Lipoxin A(4) receptor activation is distinct from that of the formyl peptide receptor in myeloid cells: Inhibition of CD11/18 expression by lipoxin A(4)-lipoxin A(4) receptor interaction

Lipoxin A(4) (LXA(4)) interacts with high-affinity receptors in human neutrophils and differentiated HL-60 cells. Recently, we characterized a myeloid-derived cDNA that encodes a LXA(4) high-affinity receptor (LXA(4)R) [Fiore, S., Maddox, J.F., Perez, H.D., and Serhan, C.N. (1994) J. Exp. Med. 180, 253-260] denoted earlier as a related N-formyl peptide receptor (RFP). To examine the selectivity of this receptor we tested its preference for specific binding of H-3-LXA(4) versus H-3-N-formylmethionyl-leucyl-phenylalanine (H-3-FMLP). When receptor-transfected Chinese hamster ovary cells were exposed to either H-3-LXA(4) or H-3-FMLP, the receptor affinity for LXA(4) exceeded by 1000-fold that of FMLP (6.1 nM vs 5 mu M). Upon differentiation, HL-60 cells acquire high-affinity binding sites and respond to both LXA(4) and FMLP. Northern blot analysis of differentiated HL-60 cells using an RFP probe showed a characteristic band at 2.1 kb. Differentiated HL-60 cells exposed to an RFP antisense oligonucleotide selectively lost H-3-LXA(4) binding as well as LXA(4)-stimulated lipid remodeling that paralleled the loss of mRNA for LXA(4)R. In contrast, the specific mRNA for the FMLP receptor, H-3-FMLP specific binding, and FMLP-induced phospholipase D activity were still observed. Treatment of human neutrophils with antisera raised against a peptide in the LXA(4)R third extracellular domain also resulted in selective abrogation of H-3-LXA(4) specific binding with polymorphonuclear leukocytes (PMN) without blocking H-3-FMLP binding. FMLP-stimulated CD11b upregulation as well as homotypic aggregation of PMN was inhibited by LXA(4) (which at 10(-9) M gave similar to 1 log unit shift to the right in the FMLP dose-response curve), The addition of LXA(4)R antisera did not alter FMLP-induced responses in PMN but completely blocked LXA(4) actions. These results indicate that altering the expression of the LXA(4)R protein by blockage of transcriptional mechanisms or hindrance of the LXA(4)R extracellular domains leads to loss of LXA(4) specific binding and blockage of LXA(4) signaling. Moreover, they indicate that in myeloid cells LXA(4)-LXA(4)R interactions are dissociable from those of FMLP and that LXA(4) regulates CD11/18 on the PMN surface.