title: Ca(2+)-dependent regulation of TrkB expression in neurons.
abstract: The neurotrophin brain-derived neurotrophic factor (BDNF), via activation of its receptor, tyrosine receptor kinase B (trkB), regulates a wide variety of cellular processes in the nervous system, including neuron survival and synaptic plasticity. Although the expression of BDNF is known to be Ca2+-dependent, the regulation of trkB expression has not been extensively studied. Here we report that depolarization of cultured mouse cortical neurons increased the expression of the full-length, catalytically active isoform of trkB without affecting expression of the truncated isoform. This increase in protein expression was accompanied by increased levels of transcripts encoding full-length, but not truncated, trkB. Depolarization also regulated transcription of the gene, TRKB, via entry of Ca2+ through voltage-gated Ca2+ channels and subsequent activation of Ca2+-responsive elements in the two TRKB promoters. Using transient transfection of neurons with TRKB promoter-luciferase constructs, we found that Ca2+ inhibited the upstream promoter P1 but activated the downstream promoter P2. Ca2+-dependent stimulation of TRKB expression requires two adjacent, non-identical CRE sites located within P2. The coordinated regulation of BDNF and trkB by Ca2+ may play a role in activity-dependent survival and synaptic plasticity by enhancing BDNF signaling in electrically active neurons.
authors.affiliation: Departments of Physiology and Anesthesiology, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA. tking001@umaryland.edu
authors.forename: Tami J
authors.initials: TJ
authors.lastname: Kingsbury
authors.forename: Peter D
authors.initials: PD
authors.lastname: Murray
authors.forename: Linda L
authors.initials: LL
authors.lastname: Bambrick
authors.forename: Bruce K
authors.initials: BK
authors.lastname: Krueger
mesh_terms: D000818:Animals; D001665:Binding Sites; D019208:Brain-Derived Neurotrophic Factor / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D015536:Down-Regulation; D005786:Gene Expression Regulation; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009474:Neurons / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D020813:Receptor, trkB / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection
chemical_list: D019208:Brain-Derived Neurotrophic Factor; D012333:RNA, Messenger; D000242:Cyclic AMP; D008156:Luciferases; D020813:Receptor, trkB; D002118:Calcium