title: Activation and induction of NUR77/NURR1 in corticotrophs by CRH/cAMP: involvement of calcium, protein kinase A, and MAPK pathways.
abstract: 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.
authors.affiliation: Laboratorio de Fisiología y Biología Molecular, Departamento de Biología, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, 1428 Buenos Aires, Argentina.
authors.forename: Damián
authors.initials: D
authors.lastname: Kovalovsky
authors.forename: Damián
authors.initials: D
authors.lastname: Refojo
authors.forename: Ana Clara
authors.initials: AC
authors.lastname: Liberman
authors.forename: Daniel
authors.initials: D
authors.lastname: Hochbaum
authors.forename: Marcelo Paez
authors.initials: MP
authors.lastname: Pereda
authors.forename: Omar A
authors.initials: OA
authors.lastname: Coso
authors.forename: Günter K
authors.initials: GK
authors.lastname: Stalla
authors.forename: Florian
authors.initials: F
authors.lastname: Holsboer
authors.forename: Eduardo
authors.initials: E
authors.lastname: Arzt
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002478:Cells, Cultured; D003346:Corticotropin-Releasing Hormone / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D051379:Mice; D009154:Mutation; D009543:Nifedipine / Q000494:pharmacology; D057105:Nuclear Receptor Subfamily 4, Group A, Member 1; D057126:Nuclear Receptor Subfamily 4, Group A, Member 2; D010766:Phosphorylation; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism; D011333:Pro-Opiomelanocortin / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D020218:Response Elements; D015398:Signal Transduction; D014157:Transcription Factors / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D050807:ets-Domain Protein Elk-1
chemical_list: D002121:Calcium Channel Blockers; D004268:DNA-Binding Proteins; C494113:Elk1 protein, mouse; C539818:Nr4a1 protein, mouse; C539883:Nr4a2 protein, mouse; D057105:Nuclear Receptor Subfamily 4, Group A, Member 1; D057126:Nuclear Receptor Subfamily 4, Group A, Member 2; D011518:Proto-Oncogene Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D011333:Pro-Opiomelanocortin; D003346:Corticotropin-Releasing Hormone; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D009543:Nifedipine; D002118:Calcium