Miyoshi E, Nishikawa A, Ihara Y, Hayashi N, Fusamoto H, Kamada T, Taniguchi N
Department of Biochemistry, Osaka University Medical School, Japan.
Cancer Res. 1994 Apr 1;54(7):1854-8.
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.
UDP-N-乙酰葡糖胺：β-D-甘露糖苷β-1,4-N-乙酰葡糖胺基转移酶III（GnT-III）是天冬酰胺连接的寡糖分支过程中的关键酶，这些寡糖存在于各种组织的表面膜蛋白和分泌性糖蛋白中。在两种人肝癌细胞系中检测了GnT-III的活性，一种是亲本细胞系Huh6，另一种是通过将3个串联的乙肝病毒基因组转染到Huh6中建立的HB611。发现Huh6和HB611之间的GnT-III活性存在显著差异（分别为136±18.3 pmol/h/mg和6.7±2.4 pmol/h/mg；平均值±标准差，P<0.001），而糖基转移酶α-3-D-甘露糖苷β-1,4-N-乙酰葡糖胺基转移酶IV、α-6-D-甘露糖苷β-1,6-N-乙酰葡糖胺基转移酶-V和β-1,4-半乳糖基转移酶在这两种细胞系中的水平几乎相同。Northern印迹分析表明，HB611中GnT-III活性降低是由于转录本减少所致。当用α干扰素处理HB611时，乙肝病毒相关mRNA的表达下降，GnT-III的活性从8.5±3.8 pmol/h/mg增加到22.0±7.2 pmol/h/mg（平均值±标准差，P<0.05）。在Huh6中未发现这种增加。使用荧光激活细胞分选分析这些细胞与红细胞植物血凝素的结合能力不同，这表明细胞表面糖链的结构可能因GnT-III活性的抑制而改变。这是关于乙肝病毒选择性抑制肝癌细胞中GnT-III活性的首次报道。
