Apoptosis induced by cadmium in human lymphoma U937 cells through Ca2+-calpain and caspase-mitochondria- dependent pathways

A free radical initiator, 2,2'-azobis (2-aminopropane) dihydrochloride enhances hyperthermia-induced apoptosis in human uterine cervical cancer cell lines

Hyperthermia-induced apoptosis and its enhancement in the presence of a temperature-dependent free radical initiator, 2,2'-azobis (2-aminopropane) dihydrochloride (AAPH) were examined in human uterine cervical cancer cell lines, CaSki and HeLa. When both cell lines were treated with hyperthermia at 44 degrees C for 60 min, minimal apoptosis was observed. When combined with nontoxic AAPH (50mM), significant enhancement of apoptosis was observed, where the initial rate of free radical formation was about twice as high than that at 37 degrees C. Augmentation of the growth delay, lipid peroxidation (LPO), activation of caspase-3 and increase in [Ca2+]i were also observed after the combined treatment. A water-soluble vitamin E, Trolox, blocked the increase in [Ca2+]i and an intracellular Ca2+ chelator, BAPTA-AM, prevented the DNA fragmentation induced by the combination. Cytochrome c release was also revealed by fluorescence microscopy. However, no significant change in mitochondrial membrane potential and expression of Bax and Bcl-2 was observed. A slight increase in Fas expression was observed only in CaSki cells after the combined treatment. These results indicate that hyperthermia and AAPH induce enhanced apoptosis and subsequent cell killing via two pathways; a pathway dependenton increase in LPO and [Ca2+]i, and a pathway associated with cytochrome c release and subsequent caspase activation without changes of mitochondrial membrane potential and Bax/Bcl-2 expression in these cell lines. Since it is known that cancer cells are generally resistant to physical and chemical stress-induced apoptosis, free radical generators like AAPH appear to be a useful thermosensitizer for hyperthermic cancer therapy.

Mitochondria-mediated caspase-independent apoptosis induced by cadmium in normal human lung cells

Cadmium, a well-known environmental hazard, has caused serious health problems in humans and animals. Accumulating evidence suggests the cadmium toxicity is mediated by oxidative stress-induced cell death. However, the molecular signaling underlying cadmium-induced apoptosis remains unclear. In this study, we demonstrate here that cadmium induced mixed types of cell death including primary apoptosis (early apoptosis), secondary necrosis (late apoptosis), and necrosis in normal human lung cells, MRC-5, as revealed by chromatin condensation, phosphatidylserine (PS) externalization, and hypodiploid DNA content. The total apoptotic cells reached a plateau of around 40.0% after 24 h exposure of 100 microM cadmium. Pretreatment with Z-Val-Ala-Asp-fluoromethylketone (Z-VAD-fmk), a broad spectrum of caspase inhibitor, could not rescue apoptotic cells from cadmium toxicity. Coincidently, we failed to detect the activation of pro-caspase-3 and cleavage of PARP by immunoblot, which implies the apoptogenic activity of cadmium in MRC-5 cells is caspase-independent. JC-1 staining also indicated that mitochondrial depolarization is a prelude to cadmium-induced apoptosis, which was accompanied by a translocation of caspase-independent pro-apoptotic factor apoptosis-inducing factor (AIF) into the nucleus as revealed by the immunofluorescence assay. In summary, this study demonstrated for the first time that cadmium induced a caspase-independent apoptotic pathway through mitochondria-mediated AIF translocation into the nucleus.

Galectin-9 induces apoptosis through the calcium-calpain-caspase-1 pathway

Galectin-9 (Gal-9) induced the apoptosis of not only T cell lines but also of other types of cell lines in a dose- and time-dependent manner. The apoptosis was suppressed by lactose, but not by sucrose, indicating that beta-galactoside binding is essential for Gal-9-induced apoptosis. Moreover, Gal-9 required at least 60 min of Gal-9 binding and possibly de novo protein synthesis to mediate the apoptosis. We also assessed the apoptosis of peripheral blood T cells by Gal-9. Apoptosis was induced in both activated CD4(+) and CD8(+) T cells, but the former were more susceptible than the latter. A pan-caspase inhibitor (Z-VAD-FMK) inhibited Gal-9-induced apoptosis. Furthermore, a caspase-1 inhibitor (Z-YVAD-FMK), but not others such as Z-IETD-FMK (caspase-8 inhibitor), Z-LEHD-FMK (caspase-9 inhibitor), and Z-AEVD-FMK (caspase-10 inhibitor), inhibited Gal-9-induced apoptosis. We also found that a calpain inhibitor (Z-LLY-FMK) suppresses Gal-9-induced apoptosis, that Gal-9 induces calcium (Ca(2+)) influx, and that either the intracellular Ca(2+) chelator BAPTA-AM or an inositol trisphosphate inhibitor 2-aminoethoxydiphenyl borate inhibits Gal-9-induced apoptosis. These results suggest that Gal-9 induces apoptosis via the Ca(2+)-calpain-caspase-1 pathway, and that Gal-9 plays a role in immunomodulation of T cell-mediated immune responses.

Caspase inhibitors as anti-inflammatory and antiapoptotic agents

The striking efficacy of Z-VAD-fmk in the various animal models presented above may reflect its ability to inhibit multiple enzymes including caspases. In accord with this, more selective, reversible inhibitors usually show low efficacy in multifactorial models such as ischaemia, but may offer some protection against NMDA-induced excitotoxicity and hepatitis. Importantly, caspase inhibitors may exhibit significant activity in vivo even when they are applied post insult. As far as the CNS is concerned, the first systemically active inhibitors have emerged. Functional recovery could be achieved in some ischaemia models, but long-term protection by caspase inhibitors is still being questioned. Recent developments in drug design enabled the first caspase inhibitors to enter the clinic. Although initially directed towards peripheral indications such as rheumatoid arthritis, caspase inhibitors will no doubt eventually be used to target CNS disorders. For this purpose the peptidic character of current inhibitors will have to be further reduced. Small molecule, nonpeptidic caspase inhibitors, which have appeared recently, indicate that this goal can be accomplished. Unfortunately, many fundamental questions still remain to be addressed. In particular, the necessary spectrum of inhibitory activity required to achieve the desired effect needs to be determined. There is also a safety aspect associated with prolonged administration. Therefore, the next therapeutic areas for broader-range caspase inhibitors are likely to involve acute treatment. Recent results with synergistic effects between MK-801 and caspase inhibitors in ischaemia suggest that caspase inhibitors may need to be used in conjunction with other drugs. It can be expected that, in the near future, research on caspases and their inhibitors will remain a rapidly developing area of biology and medicinal chemistry. More time, however, may be needed for the first caspase inhibitors to appear on the market.

Mechanisms regulating the cadmium-mediated suppression of Sp1 transcription factor activity in alveolar epithelial cells

This study demonstrates that in vitro exposure of adult rat alveolar epithelial cells to CdCl(2) decreases DNA binding activity of specificity protein 1 (Sp1), a zinc-finger transcription factor known to play a key role in eukaryotic gene expression, maintenance of homeostasis, cell cycle control, terminal differentiation, and apoptosis. Suppression of Sp1 function, as assessed by electrophoretic mobility shift assays (EMSAs), is dependent upon cadmium (Cd) dose and duration of exposure. A 45% decrease of Sp1 activity occurs as early as 30 min after Cd addition. By 2 h, Sp1 activity is reduced even further with no loss of cell viability, suggesting that Sp1 inactivation precedes cell death. If Cd is removed from cultures during these early periods of exposure, inhibition of Sp1 binding activity is reversed. Sp1 inactivation does not appear to be a generalized, non-selective response to Cd as other transcription factors are up-regulated under the same conditions. Phosphorylation is involved in Sp1 down-regulation, as evidenced by the finding that alkaline phosphatase treatment of nuclear extracts from cells exposed to Cd for 2 h helps restore Sp1 binding activity. A broad spectrum Protein Kinase C (PKC) inhibitor, GF109203X, substantially reduces the Cd-mediated effect on Sp1 suggesting that a member of the PKC family is required for Sp1 phosphorylation. More prolonged Cd exposure promotes Sp1 degradation with the appearance of cleavage products (40 and 50 kDa), as detected by Western blotting. Changes in the integrity of the Sp1 protein are accompanied by a corresponding decline in cell survival. Cd-induced cell death is substantially attenuated if cells are pretreated with antagonists of PKC activity which implies that a PKC isoform is also a participant in this process.

Calpain is activated in experimental uremia: is calpain a mediator of uremia-induced myocardial injury?

BACKGROUND

The cysteine proteases calpain and caspase-3 are known mediators of cell death. The aim of this study was to assess their contribution to the tissue damage found in experimental uremia.

METHODS

Calpain and caspase-3 activities were measured in the hearts of rats that were sham-operated (control), sham-operated and spontaneously hypertensive (SHR), and those rendered uremic by 5/6 nephrectomy (uremic). In an in vitro study, heart myoblasts (Girardi) were incubated with human serum from healthy subjects (control serum conditioned media, CSCM) or uremic patients (uremic serum conditioned media, USCM), in the presence and absence of calpain and caspase-3 inhibitors. After 48 hours the activity of calpain and caspase-3 was measured, and cell injury determined by DNA fragmentation (ELISA) and lactate dehydrogenase (LDH) release. An in situ assay was designed to study how USCM affects calpain activity over time.

RESULTS

In the in vivo study, mean calpain activities were almost identical in the control and SHR groups, but calpain and caspase-3 activities were much elevated in the uremic group (P < 0.01 and 0.001 respectively vs. control). The SHR group had significantly higher mean arterial blood pressure (P < 0.001 vs. control, 0.01 vs. uremic). In the in vitro study calpain activity and DNA fragmentation were markedly higher in USCM treated cells compared to CSCM (both P<0.05). Both were reduced in USCM cells containing calpain inhibitors (E64d, calpastatin, or PD 150606). LDH release was raised also in USCM treated cultures (P < 0.05), which only the E64d treatment could significantly reduce (P < 0.02). Caspase-3 activities were similar in USCM and CSCM groups. The in situ assay showed significant increases in calpain activity in USCM treated cells compared to CSCM after just 3.5 hours (P<0.01).

CONCLUSIONS

In vivo results suggest that the increases in calpain and caspase-3 activity in uremic rat hearts were primarily due to uremia and not to hypertension. In vitro data demonstrate that uremia-induced cell injury can be attenuated by calpain inhibition. Therefore, it is likely that calpain is a mediator of uremia-induced myocardial injury.

Apoptosis and necrosis: two distinct events induced by cadmium in cortical neurons in culture

(1) Cadmium is an extremely toxic metal commonly found in industrial workplaces, a food contaminant and a major component of cigarette smoke. Cadmium can severely damage several organs, including the brain. In this work, we have studied both the cadmium toxicity on rat cortical neurons in culture and the possible protective effect of serum. (2) Our results indicate that: (1) cadmium is taken up by the neurons in a dose and serum dependent way; (2) cadmium, at concentrations from 1 micro M or 10 micro M (depending on the absence or the presence of serum) up to 100 micro M, decreases the metabolic capacity, which was evaluated by the XTT (tetrazolium salt) test; (3) cadmium induces apoptosis and LDH (lactate dehydrogenase) release in a dose dependent way; (4) in a serum-free medium, the cadmium-induced apoptosis is accompanied by caspase-3 activation; (5) both the caspase-3 activation and the cadmium-induced apoptosis are reversed by N-acethyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO), a selective caspase-3 inhibitor, indicating that the caspase-3 pathway is involved in cadmium-induced apoptosis in cortical neurons; and (6) the cadmium concentrations which produce caspase-3 activation do not modify the intracellular ATP levels; however, higher cadmium concentrations lead to both intracellular ATP depletion and ATP release, but do not increase the caspase-3 activity, indicating that cadmium also produces cellular death by necrosis. (3) These results suggest that cadmium induces either apoptosis or necrosis in rat cortical neurons, depending on the cadmium concentration.

Mitochondrial and endoplasmic reticulum stress-induced apoptotic pathways are activated by 5-aminolevulinic acid-based photodynamic therapy in HL60 leukemia cells

We studied the mechanism of the cytotoxic effects of 5-aminolevulinic acid-based photodynamic therapy (ALA-PDT; induction with 1 mM ALA for 4 h followed by a blue light dose of 18 J/cm(2)) on the human promyelocytic leukemia cell line HL60 using biochemical and electron microscopy methods. The disruption of mitochondrial membrane potential, deltapsi(m), was paralleled by a decrease in ATP level, unmasking of the mitochondrial antigen 7A6, release of cytochrome c into the cytoplasm, activation of caspases 9 and 3 and cleavage of poly(ADP-ribose) polymerase (PARP). This was followed by DNA fragmentation. These data suggest that ALA-PDT activates the mitochondrial apoptotic pathway. The level of endoplasmic reticulum Ca(2+)-binding chaperones ERp57 and ERp72 and of anti-apoptotic proteins Bcl-2 and Bcl-x(L) was decreased whereas that of Ca(2+)-binding protein calmodulin and the stress protein HSP60 was elevated following ALA-PDT. Inhibition of the initiator caspase 9, execution caspase 3 and Ca(2+)-dependent protease m-calpain, did not prevent DNA fragmentation. We conclude that, in our in vitro model, ALA-based photodynamic treatment initiates several signaling processes in HL60 cells that lead to rapidly progressing apoptosis, which is followed by slow necrosis. Two apoptotic processes proceed in parallel, one representing the mitochondrial pathway, the other involving disruption of calcium homeostasis and activation of the endoplasmic reticulum stress-mediated pathway.

Inhibition of proteasome activity is involved in cobalt-induced apoptosis of human alveolar macrophages

Inhalation of particulate cobalt has been known to induce interstitial lung disease. There is growing evidence that apoptosis plays a crucial role in physiological and pathological settings and that the ubiquitin-proteasome system is involved in the regulation of apoptosis. Cadmium, the same transitional heavy metal as cobalt, has been reported to accumulate ubiquitinated proteins in neuronal cells. On the basis of these findings, we hypothesized that cobalt would induce apoptosis in the lung by disturbance of the ubiquitin-proteasome pathway. To evaluate this, we exposed U-937 cells and human alveolar macrophages (AMs) to cobalt chloride (CoCl(2)) and examined their apoptosis by DNA fragmentation assay, 4',6-diamidino-2'-phenylindol dihydrochloride staining, and Western blot analysis. CoCl(2) induced apoptosis and accumulated ubiquitinated proteins. Exposure to CoCl(2) inhibited proteasome activity in U-937 cells. Cobalt-induced apoptosis was mediated via mitochondrial pathway because CoCl(2) released cytochrome c from mitochondria. These results suggest that cobalt-induced apoptosis of AMs may be one of the mechanisms for cobalt-induced lung injury and that the accumulation of ubiquitinated proteins might be involved in this apoptotic process.

Cyclosporin A-sensitive permeability transition pore is involved in Cd(2+)-induced dysfunction of isolated rat liver mitochondria: doubts no more

There is dose-dependent Cd(2+)-evoked swelling of isolated rat liver mitochondria energized by complex I, II, or IV respiratory substrates in sucrose medium in the absence of added Ca(2+) and P(i), which is prevented by Sr(2+). Permeability transition effectors (ADP, CsA, EGTA, RR, DTT, ATR, P(i), and Ca(2+)) affect in a corresponding way Cd(2+)-promoted membrane permeabilization in NH(4)NO(3), KCl, and sucrose media. Maximal depression of Cd(2+)-induced swelling is achieved by simultaneous addition of ADP, Mg(2+), and CsA that produces either synergistic (NH(4)NO(3)) or additive (KCl and sucrose media) action. Sustained activation by low [Cd(2+)] of mitochondrial basal respiration in KCl medium is observed both in the absence and in the presence of rotenone and/or oligomycin but only in the latter case (rotenone+oligomycin) CsA inhibits completely Cd(2+) activation of St 4 respiration and partially reverses DNP-uncoupled respiration depressed by cadmium. Cd(2+) effects are discussed in terms of comparison with those of Zn(2+) and PhAsO.

Molecular evidence of apoptotic death in malignant brain tumors including glioblastoma multiforme: upregulation of calpain and caspase-3

Cell death in the core of human brain tumors is triggered by hypoxia and lack of nutrients, but the mode of cell death whether necrosis or apoptosis is not clearly defined. To identify the role of apoptosis in brain tumor cell death, we investigated macromolecular (RNA and protein) synthesis and activity in the central to peripheral region of benign [desmoplastic infantile ganglioglioma (DIG) and transitional meningioma (TMG)] and malignant [ependymoma (END), anaplastic astrocytoma (APA), and glioblastoma multiforme (GBM)] brain tumors derived from five patients who had not received previously radiotherapy or chemotherapy. Normal brain tissue (NBT) served as control. RT-PCR analysis of tumor tissues covering central to peripheral regions detected mRNA overexpression of pro-apoptotic gene bax in malignant tumors, indicating a commitment to apoptosis. The mRNA expression of calpain (a Ca(2+)-dependent cysteine protease) and calpastatin (endogenous calpain inhibitor) was altered resulting in an elevated calpain/calpastatin ratio. Calpain content and activity were increased, suggesting a role for calpain in cell death. In the mitochondria-dependent death pathway, caspase-9 and caspase-3 were also overexpressed in tumors. The increased caspase-3 activity cleaved poly(ADP-ribose) polymerase (PARP). Agarose gel electrophoresis detected a mixture of random and internucleosomal DNA fragmentation in malignant brain tumors. Overexpression of pro-apoptotic bax, upregulation of calpain and caspase-3, and occurrence of internucleosomal DNA fragmentation are now presented indicating that one mechanism of cell death in malignant brain tumors is apoptosis, and that enhancement of this process therapeutically may promote decreased tumor growth.

Intracellular calcium oscillations signal apoptosis rather than activation in in vitro aged mouse eggs

We have previously demonstrated that initiation of intracellular calcium ([Ca2+]i) oscillations in mouse eggs signals activation or apoptotic death depending on the age of the eggs in which the oscillations are induced. To extend these studies, mouse eggs were aged in vitro to 24, 32, and 40 h post-hCG and injected with sperm cytosolic factor (SF), adenophostin A, or sperm (intracytoplasmic sperm injection), and the times at which signs of apoptosis first appeared were examined. These treatments, which induced [Ca2+]i oscillations, caused fragmentation and other signs of programmed cell death in eggs as early as 32 h post-hCG. The susceptibility of aged eggs to apoptosis appeared to be due to cytoplasmic deficiencies, because fusion of recently ovulated eggs with aged, SF-injected eggs prevented fragmentation. Evaluation of mRNA and protein levels of the apoptotic regulatory proteins Bcl-2 and Bax showed a prominent decrease in the amounts of Bcl-2 mRNA and protein in aged eggs, whereas Bax mRNA levels did not appear to be changed. Lastly, the Ca2+ responses induced by the aforementioned Ca2+ agonists ceased in advance in aged eggs. Together, these results suggest that one or several critical cytosolic molecules involved in the regulation of Ca2+ homeostasis, and in maintaining the equilibrium between anti- and proapoptotic proteins, is either lost or inactivated during postovulatory egg aging, rendering the fertilizing Ca2+ signal into an apoptosis-inducing signal.

Enhancement of hyperthermia-induced apoptosis by local anesthetics on human histiocytic lymphoma U937 cells

The combined effects of hyperthermia at 44 degrees C and local anesthetics on apoptosis in human histiocytic lymphoma U937 cells were investigated. When the cells were exposed to hyperthermia for l0 min marginal DNA fragmentation and nuclear fragmentation were observed. In the presence of amide-type local anesthetics further enhancement was found depending on concentration. The order of the concentration required for maximum induction was the reverse order of the lipophilicity (prilocaine > lidocaine > bupivacaine). Western blotting revealed that in hyperthermia there was initial release of Ca(2+) from the intracellular store site as indicated by increased expression of the type 1 inositol-1,4,5-trisphosphate receptor. However, the combination with lidocaine did not induce any further enhancement. Lidocaine enhanced the decrease in ATP content and the increase in intracellular Ca(2+) concentration in individual cells induced by hyperthermia. In addition, superoxide formation, decrease in the mitochondrial membrane potential, and activation of intracellular caspase-3 were found in the cells treated with hyperthermia and lidocaine. All of these were suppressed in part in the presence of the intracellular Ca(2+) ion chelator BAPTA-AM (bis-(O-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl). The present results indicate that local anesthetics at optimal concentrations enhance hyperthermia-induced apoptosis via Ca(2+)- and mitochondria-dependent pathways. Initial release of Ca(2+) from intracellular store sites caused by hyperthermia and followed by the subsequent increase in the intracellular Ca(2+) concentration and the additional activation of the mitochondrial caspase-dependent pathway (partly regulated by intracellular Ca(2+) concentration) plays a crucial role in the enhancement of apoptosis induced by the combination of hyperthermia and lidocaine.

Effects of dissolved gases and an echo contrast agent on apoptosis induced by ultrasound and its mechanism via the mitochondria-caspase pathway

Human histiocytic lymphoma U937 cells were exposed to continuous 1-MHz ultrasound (US) for therapeutic use, (0 approximately 6.5 W/cm(2) (I(SPTA)). Apoptosis and its related end points were examined by flow cytometry. Fraction of cells with low mitochondria membrane potential were observed after sonication and significant superoxide and peroxide formation, increased activity of caspase-3, and DNA fragmentation revealed biochemically, were also found. The fraction of early apoptosis and secondary necrosis increased with the incubation time after sonication. Early apoptosis observed at 6 h after sonication reached its maximum at 2 min of sonication and gradually decreased. On the other hand, secondary necrosis increased with the duration of sonication. When the effects of dissolved gases, Ar, N(2), O(2), air, N(2)O and CO(2), on free radical formation due to inertial cavitation were investigated by electron spin resonance (ESR) spin trapping, formation of hydroxyl radicals and hydrogen atoms was found in solutions saturated with Ar, N(2), O(2) and air, but not with N(2)O and CO(2). Apoptosis induced by US was also dependent on the dissolved gases in the order Ar = N(2) = O(2) = air >> N(2)O = CO(2) approximately 0. These results suggest that US-induced apoptosis, which is mitochondria-caspase dependent, was linked to inertial cavitation. However, quantities of free radicals did not influence the fraction of early apoptosis and secondary necrosis. When the cells were sonicated in the presence of an echo contrast agent, Levovist; synergistic enhancement of secondary necrosis induced by US was observed at concentrations of more than 20 mg/mL. In contrast, an additive increase of early apoptosis was observed in the combined treatments. These results suggest that Levovist; acting as cavitation nuclei, enhances secondary necrosis induced by US due to an increase in the membrane damage.

Enhancement of hyperthermia-induced apoptosis by non-thermal effects of ultrasound

To determine the effect of ultrasound on hyperthermia-induced apoptosis, we exposed U937 cells (in air-saturated suspension) to continuous 1 MHz ultrasound at intensities 0.5 or 1.0 W/cm(2), considered non-thermal and sub-threshold for inertial cavitation, while at 44.0 degrees C for 10 min. We found that 0.5 W/cm(2), in combination with hyperthermia, synergistically induced apoptosis. On the other hand, 1.0 W/cm(2) in combination with hyperthermia showed an augmented instant cell lysis but no significant change in the ratio of apoptosis. This result might be useful when apoptosis induction is desired over instant cell killing in cancer therapy.

Inhibition of the MAPK and PI3K pathways enhances UDCA-induced apoptosis in primary rodent hepatocytes

The mechanisms by which bile acids induce apoptosis in hepatocytes and the signaling pathways involved in the control of cell death are not understood fully. Here, we examined the impact of mitogen-activated protein kinase (MAPK) and phosphatidyl inositol 3-kinase (PI3K) signaling on the survival of primary hepatocytes exposed to bile acids. Treatment of hepatocytes with deoxycholic acid (DCA), chenodeoxycholic acid (CDCA) or ursodeoxycholic acid (UDCA) caused sustained MAPK activation that was dependent on activation of the epidermal growth factor receptor (EGFR). Activation of MAPK was partially blocked by inhibitors of PI3K. Inhibition of DCA-, CDCA-, and UDCA-stimulated MAPK activation resulted in approximately 20%, approximately 35%, and approximately 55% apoptosis, respectively. The potentiation of DCA- and CDCA-induced apoptosis by MEK1/2 inhibitors correlated with cleavage of procaspase 3, which was blocked by inhibitors of caspase 8 (ile-Glu-Thr-Asp-p-nitroanilide [IETD]) and caspase 3 (DEVD). In contrast, the potentiation of UDCA-induced apoptosis weakly correlated with procaspase 3 cleavage, yet this effect was also blocked by IETD and DEVD. Incubation of hepatocytes with the serine protease inhibitor AEBSF reduced the death response of cells treated with UDCA and MEK1/2 inhibitor to that observed for DCA and MEK1/2 inhibitor. The apoptotic response was FAS receptor- and neutral sphingomyelinase-dependent and independent of FAS ligand expression, and neither chelation of intracellular and extracellular Ca(2+) nor down-regulation of PKC expression altered the apoptotic effects of bile acids. In conclusion, bile acid apoptosis is dependent on the production of ceramide and is counteracted by activation of the MAPK and PI3K pathways.

Calpain activation after mitochondrial permeability transition in microcystin-induced cell death in rat hepatocytes

Previous studies have shown that microcystin-LR (MLR), a specific hepatotoxin, induces onset of mitochondrial permeability transition (MPT) and apoptosis in cultured rat hepatocytes. Here we attempted to investigate the downstream events after the onset of MPT in MLR-treated hepatocytes. Various mitochondrial electron transport chain (ETC) inhibitors effectively prevented the onset of MPT, suggesting that the mitochondrial ETC plays an important role in MLR-induced MPT. MLR also induced mitochondrial cytochrome c release, which can be prevented by a specific MPT inhibitor (cyclosporin A, CsA), and by various ETC inhibitors. Interestingly, the release of cytochrome c did not activate caspase-9 and -3, the main caspases involved in apoptosis. Instead, MLR activated calpain in rat hepatocytes, probably through the increase of intracellular Ca(2+) released from mitochondria. Both ALLN and ALLM, two calpain inhibitors, significantly blocked MLR-induced calpain activation and subsequent cell death. CsA also prevented MLR-induced calpain activation and cell death, suggesting that the activation of calpain may be a post-mitochondrial event. These data demonstrate for the first time that calpain rather than caspases plays an important role in MLR-induced apoptosis.

DNA microarray analyses of genes elicited by ultrasound in human U937 cells

The gene expression of human histiocytic lymphoma cell line U937 at 6 h after 1 MHz ultrasound treatment in the presence of Ar or N(2)O gas was examined by DNA microarrays. Of the 9,182 genes analyzed, only the keratin gene was identified as down-regulated in the cells exposed to ultrasound in the presence of N(2)O where no internal cavitation was observed. In contrast, five up-regulated and two down-regulated genes were identified in the cells exposed to ultrasound in the presence of Ar where internal cavitation was apparently observed. Six changes of the gene expression were confirmed by the semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Gene expression of heme oxygenase was augmented by a factor of 6.6 in microarray and by 4.0 by RT-PCR. These results indicate that internal cavitation increased the expression of genes responsive to oxidative stress in sonicated cells but non-inertial cavitation had minimal effects on gene expression.

Enhancement of hyperthermia-induced apoptosis by a free radical initiator, 2,2'-azobis (2-amidinopropane) dihydrochloride, in human histiocytic lymphoma U937 cells

To elucidate the mechanism how a free radical initiator, 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH), induces cell death at hyperthermic temperatures, apoptosis in a human histiocytic lymphoma cell line, U937, was investigated. Free radical formation deriving from the thermal decomposition of AAPH was examined by spin trapping with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). An assay for DNA fragmentation, observation of nuclear morphological changes, and flow cytometry for phosphatidylserine (PS) externalization were used to detect apoptosis and revealed enhancement of 44.0 degrees C hyperthermia-induced apoptosis by free radicals due to AAPH. However, free radicals alone derived from AAPH did not induce apoptosis. Hyperthermia induced the production of lipid peroxidation (LPO), an increase in intracellular Ca2+ concentration ([Ca2+]i) and enhanced expression of the type 1 inositol 1,4,5-trisphosphate receptor (IP3R1). The effects of hyperthermia on LPO and [Ca2+]i were enhanced markedly by the combination with AAPH. A significant decrease in Bcl-2 expression, increase in Bax expression, a loss of mitochondrial membrane potential (delta psi m) and a marked increase in cytochrome c expression were found only in cells treated with hyperthermia and AAPH. Although an intracellular Ca2+ ion chelator, BAPTA-AM, completely inhibited DNA fragmentation, water-soluble vitamin E, Trolox, only partially suppressed DNA fragmentation and the increase in [Ca2+]i. In contrast, LPO was inhibited completely by Trolox, but no inhibition by BAPTA-AM was found. These results suggest that apoptosis induced by hyperthermia alone is due to the increase in [Ca2+]i arising from increased expression of IP3R1 and LPO. Additional increase in [Ca2+]i due to increased LPO and the activation of mitochondria-caspase dependent pathway play a major role in the enhancement of apoptosis by the combination with hyperthermia and AAPH.

The role of calpain in caspase activation during etoposide induced apoptosis in T cells

T cells treated with the drug etoposide undergo apoptotic death characterized by early evidence of nuclear damage followed by loss of mitochondrial integrity and cell lysis. Calpains and caspases are cytoplasmic proteases and there is increasing evidence of cross-talk between these proteases in death pathways. In this study we have investigated the role of calpain, in etoposide-triggered apoptosis in the 2B4 murine T cell hybridoma. Cell permeable inhibitors of calpain, ALLnM, E64 and calpeptin that block Fas ligand-Fas-mediated death in T cells, blocked etoposide-induced nuclear damage, loss of mitochondrial integrity and cell lysis. A broad spectrum peptide inhibitor of caspases, ZVAD-fmk, partially blocked nuclear damage but poorly inhibited mitochondrial damage or cell lysis triggered by etoposide. Etoposide-induced expression of the cleaved, proteolytically active form of caspase 3, and DEVD-ase activity, detected prior to nuclear damage, were blocked in the presence of calpain inhibitors. Collectively, these data describe a role for calpain in regulating etoposide-induced apoptosis via a caspase-dependent pathway in T cells.

The role of intracellular Ca(2+) in apoptosis induced by hyperthermia and its enhancement by verapamil in U937 cells

PURPOSE

The relationship between apoptosis induced by 42 degrees C and 44 degrees C hyperthermia alone or in combination with verapamil and changes in intracellular Ca(2+) concentration ([Ca(2+)]i) was investigated in U937 cells.

METHODS

Apoptosis induced by hyperthermia was assessed according to DNA fragmentation, nuclear morphologic changes, and expression of phosphatidylserine on the outside plasma cell membrane. These changes were measured by flow cytometry. The [Ca(2+)]i of individual cells after hyperthermia was monitored by a digital image-analyzing technique using Fura-2.

RESULTS

Hyperthermia-induced apoptosis reached a plateau after 6 h and was found to be both time and temperature-dependent. DNA fragmentation was maximum at 44 degrees C after 30 min. Verapamil enhanced the apoptosis induced by 42 degrees C and 44 degrees C hyperthermia in normal cells and by 44 degrees C hyperthermia in thermotolerant cells. The number of cells containing higher [Ca(2+)]i (more than 200 nM) was significantly increased by hyperthermia and further elevated by the addition of verapamil in both normal and thermotolerant cells. Apoptosis induced by hyperthermia was markedly decreased by an intracellular Ca(2+) chelator, BAPTA-AM, in a dose-dependent manner.

CONCLUSION

These results indicate that [Ca(2+)]i increase plays a crucial role in apoptosis induced by hyperthermia and the combined treatment with verapamil in normal and thermotolerant U937 cells. Furthermore, hyperthermia-combined drug therapy has potential significance in cancer therapy.