Trichosanthin induced apoptosis in HL-60 cells via mitochondrial and endoplasmic reticulum stress signaling pathways

Opportunities and challenges for ribosome-inactivating proteins in traditional Chinese medicine plants

Ribosome-inactivating proteins (RIPs) are a class of cytotoxic rRNA N-glycosylase, which widely exist in higher plants in different taxonomy, including many traditional Chinese medicinal materials and vegetables and fruits. In this paper, the traditional Chinese medicinal plants containing RIPs protein were sorted out, and their pharmacological effects and clinical applications were analyzed. Since many RIPs in traditional Chinese medicine plants exhibit antiviral and antitumor activities and show great clinical application potential, people's interest in these proteins is on the rise. This paper summarizes the possible mechanism of RIPs's anti-virus and anti-tumor effects, and discusses its potential problems and risks, laying a foundation for subsequent research on how to exert its anti-virus and anti-tumor effects.

Advances on Delivery of Cytotoxic Enzymes as Anticancer Agents

Cancer is one of the most serious human diseases, causing millions of deaths worldwide annually, and, therefore, it is one of the most investigated research disciplines. Developing efficient anticancer tools includes studying the effects of different natural enzymes of plant and microbial origin on tumor cells. The development of various smart delivery systems based on enzyme drugs has been conducted for more than two decades. Some of these delivery systems have been developed to the point that they have reached clinical stages, and a few have even found application in selected cancer treatments. Various biological, chemical, and physical approaches have been utilized to enhance their efficiencies by improving their delivery and targeting. In this paper, we review advanced delivery systems for enzyme drugs for use in cancer therapy. Their structure-based functions, mechanisms of action, fused forms with other peptides in terms of targeting and penetration, and other main results from in vivo and clinical studies of these advanced delivery systems are highlighted.

The use of miR122 and its target sequence in adeno-associated virus-mediated trichosanthin gene therapy

OBJECTIVE

Plant-derived cytotoxic transgene expression, such as trichosanthin (tcs), regulated by recombinant adeno-associated virus (rAAV) vector is a promising cancer gene therapy. However, the cytotoxic transgene can hamper the vector production in the rAAV producer cell line, human embryonic kidney (HEK293) cells. Here, we explored microRNA-122 (miR122) and its target sequence to limit the expression of the cytotoxic gene in the rAAV producer cells.

METHODS

A miR122 target (122T) sequence was incorporated into the 3' untranslated region of the tcs cDNA sequence. The firefly luciferase (fluc) transgene was used as an appropriate control. Cell line HEK293-mir122 was generated by the lentiviral vector-mediated genome integration of the mir122 gene in parental HEK293 cells. The effects of miR122 overexpression on cell growth, transgene expression, and rAAV production were determined.

RESULTS

The presence of 122T sequence significantly reduced transgene expression in the miR122-enriched Huh7 cell line (in vitro), fresh human hepatocytes (ex vivo), and mouse liver (in vivo). Also, the normal liver physiology was unaffected by delivery of 122T sequence by rAAV vectors. Compared with the parental cells, the miR122-overexpressing HEK293-mir122 cell line showed similar cell growth rate and expression of transgene without 122T, as well as the ability to produce liver-targeting rAAV vectors. Fascinatingly, the yield of rAAV vectors carrying the tcs-122T gene was increased by 77.7-fold in HEK293-mir122 cells. Moreover, the tcs-122T-containing rAAV vectors significantly reduced the proliferation of hepatocellular carcinoma cells without affecting the normal liver cells.

CONCLUSION

HEK293-mir122 cells along with the 122T sequence provide a potential tool to attenuate the cytotoxic transgene expression, such as tcs, during rAAV vector production.

Potential therapeutic compounds from traditional Chinese medicine targeting endoplasmic reticulum stress to alleviate rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease which affects about 0.5-1% of people with symptoms that significantly impact a sufferer's lifestyle. The cells involved in propagating RA tend to display pro-inflammatory and cancer-like characteristics. Medical drug treatment is currently the main avenue of RA therapy. However, drug options are limited due to severe side effects, high costs, insufficient disease retardation in a majority of patients, and therapeutic effects possibly subsiding over time. Thus there is a need for new drug therapies. Endoplasmic reticulum (ER) stress, a condition due to accumulation of misfolded proteins in the ER, and subsequent cellular responses have been found to be involved in cancer and inflammatory pathologies, including RA. ER stress protein markers and their modulation have therefore been suggested as therapeutic targets, such as GRP78 and CHOP, among others. Some current RA therapeutic drugs have been found to have ER stress-modulating properties. Traditional Chinese Medicines (TCMs) frequently use natural products that affect multiple body and cellular targets, and several medicines and/or their isolated compounds have been found to also have ER stress-modulating capabilities, including TCMs used in RA treatment by Chinese Medicine practitioners. This review encourages, in light of the available information, the study of these RA-treating, ER stress-modulating TCMs as potential new pharmaceutical drugs for use in clinical RA therapy, along with providing a list of other ER stress-modulating TCMs utilized in treatment of cancers, inflammatory diseases and other diseases, that have potential use in RA treatment given similar ER stress-modulating capacity.

Purification of Gekko Small Peptide Fraction and Its Effect of Inducing Apoptosis of EC 9706 Esophageal Cancer Cells by Inhibiting PI3K/Akt/GLUT1 Signaling Pathway

This study aimed to isolate and purify a cytotoxic extraction from Gekko japonicus, identify its components and determine its cytotoxic activity in vitro. We isolated and identified the most potent cytotoxic Gekko small peptide LH-20-15. The identification and analysis of peptide sequences of LH-20-15 were performed by de novo peptide sequencing, and two new peptides were found. LH-20-15 significantly inhibited the proliferation of human esophageal squamous carcinoma EC 9706 cells in a dose-dependent manner. Furthermore, LH-20-15 induced apoptosis in esophageal cancer cells by activating the mitochondrial apoptotic pathway. Further research showed that LH-20-15 inhibited the PI3 K/Akt/GLUT1 signaling pathway. In conclusion, LH-20-15 from Gekko japonicus is a peptide mixture and may inhibit EC 9706 cell proliferation and induce apoptosis by activating the mitochondrial apoptotic pathway. It also regulates glucose metabolism by targeting the PI3 K/Akt/GLUT1 signaling pathway. These small peptides could be new sources of natural cytotoxic ingredients against esophageal cancer with potential drug values.

ER Stress and Unfolded Protein Response in Leukemia: Friend, Foe, or Both?

The unfolded protein response (UPR) is an evolutionarily conserved adaptive signaling pathway triggered by a stress of the endoplasmic reticulum (ER) lumen compartment, which is initiated by the accumulation of unfolded proteins. This response, mediated by three sensors-Inositol Requiring Enzyme 1 (IRE1), Activating Transcription Factor 6 (ATF6), and Protein Kinase RNA-Like Endoplasmic Reticulum Kinase (PERK)—allows restoring protein homeostasis and maintaining cell survival. UPR represents a major cytoprotective signaling network for cancer cells, which frequently experience disturbed proteostasis owing to their rapid proliferation in an usually unfavorable microenvironment. Increased basal UPR also participates in the resistance of tumor cells against chemotherapy. UPR activation also occurs during hematopoiesis, and growing evidence supports the critical cytoprotective role played by ER stress in the emergence and proliferation of leukemic cells. In case of severe or prolonged stress, pro-survival UPR may however evolve into a cell death program called terminal UPR. Interestingly, a large number of studies have revealed that the induction of proapoptotic UPR can also strongly contribute to the sensitization of leukemic cells to chemotherapy. Here, we review the current knowledge on the consequences of the deregulation of UPR signaling in leukemias and their implications for the treatment of these diseases.

Role of endoplasmic reticulum oxidase 1α in H9C2 cardiomyocytes following hypoxia/reoxygenation injury

Endoplasmic reticulum (ER) oxidase 1α (ERO1α) is a glycosylated flavoenzyme that is located on the luminal side of the ER membrane, which serves an important role in catalyzing the formation of protein disulfide bonds and ER redox homeostasis. However, the role of ERO1α in myocardial hypoxia/reoxygenation (H/R) injury remains largely unknown. In the present study, ERO1α expression levels in H9C2 cardiomyocytes increased following H/R, reaching their highest levels following 3 h of hypoxia and 6 h of reoxygenation. In addition, H/R induced apoptosis, and significantly increased expression levels of ER stress (ERS) markers 78 kDa glucose-regulated protein and C/EBP homologous protein. Moreover, the genetic knockdown of ERO1α using short hairpin RNA suppressed cell apoptosis, caspase-3 activity, expression levels of cleaved caspase-12 and cytochrome c in the cytoplasm. Overall, this suggested that ERO1α knockdown may protect against H/R injury. The ERS activator tunicamycin (TM) was used to counteract the ERO1α-induced reduction in ERS; however, the percentage of apoptotic cells and the level of mitochondrial damage did not change. In conclusion, the results from the present study suggested that ERO1α knockdown may protect H9C2 cardiomyocytes from H/R injury through inhibiting intracellular ROS production and increasing intracellular levels of Ca²⁺, suggesting that ERO1α may serve an important role in H/R.

Natural Products Targeting ER Stress, and the Functional Link to Mitochondria

The endoplasmic reticulum (ER) is a dynamic organelle essential for intracellular homeostasis maintenance, controlling synthesis, the folding of secreted and membrane-bound proteins, and transport of Ca²⁺. During cellular stress, ER dysfunction leads to the activation of unfolded protein response (UPR) due to accumulated misfolded proteins in the ER. This condition is referred as ER stress. Mitochondria and ER form a site of close contact (the mitochondria-associated membrane, MAM) which is a major platform exerting important physiological roles in the regulation of intracellular Ca²⁺ homeostasis, lipid metabolism, mitochondrial fission, autophagosome formation, and apoptosis progression. Natural products have been receiving increasing attention for their ability to interfere with ER stress. Research works have focused on the capacity of these bioactive compounds to induce apoptosis by activating ER stress through the ER stress-mediated mitochondrial apoptotic pathway. In this review we discuss the role of natural products in the signaling communication between ER and mitochondria, focusing on the effects induced by ER stress including Ca²⁺ permeability transition and UPR signaling (protein kinase R-like ER kinase/mitofusin 2).

Advances on Tumor-Targeting Delivery of Cytotoxic Proteins

Great attention has been paid to cytotoxic proteins (e.g., ribosome-inactivating proteins, RIPs) possessing high anticancer activities; unlike small drugs, cytotoxic proteins can effectively retain inside the cells and avoid drug efflux mediated by multidrug resistance transporters due to the large-size effect. However, the clinical translation of these proteins is severely limited because of various biobarriers that hamper their effective delivery to tumor cells. Hence, in order to overcome these barriers, many smart drug delivery systems (DDS) have been developed. In this review, we will introduce two representative type I RIPs, trichosanthin (TCS) and gelonin (Gel), and overview the major biobarriers for protein-based cancer therapy. Finally, we outline advances on the development of smart DDS for effective delivery of these cytotoxic proteins for various applications in cancer treatment.

Neochamaejasmin A extracted from Stellera chamaejasme L. induces apoptosis involving mitochondrial dysfunction and oxidative stress in Sf9 cells

To explore the toxicity mechanisms of neochamaejasmin A (NCA), extracted from Stellera chamaejasme L., we first evaluated its cytotoxicity on the Spodoptera frugiperda (Sf9) cell line. The results confirmed that NCA inhibited Sf9 cell survival in both a dose- and time-dependent manner. Then, intracellular biochemical assays showed that NCA induced apoptosis in Sf9 cells. Evidence of apoptosis was confirmed by morphological changes and the activation of caspases-3/9. We also observed that NCA induced apoptosis via mitochondrial-dependent intrinsic apoptotic pathway by upregulating cytochrome c and proapoptotic protein (Bax) and downregulating the mitochondrial membrane potential (MMP) and antiapoptotic protein (Bcl-2). Moreover, we found a dose-dependent increase in reactive oxygen species (ROS), accumulation of lipid peroxidation product and an inactivation of the antioxidant enzymes in treated cells. Additionally, the cleavage of PARP and G2/M arrest were also detected in Sf9 cells exposed to NCA. These findings provide critical information that NCA effectively induced apoptosis in Sf9 cells through mitochondrial pathways.

Structural and Functional Investigation and Pharmacological Mechanism of Trichosanthin, a Type 1 Ribosome-Inactivating Protein

Trichosanthin (TCS) is an RNA N-glycosidase that depurinates adenine-4324 in the conserved α-sarcin/ricin loop (α-SRL) of rat 28 S ribosomal RNA (rRNA). TCS has only one chain, and is classified as type 1 ribosome-inactivating protein (RIP). Our structural studies revealed that TCS consists of two domains, with five conserved catalytic residues Tyr70, Tyr111, Glu160, Arg163 and Phe192 at the active cleft formed between them. We also found that the structural requirements of TCS to interact with the ribosomal stalk protein P2 C-terminal tail. The structural analyses suggest TCS attacks ribosomes by first binding to the C-terminal domain of ribosomal P protein. TCS exhibits a broad spectrum of biological and pharmacological activities including anti-tumor, anti-virus, and immune regulatory activities. This review summarizes an updated knowledge in the structural and functional studies and the mechanism of its multiple pharmacological effects.

Fordin: A novel type I ribosome inactivating protein from Vernicia fordii modulates multiple signaling cascades leading to anti-invasive and pro-apoptotic effects in cancer cells in vitro

Fordin, which is derived from Vernicia fordii, is a novel type I ribosome inactivating protein (RIP) with RNA N-glycosidase activity. In the present study, fordin was expressed by Escherichia coli and purified using nickel affinity chromatography. Previous studies have demonstrated RIP toxicity in a variety of cancer cell lines. To understand the therapeutic potential of fordin on tumors, the present study investigated the effects of fordin on the viability of several tumor and normal cell lines. The results demonstrated that fordin induced significant cytotoxicity in four cancer cell lines, compared with the normal cell line. Specifically, profound apoptosis and inhibition of cell invasion were observed following fordin exposure in U-2 OS and HepG2 cells; however, the molecular mechanism underlying the action of RIP remains to be fully elucidated. In the present study, it was found that the anticancer effects of fordin were associated with suppression of the nuclear factor (NF)-κB signaling pathway. In U-2 OS and HepG2 cells, fordin inhibited the expression of inhibitor of NF-κB (IκB) kinase, leading to downregulation of the phosphorylation level of IκB, which quelled the nuclear translocation of NF-κB. Fordin also reduced the mRNA and protein levels of NF-κB downstream targets associated with cell apoptosis and metastasis, particularly B-cell lymphoma-2-related protein A1 (Blf-1) and matrix metalloproteinase (MMP)-9. The inactivation of NF-κB and the reduction in the expression levels of Blf-1 and MMP-9 mediated by fordin were also confirmed by co-treatment with lipopolysaccharide or p65 small interfering RNA. These findings suggested a possible mechanism for the fordin-induced effect on tumor cell death and metastasis. The results of the present study demonstrated the multiple anticancer effects of fordin in U-2 OS and HepG2 cells, in part by inhibiting activation of the NF-κB signaling pathway.

DeBouganin Diabody Fusion Protein Overcomes Drug Resistance to ADCs Comprised of Anti-Microtubule Agents

Antibody drug conjugates (ADC), comprised of highly potent small molecule payloads chemically conjugated to a full-length antibody, represent a growing class of therapeutic agents. The targeting of cytotoxic payloads via the specificity and selectivity of the antibody has led to substantial clinical benefits. However, ADC potency can be altered by mechanisms of resistance such as overexpression of efflux pumps or anti-apoptotic proteins. DeBouganin is a de-immunized variant of bouganin, a ribosome-inactivating protein (RIP) that blocks protein synthesis, thereby leading to apoptosis. When conjugated to trastuzumab (T-deB), deBouganin was more potent than ado-trastuzumab-emtansine (T-DM1) and unaffected by resistance mechanisms to which DM1 is susceptible. To further highlight the differentiating mechanism of action of deBouganin, HCC1419 and BT-474 tumor cells that survived T-DM1 or trastuzumab-MMAE (T-MMAE) treatment were treated with an anti-HER2 C6.5 diabody–deBouganin fusion protein or T-deB. C6.5 diabody–deBouganin and T-deB were potent against HCC1419 and BT-474 cells that were resistant to T-DM1 or T-MMAE killing. The resistant phenotype involved MDR pumps, Bcl-2 family members, and the presence of additional unknown pathways. Overall, the data suggest that deBouganin is effective against tumor cell resistance mechanisms selected in response to ADCs composed of anti-microtubule payloads.

The anti-cancerous activity of recombinant trichosanthin on prostate cancer cell PC3

CONTEXT

Trichosanthin produced in the root tube of Trichosanthes kirilowii shows anti-tumor activity on a series of cancer cells including Hela, MCF-7, HL-60. But there is little information about its effect on the carcinogenesis of prostate cancer.

OBJECTIVE

This work was designed to study the role of trichosanthin on prostate cancer cells PC3.

MATERIALS AND METHODS

Trichosanthin was expressed in BL21 strain and purified by affinity chromatography. MTT assay was designed to determine the effect of trichosanthin on growth of PC3 cells at doses of 10, 20, 40, 60, 80, and 120 μg/ml. Then the effect of 50 μg/ml rTCS alone or combined with 2 μM IL-2 on PC3 cell proliferation was analyzed. And the mechanism of rTCS was studied by western blot. After that the in vivo effect of rTCS combined with IL-2 was explored in mice bearing PC3 xenograft tumor.

RESULTS

Trichosanthin was successfully expressed in BL21 and purified by 100 mM imidazole. It was shown to inhibit proliferation of PC3 cells in a dose-dependent manner with IC50 50.6 μg/ml. When combined with cytokine IL-2, a significant synergic effect was obtained. The inhibition rate on PC3 was around 50 % in combination group while only 35.5 % in single rTCS group at 50 μg/ml. Further, the expression of full length caspase-8 and Bcl-2 decreased significantly while cleaved caspase-8 and Bax were up-regulated, which suggest that caspase-8-mediated apoptosis pathway may be activated by rTCS in PC3 cells. Moreover, our data demonstrated that tumor volume and tumor weight were significantly reduced in rTCS-treated or rTCS/IL-2-treated nude mice bearing PC3 xenograft tumor compared with control. And significant difference was also found between rTCS and rTCS/IL-2 group.

CONCLUSIONS

This study demonstrates that rTCS is a potential agent with high in vitro and in vivo anti-tumor activity on PC3 cells. And rTCS combined with IL-2 is a promising strategy in treating patients with prostate cancer in future.

Pretreatment of rats with increased bioavailable berberine attenuates cerebral ischemia-reperfusion injury via down regulation of adenosine-5'monophosphate kinase activity

Berberine (BBR) exhibits multiple beneficial biological effects. However, poor bioavailability of BBR has limited its clinical application. We previously demonstrated that solid dispersion of BBR with sodium caprate (HGSD) remarkably improves its bioavailability. We examined whether this increased bioavailability of BBR could protect the brain from ischemia-reperfusion (IR) induced injury. Rats treated with HGSD, SC and saline for 7 days then subjected to cerebral ischemia reperfusion by middle cerebral artery occlusion for 2h followed 12h reperfusion. Neurological deficit scores, infarct size, SOD, MDA and NO levels were examined. P-AMPK, Bax, cleaved-Caspase-3 in brain was determined. To further probe for the mechanism of beneficial effect of HGSD, PC12 cells were incubated with serum from control or HGSD pretreated animals, incubated with 300μM H2O2 to induce apoptosis. Caspase-3 activity and cell apoptosis was evaluated. HGSD pretreatment significantly attenuated neurological deficit scores, reduced infarct size, increased SOD and decreased MDA and NO after cerebral IR injury compared to controls. Meanwhile, HGSD pretreatment significantly reduced expression of p-AMPK, Bax, cleaved-Caspase-3 after cerebral IR injury. Sodium caprate (100mg/kg/d) pretreatment alone did not exhibit any of these beneficial effects. PC12 cell apoptosis was attenuated when cells were cultured with HGSD serum compared to control. The presence of AMPK activator (AICAR) attenuated whereas AMPK inhibitor (Compound C) augmented the protective effect of HGSD serum on PC12 cell apoptosis.The results indicate that HGSD-pretreatment of rats protects the brain from ischemia-reperfusion injury and the mechanism is due to its anti-apoptotic effect mediated by decreased activation of AMPK.

Polyphyllin VII induces apoptosis in HepG2 cells through ROS-mediated mitochondrial dysfunction and MAPK pathways

Background

Paris polyphylla is an oriental folk medicine that has anticancer activities both in vivo and in vitro. Polyphyllin VII (PP7), a pennogenyl saponin from P. polyphylla has been found to exert strong anticancer activity. However, the underlying mechanisms are poorly understood. In the present study, the anticancer effect of polyphyllin VII against human liver cancer cells and the molecular mechanisms were investigated.

Methods

Cellular viability was measured by MTT assay. Apoptosis, intracellular reactive oxygen species (ROS) and mitochondrial membrane potential levels were evaluated using the InCell 2000 confocal microscope. The expression levels of apoptotic-related proteins were evaluated by Western blotting.

Results

PP7 strongly inhibited the cell growth and induced apoptosis and necrosis in hepatocellular carcinoma HepG2 cells. Meanwhile, PP7 up-regulated the levels of Bax/Bcl-2, cytochrome c, the cleaved forms of caspases-3, -8, -9, and poly (ADP-ribose) polymerase in a dose- and time-dependent manner, indicating that PP7 induced apoptosis in HepG2 cells through both intrinsic and extrinsic pathways. Moreover, PP7 provoked the production of intracellular ROS and the depolarization of mitochondrial membrane potential. Further analysis showed that PP7 significantly augmented the phosphorylation of JNK, ERK and p38, the major components of mitogen-activated protein kinase (MAPK) pathways, and the expressions of tumor suppressor proteins p53 and PTEN. In addition, PP7-induced apoptosis was remarkably attenuated by MAPK inhibitors and ROS inhibitor.

Conclusions

These results demonstrated that PP7 induced apoptotic cell death in HepG2 cells through both intrinsic and extrinsic pathways by promoting the generation of mitochondrial-mediated ROS and activating MAPK and PTEN/p53 pathways.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-016-1036-x) contains supplementary material, which is available to authorized users.

Ribosome-inactivating proteins (RIPs) and their important health promoting property

Ribosome-inactivating proteins (RIPs), widely present in plants, certain fungi and bacteria, can inhibit protein synthesis by removing one or more specific adenine residues from the large subunit of ribosomal RNAs (rRNAs).

Trichosanthin suppresses the proliferation of glioma cells by inhibiting LGR5 expression and the Wnt/β-catenin signaling pathway

Studies have indicated that trichosanthin (TCS), a bioactive protein extracted and purified from the tuberous root of Trichosanthes kirilowii (a well-known traditional Chinese medicinal plant), produces antitumor effects on various types of cancer cells. However, the effects of TCS on glioma cells are poorly understood. The objective of this study was to investigate the antitumor effects of TCS on the U87 and U251 cell lines. The in vitro effects of TCS on these two cell lines were determined using a Cell Counting Kit-8 (CCK-8) assay, Annexin V-FITC staining, DAPI staining, Transwell assays, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assays, 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethyl-imidacar-bocyanine iodide (JC-1) staining and western blotting, which was utilized to assess the expression of leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5) and key proteins in the Wnt/β-catenin signaling pathway. Our data indicated that TCS inhibited the proliferation of glioma cells in a dose- and time-dependent manner and played a role in inhibiting glioma cell invasion and migration. Additional investigation revealed that the expression levels of LGR5 and of key proteins in the Wnt/β-catenin signaling pathway were markedly decreased after TCS treatment. The results suggest that TCS may induce apoptosis in glioma cells by targeting LGR5 and repressing the Wnt/β-catenin signaling pathway. In the future, in vivo experiments should be conducted to examine the potential use of this compound as a novel therapeutic agent for gliomas.

Anti-tumor activities and apoptotic mechanism of ribosome-inactivating proteins

Ribosome-inactivating proteins (RIPs) belong to a family of enzymes that attack eukaryotic ribosomes and potently inhibit cellular protein synthesis. RIPs possess several biomedical properties, including anti-viral and anti-tumor activities. Multiple RIPs are known to inhibit tumor cell proliferation through inducing apoptosis in a variety of cancers, such as breast cancer, leukemia/lymphoma, and hepatoma. This review focuses on the anti-tumor activities of RIPs and their apoptotic effects through three closely related pathways: mitochondrial, death receptor, and endoplasmic reticulum pathways.

Fipronil induces apoptosis through caspase-dependent mitochondrial pathways in Drosophila S2 cells

Fipronil is the first phenylpyrazole insecticide widely used in controlling pests, including pyrethroid, organophosphate and carbamate insecticides. It is generally accepted that fipronil elicits neurotoxicity via interactions with GABA and glutamate receptors, although alternative mechanisms have recently been proposed. This study evaluates the genotoxicity of fipronil and its likely mode of action in Drosophila S2 cells, as an in vitro model. Fipronil administrated the concentration- and time-dependent S2 cell proliferation. Intracellular biochemical assays showed that fipronil-induced S2 cell apoptosis coincided with a decrease in the mitochondrial membrane potential and an increase reactive oxygen species generation, a significant decrease of Bcl-2 and DIAP1, and a marked augmentation of Cyt c and caspase-3. Because caspase-3 is the major executioner caspase downstream of caspase-9 in Drosophila, enzyme activity assays were used to determine the activities of caspase-3 and caspase-9. Our results indicated that fipronil effectively induced apoptosis in Drosophila S2 cells through caspase-dependent mitochondrial pathways.

Alpha-momorcharin (α-MMC) exerts effective anti-human breast tumor activities but has a narrow therapeutic window in vivo

Alpha-momorcharin (α-MMC), a ribosome inactivating protein (RIP) extracted from the seeds of Momordica charantia, exerts anti-tumor, antiviral, and anti-fungal activities. However, α-MMC has an obvious toxicity that limits its clinical application. We examined the effect of α-MMC on the inhibition of human breast cancer and assessed its general toxicity to find the therapeutic window in vivo for its potential clinical use. It was purified using column chromatography, and then injected into the xenograft nude mouse model induced by MDA-MB-231 and MCF-7. The anti-tumor efficacy was evaluated with T/C%. Next, the α-MMC was injected at a series of doses to Balb/C mice to assess its general toxicity. The MTT assay, the apoptosis test, and the cell cycle inhibition of α-MMC in human breast cancer cells were performed. In the xenografted tumors induced by MDA-MB-231 and MCF-7, α-MMC exerted an obvious inhibition effects on tumor growth at the dosage of 1.2mg/kg and 0.8 mg/kg. For in vivo toxicity experiments of α-MMC in Balb/C mice, the minimal toxic dose of α-MMC was 1.2mg/kg. Alpha-MMC induced apoptosis by increasing caspase3 activities, and the cell cycle was arrested at the G0/G1 or G2/M phases. The measurements of IC50 were 15.07 μg/mL, 33.66 μg/mL, 42.94 μg/mL for MDA-MB-231, MCF-7 and MDA-MB-453 respectively. Alpha-MMC exhibits anti-tumor effects in human breast cancer in vivo and in vitro. It inhibits breast cancer cells through the inhibition of tumor growth and induction of cell apoptosis. However, due to its obvious toxicity, α-MMC has a relatively narrow therapeutic window in vivo.

Low concentrations of trichosanthin induce apoptosis and cell cycle arrest via c-Jun N-terminal protein kinase/mitogen-activated protein kinase activation

Trichosanthin (TCS) is a type I ribosome--inactivating protein, which inhibits cell viability in human epithelial type 2 (HEp-2) and AMC-HN-8 human laryngeal epidermoid carcinoma cells. Although TCS is a potential chemotherapeutic agent, its mechanism of action remains to be elucidated. In the present study, HEp-2 and AMC-HN-8 cells were treated with different concentrations of TCS combined with or without cisplatin. After 5 days of successive treatment, different experimental groups were detected using a cell counting kit-8 and the collected supernatants were analyzed using a lactate dehydrogenase kit. Flow cytometric assays were performed to detect apoptosis and cell cycle arrest in the HEp-2 and AMC-HN-8 cells, reverse transcription quantitative polymerase chain reaction was performed to detect the levels of p27, p21WAF and western blot analysis was performed to detect changes in c-Jun N-terminal protein kinase (JNK)/phosphorylated (phospho)-JNK, p38/phospho-p38, extracellular signal-regulated kinase (ERK)/phospho-ERK, caspase-3 and caspase-9 in the HEp-2 and AMC-HN-8 cancer cells. TCS significantly inhibited the cell viability of the HEp-2 and AMC-HN-8 cells, independently of necrosis. TCS induced apoptosis and increased the percentage of HEp-2 and AMC-HN-8 cells in the S-phase of the cell cycle. In addition, the JNK/mitogen-activated protein kinase (MAPK) pathway was activated by TCS in the HEp-2 and AMC-HN-8 cells. Low concentrations of TCS also induced apoptosis and S-phase cell cycle arrest in the HEp-2 and AMC-HN-8 cells. The antitumor effects of TCS may be associated with JNK/MAPK activation.

Application of proteomics to identify the target molecules involved in Lonicera japonica-induced photokilling in human lung cancer CH27 cells

Background

The Lonicera japonica has been used as natural and healthy drink for its anti-inflammatory effect and pleasant odor in China and Taiwan.

Methods

2D electrophoresis was used to analyze the proteins involved in photoactivated Lonicera japonica-induced CH27 cell apoptosis. The fluorescent dyes MitoTracker Red CMXRos, calcein AM and JC-1 were used to elucidate mitochondrial function. The protein expression was performed by Western blotting. Fluorescent image of endoplasmic reticulum was accomplished by using ER-Tracker Green. This study used fluorescent dye CM-H₂DCFDA to detect intracellular generation of reactive oxygen species.

Results

The identified proteins can be classified into three major groups, which include proteins involved in mitochondrial function, cytoskeleton-related proteins and proteins associated with endoplasmic reticulum (ER) stress. Photoactivated Lonicera japonica caused a significant effect on the mitochondrial function and ER stress in CH27 cells. The reactive oxygen species producing was found to be involved in photoactivated Lonicera japonica-induced CH27 cell apoptosis.

Conclusion

Mitochondria and endoplasmic reticulum are the integral targets in photoactivated Lonicera japonica-induced CH27 cell apoptosis. We also demonstrated that ethyl acetate fraction of Lonicera japonica extracts caused photocytotoxicity in a dose-dependent manner in CH27 cells. This could explain the fact that the ethyl acetate fraction of Lonicera japonica extracts may contain compounds which exhibit the photosensitizing activity in CH27 cells.

Anti-tumor action of trichosanthin, a type 1 ribosome-inactivating protein, employed in traditional Chinese medicine: a mini review

Trichosanthin (TCS) as a midterm abortifacient medicine has been used clinically in traditional Chinese medicine for centuries. Additionally, TCS manifests a host of pharmacological properties, for instance, anti-HIV and anti-tumor activities. TCS has been reported to inhibit cell growth of a diversity of cancers, including cervical cancer, choriocarcinoma, and leukemia/lymphoma, etc. This article purported to review the various anti-tumor activities of TCS and the mechanism of apoptosis it induced in these tumor cells. These research progresses provide an insight into cancer research and treatment as well as disclose new pharmacological properties of the ancient but popular Chinese medicine.

Houttuynia cordata Thunb fraction induces human leukemic Molt-4 cell apoptosis through the endoplasmic reticulum stress pathway

Houttuynia cordata Thunb (HCT) is a native herb found in Southeast Asia which features various pharmacological activities against allergy, inflammation, viral and bacterial infection, and cancer. The aims of this study were to determine the cytotoxic effect of 6 fractions obtained from silica gel column chromatography of alcoholic HCT extract on human leukemic Molt-4 cells and demonstrate mechanisms of cell death. Six HCT fractions were cytotoxic to human lymphoblastic leukemic Molt-4 cells in a dose-dependent manner by MTT assay, fraction 4 exerting the greatest effects. Treatment with IC50 of HCT fraction 4 significantly induced Molt-4 apoptosis detected by annexinV-FITC/propidium iodide for externalization of phosphatidylserine to the outer layer of cell membrane. The mitochondrial transmembrane potential was reduced in HCT fraction 4-treated Molt-4 cells. Moreover, decreased expression of Bcl-xl and increased levels of Smac/Diablo, Bax and GRP78 proteins were noted on immunoblotting. In conclusion, HCT fraction 4 induces Molt-4 apoptosis cell through an endoplasmic reticulum stress pathway.

Trichosanthin inhibits breast cancer cell proliferation in both cell lines and nude mice by promotion of apoptosis

Breast cancer ranks as a common and severe neoplasia in women with increasing incidence as well as high risk of metastasis and relapse. Translational and laboratory-based clinical investigations of new/novel drugs are in progress. Medicinal plants are rich sources of biologically active natural products for drug development. The 27-kDa trichosanthin (TCS) is a ribosome inactivating protein purified from tubers of the Chinese herbal plant Trichosanthes kirilowii Maximowicz (common name Tian Hua Fen). In this study, we extended the potential medicinal applications of TCS from HIV, ferticide, hydatidiform moles, invasive moles, to breast cancer. We found that TCS manifested anti-proliferative and apoptosis-inducing activities in both estrogen-dependent human MCF-7 cells and estrogen-independent MDA-MB-231 cells. Flow cytometric analysis disclosed that TCS induced cell cycle arrest. Further studies revealed that TCS-induced tumor cell apoptosis was attributed to activation of both caspase-8 and caspase-9 regulated pathways. The subsequent events including caspase-3 activation, and increased PARP cleavage. With regard to cell morphology, stereotypical apoptotic features were observed. Moreover, in comparison with control, TCS- treated nude mice bearing MDA-MB-231 xenograft tumors exhibited significantly reduced tumor volume and tumor weight, due to the potent effect of TCS on tumor cell apoptosis as determined by the increase of caspase-3 activation, PARP cleavage, and DNA fragmentation using immunohistochemistry. Considering the clinical efficacy and relative safety of TCS on other human diseases, this work opens up new therapeutic avenues for patients with estrogen-dependent and/or estrogen-independent breast cancers.

Trichosanthin inhibits DNA methyltransferase and restores methylation-silenced gene expression in human cervical cancer cells

Epigenetic silencing of tumor suppressor genes is a well-established oncogenic process and the reactivation of tumor suppressor genes that have been silenced by promoter methylation is an attractive molecular target for cancer therapy. In this study, we investigated the demethylation activity of trichosanthin (TCS, the main bioactive component isolated from a Chinese medicinal herb) and its possible mechanism of action in cervical cancer cell lines. HeLa human cervical adenocarcinoma and CaSki human cervical squamous carcinoma cells were treated with various concentrations (0, 20, 40 and 80 µg/ml) of TCS for 48 h and the mRNA and protein expression levels of the tumor suppressor genes adenomatous polyposis coli (APC) and tumor suppressor in lung cancer 1 (TSLC1) were detected using reverse transcription (RT)-PCR and western blotting, respectively. We analyzed the methylation status of APC and TSLC1 using methylation-specific PCR (MSP). The expression levels and enzyme activity of DNA methyltransferase 1 (DNMT1) were also examined. The mRNA and protein expression levels of APC and TSLC1 were increased following treatment with various concentrations (0, 20, 40 and 80 µg/ml) of TCS for 48 h. The expression of the APC gene increased 2.55±0.29-, 3.44±0.31- and 4.36±0.14-fold, respectively. The expression of the TSLC1 gene increased 2.28±0.15-, 4.23±0.88- and 6.09±0.23-fold, respectively. MSP detection showed that TCS induced demethylation in HeLa and CaSki cells and that this demethylation activity was accompanied by the decreased expression of DNMT1 and reduced DNMT1 enzyme activity. Our experimental results demonstrate for the first time that TCS is capable of restoring the expression of methylation-silenced tumor suppressor genes and is potentially useful as a demethylation agent for the clinical treatment of human cervical cancer.

Bryonia dioica aqueous extract induces apoptosis through mitochondrial intrinsic pathway in BL41 Burkitt's lymphoma cells

ETHNOPHARMACOLOGICAL RELEVANCE

Bryonia dioica Jacq. is a climbing perennial herb with tuberous roots which is widely used in traditional medicine in Algeria for the treatment of cancers; it belongs to the genus Bryonia (Cucurbitaceae).

AIM OF THE STUDY

To investigate the cytotoxic and apoptogenic activities, the phytochemical composition and acute toxicity of the aqueous extract of Bryonia dioica roots growing in Algeria.

MATERIALS AND METHODS

Dried roots of Bryonia dioica were extracted with water (decoction). The cytotoxic effects of the aqueous extract in the Burkitt's lymphoma BL41 cell lines were evaluated by flow cytometry. Apoptosis induction was assessed by two corroborative assays; propidium iodide (PI) staining of cell DNA and flow cytometric light scatter analysis. The mitochondria membrane potential was investigated using a fluorescent dye DIOC6. The expression of caspases-3, -8, -9 and PARP was assessed by Western blot. The phytochemical screening of the roots of Bryonia dioica was performed using qualitative phytochemical standard procedures.

RESULTS

The Bryonia dioica aqueous extract induced cell death in a dose-dependent manner. The IC50 of Bryonia dioica aqueous extract was estimated to be approximately 15, 63μg/ml. This was accompanied by induction of apoptosis, activation of caspase-3 and -9, cleavage of PARP and loss of mitochondria membrane potential. Furthermore, the phytochemical screening of roots of Bryonia dioica showed the presence of various bioactive such as polyphenols, sterols and triterpenes, alkaloids, c-heterosides, carbohydrates and saponins.

CONCLUSION

The aqueous extract of Bryonia dioica induces apoptosis in the Burkitt's lymphoma BL41 cell lines via the mitochondrial pathway. The flavonoids, sterols and triterpens detected could be responsible for the cytotoxic and apoptogenic activities of the aqueous extract of Bryonia dioica. These findings suggest that Bryonia dioica could be considered as a promising source for developing novel therapeutics against Burkitt's lymphoma.

The anti-herpetic activity of trichosanthin via the nuclear factor-κB and p53 pathways

AIMS

Trichosanthin (TCS) is a type I ribosome-inactivating protein. We have previously shown that TCS induces a more potent apoptosis in infected cells over uninfected cells, but the mechanism underlying it is unclear. In this study, we explored the anti-HSV-1 mechanism of TCS through the nuclear factor-κB (NF-κB) and p53 pathways in human epithelial carcinoma (HEp-2) cells with wild type p53.

MAIN METHODS

The western blot, electrophoretic mobility shift assay, chromatin immunoprecipitation assay, enzyme-linked immunosorbent assay and cytokinesis-block micronucleus were applied in this study.

KEY FINDINGS

It was shown that TCS inhibited the HSV-1-induced NF-κB activation. Meanwhile, in HSV-1 infected cells, TCS treatment activated significantly more p53 and BAX, with no DNA damage and less S phase arrest compared with uninfected cells. The activation of BAX in infected cells correlated with the cell death signaling of p53.

SIGNIFICANCE

Taken together, these results suggest that the anti-HSV-1 effect of TCS is related to its suppression of NF-κB activation and regulation of p53-dependent cell death in infected cells.

Induction of apoptosis by ribosome inactivating proteins: importance of N-glycosidase activity

Apoptotic cell death is a fundamental process in the development and physiological homeostasis of multicellular organisms. It is associated with control of cell numbers in tissues and organs during development, with cell turnover, and with response to infection. Molecules that trigger this process in continuously proliferating cancer cells can be used as chemotherapeutic agents. Ribosome inactivating proteins (RIPs) that inhibit translation in a cell by depurinating (N-glycosidase activity) the 28S rRNA are known to serve as apoptosis inducers. However, the role of depurination activity of the RIPs in apoptosis induction is still controversial. Presently, there are three different hypotheses which propose that depurination is: (1) essential, (2) essential but not the sole factor, or (3) not essential for apoptosis induction. This article reviews various experimental outcomes on the importance of N-glycosidase activity of RIPs in the induction of apoptosis.

RNA toxins: mediators of stress adaptation and pathogen defense

RNA toxins are a group of enzymes primarily synthesized by bacteria, fungi, and plants that either cleave or depurinate RNA molecules. These proteins may be divided according to their RNA substrates: ribotoxins are nucleases that cleave ribosomal RNA (rRNA), ribosome inactivating proteins are glycosidases that remove a base from rRNA, messenger RNA (mRNA) interferases are nucleases that cleave mRNAs, and anticodon nucleases cleave transfer RNAs (tRNAs). These modifications to the RNAs may substantially alter gene expression and translation rates. Given that some of these enzymes cause cell death, it has been suggested that they function mainly in defense, either to kill competing cells or to elicit suicide and thereby limit pathogen spread from infected cells. Although good correlations have been drawn between their enzymatic functions and toxicity, recent work has shown that some RNA toxins cause apoptosis in the absence of damage to RNA and that defense against pathogens can be achieved without host cell death. Moreover, a decrease in cellular translation rate, insufficient to cause cell death, allows some organisms to adapt to stress and environmental change. Although ascribing effects observed in vitro to the roles of these toxins in nature has been challenging, recent results have expanded our understanding of their modes of action, and emphasized the importance of these toxins in development, adaptation to stress and defense against pathogens.

Induction of apoptosis in human promyelocytic leukemia HL60 cells by an extract from Erythrina suberosa stem bark

In this study, the apoptosis-inducing effect of an alcoholic extract from Erythrina suberosa stem bark (ESB) was investigated using human promyelocytic leukemia HL60 cells. Cell viability was estimated by MTT assay. We found that the ESB inhibited cell proliferation in a dose- and time-dependent manner. A series of well-documented morphological changes, such as cell shrinkage, condensation of nuclear chromatin, and nuclear fragmentation, were observed by fluorescence microscopy. The gold standard scanning electron micrographs showed apoptotic bodies and formation of blebs. Cell cycle analysis showed a significant increase in Sub G(0) population of cells above 50 μg/ml. ESB treatment resulted in a dose-dependent increase in annexin V positive cells. Increase in intracellular ROS production up to sixfold was detected in ESB-treated HL60 cells by DCFH-DA assay. Dissipation of mitochondrial membrane potential of intact cells accompanied by increase in cytosolic cytochrome c was observed, which was followed by activation of caspase-9 and -3 but not caspase-8. DNA fragmentation analysis revealed typical ladders as early as 18 h indicative of caspase-3 role in the apoptotic pathway. The overall results suggest that ESB induces mitochondria-mediated intrinsic apoptotic pathway in HL60 cells and might have therapeutic value against human leukemia.

Possible mechanisms of trichosanthin-induced apoptosis of tumor cells

Trichosanthin (TCS) is a type I ribosome-inactivating protein that is isolated from the root tubers of the Chinese medicinal herb Trichosanthes kirilowii Maximowicz. TCS has been used as an abortifacient for 1,500 years in China because of its high toxicity on trophoblasts. Over the past 20 years, TCS has been the subject of much research because of its potential antitumor activities. Many reports have revealed that TCS is cytotoxic in a variety of tumor cell lines in vitro and in vivo. Monoclonal antibody-conjugated TCS could enhance its antitumor efficacy; thus, TCS is considered to be a potential biological agent for cancer treatment. TCS is able to inhibit protein synthesis and consequently induce necrosis. Recent studies have demonstrated that TCS does indeed induce apoptosis in several tumor cell lines. Although TCS-induced apoptosis of tumor cell lines is now well known, the underlying mechanisms remain to be elucidated. The purpose of this review was to investigate the effects of TCS and its possible mechanisms of action, based on published literature and the results of our own studies.

The mechanisms of action of Tianhua(™) on antitumor activity in lung cancer cells

CONTEXT

Tianhua (TH-R) is extracted from Trichosanthes kirilowii Maxim (Cucurbitaceae) containing trichosanthin, a traditional Chinese medicine, which has been locally reported to have good anticancer effects in vivo in both animal and human models. However, there have been several reports that trichosanthin has an anticancer effect involving apoptosis.

OBJECTIVE

To investigate other anticancer effects of TH-R, various tumorigenesis parameters were verified.

MATERIALS AND METHODS

Telomerase activity, anti-apoptosis, anti-migration and immunomodulatory activity were estimated by telomeric repeat amplification protocol assay (TRAP), flow cytometry, Boyden chamber assay and ELISA assay, respectively.

RESULTS

In our studies, we are the first to find that TH-R had a cytotoxic effect on lung cancer cells in MTS assays; it could change the cell cycle distribution of human lung cancer cells (A549 cell line) and induce apoptosis. Further anti-telomerase effects in human lung adenocarcinoma A549 cells using the TRAP assay were noted. TH-R also had an aggregation effect on peripheral blood lymphocytes, but no effect on stimulating peripheral lymphocytes to produce human interferon-γ(IFN-γ). TH-R could inhibit the migration, or metastatic ability, of A549 cells by Boyden chamber assay. In the oral feeding therapy of an in vivo mouse model, there was an initial inhibition of A549 cancer cell growth, but no statistical difference after one month of therapy.

DISCUSSION AND CONCLUSION

It has been proven that medicinal herbs such as Tianhua have positive effects against cancer through preventing or inhibiting the process of lung tumorigenesis.

Targeting activating transcription factor 3 by Galectin-9 induces apoptosis and overcomes various types of treatment resistance in chronic myelogenous leukemia

Tyrosine kinase inhibitors (TKI) against Bcr-Abl are the first-line therapeutics for chronic myelogenous leukemia (CML). However, the resistance to Bcr-Abl TKIs is induced in leukemic cells not only by loss of sensitivity to TKIs through Bcr-Abl-related molecular mechanisms but also by loss of addiction to Bcr-Abl TK activity by acquiring Bcr-Abl-unrelated additional oncogenic mutations. Therefore, the identification of an additional therapeutic target has been anticipated for achievement of a complete cure and to overcome resistance to treatment. We here showed that modified human Galectin-9 (hGal9), a lectin that show specific affinity for beta-galactosides, inhibits the proliferation of five CML-derived cell lines by inducing apoptosis at their IC(50)s from 17.5 to 164.9 nmol/L. Our study revealed that activating transcription factor 3 (ATF3), a member of the ATF/cAMP-responsive element binding protein family transcription factors, is the critical mediator for cell killing by hGal9, and that Noxa is one of the downstream effector molecules of ATF3. Bim, on the other hand, the BH3-only protein essential for apoptosis by Bcr-Abl TKIs, was not associated with hGal9-induced cell death. ATF3-mediated cell death by hGal9 was not hampered by the absence of p53, the presence of mutant Abl(T315I), or by P-glycoprotein overexpression. In addition, hGal9 showed the additive growth-inhibitory effect with imatinib on CML cell lines. Collectively, hGal9 is a candidate agent that may overcome various kinds of resistance to treatment for CML and may suggest that ATF3 may be a new target molecule for the development of new treatment modalities that can overcome resistance to currently available chemotherapeutics.

Proteomic analysis reveals ATP-dependent steps and chaperones involvement in luteolin-induced lung cancer CH27 cell apoptosis

The present study applied 2D electrophoresis to analyze the proteins involved in luteolin (50 microM)-induced CH27 cell apoptosis. We found 7 proteins to be markedly changed. According to the data of analysis of these protein spots, we hypothesized that ATP synthetic pathway and heat shock proteins were involved in luteolin-induced CH27 cell apoptosis. In this study, luteolin induced a significant change in intracellular ATP levels and mitochondrial activity of CH27 cells. Further experiments demonstrated that pretreatment with forskolin blocked the luteolin-induced cell death. P38 and heat shock protein 27 may be important participants in the luteolin-induced changes in organization of actin microfilaments in this study. In addition, endoplasmic reticulum stress is also important in the luteolin-induced CH27 cell apoptosis. Our findings suggested that the function of mitochondria and endoplasmic reticulum is the integral factor in luteolin-induced CH27 cell apoptosis.

Molecular targeted therapies for diffuse large B-cell lymphoma based on apoptosis profiles

Diffuse large B-cell lymphoma (DLBCL) is the most common type of adult non-Hodgkin lymphoma and is treated with chemotherapy in combination with rituximab. Despite this aggressive therapy, the disease is fatal in 30-40% of patients. Inhibition of the apoptosis signalling pathways is strongly related to response to chemotherapy and eventual clinical outcome. In order to survive, lymphoma cells depend on disruption of the apoptosis pathway by mutations in apoptosis inducing genes or by continuous expression of anti-apoptotic proteins. The development of molecules targeting these apoptosis inhibitors provides a very promising opportunity to specifically target tumour cells without toxicity to non-malignant cells in DLBCL patients. Sensitivity for most of these antagonists can be predicted based on biological markers, suggesting the possibility of pre-defining patients who will most likely benefit from these targeted therapies. Experimental therapies aimed at restoring the upstream apoptosis pathway or targeting apoptosis inhibitors are currently being tested in clinical trials and are expected to be effective particularly in chemotherapy-refractory DLBCL, providing hope for patients who are refractory to current therapies.

Dual involvement of caspase-4 in inflammatory and ER stress-induced apoptotic responses in human retinal pigment epithelial cells

PURPOSE

To investigate the functional involvement of caspase-4 in human retinal pigment epithelial (hRPE) cells.

METHODS

Expression and activation of caspase-4 in hRPE cells were measured after stimulation with proinflammatory agents IL-1beta (2 ng/mL), TNF-alpha (20 ng/mL), lipopolysaccharide (1000 ng/mL), interferon-gamma (500 U/mL), or monocyte coculture in the absence or presence of immunomodulating agent cyclosporine (3 or 30 ng/mL), dexamethasone (10 microM), or IL-10 (100 U/mL) and endoplasmic reticulum (ER) stress inducer thapsigargin (25 nM) or tunicamycin (3 or 10 microM). The onset of ER stress was determined by expression of GRP78. The involvement of caspase-4 in inflammation and apoptosis was further examined by treating the cells with caspase-4 inhibitor Z-LEVD-fmk, caspase-1 and -4 inhibitor Z-YVAD-fmk, and pan-caspase inhibitor Z-VAD-fmk.

RESULTS

Caspase-4 mRNA expression and protein activation were induced by all the proinflammatory agents and ER stress inducers tested in this study. Caspase-4 activation was blocked or reduced by dexamethasone and IL-10. Elevated ER stress by proinflammatory agents and ER stress inducers was shown by increased expression of the ER stress marker GRP78. The induced caspase-4 and caspase-3 activities by tunicamycin and the stimulated IL-8 protein expression by IL-1beta were markedly reduced by caspase-4 inhibitor Z-LEVD-fmk. Although caspase-4 inhibitor Z-LEVD-fmk and caspase-1 and -4 inhibitor Z-YVAD-fmk reduced tunicamycin-induced hRPE apoptotic cell death by 59% and 86%, respectively, pan-caspase inhibitor Z-VAD-fmk completely abolished the induced apoptosis.

CONCLUSIONS

Caspase-4 is dually involved in hRPE proinflammatory and proapoptotic responses. Various proinflammatory stimuli and ER stress induce hRPE caspase-4 mRNA synthesis and protein activation. ER stress-induced hRPE cell death is caspase and, in part, caspase-4 dependent.

Dexamethasone enhances trichosanthin-induced apoptosis in the HepG2 hepatoma cell line

AIMS

Trichosanthin (TCS) is a type I ribosome-inactivating protein (RIP) with antitumor activities for various cancers. In this paper, we aimed to investigate whether dexamethasone, an important synthetic member of the glucocorticoid steroids, in combination with TCS can be a potential therapy in treating hepatoma.

MAIN METHODS

Cell viability was investigated using MTT assay, and apoptosis was evaluated with Hoechst 33258 staining. Western blot analysis was used to examine the changes in the expression levels of IkappaB-alpha, NF-kappaB p65 subunit and Cox-2. Additionally, we took advantage of dominant-negative IkappaB (IkappaB-DM) over-expression and chemical inhibitor PDTC to inhibit NF-kappaB activation.

KEY FINDINGS

Our results demonstrated that dexamethasone could enhance TCS-induced apoptosis in the hepatoma cell line HepG2, decreasing IC50 values from in excess of 200microg/ml to 50microg/ml. In addition, our results demonstrated that TCS could induce rapid degradation of IkappaB-alpha, nuclear translocation of NF-kappaB and decrease of COX-2 expression in HepG2 cells. Inhibition of NF-kappaB by biological (IkappaB-DM) or chemical inhibitor (PDTC) increased HepG2 cells' sensitivity to TCS, resulting in cell viability rate decreasing and apoptotic rate increasing. Simultaneously, dexamethasone increased the level of IkappaB-alpha protein and effectively inhibited TCS-induced degradation of IkappaB-alpha.

SIGNIFICANCE

These results suggest that dexamethasone could enhance trichosanthin-induced apoptosis in the HepG2, at least in part, by inhibiting the NF-kappaB signaling pathway and thus strengthening the antitumor effects of TCS, which highlights the possibility of combined drug application of TCS and dexamethasone in the clinical treatment of hepatoma.

Mechanism of the specific neuronal toxicity of a type I ribosome-inactivating protein, trichosanthin

The aim was to study the mechanism of neuronal toxicity, the cellular pathway, and the glial cell reactions induced by trichosanthin (TCS), a type I ribosome-inactivating protein (RIP). Ricin A chain (RTA) was included for comparison. TCS, RTA, and fluorescein isothiocyanate (FITC)-labeled TCS and RTA were separately injected into rat eyes. Saline or pure FITC was used as the control. Electron microscopy, confocal microscopy, and lectin and immunohistochemical staining were used to study the neurotoxic mechanism. TCS mainly induced apoptosis by causing degeneration of the mitochondria. TCS was able to enter the Müller and pigment cells. It caused a change in cell number of the following types of glial cells: a decrease in Müller cells, an increase in astrocytes, and little change in microglia. In contrast, RTA mainly induced necrosis and entered vascular endothelial cells. Astrocyte and microglia reactions were stronger in the RTA-treated retinas than those in the TCS-treated retinas. In conclusion, TCS appears to selectively enter and destroy Müller and pigment epithelia cells, which subsequently induce the death of photoreceptors. Degeneration of mitochondria is involved in the pathways of apoptosis of the photoreceptors caused by TCS. In sharp contrast, RTA can enter vascular endothelial cells and damage the vascular endothelium, resulting in retinitis and necrosis.

Diabetes- and angiotensin II-induced cardiac endoplasmic reticulum stress and cell death: metallothionein protection

We have shown cardiac protection by metallothionein (MT) in the development of diabetic cardiomyopathy (DCM) via suppression of cardiac cell death in cardiac-specific MT-overexpressing transgenic (MT-TG) mice. The present study was undertaken to define whether diabetes can induce cardiac endoplasmic reticulum (ER) stress and whether MT can prevent cardiac cell death via attenuating ER stress. Diabetes was induced by streptozotocin in both MT-TG and wild-type (WT) mice. Two weeks, and 2 and 5 months after diabetes onset, cardiac ER stress was detected by expression of ER chaperones, and apoptosis was detected by CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) and cleaved caspase-3 and caspase-12. Cardiac apoptosis in the WT diabetic mice, but not in MT-TG diabetic mice, was significantly increased 2 weeks after diabetes onset. In parallel with apoptotic effect, significant up-regulation of the ER chaperones, including glucose-regulated protein (GRP)78 and GRP94, cleaved ATF6 and phosporylated eIF2alpha, in the hearts of WT, but not MT-TG diabetic mice. Infusion of angiotensin II (Ang II) also significantly induced ER stress and apoptosis in the hearts of WT, but not in MT-TG mice. Direct administration of chemical ER stress activator tunicamycin significantly increased cardiac cell death only in WT mice. Pre-treatment with antioxidants completely prevented Ang II-induced ER stress and apoptosis in the cultured cardiac cells. These results suggest that ER stress exists in the diabetic heart, which may cause the cardiac cell death. MT prevents both diabetes- and Ang II-induced cardiac ER stress and associated cell death most likely via its antioxidant action, which may be responsible for MT's prevention of DCM.