NF-kappa B p50 Regulates C/EBP alpha Expression and Inflammatory Cytokine-Induced Neutrophil Production

NF-kappa B is a key transcriptional inducer of the inflammatory response in mature myeloid cells, and also stimulates cell survival, but its role in immature myeloid cell development has not been well characterized. C/EBP alpha is required for the development of monocytic and granulocytic myeloid cells from early progenitors, and NF-kappa B and C/EBP beta cooperatively induce several inflammatory mediators. Having found that C/EBP alpha binds NF-kappa B p50 preferentially compared with NF-kappa B p65, we have now investigated myelopoiesis in nfkb1(-/-) mice lacking NF-kappa B p50. Absence of p50 leads to a significant reduction in the number of granulocytic progenitors, CFU-granulocyte, obtained with G-CSF or GM-CSF in vitro and reduces neutrophil production in vivo in response to G-CSF, with preservation of monopoiesis in vitro in response to cytokines or LPS. To gain insight into the mechanism underlying reduced granulopoiesis in the absence of NF-kappa B p50, we assessed the expression of several myeloid regulatory proteins in lineage-negative, immature myeloid cells. Although PU.1, C/EBP beta, and STAT3 levels were unchanged, C/EBP alpha protein and RNA levels were reduced similar to 3-fold in the absence of NF-kappa B p50. In addition, NF-kappa B p50 and C/EBP alpha bound the endogenous C/EBP alpha promoter in a chromatin immuno-precipitation assay, and NF-kappa B p50 trans activated the C/EBP alpha promoter, alone or in cooperation with C/EBP alpha. Despite reduction of C/EBP alpha, G-CSFR and M-CSFR levels were maintained in total marrow and in lineage-negative cells. Together, these data indicate that acute inflammation not only activates mature myeloid cells, but also stimulates neutrophil production via NF-kappa B p50 induction of C/EBP alpha transcription. The Journal of Immunology, 2009, 182: 5757-5762.