title: An essential role for Rac/Cdc42 GTPases in cerebellar granule neuron survival.
abstract: Rho family GTPases are critical molecular switches that regulate the actin cytoskeleton and cell function. In the current study, we investigated the involvement of Rho GTPases in regulating neuronal survival using primary cerebellar granule neurons. Clostridium difficile toxin B, a specific inhibitor of Rho, Rac, and Cdc42, induced apoptosis of granule neurons characterized by c-Jun phosphorylation, caspase-3 activation, and nuclear condensation. Serum and depolarization-dependent survival signals could not compensate for the loss of GTPase function. Unlike trophic factor withdrawal, toxin B did not affect the antiapoptotic kinase Akt or its target glycogen synthase kinase-3beta. The proapoptotic effects of toxin B were mimicked by Clostridium sordellii lethal toxin, a selective inhibitor of Rac/Cdc42. Although Rac/Cdc42 GTPase inhibition led to F-actin disruption, direct cytoskeletal disassembly with Clostridium botulinum C2 toxin was insufficient to induce c-Jun phosphorylation or apoptosis. Granule neurons expressed high basal JNK and low p38 mitogen-activated protein kinase activities that were unaffected by toxin B. However, pyridyl imidazole inhibitors of JNK/p38 attenuated c-Jun phosphorylation. Moreover, both pyridyl imidazoles and adenoviral dominant-negative c-Jun attenuated apoptosis, suggesting that JNK/c-Jun signaling was required for cell death. The results indicate that Rac/Cdc42 GTPases, in addition to trophic factors, are critical for survival of cerebellar granule neurons.
authors.affiliation: Department of Pharmacology, University of Colorado Health Sciences Center and the Denver Veterans Affairs Medical Center, Denver, Colorado 80220, USA. Dan.Linseman@UCHSC.edu
authors.forename: D A
authors.initials: DA
authors.lastname: Linseman
authors.forename: T
authors.initials: T
authors.lastname: Laessig
authors.forename: M K
authors.initials: MK
authors.lastname: Meintzer
authors.forename: M
authors.initials: M
authors.lastname: McClure
authors.forename: H
authors.initials: H
authors.lastname: Barth
authors.forename: K
authors.initials: K
authors.lastname: Aktories
authors.forename: K A
authors.initials: KA
authors.lastname: Heidenreich
mesh_terms: D000199:Actins / Q000378:metabolism; D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D017209:Apoptosis; D001426:Bacterial Proteins; D001427:Bacterial Toxins / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D002470:Cell Survival; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D003599:Cytoskeleton / Q000378:metabolism; D004789:Enzyme Activation; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D015151:Immunoblotting; D007150:Immunohistochemistry; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D010766:Phosphorylation; D011188:Potassium / Q000494:pharmacology; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction; D014158:Transcription, Genetic; D020764:cdc42 GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D048051:p38 Mitogen-Activated Protein Kinases; D020744:rac GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D020741:rho GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D000199:Actins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D016895:Culture Media, Serum-Free; D011518:Proto-Oncogene Proteins; D016755:Proto-Oncogene Proteins c-jun; C031815:toxB protein, Clostridium difficile; D038341:Glycogen Synthase Kinases; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D038362:Glycogen Synthase Kinase 3; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases; D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins; D020741:rho GTP-Binding Proteins; D011188:Potassium