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Glycosylation of the Chorionic Gonadotropin Subunit Synthesized by HeLa Cells¹

Department of Biochemistry and Biophysics and Program in Molecular, Cellular, and Developmental Biology, Iowa State University, Ames, Iowa 50011

The glycoprotein hormone subunit secreted by HeLa cells was retained by concanavalin A:Sepharose and by ricin:agarose, indicating that the tumor protein has carbohydrate side chains containing both mannose and galactose residues. Lectin chromatography of the intracellular hormone suggests it is probably a precursor to the secreted protein; it was bound by concanavalin A but not by ricin, suggesting the presence of a high mannose core oligosaccharide but the absence of terminal sugar residues. The glycosylation inhibitors tunicamycin and 2-deoxy-D-glucose caused a reduction in subunit secretion comparable to their reduction of general protein synthesis but considerably less than their inhibition of protein glycosylation. Various HeLa lines secreted subunit at widely different rates, with HeLa CCL 2.2 having the highest rate of production, HeLa CCL 2.1 having the lowest, and HeLa CCL 2 being intermediate. Dose-response curves for subunit from the different HeLa lines and from tunicamycin- and deoxyglucose-treated cells were sufficiently parallel to indicate similar immunological characteristics. The incorporation of radiolabeled glucosamine and N-acetylmannosamine into secreted proteins varied among the cell lines examined and was generally comparable to their hormone production rates. Concanavalin A:Sepharose chromatography of the subunit secreted by HeLa CCL 2.2 and CCL 2.1 indicated that both proteins possess oligosaccharide side chains containing mannose while chromatography of these proteins on ricin:agarose suggested that less of the subunit from CCL 2.1 contains galactose than that from CCL 2.2.

¹ This research was sponsored by Grant CA 21534 from the National Cancer Institute, NIH.

Received 12/30/80. Accepted 5/ 7/81.