Phorbol ester inhibition of rat gonadotropin-releasing hormone promoter activity: Role of Fos and Jun in the repression of transcription

Jan M. Bruder, Andrea J. Spaulding, Margaret E. Wierman

Research output: Contribution to journalArticle

45 Scopus citations

Abstract

Treatment of GT1-7 nauronal cells with the phorbol ester, 12-O- tetradecanoyl phorbol 13-acetate (TPA), inhibits GnRH gene transcription. The present studies investigated the role of AP-1 (Fos and Jun) in this repression. Treatment of cells with TPA increased c-fos mRNA 20-fold with only a 2-fold increase in c-jun mRNA levels. In transient transfection studies, a luciferase expression vector containing fragments of the 5'- flanking DNA of the rat GnRH (rGnRH) promoter was cotransfected with Fos and Jun expression vectors to mimic the effects of TPA. A dose-dependent decrease in reporter activity was noted with increasing amounts of Fos but not with Jun overexpression. Deletion analysis mapped the region that mediates repression by AP-1 to the area between -126 and -73 base palm (bp) of the rGnRH 5'-flanking region: the same area that mediates TPA-induced repression and contains an imperfect TPA response element sequence at -99. Gel retardation assays, however, showed that a DNA fragment from -111 to -73 of the rGnRH promoter does not directly interact with Fos in GT1-7 extracts. Coexpression of Fos proteins with mutations in the DNA-binding region, the dimerization domain, or carboxy terminus partially blocked inhibition of rGnRH promoter activity. These data support a novel mechanism of AP-1 repression of GnRH transcription that is mediated by Fos interaction with other protein(s) that directly bind to the proximal rGnRH promoter.

Original languageEnglish (US)
Pages (from-to)35-44
Number of pages10
JournalMolecular Endocrinology
Volume10
Issue number1
DOIs
StatePublished - 1996
Externally publishedYes

ASJC Scopus subject areas

  • Molecular Biology
  • Endocrinology

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