Bacteriophage-encoded toxins: the lambda-holin protein causes caspase-independent non-apoptotic cell death of eukaryotic cells.
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.
Agu
Chukwuma A
CA
Research Institute of Virology and Biomedicine, University of Veterinary Medicine, Vienna, Austria.
Klein
Reinhard
R
Lengler
Johannes
J
Schilcher
Franz
F
Gregor
Wolfgang
W
Peterbauer
Thomas
T
Bläsi
Udo
U
Salmons
Brian
B
Günzburg
Walter H
WH
Hohenadl
Christine
C
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*
D014764:Viral Proteins; D020169:Caspases