Myeloid ELF-1-like factor up-regulates lysozyme transcription in epithelial cells

Lysozyme is an important component of innate immunity against common pathog ens at mucosal surfaces. We previously cloned and characterized the bovine lysozyme 5A (lys5A) promoter with the purpose of determining cis- anal tran s-acting elements controlling airway epithelial cell-specific expression. W e found that such expression is controlled by protein binding to an ETS con sensus sequence located approximately at -46 to -40 bp from the transcripti on start site. The identity of the ETS-related protein responsible for gene transactivation was unknown. In this study, we screened six ETS-related pr oteins by transient transfection into epithelial cells and fibroblasts. Res ults showed that among these factors, the myeloid Elf-1-like factor (MEF) w as the most potent. Gel shift analysis of epithelial cell nuclear extracts using a lys5A probe including the ETS-binding site (-50/-31) yielded a sing le band with retarded mobility. This band was supershifted by an antibody d irected against MEF. Supporting the possibility that MEF is responsible for functional transactivation of lysozyme in epithelial cells, we found that antisense MEF mRNA decreased lys5A promoter activity and that MEF overexpre ssion in stably transfected cells increased lysozyme mRNA and protein expre ssion, We conclude that MEF is required for epithelial cell transactivation of lysozyme.