A synthetic ceramide analog, D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol, selectively inhibits adherence during macrophage differentiation of human leukemia cells
Prior studies have demonstrated that sphingomyelin synthesis is involved in adherence during macrophage differentiation of HL-60 cells (Dressler, K. A., Kan, C.-C., and Kolesnick, R. N. (1991) J. Biol. Chem. 266, 11522-11527). The present studies show that glycosphingolipid synthesis is also involved. Initial studies demonstrated that the potent phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulates a 6- and 12-fold increase in the levels of sialosyllactosylceramide (GM3) and glucosylceramide (GlcCer), respectively, during development of an adherent macrophage population. In contrast, the level of lactosylceramide (LacCer) decreased to 20% of unstimulated controls. These effects were specific to adherent macrophages as nonadherent cells had minimal alteration in the glycosphingolipid profile. D-Threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), a competitive inhibitor of UDP-glucose:ceramide glucosyltransferase (EC 22.214.171.124), selectively blocked adherence during macrophage differentiation. PDMP markedly reduced basal levels of GlcCer, LacCer, and GM3 and prevented TPA-stimulated effects. PDMP (0.03-10 microM) reduced adherence after TPA from 30 to 6% of the total population. PDMP did not block other aspects of phorbol ester-induced macrophage differentiation including growth inhibition, expression of mRNA transcripts for the proto-oncogenes c-fos and c-myc, development of the specific enzyme markers alpha-naphthyl acetate esterase and acid phosphatase, and the gross morphologic changes associated with macrophage differentiation. PDMP appeared to have no short term or prolonged toxic effect on HL-60 cells. These studies show that PDMP selectively blocked adherence of HL-60 cells during phorbol ester-induced macrophage differentiation and suggest that this compound may be useful in the description of the biologic roles of glycosphingolipids.