Changes in nuclear morphology during apoptosis correlate with vimentin cleavage by different caspases located either upstream or downstream of Bcl-2 action.
BACKGROUND
Upon Fas stimulation, procaspase-8 is recruited to the death-inducing signalling complex where autoactivation of caspase-8 occurs. Active caspase-8 can directly activate downstream caspases (e.g. caspase-3, 6, and 7) for the execution of apoptosis (mitochondria-independent pathway), while caspase-8 can also lead to executioner caspase activation through mitochondrial damage (mitochondria-dependent pathway). Caspase activation results in the dismantling of intracellular structure through specific proteolysis.


RESULTS
We have found that an intermediate filament protein, vimentin, is cleaved at multiple sites by caspases at an early stage of apoptosis in Jurkat cells. The sequences of the two major cleavage sites in vimentin (IDVD/V and DSVD/F) suggested that these sites are cleaved by caspase-8 and caspase-3, respectively, or by close homologues of these proteases. The IDVD/V site can be cleaved by caspase-8 in vitro, and its cleavage is less sensitive to DEVD-CHO and Bcl-2 over-expression than that of the DSVD/F site in Jurkat cells. Over-expression of a mutant vimentin which was insensitive to caspase cleavage at these sites delayed the appearance of apoptotic nuclei in Jurkat cells.


CONCLUSIONS
The specific cleavage of vimentin can be used as an apoptotic marker of both apical- and mitochondria-dependent caspase activation. Apoptotic cleavage of vimentin most likely results in disruption of its filamentous structure, which may facilitate nuclear condensation and subsequent fragmentation through disruption of the cytoskeletal network.
Morishima
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Biodesign Research Group, RIKEN (the Institute of Physical and Chemical Research), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan. morishim@postman.riken.go.jp
D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D019169:Jurkat Cells; D034882:Lamins; D051379:Mice; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014746:Vimentin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019014:fas Receptor / Q000378:metabolism*
D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D034882:Lamins; D009687:Nuclear Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins; D014746:Vimentin; D019014:fas Receptor; D011065:Poly(ADP-ribose) Polymerases; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D002154:Calpain; C505409:Casp3 protein, mouse; C505526:Casp8 protein, mouse; C506434:Casp9 protein, mouse; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases