Three promoters with different tissue specificity and pathogen inducibility express the toll-like-receptor 2 (TLR2)-encoding gene in cattle

Toll-like-receptor 2 (TLR2) is a dominant receptor for perceiving presence of bacterial pathogens. The promoter controlling its tissue specific and infection induced expression in cattle was unknown. We structurally defined with 5'-RACE experiments three promoters (P1-3) controlling TLR2 expression in udder, liver and other tissues of cows suffering from E. coli mastitis. P1 is 5'-adjacent to exon 1 as defined by the prototypical TLR2 cDNA sequence. Exon 1 is spliced to the protein-encoding exon 2. P2 and P3 reside in intron 1, express exon 1A and exon 1B, respectively which are each spliced to exon 2. Infection induced massively (>30-fold) activity of P1 and P2, but not of P3 in udders and also somewhat in liver. However, the GC-rich housekeeping promoter P3 expressed exon1B in many tissues providing the wealth of TLR2-encoding transcripts. Similar induction data were obtained after challenging primary cultures of mammary epithelial cells (pbMEC) with E. coli. Reporter gene analyses in pbMEC and the liver cell line HepG2 collectively validated that P1 and constructs containing segments from P2/P3 are in principle capable to drive gene expression. Our structural data provide the basis for more detailed molecular analyses of the infection and tissue specific regulation of TLR2 expression.