title: A bacterial RTX toxin causes programmed necrotic cell death through calcium-mediated mitochondrial dysfunction.
abstract: Vibrio vulnificus, a halophilic estuarine bacterium causing fatal septicemia and necrotic wound infection, is highly cytotoxic to eukaryotic cells. We have reported that RtxA1 toxin kills host cells only after they come into contact with bacteria and plays an essential role in the pathogenesis of V. vulnificus. This study was performed to elucidate the mechanism by which the RtxA1 toxin mediates the death of HeLa cells. By using confocal microscopy and immunoblot analysis, we show that the 501-kDa RtxA1 toxin is processed into 2 fragments after its secretion into host cells. The largerN-terminal fragment (RtxA1-N; approximately 370 kDa) remained at the host cell membrane, whereas the smaller C-terminal fragment (RtxA1-C; approximately 130 kDa) was internalized into the host cell cytoplasm. RtxA1-N is believed to polymerize and form pores at the host cell membrane and to induce an increase in necrotic volume related to calcium. The RtxA1 toxin caused an increase in the intracellular Ca(2+) concentration and the subsequent activation of JNK. The cell death mechanism occurred via calcium-dependent mitochondrial pathways, which caused calcium sequestration in the mitochondria, accompanied by irreversible mitochondrial membrane dysfunction and adenosine triphosphate depletion, and was later accompanied by the disruption of the integrity of the plasma membrane.
authors.affiliation: Clinical Vaccine R&D Center, Department of Microbiology, Chonnam National University Medical School, 5 Hak-Dong, Dong-Gu, Gwangju 501–746, Korea.
authors.forename: Young Ran
authors.initials: YR
authors.lastname: Kim
authors.forename: Shee Eun
authors.initials: SE
authors.lastname: Lee
authors.forename: In-Chol
authors.initials: IC
authors.lastname: Kang
authors.forename: Kwang Il
authors.initials: KI
authors.lastname: Nam
authors.forename: Hyon E
authors.initials: HE
authors.lastname: Choy
authors.forename: Joon Haeng
authors.initials: JH
authors.lastname: Rhee
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D017209:Apoptosis; D001427:Bacterial Toxins / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D003603:Cytotoxins / Q000378:metabolism*; D004847:Epithelial Cells / Q000187:drug effects / Q000382:microbiology; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000187:drug effects* / Q000502:physiology; D051336:Mitochondrial Membranes / Q000187:drug effects / Q000502:physiology; D021381:Protein Transport; D041261:Vibrio vulnificus / Q000472:pathogenicity*
chemical_list: D001427:Bacterial Toxins; D003603:Cytotoxins; D000255:Adenosine Triphosphate; D002118:Calcium