Phosphatidylinositol 3-kinase/Akt signaling controls endothelial cell sensitivity to Fas-mediated apoptosis via regulation of FLICE-inhibitory protein (FLIP)

Rapid up-regulation of c-FLIP expression by BCR signaling through the PI3K/Akt pathway inhibits simultaneously induced Fas-mediated apoptosis in murine B lymphocytes

Cross-linking of BCR rapidly induces protection of B cells from Fas-mediated apoptosis, which has been assumed one of the important survival mechanisms of B cells during antigen stimulation. In the mouse B cell line A20, which is sensitive to Fas-mediated apoptosis, stimulation of BCR inhibited apoptosis induced via Fas upstream of caspase-8 activation with an associated rapid increase in the expression of both short and long forms of cellular caspase-8/FLICE-inhibitory protein (c-FLIP). The c-FLIP competitively inhibited the recruitment of caspase-8 to the death-inducing signaling complex (DISC), which took as long as 3h to form after the stimulation of Fas in A20 cells. Knockdown of c-FLIP by a short hairpin RNA-expressing method rendered BCR-stimulated A20 cells sensitive to Fas-mediated apoptosis. The BCR-induced rapid expression of c-FLIP was not affected by inactivation of NF-kappaB, but was inhibited by either treatment with a PI3K inhibitor, LY294002, or expression of a dominant negative PI3K p85 subunit, both of which suppressed phosphorylation of Akt and sensitized BCR-stimulated A20 cells to Fas-mediated apoptosis. Overexpression of constitutively active Akt was shown not only to up-regulate c-FLIP expression but also to render A20 cells resistant to Fas-mediated apoptosis. Moreover, treatment with LY294002 also suppressed BCR-induced up-regulation of c-FLIP expression in spleen B cells. Taken together, BCR-stimulation was shown to rapidly trigger a survival signal against simultaneously or ongoingly stimulated Fas-mediated apoptosis by promoting a PI3K/Akt signaling pathway-mediated up-regulation of c-FLIP expression.

Lipocalin 2 antagonizes the proangiogenic action of ras in transformed cells

Lipocalin 2 is an iron-binding secreted protein that converts embryonic kidney mesenchyme to epithelia. Previously, we reported that lipocalin 2 could revert 4T1-ras-transformed mesenchymal tumor cells to a more epithelial phenotype, increase E-cadherin expression, and suppress cell invasiveness in vitro and in vivo, indicating that lipocalin 2 is a metastasis suppressor. Here, we show that lipocalin 2 can suppress the ras-induced expression of vascular endothelial growth factor in 4T1 cells via down-regulation of ras mitogen-activated protein kinase and ras phosphatidylinositol-3-kinase signaling. In addition, the expression of thrombospondin-1 (an antiangiogenic molecule) was increased in tumors formed by 4T1-ras cells into which lipocalin 2 was stably introduced. Tumor angiogenesis, assessed via an intradermal tumor angiogenesis assay, was also suppressed by lipocalin 2. We also show that caveolin-1 is a critical mediator of this activity. These data provide new insights into the action of lipocalin 2 and raise the possibility that the administration of lipocalin 2 may be useful for inhibiting tumor angiogenesis, in addition to suppressing tumor metastasis, in cancers which show ras activation.

Zinc induces cell death in immortalized embryonic hippocampal cells via activation of Akt-GSK-3β signaling

Zinc is an essential catalytic and structural element of many proteins and a signaling messenger that is released by neuronal activity at many central excitatory synapses. Excessive synaptic release of zinc followed by entry into vulnerable neurons contributes severe neuronal cell death. We have previously observed that zinc-induced neuronal cell death is accompanied by Akt activation in embryonic hippocampal progenitor (H19-7) cells. In the present study, we examined the role of Akt activation and its downstream signaling events during extracellular zinc-induced neuronal cell death. Treatment of H19-7 cells with 10 microM of zinc plus zinc ionophore, pyrithione, led to increased phosphorylation of Akt at Ser-473/Thr-308 and increased Akt kinase activity. Zinc-induced Akt activation was accompanied by increased Tyr-phosphorylated GSK-3beta as well as increased GSK-3beta kinase activity. Transient overexpression of a kinase-deficient Akt mutant remarkably suppressed GSK-3beta activation and cell death. Furthermore, tau phosphorylation, but not the degradation of beta-catenin, was dependent upon zinc-induced GSK-3beta activation and contributed to cell death. The current data suggest that, following exposure to zinc, the sequential activation of Akt and GSK-3beta plays an important role directing hippocampal neural precursor cell death.

Vitamin E and Apoptosis

Vitamin E is a generic term that refers to a family of compounds that is further divided into two subgroups called tocopherols and tocotrienols. All natural forms of tocopherols and tocotrienols are potent antioxidants that regulate peroxidation reactions and controls free radical production within the body. However, it is now firmly established that many of the biological actions mediated by individual vitamin E isoforms are not dependent on their antioxidant activity. Furthermore, synthetic ether derivatives of vitamin E that no longer possess antioxidant activity also display a wide range of biological activities. One of the most intriguing therapeutic applications for natural vitamin E and vitamin E derivatives currently being investigated is their use as anticancer agents. Specific forms of vitamin E display potent apoptotic activity against a wide range of cancer cell types, while having little or no effect on normal cell function or viability. Experimental studies have also determined that the intracellular mechanisms mediating the apoptotic effects of specific vitamin E compounds display great diversity in different types of caner cells and has been found to restore multidrug resistant tumor cells sensitivity to chemotherapeutic agents. These findings strongly suggest that some natural and synthetic analogues of vitamin E can be used effectively as anticancer therapy either alone or in combination to enhance the therapeutic efficacy and reduce toxicity of other anticancer agents.

Pathomolecular effects of homocysteine on the aging process: A new theory of aging

Homocysteine has been associated with the most common age-related diseases but never associated with the acceleration of the aging process. This theoretical paper will try to demonstrate the pro-aging effects of homocysteine at the molecular, cellular, and organ level. High homocysteine levels in homocystinuria are associated with premature disease of the cardiovascular, skeletal, neurological, and other systems. These observations are similar to those noted in the aging process and should be considered as a progeroid syndrome. There is enough scientific evidence to support that homocysteine accelerates the aging process at the cellular and at the organism level. Most importantly, decreasing homocysteine levels by dietary or pharmacological interventions could prolong maximum life span in humans and/or delay the onset of the most common age-related diseases.

Mechanistic insights into diabetes mellitus and oxidative stress

Diabetes mellitus (DM) is a significant healthcare concern worldwide that affects more than 165 million individuals leading to cardiovascular disease, nephropathy, retinopathy, and widespread disease of both the peripheral and central nervous systems. The incidence of undiagnosed diabetes, impaired glucose tolerance, and impaired fasting glucose levels raises future concerns in regards to the financial and patient care resources that will be necessary to care for patients with DM. Interestingly, disease of the nervous system can become one of the most debilitating complications and affect sensitive cognitive regions of the brain, such as the hippocampus that modulates memory function, resulting in significant functional impairment and dementia. Oxidative stress forms the foundation for the induction of multiple cellular pathways that can ultimately lead to both the onset and subsequent complications of DM. In particular, novel pathways that involve metabotropic receptor signaling, protein-tyrosine phosphatases, Wnt proteins, Akt, GSK-3beta, and forkhead transcription factors may be responsible for the onset and progression of complications form DM. Further knowledge acquired in understanding the complexity of DM and its ability to impair cellular systems throughout the body will foster new strategies for the treatment of DM and its complications.

Invasive trophoblasts stimulate vascular smooth muscle cell apoptosis by a fas ligand-dependent mechanism

During pregnancy, trophoblasts migrate from the placenta into uterine spiral arteries, transforming them into wide channels that lack vasoconstrictive properties. In pathological pregnancies, this process is incomplete. To define the fundamental events involved in spiral artery remodeling, we have studied the effect of trophoblasts on vascular smooth muscle cells (SMCs). Here we demonstrate for the first time that apoptosis of SMCs can be initiated by invading trophoblasts. When trophoblasts isolated from normal placenta (primary trophoblasts) or conditioned medium was perfused into spiral or umbilical artery segments, apoptosis of SMCs resulted. Culture of human aortic SMCs (HASMCs) with primary trophoblasts, primary trophoblast-conditioned medium, or a trophoblast-derived cell line (SGHPL-4) also significantly increased SMC apoptosis. Fas is expressed by spiral artery SMCs, and a Fas-activating antibody triggered HASMC apoptosis. Furthermore, a Fas ligand (FasL)-blocking antibody significantly inhibited HASMC apoptosis induced by primary trophoblasts, SGHPL-4, or trophoblast-conditioned medium. Depleting primary trophoblast-conditioned medium of FasL also abrogated SMC apoptosis in vessels in situ. These results suggest that apoptosis triggered by the release of soluble FasL from invading trophoblasts contributes to the loss of smooth muscle from the walls of spiral arteries during pregnancy.

Cell-permeable cAMP analog suppresses 6-hydroxydopamine-induced apoptosis in PC12 cells through the activation of the Akt pathway

Although cAMP protects neuronal cells from various apoptotic stimulations, its mechanism is not fully elucidated. We report here the molecular mechanism of the 6-hydroxydopamine (6-OHDA)-induced apoptosis of pheochromocytoma PC12 cells and its suppression by 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate (pCPT-cAMP), which is a membrane permeable cAMP analog. Treatment of PC12 cells with 6-OHDA resulted in the activation of caspases and apoptosis, as detected by chromatin condensation. 6-OHDA also induced superoxide generation, Bid cleavage and mitochondrial membrane depolarization. In addition, Akt phosphorylation that was favorable to cell survival was decreased and p38 MAPK phosphorylation was increased by 6-OHDA. PC12 cell apoptosis was inhibited by pCPT-cAMP, Z-VAD-fmk (a broad-range caspase inhibitor) and tiron (a superoxide scavenger), although PC12 cell apoptosis was not inhibited by cyclosporine A (an inhibitor of mitochondrial membrane permeability transition). Moreover, pCPT-cAMP promoted Akt phosphorylation, but it did not prevent superoxide generation and mitochondrial membrane depolarization. Conversely, LY294002, an inhibitor of Akt upstream molecule PI3-kinase, enhanced 6-OHDA-induced apoptosis. These results indicated that the 6-OHDA-induced apoptosis of PC12 cells was initiated by superoxide generation followed by caspase cascade activation, which was associated with the suppressed Akt phosphorylation and increased p38 phosphorylation. It is likely that pCPT-cAMP prevented the 6-OHDA-induced apoptosis via activation of the PI3-kinase/Akt pathway without any effect on superoxide generation or mitochondrial membrane depolarization.

Enhancement of susceptibility to Fas-mediated apoptosis in oral squamous cell carcinoma cells by phosphatidylinositol 3-kinase inhibitor

In general, oral squamous cell carcinoma (OSCC) cells are relatively resistant to Fas-mediated apoptosis during in vitro culture. Here, we studied the role of survival/apoptosis associated phosphatidylinositol 3-kinase (PI 3-K)/Akt in this process. We found that both PI 3-K inhibitors, wortmannin and LY294002, markedly suppressed the phosphorylation of Akt and accelerated Fas-mediated apoptosis in OSCC cells. It was found that caspase-3 and -8 inhibitors reduced the accelerative effect of PI 3-K inhibitor on Fas-mediated apoptosis in OSCC cells, but not caspase-9 inhibitor. Although PI 3-K inhibitors did not affect the Fas expression of OSCC cells, cellular FLICE-inhibitory protein (c-FLIP) levels were markedly reduced by PI 3-K inhibitor treatment. Moreover, antisense oligonucleotide to c-FLIP confirmed that the down-regulation of c-FLIP enhanced the sensitization to Fas-mediated apoptosis in OSCC cells. These results suggest that PI 3-K/Akt signaling pathway may, in part, regulate Fas-mediated apoptosis in OSCC cells through c-FLIP expression.

Microarray analysis of Akt1 activation in transgenic mouse hearts reveals transcript expression profiles associated with compensatory hypertrophy and failure

To investigate molecular mechanisms involved in the development of cardiac hypertrophy and heart failure, we developed a tetracycline-regulated transgenic system to conditionally switch a constitutively active form of the Akt1 protein kinase on or off in the adult heart. Short-term activation (2 wk) of Akt1 resulted in completely reversible hypertrophy with maintained contractility. In contrast, chronic Akt1 activation (6 wk) induced extensive cardiac hypertrophy, severe contractile dysfunction, and massive interstitial fibrosis. The focus of this study was to create a transcript expression profile of the heart as it undergoes reversible Akt1-mediated hypertrophy and during the transition from compensated hypertrophy to heart failure. Heart tissue was analyzed before transgene induction, 2 wk after transgene induction, 2 wk of transgene induction followed by 2 days of repression, 6 wk after transgene induction, and 6 wk of transgene induction followed by 2 wk of repression. Acute overexpression of Akt1 (2 wk) leads to changes in the expression of 826 transcripts relative to noninduced hearts, whereas chronic induction (6 wk) led to changes in the expression of 1,611, of which 65% represented transcripts that were regulated during the pathological phase of heart growth. Another set of genes identified was uniquely regulated during heart regression but not growth, indicating that nonoverlapping transcription programs participate in the processes of cardiac hypertrophy and atrophy. These data define the gene regulatory programs downstream of Akt that control heart size and contribute to the transition from compensatory hypertrophy to heart failure.

Phosphatidylinositol 3-kinase/Akt positively regulates Fas (CD95)-mediated apoptosis in epidermal Cl41 cells

Fas (CD95)-mediated apoptosis is an essential mechanism for the maintenance of homeostasis, and disruption of this death pathway contributes to many human diseases. The cell survival protein kinase Akt/protein kinase B (PKB) is a known regulator of apoptosis, but its role in Fas-mediated cell death and its regulatory mechanisms are unclear. In this study, we show that stimulation of the Fas receptor by its ligand (FasL) induces rapid phosphorylation of Akt/PKB and a parallel increase in cell apoptosis in epidermal Cl41 cells. Inhibition of PI3K/Akt by dominant-negative overexpression of PI3K (Deltap85) and Akt (Akt-T308A/S473A) protects the cells from apoptosis, indicating an unexpected proapoptotic role of PI3K/Akt in the Fas signaling process. Treatment of the cells with pharmacological inhibitors of PI3K, wortmannin and 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-1 (LY294002), similarly inhibits FasL-induced apoptosis and Akt/PKB phosphorylation, indicating that PI3K is an upstream mediator of Akt/PKB and is involved in Fas-mediated cell death. Electron spin resonance studies show that FasL treatment induces rapid generation of reactive oxygen species, and inhibition of ROS by antioxidants effectively inhibits Akt/PKB signaling, suggesting that FasL activation of Akt/PKB is redox sensitive. In cells transfected with dominant-negative PI3K/Akt, Fas expression is down-regulated, but FLIP expression is unaffected. Reporter gene and mRNA expression assays show that FasL activates fas transcriptional activity and this effect is inhibited by PI3K/Akt suppression. Together, our results indicate that the PI3K/Akt, in addition to its normal prosurvival role, also plays an apoptotic role in Fas-mediated cell death through a mechanism that involves transcriptional activation of Fas receptor.

Targeting cellular FLICE-like inhibitory protein as a novel approach to the treatment of Hodgkin's lymphoma

Hodgkin's lymphoma is one of the most common lymphoid cancers, particularly among young adults. Although there have been dramatic improvements in the treatment of Hodgkin's lymphoma, leading to high cure rates in some groups, current combination chemotherapy regimes are associated with significant secondary complications in long-term survivors. Furthermore, although a proportion of patients with Hodgkin's lymphoma will be cured, there still remains a significant rate of relapse and also a smaller proportion of poor responders who will go on to die of their disease. Therefore, developments in the treatment of Hodgkin's lymphoma must be directed at improving cure rates and reducing the burden of secondary complications. In recent years, the underlying pathogenesis of Hodgkin's lymphoma has become better understood. In particular, it is emerging that a key pathogenic event in Hodgkin's lymphoma is protection from Fas-induced cell death. Recent studies by the authors' group, and others, have demonstrated that this is, in part, due to the expression by Hodgkin/Reed-Sternberg cells of the cellular Fas-associated death domain-like IL-1 converting enzyme (FLICE)-like inhibitory protein molecule, a potent inhibitor of Fas-induced death. In this review, the role of cellular FLICE-like inhibitory protein in the pathogenesis of Hodgkin's lymphoma will be explored and also the possibility of targeting this molecule in order to provide an alternative and potentially safe approach to the treatment of Hodgkin's lymphoma will be investigated.

cFLIP regulation of lymphocyte activation and development

Cellular caspase-8 (FLICE)-like inhibitory protein (cFLIP) was originally identified as an inhibitor of death-receptor signalling through competition with caspase-8 for recruitment to FAS-associated via death domain (FADD). More recently, it has been determined that both cFLIP and caspase-8 are required for the survival and proliferation of T cells following T-cell-receptor stimulation. This paradoxical finding launched new investigations of how these molecules might connect with signalling pathways that link to cell survival and growth following antigen-receptor activation. As discussed in this Review, insight gained from these studies indicates that cFLIP and caspase-8 form a heterodimer that ultimately links T-cell-receptor signalling to activation of nuclear factor-kappaB through a complex that includes B-cell lymphoma 10 (BCL-10), mucosa-associated-lymphoid-tissue lymphoma-translocation gene 1 (MALT1) and receptor-interacting protein 1 (RIP1).

Protein kinase B inhibits endostatin-induced apoptosis in HUVECs

Endostatin is a tumor-derived angiogenesis inhibitor, and the endogenous 20 kDa carboxyl-terminal fragment of collagen XVIII. In addition to inhibiting angiogenesis,endostatin inhibits tumor growth and the induction of apoptosis in several endothelial cell types. However, the mechanisms that regulate endostatin-induced apoptotic cell death are unclear. Here, we investigated apoptotic cell death and the underlying regulatory mechanisms elicited of endostatin in human umbilical vein endothelial cells (HUVECs). Endostatin was found to induce typical apoptotic features, such as, chromatin condensation and DNA fragmentation in these cells. Thus, as the phosphoinositide 3-OH kinase (PI3K)/protein kinase B (PKB) signaling pathway has been shown to prevent apoptosis in various cell types, we investigated whether this pathway could protect cells against endostatin induced apoptosis. It was found that the inhibition of PI3K/PKB significantly increased endostatin-induced apoptosis, and that endostatininduced cell death is physiologically linked to PKB-mediated cell survival through caspase-8.

An antiviral mechanism investigated with ribavirin as an RNA virus mutagen for foot-and-mouth disease virus

To prove whether error catastrophe/lethal mutagenesis is the primary antiviral mechanism of action of ribavirin against foot-and-mouth disease virus (FMDV). Ribavirin passage experiments were performed and supernatants of Rp1 to Rp5 were harvested. Morphological alterations as well as the levels of viral RNAs, proteins, and infectious particles in the BHK-21 cells infected using the supernatants of Rp1 to Rp5 and control were measured by microscope, real-time RT-PCR, western-blotting and plaque assays, respectively. The mutation frequency was measured by sequencing the complete P1- and 3D-encoding region of FMDV after a single round of virus infection from ribavirin-treated or untreated FMDV-infected cells. Ribavirin treatment for FMDV caused dramatically inhibition of multiplication in cell cultures. The levels of viral RNAs, proteins, and infectious particles in the BHK-21 cells infected were more greatly reduced along with the passage from Rp1 to Rp5, moreover, nucleocapsid protein could not be detected and no recovery of infectious virus in the supernatant or detection of intracellular viral RNA was observed at the Rp5-infected cells. A high mutation rate, giving rise to an 8-and 11-fold increase in mutagenesis and resulting in some amino acid substitutions, was found in viral RNA synthesized at a single round of virus infection in the presence of ribavirin of 1000 microM and caused a 99.7% loss in viral infectivity in contrast with parallel untreated control virus. These results suggest that the antiviral molecular mechanism of ribavirin is based on the lethal mutagenesis/error catastrophe, that is, the ribavirin is not merely an antiviral reagent but also an effective mutagen.

Salvage effect of the vascular endothelial growth factor on chemically induced acute severe liver injury in rats

BACKGROUND/AIMS

The role of the vascular endothelial growth factor (VEGF), a potent angiogenic factor, in liver regeneration following acute severe liver injury (ALI) has not been elucidated. The aims of the current study were to investigate the role of VEGF, and to find out whether VEGF can improve the outcome of ALI in rats.

METHODS

ALI was induced in male rats by combination of D-galactosamine (Gal-N) and lipopolysaccharide (LPS). The survival rate and several indices were chronologically compared with or without VEGF treatment.

RESULTS

The overall survival rate of the VEGF-treated group significantly improved as compared with the untreated group (100 vs. 27%, respectively). The serum ALT elevation, with a peak at 24 h after Gal-N+LPS intoxication, was markedly attenuated with VEGF treatment. The proliferation of hepatocytes and sinusoidal endothelial cells (SEC) was stimulated by VEGF with a peak at 36 and 96 h, respectively. The immunohistochemical analysis revealed that VEGF drastically prevented destruction of the SEC architecture in ALI. Our in vitro study showed that VEGF significantly prevented the Gal-N+LPS-induced cytotoxicity and apoptosis of SEC.

CONCLUSIONS

VEGF treatment significantly reduced the mortality rate of ALI in the rat, and it may provide a new therapeutic strategy for ALI.

FasL (CD95L/APO-1L) resistance of neurons mediated by phosphatidylinositol 3-kinase-Akt/protein kinase B-dependent expression of lifeguard/neuronal membrane protein 35

The contribution of Fas (CD95/APO-1) to cell death mechanisms of differentiated neurons is controversially discussed. Rat cerebellar granule neurons (CGNs) express high levels of Fas in vitro but are resistant to FasL (CD95L/APO-1L/CD178)-induced apoptosis. We here show that this resistance was mediated by a phosphatidylinositol 3-kinase (PI 3-kinase)-Akt/protein kinase B (PKB)-dependent expression of lifeguard (LFG)/neuronal membrane protein 35. Reduction of endogenous LFG expression by antisense oligonucleotides or small interfering RNA lead to increased sensitivity of CGNs to FasL-induced cell death and caspase-8 cleavage. The inhibition of PI 3-kinase activity sensitized CGNs to FasL-induced caspase-8 and caspase-3 processing and caspase-dependent fodrin cleavage. Pharmacological inhibition of PI 3-kinase, overexpression of the inhibitory protein IkappaB, or cotransfection of an LFG reporter plasmid with dominant-negative Akt/PKB inhibited LFG reporter activity, whereas overexpression of constitutively active Akt/PKB increased LFG reporter activity. Overexpression of LFG in CGNs interfered with the sensitization to FasL by PI 3-kinase inhibitors. In contrast to CGNs, 12 glioma cell lines, which are sensitive to FasL, did not express LFG. Gene transfer of LFG into these FasL-susceptible glioma cells protected against FasL-induced apoptosis. These results demonstrate that LFG mediated the FasL resistance of CGNs and that, under certain circumstances, e.g., inhibition of the PI 3-kinase-Akt/PKB pathway, CGNs were sensitized to FasL.

The role of cellular flice inhibitory protein (c-FLIP) in the pathogenesis and treatment of cancer

Protection from death receptor (DR)-mediated apoptosis has been proposed as an important step in the development of malignancy, enabling tumour cells not only to survive and escape antitumour immune responses, but also to develop resistance to chemotherapy or other cancer treatments. An important regulator of DR-induced death is the cellular FADD-like IL-1beta-converting enzyme inhibitory protein (c-FLIP) which, when overexpressed, can protect tumour cells from apoptosis. This review focuses on the role of c-FLIP as a tumour progression factor, with particular emphasis on recent work from the authors' laboratory concerning the contribution of c-FLIP to the pathogenesis of Hodgkin's lymphoma. The possibility of targeting c-FLIP as an approach to the treatment of cancer and, in particular, Hodgkin's lymphoma is discussed.

The Regulation of Ovarian Granulosa Cell Death by Pro- and Anti-apoptotic Molecules

In the mammalian ovary, follicular development and atresia are closely regulated by cell death and survival-promoting factors, including hormones (gonadotropins) and intraovarian regulators (gonadal steroids, cytokines, and intracellular proteins). Several hundred thousand primordial follicles are present in the mammalian ovary; however, only a limited number of primordial follicles develop to the preovulatory stage and ovulate. The others, more than 99% of follicles, will be eliminated via a degenerative process known as "atresia". The endocrinological regulatory mechanisms involved in follicular development and atresia have been characterized to a large extent, but the precise temporal and molecular mechanisms involved in the regulation of these events have remained largely unknown. Recent studies suggest that the apoptosis of ovarian granulosa cells plays a major role in follicular atresia. In this review, we provide an overview of development and atresia of follicles, and apoptosis of granulosa cells in mammals.

Regulation of Fas-mediated apoptosis in neutrophils after surgery-induced acute inflammation

BACKGROUND

Neutrophils undergo rapid Fas-mediated apoptosis during in vitro culture. The purpose of this study was to investigate the effects of surgical stress upon the Fas-mediated apoptotic response in circulating neutrophils.

MATERIALS AND METHODS

Blood samples were drawn from eight patients with a mandibular prognathism, and who had undergone a bilateral sagittal split ramus osteotomy, at 2 days before, and at 1 and 5 days after surgery. The circulating neutrophils in each blood sample were then evaluated for their susceptibility to Fas-mediated apoptosis in either the presence or the absence of autogenous plasma.

RESULTS

Fas-induced apoptosis in the neutrophils of these surgically treated patients was found to be slightly accelerated at 1 day postoperatively in the presence of FBS, compared with 2 days preoperatively and 5 days postoperatively. However, we obtained different results for these experiments in the presence of autogenous plasma. The Fas-induced apoptotic response levels in the neutrophils at day 1 postsurgery following exposure to autogenous plasma were significantly suppressed compared with the levels at both 2 days preoperatively and 5 days postoperatively. The Fas expression levels on the cell surface of the neutrophils were not altered, but the levels of soluble Fas (sFas) in the plasma were reduced to almost inverse levels during the postoperative periods. The levels of granulocyte-macrophage colony-stimulating factor, interleukin-6, and interleukin-8 levels in the plasma were also markedly raised in the plasma from each of these patients at 1 day postoperatively. However, the anti-apoptotic effects of the plasma on the Fas-mediated neutrophil apoptosis were not influenced by the addition of their neutralizing antibodies for these cytokines. The suppressive effects of postoperative plasma on Fas-mediated neutrophil apoptosis were blocked by the phosphatidylinositol 3-kinase (PI 3-K) inhibitors, LY294002, and wortmannin. Additionally, these effects were also abrogated by the extracellular signal-regulated kinase (ERK) inhibitor, PD98059, but not by the p38 mitogen-activated protein kinase inhibitor, SB203580.

CONCLUSIONS

The increase in sFas levels in the plasma of patients with acute inflammation may lead to the inhibition of Fas-mediated neutrophil apoptosis. Moreover, the activation of the PI 3-K and ERK signaling-dependent pathways may, in part, also contribute to the down-regulation of the Fas-mediated apoptotic response in neutrophils.

Employing new cellular therapeutic targets for Alzheimer's disease: a change for the better?

Alzheimer's disease is a progressive disorder that results in the loss of cognitive function and memory. Although traditionally defined by the presence of extracellular plaques of amyloid-beta peptide aggregates and intracellular neurofibrillary tangles in the brain, more recent work has begun to focus on elucidating the complexities of Alzheimer's disease that involve the generation of reactive oxygen species and oxidative stress. Apoptotic processes that are incurred as a function of oxidative stress affect neuronal, vascular, and monocyte derived cell populations. In particular, it is the early apoptotic induction of cellular membrane asymmetry loss that drives inflammatory microglial activation and subsequent neuronal and vascular injury. In this article, we discuss the role of novel cellular pathways that are invoked during oxidative stress and may potentially mediate apoptotic injury in Alzheimer's disease. Ultimately, targeting new avenues for the development of therapeutic strategies linked to mechanisms that involve inflammatory microglial activation, cellular metabolism, cell-cycle regulation, G-protein regulated receptors, and cytokine modulation may provide fruitful gains for both the prevention and treatment of Alzheimer's disease.

Driving cellular plasticity and survival through the signal transduction pathways of metabotropic glutamate receptors

Metabotropic glutamate receptors (mGluRs) share a common molecular morphology with other G protein-linked receptors, but there expression throughout the mammalian nervous system places these receptors as essential mediators not only for the initial development of an organism, but also for the vital determination of a cell's fate during many disorders in the nervous system that include amyotrophic lateral sclerosis, Parkinson's disease, Alzheimer's disease, Huntington's disease, Multiple Sclerosis, epilepsy, trauma, and stroke. Given the ubiquitous distribution of these receptors, the mGluR system impacts upon neuronal, vascular, and glial cell function and is activated by a wide variety of stimuli that includes neurotransmitters, peptides, hormones, growth factors, ions, lipids, and light. Employing signal transduction pathways that can modulate both excitatory and inhibitory responses, the mGluR system drives a spectrum of cellular pathways that involve protein kinases, endonucleases, cellular acidity, energy metabolism, mitochondrial membrane potential, caspases, and specific mitogen-activated protein kinases. Ultimately these pathways can converge to regulate genomic DNA degradation, membrane phosphatidylserine (PS) residue exposure, and inflammatory microglial activation. As we continue to push the envelope for our understanding of this complex and critical family of metabotropic receptors, we should be able to reap enormous benefits for both clinical disease as well as our understanding of basic biology in the nervous system.

NF-kappaB couples protein kinase B/Akt signaling to distinct survival pathways and the regulation of lymphocyte homeostasis in vivo

Protein kinase B (PKBalpha/Akt1) a PI3K-dependent serine-threonine kinase, promotes T cell viability in response to many stimuli and regulates homeostasis and autoimmune disease in vivo. To dissect the mechanisms by which PKB inhibits apoptosis, we have examined the pathways downstream of PKB that promote survival after cytokine withdrawal vs Fas-mediated death. Our studies show that PKB-mediated survival after cytokine withdrawal is independent of protein synthesis and the induction of NF-kappaB. In contrast, PKB requires de novo gene transcription by NF-kappaB to block apoptosis triggered by the Fas death receptor. Using gene-deficient and transgenic mouse models, we establish that NF-kappaB1, and not c-Rel, is the critical signaling molecule downstream of the PI3K-PTEN-PKB signaling axis that regulates lymphocyte homeostasis.

Expression of cellular FLICE/caspase-8 inhibitory protein is associated with malignant potential in endometrial carcinoma

This study aimed to investigate the expression of cellular Fas-associated death domain-like interleukin-1beta-converting enzyme (FLICE)/caspase-8 inhibitory protein (c-FLIP) in endometrial carcinoma and its possible implications. c-FLIP protein was detected in 42 endometrial carcinoma tissues and in 22 normal proliferative endometrial tissues by immunohistochemistry. In addition, c-FLIP messenger ribonucleic acid (mRNA) was evaluated in 20 endometrial carcinomas and in 18 normal proliferative endometria by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) using SYBR Green I(TM). The relationship between c-FLIP protein level and tumor cell proliferation and that between c-FLIP protein level and clinicopathologic parameters of patients with endometrial carcinoma was analyzed. c-FLIP protein expression was significantly higher in neoplastic tissues than in normal tissues (P < 0.01), and similar result was obtained from RT-PCR analysis of c-FLIP mRNA (P < 0.01). Furthermore, c-FLIP protein was significantly associated with proliferating cell nuclear antigen-labeling index (P < 0.01), clinical stage (P < 0.05), the presence of invasion to > 1/2 myometrium (P < 0.05), and lymph node metastasis (P < 0.01). Multivariate analysis of variance also confirmed the association of c-FLIP with clinical stage (P < 0.05) and with lymph node metastasis (P < 0.05), while its association with myometrial invasion was marginal (P = 0.059). It is concluded that c-FLIP might contribute to the carcinogenesis and aggressiveness of endometrial carcinoma and might be a useful prognostic factor in the tumor.

Epidermal growth factor receptor directed therapy in head and neck cancer

Squamous cell head and neck cancer (SCCHN) is the seventh most common cause of cancer death worldwide and its incidence is rising rapidly in developing countries. Despite recent advances in managing locally advanced SCCHN, patients with recurrent and metastatic SCCHN have a poor prognosis and little progress has been made its management. Epidermal growth factor receptor (EGFR) has been implicated in the pathogenesis of SCCHN and is a marker of poor prognosis. Recent advances in targeted therapeutics against EGFR are being investigated clinically. In this article, we review the different modalities utilized to inhibit EGFR signaling in SCCHN, including small molecule tyrosine kinase inhibitors, monoclonal antibodies, anti-sense therapy and immunotoxin conjugates. Monotherapy with EGFR inhibitors has demonstrated response rates between 5 and 15% in advanced SCCHN. However, combining EGFR inhibitors with cytotoxic chemotherapy or radiation therapy appears to augment response rates and survival. With the foundation for the use of EGFR inhibitors laid in these studies, future studies will need to optimize the delivery of these agents in combination with conventional therapies.

The sirtuin inhibitor nicotinamide enhances neuronal cell survival during acute anoxic injury through AKT, BAD, PARP, and mitochondrial associated "anti-apoptotic" pathways

Understanding the role of nicotinamide (NIC) in different cell systems represents a significant challenge in several respects. Recently, NIC has been reported to have diverse roles during cell biology. In the absence of NIC, sirtuin protein activity is enhanced and pyrazinamidase/nicotinamidase 1 (PNC1) expression, an enzyme that deaminates NIC to convert NIC into nicotinic acid, is increased to lead to lifespan extension during calorie restriction, at least in yeast. Yet, NIC may be critical for cell survival as well as the modulation of inflammatory injury during both experimental models as well as in clinical studies. We therefore investigated some of the underlying signal transduction pathways that could be critical for the determination of the neuroprotective properties of NIC. We examined neuronal injury by trypan blue exclusion, DNA fragmentation, phosphatidylserine (PS) exposure, Akt1 phosphorylation, Bad phosphorylation, mitochondrial membrane potential, caspase activity, cleavage of poly(ADP-ribose) polymerase (PARP), and mitogen-activated protein kinases (MAPKs) phosphorylation. Application of NIC (12.5 mM) significantly increased neuronal survival from 38 -/+ 3% of anoxia treated alone to 68 +/- 3%, decreased DNA fragmentation and membrane PS exposure from 67 -/+ 4% and 61 -/+ 5% of anoxia treated alone to 30 +/- 4% and 26 +/- 4% respectively. We further demonstrate that NIC functions through Akt1 activation, Bad phosphorylation, and the downstream modulation of mitochrondrial membrane potential, cytochrome c release, caspase 1, 3, and 8 - like activities, and PARP integrity to prevent genomic DNA degradation and PS externalization during anoxia. Yet, NIC does not alter the activity of either the MAPKs p38 or JNK, suggesting that protection by NIC during anoxia is independent of the p38 and JNK pathways. Additional investigations targeted to elucidate the cellular pathways responsible for the ability of NIC to modulate both lifespan extension and cytoprotection may offer critical insight for the development of new therapies for nervous system disorders.

Pigment epithelium-derived factor induces pro-survival genes through cyclic AMP-responsive element binding protein and nuclear factor kappa B activation in rat cultured cerebellar granule cells: Implication for its neuroprotective effect

Pigment epithelium-derived factor (PEDF) protects immature cerebellar granule cell neurons (CGCs) against apoptosis induced by K+ and serum deprivation. However, the precise mechanism of this protection remains unknown. We recently reported that the transcription factor nuclear factor kappa B (NF-kappaB) is activated in PEDF-treated CGCs. Although it is well known that NF-kappaB blocks apoptotic cell death through the induction of pro-survival factors, the effects of PEDF on the expression of these factors are not fully understood. In this study, we employed the use of reverse transcriptase-polymerase chain reaction to analyze the gene expression of certain pro-survival genes and found that genes such as c-IAP1, c-IAP2, FLIPs, A1/Bfl-1 and Mn-SOD were induced in PEDF-treated neurons. On the other hand, no induction was observed of the pro-apoptotic Bcl-2 family members Bax and Bid at any time from 3 to 24 h following PEDF addition. Furthermore, phosphorylation of cyclic AMP-responsive element binding protein (CREB) and increment of nuclear cyclic AMP-response element (CRE)-like DNA binding were observed in PEDF-treated CGCs. The anti-apoptotic effect of PEDF was blocked by overexpression of dominant negative CREB or a mutated form of IkappaBalpha. These results suggested that induction of both CRE- and NF-kappaB-dependent genes is required for the observed neuroprotective effects of PEDF on CGCs.

TRAIL-Induced Apoptosis in Human Vascular Endothelium Is Regulated by Phosphatidylinositol 3-Kinase/Akt through the Short Form of Cellular FLIP and Bcl-2

BACKGROUND

Apoptosis of vascular endothelial cells plays a central role in angiogenesis and atherosclerosis. This study investigates the molecular mechanisms of endothelial apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) following inhibition of phosphatidylinositol 3-kinase (PI3K). It examines downstream regulation and activation of the extrinsic and intrinsic pathways.

METHODS AND RESULTS

By flow cytometry, TRAIL receptors 2 and 3 were present to a greater extent than receptors 1 and 4. TRAIL reduced cell numbers in combination with the PI3K inhibitor LY 294002. TRAIL (100 ng/ml) with LY 294002 (20 micromol/l) activated the extrinsic pathway, causing progressive cleavage of caspase-8 and caspase-3. Activation of the intrinsic pathway proceeded by release of mitochondrial factors Smac/DIABLO and cytochrome c, and caspase-9 cleavage. LY 294002 reduced phosphorylated Akt (p-Akt), with early loss of the short form of cellular FLIP (c-FLIP(S)) and concurrent reduction of Bcl-2. Treatment with small interfering RNA against PI3K also reduced c-FLIP(S) and Bcl-2, and cotreatment with TRAIL triggered caspase-3 cleavage.

CONCLUSIONS

This study details the molecular regulation of TRAIL-induced apoptosis in vascular endothelium. Inhibition of PI3K reduces p-Akt, with concurrent reductions in c-FLIP(S) and Bcl-2, and so renders endothelium sensitive to TRAIL-induced apoptosis through the extrinsic and intrinsic pathways.

Systemic soluble Tie2 expression inhibits and regresses corneal neovascularization

This study was designed to determine if soluble Tie2 (sTie2) expression inhibits and regresses corneal neovascularization, and if VEGF contributes to its effect. The corneas of BALB/c mice were scraped and the mice were injected with either an adenovirus expressing soluble Tie2 (Ad.sTie2) or an empty adenoviral vector. When injected at the inhibition timepoint (one day prior to corneal injury), the mean percentage of neovascularized corneal area two weeks later in Ad.sTie2-treated mice vs. controls was 56.37+/-9.15% vs. 85.79+/-3.55% (p=0.04). At the regression timepoint (4 weeks after corneal scrape), the mean area of corneal neovascularization in Ad.sTie2-treated mice was 42.89+/-4.74% vs. 75.01+/-3.22% in the control group (p=0.007). VEGF expression was significantly higher in Ad.sTie2-treated mice at the inhibition timepoint and there was no significant difference at the regression timepoint. These findings suggest that sTie2 inhibits and regresses corneal neovascularization in a VEGF-independent manner.

Akt inhibition upregulates FasL, downregulates c-FLIPs and induces caspase-8-dependent cell death in Jurkat T lymphocytes

In T lymphocytes, the role of Akt in regulating Fas/Fas ligand (FasL)-mediated apoptotic signaling and death is not clearly understood. In this study, we observed that inhibition of Akt causes enhanced expression of FasL mRNA and protein and increased death-inducing signaling complex (DISC) formation with Fas-associated death domain (FADD) and procaspase-8 recruitment. Also, caspase-8 was activated at the DISC with accompanying decrease in c-FLIPs expression. FasL neutralizing antibody significantly decreased apoptotic death in the Akt-inhibited T cells. Additionally, Akt inhibition-induced Fas signaling was observed to link to the mitochondrial pathway via Bid cleavage. Further, inhibition of caspase-8 activity effectively blocked the loss of mitochondrial membrane potential and DNA fragmentation, suggesting that DISC formation and subsequent caspase-8 activation are critical initiating events in Akt inhibition-induced apoptotic death in T lymphocytes. These data demonstrate yet another important survival function governed by Akt kinase in T lymphocytes, which involves the regulation of FasL expression and consequent apoptotic signaling.

Resistance to Fas-mediated apoptosis is restored by cycloheximide through the downregulation of cellular FLIPL in NK/T-cell lymphoma

Extranodal NK/T-cell lymphoma (NKTL), nasal type, is a highly aggressive neoplasm and is strongly associated with Epstein-Barr virus (EBV). In this study, we demonstrate that EBV-positive NKTL cell lines, namely, Hank-1, NK-YS, and NK-L, are resistant to Fas-mediated apoptosis induced by anti-Fas antibodies despite high levels of Fas surface expression and no mutation in the Fas gene. Fas stimulation of Hank-1 and NK-YS cells showed little processing of caspase 8, caspase 3, or bid, although the proximal signaling molecules of the death-inducing signaling complex, namely, Fas, Fas-associated protein with a death domain, caspase 8, and bid were present in these cells. Consistent with previous reports on the hypermethylation of death associated protein (DAP) kinase in NKTLs, the promoter of DAP kinase was methylated and its mRNA not detected in Hank-1 cells. However, the restoration of DAP kinase expression by 5-aza-2'-deoxycytidine did not sensitize Hank-1 to Fas-mediated apoptosis, indicating that DAP kinase deficiency does not contribute to resistance to Fas-mediated apoptosis. Since etoposide-induced apoptosis involved caspase 3 activation in Hank-1 and NK-YS cells, the caspase 3-dependent apoptotic machinery appears to be intact. Interestingly, cotreatment of Hank-1 with cycloheximide, a protein synthesis inhibitor, markedly sensitized cells to Fas-mediated apoptosis along with caspase 8 activation and c-FLIP(L) (cellular FLICE inhibitory protein long form) downregulation. Moreover, immunohistochemistry on paraffin-embedded tissue revealed c-FLIP expression in 39% (14 of 36) of NKTL patients. Taken together, these findings indicate that c-FLIP(L)-mediated resistance to Fas contributes to the development and progression of NKTLs. This study also suggests that agents capable of downregulating c-FLIP(L) could be used to treat NKTL.

Intracellular signaling mechanisms mediating the antiproliferative and apoptotic effects of gamma-tocotrienol in neoplastic mammary epithelial cells

Tocotrienols, a subgroup within the vitamin E family of compounds, display potent antiproliferative and apoptotic activity against neoplastic mammary epithelial cells at treatment doses that have little or no effect on normal cell growth and function. Recent studies have shown that treatment with a growth inhibitory, but non-cytotoxic dose (4 microM) of gamma-tocotrienol inhibits phosphatidylinositol-3-kinase-dependent kinase (Pl3K)/Pl3K-dependent kinase 1 (PDK-1)/mitogenic signaling over a 2-3 day period following treatment exposure, and these effects were not found to be associated with an increased in either phosphatase and tensin homologue deleted from chromosome 10 (PTEN) or protein phosphatase type 2A (PP2A) phosphatase activity. In addition, this treatment caused a large decrease in NFKB transcriptional activity, apparently by suppressing I kappa B-kinase (IKK)-alpha/beta activation, an enzyme associated with inducing NFKB activation. Since Akt and NFkappaB are intimately involved in mammary tumor cell proliferation and survival, these findings strongly suggest that the antiproliferative effects of gamma-tocotrienol result, at least in part, from a reduction in Akt and NFkappa B activity. In contrast, treatment with 20 microM gamma-tocotrienol (cytotoxic dose) resulted in caspase-8 and -3 activation and apoptosis. It was also shown that this same treatment caused a rapid and large decrease in Pl3K/PDK/Akt signaling within 2-4h following treatment exposure, and a corresponding decrease in intracellular levels of FLIP, an antiapoptotic protein that inhibits caspase-8 activation. In summary, both the antiproliferative and apoptotic effects of gamma-tocotrienol appear to be mediated by a reduction in the Pl3K/PDK-1 /Akt signaling, an important pathway associated with cell proliferation and survival in neoplastic mammary epithelial cells.

Intracellular signal transduction pathway proteins as targets for cancer therapy

Circulating cytokines, hormones, and growth factors control all aspects of cell proliferation, differentiation, angiogenesis, apoptosis, and senescence. These chemical signals are propagated from the cell surface to intracellular processes via sequential kinase signaling, arranged in modules that exhibit redundancy and cross talk. This signal transduction system comprising growth factors, transmembrane receptor proteins, and cytoplasmic secondary messengers is often exploited to optimize tumor growth and metastasis in malignancies. Thus, it represents an attractive target for cancer therapy. This review will summarize current knowledge of selected intracellular signaling networks and their role in cancer therapy. The focus will be on pathways for which inhibitory agents are currently undergoing clinical testing. Original data for inclusion in this review were identified through a MEDLINE search of the literature. All papers from 1966 through March 2005 were identified by the following search terms: "signal transduction," "intracellular signaling," "kinases," "proliferation," "growth factors," and "cancer therapy." All original research and review papers related to the role of intracellular signaling in oncogenesis and therapeutic interventions relating to abnormal cell signaling were identified. This search was supplemented by a manual search of the Proceedings of the Annual Meetings of the American Association for Cancer Research, American Society of Clinical Oncology, and the American Association for Cancer Research (AARC)--European Organisation for Research and Treatment of Cancer (EORTC)--National Cancer Institute (NCI) Symposium on New Anticancer Drugs.

Therapeutic targeting of receptor tyrosine kinases in lung cancer

Lung cancer is a difficult illness with a poor overall survival. Even though combination strategies with chemotherapy, radiation therapy and surgery have all been utilised, the overall outcome for this disease continues to be relatively disappointing. In order to make a difference in the treatment of lung cancer, novel therapeutics will have to be developed. Through basic biological studies, a number of receptor tyrosine kinases have been implicated in the pathogenesis and progression of lung cancer. In this review, the authors summarise the mechanisms of several major receptor tyrosine kinases in lung cancer, especially epidermal growth factor receptor, Her2/neu, MET, vascular endothelial growth factor and KIT. The biology associated with these receptors is described, and the various novel therapeutic inhibitory strategies that are ongoing in preclinical and clinical studies for lung cancer are detailed. Through understanding of receptor tyrosine kinases and the utilisation of specific inhibitors, it is hopeful that a dramatic impact will be made on the biology and therapy for lung cancer.

Oxidative stress inactivates VEGF survival signaling in retinal endothelial cells via PI 3-kinase tyrosine nitration

In diabetic retinopathy, endothelial cell apoptosis is paradoxically increased despite upregulation of the potent pro-survival factor VEGF. We tested the hypothesis that elevated glucose levels disrupt VEGF's pro-survival function via peroxynitrite-mediated alteration of the Akt-1/p38 MAP kinase signaling pathway by studies of retinal endothelial cells in vitro. High glucose or exogenous peroxynitrite caused significant increases in apoptosis in the presence or absence of VEGF. Treatment with a peroxynitrite decomposition catalyst blocked these effects, implying a causal role of peroxynitrite. Peroxynitrite or high glucose treatment also increased phosphorylation of p38 MAP kinase, whereas phosphorylation of Akt-1 was significantly decreased in basal or VEGF-stimulated conditions. High glucose- or peroxynitrite-treated cells also showed significant increases in tyrosine nitration on the p85 subunit of PI 3-kinase that blocked PI 3-kinase and Akt-1 kinase activity. Inhibiting peroxynitrite formation or blocking tyrosine nitration of p85 restored the activity of PI 3-kinase and Akt-1 kinase, blocked phosphorylation of p38 MAP kinase and normalized pro-survival function. Transfecting the cells with constitutively active Akt-1 or inhibiting activity of p38 MAP kinase completely masked the pro-apoptotic effects of high glucose and exogenous peroxynitrite, suggesting an interaction between the Akt-1 and p38 MAP kinase pathways. In conclusion, high glucose treatment blocks the pro-survival effect of VEGF and causes accelerated endothelial cell apoptosis via the action of peroxynitrite in causing tyrosine nitration of PI 3-kinase, inhibiting activity of Akt-1 kinase and increasing the activity of p38 MAP kinase.

Angiopoietin-1 inhibits doxorubicin-induced human umbilical vein endothelial cell death by modulating fas expression and via the PI3K/Akt pathway

Angiopoietin-1 (Ang-1) is essential for the maturation of blood vessels during vasculogenesis. Besides angiogenesis, recent publications indicate that Ang-1 is also a potent survival factor for endothelial cells; however, the mechanisms by which pathways remain elusive. Doxorubicin (DOX) is a powerful anticancer drug, but its use is severely restricted by its cardiotoxicity. The authors report here that Ang-1 inhibits DOX-induced cell death in human umbilical vein endothelial cells (HUVECs). Interestingly, the DOX-induced up-regulation in Fas (CD95/APO-1) and Fas ligand expression could be blocked by Ang-1, indicating a pivotal role of Ang-1 in DOX-induced Fas and Fas ligand expression. In addition, the prevention of cell death in this model system seems to be dependent on the activation of phosphatidylinositol 3-kinase (PI3K)/Akt, as Ang-1 fails to inhibit DOX-induced cell death while PI3K/Akt pathway was blocked by the PI3K inhibitor LY294002. Moreover, Ang-1 inhibits DOX-induced up-regulation of p53 through PI3K/Akt. Therefore, Ang-1 is a potent inhibitor for DOX-induced cell death through Fas and PI3K/Akt-mediated pathways.

Oxidative stress in the brain: novel cellular targets that govern survival during neurodegenerative disease

Despite our present knowledge of some of the cellular pathways that modulate central nervous system injury, complete therapeutic prevention or reversal of acute or chronic neuronal injury has not been achieved. The cellular mechanisms that precipitate these diseases are more involved than initially believed. As a result, identification of novel therapeutic targets for the treatment of cellular injury would be extremely beneficial to reduce or eliminate disability from nervous system disorders. Current studies have begun to focus on pathways of oxidative stress that involve a variety of cellular pathways. Here we discuss novel pathways that involve the generation of reactive oxygen species and oxidative stress, apoptotic injury that leads to nuclear degradation in both neuronal and vascular populations, and the early loss of cellular membrane asymmetry that mitigates inflammation and vascular occlusion. Current work has identified exciting pathways, such as the Wnt pathway and the serine-threonine kinase Akt, as central modulators that oversee cellular apoptosis and their downstream substrates that include Forkhead transcription factors, glycogen synthase kinase-3beta, mitochondrial dysfunction, Bad, and Bcl-x(L). Other closely integrated pathways control microglial activation, release of inflammatory cytokines, and caspase and calpain activation. New therapeutic avenues that are just open to exploration, such as with brain temperature regulation, nicotinamide adenine dinucleotide modulation, metabotropic glutamate system modulation, and erythropoietin targeted expression, may provide both attractive and viable alternatives to treat a variety of disorders that include stroke, Alzheimer's disease, and traumatic brain injury.

Activating Akt and the brain's resources to drive cellular survival and prevent inflammatory injury

Protein kinase B, also known as Akt, is a serine/threonine kinase and plays a critical role in the modulation of cell development, growth, and survival. Interestingly, Akt is ubiquitously expressed throughout the body, but its expression in the nervous system is substantially up-regulated during cellular stress, suggesting a more expansive role for Akt in the nervous system that may involve cellular protection. In this regard, a body of recent work has identified a robust capacity for Akt and its downstream substrates to foster both neuronal and vascular survival during apoptotic injury. Cell survival by Akt is driven by the modulation of both intrinsic cellular pathways that oversee genomic DNA integrity and extrinsic mechanisms that control inflammatory microglial activation. A series of distinct pathways are regulated by Akt that include the Forkhead family of transcription factors, GSK-3 beta, beta-catenin, c-Jun, CREB, Bad, IKK, and p53. Culminating below these substrates of Akt are the control of caspase mediated pathways that promote genomic integrity as well as prevent inflammatory cell demise. With further levels of progress in defining the cellular role of Akt, the attractiveness of Akt as a vital and broad cytoprotectant for both neuronal and vascular cell populations should continue to escalate.

PKB/AKT and ERK regulation of caspase-mediated apoptosis by methylseleninic acid in LNCaP prostate cancer cells

Methylselenol has been implicated as an active metabolite for the anticancer effect of selenium in part through the induction of cancer cell apoptosis. Since inactivation of the AKT/protein kinase B negative regulator gene PTEN (phosphatase and tensin homologue deleted on chromosome 10) is common in prostate cancer (PCa), we compared PTEN wild-type DU145 PCa cells (low basal AKT activity) with PTEN-mutant LNCaP PCa cells (high basal AKT activity) for their apoptosis responses to the methylselenol precursor methylseleninic acid (MSeA) and sodium selenite, an inorganic salt. Our results show that LNCaP cells withstood approximately 4 times higher doses of MSeA than DU145 cells, although they were slightly more sensitive than the latter to selenite-induced apoptosis. Treatment by MSeA modestly attenuated AKT phosphorylation and increased phospho-ERK1/2 in LNCaP cells. Selenite treatment increased the phosphorylation of p53 Ser15 and both kinases, but the selenite-induced apoptosis was not influenced by chemical inhibitors of either kinase. In contrast, PI3K/AKT inhibitors greatly sensitized LNCaP cells to apoptosis induced by MSeA, accompanied by increased mitochondrial release of cytochrome c and multiple caspase activation without changing p53 Ser15 phosphorylation. The apoptosis was further accentuated by extracellular signal regulated kinases 1 and 2 (ERK1/2) inhibition without further increase in cytochrome c release. The general caspase inhibitor z-VAD-fmk completely blocked MSeA-induced apoptosis when both kinases were inhibited, whereas a caspase-8 inhibitor exerted a greater protection than did a caspase-9 inhibitor. Transfection of DU145 cells with a constitutively active AKT increased their resistance to MSeA-induced apoptosis. In summary, AKT played an important role in regulating apoptosis sensitivity of LNCaP and DU145 cells to MSeA. An MSeA-induced activation of ERK1/2 in LNCaP cells also contributed to resistance to apoptosis. However, these kinases did not significantly regulate caspase-mediated apoptosis induced by selenite in LNCaP cells. These findings support the differential involvement of these protein kinase pathways in regulating apoptosis induction by different forms of selenium.

Akt/FOXO3a signaling modulates the endothelial stress response through regulation of heat shock protein 70 expression

To identify new antiapoptotic targets of the PI3K-Akt signaling pathway in endothelial cells, adenovirus-mediated Akt1 gene transfer and oligonucleotide microarrays were used to examine Akt-regulated transcripts. DNA microarray analysis revealed that HSP70 expression underwent the greatest fold activation of 12,532 transcripts examined in human umbilical vein endothelial cells (HUVEC) transduced with constitutively active Akt1. Akt1 gene transfer increased HSP70 transcript expression by 24.8-fold as determined by quantitative PCR and promoted a dose-dependent up-regulation of HSP70 protein as determined by Western immunoblot analysis. Gene transfer of FOXO3a, a downstream target of Akt in endothelial cells, significantly suppressed both basal and stress-induced HSP70 protein expression. FOXO3a induced caspase-9-dependent apoptosis in HUVEC, and cotransduction with Ad-HSP70 rescued endothelial cells from FOXO3a-induced apoptosis under basal and stress conditions. Our results identify HSP70 as a new antiapoptotic target of Akt-FOXO3a signaling in endothelial cells that controls viability through modulation of the stress-induced intrinsic cell death pathway.

Simultaneous Inhibition of Epidermal Growth Factor Receptor (EGFR) Signaling and Enhanced Activation of Tumor Necrosis Factor-related Apoptosis-inducing Ligand (TRAIL) Receptor-mediated Apoptosis Induction by an scFv:sTRAIL Fusion Protein with Specificity for Human EGFR

Epidermal growth factor receptor (EGFR) signaling inhibition by monoclonal antibodies and EGFR-specific tyrosine kinase inhibitors has shown clinical efficacy in cancer by restoring susceptibility of tumor cells to therapeutic apoptosis induction. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising anti-cancer agent with tumor-selective apoptotic activity. Here we present a novel approach that combines EGFR-signaling inhibition with target cell-restricted apoptosis induction using a TRAIL fusion protein with engineered specificity for EGFR. This fusion protein, scFv425:sTRAIL, comprises the EGFR-blocking antibody fragment scFv425 genetically fused to soluble TRAIL (sTRAIL). Treatment with scFv425:sTRAIL resulted in the specific accretion to the cell surface of EGFR-positive cells only. EGFR-specific binding rapidly induced a dephosphorylation of EGFR and down-stream mitogenic signaling, which was accompanied by cFLIP(L) down-regulation and Bad dephosphorylation. EGFR-specific binding converted soluble scFv425:sTRAIL into a membrane-bound form of TRAIL that cross-linked agonistic TRAIL receptors in a paracrine manner, resulting in potent apoptosis induction in a series of EGFR-positive tumor cell lines. Co-treatment of EGFR-positive tumor cells with the EGFR-tyrosine kinase inhibitor Iressa resulted in a potent synergistic pro-apoptotic effect, caused by the specific down-regulation of c-FLIP. Furthermore, in mixed culture experiments binding (L)of scFv425:sTRAIL to EGFR-positive target cells conveyed a potent apoptotic effect toward EGFR-negative bystander tumor cells. The favorable characteristics of scFv425:sTRAIL, alone and in combination with Iressa, as well as its potent anti-tumor bystander activity indicate its potential value for treatment of EGFR-expressing cancers.

Insulin regulates cleavage of procaspase-9 via binding of X chromosome-linked inhibitor of apoptosis protein in HT-29 cells

Insulin significantly reduced tumor necrosis factor (TNF)-alpha-induced cleavage of procaspase-8, -9, and -3 and poly(ADP-ribose) polymerase when observed for up to 24 hours in a dose-dependent manner. Signaling pathways responsible for the inhibitory effects of insulin were investigated by using protein kinase inhibitors. Both phosphatidylinositol 3'-kinase (PI3K) and mitogen-activated protein kinase kinase pathways mediate the ability of insulin to decrease the TNF-alpha-induced cleavage of procaspase-8. In contrast, only the PI3K inhibitor reversed the effect of insulin on the TNF-alpha-induced cleavage of procaspase-9. Moreover, insulin decreased the apoptotic level induced by TNF-alpha, whereas the PI3K inhibitor enhanced it. The protein level of Apaf-1, an activator of procaspase-9, remained constant with the application of agents affecting the cleavage of procaspase-9. In examining another regulator of cleaved caspase-9, X chromosome-linked inhibitor of apoptosis protein (XIAP), we observed that TNF-alpha treatment induced fragmentation of XIAP, which was also enhanced by the PI3K inhibitor. In addition, XIAP was coimmunoprecipitated with procaspase-9. The treatment with TNF-alpha reduced the level of XIAP precipitated with procaspase-9, whereas insulin reversed this effect. Moreover, PI3K and Akt inhibitors, but not mammalian target of rapamycin inhibitor, inhibited the effect of insulin on the coprecipitation of procaspase-9 and XIAP. Our data suggest that insulin decreases the TNF-alpha-induced cleavage of procaspase-9 and subsequent apoptosis by regulating XIAP via the PI3K/Akt pathway.

NF-kappaB-regulated expression of cellular FLIP protects rheumatoid arthritis synovial fibroblasts from tumor necrosis factor alpha-mediated apoptosis

OBJECTIVE

Little apoptosis has been observed in rheumatoid arthritis (RA) synovial tissues. Tumor necrosis factor alpha (TNFalpha) is expressed in the joints of patients with RA, yet RA synovial fibroblasts are relatively resistant to apoptosis induced by TNFalpha. Recently, we demonstrated that FLIP is highly expressed in the RA joint. These studies were performed to determine if TNFalpha-induced NF-kappaB controls the expression of FLIP long (FLIP(L)) and FLIP short (FLIP(S)) in RA synovial fibroblasts and to determine the role of FLIP in the control of TNFalpha-induced apoptosis.

METHODS

RA synovial fibroblasts were isolated from RA synovial tissues and used between passages 3 and 9. RA synovial or control fibroblasts were sham infected or infected with a control adenovirus vector or one expressing the super-repressor IkappaBalpha (srIkappaBalpha). The cells were stimulated with TNFalpha or a control vehicle, and expression of FLIP(L) and FLIP(S) was determined by isoform-specific real-time polymerase chain reaction and Western blot analysis. Cell viability was determined by XTT cleavage, and apoptosis was determined by annexin V staining, DNA fragmentation, and activation of caspases 8 and 3.

RESULTS

TNFalpha induced the expression of both isoforms of FLIP messenger RNA (mRNA) in RA synovial fibroblasts; however, FLIP(L) was the dominant isoform detected by Western blot analysis. In control fibroblasts, TNFalpha induced the expression of FLIP(L) and FLIP(S) mRNA and protein. The TNFalpha-induced, but not the basal, expression of FLIP was regulated by NF-kappaB. When NF-kappaB activation was suppressed by the expression of srIkappaBalpha, TNFalpha-mediated apoptosis was induced. TNFalpha-induced apoptotic cell death was mediated by caspase 8 activation and was prevented by the ectopic expression of FLIP(L) or the caspase 8 inhibitor CrmA.

CONCLUSION

The TNFalpha-induced, but not the basal, expression of FLIP is regulated by NF-kappaB in RA synovial fibroblasts. The resistance of RA synovial fibroblasts to TNFalpha-induced apoptosis is mediated by the NF-kappaB-regulated expression of FLIP. These observations support the role of NF-kappaB and FLIP as attractive therapeutic targets in RA.

Sphingosine kinase-1 enhances endothelial cell survival through a PECAM-1-dependent activation of PI-3K/Akt and regulation of Bcl-2 family members

Sphingosine-1-phosphate (S1P), the bioactive product of sphingosine kinase (SK) activation, is a survival factor for endothelial cells. The mechanism of SK-mediated survival was investigated in endothelial cells with moderately raised intracellular SK activity. Overexpression of SK mediated survival primarily through the activation of the phosphatidyl inositol 3-kinase (PI-3K)/protein kinase B (Akt/PKB) pathway and an associated up-regulation of the antiapoptotic protein B cell lymphoma gene 2 (Bcl-2) and down-regulation of the proapoptotic protein bisindolylmaleimide (Bcl-2 interacting mediator of cell death; Bim). In addition there was an up-regulation and dephosphorylation of the junctional molecule platelet endothelial cell adhesion molecule-1 (PECAM-1), which was obligatory for activation of the PI-3K/Akt pathway, for SK-induced cell survival, and for the changes in the apoptosis-related proteins. Thus, raised intracellular SK activity induced a molecule involved in cell-cell interactions to augment cell survival through a PI-3K/Akt-dependent pathway. This is distinct from the activation of both PI-3K/Akt and mitogen-activated protein kinase (MAPK) pathways seen with exogenously added S1P. Cells overexpressing SK showed enhanced survival under conditions of serum deprivation and absence of attachment to extracellular matrix, suggesting a role for SK in the regulation of vascular phenomena that occur under conditions of stress, such as angiogenesis and survival in unattached states, as would be required for a circulating endothelial cell.

NAD+/NADH and/or CoQ/CoQH2 ratios from plasma membrane electron transport may determine ceramide and sphingosine-1-phosphate levels accompanying G1 arrest and apoptosis

To elucidate possible biochemical links between growth arrest from antiproliferative chemotherapeutic agents and apoptosis, our work has focused on agents (EGCg, capsaicin, cis platinum, adriamycin, anti-tumor sulfonylureas, phenoxodiol) that target tNOX. tNOX is a cancer-specific cell surface NADH oxidase (ECTO-NOX protein), that functions in cancer cells as the terminal oxidase for plasma membrane electron transport. When tNOX is active, coenzyme Q(10) (ubiquinone) of the plasma membrane is oxidized and NADH is oxidized at the cytosolic surface of the plasma membrane. However, when tNOX is inhibited and plasma membrane electron transport is diminished, both reduced coenzyme Q(10) (ubiquinol) and NADH would be expected to accumulate. To relate inhibition of plasma membrane redox to increased ceramide levels and arrest of cell proliferation in G(1) and apoptosis, we show that neutral sphingomyelinase, a major contributor to plasma membrane ceramide, is inhibited by reduced glutathione and ubiquinone. Ubiquinol is without effect or stimulates. In contrast, sphingosine kinase, which generates anti-apoptotic sphingosine-1-phosphate, is stimulated by ubiquinone but inhibited by ubiquinol and NADH. Thus, the quinone and pyridine nucleotide products of plasma membrane redox, ubiquinone and ubiquinol, as well as NAD(+) and NADH, may directly modulate in a reciprocal manner two key plasma membrane enzymes, sphingomyelinase and sphingosine kinase, potentially leading to G(1) arrest (increase in ceramide) and apoptosis (loss of sphingosine-1-phosphate). As such, the findings provide potential links between coenzyme Q(10)-mediated plasma membrane electron transport and the anticancer action of several clinically-relevant anticancer agents.

Rapamycin-induced endothelial cell death and tumor vessel thrombosis potentiate cytotoxic therapy against pancreatic cancer

PURPOSE

Despite current chemotherapies, pancreatic cancer remains an uncontrollable, rapidly progressive disease. Here, we tested an approach combining a recently described antiangiogenic drug, rapamycin, with standard gemcitabine cytotoxic therapy on human pancreatic tumor growth.

EXPERIMENTAL DESIGN

Tumor growth was assessed in rapamycin and gemcitabine-treated nude mice orthotopically injected with metastatic L3.6pl human pancreatic cancer cells. H&E staining was performed on tumors, along with Ki67 staining for cell proliferation and immunohistochemical terminal deoxynucleotidyl transferase-mediated nick end labeling and CD31 analysis. Rapamycin-treated tumor vessels were also directly examined in dorsal skin-fold chambers for blood flow after thrombosis induction. Cell death in human umbilical vein endothelial cells was assessed by flow cytometry after annexin-V staining.

RESULTS

Rapamycin therapy alone inhibited tumor growth and metastasis more than gemcitabine, with remarkable long-term tumor control when the drugs were combined. Mechanistically, H&E analysis revealed tumor vessel endothelium damage and thrombosis with rapamycin treatment. Indeed, dorsal skin-fold chamber analysis of rapamycin-treated tumors showed an increased susceptibility of tumor-specific vessels to thrombosis. Furthermore, terminal deoxynucleotidyl transferase-mediated nick end labeling/CD31 double staining of orthotopic tumors demonstrated apoptotic endothelial cells with rapamycin treatment, which also occurred with human umbilical vein endothelial cells in vitro. In contrast, gemcitabine was not antiangiogenic and, despite its known cytotoxicity, did not reduce proliferation in orthotopic tumors; nevertheless, rapamycin did reduce tumor proliferation.

CONCLUSIONS

Our data suggest a novel mechanism whereby rapamycin targets pancreatic tumor endothelium for destruction and thrombosis. We propose that rapamycin-based vascular targeting not only reduces tumor vascularization, it decreases the number of proliferating tumor cells to be destroyed by gemcitabine, thus introducing a new, clinically feasible strategy against pancreatic cancer.

VEGF165 and angiopoietin-1 decreased myocardium infarct size through phosphatidylinositol-3 kinase and Bcl-2 pathways

Angiogenic growth factors, vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang1) could decrease myocardial infarct size, which was assumed to be related with newly formed capillaries. We doubted that these capillaries could do this solely and the potential protective mechanisms of VEGF and Ang1 on myocardium need to be evaluated. Three types of adenoviruses encoding human VEGF(165) (Ad-VEGF(165)), human angiopoietin-1 (Ad-Ang1) and green fluorescent protein (Ad-GFP, as a parallel control) were constructed. Experiments were taken both in vitro and in vivo. As in vitro, the antiapoptosis effect of VEGF(165), Ang1 and VEGF(165)+Ang1 on cardiac myoblasts was observed, which seemed to be related with the activation of phosphatidylinositol-3 kinase and Bcl-2 pathways. As in vivo, adenoviruses were intramyocardially injected immediately after the ligation of the left anterior descending coronay arteries in rats. The results showed positive effect of VEGF(165), Ang1 and VEGF(165)+Ang1 on decreasing the myocardial infarct size at the 7th day. Myocardial PI-3K activity and Bcl-2 expression were elevated relatively at the 3rd day. The protective effect of VEGF(165) and Ang1 on the myocardium may broaden their functional research and contribute to their clinical use in the future.

Uterine spiral artery remodeling involves endothelial apoptosis induced by extravillous trophoblasts through Fas/FasL interactions

OBJECTIVE

Invasion of uterine spiral arteries by extravillous trophoblasts in the first trimester of pregnancy results in loss of endothelial and musculoelastic layers. This remodeling is crucial for an adequate blood supply to the fetus with a failure to remodel implicated in the etiology of the hypertensive disorder preeclampsia. The mechanism by which trophoblasts induce this key process is unknown. This study gives the first insights into the potential mechanisms involved.

METHODS AND RESULTS

Spiral arteries were dissected from nonplacental bed biopsies obtained at Caesarean section, and a novel model was used to mimic in vivo events. Arteries were cultured with trophoblasts in the lumen, and apoptotic changes in the endothelial layer were detected after 20 hours, leading to loss of endothelium by 96 hours. In vitro, coculture experiments showed that trophoblasts stimulated apoptosis of primary decidual endothelial cells and an endothelial cell line. This was blocked by caspase inhibition and NOK2, a FasL blocking antibody. NOK2 also abrogated trophoblast-induced endothelial apoptosis in the vessel model.

CONCLUSIONS

Extravillous trophoblast induction of endothelial apoptosis is a possible mechanism by which the endothelium is removed, and vascular remodeling may occur in uterine spiral arteries. Fas/FasL interactions have an important role in trophoblast-induced endothelial apoptosis.

Tocotrienol-induced caspase-8 activation is unrelated to death receptor apoptotic signaling in neoplastic mammary epithelial cells

Tocotrienols, a subclass in the vitamin E family of compounds, have been shown to induce apoptosis by activating caspase-8 and caspase-3 in neoplastic mammary epithelial cells. Since caspase-8 activation is associated with death receptor apoptotic signaling, studies were conducted to determine the exact death receptor/ligand involved in tocotrienol-induced apoptosis. Highly malignant +SA mouse mammary epithelial cells were grown in culture and maintained in serum-free media. Treatment with 20 microM gamma-tocotrienol decreased+SA cell viability by inducing apoptosis, as determined by positive terminal dUTP nick end labeling (TUNEL) immunocytochemical staining. Western blot analysis showed that gamma-tocotrienol treatment increased the levels of cleaved (active) caspase-8 and caspase-3. Combined treatment with caspase inhibitors completely blocked tocotrienol-induced apoptosis. Additional studies showed that treatment with 100 ng/ml tumor necrosis factor-alpha (TNF-alpha), 100 ng/ml FasL, 100 ng/ml TNF-related apoptosis-inducing ligand (TRAIL), or 1 microg/ml apoptosis-inducing Fas antibody failed to induce death in +SA cells, indicating that this mammary tumor cell line is resistant to death receptor-induced apoptosis. Furthermore, treatment with 20 microM gamma-tocotrienol had no effect on total, membrane, or cytosolic levels of Fas, Fas ligand (FasL), or Fas-associated via death domain (FADD) and did not induce translocation of Fas, FasL, or FADD from the cytosolic to the membrane fraction, providing additional evidence that tocotrienol-induced caspase-8 activation is not associated with death receptor apoptotic signaling. Other studies showed that treatment with 20 microM gamma-tocotrienol induced a large decrease in the relative intracellular levels of phospho-phosphatidylinositol 3-kinase (PI3K)-dependent kinase 1 (phospho-PDK-1 active), phospho-Akt (active), and phospho-glycogen synthase kinase3, as well as decreasing intracellular levels of FLICE-inhibitory protein (FLIP), an antiapoptotic protein that inhibits caspase-8 activation, in these cells. Since stimulation of the PI3K/PDK/Akt mitogenic pathway is associated with increased FLIP expression, enhanced cellular proliferation, and survival, these results indicate that tocotrienol-induced caspase-8 activation and apoptosis in malignant +SA mammary epithelial cells is associated with a suppression in PI3K/PDK-1/Akt mitogenic signaling and subsequent reduction in intracellular FLIP levels.