Sp1, Steroidogenic Factor 1 (SF-1), and Early Growth Response Protein 1 (Egr-1) Binding Sites Form a Tripartite Gonadotropin-Releasing Hormone Response Element in the Rat Luteinizing Hormone-  Gene Promoter: an Integral Role for SF-1

2000 ◽  
Vol 14 (8) ◽  
pp. 1235-1245 ◽  
Author(s):  
U. B. Kaiser
Keyword(s):  
Binding Sites ◽  
Growth Response ◽  
Gene Promoter ◽  
Early Growth ◽  
Gonadotropin Releasing Hormone ◽  
Hormone Response ◽  
Steroidogenic Factor 1 ◽  
Early Growth Response ◽  
Hormone Response Element ◽  
Integral Role

scholarly journals The Protein Kinase C System Acts through the Early Growth Response Protein 1 to Increase LHβ Gene Expression in Synergy with Steroidogenic Factor-1

1999 ◽  
Vol 13 (1) ◽  
pp. 106-116 ◽  
Author(s):  
Lisa M. Halvorson ◽  
Ursula B. Kaiser ◽  
William W. Chin
Keyword(s):  
Gene Expression ◽  
Protein Kinase C ◽  
Protein Kinase ◽  
Growth Response ◽  
Gene Promoter ◽  
Early Growth ◽  
Mrna Levels ◽  
Steroidogenic Factor 1 ◽  
Early Growth Response ◽  
Kinase C

Abstract Expression of the LHβ gene has been shown to be modulated by both the orphan nuclear receptor, steroidogenic factor-1 (SF-1), and the early growth response protein 1, Egr-1. It is also well known that LHβ mRNA levels are increased after hormonal activation of the protein kinase C (PKC) signaling system, for example by GnRH; however, the mechanisms by which the PKC system exerts this effect has not been fully characterized. By transient transfection of the GH3 cell line, we demonstrate that activation of the PKC system with the phorbol ester, phorbol 12-myristate 13-acetate (PMA), increases activity of region −207/+5 of the rat LHβ gene promoter (∼2-fold) and markedly augments SF-1-induced stimulation (95-fold in the presence of both factors vs. 13-fold for SF-1 alone). Mutation of the two previously identified Egr-1 sites not only prevents Egr-1 effects on the LHβ gene promoter, but also eliminates the synergistic response to PMA and SF-1 together, findings that were confirmed in a longer construct spanning region −797/+5. In the gonadotrope-derived cell line,α T3–1, these mutations eliminate the GnRH responsiveness of the− 207/+5 LHβ promoter construct. We next show that PMA treatment (GH3 and αT3–1 cells) or GnRH treatment (αT3–1 cells) induces expression of Egr-1, as detected by Egr-1 interaction with Egr-1 DNA-binding sites in the rat LHβ gene promoter sequence. Furthermore, we demonstrate that PMA increases steady-state Egr-1 mRNA levels via increased Egr-1 transcription. We conclude that PMA-induced stimulation of LHβ gene expression is achieved, at least in part, by induction of Egr-1 expression.

scholarly journals The cAMP signaling system regulates LHbeta gene expression: roles of early growth response protein-1, SP1 and steroidogenic factor-1

2004 ◽  
Vol 32 (1) ◽  
pp. 291-306 ◽  
Author(s):  
CD Horton ◽  
LM Halvorson
Keyword(s):  
Transcription Factor ◽  
Adenylate Cyclase ◽  
Promoter Activity ◽  
Growth Response ◽  
Gene Promoter ◽  
Early Growth ◽  
Steroidogenic Factor 1 ◽  
Early Growth Response ◽  
Protein Levels ◽  
Camp System

Expression of the gonadotropin genes has been shown to be modulated by pharmacological or physiological activators of both the protein kinase C (PKC) and the cAMP second messenger signaling pathways. Over the past few years, a substantial amount of progress has been made in the identification and characterization of the transcription factors and cognate cis-elements which mediate the PKC response in the LH beta-subunit (LHbeta) gene. In contrast, little is known regarding the molecular mechanisms which mediate cAMP-mediated regulation of this gene. Using pituitary cell lines, we now demonstrate that rat LHbeta gene promoter activity is stimulated following activation of the cAMP system by the adenylate cyclase activating agent, forskolin, or by the peptide, pituitary adenylate cyclase-activating peptide. The forskolin response was eliminated with mutation of a previously identified 3' cis-acting element for the early growth response protein-1 (Egr-1) when evaluated in the context of region -207/+5 of the LHbeta gene. Activation of the cAMP system increased Egr-1 gene promoter activity, Egr-1 protein levels and Egr-1 binding to the LHbeta gene promoter, supporting the role of this transcription factor in mediating the cAMP response. Analysis of a longer LHbeta promoter construct (-797/+5) revealed additional contribution by upstream Sp1 DNA-regulatory regions. Of interest, forskolin-induced stimulation of LHbeta gene promoter activity was observed to increase synergistically with introduction of the transcription factor, steroidogenic factor-1 (SF-1). Although SF-1 is a critical mediator of the cAMP response in other genes, mutation of the SF-1 DNA-binding sites in the rat LHbeta gene did not alter the forskolin response nor did forskolin increase SF-1 protein levels in a gonadotrope cell line. In a further set of experiments, it was determined that forskolin-responsiveness was maintained following mutation of the previously defined homeobox-binding element at position -100. We conclude that both Egr-1 and Sp1 contribute to cAMP-dependent transcription of the rat LHbeta gene promoter. While SF-1 does not act independently to mediate the cAMP/PKA response, SF-1 is important for magnification of this response.

scholarly journals Early Growth Response Protein 1 Binds to the Luteinizing Hormone-β Promoter and Mediates Gonadotropin-Releasing Hormone-Stimulated Gene Expression

1999 ◽  
Vol 13 (5) ◽  
pp. 752-763 ◽  
Author(s):  
Michael W. Wolfe ◽  
Gerald B. Call
Keyword(s):  
Growth Response ◽  
Early Growth ◽  
Steroidogenic Factor 1 ◽  
Response Elements ◽  
Cis Acting ◽  
Early Growth Response ◽  
Endogenous Expression ◽  
Synergistic Activation

Abstract The hypothalamic neuropeptide, GnRH, regulates the synthesis and secretion of LH from pituitary gonadotropes. Furthermore, it has been shown that the LH β-subunit gene is regulated by the transcription factors steroidogenic factor-1 (SF-1) and early growth response protein 1 (Egr1) in vitro and in vivo. The present study investigated the roles played by Egr1 and SF-1 in regulating activity of the equine LHβ-subunit promoter in the gonadotrope cell line, αT3–1, and the importance of these factors and cis-acting elements in regulation of the promoter by GnRH. All four members of the Egr family were found to induce activity of the equine promoter. The region responsible for induction by Egr was localized to the proximal 185 bp of the promoter, which contained two Egr response elements. Coexpression of Egr1 and SF-1 led to a synergistic activation of the equine (e)LHβ promoter. Mutation of any of the Egr or SF-1 response elements attenuated this synergism. Endogenous expression of Egr1 in αT3–1 cells was not detectable under basal conditions, but was rapidly induced after GnRH stimulation. Reexamination of the promoter constructs harboring mutant Egr or SF-1 sites indicated that these sites were required for GnRH induction. In fact, mutation of both Egr sites within the eLHβ promoter completely attenuated its induction by GnRH. Thus, GnRH induces expression of Egr1, which subsequently activates the eLHβ promoter. Finally, GnRH not only induced expression of Egr1, but also its corepressor, NGFI-A (Egr1) binding protein (Nab1), which can repress Egr1- induced transcription of the eLHβ promoter.

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