INDUCTION, CHARACTERIZATION, AND FUNCTIONAL COUPLING OF THE HIGH-AFFINITY CHEMOKINE RECEPTOR FOR RANTES AND MACROPHAGE INFLAMMATORY PROTEIN-1-ALPHA UPON DIFFERENTIATION OF AN EOSINOPHILIC HL-60 CELL-LINE

Eosinophilic differentiation of a pro-eosinophilic HL-60 cell line res ulted in the induction of a high affinity RANTES/macrophage inflammato ry protein-1 alpha receptor. The induced receptor is biochemically ind istinguishable in RANTES equilibrium-binding studies from the monocyti c receptor expressed on THP-1 cell membranes. Continued expression of the receptor requires the continuous presence of the inducing stimulus , and receptor site number declines without a loss of binding affinity with a t(1/2) of 11.5 h on withdrawal of the inducing stimulus. The i nduced receptor is capable of three physiologic measures of receptor c oupling, namely, ligand-induced Ca2+ fluxes, priming of the respirator y burst, and chemotaxis. Dose-dependent Ca2+ fluxes were elicited upon increasing concentrations of RANTES and MIP-1 alpha whereas no respon se was measured upon addition of MIP-1 beta or MCP-1. In addition, des ensitization studies demonstrated that previous exposure to either RAN TES or MIP-1 alpha almost completely inhibits a Ca2+ flux upon subsequ ent exposure to either ligand. Priming of the respiratory burst to PMA in differentiated cells by human rRANTES was more effective than prim ing by IL-5 or granulocyte-macrophage-CSF, whereas undifferentiated ce lls failed to secrete superoxide anion. In addition, differentiated ce lls underwent chemotaxis in response to RANTES. This provides the firs t evidence for the induction of a C-C chemokine receptor upon eosinoph ilic differentiation of a leukocyte cell line, and is in keeping with the demonstrated ability of human RANTES to induce the rapid formation of eosinophilic inflammatory sites.