An early growth response protein (Egr) 1 cis-element is required for gonadotropin-releasing hormone-induced mitogen-activated protein kinase phosphatase 2 gene expression

In pituitary gonadotropes, gonadotropin-releasing hormone (GnRH) activates all three major mitogen-activated protein kinase (MAPK) cascades. The MAPKs play key roles in transcriptional activation of GnRH-responsive genes. MAP K phosphatases (MKPs) are dual specificity protein phosphatases involved in feedback regulation of MAPK activity. Previous studies indicate that GnRH activates MKP-2 expression in gonadotropes, dependent upon activation of mu ltiple MAPKs and discrete Ca2+ signals. To further understand the transcrip tional mechanism(s) of MKP-2 induction by GnRH, we studied the activity of a 198-nucleotide MKP-2 proximal promoter region that supports GnRH responsi veness in reporter gene assays. Functional analysis of the MKP-2 promoter c onfirmed a requirement for the protein kinase C-extracellular signal-regula ted kinase (ERK) pathway and VGCC-derived Ca2+ signals in transcriptional a ctivation of the MKP-2 gene. However, the inhibitory effect of thapsigargin on MKP-2 protein expression previously identified was not mediated at the level of promoter activation, suggesting a distinct mechanism for the actio n of thapsigargin-sensitive Ca2+ signals. MGRE (MKP-2 GnRH response element ) within the MKP-2 promoter mediated promoter activation through the protei n kinase C-ERK pathway. The zinc finger transcription factor Egr-1 was iden tified in the MGRE-binding complex. Egr-1/MGRE binding was induced by GnRH in an ERK-dependent manner. Transcriptional activity of Egr-1 protein was e nhanced by GnRH treatment. In addition, overexpression of the Egr-interacti ng protein, NAB1, resulted in increased GnRH-stimulated MKP-2 gene transcri ption. Consistent with the putative role of Egr-1 in MKP-2 promoter regulat ion, Egr-1 protein expression closely correlated with the expression of MKP -2 protein in alpha T3-1 cells. Together, these data suggest that Egr-1 may be a key factor in mediating GnRH-dependent transcriptional activation of the MKP-2 gene.