Glycogen synthase kinase-3 inhibition induces glioma cell death through c-MYC, nuclear factor-kappaB, and glucose regulation

CG0009, a novel glycogen synthase kinase 3 inhibitor, induces cell death through cyclin D1 depletion in breast cancer cells

Glycogen synthase kinase 3α/β (GSK3α/β) is a constitutively active serine/threonine kinase involved in multiple physiological processes, such as protein synthesis, stem cell maintenance and apoptosis, and acts as a key suppressor of the Wnt-β-catenin pathway. In the present study, we examined the therapeutic potential of a novel GSK3 inhibitor, CG0009, in the breast cancer cell lines, BT549, HS578T, MDA-MB-231, NCI/ADR-RES, T47D, MCF7 and MDA-MB-435, from the NCI-60 cancer cell line panel. Assessment of cytotoxicity, apoptosis and changes in estrogen-signaling proteins was performed using cell viability assays, Western blotting and quantitative real-time PCR. CG0009 enhanced the inactivating phosphorylation of GSK3α at Ser21 and GSK3β at Ser9 and simultaneously decreased activating phosphorylation of GSK3β at Tyr216, and induced caspase-dependent apoptosis independently of estrogen receptor α (ERα) expression status, which was not observed with the other GSK3 inhibitors examined, including SB216763, kenpaullone and LiCl. CG0009 treatment (1 µmol/L) completely ablated cyclin D1 expression in a time-dependent manner in all the cell lines examined, except T47D. CG0009 alone significantly activated p53, leading to relocation of p53 and Bax to the mitochondria. GSK3 inhibition by CG0009 led to slight upregulation of the β-catenin target genes, c-Jun and c-Myc, but not cyclin D1, indicating that CG0009-mediated cyclin D1 depletion overwhelms the pro-survival signal of β-catenin, resulting in cell death. Our findings suggest that the novel GSK3 inhibitor, CG0009, inhibits breast cancer cell growth through cyclin D1 depletion and p53 activation, and may thus offer an innovative therapeutic approach for breast cancers resistant to hormone-based therapy.

Wnt activation promotes neuronal differentiation of glioblastoma

One of the biggest challenges in tumour research is the possibility to reprogram cancer cells towards less aggressive phenotypes. In this study, we reprogrammed primary Glioblastoma multiforme (GBM)-derived cells towards a more differentiated and less oncogenic phenotype by activating the Wnt pathway in a hypoxic microenvironment. Hypoxia usually correlates with malignant behaviours in cancer cells, but it has been recently involved, together with Wnt signalling, in the differentiation of embryonic and neural stem cells. Here, we demonstrate that treatment with Wnt ligands, or overexpression of β-catenin, mediate neuronal differentiation and halt proliferation in primary GBM cells. An hypoxic environment cooperates with Wnt-induced differentiation, in line with our finding that hypoxia inducible factor-1α (HIF-1α) is instrumental and required to sustain the expression of β-catenin transcriptional partners TCF-1 and LEF-1. In addition, we also found that Wnt-induced GBM cell differentiation inhibits Notch signalling, and thus gain of Wnt and loss of Notch cooperate in the activation of a pro-neuronal differentiation program. Intriguingly, the GBM sub-population enriched of cancer stem cells (CD133⁺ fraction) is the primary target of the pro-differentiating effects mediated by the crosstalk between HIF-1α, Wnt, and Notch signalling. By using zebrafish transgenics and mutants as model systems to visualize and manipulate in vivo the Wnt pathway, we confirm that Wnt pathway activation is able to promote neuronal differentiation and inhibit Notch signalling of primary human GBM cells also in this in vivo set-up. In conclusion, these findings shed light on an unsuspected crosstalk between hypoxia, Wnt and Notch signalling in GBM, and suggest the potential to manipulate these microenvironmental signals to blunt GBM malignancy.

Time-lapse imaging of neuroblastoma cells to determine cell fate upon gene knockdown

Neuroblastoma is the most common extra-cranial solid tumor of early childhood. Standard therapies are not effective in case of poor prognosis and chemotherapy resistance. To improve drug therapy, it is imperative to discover new targets that play a substantial role in tumorigenesis of neuroblastoma. The mitotic machinery is an attractive target for therapeutic interventions and inhibitors can be developed to target mitotic entry, spindle apparatus, spindle activation checkpoint, and mitotic exit. We present an elaborate analysis pipeline to determine cancer specific therapeutic targets by first performing a focused gene expression analysis to select genes followed by a gene knockdown screening assay of live cells. We interrogated gene expression studies of neuroblastoma tumors and selected 240 genes relevant for tumorigenesis and cell cycle. With these genes we performed time-lapse screening of gene knockdowns in neuroblastoma cells. We classified cellular phenotypes and used the temporal context of the perturbation effect to determine the sequence of events, particularly the mitotic entry preceding cell death. Based upon this phenotype kinetics from the gene knockdown screening, we inferred dynamic gene functions in mitosis and cell proliferation. We identified six genes (DLGAP5, DSCC1, SMO, SNRPD1, SSBP1, and UBE2C) with a vital role in mitosis and these are promising therapeutic targets for neuroblastoma. Images and movies of every time point of all screened genes are available at https://ichip.bioquant.uni-heidelberg.de.

PANC-1 cells proliferative response to ionizing radiation is related to GSK-3β phosphorylation

Radiotherapy may be used to treat pancreatic cancer and relieve pain. We have previously reported that histamine modulates pancreatic adenocarcinoma PANC-1 cell proliferation. This work was aimed to evaluate whether histamine improves radiosensitivity of PANC-1 cells in relation to phosphorylation/inhibition of glycogen synthase kinase-3β (GSK-3β). Immediately after γ irradiation, intracellular hydrogen peroxide was markedly decreased together with a rapid increase in catalase activity. Although histamine diminished catalase activity in nonirradiated cells, it only partially hindered the increase observed in irradiated cells and could not modify radiosensitivity. In control cells, a high expression of total and a very low expression of phosphorylated/inactive GSK-3β were found. An increment in reactive oxygen species levels produced an augmentation in GSK-3β phosphorylation and suppressed cell proliferation. In both control and histamine-treated irradiated cells, the rise in catalase activity lowered reactive oxygen species levels and only a small increase in phosphorylated GSK-3β was detected. Alternatively, 3-aminotriazole, an irreversible inhibitor of catalase, reduced the survival fraction in irradiated control cells along with an increment in phosphorylated GSK-3β. These results suggest that upon irradiation, early catalase activation may be responsible for keeping GSK-3β active conceding cells a survival advantage toward cytotoxic effects of ionizing radiation.

The glycogen synthase kinase-3β/nuclear factor-kappa B pathway is involved in cinobufagin-induced apoptosis in cultured osteosarcoma cells

Cinobufagin, a major component of cinobufacini (huachansu), is an important cardenolidal steroid. Several studies have suggested that cinobufagin has potent anti-cancer effects. The present study examines the apoptosis-inducing activity and the underlying mechanism of action of cinobufagin in osteosarcoma (OS) cells. Our results showed that cinobufagin potently inhibited the proliferation of U2OS, MG63 and SaOS-2 cells. Significant increases in G2/M cell-cycle arrest and apoptosis in OS cells were also observed. The expression levels of several apoptotic proteins were assessed after cinobufagin treatment in U2OS cells. Among them, xIAP, cIAP-1, survivin and Bcl-2 levels decreased remarkably, while the levels of Bax and cleaved-PARP increased. Furthermore, we validated the inhibition of GSK-3β/NF-κB signaling following cinobufagin treatment. Western blots showed a decrease in nuclear p65 protein expression after exposure to different concentrations of cinobufagin, while the phosphorylation of GSK-3β was simultaneously increased. Transduction with constitutively active forms of GSK-3β could protect against the downregulation of p65 and upregulation of cleaved-PARP that are induced by cinobufagin treatment. However, combined treatment with cinobufagin and SB216367 resulted in a significant reduction in p65 and an increase in cleaved-PARP in U2OS cells. Altogether, these results show that cinobufagin is a promising agent for the treatment of OS. These studies are the first to reveal the involvement of the GSK-3β/NF-κB pathway in cinobufagin-induced apoptosis.

Capsazepine, a TRPV1 antagonist, sensitizes colorectal cancer cells to apoptosis by TRAIL through ROS-JNK-CHOP-mediated upregulation of death receptors

A major problem in clinical trials of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) as cancer therapy is the development of resistance to TRAIL. Therefore, agents that can overcome TRAIL resistance have great therapeutic potential. In this study, we evaluated capsazepine, a TRPV1 antagonist, for its ability to sensitize human colon cancer cells to TRAIL-induced apoptosis. Capsazepine potentiated the effect of TRAIL, as shown by its effect on intracellular esterase activity; activation of caspase-8,-9, and -3; and colony-formation assay. Capsazepine induced death receptors (DRs) DR5 and DR4, but not decoy receptors, at the transcriptional level and in a non-cell-type-specific manner. DR induction was dependent on CCAAT/enhancer-binding protein homologous protein (CHOP), as shown by (a) the induction of CHOP by capsazepine and (b) the abolition of DR- and potentiation of TRAIL-induced apoptosis by CHOP gene silencing. CHOP induction was also reactive oxygen species (ROS)-dependent, as shown by capsazepine's ability to induce ROS and by the quenching of ROS by N-acetylcysteine or glutathione, which prevented induction of CHOP and DR5 and consequent sensitization to TRAIL. Capsazepine's effects appeared to be mediated via JNK, as shown by capsazepine's ability to induce JNK and by the suppression of both CHOP and DR5 activation by inhibition of JNK. Furthermore, ROS sequestration abrogated the activation of JNK. Finally, capsazepine downregulated the expression of various antiapoptotic proteins (e.g., cFLIP and survivin) and increased the expression of proapoptotic proteins (e.g., Bax and p53). Together, our results indicate that capsazepine potentiates the apoptotic effects of TRAIL through downregulation of cell survival proteins and upregulation of death receptors via the ROS-JNK-CHOP-mediated pathway.

Lithium exacerbates hepatic ischemia/reperfusion injury by inhibiting GSK-3β/NF-κB-mediated protective signaling in mice

Lithium (an inhibitor of GSK-3β activity) has beneficial effects on ischemia/reperfusion (I/R) injury in the central nervous system, heart and kidney. However, the role of lithium in hepatic I/R injury is unknown. The aim of this study was to assess the effects of lithium on hepatic I/R injury in a mouse model of partial hepatic I/R. Previous studies showed that lithium chloride (LiCl) can phosphorylate residue Ser9, inhibit GSK-3β activity, and improve I/R injury in other organs. In the present study, mice were pretreated with either vehicle or LiCl, which had similar effects on GSK-3β activity. Surprisingly, treatment with LiCl significantly exacerbated hepatic I/R injury, which was determined by serological and histological analyses. Acute and chronic LiCl treatment caused serious damage in hepatic I/R injury, including increased apoptosis and oxidative stress. To gain insight into the mechanism involved in this damage, the activity of nuclear factor-κB (NF-κB) (GSK-3β can regulate the transcriptional complex of NF-κB) was analyzed, which revealed that LiCl treatment significantly down-regulated the activity of NF-κB. The NF-κB-mediated protective genes were then further evaluated, including anti-apoptotic genes (RAF2, cIAP 2, Bfl-1 and cFLIP) and the antioxidant gene MnSOD. The expression of these protective genes was obviously suppressed compared with the vehicle group. Taken together, these findings show that lithium exacerbates hepatic I/R injury by suppressing the expression of GSK-3β/NF-κB-mediated protective genes.

Gliomagenesis arising from Pten- and Ink4a/Arf-deficient neural progenitor cells is mediated by the p53-Fbxw7/Cdc4 pathway, which controls c-Myc

Glioblastoma multiforme is the most common type of primary malignant brain tumor and may arise from a cell with neural stem-like properties. Deregulation of the retinoblastoma, phosphoinositide-3 kinase (PI3K), and p53 pathways are molecular hallmarks of this disease. Recent work has shown that p53(-/-)Pten(-/-) mice form gliomas in a c-Myc-dependent manner. To explore the role of the INK4A/ARF locus and Pten deletions in gliomagenesis, we generated Pten(-/-)Ink4a/Arf(-/-) mouse neural stem cells (mNSC) and such cells were highly proliferative, self-renewing, relatively refractory to differentiation, and induced both low- and high-grade glioma formation in vivo. In contrast to p53(-/-) Pten(-/-) mNSCs, however, Pten(-/-)Ink4a/Arf(-/-) mNSCs do not express appreciable levels of c-Myc in vitro, although glioma stem cells derived from thesecells did. Sequencing of Pten(-/-)Ink4a/Arf(-/-) mNSC-derived tumors revealed spontaneous mutations in Tp53 in vivo with subsequent downregulation of Fbxw7. Expression of p53 mutants in Pten(-/-)Ink4a/Arf(-/-) mNSC or knockdown of Fbxw7 resulted in reexpression of c-Myc with enhanced Pten(-/-)Ink4a/Arf(-/-) mNSC tumorigenecity. We propose that p53 mutations contribute to gliomagenesis by both allowing the overexpression of c-Myc through downregulation of Fbxw7 and by protecting against c-Myc-induced apoptosis.

Aberrant glycogen synthase kinase 3β in the development of pancreatic cancer

Development and progression of pancreatic cancer involves general metabolic disorder, local chronic inflammation, and multistep activation of distinct oncogenic molecular pathways. These pathologic processes result in a highly invasive and metastatic tumor phenotype that is a major obstacle to curative surgical intervention, infusional gemcitabine-based chemotherapy, and radiation therapy. Many clinical trials with chemical compounds and therapeutic antibodies targeting growth factors, angiogenic factors, and matrix metalloproteinases have failed to demonstrate definitive therapeutic benefits to refractory pancreatic cancer patients. Glycogen synthase kinase 3β (GSK3β), a serine/threonine protein kinase, has emerged as a therapeutic target in common chronic and progressive diseases, including cancer. Here we review accumulating evidence for a pathologic role of GSK3β in promoting tumor cell survival, proliferation, invasion, and resistance to chemotherapy and radiation in pancreatic cancer. We also discuss the putative involvement of GSK3β in mediating metabolic disorder, local inflammation, and molecular alteration leading to pancreatic cancer development. Taken together, we highlight potential therapeutic as well as preventive effects of GSK3β inhibition in pancreatic cancer.

Endothelial Wnt/β-catenin signaling inhibits glioma angiogenesis and normalizes tumor blood vessels by inducing PDGF-B expression

Wnt modulates glioma vascularization by regulating PDGF-B expression.

Endothelial Wnt/β-catenin signaling is necessary for angiogenesis of the central nervous system and blood–brain barrier (BBB) differentiation, but its relevance for glioma vascularization is unknown. In this study, we show that doxycycline-dependent Wnt1 expression in subcutaneous and intracranial mouse glioma models induced endothelial Wnt/β-catenin signaling and led to diminished tumor growth, reduced vascular density, and normalized vessels with increased mural cell attachment. These findings were corroborated in GL261 glioma cells intracranially transplanted in mice expressing dominant-active β-catenin specifically in the endothelium. Enforced endothelial β-catenin signaling restored BBB characteristics, whereas inhibition by Dkk1 (Dickkopf-1) had opposing effects. By overactivating the Wnt pathway, we induced the Wnt/β-catenin–Dll4/Notch signaling cascade in tumor endothelia, blocking an angiogenic and favoring a quiescent vascular phenotype, indicated by induction of stalk cell genes. We show that β-catenin transcriptional activity directly regulated endothelial expression of platelet-derived growth factor B (PDGF-B), leading to mural cell recruitment thereby contributing to vascular quiescence and barrier function. We propose that reinforced Wnt/β-catenin signaling leads to inhibition of angiogenesis with normalized and less permeable vessels, which might prove to be a valuable therapeutic target for antiangiogenic and edema glioma therapy.

Discovery and validation of small-molecule heat-shock protein 90 inhibitors through multimodality molecular imaging in living subjects

Up-regulation of the folding machinery of the heat-shock protein 90 (Hsp90) chaperone protein is crucial for cancer progression. The two Hsp90 isoforms (α and β) play different roles in response to chemotherapy. To identify isoform-selective inhibitors of Hsp90(α/β)/cochaperone p23 interactions, we developed a dual-luciferase (Renilla and Firefly) reporter system for high-throughput screening (HTS) and monitoring the efficacy of Hsp90 inhibitors in cell culture and live mice. HTS of a 30,176 small-molecule chemical library in cell culture identified a compound, N-(5-methylisoxazol-3-yl)-2-[4-(thiophen-2-yl)-6-(trifluoromethyl)pyrimidin-2-ylthio]acetamide (CP9), that binds to Hsp90(α/β) and displays characteristics of Hsp90 inhibitors, i.e., degradation of Hsp90 client proteins and inhibition of cell proliferation, glucose metabolism, and thymidine kinase activity, in multiple cancer cell lines. The efficacy of CP9 in disrupting Hsp90(α/β)/p23 interactions and cell proliferation in tumor xenografts was evaluated by non-invasive, repetitive Renilla luciferase and Firefly luciferase imaging, respectively. At 38 h posttreatment (80 mg/kg × 3, i.p.), CP9 led to selective disruption of Hsp90α/p23 as compared with Hsp90β/p23 interactions. Small-animal PET/CT in the same cohort of mice showed that CP9 treatment (43 h) led to a 40% decrease in (18)F-fluorodeoxyglucose uptake in tumors relative to carrier control-treated mice. However, CP9 did not lead to significant degradation of Hsp90 client proteins in tumors. We performed a structural activity relationship study with 62 analogs of CP9 and identified A17 as the lead compound that outperformed CP9 in inhibiting Hsp90(α/β)/p23 interactions in cell culture. Our efforts demonstrated the power of coupling of HTS with multimodality molecular imaging and led to identification of Hsp90 inhibitors.

Selective growth inhibition by glycogen synthase kinase-3 inhibitors in tumorigenic HeLa hybrid cells is mediated through NF-κB-dependent GLUT3 expression

Carcinogenesis and cancer progression, driven by mutations in oncogenes and tumor-suppressor genes, result in biological differences between normal and cancer cells in various cellular processes. Specific genes and signaling molecules involved in such cellular processes may be potential therapeutic targets of agents that specifically interact with the key factors in cancer cells. Increased glucose uptake is fundamental to many solid tumors and well associated with increases in glycolysis and the overexpression of glucose transporters (GLUTs) such as GLUT1 and GLUT3 at the plasma membrane. Here, we used cell-based screening to identify glycogen synthase kinase-3β (GSK-3β) inhibitors that selectively target GLUT3-expressing tumorigenic HeLa cell hybrids as compared with non-tumorigenic hybrids that express GLUT1 alone. The GSK-3 inhibitors as well as GSK-3β RNAi suppressed GLUT3 expression at the level of transcription, leading to apoptosis. This suppression was associated with NF-κB in a p53-independent manner. Furthermore, GSK-3 inhibitors exhibited a synergistic effect with anticancer agents such as adriamycin and camptothecin in GULT3-overexpressing colon cancer cells, but little effect in non-producing A431 cells. These results suggest a potential use of GSK-3 inhibitors to selectively kill cancer cells that overexpress GLUT3.

GSK-3β: A Bifunctional Role in Cell Death Pathways

Although glycogen synthase kinase-3 beta (GSK-3β) was originally named for its ability to phosphorylate glycogen synthase and regulate glucose metabolism, this multifunctional kinase is presently known to be a key regulator of a wide range of cellular functions. GSK-3β is involved in modulating a variety of functions including cell signaling, growth metabolism, and various transcription factors that determine the survival or death of the organism. Secondary to the role of GSK-3β in various diseases including Alzheimer's disease, inflammation, diabetes, and cancer, small molecule inhibitors of GSK-3β are gaining significant attention. This paper is primarily focused on addressing the bifunctional or conflicting roles of GSK-3β in both the promotion of cell survival and of apoptosis. GSK-3β has emerged as an important molecular target for drug development.

Glycogen synthase kinase-3β, NF-κB signaling, and tumorigenesis of human osteosarcoma

Background

Glycogen synthase kinase-3β (GSK-3β), a serine/threonine protein kinase, may function as a tumor suppressor or an oncogene, depending on the tumor type. We sought to determine the biological function of GSK-3β in osteosarcoma, a rare pediatric cancer for which the identification of new therapeutic targets is urgent.

Methods

We used cell viability assays, colony formation assays, and apoptosis assays to analyze the effects of altered GSK-3β expression in U2OS, MG63, SAOS2, U2OS/MTX300, and ZOS osteosarcoma cell lines. Nude mice (n = 5–8 mice per group) were injected with U2OS/MTX300, and ZOS cells to assess the role of GSK-3β in osteosarcoma growth in vivo and to evaluate the effects of inhibitors and/or anticancer drugs on tumor growth. We used an antibody array, polymerase chain reaction, western blotting, and a luciferase reporter assay to establish the effect of GSK-3β inhibition on the nuclear factor-κB (NF-κB) pathway. Immunochemistry was performed on primary tumor specimens from osteosarcoma patients (n = 74) to determine the relationship of GSK-3β activity with overall survival.

Results

Osteosarcoma cells with low levels of inactive p-Ser9-GSK-3β formed colonies in vitro and tumors in vivo more readily than cells with higher levels and cells in which GSK-3β had been silenced formed fewer colonies and smaller tumors than parental cells. Silencing or pharmacological inhibition of GSK-3β resulted in apoptosis of osteosarcoma cells. Inhibition of GSK-3β resulted in inhibition of the NF-κB pathway and reduction of NF-κB-mediated transcription. Combination treatments with GSK-3β inhibitors, NF-κB inhibitors, and chemotherapy drugs increased the effectiveness of chemotherapy drugs in vitro and in vivo. Patients whose osteosarcoma specimens had hyperactive GSK-3β, and nuclear NF-κB had a shorter median overall survival time (49.2 months) compared with patients whose tumors had inactive GSK-3β and NF-κB (109.2 months).

Conclusion

GSK-3β activity may promote osteosarcoma tumor growth, and therapeutic targeting of the GSK-3β and/or NF-κB pathways may be an effective way to enhance the therapeutic activity of anticancer drugs against osteosarcoma.

Molecular network profiling of U373MG human glioblastoma cells following induction of apoptosis by novel marine-derived anti-cancer 1,2,3,4-tetrahydroisoquinoline alkaloids

Background

Glioblastoma is the most aggressive form of brain tumors showing resistance to treatment with various chemotherapeutic agents. The most effective way to eradicate glioblastoma requires the concurrent inhibition of multiple signaling pathways and target molecules involved in the progression of glioblastoma. Recently, we obtained a series of 1,2,3,4-tetrahydroisoquinoline alkaloids with potent anti-cancer activities, including ecteinascidin-770 (ET-770; the compound 1a) and renieramycin M (RM; the compound 2a) from Thai marine invertebrates, together with a 2’-N-4”-pyridinecarbonyl derivative of ET-770 (the compound 3). We attempted to characterize the molecular pathways responsible for cytotoxic effects of these compounds on a human glioblastoma cell line U373MG.

Methods

We studied the genome-wide gene expression profile on microarrays and molecular networks by using pathway analysis tools of bioinformatics.

Results

All of these compounds induced apoptosis of U373MG cells at nanomolar concentrations. The compound 3 reduced the expression of 417 genes and elevated the levels of 84 genes, while ET-770 downregulated 426 genes and upregulated 45 genes. RM decreased the expression of 274 genes and increased the expression of 9 genes. The set of 196 downregulated genes and 6 upregulated genes showed an overlap among all the compounds, suggesting an existence of the common pathways involved in induction of apoptosis. We identified the ErbB (EGFR) signaling pathway as one of the common pathways enriched in the set of downregulated genes, composed of PTK2, AKT3, and GSK3B serving as key molecules that regulate cell movement and the nervous system development. Furthermore, a GSK3B-specific inhibitor induced apoptosis of U373MG cells, supporting an anti-apoptotic role of GSK3B.

Conclusion

Molecular network analysis is a useful approach not only to characterize the glioma-relevant pathways but also to identify the network-based effective drug targets.

Histone deacetylase inhibitors sensitize glioblastoma cells to TRAIL-induced apoptosis by c-myc-mediated downregulation of cFLIP

Glioblastoma is the most common primary brain tumor with a very poor prognosis, calling for novel treatment strategies. Here, we provide first evidence that histone deacetylase inhibitors (HDACI) prime glioblastoma cells for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) -induced apoptosis at least in part by c-myc-mediated downregulation of cellular FLICE-inhibitory protein (cFLIP). Pretreatment with distinct HDACI (MS275, suberoylanilide hydroxamic acid, valproic acid) significantly enhances TRAIL-induced apoptosis in several glioblastoma cell lines. Monitoring a panel of apoptosis-regulatory proteins revealed that MS275 reduces the expression of cFLIP(L) and cFLIP(S). This leads to decreased recruitment of cFLIP(L) and cFLIP(S) and increased activation of caspase-8 to the TRAIL death-inducing signaling complex, resulting in enhanced cleavage of caspase-8, -9 and -3 and caspase-dependent apoptosis. Also, MS275 promotes TRAIL-triggered processing of Bid, activation of Bax, loss of mitochondrial membrane potential and release of cytochrome c. MS275-mediated downregulation of cFLIP occurs at the mRNA level independent of proteasome- or caspase-mediated degradation, and is preceded by upregulation of nuclear levels of c-myc, a transcriptional repressor of cFLIP. Notably, MS275 causes increased binding of c-myc to the cFLIP promoter and reduces cFLIP promoter activity. Indeed, knockdown of c-myc partially rescues cFLIP(L) from MS275-inferred downregulation and significantly decreases TRAIL- and MS275-induced apoptosis. Also, overexpression of cFLIP(L) or cFLIP(S) significantly reduces MS275- and TRAIL-induced apoptosis. Importantly, MS275 sensitizes primary cultured glioblastoma cells towards TRAIL and cooperates with TRAIL to reduce long-term clonogenic survival of glioblastoma cells and to suppress glioblastoma growth in vivo underscoring the clinical relevance of this approach. Thus, these findings demonstrate that HDACI represent a promising strategy to prime glioblastoma for TRAIL-induced apoptosis by targeting cFLIP.

Inhibition of glycogen synthase kinase-3 activity triggers an apoptotic response in pancreatic cancer cells through JNK-dependent mechanisms

Recent evidences suggest that the activity of glycogen synthase kinase-3 (GSK3) contributes to the tumorigenic potential of pancreatic cancer cells through modulation of cell proliferation and survival. However, further investigations are needed to identify GSK3-dependent mechanisms involved in the control of pancreatic cancer cell proliferation and survival. This study was undertaken to provide further support for a role of GSK3 in pancreatic cancer cell growth as well as to identify new cellular and molecular mechanisms involved. Herein, we demonstrate that prolonged inhibition of GSK3 triggers an apoptotic response only in human pancreatic cancer cells but not in human non-transformed pancreatic epithelial cells. We show that prolonged inhibition of GSK3 activity increases Bim messenger RNA and protein expressions. Moreover, we provide evidence that activation of the c-jun N-terminal kinase (JNK) pathway is necessary for the GSK3 inhibition-mediated increase in Bim expression and apoptotic response. Finally, we demonstrate that concomitant inhibition of GSK3 potentiates the death ligand-induced apoptotic response in pancreatic cancer cells but not in non-transformed pancreatic epithelial cells and that this effect also requires JNK activity. Considering that different approaches leading to stimulation of death receptor signaling are under clinical trials for treatment of unresectable or metastatic pancreatic cancer, inhibition of GSK3 could represent an attractive new avenue to improve their effectiveness.

Emerging roles of glycogen synthase kinase 3 in the treatment of brain tumors

The constitutively active protein glycogen synthase kinase 3 (GSK3), a serine/threonine kinase, acts paradoxically as a tumor suppressor in some cancers while potentiates growth in others. Deciphering what governs its actions is vital for understanding many pathological conditions, including brain cancer. What are seemingly disparate roles of GSK3 stems from the complex regulation of many cellular functions by GSK3. This review focuses on the regulation of GSK3, its role in survival, apoptosis and DNA damage, and finally its potential therapeutic impact in brain cancer. A thorough understanding of this versatile protein is critical for improving the outcome of various diseases, especially cancer.

Identification of the couple GSK3α/c-Myc as a new regulator of hexokinase II in benzo[a]pyrene-induced apoptosis

The early apoptotic events induced by environmental pollutants with carcinogenic properties are poorly understood. Here, we focus on the early cytotoxic effects of benzo[a]pyrene (B[a]P). In F258 rat hepatic epithelial cells, B[a]P induces intrinsic apoptosis via a mitochondrial dysfunction characterized by the release of hexokinase II (HKII) from the mitochondria. Cancer cells often have an anomalous cell energy metabolism; since HKII dysfunction regulates B[a]P-induced apoptosis in F258 cells, but may also alter cell energy metabolism, HKII release from the mitochondria may represent an important B[a]P-related carcinogenic issue. Thus in the present study, we aimed at deciphering the mechanisms underlying HKII dysfunction upon B[a]P exposure. We show that while glycogen synthase kinase 3 beta (GSK3β) regulated the expression of HKII at the transcriptional level, glycogen synthase kinase 3 alpha (GSK3α) was involved in B[a]P-induced apoptosis via a decrease in c-Myc expression. The reduced level of c-Myc caused the relocation of HKII from the mitochondria to the cytosol, thereby being involved in the formation of reactive oxygen species and apoptosis. In conclusion, we show that the couple GSK3α/c-Myc plays a key role in B[a]P-induced early apoptotic cell signaling via HKII dysfunction.

Scutellaria extract and wogonin inhibit tumor-mediated induction of T(reg) cells via inhibition of TGF-β1 activity

A number of studies have implicated tumor-induced T(reg) cell activity in the sub-optimal response to therapeutic vaccines. Development of neo-adjuvant strategies targeting T(reg) cells is therefore imperative. Scutellaria extracts or constituent flavonoids have shown encouraging efficacy against various tumors, including gliomas, in both pre-clinical and clinical studies. We report here, for the first time, that Scutellaria ocmulgee leaf extract (SocL) and flavonoid wogonin could inhibit TGF-β1-induced T(reg) activity in malignant gliomas. F344 rats, subcutaneously transplanted with F98 gliomas, were treated with SocL. There was a significant inhibition of intra-tumoral TGF-β1 and T(reg) cell frequency as well as peripheral blood TGF-β1 levels in SocL-treated animals compared to the controls. SocL extract and wogonin also inhibited glioma-induced, TGF-β1-mediated T(reg) activity in vitro. SocL extract and wogonin also inhibited the secretion of IL-10 in T(reg) culture; whereas the level of IL-2 was either unchanged or marginally enhanced. We also observed an inhibition of Smad-3, GSK-3β and ERK1/2 signaling by SocL and wogonin in T(reg) cells, while phosphorylation of P38 MAPK was considerably enhanced, indicating that SocL or wogonin could inhibit the T cells' response to TGF-β1 via modulation of both Smad and non-Smad signaling pathways. Overall, this study suggests that Scutellaria can potentially reverse tumor-mediated immune suppression via inhibition of TGF-β1 secretion as well as via inhibition of T cells' response to TGF-β1. This may provide an opportunity for developing a novel adjuvant therapeutic strategy for malignant gliomas, combining Scutellaria with immunotherapy and chemo/radio-therapeutic regimen, which could potentially improve the disease outcome.

Effect of over-expressed LRIG3 on cell cycle and survival of glioma cells

This study examined the effects of over-expression of leucine-rich repeats and immunoglobulin-like domains 3 (LRIG3) on the cell cycle and survival of human glioma cell line U87 and U251 and explored the possible mechanisms. The LRIG3 gene was transduced into U87 and U251 cells respectively by using lentivirus and the transduced cells were selected by puromycin. The changes in LRIG3 mRNA and protein levels were measured by RT-PCR and Western blotting. The apoptosis rate was detected by Annexin V-FITC/PI double labeling and the cell cycle was flow cytometrically analyzed. Compared with control cells, LRIG3 mRNA expression in U251 and U87 cells transduced with pLVX-DsRed-LRIG3-Monomer-N1 were increased by 77.6% and 129.7%, and LRIG3 protein expression was raised by 141.3% and 322.7%, respectively. Cell cycle analysis showed that LRIG3 over-expression increased the percentage of cells at G(0)/G(1) phase (P<0.01). Over-expressed LRIG3 could significantly promote the apoptosis of U87 and U251 cells (P<0.05). These findings suggest that the over-expression of LRIG3 could arrest the cell cycle in G(0)/G(1) phase, and promote apoptosis of U87 and U251 cells.

Integrating diverse genomic data using gene sets

We introduce and evaluate data analysis methods to interpret simultaneous measurement of multiple genomic features made on the same biological samples. Our tools use gene sets to provide an interpretable common scale for diverse genomic information. We show we can detect genetic effects, although they may act through different mechanisms in different samples, and show we can discover and validate important disease-related gene sets that would not be discovered by analyzing each data type individually.

Differential modulatory effects of GSK-3β and HDM2 on sorafenib-induced AIF nuclear translocation (programmed necrosis) in melanoma

Background

GSK-3β phosphorylates numerous substrates that govern cell survival. It phosphorylates p53, for example, and induces its nuclear export, HDM2-dependent ubiquitination, and proteasomal degradation. GSK-3β can either enhance or inhibit programmed cell death, depending on the nature of the pro-apoptotic stimulus. We previously showed that the multikinase inhibitor sorafenib activated GSK-3β and that this activation attenuated the cytotoxic effects of the drug in various BRAF-mutant melanoma cell lines. In this report, we describe the results of studies exploring the effects of GSK-3β on the cytotoxicity and antitumor activity of sorafenib combined with the HDM2 antagonist MI-319.

Results

MI-319 alone increased p53 levels and p53-dependent gene expression in melanoma cells but did not induce programmed cell death. Its cytotoxicity, however, was augmented in some melanoma cell lines by the addition of sorafenib. In responsive cell lines, the MI-319/sorafenib combination induced the disappearance of p53 from the nucleus, the down modulation of Bcl-2 and Bcl-x_L, the translocation of p53 to the mitochondria and that of AIF to the nuclei. These events were all GSK-3β-dependent in that they were blocked with a GSK-3β shRNA and facilitated in otherwise unresponsive melanoma cell lines by the introduction of a constitutively active form of the kinase (GSK-3β-S9A). These modulatory effects of GSK-3β on the activities of the sorafenib/MI-319 combination were the exact reverse of its effects on the activities of sorafenib alone, which induced the down modulation of Bcl-2 and Bcl-x_L and the nuclear translocation of AIF only in cells in which GSK-3β activity was either down modulated or constitutively low. In A375 xenografts, the antitumor effects of sorafenib and MI-319 were additive and associated with the down modulation of Bcl-2 and Bcl-x_L, the nuclear translocation of AIF, and increased suppression of tumor angiogenesis.

Conclusions

Our data demonstrate a complex partnership between GSK-3β and HDM2 in the regulation of p53 function in the nucleus and mitochondria. The data suggest that the ability of sorafenib to activate GSK-3β and alter the intracellular distribution of p53 may be exploitable as an adjunct to agents that prevent the HDM2-dependent degradation of p53 in the treatment of melanoma.

Resveratrol suppresses constitutive activation of AKT via generation of ROS and induces apoptosis in diffuse large B cell lymphoma cell lines

Background

We have recently shown that deregulation PI3-kinase/AKT survival pathway plays an important role in pathogenesis of diffuse large B cell lymphoma (DLBCL). In an attempt to identify newer therapeutic agents, we investigated the role of Resveratrol (trans-3,4′, 5-trihydroxystilbene), a naturally occurring polyphenolic compound on a panel of diffuse large B-cell lymphoma (DLBCL) cells in causing inhibition of cell viability and inducing apoptosis.

Methodology/Principal Findings

We investigated the action of Resveratrol on DLBCL cells and found that Resveratrol inhibited cell viability and induced apoptosis by inhibition of constitutively activated AKT and its downstream targets via generation of reactive oxygen species (ROS). Simultaneously, Resveratrol treatment of DLBCL cell lines also caused ROS dependent upregulation of DR5; and interestingly, co-treatment of DLBCL with sub-toxic doses of TRAIL and Resveratrol synergistically induced apoptosis via utilizing DR5, on the other hand, gene silencing of DR5 abolished this effect.

Conclusion/Significance

Altogether, these data suggest that Resveratrol acts as a suppressor of AKT/PKB pathway leading to apoptosis via generation of ROS and at the same time primes DLBCL cells via up-regulation of DR5 to TRAIL-mediated apoptosis. These data raise the possibility that Resveratrol may have a future therapeutic role in DLBCL and possibly other malignancies with constitutive activation of the AKT/PKB pathway.

Overexpression of glycogen synthase kinase-3 in ovarian carcinoma cells with acquired paclitaxel resistance

INTRODUCTION

Acquired resistance to paclitaxel, including regimens, is one of the most significant reasons for treatment failure and death in patients with ovarian cancer, but the causes of this resistance remain unclear. However, cell cycle regulation is a key mechanism by which most chemotherapeutic agents exert their cytotoxic effects.

METHODS

We created a paclitaxel-resistant ovarian carcinoma cell line from SKOV3 cell line, and the difference of cell cycle distribution was analyzed using flow cytometry. Analysis of human cell cycle pathway complementary DNA array was performed to identify candidate genes associated with paclitaxel resistance. Gene expression changes were validated at the messenger RNA and protein levels by real-time reverse transcriptase polymerase chain reaction and Western analysis, respectively.

RESULTS

The ratio of Gap0/Gap1 phase in SKOV3-TR30 was significantly lower than that in SKOV3 (54.8% ± 6.3% vs 72.7% ± 7.6%, P = 0.035), and the ratio of G2/M phase in SKOV3-TR30 was significantly higher than that in SKOV3 (24.9% ± 6.0% vs 10.2% ± 3.5%, P = 0.021). Complementary DNA microarray analysis demonstrated enhanced glycogen synthase kinase-3α (GSK-3α) expression in paclitaxel-resistant ovarian carcinoma cells. Real-time reverse transcriptase polymerase chain reaction analysis revealed that the paclitaxel-resistant subline exhibited a 7.0 ± 1.8-fold increase in GSK-3α messenger RNA expression. There was a 3.34 ± 0.47-fold increase of total GSK-3 protein (GSK-3α/β) in SKOV3-TR30 cells validated by Western analysis.

CONCLUSIONS

This study demonstrates that enhanced expression of GSK-3 is associated with acquired resistance to paclitaxel in ovarian carcinoma cells. Glycogen synthase kinase-3 overexpression may probably be a significant contributor to chemoresistance.

Indirubins decrease glioma invasion by blocking migratory phenotypes in both the tumor and stromal endothelial cell compartments

Invasion and proliferation in neoplasia require the cooperation of tumor cell and endothelial compartments. Glycogen synthase kinase-3 (GSK-3) is increasingly recognized as a major contributor to signaling pathways that modulate invasion and proliferation. Here we show that GSK-3 inhibitors of the indirubin family reduce invasion of glioma cells and glioma-initiating cell-enriched neurospheres both in vitro and in vivo, and we show that β-catenin signaling plays an important role in mediating these effects. Indirubins improved survival in glioma-bearing mice in which a substantial decrease in blood vessel density was seen in treated animals. In addition, indirubins blocked migration of endothelial cells, suggesting that anti-invasive glioma therapy with GSK-3 inhibitors in vivo not only inhibits invasion of tumor cells, but blocks migration of endothelial cells, which is also required for tumor angiogenesis. Overall, our findings suggest that indirubin inhibition of GSK-3 offers a novel treatment paradigm to target 2 of the most important interacting cellular compartments in heterotypic models of cancer.

GSK3β inactivation induces apoptosis of leukemia cells by repressing the function of c-Myb

The level of c-Myb is a determining factor in the response of leukemia cells to GSK3β kinase inhibiton, which is of particular interest for the therapy of leukemia and cancers that have c-Myb amplifications.

Glycogen synthase kinase 3β (GSK3β) regulates diverse physiological processes, including metabolism, development, oncogenesis, and neuroprotection. GSK3β kinase activity has been reported to be critical for various types of cancer cells, but the mechanism has remained elusive. In this study we examine the mechanism by which GSK3β regulates the survival of leukemia cells. We demonstrate that upon GSK3β kinase inhibition different types of leukemia cells show severe proliferation defects as a result of apoptosis. The transcription factor c-Myb is found to be the main target of GSK3β inhibition in cell survival. GSK3β inactivation reduces the expression of c-Myb by promoting its ubiquitination-mediated degradation, thereby inhibiting the expression of c-Myb–dependent antiapoptotic genes Bcl2 and survivin. Coimmunoprecipitation, reporter assays, chromatin immunoprecipitation, and knockdown studies show that c-Myb needs to interact and cooperate with transcription factor LEF-1 in the activation of Bcl2 and survivin and that both transcription factors are required for cell survival. These data reveal an as-yet-unknown mechanism by which GSK3β controls cell survival.

Troglitazone suppresses c-Myc levels in human prostate cancer cells via a PPARγ-independent mechanism

Troglitazone is a ligand for the peroxisome proliferator activated receptor gamma (PPARγ) that decreases growth of human prostate cancer cells in vitro and in vivo. However, the mechanism by which troglitazone reduces prostate cancer cell growth is not fully understood. To understand the signaling pathways involved in troglitazone-induced decreases in prostate cancer growth, we examined the effect of troglitazone on androgen-independent C4-2 human prostate cancer cells. Initial experiments revealed troglitazone inhibited C4-2 cell proliferation by arresting cells in the G(0)/G(1) phase of the cell cycle and inducing apoptosis. Since the proto-oncogene product c-Myc regulates both apoptosis and cell cycle progression, we next examined whether troglitazone altered expression of c-Myc. Troglitazone decreased c-Myc protein levels as well as expression of downstream targets of c-Myc in a dose-dependent manner. In C4-2 cells, troglitazone-induced decreases in c-Myc protein involve proteasome-mediated degradation of c-Myc protein as well as reductions in c-Myc mRNA levels. It appears that troglitazone stimulates degradation of c-Myc by increasing c-Myc phosphorylation, for the level of phosphorylated c-Myc was elevated in prostate cancer cells exposed to troglitazone. While troglitazone dramatically decreased the amount of c-Myc within C4-2 cells, the PPARγ ligands ciglitazone, rosiglitazone and pioglitazone did not reduce c-Myc protein levels. Furthermore the down-regulation of c-Myc by troglitazone was not blocked by the PPARγ antagonist GW9662 and siRNA-mediated decreases in PPARγ protein. Thus, our data suggest that troglitazone reduces c-Myc protein independently of PPARγ.

ACSL3 and GSK-3β are essential for lipid upregulation induced by endoplasmic reticulum stress in liver cells

The endoplasmic reticulum (ER) is essential for lipid biosynthesis, and stress signals in this organelle are thought to alter lipid metabolism. Elucidating the mechanisms that underlie the dysregulation of lipid metabolism in hepatocytes may lead to novel therapeutic approaches for the treatment of lipid accumulation. We first tested the effects of several inhibitors on lipid dysregulation induced by tunicamycin, an ER stress inducer. Triacsin C, an inhibitor of long-chain acyl-CoA synthetase (ACSL) 1, 3, and 4, was the most potent among these inhibitors. We then analyzed the expression of the ACSL family during ER stress. The expression of ACSL3 was induced by ER stress in HuH-7 cells and in mice livers. ACSL3 shRNA, but not ACSL1 shRNA, inhibited the induction of lipid accumulation. GSK-3β inhibitors attenuated ACSL3 expression and the lipid accumulation induced by ER stress in HuH-7 cells. shRNA that target GSK-3β also inhibited the upregulation of ACSL3 and lipid accumulation in HuH-7 and HepG2 cells. The hepatitis B virus mutant large surface protein, which is known to induce ER stress, increased the lipid content of cells. Similarly, Triacsin C, and GSK-3β inhibitors abrogated the lipid dysregulation caused by the hepatitis B virus mutant large surface protein. Altogether, ACSL3 and GSK-3β represent novel therapeutic targets for lipid dysregulation by ER stress.

Overcoming hypoxia-induced apoptotic resistance through combinatorial inhibition of GSK-3β and CDK1

Tumor hypoxia is an inherent impediment to cancer treatment that is both clinically significant and problematic. In this study, we conducted a cell-based screen to identify small molecules that could reverse the apoptotic resistance of hypoxic cancer cells. Among the compounds, we identified were a structurally related group that sensitized hypoxic cancer cells to apoptosis by inhibiting the kinases GSK-3β and cyclin-dependent kinase (CDK) 1. Combinatorial inhibition of these proteins in hypoxic cancer cells and tumors increased levels of c-Myc and decreased expression of c-IAP2 and the central hypoxia response regulator hypoxia-inducible factor (HIF) 1α. In mice, these compounds augmented the hypoxic tumor cell death induced by cytotoxic chemotherapy, blocking angiogenesis and tumor growth. Taken together, our findings suggest that combinatorial inhibition of GSK-3β and CDK1 augment the apoptotic sensitivity of hypoxic tumors, and they offer preclinical validation of a novel and readily translatable strategy to improve cancer therapy.

Mutant K-Ras increases GSK-3β gene expression via an ETS-p300 transcriptional complex in pancreatic cancer

Glycogen synthase kinase-3 beta (GSK-3β) is overexpressed in a number of human malignancies and has been shown to contribute to tumor cell proliferation and survival. Although regulation of GSK-3β activity has been extensively studied, the mechanisms governing GSK-3β gene expression are still unknown. Using pancreatic cancer as a model, we find that constitutively active Ras signaling increases GSK-3β gene expression via the canonical mitogen-activated protein kinase signaling pathway. Analysis of the mechanism revealed that K-Ras regulates the expression of this kinase through two highly conserved E-twenty six (ETS) binding elements within the proximal region. Furthermore, we demonstrate that mutant K-Ras enhances ETS2 loading onto the promoter, and ETS requires its transcriptional activity to increase GSK-3β gene transcription in pancreatic cancer cells. Lastly, we show that ETS2 cooperates with p300 histone acetyltransferase to remodel chromatin and promote GSK-3β expression. Taken together, these results provide a general mechanism for increased expression of GSK-3β in pancreatic cancer and perhaps other cancers, where Ras signaling is deregulated.

Temozolomide induced c-Myc-mediated apoptosis via Akt signalling in MGMT expressing glioblastoma cells

PURPOSE

We investigated the molecular mechanisms underlying the cytotoxic effect of Temozolomide (TMZ) in both O(6)-methylguanine-DNA methyl transferase (MGMT) depleted as well as undepleted glioblastoma cell lines. Since TMZ is used in clinics in combination with radiotherapy, we also studied the effects of TMZ in combination with ionising radiation (IR).

METHODS

Cell colony-forming ability was measured using a clonogenic assay. Cell cycle analysis and apoptosis were evaluated by Flow Cytometry (FCM). Proteins involved in cell cycle control were detected by Western blot and co-immunoprecipitation assays.

RESULTS

Our data showed that TMZ, independent of MGMT expression, inhibited glioblastoma cell growth via an irreversible G(2) block in MGMT depleted cells or the induction of apoptosis in MGMT normal expressing cells. When TMZ was administered in combination with IR, apoptosis was greater than observed with either agent separately. This TMZ-induced apoptosis in the MGMT expressing cells occurred through Akt/Glycogen-Synthase-Kinase-3ß (GSK3ß) signalling and was mediated by Myelocytomatosis (c-Myc) oncoprotein. Indeed, TMZ phosphorylated/activated Akt led to phosphorylation/inactivation of GSK3ß which resulted in the stabilisation of c-Myc protein and subsequent modulation of the c-Myc target genes involved in the apoptotic processes.

CONCLUSION

C-Myc expression could be considered a good indicator of TMZ effectiveness.

Glycogen synthase kinase 3beta inhibition enhances repair of DNA double-strand breaks in irradiated hippocampal neurons

Prevention of cranial radiation-induced morbidity following the treatment of primary and metastatic brain cancers, including long-term neurocognitive deficiencies, remains challenging. Previously, we have shown that inhibition of glycogen synthase kinase 3β (GSK3β) results in protection of hippocampal neurons from radiation (IR)-induced apoptosis and attenuation of neurocognitive dysfunction resulting from cranial IR. In this study, we examined whether regulation of the repair of IR-induced DNA damage is one of the mechanisms involved in the radioprotective effects of neurons by inhibition of GSK3β. Specifically, this study showed that inhibition of GSK3β accelerated double strand-break (DSB) repair efficiency in irradiated mouse hippocampal neurons, as assessed by the neutral comet assay. This coincided with attenuation of IR-induced γ-H2AX foci, a well characterized in situ marker of DSBs. To confirm the effect of GSK3 activity on the efficacy of DSB repair, we further demonstrated that biochemical or genetic inhibition of GSK3 activity resulted in enhanced capacity in nonhomologous end-joining-mediated repair of DSBs in hippocampal neurons. Importantly, none of these effects were observed in malignant glioma cells. Taken together, these results suggested that enhanced repair of IR-induced DNA damage may be a novel mechanism by which inhibition of GSK3β specifically protects hippocampal neurons from IR-induced apoptosis. Furthermore, these findings warrant future investigations of the molecular mechanisms underlying the role of GSK3β in the DSB repair of normal neurons and the potential clinical application of neuroprotection with GSK3β inhibitors during cranial IR.

Hammada scoparia flavonoids and rutin kill adherent and chemoresistant leukemic cells

In search for compounds able to reduce cell adhesion-mediated drug resistance (CAM-DR), we studied effects of Hammada scoparia extracts on leukemic cells adherent or in suspension. We show that H. scoparia flavonoidic fraction and its compound rutin induce apoptosis specifically in adherent leukemic cells and abolish CAM-DR. Importantly, rutin inhibited survival of adherent leukemic progenitors (CD34(+)38(-)123(+)) but spared normal progenitors (CD34(+)38(-)). The pro-apoptotic effects of rutin were correlated with a decrease of active GSK3β and inhibitors of GSK3β reproduced rutin-induced cytotoxicity. This study uncovers the potential of H. scoparia flavonoids and rutin to overcome CAM-DR in acute myeloid leukemia.

Inhibition of glioblastoma growth by the thiadiazolidinone compound TDZD-8

BACKGROUND

Thiadiazolidinones (TDZD) are small heterocyclic compounds first described as non-ATP competitive inhibitors of glycogen synthase kinase 3β (GSK-3β). In this study, we analyzed the effects of 4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione (TDZD-8), on murine GL261 cells growth in vitro and on the growth of established intracerebral murine gliomas in vivo.

METHODOLOGY/PRINCIPAL FINDINGS

Our data show that TDZD-8 decreased proliferation and induced apoptosis of GL261 glioblastoma cells in vitro, delayed tumor growth in vivo, and augmented animal survival. These effects were associated with an early activation of extracellular signal-regulated kinase (ERK) pathway and increased expression of EGR-1 and p21 genes. Also, we observed a sustained activation of the ERK pathway, a concomitant phosphorylation and activation of ribosomal S6 kinase (p90RSK) and an inactivation of GSK-3β by phosphorylation at Ser 9. Finally, treatment of glioblastoma stem cells with TDZD-8 resulted in an inhibition of proliferation and self-renewal of these cells.

CONCLUSIONS/SIGNIFICANCE

Our results suggest that TDZD-8 uses a novel mechanism to target glioblastoma cells, and that malignant progenitor population could be a target of this compound.

NFκB inhibitors induce cell death in glioblastomas

Identification of novel target pathways in glioblastoma (GBM) remains critical due to poor prognosis, inefficient therapies and recurrence associated with these tumors. In this work, we evaluated the role of nuclear-factor-kappa-B (NFκB) in the growth of GBM cells, and the potential of NFκB inhibitors as antiglioma agents. NFκB pathway was found overstimulated in GBM cell lines and in tumor specimens compared to normal astrocytes and healthy brain tissues, respectively. Treatment of a panel of established GBM cell lines (U138MG, U87, U373 and C6) with pharmacological NFκB inhibitors (BAY117082, parthenolide, MG132, curcumin and arsenic trioxide) and NFκB-p65 siRNA markedly decreased the viability of GBMs as compared to inhibitors of other signaling pathways such as MAPKs (ERK, JNK and p38), PKC, EGFR and PI3K/Akt. In addition, NFκB inhibitors presented a low toxicity to normal astrocytes, indicating selectivity to cancerous cells. In GBMs, mitochondrial dysfunction (membrane depolarization, bcl-xL downregulation and cytochrome c release) and arrest in the G2/M phase were observed at the early steps of NFκB inhibitors treatment. These events preceded sub-G1 detection, apoptotic body formation and caspase-3 activation. Also, NFκB was found overstimulated in cisplatin-resistant C6 cells, and treatment of GBMs with NFκB inhibitors overcame cisplatin resistance besides potentiating the effects of the chemotherapeutics, cisplatin and doxorubicin. These findings support NFκB as a potential target to cell death induction in GBMs, and that the NFκB inhibitors may be considered for in vivo testing on animal models and possibly on GBM therapy.

Glycogen synthase kinase-3beta: a prognostic marker and a potential therapeutic target in human bladder cancer

PURPOSE

Although recent studies have shown glycogen synthase kinase-3β (GSK-3β), a serine/threonine kinase, as a positive regulator of pancreatic, colon, and kidney cancer cell survival and proliferation, the role of GSK-3 in bladder cancer remains unknown. Our objectives were to determine the subcellular localization of GSK-3β and to evaluate the effect of GSK-3 inhibition in bladder cancer.

EXPERIMENTAL DESIGN

We used immunohistochemical staining and nuclear/cytosolic fractionation to determine the expression pattern of GSK-3β in human urothelial carcinomas. To study the effect of GSK-3 inhibition on bladder cancer cell proliferation and survival, we used pharmacologic inhibitors of GSK-3, RNA interference, MTS assay, bromodeoxyuridine incorporation assay, quantitative reverse transcriptase-PCR, and Western blotting.

RESULTS

We found aberrant nuclear accumulation of GSK-3β in 62% (43 of 69) and 91% (21 of 23) of noninvasive and invasive human urothelial carcinomas, respectively. GSK-3β nuclear staining was significantly associated with high-grade tumors (P < 0.001), advanced stage of bladder cancer (P < 0.05), metastasis (P < 0.05), and worse cause-specific survival (P < 0.05) in bladder cancer patients. Moreover, we found that pharmacologic inhibition or genetic depletion of GSK-3β resulted in decreased viability of bladder cancer cells.

CONCLUSIONS

Our results suggest nuclear accumulation of GSK-3β as a novel prognostic marker in bladder cancer, show that GSK-3 contributes to urothelial cancer cell proliferation and survival, and identify GSK-3 as a potential therapeutic target in human bladder cancer.

Inactivation of PI3K/AKT signaling inhibits glioma cell growth through modulation of β-catenin-mediated transcription

Aberrant Wnt/β-catenin signaling contributes to the development of many cancers, including glial tumorigenesis. While cross talk between the Wnt/β-catenin and PI3K/AKT signaling pathways has been proposed, the impact of PI3K/AKT inhibition on β-catenin signaling in glioma remains unknown. In the present study, we report decreased cell proliferation and invasive ability upon the LY294002-induced inhibition of PI3K in both U251 and LN229 human glioblastoma cells in vitro. Pharmacologic inhibition of PI3K resulted in the downregulation of several members of the β-catenin pathway, including Fra-1, c-Myc, and cyclin D1. Downregulation impacted β-catenin-mediated transcription, as LY294002 decreased β-catenin/TCF transcriptional activity, determined by the reporter assay. Similar results were observed in vivo, as intratumoral injection of LY294002 downregulated the expression of the components of the β-catenin pathway and delayed tumor growth in nude mice harboring subcutaneous LN229 xenografts. These results suggest that the PI3K/AKT signaling pathway regulates glioma cell proliferation, in part via repression of the Wnt/β-catenin pathway.

Glycogen synthase kinases-3beta controls differentiation of malignant glioma cells

Malignant gliomas persist as a major disease of morbidity and mortality in adult. Differentiation therapy has emerged as a promising candidate modality. However, the mechanism related is unknown. Here, we show that glycogen synthase kinase-3beta (GSK-3beta) is highly expressed and activated during the cholera toxin-induced differentiation in sensitive C6 and U87-MG malignant glioma cells, whereas the GSK-3alpha activity remains stable. GSK-3beta inhibitors or small interfering RNA suppress the induced-differentiation in sensitive C6 cells. Conversely, overexpression of a constitutively active form of human GSK-3beta (pcDNA3-GSK-3beta-S9A) mutant in resistant U251 glioma cells restores their differentiation capabilities. In addition, GSK-3beta triggers cyclin D1 nuclear export and subsequent degradation, which is necessary for differentiation in C6 and U251 glioma cells. Analysis of human glioma tissues further revealed overexpression of active GSK-3beta. These findings suggest that GSK-3beta is a differentiation fate determinant, and shed new lights on the mechanism by which GSK-3beta regulates cyclin D1 degradation and cellular differentiation in gliomas.

Glycogen synthase kinase-3 and p38 MAPK are required for opioid-induced microglia apoptosis

Opioids have been widely applied in clinics as one of the most potent pain relievers for centuries, but their abuse has deleterious physiological effects beyond addiction. We previously reported that opioids inhibit cell growth and trigger apoptosis in lymphocytes. However, the underlying mechanism by which microglia apoptosis in response to opioids is not yet known. In this study, we show that morphine induces microglia apoptosis and caspase-3 activation in an opioid-receptor dependent manner. Morphine decreased the levels of microglia phosphorylated Akt (p-Akt) and p-GSK-3β (glycogen synthase kinase-3 beta) in an opioid-receptor dependent manner. More interestingly, GSK-3β inhibitor SB216763 significantly increases morphine-induced apoptosis in both BV-2 microglia and mouse primary microglial cells. Moreover, co-treatment of microglia with SB216763 and morphine led to a significant synergistic effect on the level of phospho-p38 mitogen-activated protein kinase (MAPK). In addition, inhibition of p38 MAPK by its specific inhibitor SB203580 significantly inhibited morphine-induced apoptosis and caspase-3 activation. Taken together, our data clearly demonstrates that morphine-induced apoptosis in microglial cells, which is mediated via GSK-3β and p38 MAPK pathways.

Glycogen synthase kinase 3 beta: can it be a target for oral cancer

Despite progress in treatment approaches for oral cancer, there has been only modest improvement in patient outcomes in the past three decades. The frequent treatment failure is due to the failure to control tumor recurrence and metastasis. These failures suggest that new targets should be identified to reverse oral epithelial dysplastic lesions. Recent developments suggest an active role of glycogen synthase kinase 3 beta (GSK3 β) in various human cancers either as a tumor suppressor or as a tumor promoter. GSK3β is a Ser/Thr protein kinase, and there is emerging evidence that it is a tumor suppressor in oral cancer. The evidence suggests a link between key players in oral cancer that control transcription, accelerated cell cycle progression, activation of invasion/metastasis and anti-apoptosis, and regulation of these factors by GSK3β. Moreover, the major upstream kinases of GSK3β and their oncogenic activation by several etiological agents of oral cancer support this hypothesis. In spite of all this evidence, a detailed analysis of the role of GSK3β in oral cancer and of its therapeutic potential has yet to be conducted by the scientific community. The focus of this review is to discuss the multitude of roles of GSK3β, its possible role in controlling different oncogenic events and how it can be targeted in oral cancer.

Delayed growth of glioma by Scutellaria flavonoids involve inhibition of Akt, GSK-3 and NF-κB signaling

Plants of the genus Scutellaria constitute one of the common components of Eastern as well as traditional American medicine against various human diseases, including cancer. In this study, we examined the in vivo anti-glioma activity of a leaf extract of Scutellaria ocmulgee (SocL) while also exploring their potential molecular mechanisms of action. Oral administration of SocL extract delayed the growth of F98 glioma in F344 rats, both in intracranial and subcutaneous tumor models. Immunohistochemistry revealed inhibition of Akt, GSK-3α/β and NF-κB phosphorylation in the subcutaneous tumors following treatment with Scutellaria. The SocL extract as well as the constituent flavonoid wogonin also showed dose- and time-dependent inhibition of Akt, GSK-3α/β and NF-κB in F98 cell cultures in vitro, as determined by western blot analysis. Pharmacologic inhibitors of PI3K and NF-κB also significantly inhibited the in vitro proliferation of F98 glioma cells, indicating the key role of these signaling molecules in the growth of malignant gliomas. Transfection of F98 cells with constitutively active mutant of AKT (AKT/CA), however, did not significantly reverse Scutellaria-mediated inhibition of proliferation, indicating that Scutellaria flavonoids either directly inhibited Akt kinase activity or acted downstream of Akt. In vitro Akt kinase assay demonstrated that the SocL extract or wogonin could indeed bind to Akt and inhibit its kinase activity. This study provides the first in vivo evidence and mechanistic support for anti-glioma activity of Scutellaria flavonoids and has implications in potential usage of Scutellaria flavonoids in adjuvant therapy for malignant tumors, including gliomas.

A New alpha5beta1 integrin-dependent survival pathway through GSK3beta activation in leukemic cells

Background

Cell survival mediated by integrin engagement has been implicated in cell adhesion-mediated drug resistance. We have recently demonstrated that the activation of glycogen synthase kinase 3 β (GSK3β) is a new pathway supporting the chemoresistance of leukemic cells adhered to fibronectin.

Methodology and Principal Findings

We show here that in conditions of serum starvation, the fibronectin receptor α₅β₁ integrin, but not α₄β₁, induced activation of GSK3β through Ser-9 dephosphorylation in adherent U937 cells. The GSK3β-dependent survival pathway occurred in adherent leukemic cells from patients but not in the HL-60 and KG1 cell lines. In adhesion, activated GSK3β was found in the cytosol/plasma membrane compartment and was co-immunoprecipitated with α₅ integrin, the phosphatase PP2A and the scaffolding protein RACK1. PP2A and its regulatory subunit B' regulated the Ser-9 phosphorylation of GSK3β. In adherent leukemic cells, α₅β₁ integrin but not α₄β₁ upregulated the resistance to TNFα-induced apoptosis. Both extrinsic and intrinsic apoptotic pathways were under the control of α₅β₁ and GSK3β.

Conclusions and Significance

Our data show that, upon serum starvation, α₅β₁ integrin engagement could regulate specific pro-survival functions through the activation of GSK3β.