Promyelocytic leukemia HL-60 cells can be induced to differentiate into granulocytic cells by various agents including retinoic acid (RA), dimethyl sulfoxide, and 6-thioguanine (6-TG). Although the induced cells are no longer capable of proliferation, a few cells continue to divide in the presence of inducers, and these cells are resistant to terminal differentiation by these inducers (R. E. Gallagher, D. A. Giangiulio, C-S. Chang, C. J. Glover, and R. L. Felsted, Blood, 68: 1402–1406, 1986).

The present study examined the structures of O-glycans attached to leukosialin, a major sialoglycoprotein in HL-60 cells, and the activities of glycosyltransferases involved in O-glycan synthesis. Leukosialin from RA-resistant and 6-TG-resistant HL-60 sublines migrated much more slowly than those from wild-type HL-60 cells when applied to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The dimethyl sulfoxide-resistant HL-60 subline, on the other hand, expressed leukosialin with a molecular weight similar to wild-type HL-60 cells. RA-resistant and 6-TG-resistant HL-60 cells were found to express a significant amount of tetrasaccharides that contain no sialic acid residue, while wild-type HL-60 cells expressed mainly disialosyl hexasaccharides and contained no detectable amount of asialo-oligosaccharides. Furthermore, wild-type HL-60 cells treated with the inducers for 4 days were found to express the same saccharides present in untreated wild-type HL-60 cells, indicating that the altered O-glycans present in RA and 6-TG sublines were not caused by a direct effect of these agents but rather are intrinsically unique to these sublines.

To better understand the mechanisms underlying the differences in O-glycans, the activities of four sialyltransferases were measured: Galβ1→3GalNAcα2→3sialyltransferase, Galβ1→4(3)GlcNAcα2→3sialyltransferase, Galβ1→4GlcNAcα2→6sialyltransferase, and GalN-Acα2→6sialyltransferase. Among them, Galβ1→3GalNAcα2→3sialyltransferase and Galβ1→4(3)GlcNAcα2→3sialyltransferase were much lower in the RA- or 6-TG-resistant HL-60 subline than in wild-type HL-60 cells. These findings indicate that the differences in O-glycans are due to the differences in α2→3sialyltransferase activities. These results strongly suggest that O-glycans associated with leukosialin may play some role in HL-60 cell differentiation.

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This work was supported by Grant R01 CA33895 from the National Cancer Institute.

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