Transcriptional regulation of beta-defensin gene expression in tracheal epithelial cells

Innate immunity provides an ever-present or rapidly inducible initial defen se against microbial infection. Among the effector molecules of this defens e in many species are broad-spectrum antimicrobial peptides. Tracheal antim icrobial peptide (TAP) was the first discovered member of the beta-defensin family of mammalian antimicrobial peptides. TAP is expressed in the ciliat ed epithelium of the bovine trachea, and its mRNA levels are dramatically i ncreased upon stimulation with bacteria or bacterial lipopolysaccharide (LP S). We report here that this induction by LPS is regulated at the level of transcription. Furthermore, the transfection of reporter gene constructs in to tracheal epithelial cells indicates that DNA sequences in the 5' flankin g region of the TAP gene, within 324 nucleotides of the transcription start site, are responsible in part for mediating gene induction. This region in cludes consensus binding sites for NF-kappa B and nuclear factor interleuki n-6 (NF IL-6) transcription factors. Gel mobility shift assays indicate tha t LPS induces NF-kappa B binding activity in the nuclei of these cells, whi le NF IL-6 binding activity is constitutively present. The gene encoding hu man beta-defensin 2, a human homologue of TAP with similar inducible expres sion patterns in the airway, was cloned and found to have conserved NF-kapp a B and NF IL-6 consensus binding sites in its 5' flanking region. Previous studies of antimicrobial peptides from insects indicated that their induct ion by infectious microbes and microbial products also occurs via activatio n of NF-kappa B-like and NF IL-6-like transcription factors. Together, thes e observations indicate that a strategy for the induction of peptide-based antimicrobial innate immunity is conserved among evolutionarily diverse org anisms.