Elena Monica Borroni

Chemokines and chemokine receptors: an overview.

Chemokines are chemotactic cytokines orchestrating leukocyte recruitment in physiological and pathological conditions. This complex system includes 42 molecules and 19 receptors and is subjected to different levels of regulation, including ligand production, post-translational modifications and degradation, as well as receptor expression and signaling activity. Here we analyze the chemokine system, with particular attention to available information on clinical situations in which chemokines or their receptors might assume diagnostic value.

Protection against inflammation- and autoantibody-caused fetal loss by the chemokine decoy receptor D6

Fetal loss in animals and humans is frequently associated with inflammatory conditions. D6 is a promiscuous chemokine receptor with decoy function, expressed in lymphatic endothelium, that recognizes and targets to degradation most inflammatory CC chemokines. Here, we report that D6 is expressed in placenta on invading extravillous trophoblasts and on the apical side of syncytiotrophoblast cells, at the very interface between maternal blood and fetus. Exposure of D6−/− pregnant mice to LPS or antiphospholipid autoantibodies results in higher levels of inflammatory CC chemokines and increased leukocyte infiltrate in placenta, causing an increased rate of fetal loss, which is prevented by blocking inflammatory chemokines. Thus, the promiscuous decoy receptor for inflammatory CC chemokines D6 plays a nonredundant role in the protection against fetal loss caused by systemic inflammation and antiphospholipid antibodies.

Unique role of junctional adhesion molecule-a in maintaining mucosal homeostasis in inflammatory bowel disease.

BACKGROUND & AIMS Junctional adhesion molecule-A (JAM-A) is localized at the tight junctions and controls leukocyte migration into the tissues. However, its functional role in inflammatory bowel disease (IBD) is unexplored. METHODS Control, Crohns disease (CD), and ulcerative colitis (UC) tissue specimens were studied for JAM-A expression, as well as the colon of mice given dextran sodium sulfate (DSS). Wild-type and JAM-A(-/-), Tie-2-Cre-JAM-A(-/-) (endothelial/hematopoietic-specific JAM inactivation) mice were studied for susceptibility to DSS. Disease activity and colonic inflammation were assessed using a disease activity index histology and endoscopy, and mucosal cytokines were measured by enzyme-linked immunosorbent assay. JAM-A function was investigated by RNA silencing in epithelial cells, and apoptosis was measured. RESULTS In both CD and UC, as well as in experimental colitis, there is a loss of epithelial but not endothelial JAM-A expression. Deletion of JAM-A results in a dramatic increase in susceptibility to DSS colitis, as assessed by weight loss, disease activity index, histologic and endoscopic severity, and strikingly high mortality rates. This is not caused by the absence of JAM-A in the endothelial or hematopoietic compartments because Tie-2-Cre-JAM-A(-/-) mice are no more susceptible to DSS colitis than wild-type animals. JAM-A(-/-) mice displayed increased intestinal permeability and inflammatory cytokine production, and marked epithelial apoptosis. Silencing of JAM-A in intestinal epithelial cells resulted in increased permeability in vitro. CONCLUSIONS Our results show a nonredundant and novel role of JAM-A in controlling mucosal homeostasis by regulating the integrity and permeability of epithelial barrier function.

The lymphatic system controls intestinal inflammation and inflammation-associated colon cancer through the chemokine decoy receptor D6

Background and aims Inflammatory CC chemokines have long been associated with cancer, but unequivocal evidence of a role in clinically relevant models of carcinogenesis is lacking. D6, a promiscuous decoy receptor that scavenges inflammatory CC chemokines, plays a non-redundant role in reducing the inflammatory response in various organs. As inflammation is a key player in the development of inflammatory bowel disease (IBD) and IBD-associated colorectal cancer, we investigated D6 expression in human colitis and colon cancer, and its role in experimental colitis and inflammation-associated colon cancer. Results In humans, D6 was mainly expressed by lymphatic vessels and leukocytes in the mucosa of individuals with IBD and colon cancer, as well as the mucosa of control individuals. Mice lacking expression of D6 were significantly more susceptible to experimental colitis than wild-type mice and failed to resolve colitis, with significantly higher levels of several pro-inflammatory chemokines. In bone marrow chimeric mice, the ability of D6 to regulate colitis was tracked to the stromal/lymphatic compartment, with no contribution of haemopoietic cells. Finally, after administration of the carcinogen azoxymethane, D6−/− mice showed increased susceptibility to colitis-associated cancer in the distal segment of the colon compared with wild-type mice. Conclusions D6 expressed on lymphatic vessels plays a key role in the control of intestinal inflammation and the development of inflammation-associated colon cancer. Our results reveal a new unexpected role for the lymphatic system in the pathogenesis of IBD and intestinal cancer, and candidate chemokines as novel players in tumour promotion and progression.

Chemokine receptors intracellular trafficking.

Chemokines coordinate leukocyte recruitment during inflammatory and immune responses through the interaction with a distinct subfamily of G protein-coupled receptors. The magnitude of the cellular response elicited by chemokines is dictated by the level of receptor expression at the plasma membrane, which is the balance of finely tuned endocytic and recycling pathways. Recent data have revealed that receptor trafficking properties can drive chemokine receptors to lysosomal degradation or recycling pathways, producing opposite effects on the strength of the intracellular signaling cascade. This review will cover recent advances on the molecular mechanisms underlying chemokine receptor internalization, recycling and degradation pathways, with particular attention to structural motifs present in receptor intracellular domains and their interacting adaptor proteins that modulate receptor trafficking and dictate proper biological response.

Recognition Versus Adaptive Up-regulation and Degradation of CC Chemokines by the Chemokine Decoy Receptor D6 Are Determined by Their N-terminal Sequence

The chemokine decoy receptor D6 controls inflammatory responses by selective recognition and degradation of most CCR1 to CCR5 agonistic ligands. CCL14 is a homeostatic chemokine present at high concentrations in the serum with a weak agonist activity on CCR1. Under inflammatory conditions, plasmin and UPA-mediated truncation of 8 amino acids generates the potent CCR1/CCR3/CCR5 isoform CCL14(9–74), which is further processed and inactivated by dipeptidyl peptidase IV/CD26 that generates CCL14(11–74). Here we report that D6 efficiently binds both CCL14 and its truncated isoforms. Like other D6 ligands, the biologically active CCL14(9–74) induces adaptive up-regulation of D6 expression on the cell membrane and is rapidly and efficiently degraded. In contrast, the D6-mediated degradation of the biologically inactive isoforms CCL14(1–74) and CCL14(11–74) is very inefficient. Thus, D6 cooperates with CD26 in the negative regulation of CCL14 by the selective degradation of its biologically active isoform. Analysis of a panel of CC chemokines and their truncated isoforms revealed that D6-mediated chemokine degradation does not correlate with binding affinity. Conversely, degradation efficiency is positively correlated with D6 adaptive up-regulation. Sequence analysis indicated that a proline residue in position 2 of D6 ligands is dispensable for binding but crucial for D6 adaptive up-regulation and efficient degradation.

β-arrestin-dependent activation of the cofilin pathway is required for the scavenging activity of the atypical chemokine receptor D6.

Far from being silent, the atypical chemokine receptor D6 depends on β-arrestin signaling to perform its scavenging function to degrade chemokines. Arresting Chemokine Scavenging Chemokines are chemoattractant cytokines, gradients of which stimulate the directed migration of cells to target sites, for example, during inflammation or infection. Chemokines signal through conventional chemokine receptors, which are G protein–coupled receptors; however, chemokines also bind to a subset of receptors, the atypical chemokine receptors (ACRs), that have no known signaling function. Borroni et al. found that chemokine binding to D6, a prototypical ACR that acts as a scavenger to degrade chemokines, activated a β-arrestin–dependent, but G protein–independent, signaling pathway involving the actin-binding protein cofilin that was required for its functions. These findings suggest that D6 is a β-arrestin–biased signaling receptor and that this pathway is required for chemokine scavenging. Chemokines promote the recruitment of leukocytes to sites of infection and inflammation by activating conventional heterotrimeric guanine nucleotide–binding protein (G protein)–coupled receptors (GPCRs). Chemokines are also recognized by a set of atypical chemokine receptors (ACRs), which cannot induce directional cell migration but are required for the generation of chemokine gradients in tissues. ACRs are presently considered “silent receptors” because no G protein–dependent signaling activity is observed after their engagement by cognate ligands. We report that engagement of the ACR D6 by its ligands activates a β-arrestin1–dependent, G protein–independent signaling pathway that results in the phosphorylation of the actin-binding protein cofilin through the Rac1–p21-activated kinase 1 (PAK1)–LIM kinase 1 (LIMK1) cascade. This signaling pathway is required for the increased abundance of D6 protein at the cell surface and for its chemokine-scavenging activity. We conclude that D6 is a signaling receptor that exerts its regulatory function on chemokine-mediated responses in inflammation and immunity through a distinct signaling pathway.

Chemokine Decoy Receptors: New Players in Reproductive Immunology

Chemokines are multifunctional molecules with roles in leukocyte trafficking and developmental processes. Both fetal and maternal components of the placenta produce chemokines, which control leukocyte trafficking observed in the placenta. Thus, chemokines play roles in the balance between protection of the developing embryo/fetus and tolerance of its hemiallogeneic tissues. Recently, a group of chemokine receptors, which include D6, DARC, and CCX-CKR, have been described as “silent” receptors by virtue of their inability to activate signal transduction events leading to cell chemoattraction. Here we review in vitro and in vivo evidence indicating that chemokine “silent” receptors regulate innate and adaptive immunity behaving as decoy receptors that support internalization and degradation of chemotactic factors, and discuss available information on their potential role in reproductive immunology.

Inflammation and prostate cancer: friends or foe?

IntroductionProstate cancer is the most common non-cutaneous malignancy diagnosed in men. Moving from histological observations since a long time, it has been recognized that innate and adaptive immunity actively participates in the pathogenesis, surveillance, and progression of prostate cancer.Materials and methodsA PubMed and Web of Science databases search was performed for studies providing evidence on the roles of the innate and adaptive immunity during the development and progression of prostate cancer.ConclusionsThere are growing evidences that chronic inflammation is involved in the regulation of cellular events in prostate carcinogenesis, including disruption of the immune response and regulation of the tumor microenvironment. This review discusses the role played by the innate and adaptive immune system in the local progression of prostate cancer, and the prognostic information that we can currently understand and exploit.

Expression of the Atypical Chemokine Receptor D6 in Human Alveolar Macrophages in COPD

BACKGROUND D6 is an atypical chemokine receptor involved in chemokine degradation and resolution of acute inflammatory responses in mice. Emerging evidence suggests that D6 might behave differently in human chronic inflammatory conditions. We, therefore, investigated the involvement of D6 in the immune responses in COPD, a chronic inflammatory condition of the lung. METHODS D6 expression was quantified by immunohistochemistry in surgical resected lung specimens from 16 patients with COPD (FEV(1), 57% ± 6% predicted) and 18 control subjects with normal lung function (nine smokers and nine nonsmokers). BAL was also obtained and analyzed by flow cytometry, immunofluorescence, and molecular analysis for further assessment of D6 involvement. RESULTS D6 expression in the lung was mainly detected in alveolar macrophages (AMs). The percentage of D6(+) AMs was markedly increased in patients with COPD as compared with both smoker and nonsmoker control subjects (P < .0005 for both). D6 expression was detected at both transcript and protein level in AMs but not in monocyte-derived macrophages. Finally, D6 expression was positively correlated with markers of immune activation (CD8(+) T lymphocytes, IL-32, tumor necrosis factor-α, B-cell activating factor of the tumor necrosis factor family, phospho-p38 mitogen-activated protein kinase) and negatively with lung function (FEV(1), FEV(1)/FVC). CONCLUSIONS D6 is expressed in AMs from patients with COPD, and its expression correlates with the degree of functional impairment and markers of immune activation. Upregulation of D6 in AMs could indicate that, besides its known scavenger activity in acute inflammation, D6 may have additional roles in chronic inflammatory conditions possibly promoting immune activation.