Modification of sialidase levels and sialoglycoconjugate pattern during erythroid and erytroleukemic cell differentiation.

Glycosphingolipids and glycoproteins play pivotal roles in the complex series of events governing cell adhesion and signal transduction. Aberrant glycosilation, typical of tumor cells, represents a key event in the induction of invasion and metastasis. Sialidases remove sialic acid residues from sialoconjugates and, in mammals, these enzymes have been proved to be involved in several cellular phenomena, including cell proliferation and differentiation, membrane function, and malignant transformation. Herein we show that only the lysosomal sialidase Neu1 and the plasma membrane-associated sialidase Neu3 are expressed in CFU-E erythroid precursors and K562 erythroleukemic cells. Tumour cells show much higher expression levels than CFU-E cells and, during differentiation, the content of the two enzymes progressively decreases. The sialoglycoconjugate pattern is different in the two cell types. In fact, the differentiating erythroid precursors show an increase of the typical erythrocyte sphingolipids, whereas K562 cells treated with butyrate show a marked increase of GD1a, GM2, PE, and ceramide. Finally, during differentiation the sialoglycoprotein content of erythroid cells shows a marked increase, and in K562 cells the process induces the synthesis of some sialoglycoprotein typical of the erythroid membrane. Overall, these results point out the great differences in sialoglycoconjugate and sialidase patterns exhibited by normal and tumour cells.