Biosynthesis, glycosylation, and secretion of rat luteinizing hormone α- and β-subunits: Differential effects of orchiectomy and gonadotropin-releasing hormone

Donna Vogel, J. A. Magner, R. J. Sherins, B. D. Weintraub

Research output: Contribution to journalArticle

Abstract

We have studied the de novo biosynthesis and secretion of LH subunits in pituitary quarters from orchiectomized and intact control adult male rats and their regulation by GnRH. After labeling with [35S]cystine ([35S]Cys), [35S]methionine, or [3H]glucosamine ([3H]GlcN) in the presence or absence of 10-8 M GnRH, tissue lysates and media were immunoprecipitated by antisera to LHβ, then LHα (after removal of TSH by immunoprecipitation with anti-TSHβ), and the products were analyzed by sodium dodecyl sulfate gradient gel electrophoresis. During a 12-min pulse labeling with [35S]methionine, three forms of immunoreactive α were labeled at 21,000, 18,000, and 12,000 mol wt. After a 30-min chase with excess unlabeled methionine, the 12,000 form increased from 57% to 69%, implying a precursor-product relationship. Neither orchiectomy nor GnRH had any effect on [35S]Cys or [3H}GlcN incorporation into intracellular or secreted total proteins. After a 6-h continuous labeling, incorporation of [35S]Cys into intracellular combined LHα in castrates was 158% of the control value, combined LHβ was 304%, and free α was 466%. The [3H]GlcN to [35S]Cys ratio, reflecting relative glycosylation, was unchanged in castrates for total proteins or LHα and somewhat decreased for LHβ and free α. Orchiectomy increased [35S]Cys-labeled secreted LHβ and free α to 183% and 231% of control values, respectively. Relative glycosylation of secreted LHα, LHβ, and free α was unchanged in castrates. Incorporation of [35S]Cys into intracellular combined LHα, LHβ and free α-subunit was unaffected by GnRH in pituitaries from intact rats. In castrates, LHα was unchanged, but LHβ and free α were slightly increased. Incorporation of [3H]GlcN into intracellular combined LHα, LHβ, and free α was increased with GnRH in both intacts and castrates, such that the 3H to 35S ratio, reflecting relative glycosylation, was also increased with GnRH. In castrates, the ratios, as a percentage of the control, were, respectively 250%, 250%, and 223% for LHα, LHβ, and free α. In intact animals, the ratios were 221%, 281%, and 143%, respectively. Incorporation of both [35S]Cys and [3H]GlcN into secreted subunits was increased in most instances, such that the 3H to 35S ratio was increased only for LHβ. These data indicate that orchiectomy stimulates LH and free α apoprotein synthesis and secretion without increasing relative glycosylation, while acute in vitro GnRH exposure increases relative glycosylation with little or no effect on apoprotein synthesis. Sex steroids and GnRH appear to regulate synthesis, glycosylation, and secretion in distinct patterns for the different subunits.

Original languageEnglish (US)
Pages (from-to)202-213
Number of pages12
JournalEndocrinology
Volume119
Issue number1
Publication statusPublished - 1986
Externally publishedYes

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ASJC Scopus subject areas

  • Endocrinology
  • Endocrinology, Diabetes and Metabolism

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