In this study, we examine the sensitivity of a panel of ovarian carcinoma cells, which includes four primary ovarian cancer cell samples, and four normal ovarian epithelium samples to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). We also examine the intracellular regulation of TRAIL-mediated apoptosis.
The sensitivity to TRAIL was determined by short-term survival assays on seven ovarian carcinoma cell lines, four primary samples of ovarian cancer, and four normal ovarian epithelium samples. We assessed the activation of the apoptotic pathway in TRAIL-resistant and -sensitive tumor cells. The expression of TRAIL receptors was determined by flow cytometry. The protein expression of FADD, XIAP, caspase-8, caspase-3, BAX, and c-FLIP were determined by immunoblot analyses.
We show that ovarian cancer cells display variable sensitivity to TRAIL-induced apoptosis although most cell lines have similar sensitivity to cisplatin. Normal ovarian epithelium samples were mostly sensitive to TRAIL. In sensitive cells, TRAIL induced caspase-8-dependent apoptosis, which subsequently led to activation of caspase-3. Both sensitive and resistant cells expressed caspase-8, caspase-3, FADD, XIAP, and c-FLIP at similar levels. A significant enhancement in cell death was observed in TRAIL-resistant cells when c-FLIP(L) levels were downregulated by RNA interference.
These data suggest that sensitivity to TRAIL and chemotherapy does not necessarily correlate in human ovarian cancer cells. Cancerous cells isolated from patients with ovarian cancer show variable sensitivity to TRAIL but most normal ovarian epithelial cells are sensitive. In human ovarian cancer cells, c-FLIP(L) may participate to the regulation of the TRAIL signaling cascade.