Mechanism of UV-induced apoptosis in human leukemia cells: roles of Ca2+/Mg(2+)-dependent endonuclease, caspase-3, and stress-activated protein kinases

Overexpression of Selenoprotein SelK in BGC-823 Cells Inhibits Cell Adhesion and Migration

Effects of human selenoprotein SelK on the adhesion and migration ability of human gastric cancer BGC-823 cells using Matrigel adhesion and transwell migration assays, respectively, were investigated in this study. The Matrigel adhesion ability of BGC-823 cells that overexpressed SelK declined extremely significantly (p < 0.01) compared with that of the cells not expressing the protein. The migration ability of BGC-823 cells that overexpressed SelK also declined extremely significantly (p < 0.01). On the other hand, the Matrigel adhesion ability and migration ability of the cells that overexpressed C-terminally truncated SelK did not decline significantly. The Matrigel adhesion ability and migration ability of human embryonic kidney HEK-293 cells that overexpressed SelK did not show significant change (p > 0.05) with the cells that overexpressed the C-terminally truncated protein. In addition to the effect on Matrigel adhesion and migration, the overexpression of SelK also caused a loss in cell viability (as measured by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H tetrazolium bromide (MTT) colorimetric assay) and induced apoptosis as shown by confocal microscopy and flow cytometry. The cytosolic free Ca2+ level of these cells was significantly increased as detected by flow cytometry. But the overexpression of SelK in HEK-293 cells caused neither significant loss in cell viability nor apoptosis induction. Only the elevation of cytosolic free Ca2+ level in these cells was significant. Taken together, the results suggest that the overexpression of SelK can inhibit human cancer cell Matrigel adhesion and migration and cause both the loss in cell viability and induction of apoptosis. The release of intracellular Ca2+ from the endoplasmic reticulum might be a mechanism whereby the protein exerted its impact. Furthermore, only the full-length protein, but not C-terminally truncated form, was capable of producing such impact. The embryonic cells were not influenced by the elevation of free Ca2+ level in cytosol, probably due to their much greater tolerance to the variation.

SOD/catalase mimetic platinum nanoparticles inhibit heat-induced apoptosis in human lymphoma U937 and HH cells

Platinum nanoparticles (Pt-NPs) are known to possess anti-tumouric activity and the ability to scavenge superoxides and peroxides indicating that they can act as superoxide dismutase (SOD)/catalase mimetics. These potentials seem useful in the protection and/or amelioration of oxidative stress-associated pathologies, but, when they are combined with a therapeutic modality that depends upon the mediation of reactive oxygen species in cell killing induction, the effect of Pt-NPs might be questionable. Here, the effects of polyacrylic acid-capped Pt-NPs (nano-Pts) on hyperthermia (HT)-induced apoptosis and the underlying molecular mechanisms were investigated in human myelomonocytic lymphoma U937 and human cutaneous T-cell lymphoma HH cells. The results showed that the pre-treatment with nano-Pts significantly inhibited HT-induced apoptosis in a dose-dependent manner. Superoxide, but not peroxides, was suppressed to varying extents. All pathways involved in apoptosis execution were also negatively affected. The results reveal that the combination of nano-Pts and HT could result in HT-desensitization.

Enhancement of macrosphelide-induced apoptosis by mild hyperthermia

Hyperthermia is a useful adjunct in cancer therapy as it can increase the effectiveness and decrease the toxicity of currently available cancer treatments such as chemotherapy and radiation. In the present study, we investigated whether 41 degrees C hyperthermia (mild HT) for 20 min can enhance macrosphelide (MS5)-induced apoptosis in human lymphoma U937 cells. Our results revealed that, compared with MS5 (5 microM) and mild HT alone, the combined treatment exhibited significant enhancement in apoptosis at 6 h, which was evaluated by observing morphological changes and DNA fragmentation. Marked increase in the reactive oxygen species (ROS) generation was observed immediately after the combined treatment. Significant increase in Fas externalization, caspase-8 and caspase-3 activation, and loss of mitochondrial membrane potential (MMP) was found after the combined treatment compared with MS5 and mild HT alone. Moreover, this combination can also alter the expression of apoptosis-related proteins as evident by the cleavage of Bid and down-regulation of Bcl-2 while no change in the expression of Bax was observed. Furthermore, an immediate rise in the intracellular calcium ion ([Ca(2+)]i) concentration was observed after the combined treatment, which continuously increased in a time-dependent manner. In addition, mild HT treatment alone also increases [Ca(2+)]i concentration without inducing apoptosis. Our data indicate that early increase in ROS generation is mainly responsible for the enhancement of apoptosis after the combined treatment.

The MIF receptor CD74 in diabetic podocyte injury

Although metabolic derangement plays a central role in diabetic nephropathy, a better understanding of secondary mediators of injury may lead to new therapeutic strategies. Expression of macrophage migration inhibitory factor (MIF) is increased in experimental diabetic nephropathy, and increased tubulointerstitial mRNA expression of its receptor, CD74, has been observed in human diabetic nephropathy. Whether CD74 transduces MIF signals in podocytes, however, is unknown. Here, we found glomerular and tubulointerstitial CD74 mRNA expression to be increased in Pima Indians with type 2 diabetes and diabetic nephropathy. Immunohistochemistry confirmed the increased glomerular and tubular expression of CD74 in clinical and experimental diabetic nephropathy and localized glomerular CD74 to podocytes. In cultured human podocytes, CD74 was expressed at the cell surface, was upregulated by high concentrations of glucose and TNF-alpha, and was activated by MIF, leading to phosphorylation of extracellular signal-regulated kinase 1/2 and p38. High glucose also induced CD74 expression in a human proximal tubule cell line (HK2). In addition, MIF induced the expression of the inflammatory mediators TRAIL and monocyte chemoattractant protein 1 in podocytes and HK2 cells in a p38-dependent manner. These data suggest that CD74 acts as a receptor for MIF in podocytes and may play a role in the pathogenesis of diabetic nephropathy.

RAGE mediates podocyte injury in adriamycin-induced glomerulosclerosis

In the kidney, the receptor for advanced glycation end products (RAGE) is principally expressed in the podocyte at low levels, but is upregulated in both human and mouse glomerular diseases. Because podocyte injury is central to proteinuric states, such as the nephrotic syndrome, the murine adriamycin nephrosis model was used to explore the role of RAGE in podocyte damage. In this model, administration of the anthracycline antibiotic adriamycin provokes severe podocyte stress and glomerulosclerosis. In contrast to wild-type animals, adriamycin-treated RAGE-null mice were significantly protected from effacement of the podocyte foot processes, albuminuria, and glomerulosclerosis. Administration of adriamycin induced rapid generation of RAGE ligands, and treatment with soluble RAGE protected against podocyte injury and glomerulosclerosis. In vitro, incubation of RAGE-expressing murine podocytes with adriamycin stimulated AGE formation, and treatment with RAGE ligands rapidly activated nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase, via p44/p42 MAP kinase signaling, and upregulated pro-fibrotic growth factors. These data suggest that RAGE may contribute to the pathogenesis of podocyte injury in sclerosing glomerulopathies such as focal segmental glomerulosclerosis.

Inhibition of UVA-induced apoptotic signaling pathway by polypeptide from Chlamys farreri in human HaCaT keratinocytes

Chronic UVA irradiation has been reported to induce photoaging and photocarcinogenesis. UVA is a potent inducer of reactive oxygen species (ROS), which can induce various biological processes, including apoptosis. Polypeptide from Chlamys farreri (PCF) is a novel marine active material isolated from the gonochoric Chinese scallop C. farreri. In our previous studies, PCF was found to be an effective antioxidant inhibiting UVA-induced ROS production and a potential inhibitory agent for UVA-induced apoptosis in the human keratinocyte cell line HaCaT. The intracellular mechanisms of how PCF protects HaCaT cells from UVA-induced apoptosis are not understood. Thus, we here investigate the effect of PCF on UVA-induced intracellular signaling of apoptosis. Pretreatment with the ROS scavenger N-acetylcysteine (NAC), the p38 MAPK inhibitor SB203580 or the caspase-3 inhibitor Ac-DEVD-CHO was found to effectively prevent UVA-induced apoptosis, indicating that ROS, p38 MAPK and caspase-3 play important roles in apoptosis. H(2)O(2)-induced apoptosis was attenuated by PCF, suggesting that PCF plays its anti-apoptotic role through its antioxidant activity. In addition, PCF treatment inhibited UVA-induced p38 MAPK activation and caspase-3 activation, as assayed by Western blot analysis and flow cytometry, respectively. Our results suggest that PCF attenuates UVA-induced apoptosis through a reduction of ROS generation and diminished p38 MAPK and caspase-3 activation.

Mechanism of cell death induction by nitroxide and hyperthermia

Heat stress and nitroxides induce reactive oxygen species (ROS) and proapoptotic effects. The underlying mechanisms remain largely elusive. Here we report that Tempo (2,2,6,6-tetramethylpiperidine-N-oxyl) is a potent thermosensitizer for promoting cell death in human leukemia U937 cells. Treatment with Tempo (10 mM, 37 degrees C/30 min) and hyperthermia (44 degrees C/30 min) induced 30 and 70-80% apoptosis, respectively, through Bax-mediated cytochrome c release and DEVDase activation. The Tempo/heat combination also caused Bax-mediated cytochrome c release, but switched heat-induced apoptosis to the particular pyknotic cell death, resulting in the irreparable inhibition of proliferation. Tempo and heat stress, but not the combination, caused an early transient elevation of H2O2/O2*- and a late induction of only O2*-, respectively. Mitochondrial Ca2+ overloads were indistinguishable after any treatment. Heat stress induced the pan-caspase inhibitor zVAD-fmk-suppressible low-Deltapsi (mitochondrial membrane potential) in 75% of cells as a result of DEVDase activation. In contrast, Tempo yielded low-Deltapsi by deprivation of the mitochondrial H+ gradient. The combined treatment induced 97% zVAD-resistant low-Deltapsi cells through irreversible mitochondrial dysfunction. Together, thus, Tempo or heat stress induced Bax-mediated mitochondrial apoptosis with the possible help of ROS or mitochondrial Ca2+, and Tempo when combined with hyperthermia acts a sensitizer by inducing irreparable pyknotic cell death through irreversible mitochondrial dysfunction.

Enhanced expression of transferrin receptor confers UV-resistance in human and monkey cells

One of the most intriguing biological subjects is cell-surface molecules that regulate the susceptibility of human cells to cell-killing effects after irradiation with far-ultraviolet light (UV, principally 254 nm wavelength). Human RSa cells have unusual sensitivity to UV-induced cell-killing. We searched for molecules on the cell-surface of RSa cells that were present in different amounts as compared to a variant of these cells, UV(r)-1 cells, which have increased resistance to UV cell-killing. Among the 21 molecules examined, the amount of transferrin receptor (TfR) protein was found to be 2-fold higher in UV(r)-1 cells compared with in RSa cells. The amounts of this protein were also higher in the UV-resistant hematopoietic cell lines, CEM6 and Daudi, as compared to the UV-sensitive cell lines, Molt4 and 697. Culturing of UV(r)-1 cells in a medium containing anti-transferrin antibodies resulted in sensitization of the cells to UV cell-killing as demonstrated by colony formation assay. Similar results were observed by treatment of the cells with TfR siRNA. In contrast, overexpression of TfR protein led to a resistance to UV cell-killing in RSa cells and monkey COS7 cells as demonstrated by both colony formation and apoptosis assay. In TfR-overexpressing cells, reduction of p53 and Bax protein was observed after UV-irradiation. Thus, TfR expression appears to be involved in the regulation of UV-resistance, possibly via modulation of the amount of p53 and Bax protein.

Role of p38 Mitogen-Activated Protein Kinase Activation in Podocyte Injury and Proteinuria in Experimental Nephrotic Syndrome

Podocytes play an important role in maintaining normal glomerular function and structure, and podocyte injury leads to proteinuria and glomerulosclerosis. The family of mitogen-activated protein kinases (MAPK; extracellular signal-regulated kinase [ERK], c-Jun N-terminal kinase, and p38) may be implicated in the progression of various glomerulopathies, but the role of MAPK in podocyte injury remains elusive. This study examined phosphorylation of p38 MAPK in clinical glomerulopathies with podocyte injury, as well as in rat puromycin aminonucleoside (PAN) nephropathy and mouse adriamycin (ADR) nephropathy. The effect of treatment with FR167653, an inhibitor of p38 MAPK, was also investigated in rodent models. In human podocyte injury diseases, the increased phosphorylation of p38 MAPK was observed at podocytes. In PAN and ADR nephropathy, the phosphorylation of p38 MAPK and ERK was marked but transient, preceding overt proteinuria. Pretreatment with FR167653 (day -2 to day 14, subcutaneously) to PAN or ADR nephropathy completely inhibited p38 MAPK activation and attenuated ERK phosphorylation, with complete suppression of proteinuria. Electron microscopy and immunohistochemistry for nephrin and connexin43 revealed that podocyte injury was markedly ameliorated by FR167653. Furthermore, early treatment with FR167653 effectively prevented glomerulosclerosis and renal dysfunction in the chronic phase of ADR nephropathy. In cultured podocytes, PAN or oxidative stress induced the phosphorylation of p38 MAPK along with actin reorganization, and FR167653 inhibited such changes. These findings indicate that the activation of MAPK is necessary for podocyte injury, suggesting that p38 MAPK and, possibly, ERK should become a potential target for therapeutic intervention in proteinuric glomerulopathies.

Xenobiotic-induced TNF-alpha expression and apoptosis through the p38 MAPK signaling pathway

Some xenobiotics, such as dichlorodiphenyltrichloroethane (DDT), bind to and activate estrogen receptors (ERs), eliciting estrogenic effects in both wildlife and humans. However, our laboratory and others have demonstrated that DDT and DDT-like compounds target non-ER pathways. In search for a molecular mechanism we recently established that DDT and its metabolites stimulate activator protein-1 (AP-1)-mediated gene expression through the p38 mitogen-activated protein kinase (MAPK) cascade. Here, we determined that DDT-induced p38 activity produces a novel environmental signaling pathway in endometrial Ishikawa and human embryonic kidney (HEK) 293 cells. Xenobiotic exposure stimulates expression of the death ligand, tumor necrosis factor-alpha (TNF-alpha) as demonstrated using RT-PCR and reporter gene assays. Furthermore, DDT-induced p38 activity led to the release of cytochrome c from the mitochondria and activation of caspase-3/7. Ultimately, DDT-treated cells underwent cell death. Taken together, these data demonstrate DDT induces both the expression of the death ligand TNF-alpha and apoptosis through a p38 MAPK-dependent mechanism.

Enhancement of apoptosis by nitric oxide released from α-phenyl-tert-butyl nitrone under hyperthermic conditions

The aim of this study was to examine whether a neuroprotector, PBN (alpha-phenyl-tert-butyl nitrone), enhances apoptosis induced by hyperthermia, which generates superoxide (O2-) intracellularly, since the release of nitric oxide (NO) from PBN under oxidative stress has been reported. When human myelomonocytic lymphoma U937 cells were treated with hyperthermia (44 degrees C, 10 min) and PBN, an increase in the concentration of nitrite in the culture medium, and a decrease in the hyperthermia-induced production of O2- was observed. Imaging using a fluorescence dye for intracellular NO, diaminofluorescein-2 diacetate (DAF-2 DA), revealed the formation of NO in the apoptotic cells treated with hyperthermia and PBN combined. Apoptotic endpoints were significantly enhanced by the combined treatment: a decrease in mitochondrial trans-membrane potential, cleavage of Bid, release of cytochrome c, and activation of caspase-8 and -3. An increase in the intracellular Ca2+ concentration ([Ca2+]i), externalization of Fas, and decrease in Hsp70 and phosphorylated HSF1 were observed following the combined treatment. Furthermore, scavengers of NO an d ONOO- significantly inhibited the enhancement of apoptosis, the externalization of Fas and the increase in [Ca2+]i. These results suggest that, (1) NO is released from PBN by hyperthermia, and subsequently reacts with O2- to form ONOO-, (2) NO and ONOO- are involved in the enhancement of apoptosis through Fas-mitochondria-caspase and [Ca2+]i-dependent pathways, and (3) a decrease in Hsp70 and phosphorylated HSF1 also contributed to the enhancement of apoptosis.

Actinonin induces apoptosis in U937 leukemia cells

We have previously shown that actinonin causes inhibition of cellular proliferation in U937 leukemia cells. In this report we demonstrate that the inhibition of cell growth by actinonin occurs through the induction of apoptosis. Signs of apoptosis at high actinonin concentration included DNA fragmentation, exposure of phosphatidylserine and condensation of cell nuclei. Apoptosis caused by actinonin was inhibited by Z-VAD-FMK, a broad specificity inhibitor of caspases, implicating the caspase pathway of apoptosis. Further, apoptosis was associated with a large increase in intracellular caspase-3 and -7 activities.

Heat shock proteins in the regulation of apoptosis: new strategies in tumor therapy: a comprehensive review

Heat shock proteins (Hsp) form the most ancient defense system in all living organisms on earth. These proteins act as molecular chaperones by helping in the refolding of misfolded proteins and assisting in their elimination if they become irreversibly damaged. Hsp interact with a number of cellular systems and form efficient cytoprotective mechanisms. However, in some cases, wherein it is better if the cell dies, there is no reason for any further defense. Programmed cell death is a widely conserved general phenomenon helping in many processes involving the reconstruction of multicellular organisms, as well as in the elimination of old or damaged cells. Here, we review some novel elements of the apoptotic process, such as its interrelationship with cellular senescence and necrosis, as well as bacterial apoptosis. We also give a survey of the most important elements of the apoptotic machinery and show the various modes of how Hsp interact with the apoptotic events in detail. We review caspase-independent apoptotic pathways and anoikis as well. Finally, we show the emerging variety of pharmacological interventions inhibiting or, just conversely, inducing Hsp and review the emergence of Hsp as novel therapeutic targets in anticancer protocols.

Signal transduction of p53-independent apoptotic pathway induced by hexavalent chromium in U937 cells

It has been reported that the hexavalent chromium compound (Cr(VI)) can induce both p53-dependent and p53-independent apoptosis. While a considerable amount of information is available on the p53-dependent pathway, only little is known about the p53-independent pathway. To elucidate the p53-independent mechanism, the roles of the Ca(2+)-calpain- and mitochondria-caspase-dependent pathways in apoptosis induced by Cr(VI) were investigated. When human lymphoma U937 cells, p53 mutated cells, were treated with 20 microM Cr(VI) for 24 h, nuclear morphological changes and DNA fragmentation were observed. Production of hydroxyl radicals revealed by electron paramagnetic resonance (EPR)-spin trapping, and increase of intracellular calcium ion concentration monitored by digital imaging were also observed in Cr(VI)-treated cells. An intracellular Ca(2+) chelator, BAPTA-AM, and calpain inhibitors suppressed the Cr(VI)-induced DNA fragmentation. The number of cells showing low mitochondrial membrane potential (MMP), high level of superoxide anion radicals (O(2)(-)), and high activity of caspase-3, which are indicators of mitochondria-caspase-dependent pathway, increased significantly in Cr(VI)-treated cells. An antioxidant, N-acetyl-l-cysteine (NAC), decreased DNA fragmentation and inhibited the changes in MMP, O(2)(-) formation, and activation of caspase-3 induced by Cr(VI). No increase of the expressions of Fas and phosphorylated JNK was observed after Cr(VI) treatment. Cell cycle analysis revealed that the fraction of G2/M phase tended to increase after 24 h of treatment, suggesting that Cr(VI)-induced apoptosis is related to the G2 block. These results indicate that Ca(2+)-calpain- and mitochondria-caspase-dependent pathways play significant roles in the Cr(VI)-induced apoptosis via the G2 block, which are independent of JNK and Fas activation. The inhibition of apoptosis and all its signal transductions by NAC suggests that intracellular reactive oxygen species (ROS) are important for both pathways in Cr(VI)-induced apoptosis of U937 cell.

Role of intracellular calcium ions and reactive oxygen species in apoptosis induced by ultrasound

Recently, we have reported that ultrasound (US)-induced apoptosis is due to inertial cavitation and that extracellular reactive oxygen species (ROS) generated by inertial cavitation are not directly correlated with the apoptosis (Honda et al. 2002). The molecular mechanism of apoptosis induced by US is not yet sufficiently clear. Here, we examine the role of intracellular calcium ions and the intracellular ROS on apoptosis induced by US. Human myelomonocytic lymphoma U937 cells were exposed to continuous 1-MHz US at an intensity of 4.9 W/cm(2) (I(SPTA)) in the presence of air, and changes of intracellular calcium ion concentration ([Ca(2+)]i) in individual cells by digital imaging, various flow cytometric analyses of endpoints of apoptosis (early apoptosis, secondary necrosis, loss of mitochondria membrane potential, superoxide formation, caspase-3 activation) and DNA fragmentation were explored. Furthermore, the effects of an intracellular calcium ion chelator (BAPTA-AM), an antioxidant (N-acetyl-L-cysteine, NAC), a calcium channel blocker (verapamil), Ca(2+)-free buffer and Levovist were also investigated. These results indicate that: 1. the mitochondria-caspase pathway and the Ca(2+)-dependent pathway play cardinal roles in apoptosis induced by US because BAPTA-AM partially inhibited DNA fragmentation, loss of mitochondria membrane potential and caspase-3 activation; 2. intracellular ROS generated from mitochondria, rather than extracellular ROS (which were directly produced by inertial cavitation in the medium), are involved in the regulation of apoptosis induced by US because addition of NAC after sonication showed effective suppression of the apoptosis; and 3. increase of [Ca(2+)]i appears to be due to nonspecific influx from outside the cells because verapamil is not effective and no increase of [Ca(2+)]i due to sonication could be observed in the Ca(2+)-free buffer.

Thyrotropin effects on ultraviolet radiation-dependent apoptosis in FRTL-5 cells

Apoptosis plays an important role within the endocrine system, particularly in the thyroid gland, although little is known about its regulation in normal thyroids. Because thyrotropin (TSH) regulates many thyroid-specific functions and cell proliferation, we investigated whether TSH can influence such mechanisms. To induce apoptosis we used UV-C radiation. The FRTL-5 rat thyroid cell strain, a cloned strain of differentiated and untransformed cells that reproduces many of the characteristics of the normal thyroid was chosen for this study. The FRTL-5 cells are a particularly suitable model because they actively proliferate when cultured in the presence of TSH (6H medium), while in TSH-free medium (5H medium) cells remain in a physiologic quiescent state for a long period of time. FRTL-5 cells in both culture conditions were irradiated with UV-C radiation (254 nm wavelength). At 48 hours after radiation, 6H cultured cells showed the characteristic signs of apoptosis. However, 5H cultured cells did not present macroscopic signs of damage, DNA fragmentation, or detectable apoptosis. Furthermore, the expression of 23 apoptosis-related genes was compared. Results indicate that Bcl2 and caspase-2 expression is enhanced, while bax, GADD45 and mdm-2 expression is reduced in irradiated cells. These data confirm that TSH plays a major role in regulating UV-induced apoptosis in FRTL-5 cells.

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.

Hematopoietic factor erythropoietin fosters neuroprotection through novel signal transduction cascades

In addition to promoting the survival, proliferation, and differentiation of immature erythroid cells, erythropoietin and the erythropoietin receptor have recently been shown to modulate cellular signal transduction pathways that extend beyond the erythropoietic function of erythropoietin. In particular, erythropoietin has been linked to the prevention of programmed cell death in neuronal systems. Although this work is intriguing, the underlying molecular mechanisms that serve to mediate neuroprotection by erythropoietin are not well understood. Further analysis illustrates that erythropoietin modulates two distinct components of programmed cell death that involve the degradation of DNA and the externalization of cellular membrane phosphatidylserine residues. Initiation of the cascades that modulate protection by erythropoietin and its receptor may begin with the activation of the Janus tyrosine kinase 2 protein. Subsequent downstream mechanisms appear to lead to the activation of multiple signal transduction pathways that include transcription factor STAT5 (signal transducers and activators of transcription), Bcl-2, protein kinase B, cysteine proteases, mitogen-activated protein kinases, protein-tyrosine phosphatases, and nuclear factor-kappaB. New knowledge of the cellular pathways regulated by erythropoietin in neuronal environments will potentially solidify the development and initiation of therapeutic strategies against nervous system disorders.

Magnesium-DNA interactions and the possible relation of magnesium to carcinogenesis. Irradiation and free radicals

Magnesium deficiency causes renal complications. The appearance of several diseases is related to its depletion in the human body. In radiotherapy, as well as in chemotherapy, especially in treatment of cancers with cis-platinum, hypomagnesaemia is observed. The site effects of chemotherapy that are due to hypomagnesaemia are decreased using Mg supplements. The role of magnesium in DNA stabilization is concentration dependent. At high concentrations there is an accumulation of Mg binding, which induces conformational changes leading to Z-DNA, while at low concentration there is deficiency and destabilization of DNA. The biological and clinical consequences of abnormal concentrations are DNA cleavage leading to diseases and cancer. Carcinogenesis and cell growth are also magnesium-ion concentration dependent. Several reports point out that the interaction of magnesium in the presence of other metal ions showed that there is synergism with Li and Mn, but there is magnesium antagonism in DNA binding with the essential metal ions in the order: Zn>Mg>Ca. In the case of toxic metals such as Cd, Ga and Ni there is also antagonism for DNA binding. It was found from radiolysis of deaerated aqueous solutions of the nucleoside 5'-guanosine monophosphate (5'-GMP) in the presence as well as in the absence of magnesium ions that, although the addition of hydroxyl radicals (*OH) has been increased by 2-fold, the opening of the imidazole ring of the guanine base was prevented. This effect was due to the binding of Mg2+ ions to N7 site of the molecule by stabilizing the five-member ring imitating cis-platinum. It was also observed using Fourier Transform Infrared spectroscopy, Raman spectroscopy and Fast Atom Bombardment mass spectrometry that *OH radicals subtract H atoms from the C1', C4' and C5' sites of the nucleotide. Irradiation of 5'-GMP in the presence of oxygen (2.5 x 10(-4) M) shows that magnesium is released from the complex. There is spectroscopic evidence that superoxide anions (O2-*) react with magnesium ions leading to magnesium release from the complex. From radiolysis data it was suggested that magnesium ions can act as radiosensitizers in the absence of oxygen, while in the presence of oxygen they act as protectors and stabilizers of DNA.

Wogonin and fisetin induce apoptosis in human promyeloleukemic cells, accompanied by a decrease of reactive oxygen species, and activation of caspase 3 and Ca(2+)-dependent endonuclease

Seven structurally related flavonoids including luteolin, nobiletin, wogonin, baicalein, apigenin, myricetin and fisetin were used to study their biological activities on the human leukemia cell line, HL-60. On MTT assay, wogonin, baicalein, apigenin, myricetin and fisetin showed obvious cytotoxic effects on HL-60 cells, with wogonin and fisetin being the most-potent apoptotic inducers among them. The cytotoxic effects of wogonin and fisetin were accompanied by the dose- and time-dependent appearance of characteristics of apoptosis including DNA fragmentation, apoptotic bodies and the sub-G1 ratio. Treatment with an apoptosis-inducing concentration of wogonin or fisetin causes rapid and transient induction of caspase 3/CPP32 activity, but not caspase 1 activity. Further, cleavage of poly(ADP-ribose) polymerase (PARP) and decrease of pro-caspase 3 protein were detected in wogonin- and fisetin-treated HL-60 cells. An increase in the pro-apoptotic protein, bax, and a decrease in the anti-apoptotic protein, Mcl-1, were detected in fisetin- and wogonin-treated HL-60 cells. However, Bcl-2, Bcl-XL, and Bad all remained unchanged in wogonin- and fisetin-treated HL-60 cells. In vitro chromatin digestion revealed that endonuclease activity was profoundly enhanced in wogonin- and fisetin-treated HL-60 cells, and the addition of ethylenediaminetetraacetic acid (EDTA) or ethyleneglycoltetraacetic acid (EGTA) into the reaction blocked endonuclease activation and at an optimum pH of 7.5. The caspase 3 inhibitor, Ac-DEVD-CHO, but not the caspase 1 inhibitor, Ac-YVAD-CHO, attenuated wogonin- and fisetin-induced DNA ladders, PARP cleavage, and endonuclease activation. Pretreatment of HL-60 cells with N-acetyl-cysteine or catalase efficiently inhibited H(2)O(2) (200 microM)-induced apoptosis, but showed no inhibitory effect on wogonin- and fisetin-induced DNA ladders, caspase 3 activation, or bax protein induction. Decrease in endogenous ROS production was detected in wogonin- and fisetin-treated HL-60 cells by DCHF-DA assay. In conclusion, our experiments indicate that a decrease in intracellular peroxide level was involved in wogonin- and fisetin-induced apoptosis; activation of caspase 3 and endonuclease, induction of bax protein and suppression of Mcl-1 protein were detected in the process.

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.

Expression of caspases-3, -6 and -8 and their relation to apoptosis in non-small cell lung carcinoma

We analyzed a set of 103 non-small cell lung carcinomas (NSCLCs) for caspase-3, -6 and -8 expression and apoptosis. Additionally, the expression of bcl-2, bax and p53 were studied. Caspase-3 positivity appeared as diffuse, cytoplasmic staining and was restricted to the tumor area. In contrast, the immunoreactivity for caspase-6 was intense, granular and mostly located in single cells or groups of tumor cells showing apoptotic morphology. The caspase-8 expression pattern was a combination of the two other caspases studied, featuring both diffuse and single-cell patterns restricted to the tumor area. No significant differences were seen in caspase -3, -6 and -8 expression between tumors of different histological types or grades. The number of apoptotic cells and bodies was significantly higher in NSCLCs, in which caspase-8 immunostaining was mainly seen in single cells (p = 0.017), whereas caspase -3 and -6 expression had no association with apoptosis. It is apparent that, in lung tissue, up-regulation of caspase expression is a phenomenon associated solely with neoplasia and reflects the readiness of the tumor cells to undergo apoptosis. Interestingly, caspases -3, -6 and -8 each have an individual staining pattern in NSCLC, perhaps reflecting their different position in the caspase hierarchy.

Glyoxal and methylglyoxal trigger distinct signals for map family kinases and caspase activation in human endothelial cells

Carbonyl compounds with diverse carbon skeletons may be differentially related to the pathogenesis of vascular diseases. In this study, we compared intracellular signals delivered into cultured human umbilical vein endothelial cells (HUVECs) by glyoxal (GO) and methylglyoxal (MGO), which differ only by a methyl group. Depending on their concentrations, GO and MGO promoted phosphorylations of ERK1 and ERK2, which were blocked by the protein-tyrosine kinase (PTK) inhibitors herbimycin A and staurosporine, thereby being PTK-dependent. GO and MGO also induced phosphorylations of JNK, p38 MAPK, and c-Jun, either PTK-dependently (GO) or -independently (MGO). Next, we found that MGO, but not GO, induced degradation of poly(ADP-ribose) polymerase (PARP) as the intracellular substrate of caspase-3. Curcumin and SB203580, which inhibit JNK and p38 MAPK signaling pathways, but not herbimycin A/staurosporine, prevented the MGO-induced PARP degradation. We then found that MGO, but not GO, reduced the intracellular glutathione level, and that cysteine, but not cystine, inhibited the MGO-mediated activation of ERK, JNK, p38 MAPK, or c-Jun more extensively than did lysine or arginine. In addition, all the signals triggered by GO and MGO were blocked by amino guanidine (AG), which traps carbonyls. These results demonstrated that GO and MGO triggered two distinct signal cascades, one for PTK-dependent control of ERK and another for PTK-independent redox-linked activation of JNK/p38 MAPK and caspases in HUVECs, depending on the structure of the carbon skeleton of the chemicals.

Fas-independent apoptosis induced by UVC in p53-mutated human epithelial tumor A431 cells through activation of caspase-8 and JNK/SAPK

A431 cells/UVC-induced apoptosis/Caspase 8/Fas/JNK/PAPK. We previously observed that p53-mutated human epithelial tumor A431 cells underwent apoptosis after ultraviolet C (UVC) irradiation through the caspases-8 and -3 pathway. Fas/FasL is known to initiate apoptosis in several cell lines via caspase-8 activation. Then, to determine if Fas/FasL mediates apoptosis in A431. we investigated Fas expression and modulation in UVC-irradiated A431 cells. A431 constitutively expressed Fas, which gradually decreased after UVC-irradiation. Pretreatment with a neutralizing anti-Fas antibody, ZB4, did not abrogate the UVC-induced apoptosis. An agonistic anti-Fas antibody, CH11, very slowly induced apoptosis in A431. suggesting that the constitutively expressed Fas had a low functional potential. Hence, UVC-induced apoptosis in A431 seems to occur independent of the Fas signal. Interestingly, however, a pretreatment with CH11 remarkably potentiated UVC-induced apoptosis. An inhibitor of caspase-8, Ac-IETD-CHO, partially inhibited UVC-induced apoptosis. JNK was phosphorylated immediately after exposure to UVC. prior to apoptotic chromatin condensation. Our data suggest that the activation of caspase-8 occurs independent of Fas upregulation, and that JNK/ SAPK contributes to UVC-induced apoptosis in human epithelial A431 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.

Se-methylselenocysteine induces apoptosis through caspase activation in HL-60 cells

Apoptosis, a programmed process of cell suicide, has been proposed as the most plausible mechanism for the chemopreventive activities of selenocompounds. In our study, we found that Se-methylselenocysteine (MSC) induced apoptosis through caspase activation in human promyelocytic leukemia (HL-60) cells. Measurements of cytotoxicity, DNA fragmentation and apoptotic morphology revealed that MSC was more efficient at inducing apoptosis than selenite, but was less toxic. Moreover, MSC increased both the apoptotic cleavage of poly(ADP-ribose) polymerase (PARP) and caspase-3 activity, whereas selenite did not. We next examined whether caspases and serine proteases are required for the apoptotic induction by MSC. A general caspase inhibitor, z-VAD-fmk, dramatically decreased cytotoxicity in MSC-treated HL-60 cells and several other apoptotic features, such as, caspase-3 activation, the apoptotic DNA ladder, TUNEL-positive staining and the DNA double-strand break. Interestingly, a general serine protease inhibitor, AAPV-cmk, also effectively inhibited MSC-mediated cytotoxicity and apoptosis. These results demonstrate that MSC is a selenocompound that efficiently induces apoptosis in leukemia cells and that proteolytic machinery, in particular caspase-3, is necessary for MSC-induced apoptosis. On the other hand, selenite-induced cell death could be derived from necrosis rather than apoptosis, since selenite did not significantly induce several apoptotic phenomena, including the activation of caspase-3.

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

Apoptosis induced by cadmium has been shown in many tissues in vivo and in cultured cells in vitro. However, its molecular mechanism is not fully understood. When the human histiocytic lymphoma cell line U937 was treated with cadmium for 12 h, evidence of apoptotic features, including change in nuclear morphology, DNA fragmentation, formation of DNA ladder in agarose gel electrophoresis, and phosphatidylserine externalization, were obtained. Moreover, loss of the mitochondrial membrane potential (Deltapsi(m)) was observed in the cadmium-treated cells and was inhibited by a broad caspase inhibitor (Z-VAD-FMK). Caspase inhibitors suppressed the DNA fragmentation in the order of Z-VAD-FMK > caspase-8 inhibitor > caspase-3 inhibitor. Expression of Bcl-x(L) and Bid decreased significantly in the cadmium-treated cells, although no apparent change in Bcl-2 and Bax expression was found. Tetrakis-(2-pyridylmethyl) ethylendiamine, a cell-permeable heavy metal chelator, partially reversed the increase of fluorescence of Fura-2 in the cadmium-treated cells. In addition, verapamil (70 microm), a voltage-dependent Ca(2+) channel blocker, inhibited the DNA fragmentation induced by cadmium less than 100 microm and decreased the fluorescence of Fura-2. Cadmium up-regulated the expression of type 1 inositol 1,4,5-trisphosphate receptor (IP(3)R) but not type 2 or type 3 IP(3)R. Calpain inhibitors I and II partially prevented DNA fragmentation. No effects of Z-VAD-FMK on the expression of type 1 IP(3)R or of calpain inhibitors on the loss of Deltapsi(m) were observed. These results suggest that cadmium possibly induced apoptosis in U937 cells through two independent pathways, the Ca(2+)-calpain-dependent pathway and the caspase-mitochondria-dependent pathway.

Nitric oxide augments release of chemokines from monocytic U937 cells: modulation by anti-inflammatory pathways

Nitric oxide (NO) appears to act as an inflammatory mediator on monocytic cells. Exogenous NO augmented release of chemokines from human promonocytic U937 cells and peripheral blood mononuclear cells. Pharmacological strategies aiming at modulation of NO-induced release of interleukin-8 (IL-8) were investigated in U937 cells in detail. Release of IL-8 was down-regulated by transforming growth factor beta2 (TGF-beta2), by the protein tyrosine-kinase inhibitor genistein, and via rises in intracellular cyclic AMP, generated by prostaglandin E(2), rolipram, pentoxifylline, forskolin, or dibutyryl-cyclic AMP. In addition, incubation with the synthetic glucocorticoid dexamethasone or suppression of activity of p38 mitogen-activated protein (MAP) kinases by SB-203580 modulated release of IL-8. Activation of p38 MAP kinases was confirmed by the demonstration of an augmented appearance of phosphorylated p38 in the presence of NO. The present data suggest that exposure to exogenous NO resembles activation of U937 cells by proinflammatory stimuli. The anti-inflammatory cytokine TGF-beta2, as well as anti-inflammatory or immunosuppressive agents such as genistein, pentoxifylline, rolipram, dexamethasone, and SB-203580 modulate inflammatory, chemokine-inducing actions of NO.

UVC-induced apoptosis in human epithelial tumor A431 cells: sequence of apoptotic changes and involvement of caspase (-8 and -3) cascade

Human epidermoid tumor A431 cells underwent apoptosis following exposure to ultraviolet C (UVC). The apoptosis was of the interphase death type, and mostly occurred within one cell cycle, independent of the cell-cycle phases. We further examined the detailed sequential order of apoptotic changes in cells after UVC exposure and the involvement of caspases using six caspase inhibitors. The loss of mitochondrial transmembrane potential (delta psi m) appeared in the earliest phase; subsequently, the chromatin condensation and DNA-fragmentation occurred. Cell shrinkage and loss of the plasma-membrane integrity, judged by propidium iodide (PI) staining, were observed in the later phase. A broad-spectrum caspase inhibitor, z-VAD-fmk, completely prevented all apoptotic changes, except for the depletion of delta psi m. Both Ac-DEVD-CHO and Ac-IETD-CHO, inhibitors of caspase -3 and -8, respectively, effectively inhibited typical chromatin condensation to almost the same extent. However, the nuclei still showed partial condensation. A caspase -9 inhibitor, Ac-LEHD-CHO, did not prevent chromatin condensation, though it partially inhibited cell-size reduction and PI-stainability. None of the caspase inhibitors could inhibit the delta psi m reduction. These results strongly suggest that the collapse of delta psi m is not a part of the central apoptotic machinery, and that caspase cascade(s), especially caspase-8 to -3, play an important role in UVC-induced apoptosis in A431.

Characterization of two DNase gamma-specific monoclonal antibodies and the in situ detection of DNase gamma in the nuclei of apoptotic rat thymocytes

Two novel monoclonal antibodies (mAbs), hg302 and hg303, raised against a synthetic peptide corresponding to the basic domain of human DNase gamma, are characterized in detail. In Western blot analysis, hg303 recognizes both wild type and C-terminal Myc-His-tagged human DNase gamma, but does not cross-react with human DNase I family members, DNase I, DNase X, or DNAS1L2. On the other hand, dot blot analysis reveals the fine specificity of hg302; it recognizes human, mouse, and rat DNase gamma, but not other DNase I family DNases under non-denaturing conditions. Furthermore, hg302 efficiently immunoprecipitates wild type, but not C-terminal Myc-His-tagged, human DNase gamma from cell lysates. In immunohistochemical analysis, hg302 strongly recognizes DNase gamma in the nuclei of X-ray irradiation-induced apoptotic, but not normal rat thymocytes. The specific detection of DNase gamma in apoptotic nuclei is confirmed by indirect-immunofluorescence analysis using TNF-alpha-induced apoptotic HeLa S3 cells transfected with DNase gamma. These results, together with the observations that DNase gamma is present in normal thymocytes and its activity is unchanged during the apoptosis, suggest that some molecular change(s), which triggers the activation of DNase gamma, occurs in response to apoptotic stimuli in the basic domain, and hg302 specifically recognizes the activated DNase gamma in immunohistochemical analysis.

A role of the Ca2+/Mg2+-dependent endonuclease in apoptosis and its inhibition by Poly(ADP-ribose) polymerase

Apoptosis is characterized by various cell morphological and biochemical features, one of which is the internucleosomal degradation of genomic DNA. The role of the human chromatin-bound Ca(2+)- and Mg(2+)-dependent endonuclease (CME) DNAS1L3 and its inhibition by poly(ADP-ribosyl)ation in the DNA degradation that accompanies apoptosis was investigated. The nuclear localization of this endonuclease is the unique feature that distinguishes it from other suggested apoptotic nucleases. Purified recombinant DNAS1L3 was shown to cleave nuclear DNA into both high molecular weight and oligonucleosomal fragments in vitro. Furthermore, exposure of mouse skin fibroblasts expressing DNAS1L3 to inducers of apoptosis resulted in oligonucleosomal DNA fragmentation, an effect not observed in cells not expressing this CME, as well as in a decrease in cell viability greater than that apparent in the control cells. Recombinant DNAS1L3 was modified by recombinant human poly(ADP-ribose) polymerase (PARP) in vitro, resulting in a loss of nuclease activity. The DNAS1L3 protein also underwent poly(ADP-ribosyl)ation in transfected mouse skin fibroblasts in response to inducers of apoptosis. The cleavage and inactivation of PARP by a caspase-3-like enzyme late in apoptosis were associated with a decrease in the extent of DNAS1L3 poly(ADP-ribosyl)ation, which likely releases DNAS1L3 from inhibition and allows it to catalyze the degradation of genomic DNA.

Critical temporal modulation of neuronal programmed cell injury

1. As a free radical, nitric oxide (NO) may be toxic to neurons through mechanisms that directly involve DNA damage. Lubeluzole, a novel benzothiazole compound, has recently been demonstrated to be neuroprotective through the signal transduction pathways of NO. We therefore examined whether neuroprotection by lubeluzole was dependent upon the molecular pathways of programmed cell death (PCD). 2. In primary hippocampal neurons, evidence of PCD was determined by hematoxylin and eosin (H&E) stain, transmission electron microscopy, and annexin-V binding. NO administration with the NO generators sodium nitroprusside (300 microM) or SIN-1 (300 microM) directly induced PCD. 3. Neurons positive for PCD increased from 22+/-3% (untreated) to 72+/-3% (NO) over a 24-hr period. Coadministration of NO and lubeluzole (750 nM), a neuroprotective concentration, actively decreased PCD expression on H&E stain from 72+/-3% (NO only) to 25+/-3% (NO and lubeluzole). Significant reduction in DNA fragmentation by lubeluzole also was evident on electron microscopy. Application of lubeluzole in concentrations that were not neuroprotective or administration of the biologically inactive R-isomer did not significantly alter NO-induced PCD, suggesting that neuroprotection by lubeluzole was intimately linked to the modulation of PCD. Lubeluzole also was able to prevent the initial stages of cellular membrane inversion labeled with annexin-V binding, an early and sensitive indicator of PCD. Interestingly, the critical period for lubeluzole to reverse PCD induction appeared to be within the first 4 hr following NO exposure. 4. Further investigation into the neuroprotective pathways that alter PCD may provide greater insight into the molecular mechanisms that ultimately determine neuronal injury.

Ectromelia virus virulence factor p28 acts upstream of caspase-3 in response to UV light-induced apoptosis

Ectromelia virus (EV) virulence factor p28 (EVp28) is a member of a family of poxvirus proteins that are defined largely by the presence of a C-terminal RING finger motif and localization to virus factories within the cytoplasm of infected cells. Previously, overexpression of the Shope fibroma virus (SFV) homologue, N1R, in vaccinia virus (VV)-infected BGMK cells was found to inhibit virus-induced apoptosis. Here, we report that both EVp28 and overexpression of SFV N1R in poxvirus-infected HeLa cells protect specifically from UV light-induced apoptosis, but not from apoptosis induced by Fas or TNF. Further, we report that both VV and EV protect from apoptosis induced by UV, Fas and TNF. Immunoblot analysis indicates that EVp28 acts upstream of caspase-3, blocking activation of the protease in response to UV irradiation. Although no difference was found in replication of an EVp28(-) mutant virus, which expresses a truncated p28 protein lacking the RING motif, compared to EV wild-type in HeLa cells, UV irradiation of infected HeLa cells reduced the replication of the EV mutant compared with wild-type EV.

Role of c-jun expression increased by heat shock- and ceramide-activated caspase-3 in HL-60 cell apoptosis. Possible involvement of ceramide in heat shock-induced apoptosis

Ceramide has emerged as a lipid mediator in apoptosis induced by a variety of stresses. As we previously showed that the activation of AP-1, a nuclear transcription factor was indispensable to ceramide-induced apoptosis in human leukemia HL-60 cells (Sawai, H., Okazaki, T., Yamamoto, H., Okano, H., Takeda, Y., Tashima, M., Sawada, H., Okuma, M., Ishikura, H., Umehara, H., and Domae, N. (1995) J. Biol. Chem. 270, 27326-27331), the role and mechanism of heat shock (HS)-increased c-jun expression in apoptosis was here investigated. HS increased morphological changes compatible with apoptosis in human leukemia HL-60 cells, and induced ceramide generation and sphingomyelin hydrolysis with an increase of neutral magnesium-dependent sphingomyelinase activity. When HS failed to induce apoptosis in HS-resistant HL-60 cells, ceramide generation was not detected, suggesting that ceramide was involved in downstream signals required for HS-induced apoptosis. Both HS and N-acetylsphingosine (C(2)-ceramide) increased the expression of c-jun/c-fos mRNAs with the peak 2 h after treatment. When we examined whether the inhibition of c-jun expression by its antisense oligodeoxynucleotides (AS) blocked HS- or C(2)-ceramide-induced apoptosis, AS of c-jun gene inhibited apoptotic morphological changes and DNA fragmentation whereas did not sense oligodeoxynucleotides. Moreover, a synthetic tetrapeptide, acetyl-Asp-Met-Gln-Asp-aldehyde (DMQD-CHO), which inhibited the formation of active form of caspase-3 more efficiently than those of caspase-4, -6, -7, and -8, blocked both caspase-3 like activity, c-jun expression and apoptosis induced by HS or C(2)-ceramide, although DMQD-CHO did not affect HS-induced ceramide generation. These results suggested that the ceramide was generated through sphingomyelin hydrolysis by HS-activated neutral, magnesium-dependent sphingomyelinase and that subsequent c-jun expression through activation of caspase-3 played a role in HS-induced HL-60 cell apoptosis.

Cleavage of Poly(ADP-ribose) polymerase measured in situ in individual cells: relationship to DNA fragmentation and cell cycle position during apoptosis

Poly(ADP-ribose) polymerase (PARP), a nuclear enzyme involved in DNA repair, is a target of caspases during apoptosis: its cleavage onto 89- and 24-kDa fragments is considered to be a hallmark of the apoptotic mode of cell death. Another hallmark is the activation of endonuclease which targets internucleosomal DNA. The aim of the present study was to reveal cell cycle phase specificity as well as the temporal and sequence relationships of PARP cleavage vis-à-vis DNA fragmentation in two model systems of apoptosis, one induced by DNA damage via cell treatment with camptothecin (CPT) (mitochondria-induced pathway) and another by the cytotoxic ligand tumor necrosis factor alpha (TNF-alpha) (cell surface death receptor pathway). PARP cleavage was detected immunocytochemically using antibody which recognizes its 89-kDa fragment (PARP p89) while DNA fragmentation was assayed by in situ labeling of DNA strand breaks. The frequency and extent of PARP cleavage as well as DNA fragmentation were measured by mutiparameter flow and laser scanning cytometry. PARP cleavage, selective to S phase cells, was detected 90 min after administration of CPT. PARP cleavage in the cells treated with TNF-alpha was not selective to any cell cycle phase and was seen already after 30 min. DNA fragmentation trailed PARP cleavage by about 30 min and showed a similar pattern of cell cycle specificity. PARP p89 was present in nuclear chromatin but at least in the early phase of apoptosis it did not colocalize with DNA strand breaks. The rate of cleavage of PARP molecules in individual cells whether induced by CPT or TNF-alpha was rapid as reflected by the paucity of cells with a mixture of cleaved and noncleaved PARP molecules. In contrast, DNA fragmentation proceeded stepwise before reaching the maximal number of DNA strand breaks. Although time windows for PARP cleavage vs DNA fragmentation were different at early stages of apoptosis, a good overall correlation between the cytometric assays of apoptotic cells identification based on these events was observed in both CPT- and TNF-alpha-treated cultures.

Changes in elemental content during apoptotic cell death studied by electron probe X-ray microanalysis

Recent data suggest that changes in ionic content, primarily potassium, play a pivotal role in the progression of apoptosis. However, the changes in total element content, i.e., sodium (Na), magnesium (Mg), phosphorous (P), chlorine (Cl), potassium (K), and calcium (Ca), during apoptosis have not been evaluated. Electron probe X-ray microanalysis (EPXMA) was used to measure total element content in U937 cells before and after the induction of apoptosis. As an experimental model we used U937 cells irradiated with ultraviolet (UV) light. Apoptosis was evaluated with phase-contrast microscopy, with scanning and transmission electron microscopy, and with the fluorescent dye bisbenzimide (Hoechst 33342). Plasma membrane permeability as a measure of cell death was determined by trypan blue dye exclusion. To investigate element content with EPXMA, cells were cryoprepared, i.e., cryofixed and freeze-dried, and analyzed as whole cells using a scanning electron microscope. We found that the UV irradiation induced rapid (within 2 h) morphological changes associated with apoptosis, such as plasma membrane blebbing, condensation of the chromatin, and the formation of membrane-bound apoptotic bodies. At this time, 95% of the apoptotic cells excluded trypan blue dye. EPXMA results demonstrated that UV light-irradiated apoptotic cells (cells with membrane-bound apoptotic bodies) had a lower Cl content (P < 0.001) and K content (P < 0.001) and a higher Na content (P < 0.001) in comparison with nonirradiated control cells. Also, P and Ca content was higher in apoptotic cells than in control cells, but this difference did not reach statistical significance. No differences were found in Mg. These data indicated that morphological changes characteristic of apoptotic cell death are related with significant changes in sodium, chlorine, and potassium content. In addition, we demonstrated that these changes in elemental composition were not associated with loss of cell membrane integrity.

The antioxidant 4b,5,9b,10-Tetrahydroindeno[1,2-b]indole inhibits apoptosis by preventing caspase activation following mitochondrial depolarization

Oxidative stress appears to have a central role in the induction of apoptosis following the exposure of cells to a range of cytotoxic insults. The modulation of apoptosis by a diverse range of antioxidants has been reported in many systems. We demonstrate, for the first time, the anti-apoptotic properties of the antioxidant, 4b, 5,9b,10-tetrahydroindeno[1,2-b]indole (THII), in Jurkat T cells subjected to a number of cytotoxic insults. THII was found to inhibit the morphological features of apoptosis in cells treated with the cytotoxic agents camptothecin, actinomycin D and ultraviolet (UV) irradiation. However, THII was unable to inhibit apoptosis induced by anti-Fas IgM. Peroxide and superoxide anion production following UV treatment was monitored, and THII was found to only partially inhibit superoxide anion production. THII was unable to inhibit mitochondrial depolarization in UV, Camptothecin or anti-Fas-treated cells. Further downstream, THII exibited strong inhibition of caspase-3 activation in UV, but not in anti-Fas-treated cells. These results suggest that THII may exert its effects downstream of mitochondrial depolarization, but upstream of caspase-3 activation.

Bax:Bcl-2 ratio modulation by bryostatin 1 and novel antitubulin agents is important for susceptibility to drug induced apoptosis in the human early pre-B acute lymphoblastic leukemia cell line, Reh

The ratio of Bax to Bcl-2 protein can determine whether cells will die via apoptosis or be protected from it. Reh was found to express a high basal level of Bcl-2 but was lacking of Bax protein expression. Treatment with bryostatin 1 induced a down-regulation in Bcl-2 protein that was not accompanied by an obvious Bax protein induction or apoptosis. These results suggest that a decreased level of Bcl-2 alone in this cell line is not sufficient for apoptosis induction. In an effort to identify the mechanism whereby apoptosis could be induced in this ALL model, we treated Reh cells with three microtubule inhibitors: dolastatin 10, auristatin PE and vincristine, in the presence and absence of bryostatin 1. When used alone, only dolastatin 10 induced apoptosis that was detected morphologically, and by flow cytometry. Western blots revealed that dolastatin 10-induced apoptosis was accompanied by the induction of Bax protein and the reduction in Bcl-2 protein. Auristatin PE and vincristine induced both Bax and Bcl-2 protein, leaving the Bax:Bcl-2 ratio constant. Reh cells pretreated for 24 h with bryostatin 1 followed by dolastatin 10, auristatin PE or vincristine showed significant apoptosis which was accompanied by Bcl-2 protein down regulation and Bax protein up regulation. We conclude that: (1) expression of bax is necessary for apoptosis-induction in this model; (2) a decrease in Bcl-2 level alone is not sufficient and might not be necessary for apoptosis-induction; and (3) the ratio of Bax:Bcl-2 plays a critical role in susceptibility to apoptosis in Reh cells. The results from this study should prove useful in guiding the clinical application of these novel agents in the treatment of acute lymphoblastic leukemia.

Neuronal intracellular pH directly mediates nitric oxide-induced programmed cell death

Neuronal injury is intricately linked to the activation of three distinct neuronal endonucleases. Since these endonucleases are exquisitely pH dependent, we investigated in primary rat hippocampal neurons the role of intracellular pH (pH(i)) regulation during nitric oxide (NO)-induced toxicity. Neuronal injury was assessed by both a 0.4% Trypan blue dye exclusion survival assay and programmed cell death (PCD) with terminal deoxynucleotidyl transferase nick-end labeling (TUNEL) 24 h following treatment with the NO generators sodium nitroprusside (300 microM), 3-morpholinosydnonimine (300 microM), or 6-(2-hyrdroxy-1-methyl-2-nitrosohydrazino)-N-methyl-1-hex anamine (300 microM). The pH(i) was measured using the fluorescent probe BCECF. NO exposure yielded a rapid intracellular acidification during the initial 30 min from pH(i) 7.36 +/- 0.01 to approximately 7.00 (p <.0001). Within 45 min, a biphasic alkaline response was evident, with pH(i) reaching 7.40 +/- 0.02, that was persistent for a 6-h period. To mimic the effect of NO-induced acidification, neurons were acid-loaded with ammonium ions to yield a pH(i) of 7.09 +/- 0.02 for 30 min. Similar to NO toxicity, neuronal survival decreased to 45 +/- 2% (24 h) and DNA fragmentation increased to 58 +/- 8% (24 h) (p <.0001). Although neuronal caspases did not play a dominant role, neuronal injury and the induction of PCD during intracellular acidification were dependent upon enhanced endonuclease activity. Furthermore, maintenance of an alkaline pH(i) of 7.60 +/- 0.02 during the initial 30 min of NO exposure prevented neuronal injury, suggesting the necessity for the rapid but transient induction of intracellular acidification during NO toxicity. Through the identification of the critical role of both NO-induced intracellular acidification and the induction of the neuronal endonuclease activity, our work suggests a potential regulatory trigger for the prevention of neuronal degeneration.

Aryl hydrocarbon receptor regulation of ceramide-induced apoptosis in murine hepatoma 1c1c7 cells. A function independent of aryl hydrocarbon receptor nuclear translocator

The relationship between aryl hydrocarbon receptor (AHR) content and susceptibility to apoptosis was examined in the murine hepatoma 1c1c7 cell line and a series of variants having different levels of AHR expression. Exposure of 1c1c7 cultures to N-acetylsphingosine (C2-ceramide) caused a concentration-dependent inhibition of cell proliferation, loss of viability, and induction of apoptosis as monitored by analyses of DNA fragmentation and caspase activation. A variant cell line (Tao) having approximately 10% of the AHR content of 1c1c7 cells also arrested following exposure to C2-ceramide, but did not undergo apoptosis. Modulation of 1c1c7 and Tao AHR contents by transfection of Ahr antisense and sense constructs, respectively, confirmed the relationship between AHR content and susceptibility to C2-ceramide-induced apoptosis. C2-ceramide also induced the apoptosis of an AHR-containing cell line lacking the aryl hydrocarbon receptor nuclear translocator protein. AHR ligands (i.e. 2,3,7,8-tetrachlorodibenzo-p-dioxin and alpha-naphthoflavone) neither induced apoptosis nor modulated the development of apoptosis in C2-ceramide-treated 1c1c7 cultures. AHR content did not affect staurosporine- or doxorubicin-induced apoptosis. These results suggest the AHR modulates aspects of ceramide signaling associated with the induction of apoptosis but not cell cycle arrest, and does so by a mechanism that is independent of its interaction with aryl hydrocarbon receptor nuclear translocator and exogenous AHR ligands.

Metabotropic glutamate receptors prevent programmed cell death through the modulation of neuronal endonuclease activity and intracellular pH

Metabotropic glutamate receptor (mGluR) activation prevents neurodegeneration against nitric oxide (NO)-induced programmed cell death (PCD). We therefore investigated whether specific neuronal endogenous deoxyribonucleases, enzymes recently identified to be responsible for the maintenance of DNA integrity, mediated mGluR protection against NO. In rat primary hippocampal neurons, injury was assessed by using a 0.4% trypan blue dye exclusion method and TUNEL assay 24 h following treatment with the NO generators sodium nitroprusside (300 microM) or SIN-1 (300 microM). DNA digestion studies using neuronal cell extracts were employed to assess specific endonuclease activity. Individual application of aurintricarboxylic acid (ATA) (10 microM), an endonuclease inhibitor, or the mGluR agonists 1S,3R-ACPD (750 microM), DHPG (750 microM), L-CCG-I (750 microM), or L-AP4 (750 microM) prior to NO exposure significantly increased neuronal survival. Yet, combination therapy with ATA (10 microM) and the mGluR agonists did not synergistically improve neuronal survival, suggesting a common pathway of protection for ATA and the mGluRs that is dependent upon the modulation of neuronal endonuclease activity. In further support of this premise, protection by the mGluR agonists 1S,3R-ACPD, DHPG, L-CCG-I, and L-AP4 was significantly decreased during enhancement of endonuclease activity with the zinc chelator, N,N,N',N',-tetrakis (2-pyridylmethyl) ethylenediamine. Antagonism of the mGluR system was ineffective against endonuclease induced DNA destruction. Further assessment with DNA digestion assays identified two distinct mechanisms to maintain DNA integrity, a Ca2+/Mg2+-dependent endonuclease inhibited by L-AP4 and a magnesium dependent endonuclease inhibited by 1S,3R-ACPD. These neuroprotective mechanisms during activation of the mGluR system were also intricately linked to the active reversal of the biphasic intracellular pH changes induced by NO. Further investigation into the molecular pathways modulated by mGluRs may identify specific mechanisms that can maintain DNA integrity during adverse cellular environments.

Coexpression of CD9 augments the ability of membrane-bound heparin-binding epidermal growth factor-like growth factor (proHB-EGF) to preserve renal epithelial cell viability

BACKGROUND

Transfection of renal epithelial cells (NRK 52E) with membrane-associated heparin-binding epidermal growth factor-like growth factor (proHB-EGF) increased renal epithelial cell survival by promoting cell-cell and cell-extracellular matrix interactions. ProHB-EGF has been shown to form a complex in the plasma membrane with the tetraspanin CD9, an interaction that significantly increases the effectiveness of proHB-EGF as a juxtacrine mitogenic agent.

METHODS

We examined whether the coexpression of proHB-EGF and CD9 would increase renal epithelial cell survival. CD9 was stably transfected into NRK 52E cells, either alone (NRKCD9) or together with proHB-EGF (NRKboth).

RESULTS

Juxtacrine mitogenic activity of NRKCD9 was no different than in cells transfected with vector alone (NRKvector), but was increased by NRKboth; juxtacrine mitogenic activity by NRKboth was twofold greater than when proHB-EGF was transfected alone (NRKproHB-EGF). When grown in 10% fetal calf serum, growth rates were similar among all transfectants. However, in 1% fetal calf serum, NRKproHB-EGF grew 50% faster than NRKvector or NRKCD9, and NRKboth grew 20% to 50% faster than NRKproHB-EGF at one, two, and three days of culture. NRKproHB-EGF attachment to plastic substratum at one, two, and three hours was 250% greater than that of NRKvector, and NRKboth was 20% to 30% greater than that of NRKproHB-EGF. Coating plates with either poly 2-hydroxyethyl methacrylate or the GRGDTP peptide prevented normal cell-extracellular matrix attachment, and NRKvector or NRKCD9 failed to attach or form cell-cell attachments. NRKproHB-EGF exhibited 300% and NRKboth exhibited 600% greater cell viability under these conditions. Expression of type I and type III collagen mRNA was enhanced similarly in NRKproHB-EGF and NRKboth, but the expression of beta1 integrin was up-regulated only in NRKboth.

CONCLUSIONS

Coexpression of proHB-EGF and CD9 may render the renal epithelial cells more resistant to disruption of cell-cell and cell-matrix interactions and could accelerate the re-establishment of these attachments.