Abstract
The fucosyl glycopeptides on the surface of promyelocytic leukemia cells (HL-60) and normal human promyelocytes before and after differentiation and maturation were studied. HL-60 cells were induced to differentiate by means of dimethyl sulfoxide (DMSO) and the tumor-promoting phorbol diester 12-O-tetradecanoylphorbol-13-acetate (TPA). DMSO-induced maturation resulted predominantly in metamyelocytes, bands, and segmented neutrophils, whereas exposure of HL-60 cells to TPA gave rise to macrophage-like cells. Fucosyl glycopeptides obtained from the cell surface of DMSO-treated, TPA-treated, and untreated cells, respectively, were investigated by gel filtration analysis and were compared with those derived from corresponding normal polymorphonuclear cells, monocytes, or macrophages and promyelocytes, respectively. Control immature promyelocytes were isolated in large quantity from normal human bone marrow by a four-step isolation procedure including density gradient centrifugation and velocity sedimentation at unit gravity. This isolation procedure resulted in up to 89% pure immature myeloid cells comprising 82% promyelocytes and myeloblasts. Fucosyl glycopeptides of the cell surface of HL-60 cells upon gel filtration appeared to be considerably larger than were those derived from mature control polymorphonuclear cells or from immature myeloid cells. DMSO exposure of HL-60 cells did not result in “normalization” of these surface glycopeptides but on the contrary accentuated the observed difference. Upon TPA treatment, the elution profile of surface glycopeptides changed considerably to a smaller size distribution. These TPA-induced glycopeptides, however, were still considerably larger than those derived from normal control monocytes or normal macrophages obtained by culturing monocytes in the presence or absence of TPA. Consequently, promyelocytic leukemia cells (HL-60), in contrast with normal promyelocytes, express cancer-related glycopeptides on their surfaces and continue to express these aberrant structures upon differentiation along both the myeloid and monocytic series. Mild acid treatment of the glycopeptides completely abolished the chromatographic differences among fucosyl glycopeptides from normal monocytes-macrophages, PMN cells, and immature myeloid cells. However, the glycopeptides of DMSO-treated, TPA-treated, and untreated HL-60 cells as compared with those of all matching control cells retained their larger size distribution after mild acid treatment and subsequent gel filtration analysis, emphasizing their difference in glycopeptide composition.
These findings justify our conclusion that, although differentiation of human leukemia cells in vitro leads to an apparent normal maturation, these matured cells still carry glycopeptides on their surface exclusively found on malignant and certain premalignant cells. They may, therefore, reflect the leukemic origin of the cells independent of their state of differentiation.