title: Synergistic effect of dexamethasone and beta-adrenergic receptor agonists on the nerve growth factor gene transcription.
abstract: Activation of beta-adrenergic receptor (betaAR) increases the synthesis of nerve growth factor (NGF) in the brain and in C6-2B glioma cells. However, in the brain, the betaAR-mediated increase in NGF expression appears to require the presence of glucocorticoids, suggesting that NGF promoter may be sensitive to cAMP and glucocorticoid-dependent transcription factors. We tested this hypothesis by exposing C6-2B glioma cells to dexamethasone (DEX) in combination with agents that increase cAMP levels and examining the DNA binding activity of two cAMP-dependent transcription factors that regulate NGF expression: cAMP responsive element binding protein (CREB) and CCAAT/enhancer binding protein delta (C/EBPdelta). Electrophoretic mobility shift assays revealed that the beta(2)AR agonist clenbuterol (CLE) or high levels of cAMP elicited a time-dependent increase in C/EBPdelta binding activity as well as phosphorylated CREB (P-CREB). When DEX, which per se showed little effect on these transcription factors, was combined with CLE, dibutyryl cAMP or isoproterenol, enhanced induction of P-CREB and C/EBP binding activity as well as NGF mRNA was observed. Moreover, the increase in NGF mRNA in the presence of DEX was prolonged compared to that obtained by CLE or other cAMP inducing agents alone. In fact, NGF mRNA levels remained significantly elevated at least for 24 h. These studies suggest that the synergistic effect of DEX on the induction of NGF mRNA may include the ability of this glucocorticoid to potentiate the betaAR-mediated induction of transcription factors.
authors.affiliation: Georgetown University Medical Center, Department of Neuroscience, Research Building, Box 571464, Washington, DC 20057, USA.
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Colangelo
authors.forename: Alessandra
authors.initials: A
authors.lastname: Mallei
authors.forename: Peter F
authors.initials: PF
authors.lastname: Johnson
authors.forename: Italo
authors.initials: I
authors.lastname: Mocchetti
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000254:growth & development / Q000378:metabolism; D051743:CCAAT-Enhancer-Binding Protein-delta; D022762:CCAAT-Enhancer-Binding Proteins / Q000187:drug effects / Q000378:metabolism; D045744:Cell Line, Tumor; D000242:Cyclic AMP / Q000378:metabolism / Q000494:pharmacology; D017362:Cyclic AMP Response Element-Binding Protein / Q000187:drug effects / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology*; D004357:Drug Synergism; D005938:Glucocorticoids / Q000378:metabolism / Q000494:pharmacology; D020932:Nerve Growth Factor / Q000235:genetics*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors; D014157:Transcription Factors / Q000187:drug effects / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics
chemical_list: D000318:Adrenergic beta-Agonists; D022762:CCAAT-Enhancer-Binding Proteins; C497254:Cebpd protein, rat; D017362:Cyclic AMP Response Element-Binding Protein; D005938:Glucocorticoids; D012333:RNA, Messenger; D011943:Receptors, Adrenergic, beta; D014157:Transcription Factors; D051743:CCAAT-Enhancer-Binding Protein-delta; D003907:Dexamethasone; D020932:Nerve Growth Factor; D000242:Cyclic AMP