Cathepsin D primes caspase-8 activation by multiple intra-chain proteolysis

J Biol Chem. 2012 Jun 15;287(25):21142-51. doi: 10.1074/jbc.M111.306399. Epub 2012 Apr 23.


During the resolution of inflammatory responses, neutrophils rapidly undergo apoptosis. A direct and fast activation of caspase-8 by cathepsin D was shown to be crucial in the initial steps of neutrophil apoptosis. Nevertheless, the activation mechanism of caspase-8 remains unclear. Here, by using site-specific mutants of caspase-8, we show that both cathepsin D-mediated proteolysis and homodimerization of caspase-8 are necessary to generate an active caspase-8. At acidic pH, cathepsin D specifically cleaved caspase-8 but not the initiator caspase-9 or -10 and significantly increased caspase-8 activity in dimerizing conditions. These events were completely abolished by pepstatin A, a pharmacological inhibitor of cathepsin D. The cathepsin D intra-chain proteolysis greatly stabilized the active site of caspase-8. Moreover, the main caspase-8 fragment generated by cathepsin D cleavage could be affinity-labeled with the active site probe biotin-VAD-fluoromethyl ketone, suggesting that this fragment is enzymatically active. Importantly, in an in vitro cell-free assay, the addition of recombinant human caspase-8 protein, pre-cleaved by cathepsin D, was followed by caspase-3 activation. Our data therefore indicate that cathepsin D is able to initiate the caspase cascade by direct activation of caspase-8. As cathepsin D is ubiquitously expressed, this may represent a general mechanism to induce apoptosis in a variety of immune and nonimmune cells.

Publication types

  • Clinical Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis / physiology*
  • Caspase 10 / chemistry
  • Caspase 10 / genetics
  • Caspase 10 / metabolism
  • Caspase 8 / chemistry
  • Caspase 8 / genetics
  • Caspase 8 / metabolism*
  • Caspase 9 / chemistry
  • Caspase 9 / genetics
  • Caspase 9 / metabolism
  • Cathepsin D / chemistry
  • Cathepsin D / genetics
  • Cathepsin D / metabolism*
  • Enzyme Activation / physiology
  • Female
  • Humans
  • Male
  • Neutrophils / cytology
  • Neutrophils / enzymology*
  • Protein Multimerization / physiology*
  • Proteolysis*
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism


  • Recombinant Proteins
  • CASP8 protein, human
  • CASP9 protein, human
  • Caspase 10
  • Caspase 8
  • Caspase 9
  • CASP10 protein, human
  • CTSD protein, human
  • Cathepsin D