CDB15:0000416 CXCL6 — CXCR1

ABSTRACT: Functional interleuin-8 (IL-8) receptors (IL-8RA and IL-8RB: CXCR1 and CXCR2, respectively) have been described in human, monkey, dog, rabbit, and guinea pig. Although three IL-8R homologues have been found in rat, only one of these, rat CXCR2, appears to be functional based on responsiveness to ligands. Similarly, CXC chemokines induce biological responses through the murine homolog of CXCR2, but the identification of functional rodent CXCR1 homologues has remained elusive. We have identified and characterized the mouse CXCR1 homologue (mCXCR1). Murine CXCR1 shares 68 and 88% amino acid identity with its human and rat counterparts, respectively. Similar to the tissue distribution pattern of rat CXCR1, we found murine CXCR1 mRNA expression predominantly in lung, stomach, bone marrow, and leukocyte-rich tissues. In contrast to previous reports, we determined that mCXCR1 is a functional receptor. We show predominant engagement of this receptor by mouse GCP-2/CXCL6, human GCP-2, and IL-8/CXCL8 by binding, stimulation of GTPgammaS exchange, and chemotaxis of mCXCR1-transfected cells. Furthermore, murine CXCR1 is not responsive to the human CXCR2 ligands ENA-78/CXCL5, NAP-2/CXCL7, GRO-alpha, -beta, -gamma/CXCL1-3, or rat CINC-1-3. In addition, we show concomitant elevation of mCXCR1 and its proposed major ligand, GCP-2, positively correlated with paw swelling in murine collagen-induced arthritis. This report represents the first description of a functional CXCR1-like receptor in rodents.

ABSTRACT: The inflammatory response is mediated by a family of chemotactic cytokines, designated chemokines. The receptor usage of the CXC chemokine granulocyte chemotactic protein-2 (GCP-2) was compared with that of interleukin-8 (IL-8) and epithelial-cell-derived neutrophil attractant-78 (ENA-78). Chemokine activities were evaluated by measurement of intracellular calcium increase and by chemotaxis and binding assays, using CXC chemokine receptor (CXCR)-transfected cell lines. GCP-2 was equally potent at inducing a rise in [Ca2+]i in both CXCR1-transfected and CXCR2-transfected cells (minimal effective concentration 3 nM). IL-8 augmented the [Ca2+]i more efficiently in CXCR1-transfectants than in CXCR2-transfectants, whereas for ENA-78, threefold higher concentrations were necessary to obtain a calcium response in CXCR1-transfected cells than in CXCR2-transfectants. GCP-2 desensitized the calcium increase induced by IL-8 in both CXCR1-transfected and CXCR2-transfected cells, but ENA-78 only affected the IL-8-induced calcium response in CXCR2-transfectants. The half-maximal effective concentrations for migration of CXCR2-transfectants in response to GCP-2 and ENA-78 were similar (0.1 nM), whereas GCP-2 was tenfold more potent than ENA-78 on CXCR1-transfectants. Half-maximal migration of CXCR1-transfected and CXCR2-transfected cells was obtained with IL-8 at concentrations of no more than 0.01 nM. Radiolabeled IL-8 could efficiently be displaced from CXCR2 by IL-8, GCP-2 and ENA-78. In contrast, only IL-8 and GCP-2 but not ENA-78, competed for 125I-IL-8 binding to CXCR1. From these data, it can be concluded that, in addition to IL-8, GCP-2, but not ENA-78, efficiently binds to both CXCR1 and CXCR2. The differential receptor usage of the structurally related ELR+ CXC chemokines GCP-2 and ENA-78 is indicative of a different role in inflammatory reactions.