Downregulation of Apaf-1 and caspase-3 by RNA interference in human glioma cells: Consequences for erucylphosphocholine-induced apoptosis

LncRNA-135528 inhibits tumor progression by up-regulating CXCL10 through the JAK/STAT pathway

Spontaneous tumor regression can be observed in many tumors, however, studies related to the altered expression of lncRNA in spontaneous glioma regression are limited, and the potential contributions of lncRNAs to spontaneous glioma regression remain unknown. To investigate the biological roles of lncRNA-135528 in spontaneous glioma regression. The cDNA fragment of lncRNA-135528 was obtained by rapid-amplification of cDNA ends (RACE) technology and cloned into the plvx-mcmv-zsgreen-puro vector. Additionally, we stably silenced or overexpressed lncRNA-135528 in G422 cells by transfecting with siRNA against lncRNA-135528 or lncRNA-135528 overexpression plasmid. Then, we examined lncRNA-135528 overexpressing and lncRNA-135528 silencing on glioma cells and its effects on CXCL10 and JAK/STAT pathways. The main findings indicated that lncRNA-135528 promoted glioma cell apoptosis, inhibited cell proliferation and arrested cell cycle progression; the up-regulation of lncRNA135528 led to significantly increased CXCL10 levels and the differential expression of mRNA associated with JAK/STAT pathway in glioma cells. lncRNA-135528 can inhibit tumor progression by up-regulating CXCL10 through the JAK/STAT pathway.

RNAi Based Approaches to the Treatment of Malignant Glioma

RNA interference (RNAi) is a recently discovered, powerful molecular mechanism that can be harnessed to engineer gene-specific silencing in mammalian tissues. A mechanism, where short double-stranded RNA (dsRNA) molecules, when introduced into cells elicit specific “knock-down” of gene expression via degradation of targeted messenger RNA, has lately become the technique of choice for analysis of gene function in oncology research. Thus, RNAi is currently being extensively evaluated as a potential therapeutic strategy against malignant gliomas, since surgical, radiological, and chemotherapeutic interventions during the past few decades have done little to improve the poor prognosis rate for patients with these dreaded tumors. This review summarizes the pre-clinical studies that are currently underway to test the validity of RNAi as a potential therapeutic strategy against malignant gliomas, and discusses the potential technical Hurdles that remain to be overcome before the technique can become a promising clinical therapy to combat this frequently lethal disease.

Inhibition of PTTG1 expression by microRNA suppresses proliferation and induces apoptosis of malignant glioma cells

The present study aimed to investigate the role of pituitary tumor-transforming gene 1 (PTTG1) in the proliferation, invasion and apoptosis of human malignant glioma U251 cells. Firstly, 2 microRNAs (miRNAs) targeting PTTG1 messenger (m)RNA were ligated into a pcDNA6.2-GW/EmGFP-miR expression vector. The recombinant plasmids, miRNA-1 and miRNA-2 (miR-2), were transfected into U251 cells using the liposome method. PTTG1 mRNA and protein levels were evaluated using quantitative polymerase chain reaction and western blot analysis. The proliferation and invasion abilities of U251 cells were determined using methylthiazol tetrazolium and Matrigel assays. Flow cytometry analysis with Annexin V/propidium iodide double staining was used to determine the percentage of apoptotic cells. PTTG1 expression was effectively suppressed by miR-2. U251 cell growth was inhibited between 10.7 and 34.7% in the miR-2 group compared with the blank group. The Matrigel assay demonstrated that the percentage of infiltrating U251 cells was significantly lower in the miR-2 group (12.3±1.0%) compared to the blank group (24.7±1.4%; P<0.001) and the negative control group (24.0±2.0%; P<0.05). A higher percentage of apoptotic U251 cells were observed in the miR-2 group compared with the blank group (53.6 vs. 32.4%) using flow cytometry due to cycle arrests at the G2/M phase. The miR-2-transfected U251 cells were subcutaneously injected into nude mice, and these mice possessed a decreased tumor tissue growth rate and higher percentage of apoptotic cells compared with the blank and negative control groups. In conclusion, PTTG1 gene expression in human malignant glioma U251 cells was effectively suppressed by exogenous miR-2. The downregulation of PTTG1 induced glioma cell apoptosis and cell cycle arrest at the G2/M phase, which inhibited cell proliferation, reverse invasion and infiltration of glioma cells.

Involvement of the extrinsic and intrinsic pathways in ultraviolet B-induced apoptosis of corneal epithelial cells

The goal of this study was to elucidate the pathway by which UVB initiates efflux of K(+) and subsequently apoptosis in human corneal limbal epithelial (HCLE) cells. The initial focus of the study was on the extrinsic pathway involving Fas. HCLE cells transfected with Fas siRNA were exposed to 80-150 mJ/cm(2) UVB and incubated in culture medium with 5.5 mM K(+). Knockdown of Fas resulted in limited reduction in UVB-induced caspase-8 and -3 activity. Patch-clamp recordings showed no difference in UVB-induced normalized K(+) currents between Fas transfected and control cells. Knockdown of caspase-8 had no effect on the activation of caspase-3 following UVB exposure, while a caspase-8 inhibitor completely eliminated UVB activation of caspase-3. This suggests that caspase-8 is a robust enzyme, able to activate caspase-3 via residual caspase-8 present after knockdown, and that caspase-8 is directly involved in the UVB activation of caspase-3. Inhibition of caspase-9 significantly decreased the activation of caspases-8 and -3 in response to UVB. Knockdown of Apaf-1, required for activation of caspase-9, resulted in a significant reduction in UVB-induced activation of caspases-9, -8, and -3. Knockdown of Apaf-1 also inhibited intrinsic and UVB-induced levels of apoptosis, as determined by DNA fragmentation measured by TUNEL assay. In UVB exposed cultures treated with caspase-3 inhibitor, the percentage of apoptotic cells was reduced to control levels, confirming the necessity of caspase-3 activation in DNA fragmentation. The lack of effect of Fas knockdown on K(+) channel activation, as well as the limited effect on activation of caspases-8 and -3, strongly suggest that Fas and the extrinsic pathway is not of primary importance in the initiation of apoptosis in response to UVB in HCLE cells. Inhibition of caspase-8 and -3 activation following inhibition of caspase-9, as well as reduction in activation of caspases-9, -8, and -3 and DNA fragmentation in response to Apaf-1 knockdown support the conclusion that the intrinsic pathway is more important in UVB-induced apoptosis in HCLE cells.

Differential effects of erufosine on proliferation, wound healing and apoptosis in colorectal cancer cell lines

The alkylphosphocholine, erucylphospho-N,N, N-trimethylpropanolamine (erufosine), has demonstrated anticancer effects in various cell lines, including leukemia, multiple myeloma, bladder, breast and oral squamous cell carcinoma cells. The purpose of the present study was to investigate its antiproliferative, antimigratory and pro-apoptotic effects in colorectal cancer cell lines, SW480 and CC531. The antiproliferative effect was determined by (3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide) (MTT) dye reduction assay following exposure to erufosine (3.1-100 µM) for 24-72 h. The antimigratory effect of erufosine (1.6-6 µM) was investigated by a wound healing assay for 12-48 h. Caspase-3/-7 activity was measured to detect apoptotic cell death. Erufosine inhibited cell proliferation in a dose- and time-dependent manner. The IC50 values following 72 h of incubation were 3.4 and 25.4 µM for SW480 and CC531 cells, respectively. erufosine at concentrations of 50 and 100 µM induced caspase-3/-7 activity concentration-dependently in SW480 cells, but only at 100 µM in CC531 cells. Incubation of SW480 cells with erufosine (1.56 µM) for 48 h inhibited migration into the scratched area by 54% as compared to the untreated cells; whereas in CC531 cells, the wound width in the erufosine-treated (1.56-6.25 µM) cells following 48 h was closed 2-fold slower than the rate in the untreated group. Erufosine (25 µM) attenuated osteonectin expression and abolished COL1A1 expression in CC531 cells. Erufosine appears to be a promising treatment agent for colorectal cancer. Rat CC531 cells are less sensitive to erufosine than human SW480 cells.

Novel small RNA expression libraries uncover hsa-miR-30b and hsa-miR-30c as important factors in anoikis resistance

MicroRNAs (miRNAs) have been widely studied in order to elucidate their biological functions. MicroRNA microarrays or miRNA overexpression libraries generated by synthesis and cloning of individual miRNAs have been used to study their different roles. In this work, we have developed a novel methodology to express mature miRNAs and other small RNAs from a double convergent RNA polymerase III promoter. We show that the generated miRNAs function similarly to those processed from primary transcripts or pri-miRNAs. This system allowed us to produce a lentiviral library expressing the whole population of small RNAs present in a metastatic cell line. A functional screening using this library led to the identification of hsa-miR-30b and hsa-miR-30c as negative regulators of cell death induced by loss of attachment (anoikis). Importantly, we demonstrated that the acquisition of anoikis resistance via these miRNAs is achieved through down-regulation of caspase 3 expression. Moreover, overexpression of these miRNAs resulted in a decrease of other types of caspase 3-dependent cell death and enhanced the survival of MCF10A acinar cells in morphogenesis assays, suggesting a putative role as oncomirs. In summary, this novel methodology provides a powerful and effective way for identifying novel small RNAs involved in a particular biological process.

A pathway from JNK through decreased ERK and Akt activities for FOXO3a nuclear translocation in response to UV irradiation

Forkhead box O (FOXO) transcription factors play an important role in physiological and pathological processes. Extracellular signal-regulated kinase (ERK) and protein kinase B (Akt) can phosphorylate FOXO and cause its degradation or cytoplasmic retention, respectively, leading to tumorigenesis. In addition, C-Jun N-terminal protein kinase (JNK) can promote FOXO nuclear localization, leading to apoptosis. Using confocal imaging of cells transfected with GFP-FOXO3a, we visualized the dynamic translocation of GFP-FOXO3a from the cytoplasm to the nucleus after UV irradiation in a time- and dose-dependent manner. We also found that UV irradiation caused activation of JNK, which in turn inactivated ERK and Akt, leading to FOXO3a translocation and Bim expression. Our results indicate that nuclear translocation of FOXO3a can be regulated by UV irradiation through the JNK-ERK/Akt pathway.

Erufosine simultaneously induces apoptosis and autophagy by modulating the Akt-mTOR signaling pathway in oral squamous cell carcinoma

We investigated the anticancer activity of erufosine in oral squamous carcinoma cell lines in terms of cell proliferation, colony formation, induction of autophagy/apoptosis, cell cycle and mTOR signaling pathway. Erufosine showed dose-dependent cytotoxicity in all cell lines, it induced autophagy as well as apoptosis, G2 cell cycle arrest and modulation of cyclin D1 expression. Further erufosine downregulated the phosphorylation of major components of mTOR pathway, like p-Akt at Ser473 and Thr308 residues, p-Raptor, p-mTOR, p-PRAS40 and its downstream substrates p-p70S6K and p-4EBP1 in a dose-dependent manner. The pre-treatment of tumor cells with p-mTOR siRNA increased cytotoxic effects of erufosine comparable to cisplatin but higher than rapamycin.

Potential involvement of F0F1-ATP(synth)ase and reactive oxygen species in apoptosis induction by the antineoplastic agent erucylphosphohomocholine in glioblastoma cell lines : a mechanism for induction of apoptosis via the 18 kDa mitochondrial translocator protein

Erucylphosphohomocholine (ErPC3, Erufosine) was reported previously to induce apoptosis in otherwise highly apoptosis-resistant malignant glioma cell lines while sparing their non-tumorigenic counterparts. We also previously found that the mitochondrial 18 kDa Translocator Protein (TSPO) is required for apoptosis induction by ErPC3. These previous studies also suggested involvement of reactive oxygen species (ROS). In the present study we further investigated the potential involvement of ROS generation, the participation of the mitochondrial respiration chain, and the role of the mitochondrial F(O)F(1)-ATP(synth)ase in the pro-apoptotic effects of ErPC3 on U87MG and U118MG human glioblastoma cell lines. For this purpose, cells were treated with the ROS chelator butylated hydroxyanisole (BHA), the mitochondrial respiration chain inhibitors rotenone, antimycin A, myxothiazol, and the uncoupler CCCP. Also oligomycin and piceatannol were studied as inhibitors of the F(O) and F(1) subunits of the mitochondrial F(O)F(1)-ATP(synth)ase, respectively. BHA was able to attenuate apoptosis induction by ErPC3, including mitochondrial ROS generation as determined with cardiolipin oxidation, as well as collapse of the mitochondrial membrane potential (Deltapsi(m)). Similarly, we found that oligomycin attenuated apoptosis and collapse of the Deltapsi(m), normally induced by ErPC3, including the accompanying reductions in cellular ATP levels. Other inhibitors of the mitochondrial respiration chain, as well as piceatannol, did not show such effects. Consequently, our findings strongly point to a role for the F(O) subunit of the mitochondrial F(O)F(1)-ATP(synth)ase in ErPC3-induced apoptosis and dissipation of Deltapsi(m) as well as ROS generation by ErPC3 and TSPO.

VDAC activation by the 18 kDa translocator protein (TSPO), implications for apoptosis

The voltage dependent anion channel (VDAC), located in the outer mitochondrial membrane, functions as a major channel allowing passage of small molecules and ions between the mitochondrial inter-membrane space and cytoplasm. Together with the adenine nucleotide translocator (ANT), which is located in the inner mitochondrial membrane, the VDAC is considered to form the core of a mitochondrial multiprotein complex, named the mitochondrial permeability transition pore (MPTP). Both VDAC and ANT appear to take part in activation of the mitochondrial apoptosis pathway. Other proteins also appear to be associated with the MPTP, for example, the 18 kDa mitochondrial Translocator Protein (TSPO), Bcl-2, hexokinase, cyclophylin D, and others. Interactions between VDAC and TSPO are considered to play a role in apoptotic cell death. As a consequence, due to its apoptotic functions, the TSPO has become a target for drug development directed to find treatments for neurodegenerative diseases and cancer. In this context, TSPO appears to be involved in the generation of reactive oxygen species (ROS). This generation of ROS may provide a link between activation of TSPO and of VDAC, to induce activation of the mitochondrial apoptosis pathway. ROS are known to be able to release cytochrome c from cardiolipins located at the inner mitochondrial membrane. In addition, ROS appear to be able to activate VDAC and allow VDAC mediated release of cytochrome c into the cytosol. Release of cytochrome c from the mitochondria forms the initiating step for activation of the mitochondrial apoptosis pathway. These data provide an understanding regarding the mechanisms whereby VDAC and TSPO may serve as targets to modulate apoptotic rates. This has implications for drug design to treat diseases such as neurodegeneration and cancer.

Synergistic inhibition of mitochondrial respiration by anticancer agent erucylphosphohomocholine and cyclosporin A

Alkylphosphocholines are a new class of anticancer agents. The mechanisms by which these drugs display their antitumor activities are not known. In this work, we show that erucylphosphohomocholine, a new antineoplastic compound, significantly decreased ATP synthesis in isolated rat liver mitochondria at a concentration of 50 microm or higher via permeabilization of the inner membrane. At a concentration of 25 microm, it induced a moderate swelling of mitochondria, a slight decrease of the inner membrane potential, and an increase in state 4 respiration without an essential influence on state 3 respiration or the outer membrane permeability to cytochrome c. We found that cyclosporin A did not prevent mitochondrial swelling induced by 25-100 microm erucylphosphohomocholine. Moreover, cyclosporin A induced a fast drop of the inner membrane potential in the presence of 25-50 microm erucylphosphohomocholine that seems to be due to a strong synergistic inhibition of the respiratory activity. The ratio of uncoupled to state 3 respiration rates increased from 1.3 +/- 0.1 with 25 microm erucylphosphohomocholine and from 1.5 +/- 0.1 with 1 microm cyclosporin A to 4.5 +/- 0.3 in the presence of both drugs. On the other hand, oligomycin or cyclosporin A protected certain cancer cell lines against erucylphosphohomocholine-induced apoptosis. This protection might be related to a prevention of cellular ATP hydrolysis by permeabilized mitochondria and to the inhibition of the classical permeability transition pore, respectively. Our findings provide new insight into the mechanisms by which these unusual alterations of mitochondria might be involved in anticancer activity of alkylphosphocholines.

Influence of co-down-regulation of caspase-3 and caspase-7 by siRNAs on sodium butyrate-induced apoptotic cell death of Chinese hamster ovary cells producing thrombopoietin

Previously, the expression of caspase-3 siRNA could not effectively inhibit sodium butyrate (NaBu)-induced apoptotic cell death of recombinant Chinese hamster ovary (rCHO) cells producing human thrombopoietin (hTPO). Caspase-3 siRNA expressing cells appeared to compensate for the lack of caspase-3 by increasing active caspase-7 levels. For the successful inhibition of NaBu-induced apoptosis of rCHO cells, both caspase-3 and caspase-7 were down-regulated using the siRNA expression vector system. Co-down-regulation of caspase-3 and caspase-7 increased cell viability and extended culture longevity in serum-free culture in the presence or absence of 1mM NaBu addition. In the cultures with 1mM NaBu addition, the maximum hTPO concentration in rCHO cells with down-regulation of both caspases was approximately 55% higher than that in rCHO cells without down-regulation of caspases and approximately 16% higher than rCHO cells with down-regulation of only caspase-3. However, in the culture with 3mM NaBu, this strategy could not dramatically enhance the culture longevity and hTPO production, compared to Bcl-2 overexpression. The different result in hTPO production between down-regulation of caspases and Bcl-2 overexpression may be because the down-regulation of caspase-3 and caspase-7, unlike Bcl-2 overexpression, could not maintain mitochondrial membrane potential in the presence of 3mM NaBu. Taken together, co-down-regulation of caspase-3 and caspase-7 is effective in regard to extension of culture longevity and enhancement of hTPO production in a serum-free culture in the presence or absence of 1mM NaBu addition.

Increased cytotoxicity of ionizing radiation in combination with membrane-targeted apoptosis modulators involves downregulation of protein kinase B/Akt-mediated survival-signaling

BACKGROUND AND PURPOSE

The membrane-targeted apoptosis modulators erucylphosphocholine (ErPC) and erucylphosphohomocholine (ErPC3) induce apoptosis in highly apoptosis resistant malignant glioma cell lines and enhance radiation-induced cell death and eradication of clonogenic tumor cells in vitro. Aim of the present study was to elucidate molecular mechanisms of combined action.

MATERIALS AND METHODS

Induction of apoptosis was evaluated by determination of nuclear morphology (fluorescence microscopy), alteration of mitochondrial function and caspase-activation (flow cytometry, Western blot). Activity of protein kinase B (PKB/Akt) and key downstream effectors involved in apoptosis regulation was verified by Western blot analysis using activation-specific antibodies.

RESULTS

Increased cytotoxicity of the combination was linked to a more efficient activation of the intrinsic apoptosis pathway with increased damage of the mitochondria and caspase-activation. Moreover, activity of the survival kinase PKB/Akt was downregulated upon treatment with ErPC/ErPC3 alone or in combination with ionizing radiation. Inhibition of PKB/Akt was associated with decreased phosphorylation and thus activation of the pro-apoptotic Bcl-2 protein Bad as well as dephosphorylation of the transcription factor FOXO3A (FKHRL1) that may be responsible for the observed increased expression of the pro-apoptotic Bcl-2 protein Bim.

CONCLUSIONS

Our data suggest a role for inhibition of PKB/Akt-mediated anti-apoptotic signaling in increased efficacy of the combination.