Invasion of epithelial cells by Campylobacter jejuni is independent of caveolae

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 dose-dependent 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.

Host Pathogen responses of chicken cells in vitro and in vivo to a diverse population of Campylobacter strains

“…A consistent role for caveolins (using filipin and genistein) in the uptake process could not be confirmed during this study. Indeed, this is consistent with a recent publication which suggests that C. jejuni invasion is independent of caveolins (Konkel et al, 2013).…”

“…Hock marks and pododermatitis are not currently used by the poultry industry as markers for Campylobacter but are used for signs of disease from other bacterial species or poor gut health. The use of ERK signalling inhibitors reduced C. jejuni invasion into the chicken cells which supports previous work (Hu et al, 2006b;Jin et al, 2003;Konkel et al, 2013;. This work could contribute to strategies to reduce…”

Taking Control: Campylobacter jejuni Binding to Fibronectin Sets the Stage for Cellular Adherence and Invasion

“…These findings are likely due to the fact that C. jejuni adhesion mutants, including a flpA mutant, are impaired in the delivery of effector proteins to host cells (Larson et al, 2013). In addition, we propose that CadF and FlpA are both involved in the activation of the β 1 integrin, which is required for C. jejuni invasion (Krause-Gruszczynska et al, 2011;Konkel et al, 2013). Studies are needed to address outstanding questions (e.g., Where does CadF bind within the FN molecule?…”

“…This figure shows the interaction of the CadF and FlpA proteins with host cell-associated FN and α 5 β 1 integrins, and the cell signaling pathways activated upon C. jejuni binding FN. C. jejuni manipulates focal adhesions (FAs) to stimulate host cell signaling and promote cell invasion (Eucker and Konkel, 2012;Konkel et al, 2013;Larson et al, 2013;. FAs are dynamic cellular structures that link ECM components, including FN, to intracellular cytoskeletal structures.…”

“…Not known is whether CadF participates in the delivery of the effector proteins to host cells. The reader is referred to other papers for detailed models of C. jejuni-host cell interactions (Krause-Gruszczynska et al, 2007Boehm et al, 2011;Eucker and Konkel, 2012;Konkel et al, 2013;. Figure 2).…”