Full length Bid is sufficient to induce apoptosis of cultured rat hippocampal neurons.
BACKGROUND
Bcl-2 homology domain (BH) 3-only proteins are pro-apoptotic proteins of the Bcl-2 family that couple stress signals to the mitochondrial cell death pathways. The BH3-only protein Bid can be activated in response to death receptor activation via caspase 8-mediated cleavage into a truncated protein (tBid), which subsequently translocates to mitochondria and induces the release of cytochrome-C. Using a single-cell imaging approach of Bid cleavage and translocation during apoptosis, we have recently demonstrated that, in contrast to death receptor-induced apoptosis, caspase-independent excitotoxic apoptosis involves a translocation of full length Bid (FL-Bid) from the cytosol to mitochondria. We induced a delayed excitotoxic cell death in cultured rat hippocampal neurons by a 5-min exposure to the glutamate receptor agonist N-methyl-D-aspartate (NMDA; 300 microM).


RESULTS
Western blot experiments confirmed a translocation of FL-Bid to the mitochondria during excitotoxic apoptosis that was associated with the release of cytochrome-C from mitochondria. These results were confirmed by immunofluorescence analysis of Bid translocation during excitotoxic cell death using an antibody raised against the amino acids 1-58 of mouse Bid that is not able to detect tBid. Finally, inducible overexpression of FL-Bid or a Bid mutant that can not be cleaved by caspase-8 was sufficient to induce apoptosis in the hippocampal neuron cultures.


CONCLUSIONS
Our data suggest that translocation of FL-Bid is sufficient for the activation of mitochondrial cell death pathways in response to glutamate receptor overactivation.
König
Hans-Georg
HG
Department of Physiology and RCSI Neuroscience Research Centre, Royal College of Surgeons in Ireland, Dublin 2, Ireland. hgkoenig@rcsi.ie <hgkoenig@rcsi.ie>
Rehm
Markus
M
Gudorf
Daniel
D
Krajewski
Stan
S
Gross
Atan
A
Ward
Manus W
MW
Prehn
Jochen H M
JH
D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000187:drug effects; D051023:BH3 Interacting Domain Death Agonist Protein / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D053181:Caspase 8 / Q000378:metabolism; D002478:Cells, Cultured; D006624:Hippocampus / Q000166:cytology* / Q000187:drug effects; D050505:Mutant Proteins / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009498:Neurotoxins / Q000494:pharmacology; D010447:Peptide Hydrolases / Q000378:metabolism; D021381:Protein Transport; D051381:Rats; D011916:Rats, Inbred F344; D017470:Receptors, Glutamate / Q000378:metabolism
D051023:BH3 Interacting Domain Death Agonist Protein; C494816:Bid protein, rat; D050505:Mutant Proteins; D009498:Neurotoxins; D017470:Receptors, Glutamate; D010447:Peptide Hydrolases; D053181:Caspase 8