ESTROGEN MODULATES EXPRESSION OF THE GLYCOSYLTRANSFERASES THAT SYNTHESIZE SULFATED OLIGOSACCHARIDES ON LUTROPIN

The glycoprotein hormone lutropin (LH) bears oligosaccharides terminat ing with the sequence SO4-4-GalNAcbeta1,4GlcNAcbeta1,2Manalpha. We hav e determined that estrogen actively modulates expression of the GalNAc - and sulfotransferases responsible for synthesis of sulfated oligosac charides on LH alpha and beta subunits. Consequently, terminal glycosy lation of LH oligosaccharides with GalNAc-4-SO4 is maintained when LH synthesis and secretion are markedly increased, as occurs during the m idcycle surge and following ovariectomy. Maintenance of sulfated oligo saccharides on LH has important biologic consequences because LH circu latory half-life as well as biologic activity at the hormone receptor level are dramatically affected by glycosylation. To our knowledge, re gulation of glycosyltransferase levels in response to specific stimuli has not been observed previously, further emphasizing the biologic si gnificance of glycosylation for expression of LH bioactivity in vivo.