Neurons exclusively express N-Bak, a BH3 domain-only Bak isoform that promotes neuronal apoptosis.
Bak is generally recognized as a multidomain, pro-apoptotic member of the Bcl-2 family. Bak and Bax are functionally redundant in non-neuronal cells and represent a mitochondrial convergence point for cell death signaling pathways. This functional redundancy, however, may not exist in neurons in which the single deletion of Bax is sufficient to confer protection against a variety of cytotoxic insults. In the present study, we demonstrate that postnatal cortical and cerebellar granule neurons exclusively express an alternatively spliced, BH3 domain-only form of Bak (N-Bak), whereas astrocytes express only the full-length, multidomain form. Overexpression of N-Bak promotes Bax translocation in HeLa cells and induces neuronal cell death in cortical, hippocampal, and cerebellar granule neurons in a Bax-dependent manner. N-Bak interacts with Bcl-XL but not BAX, suggesting an indirect mechanism for promoting Bax translocation to the mitochondria. N-Bak message and protein levels are elevated in cortical neurons in response to DNA damage, and subsequent induction of neuronal death is significantly delayed by expressing a full-length Bak antisense plasmid. These results demonstrate that postnatal neurons solely express a BH3 domain-only form of Bak, which contributes to DNA damage-induced neuronal apoptosis. The absence of full-length Bak expression explains the near exclusive requirement for Bax in neuronal apoptosis.
Uo
Takuma
T
Department of Neurological Surgery, University of Washington School of Medicine, Box 356470, Seattle, Washington 98195-6470, USA.
Kinoshita
Yoshito
Y
Morrison
Richard S
RS
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002166:Camptothecin / Q000494:pharmacology; D004249:DNA Damage; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009474:Neurons / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein
C494773:Bak1 protein, mouse; C494827:Bax protein, mouse; D008565:Membrane Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D002166:Camptothecin