The Asn-linked oligosaccharides from bovine lutropin (bLH(Pit)) are predominantly dibranched complex-type structures with the terminal sequence SO4-4GalNAcβ1,4GlcNAcβ1,2Manα. Recombinant bLH expressed in Chinese hamster ovary cells (bLH(CHO)) bears di- (60%) and tribranched (30%) complex-type oligosaccharides; however, these terminate in the sequence Siaα2,3Galβ1,4GlcNAcβ1,2Manα. In contrast to the limited spectrum of oligosaccharide structures present on recombinant bLH(CHO), the endogenous glycoproteins synthesized by CHO cells bear a heterogeneous array of Asn-linked oligosaccharides with 0, 1, 2, 3, or 4 sialic acid moieties. The sialic acid moieties on the Asn-linked oligosaccharides of both endogenous glycoproteins and recombinant bLH(CHO) are exclusively α2,3-linked, suggesting that the α2,6-sialyltransferase is not active in CHO cells. The bioactivities of bLH(Pit) and bLH(CHO) were compared using MA-10 cells following sequential digestion with neuraminidase and β-galactosidase. Neither the ED50 (dose producing 50% of the maximum response) for progesterone production (7.2 ng/ml) nor the P(max) (maximum level of progesterone produced) (470 ng/ml) was altered for bLH(Pit) by these treatments, consistent with the absence of either sialic acid or Gal on bLH(Pit). The ED50 for progesterone production by recombinant bLH(CHO) (16.4 ng/ml) was significantly greater than for bLH(Pit) but was reduced to 5.3 ng/ml following removal of terminal sialic acid. Removal of the subterminal Gal was without further effect. The P(max) for bLH(CHO) (180 ng/ml) was not altered by these treatments. The reduction in bLH(CHO) bioactivity caused by the presence of terminal sialic acid suggests that the presence of terminal sulfate on bLH(Pit) oligosaccharides may also reduce its bioactivity and may play a modulatory role in regulating hormone bioactivity.
|Number of pages||8|
|Journal||Journal of Biological Chemistry|
|State||Published - Feb 12 1990|