The killer and the executioner: how apoptosis controls malignancy

Attenuation of Polycyclic Aromatic Hydrocarbon (PAH)-Induced Carcinogenesis and Tumorigenesis by Omega-3 Fatty Acids in Mice In Vivo

Lung cancer is the leading cause of cancer death worldwide. Polycyclic aromatic hydrocarbons (PAHs) are metabolized by the cytochrome P450 (CYP)1A and 1B1 to DNA-reactive metabolites, which could lead to mutations in critical genes, eventually resulting in cancer. Omega-3 fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are beneficial against cancers. In this investigation, we elucidated the mechanisms by which omega-3 fatty acids EPA and DHA will attenuate PAH-DNA adducts and lung carcinogenesis and tumorigenesis mediated by the PAHs BP and MC. Adult wild-type (WT) (A/J) mice, Cyp1a1-null, Cyp1a2-null, or Cyp1b1-null mice were exposed to PAHs benzo[a]pyrene (BP) or 3-methylcholanthrene (MC), and the effects of omega-3 fatty acid on PAH-mediated lung carcinogenesis and tumorigenesis were studied. The major findings were as follows: (i) omega-3 fatty acids significantly decreased PAH-DNA adducts in the lungs of each of the genotypes studied; (ii) decreases in PAH-DNA adduct levels by EPA/DHA was in part due to inhibition of CYP1B1; (iii) inhibition of soluble epoxide hydrolase (sEH) enhanced the EPA/DHA-mediated prevention of pulmonary carcinogenesis; and (iv) EPA/DHA attenuated PAH-mediated carcinogenesis in part by epigenetic mechanisms. Taken together, our results suggest that omega-3 fatty acids have the potential to be developed as cancer chemo-preventive agents in people.

Chemical Decorations of "MARs" Residents in Orchestrating Eukaryotic Gene Regulation

Genome organization plays a crucial role in gene regulation, orchestrating multiple cellular functions. A meshwork of proteins constituting a three-dimensional (3D) matrix helps in maintaining the genomic architecture. Sequences of DNA that are involved in tethering the chromatin to the matrix are called scaffold/matrix attachment regions (S/MARs), and the proteins that bind to these sequences and mediate tethering are termed S/MAR-binding proteins (S/MARBPs). The regulation of S/MARBPs is important for cellular functions and is altered under different conditions. Limited information is available presently to understand the structure–function relationship conclusively. Although all S/MARBPs bind to DNA, their context- and tissue-specific regulatory roles cannot be justified solely based on the available information on their structures. Conformational changes in a protein lead to changes in protein–protein interactions (PPIs) that essentially would regulate functional outcomes. A well-studied form of protein regulation is post-translational modification (PTM). It involves disulfide bond formation, cleavage of precursor proteins, and addition or removal of low-molecular-weight groups, leading to modifications like phosphorylation, methylation, SUMOylation, acetylation, PARylation, and ubiquitination. These chemical modifications lead to varied functional outcomes by mechanisms like modifying DNA–protein interactions and PPIs, altering protein function, stability, and crosstalk with other PTMs regulating subcellular localizations. S/MARBPs are reported to be regulated by PTMs, thereby contributing to gene regulation. In this review, we discuss the current understanding, scope, disease implications, and future perspectives of the diverse PTMs regulating functions of S/MARBPs.

Using a toxicoproteomic approach to investigate the effects of thiamethoxam into the brain of Apis mellifera

Neonicotinoids have been described as toxic to bees. In this context, the A. mellifera foragers were exposed to a sublethal concentration of thiamethoxam (LC_50/100: 0,0227 ng de thiamethoxam/μL^-1 diet), a neurotoxic insecticide, for 8 days; and it was decided to investigate the insecticide effect on the brain by a shotgun proteomic approach followed by label-free quantitative-based proteomics. A total of 401 proteins were identified in the control group (CG); and a total of 350 proteins in the thiamethoxam exposed group (TMX). Quantitative proteomics data showed up 251 proteins with significant quantitative values in the TMX group. These findings demonstrated the occurrence of shared and unique proteins with altered expression in the TMX group, such as ATP synthase subunit beta, heat shock protein cognate 4, spectrin beta chain-like, mushroom body large-type Kenyon cell-specific protein 1-like, tubulin alpha-1 chain-like, arginine kinase, epidermal growth factor receptor, odorant receptor, glutamine synthetase, glutamate receptor, and cytochrome P450 4c3. Meanwhile, the proteins that were expressed uniquely in the TMX group are involved mainly in the phosphorylation, cellular protein modification, and cell surface receptor signalling processes. Interaction network results showed that identified proteins are present in five different metabolic pathways - oxidative stress, cytoskeleton control, visual process, olfactory memory, and glutamate metabolism. Our scientific outcomes demonstrated that a sublethal concentration of thiamethoxam can impair biological processes and important metabolic pathways, causing damage to the nervous system of bees, and in the long term, can compromise the nutrition and physiology of individuals from the colony.

Structure-based design, synthesis and anticancer effect of cyclic Smac-polyarginine peptides

The second mitochondria-derived activator of caspase (Smac/DIABLO) is a pro-apoptotic protein that released from mitochondria into the cytosol when cells undergo apoptosis. Smac promotes caspase activation by binding the inhibitors of apoptosis proteins (IAP), particularly XIAP and eliminating their inhibitory activity. Although the seven N-terminal amino acids AVPIAQK (SmacN7) of Smac protein is able to elicit an anticancer response by itself, it is neither cell-permeable nor stable in the cellular environment. Thus, the use of SmacN7 derivatives and mimetics is an alluring field for cancer therapy. In this study, heptamer Smac peptide was fused to a well-known octaarginine cell-penetrating peptide for promoting its intracellular access. Both therapeutic Smac part and cell-penetrating octaarginine parts of the peptide sequence constrained in a cyclic structure so as to enhance the apoptosis-inducing potential of the SmacN7 peptide. Biological assays interestingly showed that cyclic peptides P4, P5 and P7 gave rise to a significant level of cytotoxicity and apoptosis mediated cell death in multiple myeloma tumor cells (MM) comparing to linear peptide.

Histologic evaluation of Ki-67 and cleaved caspase-3 expression in feline mammary carcinoma

Objectives The purpose of this study was to evaluate histopathologic aspects of, and the expression of Ki-67 and cleaved caspase-3 in, feline mammary carcinoma (FMC). Methods Feline mammary tumors were surgically obtained by mastectomy from 30 female cats and were fixed with formalin and embedded in paraffin wax. Four-micron sections were stained with hematoxylin and eosin for histopathologic diagnosis. Ki-67 and cleaved caspase-3 were analyzed by immunohistochemistry. Results Samples were histologically confirmed as FMC. Positive immunostaining was observed in all cancer samples for both nuclear Ki-67 and cleaved caspase-3, with a mean positive staining percentage of 27.5% and 21.2%, respectively. No statistically significant correlations between Ki-67 and cleaved caspase-3 were observed within FMC. Conclusions and relevance A high proliferation index was found in feline mammary tumors. This is the first study evaluating cleaved caspase-3 expression in FMC.

Dipeptidyl Peptidase-4 Inhibitor-Associated Pancreatic Carcinoma: A Review of the FAERS Database

BACKGROUND

To date, there is limited literature regarding the association between dipeptidyl peptidase-4 (DPP-4) inhibitors and pancreatic carcinoma.

OBJECTIVE

To describe the comparative incidence of DPP-4 inhibitors and pancreatic carcinoma as reportedly available in the Food and Drug Administration (FDA) Adverse Event Reporting System (FAERS) database. The goal was to provide health care practitioners a general understanding of the drug-disease occurrence.

METHODS

This is a case/noncase study utilizing Empirica Signal software to query FAERS from November 1968 to December 31, 2013. The software was used to calculate a disproportionality statistic--namely, the empirical Bayesian geometric mean (EBGM)--for reports of DPP-4 inhibitors-associated pancreatic carcinoma. The FDA considers an EBGM significant if the fifth percentile of the distribution is at least 2, defined as an EB05 ≥ 2. With use of a disproportionality analysis, DPP-4 inhibitors were compared with all agents listed in FAERS.

RESULTS

A total of 156 patients experienced pancreatic carcinoma while receiving DPP-4 inhibitor therapy. An EB05 of 10.3 was determined for sitagliptin, 7.1 for saxagliptin, 4.9 for linagliptin, and 1.4 for alogliptin, compared with all other agents included in FAERS. Although an EB05 > 2 was achieved in 2 other antihyperglycemic agents, the findings were not consistent within their medication classes.

CONCLUSION

There appears to be a statistical association between DPP-4 inhibitor use and pancreatic carcinoma. Causality cannot be inferred from the data provided. Additional clinical studies are needed to further explore this statistical association.

The activator of apoptosis Smac-DIABLO acts as a tetramer in solution

Smac-DIABLO in its mature form (20.8 kDa) binds to baculoviral IAP repeat (BIR) domains of inhibitor of apoptosis proteins (IAPs) releasing their inhibitory effects on caspases, thus promoting cell death. Despite its apparent molecular mass (∼100 kDa), Smac-DIABLO was held to be a dimer in solution, simultaneously targeting two distinct BIR domains. We report an extensive biophysical characterization of the protein alone and in complex with the X-linked IAP (XIAP)-BIR2-BIR3 domains. Our data show that Smac-DIABLO adopts a tetrameric assembly in solution and that the tetramer is able to bind two BIR2-BIR3 pairs of domains. Our small-angle x-ray scattering-based tetrameric model of Smac-DIABLO/BIR2-BIR3 highlights some conformational freedom of the complex that may be related to optimization of IAPs binding.

Implications for chronic toxicity of benzo[a]pyrene in sea bream cultured hepatocytes: Cytotoxicity, inflammation, and cancerogenesis

Benzo[a]pyrene (B[a]P) is the most studied dangerous polycyclic aromatic hydrocarbon for its hepatotoxic, carcinogenic, mutagenic, teratogenic, and immunosuppressant effects, which can affect both wild and farmed marine fish through the trophic chain. This study investigated, for the first time, the chronic effects induced in vitro by B[a]P prolonged exposure on gilthead sea bream (Sparus aurata L.) hepatocytes, evaluating the cellular and nuclear latent damage. The purpose was to characterize the kind of B[a]P cyto- and genotoxic damage by morphological and immunocytochemical parameters applied in combination with the use of multiple assay endpoints. In light of our results, the short-term effects at higher B[a]P doses were linked to higher cytotoxicities and necrotic lysis, whereas a sustained inflammatory response at medium-low doses was perceived as a mitochondria-mediated apoptosis, both by surface and nuclear morphological changes. The strong immunoreactivity for the cleaved caspase-3 showed that the labeled cells committed suicide by apoptosis. B[a]P involvement on carcinogenesis comes from prolonged exposure at lower doses, establishing the connection between the escape from apoptosis and the selection of a tumoral phenotype. Cells colabeled with proliferating cell nuclear antigen/caspase-3 within the proliferative foci, were proliferating transformed oval stem cells, which escaped the suicide by apoptosis allowing cancer development. Finally, it was established that sea bream cultured hepatocytes are highly sensitive to chronic B[a]P exposure, as serious genotoxic effects were found even at the lowest doses.

Sclerotium rolfsii lectin induces stronger inhibition of proliferation in human breast cancer cells than normal human mammary epithelial cells by induction of cell apoptosis

Sclerotium rolfsii lectin (SRL) isolated from the phytopathogenic fungus Sclerotium rolfsii has exquisite binding specificity towards O-linked, Thomsen-Freidenreich (Galβ1-3GalNAcα1-Ser/Thr, TF) associated glycans. This study investigated the influence of SRL on proliferation of human breast cancer cells (MCF-7 and ZR-75), non-tumorigenic breast epithelial cells (MCF-10A) and normal mammary epithelial cells (HMECs). SRL caused marked, dose-dependent, inhibition of proliferation of MCF-7 and ZR-75 cells but only weak inhibition of proliferation of non-tumorigenic MCF-10A and HMEC cells. The inhibitory effect of SRL on cancer cell proliferation was shown to be a consequence of SRL cell surface binding and subsequent induction of cellular apoptosis, an effect that was largely prevented by the presence of inhibitors against caspases -3, -8, or -9. Lectin histochemistry using biotin-labelled SRL showed little binding of SRL to normal human breast tissue but intense binding to cancerous tissues. In conclusion, SRL inhibits the growth of human breast cancer cells via induction of cell apoptosis but has substantially less effect on normal epithelial cells. As a lectin that binds specifically to a cancer-associated glycan, has potential to be developed as an anti-cancer agent.

DNA binding, molecular docking and apoptotic inducing activity of nickel(ii), copper(ii) and zinc(ii) complexes of pyridine-based tetrazolo[1,5-a]pyrimidine ligands

The biological activity of metal(ii) complexes of tetrazolo[1,5-a]pyrimidine ligands show that the copper(ii) complexes may act as promising anticancer agents.

Acalypha wilkesiana extracts induce apoptosis by causing single strand and double strand DNA breaks

ETHNOPHARMACOLOGICAL RELEVANCE

The seeds of Acalypha wilkesiana have been used empirically by traditional healers in Southwest Nigeria together with other plants as a powder mixture to treat patients with breast tumours and inflammation.

AIM OF THE STUDY

There is an increasing interest among researchers in searching for new anticancer drugs from natural resources, particularly plants. This study aimed to investigate the anticancer properties of Acalypha wilkesiana extracts and the characteristics of DNA damage against brain and lung cancer cells.

MATERIALS AND METHODS

The antiproliferative activity of Acalypha wilkesiana extracts (ethyl acetate, hexane, and ethanol) was examined on human glioma (U87MG), human lung carcinoma (A549), and human lung fibroblast (MRC5) cells.

RESULTS

Cell viability MTT assay revealed that ethyl acetate extract of the plant possessed significant antiproliferative effects against both U87MG (GI(50)=28.03 ± 6.44 μg/ml) and A549 (GI(50)=89.63 ± 2.12 μg/ml) cells (p value<0.0001). The hexane extract was found to exhibit crucial antiproliferative effects on U87MG (GI(50)=166.30 ± 30.50 μg/ml) (p value<0.0001) but not on A549 cells. Neither plant extract possessed noticeable antiproliferative effects on the non-cancerous MRC5 cells (GI(50)>300 μg/ml). The ethanol extract showed no antiproliferative effects on any cell line examined. Haematoxylin & Eosin (H & E) staining and single cell gel electrophoresis (SCGE) comet assay confirmed that plant extract-treated cells underwent apoptosis and not necrosis. SCGE comet assays confirmed that plant extracts caused both single strand (SSB) and double strand (DSB) DNA breaks that led to the execution of apoptosis.

CONCLUSION

The extracts (especially ethyl acetate and hexane) of Acalypha wilkesiana possess valuable cytotoxic effects that trigger apoptosis in U87MG and A549 cancer cells through induction of DNA SSBs and DSBs.

Role of retinoic acid in the modulation of benzo(a)pyrene-DNA adducts in human hepatoma cells: implications for cancer prevention

Carcinogen-DNA adducts could lead to mutations in critical genes, eventually resulting in cancer. Many studies have shown that retinoic acid (RA) plays an important role in inducing cell apoptosis. Here we have tested the hypothesis that levels of carcinogen-DNA adducts can be diminished by DNA repair and/or by eliminating damaged cells through apoptosis. Our results showed that the levels of total DNA adducts in HepG2 cells treated with benzo(a)pyrene (BP, 2 μM)+RA (1 μM) were significantly reduced compared to those treated with BP only (P=0.038). In order to understand the mechanism of attenuation of DNA adducts, further experiments were performed. Cells were treated with BP (4 μM) for 24h to initiate DNA adduct formation, following which the medium containing BP was removed, and fresh medium containing 1 μM RA was added. The cells were harvested 24h after RA treatment. Interestingly, the levels of total DNA adducts were lower in the BP/RA group (390 ± 34) than those in the BP/DMSO group (544 ± 33), P=0.032. Analysis of cell apoptosis showed an increase in BP+RA group, compared to BP or RA only groups. Our results also indicated that attenuation of BP-DNA adducts by RA was not primarily due to its effects on CYP1A1 expression. In conclusion, our results suggest a mechanistic link between cellular apoptosis and DNA adduct formation, phenomena that play important roles in BP-mediated carcinogenesis. Furthermore, these results help understand the mechanisms of carcinogenesis, especially in relation to the chemopreventive properties of nutritional apoptosis inducers.

Glutamine prevents DMBA-induced squamous cell cancer

The etiology of oral squamous cell carcinoma has been linked to environmental carcinogens, such as activated aromatic heterocyclic radicals and epoxides. Our previous work on implantable and 7,12-dimethylbenz[a]anthracene (DMBA)-induced breast cancer showed that oral glutamine (GLN) inhibited tumor growth possibly through stimulation of host - and selective inhibition of tumor glutathione (GSH). This finding was associated with up-regulation of NK cell activity, decreased IGF-1 and TGF-beta in the circulation and downregulation of PI-3K/Akt antiapoptotic signaling in tumors. The present study was designed to investigate the effect of topically applied GLN on DMBA-induced hamster buccal pouch squamous cell carcinoma. Histopathological alterations in buccal pouches were studied by light microscopy. GLN and GSH levels in blood and buccal mucosa were determined using specific enzyme assays. The protein expression of bax, bcl-2 and PARP was determined by western blotting. H-ras and p53 genes were examined for presence of mutations using direct DNA sequencing. Fourteen weeks after DMBA application none of the GLN-supplemented animals developed tumors, while all of the control animals had well developed squamous cell carcinomas. The inhibition of DMBA-carcinogenesis by GLN application was associated with increased arterial GLN and GSH, elevated buccal mucosa GSH as well as induction of bax and PARP, and inhibition of bcl-2. H-ras and p53 were wild type. The results from this study in combination with our previous data suggest that the chemopreventive effects of GLN are exerted by enhancing the antioxidant status of the body and activation of apoptosis.

Willow bark extract (BNO1455) and its fractions suppress growth and induce apoptosis in human colon and lung cancer cells

BACKGROUND

Recently, there have been extensive efforts to evaluate the chemopreventive role of substances present in natural products. The aim of this study was to examine the effects of the main groups of compounds (salicylalcohol derivates, flavonoids, proanthocyanidins), and salicin isolated from willow bark extract BNO 1455 on proliferation and apoptosis in human colon and cancer cells.

METHODS

We used human colon cyclooxygenase-2 (COX-2)-positive HT 29 and (COX-2)-negative HCT 116 or lung COX-2 proficient A 549 and low COX-2 expressing SW2 cells. After treatment for 72 h with various concentrations of single substances and acetylsalicylic acid (ASA) as control, inhibition of cell growth and cytotoxicity were measured by colorimetric WST-1 assay and propidium iodide uptake by flow cytometry, respectively. Apoptotic cells were identified by annexin V adhesion using flow cytometry.

RESULTS

Studies on dose-dependent effects of BNO 1455 and its fractions showed anti-proliferative activity of all compounds with 50% maximal growth inhibitory concentrations (GI(50)) between 33.3 and 103.3 microg/ml for flavonoids and proanthocyanidins fractions and 50.0-243.0 microg/ml for salicylalcohol derivates and extract. Apoptosis induction was confirmed by annexin V adherence and analysis of cell morphology based on light scattering characteristics using flow cytometry in all cell lines at GI(50).

CONCLUSIONS

We showed that willow bark extract BNO 1455 an its fractions inhibit the cell growth and promote apoptosis in human colon and lung cancer cell lines irrespective of their COX-selectivity.

Apoptosis: mechanisms and relevance in cancer

Apoptosis or programmed cell death is a process with typical morphological characteristics including plasma membrane blebbing, cell shrinkage, chromatin condensation and fragmentation. A family of cystein-dependent aspartate-directed proteases, called caspases, is responsible for the proteolytic cleavage of cellular proteins leading to the characteristic apoptotic features, e.g. cleavage of caspase-activated DNase resulting in internucleosomal DNA fragmentation. Currently, two pathways for activating caspases have been studied in detail. One starts with ligation of a death ligand to its transmembrane death receptor, followed by recruitment and activation of caspases in the death-inducing signalling complex. The second pathway involves the participation of mitochondria, which release caspase-activating proteins into the cytosol, thereby forming the apoptosome where caspases will bind and become activated. In addition, two other apoptotic pathways are emerging: endoplasmic reticulum stress-induced apoptosis and caspase-independent apoptosis. Naturally occurring cell death plays a critical role in many normal processes like foetal development and tissue homeostasis. Dysregulation of apoptosis contributes to many diseases, including cancer. On the other hand, apoptosis-regulating proteins also provide targets for drug discovery and new approaches to the treatment of cancer.

Caspases in apoptotic death

Caspases are the central mediators of normal and pathological apoptotic death. They are cysteine proteases that cleave after aspartic acid. The inactive pro-enzymes are proteolytically processed and activated through mechanisms of recruitment to signalling complexes, upstream activator caspases or autoactivation. Many amplifying cascades exist in caspase activation pathways that are evolutionarily conserved. The human caspase family contains at least 10 members which form 3 groups based on substrate specificity, proteolytic targets and functional actions. The crystal structure has been solved for members from two of these groups with inhibitory peptides bound in the active site. These structures have allowed tremendous insight into mechanisms of catalysis, substrate binding and substrate specificity. Enlightened knowledge of enzyme-substrate interactions has led to the design of many inhibitors that are active in animal models of caspase-mediated cell death. Testing in animal models should lead to drugs for therapeutic intervention in the many human diseases characterised by excessive apoptotic cell death.

Molecular mechanism of arsenic trioxide inducing apoptosis in human large intestinal carcinoma cell line

AIM: To study the possible apoptosis-inducing effect of arsenic trioxide (As₂O₃) on the different types of human large intestinal carcinoma cell, and its molecular mechanisms.

METHODS: As₂O₃'s action on the cell growth, apoptosis, periodic return and the expression of related genes of the two human large intestinal carcinoma cell lines LoVo and CoLo-320 in vitro was observed by MTT assay, acridine orange (AO)/ethidiumbromide (EB) flurescent staining, electron microscopy detection, DNA gel electrophoresis, flow cytometry, and immunohistochemical staining.

RESULTS: After treated by As₂O₃ at different concentration(0.5, 1.0, 2.0, 4.0 mg/L) for various times (24, 48, 72 h), the human large intestinal carcinoma cell LoVo and CoLo-320 showed strongly inhibitory effect on growth (P < 0.05) and also the cells showed typical morphological and biochemical characteristic changes of apoptosis, with bcl-2 gene expression down-regulated, and bax and Fas gene expression up-regulated (P < 0.01).

CONCLUSION: As₂O₃ has significant apoptosis-inducing effect on large intestinal carcinoma cells, which is regulated by several genes.

Discovery of embelin as a cell-permeable, small-molecular weight inhibitor of XIAP through structure-based computational screening of a traditional herbal medicine three-dimensional structure database

The X-linked inhibitor of apoptosis (XIAP) is a promising new molecular target for the design of novel anticancer drugs aiming at overcoming apoptosis-resistance of cancer cells to chemotherapeutic agents and radiation therapy. Recent studies demonstrated that the BIR3 domain of XIAP where caspase-9 and Smac proteins bind is an attractive site for designing small-molecule inhibitors of XIAP. Through computational structure-based screening of an in-house traditional herbal medicine three-dimensional structure database of 8221 individual natural products, followed by biochemical testing of selected candidate compounds, we discovered embelin from the Japanese Ardisia herb as a small-molecular weight inhibitor that binds to the XIAP BIR3 domain. We showed that embelin binds to the XIAP BIR3 protein with an affinity similar to that of the natural Smac peptide using a fluorescence polarization-based binding assay. Our NMR analysis further conclusively confirmed that embelin interacts with several crucial residues in the XIAP BIR3 domain with which Smac and caspsase-9 bind. Embelin inhibits cell growth, induces apoptosis, and activates caspase-9 in prostate cancer cells with high levels of XIAP, but has a minimal effect on normal prostate epithelial and fibroblast cells with low levels of XIAP. In stably XIAP-transfected Jurkat cells, embelin effectively overcomes the protective effect of XIAP to apoptosis and enhances the etoposide-induced apoptosis and has a minimal effect in Jurkat cells transfected with vector control. Taken together, our results showed that embelin is a fairly potent, nonpeptidic, cell-permeable, small-molecule inhibitor of XIAP and represents a promising lead compound for designing an entirely new class of anticancer agents that target the BIR3 domain of XIAP.

Hyperforin a constituent of St John's wort (Hypericum perforatum L.) extract induces apoptosis by triggering activation of caspases and with hypericin synergistically exerts cytotoxicity towards human malignant cell lines

Hyperforin (HP) is an abundant component of St John's wort with antibiotic and antidepressive activity. We report here the ability of HP and that of polyphenolic procyanidin B2 (PB-2) to inhibit the growth of leukemia K562 and U937 cells, brain glioblastoma cells LN229 and normal human astrocytes. HP inhibited the growth of cells in vitro with GI(50) values between 14.9 and 19.9 microM. The growth inhibitory effect of PB-2 was more pronounced in leukemia cell lines K562 and U937, the GI(50) concentrations being about 12.5 microM established after 48 h incubation differed significantly (P<0.05) from those of LN229 and normal human astrocytes (103.1 and 96.7 microM), respectively. Further, HP and hypericin (HY) (a naphthodianthrone from St John's wort) acted synergistically in their inhibitory effect on leukemic (K562, U937) cell growth. Cell death occurred after 24 h treatment with HP and PB-2 by apoptosis. A dose-dependent loss of membrane phospholipid asymmetry associated with apoptosis was induced in all cell lines as evidenced by the externalization of phosphatidylserine (PS) and morphological changes in cell size and granulosity by scatter characteristics. In leukemia U937 cells, HP increased the activity of caspase-9 and caspase-3 and in K562 cells caspase-8 and caspase-3. In addition, the broad spectrum caspase inhibitor z-VAD-fmk inhibited both the appearance of PS exposure and the activation of caspases, illustrating the functional relevance of caspase activation during HP-induced apoptosis. Cytocidal effects of HP and its cooperation with HY on tumor growth inhibition in a synergistic manner make the St John's wort an interesting option in cancer warranting further in vitro and in vivo investigation.

Beta2-microglobulin induces caspase-dependent apoptosis in the CCRF-HSB-2 human leukemia cell line independently of the caspase-3, -8 and -9 pathways but through increased reactive oxygen species

Exogenous beta(2)-microglobulin (beta(2)m) induces significant apoptosis in the CCRF-HSB-2 human lymphoblastic leukemia cell line as detected by DNA fragmentation, DAPI staining and annexin V binding assay. beta(2)m treatment induced the release of cytochrome c and apoptosis-inducing factor (AIF) from the mitochondria, but no change in mitochondrial membrane potential (DeltaPsim) was observed during apoptosis, suggesting that cytochrome c may be released through a mechanism independent of mitochondrial permeability transition (MPT) pore formation. Moreover, the beta(2)m-induced release of cytochrome c and AIF from the mitochondria in CCRF-HSB-2 cells was caspase-independent, since Z-VAD-fmk, a general inhibitor of caspases, did not block the release of these factors. However, Z-VAD-fmk treatment significantly blocked beta(2)m-induced apoptosis, while Western blot analysis revealed that caspases-1, -2, -3, -6, -7, -8 and -9 are not activated during beta(2)m-induced apoptosis in these cells. These results collectively indicate that a post-mitochondrial caspase-dependent mechanism is involved in beta(2)m-induced apoptosis. Moreover, beta(2)m significantly enhanced the production of reactive oxygen species (ROS) during 12-48 hr treatment, and beta(2)m-induced apoptosis was almost totally inhibited in cells pre-treated with the antioxidant N-acetylcysteine (NAC), providing evidence that beta(2)m-induced apoptosis in CCRF-HSB-2 cells is ROS-dependent. Therefore, these results reveal that beta(2)m-induced apoptosis in CCRF-HSB-2 cells may occur through an unknown caspase-dependent and ROS-dependent mechanism(s) that is associated with cytochrome c and AIF release from mitochondria, but is independent of the caspase -3, -8 and -9 pathways.

Bax, Bcl-2, fas and Fas-L antigen expression in human seminoma: correlation with the apoptotic index

Apoptosis plays a crucial role in the regulation of spermatogenesis in male germ cells and is, at least in part, modulated by Bcl-2, Bax, and the Fas pathway. Seminomas have a favourable outcome and respond to radio-/chemotherapy with an increased rate of apoptosis. The expression of Bax, Bcl-2, Fas and Fas-ligand (Fas-L) in human seminoma was evaluated and correlated with the apoptotic index. Twenty-nine classical seminomas were examined by immunohistochemistry and Western blotting using antibodies against Bax, Bcl-2, Fas and Fas-L. Apoptosis was detected by in-situ end-labeling of fragmented DNA and the apoptotic index (AI) was determined. Expression of Fas was found in 26 (89.7%) of Fas-L in 24 seminomas (82.2%); none of the tumours expressed Bcl-2. No correlation between the AI and Fas, Fas-L or Bcl-2 expression was found. Bax was demonstrated in 20/29 tumours (69%). Bax-positive tumours showed an increased AI of 4.75 +/- 2.38% in contrast to 2.60 +/- 1.23% of the Bax-negative tumours (P = 0.002). The number of Bax-positive tumour cells and apoptotic cells revealed a significant correlation using chi2-test (P = 0.04) and linear regression (r = 0.54, P = 0.001). Therefore, Bax seems to play a determinant role in the modulation of apoptosis in human seminoma that may be linked to a favourable outcome.

Korean mistletoe lectin-induced apoptosis in hepatocarcinoma cells is associated with inhibition of telomerase via mitochondrial controlled pathway independent of p53

The extract of European mistletoe (Viscum album, L) has been used in adjuvant chemotherapy of cancer and mistletoe lectins are considered to be major active components. The present work was performed to investigate the effects of Korean mistletoe lectin (Viscum album L. coloratum agglutinin, VCA) on proliferation and apoptosis of human hepatoma cells as well as the underlying mechamisms for these effects. We showed that VCA induced apoptosis in both SK-Hep-1 (p53-positive) and Hep 3B (p53-negative) cells through p53- and p21-independent pathways. VCA induced apoptosis by down-regulation of Bcl-2 and by up-regulation of Bax functioning upstream of caspase-3 in both cell lines. In addition, we observed down-regulation of telomerase activity in both VCA-treated cells. Our results provide direct evidence of the anti-tumor potential of this biological response which comes from inhibition of telomerase and consequent inducing apoptosis. VCA-induced apoptosis is regulated by mitochondrial controlled pathway independently of p53. These findings are important for the therapy with preparation of mistletoe because they show that telomerase-dependent mechanism can be targeted by VCA in human hepatocarcinoma. Taken together, our results suggest that the VCA, considered as a telomerase-inhibitor, can be envisaged as a candidate for enhancing sensitivity of conventional anticancer drugs.

Nitric oxide and apoptosis during human head and neck squamous cell carcinoma development

PURPOSE

Apoptosis index (AI), Bcl-2, and Bax have shown prognostic significance in head and neck squamous cell carcinoma (HNSCCa). Other areas of research have implicated nitric oxide (NO) or its various intermediate species in both proapoptotic and antiapoptotic processes. We have previously shown that NO-generating enzymes are significantly increased during the stepwise progression to HNSCCa. The aim of this study was to explore the interrelationship of NO and a known consequence of NO-related oxidative stress, apoptosis, during this step-wise process.

MATERIALS AND METHODS

Formalin fixed-paraffin embedded tissue samples of 10 normal oral mucosa, 15 reactive/dysplastic lesions, and 17 HNSCCa lesions studied previously were subjected to the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP labeling (TUNEL) assay as well as immunohistochemical staining against Bcl-2, Bax, and p53. Patient charts were reviewed and clinical data were compared. The study pathologist (G.K.H) reviewed these slides blinded to patient identifiers or clinical data. The number of immunopositive cell nuclei or staining intensity was graded, noting the pattern of immunostaining. These staining characteristics were compared with the results of immunostaining previously obtained for endothelial constitutive NO synthase (ecNOS) and nitrotyrosine.

RESULTS

Compared with normal oral mucosa, the AI, Bcl-2, Bax, Bcl-2/Bax intensity and frequency ratios, and mutant p53 intensity significantly changed in reactive/dysplastic and HNSCCa lesions (P <.001 for all). Correlations between the staining characteristics of the antigens studied are presented. Furthermore, perilesional inflammatory cells showed staining in the TUNEL assay.

CONCLUSIONS

In a set of tissue samples previously well characterized, these new findings implicate a link between NO and the induction of apoptotic cell death in HNSCCa development.

Expression of Apo-3 and Apo-3L in primitive neuroectodermal tumours of the central and peripheral nervous system

Deregulation of apoptosis has been implicated in the pathogenesis, spontaneous regression and treatment resistance of neuroblastoma. A newly recognised member of the tumour necrosis factor (TNF)-family of death receptors known as Apo-3 has been mapped to human chromosome 1p36.3, a region commonly deleted in aggressive neuroblastoma. Based on its localisation and function, Apo-3 is a candidate for the putative neuroblastoma tumour suppressor gene. Therefore we analysed mRNA expression of the Apo-3 receptor/ligand (Apo-3/Apo-3L) system in a representative panel of 18 neuroblastoma cell lines, 41 primary neuroblastoma and 13 ganglioneuromas/ganglioneuroblastomas by semi-quantitative RT-PCR. We compared the level of expression with the well-established prognostic factors age, stage, histology, MYCN-amplification and TrkA expression, as well as outcome. For comparison, we studied Apo-3/Apo-3L expression in 27 central nervous system (CNS) primitive neuroectodermal tumours/medulloblastomas (PNET/medulloblastoma) and in six normal brain samples. Neuroblastoma cell lines with 1p deletion and MYCN-amplification expressed significantly lower levels of Apo-3 (P=0.009 and P=0.03, respectively) compared with neuroblastoma cell lines without 1p deletion or MYCN-amplification. The mean expression level of Apo-3L was significantly higher in ganglioneuromas/ganglioneuroblastomas compared with neuroblastomas (P=0.001) and in normal brain compared with PNET/medulloblastoma (P<0.0001). Expression of Apo-3L was significantly associated with survival in neuroblastomas (P<0.049) and in PNET/medulloblastomas (P=0.01). Expression of Apo-3 was significantly associated with survival in PNET/medulloblastomas (P=0.03). Thus, the Apo-3 receptor/ligand system might be involved in the regulation of apoptosis in neuroblastomas and PNET.

Structural analysis of a functional DIAP1 fragment bound to grim and hid peptides

The inhibitor of apoptosis protein DIAP1 suppresses apoptosis in Drosophila, with the second BIR domain (BIR2) playing an important role. Three proteins, Hid, Grim, and Reaper, promote apoptosis, in part by binding to DIAP1 through their conserved N-terminal sequences. The crystal structures of DIAP1-BIR2 by itself and in complex with the N-terminal peptides from Hid and Grim reveal that these peptides bind a surface groove on DIAP1, with the first four amino acids mimicking the binding of the Smac tetrapeptide to XIAP. The next 3 residues also contribute to binding through hydrophobic interactions. Interestingly, peptide binding induces the formation of an additional alpha helix in DIAP1. Our study reveals the structural conservation and diversity necessary for the binding of IAPs by the Drosophila Hid/Grim/Reaper and the mammalian Smac proteins.

Suppression of apoptosis: role in cell growth and neoplasia

A cell is a potentially dangerous thing. In unicellular organisms, cells divide and multiply in a manner that is chiefly determined by the availability of nutritional substrates. In a multicellular organism, each cell has a distinct growth potential that is designed to subsume a role in the function of the whole body. Departure from this path to one of uncontrolled cellular proliferation leads to cancer. For this reason, evolution has endowed cells with an elaborate set of systems that cause errant cells to self-destruct. This process of cell suicide is known as apoptosis or programmed cell death and it plays a crucial role in the growth of both normal and malignant cells. In this review, we describe the mechanisms whereby programmed cell death is induced and executed. In particular, we concentrate on how anti-apoptotic signals generated by cytokines promote cell survival and how these signal transduction pathways may be involved in the pathogenesis of neoplasia. Understanding how these processes contribute to tumorigenesis may suggest new therapeutic options.

Caspase-3 activity as a prognostic factor in colorectal carcinoma

Several techniques to determine apoptotic frequencies in tumors have been described. In this study, we report that biochemical detection of enzymatic caspase-3 activity is a simple and quantitative technique to measure apoptosis in colorectal tumor cells. The relevance of the level of apoptosis in colorectal cancer for the clinical course remains unclear. Therefore, we studied the correlation between caspase-3 activity and prognosis of the disease in relation to different factors known to be involved in apoptosis induction. High caspase-3 activity significantly correlated with a higher risk of recurrence and was preferentially found in tumors of the right side of the colon. No correlation was detected between high caspase-3 activity and altered protein expression of p53, beta-catenin, or proteins of mismatched repair genes. This indicates that high caspase-3 activity has no evident correlation with the genetic Wnt-signaling or the mismatch repair mutational pathways. The caspase-3 activity significantly correlated with CD57(+) tumor infiltrating cells. Therefore, high caspase-3 activity in right-sided tumors might be induced by a specific lymphocytic reaction.

Structural basis of caspase-7 inhibition by XIAP

The inhibitor of apoptosis (IAP) proteins suppress cell death by inhibiting the catalytic activity of caspases. Here we present the crystal structure of caspase-7 in complex with a potent inhibitory fragment from XIAP at 2.45 A resolution. An 18-residue XIAP peptide binds the catalytic groove of caspase-7, making extensive contacts to the residues that are essential for its catalytic activity. Strikingly, despite a reversal of relative orientation, a subset of interactions between caspase-7 and XIAP closely resemble those between caspase-7 and its tetrapeptide inhibitor DEVD-CHO. Our biochemical and structural analyses reveal that the BIR domains are dispensable for the inhibition of caspase-3 and -7. This study provides a structural basis for the design of the next-generation caspase inhibitors.

Natural protection from apoptosis by surfactant protein A in type II pneumocytes

Surfactant-associated protein A (SP-A) is a component of pulmonary surfactant that binds to a specific receptor (SPAR) on the surface of type II alveolar cells of the lung and regulates gene expression and surfactant secretion. Previously we have shown that activation of SPAR by SP-A binding initiates a signal through pathways that involve tyrosine phosphorylation, include IRS-1, and entail activation of phosphatidylinositol 3-kinase (PI3K). In other cell types, cytokines that activate the PI3K signaling pathway promote cell survival. Therefore we investigated whether there was an effect of SP-A on apoptosis as measured by DNA laddering, FACS analysis, TUNEL assay, and annexin V binding. SP-A protected primary cultures of rat type II alveolar cells against the apoptotic effects of etoposide and UV light and also protected the H441 human Clara lung tumor cell line against staurosporine-induced apoptosis. The protective effects of SP-A were abrogated by inhibition of either tyrosine-specific protein kinase activity or PI3K. SP-A/SPAR interaction thus initiates a signaling pathway that regulates apoptosis in type II cells. These findings may be important in understanding the pathogenesis of acute lung injury and pulmonary tumorigenesis and may suggest new therapeutic options.

Functional analysis of tumour necrosis factor-alpha-related apoptosis-inducing ligand (TRAIL): cysteine-230 plays a critical role in the homotrimerization and biological activity of this novel tumoricidal cytokine

We have determined that the mutation of the cysteine-230 residue to either glycine or serine in TRAIL (tumour necrosis factor-alpha-related apoptosis-inducing ligand) results in the formation of a structurally incompetent dimer and a consequent loss of apoptotic activity. Similarly, chemical modification of the thiol residues present in both reduced and Zn(2+)-depleted trimer converts TRAIL into an inactive dimer. We postulate that cysteine-230 plays a critical role in homotrimerization of this tumoricidal cytokine.

Prognostic significance of apoptosis in laryngeal cancer. A quantitative immunomorphological study

The main purpose of the study was to investigate the prognostic significance of apoptosis of cancer cells and to examine the relationship between apoptosis and morphological markers of the host immune response in laryngeal cancer. Apoptotic tumour cells, detected by the TUNEL technique, expression of HLA DR (an antigen belonging to human leukocyte-associated antigens class II) in cancer cells, the number of tumour infiltrating T cells (CD45RO+ cells), B cells (CD20+ cells), macrophages (CD68+ cells) and mast cells as well as the mitotic index were investigated in 28 laryngeal cancers. Sections were studied morphometrically using image analysis. Significant inverse correlations between the number of apoptotic tumour cells and HLA DR-positive tumour cells as well as between the number of apoptotic tumour cells and the number of CD45RO+ cells at the tumour periphery were observed. Analysis of survival showed that patients with high rates of apoptosis had significantly worse prognosis as compared to patients with low apoptotic rates. Differences in HLA DR expression and numbers of CD45RO+ cells were also found between groups of patients with high and low numbers of apoptotic cells. Whether these findings are due to immunosuppressive effects of apoptosis needs further investigation.

Structural and biochemical basis of apoptotic activation by Smac/DIABLO

Apoptosis (programmed cell death), an essential process in the development and homeostasis of metazoans, is carried out by caspases. The mitochondrial protein Smac/DIABLO performs a critical function in apoptosis by eliminating the inhibitory effect of IAPs (inhibitor of apoptosis proteins) on caspases. Here we show that Smac/DIABLO promotes not only the proteolytic activation of procaspase-3 but also the enzymatic activity of mature caspase-3, both of which depend upon its ability to interact physically with IAPs. The crystal structure of Smac/DIABLO at 2.2 A resolution reveals that it homodimerizes through an extensive hydrophobic interface. Missense mutations inactivating this dimeric interface significantly compromise the function of Smac/DIABLO. As in the Drosophila proteins Reaper, Grim and Hid, the amino-terminal amino acids of Smac/DIABLO are indispensable for its function, and a seven-residue peptide derived from the amino terminus promotes procaspase-3 activation in vitro. These results establish an evolutionarily conserved structural and biochemical basis for the activation of apoptosis by Smac/DIABLO.

Apoptosis: implications for inflammatory bowel disease

Cells of the intestinal mucosa live in a harsh environment and therefore rely heavily on the highly regulated process of cell death, apoptosis, to maintain tissue integrity. Imbalance in the intracellular events that modulate apoptosis may contribute to the pathogenesis of inflammatory bowel disease.

Reciprocal control of apoptosis and proliferation in cultured rat hepatoma arl-6 cells: roles of nutrient supply, serum, and oxidative stress

In order to understand how cancer cells accumulate, rat hepatoma ARL-6 cells were cultured for 8 d to identify factors involved in spontaneous cell proliferation and apoptosis. With increasing time in culture, the proportion of cells in the proliferative phases of the cell cycle and the rate of deoxyribonucleic acid (DNA) synthesis decreased. The waning of proliferation was associated with a gradual reduction of cell viability, and this was temporally related to the appearance of typical apoptotic morphology and DNA laddering. Medium replacement or supplementation with fetal calf serum (FCS) suppressed apoptosis, while medium change, but not fetal calf serum alone, enhanced cell proliferation. Apoptosis was also suppressed by dimethyl sulfoxide (DMSO), but supplementary glutathione was without effect. Expression of poly(adenosine diphosphate[ADP]-ribose)polymerase peaked on days 34 of culture, and was followed by a progressive decrease thereafter, consistent with proteolytic cleavage. This decrease was prevented to varying extents by complete medium replacement, FCS and DMSO, indicating a close temporal relationship between poly(ADP-ribose)polymerase activation and apoptosis. Expression of Fas and Bcl-2 did not change appreciably over the 8-d culture, but there was a gradual increase in Bax expression; medium change, FCS and DMSO all partly inhibited Bax expression. These data indicate that spontaneous apoptosis in cultured ARL-6 cells is inversely related to cell proliferation, and that nutrient supply, and to a lesser extent, serum-derived factors and oxidative stress modulate apoptosis in this system. Proteolytic cleavage of poly(ADP-ribose)polymerase and expression of Bax are likely to be mechanistically involved with the control of spontaneous apoptosis in ARL-6 cells, whereas changes in the levels of Fas and Bcl-2 do not play a role.

Bcl-xS and Bax induce different apoptotic pathways in PC12 cells

Apoptosis is regulated by the action of the Bcl-2 family of proteins, which includes anti- and pro-apoptotic members such as Bcl-xS and Bax. These proteins may differ from each other in structure, mechanism of action and interactions with anti-apoptotic signaling. The mechanism whereby Bax induces cell death has been studied in some cellular systems, but the mechanism of Bcl-xS-induced apoptosis is largely unknown. In this study we investigated and compared the apoptotic effects of Bcl-xS and Bax in the pheochromocytoma cell line, PC12 (a useful model system for studying neuronal apoptosis), and the extent to which they are protected by the survival factor, nerve growth factor (NGF). PC12 cells express endogenous Bcl-xS, Bax and Bcl-xL proteins. Subcellular fractionation revealed that Bax is presented mainly in the cytosolic and the heavy membrane fractions, Bcl-xS is present only in the cytosol, and the anti-apoptotic protein Bcl-xL is located mainly in the heavy membrane fraction. In contrast to the cytosolic localization of endogenous Bcl-xS, the exogenously overexpressed Bcl-xS is localized to the mitochondria. Overexpression of Bcl-xS or Bax induces cell death in the transfected cells. The cell death induced by overexpression of Bcl-xS was inhibited by coexpression of Bcl-xS with Bcl-2 or Bcl-xL, or by treatment with the broad-spectrum caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoro-methylketone (Z-VAD-FMK) or with NGF. The Bcl-2 mutants deltaC22, which lacks the transmembrane domain, and G145A (mI-3) were able to inhibit the death-inducing effect of Bcl-xS. These results therefore suggest that the apoptotic pathway induced by overexpression of Bcl-xS in PC12 cells can be controlled by Bcl-2 and Bcl-xL, is mediated by caspases, and can be inhibited by the NGF signaling pathway. The Bax-induced cell death was inhibited by co-expression of Bax with Bcl-2 or Bcl-xL, but was not inhibited by Z-VAD-FMK, NGF, or the Bcl-2 ml-3 or deltaC22 mutants. These results therefore suggest that Bax induces a caspase-independent cell death pathway which is blocked by Bcl-2 but not by the NGF signaling pathway. They further suggest that Bcl-xS and Bax induce different cell death pathways in PC12 cells.

Comparison of BCL-2 and BAX protein expression with in vitro sensitivity to ARA-C and 6TG in AML

Activity of BCL-2 protein may be antagonised by BAX protein expression, thereby affecting cellular sensitivity to chemotherapeutic drugs. We analysed the BCL-2 protein expression of blast cells from 19 patients by flow cytometry and immunocytochemistry. This was compared to in vitro sensitivity to the anthracyclines and antimetabolites using the MTT assay. We found a significant correlation between BCL-2 expression and in vitro response to two antimetabolite drugs. One of 7 patients (14%) whose cells were sensitive to ara-C expressed BCL-2 compared to 4/4 patients (100%) whose cells were resistant to ara-C in vitro (p = 0.05). Furthermore, none of the three patients whose cells were sensitive to 6-TG expressed BCL-2 compared to 6/9 patients (67%) whose cells were resistant in vitro (p = 0.045). We found no other correlation between BCL-2 expression and any other chemotherapeutic drug analysed. The ratio of BCL-2 to BAX may be more relevant clinically, therefore cells from a further 9 patients were analysed for both proteins. Whilst there was no overall relationship between BCL-2/BAX ratios and sensitivity to ara-C and 6TG, individual patients could be identified whose blast cells were resistant to ara-C and had high BCL-2/BAX ratios. Further analysis of the significance of these ratios to drug resistance may be of future prognostic value.

Apoptosis-associated generation of reactive oxygen intermediates and release of pro-inflammatory cytokines in human lymphocytes and granulocytes by extracts from the seeds of Acalypha wilkesiana

Seeds from Acalypha wilkesiana (Euphorbiaceae) are an essential component of a complex plant mixture used empirically by traditional healers in Southwest Nigeria to treat breast tumours and inflammation. To investigate their biological properties, we incubated human lymphocytes and granulocytes with aqueous and ethanolic extracts of A. wilkesiana seeds (AWS). In lymphocytes, we observed an induction of apoptosis and generation of reactive oxygen intermediates (ROI), as measured by the oxidation of hydroethidine, within 2 h, while in granulocytes, an aqueous seed extract induced the oxidative burst and enhanced phagocytosis of Escherichia coli within 10-20 min. In the supernatants of 72-h cultured lymphocytes, AWS induced the release of the pro-inflammatory cytokines tumour necrosis factor-alpha and interleukin-6, and also T-cell-associated cytokines interleukin-5 and interferon-gamma. These preliminary results encourage further investigations of this drug with both cytotoxic and immunomodulating properties.

Bcl-2 targeted to the endoplasmic reticulum can inhibit apoptosis induced by Myc but not etoposide in Rat-1 fibroblasts

Bcl-2 is a key inhibitor of a broad range of apoptotic pathways, yet neither the mechanism of action nor the role of Bcl-2 subcellular localization are well understood. The subcellular localization of Bcl-2 includes the mitochondrial membrane as well as the contiguous membrane of the endoplasmic reticulum and nuclear envelope. Most studies suggest that the ability of Bcl-2 to confer cell survival is dependent upon its localization to the mitochondria. In this manuscript, we show that Bcl-2 targeted to the endoplasmic reticulum can inhibit Myc-, but not etoposide-induced apoptosis in the Rat-1 fibroblast cell line. By contrast, wild type Bcl-2 can inhibit apoptosis triggered by either death agonist. We further show both Myc and etoposide trigger disruption of mitochondrial membrane potential (MMP) and induce poly-ADP ribose polymerase (PARP) cleavage, but release of calcium was not evident. Bcl-2 abrogates apoptosis at or upstream of MMP depletion showing that Bcl-2 does not have to reside at the mitochondria to prevent apoptosis. These results further elucidate the biochemical events associated with Myc- and etoposide-induced apoptosis and significantly advance our understanding of Bcl-2 function.

Structural basis of procaspase-9 recruitment by the apoptotic protease-activating factor 1

Caspase-9-mediated apoptosis (programmed cell death) plays a central role in the development and homeostasis of all multicellular organisms. Mature caspase-9 is derived from its procaspase precursor as a result of recruitment by the activating factor Apaf-1. The crystal structures of the caspase-recruitment domain of Apaf-1 by itself and in complex with the prodomain of procaspase-9 have been determined at 1.6 and 2.5 A resolution, respectively. These structures and other evidence reveal that each molecule of Apaf-1 interacts with a molecule of procaspase-9 through two highly charged and complementary surfaces formed by non-conserved residues; these surfaces determine recognition specificity through networks of intermolecular hydrogen bonds and van der Waals interactions. Mutation of the important interface residues in procaspase-9 or Apaf-1 prevents or reduces activation of procaspase-9 in a cell-free system. Wild-type, but not mutant, prodomains of caspase-9 completely inhibit catalytic processing of procaspase-9. Furthermore, analysis of homologues from Caenorhabditis elegans indicates that recruitment of CED-3 by CED-4 is probably mediated by the same set of conserved structural motifs, with a corresponding change in the specificity-determining residues.

Interferon-induced proteins are elevated in blood samples of patients with chemically or virally induced chronic fatigue syndrome

Overlapping symptomatologies between Chronic Fatigue Syndrome (CFS) and Chemical Sensitivity have been observed by different investigators. Therefore, it is of great importance to develop biomarker(s) for possible differentiation between viral induced CFS (without sensitivity to chemicals) versus chemically induced CFS. Since interferon induced proteins 2-5A Synthetase and Protein Kinase RNA (PKR) have been implicated in the viral induction of CFS, the objective of this study was to utilize 2-5A and PKR activity for differentiation between CFS induced by either viruses or chemicals. Based on the CDC definition and criteria, twenty CFS patients who were positive for viral genome(s) (mainly HHV6; HTLVII, EBV, and CMV) and did not have any history of exposure to toxic chemicals were included in this study. As a comparison, the second group of patients consisted of twenty individuals from the same geographical area who were negative for viral genomes but had been exposed to methyl tertiary-butyl ether concentration of up to 70 ppb and benzene concentration up to 14 ppb. All patients complained of fatigue and other symptoms overlapping between the two groups. From all 40 patients, blood was drawn, leukocyte extract was prepared and assayed for 2-5A Synthetase and PKR activity. Clinical specimens which were positive for viral genomes showed from 2.2-38.7 fold increase in 2-5A activity and 1.3-13.5 fold increase in PKR activities over the background of the healthy controls. Similarly, the second group (negative for viral genomes, but exposed to chemicals) showed a 1.1-29.2 fold increase for 2-5A Synthetase and a 1.3-11.6 fold increase for PKR when they were compared to healthy subjects. To elucidate mechanisms involved in viral versus chemical induction of 2-5A Synthetase and PKR, MDBK cell lines were cultured either in the presence or absence of HHV6, MTBE, or Benzene, heat shock proteins and interferon-beta. 2-5A and PKR activities were measured in all the above conditions. A clear induction of 2-5A and PKR was observed when MDBK cells were exposed to HHV6, MTBE, and Benzene. This induction was more significant with HSP90, HSP70, and IFN-beta indicating their involvement in the mechanism of action. However, when MDBK cells were incubated either with MTBE + Benzene or HHV6 in the presence or absence of anti IFN-beta or anti-HSP-70, the activities of both 2-5A and PKR in HHV6 infected cells were inhibited by more than 90% due to addition of anti IFN-beta, and only 20% by addition of anti-HSP70. While in MTBE + Benzene exposed cells anti IFN-beta reduced the activity of these enzymes by 40% and anti-HSP70 by more than 90%. This variation in the induction of 2-5A and PKR by anti-HSP70 or IFN-beta indicates involvement of IFN-beta in viral induction 2-5A and PKR, and HSP involvement in chemical induction of these enzymes. We conclude that 2-5A and PKR are not only biomarkers for viral induction of CFS, but biomarkers to other stressors that include MTBE and Benzene.

The point of no return: mitochondria, caspases, and the commitment to cell death

Apoptosis is a specialized mode of cell death finely regulated at the molecular level and conserved throughout evolution. In many instances during normal development or in order to maintain the homeostasis of a multicellular organism, a strategic intracellular program is initiated ensuring the fate of unwanted cells. Interference with this program has been implicated in many pathologies, particularly in cancer and autoimmune diseases. What is most important, from the organism's point of view, is that the dismissal of the outcast cells is accomplished serenely, i.e., the dying cells resign their existence without causing an inflammatory reaction. Therefore, the ability to manipulate the cell death machinery is an obvious goal of medical research. Here, we debate the idea of the point-of-no-return and propose models for the role of "initiator" and "executioner" caspases in the death program. We argue that, in many circumstances, the cells are committed to die before the execution phase of apoptosis starts. This commitment event is coordinated by the mitochondria and can be blocked by anti-apoptotic oncogenes.

Reflux-induced apoptosis of the esophageal mucosa is inhibited in Barrett's epithelium

BACKGROUND

Apoptosis maintains cell homeostasis. Altered apoptosis is involved in carcinogenesis. It was our aim to investigate whether reflux esophagitis may alter apoptosis in the esophageal mucosa and whether antireflux surgery may restore normal apoptosis.

METHODS

Apoptosis was studied preoperatively and postoperatively in esophageal biopsies of 39 patients with various grades of reflux esophagitis and in Barrett's mucosa using the TUNEL method. Biopsies were also taken from lesions of the squamous epithelium adjacent to the Barrett's mucosa.

RESULTS

Apoptosis increased with the severity of esophagitis. Apoptosis was low in Barrett's epithelium. Squamous epithelium adjacent to Barrett's mucosa showed increased apoptosis. After surgery apoptosis decreased in squamous epithelium, and it remained low in Barrett's epithelium.

CONCLUSIONS

Apoptosis in reflux esophagitis may be protective against increased proliferation. Low apoptosis following antireflux surgery indicates that surgery is effective to prevent reflux-induced cell proliferation. Inhibition of apoptosis in Barrett's may promote carcinogenesis. This may not change following surgery.

Aqueous humor-borne factor upregulates Bcl-2 expression in corneal endothelial cells

PURPOSE

To determine if factors present in the aqueous humor (AH) protect the corneal endothelium from apoptosis.

METHODS

Mouse and human corneal endothelial cells were cultured in vitro, and apoptosis was induced by nutrient deprivation. AH and supernatant from iris/ciliary body (I/CB) cell cultures were tested for their effect on corneal endothelial cell apoptosis. The effect of I/CB supernatant on Fas, Bax, and Bcl-2 gene transcription was evaluated by Northern blotting. I/CB supernatant was subjected to proteinase analysis to identify the apoptosis inhibitory factor(s).

RESULTS

Rabbit AH and supernatant from mouse I/CB cell cultures inhibited the apoptosis of mouse and human immortalized corneal endothelial cell lines. The inhibition of apoptosis was associated with an upregulation of Bcl-2 gene transcription and Bcl-2 protein expression. Bax gene expression was not significantly affected by I/CB cell supernatant. Induction of apoptosis by stimulation of the Fas receptor was unaffected by I/CB cell supernatant. Protease analyses indicated that the apoptosis inhibitory factor was a protein.

CONCLUSIONS

The inability of corneal endothelial cells to undergo mitosis renders the corneal endothelium vulnerable to loss of physiological function through cellular attrition. However, a protein(s) produced by I/CB cells and present in the AH, upregulates Bcl-2 gene transcription and protects the corneal endothelial cells from apoptosis.

Inhibition of proteasome function prevents thymocyte apoptosis: involvement of ornithine decarboxylase

We have previously shown that polyamine levels rapidly decrease in thymocytes undergoing apoptosis, and that ornithine decarboxylase increases early but too transiently to maintain elevated polyamine levels. These data led us to suppose that a precocious ornithine decarboxylase degradation might be responsible for the imbalance of polyamine metabolism. Ornithine decarboxylase is known to be degraded by the cytosolic 26S proteasome that plays an essential role in thymocyte apoptosis. In this paper we demonstrate that the inhibition of proteasome function preserves ornithine decarboxylase activity and prevents thymocytes from undergoing apoptosis after dexamethasone treatment. Since intracellular polyamine levels are also preserved, ornithine decarboxylase seems to be functionally active in maintaining polyamine homeostasis after proteasome inhibition in thymocytes. Our proposed role for the proteasome in quiescent cells upon an apoptotic stimulus is to degrade proteins like ornithine decarboxylase that are involved in the control of the cell cycle and cell survival.

Induction of apoptosis by the N-acetyl-galactosamine-specific toxic lectin from Viscum album L. is associated with a decrease of nuclear p53 and Bcl-2 proteins and induction of telomeric associations

The ribosome-inhibiting proteins from Viscum album L., i.e. the mistletoe lectins (ML), were recognized to induce apoptosis in various tumour cell lines and human lymphocytes. However, several aspects of ML-induced cell death are unclear. We report that the galNAc-binding ML III incubated with human lymphocytes mediates a very effective death signal resulting in the binding of Annexin-V and expression of mitochondrial membrane proteins Apo2.7, but also in an influx of the DNA intercalating dye propidium iodide. The addition of the ribosome-inhibiting protein Volkensin also induced Apo2.7 molecules, while Momordin, lacking a carbohydrate-binding chain, did not enter the cell membrane and thus did not affect the cells. However, we observed ML III to preferentially affect CD8+ cells with a memory phenotype (CD62L(lo)) as compared to their CD8+ CD62L(hi) counterparts, CD4+ T cells and CD19+ B cells. Furthermore, ML III did not induce sister chromatid exchange-inducing DNA lesions but reduced the intensity of telomeric signals, increased the frequencies of telomeric associations and C-anaphases and reduced nuclear Bcl-2 and p53 proteins. Whatever the exact mechanisms are, our results provide strong evidence that the ML III-mediated cytotoxicity involves distinct killing pathways, i.e. (1) primary cell death via an induction of apoptosis which may not be dependent on protein and/or RNA synthesis and may not involve p53 and Bcl-2 proteins and (2) a loss of telomeres resulting in chromosomal instability in the surviving cells which is incompatible with life. However, we cannot exclude the possibility that this effect is due to a decrease in nuclear p53 proteins.

Differential requirement for caspase 9 in apoptotic pathways in vivo

Mutation of Caspase 9 (Casp9) results in embryonic lethality and defective brain development associated with decreased apoptosis. Casp9-/- embryonic stem cells and embryonic fibroblasts are resistant to several apoptotic stimuli, including UV and gamma irradiation. Casp9-/- thymocytes are also resistant to dexamethasone- and gamma irradiation-induced apoptosis, but are surprisingly sensitive to apoptosis induced by UV irradiation or anti-CD95. Resistance to apoptosis is accompanied by retention of the mitochondrial membrane potential in mutant cells. In addition, cytochrome c is translocated to the cytosol of Casp9-/- ES cells upon UV stimulation, suggesting that Casp9 acts downstream of cytochrome c. Caspase processing is inhibited in Casp9-/- ES cells but not in thymocytes or splenocytes. Comparison of the requirement for Casp9 and Casp3 in different apoptotic settings indicates the existence of at least four different apoptotic pathways in mammalian cells.

Duplication of the DR3 gene on human chromosome 1p36 and its deletion in human neuroblastoma

The human DR3 gene, whose product is also known as Wsl-1/APO-3/TRAMP/LARD, encodes a tumor necrosis factor-related receptor that is expressed primarily on the surface of thymocytes and lymphocytes. DR3 is capable of inducing both NF-kappa B activation and apoptosis when overexpressed in mammalian cells, although its ligand has not yet been identified. We report here that the DR3 gene locus is tandemly duplicated on human chromosome band 1p36.2-p36.3 and that these genes are hemizygously deleted and/or translocated to another chromosome in neuroblastoma (NB) cell lines with amplified MYCN. Duplication of at least a portion of the DR3 gene, including the extracellular and transmembrane regions but not the cytoplasmic domain, was demonstrated by both fluorescence in situ hybridization and genomic Southern blotting. In most NB cell lines, both the DR3 and the DR3L sequences are simultaneously deleted and/or translocated to another chromosome. Finally, DR3/ Wsl-1 protein expression is quite variable among these NB cell lines, with very low or undetectable levels in 7 of 17 NB cell lines.