title: Neurotrophins elevate cAMP to reach a threshold required to overcome inhibition by MAG through extracellular signal-regulated kinase-dependent inhibition of phosphodiesterase.
abstract: Inhibitors of regeneration in myelin, such as myelin-associated glycoprotein (MAG), play an important role in preventing regeneration after CNS injury. Elevation of cAMP, either with dibutyryl-cAMP (db-cAMP) or by priming with a variety of neurotrophins, overcomes inhibition by MAG and myelin. However, activation of cAMP is not generally regarded as a signaling pathway for neurotrophins. Here we show that the NGF-like neurotrophins overcome inhibition by MAG by activating tyrosine kinase receptors. We also show that activation of extracellular signal-regulated kinase (Erk) by BDNF is required to overcome inhibition by MAG, and that activated Erk transiently inhibits phosphodiesterase 4 (PDE4), the enzyme that hydrolyzes cAMP. Inhibition of PDE4 then allows cAMP to increase and so initiates the pathway to overcome inhibition. Furthermore, we also show that basal levels of Erk activation and basal cAMP levels contribute to the effects of db-cAMP by pushing the combined levels of cAMP above a threshold required to overcome inhibition. Together, these results not only show how NGF-like neurotrophins can elevate cAMP and overcome inhibition but also point to a novel mechanism of cross talk in neurons from the Erk to the cAMP signaling pathways.
authors.affiliation: Department of Biological Sciences, Hunter College, City University of New York, New York, New York 10021, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Gao
authors.forename: Elena
authors.initials: E
authors.lastname: Nikulina
authors.forename: Wilfredo
authors.initials: W
authors.lastname: Mellado
authors.forename: Marie T
authors.initials: MT
authors.lastname: Filbin
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000037:antagonists & inhibitors*; D000818:Animals; D019208:Brain-Derived Neurotrophic Factor / Q000037:antagonists & inhibitors / Q000494:pharmacology; D003994:Bucladesine / Q000037:antagonists & inhibitors; D016466:CHO Cells; D002478:Cells, Cultured; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism*; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; D004791:Enzyme Inhibitors / Q000494:pharmacology; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D018992:Myelin-Associated Glycoprotein / Q000037:antagonists & inhibitors*; D020932:Nerve Growth Factor / Q000494:pharmacology; D009414:Nerve Growth Factors / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D017475:Receptors, Nerve Growth Factor / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D019208:Brain-Derived Neurotrophic Factor; D004791:Enzyme Inhibitors; D018992:Myelin-Associated Glycoprotein; D009414:Nerve Growth Factors; D010726:Phosphodiesterase Inhibitors; D017475:Receptors, Nerve Growth Factor; D003994:Bucladesine; D020932:Nerve Growth Factor; D000242:Cyclic AMP; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4