title: Vibrio cholerae Porin OmpU Induces Caspase-independent Programmed Cell Death upon Translocation to the Host Cell Mitochondria.
abstract: Porins, a major class of outer membrane proteins in Gram-negative bacteria, primarily act as transport channels. OmpU is one of the major porins of human pathogen, Vibrio cholerae. In the present study, we show that V. cholerae OmpU has the ability to induce target cell death. Although OmpU-mediated cell death shows some characteristics of apoptosis, such as flipping of phosphatidylserine in the membrane as well as cell size shrinkage and increased cell granularity, it does not show the caspase-3 activation and DNA laddering pattern typical of apoptotic cells. Increased release of lactate dehydrogenase in OmpU-treated cells indicates that the OmpU-mediated cell death also has characteristics of necrosis. Further, we show that the mechanism of OmpU-mediated cell death involves major mitochondrial changes in the target cells. We observe that OmpU treatment leads to the disruption of mitochondrial membrane potential, resulting in the release of cytochrome c and apoptosis-inducing factor (AIF). AIF translocates to the host cell nucleus, implying that it has a crucial role in OmpU-mediated cell death. Finally, we observe that OmpU translocates to the target cell mitochondria, where it directly initiates mitochondrial changes leading to mitochondrial membrane permeability transition and AIF release. Partial blocking of AIF release by cyclosporine A in OmpU-treated cells further suggests that OmpU may be inducing the opening of the mitochondrial permeability transition pore. All of these results lead us to the conclusion that OmpU induces cell death in target cells in a programmed manner in which mitochondria play a central role.
authors.affiliation: From the Department of Biological Sciences, Indian Institute of Science Education and Research Mohali, Knowledge City, Sector 81, SAS Nagar, Mohali 140306, Punjab, India.
authors.forename: Shelly
authors.initials: S
authors.lastname: Gupta
authors.affiliation: From the Department of Biological Sciences, Indian Institute of Science Education and Research Mohali, Knowledge City, Sector 81, SAS Nagar, Mohali 140306, Punjab, India.
authors.forename: G V R Krishna
authors.initials: GV
authors.lastname: Prasad
authors.affiliation: From the Department of Biological Sciences, Indian Institute of Science Education and Research Mohali, Knowledge City, Sector 81, SAS Nagar, Mohali 140306, Punjab, India arunika@iisermohali.ac.in.
authors.forename: Arunika
authors.initials: A
authors.lastname: Mukhopadhaya
mesh_terms: D018829:Adhesins, Bacterial / Q000378:metabolism*; D017209:Apoptosis / Q000187:drug effects*; D051033:Apoptosis Inducing Factor / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism*; D045744:Cell Line, Tumor; D002771:Cholera / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology; D006801:Humans; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins / Q000378:metabolism; D051336:Mitochondrial Membranes / Q000378:metabolism*; D000083162:Mitochondrial Permeability Transition Pore; D014734:Vibrio cholerae / Q000378:metabolism* / Q000472:pathogenicity
chemical_list: C494829:AIFM1 protein, human; D018829:Adhesins, Bacterial; D051033:Apoptosis Inducing Factor; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; C096349:OmpU protein, Vibrio cholerae; D016572:Cyclosporine; C505407:CASP3 protein, human; D053148:Caspase 3
keywords: OmpU; Vibrio cholerae; bacterial pathogenesis; cell death; mitochondria; porin; programmed cell death; virulence factor