Caspase-10 involvement in cytotoxic drug-induced apoptosis of tumor cells.

Anticancer drugs can induce tumor cell death by caspase-dependent apoptosis. The observation that procaspase-10 expression decreased in leukemic cells from acute myeloblastic leukemia patients at first relapse led us to explore the role of caspase-10 in cytotoxic drug-induced apoptosis. We show that caspase-10 is activated in etoposide-treated cells in a dose- and time-dependent manner. A caspase-10 peptide inhibitor, a caspase-10 dominant-negative mutant or a small interfering RNA (siRNA)-mediated downregulation of the enzyme negatively interfere with drug-induced cell death and caspase-2, -3, -8 and -9 activation. The extrinsic pathway to apoptosis is not involved in drug-induced caspase-10 activation that occurs downstream of Bax redistribution to mitochondria and cytochrome c release from this organelle. siRNA-mediated downregulation of Apaf-1 prevents etoposide-mediated activation of caspase-10. In a cell-free assay, cytochrome c and dATP treatment of cell extracts after immunodepletion of either caspase-3 or caspase-9 indicates that caspase-10 is activated downstream of caspase-9. Then, caspase-10 is involved in a feedback amplification loop that amplifies caspase-9 and -3 activities. Altogether, these data indicate an active role for caspase-10 in cytotoxic drug-induced tumor cell death, downstream of the mitochondria.

Modulation of apoptotic pathways triggered by cytotoxic agents.

Anticancer drugs can induce tumour cell death by apoptosis. The main pathway from specific damage induced by the drug to apoptosis involves activation of caspases in the cytosol by pro-apoptotic molecules such as cytochrome c released from the mitochondria. At least in some cell types, anticancer drugs also upregulate the expression of death receptors and sensitize tumour cells to their cognate ligands, which could be used to amplify the response to cytotoxic drugs. The Bcl-2 family of proteins, which includes anti- and pro-apoptotic molecules, regulates cell sensitivity at the mitochondrial level. Chemotherapeutic drugs modulate their expression (e.g. through p53-dependent gene transcription), their activity (e.g. by phosphorylation) and their subcellular localization (e.g. by translocation of pro-apoptotic proteins from the cytosol to the mitochondria). When interacting with tumour cells, anticancer drugs also activate lipid- and kinase-dependent signalling pathways that modulate the death response to specific damage. Protective pathways include activation of NF kappa B transcription factor, accumulation of heat shock proteins and activation of proteins involved in cell cycle regulation. The recent identification on these pathways to cell death has suggested several new strategies to improve the therapeutic efficacy of currently used anticancer drug regimens.