Characterization of a neutophil surfacer glycosaminoglycan responsible for binding of platelet factor 4
1999 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 274, no 18, 12376-12382 p.Article in journal (Refereed) Published
Platelet factor 4 (PF-4) is a platelet-derived α-chemokine that binds to and activates human neutrophils to undergo specific functions like exocytosis or adhesion. PF-4 binding has been shown to be independent of interleukin-8 receptors and could be inhibited by soluble chondroitin sulfate type glycosaminoglycans or by pretreatment of cells with chondroitinase ABC. Here we present evidence that surface-expressed neutrophil glycosaminoglycans are of chondroitin sulfate type and that this species binds to the tetrameric form of PF-4. The glycosaminoglycans consist of a single type of chain with an average molecular mass of ∼23 kDa and are composed of ∼85–90% chondroitin 4-sulfate disaccharide units type CSA (→4GlcAβ1→3GalNAc(4-O-sulfate)β1→) and of ∼10–15% di-O-sulfated disaccharide units. A major part of these di-O-sulfated disaccharide units are CSE units (→4GlcAβ1→3GalNAc(4,6-O-sulfate)β1→). Binding studies revealed that the interaction of chondroitin sulfate with PF-4 required at least 20 monosaccharide units for significant binding. The di-O-sulfated disaccharide units in neutrophil glycosaminoglycans clearly promoted the affinity to PF-4, which showed a K d ∼ 0.8 μm, as the affinities of bovine cartilage chondroitin sulfate A, porcine skin dermatan sulfate, or bovine cartilage chondroitin sulfate C, all consisting exclusively of monosulfated disaccharide units, were found to be 3–5-fold lower. Taken together, our data indicate that chondroitin sulfate chains function as physiologically relevant binding sites for PF-4 on neutrophils and that the affinity of these chains for PF-4 is controlled by their degree of sulfation.
The activation and control of polymorphonuclear granulocytes (PMN)1 are known to play an essential role in host defense against microbial invaders as well as in chronic diseases. Several members of the α-chemokine family like interleukin-8 (IL-8), neutrophil-activating peptide 2, or melanoma growth stimulatory activity have been shown to act as potent activators of PMN by binding to common IL-8 receptors (1). Such binding elicits diverse biological responses such as chemotaxis, degranulation, or adhesion. PF-4, another member of the α-subgroup of the chemokine family, is released in high concentrations from activated platelets (2,3). The functional role of PF-4 is intriguing. Highly purified PF-4 lacks any apparent biological activity for PMN but will in the presence of tumor necrosis factor α stimulate these cells to exocytose secondary granule markers or adhere tightly to different surfaces (4). These PF-4-induced functions are not elicited through binding to IL-8 receptors but by interaction with distinct binding sites different from all other chemokine receptors known so far (4,5). The action of PF-4 on PMN was shown to be sensitive to chondroitinase ABC treatment and could be inhibited by soluble chondroitin sulfate (CS), indicating that the potential receptor is of CS proteoglycan type (5).
CSs are galactosaminoglycans composed of alternating glucuronic acid and galactosamine units (→4GlcAβ1→3GalNAcβ1→)n that areO-sulfated on one or both units.2 In contrast to the glucosaminoglycans heparin and heparan sulfate (HS), they do not contain N-sulfate groups or l-iduronic acid units (except for CSB), which have been particularly implicated in protein binding to HS chains (6). The expression of glycosaminoglycans (GAGs) on neutrophils has been described previously by several authors. Pioneering work by Olsson and co-workers showed that PMN predominantly express chondroitin 4-sulfate (CSA) (7, 8), and Levitt et al. demonstrated a minor proportion of HS in these cells (9). However, as all of these analyses were done with total cell extracts, little is known about the composition and function of cell surface-expressed GAGs in PMN. Gardiner and colleagues showed that the majority of metabolically 35S-labeled compounds occurs as proteoglycans in neutrophil granules where they may enable proper storage of granule contents or exert protective functions against cellular damage (10,11). Here, we provide evidence that surface exposed CS chains serve as physiologically relevant receptors for PF-4 on PMN, and propose that this function is critically dependent on the content of sulfate groups.
Place, publisher, year, edition, pages
1999. Vol. 274, no 18, 12376-12382 p.
Medical and Health Sciences
IdentifiersURN: urn:nbn:se:uu:diva-61836DOI: 10.1074/jbc.274.18.12376OAI: oai:DiVA.org:uu-61836DiVA: diva2:89747