Regulation of death receptor-mediated apoptosis pathways

Exposure of any of two proapoptotic domains of presenilin 1-associated protein/mitochondrial carrier homolog 1 on the surface of mitochondria is sufficient for induction of apoptosis in a Bax/Bak-independent manner

Presenilin 1-associated protein/mitochondrial carrier homolog 1 (PSAP/Mtch1) is a proapoptotic outer mitochondrial membrane protein first identified as a presenilin 1-associated protein. The mechanism by which it induces apoptosis upon overexpression in cultured cells is so far unknown. We had previously reported that deletion of two independent regions of PSAP/Mtch1 is required to prevent apoptosis. We now report that mitochondrial targeting of the region containing both proapoptotic domains, or any of them independently, to the outer membrane is sufficient to induce apoptosis. On the other hand, targeting of that region to the surface of the endoplasmic reticulum does not induce apoptosis, indicating that attachment of those domains to the outer mitochondrial membrane, and not just cytosolic exposure, is a requisite for apoptosis. Overexpression of PSAP/Mtch1 in cultured cells causes mitochondrial depolarization and apoptosis that does not depend on Bax or Bak, since apoptosis is induced in mouse embryonic fibroblasts lacking these two proteins. Our results suggest that apoptosis induced by PSAP/Mtch1 likely involves the permeability transition pore.

Valproic acid sensitizes chronic lymphocytic leukemia cells to apoptosis and restores the balance between pro- and antiapoptotic proteins

Chronic lymphocytic leukemia (CLL) is one of the most common leukemias in adults in the developed world. Despite significant advances in the treatment of cancer, CLL remains incurable. The main feature of the disease is the generation of circulating B-cells with prolonged survival caused by aberrant apoptosis. In this study, we observe that valproic acid (VPA), a well-established histone deacetylase (HDAC) inhibitor, mediates apoptosis in CLL cells ex vivo through caspase activation via both the extrinsic and the intrinsic apoptosis pathways, as indicated by the activation of the caspase proteins 8 and 9, and cleavage of the proapoptotic protein BID. The Bcl-2/Bax ratio was decreased as a consequence of decreased bcl-2 mRNA levels in response to treatment with VPA. With the results presented in this study, we have identified the HDAC inhibitor VPA as restoring the apoptotic pathways in CLL cells and thus their ability to undergo apoptosis.

Serum soluble Fas levels and prediction of response to platinum-based chemotherapy in epithelial ovarian cancer

Epithelial ovarian cancer (EOC) is treated mainly by platinum-based combination chemotherapy. Chemotherapy induces apoptosis in which the Fas/Fas ligand pathway is important. Serum soluble Fas (sFas) is a biomarker of this pathway and functionally inhibits Fas-/FasL-mediated apoptosis. In this study, we have investigated the role of sFas in prediction of response to chemotherapy in EOC. Thirty-five patients were recruited and their serum sFas levels were estimated by ELISA at 4 time points-preoperative (sFas1), postoperative (sFas2), midchemotherapy (sFas3) and at the end of chemotherapy (sFas4). The response to chemotherapy was documented clinically, radiologically and by CA-125 levels, based on which, 2 groups were identified: primary chemosensitive (n = 24) and primary chemoresistant (n = 11). Based on the disease status at last follow-up, 2 groups were identified: No Evidence of Disease (n = 15) and Evidence of Disease (n = 20). The primary chemoresistant tumors showed significantly higher median sFas2 levels (p = 0.033) with the sFas2/sFas1 ratio > or =1 (p = 0.001). A multivariate Cox proportional hazards regression model identified sFas2/sFas1 ratio as a significant factor for the prediction of response to platinum-based chemotherapy (p = 0.011). Receiver operating characteristic (ROC) analysis showed that at a ratio of 1.2, sFas2/sFas1 achieved a sensitivity of 82% and specificity of 100% for prediction of chemotherapeutic response. sFas2/sFas1 and sFas3/sFas1 ratio was also higher in patients with evidence of disease (p = 0.018 and p = 0.028, respectively). Progression-free survival rates in patients with sFas2/sFas1 ratio <1 exceeded those with ratio > or =1 (p = 0.004). In conclusion, serum sFas is a useful biomarker for predicting response to platinum-based chemotherapy in EOC.

Introducing point mutations into the ATGs of the putative open reading frames of the HSV-1 gene encoding the latency associated transcript (LAT) reduces its anti-apoptosis activity

The herpes simplex virus type 1 (HSV-1) latency associated transcript (LAT) gene has anti-apoptosis activity that directly or indirectly enhances the virus's reactivation phenotype in small animal models. The first 1.5 kb of the primary 8.3 kb LAT is sufficient and some or all of it is necessary for LAT's anti-apoptosis in transient transfection assays and for LAT's ability to enhance the reactivation phenotype. Based on LAT's genomic sequence, the first 1.5 kb contains eight potential open reading frames (ORFs) defined as an ATG followed by an in frame termination codon. In this study, point mutations were introduced into the ATGs of ORFs present in the 1.5 kb fragment of LAT. Mutagenesis of all eight ATGs in LAT ORFs consistently reduced the anti-apoptotic activity of LAT in transiently transfected mouse neuroblastoma cells regardless of whether apoptosis was induced by caspase 8 or caspase 9. Mutation of the six ATGs located in the stable intron sequences within the 1.5 kb LAT had a dramatic effect on caspase 9, but not caspase 8, induced apoptosis. For both caspase 8 and caspase 9 induced apoptosis, mutating the two ATGs in the exon of the LAT 1.5 kb fragment reduced, but did not eliminate the anti-apoptotic activity of LAT. These studies suggest that altering the fine structure of regulatory RNA or expression of a putative LAT ORF regulates the anti-apoptosis activity of LAT. These studies also indicate that more than one function is present in the 1.5 kb LAT fragment.

A tale of two mitochondrial channels, MAC and PTP, in apoptosis

The crucial step in the intrinsic, or mitochondrial, apoptotic pathway is permeabilization of the mitochondrial outer membrane. Permeabilization triggers release of apoptogenic factors, such as cytochrome c, from the mitochondrial intermembrane space into the cytosol where these factors ensure propagation of the apoptotic cascade and execution of cell death. However, the mechanism(s) underlying permeabilization of the outer membrane remain controversial. Two mechanisms, involving opening of two different mitochondrial channels, have been proposed to be responsible for the permeabilization; the permeability transition pore (PTP) in the inner membrane and the mitochondrial apoptosis-induced channel (MAC) in the outer membrane. Opening of PTP would lead to matrix swelling, subsequent rupture of the outer membrane, and an unspecific release of intermembrane proteins into the cytosol. However, many believe PTP opening is a consequence of apoptosis and this channel is thought to principally play a role in necrosis, not apoptosis. Activation of MAC is exquisitely regulated by Bcl-2 family proteins, which are the sentinels of apoptosis. MAC provides specific pores in the outer membrane for the passage of intermembrane proteins, in particular cytochrome c, to the cytosol. The electrophysiological characteristics of MAC are very similar to Bax channels and depletion of Bax significantly diminishes MAC activity, suggesting that Bax is an essential constituent of MAC in some systems. The characteristics of various mitochondrial channels and Bax are compared. The involvement of MAC and PTP activities in apoptosis of disease and their pharmacology are discussed.

The interplay between pro-death and pro-survival signaling pathways in myocardial ischemia/reperfusion injury: apoptosis meets autophagy

INTRODUCTION

Programmed cell death of cardiac myocytes occurs following a bout of ischemia/reperfusion (I/R), which results in reduced function of the heart. Numerous studies, including in vivo, have shown that cell death occurs via necrosis and apoptosis following I/R. Recently, autophagy has emerged as a powerful mediator of programmed cell death, either opposing or enhancing apoptosis, or acting as an alternative form of programmed cell death distinct from apoptosis.

AIM

Here we review the apoptotic and autophagic signaling pathways, their influences on each other, and we discuss the relevance of autophagy in the heart.

Targeting death-inducing receptors in cancer therapy

Deregulated cell death pathways may lead to the development of cancer, and induction of tumor cell apoptosis is the basis of many cancer therapies. Knowledge accumulated concerning the molecular mechanisms of apoptotic cell death has aided the development of new therapeutic strategies to treat cancer. Signals through death receptors of the tumor necrosis factor (TNF) superfamily have been well elucidated, and death receptors are now one of the most attractive therapeutic targets in cancer. In particular, DR5 and DR4, death receptors of TNF-related apoptosis-inducing ligand (TRAIL or Apo2L), are interesting targets of antibody-based therapy, since TRAIL may also bind decoy receptors that may prevent TRAIL-mediated apoptosis, whereas TRAIL ligand itself selectively induces apoptosis in cancer cells. Here, we review the potential therapeutic utility of agonistic antibodies against DR5 and DR4 and discuss the possible extension of this single-antibody-based strategy when combined with additional modalities that either synergizes to cause enhanced apoptosis or further engage the cellular immune response. Rational design of antibody-based therapies combining the induction of tumor cell apoptosis and activation of tumor-specific adaptive immunity enables promotion of distinct steps of the antitumor immune response, thereby enhancing tumor-specific lymphocytes that can eradicate TRAIL/DR5-resistant mutating, large established and heterogeneous tumors in a manner that does not require the definition of individual tumor-specific antigens.

Cytokine-mediated FOXO3a phosphorylation suppresses FasL expression in hemopoietic cell lines: investigations of the role of Fas in apoptosis due to cytokine starvation

We have investigated phosphatidylinositol 3-kinase (PI3K)-dependent survival signalling pathways using several cytokines in three different hemopoietic cell lines, MC/9, FDC-P1, and TF-1. Cytokines caused PI3K- and PKB-dependent phosphorylation of FOXO3a (previously known as FKHRL1) at three distinct sites. Following cytokine withdrawal or PI3K inhibition, both of which are known to lead to apoptosis, there was a loss of FOXO3a phosphorylation, and a resulting increase in forkhead transcriptional activity, along with increased expression of Fas Ligand (FasL), which could be detected at the cell surface. Concurrently, an increase in cell surface expression of Fas was also detected. Despite the presence of both FasL and Fas, there was no detectable evidence that activation of Fas-mediated apoptotic events was contributing to apoptosis resulting from cytokine starvation or inhibition of PI3K activity. Thus, inhibition of FOXO3a activity is mediated by the PI3K-PKB pathway, but regulation of FasL is not the primary means by which cell survival is regulated in cytokine-dependent hemopoietic cells. We were also able to confirm increased expression of known FOXO3a targets, Bim and p27kip1. Together, these results support the conclusion that mitochondrial-mediated signals play the major role in apoptosis of hemopoietic cells due to loss of cytokine signalling.

Leukotriene B4 receptor antagonist LY293111 induces S-phase cell cycle arrest and apoptosis in human pancreatic cancer cells

We have previously shown that the leukotriene B4 receptor antagonist, LY293111 inhibits proliferation and induces apoptosis in human pancreatic cancer cells both in vitro and in vivo. In the current study, we investigated the molecular mechanisms of LY293111-induced apoptosis and cell cycle arrest. Two human pancreatic cancer cell lines were used in this study, MiaPaCa-2 and AsPC-1. Cell cycle analysis by flow cytometry showed a dramatic increase in the percentage of apoptotic cells as well as S-phase arrest after treatment with 250 nmol/l LY293111 for up to 48 h. Western blotting indicated that LY293111 treatment induced cytochrome c release from the mitochondria into the cytosol, accompanied by caspase-9, caspase-7 and caspase-3 activation, and cleavage of poly ADP-ribose polymerase. Caspase-8 was not activated by LY293111. A decrease was found in the expression of the antiapoptotic proteins, Bcl-2 and Mcl-1, and an increase in the proapoptotic protein, Bax. LY293111 reduced the expression of CDK2, cyclin A and cyclin E, consistent with the S-phase arrest observed in these cells. The expression of cyclin-dependent kinase inhibitors, p21 and p27 was not affected by LY293111 treatment. In conclusion, LY293111 induces apoptosis in human pancreatic cancer cells through the mitochondria-mediated pathway. LY293111 also induces S-phase arrest with downregulation of CDK2, cyclin A and cyclin E. Blockade of leukotriene B4 metabolic pathway may provide a novel treatment for human pancreatic cancer.

Links between metabolism and apoptosis in mammalian cells: applications for anti-apoptosis engineering

Production of complex recombinant proteins requires the culture of mammalian cells in bioreactors. Inherent in these cultures is the problem of cell death, which can result from nutrient depletion, byproduct accumulation, and other bioreactor stresses which signal the cell to die through apoptosis, or programmed cell death. Apoptosis is a highly regulated pathway of both pro- and anti-apoptotic proteins that promote cell survival or death, and cell engineering efforts to inhibit the apoptosis pathway have led to increased culture viability and recombinant protein production. Originally, the exclusive function of many of these pathway proteins was believed to be binding at the mitochondria and regulating apoptosis through modulation of the mitochondria permeability. While this protein functionality does still hold true, it is now evident that these proteins also include roles in the metabolic processes of the mitochondria. Furthermore, apoptosis pathway proteins in other organelles within the cell may also both modulate apoptosis and metabolism. This review first details the known links that exist between apoptosis proteins and metabolic functions in the cytosol, mitochondria, and endoplasmic reticulum. Second, the review turns to look at potentially new cell engineering strategies that are linked to metabolism for improving cell culture viability and protein production.

Hepatitis viruses: live and let die

Viral hepatitis is a diffuse inflammatory reaction of the liver caused by hepatotropic viruses. Among the hepatitis viruses, only hepatitis B virus and hepatitis C virus are able to persist in the host and cause chronic hepatitis. In the course of persistent infection, inflammation forms the pathogenetic basis of chronic hepatitis that can lead to nodular fibrosis, which can progress to cirrhosis and, eventually, hepatocellular carcinoma (HCC). Of the different antiviral defense systems employed by the host, apoptosis significantly contributes to the prevention of viral replication, dissemination, and persistence. Pathomorphologic studies have shown acidophilic bodies and hepatocyte dropout, features that are compatible with apoptosis. The number of hepatocytes showing features of apoptosis in patients with chronic hepatitis B and C was found to be higher than in healthy subjects, indicating that apoptosis is involved in the pathogenesis of these diseases. There are various data suggesting that hepatitis B and C viral proteins may modulate apoptosis. Vice versa, mechanisms of apoptosis inhibition might represent central survival strategies employed by the virus which, in the end, may contribute to HCC development. While the expression and retention of viral proteins in hepatocytes may influence the severity and progression of liver disease, the mechanisms of liver injury in viral hepatitis are defined to be due not only to the direct cytopathic effects of viruses, but also to the host immune response to viral proteins expressed by infected hepatocytes. However, the exact role of these observations in relation to pathogenesis remains to be established. The mechanism and systems are complex. This report aims to provide an overview and intends to cite only a small number of pertinent references.

Analysis of CD95 threshold signaling: triggering of CD95 (FAS/APO-1) at low concentrations primarily results in survival signaling

Recently we generated a mathematical model (Bentele, M., Lavrik, I., Ulrich, M., Stosser, S., Heermann, D. W., Kalthoff, H., Krammer, P. H., and Eils, R. (2004) J. Cell Biol. 166, 839-851) of signaling in CD95(Fas/APO-1)-mediated apoptosis. Mathematical modeling in combination with experimental data provided new insights into CD95-mediated apoptosis and allowed us to establish a threshold mechanism of life and death. Here, we further assessed the predictability of the model experimentally by a detailed analysis of the threshold behavior of CD95 signaling. Using the model predictions for the mechanism of the threshold behavior we found that the CD95 DISC (death-inducing signaling complex) is formed at the cell membrane upon stimulation with low concentrations of agonistic anti-APO-1 monoclonal antibodies; however, activation of procaspase-8 at the DISC is blocked due to high cellular FLICE-inhibitory protein recruitment into the DISC. Given that death signaling does not occur upon CD95 stimulation at low (threshold) anti-APO-1 concentrations, we also analyzed survival signaling, focusing on mitogen-activated protein kinase activation. Interestingly, we found that mitogen-activated protein kinase activation takes place under threshold conditions. These findings show that triggering of CD95 can signal both life or death, depending on the strength of the stimulus.

Novel targeted therapies in epithelial ovarian cancer: from basic research to the clinic

The development of new molecularly targeted therapies represents a high priority for the treatment of epithelial ovarian cancer. P-glycoprotein overexpression has been associated with multidrug resistance, and the use of multidrug resistance modulators, such as valspodar, is being explored in combination with chemotherapy. Human epidermal receptor (HER) family members are attractive targets for biological therapies. The addition of erlotinib or cetuximab to first-line paclitaxel- plus carboplatin-based chemotherapy is feasible and well tolerated. Gefitinib is able to inhibit the proliferation of ovarian clear-cell carcinoma in in vitro and in vivo experimental models. Single-agent trastuzumab has a limited value for recurrent epithelial ovarian cancer owing to the low frequency of HER2 overexpression and the low rate of objective responses among HER2-overexpressing patients. A Gynecologic Oncology Group Phase II trial of the proteasome inhibitor bortezomib in recurrent epithelial ovarian cancer is currently ongoing, and the combination of bortezomib and chemotherapeutic agents should be assessed. The mammalian target of rapamycin (mTOR) plays an important role in stimulating the translation of mRNAs encoding key proteins for cell growth and angiogenesis, and mTOR inhibitors, such as AP-23573 (ARIAD), deserve to be tested in selected epithelial ovarian cancer patients. The addition of intraperitoneal treatment with adenovirus containing human wild-type p53 to standard paclitaxel- plus carboplatin-based chemotherapy failed to improve the clinical outcome of patients with mutated p53 epithelial ovarian cancer. The Gynecologic Oncology Group is conducting a Phase II trial of single-agent bevacizumab (antivascular endothelial growth factor monoclonal antibody) in platinum-resistant disease. In conclusion, emerging drugs for epithelial ovarian cancer include agents designed to overcome chemoresistance, HER-targeting agents, proteasome inhibitors, mTOR inhibitors and angiogenesis inhibitors. A new paradigm of treatment could consist of chemotherapy combined with a biological agent for six cycles, and followed by chronic maintenance therapy with the biological agent alone. Advances in genomics and proteomics will elucidate the molecular mechanisms of ovarian carcinogenesis, which will hopefully lead to individualized molecular medicine in the next years.

Phellinus linteus activates different pathways to induce apoptosis in prostate cancer cells

It is known that polysaccharides extracted from the Phellinus linteus (PL) mushroom possess antitumour activity. We previously have demonstrated that high doses of PL render murine or human lung cancer cells susceptible to apoptosis. However, the molecular mechanisms of PL-mediated apoptosis have not been fully explored. In this study, we demonstrate that LNCaP cells expressing the androgen receptor (AR) are highly susceptible to apoptosis in response to treatment with high doses of PL. In this process, caspase 8 and its downstream effectors (such as BID), as well as ER stress-related, apoptotic signalling, are activated. In contrast, a moderate amount of apoptosis occurs in PC3 cells (that lack AR) after the same treatment, which does not activate ER-mediated apoptotic signalling. We also show that, in the process of PL-induced apoptosis, caspase 2 is induced in LNCaP cells, but not in PC3 cells. However, LNCaP cells that express a mutated AR or LNCaP cells treated with a caspase 2 inhibitor blocked ER stress-induced apoptotic signals. The magnitudes of the induction of apoptosis in these cells are comparable with what occurred in the PC3 cells. The data demonstrate that high doses of PL activate the AR-dependent and independent apoptotic pathways. Our study also suggests that caspase 2 is a key target in the determination of the susceptibility of prostate cancer cells to PL-induced apoptosis.

Loss of Caspase-9 Provides Genetic Evidence for the Type I/II Concept of CD95-mediated Apoptosis

The death receptor CD95 triggers apoptosis upon formation of a death-inducing signaling complex and the activation of caspase-8. Two types of CD95-mediated apoptosis have been distinguished that differ in their efficiency of death-inducing signaling complex formation and the requirement of mitochondria for caspase activation. The validity of the type I/II model, however, has been challenged, as Bcl-2 expression or the use of various CD95 agonists resulted in different apoptosis effects. By identifying a caspase-9-deficient T cell line, we now provide genetic evidence for the two-pathway model of CD95-mediated apoptosis and demonstrate that type II cells strongly depend on caspase-9. Caspase-9-deficient cells revealed strongly impaired apoptosis, caspase activation, and mitochondrial membrane depolarization upon CD95 triggering, whereas, surprisingly, activation of Bak and cytochrome c release were not inhibited. Furthermore, caspase-9-deficient cells did not switch to necrosis, and reconstitution of caspase-9 expression restored CD95 sensitivity. Finally, we also show that different death receptors have a distinct requirement for caspase-9.

Caspase-2 is activated at the CD95 death-inducing signaling complex in the course of CD95-induced apoptosis

Caspase-2 was reported to be involved in a number of apoptotic pathways triggered by various stimuli. However, the molecular mechanism of procaspase-2 activation in the course of apoptosis remains poorly defined. In this report, we demonstrate that procaspase-2 is recruited to the CD95 (Fas/APO-1) death-inducing signaling complex (DISC) in human T- and B-cell lines. We show that procaspase-2 is activated at the DISC on CD95 stimulation. Despite its presence at the DISC, caspase-2 does not initiate apoptosis on CD95 stimulation in caspase-8-deficient cell lines. Taken together, our data reveal that caspase-2 is activated at the DISC but does not play an initiating role in the CD95-induced apoptosis.

CD 95 mediated apoptosis in embryogenesis: implication in tooth development

INTRODUCTION

Understanding of apoptotic mechanisms involved in tissue shaping is of particular interest because of possible targeted modulation of the development of organ structures such as teeth. Research of CD 95 mediated apoptosis has been focused particularly on cell death in the immune system and related disorders. However, CD 95 mediated apoptosis is also involved in embryogenesis of many organs as the kidney, the lung, the intestine and tissue networks such as the nervous system.

DESIGN

Narrative review.

RESULTS

This review briefly summarizes the current knowledge of CD 95 mediated apoptosis in embryogenesis with possible implication in tooth development. CD 95 receptor and CD 95 ligand are found at early stages of tooth development. The data suggest some positive correlations with dental apoptosis distribution, particularly in the primary enamel knot where apoptosis occurs during elimination of this structure. CD 95 deficient (lpr) adult mouse tooth phenotype, however, did not show any alterations in final tooth pattern and morphology.

CONCLUSION

To date studies of apoptotic machinery during tooth development show spatial localization of many of the components together with precise and localized timing of cell death. There is still much to be learned about the regulation and importance of apoptosis in tooth development. Nevertheless, the involvement of apoptotic regulatory mechanisms interplaying with other molecules participates to the cellular cross-talk in developing tissues, which opens possible targeted modulations as suggested, e.g. for future molecular dentistry.

The Influence of Immunosuppressive Drugs on T- and B-cell Apoptosis via p53-Mediated Pathway In Vitro and In Vivo

BACKGROUND

This study was designed to assess the effects of calcineurin and inosine-5-monophosphate-dehydrogenase inhibitors on p53-mediated-apoptosis in T- and B-cells in vitro and in human heart-transplanted recipients (HTx-R).

METHODS

For in vitro experiments, peripheral blood from healthy volunteers was collected and treated either with 1 microM cyclosporin A (CsA; n = 6), 10 microM mycophenolic acid (MPA; n = 6) or 100 nM tacrolimus (TRL; n = 6). For the second part, peripheral blood was collected from HTx-R undergoing CsA-MPA (n = 11) or TRL-MPA (n = 11) therapy before (0 hr) and after (2 hr) acute drug application and from healthy volunteers (n = 11) without drug therapy. Whole blood (part 1+2) was stimulated (24 hr) with eight different concentrations of actinomycin-D (0-800 nM), an apoptosis inductor acting via p53-pathway. Apoptotic lymphocytes were measured by TUNEL and expression of Annexin-V using FACS. Drug effects were calculated by taking the effects of actinomycin-D as baseline values.

RESULTS

In vitro drug treatment with CsA, MPA, and TRL significantly (P < 0.05) decreased the apoptotic effect of actinomycin-D in T-cells in a noncompetitive manner. In HTx-R undergoing drug therapy, there was a similar antiapoptotic effect observed in both T- and B-cells (P < 0.05). Differences between 0 hr and 2 hr after acute drug application did not exist. Apoptosis induced by actinomycin-D can be completely blocked by caspase-inhibitor zVAD-FMK.

CONCLUSION

Our results suggest that, in vitro and in HTx-R, an inhibition of calcineurin and inosine-5-monophosphate-dehydrogenase by CsA, TRL, or MPA lead to an inhibition of T-and B-cell apoptosis via p53-pathway. This assay may be helpful to provide insights into mechanisms of immunosuppressive drugs in regulation of apoptosis in lymphocytes.

Impact of growth factors in the regulation of apoptosis in low-risk myelodysplastic syndromes

Increased apoptosis of hematopoietic progenitors is a hallmark of myelodysplastic syndromes (MDS) and results in ineffective hematopoiesis. Erythroid apoptosis is thought to be the main mechanism underlying the severe anemia observed in the low-risk subgroups, refractory anemia (RA) and RA with ringed sideroblasts (RARS). Treatment with erythropoietin (Epo) alone or in combination with granulocyte colony-stimulating factor (G-CSF) may significantly improve anemia and reduce bone marrow apoptosis. A synergistic effect between Epo and G-CSF has been observed in the clinic, in particular in RARS. However, the molecular mechanisms beyond the anti-apoptotic effect of these growth factors have not been fully understood. This paper outlines the potential mechanisms underlying the augmented apoptosis during the erythroid differentiation in low-risk MDS as well as the anti-apoptotic effect of the growth factors.

Apolipoprotein E epsilon 4 is associated with an increased vulnerability to cell death in Alzheimer’s disease

The presumption to suffer from Alzheimer's disease (AD) accelerates with aging. One important risk factor seems to be the isoform epsilon 4 of the apolipoprotein E gene (Apo epsilon 4), which increases the risk to develop AD at an earlier age. Furthermore, convincing evidence is provided that apoptotic cell death mechanisms play an important role in neuronal cell death in AD. In the present study, we investigated whether abnormalities in apoptosis and caspase-3 activity can be found at the level of lymphocytes and a T cell subtype, CD4 T cells, from AD patients compared to aged sex- and ApoE genotype-matched non-demented controls. Under different experimental conditions (at baseline or after in vitro incubation in the presence of proapoptotic stimuli) increased levels of apoptosis and enhanced caspase-3 activity were detected in lymphocytes from AD patients. This difference was most pronounced in the CD4(+) T cell subtype. Notably, we found a significant increase of apoptotic cells and caspase-3 activity in lymphocytes from AD patients bearing one or two alleles of the ApoE4 compared to non-E4 carriers. Again, these effects were strongest in CD4(+) T cells. Circulating amyloid-beta (A beta) levels did not differ between AD patients bearing ApoE4 and non-ApoE4 and age-matched controls. Therefore, it is likely that circulating A beta is not responsible for the observed effects, which might rather reflect an ongoing systemic response in AD, e.g. an increase in CD95 expression.

TLR-4 signaling promotes tumor growth and paclitaxel chemoresistance in ovarian cancer

Evidence suggests that an inflammatory profile of cytokines and chemokines persisting at a particular site would lead to the development of a chronic disease. Recent studies implicate bacterial infection as one possible link between inflammation and carcinogenesis; however, the crucial molecular pathways involved remain unknown. We hypothesized that one possible upstream signaling pathway leading to inflammation in carcinogenesis may be mediated by Toll-like receptors (TLR). We describe for the first time an adaptive mechanism acquired by ovarian cancer cells that allows them to promote a proinflammatory environment and develop chemoresistance. We propose that the TLR-4-MyD88 signaling pathway may be a risk factor for developing cancer and may represent a novel target for the development of biomodulators. Our work explains how bacterial products, such as lipopolysaccharide, can promote, directly from the tumor, the production of proinflammatory cytokines and the enhancement of tumor survival. In addition, we provide new evidence that links TLR-4 signaling, inflammation, and chemoresistance in ovarian cancer cells.

Is MAC the knife that cuts cytochrome c from mitochondria during apoptosis?

Apoptosis is a phenomenon fundamental to higher eukaryotes and essential to mechanisms controlling tissue homeostasis. Bcl-2 family proteins tightly control this cell death program by regulating the permeabilization of the mitochondrial outer membrane and, hence, the release of cytochrome c and other proapoptotic factors. Mitochondrial apoptosis-induced channel (MAC) is the mitochondrial apoptosis-induced channel and is responsible for cytochrome c release early in apoptosis. MAC activity is detected by patch clamping mitochondria at the time of cytochrome c release. The Bcl-2 family proteins regulate apoptosis by controlling the formation of MAC. Depending on cell type and apoptotic inducer, Bax and/or Bak are structural component(s) of MAC. Overexpression of the antiapoptotic protein Bcl-2 eliminates MAC activity. The focus of this review is a biophysical characterization of MAC activity and its regulation by Bcl-2 family proteins, and ends with some discussion of therapeutic targets.

Inhibition of the mammalian target of rapamycin (mTOR) by rapamycin increases chemosensitivity of CaSki cells to paclitaxel

Paclitaxel, a potent anti-neoplastic agent, has been found to be effective against several tumours, including cervical cancer. However, the exact mechanism underlying the cytotoxic effects of pacitaxel, especially in the survival-signalling pathway, is poorly understood. The aim of this study was to investigate the molecular pathway of the cytotoxic effect of paclitaxel in human cervical cancer cell lines. Four human cervical cancer cell lines were treated for 24 h with various concentration of paclitaxel, and the sensitivity was analysed by an MTT assay. The cell cycle progression and sub-G1 population were analysed by flow cytometry. Apoptosis was further measured by DNA fragmentation and microscope examination. The protein expression was determined by Western blot analysis. Our results showed that HeLa cells demonstrated the highest sensitivity to paclitaxel, whereas CaSki cells showed the lowest. In cervical cancer cells, paclitaxel induced apoptosis through an intrinsic pathway with prior G2/M arrest. In addition, we showed that paclitaxel downregulated the phosphorylation of Akt in both HeLa and CaSki cells. Interestingly, in CaSki cells, which were more suggestive of a resistant phenotype, paclitaxel induced the activation of mTOR as a downstream target of Akt. Pre-treatment with rapamycin inhibited activation of mTOR signalling and significantly enhanced the sensitivity of CaSki cells to paclitaxel by increasing apoptotic cell death. This effect was mediated, at least partly, through caspase activation. Overall, paclitaxel exerts its anti-tumour effects on cervical cancer cells by inducing apoptosis through intrinsic pathway, and rapamycin targeted to mTOR can sensitise paclitaxel-resistant cervical cancer cells.

The role of CAP3 in CD95 signaling: new insights into the mechanism of procaspase-8 activation

Formation of the CD95 (APO-1/Fas) death inducing signaling complex (DISC) plays a central role in CD95 signaling. Previously, CD95 DISC composition was analyzed by two-dimensional gel electrophoresis and four major cytotoxicity-associated proteins (CAP1-4) were found. CAP1 and CAP2 were defined to be unmodified and phosphorylated FADD, respectively. CAP4 was identified as procaspase-8a. CAP3, however, has remained elusive. In this study, we demonstrate that CAP3 is an intermediate of procaspase-8 processing. CAP3 is generated within seconds of DISC formation and subsequently processed to the prodomain of procaspase-8a that is known as p26 (CAP5). These findings lead to new insights into the mechanism of procaspase-8 processing and apoptosis initiation.

Down-regulation of c-FLIP contributes to the sensitization effect of 3,3'-diindolylmethane on TRAIL-induced apoptosis in cancer cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the tumor necrosis factor superfamily, which has been shown to preferentially induce apoptosis in cancer cells without adverse effects on normal cells. However, there are still some cancer cells, especially those with high malignancy, resistant to TRAIL-induced apoptosis, impeding the clinical anticancer efficiency of TRAIL. In this report, we showed that 3,3'-diindolylmethane, an indole compound derived from cruciferous vegetables, is capable of overcoming TRAIL resistance by sensitizing TRAIL-induced apoptosis in human cancer cells. Noncytotoxic concentrations of 3,3'-diindolylmethane significantly enhanced TRAIL-resistant cancer cells to TRAIL-induced apoptosis via promoting the caspase cascade, a process independent of nuclear factor-kappaB activation and cell surface TRAIL receptor expression. In the search of the molecular mechanisms involved in the sensitization activity of 3,3'-diindolylmethane, we found that combined treatment of 3,3'-diindolylmethane and TRAIL led to significant down-regulation of the cellular FLICE inhibitory protein expression (c-FLIP). Furthermore, we provided evidence showing that the reduced c-FLIP level is predominately mediated by the ubiquitin-proteasome degradation system. These findings reveal a novel anticancer property of 3,3'-diindolylmethane and suggest that this compound could have potential use in cancer therapy to overcome TRAIL resistance.

Tumor counterattack: fact or fiction?

Cancer development relies on a variety of mechanisms that facilitate tumor growth despite the presence of a functioning immune system. Understanding these mechanisms may foster novel therapeutic approaches for oncology and organ transplantation. By expression of the apoptosis-inducing protein CD95L (FasL, APO-1L, CD178), tumors may eliminate tumor-infiltrating lymphocytes and suppress anti-tumor immune responses, a phenomenon called "tumor counterattack". On the one hand, preliminary evidence of tumor counterattack in human tumors exists, and CD95L expression can prevent T-cell responses in vitro. On the other hand, CD95L-expressing tumors are rapidly rejected and induce inflammation in mice. Here, we summarize and discuss the consequences of CD95L expression of tumor cells and its contribution to immune escape.

Bax channel inhibitors prevent mitochondrion-mediated apoptosis and protect neurons in a model of global brain ischemia

Ischemic injuries are associated with several pathological conditions, including stroke and myocardial infarction. Several studies have indicated extensive apoptotic cell death in the infarcted area as well as in the penumbra region of the infarcted tissue. Studies with transgenic animals suggest that the mitochondrion-mediated apoptosis pathway is involved in ischemia-related cell death. This pathway is triggered by activation of pro-apoptotic Bcl-2 family members such as Bax. Here, we have identified and synthesized two low molecular weight compounds that block Bax channel activity. The Bax channel inhibitors prevented cytochrome c release from mitochondria, inhibited the decrease in the mitochondrial membrane potential, and protected cells against apoptosis. The Bax channel inhibitors did not affect the conformational activation of Bax or its translocation and insertion into the mitochondrial membrane in cells undergoing apoptosis. Furthermore, the compounds protected neurons in an animal model of global brain ischemia. The protective effect in the animal model correlated with decreased cytochrome c release in the infarcted area. This is the first demonstration that Bax channel activity is required in apoptosis.

Cancer-specific toxicity of apoptin is independent of death receptors but involves the loss of mitochondrial membrane potential and the release of mitochondrial cell-death mediators by a Nur77-dependent pathway

Apoptin, a small proline-rich protein derived from the chicken anaemia virus, induces cell death selectively in cancer cells. The signalling pathways of apoptin-induced, cancer cell-selective apoptosis are not well understood. Here, we demonstrate that apoptin triggers apoptosis by activating the mitochondrial/intrinsic pathway, and that it acts independently of the death receptor/extrinsic pathway. Jurkat cells deficient in either FADD or caspase-8 (which are both necessary for the extrinsic pathway) were equally as sensitive to apoptin as their parental clones. This demonstrates that apoptin is likely to act through the mitochondrial death pathway. Apoptin treatment causes a loss of mitochondrial membrane potential, and release of the mitochondrial proteins cytochrome c and apoptosis-inducing factor. Apoptin-induced cell death is counteracted by the anti-apoptotic Bcl-2 family members, Bcl-2 itself and Bcl-XL, as shown in Jurkat leukaemia cells. In addition, we describe the processing and activation of caspase-3. By contrast, cleavage of caspase-8, which is predominantly triggered by the death receptor pathway, is not observed. Furthermore, apoptin triggers the cytoplasmic translocation of Nur77, and the inhibition of Nur77 expression by siRNA significantly protects MCF7 cells from apoptin-triggered cell death. Thus, our data indicate that the apoptin death signal(s) ultimately converges at the mitochondria, and that it acts independently of the death receptor pathway.

JNK/SAPK and p38 SAPK-2 mediate mechanical stretch-induced apoptosis via caspase-3 and -9 in NRK-52E renal epithelial cells

BACKGROUND/AIMS

In renal epithelial cells, mechanical forces produced from urinary obstruction serve as potential mediators of apoptosis by activating specific intracellular signaling pathways. In this study, we sought to further define the role of JNK and p38 SAPK-2 pathway and caspase activation in stretch-induced apoptosis.

METHODS

Immortalized cell lines derived from the various components of the nephron were subjected to cyclical stretch and their differential apoptotic response was assessed. Pharmacologic inhibitors and Western blot analysis were used to assess the involvement of the MAPK pathways. Caspases' activity was assessed with ELISA and by Western blot analysis.

RESULTS

Stretch-induced apoptosis was dependent upon the cell phenotype and the degree of stretch. In NRK-52E cells, it was mediated through both JNK and p38 SAPK-2 pathways, and inhibition of either pathway reduced the degree of stretch-induced apoptosis. Stretched cells showed increased activity of caspase-3 and -9 but not -2 or -8. Stretch-induced apoptosis was modulated by inhibition of caspase-3 and to a lesser extent by caspase-9.

CONCLUSION

These findings suggest that stretch induces apoptosis in renal epithelial cells through the specific activation of JNK/SAPK and p38 SAPK-2 pathways and is dependent on the activation of caspase-3 and -9.

L'apoptose : bases fondamentales et applications médicales

Apoptosis has become a most popular concept of cell death. What makes apoptosis particularly exciting for medicine is that its dysfunctions play a central role in the pathogenesis of several human diseases. This review summarizes the considerable knowledge about the cell death pathways. The purpose of this article is to provide a background of relevance to clinicians on apoptosis, and the rationale for future therapeutic interventions directed toward the apoptotic machinery.

Regulation of the mitochondrial apoptosis-induced channel, MAC, by BCL-2 family proteins

Programmed cell death or apoptosis is central to many physiological processes and pathological conditions such as organogenesis, tissue homeostasis, cancer, and neurodegenerative diseases. Bcl-2 family proteins tightly control this cell death program by regulating the permeabilization of the mitochondrial outer membrane and, hence, the release of cytochrome c and other pro-apoptotic factors. Control of the formation of the mitochondrial apoptosis-induced channel, or MAC, is central to the regulation of apoptosis by Bcl-2 family proteins. MAC is detected early in apoptosis by patch clamping the mitochondrial outer membrane. The focus of this review is on the regulation of MAC activity by Bcl-2 family proteins. The role of MAC as the putative cytochrome c release channel during early apoptosis and insights concerning its molecular composition are also discussed.

Effects of Bcl-2 levels on Fas signaling-induced caspase-3 activation: molecular genetic tests of computational model predictions

Fas-induced apoptosis is a critical process for normal immune system development and function. Although many molecular components in the Fas signaling pathway have been identified, a systematic understanding of how they work together to determine network dynamics and apoptosis itself has remained elusive. To address this, we generated a computational model for interpreting and predicting effects of pathway component properties. The model integrates current information concerning the signaling network downstream of Fas activation, through both type I and type II pathways, until activation of caspase-3. Unknown parameter values in the model were estimated using experimental data obtained from human Jurkat T cells. To elucidate critical signaling network properties, we examined the effects of altering the level of Bcl-2 on the kinetics of caspase-3 activation, using both overexpression and knockdown in the model and experimentally. Overexpression was used to distinguish among alternative hypotheses for inhibitory binding interactions of Bcl-2 with various components in the mitochondrial pathway. In comparing model simulations with experimental results, we find the best agreement when Bcl-2 blocks the release of cytochrome c by binding to both Bax and truncated Bid instead of Bax, truncated Bid, or Bid alone. Moreover, although Bcl-2 overexpression strongly reduces caspase-3 activation, Bcl-2 knockdown has a negligible effect, demonstrating a general model finding that varying the expression levels of signal molecules frequently has asymmetric effects on the outcome. Finally, we demonstrate that the relative dominance of type I vs type II pathways can be switched by varying particular signaling component levels without changing network structure.

Apoptotic death of infiltrating cells in human cardiac allografts is regulated by IL-2, FASL, and FLIP

INTRODUCTION

In vitro studies have shown that apoptotic cell death is triggered by a IL-2-dependent activation of the Fas-FasL pathway and that this pathway can be inhibited by FLIP.

METHODS

To define whether FLIP regulates apoptotic death of graft infiltrating T-cells during IL-2-mediated rejection, we analyzed endomyocardial biopsies (EMB) from cardiac allograft recipients for CD3, DNA strand breaks (TUNEL assay), FLIP (mRNA and protein), and FasL mRNA expression.

RESULTS

Apoptosis was present in CD3+ T-cell infiltrates. The number of TUNEL-stained mononuclear cells was inversely correlated with FLIP mRNA expression levels (P=.09). FLIP protein was present in 5% to 10% of the infiltrating cells and was constitutively produced by cardiomyocytes irrespective of the rejection grade. Rejection biopsies had elevated IL-2 and FasL mRNA expression levels compared to the expression levels before and after acute rejection (P=.03 and P=.11), while FLIP mRNA expression levels were significantly decreased during rejection (P=.05).

CONCLUSION

Our results indicate that during the IL-2-induced rejection process, infiltrated T cells become more sensitive to apoptosis.

Induction of apoptosis by the synthetic retinoid MX3350-1 through extrinsic and intrinsic pathways in head and neck squamous carcinoma cells

Retinoids have shown promise in cancer prevention and therapy. As some retinoids exhibit undesirable side effects, new retinoid analogs have been synthesized. In this study, we examined the effects of the retinoid MX3350-1 on human head and neck squamous cell carcinoma (HNSCC) cell lines. MX3350-1 suppressed the growth of 7/8 HNSCC cell lines by >65%. This inhibition appeared to be due to induction of apoptosis as revealed by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. Studies with cell line UMSCC17B indicated that apoptosis was induced within 1-2 days and involved activation of caspase-8, -9, and -3. Inhibitors of these caspases suppressed MX3350-1-induced apoptosis. MX3350-1 decreased the levels of antiapoptotic Bcl-2 and Bcl-XL, increased proapoptotic Bax, induced mitochondrial membrane permeabilization (MMP), and cytochrome c release from mitochondria to cytosol. The antioxidant butylated hydroxyanisol and the MMP inhibitor cyclosporin A (Cs A) blocked apoptosis induced by MX3350-1. In contrast, retinoid receptor antagonists failed to inhibit apoptosis. MX3350-1 increased the levels of Fas-ligand, Fas, and Fas-associated death domain, and enhanced activation of procaspase-8 and cleavage of its substrate Bid. Soluble Fas rescued the cells from MX3350-1-induced apoptosis. These results demonstrate that MX3350-1 induces apoptosis by activating both extrinsic and intrinsic apoptosis pathways and suggest that further studies on the potential of this retinoid for prevention and therapy of HNSCCs are warranted.

Transfer of CD8(+) cells induces localized hair loss whereas CD4(+)/CD25(-) cells promote systemic alopecia areata and CD4(+)/CD25(+) cells blockade disease onset in the C3H/HeJ mouse model

Alopecia areata (AA) is a suspected hair follicle specific autoimmune disease. The potential for cell transfer of AA using the C3H/HeJ mouse model was examined. Cells isolated from lymph nodes and spleens of AA-affected mice using magnetic bead conjugated monoclonal antibodies were subcutaneously injected into normal C3H/HeJ recipients. Within 5 wk, all CD8(+) cell-injected mice exhibited localized hair loss exclusively at the site of injection that persisted until necropsy. In contrast, some CD4(+) and CD4(+)/CD25(-) cell-injected mice developed extensive, systemic AA, and a combination of CD8(+) and CD4(+)/CD25(-) cells injected yielded the highest frequency of systemic AA induction. CD4(+)/CD25(+) cells were less able to transfer the disease phenotype, partially blockaded systemic AA induction by CD4(+)/CD25(-) cells, and prevented CD8(+) cell-induced, injection site-localized hair loss. CD11c(+) and CD19(+) cells failed to promote significant phenotype changes. Increases in co-stimulatory ligands CD40 and CD80, plus increased leukocyte apoptosis resistance with reduced CD95, CD95L, and CD120b expression, were associated with successful alopecia induction. The results suggest that CD8(+) cells may be the primary instigators of the hair loss phenotype. However, systemic disease expression fate is, apparently determined by CD4(+)/CD25(-) cells, while CD4(+)/CD25(+) lymphocytes may play a predominantly regulatory role.

Cell size reduction induced by inhibition of the mTOR/S6K-signaling pathway protects Jurkat cells from apoptosis

In Jurkat cells, the decreased cell growth rate associated with a long-lasting deactivation of the mammalian target of rapamycin (mTOR)/p70 ribosomal S6 kinase (S6K)-signaling pathway generates a cell population of progressively reduced cellular mass and size. When promoted by rapamycin as prototype inhibitor, the mTOR deactivation-dependent cell size reduction was associated with slowed, but not suppressed, proliferation. Small-size cells were significantly protected from apoptosis induced by Fas/Apo-1 death-receptor activation (as shown by reduced procaspase cleavage and decreased catalytic activity of relevant caspases) or by stress signals-dependent mitochondrial perturbation (as shown by reduced cleavage of caspase-2, lower dissipation of mitochondrial membrane potential and decreased release of cytochorome c and apoptosis-inducing factor from mitochondria). Protection faded when reactivation of the mTOR/S6K pathway promoted the cell recovery to normal size. These results suggest that cells induced to reduce their mass by the mTOR deactivation-dependent inhibition of cell growth become more resilient to lethal assaults by curbing the cell's suicidal response.

c-FLIPR, a new regulator of death receptor-induced apoptosis

c-FLIPs (c-FLICE inhibitory proteins) play an essential role in regulation of death receptor-induced apoptosis. Multiple splice variants of c-FLIP have been described on the mRNA level; so far only two of them, c-FLIP(L) and c-FLIP(S,) had been found to be expressed at the protein level. In this report, we reveal the endogenous expression of a third isoform of c-FLIP. We demonstrate its presence in a number of T and B cell lines as well as in primary human T cells. We identified this isoform as c-FLIP(R), a death effector domain-only splice variant previously identified on the mRNA level. Impor-/tantly, c-FLIP(R) is recruited to the CD95 (Fas/APO-1) death-inducing signaling complex upon CD95 stimulation. Several properties of c-FLIP(R) are similar to c-FLIP(S): both isoforms have a short half-life, a similar pattern of expression during activation of primary human T cells, and are strongly induced in T cells upon CD3/CD28 costimulation. Taken together, our data demonstrate endogenous expression of c-FLIP(R) and similar roles of c-FLIP(R) and c-FLIP(S) isoforms in death receptor-mediated apoptosis.

Apoptosis-related factors (Fas receptor, Fas ligand, FADD) in early tooth development of the field vole (Microtus agrestis)

Fas (CD95/APO-1) belongs to the TNF receptor (TNFR) family. Fas ligand binding followed by Fas-receptor oligomerisation leads to formation of a death-inducing signal complex starting with recruitment of the Fas-adapter protein (FADD). Components of this initiation complex (Fas, Fas-L, FADD) were correlated with apoptotic cells, detected by specific DNA fragmentation and morphological criteria. Apoptotic cells can be detected throughout the embryonic development of molar teeth. Restricted temporospatial distribution suggests several important roles for apoptosis in tooth morphogenesis. However, the mechanisms employed in dental apoptosis remain unclear. Frontal sections of the field vole at stage 13.5-15.5 of embryonic development were exploited to investigate and correlate location of Fas, Fas-ligand, FADD molecules and apoptosis in developing first molars by immunohistochemistry. During these stages the primary enamel knot appears and is gradually terminated by apoptosis. Initially, apoptotic cells were demonstrated in the most superficial layer of the dental lamina. The number of TUNEL-positive cells expanded from late bud to cap stages. Restricted areas of apoptotic cells were found in the stalk and primary enamel knot. Fas, Fas-L and FADD were co-localised, particularly in the primary enamel knot, and the stalk, correlating with the occurrence of apoptosis in these areas. Fas-L, however, was also found in proliferating parts of the developing tooth germ, such as in the cervical loops. Interestingly, FADD molecules were also observed in areas, where Fas protein was not detected. According to the immunohistochemical data, Fas-mediated signalling may have a triggering or enhancing role in dental apoptosis. This remains to be functionally confirmed.

Alpha-mangostin induces Ca2+-ATPase-dependent apoptosis via mitochondrial pathway in PC12 cells

We investigated the cell death effects of eight xanthones on PC12 rat pheochromocytoma cells. Among these compounds, alpha-mangostin, from the fruit hull of Garcinia mangostana L., had the most potent effect with the EC(50) value of 4 microM. Alpha-mangostin-treated PC12 cells demonstrated typical apoptotic DNA fragmentation and caspase-3 cleavage (equivalent to activation). The flow cytometric analysis indicated that this compound induced apoptosis in time-and concentration-dependent manners. Alpha-mangostin showed the features of the mitochondrial apoptotic pathway such as mitochondrial membrane depolarization and cytochrome c release. Furthermore, alpha-mangostin inhibited the sarco(endo)plasmic reticulum Ca(2+)-ATPase markedly. There was a correlation between the Ca(2+)-ATPase inhibitory effects and the apoptotic effects of the xanthone derivatives. On the other hand, c-Jun NH(2)-terminal kinase (JNK/SAPK), one of the signaling molecules of endoplasmic reticulum (ER) stress, was activated with alpha-mangostin treatment. These results suggest that alpha-mangostin inhibits Ca(2+)-ATPase to cause apoptosis through the mitochondrial pathway.

Molecular Mechanism of Apoptosis Induced by Mechanical Forces

In all biological systems, a balance between cell proliferation/growth and death is required for normal development as well as for adaptation to a changing environment. To affect their fate, it is essential for cells to integrate signals from the environment. Recently, it has been recognized that physical forces such as stretch, strain, and tension play a critical role in regulating this process. Despite intensive investigation, the pathways by which mechanical signals are converted to biochemical responses is yet to be completely understood. In this review, we will examine our current understanding of how mechanical forces induce apoptosis in a variety of biological systems. Rather than being a degenerative event, physical forces act through specific receptor-like molecules such as integrins, focal adhesion proteins, and the cytoskeleton. These molecules in turn activate a limited number of protein kinase pathways (p38 MAPK and JNK/SAPK), which amplify the signal and activate enzymes (caspases) that promote apoptosis. Physical forces concurrently activate other signaling pathways such as PIK-3 and Erk 1/2 MAPK, which modulate the apoptotic response. The cell phenotype and the character of the physical stimuli determine which pathways are activated and, consequently, allow for variability in response to a specific stimulus in different cell types.

Infected cell protein 0 encoded by bovine herpesvirus 1 can activate caspase 3 when overexpressed in transfected cells

Infection of cattle or bovine cells with bovine herpesvirus 1 (BHV-1) leads to increased apoptosis. Previous studies indicated that BHV-1 infected cell protein 0 (bICP0), the major transcriptional regulatory protein of BHV-1, is toxic in transiently transfected cells. Point mutations within the zinc RING finger of bICP0 reduced toxicity and eliminated the ability of bICP0 to activate viral gene expression. In mouse neuroblastoma cells (neuro-2A) and bovine turbinate cells, bICP0 activated caspase 3, a key regulatory protein in the apoptotic pathway. A pro-apoptotic gene (Bax), but not bICP0, induced caspase 3 cleavage and activation by 8 h after transfection of neuro-2A cells. Conversely, bICP0 or the N-terminal 356 aa of bICP0 did not induce caspase 3 cleavage in neuro-2A cells until 30 h after transfection, suggesting that bICP0 stimulates caspase 3 cleavage by an indirect mechanism. These studies indicate that the toxic functions of bICP0 correlate with caspase 3 cleavage and activation.

Enhancement of Fas-mediated apoptosis in ageing human keratinocytes

Cellular senescence and apoptosis are two metabolically related and seemingly synergistic processes that are involved in tissue maintenance and homeostasis, anti-tumor protection, and age-related diseases. Despite this apparent co-operativity, senescence can inhibit apoptosis in certain conditions. Here, we describe senescence-apoptosis relationships in human epidermal cells by comparing apoptosis-related effector concentrations in keratinocyte cultures and epidermal skin cells at various stages of ageing. Using western blots, flow cytometry, enzyme-linked immuno-sorbent assay (ELISA) and immunofluorescence, we determined the amounts of apoptotic effectors in aged cells compared to young ones, in parallel with beta-galactosidase activity at neutral pH (senescence-associated beta-galactosidase, SA beta-gal), found to be a good indicator of cellular ageing. We observed increased levels of several Fas-mediated apoptosis effectors (Fas, Fas ligand, FADD, FLICE), both in cell cultures at advanced passages and in skin cells of aged donors (above 45 years). Furthermore, we found that while the pro-apoptotic p53 increased, the anti-apoptotic Bcl-2 declined. In spite of this, the extent of spontaneous apoptosis did not change in senescent keratinocyte cultures. The cells, however, became notably more susceptible to apoptosis when kept in exhausted growth medium, or upon Fas receptor activation by anti-Fas antibody binding. Our results are consistent with recent findings in senescent fibroblasts, showing that the death-signaling pathway is enhanced at senescence.

High molecular weight plasma proteins induce apoptosis and Fas/FasL expression in human proximal tubular cells

BACKGROUND

In proteinuria, proximal tubular epithelial cells (PTECs) are exposed to abnormally high protein concentrations, eventually leading to tubular atrophy and end-stage renal disease. The mode of cell death leading to tubular atrophy in proteinuria has not been fully established. This study examines the role of protein overload on apoptosis, necrosis and cell proliferation in primary cultures of human PTECs using plasma protein fractions representative of selective and non-selective proteinuria. The involvement of the Fas/Fas ligand (FasL) system was also investigated.

METHODS

Plasma was collected from healthy volunteers and fractionated into albumin-rich (30-100 kDa), high molecular weight (100-440 kDa) and combined (30-440 kDa) fractions. PTECs were exposed to 10 mg/ml of the protein fractions for 24, 48 and 72 h. Apoptosis was measured using fluorescein isothiocyanate (FITC)-annexinV and TUNEL. Necrosis was measured using propidium iodide, metabolic activity by MTT and cell proliferation by bromodeoxyuridine incorporation. Fas and FasL expression was analysed by western blotting.

RESULTS

Exposure to the 100-440 and 30-440 kDa fractions produced significant increases in apoptosis at all time points, whereas PTECs exposed to the 30-100 kDa fraction were not significantly different from control cells. There were no changes in the rates of necrosis as a result of protein loading. A significant reduction in metabolic activity was observed in PTECs exposed to the 100-440 and 30-440 kDa fractions, but not to the 30-100 kDa fraction. Cell proliferation was significantly reduced by 24 h in cells exposed to the 100-440 and 30-440 kDa fractions. By 48 and 72 h, all the three fractions had inhibited cell proliferation. PTECs exposed to the 100-440 and the 30-440 kDa fractions showed a significant upregulation in the expression of Fas and FasL. Overall, the high molecular weight fraction was more 'toxic' than the albumin-rich or combined fraction.

CONCLUSION

Increased apoptosis and decreased cell proliferation are the major mechanisms of cell death in human PTECs in response to protein overload. These effects may be mediated at least in part by overexpression of the Fas/FasL system. The severity of such changes is largely determined by the high molecular weight fraction (100-440 kDa) rather than the albumin-rich fraction.

Role of apoptosis in atherosclerosis and its therapeutic implications

Atherosclerotic plaques develop as a consequence of the accumulation of circulating lipid and the subsequent migration of inflammatory cells (macrophages and T-lymphocytes) and VSMCs (vascular smooth muscle cells). Advanced plaques consist of a lipid-rich core, separated from the lumen by a fibrous cap composed of VSMCs, collagen and extracellular matrix. Plaque enlargement ultimately narrows the lumen (stenosis) causing angina. However, recent studies have emphasized that acute coronary syndromes (unstable angina/myocardial infarction) are caused by lesion erosion/rupture with superimposed thrombus formation on often small non-stenotic plaques. Thus current therapies work predominantly on stabilization of plaques rather than plaque regression. Apoptosis (programmed cell death) is increasingly observed as plaques develop, although the exact mechanisms and consequences of apoptosis in the development and progression of atherosclerosis are still controversial. Increased endothelial cell apoptosis may initiate atherosclerosis, whereas apoptosis of VSMCs and macrophages localizes in ‘vulnerable’ lesions, i.e. those most likely to rupture, and at sites of rupture. This review will focus on the regulation of apoptosis of cells within the vasculature, concentrating on the relevance of apoptosis to plaque progression and clinical consequences of vascular cell apoptosis.

Replicative senescence enhances apoptosis induced by pemphigus autoimmune antibodies in human keratinocytes

We have recently shown that skin lesions of the autoimmune disease pemphigus vulgaris are associated with Fas-mediated apoptosis. Here, we describe the induction of the Fas-dependent apoptosis pathway in cultured keratinocytes by pemphigus vulgaris autoantibodies (PV-IgG), as seen from a variety of cellular, morphological and biochemical parameters. All apoptotic characters appear stronger and faster in aged cultures than in young, showing increased susceptibility of senescent keratinocytes to PV-IgG-mediated apoptotic death and culture lesions. Together with immunosenescence, this phenomenon may explain the late onset of pemphigus disease.

Fas ligand down-regulates cytokine-induced Fas receptor expression on insulinoma (NIT-1), but not islet cells, from autoimmune nonobese diabetic mice

In the pathogenesis of autoimmune type 1 diabetes, the apoptosis receptor Fas appears de novo on the surface of insulin-producing beta-cells. Fas expression is thought to be induced by proinflammatory cytokines, such as IL-1beta, interferon-gamma (IFNgamma), and TNFalpha, released by islet-infiltrating mononuclear cells. To determine whether beta-cells can modulate their sensitivity to apoptosis at the level of Fas, we investigated the effect of Fas ligand (FasL) on surface expression of Fas in NIT-1 insulinoma cells from nonobese diabetic (NOD) mice prone to autoimmune diabetes and islet cells from NOD and nonautoimmune BALB/c mice. In NIT-1 insulinoma cells, Fas expression induced by the cytokine combination IL-1beta and IFNgamma was reduced in the presence of FasL, whereas in islet cells Fas expression was unaffected by FasL. The effect of FasL on NIT-1 cells was evident during and after the induction of Fas expression by IL-1beta and IFNgamma. Thus, FasL down-regulates cytokine-induced Fas expression in NOD mouse-derived NIT-1 cells, but not in NOD or BALB/c mouse islets. The ability of NIT-1 cells to down-regulate Fas receptor in response to ligation is similar to that of a variety of tumor cells, which may use this mechanism to escape destruction by cytotoxic T cells. Islets apparently cannot protect themselves against FasL-induced apoptosis by down-regulating the Fas receptor. Understanding how NIT-1 insulinoma cells down-regulate Fas receptor in response to ligation by FasL has therapeutic implications for protecting normal beta-cells in autoimmune type 1 diabetes.

The Fas/Fas ligand system and cancer: immune privilege and apoptosis

The Fas/FasL system has been suggested to play an important role in the establishment of immune privilege status for tumors by inducing Fas-mediated apoptosis in tumor-specific lymphocytes. However, the role of cell-surface expressed FasL in tumor cell protection has recently become controversial. Our laboratory has focused on the study of the role of the Fas/FasL system in the normal tissue remodeling of the female reproductive tract and in immune-privileged organs. Our studies have demonstrated a connection between sex hormones and the regulation of the Fas/FasL pathway in immune and reproductive cells. More recently, we have investigated the resistance of tumor cells to Fas-mediated apoptosis. We have also characterized a new form of FasL, different from the classical membranal form, which is secreted by ovarian cancer cells. In this review we describe the main techniques used in these studies.

The latency-related gene encoded by bovine herpesvirus 1 can suppress caspase 3 and caspase 9 cleavage during productive infection

When the bovine herpesvirus 1 (BHV-1) latency-related (LR) gene is inserted into the latency-associated transcript (LAT) locus of a herpes simplex virus type 1 (HSV-1) LAT deletion mutant, high levels of spontaneous reactivation from latency and enhanced pathogenesis occur. The LR gene, but not LAT, inhibits caspase 3 cleavage during productive infection. Plasmids containing LAT or the LR gene inhibit caspase 3 activation in transiently transfected cells, suggesting productive infection blocks certain antiapoptotic properties of LAT. These studies demonstrate a correlation between the enhanced pathogenic potential of CJLAT and the LR gene inhibiting caspase 3 cleavage during productive infection.

Tumour necrosis factor-alpha and apoptosis in the rat temporomandibular joint

The purpose of this investigation was to investigate the roles that tumour necrosis factor-alpha (TNF-alpha) and apoptosis play during acute inflammation of the temporomandibular joint (TMJ). Adult male Sprague-Dawley rats were injected with complete Freund's adjuvant (CFA) into the TMJ or kept as uninjected controls. The TMJ tissues were removed 2 days post-injection to mimic conditions of acute inflammation and analysed for changes in expression of TNF-alpha, the receptor TNF-R1, caspase-3 and -8, and apoptosis. Concentrations of TNF-alpha, TNF-R1, caspase-3 and -8, and apoptosis were significantly elevated in CFA-injected animals compared to uninjected controls. Tissue incubation with TNF-alpha caused a significant increase in caspase-3 and -8. Also, levels of apoptosis were significantly increased during inflammation, which could be inhibited by the addition of either anti-TNF-alpha neutralising antibody or caspase inhibitors. TNF-alpha may play a significant role in the onset of acute CFA-induced TMJ inflammation, and activation of apoptosis signalling pathways may be involved.