IDENTIFICATION OF CCR6, THE SPECIFIC RECEPTOR FOR A NOVEL LYMPHOCYTE-DIRECTED CC CHEMOKINE LARC

Liver and activation-regulated chemokine (LARC) is a recently identifi ed CC chemokine that is expressed mainly in the liver. LARC functions as a selective chemoattractant for lymphocytes that express a class of receptors specifically binding to LARC with high affinity. To identif y the receptor for LARC, we examined LARC-induced calcium mobilization in cells stably expressing five CC chemokine receptors (CCR1-CCR5) an d five orphan seven-transmembrane receptors. LARC specifically induced calcium flux in K562 cells as well as 293/EBNA-1 cells stably express ing an orphan receptor GPR-CY4. LARC induced migration in 293/EBNA-1 c ells stably expressing GPR-CY4 with a bi-modal dose-response curve. LA RC fused with secreted alkaline phosphatase (LARC-SEAP) bound specific ally to Raji cells stably expressing GPR-CY4 with a K-d of 0.9 nM. Onl y LARC but not five other CC chemokines (MCP-1, RANTES, MIP-1 alpha, M IP-1 beta, and TARC) competed with LARC-SEAP for binding to GPR-CY4. B y Northern blot analysis, GPR-CY4 mRNA was expressed mainly in speen, lymph nodes, appendix, and fetal liver among various human tissues. Am ong various leukocyte subsets, GPR-CY4 mRNA was detected in lymphocyte s (CD4(+) and CD8(+) T cells and B cells) but not in natural killer ce lls, monocytes, or granulocytes. Expression of GPR-CY4 mRNA in CD4(+) and CD8(+) T cells was strongly up-regulated by IL-2. Taken together, GPR-CY4 is the specific receptor for LARC expressed selectively on lym phocytes, and LARC is a unique functional ligand for GPR-CY4. We propo se GPR-CY4 to be designated as CCR6.