Tunicamycin enhances the apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand in endometriotic stromal cells

The increase in concentration of osteoprotegerin, an antagonist of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), in the peritoneal fluid of women with endometriosis may interfere with TRAIL-induced apoptosis in endometriotic cells and promote the development of endometriosis. In the present study, the effect of tunicamycin, a possible apoptosis enhancer, on TRAIL-induced apoptosis in endometriotic stromal cells (ESC) was determined. ESC were isolated from cyst walls of ovarian endometrioma and cultured. ESC were incubated with or without tunicamycin (2 mu g/ml) for the first 16 h, and then incubated with or without TRAIL (200 ng/ml) for the following 24 h. To examine whether caspases were involved in TRAIL-induced apoptosis, z-VAD-fmk (30 mu M), a general caspase inhibitor, was added 1 h before TRAIL treatment. ESC were transfected with small interfering RNA (siRNA) for DR5, a receptor of TRAIL, before tunicamycin treatment to evaluate its role in ESC. DR5 mRNA level was determined by quantitative RT-PCR. Apoptosis in ESC was evaluated by flow cytometry. Tunicamycin increases both DR5 mRNA (P < 0.005) and TRAIL-induced apoptosis (P < 0.0001) in ESC. The increase in TRAIL-induced apoptosis in ESC by tunicamycin was suppressed (P < 0.05) by z-VAD-fmk. Transfection with DR5 siRNA suppressed the tunicamycin-induced increase in DR5 mRNA and abrogated the up-regulation of TRAIL-induced apoptosis by tunicamycin. The combined treatment with tunicamycin and TRAIL may have therapeutic potential in the treatment of endometriosis.