<i>Citrobacter rodentium</i> Infection Induces MyD88-Dependent Formation of Ubiquitinated Protein Aggregates in the Intestinal Epithelium

Citrobacter rodentium utilizes a type 3 secretion system (T3SS) to inject effector proteins into host intestinal epithelial cells, causing structural and functional changes in these cells during infection. Here, we examined the effects of C. rodentium infection on host cell protein ubiquitination in vivo. We observed the appearance of ubiquitinated protein (Ub(+)) aggregates in intestinal epithelial cells near the site of bacterial attachment. Formation of aggregates was dependent on T3SS activity and the effector translocated intimin receptor (Tir). Aggregates formed at 6 days after infection, when bacterial loads were maximal, but were absent at 12 days. Aggregates were not observed in MyD88(-/-) mice. Aggregate formation correlated with MyD88-dependent induction of NADPH oxidase 1, implicating reactive oxygen species in their formation. Aggregates were also observed in gastric tissues of mice infected with Helicobacter pylori. This is the first report describing the formation of Ub(+) aggregates in vivo during enteric infection, and reveals that this phenotype is dependent on both bacterial and host factors. Our experiments extend previous in vitro studies suggesting that Ub(+) aggregates play an important role in the initiation of immune responses to infection. Ub(+) aggregates are a novel marker of the cellular response to enteric pathogens and will be useful for studies of host-pathogen interactions in vivo.