ELEVATION OF ALPHA-2-]6 SIALYLTRANSFERASE AND ALPHA-1-]2 FUCOSYL-TRANSFERASE ACTIVITIES IN HUMAN CHORIOCARCINOMA

Structures of N-linked sugar chains are species and tissue specific an d change in the course of tumorigenesis. Sialyl linkages of human plac ental glycoproteins are exclusively Neu5Ac alpha 2-->3Gal, whereas Fuc alpha 1-->2Gal and Neu5Ac alpha 2-->6Gal residues are expressed in hu man chorionic gonadotropin and alkaline phosphatase, which are produce d in human choriocarcinoma JEG-3 and BeWo cells. In the present study, to elucidate the enzymological and molecular biological basis of the structural changes that occur in the course of tumorigenesis, (alpha 1 -->2 fucosyltransferase, alpha 2-->3 and alpha 2-->6 sialyltransferase activities, and the expression levels of the corresponding mRNAs were measured. The alpha 2-->3 sialyltransferase activity did not change a s a result of tumorigenesis; however, the alpha 2-->6 sialyltransferas e activity and alpha 1-->2 fucosyltransferase activity in JEG-3 and Be Wo cells increased to levels several times higher than those in placen ta. Competitive PCR analysis showed that the expression levels of mRNA encoding alpha 1-->2fucosyltransferase and mRNA encoding alpha 2-->6s ialyltransferase increased significantly as a result of tumorigenesis, indicating that such structural changes are regulated at the level of transcription of these glycosyltransferase genes.