title: Characterization of a MAPK scaffolding protein logic gate in gonadotropes.
abstract: In the pituitary gonadotropes, both protein kinase C (PKC) and MAPK/ERK signaling cascades are activated by GnRH. Phosphoprotein-enriched in astrocytes 15 (PEA-15) is a cytosolic ERK scaffolding protein, which is expressed in LβT2 gonadotrope cells. Pharmacological inhibition of PKC and small interfering RNA-mediated silencing of Gαq/11 revealed that GnRH induces accumulation of phosphorylated PEA-15 in a PKC-dependent manner. To investigate the potential role of PEA-15 in GnRH signaling, we examined the regulation of ERK subcellular localization and the activation of ribosomal S6 kinase, a substrate of ERK. Results obtained by cellular fractionation/Western blot analysis and immunohistochemistry revealed that GnRH-induced accumulation of phosphorylated ERK in the nucleus was attenuated when PEA-15 expression was reduced. Conversely, in the absence of GnRH stimulation, PEA-15 anchors ERK in the cytosol. Our data suggest that GnRH-induced nuclear translocation of ERK requires its release from PEA-15, which occurs upon PEA-15 phosphorylation by PKC. Additional gene-silencing experiments in GnRH-stimulated cells demonstrated that ribosomal S6 kinase activation was dependent on both PEA-15 and PKC. Furthermore, small interfering RNA-mediated knockdown of PEA-15 caused a reduction in GnRH-stimulated expression of early response genes Egr2 and c-Jun, as well as gonadotropin FSHβ-subunit gene expression. PEA-15 knockdown increased LHβ and common α-glycoprotein subunit mRNAs, suggesting a possible role in differential regulation of gonadotropin subunit gene expression. We propose that PEA-15 represents a novel point of convergence of the PKC and MAPK/ERK pathways under GnRH stimulation. PKC, ERK, and PEA-15 form an AND logic gate that shapes the response of the gonadotrope cell to GnRH.
authors: Center for Translational Systems Biology and Department of Neurology, Mount Sinai School of Medicine, Annenberg 14-94, Box 1137, One Gustave L. Levy Place, New York, New York 10029, USA.
authors: Soon Gang
authors: SG
authors: Choi
authors: Frederique
authors: F
authors: Ruf-Zamojski
authors: Hanna
authors: H
authors: Pincas
authors: Badrinath
authors: B
authors: Roysam
authors: Stuart C
authors: SC
authors: Sealfon
mesh_terms: D000818:Animals; D051017:Apoptosis Regulatory Proteins; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D044385:GTP-Binding Protein alpha Subunits / Q000235:genetics / Q000378:metabolism; D052681:Gonadotrophs / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D006062:Gonadotropins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D034622:RNA Interference; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D051017:Apoptosis Regulatory Proteins; D044385:GTP-Binding Protein alpha Subunits; D006062:Gonadotropins; C490444:Pea15 protein, mouse; D010750:Phosphoproteins; D007987:Gonadotropin-Releasing Hormone; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C069330:ribosomal protein S6 kinase, 90kDa, polypeptide 3; D011493:Protein Kinase C; D048049:Extracellular Signal-Regulated MAP Kinases