PGAM5 interacts with Bcl-rambo and regulates apoptosis and mitophagy.

Bcl-rambo, also known as BCL2L13, has been reported to regulate apoptosis, mitochondrial fragmentation, and mitophagy. However, the molecular mechanisms by which Bcl-rambo regulates these processes currently remain unclear. In the present study, we identified phosphoglycerate mutase member 5 (PGAM5) as an emerging partner interacting with Bcl-rambo through phenotypic Drosophila screening. The rough eye phenotype induced by human Bcl-rambo was partly rescued by the knockdown of pgam5-2, a mammalian ortholog of PGAM5. Bcl-rambo bound to PGAM5, and their interaction required the Bcl-rambo transmembrane domain. The co-expression of Bcl-rambo and PGAM5 promoted effector caspase activity in human embryonic kidney 293T cells. The transient overexpression of Bcl-rambo increased LC3B-II levels, which had been decreased by the co-expression of PGAM5. These results suggest that PGAM5 promotes Bcl-rambo-dependent apoptosis, but conversely interferes with Bcl-rambo-dependent mitophagy.

Evolution of the folding landscape of effector caspases.

Caspases are a family of cysteinyl proteases that control programmed cell death and maintain homeostasis in multicellular organisms. The caspase family is an excellent model to study protein evolution because all caspases are produced as zymogens (procaspases [PCPs]) that must be activated to gain full activity; the protein structures are conserved through hundreds of millions of years of evolution; and some allosteric features arose with the early ancestor, whereas others are more recent evolutionary events. The apoptotic caspases evolved from a common ancestor (CA) into two distinct subfamilies: monomers (initiator caspases) or dimers (effector caspases). Differences in activation mechanisms of the two subfamilies, and their oligomeric forms, play a central role in the regulation of apoptosis. Here, we examine changes in the folding landscape by characterizing human effector caspases and their CA. The results show that the effector caspases unfold by a minimum three-state equilibrium model at pH 7.5, where the native dimer is in equilibrium with a partially folded monomeric (PCP-7, CA) or dimeric (PCP-6) intermediate. In comparison, the unfolding pathway of PCP-3 contains both oligomeric forms of the intermediate. Overall, the data show that the folding landscape was first established with the CA and was retained for >650 million years. Partially folded monomeric or dimeric intermediates in the ancestral ensemble provide mechanisms for evolutionary changes that affect stability of extant caspases. The conserved folding landscape allows for the fine-tuning of enzyme stability in a species-dependent manner while retaining the overall caspase-hemoglobinase fold.

Design and synthesis of novel pyrazolo[3,4-d]pyrimidin-4-one bearing quinoline scaffold as potent dual PDE5 inhibitors and apoptotic inducers for cancer therapy.

PDE5 targeting represents a new and promising strategy for apoptosis induction and inhibition of tumor cell growth due to its over-expression in diverse types of human carcinomas. Accordingly, we report the synthesis of series of pyrazolo[3,4-d]pyrimidin-4-one carrying quinoline moiety (11a-r) with potential dual PDE5 inhibition and apoptotic induction for cancer treatment. These hybrids were structurally elucidated and characterized with variant spectroscopic techniques as 1H NMR, 13C NMR and elemental analysis. The assessment of their anticancer activities has been declared. All the rationalized compounds 11a-r have been selected for their cytotoxic activity screening by NCI against 60 cell lines. Compounds 11a, 11b, 11j and 11k were the most active hybrids. Among all, compound 11j was further selected for five dose tesing and it displayed outstanding activity with strong antitumor activity against the nine tumor subpanels tested with selectivity ratios ranging from 0.019 to 8.3 at the GI50 level. Further, the most active targets 11a, b, j and k were screened for their PDE5 inhibitory activity, compound 11j (with IC50 1.57 nM) exhibited the most potent PDE5 inhibitory activity. Moreover, compound 11j is also showed moderate EGFR inhibition with IC50 of 5.827 ± 0.46 µM, but significantly inhibited the Wnt/ß-catenin pathway with IC501286.96 ± 12.37 ng/mL. In addition, compound 11j induced the intrinsic apoptotic mitochondrial pathway in HepG2 cells as evidenced by the lower expression levels of the anti-apoptotic Bcl-2 protein, and the higher expression of the pro-apoptotic protein Bax, p53, cytochrome c and the up-regulated active caspase-9 and caspase-3 levels. All results confirmed by western blotting assay. Compound 11j exhibit pre G1 apoptosis and cell cycle arrest at G2/M phase. In conclusion, hybridization of quinoline moiety with the privileged pyrazolo[3,4-d]pyrimidinon-4-one structure resulted in highly potent anticancer agent, 11j, which deserves more study, in particular, in vivo and clinical investiagtions, and it is expected that these results would be applied for more drug discovery process.

GATA4-targeted compound exhibits cardioprotective actions against doxorubicin-induced toxicity in vitro and in vivo: establishment of a chronic cardiotoxicity model using human iPSC-derived cardiomyocytes.

Doxorubicin is a widely used anticancer drug that causes dose-related cardiotoxicity. The exact mechanisms of doxorubicin toxicity are still unclear, partly because most in vitro studies have evaluated the effects of short-term high-dose doxorubicin treatments. Here, we developed an in vitro model of long-term low-dose administration of doxorubicin utilizing human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Moreover, given that current strategies for prevention and management of doxorubicin-induced cardiotoxicity fail to prevent cancer patients developing heart failure, we also investigated whether the GATA4-targeted compound 3i-1000 has cardioprotective potential against doxorubicin toxicity both in vitro and in vivo. The final doxorubicin concentration used in the chronic toxicity model in vitro was chosen based on cell viability data evaluation. Exposure to doxorubicin at the concentrations of 1-3 µM markedly reduced (60%) hiPSC-CM viability already within 48 h, while a 14-day treatment with 100 nM doxorubicin concentration induced only a modest 26% reduction in hiPCS-CM viability. Doxorubicin treatment also decreased DNA content in hiPSC-CMs. Interestingly, the compound 3i-1000 attenuated doxorubicin-induced increase in pro-B-type natriuretic peptide (proBNP) expression and caspase-3/7 activation in hiPSC-CMs. Moreover, treatment with 3i-1000 for 2 weeks (30 mg/kg/day, i.p.) inhibited doxorubicin cardiotoxicity by restoring left ventricular ejection fraction and fractional shortening in chronic in vivo rat model. In conclusion, the results demonstrate that long-term exposure of hiPSC-CMs can be utilized as an in vitro model of delayed doxorubicin-induced toxicity and provide in vitro and in vivo evidence that targeting GATA4 may be an effective strategy to counteract doxorubicin-induced cardiotoxicity.

Cytosolic Gram-negative bacteria prevent apoptosis by inhibition of effector caspases through lipopolysaccharide.

The cytosolic appearance and propagation of bacteria cause overwhelming cellular stress responses that induce apoptosis under normal conditions. Therefore, successful bacterial colonization depends on the ability of intracellular pathogens to block apoptosis and to safeguard bacterial replicative niches. Here, we show that the cytosolic Gram-negative bacterium Shigella flexneri stalls apoptosis by inhibiting effector caspase activity. Our data identified lipopolysaccharide (LPS) as a bona fide effector caspase inhibitor that directly binds caspases by involving its O-antigen (O Ag) moiety. Bacterial strains that lacked the O Ag or failed to replicate within the cytosol were incapable of blocking apoptosis and exhibited reduced virulence in a murine model of bacterial infection. Our findings demonstrate how Shigella inhibits pro-apoptotic caspase activity, effectively delays coordinated host-cell demise and supports its intracellular propagation. Next to the recently discovered pro-inflammatory role of cytosolic LPS, our data reveal a distinct mode of LPS action that, through the disruption of the early coordinated non-lytic cell death response, ultimately supports the inflammatory breakdown of infected cells at later time points.

Resurrection of ancestral effector caspases identifies novel networks for evolution of substrate specificity.

Apoptotic caspases evolved with metazoans more than 950 million years ago (MYA), and a series of gene duplications resulted in two subfamilies consisting of initiator and effector caspases. The effector caspase genes (caspases-3, -6, and -7) were subsequently fixed into the Chordata phylum more than 650 MYA when the gene for a common ancestor (CA) duplicated, and the three effector caspases have persisted throughout mammalian evolution. All caspases prefer an aspartate residue at the P1 position of substrates, so each caspase evolved discrete cellular roles through changes in substrate recognition at the P4 position combined with allosteric regulation. We examined the evolution of substrate specificity in caspase-6, which prefers valine at the P4 residue, compared with caspases-3 and -7, which prefer aspartate, by reconstructing the CA of effector caspases (AncCP-Ef1) and the CA of caspase-6 (AncCP-6An). We show that AncCP-Ef1 is a promiscuous enzyme with little distinction between Asp, Val, or Leu at P4. The specificity of caspase-6 was defined early in its evolution, where AncCP-6An demonstrates a preference for Val over Asp at P4. Structures of AncCP-Ef1 and of AncCP-6An show a network of charged amino acids near the S4 pocket that, when combined with repositioning a flexible active site loop, resulted in a more hydrophobic binding pocket in AncCP-6An. The ancestral protein reconstructions show that the caspase-hemoglobinase fold has been conserved for over 650 million years and that only three substitutions in the scaffold are necessary to shift substrate selection toward Val over Asp.

Dual VEGFR-2/PIM-1 kinase inhibition towards surmounting the resistance to antiangiogenic agents via hybrid pyridine and thienopyridine-based scaffolds: Design, synthesis and biological evaluation.

Angiogenesis is a hallmark in cancer. Most antiangiogenic agents block the action of vascular endothelial growth factor (VEGF). In clinic, patients develop hypoxia-mediated resistance consistent with vascular responses to these agents. Recent studies underlying such resistance revealed hypoxia-inducible PIM-1 kinase upregulation which promotes cancer progression. PIM-1 kinase expression is thus viewed as a new resistance mechanism to antiangiogenic agents. Hence, combining PIM kinase inhibitors with anti-VEGF therapies provides synergistic antitumor response. Inspired by these facts, the current study aims at designing novel dual VEGFR-2/PIM-1 kinase inhibitors via molecular hybridization and repositioning of their pharmacophoric features. Moreover, enhancing the cytotoxic potential of the designed compounds was considered via incorporating moieties mimicking caspase 3/7 activators. Accordingly, series of novel pyridine and thieno[2,3-b]pyridine derivatives were synthesized and screened via MTT assay for cytotoxic activities against normal fibroblasts and four cancer cell lines (HepG-2, Caco-2, MCF-7 and PC-3). Compounds 3a, 9e, 10b and 10c exhibited anticancer activities at nanomolar IC50 with promising safety, activated caspase 3/7 and induced apoptosis as well as DNA fragmentation more than doxorubicin in the four cancer cell lines. Furthermore, they exerted promising dual VEGFR-2/PIM-1 kinase inhibition and significantly exhibited higher therapeutic potential to alter the expression levels of VEGF, p53 and cyclin D than doxorubicin. Interestingly, the most active anticancer compound 10b conferred the highest dual VEGFR-2/PIM-1 kinase inhibition. Finally, their in silico ligand efficiency metrics were acceptable.

The human Bcl-2 family member Bcl-rambo and voltage-dependent anion channels manifest a genetic interaction in Drosophila and cooperatively promote the activation of effector caspases in human cultured cells.

We previously reported that the Bcl-2 family member human Bcl-rambo, also known as BCL2L13, induces apoptosis in human embryonic kidney 293T cells. Mouse Bcl-rambo has recently been reported to mediate mitochondrial fragmentation and mitophagy. In the present study, we showed that the transfection of human Bcl-rambo and its microtubule-associated protein light chain 3-interacting region motif mutant (W276A/I279A) caused mitochondrial fragmentation and the perinuclear accumulation of fragmented mitochondria in human lung adenocarcinoma A549 cells. In comprehensive screening using the Drosophila model in which human Bcl-rambo was ectopically expressed in eye imaginal discs, voltage-dependent anion channels (VDAC), also known as mitochondrial porin, were found to manifest a genetic interaction with human Bcl-rambo. In addition to human adenine nucleotide translocase (ANT) 1 and ANT2, the human Bcl-rambo protein bound to human VDAC1, albeit to a lesser extent than ANT2. Moreover, human VDAC1 and human VDAC2 in particular promoted the activation of effector caspases only when they were co-expressed with human Bcl-rambo in 293T cells. Bcl-rambo induced the perinuclear accumulation of fragmented mitochondria by the knockdown of VDAC1, VDAC2, and VDAC3 in A549 cells. Thus, the present study revealed that human Bcl-rambo and VDAC cooperatively promote the activation of effector caspases in human cultured cells.

Co-imaging extrinsic, intrinsic and effector caspase activity by fluorescence anisotropy microscopy.

In order to overcome intercellular variability and thereby effectively assess signal propagation in biological networks it is imperative to simultaneously quantify multiple biological observables in single living cells. While fluorescent biosensors have been the tool of choice to monitor the dynamics of protein interaction and enzymatic activity, co-measuring more than two of them has proven challenging. In this work, we designed three spectrally separated anisotropy-based Förster Resonant Energy Transfer (FRET) biosensors to overcome this difficulty. We demonstrate this principle by monitoring the activation of extrinsic, intrinsic and effector caspases upon apoptotic stimulus. Together with modelling and simulations we show that time of maximum activity for each caspase can be derived from the anisotropy of the corresponding biosensor. Such measurements correlate relative activation times and refine existing models of biological signalling networks, providing valuable insight into signal propagation.

Immune Consequences of in vitro Infection of Human Peripheral Blood Leukocytes with Vesicular Stomatitis Virus.

BACKGROUND: Oncolytic vesicular stomatitis virus (VSV) can be delivered intravenously to target primary and metastatic lesions, but the interaction between human peripheral blood leukocytes (PBLs) and VSV remains poorly understood. Our study aimed to assess the overall immunological consequences of ex vivo infection of PBLs with VSV. METHODS: Phenotypic analysis of lymphocyte subsets and apoptosis were evaluated with flow cytometry. Caspase 3/7 activity was detected by luminescence assay. Virus release was evaluated in a murine cell line (L929). Gene expression and cytokine/chemokine secretion were assessed by real-time PCR and multiplex assay, respectively. RESULTS: Ex vivo infection of PBLs with VSV elicited upregulated expression of RIG-I, MDA-5, tetherin, IFITM3, and MxA. VSV infection triggered rapid differentiation of blood monocytes into immature dendritic cells as well as their apoptosis, which depended on caspase 3/7 activation. Monocyte differentiation required infectious VSV, but loss of CD14+ cells was also associated with the presence of a cytokine/chemokine milieu produced in response to VSV infection. CONCLUSIONS: Systemic delivery is a major goal in the field of oncolytic viruses. Our results shed further light on immune mechanisms in response to VSV infection and the underlying VSV-PBL interactions bringing hope for improved cancer immunotherapies, particularly those based on intravenous delivery of oncolytic VSV.

Starfish Apaf-1 activates effector caspase-3/9 upon apoptosis of aged eggs.

Caspase-3-related DEVDase activity is initiated upon apoptosis in unfertilized starfish eggs. In this study, we cloned a starfish procaspase-3 corresponding to mammalian effector caspase containing a CARD that is similar to the amino terminal CARD of mammalian capsase-9, and we named it procaspase-3/9. Recombinant procaspase-3/9 expressed at 15 °C was cleaved to form active caspase-3/9 which has DEVDase activity. Microinjection of the active caspase-3/9 into starfish oocytes/eggs induced apoptosis. An antibody against the recombinant protein recognized endogenous procaspase-3/9 in starfish oocytes, which was cleaved upon apoptosis in aged unfertilized eggs. These results indicate that caspase-3/9 is an effector caspase in starfish. To verify the mechanism of caspase-3/9 activation, we cloned starfish Apaf-1 containing a CARD, a NOD, and 11 WD40 repeat regions, and we named it sfApaf-1. Recombinant sfApaf-1 CARD interacts with recombinant caspase-3/9 CARD and with endogenous procaspase-3/9 in cell-free preparations made from starfish oocytes, causing the formation of active caspase-3/9. When the cell-free preparation without mitochondria was incubated with inactive recombinant procaspase-3/9 expressed at 37 °C, DEVDase activity increased and apoptosome-like complexes were formed in the high molecular weight fractions containing both sfApaf-1 and cleaved caspase-3/9. These results suggest that sfApaf-1 activation is not dependent on cytochrome c.

Protection of Insects against Viral Infection by Apoptosis-Dependent Phagocytosis.

We investigated whether phagocytosis participates in the protection of insects from viral infection using the natural host-virus interaction between Drosophila melanogaster and Drosophila C virus (DCV). Drosophila S2 cells were induced to undergo apoptotic cell death upon DCV infection. However, UV-inactivated virus was unable to cause apoptosis, indicating the need for productive infection for apoptosis induction. S2 cells became susceptible to phagocytosis by hemocyte-derived l(2)mbn cells after viral infection, and the presence of phagocytes in S2 cell cultures reduced viral proliferation. Phagocytosis depended, in part, on caspase activity in S2 cells, as well as the engulfment receptors Draper and integrin ßν in phagocytes. To validate the in vivo situation, adult flies were abdominally infected with DCV, followed by the analysis of fly death and viral growth. DCV infection killed flies in a dose-responding manner, and the activation of effector caspases was evident, as revealed by the cleavage of a target protein ectopically expressed in flies. Furthermore, hemocytes isolated from infected flies contained DCV-infected cells, and preinjection of latex beads to inhibit the phagocytic activity of hemocytes accelerated fly death after viral infection. Likewise, viral virulence was exaggerated in flies lacking the engulfment receptors, and was accompanied by the augmented proliferation of virus. Finally, phagocytosis of DCV-infected cells in vitro was inhibited by phosphatidylserine-containing liposome, and virus-infected flies died early when a phosphatidylserine-binding protein was ectopically expressed. Collectively, our study demonstrates that the apoptosis-dependent, phosphatidylserine-mediated phagocytosis of virus-infected cells plays an important role in innate immune responses against viral infection in Drosophila.

Expression of executioner procaspases and their activation by a procaspase-activating compound in chronic lymphocytic leukemia cells.

Intrinsic and extrinsic apoptotic pathways converge to activate common downstream executioner caspases (caspase-3, -6, and -7), resulting in cell death. In chronic lymphocytic leukemia (CLL), neoplastic B cells evade apoptosis owing to the overexpression of survival proteins. We hypothesized that direct activation of procaspases could bypass the apoptosis resistance induced by the upstream prosurvival proteins. The procaspase-activating compounds (PAC-1), including B-PAC-1 (L14R8), convert inactive executioner procaspases to their active cleaved forms by chelation of labile zinc ions. Both at transcript and protein levels, primary CLL cells express high levels of latent procaspases (3, -7, and -9). B-PAC-1 treatment induced CLL lymphocyte death which was higher than that in normal peripheral blood mononuclear cells or B cells, and was independent of prognostic markers and microenvironmental factors. Mechanistically, B-PAC-1 treatment activated executioner procaspases and not other Zn-dependent enzymes. Exogenous zinc completely, and pancaspase inhibitors partially, reversed B-PAC-1-induced apoptosis, elucidating the zinc-mediated mechanism of action. The cell demise relied on the presence of caspase-3/7 but not caspase-8 or Bax/Bak proteins. B-PAC-1 in combination with an inhibitor of apoptosis protein antagonist (Smac066) synergistically induced apoptosis in CLL samples. Our investigations demonstrated that direct activation of executioner procaspases via B-PAC-1 treatment bypasses apoptosis resistance and is a novel approach for CLL therapeutics.

Anticancer activity of VDR-coregulator inhibitor PS121912.

PURPOSE: PS121912 has been developed as selective vitamin D receptor (VDR)-coregulator inhibitor starting from a high throughput screening campaign to identify new agents that modulate VDR without causing hypercalcemia. Initial antiproliferative effects of PS121912 were observed that are characterized herein to enable future in vivo investigation with this molecule. METHODS: Antiproliferation and apoptosis were determined using four different cancer cell lines (DU145, Caco2, HL-60 and SKOV3) in the presence of PS121912, 1,25-(OH)2D3, or a combination of 1,25-(OH)2D3 and PS121912. VDR si-RNA was used to identify the role of VDR during this process. The application of ChIP enabled us to determine the involvement of coregulator recruitment during transcription, which was investigated by RT-PCR with VDR target genes and those affiliated with cell cycle progression. Translational changes of apoptotic proteins were determined with an antibody array. The preclinical characterization of PS121912 includes the determination of metabolic stability and CYP3A4 inhibition. RESULTS: PS121912 induced apoptosis in all four cancer cells, with HL-60 cells being the most sensitive. At sub-micromolar concentrations, PS121912 amplified the growth inhibition of cancer cells caused by 1,25-(OH)2D3 without being antiproliferative by itself. A knockout study with VDR si-RNA confirmed the mediating role of VDR. VDR target genes induced by 1,25-(OH)2D3 were down-regulated with the co-treatment of PS121912. This process was highly dependent on the recruitment of coregulators that in case of CYP24A1 was SRC2. The combination of PS121912 and 1,25-(OH)2D3 reduced the presence of SRC2 and enriched the occupancy of corepressor NCoR at the promoter site. E2F transcription factors 1 and 4 were down-regulated in the presence of PS121912 and 1,25-(OH)2D3 that in turn reduced the transcription levels of cyclin A and D, thus arresting HL-60 cells in the S or G2/M phase. In addition, proteins with hematopoietic functions such as cyclin-dependent kinase 6, histone deacetylase 9 and transforming growth factor beta 2 and 3 were down-regulated as well. Elevated levels of P21 and GADD45, in concert with cyclin D1, also mediated the antiproliferative response of HL-60 in the presence of 1,25-(OH)2D3 and PS121912. Studies at higher concentration of P121912 identified a VDR-independent pathway of antiproliferation that included the enzymatic and transcriptional activation of caspase 3/7. CONCLUSION: Overall, we conclude that PS121912 behaves like a VDR antagonist at low concentrations but interacts with more targets at higher concentrations leading to apoptosis mediated by caspase 3/7 activation. In addition, PS121912 showed an acceptable metabolic stability to enable in vivo cancer studies.

A mitochondrial-associated link between an effector caspase and autophagic flux.

It has become evident that caspases function in nonapoptotic cellular processes in addition to the canonical role for caspases in apoptotic cell death. We recently demonstrated that the Drosophila effector caspase Dcp-1 localizes to the mitochondria and positively regulates starvation-induced autophagic flux during mid-oogenesis. Loss of Dcp-1 leads to elongation of the mitochondrial network, increased levels of the adenine nucleotide translocase sesB, increased ATP levels, and a reduction in autophagy. We found that sesB is a negative regulator of autophagic flux, and Dcp-1 interacts with sesB in a nonproteolytic manner to regulate its stability, uncovering a novel mechanism of mitochondrial associated, caspase-mediated regulation of autophagy in vivo.

The Drosophila effector caspase Dcp-1 regulates mitochondrial dynamics and autophagic flux via SesB.

Increasing evidence reveals that a subset of proteins participates in both the autophagy and apoptosis pathways, and this intersection is important in normal physiological contexts and in pathological settings. In this paper, we show that the Drosophila effector caspase, Drosophila caspase 1 (Dcp-1), localizes within mitochondria and regulates mitochondrial morphology and autophagic flux. Loss of Dcp-1 led to mitochondrial elongation, increased levels of the mitochondrial adenine nucleotide translocase stress-sensitive B (SesB), increased adenosine triphosphate (ATP), and a reduction in autophagic flux. Moreover, we find that SesB suppresses autophagic flux during midoogenesis, identifying a novel negative regulator of autophagy. Reduced SesB activity or depletion of ATP by oligomycin A could rescue the autophagic defect in Dcp-1 loss-of-function flies, demonstrating that Dcp-1 promotes autophagy by negatively regulating SesB and ATP levels. Furthermore, we find that pro-Dcp-1 interacts with SesB in a nonproteolytic manner to regulate its stability. These data reveal a new mitochondrial-associated molecular link between nonapoptotic caspase function and autophagy regulation in vivo.

Role of caspase-9 in the effector caspases and genome expressions, and growth of bovine skeletal myoblasts.

Caspase-9 has been reported as the key regulator of apoptosis, however, its role in skeletal myoblast development and molecular involvements during cell growth still remains unknown. The current study aimed to present the key role of caspase-9 in the expressions of apoptotic caspases and genome, and cell viability during myoblast growth using RNA interference mediated silencing. Three small interference RNA sequences (siRNAs) targeting caspase-9 gene was designed and ligated into pSilencer plasmid vector to construct shRNA expression constructs. Cells were transfected with the constructs for 48 h. Results indicated that all three siRNAs could silence the caspase-9 mRNA expression significantly. Particularly, the mRNA expression level of caspase-9 in the cells transfected by shRNA1, shRNA2 and shRNA3 constructs were reduced by 37.85%, 68.20% and 58.14%, respectively. Suppression of caspase-9 led to the significant increases in the mRNA and protein expressions of effector caspase-3, whereas the reduction in mRNA and protein expressions of caspase-7. The microarray results showed that the suppression of caspase-9 resulted in significant upregulations of cell proliferation-, adhesion-, growth-, development- and division-regulating genes, whereas the reduction in the expressions of cell death program- and stress response-regulating genes. Furthermore, cell viability was significantly increased following the transfection. These data suggest that caspase-9 could play an important role in the control of cell growth, and knockdown of caspase-9 may have genuine potential in the treatment of skeletal muscle atrophy.

Digitoxin sensitizes glioma cells to TRAIL-mediated apoptosis by upregulation of death receptor 5 and downregulation of survivin.

Glioblastoma multiforme is the most lethal and aggressive astrocytoma among primary brain tumors in adults. However, most glioblastoma cells have been reported to be resistant to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. Here, we have shown that digitoxin (DT), a clinically approved cardiac glycoside for heart failure, can induce TRAIL-mediated apoptosis of glioblastoma cells. DT in noncytotoxic doses (20 nmol/l) can increase TRAIL-induced apoptosis in TRAIL-resistant U87MG glioblastoma cells. Treatment with DT led to apoptosis and a robust reduction in the levels of the antiapoptotic protein survivin by inducing its proteasomal degradation; however, it did not affect the levels of many other apoptosis regulators. Moreover, silencing survivin with small interfering RNAs sensitized glioma cells to TRAIL-induced apoptosis, underscoring the functional role of survivin depletion in the TRAIL-sensitizing actions of DT. We demonstrate that inactivation of survivin and death receptor 5 expression by DT is sufficient to restore TRAIL sensitivity in resistant glioma cells. Our results suggest that combining DT with TRAIL treatments may be useful in the treatment of TRAIL-resistant glioma cells.

Palmitate-induced activation of mitochondrial metabolism promotes oxidative stress and apoptosis in H4IIEC3 rat hepatocytes.

OBJECTIVE: Hepatic lipotoxicity is characterized by reactive oxygen species (ROS) accumulation, mitochondrial dysfunction, and excessive apoptosis, but the precise sequence of biochemical events leading to oxidative damage and cell death remains unclear. The goal of this study was to delineate the role of mitochondrial metabolism in mediating hepatocyte lipotoxicity. MATERIALS/METHODS: We treated H4IIEC3 rat hepatoma cells with free fatty acids in combination with antioxidants and mitochondrial inhibitors designed to block key events in the progression toward apoptosis. We then applied (13)C metabolic flux analysis (MFA) to quantify mitochondrial pathway alterations associated with these treatments. RESULTS: Treatment with palmitate alone led to a doubling in oxygen uptake rate and in most mitochondrial fluxes. Supplementing culture media with the antioxidant N-acetyl-cysteine (NAC) reduced ROS accumulation and caspase activation and partially restored cell viability. However, (13)C MFA revealed that treatment with NAC did not normalize palmitate-induced metabolic alterations, indicating that neither elevated ROS nor downstream apoptotic events contributed to mitochondrial activation. To directly limit mitochondrial metabolism, the complex I inhibitor phenformin was added to cells treated with palmitate. Phenformin addition eliminated abnormal ROS accumulation, prevented the appearance of apoptotic markers, and normalized mitochondrial carbon flow. Further studies revealed that glutamine provided the primary fuel for elevated mitochondrial metabolism in the presence of palmitate, rather than fatty acid beta-oxidation, and that glutamine consumption could be reduced through co-treatment with phenformin but not NAC. CONCLUSION: Our results indicate that ROS accumulation in palmitate-treated H4IIEC3 cells occurs downstream of altered mitochondrial oxidative metabolism, which is independent of beta-oxidation and precedes apoptosis initiation.

A high-throughput screen identifies miRNA inhibitors regulating lung cancer cell survival and response to paclitaxel.

microRNAs (miRNAs) are small RNAs endogenously expressed in multiple organisms that regulate gene expression largely by decreasing levels of target messenger RNAs (mRNAs). Over the past few years, numerous studies have demonstrated critical roles for miRNAs in the pathogenesis of many cancers, including lung cancer. Cellular miRNA levels can be easily manipulated, showing the promise of developing miRNA-targeted oligos as next-generation therapeutic agents. In a comprehensive effort to identify novel miRNA-based therapeutic agents for lung cancer treatment, we combined a high-throughput screening platform with a library of chemically synthesized miRNA inhibitors to systematically identify miRNA inhibitors that reduce lung cancer cell survival and those that sensitize cells to paclitaxel. By screening three lung cancer cell lines with different genetic backgrounds, we identified miRNA inhibitors that potentially have a universal cytotoxic effect on lung cancer cells and miRNA inhibitors that sensitize cells to paclitaxel treatment, suggesting the potential of developing these miRNA inhibitors as therapeutic agents for lung cancer. We then focused on characterizing the inhibitors of three miRNAs (miR-133a/b, miR-361-3p, and miR-346) that have the most potent effect on cell survival. We demonstrated that two of the miRNA inhibitors (miR-133a/b and miR-361-3p) decrease cell survival by activating caspase-3/7-dependent apoptotic pathways and inducing cell cycle arrest in S phase. Future studies are certainly needed to define the mechanisms by which the identified miRNA inhibitors regulate cell survival and drug response, and to explore the potential of translating the current findings into clinical applications.