Gonadotropin α subunit. Differential processing of free and combined forms in human trophoblast and transfected mouse cells

C. L. Corless, M. Bielinska, T. V. Ramabhadran, S. Daniels-McQueen, T. Otani, B. A. Reitz, D. C. Tiemeier, I. Boime

Research output: Contribution to journalArticle

40 Scopus citations

Abstract

The gonadotropins luteinizing hormone, follicle-stimulating hormone, and human chorionic gonadotropin are composed of two noncovalently linked subunits, α and β. The α subunit, identical in all three hormones, is produced in excess over the unique β subunits by pituitary and placenta, and is secreted as uncombined, or free subunit. Free α subunit from both tissues has a larger molecular weight than the dimer form. In bovine pituitary an extra O-linked oligosaccharide is added to free α subunit, and this modification has recently been detected at an analogous position (threonine 39) on human α subunit secreted by choriocarcinoma cells. To assess the contribution of N-linked and O-linked oligosaccharides to the heterogeneity of human free α subunit, we have compared free α with human chorionic gonadotropin α secreted by explants and cultured cytotrophoblasts of human first trimester placenta. We have also examined the free and combined forms of human α subunit expressed in transfected C-127 mouse mammary tumor cells. Processing of the α subunit in placental and C-127 cells was similar. Tryptic mapping of placental-derived and transfected α subunits indicated that O-glycosylation at threonine 39 was not a major modification. In the presence of the oligosaccharide processing inhibitor swainsonine the difference in size between the free and combined forms of α was eliminated in both placental and C-127 cells, indicating that the two forms of α differed in their N-linked oligosaccharides. Furthermore, the oligosaccharides of free α subunits from placental and transfected cells were resistant to endoglycosidase H, but the combined forms of α were partially sensitive to the enzyme. Thus, in human first trimester placenta and mouse C-127 cells, combination of α with human chorionic gonadotropin β alters the processing of N-linked oligosaccharides on α subunit.

Original languageEnglish (US)
Pages (from-to)14197-14203
Number of pages7
JournalJournal of Biological Chemistry
Volume262
Issue number29
StatePublished - Jan 1 1987

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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    Corless, C. L., Bielinska, M., Ramabhadran, T. V., Daniels-McQueen, S., Otani, T., Reitz, B. A., Tiemeier, D. C., & Boime, I. (1987). Gonadotropin α subunit. Differential processing of free and combined forms in human trophoblast and transfected mouse cells. Journal of Biological Chemistry, 262(29), 14197-14203.