Lithium chloride potentiates tumor necrosis factor-mediated cytotoxicity in vitro and in vivo

Lithium Enhances Autophagy and Cell Death in Skin Melanoma: An Ultrastructural and Immunohistochemical Study

Lithium is an inhibitor of glycogen synthase kinase 3 beta, which is traditionally used in the treatment of bipolar disorders and has antitumor effects. The aim of the current study was to determine if lithium salt causes autophagy and apoptosis in skin melanoma cells to enhance cell death. Light microscopy, transmission electron microscopy, immunohistochemistry, and immunofluorescence were used to study the mechanism of action of lithium carbonate in B16 melanoma cells in vivo. Proliferating cell nuclear antigen immunofluorescence assay revealed that the proliferation of B16 melanoma cells was suppressed by lithium treatment for 7 days. Electron microscopy demonstrated a significant increase in the number of autophagic vacuoles in lithium-treated cells relative to control. In addition, levels of autophagy markers LC3 beta and LAMP1 found in lithium-treated tumor xenografts were higher than levels of these markers in the control tumors. Lithium induced caspase-3 expression and apoptotic cell death in tumor cells. Thus, lithium carbonate is the compound that inhibits cell proliferation and stimulates cell death in melanoma cells through induction of autophagy and apoptosis. Stimulation of autophagy by lithium could contribute to the development of autophagic cell death in tumor cells.

High Dosage Lithium Treatment Induces DNA Damage and p57Kip2 Decrease

Lithium salt is the first-line therapeutic option for bipolar disorder and has been proposed as a potential antitumoral drug. The effects of LiCl treatment were investigated in SH-SY5Y, a human neuroblastoma cell line and an in vitro model of dopaminergic neuronal differentiation. LiCl, at the dosage used in psychiatric treatment, does not affect cell proliferation, while at higher doses it delays the SH-SY5Y cell division cycle and for prolonged usage reduces cell viability. Moreover, the ion treatment affects DNA integrity as demonstrated by accumulation of p53 and γH2AX (the phosphorylated form of H2AX histone), two important markers of genome damage. p57^Kip2, a CIP/Kip protein, is required for proper neuronal maturation and represents a main factor of response to stress including genotoxicity. We evaluated the effect of lithium on p57^Kip2 levels. Unexpectedly, we found that lithium downregulates the level of p57^Kip2 in a dose-dependent manner, mainly acting at the transcriptional level. A number of different approaches, mostly based on p57^Kip2 content handling, confirmed that the CKI/Kip reduction plays a key role in the DNA damage activated by lithium and suggests the unanticipated view that p57^Kip2 might be involved in DNA double-strand break responses. In conclusion, our study identified novel roles for p57^Kip2 in the molecular mechanism of lithium at high concentration and, more in general, in the process of DNA repair.

The Psychiatric Drug Lithium Increases DNA Damage and Decreases Cell Survival in MCF-7 and MDA-MB-231 Breast Cancer Cell Lines Expos ed to Ionizing Radiation

Background:

Breast cancer is the most common cancer among women. Radiation therapy is used for treating almost every stage of breast cancer. A strategy to reduce irradiation side effects and to decrease the recurrence of cancer is concurrent use of radiation and radiosensitizers. We studied the effect of the antimanic drug lithium on radiosensitivity of estrogen-receptor (ER)-positive MCF-7 and ER-negative, invasive, and radioresistant MDA-MB-231 breast cancer cell lines.

Methods:

MCF-7 and MDA-MB-231 breast cancer cell lines were treated with 30 mM and 20 mM concentrations of lithium chloride (LiCl), respectively. These concentrations were determined by MTT viability assay. Growth curves were depicted and comet assay was performed for control and LiCl-treated cells after exposure to X-ray. Total and phosphorylated inactive levels of glycogen synthase kinase-3beta (GSK-3β) protein were determined by ELISA assay for control and treated cells.

Results:

Treatment with LiCl decreased cell proliferation after exposure to X-ray as indicated by growth curves of MCF-7 and MDA-MB-231 cell lines within six days following radiation. Such treatment increased the amount of DNA damages represented by percent DNA in Tails of comets at 0, 1, 4, and even 24 hours after radiation in both studied cell lines. The amount of active GSK-3β was increased in LiCl-treated cells in ER-positive and ER-negative breast cancer cell lines.

Conclusion:

Treatment with LiCl that increased the active GSK-3β protein, increased DNA damages and decreased survival independent of estrogen receptor status in breast cancer cells exposed to ionizing radiation.

Mechanism of Action of the Tumor Vessel Targeting Agent NGR-hTNF: Role of Both NGR Peptide and hTNF in Cell Binding and Signaling

NGR-hTNF is a therapeutic agent for a solid tumor that specifically targets angiogenic tumor blood vessels, through the NGR motif. Its activity has been assessed in several clinical studies encompassing tumors of different histological types. The drug’s activity is based on an improved permeabilization of newly formed tumor vasculature, which favors intratumor penetration of chemotherapeutic agents and leukocyte trafficking. This work investigated the binding and the signaling properties of the NGR-hTNF, to elucidate its mechanism of action. The crystal structure of NGR-hTNF and modeling of its interaction with TNFR suggested that the NGR region is available for binding to a specific receptor. Using 2D TR-NOESY experiments, this study confirmed that the NGR-peptides binds to a specific CD13 isoform, whose expression is restricted to tumor vasculature cells, and to some tumor cell lines. The interaction between hTNF or NGR-hTNF with immobilized TNFRs showed similar kinetic parameters, whereas the competition experiments performed on the cells expressing both TNFR and CD13 showed that NGR-hTNF had a higher binding affinity than hTNF. The analysis of the NGR-hTNF-triggered signal transduction events showed a specific impairment in the activation of pro-survival pathways (Ras, Erk and Akt), compared to hTNF. Since a signaling pattern identical to NGR-hTNF was obtained with hTNF and NGR-sequence given as distinct molecules, the inhibition observed on the survival pathways was presumably due to a direct effect of the NGR-CD13 engagement on the TNFR signaling pathway. The reduced activation of the pro survival pathways induced by NGR-hTNF correlated with the increased caspases activation and reduced cell survival. This study demonstrates that the binding of the NGR-motif to CD13 determines not only the homing of NGR-hTNF to tumor vessels, but also the increase in its antiangiogenic activity.

Identifying Antigens Recognized by Cytolytic T Lymphocytes on Tumors

Identification of antigenic peptides recognized by cytolytic T lymphocytes (CTL) is a prerequisite for the development of targeted cancer immunotherapy approaches. This chapter provides a global approach for the identification of peptides recognized by CTL. It implies the identification of the HLA molecule presenting the peptide as well as the design and screening of a cDNA library derived from the tumor cells. Methods used for the identification of spliced peptides on tumors are also described.

Synthesis and Biological Activity of Novel Comenic Acid Derivatives Containing Isoxazole and Isothiazole Moieties

Methyl 5-hydroxy-4-oxo-4 H-pyran-2-carboxylate was synthesized by esterification of methanol with comenic acid under acidic catalysis. The obtained ester was alkylated with 3-(chloromethyl)-5-phenylisoxazole and 4,5-dichloro-3-(chloromethyl)isothiazole to afford corresponding conjugates containing isoxazole and isothiazole moieties which then were transformed into water-soluble Li-salts. During the bioassays of synthesized isoxazole and isothiazole derivatives of comenic acid in mixtures with first-line antitumor drug Temobel (Temozolomid) used in brain tumors chemotherapy, a synergetic effect was observed.

In Vitro Cytotoxic and Anticancer Effects of Zamzam Water in Human Lung Cancer (A594) Cell Line

BACKGROUND

Zamzam water is naturally alkaline and rich in a variety of minerals which may represent a powerful tool for cancer therapy. In this research, the cytotoxic effects of Zamzam water were investigated in human lung cancer (A549) cell line and compared with human skin fibroblasts (HSF).

METHODS

Two different preparations of Zamzam water were used: Z1, with pH adjusted to 7.2 and Z2, with no pH adjustment. The effects of both treatments on the morphology of the A549 and HSF cell lines were investigated. The cell viability of HSF and A549 cells was identified by the MTT assay and trypan blue exclusion. Detection of apoptotic cells and cell cycle analyses were determined using flow cytometry. Moreover, reactive oxygen species (ROS) were measured for both cell lines.

RESULTS

Both Zamzam water treatments, Z1 and Z2 showed reductions in the cell viability of A549 cells. Cell death occurred via necrosis among cells treated with Z2. Cell cycle arrest occurred in the G0/G1 phases for cells treated with Z2. Cellular and mitochondrial ROS productions were not affected by either treatment.

CONCLUSION

Our findings indicate that Zamzam water might have potential therapeutic efficacy for lung cancer.

Critical role of SIK3 in mediating high salt and IL-17 synergy leading to breast cancer cell proliferation

Chronic inflammation is a well-known precursor for cancer development and proliferation. We have recently demonstrated that high salt (NaCl) synergizes with sub-effective interleukin (IL)-17 to induce breast cancer cell proliferation. However, the exact molecular mechanisms mediating this effect are unclear. In our current study, we adopted a phosphoproteomic-based approach to identify salt modulated kinase-proteome specific molecular targets. The phosphoprotemics based binary comparison between heavy labelled MCF-7 cells treated with high salt (Δ0.05 M NaCl) and light labelled MCF-7 cells cultured under basal conditions demonstrated an enhanced phosphorylation of Serine-493 of SIK3 protein. The mRNA transcript and protein expression analysis of SIK3 in MCF-7 cells demonstrated a synergistic enhancement following co-treatment with high salt and sub-effective IL-17 (0.1 ng/mL), as compared to either treatments alone. A similar increase in SIK3 expression was observed in other breast cancer cell lines, MDA-MB-231, BT20, and AU565, while non-malignant breast epithelial cell line, MCF10A, did not induce SIK3 expression under similar conditions. Biochemical studies revealed mTORC2 acted as upstream mediator of SIK3 phosphorylation. Importantly, cell cycle analysis by flow cytometry demonstrated SIK3 induced G0/G1-phase release mediated cell proliferation, while SIK3 silencing abolished this effect. Also, SIK3 induced pro-inflammatory arginine metabolism, as evidenced by upregulation of the enzymes iNOS and ASS-1, along with downregulation of anti-inflammatory enzymes, arginase-1 and ornithine decarboxylase. Furthermore, gelatin zymography analysis has demonstrated that SIK3 induced expression of tumor metastatic CXCR4 through MMP-9 activation. Taken together, our data suggests a critical role of SIK3 in mediating three important hallmarks of cancer namely, cell proliferation, inflammation and metastasis. These studies provide a mechanistic basis for the future utilization of SIK3 as a key drug discovery target to improve breast cancer therapy.

Lithium inhibits tumor lymphangiogenesis and metastasis through the inhibition of TGFBIp expression in cancer cells

Metastasis is the main cause of mortality in cancer patients. Although there are many anti-cancer drugs targeting tumor growth, anti-metastatic agents are rarely developed. Angiogenesis and lymphangiogenesis are crucial for cancer progression; in particular, lymphangiogenesis is pivotal for metastasis in cancer. Here we report that lithium inhibits colon cancer metastasis by blocking lymphangiogenesis. Lithium reduces the expression of transforming growth factor-β-induced protein (TGFBIp) in colon cancer cells by inhibiting Smad3 phosphorylation via GSK3β inactivation. Moreover, lithium inhibits lymphatic endothelial cell migration, which is increased upon TGFBIp expression in tumor cells. Lithium had no significant effect on SW620 tumor growth in vitro and in vivo; however, it inhibited lymphangiogenesis in tumors. In tumor xenografts model, lithium was found to prevent metastasis to the lungs, liver, and lymph nodes by inhibiting TGFBIp-induced tumor lymphangiogenesis. Collectively, our findings demonstrate a novel role of lithium in the inhibition of colon cancer metastasis by blocking TGFBIp expression, and thereby TGFBIp-induced lymphangiogenesis, in primary tumors.

Excitotoxicity induced by kainic acid provokes glycogen synthase kinase-3 truncation in the hippocampus

In neuronal cultures, glycogen synthase kinase 3(GSK3) is truncated at the N-terminal end by calpain downstream of activated glutamate receptors. However, the in vivo biological significance of that truncation has not been explored. In an attempt to elucidate if GSK3 truncation has a pathophysiological relevance, we have used intraperitoneal injections of kainic acid (KA) in rats and intra-amygdala KA microinjections in mice as in vivo models of excitotoxicity. Spectrin cleavage analyzed by immunohistochemistry was observed in the CA1 hippocampal field in KA-intraperitoneal treated rats while the CA3 region was the hippocampal area affected after intra-amygdala KA microinjections. GSK3β immunofluorescence did not colocalize with truncated spectrin in both treatments using an antibody that recognize the N-terminal end of GSK3β. Thus, those neurons which are spectrin-positive do not show GSK3β immunolabelling. To study GSK3β truncation in vitro, we exposed organotypic hippocampal slices and cultured cortical neurons to KA leading to the truncation of GSK3 and we found that truncation was blocked by the calpain inhibitor calpeptin. These data suggest a relationship between N-terminal GSK3β truncation and excitotoxicity. Overall, our data reinforces the important relationship between glutamate receptors and GSK3 and their role in neurodegenerative processes in which excitotoxicity is involved.

Lithium inhibits growth of intracellular Mycobacterium kansasii through enhancement of macrophage apoptosis

Mycobacterium kansasii (Mk) is an emerging pathogen that causes a pulmonary disease similar to tuberculosis. Macrophage apoptosis contributes to innate host defense against mycobacterial infection. Recent studies have suggested that lithium significantly enhances the cytotoxic activity of death stimuli in many cell types. We examined the effect of lithium on the viability of host cells and intracellular Mk in infected macrophages. Lithium treatment resulted in a substantial reduction in the viability of intracellular Mk in macrophages. Macrophage cell death was significantly enhanced after adding lithium to Mk-infected cells but not after adding to uninfected macrophages. Lithium-enhanced cell death was due to an apoptotic response, as evidenced by augmented DNA fragmentation and caspase activation. Reactive oxygen species were essential for lithium-induced apoptosis. Intracellular scavenging by N-acetylcysteine abrogated the lithium-mediated decrease in intracellular Mk growth as well as apoptosis. These data suggest that lithium is associated with control of intracellular Mk growth through modulation of the apoptotic response in infected macrophages.

Neuronal apoptosis and motor deficits in mice with genetic inhibition of GSK-3 are Fas-dependent

Glycogen synthase kinase-3 (GSK-3) inhibitors have been postulated as useful therapeutic tools for the treatment of chronic neurodegenerative and neuropsychiatric diseases. Nevertheless the clinical use of these inhibitors has been limited by their common side effects. Lithium, a non-selective GSK-3 inhibitor has been classically administered to treat bipolar patients but its prescription is decreasing due to its frequent side effects such as hand tremor. This toxicity seems to be higher in the elderly and a clinical trial with lithium for Alzheimer’s disease was stopped due to high rate of discontinuation. We have previously described a mechanism for the adverse effects of chronic lithium that involves neuronal apoptosis via Fas signaling. As lithium inhibits many other enzymatic activities such as inositol monophosphatase and histone deacetylase, here we aim to genetically test whether GSK-3 inhibition induces those adverse effects through Fas receptor. For this purpose we took advantage of a transgenic mouse line with decreased GSK-3 activity (Tet/DN-GSK-3 mice) that shows increased rate of neuronal apoptosis as well as motor deficits and brought it to a Fas deficient background (lpr mice). We found that apoptosis induced by GSK-3 inhibition was absent in Fas deficient background. Interestingly, motor deficits were also absent in Fas deficient Tet/DN-GSK-3 mice. These results demonstrate that Fas signaling contributes to the neurological toxicity of GSK-3 inhibition and suggest that a combination of GSK-3 inhibitors with blockers of Fas signaling could help to improve the application of GSK-3 inhibitors to clinics.

Identifying source proteins for MHC class I-presented peptides

Identification of antigenic peptides recognized by cytolytic T lymphocytes (CTL) is a prerequisite for the development of targeted cancer immunotherapy approaches. This chapter provides a global approach for the identification of peptides recognized by CTL. It implies the identification of the HLA molecule presenting the peptide as well as the design and screening of a cDNA library derived from the tumor cells.

Lithium inhibits tumorigenic potential of PDA cells through targeting hedgehog-GLI signaling pathway

Hedgehog signaling pathway plays a critical role in the initiation and development of pancreatic ductal adenocarcinoma (PDA) and represents an attractive target for PDA treatment. Lithium, a clinical mood stabilizer for mental disorders, potently inhibits the activity of glycogen synthase kinase 3β (GSK3β) that promotes the ubiquitin-dependent proteasome degradation of GLI1, an important downstream component of hedgehog signaling. Herein, we report that lithium inhibits cell proliferation, blocks G1/S cell-cycle progression, induces cell apoptosis and suppresses tumorigenic potential of PDA cells through down-regulation of the expression and activity of GLI1. Moreover, lithium synergistically enhances the anti-cancer effect of gemcitabine. These findings further our knowledge of mechanisms of action for lithium and provide a potentially new therapeutic strategy for PDA through targeting GLI1.

Lithium enhances TRAIL-induced apoptosis in human lung carcinoma A549 cells

Non-small cell lung cancer (NSCLC) A549 cells are resistant to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. Therefore, combination therapy using sensitizing agents to overcome TRAIL resistance may provide new strategies for treatment of NSCLC. Here, we investigated whether lithium chloride (LiCl), a drug for mental illness, could sensitize A549 cells to TRAIL-induced apoptosis. We observed that LiCl significantly enhanced A549 cells apoptosis through up-regulation of death receptors DR4 and DR5 and activation of caspase cascades. In addition, G2/M arrest induced by LiCl also contributed to TRAIL-induced apoptosis. Concomitantly, LiCl strongly inhibited the activity of c-Jun N-terminal kinases (JNKs), and the inhibition of JNKs by SP600125 also induced G2/M arrest and augmented cell death caused by TRAIL or TRAIL plus LiCl. However, glycogen synthase kinase-3β (GSK3β) inhibition was not involved in TRAIL sensitization induced by LiCl. Collectively, these findings indicated that LiCl sensitized A549 cells to TRAIL-induced apoptosis through caspases-dependent apoptotic pathway via death receptors signaling and G2/M arrest induced by inhibition of JNK activation, but independent of GSK3β.

Improvement of a cytokine (TNF-α) bioassay by serum-free target cell (WEHI 164) cultivation

The elaboration of a sensitive bioassay for assessment of tumour necrosis factor alpha (TNF-α) in a defined medium is described. The assay is based on the cytotoxic effect of TNF-α on a target cell line, the murine fibrosarcoma WEHI 164 clone 13. Cytotoxicity was assessed by detecting the rate of tetrazolium salt reduction employing a spectrophotometer (ELISA-reader). A similar bioassay was used previously to assess TNF-α, though this was dependent on cell growth in a medium containing serum. By employing a synthetic serum replacement, the WEHI cells were adapted to growth in a defined medium which allowed both the propagation of the cell line and the assay to be performed under completely defined conditions. Thus, factors in serum that may influence the TNF-α assessment, such as growth factors, cytokines, soluble cytokine-receptors and macroglobulin, were avoided. The only protein required in this bioassay was insulin, while albumin was added as a carrier protein and to protect the cytokine against loss of biological activity during multiple freeze and thaw cycles. The present assay was optimised to achieve a high sensitivity and, by testing endogenous TNF-α originating from the macrophage-like cell line RAW in both the serum-free and serum-based assay, we found the highest sensitivity in the assay based on defined medium. The LC50 of recombinant mouse and human TNF-α were in the serum-free and serum-based assays considered to be 25 and 50 pg mL-1, respectively. The demonstration of a culture condition that enables long-term cultivation of target cells and a bioassay in a completely defined medium is in our opinion a substantial contribution to more reliable cytokine assessment.

Modulation of GSK-3β activity in Venezuelan equine encephalitis virus infection

Alphaviruses, including Venezuelan Equine Encephalitis Virus (VEEV), cause disease in both equine and humans that exhibit overt encephalitis in a significant percentage of cases. Features of the host immune response and tissue-specific responses may contribute to fatal outcomes as well as the development of encephalitis. It has previously been shown that VEEV infection of mice induces transcription of pro-inflammatory cytokines genes (e.g., IFN-γ, IL-6, IL-12, iNOS and TNF-α) within 6 h. GSK-3β is a host protein that is known to modulate pro-inflammatory gene expression and has been a therapeutic target in neurodegenerative disorders such as Alzheimer's. Hence inhibition of GSK-3β in the context of encephalitic viral infections has been useful in a neuroprotective capacity. Small molecule GSK-3β inhibitors and GSK-3β siRNA experiments indicated that GSK-3β was important for VEEV replication. Thirty-eight second generation BIO derivatives were tested and BIOder was found to be the most potent inhibitor, with an IC₅₀ of ∼0.5 µM and a CC₅₀ of >100 µM. BIOder was a more potent inhibitor of GSK-3β than BIO, as demonstrated through in vitro kinase assays from uninfected and infected cells. Size exclusion chromatography experiments demonstrated that GSK-3β is found in three distinct complexes in VEEV infected cells, whereas GSK-3β is only present in one complex in uninfected cells. Cells treated with BIOder demonstrated an increase in the anti-apoptotic gene, survivin, and a decrease in the pro-apoptotic gene, BID, suggesting that modulation of pro- and anti-apoptotic genes contributes to the protective effect of BIOder treatment. Finally, BIOder partially protected mice from VEEV induced mortality. Our studies demonstrate the utility of GSK-3β inhibitors for modulating VEEV infection.

Inhibition of glycogen synthase kinase-3 activity triggers an apoptotic response in pancreatic cancer cells through JNK-dependent mechanisms

Recent evidences suggest that the activity of glycogen synthase kinase-3 (GSK3) contributes to the tumorigenic potential of pancreatic cancer cells through modulation of cell proliferation and survival. However, further investigations are needed to identify GSK3-dependent mechanisms involved in the control of pancreatic cancer cell proliferation and survival. This study was undertaken to provide further support for a role of GSK3 in pancreatic cancer cell growth as well as to identify new cellular and molecular mechanisms involved. Herein, we demonstrate that prolonged inhibition of GSK3 triggers an apoptotic response only in human pancreatic cancer cells but not in human non-transformed pancreatic epithelial cells. We show that prolonged inhibition of GSK3 activity increases Bim messenger RNA and protein expressions. Moreover, we provide evidence that activation of the c-jun N-terminal kinase (JNK) pathway is necessary for the GSK3 inhibition-mediated increase in Bim expression and apoptotic response. Finally, we demonstrate that concomitant inhibition of GSK3 potentiates the death ligand-induced apoptotic response in pancreatic cancer cells but not in non-transformed pancreatic epithelial cells and that this effect also requires JNK activity. Considering that different approaches leading to stimulation of death receptor signaling are under clinical trials for treatment of unresectable or metastatic pancreatic cancer, inhibition of GSK3 could represent an attractive new avenue to improve their effectiveness.

GSK-3 Mouse Models to Study Neuronal Apoptosis and Neurodegeneration

Increased GSK-3 activity is believed to contribute to the etiology of chronic disorders like Alzheimer’s disease (AD), schizophrenia, diabetes, and some types of cancer, thus supporting therapeutic potential of GSK-3 inhibitors. Numerous mouse models with modified GSK-3 have been generated in order to study the physiology of GSK-3, its implication in diverse pathologies and the potential effect of GSK-3 inhibitors. In this review we have focused on the relevance of these mouse models for the study of the role of GSK-3 in apoptosis. GSK-3 is involved in two apoptotic pathways, intrinsic and extrinsic pathways, and plays opposite roles depending on the apoptotic signaling process that is activated. It promotes cell death when acting through intrinsic pathway and plays an anti-apoptotic role if the extrinsic pathway is occurring. It is important to dissect this duality since, among the diseases in which GSK-3 is involved, excessive cell death is crucial in some illnesses like neurodegenerative diseases, while a deficient apoptosis is occurring in others such as cancer or autoimmune diseases. The clinical application of a classical GSK-3 inhibitor, lithium, is limited by its toxic consequences, including motor side effects. Recently, the mechanism leading to activation of apoptosis following chronic lithium administration has been described. Understanding this mechanism could help to minimize side effects and to improve application of GSK-3 inhibitors to the treatment of AD and to extend the application to other diseases.

LiCl induces TNF-α and FasL production, thereby stimulating apoptosis in cancer cells

Background

The incidence of cancer in patients with neurological diseases, who have been treated with LiCl, is below average. LiCl is a well-established inhibitor of Glycogen synthase kinase-3, a kinase that controls several cellular processes, among which is the degradation of the tumour suppressor protein p53. We therefore wondered whether LiCl induces p53-dependent cell death in cancer cell lines and experimental tumours.

Results

Here we show that LiCl induces apoptosis of tumour cells both in vitro and in vivo. Cell death was accompanied by cleavage of PARP and Caspases-3, -8 and -10. LiCl-induced cell death was not dependent on p53, but was augmented by its presence. Treatment of tumour cells with LiCl strongly increased TNF-α and FasL expression. Inhibition of TNF-α induction using siRNA or inhibition of FasL binding to its receptor by the Nok-1 antibody potently reduced LiCl-dependent cleavage of Caspase-3 and increased cell survival. Treatment of xenografted rats with LiCl strongly reduced tumour growth.

Conclusions

Induction of cell death by LiCl supports the notion that GSK-3 may represent a promising target for cancer therapy. LiCl-induced cell death is largely independent of p53 and mediated by the release of TNF-α and FasL.

Key words: LiCl, TNF-α, FasL, apoptosis, GSK-3, FasL

Effect of lithium salts on lactate dehydrogenase, adenylate kinase, and 1-phosphofructokinase activities

Inhibitions of 30 nM rabbit muscle 1-phosphofructokinase (PFK-1) by lithium, potassium, and sodium salts showed inhibition or not depending upon the anion present. Generally, potassium salts were more potent inhibitors than sodium salts; the extent of inhibition by lithium salts also varied with the anion. Li(2)CO(3) was a relatively potent inhibitor of PFK-1 but LiCl and lithium acetate were not. Our results suggest that extents of inhibition by monovalent salts were due to both cations and anions, and the latter needs to be considered before inhibition can be credited to the cation. An explanation for monovalent salt inhibitions is proffered involving interactions of both cations and anions at negative and positive sites of PFK-1 that affect enzyme activity. Our studies suggest that lithium cations per se are not inhibitors: the inhibitors are the lithium salts, and we suggest that in vitro studies involving the effects of monovalent salts on enzymes should involve more than one anion.

NFAT/Fas signaling mediates the neuronal apoptosis and motor side effects of GSK-3 inhibition in a mouse model of lithium therapy

Use of lithium, the mainstay for treatment of bipolar disorder, is limited by its frequent neurological side effects and its risk for overdose-induced toxicity. Recently, lithium has also been proposed as a treatment for Alzheimer disease and other neurodegenerative conditions, but clinical trials have been hampered by its prominent side effects in the elderly. The mechanisms underlying both the positive and negative effects of lithium are not fully known. Lithium inhibits glycogen synthase kinase-3 (GSK-3) in vivo, and we recently reported neuronal apoptosis and motor deficits in dominant-negative GSK-3-transgenic mice. We hypothesized that therapeutic levels of lithium could also induce neuronal loss through GSK-3 inhibition. Here we report induction of neuronal apoptosis in various brain regions and the presence of motor deficits in mice treated chronically with lithium. We found that GSK-3 inhibition increased translocation of nuclear factor of activated T cells c3/4 (NFATc3/4) transcription factors to the nucleus, leading to increased Fas ligand (FasL) levels and Fas activation. Lithium-induced apoptosis and motor deficits were absent when NFAT nuclear translocation was prevented by cyclosporin A administration and in Fas-deficient lpr mice. The results of these studies suggest a mechanism for lithium-induced neuronal and motor toxicity. These findings may enable the development of combined therapies that diminish the toxicities of lithium and possibly other GSK-3 inhibitors and extend their potential to the treatment of Alzheimer disease and other neurodegenerative conditions.

Identification of an antiapoptotic protein complex at death receptors

Stimulation of death receptors activates the extrinsic apoptotic signaling pathway that leads to cell death. Although many steps of this apoptotic signaling cascade are known, few mechanisms that counterbalance the death signal have been described. We identified an antiapoptotic protein complex associated with death receptors that contains glycogen synthase kinase-3 (GSK3), DDX3 and cellular inhibitor of apoptosis protein-1 (cIAP-1). GSK3, DDX3 and cIAP-1 are associated in cells with each other and with death receptors. Blocking the actions of GSK3 or DDX3 potentiated caspase-3 activation induced by stimulation of four different death receptors in several types of cells. GSK3 restrained apoptotic signaling by inhibiting formation of the death-inducing signaling complex and caspase-8 activation. Stimulated death receptors surmount the antiapoptotic complex by causing GSK3 inactivation and cleavage of DDX3 and cIAP-1 to enable progression of the apoptotic signaling cascade, but the antiapoptotic complex remains functional in cancer cells resistant to death receptor stimulation, a resistance that is overcome by GSK3 inhibitors. Thus, an antiapoptotic complex of GSK3, DDX3 and cIAP-1 caps death receptors, providing a checkpoint to counterbalance apoptotic signaling.

Anti-inflammatory effects of lithium gluconate on keratinocytes: a possible explanation for efficiency in seborrhoeic dermatitis

Topical lithium (Li) gluconate has a beneficial effect on seborrhoeic dermatitis (SD), unlike oral lithium (Li) used in psychiatry. SD is an inflammatory dermatitis associated, in most of cases, with colonization by lipophilic yeasts of the genus Malassezia. However, the exact mechanism of action of Li gluconate in SD still remains unknown. The aim of our study was to investigate the effect of topical Li on cytokine secretion and innate immunity. For this purpose, we investigated first the modulatory effect of Li on two pro-inflammatory and two anti-inflammatory cytokine secretion and second, the modulatory effect of Li on Toll-like receptor (TLR) 2 and 4 expression by unstimulated and stimulated keratinocytes. Two different skin models were used: keratinocytes in monolayer and skin explants. In some of them, inflammation was induced with LPS (1 mug/ml) or zymosan (2 mg/ml). Then the skin models were incubated with Li gluconate (Labcatal*, Montrouge, France) at three different concentrations (1.6, 3, 5 mM) determined according to viability MTT test. Expression of TNFalpha, IL6, IL10, TGFbeta1, TLR2 and TLR4 was detected by immunohistochemistry (IHC). Cytokines were quantified by ELISA methods. Our results showed that the effect of Li on keratinocytes is dose-dependent. At low concentration (1.6 mM), Li enhanced TNFalpha secretion, whereas, at higher concentration (5 mM), Li significantly enhanced IL10 expression and secretion. However, there was no significant modulation of Li on IL6 and TGFbeta1 secretion. Moreover, Li at 5 mM significantly decreased TLR2 and TLR4 expressions by differentiated keratinocytes. As Li concentration during topical treatment is probably closer to 5 mM than to 1 mM, the therapeutic effect of Li gluconate in DS may be explained by two anti-inflammatory actions: an increased expression and secretion of IL10 and a decreased expression of TLR2 and TLR4 by keratinocytes. The diminution of TLR2 expression by Li may not allow MF to trigger inflammation response in lesional skin.

Upregulation of TNF-alpha production by IFN-gamma and LPS in cultured canine keratinocytes: application to monosaccharides effects

Activated keratinocytes play a key role in the cutaneous immune system by their interactions with other cell types through the production of cytokines with both autocrine and paracrine activity. But there is little knowledge about epidermal cytokines in the dog. In this study, cultured canine keratinocytes were stimulated by human recombinant interferon gamma (IFN-gamma) and lipopolysaccharide (LPS) and cell supernatants were tested for tumour necrosis factor alpha (TNF-alpha) concentration using a cell viability assay on a murine cell line. We show that IFN-gamma in combination with LPS significantly increases TNF-alpha secretion by canine keratinocytes. The best stimulations were obtained using confluent cultures and the association of IFN-gamma (400 ng/ml) and LPS (40 microg/ml). The experimental protocol we describe represents a new method for studying keratinocyte activation and its modulation in the dog. We provide an example of application of our method: the study of the effects of different monosaccharides on canine keratinocyte activation.

Neuronal apoptosis and reversible motor deficit in dominant-negative GSK-3 conditional transgenic mice

Increased glycogen synthase kinase-3 (GSK-3) activity is believed to contribute to the etiology of chronic disorders like Alzheimer's disease and diabetes, thus supporting therapeutic potential of GSK-3 inhibitors. However, sustained GSK-3 inhibition might induce tumorigenesis through beta-catenin-APC dysregulation. Besides, sustained in vivo inhibition by genetic means (constitutive knock-out mice) revealed unexpected embryonic lethality due to massive hepatocyte apoptosis. Here, we have generated transgenic mice with conditional (tetracycline system) expression of dominant-negative-GSK-3 as an alternative genetic approach to predict the outcome of chronic GSK-3 inhibition, either per se, or in combination with mouse models of disease. By choosing a postnatal neuron-specific promoter, here we specifically address the neurological consequences. Tet/DN-GSK-3 mice showed increased neuronal apoptosis and impaired motor coordination. Interestingly, DN-GSK-3 expression shut-down restored normal GSK-3 activity and re-established normal incidence of apoptosis and motor coordination. These results reveal the importance of intact GSK-3 activity for adult neuron viability and physiology and warn of potential neurological toxicity of GSK-3 pharmacological inhibition beyond physiological levels. Interestingly, the reversibility data also suggest that unwanted side effects are likely to revert if excessive GSK-3 inhibition is halted.

Targeting GSK-3: a promising approach for cancer therapy?

Glycogen synthase kinase (GSK)-3 has emerged as one of the most attractive therapeutic targets for the treatment of multiple neurological diseases, including Alzheimer's, stroke and bipolar disorders, as well as noninsulin-dependent diabetes mellitus and inflammation. Although the prominent role of GSK-3 in the adenomatous polyposis coli (APC)-beta-catenin destruction complex implies that inhibition of GSK-3 could possibly lead to tumor promotion through the activation of beta-catenin, several recent studies have shed new light on the activity of GSK-3 in cancer and provide insight into the molecular mechanisms by which it regulates tumor cell proliferation and survival of multiple human malignancies. In fact, GSK-3beta is a critical regulator of nuclear factor (NF)kappaB nuclear activity, suggesting that inhibition of GSK-3beta could be effective in the treatment of a wide variety of tumors with constitutively active NFkappaB. Herein, the authors will discuss the current understanding of the role of GSK-3 in human cancer and its potential as a therapeutic target.

The paradoxical pro- and anti-apoptotic actions of GSK3 in the intrinsic and extrinsic apoptosis signaling pathways

Few things can be considered to be more important to a cell than its threshold for apoptotic cell death, which can be modulated up or down, but rarely in both directions, by a single enzyme. Therefore, it came as quite a surprise to find that one enzyme, glycogen synthase kinase-3 (GSK3), has the perplexing capacity to either increase or decrease the apoptotic threshold. These apparently paradoxical effects now are known to be due to GSK3 oppositely regulating the two major apoptotic signaling pathways. GSK3 promotes cell death caused by the mitochondrial intrinsic apoptotic pathway, but inhibits the death receptor-mediated extrinsic apoptotic signaling pathway. Intrinsic apoptotic signaling, activated by cell damage, is promoted by GSK3 by facilitation of signals that cause disruption of mitochondria and by regulation of transcription factors that control the expression of anti- or pro-apoptotic proteins. The extrinsic apoptotic pathway entails extracellular ligands stimulating cell-surface death receptors that initiate apoptosis by activating caspase-8, and this early step in extrinsic apoptotic signaling is inhibited by GSK3. Thus, GSK3 modulates key steps in each of the two major pathways of apoptosis, but in opposite directions. Consequently, inhibitors of GSK3 provide protection from intrinsic apoptosis signaling but potentiate extrinsic apoptosis signaling. Studies of this eccentric ability of GSK3 to oppositely influence two types of apoptotic signaling have shed light on important regulatory mechanisms in apoptosis and provide the foundation for designing the rational use of GSK3 inhibitors for therapeutic interventions.

Lithium facilitates apoptotic signaling induced by activation of the Fas death domain-containing receptor

Background

Lithium, a mood stabilizer widely used to treat bipolar disorder, also is a neuroprotectant, providing neurons protection from apoptosis induced by a broad spectrum of toxic conditions. A portion of this neuroprotection is due to lithium's inhibition of glycogen synthase kinase-3. The present investigation examined if the neuroprotection provided by lithium included apoptosis induced by stimulation of the death domain-containing receptor Fas.

Results

Instead of providing protection, treatment with 20 mM lithium significantly increased apoptotic signaling induced by activation of Fas, and this occurred in both Jurkat cells and differentiated immortalized hippocampal neurons. Other inhibitors of glycogen synthase kinase-3, including 20 μM indirubin-3'-monoxime, 5 μM kenpaullone, and 5 μM rottlerin, also facilitated Fas-induced apoptotic signaling, indicating that the facilitation of apoptosis by lithium was due to inhibition of glycogen synthase kinase-3.

Conclusions

These results demonstrate that lithium is not always a neuroprotectant, and it has the opposite effect of facilitating apoptosis mediated by stimulation of death domain-containing receptors.

Tipping the balance between necrosis and apoptosis in human and murine cells treated with interferon and dsRNA

Interferons enhance the cellular antiviral response by inducing expression of protective proteins. Many of these proteins are activated by dsRNA, a typical by-product of viral infection. Here we show that type-I and type-II interferons can sensitize cells to dsRNA-induced cytotoxicity. In caspase-8- or FADD-deficient Jurkat cells dsRNA induces necrosis, instead of apoptosis. In L929sA cells dsRNA-induced necrosis involves high reactive oxygen species production. The antioxidant butylated hydroxyanisole protects cells from necrosis, but shifts the response to apoptosis. Treatment with the caspase inhibitor benzyloxycarbonyl-Val-Ala-DL-Asp(OMe)-fluoromethylketone or overexpression of Bcl-2 prevent this shift and promote necrosis. Our results suggest that a single stimulus can initiate different death-signaling pathways, leading to either necrotic or apoptotic cell death. Inhibition of key events in these signaling pathways, such as caspase activation, cytochrome c release or mitochondrial reactive oxygen species production, tips the balance between necrosis and apoptosis, leading to dominance of one of these death programs.

A MAGE-3 peptide presented by HLA-B44 is also recognized by cytolytic T lymphocytes on HLA-B18

Antigens encoded by MAGE genes are of particular interest for cancer immunotherapy because of their tumoral specificity and because they are shared by many tumors. Antigenic peptide MEVDPIGHLY, which is encoded by MAGE-3 and is known to be presented by human leukocyte antigen (HLA)-B44, is currently being used in therapeutic vaccination trials. We report here that a cytolytic T lymphocyte (CTL) clone, which is restricted by HLA-B*1801, recognizes the same peptide and, importantly, lyzes HLA-B18 tumor cells expressing MAGE-3. These results imply that the use of peptide MEVDPIGHLY can now be extended to HLA-B18 patients. We also provide evidence that, under limiting amounts of protein MAGE-3, HLA B*1801 and B*4403 compete for binding to the peptide.

Lithium sensitizes tumor cells in an NF-kappa B-independent way to caspase activation and apoptosis induced by tumor necrosis factor (TNF). Evidence for a role of the TNF receptor-associated death domain protein

We have previously shown that lithium salts can considerably increase the direct cytotoxic effect of tumor necrosis factor (TNF) on various tumor cells in vitro and in vivo. However, the underlying mechanism has remained largely unknown. Here we show that the TNF-sensitizing effect of lithium chloride (LiCl) is independent of the type of cell death, either necrosis or apoptosis. In the case of apoptosis, TNF/lithium synergism is associated with an enhanced activation of caspases and mitochondrial cytochrome c release. Sensitization to apoptosis is specific for TNF-induced apoptosis, whereas Fas-mediated or etoposide-induced apoptosis remains unaffected. LiCl also potentiates cell death induced by artificial oligomerization of a fusion protein between FKBP and the TNF receptor-associated death domain protein. TNF-induced activation of NF-kappa B-dependent gene expression is not modulated by LiCl treatment. These results indicate that LiCl enhances TNF-induced cell death in an NF-kappa B-independent way, and suggest that the TNF receptor-associated death domain protein plays a crucial role in the TNF-sensitizing effect of LiCl.

Molecular targets of lithium action

Lithium is highly effective in the treatment of bipolar disorder and also has multiple effects on embryonic development, glycogen synthesis, hematopoiesis, and other processes. However, the mechanism of lithium action is still unclear. A number of enzymes have been proposed as potential targets of lithium action, including inositol monophosphatase, a family of structurally related phosphomonoesterases, and the protein kinase glycogen synthase kinase-3. These potential targets are widely expressed, require metal ions for catalysis, and are generally inhibited by lithium in an uncompetitive manner, most likely by displacing a divalent cation. Thus, the challenge is to determine which target, if any, is responsible for a given response to lithium in cells. Comparison of lithium effects with genetic disruption of putative target molecules has helped to validate these targets, and the use of alternative inhibitors of a given target can also lend strong support for or against a proposed mechanism of lithium action. In this review, lithium sensitive enzymes are discussed, and a number of criteria are proposed to evaluate which of these enzymes are involved in the response to lithium in a given setting.

A MAGE-3 peptide recognized on HLA-B35 and HLA-A1 by cytolytic T lymphocytes

Antigens encoded by MAGE genes are of particular interest for cancer immunotherapy because of their strict tumoral specificity and because they are shared by many tumors. Antigenic peptide EVDPIGHLY encoded by MAGE-3 and known to be presented by HLA-A*0101 is currently being used in therapeutic vaccination trials. We report here that a cytolytic T-lymphocyte (CTL) clone, which is restricted by HLA-B*3501, recognizes the same peptide and, importantly, lyses HLA-B*3501 tumor cells expressing MAGE-3. These results infer that the current clinical use of peptide EVDPIGHLY can now be extended to HLA-B*3501 patients.

Requirement for glycogen synthase kinase-3beta in cell survival and NF-kappaB activation

Glycogen synthase kinase-3 (GSK-3)-alpha and -beta are closely related protein-serine kinases, which act as inhibitory components of Wnt signalling during embryonic development and cell proliferation in adult tissues. Insight into the physiological function of GSK-3 has emerged from genetic analysis in Drosophila, Dictyostelium and yeast. Here we show that disruption of the murine GSK-3beta gene results in embryonic lethality caused by severe liver degeneration during mid-gestation, a phenotype consistent with excessive tumour necrosis factor (TNF) toxicity, as observed in mice lacking genes involved in the activation of the transcription factor activation NF-kappaB. GSK-3beta-deficient embryos were rescued by inhibition of TNF using an anti-TNF-alpha antibody. Fibroblasts from GSK-3beta-deficient embryos were hypersensitive to TNF-alpha and showed reduced NF-kappaB function. Lithium treatment (which inhibits GSK-3; refs 8, 9) sensitized wild-type fibroblasts to TNF and inhibited transactivation of NF-kappaB. The early steps leading to NF-kappaB activation (degradation of I-kappaB and translocation of NF-kappaB to the nucleus) were unaffected by the loss of GSK-3beta, indicating that NF-kappaB is regulated by GSK-3beta at the level of the transcriptional complex. Thus, GSK-3beta facilitates NF-kappaB function.

Tumour necrosis factor: strategies for improving the therapeutic index

Tumour Necrosis Factor (TNF) is a cytokine initially discovered for its capacity to induce haemorrhagic necrosis of experimental tumours and later found to be endowed with potent proinflammatory activities. It was soon realised that these latter properties were at the origin of unacceptable systemic toxicity in all trials aimed at exploiting the anti-tumour activities of TNF. The present review intends to reconsider the efforts that have been devoted over the past ten years to increase the therapeutic index of TNF so to make it a useful drug for the treatment of malignancies. Overall, attempts to achieve this goal with systemically administered TNF have met little success so far. On the other hand, impressive results have been obtained with locoregional administration of TNF. Although of relatively limited clinical utility, these observations have indicated a realistic possibility for a therapeutic exploitation of TNF in tumour therapy: the delivery of systemically administered TNF to the site of tumour growth. On this basis, different targeting and pre-targeting strategies have been developed to achieve this goal. While still in their infancy, these approaches have yielded encouraging results in experimental tumour models. In the forthcoming years it will be possible to evaluate if they represent a practicable means of delivering high doses of TNF to the tumour while sparing the organism from systemic, toxic effects.

Role of YopP in suppression of tumor necrosis factor alpha release by macrophages during Yersinia infection

The Yersinia plasmid-encoded Yop virulon enables extracellular adhering bacteria to deliver toxic effector proteins inside their target cells. It includes a type III secretion system (Ysc), at least two translocator proteins (YopB, YopD), and a set of intracellular Yop effectors (YopE, YopH, YopO, YopM, and YopP). Infection of macrophages with a wild-type strain leads to low levels of tumor necrosis factor alpha (TNF-alpha) release compared to infection with plasmid-cured strains, suggesting that the virulence plasmid encodes a factor impairing the normal TNF-alpha response of infected macrophages. This effect is correlated with the inhibition of the macrophage mitogen-activated protein kinase (MAPK) activities. To identify the Yop protein responsible for the suppression of TNF-alpha release, we infected J774A.1 and PU5-1.8 macrophages with a battery of knockout Yersinia enterocolitica mutants and we quantified the TNF-alpha released. Mutants affected in secretion (yscN), in translocation (yopB and yopD), or in synthesis of all the known Yop effectors (yopH, yopO, yopP, yopE, and yopM polymutants) were unable to block the TNF-alpha response of the macrophages. In contrast, single yopE, yopH, yopO, and yopM mutants behaved like the wild-type strain. A yopP mutant elicited elevated TNF-alpha release, and complementation of the yopP mutant or the yop effector polymutant strain with yopP alone led to a drop in TNF-alpha release. In addition, YopP was also responsible for the inhibition of the extracellular signal-regulated kinase2 (ERK2) and p38 MAPK activities. These results show that YopP is the Yop effector responsible for the Yersinia-induced suppression of TNF-alpha release by infected macrophages.

Induced expression of trimerized intracellular domains of the human tumor necrosis factor (TNF) p55 receptor elicits TNF effects

The various biological activities of tumor necrosis factor (TNF) are mediated by two receptors, one of 55 kD (TNF-R55) and one of 75 kD (TNF-R75). Although the phenotypic and molecular responses elicited by TNF in different cell types are fairly well characterized, the signaling pathways leading to them are so far only partly understood. To further unravel these processes, we focused on TNF-R55, which is responsible for mediating most of the known TNF effects. Since several studies have demonstrated the importance of receptor clustering and consequently of close association of the intracellular domains for signaling, we addressed the question of whether clustering of the intracellular domains of TNF-R55 (TNF-R55i) needs to occur in structural association with the inner side of the cell membrane, where many signaling mediators are known to reside. Therefore, we investigated whether induced intracellular clustering of only TNF-R55i would be sufficient to initiate and generate a full TNF response, without the need for a full-length receptor molecule or a transmembrane region. Our results provide clear evidence that inducible forced trimerization of either TNF-R55i or only the death domain elicits an efficient TNF response, comprising activation of the nuclear factor kappaB, induction of interleukin-6, and cell killing.

Identification of genes coding for tumor antigens recognized by cytolytic T lymphocytes

Strategies have been developed to characterize tumor antigens recognized by cytolytic T lymphocytes (CTL). We use a genetic approach based on the transfection of HLA genes and cDNA libraries in COS cells to isolate the gene producing the antigenic peptide. The tumor-specific expression of this gene can be evaluated by cDNA synthesis and quantitative PCR amplification. Transfection of fragments of the isolated gene allows the identification of the region encoding the antigenic peptide. Peptides are synthesized and tested for their ability to sensitize target cells to lysis by the CTL.

Differences in the antigens recognized by cytolytic T cells on two successive metastases of a melanoma patient are consistent with immune selection

We have studied the patterns of antigens recognized by autologous cytolytic T lymphocytes (CTL) on two melanoma cell lines derived from metastases that were removed from patient LB33 at several years distance. Cell line LB33-MEL.A was obtained after surgery in 1988. A large number of CTL clones directed against LB33-MEL.A was obtained with blood lymphocytes collected from the patient in 1990. In vitro selection of melanoma cells that were resistant to these CTL clones indicated that at least five different antigens were recognized on LB33-MEL.A by autologous CTL. Four of these antigens were found to be presented by HLA-A28, B13, B44 and Cw6, respectively. The patient remained disease-free until 1993 when a metastasis was detected and was used to obtain cell line LB33-MEL.B. This cell line proved resistant to lysis by all the CTL clones directed against the LB33-MEL.A cells and showed no expression of HLA class I molecules except for HLA-A24. Using LB33-MEL.B cells to stimulate blood lymphocytes collected from the patient in 1994 we derived CTL clones that lysed these cells. All these CTL clones recognized a new antigen presented by HLA-A24. These results suggest that in patient LB33 the melanoma cells may have lost the expression of several HLA molecules under the selective pressure of an anti-tumor CTL response.

Phospholipase A2 activation in cultured mouse hepatocytes exposed to tumor necrosis factor-alpha

High concentrations of tumor necrosis factor alpha (TNF alpha) are cytotoxic to cultured hepatocytes. Impairment of energy metabolism and generation of an intracellular oxidant stress are important events in the pathogenesis of this toxicity (6). In the present study, we have examined the role of phospholipase A2 activation in TNF alpha-induced toxicity in mouse hepatocytes, since it has been reported to play a key role in TNF alpha cytolytic activity in other cell types. Recombinant murine TNF alpha (0.1 microgram/mL) caused a dose-dependent increase in PLA2 activity in cultured mouse hepatocytes. The increase in PLA2 activity was observed after only 0.5 hour of exposure (152 +/- 10% of control), and continued to increased over the first 4 hours of exposure (292 +/- 32%). However, TNF alpha-induced GSSG efflux and ATP depletion did not occur until after 2 hours of exposure. Furthermore, a small level of cytotoxicity was observed after a 24 hour incubation period. Putative PLA2 inhibitors, chlorpromazine (CPZ) and 4-bromophenacyl bromide (BPB), both prevented the TNF alpha-induced increase in PLA2 activity. They also reduced ATP depletion, GSSG efflux, and cytotoxicity. The PLA2 inhibitor, manoalide (a natural marine product), completely prevented PLA2 activation and cytotoxicity induced by TNF alpha. Pretreatment of hepatocytes with cycloheximide, to inhibit protein synthesis, increased TNF alpha-induced cytotoxicity. Cycloheximide pretreatment also potentiated PLA2 activation, ATP depletion, and GSSG efflux. CPZ and BPB both reduced the extent of PLA2 activation, ATP depletion, GSSG formation, and cytotoxicity in the cycloheximide pretreated cells exposed to TNF alpha. Taken together, these results demonstrate that TNF alpha activates PLA2, which occurs prior to other deleterious events in hepatocytes, and that inhibition of PLA2 activity reduces cell injury by TNF alpha. This suggests that PLA2 activation may lead to impairment of energy metabolism, an oxidant stress, and cytotoxicity in cells exposed to TNF alpha. Additionally, protein synthesis inhibition potentiates TNF alpha induction of PLA2 and toxicity, suggesting that there is a protein-synthesis-dependent protective mechanism in hepatocytes which ameliorates the effects induced by PLA2. These findings provide strong evidence that PLA2 activation plays an important role in the pathogenesis of toxicity induced by TNF alpha in cultured mouse hepatocytes.

Molecular mechanisms of tumor necrosis factor-induced cytotoxicity. What we do understand and what we do not

Although TNF plays an important role in several physiological and pathological conditions, the hallmark of this important cytokine has been its selective cytotoxic activity on tumor cells. Since its cloning in 1984, understanding of how TNF selectively kills tumor cells has been the subject of research in many laboratories. Here we review TNF-induced post-receptor signaling mechanisms which seem to be involved in the pathway to cytotoxicity.

Long-term action of lithium: a role for transcriptional and posttranscriptional factors regulated by protein kinase C

Lithium, a simple monovalent cation, represents one of psychiatry's most important treatments and is the most effective treatment for reducing both the frequency and severity of recurrent affective episodes. Despite extensive research, the underlying biologic basis for the therapeutic efficacy this drug remains unknown, and in recent years, research has focused on signal transduction pathways to explain lithium's efficacy in treating both poles of manic-depressive illness. Critical to attributions of therapeutic relevance to any observed biochemical effect, however, is the observation that the characteristic prophylactic action of lithium in stabilizing the profound mood cycling of bipolar disorder requires a lag period for onset and is not immediately reversed upon discontinuation of treatment. Biochemical changes requiring such prolonged administration of a drug suggest alterations at the genomic level but, until recently, little has been known about the transcriptional and posttranscriptional factors regulated by chronic drug treatment, although long-term changes in neuronal synaptic function are known to be dependent upon the selective regulation of gene expression. In this paper, we will present evidence to show that chronic lithium exerts significant transcriptional and posttranscriptional effects, and that these actions of lithium may be mediated via protein kinase C (PKC)-induced alterations in nuclear transcription regulatory factors responsible for modulating the expression of proteins involved in long-term neural plasticity and cellular response. Such target sites for chronic lithium may help unravel the processes by which a simple monovalent cation can produce a long-term stabilization of mood in individuals vulnerable to bipolar illness.

Tumor necrosis factor cytotoxicity is associated with phospholipase D activation

The activation of phospholipase D in different cell lines treated with recombinant human tumor necrosis factor (TNF) has been investigated. When the murine fibrosarcoma cell lines L929 and WEHI164c113, as well as the human promonocytic cell line U937, were prelabeled with [14C]palmitic acid or [3H]arachidonic acid, and treated with TNF in the presence of ethanol, TNF induced the synthesis of [14C]phosphatidylethanol or [3H]phosphatidylethanol, respectively, as the result of a phospholipase-D-catalyzed transphosphatidylation. TNF-induced phospholipase D activity was observed 1 h before the onset of cell killing and gradually increased thereafter. Subclones selected for resistance to TNF cytotoxicity did not show phospholipase D activation in response to TNF. In contrast, when these subclones were treated with TNF in the presence of actinomycin D, TNF cytotoxicity as well as TNF-induced phospholipase D activity could be restored. TNF cytotoxicity and TNF-induced phospholipase D activity were equally modulated by various drugs known to interfere with different steps in the TNF-signaling pathway. Phospholipase D activation was found not to be the result of cell killing per se, as a number of other cytotoxic reagents were unable to activate phospholipase D. Prelabeling of cells with [14C]lysophosphatidylcholine indicated phosphatidylcholine as one of the substrates for TNF-activated phospholipase D. In conclusion, this study demonstrates that TNF-induced cytotoxicity is associated with activation of phospholipase D.

Synergistic induction of interleukin-6 by tumor necrosis factor and lithium chloride in mice: possible role in the triggering and exacerbation of psoriasis by lithium treatment

One of the side effects of treatment of manic depressive disease with lithium salts is the triggering or aggravation of psoriasis. In a murine model, subcutaneous (s.c.) injection of a combination of tumor necrosis factor (TNF) and lithium chloride (LiCl) induces a psoriasiform inflammatory reaction. Recent studies suggest that interleukin (IL)-6 and its inducer TNF may play an important role in the pathophysiology of psoriasis. To understand the mechanism involved in the exacerbation of psoriasis by lithium salts, the IL-1, IL-6 and granulocyte-macrophage colony-stimulating factor (GM-CSF) levels in murine skin injected with TNF in combination with LiCl were studied. IL-6 levels in skin extracts of mice treated s.c. with a combination of TNF and LiCl were considerably increased as compared to the levels found in skin extracts from mice treated with TNF or LiCl alone. In contrast, in the same skin extracts IL-1 levels were not changed and GM-CSF was even not detectable. Although less pronounced, increased IL-6 levels could also be found in the sera of mice treated s.c. with TNF and LiCl. Injection with IL-1, interferon-gamma, lipopolysaccharide, or phorbol 12-myristate 13-acetate also induced IL-6 in murine skin. However, these IL-6 levels were not enhanced by co-treatment with LiCl. Likewise, on inflammatory reaction could be seen in mice treated with these agents. These results suggest a role for endogenous TNF and IL-6 in the triggering or aggravation of psoriasis in lithium-treated patients.

TNF-mediated IL6 gene expression and cytotoxicity are co-inducible in TNF-resistant L929 cells

Interleukin (IL)-6 gene induction was studied in the murine cell line, L929r2, which is resistant to the cytotoxic action of tumor necrosis factor (TNF). Increasing concentrations of TNF slightly elevated the background levels of IL6 expression as compared to non-induced cells. Under conditions where the resistant cells are sensitive to TNF by combined TNF/IFN-gamma treatment, the IL6 levels were strongly induced. This induction could be further enhanced by the addition of lithium chloride, or reduced by inhibitors of cytotoxicity, such as dexamethasone. These results confirm our earlier conclusions regarding the close relationship between TNF-mediated IL6 gene expression and the pathway leading to cytotoxicity.