Search PubMed⌕ Search

Biomedical subjects

Stephen Baghdiguian

Publications and source records attributed to Stephen Baghdiguian.

9 recordsLinked to original sources
PubMed2007

The xaxAB genes encoding a new apoptotic toxin from the insect pathogen Xenorhabdus nematophila are present in plant and human pathogens.

Xenorhabdus nematophila, a member of the Enterobacteriaceae, kills many species of insects by strongly depressing the immune system and colonizing the entire body. A peptide cytotoxin has been purified from X. nematophila broth growth, and the cytolytic effect on insect immunocytes and hemolytic effect on mammalian red blood cells of this toxin have been described (Ribeiro, C., Vignes, M., and Brehélin, M. (2003) J. Biol. Chem. 278, 3030-3039). We show here that this toxin, Xenorhabdus alpha-xenorhabdolysin (Xax), triggers apoptosis in both insect and mammalian cells. We also report the cloning and sequencing of two genes, xaxAB, encoding this toxin in X. nematophila. The expression of both genes in recombinant Escherichia coli led to the production of active cytotoxin/hemolysin. However, hemolytic activity was observed only if the two peptides were added in the appropriate order. Furthermore, we report here that inactivation of xaxAB genes in X. nematophila abolished the major cytotoxic activity present in broth growth, called C1. We also show that these genes are present in various entomopathogenic bacteria of the genera Xenorhabdus and Photorhabdus, in Pseudomonas entomophila, in the human pathogens Yersinia enterocolitica and Proteus mirabilis, and in the plant pathogen Pseudomonas syringae. This toxin cannot be classified in any known family of cytotoxins on the basis of amino acid sequences, locus organization, and activity features. It is, therefore, probably the prototype of a new family of binary toxins.

Animals↗
PubMed2006

Using Ciona to study developmental programmed cell death.

Ciona intestinalis, a member of Tunicates, the closest group to vertebrates, has emerged as an appropriate organism for the study of developmentally regulated programmed cell death. First, because massive phases of apoptosis occur all along embryogenesis. Second, because the lecithotrophic mode of development is associated with autophagic process occurring during juvenile formation. Third, because the biochemical cell death machinery is close to that found in mammals. Altogether, the Ciona system contributes to identify new specific regulatory pathways and to explain how molecular mechanisms of programmed cell death evolved from invertebrates to vertebrates.

Animals↗
PubMed2005

Fertilization regulates apoptosis of Ciona intestinalis extra-embryonic cells through thyroxine (T4)-dependent NF-kappaB pathway activation during early embryonic development.

In Ciona intestinalis, the elimination of extra-embryonic test cells during early stage of development is delayed by a fertilization signal. Test cells undergo a caspase-dependent apoptosis event repressed by thyroxine (T4)-activated NF-kappaB. When apoptosis was experimentally blocked, the hatching stage was delayed. The incubation of unfertilized eggs with a 1-h-fertilized egg extract or purified T4 restored apoptosis in test cells at a similar timing than found in fertilized eggs. Ciona expresses specific genes forming a functional IkappaB/NF-kappaB pathway. One, Ci-p65, was transiently induced upon fertilization via T4 and found to exert its anti-apoptotic role in test cells nuclei as well as in a reconstituted cell system. Blocking NF-kappaB activity by dexamethasone-induced overexpression of Ci-IkappaB abrogated the repression of apoptosis in test cells. Overall, the data are consistent for defining a central coupling role of both T4 and NF-kappaB during early embryo development.

Amino Acid Sequence↗
PubMed2005

Three-dimensional polarization sensitizes hepatocytes to Fas/CD95 apoptotic signalling.

Maintenance of epithelial cell shape and polarity determines many vital cell functions, including the appropriate response to external stimuli. Murine hepatocytes cultured in a three-dimensional Matrigel matrix formed highly polarized organoids characterized by specific localization of an ERM (ezrin/radixin/moesin) protein, radixin, at microvillus-lined membrane domains. These apical domains surrounded a lumen and were bordered by tight junctions. The hepatocyte organoids were functional as judged by the high level of albumin secretion and accumulation of bilirubin. Stimulation of the Fas/CD95 death receptor, which is highly hepatotoxic in vivo, was a strong inducer of apoptosis in the polarized organoids. This was in sharp contrast to the monolayer hepatocyte cultures, which were protected from death by exacerbated NF-kappaB signalling following engagement of the death receptors. Thus, hepatocytes in polarized, functional organoids modulate an intracellular signal transduction pathway, allowing the recapitulation of their physiological response to an apoptotic stimulus.

Animals↗
PubMed2005

Catalytically inactive human cathepsin D triggers fibroblast invasive growth.

The aspartyl-protease cathepsin D (cath-D) is overexpressed and hypersecreted by epithelial breast cancer cells and stimulates their proliferation. As tumor epithelial-fibroblast cell interactions are important events in cancer progression, we investigated whether cath-D overexpression affects also fibroblast behavior. We demonstrate a requirement of cath-D for fibroblast invasive growth using a three-dimensional (3D) coculture assay with cancer cells secreting or not pro-cath-D. Ectopic expression of cath-D in cath-D-deficient fibroblasts stimulates 3D outgrowth that is associated with a significant increase in fibroblast proliferation, survival, motility, and invasive capacity, accompanied by activation of the ras-MAPK pathway. Interestingly, all these stimulatory effects on fibroblasts are independent of cath-D proteolytic activity. Finally, we show that pro-cath-D secreted by cancer cells is captured by fibroblasts and partially mimics effects of transfected cath-D. We conclude that cath-D is crucial for fibroblast invasive outgrowth and could act as a key paracrine communicator between cancer and stromal cells, independently of its catalytic activity.

Animals↗
PubMed2003

Mechanical constraint imposed on plasma membrane through transverse phospholipid imbalance induces reversible actin polymerization via phosphoinositide 3-kinase activation.

Platelets were used to explore the effect of membrane curvature induced by phospholipid excess on cell shape and on organization of the actin cytoskeleton. We showed that the addition of short chain analogues of phospholipids to the outer leaflet of plasma membrane of resting platelets immediately induced a shape change with long filopodia formation containing newly polymerized actin. Cells recovered rapidly their discoid shape and their initial F-actin content only with the phosphatidylserine analogue, which was transported to the inner leaflet by aminophospholipid translocase. Filopodia formation and actin polymerization were inhibited in platelets pre-incubated with cytochalasin D. Both wortmannin and LY294002, two unrelated inhibitors of phosphoinositide 3-kinase, considerably reduced actin polymerization and filopodia formation. Phospholipid imbalance was accompanied by a reversible translocation of phosphoinositide 3-kinase from cytoplasm to plasma membrane. In agreement with a role for PI 3-kinase, when phospholipids were added to platelets, PtdIns(3,4)P2 increased two-fold and Akt protein was partly phosphorylated. A similar shape change was also observed in nocodazole-treated L929 fibroblasts which were incubated with the similar phospholipid analogues. In those nucleated cells, where the microtubule cytoskeleton was disrupted, a major actin-dependent membrane extension was induced by addition of short chain phospholipids that required the functional integrity of PI 3-kinase. We conclude that any physical constraint acting on plasma membrane and resulting on local changes in membrane curvature is sufficient to initiate transient actin polymerization via phosphoinositide 3-kinase activation.

Actin Cytoskeleton↗
PubMed2003

Ascidians as a vertebrate-like model organism for physiological studies of Rho GTPase signaling.

GTPases of the Rho family are evolutionarily conserved proteins that control cell shape dynamics during physiological processes as diverse as cell migration and polarity, axon outgrowth and guidance, apoptosis and phagocytosis. In mammals, 18 Rho proteins are distributed in 7 subfamilies. Rho, Rac and Cdc42 are the best-characterized ones, benefiting from the use of worm and drosophila, which only express these 3 subfamilies. An additional model would therefore help understand the physiological role of other mammalian subfamilies. We identified in genome databases the complete Rho family of two ascidians, Ciona intestinalis and Ciona savignyi, and showed that these families contain single ancestors of most mammalian Rho subfamilies. In Ciona intestinalis, all Rho genes are expressed and display specific developmental variations of mRNA expression during tadpole formation. Although C. intestinalis expresses five additional Rac compared to the closely related Ciona savignyi, only two appeared fully active in functional assays. Last, we identified in Ciona intestinalis database more than 50 Rho regulators (RhoGEFs and RhoGAPs) and 20 effector targets, whose analysis further supports the notion that Rho signaling components are of comparable complexity in mammals and ascidians. Since the tadpole of ascidians combines vertebrate-like developmental features with reduced cell number, particularly adapted to evolutionary and developmental biology studies, our data advocate this model for physiological studies of Rho signaling pathways.

Actins↗
PubMed2002

Tail regression in Ciona intestinalis (Prochordate) involves a Caspase-dependent apoptosis event associated with ERK activation.

Two apoptotic events take place during embryonic development of Ciona intestinalis. The first concerns extra-embryonic cells and precedes hatching. The second controls tail regression at metamorphosis, occurs through a polarized wave originating from tail extremity, and is caspase dependent. This was shown by: (1) in vivo incorporation of a fluorescent marker of caspase activation in different cell types of the tail; (2) detection of an activated form of caspase 3-like protein by western blotting; and (3) failure of 30% of larvae to undergo metamorphosis after treatment of fertilized eggs with a pan-caspase inhibitor. In addition, Ciona embryos express a single ERK protein, specifically phosphorylated at metamorphosis. ERK activation was shown to be located in cells of the tail. Addition of MEK inhibitor in the culture medium prevented ERK activation and metamorphosis. In silico analysis of Ciona genome pointed to 15 caspases with high homology with humans, and a single ERK gene with high homology to both mammalian ERK1 and ERK2. It is concluded that the sequence of events leading to metamorphosis includes ERK phosphorylation followed by caspase-dependent apoptosis and tail regression.

Amino Acid Sequence↗