ELC

ELC Hisayuki Nomiyama1,* and Osamu Yoshie2 1

Department of Biochemistry, Kumamoto University School of Medicine, 2-2-1 Honjo, Kumamoto, 860-0811, Japan 2 Department of Bacteriology, Kinki University School of Medicine, 377-2 Ohno-Higashi, Osaka-Sayama, Osaka, 589-8511, Japan * corresponding author tel: +81-96-373-5065, fax: +81-96-373-5066, e-mail: [email protected] DOI: 10.1006/rwcy.2000.11016.

SUMMARY

Alternative names

ELC (EBI1-ligand chemokine) (Yoshida et al., 1997), also known as MIP-3 (macrophage inflammatory protein 3 and Exodus-3, belongs to a novel class of CC chemokines that is highly expressed in lymphoid tissues and has chemotactic activity for lymphocytes, but not for monocytes or granulocytes. ELC specifically binds and signals through CCR7/EBI1/BLR2. The human gene for ELC (SCYA19) is located on chromosome 9p13, which is unusual in that most other CC chemokine genes are mapped on chromosome 17. Another CC chemokine SLC/6Ckine shares the receptor CCR7 with ELC and has its gene on the same chromosome as ELC, although they share only 32% amino acid identity. These findings suggest that ELC and SLC were derived from a common ancestor and have a role in lymphocyte homing into and trafficking within lymphoid tissues and the thymus.

ELC is also known as MIP-3 (macrophage inflammatory protein 3 ) (Rossi et al., 1997), CK -11 (chemokine -11) (designated by Human Genome Sciences; Kim et al., 1998c), and Exodus-3 (GenBank accession number U88321). A new designation will be CCL19 (CC chemokine ligand 19) (from the chemokine ligand systemic nomenclature proposed at the Keystone Symposium on Chemokines and Chemokine Receptors, 1999).

BACKGROUND

Discovery By searching the public and private EST databases, several groups independently reported the identification of the human (Rossi et al., 1997; Yoshida et al., 1997; Kim et al., 1998c) and mouse (Ngo et al., 1998) cDNAs for ELC/MIP-3 .

Structure ELC is a CC chemokine containing four conserved cysteine residues, but is distantly related to other CC chemokines. The most similar member is the CC chemokine SLC (32% identity on the human protein level), which also binds CCR7.

Main activities and pathophysiological roles Since ELC shares the CCR7 receptor with SLC, they have similar in vitro activities. However, since they differ in expression pattern and binding affinity in certain cell types (Yoshida et al., 1998b), they may have different physiological roles. The chemotactic activity of ELC combined with its restricted expression pattern suggests that this molecule functions mainly in controlling lymphocyte

1276 Hisayuki Nomiyama and Osamu Yoshie trafficking within lymphoid tissues. The roles played by ELC in secondary lymphoid tissues and in thymus are outlined below. Lymphocyte Migration in Secondary Lymphoid Tissues ELC is expressed in T cell areas of secondary lymphoid tissues and together with SLC may function in directing naõÈ ve T cells and activated B cells into the T cell areas. Although the recruitment of lymphocytes across high endothelial venules (HEVs) into lymph nodes or Peyer's patches is assumed to be mediated mainly by SLC, which is expressed at high levels by HEVs (Gunn et al., 1998), ELC may also participate in the process because ELC induces firm arrest of lymphocytes under physiological shear forces (Campbell et al., 1998b) and transendothelial migration of lymphocytes (Yoshida et al., 1998a). Upon differentiation into memory/effector cells, T cells downregulate CCR7 and leave the secondary lymphoid tissues. Upon T cell receptor stimulation, the memory/effector T cells upregulate CCR7 and home to secondary lymphoid tissues via afferent lymphatics in response to ELC and/or SLC (Sallusto et al., 1999a). Dendritic Cell Migration in Secondary Lymphoid Tissues Since ELC and SLC are potent chemokines for `mature' dendritic cells as well as lymphocytes and both are expressed in the T cell areas, they may also play a role in promoting encounter between antigenpresenting dendritic cells and T cells. However, it is not known whether ELC is expressed in lymphatic endothelium like SLC to mediate the migration of dendritic cells from tissues to afferent lymphatics (Gunn et al., 1998). Thymocyte Migration in Thymus ELC preferentially attracts mature single-positive thymocytes and positively selected double-positive thymocytes, suggesting that ELC regulates migration of these thymocytes from the cortex to the medulla and/or from the medulla into peripheral blood (Kim et al., 1998b; Ngo et al., 1998; Campbell et al., 1999).

GENE AND GENE REGULATION

Accession numbers GenBank: Human cDNA: NM_006274

Human gene: AJ223410 Mouse cDNA: AF059208

Chromosome location By somatic cell hybrid and radiation hybrid analyses, the human gene for ELC (SCYA19) was mapped to chromosome 9p13 (Rossi et al., 1997; Yoshida et al., 1997). The mouse ELC gene may be located on mouse chromosome 4 since the human ELC and SLC genes are closely linked on the chromosome (Nagira et al., 1997) and the mouse SLC mutant gene (plt) (Gunn et al., 1999) has been mapped on chromosome 4 (Nakano et al., 1998).

Relevant linkages Since the human genes for ELC and SLC are located on the same BAC clone, the genes are closely linked within a region of less than 200 kb (Nagira et al., 1997).

Cells and tissues that express the gene The human ELC mRNA was detected in the thymus, lymph nodes, and appendix at high levels, and in the spleen, trachea, small intestine, colon, and lung at lower levels (Rossi et al., 1997; Yoshida et al., 1997). The expression pattern of ELC is similar but not identical with that of SLC. However, compared with SLC, ELC is expressed at much higher levels in human thymus. Interestingly, the expression level of ELC is low in the mouse thymus (Ngo et al., 1998). By in situ hybridization, ELC has been shown to be expressed in T cell areas of secondary lymphoid tissues (Dieu et al., 1998; Ngo et al., 1998; Yoshida et al., 1998a), and the type of cells that express ELC in the T cell areas have been shown to be interdigitating dendritic cells (Ngo et al., 1998). By analyzing lymphotoxin-deficient mice, Ngo et al. (1999) showed that lymphotoxins  and are required for the expression of ELC and SLC in the T cell areas. ELC mRNA is expressed in dendritic cells 10±30 hours after induction of maturation, suggesting that dendritic cells produce ELC after homing to the T cell areas of secondary lymphoid tissues (Sallusto et al., 1998, 1999b).

ELC 1277

PROTEIN

RECEPTOR UTILIZATION

Accession numbers

ELC binds to the chemokine receptor CCR7 (Yoshida et al., 1997), which it shares with SLC (Campbell et al., 1998a; Willimann et al., 1998; Yoshida et al., 1998b). Mouse SLC has been shown to bind weakly to a CXC chemokine receptor CXCR3 (Soto et al., 1998; Jenh et al., 1999), but mouse ELC does not signal through CXCR3.

SwissProt: Human ELC: Q99731 Mouse ELC: O70460

Sequence See Figure 1.

IN VITRO ACTIVITIES

Description of protein Mature protein: Length: 77 Molecular weight: 8800 Isoelectric point: 10.16

Important homologies ELC exhibits the highest amino acid similarity to SLC (32% identity).

CELLULAR SOURCES AND TISSUE EXPRESSION

Cellular sources that produce ELC has been shown to be produced by mature dendritic cells (Ngo et al., 1998; Sallusto et al., 1999b). In human atherosclerotic plaques, ELC mRNA was frequently detected in macrophages and intimal smooth muscle cells (Reape et al., 1999). ELC mRNA was found to be upregulated in aortic smooth muscle cells stimulated with TNF and IFN and also found to be expressed by monocyte-derived macrophages but not monocytes (Reape et al., 1999).

In vitro findings ELC has been shown to be a potent chemoattractant for naõÈ ve, memory, helper, and cytotoxic T cells and thymocytes (Campbell et al., 1998a, 1999; Kim et al., 1998b,c; Ngo et al., 1998; Yoshida et al., 1998a). It also attracts B cells (Campbell et al., 1998a; Kim et al., c; Ngo et al., 1998; Yoshida et al., 1998a), mature dendritic cells (Chan et al., 1999; Dieu et al., 1998; Kellermann et al., 1999; Lin et al., 1998; Sallusto et al., 1998; Sozzani et al., 1998; Yanagihara et al., 1998), NK cells (Kim et al., 1999) and CD34+ macrophage progenitor cells (Kim et al., 1998a,b). ELC induces calcium mobilization in almost all of these cell types, but Kim et al. (1998b) reported that ELC did not mobilize detectable levels of calcium in thymocytes. Like other chemoattractants, ELC induced actin polymerization in T cells (Kim et al., 1998c). ELC, as well as SLC, SDF-1, and LARC/MIP3, has been shown to trigger almost immediate integrin-dependent adhesion of lymphocytes under flow conditions, suggesting the involvement of ELC in leukocyte±endothelial cell interactions (Campbell et al., 1998b).

Bioassays used As for other chemokines, chemotaxis assays and intracellular calcium flux measurements are widely used. In addition, transendothelial migration assays

Figure 1 Amino acid sequence for human ELC. The signal peptide is underlined. Human ELC: MALLLALSLL VLWTSPAPTL SGTNDAEDCC LSVTQKPIPG YIVRNFHYLL IKDGCRVPAV VFTTLRGRQL CAPPDQPWVE RIIQRLQRTS AKMKRRSS

1278 Hisayuki Nomiyama and Osamu Yoshie (Lin et al., 1998; Sozzani et al., 1998; Yoshida et al., 1998a) and flow chamber adhesion assays (Campbell et al., 1998b) were performed to assess the activities of ELC under more physiological conditions.

PATHOPHYSIOLOGICAL ROLES IN NORMAL HUMANS AND DISEASE STATES AND DIAGNOSTIC UTILITY

Role in experiments of nature and disease states Using RT-PCR and in situ hybridization, the ELC mRNA was detected in human atherosclerotic plaques (Reape et al., 1999). ELC mRNA was frequently expressed by macrophages and intimal smooth muscle cells in such lesions.

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