Protein synthesis-dependent but Bcl-2-independent cytochrome C release in zinc depletion-induced neuronal apoptosis

Heterotrimeric stimulatory GTP-binding proteins inhibit cisplatin-induced apoptosis by increasing X-linked inhibitor of apoptosis protein expression in cervical cancer cells

Treatment with cisplatin (cis-dichlorodiammineplatinum (II)) induces DNA double-stranded breaks and apoptosis in many human cancer cells. We have reported that heterotrimeric stimulatory GTP-binding proteins (Gαs) can modulate the apoptotic response of several cancer cells. This study investigated the effect of Gαs on apoptosis triggered by cisplatin and its underlying molecular mechanism in cervical cancer cells. Stable expression of constitutively active Gαs (GαsQL) decreased the release of cytochrome c from the mitochondria to the cytosol and cleavage of caspase-3 and poly(ADP-ribose) polymerases in HeLa cells treated with 30 μM cisplatin, indicating that Gαs inhibited cisplatin-induced apoptosis. Treatment with forskolin also inhibited apoptosis of C33A and CaSKi cervical cancer cells. Expression of GαsQL increased the expression of the X-linked inhibitor of apoptosis protein (XIAP) and partially maintained increased XIAP after cisplatin treatment. Knockdown of XIAP by siRNA augmented apoptosis. Expression of GαsQL increased XIAP mRNA; this increase was inhibited by a protein kinase A inhibitor and cAMP response element (CRE) decoy. A cAMP response element (CRE)-like element at -1396 bp in the XIAP promoter was found to mediate the induction of XIAP by Gαs. In addition, expression of GαsQL protected against the ubiquitin/proteasome-dependent degradation of the XIAP protein. This study shows that Gαs inhibits cisplatin-induced apoptosis by increasing transcription of XIAP and by decreasing degradation of XIAP protein in HeLa cervical cancer cells.

Essential role of p53 in TPEN-induced neuronal apoptosis

Depletion of intracellular zinc with N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) induces protein synthesis-dependent apoptosis. In this study, we examined the requirement for p53 as an upstream transcription factor in TPEN-induced neuronal apoptosis. Chemical or genetic blockade of p53 markedly attenuated TPEN-induced neuronal apoptosis, while the stability and activity of p53 were increased by TPEN. In addition, expression of proapoptotic genes, PUMA and NOXA, and activation of caspase-11 were increased by TPEN in a p53-dependent manner. Inhibition of p53 blocked cytochrome C release from mitochondria to cytosol and prevented caspase-3 activation. Therefore, p53 may be an essential regulatory factor for TPEN-induced neuronal apoptosis.

The involvement of caspase-11 in TPEN-induced apoptosis

The depletion of intracellular zinc with N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) induces protein synthesis-dependent apoptosis. Here we examined the involvement of caspase induction in apoptosis. Among the examined caspases, only caspase-11 was increased by TPEN. Caspase-11 activity also increased, which resulted in caspase-3 activation. Cycloheximide or actinomycin D blocked caspase-11 induction, reduced caspase-11 and -3 activation, and attenuated TPEN-induced neuronal apoptosis. Blockade of caspase-11 by a chemical inhibitor or genetic deletion attenuated TPEN-induced apoptosis, indicating a critical role of caspase-11 in TPEN-induced apoptosis. Although mitochondria-mediated caspase-9/-3 activation also contributed to TPEN-induced apoptosis, caspase-11 is likely a key inducible apoptosis-inducing protein.

Stimulatory heterotrimeric GTP-binding protein inhibits hydrogen peroxide-induced apoptosis by repressing BAK induction in SH-SY5Y human neuroblastoma cells

Heterotrimeric stimulatory GTP-binding protein (G(s)) stimulates adenylate cyclases to activate the cAMP signaling pathway. Although the cAMP pathway has been reported to be involved in apoptosis, the role of the G(s)-cAMP signaling pathway during reactive oxygen species (ROS)-mediated apoptosis, which is involved in the resistance of cancer cells to chemotherapy and radiation, is not clearly understood. Thus, in this study we aimed to investigate the role of the alpha subunit of G(s) (Galpha(s)) in the ROS-induced apoptosis of cancer cells. The stable expression of constitutively active Galpha(s) (Galpha(s)QL) inhibited the hydrogen peroxide-induced apoptosis of SH-SY5Y human neuroblastoma cells and reduced the hydrogen peroxide-induced increase in Bak and the decrease in Bcl-x(L) protein expression. Exogenous Bak expression abolished these inhibitory effects of Galpha(s)QL, but Bak small interfering RNA decreased hydrogen peroxide-induced apoptosis. Galpha(s) repressed hydrogen peroxide-induced Bak expression by inhibiting the transcription of Bak mRNA, which resulted from the inhibition of the hydrogen peroxide-induced activation of transcription factors such as AP1, NF-kappaB, and NFAT. Moreover, Galpha(s) also inhibited the hydrogen peroxide-induced binding of AP1, NF-kappaB, and NFAT to the Bak promoter. Furthermore, hydrogen peroxide-induced apoptosis was reduced by treating cells with prostaglandin E(2), which activates Galpha(s), but this was augmented by CCPA, which activates Galpha(i) causing a decrease in cAMP levels. From the results, we conclude that Galpha(s) protects neuroblastoma cells from hydrogen peroxide-induced apoptosis by repressing Bak induction, which is mediated by the inhibition of the hydrogen peroxide-induced activations of AP1, NF-kappaB, and NFAT through cAMP-PKA-CREB signaling system.

Differential effects of the ascorbyl and tocopheryl derivative on the methamphetamine-induced toxic behavior and toxicity

A previous study showed that high doses of methamphetamine induce self-injurious behavior (SIB) in rodents. Furthermore, the combination of methamphetamine and morphine increased lethality in mice. We recently surmised that the rise in SIB and mortality induced by methamphetamine and/or morphine may be related to oxidative stress. The present study was designed to determine whether an antioxidant could inhibit SIB or mortality directly induced by methamphetamine and/or morphine. The SIB induced by 20mg/kg of methamphetamine was abolished by the administration of Na L-ascorbyl-2-phosphate (APS: 300 mg/kg), but not Na DL-alpha-tocopheryl phosphate (TPNa: 200mg/kg). In contrast, APS (300 mg/kg) and TPNa (200mg/kg) each significantly attenuated the lethality induced by methamphetamine and morphine. The present study showed that the signal intensity of superoxide adduct was increased by 20mg/kg of methamphetamine in the heart and lungs, and methamphetamine plus morphine tended to increase superoxide adduct in all of the tissues measured by ESR spin trap methods. Adduct signal induced in brain by methamphetamine administration increased in significance, but in mouse administrated methamphetamine plus morphine. There are differential effects of administration of methamphetamine and coadministration of methamphetamine plus morphine on adduct signal. These results suggest that APS and TPNa are effective for reducing methamphetamine-induced toxicity and/or toxicological behavior. While APS and TPNa each affected methamphetamine- and/or morphine-induced toxicology and/or toxicological behavior, indicating that both drugs have antioxidative effects, their effects differed.

Subcellular distribution of spermidine/spermine N1-acetyltransferase

The subcellular distribution of the polyamine catabolic enzyme spermidine/spermine N(1)-acetyltransferase (SSAT) was studied in L56Br-C1 cells treated with 10 microM N(1),N(11)-diethylnorspermine (DENSPM) for 24 h. Cells were fractioned into three subcellular fractions. A particulate fraction containing the mitochondria was denoted as the mitochondrial fraction. After DENSPM treatment, an increase in SSAT activity was mainly found in the mitochondrial fraction. Western blot analysis showed an increased level of the SSAT protein in the mitochondrial fraction compared to the cytosolic fraction. Immunofluorescence microscopy and immunogold labeling transmission electron microscopy also showed a mitochondrial association of SSAT. Transmission electron microscopy revealed that the endoplasmic reticulum was devoid of ribosomes in DENSPM-treated cells, in contrast to control cells that contained ample ribosomes. An increased SSAT activity in connection with the mitochondria may be part of the mechanism of DENSPM-induced apoptosis.

Cytosolic labile zinc: a marker for apoptosis in the developing rat brain

Cytosolic zinc accumulation was thought to occur specifically in neuronal death (necrosis) following acute injury. However, a recent study demonstrated that zinc accumulation also occurs in adult rat neurons undergoing apoptosis following target ablation, and in vitro experiments have shown that zinc accumulation may play a causal role in various forms of apoptosis. Here, we examined whether intraneuronal zinc accumulation occurs in central neurons undergoing apoptosis during development. Embryonic and newborn Sprague-Dawley rat brains were double-stained for terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling (TUNEL) detection of apoptosis and immunohistochemical detection of stage-specific neuronal markers, such as nestin, proliferating cell nuclear antigen (PCNA), TuJ1 and neuronal nuclear specific protein (NeuN). The results revealed that apoptotic cell death occurred in neurons of diverse stages (neural stem cells, and dividing, young and adult neurons) throughout the brain during the embryonic and early postnatal periods. Further staining of brain sections with acid fuchsin or zinc-specific fluorescent dyes showed that all of the apoptotic neurons were acidophilic and contained labile zinc in their cell bodies. Cytosolic zinc accumulation was also observed in cultured cortical neurons undergoing staurosporine- or sodium nitroprusside (SNP)-induced apoptosis. In contrast, zinc chelation with CaEDTA or N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) reduced SNP-induced apoptosis but not staurosporine-induced apoptosis, indicating that cytosolic zinc accumulation does not play a causal role in all forms of apoptosis. Finally, the specific cytosolic zinc accumulation may have a practical application as a relatively simple marker for neurons undergoing developmental apoptosis.

Arsenic trioxide-induced death of neuroblastoma cells involves activation of Bax and does not require p53

PURPOSE

On the basis of clinical studies showing that arsenic trioxide (As(2)O(3)), via an apoptotic mechanism, and with minimal toxicity induces complete remission in patients with refractory acute promyelocytic leukemia and that multidrug-resistant and p53-mutated neuroblastoma cells are sensitive to As(2)O(3) both in vitro and in vivo, we searched for molecular mechanisms involved in the As(2)O(3)-induced neuroblastoma cell death.

EXPERIMENTAL DESIGN

We have studied the effect of As(2)O(3) on the expression and cellular localization of proteins involved in drug-induced death in two neuroblastoma cell lines with intact p53 and two with mutated p53, the latter two displaying multidrug resistance.

RESULTS

As(2)O(3) provoked Bax expression in all tested neuroblastoma cell lines, including SK-N-BE(2) cells with mutated p53 and LA-N-1 cells, which have a deleted p53. In all cell lines exposed to As(2)O(3), p21 Bax was proteolytically cleaved in a calpain-dependent way into the more proapoptotic p18 Bax, which was detected exclusively in a mitochondria-enriched subcellular fraction. As(2)O(3) also caused an increase of cytoplasmic cytochrome c, translocation of antiapoptosis-inducing factor to the nuclei, and a slight activation of caspase 3. However, inhibition of caspase 3 did not prevent cell death, whereas inhibition of Bax cleavage was associated with a decreased As(2)O(3)-induced cell death.

CONCLUSIONS

We show that multidrug-resistant neuroblastoma cells die after exposure to As(2)O(3), independent of functional p53, suggesting activation of a cytotoxic pathway different from that induced by conventional chemotherapeutic agents. We further propose that proteolytic activation of Bax is an important event in As(2)O(3)-induced cell death.

Antiapoptotic effects of roscovitine in cerebellar granule cells deprived of serum and potassium: a cell cycle-related mechanism

Neuronal apoptosis may be partly due to inappropriate control of the cell cycle. We used serum deprivation as stimulus and reduced potassium from 25 to 5mM (S/K deprivation), which induces apoptosis in cerebellar granule neurons (CGNs), to evaluate the direct correlation between re-entry in the cell cycle and apoptosis. Roscovitine (10 microM), an antitumoral drug that inhibits cyclin-dependent kinase 1 (cdk1), cdk2 and cdk5, showed a significant neuroprotective effect on CGNs deprived of S/K. S/K deprivation induced the expression of cell cycle proteins such as cyclin E, cyclin A, cdk2, cdk4 and E2F-1. It also caused CGNs to enter the S phase of the cell cycle, measured by a significant incorporation of BrdU (30% increase over control cells), which was reduced in the presence of roscovitine (10 microM). On the other hand, roscovitine modified the expression of cytochrome c (Cyt c), Bcl-2 and Bax, which are involved in the apoptotic intrinsic pathway induced by S/K deprivation. We suggest that the antiapoptotic effects of roscovitine on CGNs are due to its anti-proliferative efficacy and to an action on the mitochondrial apoptotic mechanism.

Glutathione depletion switches nitric oxide neurotrophic effects to cell death in midbrain cultures: implications for Parkinson's disease

Nitric oxide (NO) exerts neurotrophic and neurotoxic effects on dopamine (DA) function in primary midbrain cultures. We investigate herein the role of glutathione (GSH) homeostasis in the neurotrophic effects of NO. Fetal midbrain cultures were pretreated with GSH synthesis inhibitor, L-buthionine-(S,R)-sulfoximine (BSO), 24 h before the addition of NO donors (diethylamine/nitric oxide-complexed sodium and S-nitroso-N-acetylpenicillamine) at doses tested previously as neurotrophic. Under these conditions, the neurotrophic effects of NO disappeared and turned on highly toxic. Reduction of GSH levels to 50% of baseline induced cell death in response to neurotrophic doses of NO. Soluble guanylate cyclase (sGC) and cyclic GMP-dependent protein kinase (PKG) inhibitors protected from cell death for up to 10 h after NO addition; the antioxidant ascorbic acid also protected from cell death but its efficacy decreased when it was added after NO treatment (40% protection 2 h after NO addition). The pattern of cell death was characterized by an increase in chromatin condensed cells with no DNA fragmentation and with breakdown of plasmatic membrane. The inhibition of RNA and protein synthesis and of caspase activity also protected from cell death. This study shows that alterations in GSH levels change the neurotrophic effects of NO in midbrain cultures into neurotoxic. Under these conditions, NO triggers a programmed cell death with markers of both apoptosis and necrosis characterized by an early step of free radicals production followed by a late requirement for signalling on the sGC/cGMP/PKG pathway.