Thrombospondin promotes both chemotaxis and haptotaxis in neutrophil-like HL-60 cells

Differentiation of the human promyelocytic leukemia cell line HL-60 to polymorphonuclear leukocyte (PMN)-like cells with DMSO provides an important model for studying the acquisition of PMN functional responses that accompany differentiation. We showed previously that the extracellular matrix (ECM) protein thrombospondin (TSP) binds to PMN surface receptors and promotes adhesion and motility. Undifferentiated HL-60 cells did not adhere and were not motile in response to TSP, whereas cells differentiated toward PMN-like cells demonstrated both TSP-mediated adhesion and chemotaxis, with chemotaxis evident by day 2 of induction. With differentiation, a maximal response was obtained with 100 to 300 nM TSP, 10-fold lower than required for maximal PMN chemotaxis. Checkerboard analysis confirmed the directional nature of motility. mAb recognizing different domains of TSP inhibited chemotaxis, suggesting the involvement of multiple sites on TSP. Although both the NH2-terminal heparin-binding domain (HBD) and 140 kDa COOH-terminal fragment supported chemotaxis in PMN-like cells, neither fragment was as potent as intact TSP. Both pertussis and cholera toxin inhibited TSP-mediated chemotaxis, suggesting the involvement of GTP-binding proteins. The toxin effects did not indirectly result from elevated cAMP levels because high concentrations of either 8-bromo-cAMP or dibutyryl cAMP did not inhibit chemotaxis. TSP bound to nitrocellulose filters induced the directed migration (haptotaxis) of PMN-like cells rather than the random motility observed with PMN. Haptotaxis was stimulated by either the HBD or 140-kDa fragment and was inhibited by mAb against these two domains. Haptotaxis rather than random migration was confirmed by checkerboard analysis. Our results demonstrate that PMN-like HL-60 cells respond differently to TSP than human peripheral blood PMN. These differences may reflect 1) an aberration in HL-60 differentiation reflecting their leukemic phenotype 2) differentiation of HL-60 cells to a cell type characteristic of "activated" PMN.