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Participation of Omi Htra2 Serine-Protease Activity in the Apoptosis Induced by Cisplatin on SW480 Colon Cancer Cells

Abstract Apoptosis is triggered by two interconnected pathways, extrinsic and intrinsic. The intrinsic pathway is activated by genomic stress promoting mitochondrial release of apoptotic proteins. One of these proteins is Omi/Htra2, a serine protease which inactivates Inhibitor of Apoptosis Proteins (IAPs). In the present work, we assessed the participation of Omi/Htra2 in the cell death induced by the chemotherapeutic drugs 5-fluorouracil (5-FU) and cisplatin (CDDP) in SW480 colon cancer cells. CDDP and 5-FU induced apoptosis mediated by the intrinsic pathway in colon cancer cells, as demonstrated by morphological analyses, mitochondrial cytochrome c release and cleavage of caspase 3. Omi/Htra2 was also released from mitochondria of cells exposed to these drugs, as demonstrated by immunofluorescence and western blot assays of subcellular fractions. Exposure of cells to the Omi/Htra2 serine protease inhibitor UCF-101 prevented death p<0.0001 and partially suppressed reproductive cell death of cells exposed to cisplatin p<0.05, but not to 5-FU p=0.49. From these experiments we show that Omi/Htra2 serine protease activity participates in the cell death induced by CDDP but not of 5-FU in colon cancer cells.