Selective suppression of N-acetylglucosaminyltransferase III activity in a human hepatoblastoma cell line transfected with hepatitis B virus.

UDP-N-acetylglucosamine: beta-D-mannoside beta-1,4-N-acetylglucosaminyl-transferase III (GnT-III) is a key enzyme in the branching of asparagine-linked oligosaccharides, which are present in surface membrane proteins of various tissues and in secretory glycoproteins. The activity of GnT-III was assayed in 2 human hepatoblastoma cell lines, Huh6, which was the parental cell line, and HB611, which was established by transfection of 3 tandem copies of the hepatitis B virus genome into Huh6. A significant difference in GnT-III activity was found between Huh6 and HB611 (136 +/- 18.3 pmol/h/mg versus 6.7 +/- 2.4 pmol/h/mg; mean +/- SD, P < 0.001), whereas levels of the glycosyltransferases alpha-3-D-mannoside beta-1,4-N-acetylglucosaminyltransferase IV, alpha-6-D-mannoside beta-1,6-N-acetylglucosaminyltransferase-V, and beta-1,4-galactosyltransferase were almost the same in both cell lines. Northern blot analysis indicated that the decreased activity of GnT-III in HB611 was due to the decreased transcript. When HB611 was treated with interferon-alpha, expression of hepatitis B virus-related mRNA decreased, and the activity of GnT-III increased from 8.5 +/- 3.8 to 22.0 +/- 7.2 pmol/h/mg (mean +/- SD, P < 0.05). This increase was not found in Huh6. Binding capacity with erythrocyte phytohemagglutinin in these cells using fluorescence-activated cell sorter analysis was different, suggesting that the structure of sugar chain on the cell surface might be altered by suppression of GnT-III activity. This is the first report that hepatitis B virus selectively suppressed the GnT-III activity in hepatoblastoma cells.