Involvement of 5'-flanking κB-like sites within bcl-x gene in silica- induced Bcl-x expression

The present study investigated the involvement of the transcription factor NF-κB in the expression of an anti-apoptotic gene, bcl-x, using a murine macrophage cell line and peritoneal macrophages from both wild type (p50(+/+)) and NF-κB p50 gene knockout (p50(-/-)) mice. Increased expression of Bcl-x protein was observed in native and silica-exposed p50(-/-) macrophages in which the NF-κB p65-containing complex was predominantly induced. Co-transfection experiment using a bcl-x promoter reporter construct and an expression vector for NF-κB p50 or p65 indicates that p65, but not p50, upregulates the promoter activity of the bcl-x gene. DNA sequence analysis revealed that there are several κB-like sites within the 5'- flanking region of the bcl-x gene. Electrophoretic mobility shift assay suggested differences in binding of the NF-κB complexes to these putative NF-κB binding sites of the bcl-x gene.