Blood Cells With Reduced Mitochondrial Membrane Potential and Cytosolic Cytochrome C Can Survive and Maintain Clonogenicity Given Appropriate Signals to Suppress Apoptosis

Arsenic trioxide (As(2)O(3)) induces apoptosis through activation of Bax in hematopoietic cells

This study explores the roles of Bax and other Bcl-2 family members play in arsenic trioxide (As(2)O(3))-induced apoptosis. We showed that As(2)O(3) treatment triggered Bax conformational change and subsequent translocation from cytosol to mitochondria to form various multimeric homo-oligomers in IM-9 cells. On the other hand, human leukemic Jurkat cells deficient in Bax showed dramatically reduced apoptosis in response to As(2)O(3). Stable overexpression of Bcl-2 in IM-9 cells (IM-9/Bcl-2) inhibited As(2)O(3)-mediated Bax activation and apoptosis, and this inhibition could be partially averted by cell-permeable Bid-Bcl-2 homology (BH)3 peptide. Meanwhile, Bax conformational change and oligomerization induced by As(2)O(3) were not inhibited by the pancaspase inhibitor z-VAD-fmk, although Bid cleavage could be completely abolished. Bax activation by As(2)O(3) seemed to require stress-induced intracellular reactive oxygen species (ROS), since the ROS scavengers (N-acetyl-L-cysteine and lipoic acid) could completely block the conformational change and translocation of Bax from cytosol to mitochondria. These data suggest that As(2)O(3) might exert the cell killing in part by inducing Bax activation through a Bcl-2-suppressible pathway in hematopoietic cells that is caspase independent and intracellular ROS regulated.

Essential role of the voltage-dependent anion channel (VDAC) in mitochondrial permeability transition pore opening and cytochrome c release induced by arsenic trioxide

The precise molecular mechanism underlying arsenic trioxide (As(2)O(3))-induced apoptosis is a subject of extensive study. Here, we show that clinically relevant doses of As(2)O(3) can induce typical apoptosis in IM-9, a multiple myeloma cell line, in a Bcl-2 inhibitable manner. We confirmed that As(2)O(3) directly induced cytochrome c (cyto c) release from isolated mouse liver mitochondria via the mitochondrial permeability transition pore, and we further identified the voltage-dependent anion channel (VDAC) as a biological target of As(2)O(3) responsible for eliciting cyto c release in apoptosis. First, pretreatment of the isolated mitochondria with an anti-VDAC antibody specifically prevented As(2)O(3)-induced cyto c release. Second, in proteoliposome experiments, VDAC by itself was sufficient to mediate As(2)O(3)-induced cyto c release, which could be specifically inhibited by Bcl-X(L). Third, As(2)O(3) induced mitochondria membrane potential (DeltaPsim) reduction and cyto c release only in the VDAC-expressing, but not in the VDAC-deficient yeast strain. Finally, we found that As(2)O(3) induced the increased expression and homodimerization of VDAC in IM-9 cells, but not in Bcl-2 overexpressing cells, suggesting that VDAC homodimerization could potentially determine its gating capacity to cyto c, and Bcl-2 blockage of VDAC homodimerization represents a novel mechanism for its inhibition of apoptosis.

Defective caspase-3 relocalization in non-small cell lung carcinoma

Many anticancer drugs exert their cytotoxicity through DNA damage and induction of apoptosis. Small cell lung carcinoma (SCLC) and non-small cell lung carcinoma (NSCLC) have different sensitivity to treatment with radiation and chemotherapeutic agents with SCLC being more sensitive than NSCLC both in vitro and in vivo. This difference might be related to the different susceptibility of small and non-small cell lung carcinoma to undergo apoptosis. The aim of this study was to investigate if deficiencies in the apoptotic pathways can explain the intrinsic resistance of NSCLC to anti-cancer treatment. Three different triggers were used to induce apoptosis. Etoposide and gamma-radiation, which are important parts of clinical lung cancer treatment, induce DNA-damage, whereas Fas ligation induces receptor-mediated apoptotic pathways. NSCLC cells were cross-resistant to all treatments, whereas SCLC cells, which do not express pro-caspase-8, were resistant to alphaFas-, but not to DNA-damage-induced apoptosis. Cytochrome c release, activation of caspase-9 and the executioner caspase-3 were observed in both types of lung cancer cells. However, cleavage of known nuclear substrates for caspase-3, such as PARP and DFF45/ICAD, was documented only in the sensitive SCLC cells but not in the resistant NSCLC cells. Moreover, relocalization of active caspase-3 from the cytosol into the nucleus upon treatment was observed only in the SCLC cell line. These results indicate that the inhibition of apoptosis in NSCLC occurs downstream of mitochondrial changes and caspase activation, and upstream of nuclear events.

Cellular commitment to radiation-induced apoptosis

The basic elements of the machinery of programmed cell death (apoptosis) are built into all mammalian cells and are conserved evolutionarily from nematodes to humans. The workshop on Commitment to Radiation-Induced Apoptosis at the 11th International Congress of Radiation Research in Dublin, Ireland reviewed recent information regarding the basic molecular mechanisms which are fundamental to the understanding of the process of apoptosis after treatment with ionizing radiation and some other agents.