The amount and type of sialylation of
tumor cell membranes depends on the activity of a number of different
sialyltransferase enzymes. For the detection of specific activities in human
colorectal carcinoma tissue several
glycoprotein and
glycolipid acceptors were used: desialylated
fetuin,
alpha 1-acid glycoprotein,
beta 2-glycoprotein I, ovine submaxillaris
mucin, and the
gangliosides GM1, GM2, GM3 and GD1a. Because of their possible relevance for
metastasis, precursors of Le(a) and Le(x)
antigens, too, were employed, namely neoglycolipids produced by coupling LcOse4 or NeoLcOse4
oligosaccharides to L-alpha-phosphatidyl-
ethanol-
amine-dipalmitoyl. Our data indicate that human
colorectal tumor tissue contains two highly active
sialyltransferase enzymes, which are only weakly expressed in normal mucosa. These are a N-
glycan-specific alpha 2,6-sialyltransferase, which was significantly increased in metastasizing
tumors, and a Gal beta 1,3Gal-NAc-specific
sialyltransferase, which was increased in
tumors of early stages. A shift to enhanced alpha 2,6-sialylation of
membrane glycoproteins during
carcinogenesis was demonstrated by
lectin ELISA analysis of magneto-bead separated
tumor cells. Quantitative determination of specific
sialyltransferase activities may be a sensitive tool for detection and monitoring of colon
carcinoma.