Promotion of photodynamic therapy-induced apoptosis by the mitochondrial protein Smac/DIABLO: dependence on Bax.
Photodynamic therapy (PDT) using the second-generation photosensitizer phthalocyanine (Pc) 4 causes mitochondrial damage and induces apoptosis through the release of cytochrome c to the cytosol. Another protein of the mitochondrial intermembrane space, Smac/DIABLO (second mitochondria-derived activator of caspase/direct inhibitor of apoptosis-binding protein with low pI), is also released to the cytosol in response to apoptotic stimuli and promotes caspase activation by binding IAP. To investigate the possible role of Smac/DIABLO in apoptosis induced by Pc 4-PDT, we transfected Smac/DIABLO (tagged at its C-terminus with green fluorescent protein [GFP]) into MCF-7c3 cells (human breast cancer MCF-7 cells stably transfected with procaspase-3) and DU-145 cells (human prostate cancer cells that express no Bax because of a frameshift insertion mutation). Confocal microscopy showed that recombinant Smac/DIABLO, like cytochrome c, localized to mitochondria and colocalized with MitoTracker Red. Three hours after exposure of MCF-7c3 cells to PDT (200 nM Pc 4 and 150 mJ/cm2 red light), Smac/DIABLO-GFP, as well as cytochrome c, was found largely in the cytosol. In contrast, for DU-145 cells, both Smac/DIABLO-GFP and cytochrome c remained in the mitochondria after PDT. By staining with Hoechst 33,342, typical apoptotic nuclei were observed in MCF-7c3 cells, but not in DU-145 cells, after Pc 4-PDT. These results suggest that the release of Smac/DIABLO from mitochondria may be regulated by a Bax-mediated mechanism and that Smac/DIABLO may cooperate with the cytochrome c-dependent apoptosis pathway. In addition, in MCF-7c3 cells transfected by Smac/DIABLO-GFP, apoptosis induced by Pc 4-PDT was greater than in cells transfected with the GFP vector alone or in untransfected cells, as determined by flow cytometry. Thus, Smac/DIABLO promotes apoptosis after Pc 4-PDT in a Bax-dependent manner and may facilitate the passage of PDT-treated cells through the late steps of apoptosis.
Department of Radiation Oncology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-4942, USA.
Jitsuo
J
Usuda
Song-mao
SM
Chiu
Kashif
K
Azizuddin
Liang-yan
LY
Xue
Minh
M
Lam
Anna-Liisa
AL
Nieminen
Nancy L
NL
Oleinick
D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism; D005260:Female; D049452:Green Fluorescent Proteins; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008164:Luminescent Proteins / Q000235:genetics; D008297:Male; D024101:Mitochondrial Proteins / Q000378:metabolism; D018462:Photobiology; D010778:Photochemotherapy; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2; D014162:Transfection; D014407:Tumor Cells, Cultured; D051028:bcl-2-Associated X Protein
D051017:Apoptosis Regulatory Proteins; C494826:BAX protein, human; D002352:Carrier Proteins; D003574:Cytochrome c Group; C412403:DIABLO protein, human; D047908:Intracellular Signaling Peptides and Proteins; D008164:Luminescent Proteins; D024101:Mitochondrial Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D049452:Green Fluorescent Proteins