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HT22 immortalized hippocampal neurons serve as a cellular model system to study oxidative stress, an imbalance of cellular redox homeostasis. Glutamate induces HT22 cell death by inhibiting the uptake of cystine into the cells via the cystine/glutamate transport system xc-, thus leading to reduced levels of glutathione. Here, we show that glutamate-induced cell death is attenuated in HT22 cells overexpressing heat shock protein 70 or heme oxygenase-1. Moreover, supplementing the culture medium with sodium selenite completely protected HT22 against oxidative glutamate toxicity. In contrast, neither heat shock protein 70 nor heme oxygenase-1 expression or increased concentrations of sodium selenite protected HT22 cells against serum withdrawal-induced cell death. These data indicate that glutamate-induced cell death differs substantially from that induced by growth factor deprivation., (Copyright 2004 Elsevier Ireland Ltd.)

Mad2, a key component of the spindle checkpoint, is closely associated with chromosomal instability and poor prognosis in cancer. p31comet is a Mad2-interacting protein that serves as a spindle checkpoint silencer at mitosis. In this study, we showed that p31comet-induced apoptosis and senescence occur via counteraction of Mad2 activity. Upon retroviral transduction of p31comet, the majority of human cancer cell lines tested lost the ability to form colonies in a low-density seeding assay. Cancer cells with p31comet overexpression underwent distinct apoptosis and/or senescence, irrespective of p53 status, confirming the cytotoxicity of p31comet. Interestingly, both cytotoxic and Mad2 binding activities were eliminated upon deletion of the C-terminal 30 amino acids of p31comet. Point mutation or deletion of the region affecting Mad2 binding additionally abolished cytotoxic activity. Consistently, wild-type Mad2 interacting with p31comet, but not its non-binding mutant, inhibited cell death, indicating that the mechanism of p31comet-induced cell death involves Mad2 inactivation. Our results clearly suggest that the regions of p31comet affecting interactions with Mad2, including the C-terminus, are essential for induction of cell death. The finding that p31comet-induced cell death is mediated by interactions with Mad2 that lead to its inactivation is potentially applicable in anticancer therapy. [ABSTRACT FROM AUTHOR]

Since radiation-induced caspase-dependent apoptosis and ROS generation were partially prevented by HSP25 overexpression, similar to the treatment of control cells with antioxidant agents such as DPI and tiron, questions arise whether radiation-mediated ROS generation contributes to the apoptotic cell death, and also whether HSP25 overexpression can reduce ROS mediated apoptotic cell death. In the present study, radiation-induced cytochrome c release from mitochondria and activation of caspases accompanied by a decrease of mitochondrial membrane potential in Jurkat T cells were shown to be inhibited by mitochondrial complex I inhibitor rotenone, suggesting that mitochondrial ROS might be important in radiation-induced caspase-dependent apoptosis. When HSP25 was overexpressed, effects similar to the treatment of cells with the antioxidants were obtained, indicating that HSP25 suppressed radiation-induced mitochondrial alteration that resulted in apoptosis. Furthermore, activation of p38 MAP kinase by radiation was associated with radiation-induced cell death and ROS production and PKCdwas an upstream molecule for p38 MAP kinase activation, ROS generation and subsequent caspase-dependent apoptotic events. However, in the HSP25 overexpressed cells, the above-described effects were blocked. In fact, radiation-induced membrane translocation of PKCdand tyrosine phosphorylation were inhibited by HSP25. Based on the above data, we suggest that HSP25 downregulates PKCd, which is a key molecule for radiation-induced ROS generation and mitochondrial-mediated caspase-dependent apoptotic events.Oncogene (2005) 24, 3715-3725. doi:10.1038/sj.onc.1208440 Published online 4 April 2005 [ABSTRACT FROM AUTHOR]