Bacteroides fragilis Enterotoxin Induces Human ?-Defensin-2 Expression in Intestinal Epithelial Cells via a Mitogen-Activated Protein Kinase/IB Kinase/NF-B-Dependent Pathway

Enterotoxigenic Bacteroides fragilis (ETBF) produces an approximately 20-kDa heat-labile enterotoxin (BFT) that plays an essential role in mucosal inflammation. Although spontaneous disappearance of ETBF infection is common, little information is available on regulated expression of antibacterial factors in response to BFT stimulation. This study investigates the role of BFT in human ?-defensin 2 (hBD-2) induction from intestinal epithelial cells. Stimulation of HT-29 and Caco-2 intestinal epithelial cell lines with BFT resulted in the induction of hBD-2. Activation of a reporter gene for hBD-2 was dependent on the presence of NF-B binding sites. In contrast, suppression of AP-1 did not affect hBD-2 expression in BFT-stimulated cells. Inhibition of p38 mitogen-activated protein kinase (MAPK) using SB203580 and small interfering RNA (siRNA) transfection resulted in a significant reduction in BFT-induced IB kinase (IKK)/NF-B activation and hBD-2 expression. Our results suggest that a pathway including p38 MAPK, IKK, and NF-B activation is required for hBD-2 induction in intestinal epithelial cells exposed to BFT, and may be involved in the host defense following infection with ETBF.