title: Bacteriophage-encoded toxins: the lambda-holin protein causes caspase-independent non-apoptotic cell death of eukaryotic cells.
abstract: The bacteriophage-encoded holin proteins are known to promote bacterial cell lysis by forming lesions within the cytoplasmic membrane. Recently, we have shown that the bacteriophage lambda-holin protein exerts cytotoxic activity also in eukaryotic cells accounting for a reduced tumour growth in vivo. In order to elucidate the mechanisms of lambda-holin-induced mammalian cell death, detailed biochemical and morphological analyses were performed. Colocalization analyses by subcellular fractionation and organelle-specific fluorescence immunocytochemistry indicated the presence of the lambda-holin protein in the endoplasmic reticulum and in mitochondria. Functional studies using the mitochondria-specific fluorochrome JC-1 demonstrated a loss of mitochondrial transmembrane potential in response to lambda-holin expression. Morphologically, these cells exhibited unfragmented nuclei but severe cytoplasmic vacuolization representing signs of oncosis/necrosis rather than apoptosis. Consistently, Western blot analyses indicated neither an activation of effector caspases 3 and 7 nor cleavage of the respective substrate poly(ADP-ribose) polymerase (PARP) in an apoptosis-specific manner. These findings suggest that the lambda-holin protein mediates a caspase-independent non-apoptotic mode of cell death.
authors.affiliation: Research Institute of Virology and Biomedicine, University of Veterinary Medicine, Vienna, Austria.
authors.forename: Chukwuma A
authors.initials: CA
authors.lastname: Agu
authors.forename: Reinhard
authors.initials: R
authors.lastname: Klein
authors.forename: Johannes
authors.initials: J
authors.lastname: Lengler
authors.forename: Franz
authors.initials: F
authors.lastname: Schilcher
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Gregor
authors.forename: Thomas
authors.initials: T
authors.lastname: Peterbauer
authors.forename: Udo
authors.initials: U
authors.lastname: Bläsi
authors.forename: Brian
authors.initials: B
authors.lastname: Salmons
authors.forename: Walter H
authors.initials: WH
authors.lastname: Günzburg
authors.forename: Christine
authors.initials: C
authors.lastname: Hohenadl
mesh_terms: D017209:Apoptosis; D010582:Bacteriophage lambda / Q000378:metabolism / Q000472:pathogenicity*; D020169:Caspases / Q000378:metabolism*; D045744:Cell Line, Tumor / Q000473:pathology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005057:Eukaryotic Cells / Q000473:pathology*; D006367:HeLa Cells / Q000473:pathology; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D009336:Necrosis; D014764:Viral Proteins / Q000378:metabolism / Q000494:pharmacology / Q000633:toxicity*
chemical_list: D014764:Viral Proteins; D020169:Caspases