP-P can function as a kininase, but little is known about the physiological role of the cytosolic enzyme. The C. elegans genome contains a single gene encoding AP-P (W03G9.4), analysis of which predicts regions displaying high levels of amino-acid sequence homology between the predicted gene product and mammalian cytoplasmic AP-P, with the absolute conservation of key catalytic residues. The sequence of an EST (yk91g4), comprising the open reading frame of W03G9.4, confirmed the predicted genomic structure of the gene and the prediction that W03G9.4 codes for a nonsecreted protein with a molecular mass of 68 kDa. Nematodes transformed with a promoter reporter construct, W03G9.4:GFP, showed high levels of fluorescence in the intestine of larvae and adult hermaphrodites, indicating that the intestine is a major site of W03G9.4 expression. yk91g4 tagged with a hexahistidine and DLYDDDDK peptide epitope was expressed in Escherichia coli to yield, after affinity purification, a recombinant protein with a molecular mass of 71 kDa. The recombinant W03G9.4 removed the N-terminal amino acid from bradykinin (RPPGFSPFR), a Caenorhabditis elegans neuropeptide (KPSFVRFamide) and Lem Trp 1 (APSGFLGVRamide), but did not display activity towards angiotensin I (NRVYIHPFHL), des-Arg bradykinin and AF1 (KNEFIRFamide). The activity towards bradykinin was inhibited by EDTA and 1, 10 phenanthroline, as expected for a metalloenzyme, and also by apstatin (IC50, 1 microM), a selective inhibitor of mammalian AP-P. A Km of 45 microM and an optimum pH of 7-8 was observed with bradykinin as the substrate. The activity of the nematode AP-P, like its mammalian counterparts, was strongly influenced by metal ions, with Co2+, Mn2+ and Zn2+ all inhibiting the hydrolysis of bradykinin. We conclude that W03G9.4 codes for a cytoplasmic AP-P with very similar enzymatic properties to those of mammalian AP-P, and we suggest that the enzyme has a physiological role in the intracellular hydrolysis of proline-containing peptides absorbed from the lumen of the intestine.

Amino Acid Sequence↗
PubMed2001

[Incremental lower extremity CT venography, a simplified approach for the diagnosis of phlebitis in patients with pulmonary embolism].

PURPOSE: To demonstrate that incremental CT venography, performed at the time of CT pulmonary angiography, can easily diagnose deep venous thrombosis. Materials and Methods. Retrospective analysis of 152 combined incremental CT venography and CT pulmonary angiography. Results were compared to Doppler US examinations in 18 cases. RESULTS: 61% of venous thrombosis was found on incremental CT examination in case of pulmonary embolism. In 5 cases, isolated venous thrombosis was found without pulmonary embolism. The CT diagnosis of DVT was confirmed by US; CT appeared more accurate than US in the calf. CONCLUSION: CT venography combined with CT pulmonary angiography is a useful tool in order to obtain a comprehensive evaluation for thrombo-embolic disease.

Adolescent↗
PubMed2000

Cathepsin D in breast cancer: mechanisms and clinical applications, a 1999 overview.

A short review of the literature first confirms the clinical value of cathepsin D as a prognostic marker in breast cancer, when using well standardized assays. We then summarize results of studies, mostly performed in our laboratory, aimed at understanding the effect of cathepsin D overexpression on metastasis and the molecular mechanisms involved. Cathepsin D-cDNA transfection increases tumor cell proliferation in vitro and the metastatic potential of 3Y1-Ad12 embryonic rat tumorigenic cells when injected in vivo into nude mice. The mechanism by which cathepsin D increases the incidence of clinical metastasis involves increased cell growth and decreased contact inhibition rather than escape of cancer cells through the basement membrane. Different mechanisms are considered to explain this mitogenic activity. Cathepsin D could act as a protease following its activation at an acidic pH, or as a ligand of different membrane receptors at a more neutral pH. In this case cathepsin D can displace IGFII from the mannose-6-phosphate/IGFII receptor to the IGFI receptor or activate another membrane receptor to be identified. The nature of the mechanisms involved in vivo may depend on the micro environment of the tumor cells. These studies should guide in the development of new therapies aimed at inhibiting the deleterious effect of overexpressed cathepsin D.

Animals↗
PubMed2000

Measurement of the elasticity of the actin tail of Listeria monocytogenes.

We report biophysical experiments performed on the bacterium Listeria monocytogenes, a model system to study actin-based motility. Using optical tweezers and electrophoresis experiments, we find that the bacterium is firmly attached to its tail, and we demonstrate that the tail responds as an elastic gel when deformed. We have measured its elastic modulus at a value of 10(3)-10(4) Pa, which is 10 times higher than the rigidity of the eukaryotic cytoplasm. These results demonstrate that the bacterium and its tail form a very robust system, consistent with the steadyness of the motion observed in vivo. We propose an elastic model for the propulsion mechanism which takes into account the connection and thus the interaction between the actin filaments. It provides a generic description of the various aspects of actin-tail based movements.

Actins↗
PubMed2000

Morphine-like substance in leech ganglia. Evidence and immune modulation.

Binding experiments followed by measurement of nitric oxide release revealed an opiate alkaloid high affinity receptor with no affinity to opioids, representing a new mu-subtype receptor in the brain of the leech Theromyzon tessulatum. In addition, evidence of morphine-like substances was found in immunocytochemical studies and HPLC coupled to electrochemical detection (500 mV and 0.02 Hz). Based on previous evidence of the involvement of morphine as an immune response inhibitor, we demonstrate that in leech ganglia injection of lipopolysaccharide (LPS; a potent immunostimulatory agent derived from bacteria) provoked an increase in the level of ganglionic morphine-like substances after a prolonged latency period of 24 h (from 2.4 +/- 1.1 pmol per ganglion to 78 +/- 12.3 pmol per ganglion; P < 0.005; LPS injected 1 microg x mL-1); this effect is both concentration- and time-dependent. Finally, we have demonstrated that morphine, after binding to its own receptor, inhibits leech immunocyte activation through adenylate cyclase inhibition and nitric oxide release. This report confirms that morphine is an evolutionarily stable potent immunomodulator.

Adjuvants, Immunologic↗
PubMed2000

[Quid?].

Explore the source record for details and available documents.

Adult↗
PubMed1999

Activation of the CDC42 effector N-WASP by the Shigella flexneri IcsA protein promotes actin nucleation by Arp2/3 complex and bacterial actin-based motility.

To propel itself in infected cells, the pathogen Shigella flexneri subverts the Cdc42-controlled machinery responsible for actin assembly during filopodia formation. Using a combination of bacterial motility assays in platelet extracts with Escherichia coli expressing the Shigella IcsA protein and in vitro analysis of reconstituted systems from purified proteins, we show here that the bacterial protein IcsA binds N-WASP and activates it in a Cdc42-like fashion. Dramatic stimulation of actin assembly is linked to the formation of a ternary IcsA-N-WASP-Arp2/3 complex, which nucleates actin polymerization. The Arp2/3 complex is essential in initiation of actin assembly and Shigella movement, as previously observed for Listeria monocytogenes. Activation of N-WASP by IcsA unmasks two domains acting together in insertional actin polymerization. The isolated COOH-terminal domain of N-WASP containing a verprolin-homology region, a cofilin-homology sequence, and an acidic terminal segment (VCA) interacts with G-actin in a unique profilin-like functional fashion. Hence, when N-WASP is activated, its COOH-terminal domain feeds barbed end growth of filaments and lowers the critical concentration at the bacterial surface. On the other hand, the NH(2)-terminal domain of N-WASP interacts with F-actin, mediating the attachment of the actin tail to the bacterium surface. VASP is not involved in Shigella movement, and the function of profilin does not require its binding to proline-rich regions.

Actin-Related Protein 2↗
PubMed1999

Role of proteins of the Ena/VASP family in actin-based motility of Listeria monocytogenes.

Intracellular propulsion of Listeria monocytogenes is the best understood form of motility dependent on actin polymerization. We have used in vitro motility assays of Listeria in platelet and brain extracts to elucidate the function of the focal adhesion proteins of the Ena (Drosophila Enabled)/VASP (vasodilator-stimulated phosphoprotein) family in actin-based motility. Immunodepletion of VASP from platelet extracts and of Evl (Ena/VASP-like protein) from brain extracts of Mena knockout (-/-) mice combined with add-back of recombinant (bacterial or eukaryotic) VASP and Evl show that VASP, Mena, and Evl play interchangeable roles and are required to transform actin polymerization into active movement and propulsive force. The EVH1 (Ena/VASP homology 1) domain of VASP is in slow association-dissociation equilibrium high-affinity binding to the zyxin-homologous, proline-rich region of ActA. VASP also interacts with F-actin via its COOH-terminal EVH2 domain. Hence VASP/ Ena/Evl link the bacterium to the actin tail, which is required for movement. The affinity of VASP for F-actin is controlled by phosphorylation of serine 157 by cAMP-dependent protein kinase. Phospho-VASP binds with high affinity (0.5 x 10(8) M-1); dephospho-VASP binds 40-fold less tightly. We propose a molecular ratchet model for insertional polymerization of actin, within which frequent attachment-detachment of VASP to F-actin allows its sliding along the growing filament.

Actins↗
PubMed1999

Rho family GTPases control entry of Shigella flexneri into epithelial cells but not intracellular motility.

Shigella flexneri, an invasive bacterial pathogen, promotes formation of two cytoskeletal structures: the entry focus that mediates bacterial uptake into epithelial cells and the actin-comet tail that enables the bacteria to spread intracellularly. During the entry step, secretion of bacterial invasins causes a massive burst of subcortical actin polymerization leading the formation of localised membrane projections. Fusion of these membrane ruffles leads to bacterial internalization. Inside the cytoplasm, polar expression of the IcsA protein on the bacterial surface allows polymerization of actin filaments and their organization into an actin-comet tail leading to bacterial spread. The Rho family of small GTPases plays an essential role in the organization and regulation of cellular cytoskeletal structures (i.e. filopodia, lamellipodia, adherence plaques and intercellular junctions). We show here that induction of Shigella entry foci is controlled by the Cdc42, Rac and Rho GTPases, but not by RhoG. In contrast, actin-driven intracellular motility of Shigella does not require Rho GTPases. Therefore, Shigella appears to manipulate the epithelial cell cytoskeleton both by Rho GTPase-dependent and -independent processes.

Actins↗
PubMed1999

Role of collagenase in mediating in vitro alveolar epithelial wound repair.

Type II pneumocytes are essential for repair of the injured alveolar epithelium. The effect of two MMP collagenases, MMP-1 and MMP-13 on alveolar epithelial repair was studied in vitro. The A549 alveolar epithelial cell line and primary rat alveolar epithelial cell cultures were used. Cell adhesion and cell migration were measured with and without exogenous MMP-1. Wound healing of a cell monolayer of rat alveolar epithelial cell after a mechanical injury was evaluated by time lapse video analysis. Cell adhesion on type I collagen, as well as cytoskeleton stiffness, was decreased in the presence of exogenous collagenases. A similar decrease was observed when cell adhesion was tested on collagen that was first incubated with MMP-1 (versus control on intact collagen). Cell migration on type I collagen was promoted by collagenases. Wound healing of an alveolar epithelial cell monolayer was enhanced in the presence of exogenous collagenases. Our results suggest that collagenases could modulate the repair process by decreasing cell adhesion and cell stiffness, and by increasing cell migration on type I collagen. Collagen degradation could modify cell adhesion sites and collagen degradation peptides could induce alveolar type II pneumocyte migration. New insights regarding alveolar epithelial cell migration are particularly relevant to investigate early events during alveolar epithelial repair following lung injury.

Animals↗
PubMed1998

A composite genetic map of the parasitoid wasp Trichogramma brassicae based on RAPD markers.

Three linkage maps of the genome of the microhymenopteran Trichogramma brassicae were constructed from the analysis of segregation of random amplified polymorphic DNA markers in three F2 populations. These populations were composed of the haploid male progeny of several virgin F1 females, which resulted from the breeding of four parental lines that were nearly fixed for different random amplified polymorphic DNA markers and that were polymorphic for longevity and fecundity characters. As the order of markers common to the three mapping populations was found to be well conserved, a composite linkage map was constructed. Eighty-four markers were organized into five linkage groups and two pairs. The mean interval between two markers was 17.7 cM, and the map spanned 1330 cM.

Animals↗
PubMed1997

Leech immunocytes contain proopiomelanocortin: nitric oxide mediates hemolymph proopiomelanocortin processing.

This report establishes the presence of mammalian-like proopiomelanocotropic hormone (POMC), and six of its peptides, including adrenocorticotropic hormone (ACTH) and melanocyte-stimulating hormone (MSH), in the immune tissues of the leech Theromyzon tessulatum. The 25.4-kDa protein was purified by high pressure gel permeation chromatography, anti-ACTH-affinity column, and reverse-phase HPLC. Its characterization was performed by Edman degradation, enzymatic treatments, and electrospray mass spectrometry. Leech POMC exhibits considerable amino acid sequence similarity to mammalian POMC. Of the six peptides, three showed high sequence similarity to their vertebrate counterparts met-enkephalin, alpha-MSH, and ACTH: 100, 84.6, and 70%, respectively; whereas gamma-MSH, beta-endorphin, and gamma-lipotropin hormone exhibited only 45, 20, and 10% sequence identity, respectively. No dibasic amino acid residues were found at the C terminus of the gamma- and beta-MSH peptides. In contrast, the leech alpha-MSH was flanked at its C-terminal by the Gly-Arg-Lys amidation signal. ACTH and corticotropin-like intermediary pituitary peptide were also C-terminally flanked by dibasic amino acid residues. The coding region of leech POMC was obtained by reverse transcription-PCR using degenerated oligonucleotide primers. Circulating levels of ACTH and MSH were 10 and 1 fmol/microl hemolymph, respectively. Morphine, in a dose-dependent manner, increased the levels of both peptides threefold; this effect was blocked by naloxone treatment. Similar results were found with the anandamide. Leech ACTH was processed to MSH by the enzymes neutral endopeptidase (24.11) and angiotensin-converting enzyme. Leech alpha-MSH had the same activity as authentic alpha-MSH in two bioasssay systems. Taken together, the study demonstrates that POMC is present in invertebrates and its immunoregulatory actions have been conserved during evolution.

Adrenocorticotropic Hormone↗