Caspase-1α is down-regulated in human ovarian cancer cells and the overexpression of caspase-1α induces apoptosis

Caspase-1 plays a key role in the processing of cytokines and in the apoptosis of neurons and macrophages. Whether it also causes apoptosis of cancer cells has been unclear. In this study, we screened an array of apoptosis-related proteins in ovarian carcinoma cell lines and their tissue of origin, ovarian surface epithelium (OSE). Caspase-1 alpha protein was abundant in OSE and in nontumorigenic OSE with extended but limited life spans (immortalized OSE), but was reduced in the cancer lines A2780 and OVCARIO. By Western blot and immunofluorescence, caspase-1 alpha levels were greatly reduced in six of eight ovarian carcinoma lines compared with OSE. By realtime reverse transcription-PCR, steady-state transcripts of the CASP1 gene were proportional to protein levels. Caspase1 alpha overexpression caused significant apoptosis, but overexpression of a caspase-1 alpha mutant without catalytic activity did not, confirming that the effect was caspase-1 alpha-specific. Immunofluorescence of caspase-1 alpha and terminal nucleotidyl transferase-mediated dUTP-X nick end labeling colocalization clearly established a link between apoptosis and caspaselot expression. Caspase-9 and caspase-3 were activated in caspase-lot overexpressing A2780 cells, suggesting involvement of an intrinsic apoptotic pathway. Caspase-1 alpha overexpression did not change the apoptotic effect of cisplatin in A2780 and OVCARIO cells, suggesting that this agent activates a different pathway. Inummohistochernically, caspase-1 was lower in ovarian serous carcinomas than in OSE. Our study indicates, for the first time, that caspase-1 alpha is proapoptotic in ovarian cancer cells, and raises the possibility that its downregulation is one of the mechanisms which increase resistance to apoptosis in cancer cells.