Myeloid transcription factor C/EBP epsilon is involved in the positive regulation of lactoferrin gene expression in neutrophils

Targeted mutation of the myeloid transcription factor C/EBP epsilon in mice results in gram-negative septic death at 3 to 5 months of age. This study defines the underlying molecular defects in their terminal granulocytic dif ferentiation. The mRNA for the precursor protein of the cathelin-related an timicrobial peptides was almost completely absent in the bone marrow cells of C/EBP epsilon-/- mice. This finding may help explain their susceptibilit y to gram-negative sepsis, because both are bacteriocidal peptides with pot ent activity against gram-negative bacteria. Superoxide production was foun d to be reduced in both granulocytes and monocytes of C/EBP epsilon-/- mice , While gp91 phox protein levels were normal, p47phox protein levels were c onsiderably reduced in C/EBP epsilon-/- granulocytes/monocytes, possibly li miting the assembly of the NADPH oxidase, In addition, expression of mRNA o f the secondary and tertiary granule proteins, lactoferrin and gelatinase, were not detected, and levels of neutrophil collagenase mRNA were reduced i n bone marrow cells of the knock-out mice. The murine lactoferrin promoter has a putative C/EBP site close to the transcription start site. C/EBP epsi lon bound to this site in electromobility shift assay studies and mutation of this site abrogated binding to it. A mutation in the C/EBP site reduced the activity of the promoter by 35%, Furthermore, overexpression of C/EBP e psilon in U937 cells increased the activity of the wild-type lactoferrin pr omoter by 3-fold. In summary, our data implicate C/EBP epsilon as a critica l factor of host antimicrobial defense and suggests that it has a direct ro le as a positive regulator of expression of lactoferrin in vivo. (C) 1999 b y The American Society of Hematology.