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Une femme de 66 ans, auparavant en bonne sante, a consulte a l'hopital pour malaise, ballonnements et satiete rapide depuis un mois. Originaire des Philippines, elle a immigre il y [...]

A 66-year-old previously healthy woman presented to hospital with 1 month of malaise, abdominal swelling and early satiety. She had immigrated from the Philippines 40 years before and had previous [...]

Unstimulated PC12 pheochromocytoma cells contain many proteins that bound to 14-3-3s in competition with a 14-3-3-binding peptide. Additional proteins, including one of 39kDa (p39), became capable of binding to 14-3-3s in phosphatidylinositol 3-kinase-dependent responses to epidermal growth factor or nerve growth factor in vivo. The growth factor regulation was unaffected by inhibitors of the mitogen- or stress-activated protein kinase pathways, or by glucose starvation, but was blocked by amino acid starvation and only partially blocked by rapamycin. p39 in extracts of unstimulated, nutrient-fed cells, but not nutrient-starved cells, was able to bind to 14-3-3s after phosphorylation by protein kinase B (PKB) in vitro. Nutrient starvation did not affect the growth factor-stimulated activation of PKB in vivo. Either cycloheximide (CHX) or the cysteine protease inhibitor, MG132, restored the responsiveness of p39 to growth factors in nutrient-starved cells. In contrast, MG132 could not replace amino acids in supporting the growth factor-stimulated phosphorylation of two downstream targets of mTOR (mammalian target of rapamycin), namely eukaryotic initiation factor 4E binding protein 1 (4E-BP1) and p70 S6 kinase. CHX permitted complete growth factor-stimulated phosphorylation of both 4E-BP1 and p70 S6 kinase in nutrient- starved cells; however, unlike p39, phosphorylation of these proteins was blocked by rapamycin. These findings implicate PKB (or an enzyme with similar specificity) in the growth factor-triggered phosphorylation of p39. In addition, amino acidstarvation induces a CHX- and MG132-sensitive pathway that targets p39 and appears to be distinct from the mechanism of regulation of 4E-BP1 and p70 S6 kinase.

A cell-free system based on washed Leishmania majormembranes was labelled with GDP-[3H]Man in the presence of synthetic glucosaminyl-phosphatidylinositol (GlcN-PI) and N-acetylglucosaminyl-phosphatidylinositol (GlcNAc-PI). In both cases, the major radiolabelled products were Manα1-4GlcNα1-6myo-inositol1-HPO4- (sn-1,2-dipalmitoylglycerol) and Manα1-4GlcNα1-6myo-inositol1-HPO4- (sn-1-palmitoyl-2-lyso-glycerol), to which an additional D-mannose residue was added when a chase with an excess of GDP-Man was performed. The L. majorcell-free system can therefore be used to observe the actions of four enzymes, namely GlcNAc-PI de-N-acetylase, Dol-P-Man–GlcN-PI α1-4-mannosyltransferase, a phospholipase A2-like activity and a second α-mannosyltransferase activity. The substrate specificities of the first two of these enzymes were studied using a series of substrate analogues. GlcNAc-PI de-N-acetylase was tested against a variety of N-acylated GlcN-PI substrates and was able to cleave N-acetyl and N-propyl groups but not larger groups such as N-butyl, N-isobutyl, N-pentyl and N-hexyl. The Dol-P-Man–GlcN-PI α1-4-mannosyltransferase activity required the amino group of the glucosamine residue and the d-configuration of the myo-inositol residue of the GlcN-PI acceptor substrate.