Affinity labeling displays the stepwise activation of ICE-related proteases by Fas, staurosporine, and CrmA-sensitive caspase-8

Defective NOTCH signaling drives increased vascular smooth muscle cell apoptosis and contractile differentiation in bicuspid aortic valve aortopathy: A review of the evidence and future directions

Bicuspid aortic valve (BAV) disease remains the most common congenital cardiac disease and is associated with an increased risk of potentially fatal aortopathy including aortic aneurysm and dissection. Mutations in the NOTCH1 gene are one of only a few genetic anomalies identified in BAV disease; however evidence for defective NOTCH signaling, and its involvement in the characteristic histological changes of VSMC apoptosis and differentiation in ascending aortae of BAV patients is lacking. This review scrutinizes the evidence for the interactions of NOTCH signaling, cellular differentiation and apoptosis in the context of aortic VSMCs and provides focus for future research efforts in the diagnosis of BAV aortopathy and prevention of catastrophic complications through NOTCH signaling manipulation.

Functional Hepatocyte Culture and its Application to Cell Therapies

Since Berry and Friend developed methods to isolate hepatocytes from the liver by a collagenase digestion technique in 1969, studies in laboratory animals have demonstrated that hepatocyte transplantation could potentially be used for the treatment of liver failure and inborn errors of liver-based metabolism. Healthy human hepatocytes are an ideal source for hepatocyte transplantation; however, their relative scarcity is one of the major drawbacks, further compounded by the competing demands of liver transplantation. Notably, most of the hepatocytes are isolated from discarded livers that are not suitable for organ transplantation for a variety of reasons, including excessive fat content. Importantly, the hepatocyte isolation procedure itself exerts major stress on hepatocytes by the disruption of cell-to-cell and cell-to-matrix contacts, resulting in hepatocytic apoptosis. Prevention of apoptosis would maximize yield of healthy cells and maintain hepatocyte differentiated function in culture. In this review, we describe methods to prevent apoptosis by utilizing both antiapoptotic molecules and matrices. We also introduce a new type of liver tissue engineering, hepatocyte sheet transplantation, which utilizes unwoven cloth having a cellular adhesive property.

Sialic acid-binding lectin (leczyme) induces apoptosis to malignant mesothelioma and exerts synergistic antitumor effects with TRAIL

Malignant mesothelioma is a highly aggressive tumor with poor prognosis. An effective drug for treatment of malignant mesothelioma is greatly needed. Sialic acid-binding lectin (SBL) isolated from oocytes of Rana catesbeiana is a multifunctional protein which has lectin activity, ribonuclease activity and antitumor activity, so it could be developed as a new type of anticancer drug. The validity of SBL for treatment of malignant mesothelioma was assessed using three malignant mesotheliomas and a non-malignant mesothlial cell line. Effectiveness of combinatorial treatment of SBL and tumor necrosis factor-related apoptosis inducing ligand (TRAIL) was also elucidated and characterized. SBL induced tumor-selective cytotoxicity that was attributed to induction of apoptosis. Combinatorial treatment of SBL and TRAIL showed synergistic apoptosis-inducing effect. Additional experiments revealed that Bid was the mediating molecule for the synergistic effect in SBL and TRAIL. These results suggested that SBL could be a promising candidate for the therapeutics for malignant mesothelioma. Furthermore, the combinatorial treatment of SBL and TRAIL could be an effective regimen against malignant mesothelioma.

The inflammasome as a target of modulation by DNA viruses

The cellular innate immune response represents the initial reaction of a host against infecting pathogens. Host cells detect incoming microbes by way of a large and expanding array of receptors that react with evolutionarily conserved molecular patterns exhibited by microbial intruders. These receptors are responsible for initiating signaling that leads to both transcriptional activation of immunologically important genes as well as protease-dependent processing of cellular proteins. The inflammasome refers to a protein complex that functions as an activation platform for the cysteine protease caspase-1, which then processes inflammatory molecules such as IL-1β and IL-18 into functional forms. Assembly of this complex is triggered following receptor-mediated detection of pathogen-associated molecules. Receptors have been identified that are essential to inflammasome activation in response to numerous molecular patterns including virus-associated molecules such as DNA. In fact, the importance of cytoplasmic DNA as an immune stimulus is exemplified by the existence of at least nine distinct cellular receptors capable of initiating innate reactivity in response to this molecule. Viruses that employ DNA as genomic material include herpesviruses, poxviruses and adenoviruses. Each has been described as capable of inducing inflammasome-mediated activity. Interestingly, however, the cellular molecules responsible for these responses appear to vary according to host species, cell type and even viral strain. Secretion of IL-1β and IL-18 are important components of antimicrobial immunity and, as a result, pathogens have evolved factors to evade or counteract this response. This includes DNA-based viruses, many of which encode multiple redundant counteractive molecules. However, it is clear that such phenotypes are only beginning to be uncovered. The purpose of this review is to describe what is known regarding the activation of inflammasome-mediated processes in response to infection with well-examined families of DNA viruses and to discuss characterized mechanisms of manipulation and neutralization of inflammasome-dependent activity. This review aims to shed light on the biologically important phenomena regarding this virus-host interaction and to highlight key areas where important information is lacking.

Tubular cell HIV-1 gp120 expression induces caspase 8 activation and apoptosis

Renal biopsy data indicate that tubular epithelial cells serve as a reservoir for HIV-1 infection. We studied the effect of HIV-1 gp120 envelope gene expression on tubular cell apoptosis. HIV-1 gp120 was expressed in a lentiviral vector pHR-CMV-IRES2-EGFP-DeltaB. This plasmid construct was used to produce pseudotyped virus using VSV-G envelope to enhance the tropism for efficient viral transduction. Human proximal tubular (HK-2) cells were transduced and assayed for cellular injury by trypan blue exclusion, Hoechst and PI staining, TUNEL, and cell cycle staging. HIV-1 gp120-transduced HK-2 cells showed cellular injury in a time-dependent manner. Gp120-transduced cells showed 2.5-fold greater apoptosis when compared with vector-transduced cells. Cell cycle analysis did not reveal any alteration between gp120-transduced cells and vector-transduced cells. Gp120-transduced cells showed higher expression of both Fas and FasL, whereas pretreatment with anti-FasL antibody partially inhibited gp120-induced tubular cell apoptosis. Similarly, pretreatment with caspase-8 inhibitor attenuated gp120-induced HK2 cell apoptosis. Moreover, gp120-transduced cells showed activation of caspase 8. These results suggest that HIV-1 gp120 expression induces tubular cell apoptosis through the extrinsic pathway by enhancing Fas and FasL expression and activation of caspase-8.

Contractile response of norepinephrine is modulated by caspase-3 in adult rat ventricular myocytes isolated from septic rat heart

Sepsis accounts for 50% of intensive care unit deaths due to cardiac dysfunction. The cellular mechanisms following norepinephrine (NE) during sepsis are undefined. Using a septic adult rat ventricular myocyte (ARVM) paradigm, we examined the molecular mechanism responsible for the blunted contractile response of NE. We tested the hypothesis that NE-induced increases in active caspase-3 contribute to sepsis-induced ARVM contractile dysfunction. Single ARVMs were isolated from hearts harvested from sham and septic male rats. The contractile properties and expression of caspase-3 cascade proteins were determined in ARVMs treated with NE with and without QVD-OPH, prazosin and atenolol to characterize the effect of NE on their mechanical properties. Septic ARVMs exhibited a significant decrease in peak shortening (PS) compared to sham ARVMs. The effect of NE on the PS of the sham ARVMs was more pronounced compared to the septic ARVMs, suggesting a blunted contractile response of NE. NE in the presence of QVD-OPH ameliorated the sepsis-induced decrease in PS at 18h but not at 1h, while the effect of NE on sepsis-induced contractile response remained unaffected at 18h by prazosin and atenolol. An up-regulated expression of caspase-3 in NE-treated septic ARVMs was reversed by QVD-OPH, as seen by the increased number of septic ARVMs exhibiting caspase-3 fluorescence. Transfection of ARVMs using caspase-3 siRNA blocked sepsis-induced up-regulation of caspase-3 and increased PS following NE treatment. These data suggest that caspase-3 inhibition ameliorated sepsis-induced decreased ARVM contractility and blocked the blunted contractile response of NE.

Structural and functional definition of the specificity of a novel caspase-3 inhibitor, Ac-DNLD-CHO

Background

The rational design of peptide-based specific inhibitors of the caspase family members using their X-ray crystallographies is an important strategy for chemical knockdown to define the critical role of each enzyme in apoptosis and inflammation. Recently, we designed a novel potent peptide inhibitor, Ac-DNLD-CHO, for caspase-3 using a new computational screening system named the Amino acid Positional Fitness (APF) method (BMC Pharmacol. 2004, 4:7). Here, we report the specificity of the DNLD sequence against caspase-3 over other major caspase family members that participate in apoptosis by computational docking and site-directed mutagenesis studies.

Results

Ac-DNLD-CHO inhibits caspases-3, -7, -8, and -9 activities with K_i^app values of 0.68, 55.7, >200, and >200 nM, respectively. In contrast, a well-known caspase-3 inhibitor, Ac-DEVD-CHO, inhibits all these caspases with similar K_i^app values. The selective recognition of a DNLD sequence by caspase-3 was confirmed by substrate preference studies using fluorometric methylcoumarin-amide (MCA)-fused peptide substrates. The bases for its selectivity and potency were assessed on a notable interaction between the substrate Asn (N) and the caspase-3 residue Ser209 in the S₃ subsite and the tight interaction between the substrate Leu (L) and the caspase-3 hydrophobic S₂ subsite, respectively, in computational docking studies. Expectedly, the substitution of Ser209 with alanine resulted in loss of the cleavage activity on Ac-DNLD-MCA and had virtually no effect on cleaving Ac-DEVD-MCA. These findings suggest that N and L residues in Ac-DNLD-CHO are the determinants for the selective and potent inhibitory activity against caspase-3.

Conclusion

On the basis of our results, we conclude that Ac-DNLD-CHO is a reliable, potent and selective inhibitor of caspase-3. The specific inhibitory effect on caspase-3 suggests that this inhibitor could become an important tool for investigations of the biological function of caspase-3. Furthermore, Ac-DNLD-CHO may be an attractive lead compound to generate novel effective non-peptidic pharmaceuticals for caspase-mediated apoptosis diseases, such as neurodegenerative disorders and viral infection diseases.

Measurement of two caspase activities simultaneously in living cells by a novel dual FRET fluorescent indicator probe

BACKGROUND

A number of fluorescent caspase substrates and FRET-based indicators have been developed to study the in vivo activation of caspases, a conserved family of proteases critical in inflammatory, and apoptosis signaling pathways. To date, all substrates have measured only one caspase activity. Here, we describe a FRET-based probe for simultaneously measuring two distinct caspase activities in living cells.

METHODS

This probe consists of a CFP-YFP-mRFP fusion protein containing a caspase-3-cleavage motif, DEVD, between CFP and YFP, and a caspase-6-cleavage site, VEID, between YFP and mRFP. DEVDase and VEIDase activities could be assessed simultaneously by monitoring diminished FRET mediated by cleavage of either or both of these protease cleavage sites using flow cytometry.

RESULTS

DEVDase and VEIDase activities were completely inhibited by the pan-caspase inhibitor z-VAD-fmk and enhanced by DNA-damaging drugs or by anti-Fas stimulation. DEVD and VEID cleavage specificities were validated by using caspase-3-deficient MCF7-Fas cells and a caspase-6-specific inhibitor. Kinetic analysis with the FRET probe revealed that caspase-3 activation consistently preceded caspase-6 by approximately 30 min following induction of apoptosis.

CONCLUSIONS

We have developed a novel FRET-based probe for simultaneous detection of two caspase activities in living cells using flow cytometry. Simultaneous detection of two caspase activities using this probe has clearly provided information of the ordering of caspase-3 and -6 in the apoptotic pathway.

Sequential activation of caspases and synergistic beta-cell cytotoxicity by palmitate and anti-Fas antibodies

To assess the mechanism of beta-cell lipotoxicity in comparison with Fas-mediated cell death, we used a mouse beta-cell clone stably transfected with human Fas. Palmitate induced beta-cell death in correlation with medium glucose levels between 5 and 20 mmol/l, while Fas-mediated cytotoxicity was observed irrespective of glucose concentration. At the glucose level of 10 mmol/l, palmitate induced caspase-6 activity within 3 h, and caspase-3 activity after a lag period of 6 h. The activities of caspases were correlated with glucose concentration. A caspase-6 inhibitor attenuated caspase-3 activation and cell death induced by palmitate. Oxfenicine, an inhibitor of carnitine palmitoyltransferase-1, attenuated both palmitate-induced cytotoxicity and activation of caspases. Finally, beta-cell cytotoxicity caused by the combination of anti-Fas and palmitate at 25 mmol/l of glucose was greater than the sum of those induced by each. These observations suggest that palmitate induces sequential activation of caspase-6 and caspase-3 through a mitochondrial signal(s), and caspase-6 plays a primary role in the mechanism. Fas-mediated beta-cell death and lipotoxicity may share common mechanisms involving caspase activation, and thereby synergistically inducing beta-cell death, although upstream signaling pathways are distinct.

Expression of multidrug resistance proteins and accumulation of cisplatin in human non-small cell lung cancer cells

In order to understand and overcome multidrug resistance (MDR) of human non-small cell lung cancer (NSCLC), mRNA and protein expression levels of P-glycoprotein (MDR1), multidrug resistance-associated protein 1 (MRP1), and lung resistance-related protein (LRP) were investigated and compared with the chemosensitivity and the intracellular/intranuclear cisplatin accumulation of three NSCLC cell lines (Ma-10, Ma-31, and Ma-46). Ma-31 was more resistant than Ma-10 and Ma-46 to cisplatin, carboplatin, etoposide, and paclitaxel. The mRNA level of MDR1 was extremely low, and MDR1 protein was not detected in all cell lines. MRP1 mRNA expression was highest in Ma-31 and lowest in Ma-10, but there was no notable difference between the MRP1 protein expression in three cell lines. LRP mRNA/protein was equally expressed in Ma-10 and Ma-31, but was nominal in Ma-46. The intracellular/intranuclear cisplatin accumulation of the cells was determined to be Ma-31>Ma-46>Ma-10. Thus, MDR1, MRP1, and LRP mRNA and protein expression levels were not correlated with the chemosensitivity or the intracellular/intranuclear cisplatin accumulation of each cell line. The present results indicate that MDR proteins (MDR1, MRP1, and LRP) may not play an important role in the chemoresistance and drug efflux of NSCLC cells.

Molecular Mechanism of Hepatic Injury in Coinfection with Hepatitis C Virus and HIV

We have previously shown that hepatocytes exposed to hepatitis C virus (HCV) and human immunodeficiency virus (HIV) envelope proteins undergo apoptosis. In this article, we further elucidate the signaling mechanisms that mediate this effect. We found that, in human hepatocellular carcinoma (HepG2) cells, HCV E2 protein and HIV glycoprotein (gp) 120 significantly up-regulated the Fas ligand (FasL) and enhanced the formation of the Fas death-inducing signaling complex downstream of Fas receptor activation. Moreover, after stimulation with HCV E2 and HIV gp120, enhanced expression of caspases 2 and 7 and increased caspase 3 activity were observed. In addition, we showed up-regulation of the proapoptotic molecule Bid and its association with caspase 8 after treatment with these envelope proteins. We also found that HCV E2 and HIV gp120 induced a partial translocation of Bid to the mitochondria, which resulted in the release of cytochrome C and the apoptosis-inducing factor. Thus, the results of this study suggest that FasL and Bid play an important role in HCV and HIV envelope protein-induced apoptosis.

Maspin overexpression modulates tumor cell apoptosis through the regulation of Bcl-2 family proteins

BACKGROUND

Maspin is a member of serpin family with tumor suppressing activity. Recent studies of maspin in animal models strongly support maspin's role as an inhibitor against the growth of primary tumor sand the process of metastasis. However, the molecular mechanism underlying this inhibition has not been fully elucidated. In this report, we analyze the effect of maspin on tumor cell apoptosis under several stress conditions.

METHODS

Stable clones overexpressing maspin are established in the mouse mammary tumor TM40D cells. They are treated with staurosporine, TNF-alpha, and serum starvation. The rates of cell apoptosis are analyzed by TUNEL assay. Inhibitors against caspase 8 and 9 are used in the apoptosis assay. Western blot analysis and ribonuclease protection assay (RPA) are performed to examine the expression of Bcl2 family genes.

RESULTS

We report that maspin expressing tumor cells have increased rate of apoptosis when they are treated with staurosporine and serum starvation. The effect is not through extracellular maspin. Maspin-mediated apoptosis is partially blocked by caspase 8 and 9 inhibitors, and is accompanied by changes in the Bcl-2 family proteins. Maspin-expressing tumor cells have a reduced level of anti-apoptotic protein Bcl-2, and an increased level of pro-apoptotic protein Bax. The regulation is not controlled at the transcriptional level but is through selective control of Bcl-2 and Bax protein stability.

CONCLUSION

Maspin overexpression modulates tumor cell apoptosis through the regulation of Bcl2 family proteins. Such change results in an increased release of cytochrome c from mitochondria, thus the increased apoptosis in maspin-expressing cells. This evidence strongly suggests that the induction of apoptosis in maspin-overexpressing cells represents a major mechanism by which maspin inhibits breast tumor progression.

Protective effects of intracellular reactive oxygen species generated by 6-formylpterin on tumor necrosis factor-alpha-induced apoptotic cell injury in cultured rat hepatocytes

The effects of 6-formylpterin on tumor necrosis factor (TNF)-alpha-induced apoptotic cell injury were studied in cultured rat hepatocytes. The incubation of the hepatocytes with TNF-alpha and actinomycin D (ActD) induced the apoptotic cell injury. The level of aspartate transaminase (AST) in the culture supernatant increased, and the cell viability, estimated by mitochondrial respiration (MTT assay), decreased. The DNA fragmentation and the caspase 3-like activity, which are characterized to apoptosis, increased. When the hepatocytes were incubated with 100-500 microM 6-formylpterin, the intracellular formation of reactive oxygen species (ROS) was observed, and the ratio of reduced and oxidized glutathione (GSH/GSSG) of whole cell lysate decreased. The co-incubation of the TNF-alpha/ActD-treated hepatocytes with 100-500 microM 6-formylpterin attenuated the TNF-alpha/ActD-induced apoptotic cell injury. The level of AST decreased and the cell viability increased. Both the DNA fragmentation and the caspase 3-like activity decreased. The caspases, executors of apoptosis, are known to require a reduced cystein in their active site to function, and the intact intracellular GSH/GSSG is essential for the caspase activation. Therefore, our findings suggest that intracellular ROS generated by 6-formylpterin decline the intracellular redox state to an oxidant state, which suppresses the caspase activity and prevents the apoptotic cell injury of hepatocytes.

Relationship of acute lung inflammatory injury to Fas/FasL system

There is mounting evidence that apoptosis plays a significant role in tissue damage during acute lung injury. To evaluate the role of the apoptosis mediators Fas and FasL in acute lung injury, Fas (lpr)- or FasL (gld)-deficient and wild-type mice were challenged with intrapulmonary deposition of IgG immune complexes. Lung injury parameters ((125)I-albumin leak, accumulation of myeloperoxidase, and wet lung weights) were measured and found to be consistently reduced in both lpr and gld mice. In wild-type mice, lung injury was associated with a marked increase in Fas protein in lung. Inflamed lungs of wild-type mice showed striking evidence of activated caspase-3, which was much diminished in inflamed lungs from lpr mice. Intratracheal administration of a monoclonal Fas-activating antibody (Jo2) in wild-type mice induced MIP-2 and KC production in bronchoalveolar lavage fluids, and a murine alveolar macrophage cell line (MH-S) showed significantly increased MIP-2 production after incubation with this antibody. Bronchoalveolar lavage fluid content of MIP-2 and KC was substantially reduced in lpr mice after lung injury when compared to levels in wild-type mice. These data suggest that the Fas/FasL system regulates the acute lung inflammatory response by positively affecting CXC-chemokine production, ultimately leading to enhanced neutrophil influx and tissue damage.

NO means no and yes: regulation of cell signaling by protein nitrosylation

Protein nitrosylation is emerging as a key mechanism by which nitric oxide regulates cell signaling. Nitrosylation is the binding of a NO group to a metal or thiol (-SH) on a peptide or protein. Like phosphorylation, nitrosylation is a precisely targeted and rapidly reversible posttranslational modification that allows cells to flexibly and specifically respond to changes in their environment. An increasing number of proteins have been identified whose activity is regulated by intracellular nitrosylation. This review focuses on proteins regulated by endogenous nitrosylation, the chemistry underlying nitrosylation, the specificity and reversibility of nitrosylation reactions, methods to detect protein nitrosylation, and the role of coordinated protein nitrosylation/denitrosylation in cell signaling.

Role of caspases in renal tubular epithelial cell injury

The regulation of cell death has been investigated in a number of clinical disorders including renal ischemic and toxic acute renal failure. Caspases play a crucial role in the execution or final phase of cell death by cleaving and inactivating various structural and functional intracellular proteins that are essential for cell survival and proliferation. Evidence is now emerging to implicate the caspase pathway in a variety of renal diseases including the pathogenesis of acute renal failure. Among the 14 known members of the caspase family thus far identified several executioner caspases including caspases-3, -6, and -7 and the proinflammatory caspase including caspase-1 may participate in the final degradation of intracellular proteins. The activation of these caspases is regulated by the receptor- and mitochondrial-mediated cell signaling pathways as well as by the endoplasmic reticulum stress response. While the role of some caspases in renal injury is emerging, the roles of various proinflammatory and other executioner caspases remain to be determined. Although many pro- and anti-apoptotic molecules that act upstream of caspase activation have been identified, their regulation is yet to be determined in the pathogenesis of renal injury. A precise description of caspase-mediated cell death pathway and regulation of caspase activation is, therefore, critical to the understanding of the mechanism of renal injury and to the development of therapeutic targets that prevent renal diseases and preserve renal function.

Fas-associated factor 1, FAF1, is a member of Fas death-inducing signaling complex

FAF1 has been introduced as a Fas-binding protein. However, the function of FAF1 in apoptotic execution is not established. Based on the fact that FAF1 is a Fas-binding protein, we asked if FAF1 interacted with other members of the Fas-death-inducing signaling complex (Fas-DISC) such as Fas-associated death domain protein (FADD) and caspase-8. FAF1 could interact with caspase-8 and FADD in vivo as well as in vitro. The death effector domains (DEDs) of caspase-8 and FADD interacted with the amino acid 181-381 region of FAF1, previously known to have apoptotic potential. Considering that FAF1 directly binds to Fas and caspase-8, FAF1 shows similar protein-interacting characteristics to that of FADD. In the coimmunoprecipitation with an anti-Fas antibody (APO-1) in Jurkat cells, endogenous FAF1 was associated with the precipitates in which caspase-8 was present. By confocal microscopic analysis, both Fas and FAF1 were detected in the cytoplasmic membrane before Fas activation, and in the cytoplasm after Fas activation. FADD and caspase-8 colocalized with Fas in Jurkat cells validating the presence of FAF1 in the authentic Fas-DISC. Overexpression of FAF1 in Jurkat cells caused significant apoptotic death. In addition, the FAF1 deletion mutant lacking the N terminus where Fas, FADD, and caspase-8 interact protected Jurkat cells from Fas-induced apoptosis demonstrating dominant-negative phenotype. Cell death by overexpression of FAF1 was suppressed significantly in both FADD- and caspase-8-deficient Jurkat cells when compared with that in their parental Jurkat cells. Collectively, our data show that FAF1 is a member of Fas-DISC acting upstream of caspase-8.

Effects of 6-formylpterin as an internal source of hydrogen peroxide on cell death of human peripheral blood leukocytes

The intracellular generation of hydrogen peroxide (H(2)O(2)) by 6-formylpterin and its effects on the cell surface exposure of phosphatidylserine (PS) as a marker of cell death were examined in human peripheral blood leukocytes, and the effects were compared with those of exogenously administered H(2)O(2). Neutrophils, monocytes and lymphocytes were isolated from fresh blood, and cultured for 24 h in vitro. In neutrophils, the intracellular H(2)O(2) generation was observed when the cells were incubated with 100-500 microM 6-formylpterin, and the PS exposure due to spontaneous apoptosis was inhibited. The underlying mechanism of the inhibition was attributed to the suppression of both activation and activity of caspase-3. On the other hand, exogenously administered 100 microM H(2)O(2) did not affect the PS exposure. The intracellular H(2)O(2) generation was also observed in monocytes and lymphocytes. In monocytes, 500 microM 6-formylpterin induced more PS exposure than 100 microM H(2)O(2) did. In lymphocytes, up to 500 microM 6-formylpterin did not induce conspicuous PS exposure, while 100 microM H(2)O(2) induced severe PS exposure. These findings indicated that the resistance against an internal and external source of H(2)O(2) are different among leukocytes, for example, lymphocytes are poorly resistant against external H(2)O(2) but highly resistant against internal one.

Nitrosylation of cytochrome c during apoptosis

Cytochrome c released from mitochondria into the cytoplasm plays a critical role in many forms of apoptosis by stimulating apoptosome formation and subsequent caspase activation. However, the mechanisms regulating cytochrome c apoptotic activity are not understood. Here we demonstrate that cytochrome c is nitrosylated on its heme iron during apoptosis. Nitrosylated cytochrome c is found predominantly in the cytoplasm in control cells. In contrast, when cytochrome c release from mitochondria is inhibited by overexpression of the anti-apoptotic proteins B cell lymphoma/leukemia (Bcl)-2 or Bcl-X(L), nitrosylated cytochrome c is found in the mitochondria. These data suggest that during apoptosis, cytochrome c is nitrosylated in mitochondria and then rapidly released into the cytoplasm in the absence of Bcl-2 or Bcl-X(L) overexpression. In vitro nitrosylation of cytochrome c increases caspase-3 activation in cell lysates. Moreover, the inhibition of intracellular cytochrome c nitrosylation is associated with a decrease in apoptosis, suggesting that cytochrome c nitrosylation is a proapoptotic modification. We conclude that nitrosylation of the heme iron of cytochrome c may be a novel mechanism of apoptosis regulation.

Ceramide increases oxidative damage due to inhibition of catalase by caspase-3-dependent proteolysis in HL-60 cell apoptosis

We investigated through which mechanisms ceramide increased oxidative damage to induce leukemia HL-60 cell apoptosis. When 5 microm N-acetylsphingosine (C(2)-ceramide) or 20 microm H(2)O(2) alone induced little increase of reactive oxygen species (ROS) generation as judged by the 2'-7'-dichlorofluorescin diacetate method, 20 microm H(2)O(2) enhanced oxidative damage as judged by ROS accumulation, and thiobarbituric acid-reactive substance production after pretreatment with 5 microm C(2)-ceramide at least for 12 h. The treatment with a catalase inhibitor, 3-amino-1h-1,2,4-triazole, increased oxidative damage and apoptosis induced by H(2)O(2), and in contrast, purified catalase inhibited the enhancement of oxidative damage by H(2)O(2) in ceramide-pretreated cells, suggesting that the oxidative effect of ceramide is involved in catalase regulation. Indeed, C(2)-ceramide inhibited the activity of immunoprecipitated catalase and decreased the levels of catalase protein in a time-dependent manner. Moreover, acetyl-Asp-Met-Gln-Asp-aldehyde, which dominantly inhibited caspase-3 and blocked the increase of oxidative damage and apoptosis due to C(2)-ceramide-induced catalase depletion at protein and activity levels. In vitro, active and purified caspase-3, but not caspase-6, -8, and -9, inhibited catalase activity and induced the proteolysis of catalase protein whereas these in vitro effects of caspase-3 were blocked by acetyl-Asp-Met-Gln-Asp-aldehyde. Taken together, it is suggested that H(2)O(2) enhances apoptosis in ceramide-pretreated cells, because ceramide increases oxidative damage by inhibition of ROS scavenging ability through caspase-3-dependent proteolysis of catalase.

Caspase inhibitors as anti-inflammatory and antiapoptotic agents

The striking efficacy of Z-VAD-fmk in the various animal models presented above may reflect its ability to inhibit multiple enzymes including caspases. In accord with this, more selective, reversible inhibitors usually show low efficacy in multifactorial models such as ischaemia, but may offer some protection against NMDA-induced excitotoxicity and hepatitis. Importantly, caspase inhibitors may exhibit significant activity in vivo even when they are applied post insult. As far as the CNS is concerned, the first systemically active inhibitors have emerged. Functional recovery could be achieved in some ischaemia models, but long-term protection by caspase inhibitors is still being questioned. Recent developments in drug design enabled the first caspase inhibitors to enter the clinic. Although initially directed towards peripheral indications such as rheumatoid arthritis, caspase inhibitors will no doubt eventually be used to target CNS disorders. For this purpose the peptidic character of current inhibitors will have to be further reduced. Small molecule, nonpeptidic caspase inhibitors, which have appeared recently, indicate that this goal can be accomplished. Unfortunately, many fundamental questions still remain to be addressed. In particular, the necessary spectrum of inhibitory activity required to achieve the desired effect needs to be determined. There is also a safety aspect associated with prolonged administration. Therefore, the next therapeutic areas for broader-range caspase inhibitors are likely to involve acute treatment. Recent results with synergistic effects between MK-801 and caspase inhibitors in ischaemia suggest that caspase inhibitors may need to be used in conjunction with other drugs. It can be expected that, in the near future, research on caspases and their inhibitors will remain a rapidly developing area of biology and medicinal chemistry. More time, however, may be needed for the first caspase inhibitors to appear on the market.

Study of caspase inhibitors for limiting death in mammalian cell culture

Apoptosis in mammalian cell culture is associated with decreased bioproduct yields and can be inhibited through altering the intracellular signaling pathways mediating programmed cell death. In this study, we evaluated the capacity to inhibit caspases to maintain high viable cell numbers in CHO and 293 cultures. Two genetic caspase inhibitors, XIAP and CrmA, were examined along with a mutant of each, XIAP-BIR123NC, which contains three BIR domains but lacks the RING finger, and CrmA-DQMD, which has CrmA's pseudosubstrate site replaced with that of another caspase inhibitor, p35. Stable CHO pooled and 293 clonal cell lines expressing each protein were exposed to apoptotic insults, including spent medium, Sindbis virus, and etoposide. For each insult the mutated protein resulted in higher viabilities than its wild-type counterpart. However, the mutants provided different levels of protection, depending on the insult considered. CrmA-DQMD was the preferred inhibitor for spent medium-induced apoptosis, whereas XIAP-BIR123NC conferred better protection for etoposide-induced death. Addition of Z-VAD.fmk to the genetically engineered cells enhanced viabilities in the presence of spent medium or etoposide; however, the largest increases in viability were experienced by the control cells, indicating an overlap in caspase inhibition between the genetic and chemical inhibitors. Finally, parental 293 cells were treated with caspase-8 and -9 inhibitors, Z-IETD.fmk and Z-LEHD.fmk, in concert with spent medium or etoposide exposure. Spent medium-induced death was delayed more readily with the caspase-8 inhibitors, CrmA-DQMD and Z-IETD.fmk, and etoposide-induced death was stalled more so with XIAP-BIR123NC and Z-LEHD.fmk. These results suggest that the apoptosis pathways induced and the level of protection afforded by a particular caspase inhibitor may vary with the insult considered.

Downregulation of uPA inhibits migration and PI3k/Akt signaling in glioblastoma cells

The ability of glioma cells to migrate great distances from a primary tumor mass is the primary cause of tumor recurrence. The urokinase-type plasminogen activator (uPA) is a serine protease that can initiate proteolytic cascades, which result in remodeling of extracellular matrix and basement membrane, allowing cells to move across and through these barriers. The binding between uPA and its receptor uPAR also mediates several signaling events that seem to contribute to the evolution of a migratory phenotype. In this study, we determined how the downregulation of uPA affects the signaling pathways leading to cell migration. Stably transfecting human glioblastoma cells with antisense uPA decreased the amount of cell-bound uPA and disrupted actin cytoskeleton formation and cell migration. The phosphatidylinositol 3-kinase (PI3k) and Akt signaling pathway has been suggested to mediate migration in various cancer cells. The antisense-uPA clones also had less phosphorylated PI3k and Akt than control cells, a finding associated with decreased cell migration, G2/M-phase arrest, and decreased clonogenic survival. Decreased activation of PI3k and the antiapoptotic factor Akt was not sufficient to induce apoptosis in the antisense-uPA clones, but staurosporine sensitized them to apoptosis to a greater extent than control cells. These results indicate that PI3k/Akt pathway is involved in the signaling cascade required to induce cell migration and that uPA has a direct role in regulating migration.

Sauchinone, a Lignan from Saururus chinensis, Inhibits Staurosporine-Induced Apoptosis in C6 Rat Glioma Cells

Neuronal apoptosis may contribute to pathologic neuronal loss in certain disease states such as neurodegenerative diseases. Staurosporine (ST), a nonselective protein kinase inhibitor, has been shown to induce apoptosis in a variety of cells including nerve cell lines. In this study, we investigated the neuroprotective effect of sauchinone, which is a unique lignan from Saururus chinensis, on ST-induced apoptosis in C6 rat glioma cells. Sauchinone attenuated ST-induced apoptosis of C6 glioma cells as evidenced by DNA fragmentation. We also provide evidence that the inhibitory effect of sauchinone on ST-induced apoptosis involves a dose-dependent upregulation of an antiapoptotic protein, Bcl-2. Mounting evidence shows that the activation of caspases, especially caspase-3, triggers the apoptotic process. The activity of caspase-3 of ST-pretreated cells was significantly decreased upon sauchinone treatment in a dose-dependent manner. Taken together, the data demonstrate that sauchinone protects C6 glioma cells from ST-induced apoptosis in a caspase-3 dependent manner. Our findings may be critical for developing a strategy to protect nerve cells from apoptosis, suggesting the potential development of sauchinone as a neuroprotective agent.

Apoptotic mechanisms in T47D and MCF-7 human breast cancer cells

To investigate the mechanisms underlying apoptosis in breast cancer cells, staurosporine was used as an apoptotic stimulus in the human breast cancer cell lines MCF-7 and T47D. Staurosporine induced dose and time dependent increases in DNA fragmentation which was abrogated by z-VAD-fmk. MCF-7 cells did not express caspase-3, suggesting that DNA fragmentation occurred in the absence of caspase-3 and that other caspases may be involved. Staurosporine induced DEVDase activity in T47D cells suggesting the involvement of caspase-3 and/or caspase-7, yet there was no DEVDase activity in MCF-7 cells, probably ruling out the involvement caspase-7. However, staurosporine induced the cleavage of pro-caspase-6 in MCF-7 cells, but not in T47D cells. Caspase dependent PARP cleavage was detected in MCF-7 cells at 3 h, whereas only partial PARP cleavage was detected in T47D cells and then only after 24 h. Moreover, staurosporine led to cytochrome c release at 2 h in MCF-7 cells and 6 h in T47D cells. In addition, a time dependent and caspase-independent reduction of the mitochondrial transmembrane potential was observed; which appeared to occur after the release of cytochrome c. Translocation of Bax from the cytosol to mitochondria was observed in both cell types, and this preceded cytochrome c release in both T47D and MCF-7 cells. Apoptotic events in both cell types differ temporally, involving activation of different caspases and mitochondrial changes.

Calpain-mediated X-linked inhibitor of apoptosis degradation in neutrophil apoptosis and its impairment in chronic neutrophilic leukemia

The number of neutrophils in the blood and tissues is controlled by constitutive apoptotic programmed cell death and clearance by phagocytes such as macrophages. Here, we found that calpains cleave the X-linked inhibitor of apoptosis (XIAP) in vitro, producing fragments that are unable to inhibit caspase-3. These fragments were detected in normal neutrophils but were unstable and rapidly degraded. Calpain inhibition delayed tumor necrosis factor-alpha-induced apoptosis of normal neutrophils, consistent with a role for calpains in regulating the onset of apoptosis. Interestingly, neutrophils from three patients with chronic neutrophilic leukemia, a rare syndrome characterized by accumulation of mature neutrophils, exhibited decreased mu-calpain expression, diminished calpain activity, and impaired XIAP degradation. Neutrophils from these patients displayed a delay in spontaneous, Fas-stimulated, and tumor necrosis factor-alpha-induced apoptosis. These observations suggest that calpain-mediated XIAP degradation contributes to initiation of apoptosis in normal neutrophils and dysfunction of this regulatory pathway can lead to pathological neutrophil accumulation.

In situ activation of caspases and serine proteases during apoptosis detected by affinity labeling their enzyme active centers with fluorochrome-tagged inhibitors

Activation of caspases is the key event of apoptosis. To detect this event in situ we applied fluorochrome-labeled inhibitors of caspases (FLICA) as affinity labels of active centers of these enzymes. The FLICA are fluorescein- or sulforhodamine-conjugated peptide-fluoromethyl ketones that covalently, with 1:1 stoichiometry, bind to enzymatic centers of caspases; the specificity is provided by the peptide sequence of amino acids. Similarly, we applied fluorescent inhibitors of serine proteases (FLISP) to detect active sites of the latter enzymes. Exposure of live cells to FLICA of FLISP led to uptake of these ligands and their binding to activated caspases or active sites of serine proteases; the unbound reagents were removed by cell rinse. Only cells undergoing apoptosis were labeled with FLISP or FLICA. Intracellular binding sites of FLICA are consistent with known localization of caspases. Covalent binding of FLICA or FLISP allowed us to identify the labeled proteins by immunoblotting: the proteins that bound individual FLICAs had molecular weight between 17 and 22 kDa, which corresponds to large subunits of the caspases; two proteins reacting with FLISP were about 57 and 60 kDa, which suggests that they are novel enzymes. Detection of caspases or serine proteases activation can be combined with other markers of apoptosis or cell cycle for multiparametric analysis by flow or laser scanning cytometry. Being caspase inhibitors, FLICA arrest the process of apoptosis and prevent cell disintegration. The stathmo-apoptotic assay was developed, therefore, to obtain cumulative apoptotic index over a long period of time and estimate a rate of cell entry into apoptosis for cell populations.

Eicosapentaenoic acid promotes apoptosis in Ramos cells via activation of caspase-3 and -9

Eicosapentaenoic acid (EPA; 20:5n-3) may reduce the cell number in cultured leukemia/lymphoma cells owing to reduced cell proliferation, induction of cell death, or a combination of these processes. EPA has been shown to promote apoptosis in Ramos cells, and our present study was focused on a possible cell cycle arrest and the pathways by which the apoptotic process is induced. Apoptosis may proceed along the intrinsic (mitochondrial) or the extrinsic (death receptor) pathway, which are mediated via different caspases. Caspases are a class of homologous cysteine proteases recognized as pivotal mediators of apoptosis. We investigated whether EPA affects progression of the cell cycle or promotes apoptosis directly. By incorporation of [3H]thymidine and [3H]valine, we showed that DNA, as well as protein synthesis, was reduced after incubation of Ramos cells with EPA for 6 h. We monitored cell cycle distribution by 5-bromo-2'-deoxyuridine staining and observed no cell cycle arrest in the EPA-incubated cells. Incubation of cells with EPA caused PS-flipping, as demonstrated by annexin V-binding (flow cytometry), and cleavage of poly(ADP-ribose) polymerase measured by Western blot analysis. Furthermore, we observed increased activity of caspase-3 and -9, but not of caspase-8. Whereas inhibitors of caspase-3 and -9 reduced EPA-induced apoptosis, inhibition of caspase-8 did not. This suggests that EPA may promote apoptosis via the intrinsic pathway in Ramos cells. Thus, the reduction in cell number can be explained by a direct apoptotic effect of EPA rather than via cell cycle arrest.

A selective plasmin inhibitor, trans-aminomethylcyclohexanecarbonyl-L-(O-picolyl)tyrosine-octylamide (YO-2), induces thymocyte apoptosis

The treatment of rat thymocytes with YO-2, a novel inhibitor of plasmin, resulted in an increase in DNA fragmentation. DNA fragmentation was also induced by another YO compounds such as YO-0, -3, -4 and -5. These YO compounds are the inhibitor of plasmin activity. On the other hand, YO-1, -6 and -8 that hardly inhibit plasmin activity had no effect on DNA fragmentation. Analysis of fragmented DNA from thymocytes treated with YO-2 by agarose gel electrophoresis revealed that the compound caused internucleosomal DNA fragmentation. In addition, judging from a laser scanning microscopy, annexin V-positive and propidium iodide-negative cells were increased by the treatment of the cells with the compound. Moreover, chromatin condensation was observed in thymocytes treated with the compound. These results demonstrated that YO-2 induces thymocyte apoptosis. There seemed to be some correlation between the apoptosis induced by YO compounds and their plasmin inhibitory effect. However, because the other protease inhibitors including pepstatin A, leupeptin, AEBSF, DFP and E-64-d did not affect DNA fragmentation, YO compounds are likely to have unique mechanism on plasmin or to show the effect on the other plasmin-like proteases. The plasmin inhibitory activity may have an important role in YO-2-induced apoptosis. Furthermore, the stimulations of caspase-8, -9 and -3-like activities were observed in thymocytes treated with YO-2. These results suggest that YO-2 induces thymocyte apoptosis via activation of caspase cascade.

Use of fluorescently labeled caspase inhibitors as affinity labels to detect activated caspases

Activation of caspases is the key event of apoptosis and different approaches were developed to assay it. To detect their activation in situ, we applied fluorochrome labeled inhibitors of caspases (FLICA) as affinity labels of active centers of these enzymes. The FLICA ligands are fluorescein or sulforhodamine conjugated peptide-fluoromethyl ketones that covalently bind to enzymatic centers of caspases with 1:1 stoichiometry. The specificity of FLICA towards individual caspases is provided by the peptide sequence of amino acids. Exposure of live cells to FLICA results in uptake of these ligands and their binding to activated caspases; unbound FLICA is removed by cell rinse. Cells labeled with FLICA can be examined by fluorescence microscopy or subjected to quantitative analysis by cytometry. Intracellular binding sites of FLICA are consistent with known localization of caspases. Covalent binding of FLICA allowed us to identify the labeled proteins by immunoblotting: the proteins that bound individual FLICAs had molecular weight between 17 and 22 kDa, which corresponds to large subunits of the caspases. Detection of caspases activation by FLICA can be combined with other markers of apoptosis or cell cycle for multiparametric analysis. Because FLICA are caspase inhibitors they arrest the process of apoptosis preventing cell disintegration. The stathmo-apoptotic method was developed, therefore, that allows one to assay cumulative apoptotic index over long period of time and estimate the rate of cell entry into apoptosis for large cell populations. FLICA offers a rapid and convenient assay of caspases activation and can also be used to accurately estimate the incidence of apoptosis.

Lack of correlation between caspase activation and caspase activity assays in paclitaxel-treated MCF-7 breast cancer cells

MCF-7 human breast cancer cells are widely utilized to study apoptotic processes. Recent studies demonstrated that these cells lack procaspase-3. In the present study, caspase activation and activity were examined in this cell line after treatment with the microtubule poison paclitaxel. When cells were harvested 72 h after the start of a 24-h treatment with 100 nm paclitaxel, 37 +/- 5% of the cells were nonadherent and displayed apoptotic morphological changes. Although mitochondrial cytochrome c release and caspase-9 cleavage were detectable by immunoblotting, assays of cytosol and nuclei prepared from the apoptotic cells failed to demonstrate the presence of activity that cleaved the synthetic caspase substrates LEHD-7-amino-4-trifluoromethylcoumarin (LEHD-AFC), DEVD-AFC, and VEID-AFC. Likewise, the paclitaxel-treated MCF-7 cells failed to cleave a variety of caspase substrates, including lamin A, beta-catenin, gelsolin, protein kinase Cdelta, topoisomerase I, and procaspases-6, -8, and -10. Transfection of MCF-7 cells with wild type procaspase-3 partially restored cleavage of these polypeptides but did not result in detectable activities that could cleave the synthetic caspase substrates. Immunoblotting revealed that caspase-9, and -3, which were proteolytically cleaved in paclitaxel-treated MCF-7/caspase-3 cells, were sequestered in a salt-resistant sedimentable fraction rather than released to the cytosol. Immunofluorescence indicated large cytoplasmic aggregates containing cleaved caspase-3 in these apoptotic cells. These observations suggest that sequestration of caspases can occur in some model systems, causing tetrapeptide-based activity assays to underestimate the amount of caspase activation that has occurred in situ.

Characterization of zebrafish caspase-3 and induction of apoptosis through ceramide generation in fish fathead minnow tailbud cells and zebrafish embryo

Caspase-3 was cloned from zebrafish embryos and its properties were characterized to identify the biological implications of caspase in embryogenesis and apoptosis in zebrafish, which is a model organism in vertebrate developmental biology and genetics. The predicted amino acid sequence, totalling 282 amino acid residues, consisted of the prodomain and large and small subunits. Phylogenetic analysis showed that the cloned zebrafish caspase was a member of the caspase-3 subfamily with approx. 60% identity with caspase-3 from Xenopus, chicken and mammals. In addition, recombinant zebrafish caspase hydrolysed acetyl-Asp-Glu-Val-Asp-4-methyl-coumaryl-7-amide, and exhibited similar substrate specificity to the mammalian caspase-3 subfamily. Therefore this caspase was designated zebrafish caspase-3. Overexpression of zebrafish caspase-3 induced apoptosis and increased ceramide levels in fish fathead minnow tailbud cells and zebrafish embryos. Both ceramide generation and apoptosis induction were inhibited by treatment with a caspase inhibitor, benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethylketone. Moreover, zebrafish caspase-3 mRNA was present in early embryos up to the 1000-cell stage as a maternal factor, and was then expressed throughout the body after the gastrula stage by zygotic expression. These findings indicate that the isolated caspase-3 plays an important role in the induction of ceramide generation as well as apoptosis in fish cells and the zebrafish embryo, and suggest that caspase-3 functions as a modulator of the pro-apoptotic signal in development.

Discriminative disulfide-bonding affinity labeling of opioid receptor subtypes

The affinity-labeling technique is an extremely important method in receptor biochemistry. The 3-nitro-2-pyridinesulfenyl (Npys) group, attached to a mercapto group, can react only with a free thiol group (the beta-mercapto group of cysteine residue) of the target receptor molecules, forming a disulfide bond. This disulfide bonding is mediated through the thiol-disulfide exchange reaction. Unlike other labeling methods, the approach utilizing such chemically activated thiol-containing ligands is able to reproduce an unlabeled protein by treatment with dithiothreitol, a reducing reagent. This provides several unique aspects for the studies elucidating the structure-function relationships between the peptide and the receptor. Based on the SNpys affinity technique, we have achieved the discriminative disulfide-bonding affinity labeling of the three different subtypes of opioid receptors: mu, delta and kappa. This article reviews our novel affinity techniques in the in vitro receptor biochemistry.

Breast cancer cells release factors that induced apoptosis in human bone marrow stromal cells

Breast cancer is associated frequently with skeletal metastases, which cause significant morbidity. The main mechanism is an increase in osteoclast-mediated bone resorption. We postulated that osteoblasts could be other essential target cells and previously showed that conditioned medium (CM) of breast cancer cells (BCCs) inhibits the proliferation of osteoblast-like cells. In this study, we investigated the effects of BCC-secreted products on osteoprogenitor cells using a clonal fetal human bone marrow stromal preosteoblastic cell line (FHSO-6) that expresses alkaline phosphatase (ALP) activity, type I collagen (COLI), and increased osteocalcin (OC) and osteopontin under treatment with dexamethasone (Dex), 1,25-dihydroxyvitamin D [1,25(OH)2D], or recombinant human bone morphogenetic protein 2 (rhBMP-2). Treatment with MCF-7 CM inhibited FHSO-6 cell survival in a dose-dependent and irreversible manner. Morphological investigation indicated that MCF-7 CM increased both apoptotic and necrotic cell number. MCF-7 CM increased caspases activity and a broad inhibitor of caspase activity (benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethyl ketone [z-VAD-fmk]) partly reversed the CM-induced inhibition of FHSO-6 cell survival. Western blot analyses revealed an increased bax/bcl-2 ratio in MCF-7 CM-treated FHSO-6 cells. MCF-7 cells exhibit FasLigand as membrane-bound protein and as a soluble cytokine in the CM. Deprivation of MCF-7 CM from active FasLigand by saturation with a soluble Fas molecule suppressed the induction of FHSO-6 apoptosis, whereas fibroblast CM, which did not contain FasLigand, only weakly modified FHSO-6 cell survival because of increased cell necrosis. These data indicate that FasLigand secreted by BCCs induces apoptosis and necrosis of human preosteoblastic stromal cells through caspase cascade modulated by the bax and bcl-2 protein level. The induction of apoptosis in human bone marrow stromal cells by BCCs may contribute to the inappropriately low osteoblast reaction and bone formation during tumor-induced osteolysis in bone metastases.

Fas/Fas ligand system mediates epithelial injury, but not pulmonary host defenses, in response to inhaled bacteria

The Fas/Fas ligand (FasL) system has been implicated in alveolar epithelial cell apoptosis during pulmonary fibrosis and acute respiratory distress syndrome. However, Fas ligation can also lead to cell activation and cytokine production. The goal of this study was to determine the role of the Fas/FasL system in host defenses against Escherichia coli, Staphylococcus aureus, and Streptococcus pneumoniae. We administered bacteria by aerosolization into the lungs of Fas-deficient (lpr) mice and wild-type (C57BL/6) mice and measured bacterial clearance at 6 and 12 h. One hour prior to euthanasia, the mice received an intraperitoneal injection of human serum albumin (HSA) for alveolar permeability determinations. At all times after bacterial challenges, the lungs of the lpr mice contained similar or lower numbers of bacteria than those of the C57BL/6 mice. Alveolar permeability changes, as determined by bronchoalveolar lavage fluid HSA concentrations, were less severe in the lpr mice 6 h after the challenges. In response to E. coli, the lpr mice had significantly more polymorphonuclear leukocytes (PMN) and macrophage inflammatory protein 2 in the lungs, whereas histopathologic changes were less severe. In contrast, in response to the gram-positive cocci, the lpr animals had similar or lower numbers of PMN. We conclude that the Fas/FasL system contributes to the development of permeability changes and tissue injury during-gram negative bacterial pneumonia. The Fas/FasL system did not have a major role in the clearance of aerosolized bacteria from the lungs at the bacterial doses tested.

Prevention of Staurosporine-Induced Cell Death in Embryonic Chick Cardiomyocyte Is More Dependent on Caspase-2 Than Caspase-3 Inhibition and Is Independent of Sphingomyelinase Activation and Ceramide Generation

Apoptosis was induced in embryonic chick cardiomyocytes by staurosporine. Treatment of cardiomyocytes with the preferential caspase-2 inhibitor, z-VDVAD-fmk (100 microM), produced a significant (P < 0.05) although small reduction in the amount of cell death. Ac-DVED-cmk (100 microM), which preferentially inhibits caspase-3 but inhibits to a lesser extent caspase-6, -7, -8, and -10, produced a minimal decrease in cell death. The combination of the caspase-3 and -2 inhibitors produced an additive reduction in cell death after staurosporine (1 microM for 6 h) from 80.4 +/- 0.7 to 54.6 +/- 1.3%. The ability of staurosporine to activate caspase-3 was confirmed in these cardiomyocytes by measurement of caspase-3 activity. A role for ceramide formation, from sphingomyelin to induce caspase activation was unlikely, as there were no changes in cellular ceramide or sphingomyelin after staurosporine treatment of cardiomyocytes when sphingomyelin was labeled by [(3)H]palmitate for 24 h. Neither were there any changes in sphingomyelinase activity. While staurosporine effectively suppressed PKC activity, phorbol 12-myristate 13 acetate did not alter staurosporine-induced cell death or DNA fragmentation. These results demonstrate that, in this model of cardiac cell death, caspase-2 inhibition is of considerable importance, caspase-3 inhibition is of lesser significance but may produce additional effects in the combination with caspase-2 inhibition, and ceramide production from sphingomyelin is not operative in the pathway leading to caspase activation and cell death.

Staurosporine and conventional anticancer drugs induce overlapping, yet distinct pathways of apoptosis and caspase activation

Apoptosis can be induced by various stimuli including DNA-damaging anticancer drugs and the protein kinase inhibitor staurosporine. It is generally believed that the molecular events during execution of apoptosis are shared, as both anticancer drugs and staurosporine derivatives induce mitochondrial damage, cytochrome c release and the activation of the caspase-9 proteolytic cascade. In the present study we show that overexpression of a dominant-negative caspase-9 mutant abolished the activation of endogenous caspase-9, caspase-3 and the cleavage of the caspase substrate Bid in response to anticancer drug treatment. Surprisingly, however, only marginal effects were observed during staurosporine-induced apoptosis. Furthermore, we describe a Jurkat T-cell clone that is completely resistant towards different anticancer drugs, but remains sensitive towards staurosporine-induced apoptosis. In these cells only staurosporine, but neither anti-CD95 nor anticancer drugs were able to trigger caspase activity and the cleavage of caspase substrates. Our results therefore suggest that the mechanism of staurosporine-induced apoptosis is more complex and at least partially differs from anticancer drug-induced caspase activation. These distinct features of staurosporine may allow to bypass chemoresistance of tumor cells and may encourage further clinical trials for the use of staurosporine derivatives in antitumor therapy.

Caspase 8 expression and signaling in Fas injury-resistant human fetal astrocytes

Fas (APO-1/CD95) is a cell surface receptor initially identified in lymphoid cells, but more recently detected in the central nervous system under pathological, usually inflammatory, conditions. In most Fas expressing cells, triggering of Fas by its ligand or by antagonistic antibodies leads to apoptosis. Human fetal astrocytes (HFA) constitutively express Fas yet are resistant to cell death following Fas ligation. In the current study, using dissociated cultures of human fetal central nervous system-derived cells, we attempted to identify a basis for HFA resistance to Fas-mediated injury. We compared the components of the Fas signaling pathway of HFA to those of two human cell lines susceptible to Fas-mediated injury, U251 glioma and Jurkat T-cells. We found that HFA did not express caspase 8 (FLICE), the caspase primarily activated on Fas signaling. Although we could induce caspase 8 in HFA with the inflammatory cytokines IFNgamma and TNFalpha, HFA remained resistant to Fas-mediated injury. Addition of inflammatory cytokines to the extracellular milieu also increased FLIP mRNA (FLICE inhibitory protein). Furthermore, upon triggering of cytokine-treated cells with FasL, we observed upregulation of the cleavage product of FLIP (p43-FLIP) previously shown to associate with the DISC and to block caspase 8 recruitment, thereby inhibiting Fas-mediated death. Our findings indicate that caspase 8 and its regulators play a central role in determining the response to Fas ligation of HFA and support a role for Fas signaling in the developing central nervous system other than related to cytotoxicity.

Executionary pathway for apoptosis: lessons from mutant mice

Apoptosis or programmed cell death (PCD) is an evolutionarily conserved cellular process that is essential for normal development and homeostasis of multicellular organisms. Defects in the apoptosis signaling result in many diseases including autoimmune diseases and cancer. The apoptosis signaling pathway was first described genetically in the nematode Caenorhabditis elegans which serves as a framework for the more complex apoptotic pathways that exist in mammals. In this review, we will discuss the apoptotic pathways that are emerging in mammals as elucidated by studies of gene-targeted mutant mice.

Resistance to CD95-mediated apoptosis through constitutive c-FLIP expression in a non-Hodgkin's lymphoma B cell line

CD95 (Fas/Apo-1) is a transmembrane molecule that induces apoptosis and plays a central role in the regulation of the immune response. The present study describes two new B lymphoid cell lines, B593 and BR97, derived from non-Hodgkin's lymphoma, which differ in susceptibility to CD95-mediated apoptosis. While B593 cells are sensitive to CD95mediated apoptosis, BR97 cells are completely resistant. Activation of caspase-8 and caspase-3 proteases plays an important role in the CD95 signalling pathway. CD95 stimulation induced caspase-8 and caspase-3 activation in B593, but not in BR97 cells. However, activation of both caspase-8 and caspase-3 was achieved in BR97 cells treated with staurosporine. Furthermore, protein synthesis inhibition by cycloheximide restored sensitivity to CD95-mediated apoptosis and allowed activation of both caspase-8 and caspase-3 in BR97 cells. These results indicate that, in BR97 cells, both caspases are functional and suggest that CD95-apoptosis resistance may result from the presence of inhibitory factor(s). Constitutive high level expression of the apoptotic inhibitor c-FLIP was observed in the CD95-resistant BR97 cell line compared to B593. Moreover, downregulation of c-FLIP expression level by protein synthesis inhibition strictly correlated with restored sensitivity to CD95-mediated apoptosis in BR97 cells. Furthermore, we demonstrate that c-FLIP is recruited to the CD95 DISC in BR97 cells together with caspase-8 and FADD. The data presented in this study strongly suggests that, in a B-NHL-derived cell line, resistance to CD95-mediated apoptosis results from endogenous high level expression of apoptotic inhibitor c-FLIP.

Mechanisms underlying hypoxia-induced neuronal apoptosis

In vivo models of cerebral hypoxia-ischemia have shown that neuronal death may occur via necrosis or apoptosis. Necrosis is, in general, a rapidly occurring form of cell death that has been attributed, in part, to alterations in ionic homeostasis. In contrast, apoptosis is a delayed form of cell death that occurs as the result of activation of a genetic program. In the past decade, we have learned considerably about the mechanisms underlying apoptotic neuronal death following cerebral hypoxia-ischemia. With this growth in knowledge, we are coming to the realization that apoptosis and necrosis, although morphologically distinct, are likely part of a continuum of cell death with similar operative mechanisms. For example, following hypoxia-ischemia, excitatory amino acid release and alterations in ionic homeostasis contribute to both necrotic and apoptotic neuronal death. However, apoptosis is distinguished from necrosis in that gene activation is the predominant mechanism regulating cell survival. Following hypoxic-ischemic episodes in the brain, genes that promote as well as inhibit apoptosis are activated. It is the balance in the expression of pro- and anti-apoptotic genes that likely determines the fate of neurons exposed to hypoxia. The balance in expression of pro- and anti-apoptotic genes may also account for the regional differences in vulnerability to hypoxic insults. In this review, we will examine the known mechanisms underlying apoptosis in neurons exposed to hypoxia and hypoxia-ischemia.

Mammalian caspases: structure, activation, substrates, and functions during apoptosis

Apoptosis is a genetically programmed, morphologically distinct form of cell death that can be triggered by a variety of physiological and pathological stimuli. Studies performed over the past 10 years have demonstrated that proteases play critical roles in initiation and execution of this process. The caspases, a family of cysteine-dependent aspartate-directed proteases, are prominent among the death proteases. Caspases are synthesized as relatively inactive zymogens that become activated by scaffold-mediated transactivation or by cleavage via upstream proteases in an intracellular cascade. Regulation of caspase activation and activity occurs at several different levels: (a) Zymogen gene transcription is regulated; (b) antiapoptotic members of the Bcl-2 family and other cellular polypeptides block proximity-induced activation of certain procaspases; and (c) certain cellular inhibitor of apoptosis proteins (cIAPs) can bind to and inhibit active caspases. Once activated, caspases cleave a variety of intracellular polypeptides, including major structural elements of the cytoplasm and nucleus, components of the DNA repair machinery, and a number of protein kinases. Collectively, these scissions disrupt survival pathways and disassemble important architectural components of the cell, contributing to the stereotypic morphological and biochemical changes that characterize apoptotic cell death.

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

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

Tumor-induced apoptosis of T lymphocytes: elucidation of intracellular apoptotic events

Our recent studies suggest that human squamous cell carcinoma of the head and neck (SCCHN) is capable of activating an intrinsic mechanism of programmed-cell death in interacting lymphocytes in situ and in vitro. The current study used Jurkat T-cell line as a model to investigate intracellular apoptotic events in T cells interacting with SCCHN. Apoptosis induced in T lymphocytes by tumor cells was in part Fas-mediated, since it was partially, but significantly, inhibited in the presence of anti-Fas ligand Ab or in Fas-resistant Jurkat cells. The synthetic caspase inhibitors, N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (Z-VAD-FMK) and N-benzyloxycarbonyl-Asp-glu-Val-Asp-fluoromethyl ketone (Z-DEVD-FMK), effectively blocked apoptosis of Jurkat cells co-incubated with SCCHN cell lines, suggesting the involvement of caspases in tumor-induced apoptosis of lymphocytes. Overexpression of CrmA, an inhibitor of caspase-1 and caspase-8, partially inhibited tumor-induced T-cell death. Caspase-8 and caspase-3 were identified as effector molecules in the execution of tumor-induced T-cell death, since the proform enzymes were processed into active subunits during co-incubation of T cells with tumor cells. Furthermore, co-incubation with tumor cells resulted in cleavage of poly(ADP-ribose) polymerase (PARP), a common caspase-3 substrate, and in cleavage of TcR-ζ chain, shown by us to be a T-cell specific caspase-3 substrate. Overexpression of Bcl-2 did not provide protection of T cells from SCCHN-induced DNA degradation. Instead, the Bcl-2 protein was cleaved in the target T cells during their co-incubation with tumor cells. These findings demonstrate that tumor cells can trigger in T lymphocytes caspase-dependent apoptotic cascades, which are not effectively protected by Bcl-2.

Activation of apoptosis and its inhibition

The induction of apoptosis, or controlled cell death, by various stimuli has been shown to activate a cascade of endoproteases, called caspases, that cleave numerous cellular proteins necessary for cellular homeostasis. This review discusses this family of proteases together with a variety of mammalian and viral regulatory proteins that act to control this activation.