CIRCULATORY HALF-LIFE BUT NOT INTERACTION WITH THE LUTROPIN CHORIONIC-GONADOTROPIN RECEPTOR IS MODULATED BY SULFATION OF BOVINE LUTROPIN OLIGOSACCHARIDES

Certain of the glycoprotein hormones, including bovine lutropin (bLH), bear asparagine-linked oligosaccharides terminating with the sequence SO4-4GalNAc-beta-1-4GlcNAc-beta-1-2Man-alpha. To establish the biologic significance of these sulfate-bearing oligosaccharides we have compared properties of native bLH, desulfated bLH, recombinant bLH produced in Chinese hamster ovary cells that bears asparagine-linked oligosaccharides terminating with sialic acid alpha-2-3Gal-beta-1-4GlcNAc-beta-1-2Man-alpha rather than sulfated oligosaccharides (bLH/CHO), and desialyzed bLH/CHO. Using cultured MA-10 cells, a Leydig cell tumor line expressing the lutropin/chorionic gonadotropin receptor, we have found no differences in binding, cAMP production, or progesterone production between native and desulfated bLH. Sulfation of bLH oligosaccharides does not, therefore, modulate bLH bioactivity at the level of the lutropin/chorionic gonadotropin receptor. Removal of sulfate from bLH oligosaccharides and sialic acid from bLH/CHO oligosaccharides results in rapid clearance from the circulation by the hepatocyte asialoglycoprotein receptor. Thus sulfate, like sialic acid, prevents clearance from the circulation by the asialoglycoprotein receptor. The rapid removal of desulfated bLH from the circulation causes a 4- to 16-fold increase in the amount of bLH required to stimulate ovulation compared with native bLH. Particularly striking were differences in the metabolic clearance rates for native bLH and bLH/CHO, 7.3% per min and 1.7% per min, respectively. These differences were unexpected because bLH and bLH/CHO do not differ significantly in charge or size. The different metabolic clearance rates obtained for bLH and bLH/CHO indicate that the presence of sulfated rather than sialylated oligosaccharides on bLH results in a shorter circulatory half-life, which has a significant impact on in vivo bioactivity.