Inositol phosphate stimulation by LH requires the entire α Asn56 oligosaccharide

Van T. Nguyen, Vinod Singh, Vladimir Y. Butnev, Ciann M. Gray, Suzanne Westfall, John S. Davis, James A. Dias, George R. Bousfield

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

Abstract

Lentil lectin-bound, fucose-enriched hTSH was reported to stimulate both cAMP and inositol phosphate (IP) intracellular signalling pathways, whereas fucose-depleted hTSH stimulated only the cAMP pathway. Gonadotropins activate the cAMP pathway and in several studies higher concentrations activate the IP pathway. Since only the 10% of α subunit Asn56 oligosaccharides (Asn52 in humans) are fucosylated, the higher glycoprotein hormone concentrations required for IP pathway activation might be related to the abundance of competent hormone isoforms. Lentil lectin-fractionated equine (e)LHα and eFSHα preparations were combined with a truncated, des(121-149)eLHβ preparation. All four hybrid hormone preparations induced IP accumulation in porcine theca cells, suggesting that activation of the IP pathway was not dependent on fucosylation at α subunit Asn56. However, the presence of Asn56 carbohydrate was necessary for increased IP accumulation. Intact, rather than Asn56-deglycosylated eLH preparations provoked a biphasic steroidogenic response by rat testis Leydig cells, suggesting that Gαi stimulation was also sensitive to loss of Asn56 carbohydrate. While rat granulosa cells responded to human FSH preparations in a biphasic manner, a classical sigmoidal response was obtained to eFSH and Asn56-deglycosylated eFSH, suggesting that the equine preparations did not activate Gαi. Purified oLHα Asn56 oligosaccharides inhibited FSH-stimulated steroidogenesis in rat granulosa cell cultures indicating a direct role for carbohydrate in FSH action. The same carbohydrate preparation inhibited hCG-stimulated fluorescence energy transfer suggesting oligosaccharide involvement in activated LH receptor self-association.

Original languageEnglish (US)
Pages (from-to)73-86
Number of pages14
JournalMolecular and Cellular Endocrinology
Volume199
Issue number1-2
DOIs
StatePublished - Jan 31 2003

Keywords

  • Carbohydrate
  • Deglycosylation
  • Gonadotropin
  • Inositol phosphate
  • Steroidogenesis

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Endocrinology

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