Novel induction of alpha-lactalbumin-mediated lacdiNAc-R expression in vivo.

alpha-Lactalbumin (alpha-LA) is a regulatory protein by which the mammalian beta1,4-galactosyltransferase (beta1,4-galT) is induced to utilize glucose as an acceptor instead of N-acetylglucosamine (GlcNAc) during lactose synthesis in mammary gland. alpha-LA can also modulate beta1,4-galT to utilize UDP-N-acetylgalactosamine (UDP-GalNAc) as a donor towards GlcNAc acceptor substrate with high efficiency in vitro [Do, Do and Cummings (1995) J. Biol. Chem. 270, 18447-18451]. In the present study we transfected cDNA encoding bovine alpha-LA into Lec8 cells and examined whether nucleotide sugar switching of UDP-galactose (UDP-Gal) into UDP-GalNAc occurred in vivo and whether the neo-glycosylation of GalNAcbeta1,4GlcNAc-R structure was synthesized in alpha-LA-stable transfectants. Our studies demonstrate that the stable expression of alpha-LA in Lec8 cells induces the formation of GalNAcbeta1,4GlcNAc-R in vivo through the nucleotide sugar switching of beta1,4-galT.