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41.
de Marco A Volrath S Law M Fonné-Pfister R 《Biochemical and biophysical research communications》2003,301(4):873-878
CTLA-4 gene constructs were designed to express CTLA-4 exclusively in the endoplasmic reticulum (ER). Four different CTLA-4 gene constructs were transfected into HEK 293 (human embryonic kidney) and A20 (Balb/c mouse B lymphoma) cells. All constructs contained an ER retention signal and coded for CTLA-4 expression in the ER. One of the constructs, which contained the membrane part of CTLA-4, coded for an expression both on the cell surface and in the ER. Three of the expressed CTLA-4 types (including the ER-membrane-expressed form) caused a reduced surface expression of B7 in the A20 cells. Only constructs which allow dimerization of CTLA-4 showed this effect. It is assumed that intracellular CTLA-4 bound B7 and inhibited therefore the transport of B7 to the surface. The binding obviously caused also an enhanced degradation of the complexes because both proteins showed a low concentration in the transfected cell lines. CTLA-4-transfected and B7-reduced A20 cells showed a diminished costimulating activity upon T cells. This was demonstrated by a reduced proliferation of T cells from ovalbumin-immunized Balb/c mice, incubated with ovalbumin peptide-primed CTLA-4-transfected A20 cells. 相似文献
42.
Blamart D Escoubeyrou K Juillet-Leclerc A Ouahdi R Lecomte-Finiger R 《Comptes rendus biologies》2002,325(2):99-106
Nuclei (larval stage) and outer parts (adult stage) of fish otoliths from the Taiaro closed lagoon (French Polynesia) and adjacent ocean have been analysed for the C-O isotopic compositions. delta 18O values of the nuclei of both populations indicate that isotopic equilibrium is reached. This implies that the lagoonal fish population has done its complete biological cycle in the lagoon and represents an adaptation in a closed system. delta 18O values of the outer parts show a slight isotopic disequilibrium (< 0.2@1000) interpreted in term of vital effect. All the delta 13C values exhibit a strong isotopic disequilibrium related to metabolic activity. 相似文献
43.
Gélébart P Kovács T Brouland JP van Gorp R Grossmann J Rivard N Panis Y Martin V Bredoux R Enouf J Papp B 《The Journal of biological chemistry》2002,277(29):26310-26320
Calcium mobilization from the endoplasmic reticulum (ER) into the cytosol is a key component of several signaling networks controlling tumor cell growth, differentiation, or apoptosis. Sarco/endoplasmic reticulum calcium transport ATPases (SERCA-type calcium pumps), enzymes that accumulate calcium in the ER, play an important role in these phenomena. We report that SERCA3 expression is significantly reduced or lost in colon carcinomas when compared with normal colonic epithelial cells, which express this enzyme at a high level. To study the involvement of SERCA enzymes in differentiation, in this work differentiation of colon and gastric cancer cell lines was initiated, and the change in the expression of SERCA isoenzymes as well as intracellular calcium levels were investigated. Treatment of the tumor cells with butyrate or other established differentiation inducing agents resulted in a marked and specific induction of the expression of SERCA3, whereas the expression of the ubiquitous SERCA2 enzymes did not change significantly or was reduced. A similar marked increase in SERCA3 expression was found during spontaneous differentiation of post-confluent Caco-2 cells, and this closely correlated with the induction of other known markers of differentiation. Analysis of the expression of the SERCA3 alternative splice isoforms revealed induction of all three known iso-SERCA3 variants (3a, 3b, and 3c). Butyrate treatment of the KATO-III gastric cancer cells led to higher resting cytosolic calcium concentrations and, in accordance with the lower calcium affinity of SERCA3, to diminished ER calcium content. These data taken together indicate a defect in SERCA3 expression in colon cancers as compared with normal colonic epithelium, show that the calcium homeostasis of the endoplasmic reticulum may be remodeled during cellular differentiation, and indicate that SERCA3 constitutes an interesting new differentiation marker that may prove useful for the analysis of the phenotype of gastrointestinal adenocarcinomas. 相似文献
44.
45.
Hardouin J Duchateau M Canelle L Vlieghe C Joubert-Caron R Caron M 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2007,845(2):226-231
Specific and efficient selection of serum immunoglobulins, but not other proteins, on T-gel remains difficult. T-gel capacity was determined for different activation conditions and serum loadings. Mass spectrometry analysis was used to identify the proteins found in the flow-through and in the eluted fractions. Alpha-2-macroglobulin and albumin were the major contaminants of the eluates. The influence of the competition between immunoglobulins and the other serum proteins on the adsorption was also studied. Using a serum depleted in immunoglobulins (flow-through of a first chromatography on T-gel), many serum proteins were retained on the T-gel, including albumin. We conclude that T-gel selectivity is less than absolute and may reflect for a large part the experimental conditions of the adsorption. 相似文献
46.
47.
Purhonen P Lundbäck AK Lemonnier R Leblanc G Hebert H 《Journal of structural biology》2005,152(1):76-83
Melibiose permease (MelB) of Escherichia coli is a secondary transporter that couples the uptake of melibiose and various other galactosides to symport of cations that can be Na+, Li+ or H+. MelB belongs to the glycoside-pentoside-hexuronide: cation symporter family of porters and is suggested to have 12 transmembrane helices. We have determined the three-dimensional structure of MelB at 10A resolution in the membrane plane with cryo-electron microscopy from two-dimensional crystals. The three-dimensional map shows a heart-shaped molecule composed of two domains with a large central cavity between them. The structure is constricted at one side of the membrane while it is open to the other. The overall molecular shape resembles those of lactose permease and glycerol-3-phosphate transporter. However, organization of helices in MelB seems less symmetrical than in these two members of the major facilitator superfamily. 相似文献
48.
49.
Moya KL Hässig R Breen KC Volland H Di Giamberardino L 《Journal of neurochemistry》2005,92(5):1044-1053
The cellular prion protein, PrPc, is a glycosylphosphatidylinositol-anchored cell surface glycoprotein and a protease-resistant conformer of the protein may be the infectious agent in transmissible spongiform encephalopathies. PrPc is localized on growing axons in vitro and along fibre bundles that contain elongating axons in developing and adult brain. To determine whether the growth state of axons influenced the expression and axonal transport of PrPc, we examined changes in the protein following post-traumatic regeneration in the hamster sciatic nerve. Our results show (1) that PrPc in nerve is significantly increased during nerve regeneration; (2) that this increase involves an increase in axonally transported PrPc; and (3) that the PrPc preferentially targeted for the newly formed portions of the regenerating axons consists of higher molecular weight glycoforms. These results raise the possibility that PrPc may play a role in the growth of axons in vivo, perhaps as an adhesion molecule interacting with the extracellular environment through specialized glycosylation. 相似文献
50.
M. Delaigue T. Poulain P. Dabat E. Cabre Raymonde Durand B. Durand 《Biologia Plantarum》1986,28(1):23-30
Some general data on the genetic control and the possibilities of regulation of developmental paths inDrosophila are furnished. The insights to be gained from this insect will surely have implications that extend far beyond the fruit-fly.
For example, in plants, developmental programs for floral organs, implying specific proteins are known. Developmental mutants
in which mutate alleles control developmental programs for flowering were also selected in several species (Zea, Pisum, Sorghum, Cucumis, Mercurialis). Chemicals, especially phytohormones interfering with these programs are discussed. The case of sexual differentiation ofMercurialis is discussed in more detail. In this species, sex organs are controlled by sex determination genes and by auxins (male) and
cytokinins (female). Flowers of each sex can be characterized by specific mRNA populations. They were evidenced by translationin vitro in a cell-free system of the various kinds of mRNAs [poly(A), non poly(A), polysomes]. The feminisation of genetic males
by cytokinins induces the mRNA population of female type. Evidence concerning the implications of cytokinins in protein synthesis
before translation level is presented. This is also probably true for auxins, although direct evidence is lacking. 相似文献