Eotaxin Selectively Binds Heparin

Abstract

An important feature of chemokines is their ability to bind to the glycosaminoglycan (GAG) side chains of proteoglycans, predominately heparin and heparan sulfate. To date, all chemokines tested bind to immobilized heparin in vitro, as well as cell surface heparan sulfate in vitro and in vivo. These interactions play an important role in modulating the action of chemokines by facilitating the formation of stable chemokine gradients within the vascular endothelium and directing leukocyte migration, by protecting chemokines from proteolysis, by inducing chemokine oligomerization, and by facilitating transcytosis. Despite the importance of eotaxin in eosinophil differentiation and recruitment being well established, little is known about the interaction between eotaxin and GAGs and the functional consequences of such an interaction. Here we report that eotaxin binds selectively to immobilized heparin with high affinity (K d ‫؍‬ 1.23 ؋ 10 ؊8 M), but not to heparan sulfate or a range of other GAGs. The interaction of eotaxin with heparin does not promote eotaxin oligomerization but protects eotaxin from proteolysis directly by plasmin and indirectly by cathepsin G and elastase. In vivo, co-administration of eotaxin and heparin is able to significantly enhance eotaxin-mediated eosinophil recruitment in a mouse air-pouch model. Furthermore, when heparin is coadministered with eotaxin at a concentration that does not normally result in eosinophil infiltration, eosinophil recruitment occurs. In contrast, heparin does not enhance eotaxin-mediated eosinophil chemotaxis in vitro, suggesting protease protection or haptotactic gradient formation as the mechanism by which heparin enhances eotaxin action in vivo. These results suggest a role for mast cell-derived heparin in the recruitment of eosinophils, reinforcing Th2 polarization of inflammatory responses.Chemokines are a superfamily of proteins that control the migration of leukocytes to sites of inflammation during an immune response. A feature of chemokines is their ability to bind to the glycosaminoglycan (GAG) 3 side chains of proteoglycans, predominately heparin and heparan sulfate. To date, all chemokines tested bind to immobilized heparin in vitro, as well as cell surface heparan sulfate in vitro and in vivo (1). In vitro, chemokine-heparin or heparan sulfate binding may be competitively inhibited by the GAGs chondroitin sulfate and dermatan sulfate (1, 2), suggesting that some chemokines may also bind these GAGs. Different chemokines bind heparin or heparan sulfate with varying affinity (1-3), and four different models, or docking modes, have been proposed for the interaction of chemokines with heparin and heparan sulfate (4). Heparin and heparan sulfate play an important role in modulating the function of chemokines (5) and have been proposed to control chemokine action in three ways. First, it is well established that heparan sulfate immobilizes chemokines on the luminal surface of endothelial cells (6, 7), which is essential for the formation of stable chemokine...

Chemokine and chemokine receptor structure and interactions: implications for therapeutic strategies

“…Cell surface immobilization of chemokines enables them to act locally rather than as paracrine molecules, and likely prevents inappropriate activation and desensitization of receptors on cells outside the region of interest for a given physiological situation 24, 25 . Chemokine:GAG interactions have also been shown to facilitate secretion of chemokines from tumor cells 26 and T cells 26 , transcytosis across cells 27, 28 , chemokine stability 29 and even signaling 30 .…”

Interference with Glycosaminoglycan-Chemokine Interactions with a Probe to Alter Leukocyte Recruitment and Inflammation In Vivo

“…The interaction site of chemokines with their receptors is located at the chemokine aminoterminus, whereas chemokine binding to glycosaminoglycans is less well understood [11], [12]. If the binding of COAM would interfere with the chemokine receptor interaction, COAM should reduce chemotaxis.…”

“…In view of the chemical structure of COAM [19], chemokine binding to COAM might protect these chemokines from proteolytic degradation. Protection from proteolysis has been demonstrated in the case of interaction between heparin and eotaxin [12] and between heparan sulphate and IL-8 [34] or SDF-1 [35].…”

“…Leukocyte recruitment into tissues is supposed to require chemokine presentation on endothelial cells to circulating immune cells, as well as the establishment of a sustained chemotactic gradient across the vessel walls and into the extracellular matrix and tissues. GAGs are crucial molecules throughout this process by locally restraining chemokines, preventing chemokine dilution and even protection against proteolysis [11], [12]. Indeed, heparan sulphate has been shown to immobilize chemokines at the luminal endothelial cell surface [13].…”

Regulation of Chemokine Activity – A Focus on the Role of Dipeptidyl Peptidase IV/CD26

“…Indeed, interference with GAG binding by using short chemokine-derived peptides, mutated chemokines without affinity for GPCRs, and enhanced-binding properties to GAGs, or chemokine-binding aptamers, which block chemokine–GAG interactions resulted in reduced leukocyte migration in vivo (114–116). In addition, in vivo heparin binding was shown to protect CCL11 (in)directly against proteolysis mediated by plasmin, cathepsin G, and elastin and positively affects the chemotactic activity of the chemokine (117). Evidence in favor of the hypothesis that GAG binding can serve as a protective factor regarding to proteolysis was also provided by the observation that binding to heparan sulfate or heparin oligosaccharides avoids CD26-mediated proteolysis of CXCL12 (118).…”