Enhancement of Ca(2+)-dependent endonuclease activity in L1210 cells during apoptosis induced by 1-beta-D-arabinofuranosylcytosine: possible involvement of activating factor(s)

Metal ions influx is a double edged sword for the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is a common form of dementia in aged people, which is defined by two pathological characteristics: β-amyloid protein (Aβ) deposition and tau hyperphosphorylation. Although the mechanisms of AD development are still being debated, a series of evidence supports the idea that metals, such as copper, iron, zinc, magnesium and aluminium, are involved in the pathogenesis of the disease. In particular, the processes of Aβ deposition in senile plaques (SP) and the inclusion of phosphorylated tau in neurofibrillary tangles (NFTs) are markedly influenced by alterations in the homeostasis of the aforementioned metal ions. Moreover, the mechanisms of oxidative stress, synaptic plasticity, neurotoxicity, autophagy and apoptosis mediate the effects of metal ions-induced the aggregation state of Aβ and phosphorylated tau on AD development. More importantly, imbalance of these mechanisms finally caused cognitive decline in different experiment models. Collectively, reconstructing the signaling network that regulates AD progression by metal ions may provide novel insights for developing chelators specific for metal ions to combat AD.

Nuclear translocation of a leukocyte elastase Inhibitor/Elastase complex during staurosporine-induced apoptosis: role in the generation of nuclear L-DNase II activity

Using L1210 murine leukemia cells, we have previously shown that in response to treatment with drugs having different targets, apoptotic cell death occurs through at least two different signaling pathways. Here, we present evidence that nuclear extracts from staurosporine-treated cells elicit DNase II activity that is not detected in nuclear extracts from cisplatin-treated cells. This activity correlates with the accumulation of two nuclear proteins (70 and 30 kDa) which are detected by an anti-L-DNase II antibody. Partial purification of this DNase II activity suggests that the 30-kDa protein could be the nuclease responsible for staurosporine-induced DNA fragmentation. The 70-kDa protein is also recognized by an anti-elastase antibody, suggesting that it carries residues belonging to both L-DNase II and elastase. Since previous findings showed that L-DNase II was generated from the leukocyte inhibitor of elastase, we propose that the 70-kDa protein results from an SDS-stable association between these two proteins and is translocated from the cytoplasm to the nucleus during staurosporine-induced apoptosis.

Isolation and characterization of NUC70, a cytoplasmic, hematopoietic apoptotic endonuclease

Endonucleolytic DNA fragmentation is the common end point and the prevailing indicator of apoptosis. We have identified a 70-kDa endonuclease (NUC70) that is activated in drug-induced apoptosis of human hematopoietic cells. We purified NUC70 to homogeneity and generated a rabbit polyclonal antibody to distinguish it from previously identified nucleases. Biochemical characterization of isolated NUC70 demonstrates that it is Ca2+/Mg2+-dependent and active over a pH range of 6-8. When incubated with isolated HeLa nuclei, NUC70 was capable of generating internucleosomal DNA fragmentation. This endonucleolytic activity was inhibited by Zn2+, aurintricarboxylic acid, N-ethylmaleimide, spermine, and iodoacetamide. Western immunoblots using the anti-NUC70 antibody and DNA-SDS-polyacrylamide gel electrophoresis assays indicate that NUC70 expression and activity is restricted to human hematopoietic cells. No such activity was detected in human epithelial cell lines or murine hematopoietic cells. We also observed no difference in levels of NUC70 expression between apoptotic and nonapoptotic cells, suggesting that activation of NUC70 may be by posttranslational modification. We demonstrate that NUC70 activity is diminished in cells pretreated with the caspase inhibitors z-DEVD-fmk, z-VAD-fmk, and Z-CH2-Asp-DCB. Time course studies of cytoplasmic and nuclear endonuclease activities during apoptosis show that NUC70 is a cytoplasmic endonuclease that is translocated to the nucleus after the initiation of apoptosis. We confirmed this with immunostaining studies using anti-NUC70 antibody. These results demonstrate that NUC70 is an endogenous cytoplasmic endonuclease that is activated during apoptosis in a caspase-dependent mechanism.

Apoptosis in the heart: when and why?

Since mammalian cardiac myocytes essentially rely on aerobic energy metabolism, it has been assumed that cardiocytes die in a catastrophic breakdown of cellular homeostasis (i.e. necrosis), if oxygen supply remains below a critical limit. Recent observations, however, indicate that a process of gene-directed cellular suicide (i.e. apoptosis) is activated in terminally differentiated cardiocytes of the adult mammalian heart by ischemia and reperfusion, and by cardiac overload as well. Apoptosis or programmed cell death is an actively regulated process of cellular self destruction, which requires energy and de novo gene expression, and which is directed by an inborn genetic program. The final result of this program is the fragmentation of nuclear DNA into typical 'nucleosomal ladders', while the functional integrity of the cell membrane and of other cellular organelles is still maintained. The critical step in this regulated apoptotic DNA fragmentation is the proteolytic inactivation of poly-[ADP-ribose]-polymerase (PARP) by a group of cysteine proteases with some structural homologies to interleukin-1 beta-converting enzyme (ICE-related proteases [IRPs] such as apopain, yama and others). PARP catalyzes the ADP-ribosylation of nuclear proteins at the sites of spontaneous DNA strand breaks and thereby facilitates the repair of this DNA damage. IRP-mediated destruction of PARP, the 'supervisor of the genome', can be induced by activation of membrane receptors (e.g. FAS or APOI) and other signals, and is inhibited by activation of 'anti-death genes' (e.g. bcl-2). Overload-triggered myocyte apoptosis appears to contribute to the transition to cardiac failure, which can be prevented by therapeutic hemodynamic unloading. In myocardial ischemia, the activation of the apoptotic program in cardiocytes does not exclude their final destiny to catastrophic necrosis with release of cytosolic enzymes, but might be considered as an adaptive process in hypoperfused ventricular zones, sacrificing some jeopardized myocytes to regulated apoptosis, which may be less arrhythmogenic than necrosis with the primary disturbance of membrane function.