Reference : Inhibition of protein phosphatase PP1 in GH3B6, but not in GH3 cells, activates the M...
Scientific journals : Article
Life sciences : Biochemistry, biophysics & molecular biology
Inhibition of protein phosphatase PP1 in GH3B6, but not in GH3 cells, activates the MEK/ERK/c-fos pathway and the human prolactin promoter, involving the coactivator CPB/p300
Manfroid, Isabelle mailto [Université de Liège - ULg > > GIGA-Research >]
Martial, Joseph mailto [Université de Liège - ULg > Département des sciences de la vie > GIGA-R : Biologie et génétique moléculaire >]
Muller, Marc mailto [Université de Liège - ULg > Département des sciences de la vie > GIGA-R : Biologie et génétique moléculaire >]
Molecular Endocrinology (Baltimore, Md.)
Endocrine Society
Yes (verified by ORBi)
Chevy Chase
[en] Animals ; DNA-Binding Proteins/genetics/metabolism ; E1A-Associated p300 Protein ; Enzyme Inhibitors/pharmacology ; Flavonoids/pharmacology ; Humans ; Isoenzymes ; *MAP Kinase Kinase Kinase 1 ; Mitogen-Activated Protein Kinases/antagonists & inhibitors/*metabolism ; Nuclear Proteins/*metabolism ; Okadaic Acid/pharmacology ; Phosphoprotein Phosphatases/*antagonists & inhibitors/genetics/metabolism ; Pituitary Neoplasms ; Prolactin/*genetics/metabolism ; Promoter Regions, Genetic ; Protein-Serine-Threonine Kinases/metabolism ; Proto-Oncogene Proteins c-fos/drug effects/*genetics/metabolism ; Rats ; Signal Transduction ; Trans-Activators/*metabolism ; Transcription Factor AP-1/genetics/metabolism ; Transcription Factor Pit-1 ; Transcription Factors/genetics/metabolism ; Transcriptional Activation ; Tumor Cells, Cultured ; ras Proteins/drug effects/genetics/metabolism
[en] The human (hPRL) PRL gene proximal promoter (-164/+15) is the target for numerous signal transduction pathways involving protein kinases. The inhibitor of Ser/Thr-protein phosphatases okadaic acid (OA) was shown to induce this promoter in rat pituitary GH3B6 through a synergism between increased amounts of the ubiquitous factor AP-1 and the pituitary-specific factor Pit-1. Here we show that this activation results mainly from transcriptional stimulation of the c-fos promoter leading to increased AP-1 activity. We report the surprising absence of the hPRL and c-fos promoter stimulation by OA in GH3 cells, closely related to GH3B6 cells, and we use this discrepancy to dissect the precise mechanism of action. c-fos gene activation involves the mitogen-activated kinase (MAPK)-ternary complex factor (TCF) pathway and can be obtained by expressing active V12ras in both cell lines. We show that OA acts by inhibiting protein phosphatase PP1, thereby protecting MAPK kinase (MEK)1/2 and/or a MEK1/2-kinase from dephosphorylation. PP1 inhibition of MEK activation by V12ras does not occur in GH3 cells, indicating that a distinct, PP1-sensitive phosphorylation site is used in GH3B6 cells to activate the TCF pathway in GH3B6 cells. Finally, we show that the synergistic OA activation of the hPRL promoter by Pit-1 and AP-1 is independent of the Pit-1 transactivation domain and is mediated by the general coactivator (CRE-binding protein)-binding protein (CBP)/p300.

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