J. Kopitz et al., EFFECTS OF CELL-SURFACE GANGLIOSIDE SIALIDASE INHIBITION ON GROWTH-CONTROL AND DIFFERENTIATION OF HUMAN NEUROBLASTOMA-CELLS, European journal of cell biology, 73(1), 1997, pp. 1-9
Gangliosides on the external side of the plasma membrane are important
modulators of cellular functions, In previous work we had found that
in cultured human SK-N-MC neuroblastoma cells a cell surface sialidase
activity specifically cleaved terminal sialic acids from gangliosides
, leading to a shift from higher sialylated species to GM1 and a decre
ase of GM3, To further elucidate the function of the enzyme, we have n
ow examined the consequences of ganglioside sialidase inhibition, When
present in the culture medium, the ganglioside sialidase inhibitors 2
-deoxy-2,3-dehydro-N-acetylneuraminic acid (NeuAc2en), heparin, and he
paran sulfate caused dramatic changes in cell behavior, Thus, the inhi
bitors uniformly led to a complete release from contact inhibition of
growth, and to the loss of the differentiation markers neuron-specific
enolase and neurofilaments, and a decrease of cyclic AMP, In presence
of NeuAc2en, cells that normally were spread out evenly and were firm
ly attached, appeared smaller, rounded, and only loosely adherent to t
he culture vessel, Exogenous addition of vibrio cholerae sialidase mim
icked the action of the plasma membrane ganglioside sialidase by retar
ding cell proliferation and increasing intracellular acetylcholinester
ase. That the ganglioside sialidase inhibitors in the culture medium i
ndeed affected solely the cell surface enzyme and not also a lysosomal
sialidase, was demonstrated in an experiment where the desialylation
of exogenously added radioactive gangliosides was determined in absenc
e and presence of NeuAc2en and NH4Cl, an inhibitor of lysosomal functi
on, Taken together, our results suggest that the ganglioside sialidase
on the surface of SK-N-MC cells is responsible for growth control and
differentiation in this neuronal cell line.