Pro-caspase-3 overexpression sensitises ovarian cancer cells to proteasomeinhibitors

The ubiquitin-proteasome pathway plays a critical role in the degradation o f several proteins involved in the cell cycle. Dysregulation of this pathwa y leads to inhibition of cellular proliferation and the induction of apopto sis. Ubiquitination and its downstream consequences have been investigated intensively as targets for the development of drugs for tumour therapy. Her e we have investigated the mechanism of apoptosis induced by the proteasome inhibitors MG-132, lactacystin and calpain inhibitor I (ALLN), in the HEK 293 cell line and the ovarian cancer cell lines SKOV3 and OVCAR3, We have f ound strong caspase-3-like and caspase-6-like activation upon treatment of HEK 293 cells with MG-132. Using a tricistronic expression vector based on a tetracycline-responsive system we generated stable SKOV3 nd OVCAR3 cell l ines with inducible expression of pro-caspase-3, Induction of pro-caspase-3 expression in normally growing cells does not induce apoptosis, However, i n the presence of the proteasome inhibitors MG-132, lactacystin or ALLN we found that cells overexpressing pro-caspase-3 are rapidly targeted for apop tosis, Our results demonstrate that procaspase-3 can sensitise ovarian canc er cells to proteasome inhibitor-induced apoptosis, and a combination of th ese approaches might be exploited for therapy of ovarian and other cancers.