In situ trapping of activated initiator caspases reveals a role for caspase-2 in heat shock-induced apoptosis

Nat Cell Biol. 2006 Jan;8(1):72-7. doi: 10.1038/ncb1340. Epub 2005 Dec 18.


Activation of 'initiator' (or 'apical') caspases-2, -8 or -9 (refs 1-3) is crucial for induction of apoptosis. These caspases function to activate executioner caspapses that, in turn, orchestrate apoptotic cell death. Here, we show that a cell-permeable, biotinylated pan-caspase inhibitor (bVAD-fmk) both inhibited and 'trapped' the apical caspase activated when apoptosis was triggered. As expected, only caspase-8 was trapped in response to ligation of death receptors, whereas only caspase-9 was trapped in response to a variety of other apoptosis-inducing agents. Caspase-2 was exclusively activated in heat shock-induced apoptosis. This activation of caspase-2 was also observed in cells protected from heat-shock-induced apoptosis by Bcl-2 or Bcl-xL. Reduced sensitivity to heat-shock-induced death was observed in caspase-2(-/-) cells. Furthermore, cells lacking the adapter molecule RAIDD failed to activate caspase-2 after heat shock treatment and showed resistance to apoptosis in this setting. This approach unambiguously identifies the apical caspase activated in response to apoptotic stimuli, and establishes caspase-2 as a proximal mediator of heat shock-induced apoptosis.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adaptor Proteins, Signal Transducing / chemistry
  • Adaptor Proteins, Signal Transducing / genetics
  • Animals
  • Apoptosis* / drug effects
  • CRADD Signaling Adaptor Protein
  • Caspase 2
  • Caspase Inhibitors
  • Caspases / genetics
  • Caspases / metabolism
  • Caspases / physiology*
  • Hot Temperature
  • Humans
  • Jurkat Cells
  • Mice
  • Mice, Inbred BALB C
  • Mice, Inbred C57BL
  • Mice, Mutant Strains
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • bcl-X Protein / metabolism
  • fas Receptor / radiation effects


  • Adaptor Proteins, Signal Transducing
  • CRADD Signaling Adaptor Protein
  • Caspase Inhibitors
  • Cradd protein, mouse
  • Proto-Oncogene Proteins c-bcl-2
  • bcl-X Protein
  • fas Receptor
  • Caspase 2
  • Caspases