Research Article: Vibrio cholerae Cytolysin Causes an Inflammatory Response in Human Intestinal Epithelial Cells That Is Modulated by the PrtV Protease

Date Published: November 12, 2009

Publisher: Public Library of Science

Author(s): Gangwei Ou, Pramod Kumar Rompikuntal, Aziz Bitar, Barbro Lindmark, Karolis Vaitkevicius, Sun Nyunt Wai, Marie-Louise Hammarström, Adam J. Ratner.

Abstract: Vibrio cholerae is the causal intestinal pathogen of the diarrheal disease cholera. It secretes the protease PrtV, which protects the bacterium from invertebrate predators but reduces the ability of Vibrio-secreted factor(s) to induce interleukin-8 (IL-8) production by human intestinal epithelial cells. The aim was to identify the secreted component(s) of V. cholerae that induces an epithelial inflammatory response and to define whether it is a substrate for PrtV.

Partial Text: Vibrio cholerae, the causal organism of the diarrheal disease cholera, is a Gram-negative motile bacterium acquired via intake of contaminated food or water. Secreted cholera toxin (CTX) is the major factor that causes diarrhea. However, most V. cholerae vaccine candidates lacking CTX still exhibit reactogenicity in clinical trials [1]–[4]. The molecular and cellular mechanisms behind these adverse effects are still unknown. Levine et al. [5] suggested that a previously unidentified enterotoxin could cause symptoms in the absence of CTX, but its existence has been masked by the activity of CTX in the virulent strains. Proposed candidates are the Hap protease [6], [7], the multifunctional autoprocessing RTX toxin [8], and Vibrio cholera cytolysin (VCC), also called hemolysin A and El Tor hemolysin [9].

This study emerged from the previous, intriguing results of reverse molecular genetics experiments suggesting that the Vibrio protease PrtV confers an “anti-infammatory”, seemingly protective effect on human intestinal epithelium while it exerts a pathogenic effect in the intestine of the nematode C. elegans[10]. We found that PrtV executes its anti-inflammatory action by degrading secreted VCC and that BHI broth somehow protects VCC from degradation by PrtV. The latter finding was underscored by the consistent, parallel changes in capacity to induce an inflammatory response in intestinal epithelial cells and to cause lysis of red blood cells in bacterial culture supernatants depending of type of broth used, i.e. supernatants of wild type bacteria grown in LB caused little hemolysis and a low inflammatory response while supernatants of bacteria grown in BHI caused extensive hemolysis and a strong inflammatory response. The inflammatory response was characterized by increased epithelium permeability and production of IL-8 and low amounts of TNF-α by the epithelial cells. Experiments with pure VCC protein showed that VCC alone is likely to be responsible for these effects. Thus, VCC could be the causative agent of several symptoms induced by CTX-deficient strains of V. cholerae. In line with this notion, Debellis et al. [13] recently reported that VCC can cause decreased trans-tissue electrical resistance and increased chloride secretion when added at the luminal side of human colon mucosa specimens stripped of mucous layer.



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