Effects of preventing O-glycosylation on the secretion of human chorionic gonadotropin in Chinese hamster ovary cells.

Human chorionic gonadotropin (hCG) is a member of a family of heterodimeric glycoprotein hormones that have a common alpha subunit but differ in their hormone-specific beta subunits. The beta subunit of hCG (hCG beta) is unique among the beta subunits in that it contains four mucin-like O-linked oligosaccharides attached to a carboxyl-terminal extension. To study the effects of O-glycosylation on the secretion and assembly of hCG, expression vectors containing either the hCG beta gene alone or together with the hCG alpha gene were transfected into a mutant Chinese hamster ovary cell line, IdID, which exhibits a reversible defect in O-glycosylation. Our results reveal that hCG beta can be secreted normally in the absence of its O-linked oligosaccharides. hCG beta devoid of O-linked carbohydrate can also combine efficiently with hCG alpha and be secreted as an intact dimer. We conclude that in Chinese hamster ovary cells, the hCG beta O-linked chains play no role in the assembly and secretion of hCG. The normal and O-linked oligosaccharide-deficient forms of hCG secreted by these cells should prove useful in examining the role of O-linked chains on the biological function of hCG.