Comparison of sialyl- and α-1,3-galactosyltransferase activity in NIH3T3 cells transformed with ras oncogene: increased β-galactoside α-2,6-sialyltransferase

Abstract

Previous studies have indicated that transfection of NIH3T3 cells with the ras oncogene induced modifications of the terminal glycosylation of N-linked glycans which appeared in the early stage after transfection. These changes affected especially the terminal part of N-linked glycans which is substituted with α-1,3-Gal residues in NIH3T3 and with Neu5Ac residues in the ras-transformed counterpart. We have transformed NIH3T3 cells with the human c-Ha- ras oncogene, evaluated tumorigenicity and metastatic capacity in vivo and compared α-1,3-galactosyltransferase, α-2,3- and α-2,6-sialytransferases activities. By using different specific acceptors, we detected the enhancement of sialic acid transfer in transformed cells while the activity of α-1,3-galactosyltransferase remained unchanged. We showed that the higher sialyltransferase activity was due to the increase of β-galactoside α-2,6-sialyltransferase in ras-transfectant although α-2,3-sialyltransferase was weakly expressed in these cells. On the basis of binding of different lectins, we correlated these observations with changes of protein glycosylation. We concluded that altered glycosylation of ras-transformed NIH3T3 is the result of a competitive effect of the enzymes acting for terminal glycosylation of N-linked glycans and the reflection of the higher expression of α-2,6-sialyltransferase.