The appearance of [11,12–3H]lipoxin A4 (LXA4) specific binding sites was examined with human acute promyelocytic leukemic cell line 60 (HL- 60) cells exposed to either retinoic acid, phorbol 12-myristate 13- acetate (PMA), or dimethyl sulfoxide (DMSO). All three agents induced a threefold to fivefold increase in the expression of specific [11,12- 3H]LXA4 binding. Similar results were obtained in parallel with [14,15- 3H]leukotriene (LT) B4. For both 3H-ligands, homologous displacement curves were similar and independent of the agent used to induce differentiation. Specific binding of [11,12–3H]LXA4 to differentiated HL-60 cells gave a kd = 0.6 +/- 0.3 nmol/L. The appearance of both [11,12–3H]LXA4 and [14,15–3H]LTB4-specific binding sites was inhibited by actinomycin D, and LXA4 binding was sensitive to protease treatment. Specific binding of [11,12–3H]LXA4 was not evident with human platelets, red blood cells (RBCs) or the cultured B-cell (Raji), T-cell (Jurkat) lines save human endothelial cells (kd = 11.0 +/- 0.3 nmol/L). The structural specificity of induced [11,12–3H]-LXA4 recognition sites was assessed with LXB4, LTC4, LTB4, and trihydroxyhepatanoic methyl ester. Only LTC4, at 3-log molar excess, competed for 3H-LXA4-specific binding with HL-60 cells and gave a 30% reduction. The leukotriene D4 receptor antagonist SKF 104353 was ineffective in blocking [11,12- 3H]LXA4-specific binding with HL-60 cells while it competed for specific [11,12–3H]LXA4 binding with endothelial cells where LTD4 binding appears to be virtually identical to that of LXA4 binding. In addition, the LTB4 receptor antagonist ONO 4057 was ineffective at competing for [11,12–3H]LXA4 binding. When phospholipase D activation was monitored in human polymorphonuclear leukocytes (PMN) and HL-60 cells, a correlation was shown between activation and specific 3H-LXA4 binding. LXA4-induced phospholipase D (PLD) activation gave a biphasic concentration-dependent response comprised of at least two components: one phase being islet-activating protein (IAP)-sensitive (LXA4 10(-9) mol/L peak activity) and the other was staurosporine-sensitive (LXA4 10(-7) mol/L peak activity). Results indicate that HL-60 cells exposed to differentiating agents express [11,12–3H]LXA4 recognition sites also present in PMN. In addition, specific LXA4 recognition sites of myeloid cells can be distinguished by competition binding with SKF 104353 and 3H-LXA4 cross-reactivity with putative LTD4 receptors present on human endothelial cells. Moreover, they provide evidence indicating that binding of LXA4 to its recognition sites confers functional responses.

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