Transcriptional regulation of the BCL-X gene by NF-κB is an element of hypoxic responses in the rat brain

Signal transduction pathways that mediate neuronal commitment to apoptosis involve the nuclear factor kappa B (NF-κB) transcription factor. The bcl-x gene is a member of the bcl-2 family of genes that regulate apoptosis, and gives rise to two proteins, Bcl-X_L and Bcl-X_S, via alternative mRNA splicing. Bcl-X_L protein, like Bcl-2, is a dominant inhibitor of apoptotic cell death, whereas Bcl-X_S promotes apoptosis. While there is high expression of Bcl-X_L in the developing and adult brain, few transcriptional control elements have been identified in the bcl-x promoter. There are two functional nuclear factor-kappa B (NF-κB) DNA binding sites clustered upstream of the brain-specific transcription start site in the upstream promoter region of murine bcl-x. Recombinant NF-κB proteins bind to these sites. Also NF-κB overexpression, coupled with bcl-x promoter/reporter assays using a series of murine bcl-x promoter and deletion mutants, has identified the downstream 1.1kb of the bcl-x promoter as necessary for basal promoter activity and induction by NF-κB in support of the hypothesis that NF-κB can act to enhance Bcl-X_L expression via highly selective interactions with the bcl-x promoter, where NF-κB binding and promoter activation are dependent on specific DNA binding site sequences and NF-κB protein dimer composition. Hypoxia induces apoptosis in the hippocampus where the NF-κB dimers c-Rel/p50 and p50/p50 bind to the bcl-x promoter NF-κB site.