Molecular determinants of apoptosis induced by the cytotoxic ribonuclease onconase: Evidence for cytotoxic mechanisms different from inhibition of protein synthesis

Mihail S. Iordanov, Olga P. Ryabinina, John Wong, Thanh Hoai Dinh, Dianne L. Newton, Susanna M. Rybak, Bruce E. Magun

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Abstract

Cytotoxic endoribonucleases (RNases) possess a potential for use in cancer therapy. However, the molecular determinants of Rnase-induced cell death are not well understood. In this work, we identify such determinants of the cytotoxicity induced by onconase, an amphibian cytotoxic Rnase. Onconase displayed a remarkable specificity for tRNA in vivo, leaving rRNA and MRNA apparently undamaged. Onconase-treated cells displayed apoptosis-associated cell blebbing, nuclear pyknosis and fragmentation (karyorrhexis), DNA fragmentation, and activation of caspase-3-like activity. The cytotoxic action of onconase correlated with inhibition of protein synthesis; however, we present evidence for the existence of a mechanism of onconase-induced apoptosis that is independent of inhibition of protein synthesis. The caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(OMe) fluoromethyl ketone (zVADfmk), at concentrations that completely prevent apoptosis and caspase activation induced by ligation of the death receptor Fas, had only a partial protective effect on onconase-induced cell death. The proapoptotic activity of the p53 tumor suppressor protein and the Fas ligand/Fas/Fas-associating protein with death domain (FADD)/caspase-8 proapoptotic cascade were not required for onconase-induced apoptosis. Procaspases-9, -3, and -7 were processed in onconase-treated cells, suggesting the involvement of the mitochondrial apoptotic machinery in onconase-induced apoptosis. However, the onconase- induced activation of the caspase-9/caspase-3 cascade correlated with atypically little release of cytochrome c from mitochondria. In turn, the low levels of cytochrome c released from mitochondria correlated with a lack of detectable translocation of proapoptotic Bax from the cytosol onto mitochondria in response to onconase. This suggests the possibility of involvement of a different, potentially Bax- and cytochrome c-independent mechanism of caspase-9 activation in onconase-treated cells. As one possible mechanism, we demonstrate that procaspase-9 is released from mitochondria in onconase-treated cells. A detailed understanding of the molecular determinants of the cytotoxic action of onconase could provide means of positive or negative therapeutic modulation of the activity of this potent anticancer agent.

Original languageEnglish (US)
Pages (from-to)1983-1994
Number of pages12
JournalCancer Research
Volume60
Issue number7
StatePublished - Apr 1 2000

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Ribonucleases
Apoptosis
Proteins
Caspase 9
Mitochondria
Cytochromes c
Caspase 3
ranpirnase
Cell Death
Fas-Associated Death Domain Protein
Endoribonucleases
Tumor Suppressor Protein p53
Death Domain Receptors
Fas Ligand Protein
Caspase Inhibitors
Caspase 8
Amphibians
DNA Fragmentation
Blister
Caspases

ASJC Scopus subject areas

  • Cancer Research
  • Oncology

Cite this

Iordanov, M. S., Ryabinina, O. P., Wong, J., Dinh, T. H., Newton, D. L., Rybak, S. M., & Magun, B. E. (2000). Molecular determinants of apoptosis induced by the cytotoxic ribonuclease onconase: Evidence for cytotoxic mechanisms different from inhibition of protein synthesis. Cancer Research, 60(7), 1983-1994.

Molecular determinants of apoptosis induced by the cytotoxic ribonuclease onconase : Evidence for cytotoxic mechanisms different from inhibition of protein synthesis. / Iordanov, Mihail S.; Ryabinina, Olga P.; Wong, John; Dinh, Thanh Hoai; Newton, Dianne L.; Rybak, Susanna M.; Magun, Bruce E.

In: Cancer Research, Vol. 60, No. 7, 01.04.2000, p. 1983-1994.

Research output: Contribution to journalArticle

Iordanov, MS, Ryabinina, OP, Wong, J, Dinh, TH, Newton, DL, Rybak, SM & Magun, BE 2000, 'Molecular determinants of apoptosis induced by the cytotoxic ribonuclease onconase: Evidence for cytotoxic mechanisms different from inhibition of protein synthesis', Cancer Research, vol. 60, no. 7, pp. 1983-1994.
Iordanov, Mihail S. ; Ryabinina, Olga P. ; Wong, John ; Dinh, Thanh Hoai ; Newton, Dianne L. ; Rybak, Susanna M. ; Magun, Bruce E. / Molecular determinants of apoptosis induced by the cytotoxic ribonuclease onconase : Evidence for cytotoxic mechanisms different from inhibition of protein synthesis. In: Cancer Research. 2000 ; Vol. 60, No. 7. pp. 1983-1994.
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