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A novel form of free human chorionic gonadotrophin β-subunit (hCGβ) was found in serum from ElBre, a woman with epidermoid carcinoma of unknown origin. ElBre hCGβ was larger than standard (pregnancy urine) hCGβ when analysed by gel chromatography (apparent molecular weight 54 000 vs 44000). This size difference appeared to be due to a larger carboxyterminal extension (CTE) of ElBre hCGβ since thermolysin cleavage of the CTE from standard hCGβ and Elbre hCGβ yielded core products of the same size. Oligosaccharides, O-linked to serine or threonine, were present in ElBre hCGβ, presumably on its CTE as judged by the complete binding of desialylated ElBre hCGβ to immobilized peanut agglutinin (this lectin is specific for terminal galactose linked β1 3 to N-acetylgalactosamine, a disaccharide exposed after desialylation of the O-linked oligosaccharides of standard hCGβ). ElBre hCGβ, however, was incompletely recognized by antisera specific for the CTE of standard hCGβ, especially the carbohydrate-sensitive antiserum R141.

The O-linked oligosaccharides of standard hCGβ are heterogeneous in size; 13% are of the largest (hexasaccharide) form. In contrast, over 50% of the O-linked oligosaccharides in hCGβ from the JAr choriocarcinoma cell line are hexasaccharides. Like desialylated ElBre hCGβ, desialylated JAr hCGβ bound completely to peanut agglutinin, but was incompletely recognized by antisera to the hCGβ-CTE. Furthermore, JAr hCGβ was intermediate in size between standard hCGβ and ElBre hCGβ when analysed by gel chromatography (apparent molecular weight 49 000). Thus, we propose that ElBre hCGβ had an even higher proportion of large O-linked oligosaccharides than had JAr hCGβ. Moreover, the N-linked oligosaccharides of ElBre hCGβ differed from standard hCGβ; only 55% of ElBre hCGβ bound to Concanavalin A versus 89% of standard hCGβ. These data further support the concepts of aberrant glycosylation by neoplastic tissues and carbohydrate heterogeneity of hCGβ produced by various tissues.

J. Endocr. (1985) 107, 403–408