CDB15:0000216 CCL21 — CCR7

ABSTRACT: CCL21 is a human chemokine that recruits normal immune cells and metastasizing tumor cells to lymph nodes through activation of the G protein-coupled receptor CCR7. The CCL21 structure solved by NMR contains a conserved chemokine domain followed by an extended, unstructured C-terminus that is not typical of most other chemokines. A sedimentation equilibrium study showed CCL21 to be monomeric. Chemical shift mapping indicates that the CCR7 N-terminus binds to the N-loop and third β-strand of CCL21's chemokine domain. Details of CCL21-receptor recognition may enable structure-based drug discovery of novel antimetastatic agents.

ABSTRACT: Secondary Lymphoid-tissue Chemokine (SLC) is a recently identified CC chemokine that is constitutively expressed in various lymphoid tissues and is a potent and specific chemoattractant for lymphocytes. The SLC gene and the gene encoding another lymphocyte-specific CC chemokine, EBI1-ligand chemokine (ELC), form a mini-cluster at human chromosome 9p13. Here, we show that SLC is a high affinity functional ligand for chemokine receptor 7 (CCR7) that is expressed on T and B lymphocytes and a known receptor for ELC. SLC induced a vigorous calcium mobilization in murine L1.2 cells stably expressing human CCR7. SLC tagged with the secreted form of alkaline phosphatase (SLC-SEAP) showed specific binding to CCR7 that was fully competed by SLC with an IC50 of 0.5 nM. SLC also induced a vigorous chemotactic response in CCR7-expressing L1.2 cells with a typical bell-shaped dose-response curve and a maximal migration at 10 nM. When assessed using CCR7-transfected L1.2 cells, SLC and ELC were essentially equivalent in terms of cross desensitization in calcium mobilization via CCR7, cross-competition in binding to CCR7, and induction of chemotaxis via CCR7. SLC and ELC were also shown to fully share receptors expressed on cultured normal T cells known to express CCR7. Notably, however, SLC was somehow less efficient in cross-desensitization against ELC in calcium mobilization and in cross-competition with ELC for binding when assessed using cultured normal T cells. Thus, SLC and ELC, even though sharing only 32% amino acid identity, constitute a genetically and functionally highly related subgroup of CC chemokines.

ABSTRACT: The beta chemokine known as 6-C-kine, secondary lymphoid-tissue chemokine (SLC), TCA4, or Exodus-2 (herein referred to as 6CK/SLC) can trigger rapid integrin-dependent arrest of lymphocytes rolling under physiological shear and is highly expressed by high endothelial venules, specialized vessels involved in lymphocyte homing from the blood into lymph nodes and Peyer's patches. We show that 6CK/SLC is an agonist for the lymphocyte chemoattractant receptor, CCR7 (EBI-1, BLR-2), previously described as a receptor for the related beta chemokine MIP-3beta (ELC or Exodus-3). Moreover, 6CK/SLC and MIP-3beta attract the same major populations of circulating lymphocytes, including naive and memory T cells > B cells (but not natural killer cells); desensitization to MIP-3beta inhibits lymphocyte chemotaxis to 6CK/SLC but not to the alpha chemokine SDF-1 (stromal cell-derived factor); and 6CK/SLC competes for MIP-3beta binding to resting mouse lymphocytes. The findings suggest that the majority of circulating lymphocytes respond to 6CK/SLC and MIP-3beta in large part through their common receptor CCR7 and that these molecules may be important mediators of physiological lymphocyte recirculation in vivo.