The Campylobacter jejuni CiaC virulence protein is secreted from the flagellum and delivered to the cytosol of host cells

Abstract

Campylobacter jejuni is a leading cause of bacterial gastroenteritis worldwide. Acute C. jejuni-mediated disease (campylobacteriosis) involves C. jejuni invasion of host epithelial cells using adhesins (e.g., CadF and FlpA) and secreted proteins [e.g., the Campylobacter invasion antigens (Cia)]. The genes encoding the Cia proteins are up-regulated upon co-culture of C. jejuni with epithelial cells. One of the Cia proteins, CiaC, is required for maximal invasion of host cells by C. jejuni. Previous work has also revealed that CiaC is, in part, responsible for host cell cytoskeletal rearrangements that result in membrane ruffling. This study was performed to test the hypothesis that CiaC is delivered to the cytosol of host cells. To detect the delivery of CiaC into cultured epithelial cells, we used the adenylate cyclase domain (ACD) of Bordetella pertussis CyaA as a reporter. In this study, we found that export and delivery of the C. jejuni Cia proteins into human INT 407 epithelial cells required a functional flagellar hook complex composed of FlgE, FlgK, and FlgL. Assays performed with bacterial culture supernatants supported the hypothesis that CiaC delivery requires bacteria-host cell contact. We also found that CiaC was delivered to host cells by cell-associated (bound) bacteria, as judged by experiments performed with inhibitors that specifically target the cell signaling pathways utilized by C. jejuni for cell invasion. Interestingly, the C. jejuni flgL mutant, which is incapable of exporting and delivering the Cia proteins, did not induce INT 407 cell membrane ruffles. Complementation of the flgL mutant with plasmid-encoded flgL restored the motility and membrane ruffling. These data support the hypothesis that the C. jejuni Cia proteins, which are exported from the flagellum, are delivered to the cytosol of host cells.

The Intestinal Microbiota Influences Campylobacter jejuni Colonization and Extraintestinal Dissemination in Mice

“…This mutant should be attenuated in mice as C. jejuni utilizes the flagellum for both motility and secretion of virulence proteins that are delivered to host epithelial cells (29,30).…”

The Family Campylobacteraceae

“…Poly and Guerry (2008) proposed that flagella have the ability to secrete non-flagellar proteins that may be virulence associated. Larson et al (2008) and Neal-McKinney and Konkel (2012)) provide evidence that in C. jejuni, Cia is exported from the flagella and is delivered to the cytosol of host cells, thus enabling Campylobacter to attach to epithelial cells. Fimbriaelike elements and cell surface proteins (PEB1, CadF) of C. jejuni appear to function in attachment and subsequent colonization and invasion (Doig et al 1996).…”

A capsule conjugate vaccine approach to prevent diarrheal disease caused byCampylobacter jejuni

“…Flagella are critical to virulence for the organism to swim through the mucus lining of the intestine and to serve as a secretory organelle for a variety of proteins, some of which appear to play roles in invasion. [23][24][25][26][27] C. jejuni invasion is similar to that of Shigella spp., in that both usually invade the intestinal epithelium and are not generally found systemically, in contrast to Salmonella spp. The process of invasion of epithelial cells results in an influx of immune cells and cytokine release that is manifest as inflammatory diarrhea.…”