Protein kinase C inhibitor and irradiation-induced apoptosis: relevance of the cytochrome c-mediated caspase-9 death pathway.
Caspases are a family of cysteine proteases that constitute the apoptotic cell death machinery. We report the importance of the cytochrome c-mediated caspase-9 death pathway for radiosensitization by the protein kinase C (PKC) inhibitors staurosporine (STP) and PKC-412. In our genetically defined tumor cells, treatment with low doses of STP or the conventional PKC-specific inhibitor PKC-412 in combination with irradiation (5 Gy) potently reduced viability, enhanced mitochondrial cytochrome c release into the cytosol, and specifically stimulated the initiator caspase-9. Whereas treatment with each agent alone had a minimal effect, combined treatment resulted in enhanced caspase-3 activation. This was prevented by broad-range and specific caspase-9 inhibitors and absent in caspase-9-deficient cells. The tumor suppressor p53 was required for apoptosis induction by combined treatment but was dispensable for dose-dependent STP-induced caspase activation. These results demonstrate the requirement for an intact caspase-9 pathway for apoptosis-based radiosensitization by PKC inhibitors and show that STP induces apoptosis independent of p53.
Rocha
S
S
Department of Radiation Oncology, University Hospital Zurich, Switzerland.
Soengas
M S
MS
Lowe
S W
SW
Glanzmann
C
C
Fabbro
D
D
Winterhalter
K
K
Bodis
S
S
Pruschy
M
M
D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology / Q000528:radiation effects*; D053453:Caspase 9; D020169:Caspases / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects*; D003574:Cytochrome c Group / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism / Q000532:radiotherapy; D011493:Protein Kinase C / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011836:Radiation Tolerance / Q000187:drug effects* / Q000502:physiology; D019311:Staurosporine / Q000031:analogs & derivatives* / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism
D003574:Cytochrome c Group; D004791:Enzyme Inhibitors; D016159:Tumor Suppressor Protein p53; D011493:Protein Kinase C; C506433:CASP9 protein, human; D053453:Caspase 9; D020169:Caspases; D019311:Staurosporine; C059539:midostaurin