Pharmacological manipulation of cell death: clinical applications in sight?

Cyclophilin D gene ablation protects mice from ischemic renal injury

Increased oxidative stress and intracellular calcium levels and mitochondrial overloading of calcium during ischemic renal injury (IRI) favor mitochondrial membrane permeability transition pore (MPTP) opening and subsequent necrotic cell death. Cyclophilin D (CypD) is an essential component of MPTP, and recent findings implicate its role in necrotic, but not apoptotic, cell death. To evaluate the role of CypD following IRI, we tested the hypothesis that CypD gene ablation protects mice from IRI. Renal function as assessed by plasma levels of both creatinine and blood urea nitrogen was significantly reduced in CypD knockout (CypD(-/-)) mice compared with wild-type mice during the 5-day post-ischemia period. Erythrocyte trapping, tubular cell necrosis, tubular dilatation, and neutrophil infiltration were significantly decreased in CypD(-/-) mice. To define the mechanisms by which CypD deficiency protect the kidneys, an in vitro model of IRI was employed. Inhibition of CypD using cyclosporin A in oxidant-injured cultured proximal tubular cells (PTC) prevented mitochondrial membrane depolarization, reduced LDH release, ATP depletion and necrotic cell death. Similarly, oxidant-injured CypD(-/-) PTC primary cultures were protected from cytotoxicity and necrosis. To conclude, CypD gene ablation offers both functional and morphological protection in mice following IRI by decreasing necrotic cell death possibly via inhibition of MPTP and ATP depletion.

c-Jun NH2-terminal kinase activation is essential for DRAM-dependent induction of autophagy and apoptosis in 2-methoxyestradiol-treated Ewing sarcoma cells

Ewing sarcoma and osteosarcoma are two aggressive cancers that affect bones and soft tissues in children and adolescents. Despite multimodal therapy, patients with metastatic sarcoma have a poor prognosis, emphasizing a need for more effective treatment. We have shown previously that 2-methoxyestradiol (2-ME), an antitumoral compound, induces apoptosis in Ewing sarcoma cells through c-Jun NH(2)-terminal kinase (JNK) activation. In the present study, we provide evidence that 2-ME elicits macroautophagy, a process that participates in apoptotic responses, in a JNK-dependent manner, in Ewing sarcoma and osteosarcoma cells. We also found that the enhanced activation of JNK by 2-ME is partially regulated by p53, highlighting the relationship of JNK and autophagy to p53 signaling pathway. Furthermore, we showed that 2-ME up-regulates damage-regulated autophagy modulator (DRAM), a p53 target gene, in Ewing sarcoma cells through a mechanism that involves JNK activation. The silencing of DRAM expression reduced both apoptosis and autophagy triggered by 2-ME in Ewing sarcoma and osteosarcoma cells. Our results therefore identify JNK as a novel mediator of DRAM regulation. These findings suggest that 2-ME or other anticancer therapies that increase DRAM expression or function could be used to effectively treat sarcoma patients.

Identification of novel in vivo phosphorylation sites of the human proapoptotic protein BAD: pore-forming activity of BAD is regulated by phosphorylation

BAD is a proapoptotic member of the Bcl-2 protein family that is regulated by phosphorylation in response to survival factors. Although much attention has been devoted to the identification of phosphorylation sites in murine BAD, little data are available with respect to phosphorylation of human BAD protein. Using mass spectrometry, we identified here besides the established phosphorylation sites at serines 75, 99, and 118 several novel in vivo phosphorylation sites within human BAD (serines 25, 32/34, 97, and 124). Furthermore, we investigated the quantitative contribution of BAD targeting kinases in phosphorylating serine residues 75, 99, and 118. Our results indicate that RAF kinases represent, besides protein kinase A, PAK, and Akt/protein kinase B, in vivo BAD-phosphorylating kinases. RAF-induced phosphorylation of BAD was reduced to control levels using the RAF inhibitor BAY 43-9006. This phosphorylation was not prevented by MEK inhibitors. Consistently, expression of constitutively active RAF suppressed apoptosis induced by BAD and the inhibition of colony formation caused by BAD could be prevented by RAF. In addition, using the surface plasmon resonance technique, we analyzed the direct consequences of BAD phosphorylation by RAF with respect to association with 14-3-3 and Bcl-2/Bcl-X(L) proteins. Phosphorylation of BAD by active RAF promotes 14-3-3 protein association, in which the phosphoserine 99 represented the major binding site. Finally, we show here that BAD forms channels in planar bilayer membranes in vitro. This pore-forming capacity was dependent on phosphorylation status and interaction with 14-3-3 proteins. Collectively, our findings provide new insights into the regulation of BAD function by phosphorylation.

Cationic liposomes loaded with proapoptotic peptide D-(KLAKLAK)(2) and Bcl-2 antisense oligodeoxynucleotide G3139 for enhanced anticancer therapy

The treatment of cancer using macromolecular therapeutics such as oligonucleotides or peptides requires efficient delivery systems capable of intracellular penetration and may also benefit from use of a combination of therapeutics with different mechanisms of action. With this possibility in mind, we constructed cationic liposome loaded with the proapoptotic peptide, d-(KLAKLAK)(2) and the Bcl-2 antisense oligodeoxynucleotide, G3139, and determined whether the combination of the proapoptotic macromolecules in a single cationic liposome can enhance antitumor efficacy. Advantage was taken of alternating charge interaction to entrap macromolecules of opposite charge. The polycationic peptide d-(KLAKLAK)(2) was first condensed with the polyanionic oligodeoxynucleotide G3139 to obtain overall negatively charged peptide/oligodeoxynucleotide complexes. The complexes were then entrapped into DOTAP/DOPE cationic liposomes (CL). This sequential charge interaction ensured efficient entrapment of d-(KLAKLAK)(2) and G3139 with a high loading efficiency (50%) and capacity (7.5 wt %). In vitro treatment of mouse melanoma B16(F10) with CL loaded with d-(KLAKLAK)(2)/G3139 led to significantly enhanced antitumor efficacy, mediated by stimulated induction of apoptotic (caspase 3/7) activity, when compared to CL loaded with G3139 alone. Intratumoral injection of CL loaded with d-(KLAKLAK)(2)/G3139 in B16(F10) mice xenograft also led to suppressed tumor growth associated with enhanced apoptotic activity. Thus, the combination of proapoptotic peptide d-(KLAKLAK)(2) and antisense oligonucleotide G3139 in a cationic liposome led to enhanced apoptotic/antitumor efficacy and may provide a promising tool for cancer treatment.

Neurodegeneration in Alzheimer's disease: caspases and synaptic element interdependence

Extensive genetic, biochemical, and histological evidence has implicated the amyloid-β peptide (Aβ) in Alzheimer's disease pathogenesis, and several mechanisms have been suggested, such as metal binding, reactive oxygen species production, and membrane pore formation. However, recent evidence argues for an additional role for signaling mediated by the amyloid precursor protein, APP, in part via the caspase cleavage of APP at aspartate 664. Here we review the effects and implications of this cleavage event, and propose a model of Alzheimer's disease that focuses on the critical nature of this cleavage and its downstream effects.

Bz-423 superoxide signals B cell apoptosis via Mcl-1, Bak, and Bax

Bz-423 is a pro-apoptotic 1,4-benzodiazepine with therapeutic properties in murine models of lupus demonstrating selectivity for autoreactive lymphocytes. Bz-423 modulates the F(1)F(0)-ATPase, inducing the formation of superoxide within the mitochondrial respiratory chain, which then functions as a second messenger initiating apoptosis. In order to understand some of the features that contribute to the increased sensitivity of lymphocytes, we report the signaling pathway engaged by Bz-423 in a Burkitt lymphoma cell line (Ramos). Following the generation of superoxide, Bz-423-induced apoptosis requires the activation of Bax and Bak to induce mitochondrial outer membrane permeabilization and cytochrome c release. Knockdown of the BH3-only proteins Bad, Bim, Bik, and Puma inhibits Bz-423 apoptosis, suggesting that these proteins serve as upstream sensors of the oxidant stress induced by Bz-423. Treatment with Bz-423 results in superoxide-dependent Mcl-1 degradation, implicating this protein as the link between Bz-423-induced superoxide and Bax and Bak activation. In contrast to fibroblasts, B cell death induced by Bz-423 is independent of c-Jun N-terminal kinase. These results demonstrate that superoxide generated from the mitochondrial respiratory chain as a consequence of a respiratory transition can signal a specific apoptotic response that differs across cell types.

Concurrent up-regulation of BCL-XL and BCL2A1 induces approximately 1000-fold resistance to ABT-737 in chronic lymphocytic leukemia

ABT-737 and its orally active analog, ABT-263, are rationally designed inhibitors of BCL2 and BCL-XL. ABT-263 shows promising activity in early phase 1 clinical trials in B-cell malignancies, particularly chronic lymphocytic leukemia (CLL). In vitro, peripheral blood CLL cells are extremely sensitive to ABT-737 (EC50 ∼7 nM), with rapid induction of apoptosis in all 60 patients tested, independent of parameters associated with disease progression and chemotherapy resistance. In contrast to data from cell lines, ABT-737–induced apoptosis in CLL cells was largely MCL1-independent. Because CLL cells within lymph nodes are more resistant to apoptosis than those in peripheral blood, CLL cells were cultured on CD154-expressing fibroblasts in the presence of interleukin-4 (IL-4) to mimic the lymph node microenvironment. CLL cells thus cultured developed an approximately 1000-fold resistance to ABT-737 within 24 hours. Investigations of the underlying mechanism revealed that this resistance occurred upstream of mitochondrial perturbation and involved de novo synthesis of the antiapoptotic proteins BCL-XL and BCL2A1, which were responsible for resistance to low and high ABT-737 concentrations, respectively. Our data indicate that after therapy with ABT-737–related inhibitors, resistant CLL cells might develop in lymph nodes in vivo and that treatment strategies targeting multiple BCL2 antiapoptotic members simultaneously may have synergistic activity.

Mitochondrial control of platelet apoptosis: effect of cyclosporin A, an inhibitor of the mitochondrial permeability transition pore

The role of the mitochondrial permeability transition pore (MPTP) in apoptosis of nucleated cells is well documented. In contrast, the role of MPTP in apoptosis of anucleated platelets is largely unknown. The aim of this study was to elucidate the contribution of MPTP in the control of different manifestations of platelet apoptosis by analyzing the effect of cyclosporin A (CsA), a potent inhibitor of MPTP formation. Using flow cytometry, we studied the effect of pretreatment of platelets with CsA on apoptotic responses in human platelets stimulated with calcium ionophore A23187. We found that CsA inhibited A23187-stimulated platelet apoptosis, completely preventing (i) depolarization of mitochondrial inner membrane potential (DeltaPsim), (ii) activation of cytosolic apoptosis executioner caspase-3, (iii) platelet shrinkage, and (iv) fragmentation of platelets to microparticles, but (v) only partially (approximately 25%), inhibiting phosphatidylserine (PS) exposure on the platelet surface. This study shows that MPTP formation is upstream of DeltaPsim depolarization, caspase-3 activation, platelet shrinkage and microparticle formation, and stringently controls these apoptotic events in A23187-stimulated platelets but is less involved in PS externalization. These data also indicate that CsA may rescue platelets from apoptosis, preventing caspase-3 activation and inhibiting the terminal cellular manifestations of platelet apoptosis, such as platelet shrinkage and degradation to microparticles. Furthermore, the results suggest a novel potentially useful application of CsA as an inhibitor of platelet demise through apoptosis in thrombocytopenias associated with enhanced platelet apoptosis.

Pharmacological inhibition of mitochondrial membrane permeabilization for neuroprotection

Recent data have provided important clues about the molecular mechanisms underlying certain neurodegenerative diseases. Most cell death in vertebrates proceeds via the mitochondrial pathway of apoptosis. Mitochondria contain proapoptotic factors such as cytochrome c and AIF in their intermembrane space. Furthermore, mitochondrial membrane permeabilization (MMP) is a critical event during apoptosis, representing the "point of no return" of the lethal process. Modern medicine is developing an increasing number of drugs for neurodegenerative disease, but no neuroprotective treatment has yet been established. While current treatments temporarily alleviate symptoms, they do not halt disease progression. This paper briefly reviews the pharmacological inhibition of mitochondrial membrane permeabilization for neuroprotection.

PAC-1 activates procaspase-3 in vitro through relief of zinc-mediated inhibition

The direct induction of apoptosis has emerged as a powerful anticancer strategy, and small molecules that either inhibit or activate certain proteins in the apoptotic pathway have great potential as novel chemotherapeutic agents. Central to apoptosis is the activation of the zymogen procaspase-3 to caspase-3. Caspase-3 is the key "executioner" caspase, catalyzing the hydrolysis of a multitude of protein substrates within the cell. Interestingly, procaspase-3 levels are often elevated in cancer cells, suggesting a compound that directly stimulates the activation of procaspase-3 to caspase-3 could selectively induce apoptosis in cancer cells. We recently reported the discovery of a compound, PAC-1, which enhances procaspase-3 activity in vitro and induces apoptotic death in cancer cells in culture and in mouse xenograft models. Described herein is the mechanism by which PAC-1 activates procaspase-3 in vitro. We show that zinc inhibits the enzymatic activity of procaspase-3 and that PAC-1 strongly activates procaspase-3 in buffers that contain zinc. PAC-1 and zinc form a tight complex with one another, with a dissociation constant of approximately 42 nM. The combined data indicate that PAC-1 activates procaspase-3 in vitro by sequestering inhibitory zinc ions, thus allowing procaspase-3 to autoactivate itself to caspase-3. The small-molecule-mediated activation of procaspases has great therapeutic potential and thus this discovery of the in vitro mechanism of action of PAC-1 is critical to the development and optimization of other procaspase-activating compounds.

Mitochondrial outer membrane proteins assist Bid in Bax-mediated lipidic pore formation

Mitochondrial outer membrane permeabilization (MOMP) is a critical step in apoptosis and is regulated by Bcl-2 family proteins. In vitro systems using cardiolipin-containing liposomes have demonstrated the key features of MOMP induced by Bax and cleaved Bid; however, the nature of the "pores" and how they are formed remain obscure. We found that mitochondrial outer membranes contained very little cardiolipin, far less than that required for liposome permeabilization, despite their responsiveness to Bcl-2 family proteins. Strikingly, the incorporation of isolated mitochondrial outer membrane (MOM) proteins into liposomes lacking cardiolipin conferred responsiveness to cleaved Bid and Bax. Cardiolipin dependence was observed only when permeabilization was induced with cleaved Bid but not with Bid or Bim BH3 peptide or oligomerized Bax. Therefore, we conclude that MOM proteins specifically assist cleaved Bid in Bax-mediated permeabilization. Cryoelectron microscopy of cardiolipin-liposomes revealed that cleaved Bid and Bax produced large round holes with diameters of 25-100 nm, suggestive of lipidic pores. In sum, we propose that activated Bax induces lipidic pore formation and that MOM proteins assist cleaved Bid in this process in the absence of cardiolipin.

Autophagy within the antigen donor cell facilitates efficient antigen cross-priming of virus-specific CD8+ T cells

Cross-presentation of cell-associated antigen is important in the priming of CD8(+) T-cell responses to proteins that are not expressed by antigen-presenting cells (APCs). In vivo, dendritic cells are the main cross-presenting APC, and much is known regarding their ability to capture and process cell-associated antigen. In contrast, little is known about the way death effector pathways influence the efficiency of cross-priming. Here, we compared two important mechanisms of programmed cell death: classical apoptosis, as it occurs in wild-type (WT) fibroblasts, and caspase-independent cell death, which occurs with increased features of autophagy in Bax/Bak(-/-) fibroblasts. We assessed virally infected WT and Bax/Bak(-/-) fibroblasts as a source of cell-associated antigen. We found that immunization with cells undergoing autophagy before cell death was superior in facilitating the cross-priming of antigen-specific CD8(+) T cells. Strikingly, silencing of Atg5 expression inhibited priming. We interpret this to be a novel form of 'immunogenic death' with the enhanced priming efficiency being a result of persistent MHC I cross-presentation and the induction of type I interferons. These results offer the first molecular evidence that catabolic pathways, including autophagy, influence the efficiency of cross-priming. We predict that targeting the autophagy cascade may provide a therapeutic strategy for achieving robust cross-priming of viral and tumor-specific CD8(+) T cells.

The p53-cathepsin axis cooperates with ROS to activate programmed necrotic death upon DNA damage

Three forms of cell death have been described: apoptosis, autophagic cell death, and necrosis. Although genetic and biochemical studies have formulated a detailed blueprint concerning the apoptotic network, necrosis is generally perceived as a passive cellular demise resulted from unmanageable physical damages. Here, we conclude an active de novo genetic program underlying DNA damage-induced necrosis, thus assigning necrotic cell death as a form of "programmed cell death." Cells deficient of the essential mitochondrial apoptotic effectors, BAX and BAK, ultimately succumbed to DNA damage, exhibiting signature necrotic characteristics. Importantly, this genotoxic stress-triggered necrosis was abrogated when either transcription or translation was inhibited. We pinpointed the p53-cathepsin axis as the quintessential framework underlying necrotic cell death. p53 induces cathepsin Q that cooperates with reactive oxygen species (ROS) to execute necrosis. Moreover, we presented the in vivo evidence of p53-activated necrosis in tumor allografts. Current study lays the foundation for future experimental and therapeutic discoveries aimed at "programmed necrotic death."

3,4-Dideoxyglucosone-3-Ene Induces Apoptosis in Human Peritoneal Mesothelial Cells

Objective

Glucose degradation products (GDPs) are formed during heat sterilization and storage of peritoneal dialysis (PD) fluids. 3,4-dideoxyglucosone-3-ene (3,4-DGE) has been identified as the most bioreactive GDP. 3,4-DGE induces apoptosis in leukocytes and renal tubular epithelial cells. Our aim was to evaluate the apoptotic effects of 3,4-DGE on human peritoneal mesothelial cells (HPMCs).

Methods

Primary cultured HPMCs were treated with 25 or 50 μmol/L 3,4-DGE. MTT assay was used to determine cell viability. Apoptosis was measured using TUNEL assay and flow cytometry. Expressions of procaspase-3, Bax, and Bcl-2 were estimated by Western blot. Activity of caspase-3 was measured and the effect of the caspase inhibitor zVAD-fmk (Z-Val-Ala-DL-Asp-fluoromethylketone) was evaluated by TUNEL assay.

Results

3,4-DGE treatment accelerated cell death in HPMCs in a dose- and time-dependent manner. Treatment with 3,4-DGE (25 and 50 μmol/L) significantly increased apoptosis compared to control ( p < 0.05 and p < 0.01 respectively) by TUNEL assay. Flow cytometry showed treatment with 50 μmol/L 3,4-DGE significantly increased apoptosis compared to control ( p < 0.05). Decreased expression of procaspase-3 and increased activity of caspase-3 were observed in the presence of 50 μmol/L 3,4-DGE compared to control and 25 μmol/L 3,4-DGE ( p < 0.05). 3,4-DGE-induced HPMC apoptosis was decreased after pretreatment with the pan-caspase inhibitor zVAD-fmk in the 50 μmol/L 3,4-DGE-treated group ( p < 0.001). The ratio of Bcl-2 to Bax expression was decreased in the 25 μmol/L and the 50 μmol/L 3,4-DGE-treated groups compared to control ( p < 0.05).

Conclusions

3,4-DGE promotes apoptosis in HPMCs by a caspase-related mechanism.

Palladacycles catalyse the oxidation of critical thiols of the mitochondrial membrane proteins and lead to mitochondrial permeabilization and cytochrome c release associated with apoptosis

Permeabilization of the mitochondrial membrane has been extensively associated with necrotic and apoptotic cell death. Similarly to what had been previously observed for B16F10-Nex2 murine melanoma cells, PdC (palladacycle compounds) obtained from the reaction of dmpa (N,N-dimethyl-1-phenethylamine) with the dppe [1,2-ethanebis(diphenylphosphine)] were able to induce apoptosis in HTC (hepatoma, tissue culture) cells, presenting anticancer activity in vitro. To elucidate cell site-specific actions of dmpa:dppe that could respond to the induction of apoptosis in cancer cells in the present study, we investigated the effects of PdC on isolated RLM (rat liver mitochondria). Our results showed that these palladacycles are able to induce a Ca2+-independent mitochondrial swelling that was not inhibited by ADP, Mg2+ and antioxidants. However, the PdC-induced mitochondrial permeabilization was partially prevented by pre-incubation with CsA (cyclosporin A), NEM (N-ethylmaleimide) and bongkreic acid and totally prevented by DTT (dithiothreitol). A decrease in the content of reduced thiol groups of the mitochondrial membrane proteins was also observed, as well as the presence of membrane protein aggregates in SDS/PAGE without lipid and GSH oxidation. FTIR (Fourier-transform IR) analysis of PdC-treated RLM demonstrated the formation of disulfide bonds between critical thiols in mitochondrial membrane proteins. Associated with the mitochondrial permeabilization, PdC also induced the release of cytochrome c, which is sensitive to inhibition by DTT. Besides the contribution to clarify the pro-apoptotic mechanism of PdC, this study shows that the catalysis of specific protein thiol cross-linkage is enough to induce mitochondrial permeabilization and cytochrome c release.

Alteration of the mitochondrial apoptotic pathway is key to acquired paclitaxel resistance and can be reversed by ABT-737

Paclitaxel is a microtubule-targeting antineoplastic drug widely used in human cancers. Even when tumors are initially responsive, progression of disease despite continued taxane therapy is all too common in the treatment of many of the most common epithelial cancers, including breast cancer. However, the mechanisms underlying paclitaxel resistance in cancer cells are not completely understood. Our hypothesis is that changes in the intrinsic (or mitochondrial) cell death pathway controlled by the BCL-2 family are key to the development of acquired paclitaxel resistance. Here we show that paclitaxel activates the mitochondrial apoptosis pathway, which can be blocked by BCL-2 overexpression. Treatment with ABT-737, a small-molecule BCL-2 antagonist, restores sensitivity to paclitaxel in BCL-2-overexpressing cells. To investigate the importance of changes in the intrinsic apoptotic pathway in the absence of enforced BCL-2 expression, we generated two independent breast cancer cell lines with acquired resistance to apoptosis induced by paclitaxel. In these lines, acquired resistance to paclitaxel is mediated either by increased antiapoptotic BCL-2 proteins or decreased proapoptotic BCL-2 proteins. In both cases, ABT-737 can engage the mitochondrial apoptosis pathway to restore sensitivity to paclitaxel to cell lines with acquired paclitaxel resistance. In summary, these findings suggest that alterations in the intrinsic apoptotic pathway controlled by BCL-2 protein family members may be crucial to causing paclitaxel resistance. Furthermore, our results suggest that combining small-molecule BCL-2 antagonists with paclitaxel may offer benefit to patients with paclitaxel-resistant tumors, an oncologic problem of great prevalence.

Bz-423 superoxide signals apoptosis via selective activation of JNK, Bak, and Bax

Bz-423 is a proapoptotic 1,4-benzodiazepine with potent therapeutic properties in murine models of lupus and psoriasis. Bz-423 modulates the F(1)F(0)-ATPase, inducing the formation of superoxide within the mitochondrial respiratory chain, which then functions as a second messenger initiating apoptosis. Herein, we report the signaling pathway activated by Bz-423 in mouse embryonic fibroblasts containing knockouts of key apoptotic proteins. Bz-423-induced superoxide activates cytosolic ASK1 and its release from thioredoxin. A mitogen-activated protein kinase cascade follows, leading to the specific phosphorylation of JNK. JNK signals activation of Bax and Bak which then induces mitochondrial outer membrane permeabilization to cause the release of cytochrome c and a commitment to apoptosis. The response of these cells to Bz-423 is critically dependent on both superoxide and JNK activation as antioxidants and the JNK inhibitor SP600125 prevents Bax translocation, cytochrome c release, and cell death. These results demonstrate that superoxide generated from the mitochondrial respiratory chain as a consequence of a respiratory transition can signal a sequential and specific apoptotic response. Collectively, these data suggest that the selectivity of Bz-423 observed in vivo results from cell-type specific differences in redox balance and signaling by ASK1 and Bcl-2 proteins.

Effects of the JAK2 inhibitor, AZ960, on Pim/BAD/BCL-xL survival signaling in the human JAK2 V617F cell line SET-2

The Janus-associated kinase 2 (JAK2) V617F mutation is believed to play a critical role in the pathogenesis of polycythemia vera, essential thrombocythemia, and idiopathic myelofibrosis. We have characterized a novel small molecule JAK2 inhibitor, AZ960, and used it as a tool to investigate the consequences of JAK2 V617F inhibition in the SET-2 cell line. AZ960 inhibits JAK2 kinase with a K(i) of 0.00045 microm in vitro and treatment of TEL-JAK2 driven Ba/F3 cells with AZ960 blocked STAT5 phosphorylation and potently inhibited cell proliferation (GI(50)=0.025 microm). AZ960 demonstrated selectivity for TEL-JAK2-driven STAT5 phosphorylation and cell proliferation when compared with cell lines driven by similar fusions of the other JAK kinase family members. In the SET-2 human megakaryoblastic cell line, heterozygous for the JAK2 V617F allele, inhibition of JAK2 resulted in decreased STAT3/5 phosphorylation and inhibition of cell proliferation (GI(50)=0.033 microm) predominately through the induction of mitochondrial-mediated apoptosis. We provide evidence that JAK2 inhibition induces apoptosis by direct and indirect regulation of the anti-apoptotic protein BCL-xL. Inhibition of JAK2 blocked BCL-XL mRNA expression resulting in a reduction of BCL-xL protein levels. Additionally, inhibition of JAK2 resulted in decreased PIM1 and PIM2 mRNA expression. Decreased PIM1 mRNA corresponded with a decrease in Pim1 protein levels and inhibition of BAD phosphorylation at Ser(112). Finally, small interfering RNA-mediated suppression of BCL-xL resulted in apoptotic cell death similar to the phenotype observed following JAK2 inhibition. These results suggest a model in which JAK2 promotes cell survival by signaling through the Pim/BAD/BCL-xL pathway.

Dominance of cytokine- over FasL-induced impairment of the mitochondrial transmembrane potential (Deltapsim) in the pancreatic beta-cell line NIT-1

Mitochondria of pancreatic beta-cells are potential targets of intrinsic and extrinsic apoptotic pathways in the autoimmune pathogenesis of type 1 diabetes. We aimed to investigate whether cytokine- and FasLigand (FasL)-induced apoptosis is associated with impaired mitochondrial transmembrane potential (Deltapsim) in the pancreatic beta-cell line NIT-1. NIT-1 cells were exposed to the interleukin-1beta/interferon-gamma (IL-1beta/IFN-gamma) cytokine combination to induce apoptosis in vitro. Low concentrations of cytokines resulted in Deltapsim impairment, and increasing concentrations had only a minor additional effect. Treatment with the inducible nitric oxide synthase (iNOS) inhibitor Nw-nitro-L-arginine methyl ester hydrochloride (L-NAME) prevented cytokine-mediated Deltapsim impairment, implying that cytokines affect Deltapsim via nitric oxide. The broad-spectrum caspase inhibitor Z-VAD(Ome)-FMK (ZVAD) revealed dichotomic actions. In the presence of ZVAD, cytokine-induced nitrite generation was increased but cell death and Deltapsim impairment were reduced. Deltapsim impairment was also reduced by inhibitors of caspases 1, 6 and 8. Induction of Fas by IL-1beta/IFN-gamma coupled with activation by Super-FasL augmented cytokine-induced cell death. We observed a clear dominance of cytokine- over FasL-induced effects on Deltapsim. Our findings show that IL-1beta/IFN-gamma cytokines have a strong effect to impair Deltaym and prime beta-cells for apoptosis via the intrinsic pathway mediated by iNOS and caspases. Furthermore, at least in NIT-1 cells, the extrinsic FasL/Fas pathway has only a minor additive effect on cytokine-induced Deltapsim impairment.

Neuroprotective effect of Ro5-4864 following brain injury

The 18 kDa translocator protein (TSPO) is a protein complex located at the outer mitochondrial membrane and interacting with the mitochondrial permeability transition pore (mPTP), indicating its involvement in the control of mPTP opening. We intended to explore the effect of TSPO ligands, PK 11195 and Ro5-4864 on apoptosis in a rat model of cortical injury. Sprague-Dawley rats received a daily intraperitoneal injection of dimethylsulfoxide (vehicle), PK 11195, or Ro5-4864, starting 2 days prior the injury and a third injection after the injury. At 6 weeks, immunohistochemistry analysis showed that Ro5-4864 resulted in a significant increase in the number of surviving neurons and in the density of the neurofilament network in the perilesional cortex in comparison with animals of the vehicle and PK 11195 groups. In tissue samples dissected from the injured area, Ro5-4864 caused a significant reduction in activation of caspases 3 and 9 but not of caspase 8 in comparison with the vehicle and PK 11195 groups. In addition, measurements of transmembrane mitochondrial potential of mitochondria (Deltapsi(M)) isolated from normal rat brain showed that loss of Deltapsi(M) induced by recombinant Bax could be significantly reduced by Ro5-4864 in a concentration-dependent manner. Our findings indicate that the neuroprotective effect shown by Ro5-4864 in the present model of brain injury involves the mitochondrial pathway of apoptosis modulation of mPTP.

Activating PTPN11 mutants promote hematopoietic progenitor cell-cycle progression and survival

OBJECTIVE

Mutations in PTPN11, which encodes the protein tyrosine phosphatase Shp2, are commonly found in juvenile myelomonocytic leukemia (JMML). We hypothesized that PTPN11 mutations promote cell-cycle progression and confer enhanced survival to hematopoietic progenitors.

MATERIALS AND METHODS

Murine bone marrow low-density mononuclear cells were transduced with pMIEG3, pMIEG3-WT Shp2, pMIEG3-Shp2D61Y, or pMIEG3-Shp2E76K followed by cell-cycle and survival functional analysis as well as biochemical analysis for key cell-cycle and programmed cell-death regulatory proteins.

RESULTS

A higher proportion of hematopoietic progenitors bearing the gain-of-function Shp2 mutants were residing in the S or G2 phase of the cell cycle in response to low doses of granulocyte-macrophage colony-stimulating factor compared to cells transduced with empty vector (MIEG3) or with WT Shp2. Likewise, Shp2D61Y- or Shp2E76K-expressing hematopoietic cells demonstrated reduced apoptosis based on Annexin-V staining and produced increased progenitor colonies after 48 hours in minimal media compared to cells transduced with empty vector or WT Shp2. To differentiate enhanced survival vs hyperproliferation, cells were stained with PKH26 to distinguish undivided cells from divided progeny. Shp2D61Y- or Shp2E76K-expressing PKH26+ cells similarly demonstrated reduced apoptosis. Upon biochemical analysis, expression of Akt- and Erk-responsive cell-cycle and programmed cell-death regulatory proteins were altered, including increased levels of cyclin D1, Bcl2, and BclXL and reduced levels of p27, p21, and Bim.

CONCLUSION

Collectively, these data demonstrate that gain-of-function Shp2 mutants promote hematopoietic progenitor cell-cycle progression and survival and imply that agents targeting the cell cycle or promoting apoptosis may have therapeutic potential in JMML.

HIV protease inhibitors provide neuroprotection through inhibition of mitochondrial apoptosis in mice

Neuroprotection can be achieved by preventing apoptotic death of postmitotic cells. Apoptotic death can occur by either a caspase-dependent mechanism, involving cytochrome c, apoptosis protease-activating factor-1 (Apaf-1), and caspase-9, or a caspase-independent mechanism, involving apoptosis-inducing factor (AIF). HIV protease inhibitors (PIs) avert apoptosis in part by preventing mitochondrial outer membrane permeabilization (MOMP), but the precise mechanism by which they work is not known. Here, we evaluated the impact of the PIs in a mouse model of retinal detachment (RD) in vivo and in murine primary retinal cell cultures in vitro. Oral administration of the PIs nelfinavir and ritonavir significantly inhibited photoreceptor apoptosis, while preventing the translocation of AIF from mitochondria to the nucleus as well as the activation of caspase-9. RD-induced photoreceptor apoptosis was similarly inhibited in mice carrying hypomorphic mutations of the genes encoding AIF or Apaf-1. Nelfinavir attenuated apoptosis as well as mitochondrial release of AIF and cytochrome c, and subsequent activation of caspase-9 in vitro, in photoreceptor cultures exposed to starvation or monocyte chemoattractant protein-1-stimulated (MCP-1-stimulated) macrophages. Our results suggest that the MOMP inhibition by PIs involved interruption of both caspase-dependent and caspase-independent apoptosis pathways and that PIs may be clinically useful for the treatment of diseases caused by excessive apoptosis.

Over-expression of adenine nucleotide translocase 1 (ANT1) induces apoptosis and tumor regression in vivo

Background

Adenine nucleotide translocase (ANT) is located in the inner mitochondrial membrane and catalyzes the exchange of mitochondrial ATP for cytosolic ADP. ANT has been known to be a major component of the permeability transition pore complex of mitochondria and contributes to mitochondria-mediated apoptosis. Human ANT has four isoforms (ANT1, ANT2, ANT3, and ANT4), and the expression of the ANT isoforms is variable depending on the tissue and cell type, developmental stage, and proliferation status. Among the isoforms, ANT1 is highly expressed in terminally-differentiated tissues, but expressed in low levels in proliferating cells, such as cancer cells. In particular, over-expression of ANT1 induces apoptosis in cultured tumor cells.

Methods

We applied an ANT1 gene transfer approach to induce apoptosis and to evaluate the anti-tumor effect of ANT1 in a nude mouse model.

Results

We demonstrated that ANT1 transfection induced apoptosis of MDA-MB-231 cells, inactivated NF-κB activity, and increased Bax expression. ANT1-inducing apoptosis was accompanied by the disruption of mitochondrial membrane potential, cytochrome c release and the activation of caspases-9 and -3. Moreover, ANT1 transfection significantly suppressed tumor growth in vivo.

Conclusion

Our results suggest that ANT1 transfection may be a useful therapeutic modality for the treatment of cancer.

Cysteine cathepsins trigger caspase-dependent cell death through cleavage of bid and antiapoptotic Bcl-2 homologues

As a model for defining the role of lysosomal cathepsins in apoptosis, we characterized the action of the lysosomotropic agent LeuLeuOMe using distinct cellular models. LeuLeuOMe induces lysosomal membrane permeabilization, resulting in release of lysosomal cathepsins that cleave the proapoptotic Bcl-2 family member Bid and degrade the antiapoptotic member Bcl-2, Bcl-xL, or Mcl-1. The papain-like cysteine protease inhibitor E-64d largely prevented apoptosis, Bid cleavage, and Bcl-2/Bcl-xL/Mcl-1 degradation. The pancaspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp(OMe)fluoromethyl ketone failed to prevent Bid cleavage and degradation of anti-apoptotic Bcl-2 homologues but substantially decreased cell death, suggesting that cathepsin-mediated apoptosis in these cellular models mostly follows a caspase-dependent pathway. Moreover, in vitro experiments showed that one or more of the cysteine cathepsins B, L, S, K, and H could cleave Bcl-2, Bcl-xL, Mcl-1, Bak, and BimEL, whereas no Bax cleavage was observed. On the basis of inhibitor studies, we demonstrate that lysosomal disruption triggered by LeuLeuOMe occurs before mitochondrial damage. We propose that degradation of anti-apoptotic Bcl-2 family members by lysosomal cathepsins synergizes with cathepsin-mediated activation of Bid to trigger a mitochondrial pathway to apoptosis. Moreover, XIAP (X-chromosome-linked inhibitor of apoptosis) was also found to be a target of cysteine cathepsins, suggesting that cathepsins can mediate caspase-dependent apoptosis also downstream of mitochondria.

Cellular and molecular mechanisms of liver injury

Derangements in apoptosis of liver cells are mechanistically important in the pathogenesis of end-stage liver disease. Vulnerable hepatocytes can undergo apoptosis via an extrinsic, death receptor-mediated pathway, or alternatively intracellular stress can activate the intrinsic pathway of apoptosis. Both pathways converge on mitochondria, and mitochondrial dysfunction is a prerequisite for hepatocyte apoptosis. Persistent apoptosis is a feature of chronic liver diseases, and massive apoptosis is a feature of acute liver diseases. Fibrogenesis is stimulated by ongoing hepatocyte apoptosis, eventually resulting in cirrhosis of the liver in chronic liver diseases. Endothelial cell apoptosis occurs in ischemia-reperfusion injury. Natural killer and natural killer T cells remove virus-infected hepatocytes by death receptor-mediated fibrosis. Lastly, activated stellate cell apoptosis leads to slowing and resolution of apoptosis. This review summarizes recent cellular and molecular advances in the understanding of the injury mechanisms leading to end-stage liver disease.

Mitochondrial protein targets of thiol-reactive electrophiles

Mitochondria serve a pivotal role in the regulation of apoptosis or programmed cell death. Recent studies have demonstrated that reactive electrophiles induce mitochondrion-dependent apoptosis. We hypothesize that covalent modification of specific mitochondrial proteins by reactive electrophiles serves as a trigger leading to the initiation of apoptosis. In this study, we identified protein targets of the model biotin-tagged electrophile probes N-iodoacetyl- N-biotinylhexylene-diamine (IAB) and 1-biotinamido-4-(4'-[maleimidoethylcyclohexane]carboxamido)butane (BMCC) in HEK293 cell mitochondrial fractions by liquid chromatography-tandem mass spectrometry (LC-MS-MS). These electrophiles reproducibly adducted a total of 1693 cysteine residues that mapped to 809 proteins. Protein modifications were selective in that only 438 cysteine sites in 1255 cysteinyl peptide adducts (35%) and 362 of the 809 identified protein targets (45%) were adducted by both electrophiles. Of these, approximately one-third were annotated to the mitochondria following protein database analysis. IAB initiated apoptotic events including cytochrome c release, caspase-3 activation, and poly(ADP-ribose)polymerase (PARP) cleavage, whereas BMCC did not. Of the identified targets of IAB and BMCC, 44 were apoptosis-related proteins, and adduction site specificity on these targets differed between the two probes. Differences in sites of modification between these two electrophiles may reveal alkylation sites whose modification triggers apoptosis.

Proteomics for biomarker discovery in acute kidney injury

Acute kidney injury (AKI), previously referred to as acute renal failure, represents a common and devastating problem in clinical medicine. Despite significant improvements in therapeutics, the mortality and morbidity associated with AKI remain high. A major reason for this is the lack of early markers for AKI, and hence an unacceptable delay in initiating therapy. Fortunately, the application of innovative technologies such as functional genomics and proteomics to human and animal models of AKI has uncovered several novel biomarkers and therapeutic targets. The most promising of these are chronicled in this review. These include the identification of biomarker panels in plasma (neutrophil gelatinase-associated lipocalin and cystatin C) and urine (neutrophil gelatinase-associated lipocalin, kidney injury molecule-1, interleukin-18, cystatin C, alpha1-microglobulin, Fetuin-A, Gro-alpha, and meprin). It is likely that the AKI panels will be useful for timing the initial insult, and assessing the duration and severity of AKI. It is also probable that the AKI panels will distinguish between the various etiologies of AKI and predict clinical outcomes. It will be important in future studies to validate the sensitivity and specificity of these biomarker panels in clinical samples from large cohorts and from multiple clinical situations. Such studies will be facilitated markedly by the development of commercial tools for the reproducible measurement of biomarkers across different laboratories.

Transcriptional Regulation of SDHa flavoprotein by nuclear respiratory factor-1 prevents pseudo-hypoxia in aerobic cardiac cells

Nuclear respiratory factor-1 (NRF-1) is integral to the transcriptional regulation of mitochondrial biogenesis, but its control over various respiratory genes overlaps other regulatory elements including those involved in O(2) sensing. Aerobic metabolism generally suppresses hypoxia-sensitive genes, e.g. via hypoxia-inducible factor-1 (HIF-1), but mutations in Complex II-succinate dehydrogenase (SDH), a tumor suppressor, stabilize HIF-1, producing pseudo-hypoxia. In aerobic cardiomyocytes, which rely on oxidative phosphorylation, we tested the hypothesis that NRF-1 regulates Complex II expression and opposes hypoxia-inducible factor-1. NRF-1 gene silencing blocked aerobic succinate oxidation, increasing nuclear HIF-1alpha protein prior to the loss of Complex I function. We postulated that NRF-1 suppression either specifically decreases the expression of one or more SDH subunits and increases succinate availability to regulate HIF-1 prolyl hydroxylases, or stimulates mitochondrial reactive oxygen production, which interferes with HIF-1alpha degradation. Using promoter analysis, gene silencing, and chromatin immunoprecipitation, NRF-1 was found to bind to the gene promoters of two of four nuclear-encoded Complex II subunits: SDHa and SDHd, but the enzyme activity was dynamically regulated through the catalytic SDHa flavoprotein. Complex II was inactivated by SDHa silencing, which led to aerobic HIF-1alpha stabilization, nuclear translocation, and enhanced expression of glucose transporters and heme oxygenase-1. This was unrelated to mitochondrial ROS production, reversible by high alpha-ketoglutarate concentrations, and coherent with regulation of HIF-1 by succinate reported in tumor cells. These findings disclose a novel role for NRF-1 in the transcriptional control of Complex II and prevention of pseudo-hypoxic gene expression in aerobic cardiac cells.

Two independent positive feedbacks and bistability in the Bcl-2 apoptotic switch

Background

The complex interplay between B-cell lymphoma 2 (Bcl-2) family proteins constitutes a crucial checkpoint in apoptosis. Its detailed molecular mechanism remains controversial. Our former modeling studies have selected the ‘Direct Activation Model’ as a better explanation for experimental observations. In this paper, we continue to extend this model by adding interactions according to updating experimental findings.

Methodology/Principal Findings

Through mathematical simulation we found bistability, a kind of switch, can arise from a positive (double negative) feedback in the Bcl-2 interaction network established by anti-apoptotic group of Bcl-2 family proteins. Moreover, Bax/Bak auto-activation as an independent positive feedback can enforce the bistability, and make it more robust to parameter variations. By ensemble stochastic modeling, we also elucidated how intrinsic noise can change ultrasensitive switches into gradual responses. Our modeling result agrees well with recent experimental data where bimodal Bax activation distributions in cell population were found.

Conclusions/Significance

Along with the growing experimental evidences, our studies successfully elucidate the switch mechanism embedded in the Bcl-2 interaction network and provide insights into pharmacological manipulation of Bcl-2 apoptotic switch as further cancer therapies.

The Design of Gold-Based, Mitochondria-Targeted Chemotherapeutics

Recent developments in understanding the central place of mitochondria as regulators of programmed cell death have stimulated enormous interest in using them as targets for cancer chemotherapy. To overcome drug resistance and the lack of selectivity of cancer drugs in differentiating between normal and tumour cells, many strategies have been described in recent literature, including the use of delocalized lipophilic cations that selectively accumulate in tumour-cell mitochondria. Thioredoxin reductase, an enzyme involved in redox regulation and cell growth, has also emerged recently as an attractive drug target. Here we discuss the rationale for the design of lipophilic, cationic Au(i) phosphine complexes that are targeted to mitochondria of tumour cells and have potent and selective anticancer activity for cancer cells but not for normal cells. Our discovery that the thioredoxin system may be a critical target responsible for the selective toxicity provides a new strategy in the development of mitochondria-targeted chemotherapeutics.

Melatonin protects against common deletion of mitochondrial DNA-augmented mitochondrial oxidative stress and apoptosis

Defected mitochondrial respiratory chain (RC), in addition to causing a severe ATP deficiency, often augments reactive oxygen species (ROS) generation in mitochondria (mROS) which enhances pathological conditions and diseases. Previously, we demonstrated a potent endogenously RC defect-augmented mROS associated dose-dependently with a commonly seen large-scale deletion of 4977 base pairs of mitochondrial DNA (mtDNA), i.e. the common deletion (CD). As current treatments for CD-associated diseases are rather supplementary and ineffective, we investigated whether melatonin, a potential mitochondrial protector, provides beneficial protection for CD-augmented mitochondrial oxidative stress and apoptosis particularly upon the induction of a secondary oxidative stress. Detailed mechanistic investigations were performed by using laser scanning dual fluorescence imaging microscopy to provide precise spatial and temporal resolution of mitochondrial events at single cell level. We demonstrate, for the first time, that melatonin significantly prevents CD-augmented mROS formation under basal conditions as well as at early time-points upon secondary oxidative stress induced by H2O2 exposure. Thus, melatonin prevents mROS-mediated depolarization of mitochondrial membrane potential (DeltaPsim) and subsequent opening of the mitochondrial permeability transition pore (MPTP) and cytochrome c release. Moreover, melatonin prevents depletion of cardiolipin which appears to be crucial for postponing later MPTP opening, disruption of the mitochondrial membrane and apoptosis. Finally, the protection provided by melatonin is superior to those caused by the suppression of mitochondrial Ca2+ regulators including the mitochondrial Na+-Ca2) exchanger, the MPTP, and the mitochondrial Ca2+ uniporter and by antioxidants including vitamin E and mitochondria-targeted coenzyme Q, MitoQ. As RC defect-augmented endogenous mitochondrial oxidative stress is centrally involved in a variety of pathological conditions and diseases, melatonin thus may serve as a therapeutic drug to benefit many clinical conditions that involve malfunction of the mitochondria.

The effect of oxygenation level on cerebral post-traumatic apoptotsis is modulated by the 18-kDa translocator protein (also known as peripheral-type benzodiazepine receptor) in a rat model of cortical contusion

AIMS

Hyperbaric hyperoxia has been shown to reduce apoptosis in brain injury. As the 18-kDa translocator protein (TSPO), also known as peripheral-type benzodiazepine receptor, is closely associated with the mitochondrial transition pore and because of its role in mitochondrial respiration and apoptosis, we hypothesized that reduction of apoptosis by hyperoxia may involve the TSPO.

METHODS

TSPO and transferase-mediated dUTP nick end labelling (TUNEL) immunopositivity was first assessed in cortical contusion, created by dynamic cortical deformation, by immunohistochemistry in rats exposed to normoxia [(dynamic cortical deformation (DCD)], normobaric hyperoxia or hyperbaric hyperoxia [hyperbaric oxygen therapy (HBO)]. In a second step, transmembrane mitochondrial potential (Deltapsi(M)) and caspase 9 activity were assessed in the injured area in comparison with the noninjured hemisphere. Measurements were performed in DCD and HBO groups. A third group receiving both HBO and the TSPO ligand PK11195 was investigated as well.

RESULTS

TSPO correlated quantitatively and regionally with TUNEL immunopositivity in the perilesional area. Hyperoxia reduced both the number of TSPO expressing and TUNEL positive cells in the perilesional area, and this effect proved to be pressure dependent. After contusion, we demonstrated a dissipation of Deltapsi(M) in isolated mitochondria and an elevation of caspase 9 activity in tissue homogenates from the contused area, both of which could be substantially reversed by hyperbaric hyperoxia. This protective effect of hyperoxia was reversed by PK11195.

CONCLUSIONS

The present findings suggest that the protective effect of hyperoxia may be due to a negative regulation of the proapoptotic function of mitochondrial TSPO, including conservation of the mitochondrial membrane potential.

Sexual Dimorphism in Superantigen Shock Involves Elevated TNF-α and TNF-α–induced Hepatic Apoptosis

RATIONALE

There is conflicting evidence regarding sex differences in the outcome from severe sepsis and toxic shock. Superantigen-mediated toxic shock affects a higher proportion of female patients.

OBJECTIVES

The objective of the current study was to investigate sexual dimorphism in superantigen-associated sepsis and in superantigen-mediated shock and to identify the key mechanisms responsible for this sex difference.

METHODS

We measured mortality and serum cytokines after induction of sepsis with isogenic superantigen-positive and superantigen-negative Streptococcus pyogenes in HLA class II transgenics. During superantigen-mediated toxic shock, we measured mortality, T-cell responses, systemic tumor necrosis factor (TNF)-alpha and TNF receptors, TNF-alpha-induced hepatocyte apoptosis, and conditioning of these responses by tamoxifen treatment.

MEASUREMENTS AND MAIN RESULTS

In both superantigen-associated sepsis and in superantigen-mediated shock, serum TNF-alpha was increased in females compared with males. This was not attributable to a detectable difference in splenic TNF-alpha transcription; rather, serum soluble TNF receptors were higher in males. Pretreatment of females with the estrogen receptor modulator tamoxifen increased serum soluble TNF receptors, reduced the early serum TNF-alpha response, and improved mortality in females challenged with staphylococcal enterotoxin B. Lethal superantigen shock was characterized by hepatocyte apoptosis, and was reproduced by injection of TNF-alpha. Females had enhanced susceptibility to TNF-alpha-mediated lethality. TNF-alpha-induced hepatocyte apoptosis was greater in females, and was reduced by tamoxifen pretreatment.

CONCLUSIONS

Sexual dimorphism in experimental superantigen toxic shock results from increased systemic TNF-alpha in females, coupled with an increased susceptibility to TNF-alpha-induced hepatocyte apoptosis. Both processes are abrogated by estrogen receptor modulators.

Decoding caspase signaling in host immunity to the protozoan Trypanosoma cruzi

Caspases, a family of cysteinyl-aspartate-specific proteases, induce apoptosis but are also involved in signal transduction in live cells. Caspase activation and apoptosis in T lymphocytes occur following infection with parasites and might affect immune responses. Rapid progress has occurred in the development and testing of caspase inhibitors and other apoptosis blockers, which are potentially useful for treating diseases associated with the pathogenic effects of apoptosis. Pharmacological approaches and the use of genetically modified hosts can be combined in research strategies to understand how apoptosis and caspase signaling affect the immune system.

A Novel Epidermal Growth Factor Receptor Inhibitor Promotes Apoptosis in Non–Small Cell Lung Cancer Cells Resistant to Erlotinib

Non-small cell lung cancer (NSCLC) with activating mutations in the epidermal growth factor receptor (EGFR) responds to EGFR tyrosine kinase inhibitors such as erlotinib. However, secondary somatic EGFR mutations (e.g., T790M) confer resistance to erlotinib. BMS-690514, a novel panHER/vascular endothelial growth factor receptor (VEGFR) inhibitor described here, exerted antiproliferative and proapoptotic effects on NSCLC cell lines, with prominent efficacy on H1975 cells expressing the T790M mutation. In this model, BMS-690514 induced a G(1) cell cycle arrest, as well as ultrastructural hallmarks of apoptosis, mitochondrial release of cytochrome c, and activation of caspases involved in the intrinsic (e.g., caspase-2, caspase-3, caspase-7, and caspase-9), but not in the extrinsic (e.g., caspase-8), pathway. Caspase inhibition conferred partial protection against BMS-690514 cytotoxicity, pointing to the involvement of both caspase-dependent and caspase-independent effector mechanisms. Transcriptome analyses revealed the up-regulation of proapoptotic (e.g., Bim, Puma) and cell cycle inhibitory (e.g., p27(Kip1), p57(Kip2)) factors, as well as the down-regulation of antiapoptotic (e.g., Mcl1), heat shock (e.g., HSP40, HSP70, HSP90), and cell cycle promoting [e.g., cyclins B1, D1, and D3; cyclin-dependent kinase 1 (CDK1); MCM family proteins; proliferating cell nuclear antigen (PCNA)] proteins. BMS-690514-induced death of H1975 cells was modified in a unique fashion by a panel of small interfering RNAs targeting apoptosis modulators. Down-regulation of components of the nuclear factor-kappaB survival pathway (e.g., p65, Nemo/IKK gamma, TAB2) sensitized cells to BMS-690514, whereas knockdown of proapoptotic factors (e.g., Puma, Bax, Bak, caspase-2, etc.) and DNA damage-related proteins (e.g., ERCC1, hTERT) exerted cytoprotective effects. BMS-690514 is a new pan-HER/VEGFR inhibitor that may become an alternative to erlotinib for the treatment of NSCLC.

Polymer-drug conjugates as modulators of cellular apoptosis

The successful clinical application of polymer-protein conjugates (PEGylated enzymes and cytokines) and the promising results arising from clinical trials with polymer-bound chemotherapy (eg, doxorubicin or paclitaxel) have established their potential to reduce toxicity and improve activity in chemotherapy-refractory patients. Furthermore, and more important, they have also provided a firm foundation for more sophisticated second-generation constructs that deliver the newly emerging target-directed bioactive agents (eg, modulators of apoptosis, cell cycle, anti-angiogenic drugs) in addition to polymer-based drug combinations (eg, endocrine therapy and chemotherapy). This review will focus on polymer-drug conjugate modulators of cellular apoptosis to be used as single pro-apoptotic (eg, cancer) or anti-apoptotic (eg, ischemia) agents or as a combination therapy.

Modeling of the role of a Bax-activation switch in the mitochondrial apoptosis decision

We performed in silico modeling of the regulatory network of mitochondrial apoptosis through which we examined the role of a Bax-activation switch in governing the mitochondrial apoptosis decision. Two distinct modeling methods were used in this article. One is continuous and deterministic, comprised of a set of ordinary differential equations. The other, carried out in a discrete manner, is based on a cellular automaton, which takes stochastic fluctuations into consideration. We focused on dynamic properties of the mitochondrial apoptosis regulatory network. The roles of Bcl-2 family proteins in cellular responses to apoptotic stimuli were examined. In our simulations, a self-amplification process of Bax-activation is indicated. Further analysis suggests that the core module of Bax-activation is bistable in both deterministic and stochastic models, and this feature is robust to noise and wide ranges of parameter variation. When coupling with Bax-polymerization, it forms a one-way-switch, which governs irreversible behaviors of Bax-activation even with attenuation of apoptotic stimulus. Together with the growing biochemical evidence, we propose a novel molecular switch mechanism embedded in the mitochondrial apoptosis regulatory network and give a plausible explanation for the all-or-none, irreversible character of mitochondrial apoptosis.

Multifaceted targeting in cancer: the recent cell death players meet the usual oncogene suspects

Recent complicated advances towards the blueprinting of the altered molecular networks that lie behind cancer development have paved the way for targeted therapy in cancer. This directed a significant part of the research community to the development of specialized targeted agents, many of which are already available or in clinical trials. The prospect of patient-tailored therapeutic strategies, although very close to becoming a reality also raises the level of complexity of the therapeutic approach. This review summarizes the functions, in vivo expression patterns and aberrations of factors presently targeted or representing potential targets by therapeutic agents, focusing on those implicated in death receptor-induced apoptosis. The authors overview the regulation of these factors and death receptor-induced apoptosis by classical oncogenes (e.g., RAS, MYC, HER2) and their effectors/regulators, most of which are also being targeted. In addition, the importance of orthologic systemic approaches in future patient-tailored therapies are discussed.

Lysosomes and Fas-mediated liver cell death

A number of studies, mostly performed ex vivo, suggest that lysosomes are involved in apoptosis as a result of a release of their cathepsins into the cytosol. These enzymes could then contribute to the permeabilization of the outer mitochondrial membrane; they could also activate effector caspases. The present study aims at testing whether the membrane of liver lysosomes is disrupted during Fas-mediated cell death of hepatocytes in vivo, a process implicated in several liver pathologies. Apoptosis was induced by injecting mice with aFas (anti-Fas antibody). The state of lysosomes was assessed by determining the proportion of lysosomal enzymes (beta-galactosidase, beta-glucuronidase, cathepsin C and cathepsin B) present in homogenate supernatants, devoid of intact lysosomes, and by analysing the behaviour in differential and isopycnic centrifugation of beta-galactosidase. Apoptosis was monitored by measuring caspase 3 activity (DEVDase) and the release of sulfite cytochrome c reductase, an enzyme located in the mitochondrial intermembrane space. Results show that an injection of 10 microg of aFas causes a rapid and large increase in DEVDase activity and in unsedimentable sulfite cytochrome c reductase. This modifies neither the proportion of unsedimentable lysosomal enzyme in the homogenates nor the behaviour of lysosomes in centrifugation. Experiments performed with a lower dose of aFas (5 microg) indicate that unsedimentable lysosomal hydrolase activity increases in the homogenate after injection but with a marked delay with respect to the increase in DEVDase activity and in unsedimentable sulfite cytochrome c reductase. Comparative experiments ex vivo performed with Jurkat cells show an increase in unsedimentable lysosomal hydrolases, but much later than caspase 3 activation, and a release of dipeptidyl peptidase III and DEVDase into culture medium. It is proposed that the weakening of lysosomes observed after aFas treatment in vivo and ex vivo results from a necrotic process that takes place late after initiation of apoptosis.

Conjugation of a novel Apaf-1 inhibitor to peptide-based cell-membrane transporters: effective methods to improve inhibition of mitochondria-mediated apoptosis

We have identified a family of peptoids that inhibits in vitro the activity of the apoptosome, a macromolecular complex that activates mitochondrial-dependent apoptosis pathways. The analysis of peptide-based cell compatible delivery systems of the most active peptoid is presented. The active peptoid was then fused to cell penetrating peptides (CPP) as penetratin (PEN-peptoid) and HIV-1 TAT (TAT-peptoid). PEN-peptoid showed greater cell viability and as a consequence better efficiency as an apoptosis inhibitor than the TAT-peptoid. The intracellular trafficking of both inhibitors was studied by flow cytometry and confocal fluorescence microscopy. Finally, the influence of the cargo (peptoid) molecules on the conformational behavior of the CPP in buffers and in membrane mimetic environments was analyzed using circular dichroism (CD) spectroscopy.

Caspase inhibition reduces lymphocyte apoptosis and improves host immune responses to Trypanosoma cruzi infection

In experimental Chagas' disease, lymphocytes from mice infected with Trypanosoma cruzi show increased apoptosis in vivo and in vitro. Treatment with a pan-caspase blocker peptide inhibited expression of the active form of effector caspase-3 in vitro and rescued both B and T cells from cell death. Injection of the caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethyl ketone, but not a control peptide, reduced parasitemia and lymphocyte apoptosis in T. cruzi-infected mice. Moreover, treatment with caspase inhibitor throughout acute infection increased the absolute numbers of B and T cells in the spleen and lymph nodes, without affecting cell infiltrates in the heart. Following treatment, we found increased accumulation of memory/activated CD4 and CD8 T cells, and secretion of IFN-gamma by splenocytes stimulated with T. cruzi antigens. Caspase inhibition in the course of infection reduced the intracellular load of parasites in peritoneal macrophages, and increased the production of TNF-alpha and nitric oxide upon activation in vitro. Our results indicate that inhibition of caspases with a pan-caspase blocker peptide improves protective type-1 immune responses to T. cruzi infection. We suggest that mechanisms of apoptosis are potential therapeutic targets in Chagas' disease.

Brefeldin A triggers apoptosis associated with mitochondrial breach and enhances HA14-1- and anti-Fas-mediated cell killing in follicular lymphoma cells

Follicular lymphoma (FL) remains a fatal disease of increasing worldwide incidence. Since patients with FL eventually develop resistance to conventional anticancer agents, and due to BCL-2 overexpression present with profoundly compromised execution of mitochondrial pathway of apoptosis, targeting alternative pathways of cell demise may appear therapeutically beneficial. Herein we report for the first time the effects of an ER-Golgi transport inhibitor, Brefeldin A (BFA), alone and in combination with a small molecule Bcl-2 inhibitor HA14-1 or agonistic anti-Fas mAb, in the recently established human FL cell lines. All cell lines tested were sensitive to BFA-induced cytotoxicity and apoptosis. Moreover BFA-induced cell death was associated with profound ER stress, mitochondrial breach and subsequent caspase cascade activation, including caspase 2 activation. Interestingly, BFA-induced ER stress did not result in appearance of autophagic morphology in FL cells. Of importance, small molecule Bcl-2 antagonist, HA14-1 and agonistic anti-Fas mAb significantly enhanced BFA-mediated cytotoxicity and apoptosis, revealing novel and previously unexplored means to enhance ER stress-mediated cell killing in follicular lymphoma cells.

Key note lecture: toward a mechanistic taxonomy for cell death programs

BACKGROUND AND PURPOSE

Programmed cell death (pcd) plays a critical role in the development of the nervous system, as well as in its response to insult. Both anti-pcd and pro-pcd modulators play prominent roles in development and disease, including ischemic cerebrovascular disease. The purpose of this article is therefore to review the basics of programmed cell death.

METHODS

There have been over 100 000 scientific and clinical publications on the topic of programmed cell death and its most well known form, apoptosis. The principles emerging from these studies are reviewed here.

RESULTS

Programmed cell death is a form of cell death in which the cell plays an active role in its own demise. Apoptosis is the most well-defined form of pcd, but recent studies have begun to characterize an alternative program, autophagic cell death. In addition, there appear to be programmatic cell deaths that do not fit the criteria for either apoptosis or autophagic cell death, arguing that additional programs may also be available to cells.

CONCLUSIONS

Constructing a mechanistic taxonomy of all forms of pcd--based on inhibitors, activators, and identified biochemical pathways involved in each form of pcd--should offer new insight into cell deaths associated with cerebrovascular disease and other diseases, and ultimately offer new therapeutic approaches.