Choe H., Moore M. in ACKR2 that Etizolam are responsible for ligand binding. The study also highlights ACKR2-derived N-terminal peptides as being of potential therapeutic significance. leukocyte migration and are defined by the presence of variations on a conserved cysteine motif in their mature sequences (1), and the large chemokine family is divided into four subfamilies (CC, CXC, XC and CX3C) according to the specific nature of this motif. Mammals have 45 chemokines and 18 receptors that involve themselves, in sometimes very complex ways, in regulating leukocyte migration. Given this complexity, it is common to simplify chemokine, and chemokine receptor, biology by referring to them as being either homeostatic or inflammatory according to the contexts in which they predominantly function (2, 3). Thus chemokines involved in basal trafficking of leukocytes into and out of peripheral tissues and secondary lymphoid organs are referred to as homeostatic. They are typically expressed at discrete tissue locales and by discrete cell types. In contrast, inflammatory chemokines and their receptors are largely involved in responding to tissue insults, injuries, or infections. Inflammatory chemokines are not expressed at high levels at steady state but are rapidly and substantially transcriptionally activated following an inflammatory insult. These chemokines then attract inflammatory leukocytes bearing their cognate receptors, and these cells remove pathogens, engulf debris, and assist in the process of tissue repair. In addition to the 18 signaling receptors for chemokines (4), there also exists a small subfamily of atypical chemokine receptors (ACKRs)2 that are characterized by an inability to mount classical receptor signaling following ligand binding (4,C8). This subfamily currently comprises four receptors namely the Duffy antigen receptor for chemokines (DARC/ACKR1), D6/ACKR2, CXCR7/ACKR3, and CCRL1/ACKR4. We have been particularly interested in ACKR2, which was previously known as D6 (5). This receptor binds essentially all inflammatory CC-chemokines with high affinity but does not mount classical signaling responses following ligand binding (9,C11). We and others have demonstrated that ACKR2 is a highly efficient binder, internalizer, and scavenger of inflammatory CC-chemokines (12, 13). In essence, therefore, ACKR2 plays a role in removing chemokines from inflamed sites. ACKR2 is expressed in barrier tissues including the skin, gut, and lung, as well as in the syncytiotrophoblast layer of the placenta (14,C16). In adult tissues ACKR2 is prominently expressed on lymphatic endothelial cells (16, 17), although expression has also been reported on leukocytes (17,C21) and keratinocytes (22). In keeping with its chemokine scavenging role, numerous studies utilizing ACKR2-deficient Etizolam mice have demonstrated the fundamental importance of ACKR2 for the resolution of inflammatory responses (15, 23,C28). Although it was initially assumed that this involved the scavenging and degradation of chemokines throughout an inflamed area, it now appears that ACKR2 plays a more subtle role in this context by minimizing inflammatory leukocyte Etizolam interaction with lymphatic endothelial cell surfaces and therefore ensuring the openness of lymphatic channels (29,C31). Thus in ACKR2-deficient mice, lymphatic vessels Rabbit Polyclonal to Cytochrome P450 4Z1 become congested by inappropriate association with inflammatory leukocytes, and this impairs drainage of fluid, cytokines, chemokines, and cells from inflamed sites thus accounting for the impaired resolution of the inflammatory response. Notably, despite having been clearly demonstrated to be important in a range of contexts, little is known about the structure/function relationships within ACKR2 that contribute to chemokine binding. With the signaling chemokine receptors, a number of regions are known to be involved in ligand binding. Prominent among these is the N terminus and, in particular, a sulfated tyrosine motif in this region (32,C41, 43). The purpose of the present study was to determine whether mechanisms important for chemokine interactions with conventional chemokine receptors are conserved in the related atypical receptor ACKR2. In this study, we demonstrate the essential importance of sulfated tyrosine residues at the N terminus of ACKR2 for chemokine binding and internalization. In addition, we provide evidence that a peptide generated from the N terminus of ACKR2 is capable of neutralizing the activities of ACKR2 ligands. These data therefore highlight the N terminus as a key regulator of ligand binding by ACKR2 and suggest that peptides derived from this region may.