Human
glioma cell line U-373 MG expresses
CMP-NeuAc : Galbeta1,3GlcNAc alpha2,3-sialyltransferase [EC No. 2.4.99.6] (alpha2,3ST),
UDP-GlcNAc : beta-d-
mannoside beta1,6-N-acetylglucosaminyltransferase V [EC 2.4.1.155] (GnT-V) and
UDP-GlcNAc3: beta-d-
mannoside beta1,4-N-acetylglucosaminyltransferase III [EC 2.4.1.144] (GnT-III) but not
CMP-NeuAc : Galbeta1,4GlcNAc alpha2,6-sialyltransferase [EC 2.4.99.1] (alpha2,6ST) under normal culture conditions. We have previously shown that transfection of the alpha2,6ST gene into U-373 cells replaced alpha2,3-linked
sialic acids with alpha2,6
sialic acids, resulting in a marked inhibition of
glioma cell invasivity and a significant reduction in adhesivity. We now show that U-373 cells, which are typically highly resistant to cell death induced by chemotherapeutic agents (< 10% death in 18 h), become more sensitive to apoptosis following overexpression of these four
glycoprotein glycosyltransferases. U-373 cell viability showed a three-fold decrease (from 20 to 60% cell death) following treatment with
staurosporine,
C2-ceramide or
etoposide, when either alpha2,6ST and GnT-V genes were stably overexpressed. Even
glycosyltransferases typically raised in
cancer cells, such as alpha2,3ST and GnT-III, were able to decrease viability two-fold (from 20 to 40% cell death) following stable overexpression. The increased susceptibility of
glycosyltransferase-transfected U-373 cells to pro-apoptotic drugs was associated with increased
ceramide levels in Rafts, increased
caspase-3 activity and increased DNA fragmentation. In contrast, the same
glycosyltransferase overexpression protected U-373 cells against a different class of apoptotic drugs, namely the
phosphatidylinositol 3-kinase inhibitor
LY294002. Thus altered
surface protein glycosylation of a human
glioblastoma cell line can lead to lowered resistance to chemotherapeutic agents.