Rel/NF-κB represses bcl-2 transcription in pro-B lymphocytes

The mechanisms controlling programmed cell death (PCD) during early B cell development are not well understood. Members of both the Bcl-2 family of apoptosis-related proteins and the nuclear factor-kappa B/Rel (NF-kappa B/Rel) family of transcription factors are expressed differentially during B cell development. To date. however, no direct interactions between these two families have been demonstrated. The FL5.12 cell line represents a model for progenitor B cell development. Such cells reproducibly undergo PCD upon IL-3 withdrawal. The signal to enter the apoptotic pathway is mediated by a shift in the ratio of Bcl-2:Bax. While bax levels remain constant, bcl-2 transcription rate, steady-state mRNA, and protein levels decrease. Analysis of the bcl-2 promoter reveals 3 kappa B sites functionally able to bind kappa B factors from FL5.12 nuclear extracts. Cotransfection studies demonstrate that NF-kappa B factors can repress bcl-2 transcription and that site-directed mutagenesis of the kappa B motifs abolishes this repression. These studies suggest that NF-kappa B mediates PCD in pro-B cells through transcriptional repression of the survival gene bcl-2, thus shifting the bcl-2:bax ratio in favor of death-promoting complexes.