Abstract
Pulsatile secretion of GnRH is the major regulator of gonadotropin (LH, FSH) gene expression and secretion. Recently, GnRH has been shown to rapidly stimulate the expression of early growth response protein-1 (Egr-1), a transcription factor that is essential for LHbeta gene expression in the pituitary. In this study, we examined the regulatory elements and signal transduction pathways by which GnRH regulates Egr-1 transcription. Deletion analysis of the murine Egr-1 promoter identified two regions (-370 to -342 and -116 to -73) that are critical for GnRH responsiveness in alphaT3 pituitary gonadotrope cells. The first region, which contains two serum response elements (SREs), contributed about 70-80% of GnRH inducibility, whereas the second region, which contains two SREs and one Ets binding site, conferred an additional 20-30% of activity. Mutations that abolish protein binding to these SREs and Ets binding sites completely eliminated GnRH-mediated transcriptional activation of the Egr-1 promoter. Mutation of cAMP response element reduced promoter activity by 40%. Using specific protein kinase inhibitors, GnRH stimulation of Egr-1 expression was found to be dependent on PKC/ERK pathways. In addition, GnRH activated p90 ribosomal S6 kinase, which has the potential to phosphorylate serum response factor and cAMP response element binding protein. We conclude that GnRH stimulation of Egr-1 gene expression requires several distinct SREs/Ets elements and a cAMP response element and is mediated via activation of PKC/ERK signaling pathways.
Publication types
-
Research Support, U.S. Gov't, P.H.S.
MeSH terms
-
Animals
-
Binding Sites
-
Blotting, Western
-
Cells, Cultured
-
Cyclic AMP Response Element-Binding Protein / metabolism
-
DNA-Binding Proteins / genetics*
-
Early Growth Response Protein 1
-
Electrophoretic Mobility Shift Assay
-
Enzyme Activation / drug effects
-
Gene Expression Regulation / drug effects*
-
Gonadotropin-Releasing Hormone / pharmacology*
-
Immediate-Early Proteins*
-
Indoles / pharmacology
-
Maleimides / pharmacology
-
Mice
-
Mitogen-Activated Protein Kinases / metabolism
-
Phosphorylation / drug effects
-
Pituitary Gland / cytology
-
Pituitary Gland / drug effects
-
Pituitary Gland / enzymology
-
Pituitary Gland / metabolism
-
Promoter Regions, Genetic / genetics*
-
Protein Kinase C / antagonists & inhibitors
-
Protein Kinase C / metabolism
-
Proto-Oncogene Proteins / metabolism
-
Proto-Oncogene Proteins c-ets
-
Ribosomal Protein S6 Kinases / metabolism
-
Sequence Deletion / genetics
-
Serum Response Element / genetics
-
Serum Response Factor / metabolism
-
Signal Transduction / drug effects*
-
Transcription Factors / genetics*
-
Transcription Factors / metabolism
-
Transcription, Genetic / drug effects*
-
Transcription, Genetic / genetics
-
ets-Domain Protein Elk-1
Substances
-
Cyclic AMP Response Element-Binding Protein
-
DNA-Binding Proteins
-
Early Growth Response Protein 1
-
Egr1 protein, mouse
-
Immediate-Early Proteins
-
Indoles
-
Maleimides
-
Proto-Oncogene Proteins
-
Proto-Oncogene Proteins c-ets
-
Serum Response Factor
-
Transcription Factors
-
ets-Domain Protein Elk-1
-
Gonadotropin-Releasing Hormone
-
Ribosomal Protein S6 Kinases
-
Protein Kinase C
-
Mitogen-Activated Protein Kinases
-
bisindolylmaleimide I