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Expression and Differential Glycosylation of Human Sex Hormone-Binding Globulin by Mammalian Cell Lines

Wayne P. Bocchinfuso^*, Susan Warmels-Rodenhiser and Geoffrey L. Hammond

Departments of Obstetrics and Gynecology, Biochemistry, and Oncology, and Medical Research Council Group in Fetal and Neonatal, Health and Development, University of Western Ontario, London Ontario, Canada N6A 4L6

Address requests for reprints to: Geoffrey L. Hammond, Ph.D., London Regional Cancer Centre, 790 Commissioners Road East, London, Ontario, Canada N6A 4L6.

Abstract

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-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.

FOOTNOTES

This work was supported by a grant from the Medical Research Council of Canada.

^* Supported by a Victoria Hospital Corp. Graduate Studentship.

Ontario Cancer Treatment and Research Foundation Scholar.

Received for publication June 27, 1991. Revision received August 22, 1991. Accepted for publication August 22, 1991.

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