title: Different pathways mediate cytochrome c release after photodynamic therapy with hypericin.
abstract: In this study we show that overexpression of Bcl-2 in PC60R1R2 cells reveals a caspase-dependent mechanism of cytochrome c release following photodynamic therapy (PDT) with hypericin. Bcl-2 overexpression remarkably delayed cytochrome c release, procaspase-3 activation and poly(adenosine diphosphate-ribose)polymerase cleavage during PDT-induced apoptosis while it did not protect against PDT-induced necrosis. PDT-treated cells showed a reduction in the mitochondrial membrane potential which occurred with similar kinetics in PC60R1R2 and PC60R1R2/Bcl-2 cells, and was affected neither by the permeability transition pore inhibitor cyclosporin A nor by the caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (zVAD-fmk). Hypericin-induced mitochondrial depolarization coincided with cytochrome c release in PC60R1R2 cells while it precedes massive cytochrome c efflux in PC60R1R2/Bcl-2 cells. Preincubation of PC60R1R2 cells with zVAD-fmk or cyclosporin A did not prevent the mitochondrial efflux of cytochrome c, and caspase inhibition only partially protected the cells from PDT-induced apoptosis. In contrast, in PC60R1R2/Bcl-2 cells cytochrome c release and apoptosis were suppressed by addition of zVAD-fmk or cyclosporin A. These observations suggest that the progression of the PDT-induced apoptotic process in Bcl-2-overexpressing cells involves a caspase-dependent feed-forward amplification loop for the release of cytochrome c.
authors.affiliation: Division of Biochemistry, Faculty of Medicine, KULeuven, Herestraat 49, B-3000 Leuven, Belgium.
authors.forename: A
authors.initials: A
authors.lastname: Vantieghem
authors.forename: Y
authors.initials: Y
authors.lastname: Xu
authors.forename: W
authors.initials: W
authors.lastname: Declercq
authors.forename: P
authors.initials: P
authors.lastname: Vandenabeele
authors.forename: G
authors.initials: G
authors.lastname: Denecker
authors.forename: J R
authors.initials: JR
authors.lastname: Vandenheede
authors.forename: W
authors.initials: W
authors.lastname: Merlevede
authors.forename: P A
authors.initials: PA
authors.lastname: de Witte
authors.forename: P
authors.initials: P
authors.lastname: Agostinis
mesh_terms: D000818:Animals; D000873:Anthracenes; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D002460:Cell Line; D003574:Cytochrome c Group / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D004792:Enzyme Precursors / Q000378:metabolism; D019254:Genes, bcl-2; D006825:Hybridomas; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D010569:Perylene / Q000031:analogs & derivatives* / Q000494:pharmacology*; D010778:Photochemotherapy; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D051381:Rats; D015843:Serpins / Q000235:genetics; D014162:Transfection; D014764:Viral Proteins
chemical_list: D000873:Anthracenes; D003574:Cytochrome c Group; D004792:Enzyme Precursors; D015843:Serpins; D014764:Viral Proteins; D010569:Perylene; C004965:hypericin; C074641:interleukin-1beta-converting enzyme inhibitor; D011065:Poly(ADP-ribose) Polymerases; C505409:Casp3 protein, mouse; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases