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.