Bax is essential for mitochondrion-mediated apoptosis but not for cell death caused by photodynamic therapy.
The role of Bax in the release of cytochrome c from mitochondria and the induction of apoptosis has been demonstrated in many systems. Using immunocytochemical staining, we observed that photodynamic therapy (PDT) with the photosensitiser Pc 4 induced Bax translocation from the cytosol to mitochondria, and the release of cytochrome c from mitochondria as early signalling for the intrinsic pathway of apoptosis in human breast cancer MCF-7c3 cells. To test the role of Bax in apoptosis, MCF-7c3 cells were treated with Bax antisense oligonucleotides, which resulted in as much as a 50% inhibition of PDT-induced apoptosis. In the second approach, Bax-negative human prostate cancer DU-145 cells were studied. Following PDT, the hallmarks of apoptosis, including the release of cytochrome c from mitochondria, loss of mitochondrial membrane potential, caspase activation, and chromatin condensation and fragmentation, were completely blocked in these cells. Restoration of Bax expression in DU-145 cells restored apoptosis, indicating that the resistance of DU-145 cells to PDT-induced apoptosis is due to the lack of Bax rather than to another defect in the apoptotic machinery. However, despite the inhibition of apoptosis, the Bax-negative DU-145 cells were as photosensitive as Bax-replete MCF-7c3 cells, as determined by clonogenic assay. Thus, for Pc 4-PDT, the commitment to cell death occurs prior to Bax activation.
Chiu
S-M
SM
Department of Radiation Oncology and The CWRU/Ireland Comprehensive Cancer Center, School of Medicine (BRB-324), Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-4942, USA.
Xue
L-Y
LY
Usuda
J
J
Azizuddin
K
K
Oleinick
N L
NL
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000473:pathology*; D016923:Cell Death / Q000187:drug effects*; D045304:Cytochromes c / Q000378:metabolism*; D005260:Female; D007150:Immunohistochemistry; D007211:Indoles / Q000494:pharmacology; D008297:Male; D008928:Mitochondria / Q000502:physiology*; D010778:Photochemotherapy; D011471:Prostatic Neoplasms / Q000473:pathology*; D011518:Proto-Oncogene Proteins / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2; D014407:Tumor Cells, Cultured; D051028:bcl-2-Associated X Protein
D007211:Indoles; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; C107448:phthalocyanine Pc 4; D045304:Cytochromes c