GENE-EXPRESSION OF ALPHA-1-6 FUCOSYL-TRANSFERASE IN HUMAN HEPATOMA TISSUES - A POSSIBLE IMPLICATION FOR INCREASED FUCOSYLATION OF ALPHA-FETOPROTEIN

The alpha 1-6 fucosylated alpha-fetoprotein (AFP) present in serum of patients with hepatocellular carcinoma (HCC) has been employed for the differential clinical diagnosis of HCC from chronic liver diseases. T he molecular mechanism by which this alteration occurs, however, remai ns largely unknown. To address this issue, we purified GDP-L-Fuc:N-ace tyl-beta-D-glucosaminide alpha 1-6 fucosyltransferase (alpha 1-6 FucT) , an enzyme involved in the alpha 1-6 fucosylation of N-glycans from p orcine brain, as well as from a human gastric cancer cell line, and cl oned their genes. In this study, levels of alpha 1-6 FucT mRNA express ion and the activity of this enzyme for 12 human HCC tissues were exam ined and compared with that in surrounding tissues and normal livers. The mean +/- SD for alpha 1-6 FucT activity was 78 +/- 41 pmol/h/mg in normal control liver, 202 +/- 127 pmol/h/mg in adjacent uninvolved li ver tissues (chronic hepatitis: 181 +/- 106 pmol/h/mg; liver cirrhosis : 233 +/- 164 pmol/h/mg), and 194 +/- 72 pmol/h/mg in HCC tissues. The mRNA expression of alpha 1-6 FucT was also enhanced in proportion to enzymatic activity except for a few cases, suggesting that alpha 1-6 F ucT expression is increased in chronic liver diseases, especially live r cirrhosis. Transfection of alpha 1-6 FucT gene into cultured rat hep atocytes markedly increased alpha 1-6 FucT activity and led to an incr ease in lens culinaris agglutinin (LCA) binding proteins in both cell lysates and condition media. When the alpha 1-6 FucT gene was transfec ted into a human HCC cell line, Hep3B, which originally showed low lev els of alpha 1-6 FucT expression, alpha 1-6-fucosylated AFP was dramat ically increased in the condition media, Collectively, these results s uggest that the enhancement of alpha 1-6 FucT expression increased the fucosylation of several proteins, including AFP, and that the level o f alpha 1-6-fucosylated AFP in patients with HCC was in part caused by up-regulation of the alpha 1-6 FucT gene expression.