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  • Title: Distinct mechanisms of neuronal apoptosis are triggered by antagonism of Bcl-2/Bcl-x(L) versus induction of the BH3-only protein Bim.
    Author: Zimmermann AK, Loucks FA, Le SS, Butts BD, Florez-McClure ML, Bouchard RJ, Heidenreich KA, Linseman DA.
    Journal: J Neurochem; 2005 Jul; 94(1):22-36. PubMed ID: 15953346.
    Abstract:
    Primary cerebellar granule neurons (CGNs) require depolarizing extracellular potassium for their survival. Removal of depolarizing potassium triggers CGN apoptosis that requires induction of Bim, a BH3-only Bcl-2 family member. Bim is classically thought to promote apoptosis by neutralizing pro-survival Bcl-2 proteins. To determine if this is the principal function of Bim in CGNs, we contrasted Bim-mediated apoptosis to neuronal death induced by HA14-1, a BH3-domain mimetic that antagonizes Bcl-2 and Bcl-x(L). HA14-1 elicited CGN apoptosis characterized by caspase 3 and 9 activation, cytochrome c release, conformational activation of Bax, and mitochondrial depolarization. HA14-1 provoked CGN apoptosis in the absence of Bim induction and negative regulators of Bim transcription did not prevent HA14-1-induced cell death. However, the antioxidant glutathione and its precursor, N-acetyl-l-cysteine, suppressed HA14-1-induced apoptosis. Similarly, apoptosis induced by either a structurally distinct Bcl-2/Bcl-x(L) inhibitor (compound 6) or Bcl-2 antisense oligonucleotides was diminished by glutathione. In contrast, antioxidants had no effect on CGN apoptosis provoked by either removal of depolarizing potassium or overexpression of a GFP-Bim fusion protein, two models of Bim-dependent death. These data show that antagonism of Bcl-2/Bcl-x(L) function elicits oxidative stress-dependent CGN apoptosis that is mechanistically distinct from Bim-mediated cell death. These results further indicate that, although Bcl-2/Bcl-x(L) antagonism is sufficient to induce neuronal apoptosis, Bim likely promotes neuronal death by interacting with additional proteins besides Bcl-2/Bcl-x(L).
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