Expression of α-gal epitopes on HeLa cells transduced with adenovirus containing α1,3galactosyltransferase cDNA

alpha1,3Galactosyltransferase (alpha1,3GT) synthesizes alpha-gal epitopes (Galalpha1-3Galbeta1-4GlcNAc-R) on glycoconjugates in nonprimate mammals but not in humans. Transduction of a1,3GT gene into human HeLa cells by an adenovirus vector allowed for accurate kinetics studies on the appearance of a1,3GT and of its product, the alpha-gal epitope, in the transduced cells. Mouse alpha1,3GT cDNA was inserted into a replication-defective adenovirus vector. This viral vector, designated AdalphaGT, could be propagated in human 293 cells that have the viral E1 complementing gene. Transduction of HeLa cells resulted in immediate penetration of similar to20 AdalphaGT copies into each cell and the appearance of alpha1,3GT mRNA after 4h. Catalytic activity of alpha1,3GT was first detected in the cells after 6 h. The initial appearance of alpha-gal epitopes (similar to6 x 10(4)/cell) on cell surface glycoconjugates was detected 10 h posttransduction, whereas 24 h posttransduction each cell expressed 2 x 10(6) epitopes. The activity of alpha1,3GT in cells transduced with approximately two copies of AdaGT was eightfold lower than that in cells transduced with similar to20 AdalphaGT copies; however, the number of alpha-gal epitopes/cell remained closely similar. This implies that increased alpha1,3GT activity above a certain saturation level does not result in a corresponding increase in the carbohydrate product, possibly because of competing glycosyltransferases.