IL‐4 induces expression of TARC/CCL17 via two STAT6 binding sites

Abstract

A cardinal feature of allergic disorders and immune responses is enhanced leukocyte trafficking. This is largely orchestrated by chemokines. The CC chemokine thymus-and activation-regulated chemokine (TARC/CCL17) selectively attracts Th2 cells via the G protein-coupled chemokine receptor CCR4. We show here that TARC/CCL17 is expressed by human T cells upon stimulation with IL-4. Mapping of the transcriptional start site revealed the presence of two putative STAT6 binding motifs in proximity to the start position. EMSA and chromatin immunoprecipitation experiments demonstrated that STAT6 was able to bind to both motifs. A fragment of the TARC/CCL17 promoter containing both sites was tested in reporter gene assays for IL-4 inducibility. The promoter was inducible in a STAT6-deficient cell line only after introduction of functional STAT6. When mutations were inserted into one of the STAT6 motifs, IL-4-induced promoter activation was reduced. With both sites mutated, inducibility was completely abrogated. These data demonstrate collectively that T cells serve as a source of TARC/CCL17 when stimulated with IL-4 and that STAT6 is essential for this. IntroductionChemokines are structurally related 8-12-kDa chemoattractant cytokines that regulate leukocyte trafficking and inflammatory diseases. Depending on the motif displayed by the first or first two of their conserved cysteines, they have been classified into C, CC, CXC or CX3C chemokine subfamilies. Chemokines have been shown to not only regulate hemopoietic cell migration but also to be involved in a number of other physiological and pathological processes [1]. The 8-kDa thymus-and activation-regulated chemokine (TARC/CCL17) was first isolated from phytohemagglutinin-stimulated peripheral blood mononuclear cells (PBMC) by Imai et al. in 1996 [2] by means of a signal sequence trap method [3]. The TARC/CCL17 gene is located on chromosome 16q13 in a cluster with MDC/ CCL22 and Fractalkine/CX3CL1 [4]. It encodes a highly basic 94 amino acid residues long preprotein with a cleavage site between Ala23 and Ala24. The mature TARC/CCL17 protein is 71 amino acid residues in length and was shown to be constitutively expressed in thymus [2] and, upon activation with different inducers, in several cell types including PBMC [5], monocytes [6], dendritic cells [7], endothelial cells, and bronchial epithelial cells [8].Leukocytes are activated by chemokines through seven-transmembrane G protein-coupled receptors. Based on the subfamily of chemokines they bind, chemokine receptors are named XCR1, CCR1-9, CXCR1-5 and CX3CR1 [9]. The specific functional high-affinity receptor for TARC/CCL17 is the CC chemokine receptor 4 (CCR4), which has also been shown to serve as receptor for CCL22/MDC (macrophage-derived chemokine). CCR4 is predominantly Interleukin-4 (IL-4), mainly produced by Th2 T cells, mast cells, basophils and eosinophils, appears to be a crucial factor in allergic responses. IL-4 induces differentiation of allergen-specific Th2 cells and class switching towards IgE produc...

Dose-Dependent Effects of IL-17 on IL-13–Induced Airway Inflammatory Responses and Airway Hyperresponsiveness

“…1C) and increased goblet cell mucus production (assessed by periodic acid-Schiff staining; data not shown). Consistent with the ability of IL-13 to increase expression of chemokines that regulate eosinophil and lymphocyte chemotaxis (5,(37)(38)(39), the levels of mRNA encoding CCL11 (eotaxin-1), CCL17 (thymus and activation-regulated chemokine), and CCL22 (macrophage-derived chemokine) were also increased (Fig. 1C).…”

Suppressor of Cytokine Signaling 2 Is a Feedback Inhibitor of TLR-Induced Activation in Human Monocyte-Derived Dendritic Cells

“…Quantitative RT-PCR (qRT-PCR) was done as described previously (29). In brief, total RNA was isolated with TRIzol (Invitrogen, Lofer, Austria) or a Nucleospin RNA II kit (Macherey-Nagel, Düren, Germany), according to the manufacturer's instructions.…”

TARC/CCL17 gene polymorphisms and expression associated with susceptibility and coronary artery aneurysm formation in Kawasaki disease

“…TARC/CCL17, a ligand for CC chemokine receptor 4 and CC chemokine receptor 8, serves for the recruitment and migration of lymphocytes of the Th2 phenotype (8,9) and direct T-cell and macrophage recruitment into areas of allergic inflammation. In human and animal studies, it is demonstrated that TARC/CCL17 mRNA and protein are potently induced by the Th2 cytokine, interleukin-4 (IL-4), through induction of promoter binding of signal transducer and activator of transcription 6 (STAT6) (17,18). IL-4/signal transducer and activator of transcription 6 signaling during T-cell development contributes to polarized patterns of cytokine expression manifested by differentiated Th cells (19).…”