title: Insulin-like growth factor-I blocks Bcl-2 interacting mediator of cell death (Bim) induction and intrinsic death signaling in cerebellar granule neurons.
abstract: Cerebellar granule neurons depend on insulin-like growth factor-I (IGF-I) for their survival. However, the mechanism underlying the neuroprotective effects of IGF-I is presently unclear. Here we show that IGF-I protects granule neurons by suppressing key elements of the intrinsic (mitochondrial) death pathway. IGF-I blocked activation of the executioner caspase-3 and the intrinsic initiator caspase-9 in primary cerebellar granule neurons deprived of serum and depolarizing potassium. IGF-I inhibited cytochrome c release from mitochondria and prevented its redistribution to neuronal processes. The effects of IGF-I on cytochrome c release were not mediated by blockade of the mitochondrial permeability transition pore, because IGF-I failed to inhibit mitochondrial swelling or depolarization. In contrast, IGF-I blocked induction of the BH3-only Bcl-2 family member, Bim (Bcl-2 interacting mediator of cell death), a mediator of Bax-dependent cytochrome c release. The suppression of Bim expression by IGF-I did not involve inhibition of the c-Jun transcription factor. Instead, IGF-I prevented activation of the forkhead family member, FKHRL1, another transcriptional regulator of Bim. Finally, adenoviral-mediated expression of dominant-negative AKT activated FKHRL1 and induced expression of Bim. These data suggest that IGF-I signaling via AKT promotes survival of cerebellar granule neurons by blocking the FKHRL1-dependent transcription of Bim, a principal effector of the intrinsic death-signaling cascade.
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: Reid A
authors.initials: RA
authors.lastname: Phelps
authors.forename: Ron J
authors.initials: RJ
authors.lastname: Bouchard
authors.forename: Shoshona S
authors.initials: SS
authors.lastname: Le
authors.forename: Tracey A
authors.initials: TA
authors.lastname: Laessig
authors.forename: Maria L
authors.initials: ML
authors.lastname: McClure
authors.forename: Kim A
authors.initials: KA
authors.lastname: Heidenreich
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; D002352:Carrier Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology; D003574:Cytochrome c Group / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D005799:Genes, Dominant; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology* / Q000502:physiology; D048031:JNK Mitogen-Activated Protein Kinases; D008565:Membrane Proteins; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009419:Nerve Tissue Proteins; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection
chemical_list: D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; C000606778:Bcl2l11 protein, rat; D002352:Carrier Proteins; D003574:Cytochrome c Group; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; C085126:FOXO1 protein, human; C499517:FOXO3 protein, human; C499515:FOXO3 protein, rat; D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; C074639:Foxo1 protein, rat; D007334:Insulin-Like Growth Factor I; C494918:AKT1 protein, human; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; C505407:CASP3 protein, human; C506433:CASP9 protein, human; C505410:Casp3 protein, rat; C506435:Casp9 protein, rat; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases