Cyclophilins A and B (CyPA and CyPB) are cyclosporin A-binding proteins that are involved in inflammatory events. We have reported that CyPB interacts with two types of cell-surface-binding sites. The first site corresponds to a functional receptor and requires interaction with the central core of CyPB. This region is highly conserved in cyclophilins, suggesting that CyPA and CyPB might share biological activities mediated by interaction with this receptor. The second site is identified with glycosaminoglycans (GAGs), the binding region located in the N terminus of CyPB. The difference in the N-terminal extensions of CyPA and CyPB suggests that a unique interaction with GAGs might account for selective activity of CyPB. To explore this hypothesis, we analyzed the lymphocyte responses triggered by CyPA, CyPB, and CyPB KKK؊, a mutant unable to interact with GAGs. The three ligands seemed capable enough to elicit calcium signal and chemotaxis by binding to the same signaling receptor. In contrast, only CyPB enhanced firm adhesion of T cells to the extracellular matrix. This activity depended on the interactions with GAGs and signaling receptor. CyPB-mediated adhesion required CD147 presumably because it was a costimulatory molecule and was related to an activation of ␣41 and ␣47 integrins. Finally, we showed that CyPB was capable mainly to enhance T cell adhesion of the CD4 ؉ CD45RO ؉ subset. The present data indicate that CyPB rather than CyPA is a proinflammatory factor for T lymphocytes and highlight the crucial role of CyPB-GAG interaction in the chemokine-like activity of this protein.
Whereas Glc is stored in small-sized hydrosoluble glycogen particles in archaea, eubacteria, fungi, and animal cells, photosynthetic eukaryotes have resorted to building starch, which is composed of several distinct polysaccharide fractions packed into a highly organized semicrystalline granule. In plants, both the initiation of polysaccharide synthesis and the nucleation mechanism leading to formation of new starch granules are currently not understood. Ostreococcus tauri, a unicellular green alga of the Prasinophyceae family, defines the tiniest eukaryote with one of the smallest genomes. We show that it accumulates a single starch granule at the chloroplast center by using the same pathway as higher plants. At the time of plastid division, we observe elongation of the starch and division into two daughter structures that are partitioned in each newly formed chloroplast. These observations suggest that in this system the information required to initiate crystalline polysaccharide growth of a new granule is contained within the preexisting polysaccharide structure and the design of the plastid division machinery.Starch and glycogen define the most widespread form of Glc storage in living cells and consist of a-1,4 linked glucan chains with a-1,6 branches (Buléon et al., 1998; Ball and Morell, 2003). Hydrosoluble glycogen particles cannot grow greater than 40 nm in diameter because the structure becomes too crowded with Glc at the periphery of the particle to accommodate the presence of enzymes of glycogen synthesis or degradation (Meléndez et al., 1998). This limitation is due to both the higher branching level of the polymer and to its rather uniform branching pattern. There presently seems to be no other limit to the size of a starch granule than that afforded by the availability of substrate for continuing synthesis. Amylopectin, the major polysaccharide of starch, aggregates into insoluble semicrystalline material because of its asymmetrical distribution of a-1,6 linkages generating clusters of branches responsible for formation of arrays of parallel double helical structures (Buléon et al., 1998). The appearance of starch coincides with the acquisition of photosynthesis by the eukaryotic cell. No such polymer can presently be found in bacteria, archea, fungi, or animal cells. Although starch is clearly associated with the acquisition of photoautotrophy by eukaryotes, glycogen seems to be the predominant form of Glc storage within cyanobacteria and purple nonsulfur bacteria (for review, see Preiss and Romeo, 1989). In addition, nonphotosynthetic eukaryotes accumulating amylopectin-like polymers such as apicomplexa parasite heterotrophic dinoflagellates or others were always subsequently inferred to be derived from a photosynthetic eukaryote ancestor (McFadden et al., 1996). Starch has been found to accumulate in plastids in green algae and land plants, while red algae, glaucophytes, dinoflagellates, apicomplexa parasites, and cryptophytes accumulate an extraplastidial form of so-called floridean starch (Vi...
O-Linked N-acetylglucosaminylation (O-GlcNAcylation) (or O-linked N-acetylglucosamine (O-GlcNAcCells divide according to a spatially and a temporally regulated process called the cell cycle. This intricate mechanism is usually divided into four phases, namely G 1 (Gap1), S (DNA replication), G 2 (Gap2), and M (mitosis/meiosis). To ensure successful completion of its division, each phase and each checkpoint (G 0 /G 1 , G 1 /S, G 2 /M, and metaphase/anaphase) are tightly controlled by several factors that work in concert. Cyclin-dependent kinases (cdks) 1 and their specific regulators cyclins are the best described regulators monitoring the cell cycle progression. A dysregulation of these cdks leads to an uncontrolled cell division ending up in tissue cancerization (for a review, see Ref. 1).Xenopus laevis oocyte has been widely used as a model for studying the regulation of the cell cycle. The imposing size of this cell (1.3-mm diameter with a nucleus of 300 m), a total protein quantity of 25 g/oocyte, and its amenability for manipulation made this model powerful for the characterization and the identification of many key cell cycle components, such as the M phase-promoting factor (MPF) and the cytostatic factor (2, 3). During oogenesis, the oocyte accumulates nutrients and materials (mRNAs and enzymes) that will be From the ‡UMR
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