ALPHA-FETOPROTEIN-PRODUCING RENAL-CELL CARCINOMA WITH INCREASED ACTIVITY OF N-ACETYLGLUCOSAMINYLTRANSFERASE-III

N-acetylglucosaminyltransferase (GnT) III catalyzes the addition of N- acetylglucosamine through a beta 1-4 linkage to the mannose of the tri mannosyl core, resulting in conversion of the concanavalin-A-(ConA)-re active glycan into the ConA-nonreactive one. In this study, we measure d GnT III levels in serum, tumor, and surrounding normal tissues toget her with a glucosaminylation index of alpha-fetoprotein (AFP), which i s defined as the percentage of the ConA-nonreactive species in total A FP, in a case of AFP-producing renal cell carcinoma. The glucosaminyla tion index was determined by affinoelectrophoresis in the presence of ConA. GnT III was measured by using a pyridylaminated asialoagalactobi antennary sugar chain as a substrate by high-performance liquid chroma tography. The glucosaminylation index of serum AFP, the concentration of which was 68 ng/ml, was 60%. This value is much higher than observe d in hepatocellular carcinomas. The tumor tissue level of GnT III was 55.34 pmol/mg/h which was about six fold higher (9.50 pmol/mg/h) than in normal surrounding tissues. The serum level of this enzyme before s urgery was 27.65 pmol/ml/h and decreased to 5.38 pmol/ml/h thereafter in association with a depression of serum Am from 68 to 5.4 ng/ml. Thu s, an increased level of GnT III in tumor tissues could account for th e elevated conversion of a biantennary complex type sugar chain of AFP into a bisecting glucosaminylated biantennary one resulting from the addition of an N-acetylglucosamine residue at the trimannosyl core. Th is is, to our knowledge, the first report explaining the change in the carbohydrate structure of AFP with different affinity to ConA on the enzymatic basis in a renal cell carcinoma.