EXPRESSION AND DIFFERENTIAL GLYCOSYLATION OF HUMAN SEX HORMONE-BINDING GLOBULIN BY MAMMALIAN-CELL LINES

The human sex hormone-binding globulin (SHBG) gene is responsible for the production of plasma SHBG by the liver and androgen-binding protein in the testis. Cell-specific glycosylation events during synthesis may account for minor differences in the biochemical properties of SHBG and androgen-binding protein, and we have, therefore, expressed a human SHBG cDNA in chinese hamster ovary (CHO) cells and a mouse hepatoma cell line (BW-1), and compared the products to SHBG in serum. The SHBG produced in this way is a homodimer of subunits that exhibit size microheterogeneity similar to SHBG in human serum, and its affinity for 5-alpha-dihydrotestosterone (K(d) = 0.6 nM) and other steroids is essentially identical to that of natural SHBG. When medium from transfected CHO and BW-1 cells was subjected to Concanavalin-A (Con-A) chromatography, the relative amounts of SHBG retained by Con-A were 74% and 86%, respectively. In addition, when SHBG produced by CHO cells was separated into two fractions by Con-A chromatography and analyzed by polyacrylamide gel electrophoresis, SHBG that did not interact with Con-A migrated with a slightly larger apparent mol wt than that of SHBG that binds Con-A; this can be explained by the presence of triantennary, rather than biantennary, N-linked oligosaccharide chains. These data also demonstrate that the subunit microheterogeneity associated with plasma SHBG reflects differences in glycosylation during synthesis, which appear to be cell type specific.