Cleavage of Bcl-2 is an early event in chemotherapy-induced apoptosis of human myeloid leukemia cells

New synthetic phenylquinazoline derivatives induce apoptosis by targeting the pro-survival members of the BCL-2 family

Chemo-resistant cancer cells acquire robust growth potential through cell signaling mechanisms such as the down-regulation of tumor suppressors and the up-regulation of pro-survival proteins, respectively. To overcome chemo-resistance of cancer, small molecule drugs that interact with the cell signaling proteins to enhance sensitization of cancer cells toward cancer therapies are likely to be effective for the treatment of chemo-drug resistant cancer. To identify high potency small molecules, a series of ten novel phenylquinazoline derivatives were synthesized to determine their cellular effects in MCF-7 and MCF-7- cisplatin-resistant (CR) human breast cancer cells which led to the identification of two bioactive compounds, SMS-IV-20 and SMS-IV-40, that exhibited an elevated level of cytotoxicity against the human breast cancer cells and spheroid cells. In addition, both compounds enhanced chemo-sensitization of the human breast cancer cells that were genetically engineered to express the tumor suppressor and pro-apoptotic proteins, MOAP-1, Bax, and RASSF1a (MBR), suggesting that the compounds interact with the MBR signaling pathway. Furthermore, when MCF-7-CR cells were treated with SMS-IV-20 and SMS-IV-40 in the presence of ABT-737, a BCL-XL and BCL-2 inhibitor, enhanced chemo-sensitization was observed, suggesting SMS-IV-20 and SMS-IV-40 exert antagonistic activity to regulate the functional activity of BCL-2 and BCL-XL. Western blot analysis showed that both SMS-IV-20 and SMS-IV-40 induced down-regulation of BCL-2 or both BCl-2 and BCL-XL expression, respectively while promoting the release of mitochondrial Cytochrome C. Taken together, the data showed that SMS-IV-20 and SMS-IV-40 are potent activators of apoptosis that enhance chemo-sensitization through their antagonistic actions on the pro-survival activity of the BCl-2 family in human cancer cells.

Higher Serum Levels of Lactate Dehydrogenase Before Microsurgery Predict Poor Outcome of Aneurysmal Subarachnoid Hemorrhage

Introduction: We explored whether higher preoperative serum levels of lactate dehydrogenase (LDH) predicted outcome 3 months after surgery in patients with aneurysmal subarachnoid hemorrhage (aSAH) treated using microsurgical clipping in our institution.

Methods: Patients with aSAH treated at our institution between 2010 and 2018 were enrolled. The following parameters were recorded: age, sex, smoking and drinking history, medical history, Hunt–Hess and Fisher grades, aneurysm location, aneurysm size, surgical treatment, delayed cerebral ischemia (DCI), intracranial infection, hydrocephalus, pneumonia, and preoperative serum LDH levels within 24 h of aSAH. We investigated whether preoperative serum LDH levels were associated with Hunt–Hess grade, Fisher grade, and functional neurological outcome.

Results: In total, 2,054 patients with aSAH were enrolled, 874 of whom were treated using microsurgical clipping. The average serum LDH level (U/L) was significantly lower in the good outcome group (180.096 ± 50.237) than in the poor outcome group (227.554 ± 83.002; p < 0.001). After propensity score matching, the average serum LDH level (U/L) was still lower in the good outcome group (205.356 ± 76.785) than in the poor outcome group (227.119 ± 86.469; p = 0.029). The area under the receiver operating characteristic (ROC) curve was 0.702 (95% confidence interval [CI]: 0.650–0.754; p < 0.001). Based on the ROC curve, the optimal cutoff value for serum LDH levels as a predictor of poor 3-month outcome (modified Rankin Scale score > 2) was 201.5 U/L. The results revealed that Hunt–Hess grade, Fisher grade, DCI, pneumonia, and serum LDH (>201.5 U/L) were significantly associated with poor outcome. After propensity score matching, serum LDH levels > 201.5 U/L were still considered an independent risk factor for poor outcome (odds ratio: 2.426, 95% CI = 1.378–4.271, p = 0.002). Serum LDH levels were associated with Hunt–Hess and Fisher grades and were correlated with functional neurological outcomes (p < 0.001).

Conclusions: Our findings showed that higher preoperative serum levels of LDH correlated with Hunt–Hess grade, Fisher grade, and neurological functional outcome, and predicted the outcome of aSAH treated by microsurgical clipping at 3 months, which was involved in the related mechanisms of early brain injury and showed its potential clinical significance in patients with aSAH.

Dual Targeting of Aurora Kinases with AMG 900 Exhibits Potent Preclinical Activity Against Acute Myeloid Leukemia with Distinct Post-Mitotic Outcomes

Aurora kinase A and B have essential and non-overlapping roles in mitosis, with elevated expression in a subset of human cancers, including acute myeloid leukemia (AML). In this study, pan-aurora kinase inhibitor (AKI) AMG 900 distinguishes itself as an anti-leukemic agent that is more uniformly potent against a panel of AML cell lines than are isoform-selective AKIs and classic AML drugs. AMG 900 inhibited AML cell growth by inducing polyploidization and/or apoptosis. AMG 900 and aurora-B-selective inhibitor AZD1152-hQPA showed comparable cellular effects on AML lines that do not harbor a FLT3-ITD mutation. AMG 900 was active against P-glycoprotein-expressing AML cells resistant to AZD1152-hQPA and was effective at inducing expression of megakaryocyte-lineage markers (CD41, CD42) on human CHRF-288-11 cells and mouse Jak2 V617F cells. In MOLM-13 cells, inhibition of p-histone H3 by AMG 900 was associated with polyploidy, extra centrosomes, accumulation of p53 protein, apoptosis, and cleavage of Bcl-2 protein. Co-administration of cytarabine (Ara-C) with AMG 900 potentiated cell killing in a subset of AML lines, with evidence of attenuated polyploidization. AMG 900 inhibited the proliferation of primary human bone marrow cells in culture, with a better proliferation recovery profile relative to classic antimitotic drug docetaxel. In vivo, AMG 900 significantly reduced tumor burden in a systemic MOLM-13 xenograft model where we demonstrate the utility of 3'-deoxy-3'-18F-fluorothymidine [18F]FLT positron emission tomographic (PET)-CT imaging to measure the antiproliferative effects of AMG 900 in skeletal tissues in mice.

Eucalyptus microcorys leaf extract derived HPLC-fraction reduces the viability of MIA PaCa-2 cells by inducing apoptosis and arresting cell cycle

New therapeutic strategies such as the development of novel drugs and combinatorial therapies with existing chemotherapeutic agents are urgently needed to improve the clinical prognosis of pancreatic cancer. We have previously reported the antiproliferative properties of aqueous crude Eucalyptus microcorys extract against pancreatic cancer cell lines. In this study, bioassay-guided fractionation of the aqueous crude E. microcorys extract using RP-HPLC and subsequent assessment of the resultant fractions (F1-F5) for their antioxidant activity and cytotoxicity against pancreatic cancer cell lines were performed. The molecular mechanisms associated with the cytotoxicity was characterised by studying the effects of the most potent fraction-1 (F1) on apoptosis and cell cycle profiles as well as its phytochemical constituents by LC-ESI/MS/MS. F1 displayed significantly greater antioxidant activity in three different assays (p < 0.05). Moreover, F1 exhibited significantly greater antiproliferative activity (IC₅₀ = 93.11 ± 3.43 μg/mL) against MIA PaCa-2 cells compared to the other four fractions (p < 0.05). F1 induced apoptosis by regulating key apoptotic proteins- Bcl-2, Bak, Bax, cleaved PARP, procaspase-3 and cleaved caspase-3 in MIA PaCa-2 cells, suggesting the involvement of intrinsic mitochondrial apoptotic pathway and arrested cells at G2/M phase. A combination of gemcitabine and F1 exerted a greater effect on apoptosis and cell cycle arrest than F1 or gemcitabine alone (p < 0.05). LC-ESI/MS/MS revealed the tentative identities of phytochemicals present in F1 and their similarities with the phenolic compounds previously reported in Eucalyptus with antipancreatic cancer activity. Our study shows that the polyphenol and antioxidant-rich fraction of E. microcorys extract is a promising candidate for developing mono or combination therapies against pancreatic cancer.

Carfilzomib Triggers Cell Death in Chronic Lymphocytic Leukemia by Inducing Proapoptotic and Endoplasmic Reticulum Stress Responses

PURPOSE

Carfilzomib, while active in B-cell neoplasms, displayed heterogeneous response in chronic lymphocytic leukemia (CLL) samples from patients and showed interpatient variability to carfilzomib-induced cell death. To understand this variability and predict patients who would respond to carfilzomib, we investigated the mechanism by which carfilzomib induces CLL cell death.

EXPERIMENTAL DESIGN

Using CLL patient samples and cell lines, complementary knockdown and knockout cells, and carfilzomib-resistant cell lines, we evaluated changes in intracellular networks to identify molecules responsible for carfilzomib's cytotoxic activity. Lysates from carfilzomib-treated cells were immunoblotted for molecules involved in ubiquitin, apoptotic, and endoplasmic reticulum (ER) stress response pathways and results correlated with carfilzomib cytotoxic activity. Coimmunoprecipitation and pull-down assays were performed to identify complex interactions among MCL-1, Noxa, and Bak.

RESULTS

Carfilzomib triggered ER stress and activation of both the intrinsic and extrinsic apoptotic pathways through alteration of the ubiquitin proteasome pathway. Consequently, the transcription factor CCAAT/enhancer-binding protein homology protein (CHOP) accumulated in response to carfilzomib, and CHOP depletion conferred protection against cytotoxicity. Carfilzomib also induced accumulation of MCL-1 and Noxa, whereby MCL-1 preferentially formed a complex with Noxa and consequently relieved MCL-1's protective effect on sequestering Bak. Accordingly, depletion of Noxa or both Bak and Bax conferred protection against carfilzomib-induced cell death.

CONCLUSIONS

Collectively, carfilzomib induced ER stress culminating in activation of intrinsic and extrinsic caspase pathways, and we identified the CHOP protein level as a biomarker that could predict sensitivity to carfilzomib in CLL. Clin Cancer Res; 22(18); 4712-26. ©2016 AACR.

Autocrine prostaglandin E₂ signaling promotes promonocytic leukemia cell survival via COX-2 expression and MAPK pathway

The COX-2/PGE₂ pathway has been implicated in the occurrence and progression of cancer. The underlying mechanisms facilitating the production of COX-2 and its mediator, PGE₂, in cancer survival remain unknown. Herein, we investigated PGE₂-induced COX-2 expression and signaling in HL-60 cells following menadione treatment. Treatment with PGE₂ activated anti-apoptotic proteins such as Bcl-2 and Bcl-xL while reducing pro-apoptotic proteins, thereby enhancing cell survival. PGE₂ not only induced COX-2 expression, but also prevented casapse-3, PARP, and lamin B cleavage. Silencing and inhibition of COX-2 with siRNA transfection or treatment with indomethacin led to a pronounced reduction of the extracellular levels of PGE₂, and restored the menadione-induced cell death. In addition, pretreatment of cells with the MEK inhibitor PD98059 and the PKA inhibitor H89 abrogated the PGE₂-induced expression of COX-2, suggesting involvement of the MAPK and PKA pathways. These results demonstrate that PGE₂ signaling acts in an autocrine manner, and specific inhibition of PGE₂ will provide a novel approach for the treatment of leukemia. [BMB Reports 2015; 48(2): 109-114]

Antiproliferative activity of the isoindigo 5'-Br in HL-60 cells is mediated by apoptosis, dysregulation of mitochondrial functions and arresting cell cycle at G0/G1 phase

Our new compound, 5'-Br [(E)-1-(5'-bromo-2'-oxoindolin-3'-ylidene)-6-ethyl-2,3,6,9-tetrahydro-2,9-dioxo-1H-pyrrolo[3,2-f]quinoline-8-carboxylic acid], had shown strong, selective antiproliferative activity against different cancer cell lines. Here, we aim to comprehensively characterize the mechanisms associated with its cytotoxicity in the human promyelocytic leukemia HL-60 cells. We focused at studying the involvement of apoptotic pathway and cell cycle effects. 5'-Br significantly inhibited proliferation by inducing caspase-dependent apoptosis. Involvement of caspase independent mechanism is also possible due to observed inability of z-VAD-FMK to rescue apoptotic cells. 5'-Br was found to trigger intrinsic apoptotic pathway as indicated by depolarization of the mitochondrial inner membrane, decreased level of cellular ATP, modulated expression and phosphorylation of Bcl-2 leading to loss of its association with Bax, and increased release of cytochrome c. 5'-Br treated cells were found arrested at G0/G1 phase with modulation in protein levels of cyclins, dependent kinases and their inhibitors. Expression and enzymatic activity of CDK2 and CDK4 was found inhibited. Retinoblastoma protein (Rb) phosphorylation was also inhibited whereas p21 protein levels were increased. These results suggest that the antiproliferative mechanisms of action of 5'-Br could involve apoptotic pathways, dysregulation of mitochondrial functions and disruption of cell cycle checkpoint.

Dexamethasone differentially regulates Bcl-2 family proteins in human proliferative chondrocytes: role of pro-apoptotic Bid

Glucocorticoids (GCs) are widely used to treat inflammatory diseases and cancers. A multitude of undesired side effects have been reported in GC-treated patients including decreased linear bone growth. We have previously reported that GCs activate the caspase cascade and trigger Bax-mediated mitochondrial apoptosis in growth plate chondrocytes causing growth retardation in young mice. To further explore the role of mitochondrial apoptosis in GC-induced bone growth retardation, a number of pro- and anti-apoptotic proteins were studied in ex vivo cultures of human growth plate cartilage and human HCS-2/8 proliferative chondrocytes exposed to dexamethasone. Dexamethasone was found to increase the pro-apoptotic proteins Bcl-xS, Bad, and Bak as well as the proteolysis of Bid. Anti-Bid small interfering RNA partially rescued the chondrocytes from dexamethasone-induced apoptosis. Taken together, our data suggest that GC treatment differentially regulates Bcl-2 family member proteins to facilitate mitochondrial apoptosis in proliferative chondrocytes thereby contributing to GC-induced bone growth impairment. Prevention of this imbalance between pro- and anti-apoptotic Bcl-2 family proteins may provide a new strategy to protect from adverse effects of GCs on bone growth.

Cytotoxic and apoptotic effects of the oxidized derivatives of stigmasterol in the U937 human monocytic cell line

Dietary exposure to phytosterols has increased in recent years due to the incorporation of these compounds into cholesterol-lowering products. Previous studies have investigated the cytotoxic effects of the oxidized derivatives of β-sitosterol and determined that phytosterol oxidation products (POP) have a similar but less potent toxicity compared to their cholesterol equivalents. In the present study, the cytotoxicity of the oxidized derivatives of stigmasterol were investigated in the U937 cell line. The stigmasta-5,22-diene-3β,7β-diol (7β-OH), 5,6-epoxystigmasta-22,23-diol (epoxydiol), 5,6,22,23-diepoxystigmastane (diepoxide), and (22R,23R)-stigmast-5-ene-3β,22,23-triol (22R,23R-triol) derivatives were identified as the most cytotoxic, and the mode of cell death was identified as apoptosis in cells incubated with 7β-OH, epoxydiol, and diepoxide stigmasterol. The antioxidants α-tocopherol, γ-tocopherol, and β-carotene did not protect against apoptosis induced by 7β-OH and diepoxide stigmasterol; however, α-tocopherol was found to protect against epoxydiol-induced apoptosis. The cellular antioxidant, glutathione, was depleted and the apoptotic protein, Bcl-2, was down-regulated by the stigmasterol oxides identified as apoptotic.

Naturally occurring asteriscunolide A induces apoptosis and activation of mitogen-activated protein kinase pathway in human tumor cell lines

Sesquiterpene lactones have attracted much attention because they display a wide range of biological activities, including antitumor properties. Here, we show the effects of the naturally occurring sesquiterpene lactone asteriscunolide A (AS) on viability of human melanoma, leukemia and cells that overexpress antiapoptotic proteins, namely Bcl-2 and Bcl-x(L). All cell lines were sensitive to this compound, with IC(50) values of approximately 5 microM. The cytotoxic effects of AS were accompanied by a G(2)-M phase arrest of the cell cycle and a concentration- and time-dependent appearance of apoptosis as determined by DNA fragmentation, translocation of phosphatidylserine to the cell surface and sub-G(1) ratio. Apoptosis was associated with caspase-3 activity and poly(ADP-ribose) polymerase cleavage and was prevented by the nonspecific caspase inhibitor z-VAD-fmk, indicating that caspases are essential components in this pathway. The apoptotic effect of AS was also associated with (i) the release of cytochrome c from mitochondria which was accompanied by dissipation of the mitochondrial membrane potential (Delta Psi(m)) and (ii) the activation of the mitogen-activated protein kinases (MAPKs) pathway. AS-induced cell death was potentiated by inhibition of extracellular signal-regulated kinases (ERK) 1/2 signaling with U0126 and PD98059. Intracellular reactive oxygen species (ROS) seem to play a pivotal role in this process since high levels of ROS were produced early (1 h) and apoptosis was completely blocked by the free radical scavenger N-acetyl-L-cysteine (NAC). The present study demonstrates that AS-induced cell death is mediated by an intrinsic-dependent apoptotic event involving mitochondria and MAPKs, and through a mechanism dependent on ROS generation.

Flow cytometric fluorescence pulse width analysis of etoposide-induced nuclear enlargement in HCT116 cells

Fluorescence pulse width can provide size information on the fluorescence-emitting particle, such as the nuclei of propidium iodide-stained cells. To analyze nuclear size in the present study, rather than perform the simple doublet discrimination approach usually employed in flow cytometric DNA content analyses, we assessed the pulse width of the propidium iodide fluorescence signal. The anti-cancer drug etoposide is reportedly cytostatic, can induce a strong G2/M arrest, and results in nuclear enlargement. Based on these characteristics, we used etoposide-treated HCT116 cells as our experimental model system. The fluorescence pulse widths (FL2-W) of etoposide-treated (10 μM, 48 h) cells were distributed at higher positions than those of vehicle control, so the peak FL2-W value of etoposide-treated cells appeared at 400 while those of vehicle control cells appeared at 200 and 270. These results were consistent with our microscopic observations. This etoposide-induced increase in FL2-W was more apparent in G2/M phase than other cell cycle phases, suggesting that etoposide-induced nuclear enlargement preferentially occurred in G2/M phase cells rather than in G0/G1 or S phase cells.

Enhanced tissue integration during cartilage repair in vitro can be achieved by inhibiting chondrocyte death at the wound edge

OBJECTIVE

Experimental wounding of articular cartilage results in cell death at the lesion edge. The objective of this study was to investigate whether inhibition of this cell death results in enhanced integrative cartilage repair.

METHODS

Bovine articular cartilage discs (6 mm) were incubated in media containing inhibitors of necrosis (Necrostatin-1, Nec-1) or apoptosis (Z-VAD-FMK, ZVF) before cutting a 3 mm inner core. This core was left in situ to create disc/ring composites, cultured for up to 6 weeks with the inhibitors, and analyzed for cell death, sulfated glycosaminoglycan release, and tissue integration.

RESULTS

Creating the disc/ring composites resulted in a significant increase in necrosis. ZVF significantly reduced necrosis and apoptosis at the wound edge. Nec-1 reduced necrosis. Both inhibitors reduced the level of wound-induced sulfated glycosaminoglycan loss. Toluidine blue staining and electron microscopy of cartilage revealed significant integration of the wound edges in disc/ring composites treated with ZVF. Nec-1 improved integration, but to a lesser extent. Push-out testing revealed that ZVF increased adhesive strength compared to control composites.

CONCLUSIONS

This study shows that treatment of articular cartilage with cell death inhibitors during wound repair increases the number of viable cells at the wound edge, prevents matrix loss, and results in a significant improvement in cartilage-cartilage integration.

N(alpha)-tosyl-L-phenylalanine chloromethyl ketone induces caspase-dependent apoptosis in transformed human B cell lines with transcriptional down-regulation of anti-apoptotic HS1-associated protein X-1

N(alpha)-tosyl-L-phenylalanine chloromethylketone (TPCK) has been widely used to investigate signal transduction pathways that are involved in gene expression and cell survival/cell death. However, contradictory effects of TPCK on apoptosis have been reported, and the underlying signaling events leading to TPCK-induced promotion or prevention of apoptosis are not fully understood. Here, we show that TPCK induces caspase-dependent apoptosis in Epstein-Barr virus (EBV)-transformed human B cell lines with release of pro-apoptotic proteins from mitochondria. TPCK treatment also results in down-regulation of the anti-apoptotic proteins, cIAP1, cIAP2, and HAX-1, and caspase-dependent cleavage of the anti-apoptotic proteins, Bcl-2 and XIAP. Quantitative PCR analysis confirmed that the TPCK-induced down-regulation of HAX-1 occurred at the transcriptional level, and experiments using the specific pharmacological inhibitor, Bay 11-7082, suggested that HAX-1 expression is subject to regulation by the transcription factor, NF-kappaB. B cell lines derived from patients with homozygous HAX1 mutations were more sensitive to TPCK-induced apoptosis when compared with normal donor cell lines. Furthermore, N-acetylcysteine effectively blocked TPCK-induced apoptosis in EBV-transformed B cell lines and prevented the down-regulation or cleavage of anti-apoptotic proteins. Taken together, our studies demonstrate that TPCK induces apoptosis in human B cell lines and exerts multiple effects on pro- and anti-apoptotic factors.

Elevated P75NTR expression causes death of engrailed-deficient midbrain dopaminergic neurons by Erk1/2 suppression

BACKGROUND

The homeodomain transcription factors Engrailed-1 and Engrailed-2 are required for the survival of mesencephalic dopaminergic (mesDA) neurons in a cell-autonomous and gene-dose-dependent manner. Homozygote mutant mice, deficient of both genes (En1-/-;En2-/-), die at birth and exhibit a loss of all mesDA neurons by mid-gestation. In heterozygote animals (En1+/-;En2-/-), which are viable and fertile, postnatal maintenance of the nigrostriatal dopaminergic system is afflicted, leading to a progressive degeneration specific to this subpopulation and Parkinson's disease-like molecular and behavioral deficits.

RESULTS

In this work, we show that the dose of Engrailed is inversely correlated to the expression level of the pan-neurotrophin receptor gene P75NTR (Ngfr). Loss of mesDA neurons in the Engrailed-null mutant embryos is caused by elevated expression of this neurotrophin receptor: Unusually, in this case, the cell death signal of P75NTR is mediated by suppression of Erk1/2 (extracellular-signal-regulated kinase 1/2) activity. The reduction in expression of Engrailed, possibly related to the higher levels of P75NTR, also decreases mitochondrial stability. In particular, the dose of Engrailed determines the sensitivity to cell death induced by the classic Parkinson-model toxin MPTP and to inhibition of the anti-apoptotic members of the Bcl-2 family of proteins.

CONCLUSION

Our study links the survival function of the Engrailed genes in developing mesDA neurons to the regulation of P75NTR and the sensitivity of these neurons to mitochondrial insult. The similarities to the disease etiology in combination with the nigral phenotype of En1+/-;En2-/- mice suggests that haplotype variations in the Engrailed genes and/or P75NTR that alter their expression levels could, in part, determine susceptibility to Parkinson's disease.

IL-3 induces a Pim1-dependent antiapoptotic pathway in primary human basophils

The contribution of basophils in allergic disease and other Th2-type immune responses depends on their persistence at sites of inflammation, but the ligands and molecular pathways supporting basophil survival are largely unknown. The comparison of rates of apoptosis and of the expression of antiapoptotic proteins in different human granulocyte types revealed that basophils have a considerably longer spontaneous life span than neutrophils and eosinophils consistent with high levels of constitutive Bcl-2 expression. Interleukin-3 (IL-3) is the only ligand that efficiently protects basophils from apoptosis as evidenced by screening a large number of stimuli. IL-3 up-regulates the expression of the antiapoptotic proteins cIAP2, Mcl-1, and Bcl-X(L) and induces a rapid and sustained de novo expression of the serine/threonine kinase Pim1 that closely correlates with cytokine-enhanced survival. Inhibitor studies and protein transduction of primary basophils using wild-type and kinase-dead Pim1-Tat fusion-proteins demonstrate the functional importance of Pim1 induction in the IL-3-enhanced survival. Our data further indicate that the antiapoptotic Pim1-mediated pathway operates independently of PI3-kinase but involves the activation of p38 MAPK. The induction of Pim1 leading to PI3-kinase-independent survival as described here for basophils may also be a relevant antiapoptotic mechanism in other terminally differentiated leukocyte types.

Withanolide induces apoptosis in HL-60 leukemia cells via mitochondria mediated cytochrome c release and caspase activation

The present study is on the growth inhibitory effect of Withania somnifera methanolic leaf extract and its active component, withanolide on HL-60 promyelocytic leukemia cells. The decrease in survival rate of HL-60 cells was noted to be associated with a time dependent decrease in the Bcl-2/Bax ratio, leading to up regulation of Bax. Both the crude leaf extract and the active component activated the apoptotic cascade through the cytochrome c release from mitochondria. The activation of caspase 9, caspase 8 and caspase 3 revealed that caspase was a key mediator in the apoptotic pathway. DNA fragmentation analysis revealed typical ladders as early as 12h indicative of caspase 3 role in the apoptotic pathway. Flow cytometry data demonstrated an increase of sub-G1 peak upon treatment by 51% at 24h, suggesting the induction of apoptotic cell death in HL-60 cells.

Smac-mediated sensitization of human B-lymphoma cells to staurosporine- and lactacystin-triggered apoptosis is apoptosome-dependent

Second mitochondrial activator of caspase (Smac)-derived peptides have previously been shown to facilitate apoptosis of various types of cancer cells. However, it remains unclear whether the effects of such Smac agonists are dependent on apoptotic protease-activating factor-1 (Apaf-1), a key component of the apoptosome. Here, we explored the role of Apaf-1 through overexpression of this protein in the B-lymphoma cell line Raji that is defective for cytosolic Apaf-1 expression. Enforced expression of Apaf-1 rendered Raji cells sensitive to staurosporine as well as to the proteasome inhibitor, lactacystin. Importantly, co-treatment with Smac peptides resulted in a threefold higher degree of apoptosis in Apaf-1-expressing Raji cells, but not in mock-transfected cells. Smac peptides also potentiated apoptosis of the DG-75 cell line following liberation of endogenous Apaf-1 from the plasma membrane, but were ineffective when added alone. Furthermore, we observed high levels of expression in several B-lymphoma cell lines of cellular inhibitor of apoptosis protein-2 (cIAP2), and immunodepletion of cIAP2 (a target of Smac) was found to sensitize Apaf-1-overexpressing Raji cells to cytochrome c-dependent caspase activation. Collectively, these results demonstrate the importance of Apaf-1 in Smac-mediated potentiation of apoptosis of B-lymphoma-derived cells.

Bcl-2 protein family: implications in vascular apoptosis and atherosclerosis

Apoptosis has been recognized as a central component in the pathogenesis of atherosclerosis, in addition to the other human pathologies such as cancer and diabetes. The pathophysiology of atherosclerosis is complex, involving both apoptosis and proliferation at different phases of its progression. Oxidative modification of lipids and inflammation differentially regulate the apoptotic and proliferative responses of vascular cells during progression of the atherosclerotic lesion. Bcl-2 proteins act as the major regulators of extrinsic and intrinsic apoptosis signalling pathways and more recently it has become evident that they mediate the apoptotic response of vascular cells in response to oxidation and inflammation either in a provocative or an inhibitory mode of action. Here we address Bcl-2 proteins as major therapeutic targets for the treatment of atherosclerosis and underscore the need for the novel preventive and therapeutic interventions against atherosclerosis, which should be designed in the light of molecular mechanisms regulating apoptosis of vascular cells in atherosclerotic lesions.

Mitochondria in hematopoiesis and hematological diseases

Mitochondria are involved in hematopoietic cell homeostasis through multiple ways such as oxidative phosphorylation, various metabolic processes and the release of cytochrome c in the cytosol to trigger caspase activation and cell death. In erythroid cells, the mitochondrial steps in heme synthesis, iron (Fe) metabolism and Fe-sulfur (Fe-S) cluster biogenesis are of particular importance. Mutations in the specific delta-aminolevulinic acid synthase (ALAS) 2 isoform that catalyses the first and rate-limiting step in heme synthesis pathway in the mitochondrial matrix, lead to ineffective erythropoiesis that characterizes X-linked sideroblastic anemia (XLSA), the most common inherited sideroblastic anemia. Mutations in the adenosine triphosphate-binding cassette protein ABCB7, identified in XLSA with ataxia (XLSA-A), disrupt the maturation of cytosolic (Fe-S) clusters, leading to mitochondrial Fe accumulation. In addition, large deletions in mitochondrial DNA, whose integrity depends on a specific DNA polymerase, are the hallmark of Pearson's syndrome, a rare congenital disorder with sideroblastic anemia. In acquired myelodysplastic syndromes at early stage, exacerbation of physiological pathways involving caspases and the mitochondria in erythroid differentiation leads to abnormal activation of a mitochondria-mediated apoptotic cell death pathway. In contrast, oncogenesis-associated changes at the mitochondrial level can alter the apoptotic response of transformed hematopoietic cells to chemotherapeutic agents. Recent findings in mitochondria metabolism and functions open new perspectives in treating hematopoietic cell diseases, for example various compounds currently developed to trigger tumor cell death by directly targeting the mitochondria could prove efficient as either cytotoxic drugs or chemosensitizing agents in treating hematological malignancies.

Triptolide induces Bcl-2 cleavage and mitochondria dependent apoptosis in p53-deficient HL-60 cells

Triptolide, a bioactive component of the Chinese medicinal herb Tripterygium wilfordii Hook F., induces p53-mediated apoptosis in cancer cells. This study demonstrated that triptolide activated an alternative p53-independent apoptotic pathway in HL-60 cells. In the absence of an intact p53 and without changing Bax level, at nM range triptolide induced apoptosis with concomitant DNA fragmentation, S phase cell cycle arrest, mitochondrial cytochrome c release and the activation of caspases. Besides, both caspases 8 and 9 were activated and the simultaneous inhibition of both was required to completely block triptolide's apoptotic effect. Importantly, triptolide induced the appearance of a truncated 23kD Bcl-2 which was inhibited by the general caspase inhibitor Z-VAD-FMK. In the MCF-7 cells that possessed the wild type p53 but lacked caspases 3, triptolide induced cell death with an increase in p53 but Bcl-2 remained unaltered. On the other hand, transfected cells overexpressing the 28kD Bcl-2 became more resistant to triptolide and upon triptolide treatment accumulated in the G(1) instead of S phase. After 36h treatment, triptolide activated JNK pathways, at the same time inactivated the ERK and p38 pathways. However, SP600125, a specific JNK inhibitor, could not inhibit the triptolide-mediated cleavage of caspase 3, indicated that activation of JNK might not be related to the apoptotic effects of triptolide. Our data suggest that in the absence of an intact p53 and without altering Bax level triptolide induces apoptosis activates a positive amplification loop involving caspase-mediated Bcl-2 cleavage/activation, mitochondrial cytochrome c release and further activation of caspases.

Bcl-XL is qualitatively different from and ten times more effective than Bcl-2 when expressed in a breast cancer cell line

Background

Bcl-2 and Bcl-XL are anti-apoptotic paralogues that inhibit apoptosis elicited by a wide variety of stimuli, and play critical roles in cancer development and resistance to treatment. Many clinical studies have indicated that expression of these anti-apoptotic proteins in tumours is associated with poor prognosis. It has therefore been assumed that in cells the essential difference between Bcl-2 and Bcl-XL involves regulation of expression and that they are otherwise functionally similar. To examine this issue, we have compared the function of the proteins and of mutants of Bcl-2 and Bcl-XL specifically targeted to different subcellular sites.

Methods

We generated clones of the human breast cancer line MCF-7 stably expressing known amounts of Bcl-2, or Bcl-XL as determined by quantitative immunoblotting. Clones expressing equivalent amounts of wild-type and mutants of Bcl-2 and Bcl-XL with subcellular localization restricted to the cytoplasm, endoplasmic reticulum or outer mitochondrial membrane were studied in both MCF-7 and Rat-1 fibroblasts. In MCF-7 cells we measured the functional activities of these proteins in preventing apoptosis induced by four different agents (doxorubicin, ceramide, thapsigargin, TNF-α). Etoposide and low serum were used to compare the effect of Bcl-2, Bcl-XL and mutants located at the endoplasmic reticulum on induction of apoptosis in fibroblasts.

Results

We noted both qualitative and quantitative differences in the functional activity of these two anti-apoptotic proteins in cells: Bcl-2 localized to the endoplasmic reticulum inhibits apoptosis induced by ceramide and thapsigargin but not by doxorubicin or TNFα, while Bcl-XL at the endoplasmic reticulum is active against all four drugs. In fibroblasts Bcl-2 localized to the ER did not prevent cell death due to etoposide whereas Bcl-XL in the same location did. Finally in MCF-7 cells, Bcl-XL is approximately ten times more active than Bcl-2 in repressing apoptosis induced by doxorubicin. This difference can be manifest as a large difference in clonal survival.

Conclusion

When examined in the same cellular context, Bcl-2 and Bcl-XL differ substantially in the potency with which they inhibit apoptosis, mediated in part by differences in the inhibition of specific subcellular pathways.

Notch1 antiapoptotic activity is abrogated by caspase cleavage in dying T lymphocytes

Excessive signaling via the Notch1 receptor inhibits apoptosis in T lymphocytes. Since several antiapoptotic proteins are cleaved by caspases during cell death, we investigated whether Notch1 was a caspase substrate. Results demonstrate that the intracellular domain of Notch1 (NICD) is cleaved into six fragments during apoptosis in Jurkat cells or peripheral T lymphocytes. Notch1 cleavage is prevented by the caspase inhibitors DEVD-fmk and VEID-fmk or by Bcl-2 expression. Caspase-3 and caspase-6 cleave the NICD into six fragments using sites located within the NF-kappaB binding domain, the ankyrin repeats and the transactivation domain. Notch1 cleavage correlates with the loss of HES-1 expression in apoptotic T cells. Notch1 fragments cannot inhibit activation-induced cell death in a T-cell hybridoma, confirming the abrogation of Notch1 antiapoptotic activity by caspases. The ability of the NICD but not the fragments to antagonize Nur77 activity supports a role for this factor in Notch1 antiapoptotic function.

Alterations in protein expression in HL-60 cells during etoposide-induced apoptosis modulated by the caspase inhibitor ZVAD.fmk

DNA topoisomerase inhibitors induce a specific signaling cascade that promotes an active apoptotic caspase-dependent cell death process. However, little is known about the initial signals elicited by these agents. In the present study, we compared apoptosis in HL-60 cells treated either with the chemotherapeutic drug etoposide (VP16) alone or combined with the broad caspase inhibitor ZVAD.fmk. Apoptosis was assessed by changes in cell morphology and agarose gel electrophoresis of extracted cell DNA. We found that ZVAD.fmk prevents VP16-induced DNA fragmentation and the appearance of an increased number of apoptotic cells in the culture. We also compared the effects of etoposide alone or together with the pan-caspase inhibitor ZVAD.fmk on proliferating cell nuclear antigen, Bcl-2, and actin expression in human promyelocytic leukemia HL-60 cells. In addition, we screened for proteins that were initially upregulated in a caspase-dependent manner. Indeed, some proteins were induced in the cytoplasm and subsequently accumulated in the nuclei after etoposide treatment. This process was slightly inhibited by the caspase inhibitor ZVAD.fmk. We suggest that these proteins are associated with the induction of specific signaling cascades that characterize the apoptotic cell death process.

Cyclic AMP alleviates endoplasmic stress and programmed cell death induced by lipopolysaccharides in human endothelial cells

The possible protection provided by enhancement of the cAMP signal in the process of lipopolysaccharide (LPS)-induced endothelial cell death has been addressed, with special emphasis on the endoplasmic initiation of caspase-12-mediated apoptosis. Human umbilical vein endothelial cells were challenged with LPS to reduce viability after 12 h to less than 20% that of the control. Cell death was preceded by ultrastructural disintegration at the endoplasmic reticulum, PERK-phosphorylation, degradation of caspase-12-like protein and cleavage of caspase 9, resulting in apoptosis through the activation of caspase 3. Treatment with a cell-permeable cAMP analogue led to a dose-dependent reduction of cell death over time, mitigated endoplasmic reticulum disturbances, reduced phosphorylation of PERK, and the degradation of caspases 12, 9 and 3. The selective inhibition of caspase 9 completely supplanted the anti-apoptotic effects obtained by cAMP, while being without any influence on caspase 12 degradation. The data suggest that cAMP positively modulates early endoplasmic alterations and caspase activation in LPS-induced apoptosis.

On the antioxidant mechanisms of Bcl-2: a retrospective of NF-kappaB signaling and oxidative stress

Antioxidant and prooxidant signaling pathways are emanating as major players in, and regulators of, cell death and apoptosis. Redox conception of the critical role of oxidative stress in determining cell fate is being established-a foundation that craves deeper than the basic understanding of physiochemical interactions to extend beyond that into the realms of deciphering the molecular codes implicated with apoptosis. The proto-oncogene Bcl-2 is no stranger being a major player and decoder in controlling apoptosis, ostensibly via the regulation of redox equilibrium and disequilibrium. One of those potential mechanisms exhibited by Bcl-2 is its ability to counteract the detrimental effects of cell damage caused by free radicals, thereby gaining its well-known property of being an antioxidant. But the question is: what are the molecular mechanisms involved with the antioxidant role of Bcl-2 in the face of cell damage and apoptosis? Currently, a stance is being upheld in that the Bcl-2 antioxidant efficacy should be weighed against its ability to manipulate transcriptional control, through the regulation of specific transcription factors. NF-kappaB is no doubt one of the best candidates when it comes to the arena of oxidative stress, inflammation, and apoptosis. Therein, current themes in the burgeoning antioxidant role of Bcl-2 are exposed within the context of transcriptional control of NF-kappaB, thereby holding potential avenues for alleviating therapeutic approaches in the regulation of apoptosis.

The presence of 19-kDa Bcl-2 in dividing cells

The 26-kDa bcl-2 gene product inhibits apoptosis and cell proliferation. Cleavage of Bcl-2 into a 22-kDa fragment inactivates its anti-apoptotic activity and is a key event in apoptosis. Here, and in recent work, we describe massive 19-kDa Bcl-2 immunoreactivity in non-apoptotic cells, suggesting a link with viability rather than cell death. Loss of 19 kDa Bcl-2 in adriamycin-induced apoptotic cells underlines this. G2/M-phase accumulation of cells by nocodazole-treatment also results in loss of 19 kDa Bcl-2. Next to its well-documented cytoplasmic localization, a substantial pool of Bcl-2 resides in nuclei. Hampered nuclear localization of Bcl-2 leads to a loss of cell cycle repression. This has led us to point at a pivotal role for nuclear Bcl-2 in cellular proliferation. In this report, cellular fractionation of bcl-2 transfected cells in various phases of the cell cycle reveals a constitutive cytoplasmic pool of 19 kDa Bcl-2. Nuclear 19-kDa Bcl-2 immunoreactivity is far more pronounced in rapidly dividing nuclei compared with more quiescent nuclear fractions. This implicates that ongoing cell proliferation involves cleavage of nuclear Bcl-2 with a 19-kDa fragment.

2-Chlorodeoxyadenosine alone and in combination with cyclophosphamide and mitoxantrone induce apoptosis in B chronic lymphocytic leukemia cells in vivo

The purpose of the study was to determine some apoptotic events in mononuclear cells obtained from peripheral blood of patients with B-cell chronic lymphocytic leukemia (B-CLL) during and after therapy with 2-chlorodeoxyadenosine (2-CdA; C), and the combination of 2-CdA with cyclophosphamide (CC), or 2-CdA with mitoxantrone and cyclophosphamide (CMC). Western blot technique was performed to estimate expression/proteolytic degradation of generally accepted apoptotic markers, i.e., Bcl-2 protein, lamin B, PARP-1, and caspase-3 in leukemic cells isolated from blood samples of patients before treatment and subjected to drug(s) administration. The decrease of antiapoptotic protein Bcl-2 expression and proteolytic cleavage of nuclear proteins--lamin B and PARP-1 were observed in leukemic cells of patients treated according to the above therapy protocols, however, each to a different level among the studied groups. The obtained results indicated also that procaspase-3 was cleaved and activated in leukemic cells of three drug(s) treated groups. However, the cleavage of procaspase-3 and the generation of fragments with mol. mass of 17/20 kDa occurred especially effectively among patients treated according to CMC regimen. The changes in expression/proteolytic degradation of the above selected apoptotic markers, are accompanied by the appearance of apoptotic morphology in leukemic cells originated from blood of patients treated with the above drug(s) in comparison to untreated ones.

Expression of Smac/DIABLO in ovarian carcinoma cells induces apoptosis via a caspase-9-mediated pathway

We have constructed Ad CMV-Smac, a recombinant adenovirus encoding Smac/DIABLO, the recently described second mitochondrial activator of caspases. Transfection of ovarian carcinoma cells with Ad CMV-Smac at multiplicities of infection of 3-60 pfu/cell leads to increasing apoptosis in a dose-dependent manner. Western blot analysis confirms that Smac-induced apoptosis proceeds via a pathway mediated primarily by caspase-9 that can be inhibited by zLEHD-fmk and overexpression of the X-linked inhibitor of apoptosis protein (XIAP). In contrast, there is no cleavage of either caspase-8 or caspase-12. Ad CMV-Smac appears to induce apoptosis independently of cytochrome c release from mitochondria and is not inhibited by overexpression of Bcl-2. Ad CMV-Smac can combine with other proapoptotic factors, such as cisplatin, paclitaxel, and procaspase-3, to produce greater levels of apoptosis in transfected cells.

Mitochondria-mediated caspase-independent apoptosis induced by cadmium in normal human lung cells

Cadmium, a well-known environmental hazard, has caused serious health problems in humans and animals. Accumulating evidence suggests the cadmium toxicity is mediated by oxidative stress-induced cell death. However, the molecular signaling underlying cadmium-induced apoptosis remains unclear. In this study, we demonstrate here that cadmium induced mixed types of cell death including primary apoptosis (early apoptosis), secondary necrosis (late apoptosis), and necrosis in normal human lung cells, MRC-5, as revealed by chromatin condensation, phosphatidylserine (PS) externalization, and hypodiploid DNA content. The total apoptotic cells reached a plateau of around 40.0% after 24 h exposure of 100 microM cadmium. Pretreatment with Z-Val-Ala-Asp-fluoromethylketone (Z-VAD-fmk), a broad spectrum of caspase inhibitor, could not rescue apoptotic cells from cadmium toxicity. Coincidently, we failed to detect the activation of pro-caspase-3 and cleavage of PARP by immunoblot, which implies the apoptogenic activity of cadmium in MRC-5 cells is caspase-independent. JC-1 staining also indicated that mitochondrial depolarization is a prelude to cadmium-induced apoptosis, which was accompanied by a translocation of caspase-independent pro-apoptotic factor apoptosis-inducing factor (AIF) into the nucleus as revealed by the immunofluorescence assay. In summary, this study demonstrated for the first time that cadmium induced a caspase-independent apoptotic pathway through mitochondria-mediated AIF translocation into the nucleus.

Mitochondria at the heart of the cytotoxic attack

Granzyme B is a serine proteinase that acts as a key effector of cell death mediated by cytotoxic T lymphocytes. The enzyme is transferred from the cytotoxic cell to the pathogenic target cell where it cleaves and activates a number of substrates involved in the induction of apoptosis. However, recent evidence implicates mitochondria as playing an important role in both the initiation of apoptosis and control of substrate cleavage by granzyme B in cytotoxic T lymphocyte induced death. This review focuses on current research in this rapidly expanding field, specifically the role of mitochondria in cell death induced by components of cytotoxic granules in particular granzyme B.

The role of various Bcl-2 domains in the anti-proliferative effect and modulation of cellular glutathione levels: a prominent role for the BH4 domain

Reduced cell proliferation and increased levels of cellular glutathione (GSH) are characteristic for cells that overexpress the anti-apoptotic Bcl-2 protein. We investigated the influence of various Bcl-2 domains on both these characteristics. Rat CC531 colorectal cancer cells were stably transfected with the human bcl-2 gene (CCbcl2 cells) or with bcl-2 gene constructs missing a coding sequence for a func-tional domain, BH1 (CCDeltaBH1 cells), BH3 (CCDeltaBH3 cells), BH4 (CCDeltaBH4 cells) or the transmembrane region (CCDeltaTM cells). We measured GSH levels in exponentially and confluent growing bcl-2-transfected cell populations. The fraction of S-phase cells during exponential growth was significantly reduced in CCbcl2, CCDeltaBH1, CCDeltaBH3, and CCDeltaTM cells compared with parental CC531, neo-transfected CC531 and CCDeltaBH4 cells. GSH levels in these bcl-2 transfectants were significantly higher than in the parental line measured at 50% confluence; at 100% confluence they reached a similar level as found in parental cells. Independently from the presence of BH1, BH3 or TM domains, overexpression of Bcl-2 reduces cellular proliferation under conditions of increased GSH levels. This apparent link is lost in CCDeltaBH4 cells; these cells are not reduced in cellular proliferation and harbour significantly higher GSH levels than found in the other transfectants. Studies on the subcellular localization revealed an extremely low expression of the Bcl-2 protein lacking the N-terminal BH4 domain in nuclear fractions. Nuclear translocation of Bcl-2 requires the presence of the BH4 domain and seems prominent in reducing cellular proliferation.

The involvement of diadenosine 5',5"'-P1,P4-tetraphosphate in cell cycle arrest and regulation of apoptosis

Diadenosine oligophosphates (Ap(n)A) have been proposed to function as intracellular and extracellular signaling molecules in animal cells. Here, we have examined the cellular and molecular mechanisms underlying the induction of apoptosis by diadenosine 5',5"'-P(1),P(4)-tetraphosphate (Ap(4)A). We have shown a dose-dependent apoptotic response in cells treated with Ap(4)A. Flow cytometric analysis indicated an involvement of Ap(4)A at an early stage of G1/S arrest. No difference in the amount of p21(waf1) was observed in HL60 cells treated with Ap(4)A compared to control cells. The level of retinoblastoma protein (pRb) dropped dramatically when apoptosis was extensive. The cleavage of pRb was abrogated if Ap(4)A-treated cells were incubated with general caspase inhibitor zVAD-fmk. Ap(4)A also induced a profound decrease in the level of the Bcl-2 protein. The lack of effect of Ap(4)A on CDK1 activity indicated that Ap(4)A is not involved in "aberrant mitosis". We suggest that in vivo Ap(4)A may play a significant role in tumor growth suppression by inducing apoptosis.

Viral versus cellular BCL-2 proteins

All gamma herpesviruses and a few other viruses encode at least one homologue of the mammalian cell death inhibitor BCL-2. Gamma herpesviruses are associated with human and animal lymphoid and epithelial tumours. However, the role of these viral BCL-2 homologues in the virus replication cycle or in human disease is not known, though recent developments show progress in this area. The structure of viral BCL-2 family protein, KSBcl-2, is similar to that of cellular family members, but viral BCL-2 proteins differ functionally from the cellular proteins, apparently escaping the regulatory mechanisms to which their cellular counterparts are subjected. Thus, exploring the biochemical and biological functions of the viral BCL-2 family proteins will increase our understanding of their role in virus infections and will undoubtedly teach us something about their cellular kin.

Redox Regulation of Apoptosis before and after Cytochrome C Release

Programmed cell death, or apoptosis, is one of the most studied areas of modern biology. Apoptosis is a genetically regulated process, which plays an essential role in the development and homeostasis of higher organisms. Mitochondria, known to play a central role in regulating cellular metabolism, was found to be critical for regulating apoptosis induced under both physiological and pathological conditions. Mitochondria are a major source of reactive oxygen species (ROS) but they can also serve as its target during the apoptosis process. Release of apoptogenic factors from mitochondria, the best known of which is cytochrome c, leads to assembly of a large apoptosis-inducing complex called the apoptosome. Cysteine proteases (called caspases) are recruited to this complex and, following their activation by proteolytic cleavage, activate other caspases, which in turn target for specific cleavage a large number of cellular proteins. The redox regulation of apoptosis during and after cytochrome c release is an area of intense investigation. This review summarizes what is known about the biological role of ROS and its targets in apoptosis with an emphasis on its intricate connections to mitochondria and the basic components of cell death.

Chemotherapy induces bcl-2 cleavage in lymphoid leukemic cell lines

Bcl-2 is the major anti-apoptotic protein evaluated in studies aimed at understanding programmed cell death. Recent work suggests that the biological activity of Bcl-2 is modulated by proteolytic cleavage, with a 23 kDa cleaved Bcl-2 product having pro-apoptotic activity. In the current study we evaluated the effect of chemotherapy on Bcl-2 cleavage in B lineage leukemic cell lines. JM-1, SUP-B 15 and RS4 leukemic cell lines cleaved Bcl-2 to its 23 kDa form when exposed to the chemotherapeutic agents 1-beta-D-arabinofuranosyl-cytosine (Ara-C) or etoposide (VP-16). Chemotherapy induced Bcl-2 cleavage was blunted by inhibition of caspase activity. Co-culture of leukemic cells with bone marrow stromal cells during chemotherapy exposure resulted in reduced levels of 23 kDa Bcl-2 protein. These observations suggest that the bone marrow microenvironment may contribute to maintenance of residual leukemic disease during treatment by reducing generation of pro-apoptotic 23 kDa Bcl-2.

Caspase-9 inhibition after focal cerebral ischemia improves outcome following reversible focal ischemia

Cerebral ischemia initiates a program of cell death known as apoptosis. Early steps in these death promoting events are the release of cytochrome c from the mitochondria and activation of caspase-9. The purpose of this report is to determine if the administration of a specific caspase-9 inhibitor, Z-Leu-Glu(Ome)-His-Asp(Ome)-FMK x TFA (Z-LEHD-FMK) would attenuate apoptosis and the resultant brain injury after ischemia. Adult Wistar rats underwent 3 h of temporary middle cerebral artery occlusion (MCAO) followed by 24 h of reperfusion. An intraventricular injection of 4.8 microg of Z-LEHD-FMK was given 15-min postreperfusion. Administration of the caspase-9 inhibitor, Z-LEHD-FMK, to the experimental group (n = 12) reduced total infarction volume by 49% (p < 0.05) and improved neurological outcome by 63% (p < 0.01) as compared to the control group (n = 12). Western blot analysis of animals that underwent ischemia-reperfusion showed the appearance of the active form of caspase-9. Inhibition of caspase-9, the apical caspase in cytochrome-c-dependent apoptosis, is an effective intervention to attenuate neurological injury after focal ischemia.

Epstein-Barr virus BALF1 is a BCL-2-like antagonist of the herpesvirus antiapoptotic BCL-2 proteins

Cellular BCL-2 family proteins can inhibit or induce programmed cell death in part by counteracting the activity of other BCL-2 family members. All sequenced gammaherpesviruses encode a BCL-2 homologue that potently inhibits apoptosis and apparently escapes some of the regulatory mechanisms that govern the functions of their cellular counterparts. Examples of these protective proteins include BHRF1 of Epstein-Barr virus (EBV) and KSBcl-2 of Kaposi's sarcoma-associated herpesvirus, also known as human herpesvirus 8. The gamma-1 subgroup of these viruses, such as EBV, encodes a second BCL-2 homologue. We have now found that this second BCL-2 homologue encoded by EBV, BALF1, inhibits the antiapoptotic activity of EBV BHRF1 and of KSBcl-2 in several transfected cell lines. However, BALF1 failed to inhibit the cellular BCL-2 family member, BCL-x(L). Thus, BALF1 acts as a negative regulator of the survival function of BHRF1, similar to the counterbalance observed between cellular BCL-2 family members. Unlike the cellular BCL-2 family antagonists, BALF1 lacked proapoptotic activity and could not be converted into a proapoptotic factor in a manner similar to cellular BCL-2 proteins by caspase cleavage or truncation of the N terminus. Coimmunoprecipitation experiments and immunofluorescence assays suggest that a minimal amount, if any, of the BHRF1 and BALF1 proteins colocalizes inside cells, suggesting that mechanisms other than direct interaction explain the suppressive function of BALF1.

The role of apoptosis in response to photodynamic therapy: what, where, why, and how

Photodynamic therapy (PDT), a treatment for cancer and for certain benign conditions, utilizes a photosensitizer and light to produce reactive oxygen in cells. PDT is primarily employed to kill tumor and other abnormal cells, so it is important to ask how this occurs. Many of the photosensitizers currently in clinical or pre-clinical studies of PDT localize in or have a major influence on mitochondria, and PDT is a strong inducer of apoptosis in many situations. The purpose of this review is to critically evaluate all of the recently published research on PDT-induced apoptosis, with a focus on studies providing mechanistic insights. Components of the mechanism whereby PDT causes cells to undergo apoptosis are becoming understood, as are the influences of several signal transduction pathways on the response. Future research should be directed to elucidating the role(s) of the multiple steps in apoptosis in directing damaged cells to an apoptotic vs. necrotic pathway and for producing tumor ablation in conjunction with tissue-level mechanisms operating in vivo.

Regulation of apoptotic cell death by cytokines in a human salivary gland cell line: distinct and synergistic mechanisms in apoptosis induced by tumor necrosis factor alpha and interferon gamma

We examined the mechanisms of apoptosis in a human salivary gland (HSG) cell line induced by tumor necrosis factor (TNF) alpha and interferon (IFN) gamma. DNA fragmentation and the activation of caspase-3 were determined in HSG cells cultured with TNF-alpha or IFN-gamma. Mitochondrial dysfunction also appeared to be involved in the process because a disruption of mitochondrial transmembrane potential with the activation of caspase-9 was demonstrated in TNF-alpha- and IFN-gamma-stimulated HSG cells. Activation of caspase-8 was thought to be essential in TNF-alpha--induced apoptosis of HSG cells; however, the activation of caspase-8 was not involved in IFN-gamma-induced apoptosis of HSG cells. In contrast, Bcl-2 appeared to be an indispensable regulatory molecule in IFN-gamma-induced, but not in TNF-alpha-induced, apoptosis of HSG cells because its expression was inhibited in IFN-gamma-stimulated, but not in TNF-alpha-stimulated, cells. The inhibitory effect of IFN-gamma in Bcl-2 expression was enhanced by coadministration of TNF-alpha and, interestingly, apoptosis of HSG cells, as assessed by DNA fragmentation and the activation of caspase-9 and caspase-3, and disruption of mitochondrial transmembrane potential was also synergistically augmented by TNF-alpha and IFN-gamma. Our results suggest that cytokines expressed in the salivary glands of patients with Sjögren syndrome play an important role in regulating apoptosis of acinar-ductal epithelial cells through distinct and synergistic mechanisms, thereby modulating salivary gland function in patients with Sjögren syndrome.

Pro-apoptotic cleavage products of Bcl-xL form cytochrome c-conducting pores in pure lipid membranes

During apoptotic cell death, cells usually release apoptogenic proteins such as cytochrome c from the mitochondrial intermembrane space. If Bcl-2 family proteins induce such release by increasing outer mitochondrial membrane permeability, then the pro-apoptotic, but not anti-apoptotic activity of these proteins should correlate with their permeabilization of membranes to cytochrome c. Here, we tested this hypothesis using pro-survival full-length Bcl-x(L) and pro-death Bcl-x(L) cleavage products (DeltaN61Bcl-x(L) and DeltaN76Bcl-x(L)). Unlike Bcl-x(L), DeltaN61Bcl-x(L) and DeltaN76Bcl-x(L) caused the release of cytochrome c from mitochondria in vivo and in vitro. Recombinant DeltaN61Bcl-x(L) and DeltaN76Bcl-x(L), as well as Bcl-x(L), cleaved in situ by caspase 3-possessed intrinsic pore-forming activity as demonstrated by their ability to efficiently permeabilize pure lipid vesicles. Furthermore, only DeltaN61Bcl-x(L) and DeltaN76Bcl-x(L), but not Bcl-x(L), formed pores large enough to release cytochrome c and to destabilize planar lipid bilayer membranes through reduction of pore line tension. Because Bcl-x(L) and its C-terminal cleavage products bound similarly to lipid membranes and formed oligomers of the same size, neither lipid affinity nor protein-protein interactions appear to be solely responsible for the increased membrane-perturbing activity elicited by Bcl-x(L) cleavage. Taken together, these data are consistent with the hypothesis that Bax-like proteins oligomerize to form lipid-containing pores in the outer mitochondrial membrane, thereby releasing intermembrane apoptogenic factors into the cytosol.

Proteolytic loss of bcl-x(L) in FL5.12 Cells undergoing apoptosis induced by MK886

Apoptosis induced in the IL3-dependent murine pro-B lymphocytic (FL5.12) cell line by the 5-lipoxygenase activating protein inhibitor MK886 is accompanied by the rapid loss of the anti-apoptotic bcl-x(L) and bcl-2, but not the proapoptotic bax proteins (Datta et al., J. Biol. Chem. 273, 28163-28169, 1998). Since several reports indicate important roles for noncaspase proteases in apoptosis, the participation of lysosomes, as well as serine, cysteine, or aspartic acid proteases, in the effects of MK886 were investigated. Consistent with the involvement of various proteases, lysosomal degranulation was evident, as observed by a decrease in acridine orange fluorescence at 2 h and an increase in cytosolic beta-hexosaminidase activity at 4 h after treating FL5.12 cells with 10 microM MK886. The disappearance of bcl-x(L) from FL5.12 cells upon MK886 treatment was prevented in a dose-dependent manner by pretreatment with leupeptin, pepstatin, phenylmethylsulfonyl fluoride, or the broad-spectrum caspase inhibitor Boc-D-FMK. Each of the noncaspase protease inhibitors partially inhibited MK886-induced apoptosis as measured by phosphatidylserine externalization and DNA fragmentation. The noncaspase inhibitors also blocked about half of the increase in caspase-3-like activity. Boc-D-FMK completely inhibited this enzyme and prevented apoptosis. None of the inhibitors were able to directly inhibit activated caspase-3 in cell lysates, suggesting their effects were upstream of caspase activation. These observations suggest the involvement of various proteases, possibly originating from lysosomes, upstream of active caspase-3, in the loss of bcl-x(L) protein and in the signaling pathway of MK886-induced apoptosis in FL5.12 cells. This pathway may be unique to MK886 since these same protease inhibitors had only minimal effects on etoposide-induced apoptosis and the accompanying moderate loss of bcl-x(L) in FL5.12 cells.

Mitochondrial permeability transition induced by the anticancer drug etoposide

Etoposide (VP-16) is widely used for the treatment of several forms of cancer. The cytotoxicity of VP-16 has been assigned to the induction of apoptotic cell death but the signaling pathway for VP-16-induced apoptosis is essentially unknown. There is some evidence that this process depends on events associated with the loss of mitochondrial membrane potential (Delta Psi) and/or release of apoptogenic factors, putatively as a consequence of mitochondrial permeability transition (MPT) induction. This work evaluates the interference of VP-16 with MPT in vitro, which is characterized by the Ca(2+)-dependent depolarization of Delta Psi, the release of matrix Ca(2+) and by extensive swelling of mitochondria. Delta Psi depolarization and Ca(2+) release were measured with ion-selective electrodes, and mitochondrial swelling was monitored spectrophotometrically. Incubation of rat liver mitochondria with VP-16 results in a concentration-dependent induction of MPT, evidenced by an increased sensitivity to Ca(2+)-induced swelling, depolarization of Delta Psi, Ca(2+) release by mitochondria and stimulation of state 4 oxygen consumption. All of these effects are prevented by preincubating the mitochondria with cyclosporine A, a potent and specific inhibitor of the MPT. Therefore, VP-16 increases the sensitivity of isolated mitochondria to the Ca(2+)-dependent induction of the MPT. Together, these data provide a possible mechanistic explanation for the previously reported effects of VP-16 on apoptosis induction.