Expression of aberrant O-glycans attached to leukosialin in differentiation-deficient HL-60 cells.
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: Gal beta 1----3GalNAc alpha 2----3sialyltransferase, Gal beta 1----4(3) GlcNAc alpha 2----3sialyltransferase, Gal beta 1----4GlcNAc alpha 2----6sialyltransferase, and GalNAc alpha 2----6sialyltransferase. Among them, Gal beta 1----3GalNAc alpha 2----3sialyltransferase and Gal beta 1----4(3)GlcNAc alpha 2----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 alpha 2----3sialyltransferase activities. These results strongly suggest that O-glycans associated with leukosialin may play some role in HL-60 cell differentiation.
Saitoh
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La Jolla Cancer Research Foundation, Cancer Research Center, California 92037.
Gallagher
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RE
Fukuda
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D015703:Antigens, CD; D002454:Cell Differentiation / Q000187:drug effects; D004351:Drug Resistance; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D015473:Leukemia, Promyelocytic, Acute / Q000378:metabolism* / Q000473:pathology; D051917:Leukosialin; D011134:Polysaccharides / Q000096:biosynthesis / Q000737:chemistry*; D012795:Sialoglycoproteins / Q000737:chemistry*; D012799:Sialyltransferases / Q000032:analysis; D013866:Thioguanine / Q000494:pharmacology; D014212:Tretinoin / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000378:metabolism / Q000473:pathology
D015703:Antigens, CD; D051917:Leukosialin; D011134:Polysaccharides; C465014:SPN protein, human; D012795:Sialoglycoproteins; D014212:Tretinoin; D012799:Sialyltransferases; D013866:Thioguanine