THE O-LINKED OLIGOSACCHARIDE STRUCTURES ARE STRIKING DIFFERENT ON PREGNANCY AND CHORIOCARCINOMA HCG*

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Abstract
HCG is a glycoprotein hormone which is detected in the serum and urine of pregnant women and of patients with hydatidiform mole and choriocarcinoma. The molecule contains 4 O-linked sugar chains. In an effort to identify cancer markers, the structures of these sugar units on the hCG produced in pregnancy and choriocarcinoma were compared. hCG molecules in patient urines were purified by immuno-affinity chromatography and gel filtration. .beta.-Elimination was used to cleave the O-linked sugar units, radioactive sodium borohydirde to label them, and gel filtration on Bio-Gel P4 to size them and compare their elution volumes with those of standard oligosaccharides of known structure. A trisaccharide, NeuAc.alpha.2-3Gal.beta.1-3Ga1NAc-, was found to be the principal unit attached to urinary hCG from pregnant women (10 samples). A hexasaccharide, NeuAc.alpha.2-3Gal.beta.1-3(NeuAc.alpha.2-3Gal.beta.1-4 GlcNAc.beta.1-6)GalNAc-, which accounted for just 6% (mean, range 0-14%) of the O-linked sugar units on pregnancy hCG, was the principal unit (mean 52% of total, range 50-56%) attached to the hCG from choriocarcinoma patient urines (3 samples). These results indicate that hexasaccharide-abundant hCG is an indicator of choriocarcinoma.