title: Neuronal apoptosis induced by selective inhibition of Rac GTPase versus global suppression of Rho family GTPases is mediated by alterations in distinct mitogen-activated protein kinase signaling cascades.
abstract: Rho family GTPases play integral roles in neuronal differentiation and survival. We have shown previously that Clostridium difficile toxin B (ToxB), an inhibitor of RhoA, Rac1, and Cdc42, induces apoptosis of cerebellar granule neurons (CGNs). In this study, we compared the effects of ToxB to a selective inhibitor of the Rac-specific guanine nucleotide exchange factors Tiam1 and Trio (NSC23766). In a manner similar to ToxB, selective inhibition of Rac induces CGN apoptosis associated with enhanced caspase-3 activation and reduced phosphorylation of the Rac effector p21-activated kinase. In contrast to ToxB, caspase inhibitors do not protect CGNs from targeted inhibition of Rac. Also dissimilar to ToxB, selective inhibition of Rac does not inhibit MEK1/2/ERK1/2 or activate JNK/c-Jun. Instead, targeted inhibition of Rac suppresses distinct MEK5/ERK5, p90Rsk, and Akt-dependent signaling cascades known to regulate the localization and expression of the Bcl-2 homology 3 domain-only protein Bad. Adenoviral expression of a constitutively active mutant of MEK5 is sufficient to attenuate neuronal cell death induced by selective inhibition of Rac with NSC23766 but not apoptosis induced by global inhibition of Rho GTPases with ToxB. Collectively, these data demonstrate that global suppression of Rho family GTPases with ToxB causes a loss of MEK1/2/ERK1/2 signaling and activation of JNK/c-Jun, resulting in diminished degradation and enhanced transcription of the Bcl-2 homology 3 domain-only protein Bim. In contrast, selective inhibition of Rac induces CGN apoptosis by repressing unique MEK5/ERK5, p90Rsk, and Akt-dependent prosurvival pathways, ultimately leading to enhanced expression, dephosphorylation, and mitochondrial localization of proapoptotic Bad.
authors: From the Research Service, Veterans Affairs Medical Center, Denver, Colorado 80220, the Department of Biological Sciences and Eleanor Roosevelt Institute, University of Denver, Denver, Colorado 80208.
authors: Trisha R
authors: TR
authors: Stankiewicz
authors: the Department of Biological Sciences and Eleanor Roosevelt Institute, University of Denver, Denver, Colorado 80208.
authors: Sai Anandi
authors: SA
authors: Ramaswami
authors: From the Research Service, Veterans Affairs Medical Center, Denver, Colorado 80220.
authors: Ron J
authors: RJ
authors: Bouchard
authors: the Institute for Experimental and Clinical Pharmacology and Toxicology, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany, and.
authors: Klaus
authors: K
authors: Aktories
authors: From the Research Service, Veterans Affairs Medical Center, Denver, Colorado 80220, the Department of Biological Sciences and Eleanor Roosevelt Institute, University of Denver, Denver, Colorado 80208, the Division of Clinical Pharmacology and Toxicology, Department of Medicine and Neuroscience Program, University of Colorado Denver, Aurora, Colorado 80045 dan.linseman@ucdenver.edu.
authors: Daniel A
authors: DA
authors: Linseman
mesh_terms: D000634:Aminoquinolines / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001426:Bacterial Proteins / Q000494:pharmacology; D001427:Bacterial Toxins / Q000494:pharmacology; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology; D005260:Female; D015151:Immunoblotting; D048671:MAP Kinase Kinase 5 / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008856:Microscopy, Fluorescence; D048054:Mitogen-Activated Protein Kinase 7 / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011743:Pyrimidines / Q000494:pharmacology; D017207:Rats, Sprague-Dawley; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D051025:bcl-Associated Death Protein / Q000378:metabolism; D020744:rac GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020741:rho GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D000634:Aminoquinolines; D001426:Bacterial Proteins; D001427:Bacterial Toxins; C494821:Bad protein, rat; C487513:NSC 23766; D011743:Pyrimidines; D051025:bcl-Associated Death Protein; C031815:toxB protein, Clostridium difficile; D051057:Proto-Oncogene Proteins c-akt; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D048054:Mitogen-Activated Protein Kinase 7; D048671:MAP Kinase Kinase 5; C482565:Map2k5 protein, rat; D020744:rac GTP-Binding Proteins; D020741:rho GTP-Binding Proteins
keywords: Apoptosis; B Cell Lymphoma 2 (Bcl-2); Bad; ERK; MEK; NSC23766; Neurodegeneration; Rac (Rac GTPase)