The Herbal Compound Cryptotanshinone Restores Sensitivity in Cancer Cells That Are Resistant to the Tumor Necrosis Factor-related Apoptosis-inducing Ligand

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) selectively induces apoptosis and kills cancer cells but not normal cells. However, TRAIL resistance due to low level of TRAIL receptor expression is widely found in cancer cells and hampers its development for cancer treatment. Thus, the agents that can sensitize the tumor cells to TRAIL-mediated apoptosis are urgently needed. We investigated whether tanshinones, the major bioactive compounds of Salvia miltiorrhiza (danshen), can up-regulate TRAIL receptor expression. Among the major tanshinones being tested, cryptotanshinone (CT) showed the best ability to induce TRAIL receptor 2 (DR5) expression. We further showed that CT was capable of promoting TRAIL-induced cell death and apoptosis in A375 melanoma cells. CT-induced DR5 induction was not cell type-specific, as DR5 induction was observed in other cancer cell types. DR5 knockdown abolished the enhancing effect of CT on TRAIL responses. Mechanistically, induction of the DR5 by CT was found to be p53-independent but dependent on the induction of CCAAT/enhancer-binding protein-homologous protein (CHOP). Knockdown of CHOP abolished CT-induced DR5 expression and the associated potentiation of TRAIL-mediated cell death. In addition, CT-induced ROS production preceded up-regulation of CHOP and DR5 and consequent sensitization of cells to TRAIL. Interestingly, CT also converted TRAIL-resistant lung A549 cancer cells into TRAIL-sensitive cells. Taken together, our results indicate that CT can potentiate TRAIL-induced apoptosis through up-regulation of DR5.     

Induction of Cell Death through Alteration of Oxidants and Antioxidants in Lung Epithelial Cells Exposed to High Energy Protons

Radiation affects several cellular and molecular processes, including double strand breakage and modifications of sugar moieties and bases. In outer space, protons are the primary radiation source that poses a range of potential health risks to astronauts. On the other hand, the use of proton irradiation for tumor radiation therapy is increasing, as it largely spares healthy tissues while killing tumor tissues. Although radiation-related research has been conducted extensively, the molecular toxicology and cellular mechanisms affected by proton irradiation remain poorly understood. Therefore, in this study, we irradiated rat lung epithelial cells with different doses of protons and investigated their effects on cell proliferation and death. Our data show an inhibition of cell proliferation in proton-irradiated cells with a significant dose-dependent activation and repression of reactive oxygen species and antioxidants glutathione and superoxide dismutase, respectively, compared with control cells. In addition, the activities of apoptosis-related genes such as caspase-3 and -8 were induced in a dose-dependent manner with corresponding increased levels of DNA fragmentation in proton-irradiated cells compared with control cells. Together, our results show that proton irradiation alters oxidant and antioxidant levels in cells to activate the apoptotic pathway for cell death.     

Vitellogenin Recognizes Cell Damage through Membrane Binding and Shields Living Cells from Reactive Oxygen Species

Large lipid transfer proteins are involved in lipid transportation and diverse other molecular processes. These serum proteins include vitellogenins, which are egg yolk precursors and pathogen pattern recognition receptors, and apolipoprotein B, which is an anti-inflammatory cholesterol carrier. In the honey bee, vitellogenin acts as an antioxidant, and elevated vitellogenin titer is linked to prolonged life span in this animal. Here, we show that vitellogenin has cell and membrane binding activity and that it binds preferentially to dead and damaged cells. Vitellogenin binds directly to phosphatidylcholine liposomes and with higher affinity to liposomes containing phosphatidylserine, a lipid of the inner leaflet of cell membranes that is exposed in damaged cells. Vitellogenin binding to live cells, furthermore, improves cell oxidative stress tolerance. This study can shed more light on why large lipid transfer proteins have a well conserved α-helical domain, because we locate the lipid bilayer-binding ability of vitellogenin largely to this region. We suggest that recognition of cell damage and oxidation shield properties are two mechanisms that allow vitellogenin to extend honey bee life span.     

Artesunate Induces Cell Death in Human Cancer Cells via Enhancing Lysosomal Function and Lysosomal Degradation of Ferritin

Artesunate (ART) is an anti-malaria drug that has been shown to exhibit anti-tumor activity, and functional lysosomes are reported to be required for ART-induced cancer cell death, whereas the underlying molecular mechanisms remain largely elusive. In this study, we aimed to elucidate the molecular mechanisms underlying ART-induced cell death. We first confirmed that ART induces apoptotic cell death in cancer cells. Interestingly, we found that ART preferably accumulates in the lysosomes and is able to activate lysosomal function via promotion of lysosomal V-ATPase assembly. Furthermore, we found that lysosomes function upstream of mitochondria in reactive oxygen species production. Importantly, we provided evidence showing that lysosomal iron is required for the lysosomal activation and mitochondrial reactive oxygen species production induced by ART. Finally, we showed that ART-induced cell death is mediated by the release of iron in the lysosomes, which results from the lysosomal degradation of ferritin, an iron storage protein. Meanwhile, overexpression of ferritin heavy chain significantly protected cells from ART-induced cell death. In addition, knockdown of nuclear receptor coactivator 4, the adaptor protein for ferritin degradation, was able to block ART-mediated ferritin degradation and rescue the ART-induced cell death. In summary, our study demonstrates that ART treatment activates lysosomal function and then promotes ferritin degradation, subsequently leading to the increase of lysosomal iron that is utilized by ART for its cytotoxic effect on cancer cells. Thus, our data reveal a new mechanistic action underlying ART-induced cell death in cancer cells.     

p53-induced gene 3 mediates cell death induced by glutathione peroxidase 3

Expression of glutathione peroxidase 3 (GPx3) is down-regulated in a variety of human malignancies. Both methylation and deletion of GPx3 gene underlie the alterations of GPx3 expression in prostate cancer. A strong correlation between the down-regulation of GPx3 expression and progression of prostate cancer and the suppression of prostate cancer xenografts in SCID mice by forced expression of GPx3 suggests a tumor suppression role of GPx3 in prostate cancer. However, the mechanism of GPx3-mediated tumor suppression remains unclear. In this report, GPx3 was found to interact directly with p53-induced gene 3 (PIG3). Forced overexpression of GPx3 in prostate cancer cell lines DU145 and PC3 as well as immortalized prostate epithelial cells RWPE-1 increased apoptotic cell death. Expression of GPx3(x73c), a peroxidase-negative OPAL codon mutant, in DU145 and PC3 cells also increased cell death. The induced expression of GPx3 in DU145 and PC3 cells resulted in an increase in reactive oxygen species and caspase-3 activity. These activities were abrogated by either knocking down PIG3 or mutating the PIG3 binding motif in GPx3 or binding interference from a peptide corresponding to PIG3 binding motif in GPx3. In addition, UV-treated RWPE-1 cells underwent apoptotic death, which was partially prevented by knocking down GPx3 or PIG3, suggesting that GPx3-PIG3 signaling is critical for UV-induced apoptosis. Taken together, these results reveal a novel signaling pathway of GPx3-PIG3 in the regulation of cell death in prostate cancer.     

Inhibition of Glutathione Peroxidase Mediates the Collateral Sensitivity of Multidrug-resistant Cells to Tiopronin

Multidrug resistance (MDR) is a major obstacle to the successful chemotherapy of cancer. MDR is often the result of overexpression of ATP-binding cassette transporters following chemotherapy. A common ATP-binding cassette transporter that is overexpressed in MDR cancer cells is P-glycoprotein, which actively effluxes drugs against a concentration gradient, producing an MDR phenotype. Collateral sensitivity (CS), a phenomenon of drug hypersensitivity, is defined as the ability of certain compounds to selectively target MDR cells, but not the drug-sensitive parent cells from which they were derived. The drug tiopronin has been previously shown to elicit CS. However, unlike other CS agents, the mechanism of action was not dependent on the expression of P-glycoprotein in MDR cells. We have determined that the CS activity of tiopronin is mediated by the generation of reactive oxygen species (ROS) and that CS can be reversed by a variety of ROS-scavenging compounds. Specifically, selective toxicity of tiopronin toward MDR cells is achieved by inhibition of glutathione peroxidase (GPx), and the mode of inhibition of GPx1 by tiopronin is shown in this report. Why MDR cells are particularly sensitive to ROS is discussed, as is the difficulty in exploiting this hypersensitivity to tiopronin in the clinic.     

SOD2 to SOD1 Switch in Breast Cancer

Cancer cells are characterized by elevated levels of reactive oxygen species, which are produced mainly by the mitochondria. The dismutase SOD2 localizes in the matrix and is a major antioxidant. The activity of SOD2 is regulated by the deacetylase SIRT3. Recent studies indicated that SIRT3 is decreased in 87% of breast cancers, implying that the activity of SOD2 is compromised. The resulting elevation in reactive oxygen species was shown to be essential for the metabolic reprograming toward glycolysis. Here, we show that SOD2 itself is down-regulated in breast cancer cell lines. Further, activation of oncogenes, such as Ras, promotes the rapid down-regulation of SOD2. Because in the absence of SOD2, superoxide levels are elevated in the matrix, we reasoned that mechanisms must exist to retain low levels of superoxide in other cellular compartments especially in the intermembrane space of the mitochondrial to avoid irreversible damage. The dismutase SOD1 also acts as an antioxidant, but it localizes to the cytoplasm and the intermembrane space of the mitochondria. We report here that loss of SOD2 correlates with the overexpression of SOD1. Further, we show that mitochondrial SOD1 is the main dismutase activity in breast cancer cells but not in non-transformed cells. In addition, we show that the SOD1 inhibitor LCS-1 leads to a drastic fragmentation and swelling of the matrix, suggesting that in the absence of SOD2, SOD1 is required to maintain the integrity of the organelle. We propose that by analogy to the cadherin switch during epithelial-mesenchymal transition, cancer cells also undergo a SOD switch during transformation.     

Protease Activity of Procaspase-8 Is Essential for Cell Survival by Inhibiting Both Apoptotic and Nonapoptotic Cell Death Dependent on Receptor-interacting Protein Kinase 1 (RIP1) and RIP3

Caspase-8 has an important role as an initiator caspase during death receptor-mediated apoptosis. Moreover, it has been reported to contribute to the regulation of cell fate in various types of cells including T-cells. In this report, we show that caspase-8 has an essential role in cell survival in mouse T-lymphoma-derived L5178Y cells. The knockdown of caspase-8 expression decreased the growth rate and increased cell death, both of which were induced by the absence of protease activity of procaspase-8. The cell death was associated with reactive oxygen species (ROS) accumulation, caspase activation, and autophagosome formation. The cell death was inhibited completely by treatment with ROS scavengers, but only partly by treatment with caspase inhibitors, expression of Bcl-xL, and knockdown of caspase-3 or Atg-7 which completely inhibits apoptosis or autophagosome formation, respectively, indicating that apoptosis and autophagy-associated cell death are induced simultaneously by the knockdown of caspase-8 expression. Further analysis indicated that RIP1 and RIP3 regulate this multiple cell death, because the cell death as well as ROS production was completely inhibited by not only treatment with the RIP1 inhibitor necrostatin-1, but also by knockdown of RIP3. Thus, in the absence of protease activity of procaspase-8, RIP1 and RIP3 simultaneously induce not only nonapoptotic cell death conceivably including autophagic cell death and necroptosis but also apoptosis through ROS production in mouse T-lymphoma cells.     

Caspase 1 Activation Is Protective against Hepatocyte Cell Death by Up-regulating Beclin 1 Protein and Mitochondrial Autophagy in the Setting of Redox Stress

Caspase 1 activation can be induced by oxidative stress, which leads to the release of the proinflammatory cytokines IL1β and IL18 in myeloid cells and a potentially damaging inflammatory response. However, little is known about the role of caspase 1 in non-immune cells, such as hepatocytes, that express and activate the inflammasome but do not produce a significant amount of IL1β/IL18. Here we demonstrate that caspase 1 activation protects against cell death after redox stress induced by hypoxia/reoxygenation in hepatocytes. Mechanistically, we show that caspase 1 reduces mitochondrial respiration and reactive oxygen species by increasing mitochondrial autophagy and subsequent clearance of mitochondria in hepatocytes after hypoxia/reoxygenation. Caspase 1 increases autophagic flux through up-regulating autophagy initiator beclin 1 during redox stress and is an important cell survival factor in hepatocytes. We find that during hemorrhagic shock with resuscitation, an in vivo mouse model associated with severe hepatic redox stress, caspase 1 activation is also protective against liver injury and excessive oxidative stress through the up-regulation of beclin 1. Our findings suggest an alternative role for caspase 1 activation in promoting adaptive responses to oxidative stress and, more specifically, in limiting reactive oxygen species production and damage in cells and tissues where IL1β/IL18 are not highly expressed.     

Nimbolide sensitizes human colon cancer cells to TRAIL through reactive oxygen species- and ERK-dependent up-regulation of death receptors, p53, and Bax

TNF-related apoptosis-inducing ligand (TRAIL) shows promise as a cancer treatment, but acquired tumor resistance to TRAIL is a roadblock. Here we investigated whether nimbolide, a limonoid, could sensitize human colon cancer cells to TRAIL. As indicated by assays that measure esterase activity, sub-G(1) fractions, mitochondrial activity, and activation of caspases, nimbolide potentiated the effect of TRAIL. This limonoid also enhanced expression of death receptors (DRs) DR5 and DR4 in cancer cells. Gene silencing of the receptors reduced the effect of limonoid on TRAIL-induced apoptosis. Using pharmacological inhibitors, we found that activation of ERK and p38 MAPK was required for DR up-regulation by nimbolide. Gene silencing of ERK abolished the enhancement of TRAIL-induced apoptosis. Moreover, our studies indicate that the limonoid induced reactive oxygen species production, which was required for ERK activation, up-regulation of DRs, and sensitization to TRAIL; these effects were mimicked by H(2)O(2). In addition, nimbolide down-regulated cell survival proteins, including I-FLICE, cIAP-1, cIAP-2, Bcl-2, Bcl-xL, survivin, and X-linked inhibitor of apoptosis protein, and up-regulated the pro-apoptotic proteins p53 and Bax. Interestingly, p53 and Bax up-regulation by nimbolide was required for sensitization to TRAIL but not for DR up-regulation. Overall, our results indicate that nimbolide can sensitize colon cancer cells to TRAIL-induced apoptosis through three distinct mechanisms: reactive oxygen species- and ERK-mediated up-regulation of DR5 and DR4, down-regulation of cell survival proteins, and up-regulation of p53 and Bax.     

肿瘤微环境中ROS介导IgG表达对膀胱癌细胞增殖和侵袭能力的影响

摘要 目的：探讨肿瘤微环境（TME）中活性氧（ROS）介导免疫球蛋白G（IgG）表达对膀胱癌EJ细胞增殖、迁移和侵袭能力的影响。方法：临床收集的18例膀胱癌患者样本,通过Western blot法检测膀胱癌和癌旁正常组织样本中IgG表达量。利用免疫荧光染色（IF）技术分别对膀胱癌组织和癌旁正常组织中ROS和IgG分子进行共定位和相对定量分析。将活性氧清除剂N-乙酰基-L-半胱氨酸（NAC）加入膀胱癌细胞EJ中,实验分为3组：空白组（EJ细胞）、阴性对照组（EJ+PBS）、实验组（EJ+PBS+NAC）,10 mM NAC药物处理48小时后,运用DHE-ROS荧光探针技术和Western blot实验检测药物NAC对ROS和IgG相对表达水平的影响;通过克隆集落形成实验、划痕实验、Transwell实验检测去除ROS后对膀胱癌细胞增殖、迁移和侵袭的影响。结果：人体膀胱癌组织中ROS和IgG分子表达水平显著高于癌旁正常组织（P<0.001）;荧光显微镜显示膀胱肿瘤组织中正常膀胱尿路上皮细胞组织被肿瘤细胞严重破坏,结构紊乱不规则,IgG和ROS表达水平均升高,而癌旁组织膀胱尿路上皮组织的结构均匀规则;NAC药物处理EJ细胞后,与空白组和阴性对照组相比ROS和IgG表达显著降低,同时实验组细胞的增殖、迁移和侵袭能力明显下降（P<0.01）。结论：ROS和IgG在临床膀胱癌组织和体外膀胱癌细胞株EJ中均显著高表达,在肿瘤微环境中ROS通过调控IgG表达,从而促进膀胱癌细胞的增殖、迁移、侵袭。ROS和IgG可能成为膀胱癌早期诊断和生物治疗的临床新靶点。     

Constitutive Activation of Epidermal Growth Factor Receptor Promotes Tumorigenesis of Cr(VI)-transformed Cells through Decreased Reactive Oxygen Species and Apoptosis Resistance Development

Hexavalent chromium (Cr(VI)) compounds are well-established lung carcinogens. Epidermal growth factor receptor (EGFR) is a tyrosine kinase transmembrane receptor that regulates cell survival, tumor invasion, and angiogenesis. Our results show that chronic exposure of human bronchial epithelial (BEAS-2B) cells to Cr(VI) is able to cause malignant cell transformation. These transformed cells exhibit apoptosis resistance with reduced poly ADP-ribose polymerase cleavage (C-PARP) and Bax expression and enhanced expressions of Bcl-2 and Bcl-xL. These transformed cells also exhibit reduced capacity of reactive oxygen species (ROS) generation along with elevated expression of antioxidant manganese superoxide dismutase 2 (SOD2). The expression of this antioxidant was also elevated in lung tumor tissue from a worker exposed to Cr(VI) for 19 years. EGFR was activated in Cr(VI)-transformed BEAS-2B cells, lung tissue from animals exposed to Cr(VI) particles, and human lung tumor tissue. Further study indicates that constitutive activation of EGFR in Cr(VI)-transformed cells was due to increased binding to its ligand amphiregulin (AREG). Inhibition of EGFR or AREG increased Bax expression and reduced Bcl-2 expression, resulting in reduced apoptosis resistance. Furthermore, inhibition of AREG or EGFR restored capacity of ROS generation and decreased SOD2 expression. PI3K/AKT was activated, which depended on EGFR in Cr(VI)-transformed BEAS-2B cells. Inhibition of PI3K/AKT increased ROS generation and reduced SOD2 expression, resulting in reduced apoptosis resistance with commitment increase in Bax expression and reduction of Bcl-2 expression. Xenograft mouse tumor study further demonstrates the essential role of EGFR in tumorigenesis of Cr(VI)-transformed cells. In summary, the present study suggests that ligand-dependent constitutive activation of EGFR causes reduced ROS generation and increased antioxidant expression, leading to development of apoptosis resistance, contributing to Cr(VI)-induced tumorigenesis.     

Mitochondrial dysfunction and oxidative stress contribute to the pathogenesis of spinocerebellar ataxia type 12 (SCA12)

Spinal cerebellar ataxia type 12 (SCA12) has been attributed to the elevated expression of ppp2r2b. To better elucidate the pathomechanism of the neuronal disorder and to search for a pharmacological treatment, Drosophila models of SCA12 were generated by overexpression of a human ppp2r2b and its Drosophila homolog tws. Ectopic expression of ppp2r2b or tws caused various pathological features, including neurodegeneration, apoptosis, and shortened life span. More detailed analysis revealed that elevated ppp2r2b and tws induced fission of mitochondria accompanied by increases in cytosolic reactive oxygen species (ROS), cytochrome c, and caspase 3 activity. Transmission electron microscopy revealed that fragmented mitochondria with disrupted cristae were engulfed by autophagosomes in photoreceptor neurons of flies overexpressing tws. Additionally, transgenic flies were more susceptible to oxidative injury induced by paraquat. By contrast, ectopic Drosophila Sod2 expression and antioxidant treatment reduced ROS and caspase 3 activity and extended the life span of the SCA12 fly model. In summary, our study demonstrates that oxidative stress induced by mitochondrial dysfunction plays a causal role in SCA12, and reduction of ROS is a potential therapeutic intervention for this neuropathy.     

Gefitinib-mediated Reactive Oxygen Specie (ROS) Instigates Mitochondrial Dysfunction and Drug Resistance in Lung Cancer Cells

Therapeutic benefits offered by tyrosine kinase inhibitors (TKIs), such as gefitinib (Iressa) and erlotinib (Tarceva), are limited due to the development of resistance, which contributes to treatment failure and cancer-related mortality. The aim of this study was to elucidate mechanistic insight into cellular perturbations that accompany acquired gefitinib resistance in lung cancer cells. Several lung adenocarcinoma (LAD) cell lines were screened to characterize epidermal growth factor receptor (EGFR) expression and mutation profile. To circumvent intrinsic variations between cell lines with respect to response to drug treatments, we generated gefitinib-resistant H1650 clone by long-term, chronic culture under gefitinib selection of parental cell line. Isogenic cells were analyzed by microarray, Western blot, flow cytometry, and confocal and transmission electron microscope. We observed that although chronic gefitinib treatment provided effective action against its primary target (aberrant EGFR activity), secondary effects resulted in increased cellular reactive oxygen species (ROS). Gefitinib-mediated ROS correlated with epithelial-mesenchymal transition, as well as striking perturbation of mitochondrial morphology and function. However, gefitinib treatment in the presence of ROS scavenger provided a partial rescue of mitochondrial aberrations. Furthermore, withdrawal of gefitinib from previously resistant clones correlated with normalized expression of epithelial-mesenchymal transition genes. These findings demonstrate that chronic gefitinib treatment promotes ROS and mitochondrial dysfunction in lung cancer cells. Antioxidants may alleviate ROS-mediated resistance.     

Serine Phosphorylation of the Insulin-like Growth Factor I (IGF-1) Receptor C-terminal Tail Restrains Kinase Activity and Cell Growth

Insulin-like growth factor I receptor (IGF-1R) signaling is essential for cell, organ, and animal growth. The C-terminal tail of the IGF-1R exhibits regulatory function, but the mechanism is unknown. Here, we show that mutation of Ser-1248 (S1248A) enhances IGF-1R in vitro kinase activity, autophosphorylation, Akt/mammalian target of rapamycin activity, and cell growth. Ser-1248 phosphorylation is mediated by GSK-3β in a mechanism that involves a priming phosphorylation on Ser-1252. GSK-3β knock-out cells exhibit reduced IGF-1R cell surface expression, enhanced IGF-1R kinase activity, and signaling. Examination of crystallographic structures of the IGF-1R kinase domain revealed that the (1248)SFYYS(1252) motif adopts a conformation tightly packed against the kinase C-lobe when Ser-1248 is in the unphosphorylated state that favors kinase activity. S1248A mutation is predicted to lock the motif in this position. In contrast, phosphorylation of Ser-1248 will drive profound structural transition of the sequence, critically affecting connection of the C terminus as well as exposing potential protein docking sites. Decreased kinase activity of a phosphomimetic S1248E mutant and enhanced kinase activity in mutants of its predicted target residue Lys-1081 support this auto-inhibitory model. Thus, the SFYYS motif controls the organization of the IGF-1R C terminus relative to the kinase domain. Its phosphorylation by GSK-3β restrains kinase activity and regulates receptor trafficking and signaling.