Ephrin-B3 binds specifically to B lymphocytes in blood and induces migration.

Eph receptors and ephrin ligands have been shown to be differentially expressed on leucocytes. Here, we show that one member of the ephrin-B subfamily of ephrins, ephrin-B3, specifically binds to B lymphocytes in blood. No binding was observed to T lymphocytes or monocytes. The ephrin-B3 binding receptor on B lymphocytes is so far not identified, but our results here indicate that ephrin-B3 binds to a protein not belonging to the Eph receptor family. Recently, we have shown that ephrin-B3 binds to a sulphated cell surface receptor on HEK293T cells and that this binding can be blocked with heparin. Ephrin-B3 binding to B lymphocytes is partially affected by heparin, and a basic amino acid in the extracellular juxtamembrane region, Arg-188, is here shown to be involved in this binding. The functional consequence of ephrin-B3 binding to B lymphocytes is induced migration, in particular of the memory cells. To conclude, ephrin-B3 binds to B lymphocytes, most likely via a non-classical receptor, and induces migration of the memory B cell subpopulation.

Protein core-dependent glycosaminoglycan modification and glycosaminoglycan-dependent polarized sorting in epithelial Madin-Darby canine kidney cells.

The proteoglycan serglycin (SG) fused to green fluorescent protein (GFP) is secreted predominantly from the apical surface of polarized epithelial Madin-Darby canine kidney (MDCK) cell monolayers, but the minor fraction secreted basolaterally carries more intensely sulfated glycosaminoglycan (GAG) chains (Tveit H, Dick G, Skibeli V, Prydz K. 2005. A proteoglycan undergoes different modifications en route to the apical and basolateral surfaces of Madin-Darby canine kidney cells. J Biol Chem 280: 29596-29603). To investigate whether the domain with GAG attachment sites in SG (i) is sufficient to drive apical protein sorting and (ii) independently generates the sulfation differences observed in the apical and basolateral pathways, the GAG domain of SG was fused into the junction of rat growth hormone (rGH) and GFP and expressed in MDCK cells, either with or without two N-glycosylation sites in the rGH part. Both variants acquired chondroitin sulfate GAG chains and were secreted predominantly to the apical medium, to the same extent as rGH-GFP with two N-glycosylation sites only, and different from the nonsorted variant lacking glycosylation sites. Transfer of the GAG attachment domain from SG to the new rGH context abolished the differences in sulfation intensity and positions observed for SG in the apical and basolateral secretory routes. Thus, these differences are coded by elements outside the GAG attachment domain.

Serglycin--structure and biology.

Serglycin is a proteoglycan found in hematopoietic cells and endothelial cells. It has important functions related to formation of several types of storage granules. In connective tissue mast cells the covalently attached glycosaminoglycan is heparin, whereas mucosal mast cells and activated macrophages contain oversulfated chondroitin sulfate (type E). In mast cells, serglycin interact with histamine, chymase, tryptase and carboxypeptidase, in neutrophils with elastase, in cytotoxic T cells with granzyme B, in endothelial cells with tissue-type plasminogen activator and in macrophages with tumor necrosis factor-alpha. Serglycin is important for the retention of key inflammatory mediators inside storage granules and secretory vesicles. Serglycin can further modulate the activities of partner molecules in different ways after secretion from activated immune cells, through protection, transport, activation and interactions with substrates or target cells. Serglycin is a proteoglycan with important roles in inflammatory reactions.