The collagen-breakdown product N-acetyl PGP does not interact directly with human CXCR1 and CXCR2

Inflammatory Bowel Diseases (IBD) and Chronic Obstructive Pulmonary Diseases (COPD) are diseases characterized by a significant accumulation of leukocytes in the bowel and pulmonary mucosa, respectively. Chemokines and their receptors are the key mediators involved in this infiltration of leukocytes. Since CXCR1 and CXCR2 are both expressed on neutrophils, these receptors are prime targets in the treatment of IBD and COPD. Recently, Weathington and colleagues (2006, Nature Medicine) have shown that the collagen breakdown product N- acetyl-proline-glycine-proline (N-α-PGP) is able to attract neutrophils, HL60 cells and CXCR1 or CXCR2 expressing RBL-2H3 cells. Furthermore, they showed that this chemotaxis was dependent on CXCR1 and CXCR2 receptors both in vitro as well in vivo. As such, N-α-PGP can be a potential player in IBD and COPD. However, we showed in [125I]-CXCL8 binding studies that N-α-PGP does not bind to human CXCR1 or CXCR2 on HEK293T cells expressing these receptors. Furthermore, N- α-PGP is not able to activate human CXCR1 and CXCR2 in several functional assays (chemotaxis of L1.2 cells expressing human CXCR1 and CXCR2, inositol phosphate accumulation in HEK293T cells and β-arrestin recruitment assays in PathHunter™HEK293 cells). Therefore, we conclude the N-α-PGP does not directly interact with human CXCR1 and CXCR2. Additional studies have shown that N-α-PGP is capable to activate neutrophils to release CXCL8. On its turn, CXCL8 can activate CXCR1 and CXCR2-mediated signaling. Taken together, N-α-PGP indirectly signals via CXCR1 and CXCR2. As such, N-α- PGP, CXCR1 and CXCR2 are important targets in inflammatory diseases.