Induction of type 1 programmed cell death in U937 cells by the antioxidant, butylated hydroxy-toluene or the free radical spin trap, NTBN

Differential sensitization of different prostate cancer cells to apoptosis

Although protein kinase C (PKC) plays an important role in sensitizing prostate cancer cells to apoptosis, and suppression of PKC is able to trigger an apoptotic crisis in cells harboring oncogenic ras, little is known about whether dyregulation of Ras effectors in prostate cancer cells, together with loss of PKC, is synthetically lethal. The current study aims at investigating whether prostate cancer cells with aberrant Ras effector signaling are sensitive to treatment with HMG (a PKC inhibitor) for the induction of apoptosis. We show that prostate cancer DU145 cells expressing a high level of JNK1 become susceptible to apoptosis after treatment with HMG, in which caspase 8 is activated and cytochrome c is released to the cytosol. In contrast, the addition of HMG sensitizes LNCaP or PC3 prostate cancer cells harboring an active Akt to apoptosis, in which ROS is upregulated to induce the UPR and GADD153 expression. The concurrent activation of JNK1 and Akt has an additive effect on apoptosis following PKC suppression. Thus, the data identify Akt and JNK1 as potential targets in prostate cancer cells for PKC inhibition-induced apoptosis.

Intracellular redox status and oxidative stress: implications for cell proliferation, apoptosis, and carcinogenesis

Oxidative stress can be defined as the imbalance between cellular oxidant species production and antioxidant capability. Reactive oxygen species (ROS) are involved in a variety of different cellular processes ranging from apoptosis and necrosis to cell proliferation and carcinogenesis. In fact, molecular events, such as induction of cell proliferation, decreased apoptosis, and oxidative DNA damage have been proposed to be critically involved in carcinogenesis. Carcinogenicity and aging are characterized by a set of complex endpoints, which appear as a series of molecular reactions. ROS can modify many intracellular signaling pathways including protein phosphatases, protein kinases, and transcription factors, suggesting that the majority of the effects of ROS are through their actions on signaling pathways rather than via non-specific damage of macromolecules; however, exact mechanisms by which redox status induces cells to proliferate or to die, and how oxidative stress can lead to processes evoking tumor formation are still under investigation.

Modulation of intracellular signaling pathways to induce apoptosis in prostate cancer cells

An understanding of the molecular pathways defining the susceptibility of prostate cancer, especially refractory prostate cancer, to apoptosis is the key for developing a cure for this disease. We previously demonstrated that up-regulating Ras signaling, together with suppression of protein kinase C (PKC), induces apoptosis. Dysregulation of various intracellular signaling pathways, including those governed by Ras, is the important element in the development of prostate cancer. In this study, we tested whether it is possible to modulate the activities of these pathways and induce an apoptotic crash among them in prostate cancer cells. Our data showed that DU145 cells express a high amount of JNK1 that is phosphorylated after endogenous PKC is suppressed, which initiates caspase 8 cleavage and cytochrome c release, leading to apoptosis. PC3 and LNCaP cells contain an activated Akt. The inhibition of PKC further augments Akt activity, which in turn induces ROS production and the accumulation of unfolded proteins in the endoplasmic reticulum, resulting in cell death. However, the concurrent activation of JNK1 and Akt, under the condition of PKC abrogation, dramatically augment the magnitude of apoptosis in the cells. Thus, our study suggests that Akt, JNK1, and PKC act in concert to signal the intracellular apoptotic machinery for a full execution of apoptosis in prostate cancer cells.

Induction of apoptosis by 9,10-dimethyl-1,2-benzanthracene in cultured preovulatory rat follicles is preceded by a rise in reactive oxygen species and is prevented by glutathione

The polycyclic aromatic hydrocarbon (PAH) 9,10-dimethyl-1,2-benzanthracene (DMBA) destroys primordial, primary, and secondary ovarian follicles in rodents, but its effects on antral follicles have received limited attention. PAHs are metabolized to reactive species, some of which can undergo redox cycling to generate reactive oxygen species (ROS). We previously showed that ROS initiate apoptosis in preovulatory follicles cultured without gonadotropin support and that glutathione (GSH) depletion induces apoptosis in the presence of gonadotropins. In the present study, we tested the hypothesis that DMBA induces apoptosis in preovulatory follicles, which is mediated by ROS and prevented by GSH. Preovulatory follicles were isolated from ovaries of 25-day-old rats 48 h after the injection of 10 IU of eCG and were cultured with DMBA in the presence of FSH for 2 to 48 h. DMBA induced granulosa cell (GC) and theca cell (TC) apoptosis at 48 h, as judged by TUNEL and activated caspase-3 immunostaining. DMBA treatment also increased the numbers of GCs and TCs that immunostained for the proapoptotic protein BAX. Follicular ROS levels were significantly increased in DMBA-treated follicles at 12, 24, and 48 h. GSH supplementation protected against and GSH depletion enhanced the induction of apoptosis in GCs and TCs by DMBA. These findings suggest that GSH is a critical protective mechanism against DMBA-induced apoptosis in antral follicles and that ROS generation may mediate DMBA-induced GC apoptosis.

Toluene inhalation induced 8-hydroxy-2'-deoxyguanosine formation as the peroxidative degeneration in rat organs

The effect of toluene inhalation on oxidative damage in rat organs was examined. Male Wistar rats was inhaled toluene (1500 ppm for 4 h a day) for 7 days. Quantitatively and immunohistochemically, oxidative DNA damage, lipid peroxide (LPO) and superoxide dismutase (SOD) were examined. As a marker of the oxidative DNA damage, 8-hydroxy-2'-deoxyguanosine (8-OH-dG) immunoreactivity increased in the lung, liver and kidney. The amount of 8-OH-dG also increased in liver and kidney significantly. In the testis, the amount of 8-H-dG did not increase, however 8-OH-dG immunoreactivity enhanced in the spermatogonia. SOD immunoreactivity increased in the lung, liver and kidney. However, 4-hydroxy-nonenal immunoreactivity and the amount of LPO did not change in each organ. Thus, oxidative damage by toluene is mainly DNA damage, especially, the oxidative DNA damage observed in the lung, liver and kidney for the increase of the immunoreactivity and amount of 8-OH-dG.

Selected features of nonendocrine pancreatic cancer

We survey some interesting features of gene expression in nonendocrine pancreatic cancer, the response to some less widely known agents as they impact on pancreatic cell proliferation and programmed death, and several developing approaches to therapy. The proliferative and cellular suicide responses of Panc-1 cells to the free radical spin trap, NTBN, and to the 5-lipoxygenease inhibitor, MK 886, the latter assessed with CLONTECH Atlas Human cDNA Array 1, are reviewed. Difficulties in identifying those factors whose suppression or augmentation could result in inhibition of malignantly transformed cell properties are considered.

The mode of cell death in H-358 lung cancer cells cultured with inhibitors of 5-lipoxygenase or the free radical spin trap, NTBN

The 5-lipoxygenase inhibitors SC41661A and MK886 with different mechanisms of action and the free radical spin trap, NTBN inhibit proliferation of the human bronchiolar lung cancer cell line NCI H-358 (5807 CRL). With continued culture, the agents induced a form of programmed cell death in which DNA laddering was not detected and ultrastructural changes were not characteristic of classic 'type 1' cellular suicide. The changes were more consistent with a type 2 cytosolic, autophagic form of PCD. MK886 induced strikingly abnormal mitochondrial morphology. Since the lipoxygenase inhibitors and NTBN induce classic type 1 PCD in U937 monoblastoid cells, these agents can activate either pathway, depending upon cell type. It is not certain whether activation of type 1 or 2 pathways depends entirely upon cell lineage and/or initiating agent, if all cells retain both pathways, and if type 1 PCD a more effective mediator of the process. These are all relevant questions for assessing the impact of PCD on malignant cell survival and considering ways in which it might be enhanced.