Role of endoplasmic reticulum depletion and multidomain proapoptotic BAX and BAK proteins in shaping cell death after hypericin-mediated photodynamic therapy.
Both the commitment event and the modality of cell death in photodynamic therapy (PDT) remain poorly defined. We report that PDT with endoplasmic reticulum (ER)-associating hypericin leads to an immediate loss of SERCA2 protein levels, causing disruption of Ca2+ homeostasis and cell death. Protection of SERCA2 protein rescues ER-Ca2+ levels and prevents cell death, suggesting that SERCA2 photodestruction with consequent incapability of the ER to maintain intracellular Ca2+ homeostasis is causal to cell killing. Apoptosis is rapidly initiated after ER-Ca2+ depletion and strictly requires the BAX/BAK gateway at the mitochondria. Bax-/-Bak-/- double-knockout (DKO) cells are protected from apoptosis but undergo autophagy-associated cell death as revealed by electron microscopy and biochemical analysis. Autophagy inhibitors, but not caspase antagonists, significantly reduce death of DKO cells, suggesting that sustained autophagy is lethal. Thus, following ER photodamage and consequent disruption of Ca2+ homeostasis, BAX and BAK proteins model PDT-mediated cell killing, which is executed through apoptosis in their presence or via an autophagic pathway in their absence.
Buytaert
Esther
E
Department of Molecular and Cell Biology, Faculty of Medicine, Catholic University of Leuven, Leuven, Belgium.
Callewaert
Geert
G
Hendrickx
Nico
N
Scorrano
Luca
L
Hartmann
Dieter
D
Missiaen
Ludwig
L
Vandenheede
Jackie R
JR
Heirman
Ingeborg
I
Grooten
Johan
J
Agostinis
Patrizia
P
D000818:Animals; D000873:Anthracenes; D017209:Apoptosis / Q000187:drug effects*; D001343:Autophagy / Q000187:drug effects / Q000528:radiation effects; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D005347:Fibroblasts / Q000378:metabolism; D017353:Gene Deletion; D006801:Humans; D051379:Mice; D010569:Perylene / Q000031:analogs & derivatives* / Q000494:pharmacology; D010778:Photochemotherapy; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000235:genetics / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism*
D000873:Anthracenes; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D010569:Perylene; C004965:hypericin; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; C506946:ATP2A2 protein, human; C506947:Atp2a2 protein, mouse; D000252:Calcium-Transporting ATPases; D002118:Calcium