The signaling pathway of Campylobacter jejuni-induced Cdc42 activation: Role of fibronectin, integrin beta1, tyrosine kinases and guanine exchange factor Vav2
- Equal contributors
1 From the School for Biomedical and Biomolecular Science, University College Dublin, Belfield Campus, Dublin-4, Ireland
2 the Department of Microbiology, Otto von Guericke University, Leipziger Str. 44, D-39120 Magdeburg, Germany
3 the Department of Medical Microbiology, Helmholtz Center for Infection Research, Inhoffen Str. 7, D-38124 Braunschweig, Germany
4 the Department of Molecular Medicine, Max-Planck-Institute for Biochemistry, Martinsried, Germany
5 the Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, Budapest, Hungary
6 the Department of Biological Sciences, Alabama State University, Montgomery, AL 36104, USA
Cell Communication and Signaling 2011, 9:32 doi:10.1186/1478-811X-9-32Published: 28 December 2011
Host cell invasion by the foodborne pathogen Campylobacter jejuni is considered as one of the primary reasons of gut tissue damage, however, mechanisms and key factors involved in this process are widely unclear. It was reported that small Rho GTPases, including Cdc42, are activated and play a role during invasion, but the involved signaling cascades remained unknown. Here we utilised knockout cell lines derived from fibronectin-/-, integrin-beta1-/-, focal adhesion kinase (FAK)-/- and Src/Yes/Fyn-/- deficient mice, and wild-type control cells, to investigate C. jejuni-induced mechanisms leading to Cdc42 activation and bacterial uptake.
Using high-resolution scanning electron microscopy, GTPase pulldowns, G-Lisa and gentamicin protection assays we found that each studied host factor is necessary for induction of Cdc42-GTP and efficient invasion. Interestingly, filopodia formation and associated membrane dynamics linked to invasion were only seen during infection of wild-type but not in knockout cells. Infection of cells stably expressing integrin-beta1 variants with well-known defects in fibronectin fibril formation or FAK signaling also exhibited severe deficiencies in Cdc42 activation and bacterial invasion. We further demonstrated that infection of wild-type cells induces increasing amounts of phosphorylated FAK and growth factor receptors (EGFR and PDGFR) during the course of infection, correlating with accumulating Cdc42-GTP levels and C. jejuni invasion over time. In studies using pharmacological inhibitors, silencing RNA (siRNA) and dominant-negative expression constructs, EGFR, PDGFR and PI3-kinase appeared to represent other crucial components upstream of Cdc42 and invasion. siRNA and the use of Vav1/2-/- knockout cells further showed that the guanine exchange factor Vav2 is required for Cdc42 activation and maximal bacterial invasion. Overexpression of certain mutant constructs indicated that Vav2 is a linker molecule between Cdc42 and activated EGFR/PDGFR/PI3-kinase. Using C. jejuni mutant strains we further demonstrated that the fibronectin-binding protein CadF and intact flagella are involved in Cdc42-GTP induction, indicating that the bacteria may directly target the fibronectin/integrin complex for inducing signaling leading to its host cell entry.
Collectively, our findings led us propose that C. jejuni infection triggers a novel fibronectin→integrin-beta1→FAK/Src→EGFR/PDGFR→PI3-kinase→Vav2 signaling cascade, which plays a crucial role for Cdc42 GTPase activity associated with filopodia formation and enhances bacterial invasion.