Expression of Bactericidal/Permeability-Increasing protein requires C/EBPε

Bactericidal/permeability-increasing protein (BPI) is a 55-kd cationic protein found mainly in neutrophil primary granules. BPI shows cytotoxicity against Gram-negative bacteria. In this study, we studied the role of a myeloid-specific transcription factor, CCAAT/enhancer binding protein epsilon (C/EBP epsilon), in the regulation of BPI gene expression. A patient with neutrophil-specific granule deficiency with a homozygous inactivating mutation in the CEBP epsilon gene showed severely impaired expression of both BPI messenger RNA (mRNA) and BPI protein. Both U937 and NB4 cells treated with 10(-7) M all-trans retinoic acid (ATRA) for 6 days displayed increased levels of BPI protein and accompanying up-regulated C/EBP epsilon expression. Chromatin-immunoprecipitation analysis and electrophoretic mobility shift assays revealed binding of the C/EBP epsilon protein to the C/EBP-binding site in the BPI gene promoter. U937 cells stably transfected with a zinc-inducible C/EBP epsilon expression vector showed a 30-fold increase in BPI mRNA levels compared with cells transfected with control empty vector after culturing for 48 hours with 100 mu M ZnSO4. BPI mRNA expression was severely reduced in the bone marrow of C/EBP epsilon-deficient mice compared with wild-type mice. Expression of BPI in human cord blood cells was increased by incubation with 10(-7) M ATRA for 48 hours. These results demonstrate the requirement for C/EBP epsilon in mediating BPI gene expression in myeloid cells in vitro and in vivo.