Post-translational control of chemokines: A role for decoy receptors?

Cancer Research UK Beatson Laboratories, The Beatson Institute for Cancer Research, Garscube Estate, Switchback Road, Glasgow G61 1BD, UK.
Immunology Letters (Impact Factor: 2.51). 02/2005; 96(2):163-74. DOI: 10.1016/j.imlet.2004.08.018
Source: PubMed


It is well-established that chemokines play a critical role in the orchestration of inflammation and immunity. Interactions between chemokines and their receptors are essential for the homing of specific subsets of leukocytes to their functional microenvironments. They also influence other diverse biological processes such as development, leukocyte activation, Th1/Th2 polarisation, tumour metastasis, angiogenesis, and HIV pathogenesis. However, despite their importance, only now are we beginning to understand the complex regulation brought to bear on these molecules. In this review, we discuss a number of these key chemokine regulators that exert their influence once these proteins have been synthesised. We examine (i) chemokine storage, release, and presentation, (ii) protease regulation, (iii) viral manipulation of host chemokines, and (iv) natural mammalian receptor antagonists. Principally, the growing evidence for a role for decoy receptors in the chemokine system is discussed. In particular, the potential decoy function of the 'silent' pro-inflammatory chemokine receptor D6 is described alongside two other candidate decoy receptor molecules, DARC, and CCX-CKR. Dissecting the biological and pathological function of these chemokine controllers will lead to a deeper understanding of chemokine regulation, and may reveal novel strategies to therapeutically modify the chemokine system.

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    • "In each case, these strategies are specific for the blockade of single ligands or receptors. Given the multiple redundancy within both chemokines and their receptors, it seems likely that a strategy to simultaneously modulate a number of chemokines will have a clinical advantage (11); indeed, naturally occurring chemokine “scavenger” receptors such as D6 and DARC can perform this function in vivo by clearance of groups of chemokines (12). Notably, GPCR agonists, including the chemokines, can induce both homologous and heterologous receptor tolerance, suggesting that single agents might negate the potential of a cell to respond to multiple chemokines (5). "
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    ABSTRACT: Interaction between chemokines and heparan sulfate (HS) is essential for leukocyte recruitment during inflammation. Previous studies have shown that a non-HS-binding mutant form of the inflammatory chemokine CCL7 can block inflammation produced by wild-type chemokines. This study examined the anti-inflammatory mechanism of a non-HS-binding mutant of the homeostatic chemokine CXCL12. Initial experiments demonstrated that mutant CXCL12 was an effective CXCR4 agonist. However, this mutant chemokine failed to promote transendothelial migration in vitro and inhibited the haptotactic response to wild-type CCL7, CXCL12, and CXCL8, and naturally occurring chemoattractants in synovial fluid from the rheumatoid synovium, including CCL2, CCL7, and CXCL8. Notably, intravenous administration of mutant CXCL12 also inhibited the recruitment of leukocytes to murine air pouches filled with wild-type CXCL12. Following intravenous administration, wild-type CXCL12 was cleared from the circulation rapidly, while the mutant chemokine persisted for >24 h. Chronic exposure to mutant CXCL12 in the circulation reduced leukocyte-surface expression of CXCR4, reduced the chemotactic response of these cells to CXCL12, and inhibited normal chemokine-mediated induction of adhesion between the alpha4beta1 integrin, VLA-4, and VCAM-1. These data demonstrate that systemic administration of non-HS-binding variants of CXCL12 can mediate a powerful anti-inflammatory effect through chemokine receptor desensitization.
    Full-text · Article · Sep 2009 · The FASEB Journal
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    • "Several papers have focused recently on “scavenger receptors” which are “atypical” receptors playing a role in scavenging or altering the localization of chemoattractant molecules such as chemokines and complement molecules [8, 10, 25]. The “atypical” receptor family comprised the receptors D6, the Duffy Antigen/Receptor for Chemokines and CCRL1/CCX-CKR [8, 10]. CCRL1 was described in mice and humans but there was no data about this receptor in the pig [9, 16, 34, 37]. "
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    ABSTRACT: Salmonella enterica subspecies enterica serovar Typhimurium, commonly called S. Typhimurium, can cause intestinal infections in humans and various animal species such as swine. To analyze the host response to Salmonella infection in the pig we used an in vivo gut loop model, which allows the analysis of multiple immune responses within the same animal. Four jejunal gut-loops were each inoculated with 3 x 10(8) cfu of S. Typhimurium in 3 one-month-old piglets and mRNA expressions of various cytokines, chemokines, transcription factors, antimicrobial peptides, toll like and chemokine receptors were assessed by quantitative real-time PCR in the Peyer's patch and the gut wall after 24 h. Several genes such as the newly cloned CCRL1/CCX-CKR were assessed for the first time in the pig at the mRNA level. Pro-inflammatory and T-helper type-1 (Th1) cytokine mRNA were expressed at higher levels in infected compared to non-infected control loops. Similarly, some B cell activation genes, NOD2 and toll like receptor 2 and 4 transcripts were more expressed in both tissues while TLR5 mRNA was down-regulated. Interestingly, CCL25 mRNA expression as well as the mRNA expressions of its receptors CCR9 and CCRL1 were decreased both in the Peyer's patch and gut wall suggesting a potential Salmonella strategy to reduce lymphocyte homing to the intestine. In conclusion, these results provide insight into the porcine innate mucosal immune response to infection with entero-invasive microorganisms such as S. Typhimurium. In the future, this knowledge should help in the development of improved prophylactic and therapeutic approaches against porcine intestinal S. Typhimurium infections.
    Full-text · Article · Nov 2008 · Veterinary Research
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    • "In summary, chemokines are important, multifunctional mediators of inflammation and immunity. The complexity of their biological role is suggested by many of their features, from the large number of members in the superfamily, to their complex ligand–receptor interactions, the multiple conformations of the receptor (homo-and hetero-dimerization ), as well as naturally-occurring splice variants, polymorphisms , and post-translational modifications (observed with locally released proteases); which all play a role in finely tuning their local biological actions (Mellado et al, 2001; Comerford and Nibbs, 2005). "
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    ABSTRACT: Healthy individuals initiate an immediate immune response to microbes by using a set of germline-encoded receptors that recognize common molecular patterns found on the surface of pathogens that are distinct from self-antigens. This innate immune response is the first line of defense against microorganisms in vertebrates, and constitutes the only immune response in plants and invertebrates. The innate immune system includes cellular components, as well as a host of soluble products (antimicrobial peptides, complement fragments, cytokines, and chemokines). The adaptive immune response, which provides long-lasting protection, takes days to develop and requires somatic mutations leading to the development of antigen-specific T cell receptors (cell-mediated immunity) and immunoglobulins (humoral immunity). Members of the chemokine superfamily are crucially involved in both innate and adaptive responses. We review the biological actions of the chemokine superfamily, focusing on several functions that are relevant for both immune responses, such as cell recruitment, microbicidal activity, cell activation, polarization of CD4+ T cells, and effects on structural cells. In particular, we will illustrate the central role that chemokines play in host defense, best demonstrated by the tremendous number of chemokine and chemokine receptor homologs found in microbial genomes, which deflect the immune response of the host.
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