O-Glycosylation of Proteins in the Normal and Neoplastic Trophoblast
hCG is a glycoprotein hormone composed of two dissimilar subunits, α and β, joined non-covalently. The hormone, in addition to having N-linked sugar units, two on each subunit, contains four O-linked structures, all attached to the COOHsegment of the β subunit (Birken and Canfield, 1977; Cole et al., 1985). Gonadotropin large free α (LFA) is an oversized (Mr=24,000) non-combining form of the glycoprotein hormone common α-subunit (Mr=22,000). LFA can contain a single O-linked sugar unit attached to Thr 39 which may in part account for its size difference with the α-subunit incorporated into glycoprotein hormones (Cole et al, 1984a; Parsons and Pierce, 1984). Both hCG and LFA are secreted by the normal trophoblast in pregnancy and by the neoplastic trophoblast in hydatidiform mole and choriocarcinoma (Hussa, 1981; Cole et al., 1983; Cole et al., 1984b).
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- Birken, S.G., Agosto, G., Canfield, R.E., Amr, S., and Nisula, B. (1981) Antisera sensitive to the carbohydrate in the COOH-terminal region of hCG beta: Novel antibodies of clinical significance. Abstract of the 63rd Annual Meeting of the Endocrine Society, Cincinnati.Google Scholar
- Cole, L.A., Hartle, R.J., Laferla, J.J., and Ruddon, R.W. (1983) Detection of the free beta subunit of human chorionic gonadotropin (HCG) in cultures of normal and malignant trophoblast cells, pregnancy sera, and sera of patients with choriocarcinoma. Endocrinol. 113, 1176–1178.CrossRefGoogle Scholar
- Cole, L.A. (1985) Structures of the 0-linked oligosaccharides on human chorionic gonadotropin molecules produced by cancer cells. Abstract of the AAP/ASCI/AFCR Meetings, Washington, DC.Google Scholar
- Funakoshi, I. and Yamashina, I. (1982) Structures of 0-glycosidically linked sugar units from plasma membranes of an ascites hepatoma, AH66. J. Biol. Chem. 257, 3787.Google Scholar
- Hussa, R.O. (1981) Human chorionic gonadotropin, a clinical marker: review of its biosynthesis. Ligand. Rev. 3, 1–43.Google Scholar
- Imamura, S., Armstrong, E.G., Birken, S., and Cole, L.A. (1984) Highly specific and sensitive measurements of asialo hCG with lectin-antibody sandwich assays. Abstracts of the 7th International Congress of Endocrinology, Quebec City, Canada.Google Scholar
- Warren, L., Buck, C.A., and Tuszynski, G.P. (1978) Glycopeptide changes and malignant transformation: A possible role for carbohydrate in malignant behavior. Biochem. Biophys. Acta 516, 97–127.Google Scholar