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Infection and Immunity, December 2006, p. 6557-6570, Vol. 74, No. 12
0019-9567/06/$08.00+0     doi:10.1128/IAI.00591-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Expression of Pseudomonas aeruginosa Toxin ExoS Effectively Induces Apoptosis in Host Cells{triangledown}

Jinghua Jia,1 Yanping Wang,2 Lei Zhou,1 and Shouguang Jin1*

Department of Molecular Genetics and Microbiology, University of Florida College of Medicine, Gainesville, Florida 32610,1 Tianjin Key Laboratory of Food Nutrition and Safety, Tianjin University of Science and Technology, Tianjin 300222, China2

Received 20 April 2006/ Returned for modification 31 May 2006/ Accepted 4 September 2006

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that primarily infects immunocompromised individuals and patients with cystic fibrosis. Invasive strains of P. aeruginosa are known to induce apoptosis at a high frequency in HeLa cells and in many other cell lines, a process that is dependent on the ADP-ribosylation (ADPRT) activity of a type III secreted protein ExoS. In our previous report, it was proposed that P. aeruginosa secreting ExoS, upon infection, shuts down host cell survival signal pathways by inhibiting ERK1/2 and p38 activation, and it activates proapoptotic pathways through activation of JNK1/2, leading ultimately to cytochrome c release and activation of caspases. In this study, we demonstrate that the expression of ExoS in HeLa cells by eukaryotic expression vector effectively caused apoptosis in an ADPRT activity-dependent manner, indicating that ExoS alone is sufficient to trigger apoptotic death of host cells independent of any other bacterial factors. By expressing an EGFP-ExoS fusion protein, we were able to directly correlate the death of HeLa cells with the presence of intracellular ExoS and further proved the dependence of this process on both JNK activation and mitochondrial proapoptotic event. The cellular pathway responsible for the ExoS-induced cytotoxicity appears to be well conserved, since the expression of the ADPRT-competent ExoS also induced rapid cell death in the Drosophila melanogaster S2 cell lines. The presented study not only highlights the ability of ExoS ADPRT to modulate host cell signaling, eventually leading to apoptosis, but also establishes ExoS as a valuable tool, in principle, for the elucidation of apoptosis mechanisms.

* Corresponding author. Mailing address: Department of Molecular Genetics and Microbiology, P.O. Box 100266, University of Florida, Gainesville, FL 32610. Phone: (352) 392-8323. Fax: (352) 392-3133. E-mail: sjin{at}mgm.ufl.edu.

{triangledown} Published ahead of print on 11 September 2006.

Editor: J. B. Bliska

Infection and Immunity, December 2006, p. 6557-6570, Vol. 74, No. 12
0019-9567/06/$08.00+0     doi:10.1128/IAI.00591-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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