Calpain-induced Bax-cleavage product is a more potent inducer of apoptotic cell death than wild-type Bax

Changes in calpain-2 expression during glioblastoma progression predisposes tumor cells to temozolomide resistance by minimizing DNA damage and p53-dependent apoptosis

BACKGROUND

Glioblastoma multiforme (GBM) is characterized by an unfavorable prognosis for patients affected. During standard-of-care chemotherapy using temozolomide (TMZ), tumors acquire resistance thereby causing tumor recurrence. Thus, deciphering essential molecular pathways causing TMZ resistance are of high therapeutic relevance.

METHODS

Mass spectrometry based proteomics were used to study the GBM proteome. Immunohistochemistry staining of human GBM tissue for either calpain-1 or -2 was performed to locate expression of proteases. In vitro cell based assays were used to measure cell viability and survival of primary patient-derived GBM cells and established GBM cell lines after TMZ ± calpain inhibitor administration. shRNA expression knockdowns of either calpain-1 or calpain-2 were generated to study TMZ sensitivity of the specific subunits. The Comet assay and ɣH2AX signal measurements were performed in order to assess the DNA damage amount and recognition. Finally, quantitative real-time PCR of target proteins was applied to differentiate between transcriptional and post-translational regulation.

RESULTS

Calcium-dependent calpain proteases, in particular calpain-2, are more abundant in glioblastoma compared to normal brain and increased in patient-matched initial and recurrent glioblastomas. On the cellular level, pharmacological calpain inhibition increased the sensitivities of primary glioblastoma cells towards TMZ. A genetic knockdown of calpain-2 in U251 cells led to increased caspase-3 cleavage and sensitivity to neocarzinostatin, which rapidly induces DNA strand breakage. We hypothesize that calpain-2 causes desensitization of tumor cells against TMZ by preventing strong DNA damage and subsequent apoptosis via post-translational TP53 inhibition. Indeed, proteomic comparison of U251 control vs. U251 calpain-2 knockdown cells highlights perturbed levels of numerous proteins involved in DNA damage response and downstream pathways affecting TP53 and NF-κB signaling. TP53 showed increased protein abundance, but no transcriptional regulation.

CONCLUSION

TMZ-induced cell death in the presence of calpain-2 expression appears to favor DNA repair and promote cell survival. We conclude from our experiments that calpain-2 expression represents a proteomic mode that is associated with higher resistance via "priming" GBM cells to TMZ chemotherapy. Thus, calpain-2 could serve as a prognostic factor for GBM outcome.

Subtype-selective induction of apoptosis in translocation-related sarcoma cells induced by PUMA and BIM upon treatment with pan-PI3K inhibitors

Translocation-related sarcomas (TRSs) harbor an oncogenic fusion gene generated by chromosome translocation and account for approximately one-third of all sarcomas; however, effective targeted therapies have yet to be established. We previously reported that a pan-phosphatidylinositol 3-kinase (PI3K) inhibitor, ZSTK474, was effective for the treatment of sarcomas in a phase I clinical trial. We also demonstrated the efficacy of ZSTK474 in a preclinical model, particularly in cell lines from synovial sarcoma (SS), Ewing's sarcoma (ES) and alveolar rhabdomyosarcoma (ARMS), all of which harbor chromosomal translocations. ZSTK474 selectively induced apoptosis in all these sarcoma cell lines, although the precise mechanism underlying the induction of apoptosis remained unclear. In the present study, we aimed to determine the antitumor effect of PI3K inhibitors, particularly with regards to the induction of apoptosis, against various TRS subtypes using cell lines and patient-derived cells (PDCs). All of the cell lines derived from SS (six), ES (two) and ARMS (one) underwent apoptosis accompanied by the cleavage of poly-(ADP-ribose) polymerase (PARP) and the loss of mitochondrial membrane potential. We also observed apoptotic progression in PDCs from SS, ES and clear cell sarcoma (CCS). Transcriptional analyses revealed that PI3K inhibitors triggered the induction of PUMA and BIM and the knockdown of these genes by RNA interference efficiently suppressed apoptosis, suggesting their functional involvement in the progression of apoptosis. In contrast, TRS-derived cell lines/PDCs from alveolar soft part sarcoma (ASPS), CIC-DUX4 sarcoma and dermatofibrosarcoma protuberans failed to undergo apoptosis nor induce PUMA and BIM expression, as well as cell lines derived from non-TRSs and carcinomas. Thus, we conclude that PI3K inhibitors induce apoptosis in selective TRSs such as ES and SS via the induction of PUMA and BIM and the subsequent loss of mitochondrial membrane potential. This represents proof of concept for PI3K-targeted therapy, particularly such TRS patients.

PACAP-derived mutant peptide MPAPO protects trigeminal ganglion cell and the retina from hypoxic injury through anti-oxidative stress, anti-apoptosis, and promoting axon regeneration

The purpose of this study was to determine whether the MPAPO, derived peptide of pituitary adenylate cyclase-activating polypeptide (PACAP), would protect trigeminal ganglion cells (TGCs) and the mice retinas from a hypoxic insult. The nerve endings of the ophthalmic nerve of the trigeminal nerve are widely distributed in eye tissues. In TGCs after hypoxia exposure, we discovered that reactive oxygen species level, the contents of cytosolic cytochrome c and cleaved-caspase-3 were significantly increased, in the meanwhile, m-Calpain was activated and cytoskeleton proteins (αII-spectrin and Synapsin) were degraded, neurites of TGCs disappeared, but these effects were reversed in TGCs treated with MPAPO. The structure of the mice retinas after hypoxic exposure was disordered. Increased lipid peroxidation (LPO), decreased glutathione (GSH) levels, and decreased superoxide dismutase (SOD) activity, positive cells of terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL), the disintegration of nerve fibers was examined in the retinas following a hypoxic insult. Disordered retina was attenuated with MPAPO eye drops, as well as hypoxia-induced apoptosis in the developing retina, increase in LPO, and decrease in GSH levels and SOD activity of the retina. Moreover, the disintegrated retinal nerve fibers were reassembled after MPAPO treatment. These results suggest that hypoxia induces oxidative stress, apoptosis, and neurites disruption, while MPAPO is remarkably protective against these adverse effects of hypoxia in TGCs and the developing retinas by specifically activating PAC1 receptor.

Calpain-calpastatin system and cancer progression

The calpain system is required by many important physiological processes, including the cell cycle, cytoskeleton remodelling, cellular proliferation, migration, cancer cell invasion, metastasis, survival, autophagy, apoptosis and signalling, as well as the pathogenesis of a wide range of disorders, in which it may function to promote tumorigenesis. Calpains are intracellular conserved calcium-activated neutral cysteine proteinases that are involved in mediating cancer progression via catalysing and regulating the proteolysis of their specific substrates, which are important signalling molecules during cancer progression. μ-calpain, m-calpain, and their specific inhibitor calpastatin are the three molecules originally identified as comprising the calpain system and they contain several crucial domains, specific motifs, and functional sites. A large amount of data supports the roles of the calpain-calpastatin system in cancer progression via regulation of cellular adhesion, proliferation, invasion, metastasis, and cellular survival and death, as well as inflammation and angiogenesis during tumorigenesis, implying that the inhibition of calpain activity may be a potential anti-cancer intervention strategy targeting cancer cell survival, invasion and chemotherapy resistance.

Elevation of Cleaved p18 Bax Levels Associated with the Kinetics of Neuronal Cell Death during Japanese Encephalitis Virus Infection

Japanese encephalitis virus (JEV) infection induces uncontrolled neuronal apoptosis, leading to irreversible brain damage. However, the mechanism of JEV-induced neuronal apoptosis has not been clearly elucidated. This study aimed to investigate both virus replication and neuronal cell apoptosis during JEV infection in human neuroblastoma SH-SY5Y cells. As a result, the kinetic productions of new viral progeny were time- and dose-dependent. The stimulation of SH-SY5Y cell apoptosis was dependent on the multiplicity of infections (MOIs) and infection periods, particularly during the late period of infection. Interestingly, we observed that of full-length Bax (p21 Bax) level started to decrease, which corresponded to the increased level of its cleaved form (p18 Bax). The formation of p18 Bax resulting in cytochrome c release into the cytosol appeared to correlate with JEV-induced apoptotic cell death together with the activation of caspase-3/7 activity, especially during the late stage of a robust viral infection. Therefore, our results suggest another possible mechanism of JEV-induced apoptotic cell death via the induction of the proteolysis of endogenous p21 Bax to generate p18 Bax. This finding could be a new avenue to facilitate novel drug discovery for the further development of therapeutic treatments that could relieve neuronal damage from JEV infection.

Zinc(II) phthalocyanines as photosensitizers for antitumor photodynamic therapy

Photodynamic therapy (PDT) is a highly specific and clinically approved method for cancer treatment in which a nontoxic drug known as photosensitizer (PS) is administered to a patient. After selective tumor irradiation, an almost complete eradication of the tumor can be reached as a consequence of reactive oxygen species (ROS) generation, which not only damage tumor cells, but also lead to tumor-associated vasculature occlusion and the induction of an immune response. Despite exhaustive investigation and encouraging results, zinc(II) phthalocyanines (ZnPcs) have not been approved as PSs for clinical use yet. This review presents an overview on the physicochemical properties of ZnPcs and biological results obtained both in vitro and in more complex models, such as 3D cell cultures, chicken chorioallantoic membranes and tumor-bearing mice. Cell death pathways induced after PDT treatment with ZnPcs are discussed in each case. Finally, combined therapeutic strategies including ZnPcs and the currently available clinical trials are mentioned.

Axon injury signaling and compartmentalized injury response in glaucoma

Axonal degeneration is an active, highly controlled process that contributes to beneficial processes, such as developmental pruning, but also to neurodegeneration. In glaucoma, ocular hypertension leads to vision loss by killing the output neurons of the retina, the retinal ganglion cells (RGCs). Multiple processes have been proposed to contribute to and/or mediate axonal injury in glaucoma, including: neuroinflammation, loss of neurotrophic factors, dysregulation of the neurovascular unit, and disruption of the axonal cytoskeleton. While the inciting injury to RGCs in glaucoma is complex and potentially heterogeneous, axonal injury is ultimately thought to be the key insult that drives glaucomatous neurodegeneration. Glaucomatous neurodegeneration is a complex process, with multiple molecular signals contributing to RGC somal loss and axonal degeneration. Furthermore, the propagation of the axonal injury signal is complex, with injury triggering programs of degeneration in both the somal and axonal compartment. Further complicating this process is the involvement of multiple cell types that are known to participate in the process of axonal and neuronal degeneration after glaucomatous injury. Here, we review the axonal signaling that occurs after injury and the molecular signaling programs currently known to be important for somal and axonal degeneration after glaucoma-relevant axonal injuries.

Immunohistochemical Localization of Calpains in the Amphibian Xenopus laevis

Though histochemical techniques have been used for decades, they are still very important in basic research. They make it possible to work on fixed tissues and provide a large amount of information in a relatively short time and at a low cost. Here we describe methods for indirect immunohistochemistry and immunofluorescence on sections of tadpoles and tissues of adult amphibians belonging to the species Xenopus laevis. The objective is to localize calpains within tissues in order to understand their involvement in cellular processes.

Lysosomal permeabilization and endoplasmic reticulum stress mediate the apoptotic response induced after photoactivation of a lipophilic zinc(II) phthalocyanine

We have previously reported that the phototoxic action of the lipophilic phthalocyanine Pc9 (2,9(10),16(17),23(24) tetrakis[(2-dimethylamino)ethylsulfanyl]phthalocyaninatozinc(II)) encapsulated into poloxamine micelles is related to the induction of an apoptotic response in murine colon CT26 carcinoma cells. In the present study, we explored the intracellular signals contributing to the resulting apoptotic death. We found that Pc9-T1107 arrests cell cycle progression immediately after irradiation promoting then an apoptotic response. Thus, 3 h after irradiation the percentage of hypodiploid cells increased from 5.9 ± 0.6% to 23.1 ± 0.1%; activation of caspases 8 and 9 was evident; the population of cells with loss of mitochondrial membrane potential increased from 1.1 ± 0.4% to 44.0 ± 9.3%; the full-length forms of Bid and PARP-1 were cleaved; and a 50% decrease of the expression levels of the anti-apoptotic proteins Bcl-2 and Bcl-X_L was detected. We also found that the photosensitizer, mainly retained in lysosomes and endoplasmic reticulum (ER), promotes the permeabilization of lysosomal membranes and induces ER stress. Lysosomal membrane permeabilization was demonstrated by the reduction of acridine orange lysosome fluorescence, the release of Cathepsin D into the cytosol and ∼50% decrease of Hsp70, a chaperone recognized as a lysosomal stabilizer. Cathepsin D also contributed to Bid cleavage and caspase 8 activation. The oxidative damage to the ER induced an unfolded protein response characterized, 3 h after irradiation, by a 3-fold increase in cytosolic Ca²⁺ levels and 3-4 times higher expression of ER chaperones GRP78/BIP, calnexin, Hsp90 and Hsp110. The cell death signaling promoted by cytosolic Ca²⁺, calpains and lysosomal proteases was partially abolished by the Ca²⁺ chelator BAPTA-AM, the calpain inhibitor PD 150606 and proteases inhibitors. Furthermore, Bax down-regulation observed in Pc9-treated cells was undetectable in the presence of PD 150606, indicating that calpains contribute to Bax proteolytic damage. In summary, our results indicate that photoactivation of Pc9-T1107 led to lysosomal membrane permeabilization, induction of ER stress and activation of a caspase-dependent apoptotic cell death.

The combination of a sphingosine kinase 2 inhibitor (ABC294640) and a Bcl-2 inhibitor (ABT-199) displays synergistic anti-myeloma effects in myeloma cells without a t(11;14) translocation

Multiple myeloma (MM) remains an incurable disease in need of the development of novel therapeutic agents and drug combinations. ABT‐199 is a specific Bcl‐2 inhibitor in clinical trials for MM; however, its activity as a single agent was limited to myeloma patients with the t(11;14) translocation who acquire resistance due to co‐expression of Mcl‐1 and Bcl‐xL. These limitations preclude its use in a broader patient population. We have recently found that a sphingosine kinase 2‐specific inhibitor (ABC294640) induces apoptosis in primary human CD138⁺ cells and MM cell lines. ABC294640 is currently in phase I/II clinical trials for myeloma (clinicaltrials.gov: #NCT01410981). Interestingly, ABC294640 down‐regulates c‐Myc and Mcl‐1, but does not have any effects on Bcl‐2. We first evaluated the combinatorial anti‐myeloma effect of ABC294640 and ABT‐199 in vitro in 7 MM cell lines, all of which harbor no t(11;14) translocation. Combination index calculation demonstrated a synergistic anti‐myeloma effect of the combination of ABC294640 and ABT‐199. This synergistic anti‐myeloma effect was maintained even in the presence of bone marrow (BM) stromal cells. The combination of ABC294640 and ABT‐199 led to enhanced cleavage of PARP and caspase‐3/9 and increased Annexin‐V expression, consistent with the induction of apoptosis by the combination treatment. In addition, the combination of ABC294640 and ABT‐199 resulted in the down‐regulation of the anti‐apoptotic proteins Mcl‐1, Bcl‐2, and Bcl‐xL and the cleavage of Bax and Bid. The combination induced both the mitochondrial mediated‐ and caspase‐mediated apoptosis pathways. Finally, the combination of ABC294640 and ABT‐199 resulted in augmented anti‐myeloma effect in vivo in a mouse xenograft model. These findings demonstrate that the co‐administration of ABC294640 and ABT‐199 exhibits synergistic anti‐myeloma activity in vitro and in vivo, providing justification for a clinical study of this novel combination in patients with relapsed/refractory multiple myeloma.

Enhanced Phosphorylation of Bax and Its Translocation into Mitochondria in the Brains of Individuals Affiliated with Alzheimer's Disease

Background:

Despite increased neuronal death, senile plaques, and neurofibrillary tangles observed in patients suffering from Alzheimer’s disease (AD), the detailed mechanism of cell death in AD is still poorly understood.

Method:

We hypothesized that p38 kinase activates and then phosphorylates Bax, leading to its translocation to mitochondria in AD brains compared to controls. The aim of this study was to investigate the role of p38 kinase in phosphorylation and sub-cellular localization of pro-apoptotic Bax in the frontal cortex of the brains from AD and control subjects. Increased oxidative stress in AD individuals compared to control was evaluated by measuring the levels of carbonylated proteins and oxidized peroxiredoxin, an antioxidant enzyme. The relative amounts of p38 kinase and phospho-Bax in mitochondria in AD brains and controls were determined by immunoblot analysis using the respective antibody against each protein following immunoprecipitation.

Results:

Our results showed that the levels of oxidized peroxiredoxin-SO₃ and carbonylated proteins are significantly elevated in AD brains compared to controls, demonstrating the increased oxidative stress.

Conclusion:

The amount of phospho-p38 kinase is increased in AD brains and the activated p38 kinase appears to phosphorylate Thr residue(s) of Bax, which leads to its mitochondrial translocation, contributing to apoptosis and ultimately, neurodegeneration.

The functional domains for Bax∆2 aggregate-mediated caspase 8-dependent cell death

Bax∆2 is a functional pro-apoptotic Bax isoform having alterations in its N-terminus, but sharing the rest of its sequence with Baxα. Bax∆2 is unable to target mitochondria due to the loss of helix α1. Instead, it forms cytosolic aggregates and activates caspase 8. However, the functional domain(s) responsible for BaxΔ2 behavior have remained elusive. Here we show that disruption of helix α1 makes Baxα mimic the behavior of Bax∆2. However, the other alterations in the Bax∆2 N-terminus have no significant impact on aggregation or cell death. We found that the hallmark BH3 domain is necessary but not sufficient for aggregation-mediated cell death. We also noted that the core region shared by Baxα and Bax∆2 is required for the formation of large aggregates, which is essential for BaxΔ2 cytotoxicity. However, aggregation by itself is unable to trigger cell death without the C-terminus. Interestingly, the C-terminal helical conformation, not its primary sequence, appears to be critical for caspase 8 recruitment and activation. As Bax∆2 shares core and C-terminal sequences with most Bax isoforms, our results not only reveal a structural basis for Bax∆2-induced cell death, but also imply an intrinsic potential for aggregate-mediated caspase 8-dependent cell death in other Bax family members.

Release of Cytochrome C from Bax Pores at the Mitochondrial Membrane

How cytochrome C is released from the mitochondria to the cytosol via Bax oligomeric pores, a process which is required for apoptosis, is still a mystery. Based on experimentally measured residue-residue distances, we recently solved the first atomic model for Bax oligomeric pores at the membranes using computational approaches. Here, we investigate the mechanism at the microsecond time- and nanometer space- scale using MD simulations. Our free energy landscape depicts a low barrier for the permeation of cytochrome C into the Bax C-terminal mouth, with the pathway proceeding to the inner cavity and exiting via the N-terminal mouth. Release is guided by organized charged/hydrophilic surfaces. The hydrophilicity and negative charge of the pore surface gradually increase along the release pathway from the pore entry to the exit opening. Rather than inert passing of the cytochrome C through a rigid pore, the flexible pore may selectively aid the cytochrome C passage. Once the Bax pore is formed in the membrane, with a low energy barrier, the release of cytochrome C may be readily achieved through energy fluctuations. Collectively, our work provides mechanistic insight in atomic detail into the release of cytochrome C through Bax oligomeric pores.

Mannich bases of 1,2,4-triazole-3-thione containing adamantane moiety: Synthesis, preliminary anticancer evaluation, and molecular modeling studies

A series of 18 novel N-Mannich bases derived from 5-adamantyl-1,2,4-triazole-3-thione was synthesized and characterized using NMR spectroscopy and X-ray diffraction technique. All derivatives were evaluated for their anticancer potential against four human cancer cell lines. Several tested compounds exerted good cytotoxic activities on K562 and HL-60 cell lines, along with pronounced selectivity, showing lower cytotoxicity against normal fibroblasts MRC-5 compared to cancer cells. The effects of compounds 5b, 5e, and 5j on the cell cycle were investigated by flow cytometric analysis. It was found that these compounds cause the accumulation of cells in the subG1 and G1 phases of the cell cycle and induce caspase-dependent apoptosis, while the anti-angiogenic effects of 5b, 5e, and 5j have been confirmed in EA.hy926 cells using a tube formation assay. Further, the interaction of Bax protein with compound 5b was investigated by means of molecular modeling, applying the combined molecular docking/molecular dynamics approach.

Ibulocydine sensitizes human hepatocellular carcinoma cells to TRAIL-induced apoptosis via calpain-mediated Bax cleavage

Tumor necrosis factor-related apoptosis-induced ligand (TRAIL) induces apoptosis selectively in cancer cells without affecting the majority of normal human cells. However, hepatocellular carcinoma (HCC) cells often display resistance to TRAIL-induced apoptosis. Ibulocydine (IB) is an isobutyrate ester pro-drug of a novel synthetic Cdk inhibitor that targets Cdk7 and Cdk9. In this study, we show that treatment with subtoxic doses of IB in combination with TRAIL displays potent cytotoxicity in TRAIL-resistant human HCC cells. Combination of IB and TRAIL was found to synergistically induce apoptosis through activation of caspases, which was blocked by a pan-caspase inhibitor (zVAD). Although the expression of Mcl-1 and survivin were reduced by IB plus TRAIL, overexpression of Mcl-1 and survivin did not block the cell death induced by co-treatment. Moreover, overexpression of Bcl-xL did not significantly interfere with the cell death induced by co-treatment of IB and TRAIL. Interestingly, the combination treatment induced cleavage of Bax, which was translocated to mitochondria upon induction of apoptosis. Furthermore, down-regulation of Bax by small interfering RNA effectively reduced the cell death and loss of mitochondrial membrane potential (MMP) caused by co-treatment with IB and TRAIL. Finally, pre-treatment of HCC cells with a calpain inhibitor effectively blocked IB plus TRAIL-induced cleavage of Bax and apoptosis. Collectively, our results demonstrate that IB increases the sensitivity of human HCC cells to TRAIL via mitochondria signaling pathway mediated by calpain-induced cleavage of Bax, suggesting that combined treatment with IB and TRAIL may offer an effective therapeutic strategy for human HCC.

Pluronic-based micelle encapsulation potentiates myricetin-induced cytotoxicity in human glioblastoma cells

As one of the natural herbal flavonoids, myricetin has attracted much research interest, mainly owing to its remarkable anticancer properties and negligible side effects. It holds great potential to be developed as an ideal anticancer drug through improving its bioavailability. This study was performed to investigate the effects of Pluronic-based micelle encapsulation on myricetin-induced cytotoxicity and the mechanisms underlying its anticancer properties in human glioblastoma cells. Cell viability was assessed using a methylthiazol tetrazolium assay and a real-time cell analyzer. Immunoblotting and quantitative reverse transcriptase polymerase chain reaction techniques were used for determining the expression levels of related molecules in protein and mRNA. The results indicated that myricetin-induced cytotoxicity was highly potentiated by the encapsulation of myricetin. Mitochondrial apoptotic pathway was demonstrated to be involved in myricetin-induced glioblastoma cell death. The epidermal growth factor receptor (EGFR)/PI3K/Akt pathway located in the plasma membrane and cytosol and the RAS-ERK pathway located in mitochondria served as upstream and downstream targets, respectively, in myricetin-induced apoptosis. MiR-21 inhibitors interrupted the expression of EGFR, p-Akt, and K-Ras in the same fashion as myricetin-loaded mixed micelles (MYR-MCs) and miR-21 expression were dose-dependently inhibited by MYR-MCs, indicating the interaction of miR-21 with MYR-MCs. This study provided evidence supportive of further development of MYR-MC formulation for preferentially targeting mitochondria of glioblastoma cells.

Potassium increases the antitumor effects of ascorbic acid in breast cancer cell lines in vitro

Ascorbic acid (A) has been demonstrated to exhibit anti-cancer activity in association with chemotherapeutic agents. Potassium (K) is a regulator of cellular proliferation. In the present study, the biological effects of A and K bicarbonate, alone or in combination (A+K), on breast cancer cell lines were evaluated. The survival of cancer cells was determined by sulforhodamine B cell proliferation assay, while analysis of the cell cycle distribution was conducted via fluorescence-activated cell sorting. In addition, the expression of signaling proteins was analyzed upon treatment. The results indicated that there was a heterogeneous response of the different cell lines to A and K, and the best effects were achieved by A+K and A treatment. The interaction between A+K indicated an additive or synergistic effect. In addition, A+K increased the percentage of cells in the sub-G1 phase of the cell cycle, and was the most effective treatment in activating the degradation of poly(adenosine diphosphate-ribose) polymerase-1. In the breast cancer cell line MCF-7, A+K induced the appearance of the 18 kDa isoform of B-cell lymphoma-2-associated X protein (Bax), which is a more potent inducer of apoptosis than the full-length Bax-p21. The effects of A and K on the phosphorylation of extracellular signal-regulated kinase (ERK)1 and ERK2 were heterogeneous. In addition, treatment with K, A and A+K inhibited the expression of nuclear factor-κB. Overall, the results of the present study indicated that K potentiated the anti-tumoral effects of A in breast cancer cells in vitro.

Nuclear localization of the caspase-3-cleaved form of p73 in anoikis

The transcription factor p73 is a homologue of p53 that can be expressed as pro- or anti-apoptotic isoforms. Unlike p53, p73 is rarely mutated or lost in cancers and it is found to replace defective p53 inducing apoptosis. Here, we investigated the p73 involvement in anoikis, a type of apoptosis caused by inadequate cell-matrix interactions. Breast cancer cell lines with different p53 status were treated with doxorubicin (DOX) or docetaxel (DOC) and cells detached from the extracellular matrix were analyzed. We demonstrate for the first time that DOX-induced cell detachment is associated with p73 cleavage and caspase activation, independently of the p53 status. However, we did not detect p73 cleavage or caspase activation in detached cells under DOC treatment. Overexpressing the apoptotic isoform of p73 led to cell detachment associated with p73 cleavage and caspase activation. Interestingly, p73 cleaved forms localize to the nucleus during the late phase of cell death indicating an increase in the transcriptional activity. Our study suggests that the cleavage of p73 on specific sites may release its pro-apoptotic function and contribute to cell death.

Suppression of the Arboviruses Dengue and Chikungunya Using a Dual-Acting Group-I Intron Coupled with Conditional Expression of the Bax C-Terminal Domain

In portions of South Asia, vectors and patients co-infected with dengue (DENV) and chikungunya (CHIKV) are on the rise, with the potential for this occurrence in other regions of the world, for example the United States. Therefore, we engineered an antiviral approach that suppresses the replication of both arboviruses in mosquito cells using a single antiviral group I intron. We devised unique configurations of internal, external, and guide sequences that permit homologous recognition and splicing with conserved target sequences in the genomes of both viruses using a single trans-splicing Group I intron, and examined their effectiveness to suppress infections of DENV and CHIKV in mosquito cells when coupled with a proapoptotic 3' exon, ΔN Bax. RT-PCR demonstrated the utility of these introns in trans-splicing the ΔN Bax sequence downstream of either the DENV or CHIKV target site in transformed Aedes albopictus C6/36 cells, independent of the order in which the virus specific targeting sequences were inserted into the construct. This trans-splicing reaction forms DENV or CHIKV ΔN Bax RNA fusions that led to apoptotic cell death as evidenced by annexin V staining, caspase, and DNA fragmentation assays. TCID50-IFA analyses demonstrate effective suppression of DENV and CHIKV infections by our anti-arbovirus group I intron approach. This represents the first report of a dual-acting Group I intron, and demonstrates that we can target DENV and CHIKV RNAs in a sequence specific manner with a single, uniquely configured CHIKV/DENV dual targeting group I intron, leading to replication suppression of both arboviruses, and thus providing a promising single antiviral for the transgenic suppression of multiple arboviruses.

Calpain in Breast Cancer: Role in Disease Progression and Treatment Response

The calpains are a family of intracellular cysteine proteases that function in a wide array of cellular activities, including cytoskeletal remodelling, survival and apoptosis. The ubiquitously expressed micro (µ)-calpain and milli (m)-calpain are archetypal family members that require calcium for function and can be inhibited by their endogenous inhibitor calpastatin. This review describes the role of the calpain system in the prognosis of breast cancer and disease progression, in addition to the role of the calpain system in the response to breast cancer treatments, including chemotherapeutic, endocrine and targeted therapies.

The novel protective role of P27 in MLN4924-treated gastric cancer cells

The tumor-suppressor gene cyclin-dependent kinase inhibitor 1B (P27) is downregulated in gastric cancer cells mainly through proteolytic degradation mediated by the SKP-Cullin1-F-Box (SCF) complex. But the correlation between its downregulation and gastric cancer prognosis still remains indefinite. MLN4924, an anti-tumor agent, which suppresses the SCF complex by inhibiting Cullin1 neddylation, emerges as a promising tool to elucidate its functions in gastric cancer cells. In this study, MLN4924 induced significant growth inhibition of gastric cancer cells in a dose-dependent manner, along with the simultaneous accumulation of P27 and cell cycle abnormalities such as G2/M arrest. Importantly, we found that P27 silencing in MLN4924-treated cells resulted in an enhancement of growth inhibition both in vitro and in vivo. Mechanism analysis revealed the antagonism effects of antioxidants to this excess apoptosis, suggesting reactive oxygen species (ROS) overproduction especially in the mitochondria was the principal cause of the augmentation. Moreover, the robust ROS attacked the mitochondria to initiate collapse of the mitochondrial membrane permeability and the exportation of apoptosis-inducing factor (AIF), IAP-binding mitochondrial protein (SMAC/DIABLO) and cytochrome c. Finally, we also found that P27 knockdown affected the expression profile of several critical BH3 family members to amplify the mitochondrial dysfunction and apoptosis. In summary, our findings unveiled a protective role of P27 by maintaining mitochondrial membrane permeability in MLN4924-treated gastric cancer cells, and therefore highlighted the potential combination of MLN4924 with P27 inhibition to improve its therapeutic efficacy.

Lysophosphatidic Acid Inhibits Apoptosis Induced by Cisplatin in Cervical Cancer Cells

Cervical cancer is the second most common cause of cancer death in women worldwide. Lysophosphatidic acid (LPA) level has been found significantly increased in the serum of patients with ovarian, cervical, and colon cancers. LPA level in cervical cancer patients is significantly higher than in healthy controls. LPA receptors were found highly expressed in cervical cancer cells, suggesting LPA may play a role in the development of cervical cancer. The aim of this study is to investigate the effect of LPA on the apoptosis induced by cisplatin (DDP) in cervical cancer cell line and the underlying changes in signaling pathways. Our study found that cisplatin induced apoptosis of Hela cell through inhibiting expression of Bcl-2, upregulating the expression of Bax, Fas-L, and the enzyme activity of caspase-3 (p < 0.05); LPA significantly provided protection against the apoptosis induced by cisplatin by inhibiting the above alterations in apoptotic factor caused by cisplatin (p < 0.05). Moreover, PI3K/AKT pathway was found to be important for the LPA antiapoptosis effect, and administration of PI3K/AKT partially reversed the LPA-mediated protection against cisplatin-induced apoptosis (p < 0.05). These findings have shed new lights on the LPA bioactivity in cervical cancer cells and pointed to a possible sensitization scheme through combined administration of PI3K inhibitor and cisplatin for better treatment of cervical cancer patients, especially those with elevated LPA levels.

Effect of enhanced expression of connexin 43 on sunitinib-induced cytotoxicity in mesothelioma cells

Connexin (Cx) makes up a type of intercellular channel called gap junction (GJ). GJ plays a regulatory role in cellular physiology. The Cx expression level is often decreased in cancer cells compared to that in healthy ones, and the restoration of its expression has been shown to exert antiproliferative effects. This work aims to evaluate the effect of the restoration of connexin 43 (Cx43) (the most ubiquitous Cx subtype) expression on sunitinib (SU)-induced cytotoxicity in malignant mesothelioma (MM) cells. Increased Cx43 expression in an MM cell line (H28) improved the ability of SU to inhibit receptor tyrosine kinase (RTK) signaling. Moreover, higher Cx43 expression promoted SU-induced apoptosis. The cell viability test revealed that Cx43 enhanced the cytotoxic effect of SU in a GJ-independent manner. The effect of Cx43 on a proapoptotic factor, Bax, was then investigated. The interaction between Cx43 and Bax was confirmed by immunoprecipitation. Furthermore, higher Cx43 expression increased the production of a cleaved (active) form of Bax during SU-induced apoptosis with no alteration in total Bax expression. These findings indicate that Cx43 most likely increases sensitivity to SU in H28 through direct interaction with Bax. In conclusion, we found that Cx43 overcame the chemoresistance of MM cells.

Disruption of dengue virus transmission by mosquitoes

Current control efforts for mosquito-borne arboviruses focus on mosquito control involving insecticide applications, which are becoming increasingly ineffective and unsustainable in urban areas. Mosquito population replacement is an alternative arbovirus control concept aiming at replacing virus-competent vector populations with laboratory-engineered incompetent vectors. A prerequisite for this strategy is the design of robust anti-pathogen effectors that can ultimately be genetically driven through a wild-type population. Several anti-pathogen effector concepts have been developed that target the RNA genomes of arboviruses such as dengue virus in a highly sequence-specific manner. Design principles are based on long inverted-repeat RNA triggered RNA interference, catalytic hammerhead ribozymes, and trans-splicing Group I Introns that are able to induce apoptosis in virus-infected cells following splicing with target viral RNA.

Inhibition of Integrin-HER2 signaling by Cucurbitacin B leads to in vitro and in vivo breast tumor growth suppression

HER2, an oncogenic receptor is overexpressed in about 25-30% of breast cancer patients. HER2 has been shown to play role in tumor promotion by having cross-talk with multiple oncogenic pathways in cancer cells. Our results show that Cucurbitacin B (CuB), a triterpenoid steroidal compound inhibited the growth of various breast cancer cells with an IC50 ranging from 18-50nM after 48 and 72 h of treatment. Our study also revealed the significant inhibitory effects of CuB on HER2 and integrin signaling in breast cancer. Notably, CuB inhibited ITGA6 and ITGB4 (integrin α6 & integrin β4), which are overexpressed in breast cancer. Furthermore, CuB also induced the expression of major ITGB1and ITGB3, which are known to cause integrin-mediated cell death. In addition, we observed that TGFβ treatment resulted in the increased association of HER2 with ITGA6 and this association was inhibited by CuB treatment. Efficacy of CuB was tested in vivo using two different orthotopic models of breast cancer. MDA-MB-231 and 4T-1 cells were injected orthotopically in the mammary fat pad of female athymic nude mice or BALB/c mice respectively. Our results showed that CuB administration inhibited MDA-MB-231 orthotopic tumors by 55%, and 4T-1 tumors by 40%. The 4T-1 cells represent stage IV breast cancer and form very aggressive tumors. CuB mediated breast tumor growth suppression was associated with the inhibition of HER2/integrin signaling. Our results suggest novel targets of CuB in breast cancer in vitro and in vivo.

Thy28 protects against anti-CD3-mediated thymic cell death in vivo

Apoptotic cell death plays a pivotal role in the development and/or maintenance of several tissues including thymus. Deregulated thymic cell death is associated with autoimmune diseases including experimental autoimmune encephalomyelitis (EAE), a prototype murine model for analysis of human multiple sclerosis. Because Thy28 expression is modulated during thymocyte development, we tested whether Thy28 affects induction of EAE as effectively as antigen-induced thymocyte deletion using Thy28 transgenic (TG) mice. Thy28 TG mice showed partial resistance to anti-CD3 monoclonal antibody (mAb)-induced thymic cell death in vivo, as assessed by annexin V-expression and loss of mitochondrial membrane potential. The resistance to anti-CD3 mAb-induced cell death in Thy28 TG mice appeared to correlate with a decreased c-Jun N-terminal kinase phosphorylation and reduced down-regulation of Bcl-xL. Moreover, thymic hyperplasia was detected in Thy28 TG mice, although thymocyte development was unaltered. Development of peripheral lymphoid tissues including spleen and lymph nodes was also unaltered. Thy28 TG spleen T cells showed an increased production of IFN-γ, but not IL-17, in response to both anti-CD3 and anti-CD28 mAbs. Finally, Thy28 TG mice displayed accelerated induction of EAE as assessed by disease incidence, clinical score, and pathology following immunization with myelin oligodendrocyte glycoprotein compared with control WT mice. These findings suggest that modulation of Thy28 expression plays a crucial role in the determination of thymic cell fate, which may contribute to the development of EAE through proinflammatory cytokine production.

Melatonin Reverses Fas, E2F-1 and Endoplasmic Reticulum Stress Mediated Apoptosis and Dysregulation of Autophagy Induced by the Herbicide Atrazine in Murine Splenocytes

Exposure to the herbicide Atrazine (ATR) can cause immunotoxicity, apart from other adverse consequences for animal and human health. We aimed at elucidating the apoptotic mechanisms involved in immunotoxicity of ATR and their attenuation by Melatonin (MEL). Young Swiss mice were divided into control, ATR and MEL+ATR groups based on daily (x14) intraperitoneal administration of the vehicle (normal saline), ATR (100 mg/kg body weight) and MEL (20 mg/kg body weight) with ATR. Isolated splenocytes were processed for detection of apoptosis by Annexin V-FITC and TUNEL assays, and endoplasmic reticulum (ER) stress by immunostaining. Key proteins involved in apoptosis, ER stress and autophagy were quantified by immunoblotting. ATR treatment resulted in Fas-mediated activation of caspases 8 and 3 and inactivation of PARP1 which were inhibited significantly by co-treatment with MEL. MEL also attenuated the ATR-induced, p53 independent mitochondrial apoptosis through upregulation of E2F-1 and PUMA and suppression of their downstream target Bax. An excessive ER stress triggered by ATR through overexpression of ATF-6α, spliced XBP-1, CREB-2 and GADD153 signals was reversed by MEL. MEL also reversed the ATR-induced impairment of autophagy which was indicated by a decline in BECN-1, along with significant enhancement in LC3B-II and p62 expressions. Induction of mitochondrial apoptosis, ER stress and autophagy dysregulation provide a new insight into the mechanism of ATR immunotoxicity. The cytoprotective role of MEL, on the other hand, was defined by attenuation of ER stress, Fas-mediated and p53 independent mitochondria-mediated apoptosis as well as autophagy signals.

Leiomyoma cells in 3-dimensional cultures demonstrate an attenuated response to fasudil, a rho-kinase inhibitor, when compared to 2-dimensional cultures

Uterine leiomyomata are common benign tumors in women of reproductive age and demonstrate an attenuated response to mechanical signaling that involves Rho and integrins. To further characterize the impairment in Rho signaling, we studied the effect of Rho-kinase inhibitor, fasudil, on extracellular matrix production, in 2-dimensional (2D) and 3-dimensional (3D) cultures of leiomyoma and myometrial cells. Leiomyoma 2D cultures demonstrated a rapid decrease in gene transcripts and protein for fibronectin, procollagen 1A, and versican. In 3D cultures, fibronectin and procollagen 1A proteins demonstrated increased levels at lower concentrations of fasudil, followed by a concentration-dependent decrease. Versican protein increased up to 3-fold, whereas fibromodulin demonstrated a significant decrease of 1.92-fold. Myometrial 2D or 3D cultures demonstrated a decrease in all proteins after 72 hours of treatment. The 3D leiomyoma cultures demonstrated a significant increase in active RhoA, followed by a concentration-dependent decrease at higher concentrations. A concentration-dependent increase in phospho-extracellular regulated signal kinase and proapoptotic protein Bax was observed in 3D leiomyoma cultures. Fasudil relaxed the contraction of the 3D collagen gels caused by myometrium and leiomyoma cell growth. These findings indicate that the altered state of Rho signaling in leiomyoma was more clearly observed in 3D cultures. The results also suggest that fasudil may have clinical applicability for treatment of uterine leiomyoma.

Effective suppression of dengue virus using a novel group-I intron that induces apoptotic cell death upon infection through conditional expression of the Bax C-terminal domain

INTRODUCTION

Approximately 100 million confirmed infections and 20,000 deaths are caused by Dengue virus (DENV) outbreaks annually. Global warming and rapid dispersal have resulted in DENV epidemics in formally non-endemic regions. Currently no consistently effective preventive measures for DENV exist, prompting development of transgenic and paratransgenic vector control approaches. Production of transgenic mosquitoes refractory for virus infection and/or transmission is contingent upon defining antiviral genes that have low probability for allowing escape mutations, and are equally effective against multiple serotypes. Previously we demonstrated the effectiveness of an anti-viral group I intron targeting U143 of the DENV genome in mediating trans-splicing and expression of a marker gene with the capsid coding domain. In this report we examine the effectiveness of coupling expression of ΔN Bax to trans-splicing U143 intron activity as a means of suppressing DENV infection of mosquito cells.

RESULTS

Targeting the conserved DENV circularization sequence (CS) by U143 intron trans-splicing activity appends a 3' exon RNA encoding ΔN Bax to the capsid coding region of the genomic RNA, resulting in a chimeric protein that induces premature cell death upon infection. TCID50-IFA analyses demonstrate an enhancement of DENV suppression for all DENV serotypes tested over the identical group I intron coupled with the non-apoptotic inducing firefly luciferase as the 3' exon. These cumulative results confirm the increased effectiveness of this αDENV-U143-ΔN Bax group I intron as a sequence specific antiviral that should be useful for suppression of DENV in transgenic mosquitoes. Annexin V staining, caspase 3 assays, and DNA ladder observations confirm DCA-ΔN Bax fusion protein expression induces apoptotic cell death.

CONCLUSION

This report confirms the relative effectiveness of an anti-DENV group I intron coupled to an apoptosis-inducing ΔN Bax 3' exon that trans-splices conserved sequences of the 5' CS region of all DENV serotypes and induces apoptotic cell death upon infection. Our results confirm coupling the targeted ribozyme capabilities of the group I intron with the generation of an apoptosis-inducing transcript increases the effectiveness of infection suppression, improving the prospects of this unique approach as a means of inducing transgenic refractoriness in mosquitoes for all serotypes of this important disease.

Natural compound Alternol induces oxidative stress-dependent apoptotic cell death preferentially in prostate cancer cells

Prostate cancers at the late stage of castration resistance are not responding well to most of current therapies available in clinic, reflecting a desperate need of novel treatment for this life-threatening disease. In this study, we evaluated the anticancer effect of a recently isolated natural compound, Alternol, in multiple prostate cancer cell lines with the properties of advanced prostate cancers in comparison to prostate-derived nonmalignant cells. As assessed by trypan blue exclusion assay, significant cell death was observed in all prostate cancer cell lines except DU145 but not in nonmalignant (RWPE-1 and BPH1) cells. Further analyses revealed that Alternol-induced cell death was an apoptotic response in a dose- and time-dependent manner, as evidenced by the appearance of apoptosis hallmarks such as caspase-3 processing and PARP cleavage. Interestingly, Alternol-induced cell death was completely abolished by reactive oxygen species scavengers N-acetylcysteine and dihydrolipoic acid. We also demonstrated that the proapoptotic Bax protein was activated after Alternol treatment and was critical for Alternol-induced apoptosis. Animal xenograft experiments in nude mice showed that Alternol treatment largely suppressed tumor growth of PC-3 xenografts but not Bax-null DU-145 xenografts in vivo. These data suggest that Alternol might serve as a novel anticancer agent for patients with late-stage prostate cancer.

Calcium paradox induces apoptosis in the isolated perfused Rana ridibunda heart: involvement of p38-MAPK and calpain

“Calcium paradox” as a term describes the deleterious effects conferred to a heart perfused with a calcium-free solution followed by repletion, including loss of mechanical activity and sarcomere disruption. Given that the signaling mechanisms triggered by calcium paradox remain elusive, in the present study, we tried to investigate them in the isolated perfused heart from Rana ridibunda. Calcium paradox was found to markedly activate members of the MAPKs (p43-ERK, JNKs, p38-MAPK). In addition to lactate dehydrogenase (LDH) release in the perfusate (indicative of necrosis), we also confirmed the occurrence of apoptosis by using the TUNEL assay and identifying poly(ADP-ribose) polymerase (PARP) fragmentation and upregulated Bax expression. Furthermore, using MDL28170 (a selective calpain inhibitor), a role for this protease was revealed. In addition, various divalent cations were shown to exert a protective effect against the calcium paradox. Interestingly, SB203580, a p38-MAPK inhibitor, alleviated calcium-paradox-conferred apoptosis. This result indicates that p38-MAPK plays a pro-apoptotic role, contributing to the resulting myocardial dysfunction and cell death. To our knowledge, this is the first time that the calcium paradox has been shown to induce apoptosis in amphibians, with p38-MAPK and calpain playing significant roles.

Bile acids induce apoptosis selectively in androgen-dependent and -independent prostate cancer cells

Prostate cancer is a prevalent age-related disease in North America, accounting for about 15% of all diagnosed cancers. We have previously identified lithocholic acid (LCA) as a potential chemotherapeutic compound that selectively kills neuroblastoma cells while sparing normal human neurons. Now, we report that LCA inhibits the proliferation of androgen-dependent (AD) LNCaP prostate cancer cells and that LCA is the most potent bile acid with respect to inducing apoptosis in LNCaP as well as androgen-independent (AI) PC-3 cells, without killing RWPE-1 immortalized normal prostate epithelial cells. In LNCaP and PC-3 cells, LCA triggered the extrinsic pathway of apoptosis and cell death induced by LCA was partially dependent on the activation of caspase-8 and -3. Moreover, LCA increased cleavage of Bid and Bax, down-regulation of Bcl-2, permeabilization of the mitochondrial outer membrane and activation of caspase-9. The cytotoxic actions of LCA occurred despite the inability of this bile acid to enter the prostate cancer cells with about 98% of the nominal test concentrations present in the extracellular culture medium. With our findings, we provide evidence to support a mechanism of action underlying the broad anticancer activity of LCA in various human tissues.

Interconnections between apoptotic, autophagic and necrotic pathways: implications for cancer therapy development

The rapid accumulation of knowledge on apoptosis regulation in the 1990s was followed by the development of several experimental anticancer- and anti-ischaemia (stroke or myocardial infarction) drugs. Activation of apoptotic pathways or the removal of cellular apoptotic inhibitors has been suggested to aid cancer therapy and the inhibition of apoptosis was thought to limit ischaemia-induced damage. However, initial clinical studies on apoptosis-modulating drugs led to unexpected results in different clinical conditions and this may have been due to co-effects on non-apoptotic interconnected cell death mechanisms and the ‘yin-yang’ role of autophagy in survival versus cell death. In this review, we extend the analysis of cell death beyond apoptosis. Upon introduction of molecular pathways governing autophagy and necrosis (also called necroptosis or programmed necrosis), we focus on the interconnected character of cell death signals and on the shared cell death processes involving mitochondria (e.g. mitophagy and mitoptosis) and molecular signals playing prominent roles in multiple pathways (e.g. Bcl2-family members and p53). We also briefly highlight stress-induced cell senescence that plays a role not only in organismal ageing but also offers the development of novel anticancer strategies. Finally, we briefly illustrate the interconnected character of cell death forms in clinical settings while discussing irradiation-induced mitotic catastrophe. The signalling pathways are discussed in their relation to cancer biology and treatment approaches.

Mitochondrial peroxiredoxin-5 as potential modulator of mitochondria-ER crosstalk in MPP+-induced cell death

Peroxiredoxin-5 (PRDX5) is an antioxidant enzyme which differs from the other peroxiredoxins with regards to its enzymatic mechanism, its high affinity for organic peroxides and peroxynitrite and its wide subcellular distribution. In particular, the mitochondrial isoform of PRDX5 confers a remarkable cytoprotection toward oxidative stress to mammalian cells. Mitochondrial dysfunction and disruption of Ca²⁺ homeostasis are implicated in neurodegeneration. Growing evidence supports that endoplasmic reticulum (ER) could operate in tandem with mitochondria to regulate intracellular Ca²⁺ fluxes in neurodegenerative processes. Here, we overexpressed mitochondrial PRDX5 in SH-SY5Y cells to dissect the role of this enzyme in 1-methyl-4-phenylpyridinium (MPP)⁺-induced cell death. Our data show that mitochondria-dependent apoptosis triggered by MPP⁺, assessed by the measurement of caspase-9 activation and mitochondrial DNA damage, is prevented by mitochondrial PRDX5 overexpression. Moreover, PRDX5 overexpression blocks the increase in intracellular Ca²⁺, Ca²⁺-dependent activation of calpains and Bax cleavage. Finally, using Ca²⁺ channel inhibitors (Nimodipine, Dantrolene and 2-APB), we show that Ca²⁺ release arises essentially from ER stores through 1,4,5-inositol-trisphosphate receptors (IP3 R). Altogether, our results suggest that the MPP⁺ mitochondrial pathway of apoptosis is regulated by mitochondrial PRDX5 in a process that could involve redox modulation of Ca²⁺ transporters via a crosstalk between mitochondria and ER.

Autophagy, apoptosis, mitoptosis and necrosis: interdependence between those pathways and effects on cancer

Cell death is a fundamental ingredient of life. Thus, not surprisingly more than one form of cell death exists. Several excellent reviews on various forms of cell death have already been published but manuscripts describing interconnection and interdependence between such processes are uncommon. Here, what follows is a brief introduction on all three classical forms of cell death, followed by a more detailed insight into the role of p53, the master regulator of apoptosis, and other forms of cell death. While discussing p53 and also the role of caspases in cell death forms, we offer insight into the interplay between autophagy and apoptosis, or necrosis, where autophagy may initially serve pro-survival functions. The review moves further to present some details about less researched forms of programmed cell death, namely necroptosis, necrosis and mitoptosis. These "mixed" forms of cell death allow us to highlight the interconnected nature of cell death forms, particularly apoptosis and necrosis. The interdependence between apoptosis, autophagy and necrosis, and their significance for cancer development and treatment are also analyzed in further parts of the review. In the concluding parts, the afore-mentioned issues will be put in perspective for the development of novel anti-cancer therapies.

Molecular and enzymatic characterization of XMRV protease by a cell-free proteolytic analysis

Xenotropic murine leukemia virus-related virus (XMRV) is a virus generated under artificial conditions by the recombination of 2 murine leukemia virus (MLV) proviruses, PreXMRV-1 and PreXMRV-2, during the in vivo passage of human prostate cancer cells in athymic nude mice. The molecular etiology of XMRV infection has not been characterized and its implication in human prostate cancer progression remains equivocal. As a step toward resolving this issue we developed an in vitro enzymatic assay system to characterize XMRV protease (PR)-mediated cleavage of host-cell proteins. Enzymatically-active XMRV PR protein was synthesized using a wheat-germ cell-free system. By monitoring cleavage activity of XMRV PR by AlphaScreen and 2-color immunoblot analyses, we revealed that the catalytic activity of XMRV PR is selectively blocked by the HIV PR inhibitor, Amprenavir, and identified several human tumor suppressor proteins, including PTEN and BAX, to be substrates of XMRV PR. This system may provide an attractive means for analyzing the function of retrovirus proteases and provide a technology platform for drug screening.

Regulation and physiological roles of the calpain system in muscular disorders

Calpains, a family of Ca(2+)-dependent cytosolic cysteine proteases, can modulate their substrates' structure and function through limited proteolytic activity. In the human genome, there are 15 calpain genes. The most-studied calpains, referred to as conventional calpains, are ubiquitous. While genetic studies in mice have improved our understanding about the conventional calpains' physiological functions, especially those essential for mammalian life as in embryogenesis, many reports have pointed to overactivated conventional calpains as an exacerbating factor in pathophysiological conditions such as cardiovascular diseases and muscular dystrophies. For treatment of these diseases, calpain inhibitors have always been considered as drug targets. Recent studies have introduced another aspect of calpains that calpain activity is required to protect the heart and skeletal muscle against stress. This review summarizes the functions and regulation of calpains, focusing on the relevance of calpains to cardiovascular disease.

PKC-δ mediates interferon-α-induced apoptosis through c-Jun NH₂-terminal kinase activation

Background

Interferon-α (IFN-α) exerts an anti-tumor effect at least through induction of apoptosis in a variety of types including B lymphoma cells. We recently found that IFN-α induced a sustained activation of c-Jun NH₂-terminal kinase1 (JNK1), which is implicated in activation of the tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) promoter. In the present study, we explored upstream component(s) of the prolonged IFN-α-initiated activation of JNK1.

Results

IFN-α caused activation of PKC-δ in Daudi B lymphoma cells and myeloma U266 cells, as detected by Western blotting using a monoclonal antibody specific for the phosphorylated form of PKC-δ. The dominant-negative form of mutant PKC-δ (dnPKC-δ) reduced the IFN-α-induced JNK1 activation, TRAIL promoter activity, loss of mitochondrial membrane potential (ΔΨm), and increase in propidium iodide (PI) positive cells. The IFN-α-induced activation of JNK1 and the TRAIL promoter was also attenuated by the PKC-δ inhibitor rottlerin. Moreover, a constitutively active form of mutant PKC-δ enhanced the IFN-α-induced TRAIL promoter activity and loss of ΔΨm in Daudi B lymphoma cells. In addition, IFN-α-induced Ser727 phosphorylation of Stat1 was also abrogated by dnPKC-δ.

Conclusions

IFN-α induced JNK1 activation via PKC-δ, leading to upregulation of TRAIL. The interaction of the consequent enhanced TRAIL expression with TRAIL-receptor results in a loss of ΔΨm and increase in PI positive cells. The IFN-α-induced apoptotic events may also be affected by the Ser727-Stat1 induced by PKC-δ-mediated signaling component(s).

Thy28 partially prevents apoptosis induction following engagement of membrane immunoglobulin in WEHI-231 B lymphoma cells

Thy28 protein is conserved among plants, bacteria, and mammalian cells. Nuclear Thy28 protein is substantially expressed in testis, liver, and immune cells such as lymphocytes. Lymphocyte apoptosis plays a crucial role in homeostasis and formation of a diverse lymphocyte repertoire. In this study, we examined whether Thy28 affects induction of apoptosis in WEHI-231 B lymphoma cells following engagement of membrane immunoglobulin (mIg). Once they were established, the Thy28-overexpressing WEHI-231 cells showed similar expression levels of IgM and class I major histocompatibility complex (MHC) molecule compared with controls. The Thy28-overexpressing cells were considerably resistant to loss of mitochondrial membrane potential (ΔΨm), caspase-3 activation, and increase in annexin-positive cells upon mIg engagement. These changes were concomitant with an increase in G1 phase associated with upregulation of p27^Kip1. The anti-IgM-induced sustained activation of c-Jun N-terminal kinase (JNK), which was associated with late-phase hydrogen peroxide (H₂O₂) production, was partially reduced in the Thy28-expressing cells relative to controls. Taken together, the data suggest that in WEHI-231 B lymphoma cells, Thy28 regulates mIg-mediated apoptotic events through the JNK-H₂O₂ activation pathway, concomitant with an accumulation of cells in G1 phase associated with upregulation of p27^Kip1 in WEHI-231 B lymphoma cells.

The anti-tumour compound, RH1, causes mitochondria-mediated apoptosis by activating c-Jun N-terminal kinase

BACKGROUND AND PURPOSE

2,5-diaziridinyl-3-(hydroxymethyl)-6-methyl-1,4-benzoquinone (RH1) is a bioreductive agent that is activated by the two-electron reductase NAD(P)H quinone oxidoreductase 1 (NQO1). Although the cytotoxic efficacy of RH1 against tumours has been studied extensively, the molecular mechanisms underlying this anti-cancer activity have not yet been fully elucidated.

EXPERIMENTAL APPROACH

2,5-diaziridinyl-3-(hydroxymethyl)-6-methyl-1,4-benzoquinone-induced apoptosis and related signalling pathways in NQO1-negative and NQO1-overexpressing cells were evaluated. The role of p53 in RH1-induced cell death was investigated using parental and p53-deficient RKO human colorectal cancer cells by assaying clonogenic cell survival. Specific inhibitors and siRNAs targeting factors involved in RH1-induced apoptosis were used to clarify the roles played by such factors in RH1-activated apoptotic signalling pathways.

KEY RESULTS

2,5-diaziridinyl-3-(hydroxymethyl)-6-methyl-1,4-benzoquinone induced apoptosis and clonogenic death, dependent on NQO1 and p53. Treatment of NQO1-overexpressing cells with RH1 caused rapid disruption of mitochondrial membrane potential, nuclear translocation of apoptosis-inducing factor (AIF) and endonuclease G (Endo G) from mitochondria, and subsequent caspase-independent apoptotic cell death. siRNA targeting AIF and Endo G effectively attenuated RH1-induced apoptotic cell death. Moreover, RH1 induced cleavage of Bax, which targets mitochondria. RH1 significantly activated the c-Jun N-terminal kinase (JNK) pathway, and inhibition of this pathway suppressed RH1-induced mitochondria-mediated apoptosis. RH1-induced generation and mitochondrial translocation of cleaved Bax were blocked by the JNK inhibitor, SP600125. Inhibition of JNK with SP600125 attenuated the mitochondrial translocation of JNK.

CONCLUSIONS AND IMPLICATIONS

2,5-diaziridinyl-3-(hydroxymethyl)-6-methyl-1,4-benzoquinone activated JNK, resulting in mitochondria-mediated apoptotic cell death that was NQO1-dependent.

β-lapachone significantly increases the effect of ionizing radiation to cause mitochondrial apoptosis via JNK activation in cancer cells

Background

β-lapachone (β-lap), has been known to cause NQO1-dependnet death in cancer cells and sensitize cancer cells to ionizing radiation (IR). We investigated the mechanisms underlying the radiosensitization caused by β-lap.

Methodology/Principal Findings

β-lap enhanced the effect of IR to cause clonogenic cells in NQO1⁺-MDA-MB-231 cells but not in NQO1⁻-MDA-MB-231 cells. β-lap caused apoptosis only in NQO1⁺ cells and not in NQO1⁻ cells and it markedly increased IR-induced apoptosis only in NQO1⁺ cells. Combined treatment of NQO1⁺ cells induced ROS generation, triggered ER stress and stimulated activation of ERK and JNK. Inhibition of ROS generation by NAC effectively attenuated the activation of ERK and JNK, induction of ER stress, and subsequent apoptosis. Importantly, inhibition of ERK abolished ROS generation and ER stress, whereas inhibition of JNK did not, indicating that positive feedback regulation between ERK activation and ROS generation triggers ER stress in response to combined treatment. Furthermore, prevention of ER stress completely blocked combination treatment-induced JNK activation and subsequent apoptotic cell death. In addition, combined treatment efficiently induced the mitochondrial translocation of cleaved Bax, disrupted mitochondrial membrane potential, and the nuclear translocation of AIF, all of which were efficiently blocked by a JNK inhibitor. Caspases 3, 8 and 9 were activated by combined treatment but inhibition of these caspases did not abolish apoptosis indicating caspase activation played a minor role in the induction of apoptosis.

Conclusions/Significance

β-lap causes NQO1-dependent radiosensitization of cancer cells. When NQO1⁺ cells are treated with combination of IR and β-lap, positive feedback regulation between ERK and ROS leads to ER stress causing JNK activation and mitochondrial translocation of cleaved Bax. The resultant decrease in mitochondrial membrane leads to translocation of AIF and apoptosis.

Endoplasmic reticulum stress-induced JNK activation is a critical event leading to mitochondria-mediated cell death caused by β-lapachone treatment

Background

β-lapachone (β-lap) is a bioreductive agent that is activated by the two-electron reductase NAD(P)H quinone oxidoreductase 1 (NQO1). Although β-lap has been reported to induce apoptosis in various cancer types in an NQO1-dependent manner, the signaling pathways by which β-lap causes apoptosis are poorly understood.

Methodology/Principal Findings

β-lap-induced apoptosis and related molecular signaling pathways in NQO1-negative and NQO1-overexpressing MDA-MB-231 cells were investigated. Pharmacological inhibitors or siRNAs against factors involved in β-lap-induced apoptosis were used to clarify the roles played by such factors in β-lap-activated apoptotic signaling pathways. β-lap leads to clonogenic cell death and apoptosis in an NQO1- dependent manner. Treatment of NQO1-overexpressing MDA-MB-231 cells with β-lap causes rapid disruption of mitochondrial membrane potential, nuclear translocation of AIF and Endo G from mitochondria, and subsequent caspase-independent apoptotic cell death. siRNAs targeting AIF and Endo G effectively attenuate β-lap-induced clonogenic and apoptotic cell death. Moreover, β-lap induces cleavage of Bax, which accumulates in mitochondria, coinciding with the observed changes in mitochondria membrane potential. Pretreatment with Salubrinal (Sal), an endoplasmic reticulum (ER) stress inhibitor, efficiently attenuates JNK activation caused by β-lap, and subsequent mitochondria-mediated cell death. In addition, β-lap-induced generation and mitochondrial translocation of cleaved Bax are efficiently blocked by JNK inhibition.

Conclusions/Significance

Our results indicate that β-lap triggers induction of endoplasmic reticulum (ER) stress, thereby leading to JNK activation and mitochondria-mediated apoptosis. The signaling pathways that we revealed in this study may significantly contribute to an improvement of NQO1-directed tumor therapies.