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Dysfunctional apoptosome activation in ovarian cancer: implications for chemoresistance
J Rebecca Liu1, Anthony W Opipari, Lijun Tan
1Department of Obstetrics and Gynecology, University of Michigan Medical School, L4000 Women's Hospital, 1500 East Medical Center Drive, Ann Arbor, MI 48109, USA. rliu@umich.edu
Abstract:
Alterations in the regulation of apoptosis may contribute to the pathogenesis of cancer and resistance of tumor cells to chemotherapy. In mammalian cells, nonreceptor-mediated apoptosis occurs predominantly via assembly of a cytochrome c-dependent apoptosome complex containing caspase-9 and apoptotic protease-activating factor-1 (Apaf-1). We show here that cytosolic extracts from human ovarian carcinoma cell lines and primary ovarian tumor samples are deficient in their ability to activate procaspase-9 in the presence of cytochrome c and dATP when compared with control extracts. SKOV3, a human ovarian carcinoma cell line with diminished apoptosome activity, was significantly more resistant to chemotherapy-induced apoptosis than cell lines with functional Apaf-1 activity. This dysfunctional apoptosome activity was not explained by reduced expression levels of caspase-9 or Apaf-1. Moreover, expression levels of known inhibitors of the apoptosome, including heat shock protein 70, heat shock protein 90, or X-linked inhibitor of apoptosis, did not correlate with functional activity of the apoptosome. SKOV3, an ovarian cancer cell line with dysfunctional apoptosome activity, retains the ability to form the Apaf-1 oligomer; however, there is a diminished amount of caspase-9 in the apoptosome. The reduction in the amount of caspase-9 in the apoptosome in the SKOV3 cell line was associated with diminished caspase-3 activity. Dysfunctional apoptosome activation may contribute both to the pathogenesis of ovarian carcinoma and to chemoresistance.
Insights
Dysfunctional apoptosome activation, crucial for programmed cell death, is observed in ovarian cancer cells, contributing to chemoresistance. This defect involves reduced caspase-9 incorporation into the apoptosome complex.
Area of Science:
- Cellular Biology
- Molecular Oncology
- Biochemistry
Background:
- Apoptosis regulation is critical in cancer pathogenesis and chemotherapy resistance.
- Nonreceptor-mediated apoptosis involves the cytochrome c-dependent apoptosome complex, including caspase-9 and apoptotic protease-activating factor-1 (Apaf-1).
Purpose of the Study:
- To investigate apoptosome activity in human ovarian carcinoma cell lines and primary tumors.
- To determine the role of apoptosome dysfunction in chemoresistance of ovarian cancer cells.
Main Methods:
- Assessed procaspase-9 activation in cytosolic extracts from ovarian cancer cell lines and tumors.
- Compared chemotherapy-induced apoptosis in ovarian cancer cell lines with functional versus diminished apoptosome activity.
- Analyzed expression levels of caspase-9, Apaf-1, and known apoptosome inhibitors (HSP70, HSP90, XIAP).
- Investigated Apaf-1 oligomerization and caspase-9/caspase-3 activity in SKOV3 cells.
Main Results:
- Cytosolic extracts from ovarian carcinoma samples showed deficient procaspase-9 activation compared to controls.
- SKOV3 cells, exhibiting diminished apoptosome activity, were significantly more resistant to chemotherapy-induced apoptosis.
- Reduced apoptosome activity was not due to lower expression of caspase-9 or Apaf-1, nor correlated with known inhibitor levels.
- SKOV3 cells formed Apaf-1 oligomers but had diminished caspase-9 within the complex, leading to reduced caspase-3 activity.
Conclusions:
- Dysfunctional apoptosome activation, characterized by impaired caspase-9 recruitment, is present in ovarian cancer.
- This defect contributes to the pathogenesis of ovarian carcinoma and confers resistance to chemotherapy.
- Targeting apoptosome function may offer novel therapeutic strategies for ovarian cancer.