CRK and infection: We therefore propose that during infection of NCI-H292 cells by P. aeruginosa, two mechanisms occur: Firstly, the ADPRT activity of ExoT limits the production of phosphorylated CrkII by preventing the interaction between CrkII and Abl74,88, and secondly, the phosphatase activity of PTP1B further reduces the level of previously phosphorylated CrkII.