Morphological assessment of non-human primate models of osteoarthritis: Comparisons of HR-MRI with CT arthrography (CTA)

International audienc

Clonage moléculaire et caractérisation de SHIP2, une nouvelle inositols et phosphatidylinositols polyphosphates 5-phosphatase qui contrôle la voie de signalisation de la PI 3-kinase.

Doctorat en Sciencesinfo:eu-repo/semantics/nonPublishe

Clonage moléculaire et caractérisation de SHIP2, une nouvelle inositols et phosphatidylinositols polyphosphates 5-phosphatase qui contrôle la voie de signalisation de la PI 3-kinase.

Doctorat en Sciencesinfo:eu-repo/semantics/nonPublishe

The diversity and possible functions of the inositol polyphosphate 5-phosphatases

Distinct forms of inositol and phosphatidylinositol polyphosphate 5-phosphatases selectively remove the phosphate from the 5-position of the inositol ring from both soluble and lipid substrates, i.e. inositol 1,4,5-trisphosphate (Ins(1,4,5)P3), inositol 1,3,4, 5-tetrakisphosphate (Ins(1,3,4,5)P4), phosphatidylinositol 4, 5-bisphosphate (PtdIns(4,5)P2) or phosphatidylinositol 3,4, 5-trisphosphate (PtdIns(3,4,5)P3). In mammalian cells, this family contains a series of distinct genes and splice variants. All inositol polyphosphate 5-phosphatases share a 5-phosphatase domain and various protein modules probably responsible for specific cell localisation or recruitment (SH2 domain, proline-rich sequences, prenylation sites, etc.). Type I Ins(1,4,5)P3 5-phosphatase also uses Ins(1,3,4,5)P4 but not the phosphoinositides as substrates. This enzyme is targeted to specific membranes by means of a prenylation site. Type II 5-phosphatases can use both PtdIns(4,5)P2 and PtdIns(3,4,5)P3 as substrates. Five mammalian enzymes and multiple splice variants are known: INPP5P or inositol polyphosphate 5-phosphatase II, OCRL (a Golgi protein implicated in the Lowe oculocerebrorenal syndrome), synaptojanin (a protein involved in the recycling of synaptic vesicles), SHIP 1 and SHIP 2 (or SH2-containing inositol 5-phosphatases). As discussed in this review, the substrate specificity, regulatory mechanisms, subcellular localisation and tissue specificity indicate that the different 5-phosphatase isoforms may play specific roles. As known in the dephosphorylation of tyrosine containing substrates by the tyrosine protein phosphatases or in the metabolism of cyclic nucleotides by the cyclic nucleotide phosphodiesterases, inositol polyphosphate 5-phosphatases directly participate in the control of second messengers in response to both activation or inhibitory cell signalling.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

The SH2 domain containing inositol 5-phosphatase SHIP2 associates to the immunoreceptor tyrosine-based inhibition motif of FcγRIIB in B cells under negative signaling

FcγRIIB are single-chain low-affinity receptors for IgG that bear an immunoreceptor tyrosine-based inhibition motif (ITIM) in their intracytoplasmic domain and that negatively regulate immunoreceptor tyrosine-based activation motif (ITAM)-dependent cell activation. In B cells, coaggregation of the B cell receptor (BCR) and FcγRIIB leads to an inhibition of B cell activation. Inhibitory properties of FcγRIIB have been related to the recruitment of SHIP, an SH2 domain-containing inositol 5-phosphatase (referred to as SHIP1), via ITIM phosphorylated FcγRIIB. Here, we demonstrate that the second SH2 domain-containing inositol 5-phosphatase SHIP2 could also bind to the FcγRIIB ITIM. As a model, a FcγRIIB deficient B cell line (IIA1.6), transfected with a cDNA encoding either w.t. FcγRIIB1' or FcγRIIB1' whose ITIM tyrosine was mutated has been used. SHIP2 tyrosine phosphorylation and association to the adaptator protein Shc were only found in transfectants expressing w.t. FcγRIIB1'. SHIP2 was also found to bind to a phosphopeptide corresponding to the ITIM sequence of FcγRIIB. There was no binding to the nonphosphorylated peptide. Finally, both SHIP2 and SHIP1 were coprecipitated with FcγRIIB1' upon coaggregation with BCR in IIA1.6 transfectants. Copyright (C) 2000 Elsevier Science B.V.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Hyperosmotic stress stimulates inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate formation independently of bis-diphosphoinositol tetrakisphosphate modulation.

Hyperosmotic stress induces water diffusion out of the cell, resulting in cell shrinkage, and leading to DNA damage, cell cycle arrest, and cytoskeletal reorganization. A previous report showed that low concentrations of sorbitol (200mM) could increase up to 25-fold the concentration of InsP(8) in animal cells. Here, we investigate the effect of sorbitol (200mM) on the inositol 1,4,5-trisphosphate (InsP(3)) and inositol 1,3,4,5-tetrakisphosphate (InsP(4)) pathway. A 3- to 4-fold increase in InsP(3) and InsP(4) levels after sorbitol challenge was observed. It was prevented by the phospholipase C inhibitor U-73122 but was insensitive to the MAP kinase inhibitor U0126. We also observed an increase in the free intracellular [Ca(2+)] and the occurrence of Ca(2+) oscillations in response to sorbitol. A hyperosmotic stress could therefore affect the levels of both hyperphosphorylated inositol phosphates and InsP(3)/InsP(4)-signalling molecules.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

Radical‐Initiated Dismutation of Hydrosiloxanes by Catalytic Potassium‐Graphite

International audienceFormation of higher‐value products from cheaper silicone precursors such as polymethylhydrosiloxane (PMHS) is a challenge for silicon chemistry. Here, we show that catalytic amount (<0.5 mol %) of potassium graphite (KC8) can be used as an efficient radical initiator for the cleavage of Si−O bonds of hydrosiloxanes. Methylsilane and dimethylsilane are quantitatively obtained from PMHS and TMDS (1,1,3,3‐tetramethyldisiloxane), respectively. Taking advantage of the high reactivity of the newly formed silane, the reduction of carbonyl functionalities with KC8 in catalytic amount was further performed. Mechanistic investigations suggest that both the dismutation of the initial hydrosiloxane and the reduction of carbonyl derivatives by hydrosilylation are initiated with a radical pathway

The influence of anionic lipids on SHIP2 phosphatidylinositol 3,4,5-trisphosphate 5-phosphatase activity.

The SH2 domain containing inositol 5-phosphatase 2 (SHIP2) catalyzes the dephosphorylation of phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P(3)) to phosphatidylinositol 3,4-bisphosphate (PtdIns(3,4)P(2)) and participates in the insulin signalling pathway in vivo. In a comparative study of SHIP2 and the phosphatase and tensin homologue deleted on chromosome 10 (PTEN), we found that their lipid phosphatase activity was influenced by the presence of vesicles of phosphatidylserine (PtdSer). SHIP2 PtdIns(3,4,5)P(3) 5-phosphatase activity was greatly stimulated in the presence of vesicles of PtdSer. This effect appears to be specific for di-C8 and di-C16 fatty acids of PtdIns(3,4,5)P(3) as substrate. It was not observed with inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P(4)) another in vitro substrate of SHIP2, nor with Type I Ins(1,4,5)P(3)/Ins(1,3,4,5)P(4) 5-phosphatase activity, an enzyme which acts on soluble inositol phosphates. Vesicles of phosphatidylcholine (PtdCho) stimulated only twofold PtdIns(3,4,5)P(3) 5-phosphatase activity of SHIP2. Both a minimal catalytic construct and the full length SHIP2 were sensitive to the stimulation by PtdSer. In contrast, PtdIns(3,4,5)P(3) 5-phosphatase activity of the Skeletal muscle and Kidney enriched Inositol Phosphatase (SKIP), another member of the mammaliam Type II phosphoinositide 5-phosphatases, was not sensitive to PtdSer. Our enzymatic data establish a specificity in the control of SHIP2 lipid phosphatase activity with PtdIns(3,4,5)P(3) as substrate which is depending on the fatty acid composition of the substrate.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

The two SH2-domain-containing inositol 5-phosphatases SHIP1 and SHIP2 are coexpressed in human T lymphocytes.

The activation of many hematopoietic cells via cytokine receptors, as well as B and T cell receptors, leads to the tyrosine phosphorylation of Shc and its association with both Grb2-Sos1 complexes and with a 145 kDa protein referred to as the SH2 containing inositol 5-phosphatase (SHIP1). In a search of putative 5-phosphatase isoenzymes, we have isolated a second SH2 domain containing inositol 5-phosphatase, referred to as (SHIP2). Both SHIP1 and SHIP2 are coexpressed in human T lymphocytes. This was shown at the protein level by Western blot analysis in transformed T cell lines and in peripheral blood T lymphocytes either unstimulated or after in vitro activation through TCR-CD3 complex. SHIP1 protein level was not modulated after activation of T lymphocytes, in contrast to SHIP2, which was increased after long-term stimulation. SHIP1 was tyrosine phosphorylated in resting naive T cells. This was not observed in the transformed T cell lines. T lymphocyte is therefore a model of coexpression of the two SH2-containing inositol 5-phosphatases SHIP1 and SHIP2.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe