ExoS of Pseudomonas aeruginosa induces apoptosis through a Fas receptor/caspase 8-independent pathway in HeLa cells.
Pseudomonas aeruginosa infection is a serious complication in immunocompromised individuals and in patients with cystic fibrosis. We have previously shown that the type III secreted effector ExoS triggers apoptosis in various cultured cell lines via its ADP-ribosyltransferase (ADPRT) activity. The apoptosis process was further shown to involve intrinsic signalling pathway requiring c-Jun N-terminal kinase (JNK)-initiated mitochondrial pathway. In the present study, we investigated the role of Fas pathway activation in P. aeruginosa-induced apoptosis. P. aeruginosa infection resulted in caspase 8 cleavage in HeLa cells, which was inhibited by overexpression of a dominant negative version of Fas-associated death domain (FADD), suggesting that Fas pathway was activated. In fact, confocal laser scanning microscopy showed that P. aeruginosa induced clustering of FasR. In addition, the ADPRT activity of the ExoS was required for the induction of FasR clustering and caspase 8 cleavage. However, blocking the FasR-FasL interaction by antagonistic antibodies to FasR or to FasL had no effect on P. aeruginosa-induced caspase 8 and caspase 3 activation, neither did the silencing of FasR by small interfering RNA (siRNA), suggesting that caspase 8 activation through the FADD bypasses FasR/FasL-mediated signalling. Thus, FADD-mediated caspase 8 activation involves intracellular ExoS in an ADPRT-dependent manner. Furthermore, silencing of caspase 8 by siRNA did not interfere with P. aeruginosa-induced apoptosis, whereas it rendered HeLa cells markedly increased resistance towards FasL-induced apoptosis. In conclusion, our findings indicate that ExoS of P. aeruginosa induces apoptosis through a mechanism that is independent of Fas receptor/caspase 8 pathway.
Alaoui-El-Azher
Mounia
M
Department of Molecular Genetics and Microbiology, University of Florida College of Medicine, Gainesville, FL 32610, USA.
Jia
Jinghua
J
Lian
Wei
W
Jin
Shouguang
S
D036002:ADP Ribose Transferases / Q000502:physiology*; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000906:Antibodies / Q000378:metabolism; D017209:Apoptosis; D001427:Bacterial Toxins; D053181:Caspase 8; D020169:Caspases / Q000235:genetics / Q000502:physiology*; D053222:Fas Ligand Protein; D053200:Fas-Associated Death Domain Protein; D006367:HeLa Cells; D006801:Humans; D008562:Membrane Glycoproteins / Q000276:immunology / Q000378:metabolism; D018613:Microscopy, Confocal; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011550:Pseudomonas aeruginosa / Q000502:physiology*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D048069:Tumor Necrosis Factors / Q000276:immunology / Q000378:metabolism; D019014:fas Receptor / Q000235:genetics / Q000276:immunology / Q000502:physiology*
D048868:Adaptor Proteins, Signal Transducing; D000906:Antibodies; D001427:Bacterial Toxins; C505533:FADD protein, human; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D053200:Fas-Associated Death Domain Protein; D008562:Membrane Glycoproteins; D034741:RNA, Small Interfering; D048069:Tumor Necrosis Factors; D019014:fas Receptor; D036002:ADP Ribose Transferases; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; C444820:exoenzyme S; C505530:CASP8 protein, human; D053181:Caspase 8; D020169:Caspases