Activation of β1,3-N-Acetylglucosaminyltransferase-2 (β3Gn-T2) by β3Gn-T8: POSSIBLE INVOLVEMENT OF β3Gn-T8 IN INCREASING POLY-N-ACETYLLACTOSAMINE CHAINS IN DIFFERENTIATED HL-60 CELLS*

摘要

Enzymatic activities of some glycosyltransferases are markedly increased via complex formation with other transferases or cofactor proteins. We previously showed that β1,3-N-acetylglucosaminyltransferase-2 (β3Gn-T2) and β3Gn-T8 can form a heterodimer in vitro and that the complex exhibits much higher enzymatic activity than either enzyme alone (Seko, A., and Yamashita, K. (2005) Glycobiology 15, 943–951). Here we examined this activation and the biological significance of complex formation in differentiated HL-60 cells. β3Gn-T2 and -T8 were co-immunoprecipitated from the lysates of both-transfected COS-7 cells, indicating their association in vivo. We prepared inactive mutants of both enzymes by destroying the DXD motifs. The mixture of mutated β3Gn-T2 and intact β3Gn-T8 did not exhibit any activation, whereas the mixture of intact β3Gn-T2 and mutated β3Gn-T8 had increased activity, indicating the activation of β3Gn-T2 via complex formation. Next, we compared expression levels of β3Gn-T1-T8 in HL-60 cells and DMSO-treated differentiated HL-60 cells, which produce larger poly-N-acetyllactosamine chains. The expression level of β3Gn-T8 in the differentiated cells was 2.6-fold higher than in the untreated cells. Overexpression of β3Gn-T8, but not β3Gn-T2, induced an increase in poly-N-acetyllactosamine chains in HL-60 cells. These results raise a possibility that up-regulation of β3Gn-T8 in differentiated HL-60 cells increases poly-N-acetyllactosamine chains by activating intrinsic β3Gn-T2.