R. Seidenfaden et al., Control of NCAM polysialylation by the differential expression of polysialyltransferases ST8Siall and ST8SialV, EUR J CELL, 79(10), 2000, pp. 680-688
Polysialic acid (PSA) is a developmentally regulated carbohydrate consistin
g of alpha -2,8-linked sialic acid residues attached to the neural cell adh
esion molecule NCAM. PSA promotes plasticity of cell-cell interactions in t
he nervous system and appears linked to the malignant potential of several
tumors. Two enzymes, the polysialyltransferases ST8SiaII (STX) and ST8SiaIV
(PST) have been identified and shown to be independently able to synthesiz
e PSA. However, in vivo studies have demonstrated that in the majority of P
SA-positive tissues the two polysialyltransferases are expressed simultaneo
usly. Therefore, this study was undertaken to elucidate in which way the in
dividual enzymes contribute to PSA expression under in vivo conditions. Usi
ng a semiquantitative RT-PCR strategy PSA-positive human tumor cell lines w
ere screened for expression of ST8SiaII and ST8SiaIV at the mRNA level. Div
ergent patterns observed in some cell lines suggest that polysialyltransfer
ases are independently regulated at the transcriptional level. In subsequen
t analyses the different mRNA levels of ST8SiaII and STgSiaIV in these tumo
r cells were correlated with the degree of PSA expression and the cellular
capacity to rapidly synthesize PSA. Our data indicate that STgSiaIV is the
major regulator of NCAM polysialylation in vivo.