C/Ebp-Epsilon Is a Myeloid-Specific Activator of Cytokine, Chemokine, and Macrophage-Colony-Stimulating Factor Receptor Genes

C/EBP epsilon is a member of the CCAAT/enhancer binding protein family of basic region/leucine zipper transcriptional activators. The C/EBP epsilon protein is highly conserved between rodents and humans, and its domain structure is very similar to C/EBP alpha, In mice C/EBP epsilon mRNA is only detected in hematopoietic tissues, including embryonic liver and adult bone marrow and spleen. Within the hematopoietic system, C/EBP epsilon is expressed primarily in myeloid cells, including promyelocytes, myelomonocytes, and their differentiated progeny. To identify potential functions of C/EBP epsilon, cell lines overexpressing the C/EBP epsilon protein were generated in the P388 lymphoblastic cell line. In contrast to the parental cell line, C/EBPE-expressing cell lines displayed lipopolysaccharide-inducible expression of the interleukin-6 and monocyte chemoattractant protein 1 (MCP-1) genes as well as elevated basal expression of the MIP-1 alpha and MIP-1 beta chemokine genes. In the EML-C1 hematopoietic stem cell line, C/EBP epsilon mRNA levels increased as the cells progressed along the myeloid lineage, just preceding activation of the gene encoding the receptor for macrophage-colony-stimulating factor (M-CSFR). M-CSFR expression was stimulated in C/EBP epsilon-expressing P388 cell lines, when compared with either the parental P388 cells or P388 cell lines expressing either C/EBP alpha or C/EBP beta, These results suggest that C/EBP epsilon may be an important regulator of differentiation of a subset of myeloid cell types and may also participate in the regulation of cytokine gene expression in mature cells. [References: 43]

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