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Molecular and Cellular Biology, April 1999, p. 2567-2576, Vol. 19, No. 4
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Egr-1 Is a Downstream Effector of GnRH and Synergizes by Direct Interaction with Ptx1 and SF-1 To Enhance Luteinizing Hormone beta  Gene Transcription

Jacques J. Tremblay and Jacques Drouin*

Laboratoire de Génétique Moléculaire, Institut de Recherches Cliniques de Montréal, Montréal, Québec, Canada H2W 1R7

Received 29 May 1998/Returned for modification 12 August 1998/Accepted 11 January 1999

Pituitary gonadotropins are critical regulators of gonadal development and function. Expression and secretion of the mature hormones are regulated by gonadotropin-releasing hormone (GnRH), which is itself secreted from the hypothalamus. GnRH stimulation of gonadotropin expression and secretion occurs through the G-protein-linked phospholipase C/inositol triphosphate intracellular signaling pathway, which ultimately leads to protein kinase C (PKC) activation and increased intracellular calcium levels. Transcription factors mediating the effects of GnRH-induced signals on transcription of gonadotropin genes have not yet been identified. Recent studies have identified key factors involved in luteinizing hormone beta  (LHbeta ) gonadotropin gene transcription: the nuclear receptor SF-1, the bicoid-related homeoprotein Ptx1 (Pitx1), and the immediate-early Egr-1 gene. We now show that GnRH is a potent stimulator of Egr-1, but not Ptx1 or SF-1, expression. Further, Egr-1 activation of the LHbeta promoter is specifically enhanced by PKC, in agreement with a role for Egr-1 in mediating a GnRH effect on transcription. Egr-1 interacts directly with Ptx1 and with SF-1, leading to an enhancement of Ptx1- and SF-1-induced LHbeta transcription. Thus, Egr-1 is a likely transcriptional mediator of GnRH-induced signals for activation of the LHbeta gene.

* Corresponding author. Mailing address: Laboratoire de Génétique Moléculaire, Institut de Recherches Cliniques de Montréal, 110 des Pins Ouest, Montréal, Québec, Canada H2W 1R7. Phone: (514) 987-5680. Fax: (514) 987-5575. E-mail: drouinj{at}ircm.qc.ca.

Molecular and Cellular Biology, April 1999, p. 2567-2576, Vol. 19, No. 4
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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