Glycosaminoglycans interact selectively with chemokines and modulate receptor binding and cellular responses

Chemokines selectively recruit and activate a variety of cells during infla mmation. Interactions between cell surface glycosaminoglycans (GAGs) and ch emokines drive the formation of haptotactic or immobilized gradients of che mokines at the site of inflammation, directing this recruitment. Chemokines bind to glycosaminoglycans on human umbilical vein endothelial cells (HUVE Cs) with affinities in the micromolar range: RANTES > MCP-1 > IL-8 > MIP-1 alpha. This binding can be competed with by soluble glycosaminoglycans: hep arin, heparin sulfate, chondroitin sulfate, and dermatan sulfate. RANTES bi nding showed the widest discrimination between glycosaminoglycans (700-fold ), whereas MIP-1 alpha was the least selective. Almost identical results we re obtained in an assay using heparin sulfate beads as the source of immobi lized glycosaminoglycan. The binding of chemokines to glycosaminoglycan fra gments has a strong: length dependence, and optimally requires both N- and O-sulfation. Isothermal titration calorimetry data confirm these results; I L-8 binds heparin fragments with a K-d of 0.39-2.63 mu M, and requires five saccharide units to bind each monomer of chemokine. In membranes from cell s expressing the G-protein-coupled chemokine receptors CXCR1, CXCR2, and CC R1, soluble GAGs inhibit the binding of chemokine ligands to their receptor s, Consistent with this, heparin and heparin sulfate could inhibit IL-8-ind uced neutrophil calcium flux. Chemokines can therefore form complexes with both cell surface and soluble GAGs; these interactions have different funct ions. Soluble GAG chemokines complexes are unable to bind the receptor, res ulting in a block of the biological activity. Previously, we have shown tha t cell surface GAGs present chemokines to the G-protein-coupled receptors, by increasing the local concentration of protein. A model is presented whic h brings together all of these data. The selectivity in the chemokine-GAG i nteraction suggests selective disruption of the haptotactic gradient may be an achievable therapeutic approach in inflammatory disease.