Glycosaminoglycan binding and oligomerization are essential for the <i>in vivo</i> activity of certain chemokines

TLDR

During organogenesis, immunosurveillance, and inflammation, chemokines selectively recruit leukocytes by activating seven‑transmembrane‑spanning receptors, and it has been suggested that a haptotactic gradient formed by immobilization on cell surface glycosaminoglycans (GAGs) is important, though this has not been experimentally demonstrated in vivo. The study investigated how mutations in the GAG binding sites of CCL2, CCL4, and CCL5 affect their ability to recruit cells in vivo. They generated GAG‑binding mutants of CCL2, CCL4, and CCL5 and evaluated their cell‑recruiting activity after intraperitoneal injection. Mutant chemokines retain in vitro chemotactic activity but fail to recruit cells in vivo, and monomeric variants are also inactive in vivo, demonstrating that GAG binding and oligomerization are essential for in vivo activity but not for receptor activation in vitro.

Abstract

During organogenesis, immunosurveillance, and inflammation, chemokines selectively recruit leukocytes by activating seven-transmembrane-spanning receptors. It has been suggested that an important component of this process is the formation of a haptotactic gradient by immobilization of chemokines on cell surface glycosaminoglycans (GAGs). However, this hypothesis has not been experimentally demonstrated in vivo . In the present study we investigated the effect of mutations in the GAG binding sites of three chemokines, monocyte chemoattractant protein-1/CC chemokine ligand (CCL)2, macrophage-inflammatory protein-1β/CCL4, and RANTES/CCL5, on their ability to recruit cells in vivo . These mutant chemokines retain chemotactic activity in vitro , but they are unable to recruit cells when administered intraperitoneally. Additionally, monomeric variants, although fully active in vitro , are devoid of activity in vivo . These data demonstrate that both GAG binding and the ability to form higher-order oligomers are essential for the activity of particular chemokines in vivo , although they are not required for receptor activation in vitro . Thus, quaternary structure of chemokines and their interaction with GAGs may significantly contribute to the localization of leukocytes beyond migration patterns defined by chemokine receptor interactions.