Title: Induction and molecular effectors of autophagy and apoptosis in ER-damaged cells after photodynamic therapy
Authors: Dewaele, Michael
Buytaert, Esther
Van Kelst, Sofie
de Witte, Peter
Martinet, Wim
Agostinis, Patrizia #
Issue Date: 2008
Conference: Oncoforum location:Leuven, Belgium date:15 February
Abstract: Induction and molecular effectors of autophagy and apoptosis in ER-damaged cells after photodynamic therapy

Michael Dewaele1, Esther Buytaert1, Sofie Van Kelst1, Peter de Witte1, Wim Martinet2,
and Patrizia Agostinis1

1Dept. Molecular Cell Biology, Faculty of Medicine, Catholic University of Leuven, Belgium 2Division of Pharmacology, University of Antwerp, Belgium.

Photodynamic therapy (PDT) is an anticancer therapy utilizing cytotoxic reactive oxygen species (ROS) produced after irradiation of a photosensitizer with visible light, to kill the cancer cells1. Light activation of the ER-associated photosensitizer hypericin causes an immediate photooxidative damage to the sarco(endo)plasmic Ca2+-ATPase (SERCA) pump, due to the local generation of 1O2. This event results in the rapid loss of ER Ca2+ homeostasis which leads to ER-stress and subsequent cell death, through the induction of both caspase-dependent (apoptotic cell death) and –independent (autophagic cell death) pathways. Previous investigation in murine embryonic fibroblasts (MEFs) lacking both Bax and Bak (DKO) two pro-apoptotic Bcl-2 proteins that are essential for apoptosis induction in this ER stress paradigm, has implicated autophagic cell death as a major caspase-independent subroutine to cell death after PDT2. However, the exact role of autophagy in apoptosis-competent cells as well as the cross-communication between apoptosis and autophagy remained largely unclear.
In this study we show that in apoptosis-competent cells, such as in the human HeLa cancer cells or in the rat bladder cancer AY27 cells, the induction of apoptotic cell death occurs concomitantly with the onset of autophagy, suggesting that both pathways are simultaneously propagated in response to PDT-mediated ER stress. However, both the intensity and kinetics of the autophagic process are enhanced in the absence of caspase signalling, either caused by Bax/Bak or Apaf-1 genetic deficiency in MEFs or by pharmacological inhibition of caspases in cancer cells. Under conditions of caspase inhibition photosensitized cells are fated to die with the phenotypic manifestations of autophagy. To study the role of autophagy in apoptosis-competent cells we used MEFs in which the expression of the essential atg-gene Atg5, can be completely suppressed by the presence of doxycycline which render these cells autophagy-defective. Interestingly, the doxycycline-mediated knock-down of Atg5, does not only inhibit autophagy but also hampers the release of cytochrome c, caspase-activation and subsequent apoptosis in response to PDT.
These data point at a complex level of cross-communication between apoptosis and autophagy in PDT treated cells and indicate that key autophagy genes have a potential role in propagating apoptosis. We are currently elucidating the role of other other Atg-genes, like Beclin1, in vitro and the in vivo effect of Atg5 deficiency in tumor-bearing mice after PDT.

1Dolmans et al, (2003) Nat Rev Cancer 3:380-7
2Buytaert et al, (2006) FASEB J. 20:756-8
Publication status: accepted
KU Leuven publication type: AMa
Appears in Collections:Laboratory of Cell Death Research & Therapy
Laboratory of Dermatology
Laboratory for Pharmaceutical Biology (-)
Laboratory for Molecular Cancer Biology
# (joint) last author

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