The enterohaemorrhagic escherichia coli effector EspW triggers actin remodelling in a Rac1 dependent manner

Abstract

Enterohaemorrhagic Escherichia coli (EHEC) is a diarrheagenic pathogen that colonizes the gut mucosa by forming attaching-and-effacing lesions. EHEC employs a type III secretion system (T3SS) to translocate 50 effector proteins that hijack and manipulate host cell signalling pathways, which contribute to subversion of immune responses, colonization and disease. The role of many effectors during infection remains unclear. This study aimed to identify the function of the T3SS effector protein EspW. Although EspW is an EHEC effector, we found that it is present in the prototypes strains EPEC E11 and B171. Furthermore, screening a collection of clinical EPEC isolates revealed that espW is present in 52% of the tested stains, suggesting that EspW is an important virulence factor. We report that EspW modulates actin dynamics in a Rac1-dependant manner. Ectopic expression of EspW results in formation of unique membrane protrusions. Infection of Swiss cells with an EHEC espW deletion mutant induces cell shrinkage that could be overcomed by Rac1 activation via expression of the bacterial GEF, EspT. EspW contains a QLSI motif, similar to the QxSI sequence found in the catalytic loops of the effectors EspM and Map, which activate RhoA and Rac-1, respectively. We found that I237 within that motif is essential for the activity of EspW during ectopic expression and infection. Furthermore, using a yeast two hybrid screen we identified the motor protein Kif15 as a potential interacting partner of EspW. Kif15 and EspW co-localized in co-transfected cells, while ectopically expressed Kif15 localized to the actin pedestals following EHEC infection. The data suggest that Kif15 recruits EspW to the site of bacterial attachment, which in turn activates Rac1, resulting in modifications of the actin cytoskeleton that are essential to maintain cell shape during infection.