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Repression of gonadotropin-releasing hormone gene expression by androgen receptor


Gonadotropin-releasing hormone (GnRH) is the central regulator of the hypothalamic-pituitary-gonadal axis. Steroid hormones synthesized and released by the gonads, such as androgens, negatively feedback to the hypothalamus to regulate GnRH synthesis and secretion, and precise regulation is vital for proper reproductive function. In vitro experiments, utilizing the GnRH immortalized neuronal cell line, GT1-7, were performed to elucidate the mechanisms by which androgen receptor (AR) disrupts GnRH transcription. We show that methyltrienolone (R1881), an AR agonist, represses GnRH expression through the proximal promoter (GnRHp) as well as the distal enhancer (GnRHe) and causes increased AR interaction with those regions. Classical gene regulation by AR involves binding to androgen responsive elements (AREs). However, GnRHp and GnRHe do not contain putative AREs. Thus, repression may be occurring via AR interaction with DNA-bound transcription factors or with co-factors. We find that multiple regions, including the -91/-86 region in GnRHp, are required for AR-mediated repression rather than a single transcription factor-binding site. On the other hand, repression of GnRHe maps to the -1800/-1766 region and may require nucleotides -1789/-1787. AR and thyroid transcription factor-1 (TTF-1 or Nkx2.1) may be part of unknown protein complexes binding to the -1795/-1790 and - 1792/-1784 regions of GnRHe, respectively. Interestingly, we also find that R1881 suppresses the activity of Rous sarcoma virus promoter (RSVp) when three copies of the Nkx2.1 consensus binding sequence are positioned directly upstream of RSVp. In conclusion, AR activation by R1881 represses GnRH expression by utilizing multiple sites throughout GnRHp, the 1800/-1766 region of GnRHe, and possibly involves Nkx2.1

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