Bcl-2 inhibits Bax translocation from cytosol to mitochondria during drug-induced apoptosis of human tumor cells

Static mechanical stress induces apoptosis in rat endplate chondrocytes through MAPK and mitochondria-dependent caspase activation signaling pathways

Mechanical stress has detrimental effects on cartilaginous endplate chondrocytes due to apoptosis in vivo and in vitro. In this study, we investigated the possible apoptosis signaling pathways induced by mechanical stress in cultured rat cervical endplate chondrocytes. Static mechanical load significantly reduced cell viability in a time- and load-dependent manner, as demonstrated by the Cell Counting Kit-8 (CCK-8) assay. Chondrocyte apoptosis induced by mechanical stress was confirmed by annexin V/propidium iodide (PI) staining and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL). Western blot analysis revealed that static load-induced chondrocyte apoptosis was accompanied by increased phosphorylation of c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase 1/2 (ERK1/2), and p38 mitogen-activated protein kinase (MAPK). The loss of mitochondrial membrane potential (ΔΨm), increased Cytochrome c release, and activated Caspase-9 and Caspase-3, indicating that the mitochondrial pathway is involved in mechanical stress-induced chondrocyte apoptosis. Treatment with inhibitors of JNK (SP600125), p38 MAPK (SB203580), and ERK (PD98059) prior to mechanical stimulation reversed both the static load-induced chondrocyte apoptosis and the activation of JNK, p38 MAPK, and ERK. Taken together, the data presented in this study demonstrate that mechanical stress induces apoptosis in rat cervical endplate chondrocytes through the MAPK-mediated mitochondrial apoptotic pathway.

Reactive oxygen species induce cell death via Akt signaling in rat osteoblast-like cell line ROS 17/2.8

In bones, osteoblasts are responsible for bone formation. The cell death of osteoblasts may cause a series of bone diseases and lead to bone loss, such as osteoarthrosis, hyperparathyroidism, and Paget's disease. Reactive oxygen species (ROS) are reported as a main factor for osteoblast cell death and further several bone diseases. However, the detailed mechanism is still largely unknown. Here, we found that ROS could induce cell death of rat osteoblast-like cell line ROS 17/2.8 via Akt (protein kinase B). Also, the mammalian target of rapamycin signaling was involved in this process. Our findings could help to reveal the cellular mechanism of osteoblast cell death, which is served for the pursuit of clinical treatment targets of relative bone diseases.

Knockdown of ZFX inhibits gastric cancer cell growth in vitro and in vivo via downregulating the ERK-MAPK pathway

Zinc finger protein X-linked (ZFX) is a zinc finger transcription factor encoded on the X chromosome. Here, we found that ZFX expression was significantly upregulated in gastric cancer (GC) cell lines and tissues. Knockdown of ZFX induced significant apoptosis and cell cycle arrest in SGC7901 and MGC803 cells. Moreover, we demonstrated for the first time that knockdown of ZFX inhibited gastric cancer cell growth in vitro and in vivo via downregulating the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK-MAPK) pathway. Therefore, ZFX play a prominent role in GC tumorigenicity and may have potential applications in the diagnosis or treatment of GC.

Ischemic preconditioning and the gene expression of enteric endothelial cell biology of rats submitted to intestinal ischemia and reperfusion

PURPOSE

To investigate the effects of ischemic preconditioning (IPC) on the expression of pro and anti-apoptotic genes in rat endothelial cells undergoing enteric ischemia (I) and reperfusion (R).

METHODS

Thirty rats underwent clamping of the superior mesenteric vessels. Sham group (GS) laparotomy only; Ischemia (GI): intestinal ischemia (60 min); Ischemia and Reperfusion (GIR): ischemia (60 min) and reperfusion (120 min); Ischemia and intestinal ischemic preconditioning (GI + IPC) : 5 minutes of ischemia followed by 10 min of reperfusion before sustained ischemia (60 min) ischemia and reperfusion and IPC (GIR + IPC): 5 min ischemia followed by 10 min of reperfusion before sustained ischemia (60min) and reperfusion (120 min). Rat Endothelial Cell Biology (PCR array) to determine the expression of genes related to endothelial cell biology.

RESULTS

Gene expression of pro-apoptotic markers (Casp1, Casp6, Cflar, Fas, and Pgl) was down regulated in GI+IPC and in GIR + IPC. In contrast, the expression of anti-apoptotic genes (Bcl2 and Naip2), was up-regulated in GI + IPC and in GIR + IPC.

CONCLUSION

Ischemic preconditioning may protect against cell death caused by ischemia and reperfusion.

Analysis of the cytoprotective role of α-crystallins in cell survival and implication of the αA-crystallin C-terminal extension domain in preventing Bax-induced apoptosis

α-Crystallins, initially described as the major structural proteins of the lens, belong to the small heat shock protein family. Apart from their function as chaperones, α-crystallins are involved in the regulation of intracellular apoptotic signals. αA- and αB-crystallins have been shown to interfere with the mitochondrial apoptotic pathway triggering Bax pro-apoptotic activity and downstream activation of effector caspases. Differential regulation of α-crystallins has been observed in several eye diseases such as age-related macular degeneration and stress-induced and inherited retinal degenerations. Although the function of α-crystallins in healthy and diseased retina remains poorly understood, their altered expression in pathological conditions argue in favor of a role in cellular defensive response. In the Rpe65⁻/⁻ mouse model of Leber's congenital amaurosis, we previously observed decreased expression of αA- and αB-crystallins during disease progression, which was correlated with Bax pro-death activity and photoreceptor apoptosis. In the present study, we demonstrated that α-crystallins interacted with pro-apoptotic Bax and displayed cytoprotective action against Bax-triggered apoptosis, as assessed by TUNEL and caspase assays. We further observed in staurosporine-treated photoreceptor-like 661W cells stably overexpressing αA- or αB-crystallin that Bax-dependent apoptosis and caspase activation were inhibited. Finally, we reported that the C-terminal extension domain of αA-crystallin was sufficient to provide protection against Bax-triggered apoptosis. Altogether, these data suggest that α-crystallins interfere with Bax-induced apoptosis in several cell types, including the cone-derived 661W cells. They further suggest that αA-crystallin-derived peptides might be sufficient to promote cytoprotective action in response to apoptotic cell death.

Suppression of CLIC4/mtCLIC enhances hydrogen peroxide-induced apoptosis in C6 glioma cells

CLIC4/mtCLIC (referred to here as CLIC4) is one of the seven-member family of chloride intracellular channels (CLIC). CLIC4 localizes to the mitochondria, nucleus, cytoplasm and other organellular compartments and participates in the apoptotic response to stress. However, the role of CLIC4 in oxidative stress and apoptosis is not well understood. In this study, we showed the important role of CLIC4 in apoptosis of C6 glioma cells induced by hydrogen peroxide (H2O2). Our results showed that CLIC4 protein expression was upregulated following H2O2-induced C6 cell apoptosis. The upregulation of CLIC4 protein expression was paralleled with an increased Bax/Bcl-2 ratio, cytochrome c and cleaved caspase-3 protein expression upon H2O2-induced C6 cell apoptosis. Suppression of CLIC4 expression by RNA interference enhanced cell apoptosis, but the ratio of Bax/Bcl-2 was not involved in this process. Dissipation of mitochondrial membrane potential and nuclear translocation of CLIC4 were involved in the activation of apoptosis induced by H2O2. Our data indicate that CLIC4 protein may be a key element in the apoptotic response to oxidative stress.

Signaling cascades initiated by TSLP-mediated signals in different cell types

Thymic stromal lymphopoietin (TSLP) has been well characterized as a consequence of its ability to modulate allergic and neoplastic diseases. However, downstream signaling mediated by TSLP varies significantly between the cell type and species examined. Since this observation is often overlooked and in some cases ignored, this review aims to consolidate the molecular pathways activated by TSLP receptors expressed by various human and mouse cell types.

Effects of DNA methyltransferase inhibitors (DNMTIs) on MDS-derived cell lines

DNA methyltransferase inhibitors (DNMTIs), including decitabine (DAC) and azacitidine (AZA), have recently been highlighted for the treatment of high-risk myelodysplastic syndrome (MDS); however, their action mechanisms have not been clearly defined. Therefore, we investigated the effects of DNMTIs on MDS-derived cell lines in vitro. An MDS-derived cell line MDS92 and its blastic subline MDS-L and HL-60 were used. All three cell lines were sensitive to DNMTIs, but MDS-L was the most susceptible. DAC-induced cell death in MDS-L was preceded by DNA damage-induced G2 arrest via a p53-independent pathway. AZA did not influence the pattern of cell cycle, although it induced DNA damage response. The IC(50) of DAC or AZA on MDS-L cells was associated with the dose inducing the maximal hypomethylation in long interspersed nuclear elements-1 (LINE-1) methylation assay. AZA suppressed the level of methylation in a time-dependent manner (days 4, 7, and 10), whereas DAC maintained the level of methylation from day 4 to 11. The protein expression of DNMT1 and DNMT3a decreased with the suppression of growth and methylation. We conclude that this study provides in vitro models for understanding the effects of DNMTIs on cell growth and gene regulation, including differences in the possible action mechanism of DAC and AZA.

Efficient inhibition of intraperitoneal ovarian cancer growth in nude mice by liposomal delivery of short hairpin RNA against STAT3

AIM

Signal transducer and activator of transcription 3 (STAT3) plays an important role in the tumor formation, prognosis and chemoresistance of ovarian cancer. Our goal was to investigate the effect of silencing STAT3 on ovarian cancer cell apoptosis, proliferation, angiogenesis and expression of key targets in vitro and in vivo.

METHODS

The ovarian cancer cell lines A2780CP and A2780s were used. STAT3 was knocked down by the plasmid-based short hairpin RNA (shRNA) expression system. In vitro, a colony formation assay and Hoechst staining were used to examine cell proliferation and apoptosis. The expression level of STAT3 and apoptosis-related proteins were determined by Western blot. The A2780CP intraperitoneal model was used to evaluate the effect of shSTAT3 on tumor growth in mice. Proliferation, apoptosis, and angiogenesis in tumor tissues were measured by proliferating cell nuclear antigen, TUNEL and CD31 immunostaining, respectively.

RESULTS

Treatment with shSTAT3 resulted in apoptosis and inhibition of cell proliferation in vitro. Western blot analysis demonstrated that shSTAT3 induced the expression of cleaved caspase-3 and reduced the expression of survivin, Bcl-2 and vascular endothelial growth factor. In vivo, the tumor weight was reduced to 13.46% of 5% glucose by shSTAT3/lipoplexes (P < 0.01), accompanied with apoptosis induction (P < 0.01), proliferation inhibition (P < 0.01) and angiogenesis inhibition (P < 0.01).

CONCLUSIONS

We find that treatment with shSTAT3 inhibits tumor growth in vitro and in vivo by inducing apoptosis and inhibiting cell proliferation. This work should provide the scientific foundation for future investigation of shSTAT3 as a strategy for ovarian cancer gene therapy and the combination of gene therapy with chemotherapy.

Wentilactone B from Aspergillus wentii induces apoptosis and inhibits proliferation and migration of human hepatoma SMMC-7721 cells

Wentilactone B (EN-48-57) is one of the six derivatives separated from Aspergillus wentii (EN-48). Of these derivatives, Wentilactone B exerted a more significant antibacterial and cytotoxic activity in several tumor cell lines. The present study demonstrates that Wentilactone B could efficiently induce SMMC-7721 cells apoptosis, but not normal hepatic cells, as measured by an inverted microscope, 4',6-diamidino-2-phenylindole staining and flow cytometry. In addition, Wentilactone B could inhibit the metastasis of SMMC-7721 cells, which was detected by colony formation, scratch migration and a transwell assay, and could induce a series of intracellular events, including the down-regulation of CD44 and epidermal growth factor receptor proteins. In conclusion, Wentilactone B inhibited the growth of SMMC-7721 cells by triggering apoptosis and inhibiting metastasis.

Enhanced apoptosis of ovarian cancer cells via nanocarrier-mediated codelivery of siRNA and doxorubicin

A folate conjugated ternary copolymer, FA–PEG–PEI–PCL, of poly(ethylene glycol) (PEG), poly(ethylene imine) (PEI), and poly(ɛ-caprolactone) (PCL) was synthesized. The copolymer self-assembled into cationic micelles capable of co-delivering siRNA and the anticancer drug doxorubicin (DOX). This dual functional nanocarrier demonstrated low cytotoxicity and high performance in drug/siRNA delivery. Upon the codelivery of siRNA, targeting the Bcl-2 gene, and DOX, using the folate-targeted nanocarrier, DOX-induced apoptosis in the skov-3 cells overexpressing folate receptor was significantly enhanced through a mechanism of downregulating the antiapoptotic protein Bcl-2, while simultaneously upregulating the proapoptotic protein Bax. This work suggested that the combination of Bcl-2 siRNA and DOX therapies is feasible, based on our dual functional nanocarrier, which set up a good basis for a future in vivo test.

Isoflurane induces endothelial apoptosis of the post-hypoxic blood-brain barrier in a transdifferentiated human umbilical vein endothelial cell model

Isoflurane is a popular volatile anesthetic agent used in humans as well as in experimental animal research. In previous animal studies of the blood-brain barrier (BBB), observations towards an increased permeability after exposure to isoflurane are reported. In this study we investigated the effect of a 2-hour isoflurane exposure on apoptosis of the cerebral endothelium following 24 hours of hypoxia in an in vitro BBB model using astrocyte-conditioned human umbilical vein endothelial cells (AC-HUVECs). Apoptosis of AC-HUVECs was investigated using light microscopy of the native culture for morphological changes, Western blot (WB) analysis of Bax and Bcl-2, and a TUNEL assay. Treatment of AC-HUVECs with isoflurane resulted in severe cellular morphological changes and a significant dose-dependent increase in DNA fragmentation, which was observed during the TUNEL assay analysis. WB analysis confirmed increases in pro-apoptotic Bax levels at 4 hours and 24 hours and decreases in anti-apoptotic Bcl-2 in a dose-dependent manner compared with the control group. These negative effects of isoflurane on the BBB after a hypoxic challenge need to be taken into account not only in experimental stroke research, but possibly also in clinical practice.

Aqueous fraction of Nephelium ramboutan-ake rind induces mitochondrial-mediated apoptosis in HT-29 human colorectal adenocarcinoma cells

The aim of this study was to investigate the cytotoxic and apoptotic effects of Nephelium ramboutan-ake (pulasan) rind in selected human cancer cell lines. The crude ethanol extract and fractions (ethyl acetate and aqueous) of N. ramboutan-ake inhibited the growth of HT-29, HCT-116, MDA-MB-231, Ca Ski cells according to MTT assays. The N. ramboutan-ake aqueous fraction (NRAF) was found to exert the greatest cytotoxic effect against HT-29 in a dose-dependent manner. Evidence of apoptotic cell death was revealed by features such as chromatin condensation, nuclear fragmentation and apoptotic body formation. The result from a TUNEL assay strongly suggested that NRAF brings about DNA fragmentation in HT-29 cells. Phosphatidylserine (PS) externalization on the outer leaflet of plasma membranes was detected with annexin V-FITC/PI binding, confirming the early stage of apoptosis. The mitochondrial permeability transition is an important step in the induction of cellular apoptosis, and the results clearly suggested that NRAF led to collapse of mitochondrial transmembrane potential in HT-29 cells. This attenuation of mitochondrial membrane potential (Δψm) was accompanied by increased production of ROS and depletion of GSH, an increase of Bax protein expression, and induced-activation of caspase-3/7 and caspase-9. These combined results suggest that NRAF induces mitochondrial-mediated apoptosis.

The cardioprotective efficacy of TVP1022 in a rat model of ischaemia/reperfusion

BACKGROUND AND PURPOSE

Because myocardial infarction is a major cause of morbidity and mortality worldwide, protecting the heart from the ischaemia and reperfusion (I/R) damage is the focus of intense research. Based on our in vitro findings showing that TVP1022 (the S-enantiomer of rasagiline, an anti-Parkinsonian drug) possesses cardioprotective effects, in the present study we investigated the hypothesis that TVP1022 can attenuate myocardial damage in an I/R model in rats.

EXPERIMENTAL APPROACH

The model consisted of 30-min occlusion of the left anterior descending artery followed by 4 or 24 h reperfusion. In addition, we investigated the possible mechanisms of cardioprotection in H9c2 cells and neonatal rat ventricular myocytes (NRVM) exposed to oxidative stress induced by H(2) O(2) .

KEY RESULTS

TVP1022 (20 and 40 mg·kg(-1) ) administered 5 min before reperfusion followed by an additional dose 4 h after reperfusion reduced the infarct size and attenuated the decline in ventricular function. TVP1022 also attenuated I/R-induced deterioration in cardiac mitochondrial integrity evaluated by mitochondrial swelling capacity. In vitro, using H9c2 cells and NRVM, TVP1022 attenuated both serum free- and H(2) O(2) -induced damage, preserved mitochondrial membrane potential and Bcl-2 levels, inhibited mitochondrial cytochrome c release and the increase in cleaved caspase 9 and 3 levels, and enhanced the phosphorylation of protein kinase C and glycogen synthase kinase-3β.

CONCLUSIONS AND IMPLICATIONS

TVP1022 provided cardioprotection in a model of myocardial infarction, and therefore should be considered as a novel adjunctive therapy for attenuating myocardial damage resulting from I/R injuries.

Treatment with a BH3 mimetic overcomes the resistance of latency III EBV (+) cells to p53-mediated apoptosis

P53 inactivation is often observed in Burkitt's lymphoma (BL) cells due to mutations in the p53 gene or overexpression of its negative regulator, murine double minute-2 (MDM2). This event is now considered an essential part of the oncogenic process. Epstein–Barr virus (EBV) is strongly associated with BL and is a cofactor in its development. We previously showed that nutlin-3, an antagonist of MDM2, activates the p53 pathway in BL cell lines harboring wild-type p53. However, nutlin-3 strongly induced apoptosis in EBV (−) or latency I EBV (+) cells, whereas latency III EBV (+) cells were much more resistant. We show here that this resistance to apoptosis is also observed in latency III EBV (+) lymphoblastoid cell lines. We also show that, in latency III EBV (+) cells, B-cell lymphona 2 (Bcl-2) is selectively overproduced and interacts with Bcl-2-associated X protein (Bax), preventing its activation. The treatment of these cells with the Bcl-2-homology domain 3 mimetic ABT-737 disrupts Bax/Bcl-2 interaction and allows Bax activation by nutlin-3. Furthermore, treatment with these two compounds strongly induces apoptosis. Thus, a combination of Mdm2 and Bcl-2 inhibitors might be a useful anti-cancer strategy for diseases linked to EBV infection.

Molecular biology of Bax and Bak activation and action

Bax and Bak are two nuclear-encoded proteins present in higher eukaryotes that are able to pierce the mitochondrial outer membrane to mediate cell death by apoptosis. Thus, organelles recruited by nucleated cells to supply energy can be recruited by Bax and Bak to kill cells. The two proteins lie in wait in healthy cells where they adopt a globular α-helical structure, seemingly as monomers. Following a variety of stress signals, they convert into pore-forming proteins by changing conformation and assembling into oligomeric complexes in the mitochondrial outer membrane. Proteins from the mitochondrial intermembrane space then empty into the cytosol to activate proteases that dismantle the cell. The arrangement of Bax and Bak in membrane-bound complexes, and how the complexes porate the membrane, is far from being understood. However, recent data indicate that they first form symmetric BH3:groove dimers which can be linked via an interface between the α6-helices to form high order oligomers. Here, we review how Bax and Bak change conformation and oligomerize, as well as how oligomers might form a pore. This article is part of a Special Issue entitled Mitochondria: the deadly organelle.

Fluoxetine affects antioxidant system and promotes apoptotic signaling in Wistar rat liver

Selective serotonin reuptake inhibitors (SSRI) are a treatment of choice for stress related disorders including clinical depression and a range of anxiety-related disorders. In the experimental animals, chronic stress paradigms are considered as a model of depression, and in that context are used for examining the effects of different drug treatments. The present research was designed to investigate the effect of SSRI fluoxetine on antioxidant status and apoptotic signaling in Wistar rat liver, which is a central organ for activation and detoxification of many xenobiotics and reactive oxygen species. We also investigated whether chronic fluoxetine treatment exhibits the same effects in the liver of control animals vs. animals stressed by chronic psychosocial isolation. Our results revealed that fluoxetine downregulated the activity of superoxide dismutases and upregulated the activity of glutathione peroxidase in both rat groups, while elevating glutathione reductase activity and total antioxidant status only in stressed animals. These results suggested that fluoxetine interfered with stress-induced pathways of oxidative defense in the liver. In addition, in both experimental groups, fluoxetine induced several hallmarks of apoptosis in the liver, including a decrease in Bcl-2 expression and increased DNA fragmentation. However, apoptotic alterations were more pronounced in stressed animals, suggesting that stress related oxidative damage could have primed apoptotic effects of fluoxetine.

Anti-tumor effects of dihydroartemisinin on human osteosarcoma

Dihydroartemisinin (DHA) exhibits antitumor activity against a wide spectrum of cancer cells. However, whether DHA has anti-tumor effect on human osteosarcoma cells remains unknown. This study aims to investigate the anti-tumor activity of DHA and the underlying mechanisms in human osteosarcoma cell lines with different p53 mutation statuses. Four human osteosarcoma cell lines were treated with different concentrations of DHA. Then, cell proliferation was determined by the CCK-8 viability assay; apoptosis and cell cycle progression were evaluated by flow cytometry; protein expression was analyzed by western blot assay; and NF-kB activity was examined by luciferase assay. The results demonstrated that DHA treatment could inhibit the proliferation of four osteosarcoma cell lines in a dose-dependent manner. P53 wild-type osteosarcoma cells were more sensitive to DHA. Moreover, the percentage of apoptotic cell and cell arrest in G₂/M phase was increased upon DHA treatment in a dose-dependent manner. Mechanistically, DHA activated caspase-3, caspase-8, and caspase-9; upregulated the expression of Bax, FAS, and cyclin D1; downregulated the expression of Bcl-2, Cdc25B, and cyclin B1; and inhibited the activity of NF-кB. In conclusion, DHA has significant anticancer effects against human osteosarcoma cells, which include induction of apoptosis and cell cycle arrest. The p53 gene may play a certain role in the DHA-induced human osteosarcoma apoptosis and cell cycle arrest. DHA is a novel anti-osteosarcoma drug candidate that merits further study.

Combination of taxol and Bcl-2 siRNA induces apoptosis in human glioblastoma cells and inhibits invasion, angiogenesis and tumour growth

Taxol is a powerful chemotherapeutic agent that binds to microtubules to prevent tumour cell division. However, a traditional high dose of taxol may also induce apoptosis in normal cells. The anti-apoptotic molecule Bcl-2 is up-regulated in tumour cells to prevent apoptosis. We designed this study to determine whether use of a low dose of taxol and anti-apoptotic Bcl-2 gene silencing would effectively induce apoptosis in human glioblastoma U251MG cells and also inhibit invasion, angiogenesis and intracranial as well as subcutaneous tumour growth. We treated the cells with either 100 nM taxol or transfected with a plasmid vector expressing Bcl-2 siRNA or both agents together for 72 h. Knockdown of Bcl-2 potentiated efficacy of taxol for cell death. Fluorescence-activated cell sorting analysis, double immunofluorescent staining and TUNEL assay demonstrated apoptosis in about 70% of the cells after treatment with the combination of taxol and Bcl-2 siRNA. In vitro Matrigel invasion assay demonstrated dramatic decrease in glioblastoma cell invasion and in vivo angiogenesis assay showed complete inhibition of neovascularization in athymic nude mice after treatment with the combination. Further, treatment with the combination of taxol and Bcl-2 siRNA caused suppression of intracranial tumour growth and subcutaneous solid tumour development. In conclusion, our results indicate that the combination of taxol and Bcl-2 siRNA effectively induces apoptosis and inhibits glioblastoma cell invasion, angiogenesis and intracranial as well as subcutaneous tumour growth. Therefore, the combination of a low dose of taxol and Bcl-2 siRNA is a promising therapeutic strategy for controlling the aggressive growth of human glioblastoma.

A switch from life to death in endoplasmic reticulum stressed β-cells

β-Cell death is an important pathogenic component of both type 1 and type 2 diabetes. Recent findings indicate that cell signalling pathways emanating from the endoplasmic reticulum (ER) play an important role in the regulation of β-cell death during the progression of diabetes. Homeostasis within the ER must be maintained to produce properly folded secretory proteins, such as insulin, in response to the body's need for them. However, the sensitive protein-folding environment in the ER can be perturbed by genetic and environmental factors leading to ER stress. To counteract ER stress, β-cells activate cell signalling pathways termed the unfolded protein response (UPR). The UPR functions as a binary switch between life and death, regulating both survival and death effectors. The outcome of this switch depends on the nature of the ER stress condition, the regulation of UPR activation and the expression and activation of survival and death components. This review discusses the mechanisms and the components in this switch and highlights the roles of this UPR's balancing act between life and death in β-cells.

Caspase-3 and Bcl-2 expression in glioblastoma: an immunohistochemical study

The unfavorable prognosis of malignant gliomas can also be explained by the incomplete knowledge of their molecular pathways. Studies regarding the regulatory process of apoptosis in glioblastoma (GBM), the most common malignant glioma, are few, and better knowledge of the expression of pro and anti-apoptotic proteins could collaborate with the development of new treatments founded on molecular basis. The objective of this study was to evaluate by immunohistochemistry the expression of caspase-3 and Bcl-2 in 30 samples of GBMs. The expression of caspase-3 (mean 17.67%) was lower than Bcl-2 (mean 30.92%), a statistically significant result (p<0.0001), suggesting low apoptotic activity in these tumors. Other studies of proteins related to the intrinsic and extrinsic pathway of apoptosis are required to provide additional information of this mechanism in GBMs.

Serine phosphorylation of glutathione S-transferase P1 (GSTP1) by PKCα enhances GSTP1-dependent cisplatin metabolism and resistance in human glioma cells

Recently, we reported that the human GSTP1 is phosphorylated and functionally activated by the PKC class of serine/threonine kinases. In this study, we investigated the contribution of this post-translational modification of GSTP1 to tumor cisplatin resistance. Using two malignant glioma cell lines, MGR1 and MGR3, the ability of PKCα-phosphorylated GSTP1 to catalyze the conjugation of cisplatin to glutathione was assessed and correlated with cisplatin sensitivity and cisplatin-induced DNA interstrand cross-links and apoptosis of the cells. The results showed PKCα activation and associated phosphorylation of GSTP1 to correlate significantly with increased glutathionylplatinum formation, decreased DNA interstrand cross-link formation and increased cisplatin resistance. Following PKC activation, the IC(50) of cisplatin increased from 13.63μM to 36.49μM in MGR1 and from 20.75μM to 38.45μM in MGR3. In both cell lines, siRNA-mediated GSTP1 or PKCα transcriptional suppression similarly decreased cisplatin IC(50) and was associated with decreased intracellular levels of glutathionylplatinum metabolite. Combined inhibition/transcriptional suppression of both PKCα and GSTP1 was synergistic in enhancing cisplatin sensitivity. Although, cisplatin-induced apoptosis was associated with the translocation of Bax to mitochondria, release of cytochrome c and caspase-3/7 activation, the levels of relocalized Bax and cytochrome c were significantly greater following GSTP1 knockdown. These results support a mechanism of cisplatin resistance mediated by the PKCα-dependent serine phosphorylation of GSTP1 and its associated increased cisplatin metabolism, and suggest the potential of simultaneous targeting of GSTP1 and PKCα to improve the efficacy of cisplatin therapy.

Pim-1 kinase protects mitochondrial integrity in cardiomyocytes

RATIONALE

Cardioprotective signaling mediates antiapoptotic actions through multiple mechanisms including maintenance of mitochondrial integrity. Pim-1 kinase is an essential downstream effector of AKT-mediated cardioprotection but the mechanistic basis for maintenance of mitochondrial integrity by Pim-1 remains unexplored. This study details antiapoptotic actions responsible for enhanced cell survival in cardiomyocytes with elevated Pim-1 activity.

OBJECTIVE

The purpose of this study is to demonstrate that the cardioprotective kinase Pim-1 acts to inhibit cell death by preserving mitochondrial integrity in cardiomyocytes.

METHODS AND RESULTS

A combination of biochemical, molecular, and microscopic analyses demonstrate beneficial effects of Pim-1 on mitochondrial integrity. Pim-1 protein level increases in the mitochondrial fraction with a corresponding decrease in the cytosolic fraction of myocardial lysates from hearts subjected to 30 minutes of ischemia followed by 30 minutes of reperfusion. Cardiac-specific overexpression of Pim-1 results in higher levels of antiapoptotic Bcl-X(L) and Bcl-2 compared to samples from normal hearts. In response to oxidative stress challenge, Pim-1 preserves the inner mitochondrial membrane potential. Ultrastructure of the mitochondria is maintained by Pim-1 activity, which prevents swelling induced by calcium overload. Finally, mitochondria isolated from hearts created with cardiac-specific overexpression of Pim-1 show inhibition of cytochrome c release triggered by a truncated form of proapoptotic Bid.

CONCLUSION

Cardioprotective action of Pim-1 kinase includes preservation of mitochondrial integrity during cardiomyopathic challenge conditions, thereby raising the potential for Pim-1 kinase activation as a therapeutic interventional approach to inhibit cell death by antagonizing proapoptotic Bcl-2 family members that regulate the intrinsic apoptotic pathway.

The binary switch between life and death of endoplasmic reticulum-stressed beta cells

PURPOSE OF REVIEW

beta-Cell death is an important pathogenic component of both type 1 and type 2 diabetes. However, the specific molecular pathways and interactions involved in this process are not completely understood. Increasing evidence indicates that a type of cell stress called endoplasmic reticulum stress (ER stress) plays an important role in beta-cell death. In the present article, we discuss a potential paradigm of ER stress-mediated beta-cell death.

RECENT FINDINGS

Upon ER stress conditions, a signaling network termed the unfolded protein response (UPR) is activated. The UPR regulates adaptive effectors to attenuate ER stress and restore ER homeostasis promoting cell survival. Paradoxically the UPR also regulates apoptotic effectors. When adaptive effectors fail to attenuate ER stress, these apoptotic effectors take into effect leading to cell death. The nature of this switch between life and death is currently under study.

SUMMARY

Depending on the nature of the stress condition, the UPR either protects beta cells or promotes their death. The mechanisms of this switch are not well understood but involve the balance between adaptive and apoptotic factors regulated by the UPR. In the present article, we review examples of this UPR balancing act between life and death and the potential mechanisms involved.

Enhanced apoptotic propensity in diabetic cardiac mitochondria: influence of subcellular spatial location

Cardiovascular complications, such as diabetic cardiomyopathy, account for the majority of deaths associated with diabetes mellitus. Mitochondria are particularly susceptible to the damaging effects of diabetes mellitus and have been implicated in the pathogenesis of diabetic cardiomyopathy. Cardiac mitochondria consist of two spatially distinct subpopulations, termed subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM). The goal of this study was to determine whether subcellular spatial location is associated with apoptotic propensity of cardiac mitochondrial subpopulations during diabetic insult. Swiss Webster mice were subjected to intraperitoneal injection of streptozotocin or citrate saline vehicle. Ten weeks following injection, diabetic hearts displayed increased caspase-3 and caspase-9 activities, indicating enhanced apoptotic signaling (P < 0.05, for both). Mitochondrial size (forward scatter) and internal complexity (side scatter) were decreased in diabetic IFM (P < 0.05, for both) but not in diabetic SSM. Mitochondrial membrane potential (Delta(Psim)) was lower in diabetic IFM (P < 0.01) but not in diabetic SSM. Mitochondrial permeability transition pore (mPTP) opening was increased in diabetic compared with control IFM (P < 0.05), whereas no differences were observed in diabetic compared with control SSM. Examination of mPTP constituents revealed increases in cyclophilin D in diabetic IFM. Furthermore, diabetic IFM possessed lower cytochrome c and BcL-2 levels and increased Bax levels (P < 0.05, for all 3). No significant changes in these proteins were observed in diabetic SSM compared with control. These results indicate that diabetes mellitus is associated with an enhanced apoptotic propensity in IFM, suggesting a differential apoptotic susceptibility of distinct mitochondrial subpopulations based upon subcellular location.

Arsenite induces apoptosis in human mesenchymal stem cells by altering Bcl-2 family proteins and by activating intrinsic pathway

PURPOSE

Environmental exposure to arsenic is an important public health issue. The effects of arsenic on different tissues and organs have been intensively studied. However, the effects of arsenic on bone marrow mesenchymal stem cells (MSCs) have not been reported. This study is designed to investigate the cell death process caused by arsenite and its related underlying mechanisms on MSCs. The rationale is that absorbed arsenic in the blood circulation can reach to the bone marrow and may affect the cell survival of MSCs.

METHODS

MSCs of passage 1 were purchased from Tulane University, grown till 70% confluency level and plated according to the experimental requirements followed by treatment with arsenite at various concentrations and time points. Arsenite (iAs(III)) induced cytotoxic effects were confirmed by cell viability and cell cycle analysis. For the presence of canonic apoptosis markers; DNA damage, exposure of intramembrane phosphotidylserine, protein and m-RNA expression levels were analyzed.

RESULTS

iAs(III) induced growth inhibition, G2-M arrest and apoptotic cell death in MSCs, the apoptosis induced by iAs(III) in the cultured MSCs was, via altering Bcl-2 family proteins and by involving intrinsic pathway.

CONCLUSION

iAs(III) can induce apoptosis in bone marrow-derived MSCs via Bcl-2 family proteins, regulating intrinsic apoptotic pathway. Due to the multipotency of MSC, acting as progenitor cells for a variety of connective tissues including bone, adipose, cartilage and muscle, these effects of arsenic may be important in assessing the health risk of the arsenic compounds and understanding the mechanisms of arsenic-induced harmful effects.

Computational analysis of dynamical responses to the intrinsic pathway of programmed cell death

Multicellular organisms shape development and remove aberrant cells by programmed cell death ("apoptosis"). Because defective cell death (too little or too much) is implicated in various diseases (like cancer and autoimmunity), understanding how apoptosis is regulated is an important goal of molecular cell biologists. To this end, we propose a mathematical model of the intrinsic apoptotic pathway that captures three key dynamical features: a signal threshold to elicit cell death, irreversible commitment to the response, and a time delay that is inversely proportional to signal strength. Subdividing the intrinsic pathway into three modules (initiator, amplifier, executioner), we use computer simulation and bifurcation theory to attribute signal threshold and time delay to positive feedback in the initiator module and irreversible commitment to positive feedback in the executioner module. The model accounts for the behavior of mutants deficient in various genes and is used to design experiments that would test its basic assumptions. Finally, we apply the model to study p53-induced cellular responses to DNA damage. Cells first undergo cell cycle arrest and DNA repair, and then apoptosis if the damage is beyond repair. The model ascribes this cell-fate transition to a transformation of p53 from "helper" to "killer" forms.

Kazrin F is involved in apoptosis and interacts with BAX and ARC

Kazrin has recently been identified as a functional protein that is involved in cell-cell junctions and in signal transduction. Here, we identified a new isoform, Kazrin F, which is 518 aa in length and has 97 aa unique at the N-terminus. Knockdown of Kazrin F using siRNA caused cell apoptosis and a marked decrease in cell viability measured by MTT and TUNEL assays. Co-immunoprecipitation analysis revealed that Kazrin F interacts with ARC (apoptosis repressor with caspase recruitment domain) and Bax (Bcl-2-associated X protein). Co-localization of Kazrin F with ARC and Bax in the cytoplasm was determined by immunofluorescence analysis. These results suggested that Kazrin F might play an important role in regulating cellular apoptosis by interacting with ARC and Bax.

Necrostatin-1 reverts shikonin-induced necroptosis to apoptosis

Degterev et al. previously demonstrated that death receptor mediated apoptosis could be diverted to necroptosis when apoptosis signaling was blocked, suggesting that necroptosis may function as a backup mechanism to insure the elimination of damaged cells under certain conditions when apoptosis was inhibited. Here, we show that shikonin-induced necroptosis can be reverted to apoptosis in the presence of necrostatin-1 (Nec-1), a specific necroptosis inhibitor and that the death mode switch is at least partially due to the conversion from mitochondrial inner membrane permeability to mitochondrial outer membrane permeability, which is associated with Bax translocation. The data combined with the previous reports support a notion that apoptosis and necroptosis may function as reciprocal backup mechanisms of cellular demise. To the best of our knowledge, this is the first study to document a conversion from necroptosis to apoptosis.

Induction of apoptosis of detached oral squamous cell carcinoma cells by safingol. Possible role of Bim, focal adhesion kinase and endonuclease G

The protein kinase C (PKC) inhibitor safingol increased rounding and detachment of human oral squamous cell carcinoma (SCC) cells in monolayer cultures. When dissociated cells were incubated in the presence of safingol, cell adhesion was prevented and cell viability was lost gradually, while most cells survived in the absence of safingol even if their attachment was blocked by coating the culture plates with polyhydroxyethyl methacrylate. Flow cytometric analysis and agarose gel electrophoresis of cellular DNA revealed an increase in the proportion of sub-G(1) cells and DNA fragmentation, indicating that safingol induced apoptosis of dissociated cells. During the induction of apoptosis in cell suspensions by safingol, there was an increase of the pro-apoptotic BH-3 only protein Bim and decrease of pro-survival Bcl-2 family proteins Bcl-xL and mitochondrial pro-apoptogenic factor endonuclease G translocated to the nucleus. The level of phosphorylated focal adhesion kinase (FAK) required for cell survival also rapidly decreased, followed by a decrease in the protein level. The introduction of siRNA against PKCalpha into SAS cells resulted in an increase of Bim, a decrease of Bcl-xL, the translocation of endonuclease G, and a decrease in the phosphorylation of FAK. These results suggest that Bim, Bcl-xL, FAK and endonuclease G are involved in safingol-induced apoptosis of detached oral SCC cells. Safingol can be used to induce apoptosis with cell detachment, anoikis, of oral SCC cells.

Bcl-2 family proteins as regulators of oxidative stress

The Bcl-2 family of proteins includes pro- and anti-apoptotic factors acting at mitochondrial and microsomal membranes. An impressive body of published studies, using genetic and physical reconstitution experiments in model organisms and cell lines, supports a view of Bcl-2 proteins as the critical arbiters of apoptotic cell death decisions in most circumstances (excepting CD95 death receptor signaling in Type I cells). Evasion of apoptosis is one of the hallmarks of cancer [Hanahan D, Weinberg RA. The hallmarks of cancer. Cell 2000;100:57-70], relevant to tumorigenesis as well as resistance to cytotoxic drugs, and deregulation of Bcl-2 proteins is observed in many cancers [Manion MK, Hockenbery DM. Targeting BCL-2-related proteins in cancer therapy. Cancer Biol Ther. 2003;2:S105-14; Olejniczak ET, Van Sant C, Anderson MG, Wang G, Tahir SK, Sauter G, et al. Integrative genomic analysis of small-cell lung carcinoma reveals correlates of sensitivity to bcl-2 antagonists and uncovers novel chromosomal gains. Mol Cancer Res. 2007;5:331-9]. The rekindled interest in aerobic glycolysis as a cancer trait raises interesting questions as to how metabolic changes in cancer cells are integrated with other essential alterations in cancer, e.g. promotion of angiogenesis and unbridled growth signals. Apoptosis induced by multiple different signals involves loss of mitochondrial homeostasis, in particular, outer mitochondrial membrane integrity, releasing cytochrome c and other proteins from the intermembrane space. This integrative process, controlled by Bcl-2 family proteins, is also influenced by the metabolic state of the cell. In this review, we consider the role of reactive oxygen species, a metabolic by-product, in the mitochondrial pathway of apoptosis, and the relationships between Bcl-2 functions and oxidative stress.

Bcl-2 family proteins as regulators of oxidative stress

The Bcl-2 family of proteins includes pro- and anti-apoptotic factors acting at mitochondrial and microsomal membranes. An impressive body of published studies, using genetic and physical reconstitution experiments in model organisms and cell lines, supports a view of Bcl-2 proteins as the critical arbiters of apoptotic cell death decisions in most circumstances (excepting CD95 death receptor signaling in Type I cells). Evasion of apoptosis is one of the hallmarks of cancer [Hanahan D, Weinberg RA. The hallmarks of cancer. Cell 2000;100:57-70], relevant to tumorigenesis as well as resistance to cytotoxic drugs, and deregulation of Bcl-2 proteins is observed in many cancers [Manion MK, Hockenbery DM. Targeting BCL-2-related proteins in cancer therapy. Cancer Biol Ther. 2003;2:S105-14; Olejniczak ET, Van Sant C, Anderson MG, Wang G, Tahir SK, Sauter G, et al. Integrative genomic analysis of small-cell lung carcinoma reveals correlates of sensitivity to bcl-2 antagonists and uncovers novel chromosomal gains. Mol Cancer Res. 2007;5:331-9]. The rekindled interest in aerobic glycolysis as a cancer trait raises interesting questions as to how metabolic changes in cancer cells are integrated with other essential alterations in cancer, e.g. promotion of angiogenesis and unbridled growth signals. Apoptosis induced by multiple different signals involves loss of mitochondrial homeostasis, in particular, outer mitochondrial membrane integrity, releasing cytochrome c and other proteins from the intermembrane space. This integrative process, controlled by Bcl-2 family proteins, is also influenced by the metabolic state of the cell. In this review, we consider the role of reactive oxygen species, a metabolic by-product, in the mitochondrial pathway of apoptosis, and the relationships between Bcl-2 functions and oxidative stress.

Gene silencing for epidermal growth factor receptor variant III induces cell-specific cytotoxicity

Epidermal growth factor receptor variant III (EGFRvIII) is a constitutively active mutant form of EGFR that is expressed in 40% to 50% of gliomas and several other malignancies. Here, we describe the therapeutic effects of silencing EGFRvIII on glioma cell lines in vitro and in vivo. A small interfering RNA molecule against EGFRvIII was introduced into EGFRvIII-expressing glioma cells (U87Delta) by electroporation resulting in complete inhibition of expression of EGFRvIII as early as 48 h post-treatment. During EGFRvIII silencing, a decrease in the proliferation and invasiveness of U87Delta cells was accompanied by an increase in apoptosis (P < 0.05). Notably, EGFRvIII silencing inhibited the signal transduction machinery downstream of EGFRvIII as evidenced by decreases in the activated levels of Ras and extracellular signal-regulated kinase. A lentivirus capable of expressing anti-EGFRvIII short hairpin RNA was also able to achieve progressive silencing of EGFRvIII in U87Delta cells in addition to inhibiting cell proliferation, invasiveness, and colony formation in a significant manner (P < 0.05). Silencing EGFRvIII in U87Delta cultures with this virus reduced the expression of factors involved in epithelial-mesenchymal transition including N-cadherin, beta-catenin, Snail, Slug, and paxillin but not E-cadherin. The anti-EGFRvIII lentivirus also affected the cell cycle progression of U87Delta cells with a decrease in G(1) and increase in S and G(2) fractions. In an in vivo model, tumor growth was completely inhibited in severe combined immunodeficient mice (n = 10) injected s.c. with U87Delta cells treated with the anti-EGFRvIII lentivirus (P = 0.005). We conclude that gene specific silencing of EGFRvIII is a promising strategy for treating cancers that contain this mutated receptor.

Pinocembrin prevents glutamate-induced apoptosis in SH-SY5Y neuronal cells via decrease of bax/bcl-2 ratio

Pinocembrin is the most abundant flavonoids in propolis, and has been proven to have antioxidant, antibacterial and anti-inflammatory property. To assess the protective effects of pinocembrin on neurons, SH-SY5Y neuronal cells were pretreated with pinocembrin for 2 h followed by co-treatment with glutamate (2 mM) for 12 h. Cell viability was determined by(3,4,5-dimethylthiazol-2-yl)-2,5-diphenylte-trazolium bromide assay, and apoptosis was confirmed by cell morphology, capillary zone electrophoresis and flow cytometry assay. Cell morphology was evaluated with Hoechst33258/PI dye. Treatment with pinocembrin (10(-5), 10(-6), 10(-7) mol/l) increased cell viability dose-dependently, inhibited LDH release and attenuated apoptosis. Intracellular free [Ca(2+)] was increased after glutamate exposure, and this increase was attenuated in cells treated with pinocembrin. bax mRNA expression increased remarkably following glutamate exposure and pinocembrin treatment manifested a reduction effect. bcl-2 mRNA expression changes were not detected in groups with or without pinocembrin. Western blotting results indicated that pinocembrin treatment reduced the expression of Bax and had no effect on Bcl-2, thus decreased the Bax-Bcl-2 ratio, which is in consistent with the gene expression result. Pinocembrin could also down-regulate the expression of p53 protein, and inhibit the release of cytochrome c from mitochondria to cytosol. Thus we conclude that pinocembrin exerts its neuroprotective effects in glutamate injury model partly by inhibiting p53 expression, thus Bax-Bcl-2 ratio, and the release of cytochrome c.

Bcl-2 siRNA augments taxol mediated apoptotic death in human glioblastoma U138MG and U251MG cells

The anti-neoplastic drug taxol binds to beta-tubulin to prevent tumor cell division, promoting cell death. However, high dose taxol treatment may induce cell death in normal cells too. The anti-apoptotic molecule Bcl-2 is upregulated in many cancer cells to protect them from apoptosis. In the current study, we knocked down Bcl-2 expression using cognate siRNA during low-dose taxol treatment to induce apoptosis in two human glioblastoma U138MG and U251MG cell lines. The cells were treated with either 100 nM taxol or 100 nM Bcl-2 siRNA or both for 72 h. Immunofluorescent stainings for calpain and active caspase-3 showed increases in expression and co-localization of these proteases in apoptotic cells. Fluorometric assays demonstrated increases in intracellular free [Ca(2+)], calpain, and caspase-3 indicating augmentation of apoptosis. Western blotting demonstrated dramatic increases in the levels of Bax, Bak, tBid, active caspases, DNA fragmentation factor-40 (DFF40), cleaved fragments of lamin, fodrin, and poly(ADP-ribose) polymerase (PARP) during apoptosis. The events related to apoptosis were prominent more in combination therapy than in either treatment alone. Our current study demonstrated that Bcl-2 siRNA significantly augmented taxol mediated apoptosis in different human glioblastoma cells through induction of calpain and caspase proteolytic activities. Thus, combination of taxol and Bcl-2 siRNA offers a novel therapeutic strategy for controlling the malignant growth of human glioblastoma cells.

Cytotoxic effects of curcumin on osteosarcoma cell lines

Curcumin (diferuloylmethane), one of the main components of the Indian spice turmeric, is known to possess potent anti-inflammatory and anti-oxidant properties. In addition, curcumin has also been shown to have in vitro and in vivo efficacy against a variety of malignancies. In the current study we examined the cytotoxic effect of curcumin on seven osteosarcoma (OS) cell lines with varying degrees of in vivo metastatic potential. Curcumin inhibited the growth of all OS cell lines tested with half-maximal inhibitory concentration values ranging from 14.4 to 24.6 microM. Growth inhibition was associated with a dose dependent increase in the number of apoptotic cells and accumulation of cells in the G(2)/M phase of the cell cycle. Curcumin treatment also resulted in cleavage of caspase-3 and poly adenosine diphosphate-ribose polymerase. Moreover, curcumin treatment was associated with an increase in cellular levels of the apoptotic B-cell leukemia/lymphoma 2 (Bcl-2)-associated X protein and a decrease in cellular content of the anti-apoptotic protein Bcl-2. In addition, curcumin treatment also inhibited the migration of OS cell lines. These data indicate that the potent cytotoxic activity of curcumin on OS cell lines is mediated by induction of apoptotic processes. Thus, curcumin has potential to be a novel OS chemotherapeutic agent.

Ribosomal protein S19 deficiency leads to reduced proliferation and increased apoptosis but does not affect terminal erythroid differentiation in a cell line model of Diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) is a congenital red-cell aplasia in which 25% of the patients have a mutation in the ribosomal protein (RP) S19 gene. It is not known how the RPS19 deficiency impairs erythropoiesis and proliferation of hematopoietic progenitors. To elucidate molecular mechanisms in RPS19-deficient DBA, we analyzed the effects of RPS19 deficiency on erythropoietin (EPO)-induced signal transduction, cell cycle, and apoptosis in RPS19-deficient TF-1 cells. We did not find any abnormality in EPO-induced signal transduction. However, RPS19-deficient TF-1 cells showed G0/G1 arrest (82% vs. 58%; p < .05) together with accumulation of p21 and p27. The fraction of apoptotic cells detected by Annexin V analysis also increased compared with control cells (13% vs. 3.1%; p < .05). Western blot analysis of apoptosis-related proteins showed that the level of bcl-2 and Bad was decreased and Bax was increased in RPS19-deficient TF-1 cells. Moreover, primary CD34-positive cells from DBA patients detected by Annexin V analysis also generated a higher number of apoptotic cells compared with normal CD34-positive cells during in vitro culture (38% vs. 8.9%; n = 5; p < .001). Finally, we show that although RPS19 silencing reduces EPO-induced development of erythroid progenitors expressing glycophorin A (GPA), RPS19 silencing in cells already expressing GPA does not affect GPA expression. These findings indicate that RPS19 deficiency causes apoptosis and accelerated loss of erythroid progenitors in RPS19-deficient DBA.

Restoration of tissue factor pathway inhibitor-2 in a human glioblastoma cell line triggers caspase-mediated pathway and apoptosis

PURPOSE

The induction of apoptotic pathways in cancer cells offers a novel and potentially useful approach to improve patient responses to conventional chemotherapy. Tissue factor pathway inhibitor-2 (TFPI-2) is a protease inhibitor that is abundant in the extracellular matrix and highly expressed in noninvasive cells but absent or undetectable in highly invasive human glioblastoma cells.

EXPERIMENTAL DESIGN

Using a recombinant adeno-associated viral vector carrying human TFPI-2 cDNA, we stably expressed TFPI-2 in U-251 cells, a highly invasive human glioblastoma cell line. Our previous studies showed that restoration of TFPI-2 in glioblastomas effectively prevents cell proliferation, angiogenesis, and tumor invasion. In this study, we determined whether TFPI-2 restoration could induce apoptosis through the caspase-mediated signaling pathway.

RESULTS

The results from nuclear chromatin staining, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay, and fluorescence-activated cell sorting analysis showed increased apoptosis in U-251 cells after restoration of TFPI-2. Caspase-9 and caspase-3 activity assays showed increased activity, indicating enhanced apoptosis. Immunofluorescence for cleaved caspase-9 and caspase-3 depicted increased expression and colocalization of both molecules. Western blot analysis showed increased transcriptional activities of Fas ligand, tumor necrosis factor-alpha, Bax, Fas-associated death domain, and tumor necrosis factor receptor 1-associated death domain as well as elevated levels of cleaved caspases and poly(ADP-ribose) polymerase. Semiquantitative reverse transcription-PCR depicted increased expression of tumor necrosis factor-alpha and Fas ligand and the related death domains tumor necrosis factor receptor 1-associated death domain and Fas-associated death domain.

CONCLUSIONS

Taken together, these results show that restoration of TFPI-2 activates both intrinsic and extrinsic caspase-mediated, proapoptotic signaling pathways and induces apoptosis in U-251 cells. Furthermore, our study suggests that recombinant adeno-associated viral vector-mediated gene expression offers a novel tool for cancer gene therapy.