Invasion of epithelial cells by Campylobacter jejuni is independent of caveolae
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RESEARCH
Open Access
Invasion of epithelial cells by Campylobacter jejuni is independent of caveolae Michael E Konkel*, Derrick R Samuelson, Tyson P Eucker, Eric A Shelden and Jason L O'Loughlin
Abstract Caveolae are 25–100 nm flask-like membrane structures enriched in cholesterol and glycosphingolipids. Researchers have proposed that Campylobacter jejuni require caveolae for cell invasion based on the finding that treatment of cells with the cholesterol-depleting compounds filipin III or methyl-β-cyclodextrin (MβCD) block bacterial internalization in a dosedependent manner. The purpose of this study was to determine the role of caveolae and caveolin-1, a principal component of caveolae, in C. jejuni internalization. Consistent with previous work, we found that the treatment of HeLa cells with MβCD inhibited C. jejuni internalization. However, we also found that the treatment of HeLa cells with caveolin-1 siRNA, which resulted in greater than a 90% knockdown in caveolin-1 protein levels, had no effect on C. jejuni internalization. Based on this observation we performed a series of experiments that demonstrate that MβCD acts broadly, disrupting host cell lipid rafts and C. jejuni-induced cell signaling. More specifically, we found that MβCD inhibits the cellular events necessary for C. jejuni internalization, including membrane ruffling and Rac1 GTPase activation. We also demonstrate that MβCD disrupted the association of the β1 integrin and EGF receptor, which are required for the maximal invasion of epithelial cells. In agreement with these findings, C. jejuni were able to invade human Caco-2 cells, which are devoid of caveolae, at a level equal to that of HeLa cells. Taken together, the results of our study demonstrate that C. jejuni internalization occurs in a caveolae-independent manner. Keywords: Lipid rafts, Caveolin-1, Cell signaling, Focal complex, Membrane ruffling
Lay abstract Campylobacter jejuni is responsible for a significant proportion of human morbidity and mortality in both developing and developed countries. Most cases of campylobacteriosis result from consumption of foods crosscontaminated with undercooked chicken products. Acute disease is dependent upon the ability of C. jejuni to bind and invade the cells lining the human gastrointestinal tract. While significant progress has been made in identifying and characterizing the bacterial components that contribute to the development of disease in humans, how the bacterium manipulates the host intestinal cells during infection is less well-defined. For more than a decade researchers have proposed that C. jejuni invasion of intestinal cells requires specialized structures called caveolae. We present evidence demonstrating that C. jejuni internalization is not dependent on caveolae, but requires the cellular components that comprise the * Correspondence: [email protected] School of Molecular Biosciences, College of Veterinary Medicine, Washington State University, Life Sciences Bldg. Room 302c, Pullman, WA, USA
focal complex. Our data provide
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