Generation of reactive oxygen species (ROS) and activation of caspase cascade are both indispensable in Fas-mediated apoptotic signaling. Although ROS was presumed to affect the activity of the caspase cascade on the basis of findings that antioxidants inhibited the activation of caspases and that the stimulation of ROS by itself activated caspases, the mechanism by which these cellular events are integrated in Fas signaling is presently unclear. In this study, using human T cell leukemia Jurkat cells as well as an in vitro reconstitution system, we demonstrate that ROS are required for the formation of apoptosome. We first showed that ROS derived from mitochondrial permeability transition positively regulated the apoptotic events downstream of mitochondrial permeability transition. Then, we revealed that apoptosome formation in Fas-stimulated Jurkat cells was clearly inhibited by N-acetyl-l-cysteine and manganese superoxide dismutase by using both the immunoprecipitation and size-exclusion chromatography methods. To confirm these in vivo findings, we next used an in vitro reconstitution system in which in vitro-translated apoptotic protease-activating factor 1 (Apaf-1), procaspase-9, and cytochrome c purified from human placenta were activated by dATP to form apoptosome; the formation of apoptosome was markedly inhibited by reducing reagents such as DTT or reduced glutathione (GSH), whereas hydrogen peroxide prevented this inhibition. We also found that apoptosome formation was substantially impaired by GSH-pretreated Apaf-1, but not GSH-pretreated procaspase-9 or GSH-pretreated cytochrome c. Collectively, these results suggest that ROS plays an essential role in apoptosome formation by oxidizing Apaf-1 and the subsequent activation of caspase-9 and -3.
A case of a 53-year-old female patient with reactive lymphoid hyperplasia (RLH), clinically designated as pseudolymphoma of the liver is described in this article. The patient was admitted to our hospital for further evaluation of hepatic tumors incidentally discovered at another hospital. Various diagnostic methods, including ultrasonography (US), computerized tomography (CT), magnetic resonance imaging (MRI) and hepatic angiography displayed three small lesions in the liver with outstanding findings consistent with hepatocellular carcinoma (HCC). Surgical resection was performed and the three lesions were microscopically diagnosed as RLH of the liver. The lesions comprised a massive infiltration of lymphoid cells with follicles and hyalinized interfollicular spaces. Immunohistochemical examination revealed that infiltrating lymphocytes had no prominent nuclear atypia and polyclonality. RLH of the liver is a very rare condition and only twelve cases have been reported in the English literature. Majority of the reported cases were middle-aged women and about half of them had some immunologic abnormalities such as autoimmune thyroiditis, Sjogren's syndrome, primary immunodeficiency, primary biliary cirrhosis. Since they are often clinically misdiagnosed as HCC, surgery is the choice of treatment for these patients. Although their pathology resembles malignant lymphoma, the clinical course is completely benign. The authors propose that RLH of the liver can be discriminated from HCC by its clinical features.
In the present study, we used mitochondrial DNA-depleted Jurkat subclones (ρ0 cells) to demonstrate that Fas agonistic Ab (CH-11), at the concentrations that evoke apoptotic death of the parental Jurkat cells, induced necrosis mainly through generation of excess reactive oxygen species, lysosomal rupture, and sequential activation of cathepsins B and D, and in minor part through activation of receptor-interacting protein (RIP). In the ρ0 cells treated with CH-11, ATP supplementation converted necrosis into apoptosis by the formation of the apoptosome and subsequent activation of procaspase-3. In these ATP-supplemented ρ0 cells (ATP-ρ0), generation of excess ROS and lysosomal rupture were still seen, yet cathepsins B and D were inactivated and RIP was degraded. The conversion of necrosis to apoptosis, RIP degradation, and cathepsin inactivation in ATP- ρ0 cells were blocked by caspase-3 inhibitors. Activities of cathepsins B and D in the lysate of necrotic ρ0 cells were inhibited by the addition of apoptotic parental Jurkat cell lysate. Thus, apoptosis may supercede necrosis.
We came across a rare case of acute megakaryocytic leukemia, the clinical course of which was relatively chronic and nonaggressive. This case was complicated with generalized severe osteosclerosis (OS). The medium in which blastic cells from the patient were cultured showed a strong activity to enhance the expression of an osteosclerotic cytokine, osteoprotegerin (OPG), as revealed by real-time quantitative RT-PCR and Western blot analysis. The OPG-inducing activity of the culture medium was neutralized by the anti-interleukin-11 (IL-11) antibody. These results indicate that IL-11 produced by the blasts was a causative factor of the OS observed in this patient. Am.
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