Mechanism and consequences of uropathogenic Escherichia coli entry into host cells

Urinary tract infections (UTIs) are predominantly caused by strains of uropathogenic Escherichia coli (UPEC, a major subgroup of extraintestinal pathogenic E. coli.) Most UPEC isolates encode filamentous adhesive organelles called type 1 pili that promote bacterial colonization and invasion of the host urothelium. The FimH adhesin, present at the distal tips of type 1 pili, interacts with host alpha3beta1 integrin receptors and triggers localized actin rearrangements that lead to internalization of adherent bacteria via a zipper-like mechanism. Actin dynamics during UPEC invasion were found to be controlled by host factors that are commonly associated with integrin-linked signaling cascades and the regulation and development of focal adhesions. Specifically, FimH-mediated bacterial invasion required activation of actin-nucleating WAVE2 complexes via a process that is positively regulated by microtubules, the microtubule-associated histone deacetylase HDAC6, and kinesin-1 motor complexes. Our results suggest that by altering acetylation levels of alpha-tubulin, HDAC6 modulates the recruitment and directional trafficking of kinesin-1, which in turn functions in the delivery of regulatory factors to sites of bacterial entry. One or more of these factors may in turn act to counter the effects of the Rho kinase ROCK, which along with two other actin-nucleating factors, N-WASP and hDia2, negatively affects UPEC entry into bladder cells. These results highlight a complex interplay among UPEC, the actin and microtubule cytoskeletal networks, and integrin-linked signaling cascades during the invasion process. Interestingly, many of the host factors identified here as key facilitators of UPEC entry, including the adaptor protein paxillin, are subsequently degraded during the course of infection with UPEC. Degradation was attributed to the secretion of sublytic concentrations of the pore-forming toxin alpha-hemolysin (HlyA), which is expressed by many UPEC isolates. These proteolytic events were not observed with two other pore-forming toxins, alpha-toxin and aerolysin, and involved the HlyA-induced activation of Nalpha-Tosyl-L-lysine chloromethyl ketone hydrochloride (TLCK)-sensitive host serine proteases. These observations suggest a novel means by which HlyA produced by UPEC and related pathogens can promote tissue damage and possibly inactivate effector immune cells.