A role for mitogen-activated protein kinase in mediating activation of the glycoprotein hormone alpha-subunit promoter by gonadotropin-releasing hormone.
Gonadotropin-releasing hormone (GnRH) interacts with a G protein-coupled receptor and increases the transcription of the glycoprotein hormone alpha-subunit gene. We have explored the possibility that mitogen-activated protein kinase (MAPK) plays a role in mediating GnRH effects on transcription. Activation of the MAPK cascade by an expression vector for a constitutively active form of the Raf-1 kinase led to stimulation of the alpha-subunit promoter in a concentration-dependent manner. GnRH treatment was found to increase the phosphorylation of tyrosine residues of MAPK and to increase MAPK activity, as determined by an immune complex kinase assay. A reporter gene assay using the MAPK-responsive, carboxy-terminal domain of the Elk1 transcription factor was also consistent with GnRH-induced activation of MAPK. Interference with the MAPK pathway by expression vectors for kinase-defective MAPKs or vectors encoding MAPK phosphatases reduced the transcription-stimulating effects of GnRH. The DNA sequences which are required for responses to GnRH include an Ets factor-binding site. An expression vector for a dominant negative form of Ets-2 was able to reduce GnRH effects on expression of the alpha-subunit gene. These findings provide evidence that GnRH treatment leads to activation of the MAPK cascade in gonadotropes and that activation of MAPK contributes to stimulation of the alpha-subunit promoter. It is likely that an Ets factor serves as a downstream transcriptional effector of MAPK in this system.
Roberson
M S
MS
Department of Cell Biology and Anatomy, Oregon Health Sciences University, Portland 97201, USA.
Misra-Press
A
A
Laurance
M E
ME
Stork
P J
PJ
Maurer
R A
RA
D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002460:Cell Line; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D006065:Gonadotropins, Pituitary / Q000096:biosynthesis* / Q000235:genetics; D017874:Immediate-Early Proteins / Q000096:biosynthesis; D051379:Mice; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D017027:Protein Tyrosine Phosphatases / Q000096:biosynthesis; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf; D015682:Retroviridae Proteins, Oncogenic / Q000378:metabolism; D015398:Signal Transduction; D014158:Transcription, Genetic; D014162:Transfection
D006065:Gonadotropins, Pituitary; D017874:Immediate-Early Proteins; D011518:Proto-Oncogene Proteins; D015682:Retroviridae Proteins, Oncogenic; C050379:oncogene proteins v-ets; D007987:Gonadotropin-Releasing Hormone; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D017027:Protein Tyrosine Phosphatases