Reactive oxygen species induced by proteasome inhibition in neuronal cells mediate mitochondrial dysfunction and a caspase-independent cell death

While increasing evidence shows that proteasome inhibition triggers oxidative damage, mitochondrial dysfunction and death in neuronal cells, the regulatory relationship among these events is unclear. Using mouse neuronal cells we show that the cytotoxicity induced by mild (0.25 μM) and potent (5.0 μM) doses of the proteasome inhibitor, N-Benzyloxycarbonyl-Ile-Glu (O-t-butyl)-Ala-leucinal, (PSI) involved a dose-dependent increase in caspase activation, overproduction of reactive oxygen species (ROS) and a mitochondrial dysfunction manifested by the translocation of the proapoptotic protein, Bax, from the cytoplasm to the mitochondria, membrane depolarization and the release of cytochrome c and the apoptosis inducing factor (AIF) from mitochondria to the cytoplasm and nucleus, respectively. Whereas caspase or Bax inhibition failed to prevent mitochondrial membrane depolarization and neuronal cell death, pretreatments with the antioxidant N-acetyl-l-cysteine (NAC) or overexpression of the antiapoptotic protein Bcl-xL abrogated these events in cells exposed to mild levels of PSI. These findings implicated ROS as a mediator of PSI-induced cytotoxicity. However, depletions in glutathione and Bcl-xL with potent proteasome inhibition exacerbated this response whereupon survival required the cooperative protection of NAC with Bcl-xL overexpression. Collectively, ROS induced by proteasome inhibition mediates a mitochondrial dysfunction in neuronal cells that culminates in death through caspase- and Bax-independent mechanisms. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Reactive oxygen species generation and mitochondrial dysfunction for the initiation of apoptotic cell death in human hepatocellular carcinoma HepG2 cells by a cyclic dipeptide Cyclo(-Pro-Tyr)

Molecular Biology Reports - Cyclic dipeptides are increasingly gaining importance as considering its significant biological and pharmacological activities. This study was aimed to investigate the...     

Reactive oxygen species-mediated mitochondrial pathway is involved in Baohuoside I-induced apoptosis in human non-small cell lung cancer

Baohuoside I (also known as Icariside II) is a flavonoid isolated from Epimedium koreanum Nakai. Although Baohuoside I exhibits anti-inflammatory and anti-cancer activities, its molecular targets/pathways in human lung cancer cells are poorly understood. Therefore, in the present study, we investigated the usefulness of Baohuoside I as a potential apoptosis-inducing cytotoxic agent using human adenocarcinoma alveolar basal epithelial A549 cells as in vitro model. The apoptosis induced by Baohuoside I in A549 cells was confirmed by annexin V/propidium iodide double staining, cell cycle analysis and dUTP nick end labeling. Further research revealed that Baohuoside I accelerated apoptosis through the mitochondrial apoptotic pathway, involving the increment of BAX/Bcl-2 ratio, dissipation of mitochondrial membrane potential, transposition of cytochrome c, caspase 3 and caspase 9 activation, degradation of poly (ADP-ribose) polymerase and the over-production of reactive oxygen species (ROS). A pan-caspase inhibitor, Z-VAD-FMK, only partially prevented apoptosis induced by Baohuoside I, while NAC, a scavenger of ROS, diminished its effect more potently. In addition, the apoptotic effect of Baohuoside I was dependent on the activation of ROS downstream effectors, JNK and p38(MAPK), which could be almost abrogated by using inhibitors SB203580 (an inhibitor of p38(MAPK)) and SP600125 (an inhibitor of JNK). These findings suggested that Baohuoside I might exert its cytotoxic effect via the ROS/MAPK pathway.     

Claudin-7 suppresses the cytotoxicity of TRAIL-expressing mesenchymal stem cells in H460 human non-small cell lung cancer cells

Evidence suggests that the cytokine tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising candidate for cancer therapeutics. Studies have also shown that claudin-7 (CLDN7) expression is variably dysregulated in various malignant neoplasms, with a role in lung cancer that has not been definitively decided. This work investigated the differential sensitivity of CLDN7-overexpressing human NSCLC H460 cells to TRAIL in vitro and in mouse xenografts, and explored the molecular mechanisms responsible for these effects. NCI-H460 cells were transfected or not with green fluorescent protein-tagged CLDN7. Each group was then exposed to mesenchymal stem cells (MSCs) or red fluorescent protein-tagged MSCs transduced with lentivirus expressing membrane-bound TRAIL. The effects and related mechanisms of these treatments were evaluated in vitro, and in vivo in murine xenografts. Our results indicate that TRAIL induced apoptosis in H460 cells in vitro, and in established xenograft tumors TRAIL was associated with a decrease in tumor size, tumor weight, and circulating tumor cells. CLDN7 was found to inhibit the MEK/ERK signaling pathway, leading to inhibition of death receptor 5 (TNFRSF10B). The cytotoxicity of TRAIL was confirmed in H460 cells and in vivo, and CLDN7 suppressed the cytotoxicity of TRAIL in H460 cells. Our results indicate that TRAIL may be a useful therapy to enhance apoptosis in CLDN7-negative lung cancer cells.     

Flavokawain B induces apoptosis of non-small cell lung cancer H460 cells via Bax-initiated mitochondrial and JNK pathway

Flavokawain B (FKB) possesses strong anti-neoplastic activity against many cancer cells. Here we assessed its antitumor activity and molecular mechanisms in lung cancer H460 cells in vitro. FKB significantly inhibited cell proliferation and caused arrest of the cell cycle G2-M of H460 cells in a dose-dependent manner. FKB also inducted apoptosis, which was associated with cytochrome c release, caspase-7 and caspase-9 activation and Bcl-xL/Bax dys-regulation. FKB significantly down-regulated survivin and XIAP, and the inhibitory effect induced by FKB was greatly attenuated by through over-expression of survivin or Bax(-/-) MEFs. Furthermore, FKB activated the mitogen-activated protein kinases and the JNK inhibitor SP600125 significantly decreased the growth-inhibitory and apoptotic effects of FKB. Together, these results suggest the anti-lung cancer potential of flavokawain B for the prevention and treatment of lung cancer.     

The hierarchical relationship between MAPK signaling and ROS generation in human leukemia cells undergoing apoptosis in response to the proteasome inhibitor Bortezomib

The hierarchy of events accompanying induction of apoptosis by the proteasome inhibitor Bortezomib was investigated in Jurkat lymphoblastic and U937 myelomonocytic leukemia cells. Treatment of Jurkat or U937 cells with Bortezomib resulted in activation of c-Jun-N-terminal kinase (JNK) and p38 MAPK (mitogen-activated protein kinase), inactivation of extracellular signal-regulating kinase 1/2 (ERK1/2), cytochrome c release, caspase-9, -3, and -8 activation, and apoptosis. Bortezomib-mediated cytochrome c release and caspase activation were blocked by the pharmacologic JNK inhibitor SP600125, but lethality was not diminished by the p38 MAPK inhibitor SB203580. Inducible expression of a constitutively active MEK1 construct blocked Bortezomib-mediated ERK1/2 inactivation, significantly attenuated Bortezomib lethality, and unexpectedly prevented JNK activation. Conversely, pharmacologic MEK/ERK1/2 inhibition promoted Bortezomib-mediated JNK activation and apoptosis. Lastly, the antioxidant N-acetyl-l-cysteine (LNAC) attenuated Bortezomib-mediated reactive oxygen species (ROS) generation, ERK inactivation, JNK activation, mitochondrial dysfunction, and apoptosis. In contrast, enforced MEK1 and ERK1/2 activation or JNK inhibition did not modify Bortezomib-induced ROS production. Together, these findings suggest that in human leukemia cells, Bortezomib-induced oxidative injury operates at a proximal point in the cell death cascade to antagonize cytoprotective ERK1/2 signaling, promote activation of the stress-related JNK pathway, and to trigger mitochondrial dysfunction, caspase activation, and apoptosis. They also suggest the presence of a feedback loop wherein Bortezomib-mediated ERK1/2 inactivation contributes to JNK activation, thereby amplifying the cell death process.     

Reactive oxygen species generation is independent of de novo sphingolipids in apoptotic photosensitized cells

Our recent studies have shown that the de novo sphingolipids play a role in apoptosis of photosensitized cells. To elucidate the involvement of the de novo sphingolipids in reactive oxygen species (ROS) production and mitochondrial depolarization during apoptosis, the stress inducer photodynamic therapy (PDT) with the photosensitizer Pc 4 was used. In Jurkat cells PDT-triggered ROS production or mitochondrial membrane potential (deltapsi(m)) loss was not prevented by the de novo sphingolipid synthesis inhibitor ISP-1. However, PDT + C16-ceramide led to enhanced mitochondrial depolarization and DEVDase activation. The superoxide dismutase mimic manganese (III) tetrakis (4-benzoic acid) porphyrin (MnTBAP) protected Jurkat cells from ROS generation and apoptosis, but not from deltapsi(m) reduction. Sphinganine or C16-ceramide counteracted MnTBAP-induced protection from apoptosis in Jurkat, as well as CHO cells. In LY-B cells, CHO-derived mutants deficient in serine palmitoyltransferase (SPT) activity and the de novo sphingolipid synthesis, mitochondrial depolarization, but not ROS generation, was suppressed post-PDT. In LY-B cells transfected with the SPT component LCB1, deltapsi(m) collapse post-PDT was restored. The data support the following hypotheses: MnTBAP protects against apoptosis via steps downstream of deltapsi(m) loss; de novo sphingolipids are not required for ROS generation, but can play a role in deltapsi(m) dissipation in photosensitized apoptotic cells.     

Reactive oxygen species stimulate mitochondrial allele segregation toward homoplasmy in human cells

Mitochondria that contain a mixture of mutant and wild-type mitochondrial (mt) DNA copies are heteroplasmic. In humans, homoplasmy is restored during early oogenesis and reprogramming of somatic cells, but the mechanism of mt-allele segregation remains unknown. In budding yeast, homoplasmy is restored by head-to-tail concatemer formation in mother cells by reactive oxygen species (ROS)–induced rolling-circle replication and selective transmission of concatemers to daughter cells, but this mechanism is not obvious in higher eukaryotes. Here, using heteroplasmic m.3243A > G primary fibroblast cells derived from MELAS patients treated with hydrogen peroxide (H₂O₂), we show that an optimal ROS level promotes mt-allele segregation toward wild-type and mutant mtDNA homoplasmy. Enhanced ROS level reduced the amount of intact mtDNA replication templates but increased linear tandem multimers linked by head-to-tail unit-sized mtDNA (mtDNA concatemers). ROS-triggered mt-allele segregation correlated with mtDNA-concatemer production and enabled transmission of multiple identical mt-genome copies as a single unit. Our results support a mechanism by which mt-allele segregation toward mt-homoplasmy is mediated by concatemers.     

BCI induces apoptosis via generation of reactive oxygen species and activation of intrinsic mitochondrial pathway in H1299 lung cancer cells

The compound(E)-2-benzylidene-3-(cyclohexylamino)-2,3-dihydro-1 H-inden-1-one(BCI) is known as an inhibitor of dual specific phosphatase 1/6 and mitogen-activated protein kinase. However, its precise anti-lung cancer mechanism remains unknown. In this study, the effects of BCI on the viability of non-small cell lung cancer cell lines NCI-H1299, A549, and NCI-H460 were evaluated. We confirmed that BCI significantly inhibited the viability of p53(-) NCI-H1299 cells as compared to NCI-H460 and A549 cells, which express wild-type p53. Furthermore, BCI treatment increased the level of cellular reactive oxygen species and pre-treatment of cells with N-acetylcysteine markedly attenuated BCI-mediated apoptosis of NCI-H1299 cells. BCI induced cellular morphological changes, inhibited viability, and produced reactive oxygen species in NCI-H1299 cells in a dose-dependent manner. BCI induced processing of caspase-9, caspase-3, and poly ADP-ribose polymerase as well as the release of cytochrome c from the mitochondria into the cytosol. In addition, BCI downregulated Bcl-2 expression and enhanced Bax expression in a dose-dependent manner in NCI-H1299 cells. However, BCI failed to modulate the expression of the death receptor and extrinsic factor caspase-8 and Bid, a linker between the intrinsic and extrinsic apoptotic pathways in NCI-H1299 cells. Thus, BCI induces apoptosis via generation of reactive oxygen species and activation of the intrinsic pathway in NCI-H1299 cells.     

Caudatin induces caspase-dependent apoptosis in human glioma cells with involvement of mitochondrial dysfunction and reactive oxygen species generation

Caudatin as one species of C-21 steroidal from Cynanchum bungei decne displays potential anticancer activity. However, the underlying mechanisms remain elusive. In the present study, the growth suppressive effect and mechanism of caudatin on human glioma U251 and U87 cells were evaluated in vitro. The results indicated that caudatin significantly inhibited U251 and U87 cell growth in both a time- and dose-dependent manner. Flow cytometry analysis revealed that caudatin-induced cell growth inhibition was achieved by induction of cell apoptosis, as convinced by the increase of Sub-G1 peak, PARP cleavage and activation of caspase-3, caspase-7 and caspase-9. Caudatin treatment also resulted in mitochondrial dysfunction which correlated with an imbalance of Bcl-2 family members. Further investigation revealed that caudatin triggered U251 cell apoptosis by inducing reactive oxygen species (ROS) generation through disturbing the redox homeostasis. Moreover, pretreatment of caspase inhibitors apparently weakens caudatin-induced cell killing, PARP cleavage and caspase activation and eventually reverses caudatin-mediated apoptosis. Importantly, caudatin significantly inhibited U251 tumour xenografts in vivo through induction of cell apoptosis involving the inhibition of cell proliferation and angiogenesis, which further validate its value in combating human glioma in vivo. Taken together, the results described above all suggest that caudatin inhibited human glioma cell growth by induction of caspase-dependent apoptosis with involvement of mitochondrial dysfunction and ROS generation.     

Anwulignan is a novel JAK1 inhibitor that suppresses non-small cell lung cancer growth

Anwulignan is a monomer compound derived from Schisandra sphenanthera lignans. It has been reported to possess a spectrum of pharmacological activities, including anti-bacterial, anti-inflammatory, anticancer and hepatoprotective properties. However, its anticancer capacity and molecular mechanism(s) against non-small cell lung cancer (NSCLC) have not been fully elucidated. Anwulignan significantly inhibited cell growth and increased G1-phase cell cycle arrest in NSCLC cells. Anwulignan strongly attenuates the JAK1/STAT3 signalling pathway by directly targeting JAK1 protein kinase activity in vitro. The anticancer activity by Anwulignan is dependent upon the JAK1 protein expression. Remarkably, Anwulignan strongly inhibited tumour growth in vivo. In conclusion, Anwulignan is a novel JAK1 inhibitor that may have therapeutic implications for NSCLC management.     

The proliferative inhibition and apoptotic mechanism of Saikosaponin D in human non-small cell lung cancer A549 cells

Saikosaponin D is a saponin extract derived from several species of Bupleurum (Umbelliferae), which is used for the treatment of various liver diseases in traditional Chinese medicine. In this study, we report that Saikosaponin D inhibits the cell growth of human lung cancer cell line A549 and provide a molecular understanding of this effect. The results showed that Saikosaponin D inhibited the proliferation of A549 by inducing apoptosis and blocking cell cycle progression in the G1 phase. ELISA assay showed that Saikosaponin D significantly increased the expression of p53 and p21/WAF1 protein, contributing to cell cycle arrest. An enhancement in Fas/APO-1 and its two form ligands, membrane-bound Fas ligand (mFasL) and soluble Fas ligand (sFasL), as well as Bax protein, was responsible for the apoptotic effect induced by Saikosaponin D. Taken together, our study suggests that the induction of p53 and activity of the Fas/FasL apoptotic system may participate in the antiproliferative activity of Saikosaponin D in A549 cells.     

Reactive oxygen species induced by Streptococcus pyogenes invasion trigger apoptotic cell death in infected epithelial cells

Streptococcus pyogenes (group A streptococcus, GAS), one of the most common pathogens of humans, attaches and invades into human pharyngeal or skin epithelial cells. We have previously reported that induction of apoptosis is associated with GAS invasion, which induces mitochondrial dysfunction and apoptotic cell death. We demonstrate here that GAS‐induced apoptosis is mediated by reactive oxygen species (ROS) production. Both the induction of apoptosis and ROS production markedly increased upon invasion of wild‐type GAS strain JRS4 into HeLa cells; however, the apoptotic response was not observed in fibronectin‐binding protein F1‐disrupted mutant SAM1‐infected cells. In Bcl‐2‐overexpressing HeLa cells (HBD98‐2‐4), the induction of apoptosis, ROS production and mitochondrial dysfunction were significantly suppressed, whereas the numbers of invaded GAS was not different between HeLa (mock cells) and the HeLa HBD98‐2‐4 cells. Whereas Rac1 activation occurred during GAS invasion, ROS production in GAS‐infected cells was clearly inhibited by transfection with the Rac1 mutants (L37 or V12L37), but not by the dominant active mutant (V12L61) or by the dominant negative mutant (N17). These observations indicate that GAS invasion triggers ROS production through Rac1 activation and generated ROS induced mitochondrial dysfunction leading to cellular apoptosis.     

Reactive oxygen species production and mitochondrial dysfunction contribute to quercetin induced death in Leishmania amazonensis

Background

Leishmaniasis, a parasitic disease caused by protozoa of the genus Leishmania, affects more than 12 million people worldwide. Quercetin has generated considerable interest as a pharmaceutical compound with a wide range of therapeutic activities. One such activity is exhibited against the bloodstream parasite Trypanosoma brucei and amastigotes of Leishmania donovani. However, the mechanism of protozoan action of quercetin has not been studied.

Methodology/Principal Findings

In the present study, we report here the mechanism for the antileishmanial activity of quercetin against Leishmania amazonensis promastigotes. Quercetin inhibited L. amazonensis promastigote growth in a dose- and time- dependent manner beginning at 48 hours of treatment and with maximum growth inhibition observed at 96 hours. The IC₅₀ for quercetin at 48 hours was 31.4 µM. Quercetin increased ROS generation in a dose-dependent manner after 48 hours of treatment. The antioxidant GSH and NAC each significantly reduced quercetin-induced cell death. In addition, quercetin caused mitochondrial dysfunction due to collapse of mitochondrial membrane potential.

Conclusions/Significance

The effects of several drugs that interfere directly with mitochondrial physiology in parasites such as Leishmania have been described. The unique mitochondrial features of Leishmania make this organelle an ideal drug target while minimizing toxicity. Quercetin has been described as a pro-oxidant, generating ROS which are responsible for cell death in some cancer cells. Mitochondrial membrane potential loss can be brought about by ROS added directly in vitro or induced by chemical agents. Taken together, our results demonstrate that quercetin eventually exerts its antileishmanial effect on L. amazonensis promastigotes due to the generation of ROS and disrupted parasite mitochondrial function.     

Marchantin M: a novel inhibitor of proteasome induces autophagic cell death in prostate cancer cells

We previously reported that marchantin M (Mar) is an active agent to induce apoptosis in human prostate cancer (PCa), but the molecular mechanisms of action remain largely unknown. Here, we demonstrate that Mar potently inhibited chymotrypsin-like and peptidyl-glutamyl peptide-hydrolyzing activities of 20S proteasome both in in vitro and intracellular systems and significantly induced the accumulation of polyubiquitinated proteins in PCa cells. The computational modeling analysis suggested that Mar non-covalently bound to active sites of proteasome β5 and β1 subunits, resulting in a non-competitive inhibition. Proteasome inhibition by Mar subsequently resulted in endoplasmic reticulum (ER) stress, as evidenced by elevated glucose-regulated protein 78 and CHOP, increased phospho-eukaryotic translation initiation factor 2α (eIF_2α), splicing of X-box-binding protein-1 and dilation of the ER. However, Mar-mediated cell death was not completely impaired by a pan inhibitor of caspases. Further studies revealed that the Mar-induced cell death was greatly associated with the activation of autophagy, as indicated by the significant induction of microtubule-associated protein-1 light chain-3 beta (LC3B) expression and conversion. Electron microscopic and green fluorescent protein-tagged LC3B analyses further demonstrated the ability of autophagy induction by Mar. Time kinetic studies revealed that Mar induced a rapid and highly sustained processing of LC3B in treated cells and simultaneously decreased the expression of p62/SQSTM1. Pharmacological blockade or knockdown of LC3B and Atg5 attenuated Mar-mediated cell death. The autophagic response triggered by Mar required the activation of RNA-dependent protein kinase-like ER kinase/eIF_2α and suppression of the phosphatidylinositol-3 kinase/Akt/mammalian target of rapamycin axis via preventing activation and expression of Akt. Our results identified a novel mechanism for the cytotoxic effect of Mar, which strengthens it as a potential agent in cancer chemotherapy.     

Nano neodymium oxide induces massive vacuolization and autophagic cell death in non-small cell lung cancer NCI-H460 cells

Neodymium, a rare earth element, was known to exhibit cytotoxic effects and induce apoptosis in certain cancer cells. Here we show that nano-sized neodymium oxide (Nano Nd2O3) induced massive vacuolization and cell death in non-small cell lung cancer NCI-H460 cells at micromolar equivalent concentration range. Cell death elicited by Nano Nd2O3 was not due to apoptosis and caspases were not involved. Electron microscopy and acridine orange staining revealed extensive autophagy in the cytoplasm of the cells treated by Nano Nd2O3. Autophagy induced by Nano Nd2O3 was accompanied by S-phase cell cycle arrest, mild disruption of mitochondrial membrane potential, and inhibition of proteasome activity. Bafilomycin A1, but not 3-MA, induced apoptosis while inhibiting autophagy. Our results revealed a novel biological function for Nano Nd2O3 and may have implications for the therapy of non-small cell lung cancer.     

Adenovirus vector-mediated FAM176A overexpression induces cell death in human H1299 non-small cell lung cancer cells

FAM176A (family with sequence similarity 176 member A) is a novel molecule related to programmed cell death. A decreased expression of FAM176A has been found in several types of human tumors in including lung cancers. In the present study, we investigated the biological activities of FAM176A on the human non–small cell lung cancer cell line H1299 cells. We constructed a recombinant adenovirus 5-FAM176A vector (Ad5-FAM176A) and evaluated the expression and anti-tumor activities in vitro. Cell viability analysis revealed that the adenovirus-mediated increase of FAM176A inhibited the growth of the tumor cells in a dose- and time-dependent manner. This inhibitory effect was mediated by both autophagy and apoptosis that involved caspase activation. In addition, cell cycle analysis suggested that Ad5-FAM176A could induce cell cycle arrest at the G2/M phase, all of which suggested that adenovirus-mediated FAM176A gene transfer might present a new therapeutic approach for lung cancer treatment. [BMB Reports 2014; 47(2): 104-109]