Signal transducer and activator of transcription-3: a molecular hub for signaling pathways in gliomas

Additive effect on survival of Raf kinase inhibitor protein and signal transducer and activator of transcription 3 in high-grade glioma

BACKGROUND

Animal studies have shown cooperative contribution of the Ras/Raf/MAPK and PI3K/Akt/mTOR signaling pathways in glioblastoma formation. However, this joint action has not yet been confirmed in human studies.

METHODS

The expression of Raf kinase inhibitory protein (RKIP) was examined in 159 patients with high-grade and low-grade gliomas and correlated with previously obtained data on the activation of signal transducer and activator of transcription 3 (STAT3), a downstream effector of the PI3K/Akt/mTOR signaling pathway.

RESULTS

RKIP expression was associated with a longer overall survival in high-grade glioma cases without showing a direct or inverse correlation with tyrosine-705 phosphorylation of STAT3 (pSTAT3). Notably, RKIP-positive and pSTAT3 negative cases demarcate a patients group with exceptionally long survival, exceeding the prognostic impact of each single marker.

CONCLUSIONS

The results of this study indicated that 1) RKIP expression correlates with tumor grade and is a marker for good prognosis in high-grade gliomas; 2) RKIP expression and lack of pSTAT3 have a cumulative prognostic impact; and 3) RKIP and pSTAT3 are likely to operate independently to influence survival. These findings represented the first human evidence of an additive effect of 2 distinct signaling pathways in high-grade glioma, suggesting that simultaneous inhibition of multiple pathways should be considered as a treatment strategy for these patients.

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.

Tumor heterogeneity is an active process maintained by a mutant EGFR-induced cytokine circuit in glioblastoma

Human solid tumors frequently have pronounced heterogeneity of both neoplastic and normal cells on the histological, genetic, and gene expression levels. While current efforts are focused on understanding heterotypic interactions between tumor cells and surrounding normal cells, much less is known about the interactions between and among heterogeneous tumor cells within a neoplasm. In glioblastoma multiforme (GBM), epidermal growth factor receptor gene (EGFR) amplification and mutation (EGFRvIII/DeltaEGFR) are signature pathogenetic events that are invariably expressed in a heterogeneous manner. Strikingly, despite its greater biological activity than wild-type EGFR (wtEGFR), individual GBM tumors expressing both amplified receptors typically express wtEGFR in far greater abundance than the DeltaEGFR lesion. We hypothesized that the minor DeltaEGFR-expressing subpopulation enhances tumorigenicity of the entire tumor cell population, and thereby maintains heterogeneity of expression of the two receptor forms in different cells. Using mixtures of glioma cells as well as immortalized murine astrocytes, we demonstrate that a paracrine mechanism driven by DeltaEGFR is the primary means for recruiting wtEGFR-expressing cells into accelerated proliferation in vivo. We determined that human glioma tissues, glioma cell lines, glioma stem cells, and immortalized mouse Ink4a/Arf(-/-) astrocytes that express DeltaEGFR each also express IL-6 and/or leukemia inhibitory factor (LIF) cytokines. These cytokines activate gp130, which in turn activates wtEGFR in neighboring cells, leading to enhanced rates of tumor growth. Ablating IL-6, LIF, or gp130 uncouples this cellular cross-talk, and potently attenuates tumor growth enhancement. These findings support the view that a minor tumor cell population can potently drive accelerated growth of the entire tumor mass, and thereby actively maintain tumor cell heterogeneity within a tumor mass. Such interactions between genetically dissimilar cancer cells could provide novel points of therapeutic intervention.

Inhibition of the JAK-2/STAT3 signaling pathway impedes the migratory and invasive potential of human glioblastoma cells

The objective of current treatment strategies for glioblastoma (GBM) is cytoreduction. Unfortunately, the deleterious migratory and invasive behavior of glial tumors remains largely unattended. The transcription factor signal transducer and activator of transcription (STAT) 3 is known to be involved in the development and progression of many different tumor types, including malignant gliomas. Beside other biological effects, STAT3 controls cell proliferation and tissue remodeling, processes common to both wound healing and tumor dissemination. Here, we report on impeded migratory and invasive potential of five different glioblastoma cell lines after treatment with AG490, a pharmacological inhibitor of the upstream STAT3 activator Janus kinase (JAK) 2. STAT3 was constitutively activated in all the cell lines tested, and treatment with AG490 eliminated the biologically active, tyrosine705-phosphorylated form of STAT3 in a dose-dependent fashion, as determined by Western blot analysis. Inhibition of activated STAT3 was paralleled by a decrease in transcriptional expression of the STAT3 target genes MMP-2 and MMP-9, and led to reduced proteolytic activity, as determined by zymography. Accordingly, the migratory behavior of all five GBM cell lines was impeded in monolayer wound-healing assays; invasive capacity in matrigel-coated trans-well assays was also hampered by treatment with AG490. The proliferative activity of the cell lines was also significantly reduced after treatment with AG490. The effects elicited by STAT3 inhibition were observed in both PTEN-expressing and PTEN-deficient cells. Because pharmacological inhibition of the JAK-2/STAT3 signaling pathway affects not only tumor cell proliferation but also the characteristic features of malignant gliomas, i.e. migration and invasion pertinent to invariable tumor recurrence and high morbidity, our findings support the idea that STAT3 is a suitable target in the treatment of brain tumors.

NF-kappaB and STAT3 signaling in glioma: targets for future therapies

Glioblastoma remains the most clinically challenging tumor of the CNS, as evidenced by the dismal change in overall survival over the past 50 years. However, recent advances in high-throughput screening techniques have given rise to a wealth of new information regarding the aberrant signaling pathways that drive the tumor phenotype. Two of these so-called 'oncopathways' are NF-kappaB and JAK/STAT. This review will describe the basic mechanisms of these pathways, explore the relevance of NF-kappaB and JAK/STAT signaling in glioblastoma, and look ahead to experimental compounds that will integrate our knowledge of these pathways into existing therapies.

A novel small molecule, LLL12, inhibits STAT3 phosphorylation and activities and exhibits potent growth-suppressive activity in human cancer cells

Constitutive activation of signal transducer and activator of transcription 3 (STAT3) signaling is frequently detected in cancer, promoting its emergence as a promising target for cancer treatment. Inhibiting constitutive STAT3 signaling represents a potential therapeutic approach. We used structure-based design to develop a nonpeptide, cell-permeable, small molecule, termed as LLL12, which targets STAT3. LLL12 was found to inhibit STAT3 phosphorylation (tyrosine 705) and induce apoptosis as indicated by the increases of cleaved caspase-3 and poly (ADP-ribose) polymerase in various breast, pancreatic, and glioblastoma cancer cell lines expressing elevated levels of STAT3 phosphorylation. LLL12 could also inhibit STAT3 phosphorylation induced by interleukin-6 in MDA-MB-453 breast cancer cells. The inhibition of STAT3 by LLL12 was confirmed by the inhibition of STAT3 DNA binding activity and STAT3-dependent transcriptional luciferase activity. Downstream targets of STAT3, cyclin D1, Bcl-2, and survivin were also downregulated by LLL12 at both protein and messenger RNA levels. LLL12 is a potent inhibitor of cell viability, with half-maximal inhibitory concentrations values ranging between 0.16 and 3.09 microM, which are lower than the reported JAK2 inhibitor WP1066 and STAT3 inhibitor S3I-201 in six cancer cell lines expressing elevated levels of STAT3 phosphorylation. In addition, LLL12 inhibits colony formation and cell migration and works synergistically with doxorubicin and gemcitabine. Furthermore, LLL12 demonstrated a potent inhibitory activity on breast and glioblastoma tumor growth in a mouse xenograft model. Our results indicate that LLL12 may be a potential therapeutic agent for human cancer cells expressing constitutive STAT3 signaling.

STAT3 tyrosine phosphorylation influences survival in glioblastoma

Signal transducer and activator of transcription protein 3 (STAT3) is a regulator of central nervous system (CNS) development and a promising therapeutic target in human cancers. Activation of STAT3 promotes oncogenesis in a variety of tissues, but knowledge of its role in glioblastoma is still limited. Recent results indicate that STAT3 acts as a tumor suppressor or an oncogene depending upon the genetic background of the tumor. Here we immunohistochemically assessed Y705-phosphorylated STAT3 (pY705-STAT3) in formalin-fixed, paraffin-embedded specimens of 111 patients with supratentorial glioblastomas and 25 patients with supratentorial grade III gliomas. We found that glioblastoma patients with high or very high numbers of pY705-STAT3-positive tumor cells had significantly shorter overall survival than those with no or low numbers (P = 0.001, Cox regression). Interestingly the proportion of grade III glioma cases with high or very high numbers of pY705-STAT3-positive tumor cells was similar to that in glioblastoma. Our findings provide evidence that activation of STAT3 by Y705 phosphorylation is linked with clinically more aggressive behavior in glioblastomas, but is most likely not associated with tumor progression of grade III gliomas. In sum, our results suggest that STAT3 inhibition should be considered as a therapeutic approach in malignant gliomas.

Sorafenib induces growth arrest and apoptosis of human glioblastoma cells through the dephosphorylation of signal transducers and activators of transcription 3

Glioblastoma is the most common type of primary brain tumor and is rapidly progressive with few treatment options. Here, we report that sorafenib (< or =10 micromol/L) inhibited cell proliferation and induced apoptosis in two established cell lines (U87 and U251) and two primary cultures (PBT015 and PBT022) from human glioblastomas. The effects of sorafenib on these tumor cells were associated with inhibiting phosphorylated signal transducers and activators of transcription 3 (STAT3; Tyr705). Expression of a constitutively activated STAT3 mutant partially blocked the effects of sorafenib, consistent with a role for STAT3 inhibition in the response to sorafenib. Phosphorylated Janus-activated kinase (JAK)1 was inhibited in U87 and U251 cells, whereas phosphorylated JAK2 was inhibited in primary cultures. Sodium vanadate, a general inhibitor of protein tyrosine phosphatases, blocked the inhibition of phosphorylation of STAT3 (Tyr705) induced by sorafenib. These data indicate that the inhibition of STAT3 activity by sorafenib involves both the inhibition of upstream kinases (JAK1 and JAK2) of STAT3 and increased phosphatase activity. Phosphorylation of AKT was also reduced by sorafenib. In contrast, mitogen-activated protein kinases were not consistently inhibited by sorafenib in these cells. Two key cyclins (D and E) and the antiapoptotic protein Mcl-1 were downregulated by sorafenib in both cell lines and primary cultures. Our data suggest that inhibition of STAT3 signaling by sorafenib contributes to growth arrest and induction of apoptosis in glioblastoma cells. These findings provide a rationale for potential treatment of malignant gliomas with sorafenib. Mol Cancer Ther; 9(4); 953-62. (c)2010 AACR.

Disruption of astrocyte STAT3 signaling decreases mitochondrial function and increases oxidative stress in vitro

BACKGROUND

Astrocytes exert a wide variety of functions in health and disease and respond to a wide range of signaling pathways, including members of the Janus-kinase signal transducers and activators of transcription (Jak-STAT) family. We have recently shown that STAT3 is an important regulator of astrocyte reactivity after spinal cord injury in vivo[1].

METHODOLOGY/PRINCIPAL FINDINGS

Here, we used both a conditional gene deletion strategy that targets the deletion of STAT3 selectively to astrocytes (STAT3-CKO), and a pharmacological inhibitor of JAK-2, AG490, in cultured astrocytes in vitro, to investigate potential functions and molecules influenced by STAT3 signaling in relation to mitochondrial function and oxidative stress. Our findings show that the absence of STAT3 signaling in astrocytes leads to (i) increased production of superoxide anion and other reactive oxygen species and decreased level of glutathione, (ii) decreased mitochondrial membrane potential and decreased ATP production, and (iii) decreased rate of cell proliferation. Many of the differences observed in STAT3-CKO astrocytes were distinctly altered by exposure to rotenone, suggesting a role for complex I of the mitochondrial electron transport chain. Gene expression microarray studies identified numerous changes in STAT3-CKO cells that may have contributed to the identified deficits in cell function.

CONCLUSIONS/SIGNIFICANCE

Taken together, these STAT3-dependent alterations in cell function and gene expression have relevance to both reactive gliosis and to the support and protection of surrounding cells in neural tissue.

The neurofibromatosis type 1 tumor suppressor controls cell growth by regulating signal transducer and activator of transcription-3 activity in vitro and in vivo

Neurofibromatosis type 1 (NF1) is a common cancer predisposition syndrome in which affected individuals develop benign and malignant nerve tumors. The NF1 gene product neurofibromin negatively regulates Ras and mammalian target of rapamycin (mTOR) signaling, prompting clinical trials to evaluate the ability of Ras and mTOR pathway inhibitors to arrest NF1-associated tumor growth. To discover other downstream targets of neurofibromin, we performed an unbiased cell-based high-throughput chemical library screen using NF1-deficient malignant peripheral nerve sheath tumor (MPNST) cells. We identified the natural product, cucurbitacin-I (JSI-124), which inhibited NF1-deficient cell growth by inducing apoptosis. We further showed that signal transducer and activator of transcription-3 (STAT3), the target of cucurbitacin-I inhibition, was hyperactivated in NF1-deficient primary astrocytes and neural stem cells, mouse glioma cells, and human MPNST cells through Ser(727) phosphorylation, leading to increased cyclin D1 expression. STAT3 was regulated in NF1-deficient cells of murine and human origin in a TORC1- and Rac1-dependent manner. Finally, cucurbitacin-I inhibited the growth of NF1-deficient MPNST cells in vivo. In summary, we used a chemical genetics approach to reveal STAT3 as a novel neurofibromin/mTOR pathway signaling molecule, define its action and regulation, and establish STAT3 as a tractable target for future NF1-associated cancer therapy studies.

STAT3 signalling pathway is involved in the activation of microglia induced by 2.45 GHz electromagnetic fields

PURPOSE

Microglia activation plays a pivotal role in the initiation and progression of central nervous system (CNS) insult. The aim of the present work was to investigate the activation of microglia and involvement of signal transducer and activator of transcription 3 (STAT3) in microglia activation after 2.45 GHz electromagnetic fields (EMF) exposure.

MATERIALS AND METHODS

In this study, murine N9 microglial cells were exposed to 2.45 GHz EMF, the protein expressions of STAT3, Janus Tyrosine kinase 1 and 2(JAK1 and JAK2), phosphor-(Try705)STAT3 and DNA binding activity of STAT3 were examined by Western blot analysis and electrophoresis mobility shift assay (EMSA). Levels of the nitric oxide (NO) derivative nitrite were determined in the culture medium by the Griess reaction. The mRNA expression of tumour necrosis factor alpha (TNF-alpha) and inducible nitric oxide synthase (iNOS) were detected by reverse transcription and polymerase chain reaction (RT-PCR).

RESULTS

A significant increase of STAT3 DNA-binding ability was noted after exposure. Consistent with this, EMF rapidly induced phosphorylation of STAT3 and activated JAK1 and JAK2. In addition, EMF exposure increased transcription levels of the inflammation-associated genes, iNOS and TNF-alpha, which are reported to contain STAT-binding elements in their promoter region. P6, a JAK inhibitor, reduced induction of iNOS and TNF-alpha, nuclear factor binding activity, and activation of STAT3 in EMF-stimulated microglia.

CONCLUSION

These results provide evidence that EMF exposure can initiate the activation of microglia cells and STAT3 signalling involves in EMF-induced microglial activation.

The phosphorylation of ephrin-B2 ligand promotes glioma cell migration and invasion

To reveal molecular drivers of glioma invasion, two distinct glioblastoma (GBM) cell phenotypes (invading cells and tumor core cells) were collected from 19 GBM specimens using laser capture microdissection. Isolated RNA underwent whole human genome expression profiling to identify differentially expressed genes. Pathway enrichment analysis highlighted the bidirectional receptor/ligand tyrosine kinase system, EphB/ephrin-B, as the most tightly linked system to the invading cell phenotype. Clinical relevance of ephrin-B genes was confirmed in a clinically annotated expression data set of 195 brain biopsy specimens. Levels of ephrin-B1 and -B2 mRNA were significantly higher in GBM (n = 82) than in normal brain (n = 24). Kaplan-Meier analysis demonstrated ephrin-B2, but not ephrin-B1, expression levels were significantly associated with short term survival in malignant astrocytomas (n = 97, p = 0.016). In human brain tumor specimens, the production and phosphorylation of ephrin-B2 were high in GBM. Immunohistochemistry demonstrated ephrin-B2 localization primarily in GBM cells but not in normal brain. A highly invasive glioma cell line, U87, expressed high levels of ephrin-B2 compared with relatively less invasive cell lines. Treatment with EphB2/Fc chimera further enhanced migration and invasion of U87 cells, whereas treatment with an ephrin-B2 blocking antibody significantly slowed migration and invasion. Forced expression of ephrin-B2 in the U251 cell line stimulated migration and invasion in vitro and ex vivo, concomitant with tyrosine phosphorylation of ephrin-B2. These results demonstrate that high expression of ephrin-B2 is a strong predictor of short-term survival and that ephrin-B2 plays a critical role in glioma invasion rendering this signaling pathway as a potential therapeutic target.

Visualization of Stat3 and Stat5 transactivation activity with specific response element dependent reporter constructs integrated into lentiviral gene transfer vectors

BACKGROUND

Signal transducer and activator of transcription 3 and 5 (Stat3 and Stat5) play important roles in cell differentiation, proliferation, apoptosis and inflammation. They are transiently activated by ligand-receptor interactions in normal cells but are often found to be constitutively active in cancer cells. Analysis of their activation pattern is therefore important for the description of developmental processes and the understanding of cellular transformation.

MATERIALS AND METHODS

To visualize Stat3 and Stat5 transactivation activity in different cell types, we designed novel reporter constructs. These constructs comprise Stat3 or Stat5 specific promoter elements and reporter genes encoding β-galactosidase or fluorescent proteins. These constructs were integrated into lentiviral gene transfer vectors facilitating efficient transduction of most cell types.

RESULTS

The lentiviral reporter constructs were used to infect different cell types and their inducibility by activated Stat3 or Stat5 was measured. The Stat3-mCherry reporter was active in transduced tumor cells, which exhibit high levels of phosphorylated Stat3 and it was inducible in HepG2 liver cells by interleukin-6 treatment. The Stat5-LacZ reporter was active in cultured cells upon hormone induction of Stat5 and in primary mammary epithelial cells transplanted into cleared fat pads of mice during late pregnancy.

CONCLUSION

These novel reporter constructs are valuable tools to investigate and to distinguish between Stat3 and Stat5 activity in primary cells and cancer cells. They will also be useful in the discovery of drugs targeting Stat3 or Stat5. They can also be employed to generate transgenic mice and track Stat activity during development.

Challenges in clinical design of immunotherapy trials for malignant glioma

Glioblastoma multiforme (GBM) is the most common and lethal primary malignant brain tumor. The traditional treatments for GBM, including surgery, radiation, and chemotherapy, only modestly improve patient survival. Therefore, immunotherapy has emerged as a novel therapeutic modality. Immunotherapeutic strategies exploit the immune system's ability to recognize and mount a specific response against tumor cells, but not normal cells. Current immunotherapeutic approaches for glioma can be divided into 3 categories: immune priming (active immunotherapy), immunomodulation (passive immunotherapy), and adoptive immunotherapy. Immune priming sensitizes the patient's immune cells to tumor antigens using various vaccination protocols. In the case of immunomodulation, strategies are aimed at reducing suppressive cytokines in the tumor microenvironment or using immune molecules to specifically target tumor cells. Adoptive immunotherapy involves harvesting the patient's immune cells, followed by ex vivo activation and expansion before reinfusion. This article provides an overview of the interactions between the central nervous system and the immune system, and discusses the challenges facing current immunotherapeutic strategies.

Visfatin through STAT3 activation enhances IL-6 expression that promotes endothelial angiogenesis

Signal transducer and activator of transcription 3 (STAT3) acts as a mediator and biomarker in endothelial activation. We have recently shown that a novel adipokine visfatin promotes endothelial angiogenesis. The present study was to determine whether visfatin affects STAT3 activity and to explore the potential target gene(s). Here, we found that visfatin induced the activation of STAT3, as characterized by increased tyrosine phosphorylation, nuclear translocation, and DNA-binding activity in human endothelial cells. In addition, visfatin significantly upregulated mRNA and protein levels of endothelial interleukin-6 (IL-6), which was blocked by a specific inhibitor of STAT3 signaling and by the transfection of siRNA specific for STAT3. Furthermore, visfatin-induced angiogenesis was reduced by the inhibition of STAT3 signaling or neutralization of IL-6 function, as measured by tube formation, rat aortic ring assay, and mouse Matrigel plug assay. Taken together, our results provide the first example of STAT3-dependent endothelial IL-6 induction by visfatin and of the role of IL-6 in mediating visfatin-induced angiogenesis.

Manumycin inhibits STAT3, telomerase activity, and growth of glioma cells by elevating intracellular reactive oxygen species generation

The poor prognosis of glioblastoma multiforme and lack of effective therapy have necessitated the identification of new treatment strategies. We have previously reported that elevation of oxidative stress induces apoptosis of glioma cells. Because the farnesyltransferase inhibitor manumycin is known to induce reactive oxygen species (ROS) generation, we evaluated the effects of manumycin on glioma cells. Manumycin induced glioma cell apoptosis by elevating ROS generation. Treatment with the ROS inhibitor N-acetylcysteine blocked manumycin-induced apoptosis, caspase-3 activity, and PARP expression, indicating the involvement of increased ROS in the proapoptotic activity of manumycin. This heightened ROS level was accompanied by a concurrent decrease in antioxidants such as superoxide dismutase (SOD-1) and thioredoxin (TRX-1). SOD-1 overexpression protects glioma cells from manumycin-induced apoptosis. In addition, small interfering RNA-mediated knockdown of SOD-1 and TRX-1 expression also increased ROS generation and sensitivity of glioma cells to manumycin-induced cell death. Interestingly, suppressing ROS generation prevented manumycin-induced Ras inhibition. This study reports for the first time that Ras inhibition by manumycin is due to heightened ROS levels. We also report for the first time that manumycin inhibits the phosphorylation of signal transducer and activator of transcription 3 and telomerase activity in a ROS-dependent manner, which plays a crucial role in glioma resistance to apoptosis. In addition manumycin (i) induced the DNA-damage repair response, (ii) affected cell-cycle-regulatory molecules, and (iii) impaired the colony-forming ability of glioma cells in a ROS-dependent manner.

STAT3 in CD4+ T helper cell differentiation and inflammatory diseases

Jak/STAT pathways influence cell-fate decisions made by differentiating naïve T cells, regulate the intensity and duration of inflammatory responses and are implicated in pathogenic mechanisms of a number of chronic inflammatory diseases. Among the STATs, the STAT3 protein has emerged as an important determinant of whether the naïve T cell differentiates into regulatory (Treg) or an inflammatory (Th17) T cell lineage. STAT3 also has potent anti-inflammatory effects and regulates critical cellular processes such as, cell growth, apoptosis and transcription of inflammatory genes. Dysregulation of STAT3 pathway has therefore been implicated in the development of chronic inflammatory diseases, as well as, a number of malignant and neurodegenerative diseases. This review focuses on recent findings regarding the role of STAT3 in immunity, with particular emphasis on T cell lineage specification and disease etiology. New insights from animal models of uveitis, multiple sclerosis and inflammatory bowel diseases are discussed as exemplars of critical roles that STAT3 pathways play in inflammatory diseases and on how inhibiting STAT3 can be exploited to mitigate pathogenic autoimmunity.

Molecular and phenotypic characterisation of paediatric glioma cell lines as models for preclinical drug development

BACKGROUND

Although paediatric high grade gliomas resemble their adult counterparts in many ways, there appear to be distinct clinical and biological differences. One important factor hampering the development of new targeted therapies is the relative lack of cell lines derived from childhood glioma patients, as it is unclear whether the well-established adult lines commonly used are representative of the underlying molecular genetics of childhood tumours. We have carried out a detailed molecular and phenotypic characterisation of a series of paediatric high grade glioma cell lines in comparison to routinely used adult lines.

PRINCIPAL FINDINGS

All lines proliferate as adherent monolayers and express glial markers. Copy number profiling revealed complex genomes including amplification and deletions of genes known to be pivotal in core glioblastoma signalling pathways. Expression profiling identified 93 differentially expressed genes which were able to distinguish between the adult and paediatric high grade cell lines, including a number of kinases and co-ordinated sets of genes associated with DNA integrity and the immune response.

SIGNIFICANCE

These data demonstrate that glioma cell lines derived from paediatric patients show key molecular differences to those from adults, some of which are well known, whilst others may provide novel targets for evaluation in primary tumours. We thus provide the rationale and demonstrate the practicability of using paediatric glioma cell lines for preclinical and mechanistic studies.

Transient and etiology-related transcription regulation in cirrhosis prior to hepatocellular carcinoma occurrence

AIM: To search for transcription dysregulation that could (1) differentiate hepatocellular carcinoma (HCC)-free from HCC-related cirrhosis (2) differentiate HCC-free cirrhosis related to HCV from that related to alcohol intake.

METHODS: Using microarray analysis, we compared transcript levels in HCC-free cirrhosis (alcoholism: 7; hepatitis C: 7), HCC-associated cirrhosis (alcoholism: 10; hepatitis C: 10) and eight control livers. The identified transcripts were validated by qRT-PCR in an independent cohort of 45 samples (20 HCC-free cirrhosis; 15 HCC-associated cirrhosis and 10 control livers). We also confirmed our results by immunohistochemistry.

RESULTS: In HCC-free livers, we identified 70 transcripts which differentiated between alcoholic-related cirrhosis, HCV-related cirrhosis and control livers. They mainly corresponded to down-regulation. Dysregulation of Signal Transduction and Activator of Transcription-3 (STAT-3) was found along with related changes in STAT-3 targets which occurred in an etiology-dependent fashion in HCC-free cirrhosis. In contrast, in HCC, such transcription dysregulations were not observed.

CONCLUSION: We report that transcriptional dysregulations exist in HCC-free cirrhosis, are transiently observed prior to detectable HCC onset and may be appear like markers from cirrhosis to HCC transition.

Phosphatidylinositol 3-kinase/AKT pathway regulates the endoplasmic reticulum to golgi traffic of ceramide in glioma cells: a link between lipid signaling pathways involved in the control of cell survival

Different lines of evidence indicate that both aberrant activation of the phosphatidylinositol 3-OH kinase (PI3K)/Akt survival pathway and down-regulation of the death mediator ceramide play a critical role in the aggressive behavior, apoptosis resistance, and adverse clinical outcome of glioblastoma multiforme. Furthermore, the inhibition of the PI3K/Akt pathway and the up-regulation of ceramide have been found functional to the activity of many cytotoxic treatments against glioma cell lines and glioblastomas as well. A reciprocal control between PI3K/Akt and ceramide signaling in glioma cell survival/death is suggested by data demonstrating a protective role of PI3K/Akt on ceramide-induced cell death in glial cells. In this study we investigated the role of the PI3K/Akt pathway in the regulation of the ceramide metabolism in C6 glioma cells, a cell line in which the PI3K/Akt pathway is constitutively activated. Metabolic experiments performed with different radioactive metabolic precursors of sphingolipids and microscopy studies with fluorescent ceramides demonstrated that the chemical inhibition of PI3K and the transfection with a dominant negative Akt strongly inhibited ceramide utilization for the biosynthesis of complex sphingolipids by controlling the endoplasmic reticulum (ER) to Golgi vesicular transport of ceramide. These findings constitute the first evidence for a PI3K/Akt-dependent regulation of vesicle-mediated movements of ceramide in the ER-Golgi district. Moreover, the findings also suggest the activation of the PI3K/Akt pathway as crucial to coordinate the biosynthesis of membrane complex sphingolipids with cell proliferation and growth and/or to maintain low ceramide levels, especially as concerns those treatments that promote ceramide biosynthesis in the ER.

Loss of protein inhibitors of activated STAT-3 expression in glioblastoma multiforme tumors: implications for STAT-3 activation and gene expression

PURPOSE

STATs activate transcription in response to numerous cytokines, controlling proliferation, gene expression, and apoptosis. Aberrant activation of STAT proteins, particularly STAT-3, is implicated in the pathogenesis of many cancers, including GBM, by promoting cell cycle progression, stimulating angiogenesis, and impairing tumor immune surveillance. Little is known about the endogenous STAT inhibitors, the PIAS proteins, in human malignancies. The objective of this study was to examine the expression of STAT-3 and its negative regulator, PIAS3, in human tissue samples from control and GBM brains.

EXPERIMENTAL DESIGN

Control and GBM human tissues were analyzed by immunoblotting and immunohistochemistry to determine the activation status of STAT-3 and expression of the PIAS3 protein. The functional consequence of PIAS3 inhibition by small interfering RNA or PIAS3 overexpression in GBM cells was determined by examining cell proliferation, STAT-3 transcriptional activity, and STAT-3 target gene expression. This was accomplished using [(3)H]TdR incorporation, STAT-3 dominant-negative constructs, reverse transcription-PCR, and immunoblotting.

RESULTS AND CONCLUSIONS

STAT-3 activation, as assessed by tyrosine and serine phosphorylation, was elevated in GBM tissue compared with control tissue. Interestingly, we observed expression of PIAS3 in control tissue, whereas PIAS3 protein expression in GBM tissue was greatly reduced. Inhibition of PIAS3 resulted in enhanced glioblastoma cellular proliferation. Conversely, PIAS3 overexpression inhibited STAT-3 transcriptional activity, expression of STAT-3-regulated genes, and cell proliferation. We propose that the loss of PIAS3 in GBM contributes to enhanced STAT-3 transcriptional activity and subsequent cell proliferation.