RT Journal Article
SR Electronic
T1 Insulin-Like Growth Factor-I Blocks Bcl-2 Interacting Mediator of Cell Death (Bim) Induction and Intrinsic Death Signaling in Cerebellar Granule Neurons
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 9287
OP 9297
DO 10.1523/JNEUROSCI.22-21-09287.2002
VO 22
IS 21
A1 Daniel A. Linseman
A1 Reid A. Phelps
A1 Ron J. Bouchard
A1 Shoshona S. Le
A1 Tracey A. Laessig
A1 Maria L. McClure
A1 Kim A. Heidenreich
YR 2002
UL http://www.jneurosci.org/content/22/21/9287.abstract
AB 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.