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. MAPK 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 multiple MAPKs and discrete Ca(2+) signals. To further understand the transcriptional mechanism(s) of MKP-2 induction by GnRH, we studied the activity of a 198-nucleotide MKP-2 proximal promoter region that supports GnRH responsiveness in reporter gene assays. Functional analysis of the MKP-2 promoter confirmed a requirement for the protein kinase C-extracellular signal-regulated kinase (ERK) pathway and VGCC-derived Ca(2+) signals in transcriptional activation 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 action of thapsigargin-sensitive Ca(2+) signals. MGRE (MKP-2 GnRH response element) within the MKP-2 promoter mediated promoter activation through the protein kinase C-ERK pathway. The zinc finger transcription factor Egr-1 was identified 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 enhanced by GnRH treatment. In addition, overexpression of the Egr-interacting protein, NAB1, resulted in increased GnRH-stimulated MKP-2 gene transcription. Consistent with the putative role of Egr-1 in MKP-2 promoter regulation, 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.
Zhang
T
T
Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA.
Wolfe
M W
MW
Roberson
M S
MS
D000818:Animals; D001483:Base Sequence; D020013:Calcium Signaling; D002460:Cell Line; D004247:DNA; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D054637:Dual-Specificity Phosphatases; D051766:Early Growth Response Protein 1; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology*; D017874:Immediate-Early Proteins; D008156:Luciferases / Q000235:genetics; D051379:Mice; D054639:Mitogen-Activated Protein Kinase Phosphatases; D008969:Molecular Sequence Data; D011493:Protein Kinase C / Q000378:metabolism; D054648:Protein Phosphatase 2; D017027:Protein Tyrosine Phosphatases / Q000235:genetics*; D014157:Transcription Factors / Q000737:chemistry / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology*
D004268:DNA-Binding Proteins; D051766:Early Growth Response Protein 1; C486109:Egr1 protein, mouse; C486110:Egr1 protein, rat; D017874:Immediate-Early Proteins; D014157:Transcription Factors; D007987:Gonadotropin-Releasing Hormone; D004247:DNA; D008156:Luciferases; D011493:Protein Kinase C; D054639:Mitogen-Activated Protein Kinase Phosphatases; D054648:Protein Phosphatase 2; C490583:DUSP4 protein, human; D054637:Dual-Specificity Phosphatases; D017027:Protein Tyrosine Phosphatases