pERK, pAkt and pBad: A Possible Role in Cell Proliferation and Sustained Cellular Survival During Tumorigenesis and Tumor Progression in ENU Induced Transplacental Glioma Rat Model

A modular microfluidic platform to study how fluid shear stress alters estrogen receptor phenotype in ER+ breast cancer cells

Metastatic breast cancer leads to poor prognoses and worse outcomes in patients due to its invasive behavior and poor response to therapy. It is still unclear what biophysical and biochemical factors drive this more aggressive phenotype in metastatic cancer; however recent studies have suggested that exposure to fluid shear stress in the vasculature could cause this. In this study a modular microfluidic platform capable of mimicking the magnitude of fluid shear stress (FSS) found in human vasculature was designed and fabricated. This device provides a platform to evaluate the effects of FSS on MCF-7 cell line, an estrogen receptor positive (ER+) breast cancer cell line, during circulation in the vessels. Elucidation of the effects of FSS on MCF-7 cells was carried out utilizing two approaches: single cell analysis and bulk analysis. For single cell analysis, cells were trapped in a microarray after exiting the serpentine channel and followed by immunostaining on the device (on-chip). Bulk analysis was performed after cells were collected in a microtube at the outlet of the microfluidic serpentine channel for western blotting (off-chip). It was found that cells exposed to an FSS magnitude of 10 dyn/cm2 with a residence time of 60 s enhanced expression of the proliferation marker Ki67 in the MCF-7 cell line at a single cell level. To understand possible mechanisms for enhanced Ki67 expression, on-chip and off-chip analyses were performed for pro-growth and survival pathways ERK, AKT, and JAK/STAT. Results demonstrated that after shearing the cells phosphorylation of p-AKT, p-mTOR, and p-STAT3 were observed. However, there was no change in p-ERK1/2. AKT is a mediator of ER rapid signaling, analysis of phosphorylated ERα was carried out and no significant differences between sheared and non-sheared populations were observed. Taken together these results demonstrate that FSS can increase phosphorylation of proteins associated with a more aggressive phenotype in circulating cancer cells. These findings provide additional information that may help inform why cancer cells located at metastatic sites are usually more aggressive than primary breast cancer cells.

The Essential Role of microRNAs in Inflammatory and Autoimmune Skin Diseases-A Review

The etiopathogenesis of autoimmune skin diseases is complex and still not fully understood. The role of epigenetic factors is emphasized in the development of such diseases. MicroRNAs (miRNAs), a group of non-coding RNAs (ncRNAs-non-coding RNAs), are one of the important post-transcriptional epigenetic factors. miRNAs have a significant role in the regulation of the immune response by participating in the process of the differentiation and activation of B and T lymphocytes, macrophages, and dendritic cells. Recent advances in research on epigenetic factors have provided new insights into the pathogenesis and potential diagnostic and therapeutic targets of many pathologies. Numerous studies revealed a change in the expression of some microRNAs in inflammatory skin disorders, and the regulation of miRNA expression is a promising therapeutic goal. This review presents the state of the art regarding changes in the expression and role of miRNAs in inflammatory and autoimmune skin diseases, including psoriasis, atopic dermatitis, vitiligo, lichen planus, hidradenitis suppurativa, and autoimmune blistering diseases.

PODNL1 Methylation Serves as a Prognostic Biomarker and Associates with Immune Cell Infiltration and Immune Checkpoint Blockade Response in Lower-Grade Glioma

Lower-grade glioma (LGG) is a diffuse infiltrative tumor of the central nervous system, which lacks targeted therapy. We investigated the role of Podocan-like 1 (PODNL1) methylation in LGG clinical outcomes using the TCGA-LGG transcriptomics dataset. We identified four PODNL1 CpG sites, cg07425555, cg26969888, cg18547299, and cg24354933, which were associated with unfavorable overall survival (OS) and disease-free survival (DFS) in univariate and multivariate analysis after adjusting for age, gender, tumor-grade, and IDH1-mutation. In multivariate analysis, the OS and DFS hazard ratios ranged from 0.44 to 0.58 (p < 0.001) and 0.62 to 0.72 (p < 0.001), respectively, for the four PODNL1 CpGs. Enrichment analysis of differential gene and protein expression and analysis of 24 infiltrating immune cell types showed significantly increased infiltration in LGGs and its histological subtypes with low-methylation levels of the PODNL1 CpGs. High PODNL1 expression and low-methylation subgroups of the PODNL1 CpG sites were associated with significantly increased PD-L1, PD-1, and CTLA4 expressions. PODNL1 methylation may thus be a potential indicator of immune checkpoint blockade response, and serve as a biomarker for determining prognosis and immune subtypes in LGG.

miRNAs Flowing Up and Down: The Concerto of Psoriasis

Psoriasis is a chronic immune-mediated skin disease, whose hallmarks include keratinocyte hyperproliferation and CD4⁺ T cell subsets imbalance. Dysregulated microRNAs (miRNAs) identified in psoriasis have been shown to affect keratinocyte and T cell functions, with studies on the molecular mechanisms and intrinsic relationships of the miRNAs on the way. Here, we focus on the dysregulated miRNAs that contribute to the two hallmarks of psoriasis with the miRNA target genes confirmed. We review a network, in which, upregulated miR-31/miR-203/miR-155/miR-21 and downregulated miR-99a/miR-125b facilitate the excessive proliferation and abnormal differentiation of psoriatic keratinocytes; upregulated miR-210 and downregulated miR-138 work in concert to distort CD4⁺ T cell subsets balance in psoriasis. The miRNAs exert their functions through regulating key psoriasis-associated transcription factors including NF-κB and STAT3. Whether flowing up or down, these miRNAs collaborate to promote the development and maintenance of psoriasis.

The role of inflammation in subventricular zone cancer

The adult subventricular zone (SVZ) stem cell niche has proven vital for discovering neurodevelopmental mechanisms and holds great potential in medicine for neurodegenerative diseases. Yet the SVZ holds a dark side - it can become tumorigenic. Glioblastomas can arise from the SVZ via cancer stem cells (CSCs). Glioblastoma and other brain cancers often have dismal prognoses since they are resistant to treatment. In this review we argue that the SVZ is susceptible to cancer because it contains stem cells, migratory progenitors and unusual inflammation. Theoretically, SVZ stem cells can convert to CSCs more readily than can postmitotic neural cells. Additionally, the robust long-distance migration of SVZ progenitors can be subverted upon tumorigenesis to an infiltrative phenotype. There is evidence that the SVZ, even in health, exhibits chronic low-grade cellular and molecular inflammation. Its inflammatory response to brain injuries and disease differs from that of other brain regions. We hypothesize that the SVZ inflammatory environment can predispose cells to novel mutations and exacerbate cancer phenotypes. This can be studied in animal models in which human mutations related to cancer are knocked into the SVZ to induce tumorigenesis and the CSC immune interactions that precede full-blown cancer. Importantly inflammation can be pharmacologically modulated providing an avenue to brain cancer management and treatment. The SVZ is accessible by virtue of its location surrounding the lateral ventricles and CSCs in the SVZ can be targeted with a variety of pharmacotherapies. Thus, the SVZ can yield aggressive tumors but can be targeted via several strategies.

MiR-155 promotes cell proliferation and inhibits apoptosis by PTEN signaling pathway in the psoriasis

MicroRNAs (miRNAs) have been demonstrated to contribute to malignant progression in psoriasis development. The purposes of the study was to evaluated the effects of miRNA-155 on cell proliferation, migration and apoptosis in psoriasis development via PTEN singaling pathway and identify its direct target protein. Quantitative real-time RT-PCR (qRT-PCR) was performed to examine the level of miR-155 in psoriasis cells, miR-155 was downregulated in a psoriasis cell line Hacat by transfected with small interfering RNA (siRNA), respectively. Cell survival was detected by the MTT assay and colony formation assay. Cell migration and invasion were measured via wound-healing assayand transwell assay. In addition, cell cycle and apoptosis about psoriasis cells was measured by flow cytometry. In this study, qRT-PCR assay showed that the expressions of miR-155 mRNA in psoriasis tissues were significantly higher than that in normal tissues. The assays about cell growth and proliferation showed that miR-155 knockdown led to a significant decrease in cell proliferation which was determined by MTT assay and colony formation assay compared to those of Lv-NC cells. Flow cytometry analysis showed that depletion of miR-155 could cause cell cycle change and the number of apoptotic cells was significantly increased in Lv-miR155 cells compared with control cells. In addition, the expression of several apoptosis-related factors were dramatically changed, such as PTEN, PIP₃, AKT, p-AKT, Bax and Bcl-2. Our findings indicate that down-regulation of miR-155 significantly inhibits proliferation, migration, invasion and promotes apoptosis through PTEN singaling pathway in psoriasis cells. miR-155 might function as an oncogene miRNA in the progress of psoriasis.

Pro-apoptotic effects of rHSG on C6 glioma cells

Our previous in vitro study demonstrated that the rat hyperplasia suppressor gene (rHSG) inhibited the proliferation of C6 cells. In the present study, we investigated further the effects of rHSG overexpression on the apoptosis of C6 cells and the possible pathways involved. Hoechst 33342/PI double staining and comet assay were used to examine the morphological characteristics of apoptosis and to examine the effects of rHSG on the apoptosis of the C6 cells. Western blot analysis was used to determine the effects of rHSG overexpression on the protein expression levels of poly(ADP-ribose) polymerase (PARP), cleaved caspase-3, phosphorylated extracellular signal-regulated kinase 1/2 (p-Erk1/2), phosphorylated Akt (p-Akt) and phosphoinositide 3-kinase (PI3K)/Akt, as well as on the mitogen-activated protein kinase (MAPK) pathways induced by insulin-like growth factor (IGF)-1. Our results revealed that the C6 cells transfected with the rHSG adenoviral vector (Adv-rHSG-GFP group) efficiently expressed rHSG protein; Hoechst 33342/PI double staining and comet assay revealed that rHSG increased C6 cell apoptosis and induced DNA damage. Western blot analysis indicated that rHSG overexpression significantly increased the level of full-length PARP at 24 and 72 h (P<0.01), but decreased the level at 48 h following transfection (P<0.01), while the proteins levels of cleaved PARP and cleaved caspase-3 increased significantly (P<0.01). The protein expression of p-Erk1/2 and p-Akt began to decrease at 48 h post-transfection (P<0.01). In addition, the protein levels of Akt and Erk1/2 induced by IGF-1 were significantly inhibited. On the whole, the findings of the present study demonstrate that rHSG overexpression induces the apoptosis of rat glioma cells, and that these effects may involve the PI3K/Akt and MAPK pathways.

Identification of a Novel lincRNA-p21-miR-181b-PTEN Signaling Cascade in Liver Fibrosis

Previously, we found that long intergenic noncoding RNA-p21 (lincRNA-p21) inhibits hepatic stellate cell (HSC) activation and liver fibrosis via p21. However, the underlying mechanism of the antifibrotic role of lincRNA-p21 in liver fibrosis remains largely unknown. Here, we found that lincRNA-p21 expression was significantly downregulated during liver fibrosis. In LX-2 cells, the reduction of lincRNA-p21 induced by TGF-β1 was in a dose- and time-dependent manner. lincRNA-p21 expression was reduced in liver tissues from patients with liver cirrhosis when compared with that of healthy controls. Notably, lincRNA-p21 overexpression contributed to the suppression of HSC activation. lincRNA-p21 suppressed HSC proliferation and induced a significant reduction in α-SMA and type I collagen. All these effects induced by lincRNA-p21 were blocked down by the loss of PTEN, suggesting that lincRNA-p21 suppressed HSC activation via PTEN. Further study demonstrated that microRNA-181b (miR-181b) was involved in the effects of lincRNA-p21 on HSC activation. The effects of lincRNA-p21 on PTEN expression and HSC activation were inhibited by miR-181b mimics. We demonstrated that lincRNA-p21 enhanced PTEN expression by competitively binding miR-181b. In conclusion, our results disclose a novel lincRNA-p21-miR-181b-PTEN signaling cascade in liver fibrosis and suggest lincRNA-p21 as a promising molecular target for antifibrosis therapy.

Anti-VEGFR2 driven nuclear translocation of VEGFR2 and acquired malignant hallmarks are mutation dependent in glioblastoma

OBJECTIVE

Anti-angiogenic therapies (AATs), targeting VEGF-VEGFR pathways, are being used as an adjuvant to normalize glioblastoma (GBM) vasculature. Unexpectedly, clinical trials have witnessed transient therapeutic effect followed by aggressive tumor recurrence. In pre-clinical studies, targeting VEGFR2 with vatalanib, increased GBM growth under hypoxic microenvironment. There is limited understanding of these unanticipated results. Here, we investigated tumor cell associated phenotypes in response to VEGFR2 blockade.

METHODS

Human U251 cells were orthotopically implanted in mice (day 0) and were treated with vehicle or vatalanib on day 8. Tumor specimens were collected for immunohistochemistry and protein array. Nuclear translocation of VEGFR2 was analyzed through IHC and western blot. In vitro studies were performed in U251 (p53 and EGFR mutated) and U87 (p53 and EGFR wildtype) cells following vehicle or vatalanib treatments under normoxia (21% O₂) and hypoxia (1% O₂). Proliferation, cell cycle and apoptosis assays were done to analyze tumor cell phenotypes after treatments.

RESULTS

Vatalanib treated animals displayed distinct patterns of VEGFR2 translocation into nuclear compartment of U251 tumor cells. In vitro studies suggest that vatalanib significantly induced nuclear translocation of VEGFR2, characterized in chromatin bound fraction, especially in U251 tumor cells grown under normoxia and hypoxia. Anti-VEGFR2 driven nuclear translocation of VEGFR2 was associated with increased cell cycle and proliferation, decreased apoptosis, and displayed increased invasiveness in U251 compared to U87 cells.

CONCLUSIONS

Study suggests that AAT- induced molecular and phenotypic alterations in tumor cells are associated with mutation status and are responsible for aggressive tumor growth. Therefore, mutation status of the tumor in GBM patients should be taken in to consideration before applying targeted therapy to overcome unwanted effects.

Curcumin up-regulates phosphatase and tensin homologue deleted on chromosome 10 through microRNA-mediated control of DNA methylation--a novel mechanism suppressing liver fibrosis

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) has been reported to play a role in the suppression of activated hepatic stellate cells (HSCs). Moreover, it has been demonstrated that hypermethylation of the PTEN promoter is responsible for the loss of PTEN expression during HSC activation. Methylation is now established as a fundamental regulator of gene transcription. MicroRNAs (miRNAs), which can control gene expression by binding to their target genes for degradation and/or translational repression, were found to be involved in liver fibrosis. However, the mechanism responsible for miRNA-mediated epigenetic regulation in liver fibrosis still remained unclear. In the present study, curcumin treatment significantly resulted in the inhibition of cell proliferation and an increase in the apoptosis rate through the up-regulation of PTEN associated with a decreased DNA methylation level. Only DNA methyltransferase 3b (DNMT3b) was reduced in vivo and in vitro after curcumin treatment. Further studies were performed aiming to confirm that the knockdown of DNMT3b enhanced the loss of PTEN methylation by curcumin. In addition, miR-29b was involved in the hypomethylation of PTEN by curcumin. MiR-29b not only was increased by curcumin in activated HSCs, but also was confirmed to target DNMT3b by luciferase activity assays. Curcumin-mediated PTEN up-regulation, DNMT3b down-regulation and PTEN hypomethylation were all attenuated by miR-29b inhibitor. Collectively, it is demonstrated that curcumin can up-regulate miR-29b expression, resulting in DNMT3b down-regulation in HSCs and epigenetically-regulated PTEN involved in the suppression of activated HSCs. These results indicate that miRNA-mediated epigenetic regulation may be a novel mechanism suppressing liver fibrosis.

The adenosine A3 receptor agonist Cl-IB-MECA induces cell death through Ca²⁺/ROS-dependent down regulation of ERK and Akt in A172 human glioma cells

Adenosine A(3) receptor (A3AR) is coupled to G proteins that are involved in a variety of intracellular signaling pathways and physiological functions. 2-Chloro-N(6)-(3-iodobenzyl) adenosine-5'-N-methylcarboxamide (Cl-IB-MECA), an agonist of A3AR, has been reported to induce cell death in various cancer cells. However, the effect of CI-IB-MECA on glioma cell growth is not clear. This study was undertaken to examine the effect of CI-IB-MECA on glioma cell viability and to determine its molecular mechanism. CI-IB-MECA inhibited cell proliferation and induced cell death in a dose- and time-dependent manner. Treatment of CI-IB-MECA resulted in an increase in intracellular Ca(2+) followed by enhanced reactive oxygen species (ROS) generation. EGTA and N-acetylcysteine (NAC) blocked the cell death induced by CI-IB-MECA, suggesting that Ca(2+) and ROS are involved in the Cl-IB-MECA-induced cell death. Western blot analysis showed that CI-IB-MECA induced the down-regulation of extracellular signal-regulated kinases (ERK) and Akt, which was prevented by EGTA, NAC, and the A3AR antagonist MRS1191. Transfection of constitutively active forms of MEK, the upstream kinase of ERK, and Akt prevented the cell death. CI-IB-MECA induced caspase-3 activation and the CI-IB-MECA-induced cell death was blocked by the caspase inhibitors DEVD-CHO and z-VAD-FMK. In addition, expression of XIAP and Survivin were decreased in cells treated with Cl-IB-MECA. Collectively, these findings demonstrate that CI-IB-MECA induce a caspase-dependent cell death through suppression of ERK and Akt mediated by an increase in intracellular Ca(2+) and ROS generation in human glioma cells. These suggest that A3AR agonists may be a potential therapeutic agent for induction of apoptosis in human glioma cells.

DNMT1-mediated PTEN hypermethylation confers hepatic stellate cell activation and liver fibrogenesis in rats

Hepatic stellate cell (HSC) activation is an essential event during liver fibrogenesis. Phosphatase and tension homolog deleted on chromosome 10 (PTEN), a tumor suppressor, is a negative regulator of this process. PTEN promoter hypermethylation is a major epigenetic silencing mechanism in tumors. The present study aimed to investigate whether PTEN promoter methylation was involved in HSC activation and liver fibrosis. Treatment of activated HSCs with the DNA methylation inhibitor 5-aza-2'-deoxycytidine (5-azadC) decreased aberrant hypermethylation of the PTEN gene promoter and prevented the loss of PTEN expression that occurred during HSC activation. Silencing DNA methyltransferase 1 (DNMT1) gene also decreased the PTEN gene promoter methylation and upregulated the PTEN gene expression in activated HSC-T6 cells. In addition, knockdown of DNMT1 inhibited the activation of both ERK and AKT pathways in HSC-T6 cells. These results suggest that DNMT1-mediated PTEN hypermethylation caused the loss of PTEN expression, followed by the activation of the PI3K/AKT and ERK pathways, resulting in HSC activation.

The proteasome inhibitor MG-132 induces AIF nuclear translocation through down-regulation of ERK and Akt/mTOR pathway

Anticancer activity of proteasome inhibitors has been demonstrated in various cancer cell types. However, mechanisms by which they exert anticancer action were not fully understood. The present study was undertaken to examine the effect of the proteasome inhibitor MG-132 and the underlying mechanism in glioma cells. MG-132 caused alterations in mitochondrial membrane potential and apoptosis-inducing factor (AIF) nuclear translocation. MG-132 induced reduction in ERK and Akt activation. The transient transfection of constitutively active forms of MEK, an upstream of ERK, and Akt blocked the MG-132-induced cell death. Similarly to down-regulation of Akt, expression levels of mTOR were inhibited by MG-132. Addition of rapamycin, an inhibitor of mTOR, caused stimulation of the MG-132-induced cell death. There were no significant changes in levels of XIAP, survivin, and Bax. Overexpression of constitutively active forms of MEK and Akt blocked the MG-132-induced AIF nuclear translocation. These findings indicate that MG-132 induces AIF nuclear translocation through down-regulation of ERK and Akt/mTOR pathways. These data suggest that proteasome inhibitors may serve as potential therapeutic agents for malignant human gliomas.

c-Jun N terminal kinases (JNK) are activated in the brain during the pathology of experimental cerebral malaria

Experimental cerebral malaria (ECM) resulting from Plasmodium berghei ANKA (PbA) infection in C57BL/6J mice manifests cell death in the brain. However, the precise molecular and biochemical mechanisms regulating cell death during ECM remains unknown. In this study we have examined, the role of a stress activated protein kinase called c-Jun N terminal kinase during the pathology of ECM. We report in this study, for the first time the activation of all key elements in the JNK pathway like p-MKK4, p-JNK and p-c-Jun in mouse brain during ECM. Concomitant with such activation was the up regulation of p-JNK and its translocation into the nucleus leading to the phosphorylation of its major substrate c-Jun. These observations show the neuronal induction of p-JNK and its critical role as a mediator in neuronal cell death during ECM.

Immunohistochemical Characterization of Canine Neuroepithelial Tumors

The expression of cell differentiation and proliferation markers of canine neuroepithelial tumors was examined immunohistochemically to identify the histogenesis of these tumors. Astrocytomas ( n = 4) consisted of cells positive for glial fibrillary acidic protein (GFAP) and nestin and a few cells positive for doublecortin (DCX). Immunoreactive cells for receptor tyrosine kinases (epidermal growth factor receptor and c-erbB2) and their downstream molecules (phospho-extracellular signal-regulated kinase 1/2 and phospho-Akt) were often detected in astrocytomas, especially in medium- and high-grade tumors. Gliomatosis cerebri ( n = 3) consisted of cells positive for ionized calcium–binding adaptor molecule 1 and GFAP, including a minor population of cells positive for nestin, DCX, and beta III tubulin, suggesting their glial differentiation. In choroid plexus tumors ( n = 4), most tumor cells were positive for cytokeratins AE1/AE3 and 18, and few were positive for GFAP. The majority of cells of oligodendrogliomas ( n = 5) were DCX positive, but the tumors also contained minor populations of cells positive for GFAP, nestin, or beta III tubulin. Primitive neuroectodermal tumors (PNETs; n = 2) consisted of heterogeneous cell populations, and the tumor cells were positive for nestin, beta III tubulin, and DCX, suggesting glial and neuronal differentiation. The major population of neuroblastoma cells ( n = 3) were positive for beta III tubulin and DCX, suggesting single neuronal differentiation. As for antiapoptotic cell death molecules, most tumor cells in the choroid plexus tumors, PNETs, and neuroblastomas were intensely positive for Bcl-2 and Bcl-xL, whereas those in gliomatosis cerebri were almost negative. In astrocytomas, Bcl-xL-positive cells predominated over Bcl-2-positive cells, but the opposite was observed in oligodendrogliomas. The immunohistochemical results were analyzed by hierarchical clustering, and the constructed dendrogram clearly indicated a novel position of oligodendrogliomas: the primitive glial and neuronal differentiation.

Wnt/beta-catenin/Tcf signaling pathway activation in malignant progression of rat gliomas induced by transplacental N-ethyl-N-nitrosourea exposure

Although Wnt/beta-catenin/Tcf signaling pathway has been shown to be a crucial factor in the development of many cancers, little is known about its role in glioma malignancy. In the present study, we report the first evidence that Wnt/beta-catenin/Tcf signaling pathway is constitutively activated in experimental gliomas induced by single transplacental dose of N-ethyl-N-nitrosourea (ENU). In the present study we analyzed ENU induced rat gliomas of different stages (P90, P135 and P180) for the expression of beta-catenin, Lef1, Tcf4 and their targets c-Myc, N-Myc and cyclin D1. Western blot analysis revealed upregulation of beta-catenin, Lef1, Tcf4, c-Myc, N-Myc and cyclin D1 in gliomas compared to controls and their levels were progressively increased from initial stage (P90) to progression stage (P180). In consistent with this, immunohistochemistry revealed the cytoplasmic and nuclear accumulation of beta-catenin, and nuclear positivity was evident for Lef1, Tcf4, c-Myc, N-Myc and cyclin D1. Based on these results, we conclude that Wnt/beta-catenin pathway may play a major role in the tumorigenesis and tumor progression in ENU induced rat gliomas.

Underlying mechanism of quercetin-induced cell death in human glioma cells

There has been considerable interest in recent years in the anti-tumor activities of flavonoids. Quercetin, a ubiquitous bioactive flavonoid, can inhibit proliferation and induce apoptosis in a variety of cancer cells. However, the precise molecular mechanism by which quercetin induces apoptosis in cancer cells is poorly understood. The present study was undertaken to examine the effect of quercetin on cell viability and to determine its underlying mechanism in human glioma cells. Quercetin resulted in loss of cell viability in a dose- and time-dependent manner and the decrease in cell viability was mainly attributed to cell death. Quercetin did not increase reactive oxygen species (ROS) generation and the quercetin-induced cell death was also not affected by antioxidants, suggesting that ROS generation is not involved in loss of cell viability. Western blot analysis showed that quercetin treatment caused rapid reduction in phosphorylation of extracellular signal-regulated kinase (ERK) and Akt. Transient transfection with constitutively active forms of MEK and Akt protected against the quercetin-induced loss of cell viability. Quercetin-induced depolarization of mitochondrial membrane potential. Caspase activity was stimulated by quercetin and caspase inhibitors prevented the quercetin-induced loss of cell viability. Quercetin resulted in a decrease in expression of survivin, antiapoptotic proteins. Taken together, these findings suggest that quercetin results in human glioma cell death through caspase-dependent mechanisms involving down-regulation of ERK, Akt, and survivin.