Sang-Hoon Rhee

Genetic evidence indicating that TOLL-like receptor 4 (Tlr4) is the lipopolysaccharide (LPS) receptor in mice was reported. However, biochemical evidence that murine Tlr4 confers LPS responsiveness has not been convincingly demonstrated. Inducible cyclooxygenase (COX-2) is selectively expressed in LPS-stimulated macrophages in part mediated through the activation of NF kappa B. Thus, we determined whether murine Tlr4 confers LPS responsiveness as evaluated by the activation of NF kappa B and COX

Commensal and enteroinvasive microbes in the human gut release bacterial flagellin, a specific microbial ligand of Toll-like receptor 5 (TLR5). However, the pathophysiological role of bacterial flagellin in gastrointestinal inflammation has not been determined. Here we evaluated the role of bacterial flagellin using native human colonic mucosa and the mouse colitis model of dextran sulfate sodium (DSS). We demonstrate that, in intact human colonic mucosa, the flagellin/TLR5 response occurs only

Lipopolysaccharide (LPS), a main constituent of Gram-negative bacterial membrane, specifically activates Toll-like receptor 4, leading to the production of pleiotropic cytokines/chemokines which in turn regulate inflammatory and innate and subsequent adaptive immune responses. Given that human gut harbors a large collection of commensal bacteria, LPS released by gut microbes is able to make the great impact on gut homeostasis through the intracellular signaling pathways engaged by host-microbial

Engagement of Toll-like receptor (TLR) proteins activates multiple signal transduction pathways. These studies show that engagement of TLR2 and TLR4 leads to rapid phosphorylation of the transcription factor STAT1 at serine 727 (Ser-727 STAT1) in murine macrophages. Only TLR4 engagement induced STAT1 phosphorylation at tyrosine 701, although this response was delayed compared with Ser-727 STAT1 phosphorylation. Inhibition of phosphatidylinositol 3'-kinase using LY294002 blocked TLR4-induced STAT

Bacterial flagellin, recognized by Toll-like receptor (TLR) 5, is suggested to be involved in colonic inflammation. However, the detailed signaling mechanisms mediated by flagellin/TLR5 engagement are not clear. Here we dissected the biochemical mechanism by which TLR5 engagement mediates phosphatidylinositol 3-kinase (PI3K) activation in colonic epithelial cells. We demonstrate that silencing TLR5 expression in nontransformed human colonic epithelial cells blocks flagellin-induced PI3K activati

Toll-like receptors (TLRs) associate with adaptor molecules (MyD88, Mal/TIRAP, TRAM, and TRIF) to mediate signaling of host-microbial interaction. For instance, TLR4 utilizes the combination of both Mal/TIRAP-MyD88 (MyD88-dependent pathway) and TRAM-TRIF (MyD88-independent pathway). However, TLR5, the specific receptor for flagellin, is known to utilize only MyD88 to elicit inflammatory responses, and an involvement of other adaptor molecules has not been suggested in TLR5-dependent signaling. H

Flagellin, a specific ligand for Toll-like receptor 5 (TLR5), is a molecular pattern associated with several bacterial species. Recently, TLR signaling has been intensively studied. However, TLR5-associated signaling in non-transformed colonocytes has not been investigated. Here we studied the expression of cytokines induced by flagellin in non-transformed human colonic NCM460 cells and the signaling mechanisms mediating these responses. Cytokine expression array experiments showed that exposure

Frequency of gram-negative bacteria is markedly enhanced in inflamed gut, leading to augmented LPS in the intestine. Although LPS in the intestine is considered harmless and, rather, provides protective effects against epithelial injury, it has been suggested that LPS causes intestinal inflammation, such as necrotizing enterocolitis. Therefore, direct effects of LPS in the intestine remain to be studied. In this study, we examine the effect of LPS in the colon of mice instilled with LPS by recta

Microbial recognition by multicellular organisms is initially accomplished by a group of pattern recognition receptors which are specialized to recognize microbe-associated molecular patterns (MAMPs) such as lipopolysaccharide, bacterial lipoprotein, CpG DNA motif, double strand RNA and flagellin. Toll-like receptors (TLRs) are the representative pattern recognition receptors, and microbial recognition by TLRs elicits innate and inflammatory responses. Ten TLR family members have been presently

Defective IL-10 allele is a risk factor for intestinal inflammation. Indeed, IL-10(-/-) mice are predisposed to spontaneous colitis in the presence of intestinal microbiota, indicating that microbial factors contribute to developing intestinal inflammation. By recognizing flagellin, TLR5 plays a quintessential role in microbial recognition in intestinal epithelial cells. Here, we treated flagellin (1.0 μg/mouse/d) in mouse colon and found that it elicited colonic inflammation in IL-10(-/-) mice,

Proteolytic modification of pattern recognition receptors and their signaling adaptor molecules has recently emerged as an essential cellular event to regulate immune and inflammatory responses. Here we show that the TIR domain containing adaptor-inducing interferon-beta (TRIF), an adaptor molecule mediating TLR3 signaling and MyD88-independent signaling of TLR4, plays an inhibitory role in TLR5-elicited responses by inducing proteolytic degradation of TLR5. TRIF overexpression in human embryoni