The product of a novel growth factor-activated gene, fic, is a biologically active "C-C"-type cytokine

Monitoring Scavenging Activity of Chemokine Receptors

Migration and positioning of cells is fundamental for complex functioning of multicellular organisms. During an immune response, cells are recruited from remote distances to a distinct location. Cells that are passively transported leave the circulation stimulated by locally produced signals and follow chemotactic cues to reach specific destinations. Such gradients are short (<150 μm) and require a source of production where the concentration is the highest and a sink in apposition where the attractant dissipates and the concentration is the lowest. Several straight forward methods exist to identify in vitro and in vivo cells producing chemoattractants. This can be achieved at the transcriptional level and by measuring secreted proteins. However, to demonstrate the activity of sinks in vitro and in vivo is more challenging. Cell-mediated dissipation of an attractant must be revealed by measuring its uptake and subsequent destruction. Elimination of chemoattractants such as chemokines can be monitored in vitro using radiolabeled ligands or more elegantly with fluorescent-labeled chemoattractants. The latter method can also be used in vivo and enables to monitor the process in real time using time-lapse video microscopy. In this chapter, we describe methods to produce fluorescently labeled chemokines either as fusion proteins secreted from insect cells or as recombinant bacterial proteins that can enzymatically be labeled. We discuss methods that were successfully used to demonstrate sink activities of scavenger receptors. Moreover, fluorescent chemokines can be used to noninvasively analyze receptor expression and activity in living cells.

The MCP/eotaxin subfamily of CC chemokines

Migration of leukocytes from the bone marrow to the circulation, the primary lymphoid organs and inflammatory sites is directed by chemokines and specific receptor interactions. Besides the role of this group of low molecular weight cytokines in leukocyte attraction and activation, anti-HIV and hematopoietic activities were also attributed to chemokines. On the basis of the number and arrangement of the conserved cysteines, chemokines are subdivided in two multi-member families, namely the CXC and CC chemokines, whereas fractalkine (CX3C) and lymphotactin (C) are unique relatives. The CC chemokines possess four cysteines of which the first two are adjacent. Functionally, they form a rather heterogeneous family. Here, the focus is on the monocyte chemotactic proteins and eotaxin which, on a structural basis, can be considered as a CC chemokine subfamily. Not only the protein sequences, but also the gene structures, chromosomal location, biological activities and receptor usage exhibit considerable similarities. The review is complemented with a comparison of the biological functions of the MCP/eotaxin-subfamily in physiology and pathology.

Chemokines and chemokine receptors during activation and deactivation of monocytes and dendritic cells and in amplification of Th1 versus Th2 responses

Chemokines are a superfamily of small cytokines which are generally chemotactic for leukocytes. The general features of chemokines and their receptors are reviewed. Recent evidence indicates that receptor expression dictates the spectrum of action of chemokines, as shown recently for Th1 and Th2 cells. Chemokines represent amplification loops of polarized Th1 and Th2 responses. Receptor expression is tightly regulated during differentiation, activation, and deactivation of mononuclear phagocytes and dendritic cells. Thus, regulation of receptor expression is crucial as a set point of the chemokine system.

Abnormalities in monocyte recruitment and cytokine expression in monocyte chemoattractant protein 1-deficient mice

Monocyte chemoattractant protein 1 (MCP-1) is a CC chemokine that attracts monocytes, memory T lymphocytes, and natural killer cells. Because other chemokines have similar target cell specificities and because CCR2, a cloned MCP-1 receptor, binds other ligands, it has been uncertain whether MCP-1 plays a unique role in recruiting mononuclear cells in vivo. To address this question, we disrupted SCYA2 (the gene encoding MCP-1) and tested MCP-1-deficient mice in models of inflammation. Despite normal numbers of circulating leukocytes and resident macrophages, MCP-1(-/-) mice were specifically unable to recruit monocytes 72 h after intraperitoneal thioglycollate administration. Similarly, accumulation of F4/80+ monocytes in delayed-type hypersensitivity lesions was impaired, although the swelling response was normal. Development of secondary pulmonary granulomata in response to Schistosoma mansoni eggs was blunted in MCP-1(-/-) mice, as was expression of IL-4, IL-5, and interferon gamma in splenocytes. In contrast, MCP-1(-/-) mice were indistinguishable from wild-type mice in their ability to clear Mycobacterium tuberculosis. Our data indicate that MCP-1 is uniquely essential for monocyte recruitment in several inflammatory models in vivo and influences expression of cytokines related to T helper responses.

Defects in macrophage recruitment and host defense in mice lacking the CCR2 chemokine receptor

Chemokines are a structurally related family of cytokines that are important for leukocyte trafficking. The C-C chemokine monocyte chemoattractant protein-1 (MCP-1) is a potent monocyte activator in vitro and has been associated with monocytic infiltration in several inflammatory diseases. One C-C chemokine receptor, CCR2, has been identified that mediates in vitro responses to MCP-1 and its close structural homologues. CCR2 has also recently been demonstrated to be a fusion cofactor for several HIV isolates. To investigate the normal physiological function of CCR2, we generated mice with a targeted disruption of the ccr2 gene. Mice deficient for CCR2 developed normally and had no hematopoietic abnormalities. However, ccr2(-/-) mice failed to recruit macrophages in an experimental peritoneal inflammation model. In addition, these mice were unable to clear infection by the intracellular bacteria, Listeria monocytogenes. These results suggest that CCR2 has a nonredundant role as a major mediator of macrophage recruitment and host defense against bacterial pathogens and that MCP-1 and other CCR2 ligands are effectors of those functions.

Serum- and polypeptide growth factor-inducible gene expression in mouse fibroblasts

Complex cellular processes such as proliferation, differentiation, and apoptosis are regulated in part by extracellular signaling molecules: for example, polypeptide growth factors, cytokines, and peptide hormones. Many polypeptide growth factors exert their mitogenic effects by binding to specific cell surface receptor protein tyrosine kinases. This interaction triggers numerous biochemical responses, including changes in phospholipid metabolism, the activation of a protein phosphorylation cascade, and the enhanced expression of specific immediate-early, delayed-early, or late response genes. In this review, I summarize the major findings obtained from studies investigating the effects of serum or individual polypeptide growth factors on gene expression in murine fibroblasts. Several experimental approaches, including differential hybridization screening of cDNA libraries and differential display, have been employed to identify mRNA species that are expressed at elevated levels in serum- or polypeptide growth factor-stimulated cells. These studies have demonstrated that serum- and growth factor-inducible genes encode a diverse family of proteins, including DNA-binding transcription factors, cytoskeletal and extracellular matrix proteins, metabolic enzymes, secreted chemokines, and serine-threonine kinases. Some of these gene products act as effectors of specific cell cycle functions (e.g., enzymes involved in nucleotide and DNA synthesis), others are required to successfully convert a metabolically inactive cell to a metabolically active cell that will eventually increase in size and then divide (e.g., glucose-metabolizing enzymes), and some actually function as positive or negative regulators of cell cycle progression. In conclusion, research conducted during the past 15 years on serum- and growth factor-regulated gene expression in murine fibroblasts has provided significant insight into mitogenic signal transduction and cell growth control.

Production and purification of novel secreted human proteins

Our objective during the last year was to produce and purify 50-80 novel, secreted human proteins identified via high throughput cDNA sequencing and computer analysis. We chose the baculovirus expression vector system in order to obtain secreted, correctly folded, bioactive proteins. Recombinant (re-)baculoviruses (BV) were plaque purified, and pulse-labeling was used to verify the synthesis and secretion of the re-proteins. N-terminal microsequencing was performed to simultaneously confirm the identity of the protein(s) as well as the signal peptide (SP) cleavage site(s). Following sequence confirmation, the proteins were purified to homogeneity and functional assays carried out to determine potential therapeutic applications. We identified proteins with antiviral activity, several novel growth factors, proteins influencing the differentiation of specific cell types, novel proteases and protease inhibitors among others. Certain proteins were expressed both in insect cells and in CHO stable cell lines. In the cases analyzed, we found that the same SP cleavage site was utilized in the two expression systems. Significant differences were observed in the carbohydrate moieties attached to the proteins, though no effects on the biological activity due to these differences have been demonstrated. The BV system has served as a viable alternative for the high throughput, high fidelity expression of many novel secreted human genes. To date, more than 75 new genes have been expressed, and the re-proteins purified. This expression system combines many favorable traits including relative speed, moderate cost but perhaps most importantly, the production of biologically active proteins.

Murine monocyte chemoattractant protein (MCP)-5: a novel CC chemokine that is a structural and functional homologue of human MCP-1

The chemokines are a large family of cytokines that control the recruitment of leukocytes in immune and inflammatory responses. We describe the isolation of a novel murine CC chemokine that, based on its biological and structural features, we have named monocyte chemoattractant protein (MCP)-5. MCP-5 mapped to the CC chemokine cluster on mouse chromosome 11 and was most closely related to human MCP-1 in structure (66% amino acid identity). Purified recombinant MCP-5 protein was a potent chemoattractant for peripheral blood monocytes, was only weakly active on eosinophils at high doses, and was inactive on neutrophils. MCP-5 induced a calcium flux in peripheral blood mononuclear cells, but not in purified murine eosinophils or neutrophils. Consistent with these results, MCP-5 induced a calcium flux in human embryonic kidney (HEK)-293 cells transfected with human and murine CCR2, a CC chemokine receptor expressed on monocytes. MCP-5 did not induce a calcium flux in HEK-293 cells transfected with CCR1, CCR3, or CCR5. Constitutive expression of MCP-5 mRNA was detected predominantly in lymph nodes, and its expression was markedly induced in macrophages activated in vitro and in vivo. Moreover, MCP-5 expression was up-regulated in the lungs of mice following aerosolized antigen challenge of sensitized mice, and during the host response to infection with Nippostrongylus brasiliensis. These data indicate that MCP-5 is a novel and potent monocyte active chemokine that is involved in allergic inflammation and the host response to pathogens.

Leukocyte migration and activation by murine chemokines

Chemokines are a family of chemotactic cytokines which attract different types of leukocytes. This property, combined with some additional inflammatory and growth-regulatory activities, demonstrate their crucial role in the immune system. Chemokines are low molecular weight proteins and possess a typical positioning of four conserved cysteines. This family is further subdivided in two subfamilies depending on whether the first two cysteines are adjacent or not (CC and CXC chemokines, respectively). The CXC chemokines (including interleukin-8) predominantly attract neutrophils, whereas CC chemokines induce migration of monocytes, as well as other leukocyte cell types. In this article, the general characteristics of chemokines are reviewed. Furthermore, the murine CC chemokines, JE/MCP-1, MCP-3/MARC, MIP-1 alpha, MIP-1 beta, RANTES, TCA3, C10/MRP-1, MRP-2, and eotaxin, are discussed more in detail.

Chemokines: a superfamily of chemotactic cytokines

Chemokines are a bipartite family of chemotactic proteins that bear the structural hallmark of four cysteine residues, the first two of which are in tandem. The spectrum of action of chemokines encompasses a large number of leukocyte populations, including monocytes, granulocytes, lymphocytes, NK and dendritic cells. Although the spectrum of action of chemokines largely overlaps, clear differences are still present. Chemokines play an important role in the recruitment of leukocytes at the site of inflammation, allergic reaction and tumors. Available information on receptor usage by MCP-1 and related chemokines and signal transduction pathways is reviewed. The better understanding of signaling mechanisms will provide a new basis for the development of therapeutic strategies.

Cloning and functional expression of mCCR2, a murine receptor for the C-C chemokines JE and FIC

The C-C chemokines human monocyte chemoattractant protein-1 and -3 (MCP-1 and MCP-3) and mouse JE and FIC are potent activators of monocytes. Several receptors for MCP-1 and MCP-3 have been cloned from human monocytic cell lines, and one of these receptors, CCR2B, binds both MCP-l and MCP-3. Thus far, no murine receptors for JE or FIC have been reported. We have cloned a novel murine C-C chemokine receptor, designated mouse CCR2 (mCCR2), from the mouse monocyte cell line WEHI265.1. The predicted 373-amino acid sequence of mCCR2 shows highest identity (80%) with CCR2B. When stably expressed in human embryonic kidney 293 cells, mCCR2 specifically bound 125I-JE with high affinity. FIC was less potent than JE in competing 125I-JE binding to mCCR2-expressing cells, while three other mouse chemokines, MIP-1alpha, C10, and N51/KC, did not compete. mccr2 mRNA expression was detected in elicited peritoneal macrophages as well as in several mouse organs. The cloning of mCCR2 provides an important tool to investigate monocyte/macrophage responses to JE and FIC, to identify other targets for their action, and potentially to study models of CCR2 function in the mouse.

Molecular cloning of human eotaxin, an eosinophil-selective CC chemokine, and identification of a specific eosinophil eotaxin receptor, CC chemokine receptor 3

The CC chemokine eotaxin is a selective chemoattractant for guinea pig eosinophils, first purified from bronchoalveolar lavage fluid in a guinea pig model of allergic airway inflammation. We have now isolated the gene and cDNA for a human counterpart of eotaxin. The gene maps to chromosome 17 and is expressed constitutively at high levels in small intestine and colon, and at lower levels in various other tissues. The deduced mature protein sequence is 66% identical to human monocyte chemoattractant protein-1, and 60% identical to guinea pig eotaxin. Recombinant human eotaxin produced in insect cells induced a calcium flux response in normal human eosinophils, but not in neutrophils or monocytes. The response could not be desensitized by pretreatment of eosinophils with other CC chemokines, suggesting a unique receptor. In this regard, we show that human eotaxin is a potent and highly specific agonist for CC chemokine receptor 3, a G protein-coupled receptor selectively expressed in human eosinophils. Thus eotaxin and CC chemokine receptor 3 may be host factors highly specialized for eosinophil recruitment in inflammation, and may be good targets for the development of selective drugs for inflammatory diseases where eosinophils contribute to pathogenesis, such as asthma.

Chemokines and renal disease

Chemokines are low molecular weight inflammatory cytokines with chemoattractant properties as their major biologic effect. They are classified into at least two families. C-X-C chemokines (alpha subfamily) act primarily on neutrophils, while C-C chemokines act preferentially on monocytes. Chemokine receptors are G protein-coupled receptors that form a family of structurally and functionally related proteins. Chemokines are induced in cells and tissue in response to proinflammatory cytokines. They are produced by glomerular, tubular interstitial, and blood vessel cells. There is good evidence that chemokines contribute to neutrophil and mononuclear cell infiltration in glomeruli and interstitium. Their expression is increased in renal disease, and neutralization studies using antibodies in vivo demonstrated a role for certain chemokines in mediating renal pathology and proteinuria. Interleukin-8, RANTES, and monocyte chemotactic peptide are the best-studied chemokines in the kidney. Development of specific antibodies and receptor antagonists should help establish the precise role of these mediators in renal disease. Important therapeutic implications may result from this work.

Cloning and differential tissue-specific expression of three mouse beta chemokine receptor-like genes, including the gene for a functional macrophage inflammatory protein-1 alpha receptor

Macrophage inflammatory protein-1 alpha (MIP-1 alpha) and RANTES, members of the beta chemokine family of leukocyte chemoattractants, bind to a common seven-transmembrane-domain human receptor. We have now cloned three related mouse genes: one for a selective MIP-1 alpha receptor (MIP-1 alpha R) and two for orphan receptors provisionally designated MIP-1 alpha receptor-like 1 and 2 (MIP-1 alpha RL1 and 2). Their deduced sequences are 80, 62, and 63% identical to the human MIP-1 alpha/RANTES receptor, respectively. K562 cells stably transfected with MIP-1 alpha R specifically bound 125I-human MIP-1 alpha and 125I-human RANTES with high affinity. The rank order of beta chemokine competition for 125I-human MIP-1 alpha binding was human MIP-1 alpha > mouse MIP-1 alpha approximately RANTES approximately MIP-1 beta > MCP-1. However, human RANTES was approximately 100-fold less potent as a calcium-mobilizing agonist for MIP-1 alpha R than either human or mouse MIP-1 alpha, which matched the selectively of mouse leukocytes for calcium mobilization by MIP-1 alpha and RANTES. No other beta or alpha chemokines tested were agonists for MIP-1 alpha R. RNA for all three genes was detected in mouse leukocytes, but unique patterns of expression were identified in solid organs: MIP-1 alpha R, heart, spleen, and lung; MIP-1 alpha RL1, skeletal muscle; and MIP-1 alpha RL2, spleen and liver. These data identify potentially important new targets for beta chemokine action in the mouse.

Glucocorticoid-attenuated response genes encode intercellular mediators, including a new C-X-C chemokine

A major part of the anti-inflammatory effect of glucocorticoids is attributable to their attenuation of the induction of genes whose products mediate intercellular interactions, e.g. cytokines and the inducible forms of prostaglandin synthase and nitric oxide synthase. We hypothesized that (i) there exists a class of immediate-early/primary response genes whose induction by inflammatory agents, mitogens, and other stimuli is attenuated by glucocorticoids, and (ii) the products of these glucocorticoid-attenuated response genes (GARGs) function predominantly in paracrine cell processes. We constructed a lambda cDNA library from transforming growth factor beta 1-pretreated murine Swiss 3T3 cells stimulated with lipopolysaccharide (LPS) or serum in the presence of cycloheximide, screened 15,000 plaques by differential hybridization, and cloned 12 LPS-induced, dexamethasone-attenuated cDNAs. Seven were previously known. Six of these encode intercellular mediators (thrombospondin-1, MCSF, JE/MCP-1, MARC/fic/MCP-3, crg2/IP-10, and cyr61); one encodes a protein of unknown function (IRG2). Thus, a large majority of these GARG cDNAs encode intercellular mediators, as hypothesized. Of the five GARG cDNAs not previously known, one encodes a novel member of the CXC chemokine family, designated LIX (LPS-induced CXC chemokine). The predicted LIX protein has a 40-amino acid signal sequence and a 92-amino acid mature peptide with a distinctive COOH-terminal region. Surprisingly, segments of the 3'-untranslated regions of LIX and two other CXC chemokines have substantially greater nucleotide sequence homology than do their coding regions. These segments may perform an unknown regulatory function. The LIX message is strongly induced by LPS in fibroblasts, but not in macrophages, suggesting that LIX may participate in the recruitment of inflammatory cells by injured or infected tissue.

A sub-set of immediate early mRNAs induced by tumor necrosis factor-alpha during cellular cytotoxic and non-cytotoxic responses

TNF-alpha is a multifunctional cytokine which is cytotoxic for some cell lines. In order to characterize the early genomic response to TNF-alpha, we have analyzed the induction of a sub-set of serum-inducible immediate early genes in WEHI-S and L929 fibrosarcoma cell lines, which are sensitive to TNF-alpha, and in the 3T3-LI pre-adipocytic cell line, which is resistant to TNF-alpha cytotoxicity. Among 77 immediate early mRNAs screened by dot blot and/or Northern blot analyses, the expression of 23 mRNAs was found to be induced by TNF-alpha. Ten of these mRNAs encode proteins known to function as pro-inflammatory cytokines or transcription factors, while 13 others have as yet uncharacterized activities. The magnitude of c-fos induction by TNF-alpha inversely correlated with cell-type-specific cytotoxicity. Rapid and transient mRNA responses were observed in the TNF-alpha-resistant cells, whereas a slower and more persistent response was characteristic for TNF-alpha-sensitive cells. The prolonged induction of immediate early mRNAs may contribute to TNF-alpha-induced cellular cytotoxic responses.