Different pathways mediate cytochrome c release after photodynamic therapy with hypericin
A Vantieghem1, Y Xu, W Declercq
1Division of Biochemistry, Faculty of Medicine, KULeuven, Herestraat 49, B-3000 Leuven, Belgium.
Photochemistry and Photobiology
|September 8, 2001
Summary
Overexpression of Bcl-2 delays cytochrome c release during photodynamic therapy (PDT)-induced apoptosis. This suggests a caspase-dependent amplification loop for cytochrome c release in Bcl-2-overexpressing cells.
Area of Science:
- Cell Biology
- Biochemistry
- Oncology
Background:
- Photodynamic therapy (PDT) induces apoptosis via various cellular mechanisms.
- Bcl-2 is a key regulator of apoptosis, often overexpressed in cancer cells.
- Understanding the role of Bcl-2 in PDT response is crucial for cancer treatment strategies.
Purpose of the Study:
- To investigate the mechanism of cytochrome c release during hypericin-induced PDT in cells overexpressing Bcl-2.
- To elucidate the role of caspases and mitochondrial membrane potential in PDT-induced apoptosis in the presence of Bcl-2.
- To determine if Bcl-2 overexpression alters the kinetics or pathways of apoptosis induction.
Main Methods:
- Utilized PC60R1R2 and PC60R1R2/Bcl-2 cell lines.
- Administered hypericin-based photodynamic therapy (PDT).
- Assessed cytochrome c release, procaspase-3 activation, poly(ADP-ribose)polymerase cleavage, and mitochondrial membrane potential.
- Employed caspase inhibitors (zVAD-fmk) and permeability transition pore inhibitors (cyclosporin A).
Main Results:
- Bcl-2 overexpression significantly delayed cytochrome c release, procaspase-3 activation, and PARP cleavage during PDT-induced apoptosis.
- Bcl-2 did not protect against PDT-induced necrosis.
- Mitochondrial membrane potential reduction occurred similarly in both cell types and was unaffected by inhibitors.
- Caspase inhibition partially protected cells from apoptosis in non-Bcl-2 overexpressing cells, but suppressed cytochrome c release and apoptosis in Bcl-2 overexpressing cells.
Conclusions:
- Bcl-2 overexpression reveals a caspase-dependent mechanism for cytochrome c release in PDT.
- A caspase-dependent feed-forward amplification loop for cytochrome c release is implicated in PDT-induced apoptosis in Bcl-2-overexpressing cells.
- The findings highlight distinct apoptotic pathways modulated by Bcl-2 during PDT.
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