Epithelial cell contact-induced alterations in Salmonella enterica serovar Typhi lipopolysaccharide are critical for bacterial internalization

Abstract

SummaryThe invasion of Pseudomonas aeruginosa and Salmonella enterica serovar Typhi into epithelial cells depends on the cystic fibrosis transmembrane conductance regulator (CFTR) protein as an epithelial receptor. In the case of P. aeruginosa, the bacterial ligand for CFTR is the outer core oligosaccharide portion of the lipopolysaccharide (LPS). To determine whether serovar Typhi LPS is also a bacterial ligand mediating internalization, we used both P. aeruginosa and serovar Typhi LPS as a competitive inhibitor of serovar Typhi invasion into the epithelial cell line T84. P. aeruginosa LPS containing a complete core efficiently inhibited serovar Typhi invasion. However, neither killed wild-type Typhi cells nor purified LPS were effective inhibitors. LPS from mutant Typhi strains defective in O side-chain synthesis, but with an apparently normal core, was capable of inhibiting invasion, but LPS obtained from a deeper rough mutant strain with alterations in fast-migrating core oligosaccharide failed to inhibit invasion. Lastly, exposure of wild-type serovar Typhi to T84 cultures before heat killing resulted in a structural alteration in its LPS that allowed the heat-killed cells to inhibit invasion of wild-type serovar Typhi. These data indicate that the serovar Typhi LPS core, like the P. aeruginosa LPS core, is a ligand mediating internalization of bacteria by epithelial cells, and that exposure of this ligand on wild-type Typhi is induced by the bacteria's interaction with host cells.

Salmonella enterica Serovar Typhi Modulates Cell Surface Expression of Its Receptor, the Cystic Fibrosis Transmembrane Conductance Regulator, on the Intestinal Epithelium

“…In summary, we have shown that the CFTR protein, which [15]) and the cellular localization of its host receptor (CFTR). A heat-and proteasesensitive factor produced by serovar Typhi is necessary for CFTR redistribution.…”

“…One mutant strain of serovar Typhi that produces truncated LPS core is not capable of binding the CFTR protein and has a greatly reduced ability to enter epithelial cells, while another isogenic mutant producing a slightly larger LPS core interacts with CFTR normally and has an invasive phenotype (15). We are currently analyzing these LPS mutants in an attempt to identify the precise region of the LPS that serves as the CFTR-binding ligand.…”

“…On wild-type serovar Typhi, this LPS-based ligand is blocked from interacting with its epithelial cell receptor. Alterations in the LPS, triggered by bacterium-epithelial cell contact, allow wild-type serovar Typhi LPS to bind its epithelial cell receptor (15).…”

Resistance toPseudomonas aeruginosaChronic Lung Infection Requires Cystic Fibrosis Transmembrane Conductance Regulator-Modulated Interleukin-1 (IL-1) Release and Signaling through the IL-1 Receptor

“…We and others have shown that this interaction between WT-CFTR and P. aeruginosa leads to internalization of the bacterium by respiratory epithelial cells via lipid raft formation (25,56), induction of nuclear translocation of NF-B (42), activation of Src-like tyrosine kinases p59Fyn and p60Src followed by tyrosine phosphorylation of additional epithelial cell proteins (12), transcriptional activation of genes for interleukin-6 (IL-6), IL-8, CXCL1, and intercellular adhesion molecule 1 (40), and rapid apoptosis to resolve the infection (8). Multiple groups have additionally shown that binding of Salmonella enterica serovar Typhi pili and/or LPS to CFTR also mediates intestinal epithelial cell uptake of this organism (21,28,35,50). Overall, the lack of functional CFTR has been shown to affect a number of responses of the lung to P. aeruginosa, which appears to lead to a dampened early innate immune response allowing the organisms to eventually establish a chronic infection (34).…”

Commensal Bacteria Increase Invasion of Intestinal Epithelium bySalmonella entericaSerovar Typhi

“…Previous work (12,18) has demonstrated that the availability of CFTR on the epithelial plasma membrane correlates positively with serovar Typhi translocation to the gastric submucosa. This is likely due to the increased availability of epithelial CFTR for binding by its serovar Typhi-based ligand, lipopolysaccharide (13). Therefore, I determined whether commensal-stimulated redistribution of the CFTR receptor increased serovar Typhiepithelium adhesion.…”