title: Regulation of somatostatin gene expression by brain derived neurotrophic factor in fetal rat cerebrocortical cells.
abstract: Brain derived neurotrophic factor (BDNF) increases the levels of somatostatin (SS) and its mRNA. To test the hypothesis that the regulation of SS synthesis by BDNF occurs at the transcriptional level and requires specific promoter sequences, cerebrocortical and PC12trkB neurons were transiently transfected with different constructs of the SS promoter fused to the luciferase and CAT reporter genes. We demonstrated that BDNF triggered the transcription of the SS gene through the CRE sequence located in the SS promoter. BDNF and SS are genes regulated by K(+)-induced neuronal activity. Using BDNF blocking antibodies, we investigated whether K(+)-induced BDNF was required for K(+)-dependent SS mRNA induction. We found that K(+)-induced SS mRNA was partially prevented when BDNF was blocked. This finding indicated that BDNF mediated the induction of SS mRNA by K(+) depolarization. To identify the mechanisms by which BDNF activates SS gene transcription we first elucidated the signaling pathways activated by BDNF in cerebrocortical cells. We confirmed that BDNF activates the MAPK/ERKs and PI3K/Akt pathways. Both signaling pathways are, in turn, implicated in the activation of CREB by BDNF. In addition we observed that the PKA inhibitors, H89 and Rp-cAMPS decreased BDNF-induced CREB activation. These findings suggested that BDNF-induced CREB activation was also mediated by the cAMP/PKA pathway. We next elucidated the mechanism by which BDNF induces SS mRNA. We observed that H89, PD0998059, KN62 and LY294002 diminished BDNF-induced SS mRNA suggesting that BDNF-induced SS mRNA is mediated by the activation of cAMP/PKA, MAPK/ERKs, CaMK and PI3K pathways.
authors.affiliation: Endocrinology Service, Hospital Ramón y Cajal, Madrid, Spain.
authors.forename: Isabel
authors.initials: I
authors.lastname: Sánchez-Muñoz
authors.forename: Franco
authors.initials: F
authors.lastname: Sánchez-Franco
authors.forename: Mario
authors.initials: M
authors.lastname: Vallejo
authors.forename: Antonio
authors.initials: A
authors.lastname: Fernández
authors.forename: Nuria
authors.initials: N
authors.lastname: Palacios
authors.forename: Miriam
authors.initials: M
authors.lastname: Fernández
authors.forename: María
authors.initials: M
authors.lastname: Sánchez-Grande
authors.forename: Lucinda
authors.initials: L
authors.lastname: Cacicedo
mesh_terms: D000818:Animals; D015153:Blotting, Western; D019208:Brain-Derived Neurotrophic Factor / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004558:Electric Stimulation; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D007074:Immunoglobulin G / Q000302:isolation & purification; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011188:Potassium / Q000494:pharmacology; D011247:Pregnancy; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D050436:Regulatory Elements, Transcriptional; D015398:Signal Transduction / Q000187:drug effects; D013004:Somatostatin / Q000096:biosynthesis* / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
chemical_list: D019208:Brain-Derived Neurotrophic Factor; D017362:Cyclic AMP Response Element-Binding Protein; D004791:Enzyme Inhibitors; D007074:Immunoglobulin G; D000081082:Phosphoinositide-3 Kinase Inhibitors; D012333:RNA, Messenger; D013004:Somatostatin; D017868:Cyclic AMP-Dependent Protein Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D020928:Mitogen-Activated Protein Kinases; D011188:Potassium