title: Involvement of both caspase-dependent and -independent pathways in apoptotic induction by hexaminolevulinate-mediated photodynamic therapy in human lymphoma cells.
abstract: Photodynamic therapy (PDT) is a cancer treatment based on the interaction of a photosensitizer, light and oxygen. PDT with the endogenous photosensitizer, protoporphyrin IX (PpIX) induced by 5-aminolevulinic acid (ALA) or its derivatives is a modification of this treatment modality with successful application in dermatology. However, the mechanism of cell destruction by ALA-PDT has not been elucidated. In this study a human T-cell lymphoma Jurkat cell line was treated with PDT using hexaminolevulinate (HAL, hexylester of ALA). Four hours following treatment nearly 80% of the cells exhibited typical apoptotic features. Mitochondrial pro-apoptotic proteins were evaluated by Western blots in subcellular fractionated samples. PDT caused cytosolic translocation of cytochrome c and nuclear redistribution of apoptosis-inducing factor (AIF), but the release of mitochondrial Smac/DIABLO, Omi/HtrA2 and EndoG was not observed. The release of cytochrome c was followed by the cleavage of caspase-9 and caspase-3 as well as its downstream substrates, together with oligonucleosomal DNA fragmentation. The pan-caspases inhibitor, z-VAD.fmk, prevented oligonucleosomal DNA fragmentation, but failed to inhibit PDT-mediated apoptosis. The apoptotic induction by AIF-mediated caspase-independent pathway was also found after HAL-PDT with large-scale DNA fragmentation in the presence of z-VAD.fmk. These results demonstrate that cytochrome c-mediated caspase-dependent pathway and AIF-induced caspase-independent pathway are simultaneously involved in the apoptotic induction by PDT. When the cytochrome c-induced caspase-dependent pathway is blocked, the cells go into apoptosis via AIF-mediated pathway, clearly demonstrating that the cytochrome c-mediated caspase-dependent pathway is not required for such apoptotic induction. This finding may have an impact on improved PDT effectiveness.
authors.affiliation: Pathology Clinic, Rikshospitalet-Radiumhospitalet HF Medical Center, Faculty Division Radiumhospitalet, University of Oslo, Norway.
authors.forename: Ingegerd Eggen
authors.initials: IE
authors.lastname: Furre
authors.forename: Michael T N
authors.initials: MT
authors.lastname: Møller
authors.forename: Susan
authors.initials: S
authors.lastname: Shahzidi
authors.forename: Jahn M
authors.initials: JM
authors.lastname: Nesland
authors.forename: Qian
authors.initials: Q
authors.lastname: Peng
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000622:Aminolevulinic Acid / Q000031:analogs & derivatives* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects*; D051033:Apoptosis Inducing Factor / Q000378:metabolism; D020169:Caspases / Q000378:metabolism*; D045304:Cytochromes c / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D019169:Jurkat Cells; D015458:Leukemia, T-Cell / Q000188:drug therapy*; D053078:Membrane Potential, Mitochondrial; D008928:Mitochondria / Q000378:metabolism; D010778:Photochemotherapy; D011524:Protoporphyrins / Q000378:metabolism
chemical_list: C494829:AIFM1 protein, human; D000590:Amino Acid Chloromethyl Ketones; D051033:Apoptosis Inducing Factor; D004791:Enzyme Inhibitors; D011524:Protoporphyrins; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D000622:Aminolevulinic Acid; D045304:Cytochromes c; C028025:protoporphyrin IX; D020169:Caspases; C419924:5-aminolevulinic acid hexyl ester