title: A myocyte enhancer factor 2D (MEF2D) kinase activated during neuronal apoptosis is a novel target inhibited by lithium.
abstract: Depolarization promotes the survival of cerebellar granule neurons via activation of the transcription factor myocyte enhancer factor 2D (MEF2D). Removal of depolarization induces hyperphosphorylation of MEF2D on serine/threonine residues, resulting in its decreased DNA binding and susceptibility to caspases. The subsequent loss of MEF2-dependent gene transcription contributes to the apoptosis of granule neurons. The kinase(s) that phosphorylates MEF2D during apoptosis is currently unknown. The serine/threonine kinase, glycogen synthase kinase-3 beta (GSK-3 beta), plays a pro-apoptotic role in granule neurons. To investigate a potential role for GSK-3 beta in MEF2D phosphorylation, we examined the effects of lithium, a non-competitive inhibitor of GSK-3 beta, on MEF2D activity in cultured cerebellar granule neurons. Lithium inhibited caspase-3 activation and chromatin condensation in granule neurons induced to undergo apoptosis by removal of depolarizing potassium and serum. Concurrently, lithium suppressed the hyperphosphorylation and caspase-mediated degradation of MEF2D. Moreover, lithium sustained MEF2 DNA binding and transcriptional activity in the absence of depolarization. Lithium also attenuated MEF2D hyperphosphorylation and apoptosis induced by calcineurin inhibition under depolarizing conditions, a GSK-3 beta-independent model of neuronal death. In contrast to lithium, MEF2D hyperphosphorylation was not inhibited by forskolin, insulin-like growth factor-I, or valproate, three mechanistically distinct inhibitors of GSK-3 beta. These results demonstrate that the kinase that phosphorylates and inhibits the pro-survival function of MEF2D in cerebellar granule neurons is a novel lithium target distinct from GSK-3 beta.
authors.affiliation: Department of Pharmacology, University of Colorado Health Sciences Center and the Denver Veterans Affairs Medical Center, Denver, Colorado 80262, USA.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Linseman
authors.forename: Brandon J
authors.initials: BJ
authors.lastname: Cornejo
authors.forename: Shoshona S
authors.initials: SS
authors.lastname: Le
authors.forename: Mary Kay
authors.initials: MK
authors.lastname: Meintzer
authors.forename: Tracey A
authors.initials: TA
authors.lastname: Laessig
authors.forename: Ron J
authors.initials: RJ
authors.lastname: Bouchard
authors.forename: Kim A
authors.initials: KA
authors.lastname: Heidenreich
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001798:Blood Proteins / Q000494:pharmacology; D065095:Calcineurin Inhibitors; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors; D000071679:Glycogen Synthase Kinase 3 beta; D008094:Lithium / Q000494:pharmacology*; D064326:MEF2 Transcription Factors; D018006:Myogenic Regulatory Factors; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D010770:Phosphotransferases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D001798:Blood Proteins; D065095:Calcineurin Inhibitors; D061945:Caspase Inhibitors; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D064326:MEF2 Transcription Factors; D018006:Myogenic Regulatory Factors; D014157:Transcription Factors; D005576:Colforsin; D004247:DNA; D008094:Lithium; D010770:Phosphotransferases; D000071679:Glycogen Synthase Kinase 3 beta; D038362:Glycogen Synthase Kinase 3; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases; D011188:Potassium