Two mechanisms of caspase 9 processing in double-stranded RNA- and virus-triggered apoptosis

M. S. Iordanov, O. P. Ryabinina, P. Schneider, B. E. Magun

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


Viral double-stranded RNA (dsRNA) is a ubiquitous intracellular "alert signal" used by cells to detect viral infection and to mount anti-viral responses. DsRNA triggers a rapid (complete within 2-4 h) apoptosis in the highly-susceptible HeLa cell line. Here, we demonstrate that the apical event in this apoptotic cascade is the activation of procaspase 8. Downstream of caspase 8, the apoptotic signaling cascade bifurcates into a mitochondria-independent caspase 8/caspase 3 arm and a mitochondria-dependent, caspase 8/Bid/Bax/Bak/cytochrome c arm. Both arms impinge upon, and activate, procaspase 9 via two different cleavage sites within the procaspase 9 molecule (D330 and D315, respectively). This is the first in vivo demonstration that the "effector" caspase 3 plays an "initiator" role in the regulation of caspase 9. The dsRNA-induced apoptosis is potentiated by the inhibition of protein synthesis, whose role is to accelerate the execution of all apoptosis steps downstream of, and including, the activation of caspase 8. Thus, efficient apoptosis in response to viral dsRNA results from the co-operation of the two major apical caspases (8 and 9) and the dsRNA-activated protein kinase R (PKR)/ribonuclease L (RNase L) system that is essential for the inhibition of protein synthesis in response to viral infection.

Original languageEnglish (US)
Pages (from-to)153-166
Number of pages14
Issue number1
StatePublished - Jan 2005
Externally publishedYes


  • Apoptosis
  • Caspases
  • Double-stranded RNA
  • Encephalomyocarditis virus

ASJC Scopus subject areas

  • Pharmacology
  • Pharmaceutical Science
  • Clinical Biochemistry
  • Cell Biology
  • Biochemistry, medical
  • Cancer Research


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