title: Inositol phosphate stimulation by LH requires the entire alpha Asn56 oligosaccharide.
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 alpha subunit Asn(56) oligosaccharides (Asn(52) 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)LHalpha and eFSHalpha preparations were combined with a truncated, des(121-149)eLHbeta 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 alpha subunit Asn(56). However, the presence of Asn(56) carbohydrate was necessary for increased IP accumulation. Intact, rather than Asn(56)-deglycosylated eLH preparations provoked a biphasic steroidogenic response by rat testis Leydig cells, suggesting that Galpha(i) stimulation was also sensitive to loss of Asn(56) carbohydrate. While rat granulosa cells responded to human FSH preparations in a biphasic manner, a classical sigmoidal response was obtained to eFSH and Asn(56)-deglycosylated eFSH, suggesting that the equine preparations did not activate Galpha(i). Purified oLHalpha Asn(56) 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.
authors.affiliation: Department of Biological Sciences, Box 26, Wichita State University, 1845 Fairmount, KS 67260-0026, USA.
authors.forename: Van T
authors.initials: VT
authors.lastname: Nguyen
authors.forename: Vinod
authors.initials: V
authors.lastname: Singh
authors.forename: Vladimir Y
authors.initials: VY
authors.lastname: Butnev
authors.forename: Ciann M
authors.initials: CM
authors.lastname: Gray
authors.forename: Suzanne
authors.initials: S
authors.lastname: Westfall
authors.forename: John S
authors.initials: JS
authors.lastname: Davis
authors.forename: James A
authors.initials: JA
authors.lastname: Dias
authors.forename: George R
authors.initials: GR
authors.lastname: Bousfield
mesh_terms: D000818:Animals; D001216:Asparagine; D004305:Dose-Response Relationship, Drug; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D005643:Fucose / Q000378:metabolism; D006031:Glycosylation; D006107:Granulosa Cells / Q000378:metabolism; D006736:Horses; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism*; D007985:Leydig Cells / Q000378:metabolism; D007986:Luteinizing Hormone / Q000737:chemistry / Q000494:pharmacology*; D008297:Male; D009844:Oligosaccharides / Q000737:chemistry / Q000494:pharmacology*; D051381:Rats; D015398:Signal Transduction; D013256:Steroids / Q000096:biosynthesis; D013329:Structure-Activity Relationship; D013552:Swine; D013799:Theca Cells / Q000378:metabolism
chemical_list: D007295:Inositol Phosphates; D009844:Oligosaccharides; D013256:Steroids; D005643:Fucose; D001216:Asparagine; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone