Defective cytochrome c-dependent caspase activation in ovarian cancer celllines due to diminished or absent apoptotic protease activating factor-1 activity

Apoptosis via the mitochondrial pathway requires release of cytochrome c in to the cytosol to initiate formation of an oligomeric apoptotic protease-ac tivating factor-1 (APAF-1) apoptosome. The apoptosome recruits and activate s caspase-9, which in turn activates caspase-3 and -7, which then kill the cell by proteolysis. Because inactivation of this pathway may promote oncog enesis, we examined 10 ovarian cancer cell lines for resistance to cytochro me c-dependent caspase activation using a cell-free system. Strikingly, we found that cytosolic extracts from all cell lines had diminished cytochrome c-dependent caspase activation compared with normal ovarian epithelium ext racts. The resistant cell lines expressed APAF-1 and caspase-9, -3, and -7; however, each demonstrated diminished APAF-1 activity relative to the norm al ovarian epithelium cell lines. A competitive APAF-1 inhibitor may accoun t for the diminished APAF-1 activity because we did not detect dominant APA F-1 inhibitors, altered APAF-1 isoform expression, or APAF-1 deletion, degr adation, or mutation. Lack of APAF-1 activity correlated in some but not al l cell lines with resistance to apoptosis. These data suggest that regulati on of APAF-1 activity may be important for apoptosis regulation in some ova rian cancers.