Opposing changes in N-acetylglucosaminyltransferase-V and -III during the cell cycle and all-trans retinoic acid treatment of hepatocarcinoma cell line

The changes in N-acetylglucosaminyltransferase-V and -III (GnT-V, GnT-III) during the cell-cycle of synchronized 7721 human hepatocarcinoma cell line were investigated. Using an HPLC method to assay GnT and flow cytometry (FC M) for cell cycle analysis, it was found that GnT-V showed the highest acti vity, but GnT-III reached the lowest activity when G(2)/M cells were most a bundant. In contrast, GnT-V declined to the minimum while GnT-III elevated to maximum when G(0)/G(1) cells were most predominant. The opposing changes were more obvious when the activities of GnT-V and GnT-III were expressed as relative activities (activity of GnT-V or GnT-III/the sum of activities of GnT-V plus GnT-IV plus GnT-III). These opposing changes of GnT-V and GnT -III during the cell cycle might result from the different regulatory mecha nisms of GnT-V and GnT-III expression in the cell cycle. The alterations in the structures of cell surface N-glycans were compatible with the changes of the activities of GnTs. The results from immunocytochemistry and Norther n blot showed that the protein and mRNA contents of GnT-V were not signific antly changed during the cell cycle. The activity of a cell cycle regulatin g protein kinase, p34(cdc2) kinase, correlated to the activity of GnT-V. Th ese findings suggested that the change of GnT-V activity in cell cycle was not the consequence of the alteration of gene transcription or enzyme prote in synthesis, but might be caused by the post-translational regulation. The decrease in GnT-V and the corresponding increase in GnT-III activities wer e also found after the cells were treated with all-trans retinoic acid (ATR A), and the mechanism of this might be different from that in the cell cycl e. (C) 2000 Elsevier Science B.V. All rights reserved.