The role of oct-1 in the regulation of tracheal antimicrobial peptide (TAP) and lingual antimicrobial peptide (LAP) expression in bovine mammary epithelial cells.

Lingual antimicrobial peptide (LAP) and tracheal antimicrobial peptide (TAP) are two important β-defensins of antimicrobial peptide family, which are evolutionarily conserved effector molecules of the innate immune response. Although known to be sensitive to pathogenic challenge, the control of their expression remains unclear. Both LAP and TAP genes showed constitutive and inducible expression in bovine mammary epithelial tissues, and the aim of this study was to investigate the mechanisms underlying their expression and regulation. Reporter plasmids fused with 5' regions of the two gene promoter regions were constructed and transiently transfected into a bovine mammary epithelial (BME) cell line. Initial serial deletion of the promoter regions from both genes identified two positive regulatory elements within the 1 kb regions upstream the transcription start sites, which co-operatively contribute to LAP and TAP gene expression. Further luciferase reporter assays revealed that an enhancer and a 61-bp region proximal to both genes are important for basal expression and regulation of transcription. Electrophoretic mobility shift assays (EMSA) indicated the involvement of the Oct-1 protein-DNA complex in regulating the promoter activity, which was confirmed by super shift EMSA with Oct-1 antibody and by knockdown of Oct-1 with small interfering RNA. The Oct-1 binding motif was also shown to be responsive to phorbol 12-myristate 13-acetate but not LPS stimulation. The results from this study clearly demonstrate the involvement of the Oct-1 transcription factor in the regulation of LAP and TAP expression.