Development of specific functionally active receptors for platelet-activating factor in HL-60 cells following granulocytic differentiation.

Abstract

A human promyelocytic leukemia cell line (undifferentiated HL-60 cells) as well as a granulocyte form of HL-60 cells induced in vitro by exposure to dimethyl sulfoxide were examined for binding, metabolism, and biological responses to platelet-activating factor (PAF). Undifferentiated and differentiated HL-60 cells each exhibit a high capacity to incorporate and metabolize [3H]PAF at 37 degrees C; however, the amount of [3H]PAF that is assimilated by both cell populations is greatly reduced and its metabolism abolished at less than or equal to 4 degrees C. At 0 degrees C HL-60 granulocytes bind more [3H]PAF than their undifferentiated counterparts. Binding to differentiated cells reaches equilibrium within 80 min and is saturable, reversible and specific; PAF receptor antagonists WEB 2086, L-659,989, BN 52021, and kadsurenone abolish this specific [3H]PAF binding. In contrast, [3H]PAF uptake by undifferentiated HL-60 cells is neither saturable nor sensitive to specific receptor antagonists. Scatchard analyses reveal 5850 +/- 850 binding sites per differentiated HL-60 cell with a dissociation constant of 0.66 +/- 0.15 nM. In the presence of cytochalasin B, PAF (200 nM) induces degranulation only in differentiated cells and this response also is blocked by PAF receptor antagonists. Our results demonstrate that HL-60 cells develop specific and functionally active PAF receptors only after chemically induced differentiation into granulocytes.