Different mechanisms for suppression of apoptosis by cytokines and calcium mobilizing compounds

Inhibition of the sarco/endoplasmic reticulum (ER) Ca2+-ATPase by thapsigargin analogs induces cell death via ER Ca2+ depletion and the unfolded protein response

Calcium (Ca²⁺) is a fundamental regulator of cell signaling and function. Thapsigargin (Tg) blocks the sarco/endoplasmic reticulum (ER) Ca²⁺-ATPase (SERCA), disrupts Ca²⁺ homeostasis, and causes cell death. However, the exact mechanisms whereby SERCA inhibition induces cell death are incompletely understood. Here, we report that low (0.1 μm) concentrations of Tg and Tg analogs with various long-chain substitutions at the O-8 position extensively inhibit SERCA1a-mediated Ca²⁺ transport. We also found that, in both prostate and breast cancer cells, exposure to Tg or Tg analogs for 1 day caused extensive drainage of the ER Ca²⁺ stores. This Ca²⁺ depletion was followed by markedly reduced cell proliferation rates and morphological changes that developed over 2-4 days and culminated in cell death. Interestingly, these changes were not accompanied by bulk increases in cytosolic Ca²⁺ levels. Moreover, knockdown of two key store-operated Ca²⁺ entry (SOCE) components, Orai1 and STIM1, did not reduce Tg cytotoxicity, indicating that SOCE and Ca²⁺ entry are not critical for Tg-induced cell death. However, we observed a correlation between the abilities of Tg and Tg analogs to deplete ER Ca²⁺ stores and their detrimental effects on cell viability. Furthermore, caspase activation and cell death were associated with a sustained unfolded protein response. We conclude that ER Ca²⁺ drainage and sustained unfolded protein response activation are key for initiation of apoptosis at low concentrations of Tg and Tg analogs, whereas high cytosolic Ca²⁺ levels and SOCE are not required.

Tacrolimus Protects Podocytes from Injury in Lupus Nephritis Partly by Stabilizing the Cytoskeleton and Inhibiting Podocyte Apoptosis

Objective

Several studies have reported that tacrolimus (TAC) significantly reduced proteinuria in lupus nephritis (LN) patients and mouse models. However, the mechanism for this effect remains undetermined. This study explored the mechanism of how TAC protects podocytes from injury to identify new targets for protecting renal function.

Methods

MRL/lpr mice were given TAC at a dosage of 0.1 mg/kg per day by intragastric administration for 8 weeks. Urine and blood samples were collected. Kidney sections (2μm) were stained with hematoxylin-eosin (HE), periodic acid-Schiff base (PAS) and Masson's trichrome stain. Mouse podocyte cells (MPC5) were treated with TAC and/or TGF-β₁ for 48h. The mRNA levels and protein expression of synaptopodin and Wilms’ tumor 1 (WT1) were determined by real-time PCR, Western blotting and/or immunofluorescence, respectively. Flow cytometry was used to detect cell apoptosis with annexin V. Podocyte foot processes were observed under transmission electron microscopy. IgG and C3 deposition were assessed with immunofluorescence assays and confocal microscopy.

Results

Synaptopodin expression significantly decreased in MRL/lpr disease control mice, accompanied by increases in 24-h proteinuria, blood urea nitrogen, and serum creatinine. TAC, however, reduced proteinuria, improved renal function, attenuated renal pathology, restored synaptopodin expression and preserved podocyte numbers. In MPC5 cells, TGF-β₁ enhanced F-actin damage in podocytes and TAC stabilized it. TAC also decreased TGF-β₁-induced podocyte apoptosis in vitro and inhibited foot process fusion in MRL/lpr mice. In addition, our results also showed TAC inhibited glomerular deposition of IgG and C3.

Conclusion

This study demonstrated that TAC reduced proteinuria and preserved renal function in LN through protecting podocytes from injury partly by stabilizing podocyte actin cytoskeleton and inhibiting podocyte apoptosis.

Obesity related adipokines and colorectal cancer: a review and meta-analysis

Obesity has been considered as an important risk factor for the development of colorectal cancer (CRC), but the association has not been fully elucidated. Obesity is linked significantly to adipose tissue dysfunction and to alteration of adipokines in blood; in particular, obesity-induced inflammation is thought to be an important link between obesity and colorectal cancer. Based on epidemiological studies, we undertook a systematic review to understand the association of circulating levels of selected adipokines, including adiponectin, leptin, resistin, IL-6 and TNF-α, with the level of CRC risk. Most prospective studies suggested protective effects of adiponectin, but these were attenuated by body mass index (BMI) and waist circumference (WC) data in our meta-analysis. On the other hand, meta-analyses for leptin and CRC did not demonstrate any association, similar to the results of systematic review. Although it proved difficult to determine whether other selected adipokines (resistin, IL-6 and TNF-α) were related to CRC risk due to small number of reports, the present systematic review suggested a positive association with elevated resistin levels but null associations with IL-6 and TNF-α.

Lessons learned from gene expression profiling of cutaneous T-cell lymphoma

Gene expression studies of cutaneous T-cell lymphoma (CTCL) span a decade, yet the pathogenesis is poorly understood and diagnosis remains a challenge. This review examines the varied approaches to gene expression analysis of CTCL, with emphasis on cell populations, control selection and expression data collection. Despite discordant results, several dysregulated genes have been identified across multiple studies, including PLS3, KIR3DL2, TWIST1 and STAT4. Here, we provide an overview of the most consistently expressed genes across different studies and bring them together through common pathways biologically relevant to CTCL. Four pathways - evasion of activation-induced cell death, T helper 2 lymphocyte differentiation, transforming growth factor-β receptor expression, and tumour necrosis factor receptor ligands - appear to encompass the most frequently affected genes, hypothetically providing insight into the disease pathogenesis.

S100A6 (calcyclin) enhances the sensitivity to apoptosis via the upregulation of caspase-3 activity in Hep3B cells

S100A6 (calcyclin) is a small calcium-binding protein which has been implicated in several cellular processes such as cell cycle progression, cytoskeleton rearrangement, and exocytosis. Also the upregulation of S100A6 has been reported in a variety of tumors and linked to metastasis. However, exact intracellular roles of S100A6 related with apoptosis have not been clarified yet. Here we demonstrated that the upregulation of S100A6 enhances the cell death rate compared to the control under the apoptotic conditions. In exogenously S100A6 induced Hep3B cells, cell viability was significantly decreased compared with mock and S100A6-knockdown cells under calcium ionophore A23187 treatment. The exogenously introduced S100A6 significantly affected the caspase-3-like activity in programmed cell death through the enhanced caspase-3 expression, which was verified by promoter assay in wild or mutant S100A6-transfected Hep3B cells. Next, the promoter activity of caspase-3 was increased by 2.5-folds in wild-type S100A6-transfected cells compared to mutant 2 (E67K, mutant of EF-hand motif) or control. Our results suggest that S100A6 might be involved in the processing of apoptosis by modulating the transcriptional regulation of caspase-3.

Circulating levels of inflammatory cytokines and risk of colorectal adenomas

The association between obesity and colorectal neoplasia may be mediated by inflammation. Circulating levels of C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) are elevated in the obese. Adipose tissue can produce and release the inflammatory cytokines that are potentially procarcinogenic. We examined circulating levels of CRP, IL-6, and TNF-alpha in relation to risk factors and the prevalence of colorectal adenomas. Plasma levels of CRP, IL-6, and TNF-alpha were quantified in 873 participants (242 colorectal adenoma cases and 631 controls) in a colonoscopy-based cross-sectional study conducted between 1998 and 2002. Multivariable logistic regression was used to estimate associations between known risk factors for colorectal neoplasia and circulating levels of inflammatory cytokines and associations between inflammatory cytokines and colorectal adenomas. Several known risk factors for colorectal neoplasia were associated with higher levels of inflammatory cytokines, including older age, current smoking, and increasing adiposity. The prevalence of colorectal adenomas was associated with higher concentrations of IL-6 and TNF-alpha and, to a lesser degree, with CRP. For IL-6, adjusted odds ratios (OR) for colorectal adenomas were 1.79 [95% confidence interval (CI), 1.19-2.69] for the second highest plasma level and 1.85 (95% CI, 1.24-2.75) for the highest level compared with the reference level. A similar association was found with TNF-alpha, with adjusted ORs of 1.56 (95% CI, 1.03-2.36) and 1.66 (95% CI, 1.10-2.52), respectively. Our findings indicate that systemic inflammation might be involved in the early development of colorectal neoplasia.

Anti-angiogenic effects of liposomal prednisolone phosphate on B16 melanoma in mice

Prednisolone phosphate (PLP) encapsulated in long-circulating liposomes can inhibit tumor growth after intravenous administration (i.v.). These antitumor effects of liposomal PLP are the result of the tumor-targeting property of the liposome formulation. The mechanism by which liposomal PLP inhibits tumor growth is unclear. We investigated the effects of liposome-encapsulated PLP versus free PLP on angiogenic protein production in tumor tissue in vivo and on viability and proliferation of tumor and endothelial cells in vitro. In vivo, liposomal PLP had a stronger reducing effect on pro-angiogenic protein levels than free PLP, whereas levels of anti-angiogenic proteins were hardly affected. Cell viability was only slightly affected with either treatment. Liposomal PLP had strong anti-proliferative effects on human umbilical vein endothelial cells, whereas free PLP had hardly any effect. Taken together, the present study points to a strong inhibitory effect of liposomal PLP on tumor angiogenesis by reduction of the intratumoral production of the majority of pro-angiogenic factors studied and direct inhibition of endothelial cell proliferation, which is the result of high prolonged levels of prednisolone in the tumor by liposomal delivery.

The mitochondrial ADPR link between Ca2+ store release and Ca2+ influx channel opening in immune cells

The regulation of non-voltage-operated Ca2+ channels in the plasma membrane remains unclear. However, there is often a link between the physiological release of Ca2+ from intracellular stores and opening of Ca2+ influx channels on the plasma membrane. This route has been referred to variously as store-operated Ca2+ entry (SOC), capacitative Ca2+ entry, and Ca2+ release-activated channel opening (CRAC), and often underlies the large changes in cytosolic free Ca2+ that accompany many stimuli in a wide variety of cell types. The linkage between Ca2+ store release and opening of Ca2+ channels on the plasma membrane has remained elusive for a number of years, perhaps in part because different mechanisms exist for this linkage, and are used to differing extents by different cells. We suggest here that one of the mechanisms that may operate in cells of the immune system, but that may be important elsewhere, involves the release of mitochondrial adenosine diphosphate ribose (ADPR) or nicotinamide adenine dinucleotide (NAD+). There is accumulating evidence to support each of the steps necessary for a complete description of this "Ca2+ store release to plasma membrane channel opening" link, but to our knowledge they have not been connected before to make a coherent model.-

Extracellular ATP inhibits apoptosis and maintains cell viability by inducing autocrine production of interleukin-4 in a myeloid progenitor cell line

Interleukin-3 (IL-3)-dependent myeloid progenitor cell FDC.P2 is induced to undergo apoptotic cell death upon IL-3 depletion. Extracellular adenosine triphosphate (ATP) was found to prevent apoptosis and maintain cell viability of FDC.P2 cells upon IL-3 withdrawal. The antiapoptotic effect of ATP required extracellular Ca2+. Furthermore, FK506, a specific inhibitor of calcium/calmodulin-dependent protein phosphatase calcineurin, inhibited the antiapoptotic effect of ATP. As one of cytokines whose expression is dependent on the activation of calcineurin, interleukin-4 (IL-4) played a critical role in ATP-mediated cell survival of FDC.P2 cells because neutralizing antibody against IL-4 effectively abrogated the antiapoptotic activity of ATP. Moreover, ATP treatment induced a significant amount of secreted IL-4 that was sufficient to maintain cell viability. Taken together, our present results demonstrate that extracellular ATP triggers autocrine production of IL-4 through calcium-dependent activation of calcineurin and secreted IL-4 substitutes IL-3 in protecting FDC.P2 cells from apoptosis even in the absence of IL-3.

Brain response to traumatic brain injury in wild-type and interleukin-6 knockout mice: a microarray analysis

Traumatic injury to the brain is one of the leading causes of injury-related death or disability. Brain response to injury is orchestrated by cytokines, such as interleukin (IL)-6, but the full repertoire of responses involved is not well known. We here report the results obtained with microarrays in wild-type and IL-6 knockout mice subjected to a cryolesion of the somatosensorial cortex and killed at 0, 1, 4, 8 and 16 days post-lesion. Overall gene expression was analyzed by using Affymetrix genechips/oligonucleotide arrays with approximately 12,400 probe sets corresponding to approximately 10,000 different murine genes (MG_U74Av2). A robust, conventional statistical method (two-way anova) was employed to select the genes significantly affected. An orderly pattern of gene responses was clearly detected, with genes being up- or down-regulated at specific timings consistent with the processes involved in the initial tissue injury and later regeneration of the parenchyma. IL-6 deficiency showed a dramatic effect in the expression of many genes, especially in the 1 day post-lesion timing, which presumably underlies the poor capacity of IL-6 knockout mice to cope with brain damage. The results highlight the importance of IL-6 controlling the response of the brain to injury as well as the suitability of microarrays for identifying specific targets worthy of further study.

BCL2 and JUNB abnormalities in primary cutaneous lymphomas

BACKGROUND

BCL2 is upregulated in nodal and extranodal B-cell non-Hodgkin's lymphomas, with a consequent antiapoptotic effect. However, loss of BCL2 has also been noted in some malignancies, suggesting a different molecular pathogenesis.

OBJECTIVES

To investigate genomic and protein expression status of BCL2 and to compare the results with that of JUNB in primary cutaneous lymphomas (PCLs).

METHODS

We analysed gene copy number of BCL2 and JUNB in 88 DNA samples from 80 patients with PCL consisting of Sézary syndrome/mycosis fungoides (SS/MF), primary cutaneous B-cell lymphoma (PCBCL) and primary cutaneous CD30+ anaplastic large cell lymphoma (C-ALCL) by the use of real-time polymerase chain reaction (PCR) and immunohistochemistry (IHC). Real-time PCR and IHC findings were subsequently compared with the results of additional fluorescent in situ hybridization (FISH) analysis of 23 cases of SS and Affymetrix cDNA expression microarray study of two primary cutaneous T-cell lymphoma (CTCL) cell lines.

RESULTS

Real-time PCR analysis showed loss of BCL2 gene copy number in 22 of 80 PCL cases (28%), including 17 of 42 SS/MF, three of 13 C-ALCL and two of 33 PCBCL samples, and gain of BCL2 in four PCBCL samples. Gain of JUNB was identified in 18 of 71 PCL cases (25%), including nine of 35 SS/MF, seven of 13 C-ALCL and two of 31 PCBCL samples. IHC analysis revealed absent nuclear expression of BCL2 protein in 47 of 73 PCL cases, comprising 28 of 36 SS/MF, eight of eight C-ALCL and 11 of 29 PCBCL cases. In contrast, BCL2 protein expression was detected in 26 of 73 PCL cases, consisting of 18 of 29 PCBCL and eight of 36 SS/MF cases. JUNB protein expression was present in tumour cells from 30 of 33 of SS/MF and eight of eight C-ALCL, and was absent in tumour cells from 18 of 27 PCBCL cases. A comparison between BCL2 and JUNB revealed loss of BCL2 and gain of JUNB in five of 35 SS/MF samples, and expression of JUNB protein and absent BCL2 expression in 25 SS/MF and eight of eight C-ALCL cases. In contrast, expression of BCL2 and absent JUNB expression were detected in 67% of PCBCL cases. Additional FISH analysis revealed deletion of BCL2 in 19 of 23 SS cases (83%), including eight cases with BCL2 loss shown by real-time PCR. Furthermore, Affymetrix expression microarray demonstrated decreased expression of proapoptotic and antiapoptotic genes involved in BCL2 signalling pathways such as BOK, BIM, HRK, RASA1 and STAT2 in two CTCL cell lines with BCL2 loss and absent BCL2 expression. Increased expression of JUNB was also identified in the MF cell line.

CONCLUSIONS

These findings provide a comprehensive assessment of BCL2 and JUNB status in PCL, and suggest that there is a selection pressure in a subset of CTCL cases for tumour cells showing BCL2 loss and upregulation of JUNB primarily through chromosomal deletion and amplification, respectively.

Induction in myeloid leukemic cells of genes that are expressed in different normal tissues

Using DNA microarray and cluster analysis of expressed genes in a cloned line (M1-t-p53) of myeloid leukemic cells, we have analyzed the expression of genes that are preferentially expressed in different normal tissues. Clustering of 547 highly expressed genes in these leukemic cells showed 38 genes preferentially expressed in normal hematopoietic tissues and 122 other genes preferentially expressed in different normal nonhematopoietic tissues, including neuronal tissues, muscle, liver, and testis. We have also analyzed the genes whose expression in the leukemic cells changed after activation of WT p53 and treatment with the cytokine IL-6 or the calcium mobilizer thapsigargin. Of 620 such genes in the leukemic cells that were differentially expressed in normal tissues, clustering showed 80 genes that were preferentially expressed in hematopoietic tissues and 132 genes in different normal nonhematopoietic tissues that also included neuronal tissues, muscle, liver, and testis. Activation of p53 and treatment with IL-6 or thapsigargin induced different changes in the genes preferentially expressed in these normal tissues. These myeloid leukemic cells thus express genes that are expressed in normal nonhematopoietic tissues, and various treatments can reprogram these cells to induce other such nonhematopoietic genes. The results indicate that these leukemic cells share with normal hematopoietic stem cells the plasticity of differentiation to different cell types. It is suggested that this reprogramming to induce in malignant cells genes that are expressed in different normal tissues may be of clinical value in therapy.

1alpha,25(OH)(2)D(3) regulates NF-kappaB DNA binding activity in cultured normal human keratinocytes through an increase in IkappaBalpha expression

NF-kappaB is a dimeric transcription factor which regulates transcription of a number of different genes including IL-8 and p53. In resting cells NF-kappaB is usually retained in an inactive state in the cytoplasm through binding to a member of the inhibitory kappaB (IkappaB) protein family. The purpose of this study was to determine the effect of 1alpha,25(OH)(2)D(3) on NF-kappaB activation in both unstimulated and stimulated (IL-1alpha) cultured normal human keratinocytes. NF-kappaB DNA binding activity was determined by EMSA using two different oligonucleotides containing the kappaB sequence from either the IL-8 or the p53 promoter. IkappaBalpha and p53 expression was determined by Western blotting and IL-8 expression by ELISA. In unstimulated keratinocytes no NF-kappaB binding to the IL-8 kappaB binding sequence was detectable, whereas stimulation with IL-1alpha (10 ng/ml) led to a significant ( P<0.05) induction of NF-kappaB binding. In contrast NF-kappaB binding to the p53 kappaB binding sequence was detectable in unstimulated cells, although it was significantly increased after IL-1alpha (10 ng/ml) stimulation. Incubation with 1alpha,25(OH)(2)D(3) (10(-8)-10(-7) M) was shown to significantly ( P<0.05) stimulate the expression of IkappaBalpha and in parallel experiments with normal human keratinocytes stimulated with IL-1alpha (10 ng/ml) a significant ( P<0.05) time and dose-dependent decrease in NF-kappaB binding to the IL-8 kappaB binding sequence and in IL-8 expression were seen. A less-pronounced decrease in NF-kappaB binding to the p53 kappaB response element was seen after preincubation with 1alpha,25(OH)(2)D(3) and IL-1alpha stimulation, and it did not result in any change in p53 expression. These results demonstrate that 1alpha,25(OH)(2)D(3) inhibits NF-kappaB binding to the IL-8 kappaB binding sequence more potently than binding to the p53 kappaB binding sequence. We propose that this selectivity may be mediated through an increased expression of IkappaBalpha which leads to an inhibition of specific NF-kappaB subunits resulting in a selective regulation of NF-kappaB-induced gene transcription.

Signalling shutdown strategies in aging immune cells

It is important for the resolution of inflammation that the number and activity of immune cells are reduced. Clearance of immune cells may be achieved by apoptosis and phagocytosis of cell fragments by macrophages. However, signalling shutdown by immune cells committed to apoptosis occurs early in the progression of these cells towards fragmentation and, it could be argued, is a key feature of apoptosis. There is surprisingly little known about the mechanisms that underlie this signalling shutdown, in particular the shutdown of Ca(2+) influx. The consequences and the potential mechanisms by which Ca(2+) influx shutdown is achieved are discussed. In addition, the potential consequences for cell signalling of cytochrome c release from mitochondria and of phosphatidyl-serine externalization are discussed. The aim of the review is therefore to highlight the evidence for various signalling shutdown strategies in immune cells that may limit their activity during progression towards apoptosis.

Raising intracellular calcium attenuates neuronal apoptosis triggered by staurosporine or oxygen-glucose deprivation in the presence of glutamate receptor blockade

The relationship between intracellular Ca(2+) ([Ca(2+)](i)) regulation and programmed cell death is not well-defined; both increases and decreases in [Ca(2+)](i) have been observed in cells undergoing apoptosis. We determined [Ca(2+)](i) in cultured murine cortical neurons undergoing apoptosis after exposure to staurosporine or following oxygen-glucose deprivation in the presence of glutamate receptor antagonists. Neuronal [Ca(2+)](i) was decreased 1-4 h after exposure to staurosporine (30 nM). A [Ca(2+)](i) decrease was also observed 1 h after the end of the oxygen-glucose deprivation period when MK-801 and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) were added to the bathing medium during the deprivation period. A similar decrease in [Ca(2+)](i) produced by reducing extracellular Ca(2+) or chelating intracellular Ca(2+) was sufficient to induce neuronal apoptosis. Raising [Ca(2+)](i) either by activating voltage-sensitive Ca(2+) channels with (-) Bay K8644 or by application of low concentrations of kainate attenuated both staurosporine and oxygen-glucose deprivation-induced apoptosis.

Inhibition of p53-induced apoptosis without affecting expression of p53-regulated genes

Using DNA microarray and clustering of expressed genes we have analyzed the mechanism of inhibition of wild-type p53-induced apoptosis by the cytokine interleukin 6 (IL-6) and the calcium mobilizer thapsigargin (TG). Clustering analysis of 1,786 genes, the expression level of which changed after activation of wild-type p53 in the absence or presence of IL-6 or TG, showed that these compounds did not cause a general inhibition of the ability of p53 to up-regulate or down-regulate gene expression. Expression of various p53 targets implicated as mediators of p53-induced apoptosis was also not affected by IL-6 or TG. These compounds thus can bypass the effect of wild-type p53 on gene expression and inhibit apoptosis. IL-6 and TG activated different p53-independent pathways of gene expression that include up-regulation of antiapoptotic genes. IL-6 and TG also activated different differentiation-associated genes. The ability of compounds such as cytokines and calcium mobilizers to inhibit p53-mediated apoptosis without generally inhibiting gene expression regulated by p53 can facilitate tumor development and tumor resistance to radiation and chemotherapy in cells that retain wild-type p53.

Calcium induces cell survival and proliferation through the activation of the MAPK pathway in a human hormone-dependent leukemia cell line, TF-1

Survival and proliferation of cells of a human myelo-erythroid CD34+ leukemia cell line (TF-1) depend on the presence of granulocyte-macrophage colony-stimulating factor or interleukin-3. Upon hormone withdrawal these cells stop proliferating and undergo apoptotic process. In this report we demonstrate that a controlled increase in [Ca2+]i induces hormone-independent survival and proliferation of TF-1 cells. We found that moderate elevation of [Ca2+]i by the addition of cyclopiasonic-acid protected TF1 cells from apoptosis. Furthermore, a higher, but transient elevation of [Ca2+]i by ionomycin treatment induced cell proliferation. In both cases caspase-3 activity was reduced, and Bcl-2 was up-regulated. Higher elevation of [Ca2+]i by ionomycin induced MEK-dependent biphasic ERK1/2 activation, sufficient to move the cells from G0/G1 to S/M phases. Meanwhile, activation of ERK1/2, phosphorylation of the Elk-1 transcription factor, and, consequently, a substantial elevation of Egr-1 and c-Fos levels and AP-1 DNA binding were observed. Moderate elevation of [Ca2+]i, on the other hand, caused a delayed monophasic activation of ERK1/2 and Elk-1 that was accompanied with only a small increase of Egr-1 and c-Fos levels and AP-1 DNA binding. The specific MEK-1 kinase inhibitor, PD98059, inhibited all the effects of increasing [Ca2+]i, indicating that the MAPK/ERK pathway activation is essential for TF-1 cell survival and proliferation. Based on these results we suggest that the elevation of the [Ca2+]i may influence the cytokine dependence of hemopoietic progenitors and may contribute to pathological hematopoiesis.

Downregulation of p21(waf/cip-1) mediates apoptosis of human hepatocellular carcinoma cells in response to interferon-gamma

There is no effective treatment for advanced hepatocellular carcinoma (HCC). We therefore explored the molecular mechanisms of interferon-gamma (IFN-gamma)-mediated growth regulation in human HCC cell lines. IFN-gamma receptor expression, signal transduction, and regulation of effectors were examined by RT-PCR, immunoprecipitation, immunoblotting, and reporter gene assays. Growth and apoptosis were determined based on cell numbers, cell cycle analyses, kinase assays, DNA fragmentation, and PARP cleavage. HCC cell lines express functionally intact IFN-gamma receptors and downstream effectors. IFN-gamma profoundly inhibited growth of HCC cells via two different mechanisms: inhibition of G1 cell cycle progression and induction of apoptosis. Analyses in SK-Hep-1 cells revealed a deficient cyclin D induction in IFN-gamma-treated cells, resulting in reduced activity of CDK4 and CDK2 kinases and pRB hypophosphorylation. In contrast, apoptosis prevailed in IFN-gamma-treated HepG2 cultures. A survey of apoptosis relevant IFN-gamma effectors including IRF-1, caspase-1, caspase-3, and p21(waf/cip-1) documented a dramatic transcriptional downregulation of p21(waf/cip-1) exclusively in apoptosis-susceptible HepG2 cells. Reconstitution of p21(waf/cip-1) rescued HepG2 cells from IFN-gamma-induced apoptosis, indicating that p21(waf/cip-1) reduction was required for apoptosis execution. Inversely, downregulation of p21(waf/cip-1) sensitized SK-Hep-1 cells to IFN-gamma-induced apoptosis. Thus, downregulation of p21(waf/cip-1) in HCC cells functions as a novel, critical determinant of alternative growth inhibitory pathways in response to IFN-gamma.

Cytokine control of developmental programs in normal hematopoiesis and leukemia

The establishment of a system for in vitro clonal development of hematopoietic cells made it possible to discover the cytokines that regulate hematopoiesis. These cytokines include colony stimulating factors and others, which interact in a network, and there is a cytokine cascade which couples growth and differentiation. A network allows considerable flexibility and a ready amplification of response to a particular stimulus. A network may also be necessary to stabilize the whole system. Cells called hematopoietic stem cells (HSC) can repopulate all hematopoietic lineages in lethally irradiated hosts, and under appropriate conditions give rise to neuronal, muscle, and epithelial cells. Granulocyte colony stimulating factor induces migration of both HSC and in vitro colony forming cells from the bone marrow to peripheral blood. Granulocyte colony stimulating factor is also used clinically to repair irradiation and chemotherapy associated suppression of normal hematopoiesis in cancer patients, and to stimulate normal granulocyte development in patients with infantile congenital agranulocytosis. It is suggested that there may also be appropriate conditions under which in vitro colony forming cells have a wider differentiation potential similar to that shown by HSC. An essential part of the developmental program is cytokine suppression of apoptosis by changing the balance in expression of apoptosis inducing and suppressing genes. Decreasing the level of cytokines that suppress therapeutic induction of apoptosis in malignant cells can improve cancer therapy. Cytokines and some other compounds can reprogram abnormal developmental programs in leukemia, so that the leukemic cells differentiate to mature non dividing cells, and this can also be used for therapy. There is considerable plasticity in the developmental programs of normal and malignant cells.

Lysosomal destabilization in p53-induced apoptosis

The tumor suppressor wild-type p53 can induce apoptosis. M1-t-p53 myeloid leukemic cells have a temperature-sensitive p53 protein that changes its conformation to wild-type p53 after transfer from 37 degrees C to 32 degrees C. We have now found that these cells showed an early lysosomal rupture after transfer to 32 degrees C. Mitochondrial damage, including decreased membrane potential and release of cytochrome c, and the appearance of apoptotic cells occurred later. Lysosomal rupture, mitochondrial damage, and apoptosis were all inhibited by the cytokine IL-6. Some other compounds can also inhibit apoptosis induced by p53. The protease inhibitor N-tosyl-l-phenylalanine chloromethyl ketone inhibited the decrease in mitochondrial membrane potential and cytochrome c release, the Ca(2+)-ATPase inhibitor thapsigargin inhibited only cytochrome c release, and the antioxidant butylated hydroxyanisole inhibited only the decrease in mitochondrial membrane potential. In contrast to IL-6, these other compounds that inhibited some of the later occurring mitochondrial damage did not inhibit the earlier p53-induced lysosomal damage. The results indicate that apoptosis is induced by p53 through a lysosomal-mitochondrial pathway that is initiated by lysosomal destabilization, and that this pathway can be dissected by using different apoptosis inhibitors. These findings on the induction of p53-induced lysosomal destabilization can also help to formulate new therapies for diseases with apoptotic disorders.

2-Methoxyestradiol-induced caspase-3 activation and apoptosis occurs through G(2)/M arrest dependent and independent pathways in gastric carcinoma cells

BACKGROUND

2-Methoxyestradiol (2-Me), one of the estrogen metabolites, has recently been found to possess anti-angiogenesis activity in vivo. Many chemotherapeutic agents, such as taxol, docetaxel, and vinblastine, interact with microtubules and then induce apoptosis. It has been suggested that 2-Me acts on microtubules and results in G(2)/M-cycle arrest of tumor cells. Whether 2-Me induces apoptosis in gastric carcinoma cell lines is not known. Moreover, reactive oxygen species (ROS) produced by 2-Me may be involved in cytotoxicity of tumor cells. Thus, another objective of this study was to evaluate the relation between cell cycle arrest, ROS formation, and caspase activity levels after 2-Me treatment in gastric carcinoma cells.

METHODS

It was determined whether 2-Me directly induced apoptosis in two gastric carcinoma cell lines (SC-M1 and NUGC-3) through caspase-3 and caspase-8 activation and, eventually, induced DNA fragmentation. To clarify the effect of 2-Me-induced G(2)/M arrest in apoptosis, calcium ionophore, A23187, and thapsigargin were used to modulate 2-Me-induced cell cycle responses. Moreover, the role of 2-Me-induced ROS formation in the cell cycle responses also was evaluated.

RESULTS

It was found that 2-Me treatment resulted in G(2)/M-cycle arrest, caspase-8 and caspase-3 activation, and DNA fragmentation. In addition, the 2-Me induced, concomitant increases of peroxide and superoxide anions were correlated with G(2)/M-cycle arrest. Treatment with calcium ionophore A23187 and thapsigargin partially reversed the 2-Me-induced G(2)/M-cycle arrest, with a concomitant decrease in both peroxide and superoxide levels. Moreover, A23187 blocked the 2-Me-induced caspase-3 activation, whereas thapsigargin had no effect. Treatment with calcium channel blockers did not affect 2-Me-induced cell cycle arrest or caspase-3 activation.

CONCLUSIONS

These results suggest that the 2-Me-induced apoptosis of gastric carcinoma cells by DNA fragmentation accompanied caspase activation. Elevation of free radicals was associated with G(2)/M-cycle arrest. The induction of G(2)/M-cycle arrest is not a prerequisite for caspase activation.

Ion homeostasis and apoptosis

Alterations in the transmembrane gradients of several physiological ions may influence programmed cell death. In particular, recent data suggest that increases in intracellular calcium may either promote or inhibit apoptosis, depending on the level, timing and location, whereas loss of intracellular potassium promotes apoptosis.

Cyclosporine reduces left ventricular mass with chronic aortic banding in mice, which could be due to apoptosis and fibrosis

A tacit assumption in studies of left ventricular (LV) hypertrophy is that left ventricular/body weight (LV/BW) reflects the extent of myocyte hypertrophy. The goal of the current investigation was to determine if there was another explanation for the reduced LV/BW observed after inhibiting calcineurin with cyclosporine during the development of pressure overload LV hypertrophy as compared with animals that did not receive cyclosporine. Accordingly, we examined the prevalence of fibrosis and apoptosis and measured cell size in the hearts from mice at 1 and 3 weeks after transverse aortic banding with and without chronic cyclosporine. Although LV/BW, compared to aortic banded vehicle treated mice, was reduced by 30% in aortic banded cyclosporine treated mice, myocyte cross sectional area was similar in both banded groups (346+/-9 microm2 v 336+/-13 microm2). The volume percent interstitial fibrosis was greater in aortic banded cyclosporine treated animals (1.4+/-0.2%) compared with aortic banded vehicle treated animals (0.9+/-0.2%, P<0.05) or in sham animals (0.6+/-0.1%). Surprisingly, lesions including myocytes containing iron were observed and were most prominent in aortic banded cyclosporine treated animals. Apoptosis, quantitated with TUNEL staining as percent of myocytes, was increased in aortic banded cyclosporine treated animals at 7 days (1.6+/-0.4%) compared with aortic banded vehicle treated animals (0.4+/-0.1%, P<0.01) and was still increased at 21 days. Immunoblotting demonstrated a decrease in the phosphorylation of Akt and Bad, and also Bcl-2 levels were reduced in aortic banded cyclosporine treated animals at 7 days compared with aortic banded vehicle treated animals. These proteins protect against apoptosis, and support the concept that cyclosporine inhibited the calcineurin pathway, resulting in enhanced apoptosis. Thus, the decrease in LV/BW in the aortic banded cyclosporine treated animals actually may be due, at least in part, to cell loss and death, as reflected by the enhanced fibrosis and apoptosis and the focal iron deposits in myocytes.

2-Methoxyestradiol-induced caspase-3 activation and apoptosis occurs through G(2)/M arrest dependent and independent pathways in gastric carcinoma cells

BACKGROUND

2-Methoxyestradiol (2-Me), one of the estrogen metabolites, has recently been found to possess anti-angiogenesis activity in vivo. Many chemotherapeutic agents, such as taxol, docetaxel, and vinblastine, interact with microtubules and then induce apoptosis. It has been suggested that 2-Me acts on microtubules and results in G(2)/M-cycle arrest of tumor cells. Whether 2-Me induces apoptosis in gastric carcinoma cell lines is not known. Moreover, reactive oxygen species (ROS) produced by 2-Me may be involved in cytotoxicity of tumor cells. Thus, another objective of this study was to evaluate the relation between cell cycle arrest, ROS formation, and caspase activity levels after 2-Me treatment in gastric carcinoma cells.

METHODS

It was determined whether 2-Me directly induced apoptosis in two gastric carcinoma cell lines (SC-M1 and NUGC-3) through caspase-3 and caspase-8 activation and, eventually, induced DNA fragmentation. To clarify the effect of 2-Me-induced G(2)/M arrest in apoptosis, calcium ionophore, A23187, and thapsigargin were used to modulate 2-Me-induced cell cycle responses. Moreover, the role of 2-Me-induced ROS formation in the cell cycle responses also was evaluated.

RESULTS

It was found that 2-Me treatment resulted in G(2)/M-cycle arrest, caspase-8 and caspase-3 activation, and DNA fragmentation. In addition, the 2-Me induced, concomitant increases of peroxide and superoxide anions were correlated with G(2)/M-cycle arrest. Treatment with calcium ionophore A23187 and thapsigargin partially reversed the 2-Me-induced G(2)/M-cycle arrest, with a concomitant decrease in both peroxide and superoxide levels. Moreover, A23187 blocked the 2-Me-induced caspase-3 activation, whereas thapsigargin had no effect. Treatment with calcium channel blockers did not affect 2-Me-induced cell cycle arrest or caspase-3 activation.

CONCLUSIONS

These results suggest that the 2-Me-induced apoptosis of gastric carcinoma cells by DNA fragmentation accompanied caspase activation. Elevation of free radicals was associated with G(2)/M-cycle arrest. The induction of G(2)/M-cycle arrest is not a prerequisite for caspase activation.

Calcium is a key signaling molecule in beta-lapachone-mediated cell death

beta-Lapachone (beta-Lap) triggers apoptosis in a number of human breast and prostate cancer cell lines through a unique apoptotic pathway that is dependent upon NQO1, a two-electron reductase. Downstream signaling pathway(s) that initiate apoptosis following treatment with beta-Lap have not been elucidated. Since calpain activation was suspected in beta-Lap-mediated apoptosis, we examined alterations in Ca(2+) homeostasis using NQO1-expressing MCF-7 cells. beta-Lap-exposed MCF-7 cells exhibited an early increase in intracellular cytosolic Ca(2+), from endoplasmic reticulum Ca(2+) stores, comparable to thapsigargin exposures. 1,2-Bis-(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester, an intracellular Ca(2+) chelator, blocked early increases in Ca(2+) levels and inhibited beta-Lap-mediated mitochondrial membrane depolarization, intracellular ATP depletion, specific and unique substrate proteolysis, and apoptosis. The extracellular Ca(2+) chelator, EGTA, inhibited later apoptotic end points (observed >8 h, e.g. substrate proteolysis and DNA fragmentation), suggesting that later execution events were triggered by Ca(2+) influxes from the extracellular milieu. Collectively, these data suggest a critical, but not sole, role for Ca(2+) in the NQO1-dependent cell death pathway initiated by beta-Lap. Use of beta-Lap to trigger an apparently novel, calpain-like-mediated apoptotic cell death could be useful for breast and prostate cancer therapy.

Inhibition of Na+,K+-ATPase by interferon gamma down-regulates intestinal epithelial transport and barrier function

BACKGROUND & AIMS

To determine how interferon (IFN)-gamma inhibits epithelial barrier and ion transport functions, intestinal T84 cells were studied.

METHODS

Acute and chronic effects of IFN-gamma on T84 barrier function, Na+,K+-adenosine triphosphatase (ATPase) activity, and certain ion transport and tight junctional proteins were determined. To assess the role of Na+,K+-ATPase and intracellular Na+, similar studies with the Na+,K+-ATPase inhibitor ouabain and Na+ ionophore monensin were performed. To determine the role of nitric oxide (NO), the NO donor SPER-NO was used.

RESULTS

IFN-gamma acutely (<6 hour) decreased cellular Na+,K+-ATPase activity, followed later (>24 hours) by decreases in expression of Na/K/2Cl, the alpha subunit of Na+,K+-ATPase, occludin, and ZO-1. In contrast, cystic fibrosis transmembrane conductance regulator or the Na+ pump beta subunit were unchanged. Ouabain and monensin caused nearly identical changes to IFN-gamma. Incubation in low Na+ media significantly blunted the chronic effects of IFN-gamma. Hypotonic-induced cell swelling, in contrast, had effects similar to IFN-gamma but did not alter the expression of the Na+ pump alpha subunit. The NO donor SPER-NO rapidly inhibited Na+,K+-ATPase and also down-regulated transport and barrier proteins.

CONCLUSIONS

IFN-gamma inhibition of Na+,K+-ATPase activity acutely causes increases in intracellular Na(i) concentration and cell volume, which are distinct signaling events that ultimately result in a leaky and dysfunctional epithelium associated with chronic inflammation.

Regulation of p53 stability and p53-dependent apoptosis by NADH quinone oxidoreductase 1

The tumor suppressor gene wild-type p53 encodes a labile protein that accumulates in cells after different stress signals and can cause either growth arrest or apoptosis. One of the p53 target genes, p53-inducible gene 3 (PIG3), encodes a protein with significant homology to oxidoreductases, enzymes involved in cellular responses to oxidative stress and irradiation. This fact raised the possibility that cellular oxidation-reduction events controlled by such enzymes also may regulate the level of p53. Here we show that NADH quinone oxidoreductase 1 (NQO1) regulates p53 stability. The NQO1 inhibitor dicoumarol caused a reduction in the level of both endogenous and gamma-irradiation-induced p53 in HCT116 human colon carcinoma cells. This reduction was prevented by the proteasome inhibitors MG132 and lactacystin, suggesting enhanced p53 degradation in the presence of dicoumarol. Dicoumarol-induced degradation of p53 also was prevented in the presence of simian virus 40 large T antigen, which is known to bind and to stabilize p53. Cells overexpressing NQO1 were resistant to dicoumarol, and this finding indicates the direct involvement of NQO1 in p53 stabilization. NQO1 inhibition induced p53 degradation and blocked wild-type p53-mediated apoptosis in gamma-irradiated normal thymocytes and in M1 myeloid leukemic cells that overexpress wild-type p53. Dicoumarol also reduced the level of p53 in its mutant form in M1 cells. The results indicate that NQO1 plays an important role in regulating p53 functions by inhibiting its degradation.

Regulation of p53 stability and p53-dependent apoptosis by NADH quinone oxidoreductase 1

The tumor suppressor gene wild-type p53 encodes a labile protein that accumulates in cells after different stress signals and can cause either growth arrest or apoptosis. One of the p53 target genes, p53-inducible gene 3 (PIG3), encodes a protein with significant homology to oxidoreductases, enzymes involved in cellular responses to oxidative stress and irradiation. This fact raised the possibility that cellular oxidation-reduction events controlled by such enzymes also may regulate the level of p53. Here we show that NADH quinone oxidoreductase 1 (NQO1) regulates p53 stability. The NQO1 inhibitor dicoumarol caused a reduction in the level of both endogenous and gamma-irradiation-induced p53 in HCT116 human colon carcinoma cells. This reduction was prevented by the proteasome inhibitors MG132 and lactacystin, suggesting enhanced p53 degradation in the presence of dicoumarol. Dicoumarol-induced degradation of p53 also was prevented in the presence of simian virus 40 large T antigen, which is known to bind and to stabilize p53. Cells overexpressing NQO1 were resistant to dicoumarol, and this finding indicates the direct involvement of NQO1 in p53 stabilization. NQO1 inhibition induced p53 degradation and blocked wild-type p53-mediated apoptosis in gamma-irradiated normal thymocytes and in M1 myeloid leukemic cells that overexpress wild-type p53. Dicoumarol also reduced the level of p53 in its mutant form in M1 cells. The results indicate that NQO1 plays an important role in regulating p53 functions by inhibiting its degradation.

Hepatocyte growth factor, but not insulin-like growth factor I, protects podocytes against cyclosporin A-induced apoptosis

Cyclosporin A (CsA) nephropathy is associated with altered expression of apoptosis regulatory genes such as Fas-ligand and Bcl-2 family members in the glomerular, tubulointerstitial, and vascular compartments. Both hepatocyte growth factor (HGF) and insulin-like growth factor (IGF-I) protect against apoptosis, and HGF specifically up-regulates Bcl-xL, a protein that regulates apoptosis. We investigated whether Bcl-xL and Fas/Fas-ligand were regulated by CsA in cultured podocytes and whether CsA-induced apoptosis was prevented by HGF or IGF-I. A murine podocyte cell line was treated with CsA in the presence or absence of HGF or IGF-I. Apoptosis was quantitated by ELISA and by flow cytometry; Bcl-xL, Fas, and Fas-ligand were measured by Western blotting. Inhibitors of MAP kinase/ERK kinase (MEK)-1 and of phosphatidylinositol 3'-kinase (PI3'-K) were used to determine the signaling pathways involved in Bcl-xL regulation. Apoptosis was induced by CsA in a dose- and time-dependent fashion. CsA also decreased Bcl-xL levels. HGF, but not IGF-I, prevented apoptosis and restored Bcl-xL levels. The regulation of Bcl-xL by HGF was mediated by the PI3'-K but not by the MEK-1 pathway. In summary, we showed that CsA induces apoptosis in podocytes. Apoptosis was prevented by pretreatment with HGF but not IGF-I. Decreased apoptosis appeared to be mediated by regulation of Bcl-xL via the PI3'-K pathway. Our data suggest that the effect of CsA on podocytes may contribute to the glomerular damage and that HGF could provide protection.

Kinases: positive and negative regulators of apoptosis

Cells sense and respond to extracellular factors via receptors on the cell surface that trigger intracellular signaling pathways. The signals received by the receptors on hematopoietic cells often determine if the cell proliferates, survives or undergoes apoptosis. Apoptosis can be induced by almost any cytotoxic stimuli. These stimuli may be an absence of signals arising from cellular receptors, stimulation of specific ligand receptors on the cell surface, chemotherapeutic agents, and ionizing radiation or oxygen radicals, as well as a number of other factors. Cellular kinases and phosphatases participate in signaling cascades that influence this process. We review the ability of the calmodulin-dependent-kinases, I-kappaB kinases, PI3-kinases, Jakkinases, PKC, PKA, and MAP kinase signaling pathways (Erk, Jnk, and p38), to influence the apoptotic process. In addition, we discuss the cross-talk that exists between signaling cascades that are pro-apoptotic and anti-apoptotic.

A selective requirement for elevated calcium in DNA degradation, but not early events in anti-Fas-induced apoptosis

Jurkat cells undergo apoptosis in response to anti-Fas antibody through a caspase-dependent death cascade in which calcium signaling has been implicated. We have now evaluated the role of calcium during this death cascade at the single cell level in real time utilizing flow cytometric analysis and confocal microscopy. Fluo-3 and propidium iodide were employed to evaluate calcium fluxes and to discriminate between viable and non-viable cells, respectively. Anti-Fas treatment of Jurkat cells resulted in a sustained increase in intracellular calcium commencing between 1 and 2 h after treatment and persisting until subsequent loss of cell membrane integrity. The significance of this rise in calcium was evaluated by buffering intracellular calcium with BAPTA and/or removing calcium from the extracellular medium and monitoring the effects of these manipulations on calcium signaling and components of the apoptotic process. Complete inhibition of the anti-Fas induced rise in intracellular calcium required both chelation of [Ca(2+)](i) and removal of extracellular calcium. Interestingly, this condition did not abrogate several events in Fas-induced apoptosis including cell shrinkage, mitochondrial depolarization, annexin binding, caspase activation, and nuclear poly(A)DP-ribose polymerase cleavage. Furthermore, calcium-free conditions in the absence of anti-Fas antibody weakly induced these apoptotic components. In marked contrast, calcium depletion did not induce DNA degradation in control cells, and inhibited apoptotic DNA degradation in response to anti-Fas. These data support the concept that the rise in intracellular calcium is not a necessary component for the early signal transduction pathways in anti-Fas-induced apoptosis in Jurkat cells, but rather is necessary for the final degradation of chromatin via nuclease activation.

Characterization of calcium release-activated apoptosis of LNCaP prostate cancer cells

Apoptosis inhibition rather than enhanced cellular proliferation occurs in prostate cancer (CaP), the most commonly diagnosed malignancy in American men. Therefore, it is important to characterize residual apoptotic pathways in CaP cells. When intracellular Ca(2+) stores are released and plasma membrane "store-operated" Ca(2+) entry channels subsequently open, cytosolic [Ca(2+)] increases and is thought to induce apoptosis. However, cells incapable of releasing Ca(2+) stores are resistant to apoptotic stimuli, indicating that Ca(2+) store release is also important. We investigated whether release of intracellular Ca(2+) stores is sufficient to induce apoptosis of the CaP cell line LNCaP. We developed a method to release stored Ca(2+) without elevating cytosolic [Ca(2+)]; this stimulus induced LNCaP cell apoptosis. We compared the apoptotic pathways activated by intracellular Ca(2+) store release with the dual insults of store release and cytosolic [Ca(2+)] elevation. Earlier processing of caspases-3 and -7 occurred when intracellular store release was the sole Ca(2+) perturbation. Apoptosis was attenuated in both conditions in stable transfected cells expressing antiapoptotic proteins Bclx(L) and catalytically inactive caspase-9, and in both scenarios inactive caspase-9 became complexed with caspase-7. Thus, intracellular Ca(2+) store release initiates an apoptotic pathway similar to that elicited by the dual stimuli of cytosolic [Ca(2+)] elevation and intracellular store release.

Calcineurin-mediated hypertrophy protects cardiomyocytes from apoptosis in vitro and in vivo: An apoptosis-independent model of dilated heart failure

We have previously shown that the calcium-calmodulin-regulated phosphatase calcineurin (PP2B) is sufficient to induce cardiac hypertrophy that transitions to heart failure in transgenic mice. Given the rapid onset of heart failure in these mice, we hypothesized that calcineurin signaling would stimulate myocardial cell apoptosis. However, utilizing multiple approaches, we determined that calcineurin-mediated hypertrophy protected cardiac myocytes from apoptosis, suggesting a model of heart failure that is independent of apoptosis. Adenovirally mediated gene transfer of a constitutively active calcineurin cDNA (AdCnA) was performed in cultured neonatal rat cardiomyocytes to elucidate the mechanism whereby calcineurin affected myocardial cell viability. AdCnA infection, which induced myocyte hypertrophy and atrial natriuretic factor expression, protected against apoptosis induced by 2-deoxyglucose or staurosporine, as assessed by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL) labeling, caspase-3 activation, DNA laddering, and cellular morphology. The level of protection conferred by AdCnA was similar to that of adenoviral Bcl-x(L) gene transfer or hypertrophy induced by phenylephrine. In vivo, failing hearts from calcineurin-transgenic mice did not demonstrate increased TUNEL labeling and, in fact, demonstrated a resistance to ischemia/reperfusion-induced apoptosis. We determined that the mechanism whereby calcineurin afforded protection from apoptosis was partially mediated by nuclear factor of activated T cells (NFAT3) signaling and partially by Akt/protein kinase B (PKB) signaling. Although calcineurin activation protected myocytes from apoptosis, inhibition of calcineurin with cyclosporine was not sufficient to induce TUNEL labeling in Gqalpha-transgenic mice or in cultured cardiomyocytes. Collectively, these data identify a calcineurin-dependent mouse model of dilated heart failure that is independent of apoptosis.

Annexin V counteracts apoptosis while inducing Ca(2+) influx in human lymphocytic T cells

We have previously shown that when annexin V is present during the execution of a cell death program, apoptosis is delayed. This is reflected by the inhibition of DNA cleavage and of the release of apoptotic membrane particles, and by reduction of the proteolytic processing of caspase-3. Here, we have studied the mechanism(s) through which annexin V counteracts apoptosis in the human CEM T cell line. The degree of apoptosis inhibition was associated with an increase of intracellular Ca(2+) concentration ([Ca(2+)](i)). Reduction of the extracellular Ca(2+) concentration by EGTA abolished the anti-apoptotic effect, suggesting that annexin V favors Ca(2+) influx and that Ca(2+) acts as an inhibitor rather than an activator of apoptosis in CEM T cells. The effects on apoptosis and [Ca(2+)](i) of several modified annexins with different electrophysiological properties indicate that the N-terminal domain of annexin V is necessary for the Ca(2+)-dependent anti-apoptotic action of annexin V. These results suggest that annexin V regulates membrane Ca(2+) permeability and is protective against apoptosis by increasing [Ca(2+)](i) in CEM T cells.

Suppression or induction of apoptosis by opposing pathways downstream from calcium-activated calcineurin

Ca(2+)-mobilizing compounds such as the Ca(2+) ionophore A23187 or the endoplasmic reticulum Ca(2+) ATPase inhibitor thapsigargin can suppress or induce apoptosis in the same cells. The use of different calcineurin inhibitors has shown that both suppression and induction of apoptosis by the Ca(2+)-mobilizing compounds were mediated by calcineurin activation. Ca(2+)-mobilizing compounds activated p38 and p44/42 mitogen-activated protein kinases (MAPKs). Induction of apoptosis by the Ca(2+)-mobilizing compounds was suppressed by an inhibitor of p38 MAPK but not by an inhibitor of p44/42 MAPK. These MAPK inhibitors did not suppress apoptosis induction by wild-type p53 or by withdrawal of IL-6 from IL-6-dependent cells that are mediated by calcineurin-independent pathways. These MAPK inhibitors also did not affect the ability of Ca(2+)-mobilizing compounds to suppress apoptosis. The results indicate that (i) Ca(2+)- mobilizing compounds activate different and opposing pathways that diverge downstream from calcineurin activation that can either suppress or induce apoptosis in the same cells; (ii) p38 MAPK but not p44/42 MAPK is involved in induction of apoptosis but not in its suppression by the Ca(2+)-mobilizing compounds; and (iii) neither p38 nor p44/42 MAPKs mediate induction of apoptosis by some calcineurin-independent pathways.

Calcium signaling and cytotoxicity

The divalent calcium cation Ca(2+) is used as a major signaling molecule during cell signal transduction to regulate energy output, cellular metabolism, and phenotype. The basis to the signaling role of Ca(2+) is an intricate network of cellular channels and transporters that allow a low resting concentration of Ca(2+) in the cytosol of the cell ([Ca(2+)]i) but that are also coupled to major dynamic and rapidly exchanging stores. This enables extracellular signals from hormones and growth factors to be transduced as [Ca(2+)]i spikes that are amplitude and frequency encoded. There is considerable evidence that a number of toxic environmental chemicals target these Ca(2+) signaling processes, alter them, and induce cell death by apoptosis. Two major pathways for apoptosis will be considered. The first one involves Ca(2+)-mediated expression of ligands that bind to and activate death receptors such as CD95 (Fas, APO-1). In the second pathway, Ca(2+) has a direct toxic effect and its primary targets include the mitochondria and the endoplasmic reticulum (ER). Mitochondria may respond to an apoptotic Ca(2+) signal by the selective release of cytochrome c or through enhanced production of reactive oxygen species and opening of an inner mitochondrial membrane pore. Toxic agents such as the environmental pollutant tributyltin or the natural plant product thapsigargin, which deplete the ER Ca(2+) stores, will induce as a direct result of this effect the opening of plasma membrane Ca(2+) channels and an ER stress response. In contrast, under some conditions, Ca(2+) signals may be cytoprotective and antagonize the apoptotic machinery.