ExoS of Pseudomonas aeruginosa binds to a human KIF7 to induce cytotoxicity in cultured human bronchial epithelial cells.

The lungs are a major site of Pseudomonas aeruginosa infection in patients with compromised immune systems. P. aeruginosa secretes a number of toxins by a type III secretion system, and these are important in virulence. One of these toxins, ExoS can induce a cytotoxic effect and is associated with the ability to produce lung damage. ExoS is a bifunctional toxin, with N-terminal GTPase-activating protein (GAP) activity and a C-terminal ADP ribosyl transferase (ADPRT) domain. Although these two domains have numerous potential cellular targets, the overall mechanism of ExoS-induced cytotoxicity remains unclear. We carried out a yeast two-hybrid screen using the ExoS truncation mutant ExoSΔ (residue 1-388), which lacks the 14-3-3 binding site in the ADPRT domain, to identify unknown cellular targets associated with ExoS-induced cytotoxicity. We identified the mammalian factor, kinesin family member 7 (KIF7), which is involved in Hedgehog signaling, as a binding partner for ExoSΔC2. A pull-down assay revealed that ExoS bound to the truncated KIF7 gene encoding the N-terminal domain (residues 1-109) of KIF7. Yeast two-hybrid analysis showed that the ADPRT domain (residues 234-354) of ExoS bound to the truncated KIF7. Furthermore, exoS gene expression and silencing the expression of KIF7 both caused significant cytotoxicity in cultured human bronchial epithelial cells (BEAS-2B). Taken together, our results suggest that ExoS could induce cytotoxicity in BEAS-2B cells by interacting with KIF7.