Scatter factor/hepatocyte growth factor stimulation of glioblastoma cell cycle progression through G(1) is c-Myc dependent and independent of p27 suppression, Cdk2 activation, or E2F1-dependent transcription

Current understanding of epigenetics role in melanoma treatment and resistance

Melanoma is the most aggressive form of skin cancer resulting from genetic mutations in melanocytes. Several factors have been considered to be involved in melanoma progression, including genetic alteration, processes of damaged DNA repair, and changes in mechanisms of cell growth and proliferation. Epigenetics is the other factor with a crucial role in melanoma development. Epigenetic changes have become novel targets for treating patients suffering from melanoma. These changes can alter the expression of microRNAs and their interaction with target genes, which involves cell growth, differentiation, or even death. Given these circumstances, we conducted the present review to discuss the melanoma risk factors and represent the current knowledge about the factors related to its etiopathogenesis. Moreover, various epigenetic pathways, which are involved in melanoma progression, treatment, and chemo-resistance, as well as employed epigenetic factors as a solution to the problems, will be discussed in detail.

C-Myc Signaling Pathway in Treatment and Prevention of Brain Tumors

Brain tumors are responsible for high morbidity and mortality worldwide. Several factors such as the presence of blood-brain barrier (BBB), sensitive location in the brain, and unique biological features challenge the treatment of brain tumors. The conventional drugs are no longer effective in the treatment of brain tumors, and scientists are trying to find novel therapeutics for brain tumors. In this way, identification of molecular pathways can facilitate finding an effective treatment. c-Myc is an oncogene signaling pathway capable of regulation of biological processes such as apoptotic cell death, proliferation, survival, differentiation, and so on. These pleiotropic effects of c-Myc have resulted in much fascination with its role in different cancers, particularly brain tumors. In the present review, we aim to demonstrate the upstream and down-stream mediators of c-Myc in brain tumors such as glioma, glioblastoma, astrocytoma, and medulloblastoma. The capacity of c-Myc as a prognostic factor in brain tumors will be investigated. Our goal is to define an axis in which the c-Myc signaling pathway plays a crucial role and to provide direction for therapeutic targeting in these signaling networks in brain tumors.

HGF/MET Signaling in Malignant Brain Tumors

Hepatocyte growth factor (HGF) ligand and its receptor tyrosine kinase (RTK) mesenchymal-epithelial transition factor (MET) are important regulators of cellular processes such as proliferation, motility, angiogenesis, and tissue regeneration. In healthy adult somatic cells, this ligand and receptor pair is expressed at low levels and has little activity except when tissue injuries arise. In cancer cells, HGF/MET are often overexpressed, and this overexpression is found to correlate with tumorigenesis, metastasis, and poorer overall prognosis. This review focuses on the signaling of these molecules in the context of malignant brain tumors. RTK signaling pathways are among the most common and universally dysregulated pathways in gliomas. We focus on the role of HGF/MET in the following primary malignant brain tumors: astrocytomas, glioblastomas, oligodendrogliomas, ependymomas, and embryonal central nervous system tumors (including medulloblastomas and others). Brain metastasis, as well as current advances in targeted therapies, are also discussed.

Identification of subsets of IDH-mutant glioblastomas with distinct epigenetic and copy number alterations and stratified clinical risks

Background

IDH-mutant glioblastoma is classified by the 2016 CNS WHO as a group with good prognosis. However, the actual number of cases examined in the literature is relatively small. We hypothesize that IDH-mutant glioblastoma is not a uniform group and should be further stratified.

Methods

We conducted methylation profiles and estimated copy number variations of 57 IDH-mutant glioblastomas.

Results

Our results showed that 59.6% and 40.4% of tumors belonged to glioma-CpG island methylator phenotype (G-CIMP)-high and G-CIMP-low methylation subgroups, respectively. G-CIMP-low subgroup was associated with significantly worse overall survival (OS) as compared to G-CIMP-high (P = .005). CDKN2A deletion (42.1%) was the most common gene copy number variation, and was significantly associated with G-CIMP-low subgroup (P = .004). Other frequent copy number changes included mesenchymal-epithelial transition (MET) (5.3%), CCND2 (19.3%), PDGFRA (14.0%), CDK4 (12.3%), and EGFR (12.3%) amplification. Both CDKN2A deletion (P = .036) and MET amplification (P < .001) were associated with poor OS in IDH-mutant glioblastomas. Combined epigenetic signature and gene copy number variations separated IDH-mutant glioblastomas into Group 1 (G-CIMP-high), Group 2 (G-CIMP-low without CDKN2A nor MET alteration), and Group 3 (G-CIMP-low with CDKN2A and/or MET alteration). Survival analysis revealed Groups 1 and 2 exhibited a favorable OS (median survival: 619 d [20.6 mo] and 655 d [21.8 mo], respectively). Group 3 exhibited a significant shorter OS (median survival: 252 d [8.4 mo]). Multivariable analysis confirmed the independent prognostic significance of our Groups.

Conclusions

IDH-mutant glioblastomas should be stratified for risk with combined epigenetic signature and CDKN2A/MET status and some cases have poor outcome.

MicroRNA-Directed Cancer Therapies: Implications in Melanoma Intervention

Acquired tumor resistance to cancer therapies poses major challenges in the treatment of cancers including melanoma. Among several signaling pathways or factors that affect neocarcinogenesis, cancer progression, and therapies, altered microRNAs (miRNAs) expression has been identified as a crucial player in modulating the key pathways governing these events. While studies in the miRNA field have grown exponentially in the last decade, much remains to be discovered, particularly with respect to their roles in cancer therapies. Since immune and nonimmune signaling cascades prevail in cancers, identification and evaluation of miRNAs, their molecular mechanisms and cellular targets involved in the underlying development of cancers, and acquired therapeutic resistance would help in devising new strategies for the prognosis, treatment, and an early detection of recurrence. Importantly, in-depth validation of miRNA-targeted molecular events could lead to the development of accurate progression-risk biomarkers, improved effectiveness, and improved patient responses to standard therapies. The current review focuses on the roles of miRNAs with recent updates on regulated cell cycle and proliferation, immune responses, oncogenic/epigenetic signaling pathways, invasion, metastasis, and apoptosis, with broader attention paid to melanomagenesis and melanoma therapies.

Negative control of the HGF/c-MET pathway by TGF-β: a new look at the regulation of stemness in glioblastoma

Multiple target inhibition has gained considerable interest in combating drug resistance in glioblastoma, however, understanding the molecular mechanisms of crosstalk between signaling pathways and predicting responses of cancer cells to targeted interventions has remained challenging. Despite the significant role attributed to transforming growth factor (TGF)-β family and hepatocyte growth factor (HGF)/c-MET signaling in glioblastoma pathogenesis, their functional interactions have not been well characterized. Using genetic and pharmacological approaches to stimulate or antagonize the TGF-β pathway in human glioma-initiating cells (GIC), we observed that TGF-β exerts an inhibitory effect on c-MET phosphorylation. Inhibition of either mitogen-activated protein kinase (MAPK)/ extracellular signal-regulated kinase (ERK) or phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB/AKT) signaling pathway attenuated this effect. A comparison of c-MET-driven and c-MET independent GIC models revealed that TGF-β inhibits stemness in GIC at least in part via its negative regulation of c-MET activity, suggesting that stem cell (SC) maintenance may be controlled by the balance between these two oncogenic pathways. Importantly, immunohistochemical analyses of human glioblastoma and ex vivo single-cell gene expression profiling of TGF-β and HGF confirm the negative interaction between both pathways. These novel insights into the crosstalk of two major pathogenic pathways in glioblastoma may explain some of the disappointing results when targeting either pathway alone in human glioblastoma patients and inform on potential future designs on targeted pharmacological or genetic intervention.

Role and Therapeutic Targeting of the HGF/MET Pathway in Glioblastoma

Glioblastoma (GBM) is a lethal brain tumor with dismal prognosis. Current therapeutic options, consisting of surgery, chemotherapy and radiation, have only served to marginally increase patient survival. Receptor tyrosine kinases (RTKs) are dysregulated in approximately 90% of GBM; attributed to this, research has focused on inhibiting RTKs as a novel and effective therapy for GBM. Overexpression of RTK mesenchymal epithelial transition (MET), and its ligand, hepatocyte growth factor (HGF), in GBM highlights a promising new therapeutic target. This review will discuss the role of MET in cell cycle regulation, cell proliferation, evasion of apoptosis, cell migration and invasion, angiogenesis and therapeutic resistance in GBM. It will also discuss the modes of deregulation of HGF/MET and their regulation by microRNAs. As the HGF/MET pathway is a vital regulator of multiple pro-survival pathways, efforts and strategies for its exploitation for GBM therapy are also described.

E2F transcription factors associated with up-regulated genes in glioblastoma

BACKGROUND

Glioblastoma is considered to the most common and malignant brain tumor in adults. Patients have a median survival of approximately one year from diagnosis due to poor response to therapy.

OBJECTIVE

We applied bioinformatics approaches to predict transcription factors (TF) that are deregulated in glioblastoma in an attempt to point out molecular targets for therapy.

METHODS

Up-regulated genes in glioblastoma selected from public microarray data were submitted to two TF association analyses. Thereafter, the expression levels of TF obtained in the overlap of analyses were assessed by RT-qPCR carried out in seven glioblastoma cell lines (T98, U251, U138, U87, U343, M059J, and M059K).

RESULTS

E2F1 and E2F4 were highlighted in both TF analyses. However, only E2F1 was confirmed as significantly up-regulated in all glioblastoma cell lines in vitro.

CONCLUSION

E2F1 is a potential common regulator of differentially expressed genes in glioblastoma, despite the genetic heterogeneity of tumor cells.

Non-coding RNAs in skin cancers: An update

Skin cancers are the most common form of cancer in humans. They can largely be categorized into Melanoma and Non-melanoma skin cancers. The latter mainly includes Squamous Cell Carcinoma (SCC) and Basal Cell Carcinoma (BCC), and have a higher incidence than melanomas. There has been a recent emergence of interest in the role of non-coding RNA's in pathogenesis of skin cancers. The transcripts which lack any protein coding capacity are called non-coding RNA. These non-coding RNA are further classified based on their length; small non-coding RNA (<200 nucleotides) and long non-coding RNA (>200 nucleotides). ncRNA They are involved at multiple transcriptional, post transcriptional and epigenetic levels, modulating cell proliferation, angiogenesis, senescence and apoptosis. Their expression pattern has also been linked to metastases, drug resistance and long term prognosis. They have both diagnostic and prognostic significance for skin cancers, and can also be a target for future therapies for cutaneous malignancies. More research is needed to further utilize their potential as therapeutic targets.

E2F1 transcription factor and its impact on growth factor and cytokine signaling

E2F1 is a transcription factor involved in cell cycle regulation and apoptosis. The transactivation capacity of E2F1 is regulated by pRb. In its hypophosphorylated form, pRb binds and inactivates DNA binding and transactivating functions of E2F1. The growth factor stimulation of cells leads to activation of CDKs (cyclin dependent kinases), which in turn phosphorylate Rb and hyperphosphorylated Rb is released from E2F1 or E2F1/DP complex, and free E2F1 can induce transcription of several genes involved in cell cycle entry, induction or inhibition of apoptosis. Thus, growth factors and cytokines generally utilize E2F1 to direct cells to either fate. Furthermore, E2F1 regulates expressions of various cytokines and growth factor receptors, establishing positive or negative feedback mechanisms. This review focuses on the relationship between E2F1 transcription factor and cytokines (IL-1, IL-2, IL-3, IL-6, TGF-beta, G-CSF, LIF), growth factors (EGF, KGF, VEGF, IGF, FGF, PDGF, HGF, NGF), and interferons (IFN-α, IFN-β and IFN-γ).

Targeting MET for glioma therapy

Glioblastoma multiforme is the most common and most lethal of all primary brain tumors. Even with the standard therapy, life expectancy is still poor, with an average survival of approximately 14 months following initial diagnosis. Hence, there is an urgent need for novel treatment strategies that inhibit proliferation and angiogenesis in high-grade gliomas. One such strategy consists of inhibiting receptor tyrosine kinases, including MET and/or its ligand hepatocyte growth factor (HGF). Because of their widespread involvement in human cancer, HGF and MET have emerged as promising therapeutic targets, and some inhibitory agents that target them have already entered clinical trials. In this paper, the authors highlight recent evidence implicating HGF/MET pathway deregulation in glioblastoma multiforme, discuss therapeutic approaches to inhibit HGF/MET signaling, and summarize ongoing clinical trials targeting this pathway.

The role of microRNAs and long non-coding RNAs in the pathology, diagnosis, and management of melanoma

Melanoma is frequently lethal and its global incidence is steadily increasing. Despite the rapid development of different modes of targeted treatment, durable clinical responses remain elusive. A complete understanding of the molecular mechanisms that drive melanomagenesis is required, both genetic and epigenetic, in order to improve prevention, diagnosis, and treatment. There is increased appreciation of the role of microRNAs (miRNAs) in melanoma biology, including in proliferation, cell cycle, migration, invasion, and immune evasion. Data are also emerging on the role of long non-coding RNAs (lncRNAs), such as SPRY4-IT1, BANCR, and HOTAIR, in melanomagenesis. Here we review the data on the miRNAs and lncRNAs implicated in melanoma biology. An overview of these studies will be useful for providing insights into mechanisms of melanoma development and the miRNAs and lncRNAs that might be useful biomarkers or future therapeutic targets.

The role of ubiquitin-proteasome system in glioma survival and growth

High-grade gliomas represent a group of aggressive brain tumors with poor prognosis due to an inherent capacity of persistent cell growth and survival. The ubiquitin-proteasome system (UPS) is an intracellular machinery responsible for protein turnover. Emerging evidence implicates various proteins targeted for degradation by the UPS in key survival and proliferation signaling pathways of these tumors. In this review, we discuss the involvement of UPS in the regulation of several mediators and effectors of these pathways in malignant gliomas.

Interactions between SAP155 and FUSE-binding protein-interacting repressor bridges c-Myc and P27Kip1 expression

Oncogenic c-Myc plays a critical role in cell proliferation, apoptosis, and tumorigenesis, but the precise mechanisms that drive this activity remain largely unknown. P27Kip1 (CDKN1B) arrests cells in G1, and SAP155 (SF3B1), a subunit of the essential splicing factor 3b (SF3b) subcomplex of the spliceosome, is required for proper P27 pre-mRNA splicing. FUSE-binding protein-interacting repressor (FIR), a splicing variant of PUF60 lacking exon5, is a c-Myc transcriptional target that suppresses the DNA helicase p89 (ERCC3) and is alternatively spliced in colorectal cancer lacking the transcriptional repression domain within exon 2 (FIRΔexon2). FIR and FIRΔexon2 form a homo- or hetero-dimer that complexes with SAP155. Our study indicates that the FIR/FIRΔexon2/SAP155 interaction bridges c-Myc and P27 expression. Knockdown of FIR/FIRΔexon2 or SAP155 reduced p27 expression, inhibited its pre-mRNA splicing, and reduced CDK2/Cyclin E expression. Moreover, spliceostatin A, a natural SF3b inhibitor, markedly inhibited P27 expression by disrupting its pre-mRNA splicing and reduced CDK2/Cyclin E expression. The expression of P89, another FIR target, was increased in excised human colorectal cancer tissues. Knockdown of FIR reduced P89; however, the effects on P27 and P89 expression are not simply or directly related to altered FIR expression levels, indicating that the mechanical or physical interaction of the SAP155/FIR/FIRΔexon2 complex is potentially essential for sustained expression of both P89 and P27. Together, the interaction between SAP155 and FIR/FIRΔexon2 not only integrates cell-cycle progression and c-Myc transcription by modifying P27 and P89 expression but also suggests that the interaction is a potential target for cancer screening and treatment.

Induction of UGT1A1 and CYP2B6 by an antimitogenic factor in HepG2 cells is mediated through suppression of cyclin-dependent kinase 2 activity: cell cycle-dependent expression

Hepatocyte growth factor (HGF), an antimitogenic factor for HepG2 cells, increased mRNA and protein levels of UGT1A1 and CYP2B6, as well as the endogenous cyclin-dependent kinase (CDK) inhibitors p16, p21, and p27 in HepG2 cells but not in HuH6, Caco2, or MCF7 cells. Treatment with 1,4-diamino-2,3-dicyano-1,4-bis(methylthio)butadiene (U0126) (an extracellular signal-regulated kinase inhibitor) suppressed the HGF-induced expression of UGT1A1 and CYP2B6, as well as p16, p21, and p27 in HepG2 cells. The CDK inhibitor roscovitine also enhanced the expression of UGT1A1, CYP2B6, and CYP3A4. Transfection of anti-CDK2 siRNA led to elevated levels of UGT1A1, CYP2B6, and CYP3A4 in HepG2 and SW480 cells, whereas anti-CDK4 small interfering RNA (siRNA) did not significantly enhance the expression of these enzymes. In fact, CDK2 activity was decreased in HGF-treated HepG2 cells. In cells arrested in S phase by a thymidine block and then released into a synchronous cell cycle, there was a clear dissociation among the activation of CDK2 and the expression of UGT1A1, CYP2B6, and CYP3A4. Furthermore, the induction of CYP3A4 but not UGT1A1 or CYP2B6 mRNA expression by roscovitine was repressed in pregnane X receptor (PXR) siRNA-transfected HepG2 cells. Transfection with constitutive androstane receptor siRNA or PXR siRNA in HepG2 cells did not repress the HGF-stimulated expression of UGT1A1 mRNA. Taken together, our results show that the expression of UGT1A1 and CYP2B6 is negatively regulated through a CDK2 signaling pathway linked to cell cycle progression in HepG2 and SW480 cells, the mechanism of which may differ from that of CYP3A4 expression through PXR phosphorylated by CDK2.

Cyr61 mediates hepatocyte growth factor-dependent tumor cell growth, migration, and Akt activation

Certain tumor cell responses to the growth factor-inducible early response gene product CCN1/Cyr61 overlap with those induced by the hepatocyte growth factor (HGF)/c-Met signaling pathway. In this study, we investigate if Cyr61 is a downstream effector of HGF/c-Met pathway activation in human glioma cells. A semiquantitative immunohistochemical analysis of 112 human glioma and normal brain specimens showed that levels of tumor-associated Cyr61 protein correlate with tumor grade (P < 0.001) and with c-Met protein expression (r(2) = 0.4791, P < 0.0001). Purified HGF rapidly upregulated Cyr61 mRNA (peak at 30 minutes) and protein expression (peak at 2 hours) in HGF(-)/c-Met(+) human glioma cell lines via a transcription- and translation-dependent mechanism. Conversely, HGF/c-Met pathway inhibitors reduced Cyr61 expression in HGF(+)/c-Met(+) human glioma cell lines in vitro and in HGF(+)/c-Met(+) glioma xenografts. Targeting Cyr61 expression with small interfering RNA (siRNA) inhibited HGF-induced cell migration (P < 0.01) and cell growth (P < 0.001) in vitro. The effect of Cyr61 on HGF-induced Akt pathway activation was also examined. Cyr61 siRNA had no effect on the early phase of HGF-induced Akt phosphorylation (Ser(473)) 30 minutes after stimulation with HGF. Cyr61 siRNA inhibited a second phase of Akt phosphorylation measured 12 hours after cell stimulation with HGF and also inhibited HGF-induced phosphorylation of the Akt target glycogen synthase kinase 3alpha. We treated preestablished subcutaneous glioma xenografts with Cyr61 siRNA or control siRNA by direct intratumoral delivery. Cyr61 siRNA inhibited Cyr61 expression and glioma xenograft growth by up to 40% in a dose-dependent manner (P < 0.05). These results identify a Cyr61-dependent pathway by which c-Met activation mediates cell growth, cell migration, and long-lasting signaling events in glioma cell lines and possibly astroglial malignancies.

Expression of hepatocyte growth factor and its receptor c-Met in human pituitary adenomas

Hepatocyte growth factor (HGF) and its receptor c-Met have been known as key determinants of growth and angiogenesis in some brain tumors like gliomas, meningiomas, and schwannomas. But little is known about their expression in pituitary adenomas. In this study, the expression of HGF and c-Met in pituitary adenomas of different histology types was investigated by immunohistochemistry, and correlative analysis of their expression with microvessel density (MVD), Ki-67 expression, and other clinicopathologic factors was made. The results showed that the expression of HGF and c-Met exists in 98% (64 of 65) and 92% (60 of 65) pituitary adenomas, respectively, and co-expression of them existed in 91% (59 of 65) adenomas. HGF had significant correlation with MVD (Spearman's correlation coefficient, r = .31, P = .01) and Ki-67 (r = .32, P = .01). c-Met had significant correlation with MVD (r = .30, P = .02) and Ki-67 (r = .38, P = .00). HGF and c-Met expression had no significant correlation with age or extrasellar extension. There were no significant differences in HGF and c-Met expression between pituitary adenomas of different histology types. The results indicate that HGF and c-Met are widely expressed in pituitary adenomas, and their expression correlates with MVD and Ki-67 expression.

Acyl-CoA synthetase VL3 knockdown inhibits human glioma cell proliferation and tumorigenicity

The contribution of lipid metabolic pathways to malignancy is poorly understood. Expression of the fatty acyl-CoA synthetase ACSVL3 was found to be markedly elevated in clinical malignant glioma specimens but nearly undetectable in normal glia. ACSVL3 levels correlated with the malignant behavior of human glioma cell lines and glioma cells propagated as xenografts. ACSVL3 expression was induced by the activation of oncogenic receptor tyrosine kinases (RTK) c-Met and epidermal growth factor receptor. Inhibiting c-Met activation with neutralizing anti-hepatocyte growth factor monoclonal antibodies reduced ACSVL3 expression concurrent with tumor growth inhibition in vivo. ACSVL3 expression knockdown using RNA interference, which decreased long-chain fatty acid activation, inhibited anchorage-dependent and anchorage-independent glioma cell growth by approximately 70% and approximately 90%, respectively. ACSVL3-depleted cells were less tumorigenic than control cells, and subcutaneous xenografts grew approximately 60% slower than control tumors. Orthotopic xenografts produced by ACSVL3-depleted cells were 82% to 86% smaller than control xenografts. ACSVL3 knockdown disrupted Akt function as evidenced by RTK-induced transient decreases in total and phosphorylated Akt, as well as glycogen synthase kinase 3beta, via a caspase-dependent mechanism. Expressing constitutively active myr-Akt rescued cells from the anchorage-dependent and anchorage-independent growth inhibitory effects of ACSVL3 depletion. These studies show that ACSVL3 maintains oncogenic properties of malignant glioma cells via a mechanism that involves, in part, the regulation of Akt function.

Prognostic significance of c-Met expression in glioblastomas

BACKGROUND

The authors investigated whether expression of c-Met protein in glioblastomas is associated with overall survival and biologic features representing tumor invasiveness in patients with glioblastomas.

METHODS

Paraffin-embedded specimens of glioblastomas from 62 patients treated in a single institution were assessed by immunohistochemical (IHC) analysis of c-Met expression. On the basis of the clinical data for these patients, the association between c-Met expression and clinicobiologic features representing tumor invasiveness was analyzed.

RESULTS

c-Met overexpression was detected in 29.0% (18 of 62) of glioblastomas. In patients with c-Met overexpression, the median survival was 11.7 months (95% confidence interval [95% CI], 9.9 months-13.5 months), compared with a median survival of 14.3 months (95% CI, 7.6 months-21.0 months) for patients whose tumors had no or little expression of c-Met (P=.031). On the radiographic analysis, 9 of 18 patients (50%) with tumors overexpressing c-Met demonstrated invasive and multifocal lesions on the initial magnetic resonance images, whereas only 9 of 44 patients (20.5%) with tumors that expressed no or little c-Met demonstrated these features (P=.030). Using immunohistochemistry, we also found a significant association between c-Met expression and matrix metalloproteinase-2,-9 (P=.020 and P=.013). Furthermore, Myc overexpression was found to be closely correlated with c-Met overexpression on IHC analysis (P=.004).

CONCLUSIONS

The authors suggest that c-Met overexpression is associated with shorter survival time and poor treatment response in glioblastomas, the mechanism for which is elevated tumor invasiveness on the molecular and clinical phenotypes. This implies that more effective therapeutic strategies targeting c-Met receptors may have important clinical implication.

Hepatocyte growth factor enhances death receptor-induced apoptosis by up-regulating DR5

BACKGROUND

Hepatocyte growth factor (HGF) and its receptor c-MET are commonly expressed in malignant gliomas and embryonic neuroectodermal tumors including medulloblastoma and appear to play an important role in the growth and dissemination of these malignancies. Dependent on cell context and the involvement of specific downstream effectors, both pro- and anti-apoptotic effects of HGF have been reported.

METHODS

Human medulloblastoma cells were treated with HGF for 24-72 hours followed by death receptor ligand TRAIL (Tumor necrosis factor-related apoptosis-inducing ligand) for 24 hours. Cell death was measured by MTT and Annexin-V/PI flow cytometric analysis. Changes in expression levels of targets of interest were measured by Northern blot analysis, quantitative reverse transcription-PCR, Western blot analysis as well as immunoprecipitation.

RESULTS

In this study, we show that HGF promotes medulloblastoma cell death induced by TRAIL. TRAIL alone triggered apoptosis in DAOY cells and death was enhanced by pre-treating the cells with HGF for 24-72 h prior to the addition of TRAIL. HGF (100 ng/ml) enhanced TRAIL (10 ng/ml) induced cell death by 36% (P<0.001). No cell death was associated with HGF alone. Treating cells with PHA-665752, a specific c-Met receptor tyrosine kinase inhibitor, significantly abrogated the enhancement of TRAIL-induced cell death by HGF, indicating that its death promoting effect requires activation of its canonical receptor tyrosine kinase. Cell death induced by TRAIL+HGF was predominately apoptotic involving both extrinsic and intrinsic pathways as evidenced by the increased activation of caspase-3, 8, 9. Promotion of apoptosis by HGF occurred via the increased expression of the death receptor DR5 and enhanced formation of death-inducing signal complexes (DISC).

CONCLUSION

Taken together, these and previous findings indicate that HGF:c-Met pathway either promotes or inhibits medulloblastoma cell death via pathway and context specific mechanisms.

Drug development against metastasis-related genes and their pathways: a rationale for cancer therapy

It is well recognized that the majority of cancer related deaths is caused by metastatic diseases. Therefore, there is an urgent need for the development of therapeutic intervention specifically targeted to the metastatic process. In the last decade, significant progress has been made in this research field, and many new concepts have emerged that shed light on the molecular mechanism of metastasis cascade which is often portrayed as a succession of six distinct steps; localized invasion, intravasation, translocation, extravasation, micrometastasis and colonization. Successful metastasis is dependent on the balance and complex interplay of both the metastasis promoters and suppressors in each step. Therefore, the basic strategy of our interventions is aimed at either blocking the promoters or potentiating the suppressors in this disease process. Toward this goal, various kinds of antibodies and small molecules have been designed. These include agents that block the ligand-recepter interaction of metastasis promoters (HGF/c-Met), antagonize the metastasis-promoting enzymes (AMF, uPA and MMP) and inhibit the transcriptional activity of metastasis promoter (beta-Catenin). On the other hand, the intriguing roles of metastasis suppressors and their signal pathways have been extensively studied and various attempts have been made to potentiate these factors. Small molecules have been developed to restore the expression or mimic the function of metastasis-suppressor genes such as NM23, E-cadherin, Kiss-1, MKK4 and NDRG1, and some of them are under clinical trials. This review summarizes our current understanding of the molecular pathway of tumor metastasis and discusses strategies and recent development of anti-metastatic drugs.

Transcription-dependent epidermal growth factor receptor activation by hepatocyte growth factor

The mechanisms and biological implications of coordinated receptor tyrosine kinase coactivation remain poorly appreciated. Epidermal growth factor receptor (EGFR) and c-Met are frequently coexpressed in cancers, including those associated with hepatocyte growth factor (HGF) overexpression, such as malignant astrocytoma. In a previous analysis of the HGF-induced transcriptome, we found that two EGFR agonists, transforming growth factor-alpha and heparin-binding epidermal growth factor-like growth factor (HB-EGF), are prominently up-regulated by HGF in human glioma cells. We now report that stimulating human glioblastoma cells with recombinant HGF induces biologically relevant EGFR activation. EGFR phosphorylation at Tyr(845) and Tyr(1068) increased 6 to 24 h after cell stimulation with HGF and temporally coincided with the induction of transforming growth factor-alpha (~5-fold) and HB-EGF (~23-fold) expression. Tyr(845) and Tyr(1068) phosphorylation, in response to HGF, was inhibited by cycloheximide and actinomycin D, consistent with a requirement for DNA transcription and RNA translation. Specifically, blocking HB-EGF binding to EGFR with the antagonist CRM197 inhibited HGF-induced EGFR phosphorylation by 60% to 80% and inhibited HGF-induced S-G(2)-M transition. CRM197 also inhibited HGF-induced anchorage-dependent cell proliferation but had no effect on HGF-mediated cytoprotection. These findings establish that EGFR can be activated with functional consequences by HGF as a result of EGFR ligand expression. This transcription-dependent cross-talk between the HGF receptor c-Met and EGFR expands our understanding of receptor tyrosine kinase signaling networks and may have considerable consequences for oncogenic mechanisms and cancer therapeutics.

Ribotoxic stress sensitizes glioblastoma cells to death receptor induced apoptosis: requirements for c-Jun NH2-terminal kinase and Bim

A prominent feature of glioblastoma is its resistance to death receptor-mediated apoptosis. In this study, we explored the possibility of modulating death receptor-induced cell death with the c-Jun-NH2-terminal kinase (JNK) activator anisomycin. Anisomycin activates JNK by inactivating the ribosome and inducing "ribotoxic stress." We found that anisomycin and death receptor ligand anti-Fas antibody CH-11 or tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) synergistically induce apoptosis in multiple human glioblastoma cell lines. For example, in U87 cells, anisomycin reduced the IC50 of CH-11 by more than 20-fold (from 500 to 25 ng/mL). Cell viability in response to anisomycin, CH-11, and their combination was 79%, 91%, and 28% (P<0.001), respectively. Anisomycin and TRAIL were found to be similarly synergistic in glioblastoma cells maintained as tumor xenografts. The potentiation of death receptor-dependent cell death by anisomycin was specific because emetine, another ribosome inhibitor that does not induce ribotoxic stress or activate JNK, did not have a similar effect. Synergistic cell death was predominantly apoptotic involving both extrinsic and intrinsic pathways. Expression of Fas, FasL, FLIP, and Fas-associated death domain (FADD) was not changed following treatment with anisomycin+CH-11. JNK was activated 10- to 22-fold by anisomycin+CH-11 in U87 cells. Inhibiting JNK activation with pharmacologic inhibitors of JNKK and JNK or with dominant negative mitogen-activated protein kinase (MAPK) kinase kinase 2 (MEKK2) significantly prevented cell death induced by the combination of anisomycin+CH-11. We further found that anisomycin+CH-11 up-regulated the proapoptotic protein Bim by approximately 14-fold. Simultaneously inhibiting Bim expression and JNK activation additively desensitized U87 cells to anisomycin+CH-11. These findings show that anisomycin-induced ribotoxic stress sensitizes glioblastoma cells to death receptor-induced apoptosis via a specific mechanism requiring both JNK activation and Bim induction.

The scatter factor/hepatocyte growth factor: c-met pathway in human embryonal central nervous system tumor malignancy

Embryonal central nervous system (CNS) tumors, which comprise medulloblastoma, are the most common malignant brain tumors in children. The role of the growth factor scatter factor/hepatocyte growth factor (SF/HGF) and its tyrosine kinase receptor c-Met in these tumors has been until now completely unknown. In the present study, we show that human embryonal CNS tumor cell lines and surgical tumor specimens express SF/HGF and c-Met. Furthermore, c-Met mRNA expression levels statistically significantly correlate with poor clinical outcome. Treatment of medulloblastoma cells with SF/HGF activates c-Met and downstream signal transduction as evidenced by c-Met, mitogen-activated protein kinase, and Akt phosphorylation. SF/HGF induces tumor cell proliferation, anchorage-independent growth, and cell cycle progression beyond the G1-S checkpoint. Using dominant-negative Cdk2 and a degradation stable p27 mutant, we show that cell cycle progression induced by SF/HGF requires Cdk2 function and p27 inhibition. SF/HGF also protects medulloblastoma cells against apoptosis induced by chemotherapy. This cytoprotective effect is associated with reduction of proapoptotic cleaved poly(ADP-ribose) polymerase and cleaved caspase-3 proteins and requires phosphoinositide 3-kinase activity. SF/HGF gene transfer to medulloblastoma cells strongly enhances the in vivo growth of s.c. and intracranial tumor xenografts. SF/HGF-overexpressing medulloblastoma xenografts exhibit increased invasion and morphologic changes that resemble human large cell anaplastic medulloblastoma. This first characterization establishes SF/HGF:c-Met as a new pathway of malignancy with multifunctional effects in human embryonal CNS tumors.

Scatter factor/hepatocyte growth factor in brain tumor growth and angiogenesis

The multifunctional growth factor scatter factor/hepatocyte growth factor (SF/HGF) and its receptor tyrosine kinase c-Met have emerged as key determinants of brain tumor growth and angiogenesis. SF/HGF and c-Met are expressed in brain tumors, the expression levels frequently correlating with tumor grade, tumor blood vessel density, and poor prognosis. Overexpression of SF/HGF and/or c-Met in brain tumor cells enhances their tumorigenicity, tumor growth, and tumor-associated angiogenesis. Conversely, inhibition of SF/HGF and c-Met in experimental tumor xenografts leads to inhibition of tumor growth and tumor angiogenesis. SF/HGF is expressed and secreted mainly by tumor cells and acts on c-Met receptors that are expressed in tumor cells and vascular endothelial cells. Activation of c-Met leads to induction of proliferation, migration, and invasion and to inhibition of apoptosis in tumor cells as well as in tumor vascular endothelial cells. Activation of tumor endothelial c-Met also induces extracellular matrix degradation, tubule formation, and angiogenesis in vivo. SF/HGF induces brain tumor angiogenesis directly through only partly known mechanisms and indirectly by regulating other angiogenic pathways such as VEGF. Different approaches to inhibiting SF/HGF and c-Met have been recently developed. These include receptor antagonism with SF/HGF fragments such as NK4, SF/HGF, and c-Met expression inhibition with U1snRNA/ribozymes; competitive ligand binding with soluble Met receptors; neutralizing antibodies to SF/HGF; and small molecular tyrosine kinase inhibitors. Use of these inhibitors in experimental tumor models leads to inhibition of tumor growth and angiogenesis. In this review, we summarize current knowledge of how the SF/HGF:c-Met pathway contributes to brain tumor malignancy with a focus on glioma angiogenesis.

Proliferation and invasion: plasticity in tumor cells

Invasive and proliferative phenotypes are fundamental components of malignant disease, yet basic questions persist about whether tumor cells can express both phenotypes simultaneously and, if so, what are their properties. Suitable in vitro models that allow characterization of cells that are purely invasive are limited because proliferation is required for cell maintenance. Here, we describe glioblastoma cells that are highly invasive in response to hepatocyte growth factor/scatter factor (HGF/SF). From this cell population, we selected subclones that were highly proliferative or displayed both invasive and proliferative phenotypes. The biological activities of invasion, migration, urokinase-type plasminogen activation, and branching morphogenesis exclusively partitioned with the highly invasive cells, whereas the highly proliferative subcloned cells uniquely displayed anchorage independent growth in soft agar and were highly tumorigenic as xenografts in immune-compromised mice. In response to HGF/SF, the highly invasive cells signal through the MAPK pathway, whereas the selection of the highly proliferative cells coselected for signaling through Myc. Moreover, in subcloned cells displaying both invasive and proliferative phenotypes, both signaling pathways are activated by HGF/SF. These results show how the mitogen-activated protein kinase and Myc pathways can cooperate to confer both invasive and proliferative phenotypes on tumor cells and provide a system for studying how transitions between invasion and proliferation can contribute to malignant progression.

Targeting the c-Met Pathway Potentiates Glioblastoma Responses to γ-Radiation

PURPOSE

Resistance to current cytotoxic therapies limits the treatment of most solid malignancies. This results, in part, from the overactivation of receptor tyrosine kinases and their downstream pathways in tumor cells and their associated vasculature. In this report, we ask if targeting the multifunctional mitogenic, cytoprotective, and angiogenic scatter factor/hepatocyte growth factor (SF/HGF)/c-Met pathway potentiates antitumor responses to gamma-radiation.

EXPERIMENTAL DESIGN

Endogenous expression of SF/HGF and c-Met was targeted in U87 MG human malignant glioma cells and xenografts using chimeric U1/ribozymes. The effects of U1/ribozymes +/- gamma-radiation on glioma cell proliferation, apoptosis, xenograft growth, and animal survival were examined.

RESULTS

U1/ribozymes knocked down SF/HGF and c-Met mRNA and protein levels, sensitized cells to gamma-radiation (P < 0.005), and enhanced radiation-induced caspase-dependent cytotoxicity in vitro (P < 0.005). Intravenous U1/ribozyme therapy as liposome/DNA complexes or radiation alone modestly and transiently inhibited the growth of s.c. U87 xenografts. Combining the therapies caused tumor regression and a 40% tumor cure rate. In animals bearing intracranial xenografts, long-term survival was 0% in response to radiation, 20% in response to intratumoral adenoviral-based U1/ribozyme delivery, and 80% (P < 0.0005) in response to combining U1/ribozymes with radiation. This apparent synergistic antitumor response was associated with a approximately 70% decrease in cell proliferation (P < 0.001) and a approximately 14- to 40-fold increase in apoptosis (P < 0.0001) within xenografts.

CONCLUSIONS

Targeting the SF/HGF/c-Met pathway markedly potentiates the anti-glioma response to gamma-radiation. Clinical trials using novel SF/HGF/c-Met pathway inhibitors in glioma and other malignancies associated with c-Met activation should ultimate include concurrent radiation and potentially other cytotoxic therapeutics.

Hepatocyte growth factor, its receptor, and their potential value in cancer therapies

Hepatocyte growth factor plays multiple roles in cancer, by acting as a motility and invasion stimulating factor, promoting metastasis and tumour growth. Furthermore, it acts as a powerful angiogenic factor. The pivotal role of this factor in cancer has indicated HGF as being a potential target in cancer therapies. The past few years have seen rapid progress in developing tools in targeting HGF, in the context of cancer therapies, including development of antagonists, small compounds, antibodies and genetic approaches. The current article discusses the potential value of HGF and its receptor as targets in cancer therapies, the current development in anti-HGF research, and the clinical value of HGF in prognosis and treatment.

Neuronal pentraxin 1: a novel mediator of hypoxic-ischemic injury in neonatal brain

Neonatal hypoxic-ischemic brain injury is a major cause of neurological disability and mortality. Its therapy will likely require a greater understanding of the discrete neurotoxic molecular mechanism(s) triggered by hypoxia-ischemia (HI). Here, we investigated the role of neuronal pentraxin 1 (NP1), a member of a newly recognized subfamily of "long pentraxins," in the HI injury cascade. Neonatal brains developed marked infarcts in the ipsilateral cerebral hemisphere at 24 hr and showed significant loss of ipsilateral striatal, cortical, and hippocampal volumes at 7 d after HI compared with the contralateral hemisphere and sham controls. Immunofluorescence analyses revealed elevated neuronal expression of NP1 in the ipsilateral cerebral cortex from 6 hr to 7 d and in the hippocampal CA1 and CA3 regions from 24 hr to 7 d after HI. These same brain areas developed infarcts and terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling-positive cells within 24-48 hr of HI. In primary cortical neurons, NP1 protein was induced >2.5-fold (p < 0.001) after their exposure to hypoxia that caused approximately 30-40% neuronal death. Transfecting cortical neurons with antisense oligodeoxyribonucleotides directed against NP1 mRNA (NP1AS) significantly inhibited (p < 0.01) hypoxia-induced NP1 protein induction and neuronal death (p < 0.001), demonstrating a specific requirement of NP1 in hypoxic neuronal injury. NP1 protein colocalized and coimmunoprecipitated with the fast excitatory AMPA glutamate receptor subunit (GluR1) in primary cortical neurons, and hypoxia induced a time-dependent increase in NP1-GluR1 interactions. NPIAS also protected against AMPA-induced neuronal death (p < 0.05), implicating a role for NP1 in the excitotoxic cascade. Our results show that NP1 induction mediates hypoxic-ischemic injury probably by interacting with and modulating GluR1 and potentially other excitatory glutamate receptors.

TGF-beta signaling in fibroblasts modulates the oncogenic potential of adjacent epithelia

Stromal cells can have a significant impact on the carcinogenic process in adjacent epithelia. The role of transforming growth factor-beta (TGF-beta) signaling in such epithelial-mesenchymal interactions was determined by conditional inactivation of the TGF-beta type II receptor gene in mouse fibroblasts (Tgfbr2fspKO). The loss of TGF-beta responsiveness in fibroblasts resulted in intraepithelial neoplasia in prostate and invasive squamous cell carcinoma of the forestomach, both associated with an increased abundance of stromal cells. Activation of paracrine hepatocyte growth factor (HGF) signaling was identified as one possible mechanism for stimulation of epithelial proliferation. Thus, TGF-beta signaling in fibroblasts modulates the growth and oncogenic potential of adjacent epithelia in selected tissues.

Vascular endothelial growth factor mediates vasogenic edema in acute lead encephalopathy

Brain injury from inorganic Pb(2+) is considered the most important environmental childhood health hazard worldwide. The microvasculature of the developing brain is uniquely susceptible to high level Pb(2+) toxicity (ie, Pb(2+) encephalopathy) characterized by cerebellar hemorrhage, increased blood-brain barrier permeability, and vasogenic edema. However, the specific molecular mediators of Pb(2+) encephalopathy have been elusive. We found that Pb(2+) induces vascular endothelial growth factor/vascular permeability factor (VEGF) in cultured astrocytes (J Biol Chem, 2000;275:27874-27882). The study presented here asks if VEGF dysregulation contributes mechanistically to Pb(2+) encephalopathy. Neonatal rats exposed to 4% Pb-carbonate develop the histopathological features of Pb(2+) encephalopathy seen in children. Cerebellar VEGF expression increased approximately twofold (p < 0.01) concurrent with the development of cerebellar microvascular hemorrhage, enhanced vascular permeability to serum albumin, and vasogenic cerebellar edema (p < 0.01). No change in VEGF expression occurred in cerebral cortex that does not develop these histopathological complications of acute Pb(2+) intoxication. Pb(2+) exposure increased phosphorylation of cerebellar Flk-1 VEGF receptors and the Flk-1 inhibitor CEP-3967 completely blocked cerebellar edema formation without affecting microhemorrhage formation or blood-brain barrier permeability. This establishes that Pb(2+)-induced vasogenic edema formation develops via a Flk-1-dependent mechanism and suggests that the vascular permeability caused by Pb(2+) is Flk-1 independent.

Targeted expression of HGF/SF in mouse mammary epithelium leads to metastatic adenosquamous carcinomas through the activation of multiple signal transduction pathways

Overexpression of hepatocyte growth factor (HGF), also called scatter factor (SF), and its receptor c-Met are associated with poor prognosis for cancer patients. In particular, breast cancer cells can produce HGF that acts in a paracrine as well as in an autocrine manner. Therefore, HGF and c-Met are putative targets for cancer therapy. To explore HGF/c-Met signaling in breast cancer, we have generated transgenic mice expressing HGF specifically in mammary epithelium under the transcriptional control of the whey acidic protein (WAP) gene promoter. WAP-HGF transgenic females developed hyperplastic ductal trees and multifocal invasive tumors after several pregnancies, some of which progressed to lung metastases. Tumors produced HGF and displayed phosphorylated c-Met, which correlated with increased Akt as well as c-myc activation. A high growth rate, as demonstrated by Ki67 nuclear antigen staining, and a lack of progesterone receptor were characteristic of the tumors. Immunohistochemical analysis revealed areas of osteopontin (Opn) expression in WAP-HGF tumors and lung metastases in agreement with a previously reported role for Opn in invasive growth. We suggest that these mice may serve as a new breast cancer model for the evaluation of the effects of unscheduled HGF expression in breast cancer.

Hepatocyte growth factor activates CCAAT enhancer binding protein and cell replication via PI3-kinase pathway

Hepatocyte growth factor (HGF), a ligand of c-Met receptor, stimulates activation of cellular kinases via phosphatidylinositol 3-kinase (PI3-kinase). CCAAT/enhancer binding protein (C/EBP) controls cell cycle progression. The present study was designed to determine whether HGF activates C/EBP in association with the S-phase entrance for cell replication and whether PI3-kinase contributes to the activation of C/EBP. Treatment of H4IIE cells, a hepatocyte-derived cell line, with HGF increased protein binding to the C/EBP binding site at an early time. Immunodepletion, subcellular fractionation, and confocal microscopic analyses showed that the HGF-induced C/EBP DNA binding activity depended on nuclear translocation of C/EBP beta. Whereas stable transfection of the p110 catalytic subunit of PI3-kinase enhanced HGF-mediated nuclear translocation of C/EBP beta and DNA binding, stable transfection of p85 subunit or chemical inhibition of PI3-kinase completely blocked C/EBP activation. HGF increased luciferase reporter activity in cells transfected with a mammalian cell expression vector containing -1.65 kilobase rGSTA2 promoter comprising C/EBP response element (pGL-1651). Whereas transfection with pCMV500, a control vector, allowed pGL-1651 to respond to HGF, expression of dominant negative mutant C/EBP completely inhibited the ability of HGF to stimulate the reporter gene expression. Flow cytometric analysis showed that HGF caused an increase in the area of S phase with a reciprocal decrease in that of G(1) phase, suggesting that HGF promoted cell cycle progression to S phase. In conclusion, HGF induces nuclear translocation of C/EBP beta via the PI3-kinase pathway and stimulates C/EBP DNA binding and gene transcription and that the PI3-kinase-mediated C/EBP activation by HGF may contribute to cell replication.