THE FAR UPSTREAM CHICKEN LYSOZYME ENHANCER AT -6.1-KILOBASE, BY INTERACTING WITH NF-M, MEDIATES LIPOPOLYSACCHARIDE-INDUCED EXPRESSION OF THE CHICKEN LYSOZYME GENE IN CHICKEN MYELOMONOCYTIC CELLS

Macrophages respond to lipopolysaccharide (LPS) with the activation of various genes, including the lysozyme gene. Here, we show that the le vel of lysozyme mRNA increases following treatment of chicken myelomon ocytic HD11 cells with LPS. By transient and stable transfection of th e chloramphenicol acetyltransferase (CAT) gene controlled by regulator y elements of the lysozyme gene, we identified a subfragment of the -6 .1 kilobase (kb) lysozyme enhancer that mediates the LPS-induced lysoz yme expression. This subfragment contains two elements (D and E), each of which matches the highly degenerate consensus sequence of binding sites for C/EBP-like transcription factors. Furthermore, we found prot ein complexes to interact with elements D and E whose binding activity to elements D and E is LPS-inducible in myelomonocytic HD11 cells. Im muno-mobility shift assays show that NF-M, a myeloid-specific C/EBP be ta-related transcription factor is an essential component of these pro tein complexes. Mutations of the C/EBP binding sites within D and E ca use a reduction of basal activity and abolish LPS responsiveness of th e -6.1 kb lysozyme enhancer. These results show that the -6.1 kb lysoz yme enhancer, in addition to its role in cell type-specific expression , can mediate, by interacting with NF-M, LPS-induced expression of the lysozyme gene in chicken myelomonocytic cells.