Alpha 2-->3sialyltransferase associated with the synthesis of CA 19-9 in colorectal tumors

A novel assay method specific for alpha 2-->3sialyltransferase that seems to be responsible for the synthesis of CA 19-9 antigen was developed and the levels of the enzyme in colorectal tumor tissues were measured and compared with the levels of alpha 1-->4fucosyltransferase and the CA 19-9 antigen.

Lacto-N-biose I (Gal beta 1-->3GlcNAc beta, Lewis(c) [Le(c)]) and 6-O-methyl-Le(c) (Gal beta 1-->3[6OMe]GlcNAc beta) were synthesized and covalently attached to bovine serum albumin (BSA). These two substrates were incubated with extracts from colorectal tissues in the presence of cytidine 5'-monophospho-N-acetylneuraminic acid (CMP-NeuAc) and their resulting products were detected by a sequential use of anti-BSA monoclonal antibody-coated beads and 125I-labelled anti-sialylated Le(c) antibody. Levels of alpha 2-->3sialyltransferase and alpha 1-->4fucosyltranferase activities and CA 19-9 antigen were measured in the extracts from colorectal tumors and their adjacent normal tissues.

6-O-Methyl-Le(c)-BSA showed a strong acceptor activity compared with Le(c)-BSA and was used as a specific acceptor for alpha 2-->3sialyltransferase. Similar elevation patterns alpha 2-->3sialyltransferase activities and CA 19-9 antigen levels were observed in tumor extracts but no clear correlation was present between the level of alpha 1-->4fucosyltransferase activities and CA 19-9 antigen levels were observed in tumor extracts but no clear correlation was present between the level of alpha 1-->4fucosyltransferase activities and CA 19-9 antigen levels in the same extracts.

The accumulation of CA 19-9 antigen in colorectal tumors might be caused mainly by the activation of alpha 2-->3sialyltransferase but not by that of alpha 1-->fucosyltransferase.