Differential NF-κB regulation of bcl-x gene expression in hippocampus and basal forebrain in response to hypoxia

Cell death often occurs after hypoxic/ischemic injury to the central nervous system. Changes in levels of the anti-apoptotic Bcl-X-L protein may be a determining factor in hypoxia-induced neuronal apoptosis. The transcription factor NF-kappaB regulates bcl-x gene expression. In this study, we examined the role of NF-kappaB in the regulation of bcl-x in hypoxia-induced cell death. Rat hippocampus and basal forebrain tissues were collected at different time points after hypoxia (7%O-2, 93% N-2 for 10 or 20 min). We found that 1) hypoxia induced apoptosis in the hippocampus and basal forebrain; 2) the NF-kappaB dimers c-Rel/p50 and p50/p50 bound to the bcl-x promoter NF-kappaB sequence (CS4) in the hippocampus, but only p50/p50 bound to the CS4 sequence in the basal forebrain and hypoxia-induced differential binding patterns of c-Rel/p50 and p50/p50 correlated with the bcl-x expression pattern in the hippocampus; 3) the hypoxiainduced patterns of binding of c-Rel/p50 to the bcl-x promoter CS4 sequence were different from those to the IgG-kappaB enhancer sequence, whereas those of p50/p50 were similar to both sequences; 4) nuclear protein levels of c-Rel, but not p50, correlated with the c-Rel/p50 DNA binding patterns to the bcl-x CS4 site; and 5) there were differential responses to hypoxia among the different NF-kappaB protein subunits, These results suggest that there is a tissue-specific regulation of bcl-x gene expression by NF-kappaB in hypoxia-induced cell death in the hippocampus. The absence of these regulating features in the basal forebrain may account for the early appearance of apoptosis in response to hypoxia as compared with that in hippocampus, (C) 2001 Wiley-Liss, Inc.