Bacteroides fragilisEnterotoxin Induces Human β-Defensin-2 Expression in Intestinal Epithelial Cells via a Mitogen-Activated Protein Kinase/IκB Kinase/NF-κB-Dependent Pathway

Abstract

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 β-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-κB 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 IκB kinase (IKK)/NF-κB activation and hBD-2 expression. Our results suggest that a pathway including p38 MAPK, IKK, and NF-κB 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.

Bacteroides fragilis enterotoxin upregulates lipocalin-2 expression in intestinal epithelial cells

“…32 Purification of BFT and Cell Culture Conditions BFT was purified from the culture supernatant of a highly toxigenic ETBF strain as described previously. 10,[25][26][27][28][29][30]33 BFT preparation purity was confirmed by sodium dodecyl sulfatepolyacrylamide gel electrophoresis (SDS-PAGE). Typical preparations of BFT contained 0.5-1.2 mg protein/ml as measured by the BCA protein assay.…”

“…Moreover, there is no evidence of BFT-induced MAPKs or AP-1 activation leading to Lcn-2 expression, although those signaling molecules have been reported to be activated in intestinal epithelial cells exposed to BFT. 10,[25][26][27][28][29][30][31] In the studies reported here, we investigated the regulation of Lcn-2 expression in response to BFT stimulation, and found that stimulation with BFT upregulates Lcn-2 expression in intestinal epithelial cells through the activation of MAPKs and the AP-1 signaling pathway.…”

“…[6][7][8][9] Recently, we demonstrated that stimulation of intestinal epithelial cells with BFT enhanced the expression of the antibacterial peptide human b-defensin (hBD)-2. 10 However, it is possible that other antibacterial factors may be upregulated in the ETBF-infected area of the intestine and contribute to regulation of enteric inflammation.…”

Extracellular HIV-1 Tat Induces Human Beta-Defensin-2 Production Via NF-kappaB/AP-1 Dependent Pathways in Human B Cells

“…The mitogen-activated protein kinases (MAPKs) such as p38, JNK and ERK protein kinase are involved in the signaling cascades leading to hBD-2 expression upon various stimuli (Jang et al, 2004;Méndez-Samperio et al, 2007;Yoon et al, 2010). We observed that JNK inhibitor, but not ERK and p38 MAPK inhibitors, suppressed HIV-1 Tat-induced mRNA expression of hBD-2 as well as the production of hBD-2 ( Fig.…”

“…Previous studies have indicated that the activity of MAP kinases such as p38, JNK and ERK protein kinase is involved in hBD-2 expression upon various stimuli (Jang et al, 2004;Méndez-Samperio et al, 2007;Yoon et al, 2010). To further analyze the effect of the MAPK superfamily pathway on HIV-1 Tat-mediated hBD-2 production, we measured HIV-1 Tat-induced hBD-2 production in the presence of pathway-specific inhibitors.…”