Activation and induction of Nur77/Nurr1 in corticotrophs by CRH/cAMP: Involvement of calcium, protein kinase a, and MAPK pathways

• Autores: Kovalovsky, D.; Refojo, D.; Liberman, A.C.; Hochbaum, D.; Pereda, M.P.; Coso, O.A.; Stalla, G.K.; Holsboer, F.; Arzt, E.
• Año de publicación: 2002
• Idioma: inglés
• Tipo de recurso: artículo
• Fuente: Mol. Endocrinol. 2002;16(7):1638-1651
• Materia: corticosteroid receptor; cyclic AMP dependent protein kinase; mitogen activated protein kinase; proopiomelanocortin; protein kinase (calcium,calmodulin); calcium; calcium channel blocking agent; cell receptor; corticotropin releasing factor; cyclic AMP; DNA binding protein; Elk1 protein, mouse; nifedipine; nuclear receptor Nur77; Nurr1 nuclear receptor; oncoprotein; steroid receptor; transcription factor; transcription factor Elk 1; animal cell; article; cell type; corticotropin release; enzyme activation; enzyme induction; gene overexpression; hypothalamus hypophysis adrenal system; nonhuman; point mutation; priority journal; protein phosphorylation; stimulus response; stress; transcription regulation; animal; cell culture; cytology; DNA responsive element; drug effect; genetic transcription; genetics; hypophysis; metabolism; mouse; mutation; phosphorylation; promoter region; signal transduction; Animalia; Animals; Calcium; Calcium Channel Blockers; Cells, Cultured; Corticotropin-Releasing Hormone; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; DNA-Binding Proteins; ets-Domain Protein Elk-1; MAP Kinase Signaling System; Mice; Mutation; Nifedipine; Phosphorylation; Pituitary Gland; Pro-Opiomelanocortin; Promoter Regions (Genetics); Proto-Oncogene Proteins; Receptors, Cytoplasmic and Nuclear; Receptors, Steroid; Response Elements; Signal Transduction; Transcription Factors; Transcription, Genetic
• Institución: Universidad Nacional de Buenos Aires. Facultad de Ciencias Exactas y Naturales

Nur factors are critical for proopiomelanocortin (POMC) induction by CRH in corticotrophs, but the pathways linking CRH to Nur are unknown. In this study we show that in AtT-20 corticotrophs CRH and cAMP induce Nur77 and Nurr1 expression and transcription at the NurRE site by protein kinase A (PKA) and calcium-dependent and -independent mechanisms. Calcium pathways depend on calmodulin kinase II (CAMKII) activity, and calcium-independent pathways are accounted for in part by MAPK activation (Rap1/B-Raf/MAPK-ERK kinase/ERK1/2), demonstrated by the use of molecular and pharmacological tools. ATT-20 corticotrophs express B-Raf, as do other cells in which cAMP stimulates MAPK. CRH/cAMP stimulated ERK2 activity and increased transcriptional activity of a Gal4-Elk1 protein, which was blocked by overexpression of dominant negative mutants and kinase inhibitors and stimulated by expression of B-Raf. The MAPK kinase inhibitors did not affect Nur77 and Nurr1 mRNA induction but blocked CRH or cAMP-stimulated Nur transcriptional activity. Moreover, MAPK stimulated phosphorylation and transactivation of Nur77. The functional impact of these pathways was confirmed at the POMC promoter. In conclusion, in AtT-20 corticotrophs the CRH/cAMP signaling that leads to Nur77/Nurr1 mRNA induction and transcriptional activation, and thus POMC expression, is dependent on protein kinase A and involves calcium/calmodulin kinase II (Nur induction/activation) and MAPK calcium-dependent and -independent (Nur phosphorylation-activation) pathways.