Neural cell adhesion molecule L1 in gliomas: correlation with TGF-beta and p53

Communication of Glioma cells with neuronal plasticity: What is the underlying mechanism?

There has been a significantly rising discussion on how neuronal plasticity communicates with the glioma growth and invasion. This literature review aims to determine which neurotransmitters, ion channels and signaling pathways are involved in this context, how information is transferred from synaptic sites to the glioma cells and how glioma cells apply established mechanics of synaptic plasticity for their own increment. This work is a compilation of some outstanding findings related to the influence of the glutamate, calcium, potassium, chloride and sodium channels and other important brain plasticity molecules over the glioma progression. These topics also include the relevant molecular signaling data which could prove to be helpful for an effective clinical management of brain tumors in the future.

L1CAM High Expression Associates with Poor Prognosis in Glioma but Does Not Correlate with C11orf95-RELA Fusion

The latest WHO guideline of CNS tumor defined a RELA fusion-positive ependymoma type with extremely poor prognosis, and the expression of L1CAM was correlated well with the presence of RELA fusion. However, the L1CAM protein expression in large sample gliomas other than ependymoma, its relationship with the RELA gene and its prognostic significance remained unknown. We examined the expression of L1CAM in 565 glioma cases (WHO grade I-IV). The L1CAM IHC-positive cases were selected to test RELA fusion with FISH break-apart probes. L1CAM was positive in 109 cases (19.29%) of all 565 glioma cases, with 18.27% in low-grade gliomas and 19.84% in high-grade gliomas, respectively. Unlike ependymoma, L1CAM protein expression was not correlated with the C11orf95-RELA fusion gene in other gliomas, but it had correction with the patient age (older than 45-year-old, p = 0.006), ATRX mutation (p = 0.003) and Ki67 (p = 0.007). High expression of L1CAM was an independent prognostic factor in our cohort. Further analysis demonstrated that L1CAM strong positive expression was significantly associated with poor prognosis in gliomas, both in our cohort (p < 0.001) and TCGA (p < 0.009) dataset. Although uncorrelated with C11orf95-RELA fusion, L1CAM was a significant poor prognostic marker in glioma patients. More aggressive treatment should be taken for these patients and L1CAM might be a promising therapeutic target in glioma.

Review of ependymomas: assessment of consensus in pathological diagnosis and correlations with genetic profiles and outcome

We focused on histological and immunohistochemical characteristics of ependymoma (EPN) with molecular profiles to develop more reproducible criteria of the diagnosis. Three expert neuropathologists reviewed the pathology of 130 samples from the Japan Pediatric Molecular Neuro-Oncology Group study. Confirmed cases were assessed for histology, surrogate markers, molecular subgrouping, and survival data. We reached a consensus regarding the diagnosis of EPNs in 100% of spinal cord tumors and 93% of posterior fossa (PF) tumors that had been diagnosed as EPNs by local pathologists, whereas we reached a consensus regarding only 77% of the local diagnosis of supratentorial (ST) EPNs. Among the PF-EPNs, most of anaplastic ependymomas (AEPNs) were defined as EPN-A by methylation profiling, which was significantly correlated with the subgroup assignment. Regarding prognosis, the overall survival of patients with PF-EPN was significantly better than that of patients with PF AEPN (p = 0.01). Histologically, all ependymoma, RELA fusion-positive (EPN-RELA) qualified as Grade III. Both L1 cell adhesion molecule and nuclear factor kappaB p65 antibodies showed good sensitivity for detecting EPN-RELA. This study indicated that the expert consensus pathological diagnosis could correlate well with the molecular classifications in EPNs. ST EPNs should be diagnosed more carefully by histological and molecular analyses.

Long non-coding RNA PVT1 promotes glioma cell proliferation and invasion by targeting miR-200a

Glioma is a type of malignant tumor accounting for 80% of all brain cancer morbidity. The long non-coding RNA (lncRNA) PVT1 has been demonstrated to be an oncogenic lncRNA in other types of cancer. However, the role of PVT1 in glioma is still unknown. The aim of the present study was to investigate the role of PVT1 in glioma, and its potential association with microRNA (miR)-200a. miR-200a mimics and small interfering (si)RNA transfection were utilized to construct miR-200a overexpression and knockdown models to investigate the effect of miR-200a on glioma cells. Slow-virus infection was used to transfect cells. Western blotting and reverse transcription-quantitative polymerase chain reaction were applied for the quantitative analysis of mRNA and protein expression. Apoptosis of podocytes was detected by terminal deoxynucleotidyl-transferase-mediated dUTP nick end labelling staining. PVT1 expression in glioma was upregulated. In vitro, PVT1 silencing via transfection with si-PVT1 suppressed proliferation and invasion and induced G0/G1 phase arrest. Luciferase reporter assay revealed the association between miR-200a and the PVT1 3'-untranslated region. Furthermore, experiments examining both miR-200a and PVT1 indicated that miR-200a could reverse the effects of PVT1 on glioma cell phenotypes. The present study reveals the overexpression of PVT1 in glioma tissue and cells and the oncogenic role of PVT1 in gliomagenesis via sponging miR-200a, thus providing a potential biomarker for the early detection of glioma and prognosis prediction.

Increased L1CAM (CD171) levels are associated with glioblastoma and metastatic brain tumors

L1 cell adhesion molecule (L1CAM) is a member of the immunoglobulin-like cell-adhesion molecule family that was shown to be associated with a worse prognosis in several human cancers. L1 ectodomain shedding via vesicles or exosomes has been detected in extracellular fluids after cleavage from the cell surface by metalloproteases. We evaluated the presence of L1CAM in cyst fluid and tissue from glioblastomas or brain metastases.The amount of L1CAM in cyst fluid of 9 glioblastomas and 11 brain metastases was assessed using enzyme-linked immunosorbent assay (ELISA). Corresponding tumor tissue slices were stained immunohistochemically for L1CAM. Cerebrospinal fluid of 20 non-tumor patients served as controls.Mean levels of L1CAM in tumor cyst fluid were significantly higher in glioblastoma (6118 ± 4095 ng/mL) and metastasis patients (8001 ± 6535 ng/mL) than in CSF of control patients (714 ± 22 ng/mL). The immunohistochemical expression of L1CAM in corresponding tissue was significantly higher in metastases than in glioblastomas.The present study demonstrates high levels of L1CAM in cyst fluid of glioblastoma and metastatic brain tumors. Soluble L1CAM may represent a motility promoting molecule in cancer progression, a co-factor for development of tumor cysts and a target for new treatment strategies.

Neuroblastoma Origin and Therapeutic Targets for Immunotherapy

Neuroblastoma is a pediatric solid cancer of heterogeneous clinical behavior. The unique features of this type of cancer frequently hamper the process of determining clinical presentation and predicting therapy effectiveness. The tumor can spontaneously regress without treatment or actively develop and give rise to metastases despite aggressive multimodal therapy. In recent years, immunotherapy has become one of the most promising approaches to the treatment of neuroblastoma. Still, only one drug for targeted immunotherapy of neuroblastoma, chimeric monoclonal GD2-specific antibodies, is used in the clinic today, and its application has significant limitations. In this regard, the development of effective and safe GD2-targeted immunotherapies and analysis of other potential molecular targets for the treatment of neuroblastoma represents an important and topical task. The review summarizes biological characteristics of the origin and development of neuroblastoma and outlines molecular markers of neuroblastoma and modern immunotherapy approaches directed towards these markers.

Prognostic value and clinicopathologic characteristics of L1 cell adhesion molecule (L1CAM) in a large series of vulvar squamous cell carcinomas

Background

Vulvar cancer treatment is mostly curative, but also has high morbidity rates. In a search for markers that can identify patients at risk of metastases, we investigated the prognostic value of L1-cell adhesion molecule (L1CAM) in large series of vulvar squamous cell carcinomas (VSCCs). L1CAM promotes cell motility and is an emerging prognostic factor for metastasis in many cancer subtypes.

Results

L1CAM expression was observed at the invasive front or in spray-patterned parts of 17% of the tumours. L1CAM-positive tumours expressed vimentin more often, but L1CAM expression was not associated with TP53 or CTNNB1 mutations. Five-year survival was worse for patients with L1CAM expression (overall survival 46.1% vs 63.6%, P=.014, disease specific survival 63.8% vs 80.0%, P=.018). Multivariate analysis indicates L1CAM expression as an independent prognostic marker (HR 2.9, 95% CI 1.10–7.68). An in vitro spheroid invasion assay showed decreased invasion of L1CAM-expressing VSCC spindle cells after treatment with L1CAM-neutralising antibodies.

Materials and Methods

Paraffin-embedded tumour tissue from two cohorts (N=103 and 245) of primary VSCCs were stained for L1CAM, vimentin and E-cadherin. Patients of the first cohort were tested for human papilloma virus infection and sequenced for TP53 and CTNNB1 (β-catenin) mutations. The expression of L1CAM was correlated to clinical characteristics and patient survival.

Conclusion

This is the first study to show high L1CAM-expression at the infiltrating margin of VSCC's. L1CAM-expressing VSCCs had a significantly worse prognosis compared to L1CAM-negative tumours. The highest expression was observed in spindle-shaped cells, where it might be correlated to their invasive capacity.

Copy number variation, increased gene expression, and molecular mechanisms of neurofascin in lung cancer

Metastasis and cell adhesion are key aspects of cancer progression. Neurofascin (NFASC) is a member of the immunoglobulin superfamily of adhesion molecules and, while studies on NFASC are inadequate, other members have been indicated pivotal roles in cancer progression and metastasis. This study aimed at increasing the knowledge on the involvement of adhesion molecules in lung cancer progression by studying the regulation and role of NFASC in non‐small cell lung cancer (NSCLC). Here, copy number variations in the NFASC gene were analyzed in tumor and non‐tumorous lung tissues of 204 NSCLC patients. Frequent gene amplifications (OR = 4.50, 95%CI: 2.27‐8.92, P ≤ 0.001) and increased expression of NFASC (P = 0.034) were identified in tumors of NSCLC patients. Furthermore, molecular mechanisms of NFASC in lung cancer progression were evaluated by investigating the effects of NFASC silencing on cell proliferation, viability, migration, and invasion using siRNA technology in four NSCLC cell lines. Silencing of NFASC did not affect cell proliferation or viability but rather decreased NSCLC cell migration (P ≤ 0.001) and led to morphological changes, rearrangements in the actin cytoskeleton and changes in F‐actin networks in migrating NSCLC cell lines. This study is the first to report frequent copy number gain and increased expression of NFASC in NSCLC. Moreover, these data suggest that NFASC is a novel regulator of NSCLC cell motility and support a role of NFASC in the regulation of NSCLC progression.

L1 cell adhesion molecule as a therapeutic target in cancer

L1 cell adhesion molecule (L1CAM) is the prototype member of the L1-family of closely related neural adhesion molecules. L1CAM is differentially expressed in the normal nervous system as well as pathological tissues and displays a wide range of biological activities. In human malignancies, L1CAM plays a vital role in tumor growth, invasion and metastasis. Recently, increasing evidence has suggested that L1CAM exerts a variety of functions at different steps of tumor progression through a series of signaling pathways. In addition, L1CAM has been identified as a promising target for cancer therapy by using synthetic and natural inhibitors. In this review, we provide an up-to-date overview of the role of L1CAM involved in cancers and the rationale for L1CAM as a novel molecular target for cancer therapy.

Glioblastoma multiforme: Pathogenesis and treatment

Each year, about 5-6 cases out of 100,000 people are diagnosed with primary malignant brain tumors, of which about 80% are malignant gliomas (MGs). Glioblastoma multiforme (GBM) accounts for more than half of MG cases. They are associated with high morbidity and mortality. Despite current multimodality treatment efforts including maximal surgical resection if feasible, followed by a combination of radiotherapy and/or chemotherapy, the median survival is short: only about 15months. A deeper understanding of the pathogenesis of these tumors has presented opportunities for newer therapies to evolve and an expectation of better control of this disease. Lately, efforts have been made to investigate tumor resistance, which results from complex alternate signaling pathways, the existence of glioma stem-cells, the influence of the blood-brain barrier as well as the expression of 0(6)-methylguanine-DNA methyltransferase. In this paper, we review up-to-date information on MGs treatment including current approaches, novel drug-delivering strategies, molecular targeted agents and immunomodulative treatments, and discuss future treatment perspectives.

Epithelial-to-mesenchymal transition in paired human primary and recurrent glioblastomas

Patients with highly malignant glioblastomas have a short median survival time mainly due to aggressive relapses after therapeutic treatment. Beside others, they achieve their progressive character via epithelial-to-mesenchymal transition (EMT). However, comprehensive investigations on EMT in paired primary-recurrent glioblastoma pairs are presently not available. Thus, in our present study we examined the expression profile of different EMT-markers in 17 matched primary and recurrent glioblastomas by qPCR and double-immunofluorescence stainings to identify EMT marker expressing cell types. Additionally, we analyzed the influence of temozolomide on EMT marker expression in vitro. In comparison to primary tumors, expression of β-catenin (p<0.05), Snail1 (p<0.05), Snail2/Slug (p<0.05), biglycan (p<0.05) and Twist1 (p<0.01) was downregulated in recurrence whereas L1CAM showed upregulation (p<0.05; qPCR). Expression of desmoplakin, vimentin, fibronectin and TGF-β1 with its receptors TGF-βR1 and TGF-βR2 was almost unchanged. Comparing each individual pair, five different 'EMT groups' within our glioblastoma collective were identified according to the regulation of mRNA expression of GFAP, desmoplakin, Snail1, Snail2, Twist1 and vimentin. Additionally, double-stainings of EMT markers in combination with cell specific markers (glial fibrillary acidic protein, CD11b, von Willebrand factor) revealed that EMT markers were expressed in a complex pattern with all three cellular types as possible sources. Temozolomide treatment significantly induced mRNA expression of nearly all investigated EMT markers in T98G glioma cells. Thus, EMT seems to be involved in glioma progression in a complex way requiring an individualized analysis, and is influenced by commonly used therapeutic options in glioma therapy.

Transcription factors and microRNA-co-regulated genes in gastric cancer invasion in ex vivo

Aberrant miRNA expression abnormally modulates gene expression in cells and can contribute to tumorigenesis in humans. This study identified functionally relevant differentially expressed genes using the transcription factors and miRNA-co-regulated network analysis for gastric cancer. The TF-miRNA co-regulatory network was constructed based on data obtained from cDNA microarray and miRNA expression profiling of gastric cancer tissues. The network along with their co-regulated genes was analyzed using Database for Annotation, Visualization and Integrated Discovery (DAVID) and Transcriptional Regulatory Element Database (TRED). We found eighteen (17 up-regulated and 1 down-regulated) differentially expressed genes that were co-regulated by transcription factors and miRNAs. KEGG pathway analysis revealed that these genes were part of the extracellular matrix-receptor interaction and focal adhesion signaling pathways. In addition, qRT- PCR and Western blot data showed an increase in COL1A1 and decrease in NCAM1 mRNA and protein levels in gastric cancer tissues. Thus, these data provided the first evidence to illustrate that altered gene network was associated with gastric cancer invasion. Further study with a large sample size and more functional experiments is needed to confirm these data and contribute to diagnostic and treatment strategies for gastric cancer.

Neuregulin 1 enhances cell adhesion molecule l1 expression in human glioma cells and promotes their migration as a function of malignancy

Similar functions of L1, a cell adhesion molecule, and the cytokine neuregulin 1 (Nrg1) have been suggested in tumorigenesis and the promotion of metastasis. We studied the relationships of Nrg1 and L1 expression in human gliomas. Using immunofluorescence staining on a human glioma tissue microarray, we found a positive correlation between levels of L1 and Nrg1α or Nrg1β expression; expression tended to increase with increasing WHO (World Health Organization) tumor grade. L1 was also found to colocalize with either Nrg1 isoform. In cultures of U87-MG human glioblastoma and human U251 and SHG-44 glioma cells, the base levels of full-length L1 expression were increased by the 2 Nrg1 molecules in the nanomolar range, and Nrg1 siRNA downregulated full-length L1 expression in these tumor cell lines. U87-MG cells treated with either Nrg1 isoform also showed enhanced migration when compared with that treated with vehicle control. In addition, administration of either lapatinib (a dual inhibitor of both the epidermal growth factor receptor and ErbB-2) or erlotinib (an inhibitor of the epidermal growth factor receptor) in combination with either Nrg1α or Nrg1β inhibited the L1 expression elicited by these cytokines in U87-MG cells. Together, our data suggest that Nrg1 regulates L1 expression in gliomas, and that Nrg1 may contribute to malignancy by upregulating the L1 expression in glioblastoma cells, thereby enhancing their migration.

The neural adhesion molecule L1CAM confers chemoresistance in human glioblastomas

Glioblastoma multiforme (GBM) represents the most common and malignant brain tumor. GBM tissues exhibit elevated expression of the transforming growth factor-beta1 (TGF-β1) and the adhesion molecule L1CAM. This study investigated the mechanism of L1CAM regulation in GBM cells and its role in the mediation of chemoresistance. L1CAM expression levels varied in GBM cells being highest in A172 cells and low in T98G cells. Inhibition of TGF-β1 signaling in A172 cells reduced L1CAM expression and vice versa stimulation with exogenous TGF-β1 led to upregulation of L1CAM in T98G cells. Additionally, TGF-β1 and L1CAM expression increased during differentiation of glioma stem-like cells. L1CAM expressing GBM cells and differentiated glioma stem-like cells showed a reduced apoptotic response after treatment with the chemotherapeutic drug temozolomide. Accordingly, siRNA-mediated knock-down of L1CAM in A172 cells and differentiated glioma stem-like cells increased chemosensitivity, whereas overexpression of L1CAM in T98G cells and glioma spheroids diminished the apoptotic response. Elevated L1CAM expression caused a diminished expression of caspase-8 in GBM and differentiated glioma stem-like cells. These data show that TGF-β1 dependent upregulation of L1CAM expression in GBM cells leads to the downregulation of caspase-8 and apoptosis resistance pointing to L1CAM as potential target for improved therapy of GBM patients.

Immunotherapy targeting glioma stem cells--insights and perspectives

INTRODUCTION

Glioblastoma multiforme (GBM) is the most aggressive and lethal primary malignant brain tumor. Although progress has been made in current conventional therapies for GBM patients, the effect of these advances on clinical outcomes has been disappointing. Recent research into the origin of cancers suggest that GBM cancer stem cells (GSC) are the source of initial tumor formation, resistance to current conventional therapeutics and eventual patient relapse. Currently, there are very few studies that apply immunotherapy to target GSC.

AREAS COVERED

CD133, a cell surface protein, is used extensively as a surface marker to identify and isolate GSC in malignant glioma. We discuss biomarkers such as CD133, L1-cell adhesion molecule (L1-CAM), and A20 of GSC. We review developing novel treatment modalities, including immunotherapy strategies, to target GSC.

EXPERT OPINION

There are very few reports of preclinical studies targeting GSC. Identification and validation of unique molecular signatures and elucidation of signaling pathways involved in survival, proliferation and differentiation of GSC will significantly advance this field and provide a framework for the rational design of a new generation of antigen-specific, anti-GSC immunotherapy- and nanotechnology-based targeted therapyies. Combined with other therapeutic avenues, GSC-targeting therapies may represent a new paradigm to treat GBM patients.

L1 stimulation of human glioma cell motility correlates with FAK activation

The neural adhesion/recognition protein L1 (L1CAM; CD171) has been shown or implicated to function in stimulation of cell motility in several cancer types, including high-grade gliomas. Our previous work demonstrated the expression and function of L1 protein in stimulation of cell motility in rat glioma cells. However, the mechanism of this stimulation is still unclear. This study further investigated the function of L1 and L1 proteolysis in human glioblastoma multiforme (GBM) cell migration and invasion, as well as the mechanism of this stimulation. L1 mRNA was found to be present in human T98G GBM cell line but not in U-118 MG grade III human glioma cell line. L1 protein expression, proteolysis, and release were found in T98G cells and human surgical GBM cells by Western blotting. Exosome-like vesicles released by T98G cells were purified and contained full-length L1. In a scratch assay, T98G cells that migrated into the denuded scratch area exhibited upregulation of ADAM10 protease expression coincident with loss of surface L1. GBM surgical specimen cells exhibited a similar loss of cell surface L1 when xenografted into the chick embryo brain. When lentivirally introduced shRNA was used to attenuate L1 expression, such T98G/shL1 cells exhibited significantly decreased cell motility by time lapse microscopy in our quantitative Super Scratch assay. These cells also showed a decrease in FAK activity and exhibited increased focal complexes. L1 binding integrins which activate FAK were found in T98G and U-118 MG cells. Addition of L1 ectodomain-containing media (1) rescued the decreased cell motility of T98G/shL1 cells and (2) increased cell motility of U-118 MG cells but (3) did not further increase T98G cell motility. Injection of L1-attenuated T98G/shL1 cells into embryonic chick brains resulted in the absence of detectable invasion compared to control cells which invaded brain tissue. These studies support a mechanism where glioma cells at the edge of a cell mass upregulate ADAM10 to proteolyze surface L1 and the resultant ectodomain increases human glioma cell migration and invasion by binding to integrin receptors, activating FAK, and increasing turnover of focal complexes.

L1 Cell adhesion molecule (L1CAM) expression at the cancer invasive front is a novel prognostic marker of pancreatic ductal adenocarcinoma

BACKGROUND AND OBJECTIVES

Pancreatic ductal adenocarcinoma (PDAC) is one of the most extremely aggressive cancers with a poor prognosis after curative resection. L1 cell adhesion molecule (L1CAM) is a 200-220 kDa type I transmembrane glycoprotein of the immunoglobulin superfamily, which has been shown to affect the prognosis of several cancers. No clinicopathological significance of L1CAM expression has been examined at the invasive front of PDAC. In this study, we examined the relationship between L1CAM expression and clinicopathological features in PDAC by immunohistochemistry.

METHODS

One hundred seven surgically resected specimens of PDAC were immunohistochemically examined using a monoclonal antibody against L1CAM.

RESULTS

Positive expression of L1CAM was found in 23 of 107 cases with PDAC. In most cases (21/23), L1CAM expression was localized at the invasive front of the tumor tissue. Positive expression of L1CAM was significantly correlated with the histological grade, lymph node involvement, and distant metastasis. In univariate analysis, a positive expression of L1CAM was associated with short overall survival (P = 0.0002), and this was significant in multivariate analysis (P = 0.009).

CONCLUSIONS

L1CAM could play an important role in the invasive process in vivo, and is thought to be a good indicator of prognosis in PDAC.

Stimulation of glioma cell motility by expression, proteolysis, and release of the L1 neural cell recognition molecule

Background

Malignant glioma cells are particularly motile and can travel diffusely through the brain parenchyma, apparently without following anatomical structures to guide their migration. The neural adhesion/recognition protein L1 (L1CAM; CD171) has been implicated in contributing to stimulation of motility and metastasis of several non-neural cancer types. We explored the expression and function of L1 protein as a stimulator of glioma cell motility using human high-grade glioma surgical specimens and established rat and human glioma cell lines.

Results

L1 protein expression was found in 17 out of 18 human high-grade glioma surgical specimens by western blotting. L1 mRNA was found to be present in human U-87/LacZ and rat C6 and 9L glioma cell lines. The glioma cell lines were negative for surface full length L1 by flow cytometry and high resolution immunocytochemistry of live cells. However, fixed and permeablized cells exhibited positive staining as numerous intracellular puncta. Western blots of cell line extracts revealed L1 proteolysis into a large soluble ectodomain (~180 kDa) and a smaller transmembrane proteolytic fragment (~32 kDa). Exosomal vesicles released by the glioma cell lines were purified and contained both full-length L1 and the proteolyzed transmembrane fragment. Glioma cell lines expressed L1-binding αvβ5 integrin cell surface receptors. Quantitative time-lapse analyses showed that motility was reduced significantly in glioma cell lines by 1) infection with an antisense-L1 retroviral vector and 2) L1 ectodomain-binding antibodies.

Conclusion

Our novel results support a model of autocrine/paracrine stimulation of cell motility in glioma cells by a cleaved L1 ectodomain and/or released exosomal vesicles containing L1. This mechanism could explain the diffuse migratory behavior of high-grade glioma cancer cells within the brain.

L1 cell adhesion molecules as regulators of tumor cell invasiveness

Fast growing malignant cancers represent a major therapeutic challenge. Basic cancer research has concentrated efforts to determine the mechanisms underlying cancer initiation and progression and reveal candidate targets for future therapeutic treatment of cancer patients. With known roles in fundamental processes required for proper development and function of the nervous system, L1-CAMs have been recently identified as key players in cancer biology. In particular L1 has been implicated in cancer invasiveness and metastasis, and has been pursued as a powerful prognostic factor, indicating poor outcome for patients. Interestingly, L1 has been shown to be important for the survival of cancer stem cells, which are thought to be the source of cancer recurrence. The newly recognized roles for L1CAMs in cancer prompt a search for alternative therapeutic approaches. Despite the promising advances in cancer basic research, a better understanding of the molecular mechanisms dictating L1-mediated signaling is needed for the development of effective therapeutic treatment for cancer patients.

The intracellular interactions of the L1 family of cell adhesion molecules

The L1 family of CAMs (cell adhesion molecules) has long aroused the interest of researchers, but primarily the extracellular interactions of these proteins have been elucidated. More recently, attention has turned to the intracellular signalling potentiated by transmembrane proteins and the cytoplasmic proteins with which they can interact. The present review brings up to date the current body of published knowledge for the intracellular interactions of L1-CAM family proteins and the potential importance of these interactions for the mechanisms of L1-CAM action.

L1 cell adhesion molecule (L1CAM) in invasive tumors

The L1 cell adhesion molecule (L1CAM) belongs to the immunoglobulin superfamily and was originally identified in the nervous system. Recent studies demonstrated L1CAM expression in various types of cancer, predominantly at the invasive front of tumors and in metastases, suggesting its involvement in advanced stages of tumor progression. Overexpression of L1CAM in normal and cancer cells increased motility, enhanced growth rate and promoted cell transformation and tumorigenicity. Moreover, the expression of L1CAM in tumor cells conferred the capacity to form metastases. These properties of L1CAM, in addition to its cell surface localization, make it a potentially useful diagnostic marker for cancer progression and a candidate for anti-cancer therapy. We review the role of L1CAM in cancer progression with particular emphasis on colon cancer, and the potential of anti-L1CAM antibodies as a therapeutic tool for cancer.

Transforming growth factor-beta (TGF-beta) and brain tumours

Since its discovery in the late 1970s considerable research has linked transforming growth factor-beta (TGF-beta) to several human diseases such as fibrosis, auto-immunity and cancer. TGF-beta acts initially as a growth inhibitory factor in early stages of tumour development. In contrast, as tumours evolve, they develop mechanisms to evade the growth-regulatory effects of TGF-beta, resulting in greater tumour invasiveness, increased metastatic potential and inhibition of surrounding immune responses. However, although extensively studied, the molecular mechanisms that trigger tumour cells to "switch" from TGF-beta-inhibited to TGF-beta-promoted are still not fully understood. Contradictory studies that demonstrate opposite cellular effects mediated by TGF-beta are abundant throughout the literature. This review summarizes the current molecular mechanisms involved in the tumour suppressive and tumour progressive characteristics of TGF-beta in brain tumours. Potential therapeutic agents that target TGF-beta and related proteins being evaluated against brain tumours is also discussed.

Cell adhesion molecule L1 disrupts E-cadherin-containing adherens junctions and increases scattering and motility of MCF7 breast carcinoma cells

The first steps of invasion and metastasis include the dissociation of adherens junctions and the induction of migratory phenotype, through a program that resembles epithelial-mesenchymal transition (EMT). The L1 cell adhesion molecule, which is normally found primarily in the brain, was recently shown to be expressed in different types of cancer and to have tumor-promoting activity. We now find that L1 mediates EMT-like events in MCF7 breast carcinoma cells. MCF7 predominantly expresses the nonneuronal isoform of L1, as do 16 of 17 other cell lines derived from different types of cancer. L1 protein expression in MCF7 cells, which form E-cadherin-containing adherens junctions, is inversely related to cell density. Analysis of MCF7 cells with overexpression or knockdown of nonneuronal L1 isoform revealed that L1 expression leads to the disruption of adherens junctions and increases beta-catenin transcriptional activity. As a result, L1 expression promotes the scattering of epithelial cells from compact colonies. Expression of the full-length L1 protein, but not of its soluble extracellular moiety, increases the motility of the MCF7 epithelial monolayer in a wound-healing assay, in which L1 expression is preferentially observed and required in cells leading the movement of the monolayer. Based on these results, we propose a model for the role of L1 as a trigger of EMT-like events in transformed epithelial cells.

Proteomic identification of the wt-p53-regulated tumor cell secretome

Tumor-stroma interactions play a major role in tumor development, maintenance and progression. Yet little is known on how the genetic alterations that underlie cell transformation elicit cell extrinsic changes modulating heterotypic cell interactions. We hypothesized that these events involve a modification in the complement of secreted proteins by the cell, acting as mediators of intercellular communication. To test this hypothesis, we examined the role of wt-p53, a major tumor suppressor, on the tumor microenvironment through its regulation of secreted factors. Using a combination of 2-DE and cICAT proteomic techniques, we found a total of 111 secreted proteins, 39 of which showed enhanced and 21 inhibited secretion in response to wt-p53 expression. The majority of these were not direct targets of p53 transcription factor activity, suggesting a novel role for wt-p53 in the control of intracellular protein trafficking and/or secreted protein stability. Evidence for p53-controlled post-translational modifications on nine secreted proteins was also found. These findings will enhance our understanding of wt-p53 modulated interactions of the tumor with its environment.

Human and Rat Glioma Growth, Invasion, and Vascularization in a Novel Chick Embryo Brain Tumor Model

The mechanisms that control the insidiously invasive nature of malignant gliomas are poorly understood, and their study would be facilitated by an in vivo model that is easy to manipulate and inexpensive. The developing chick embryo brain was assessed as a new xenograft model for the production, growth, and study of human and rat glioma cell lines. Three established glioma lines (U-87 MG, C6, and 9L) were injected into chick embryo brain ventricles on embryonic day (E) 5 and brains were examined after several days to two weeks after injection. All glioma lines survived, produced vascularized intraventricular tumors, and invaded the brain in a manner similar to that in rodents. Rat C6 glioma cells spread along vasculature and also invaded the neural tissue. Human U-87 glioma cells migrated along vasculature and exhibited slight invasion of neural tissue. Rat 9L gliosarcoma cells were highly motile, but migrated only along the vasculature. A derivative of 9L cells that stably expressed the cell surface adhesion molecule NgCAM/L1 was produced and also injected into chick embryo brain ventricles to see if this protein could facilitate tumor cell migration away from the vasculature into areas such as axonal tracts. 9L/NgCAM cells, however, did not migrate away from the vasculature and, thus, this protein alone cannot be responsible for diffuse invasiveness of some gliomas. 9L/NgCAM cell motility was assessed in vitro using sophisticated time-lapse microscopy and quantitative analysis, and was significantly altered compared to parental 9L cells. These studies demonstrate that the chick embryo brain is a successful and novel xenograft model for mammalian gliomas and demonstrate the potential usefulness of this new model for studying glioma tumor cell growth, vascularization, and invasiveness.

Clinicopathological study of cellular proliferation and invasion in gliomatosis cerebri: important role of neural cell adhesion molecule L1 in tumour invasion

BACKGROUND/AIMS

In patients with gliomatosis cerebri (GC), glial fibrillary acidic protein (GFAP) positive cells invade the entire brain, particularly the white matter. Because the nosological definition and histogenesis of GC remain controversial, the morphology and immunohistochemical staining patterns of neoplastic GC cells were compared with those of other gliomas.

METHODS

An immunohistochemical analysis of neoplastic cells from four patients with GC and 20 with astrocytic tumours using antibodies against Ki-67, GFAP, and L1, the last of which is a neural cell adhesion molecule putatively related to glioma invasion.

RESULTS

GC tumour cells can be divided into two types, those mainly composed of strongly GFAP and L1 positive gemistocytic cells, the other composed of small, GFAP and L1 negative spindle shaped cells. The two types did not differ with respect to Ki-67 positivity. Cells from patients with other gliomas were positive for GFAP but concurrent L1 expression was negative or weakly positive.

CONCLUSION

The strong expression of L1 in patients with GC and its poor expression in the 20 patients with other types of glioma, including those with GFAP positive gemistocytic astrocytomas, suggest that L1 expression may play a role in the histogenesis of GC.

Glioma cell invasion: regulation of metalloproteinase activity by TGF-beta

Matrix metalloproteinases (MMPs) are a family of extracellular endopeptidases that selectively degrade components of the extracellular matrix. MMPs are implicated in tumor cell invasion because they mediate the breakdown of the basal membrane. In addition, they seem to be important for the creation and maintenance of a microenvironment that facilitates tumor cell survival. Among the essential characteristics of human malignant gliomas are infiltrative growth, angiogenesis and suppression of antitumor immune surveillance. Transforming growth factor-beta (TGF-beta) is intimately involved in the regulation of these processes. We have previously demonstrated that TGF-beta promotes the migration of LN- 18 and LN-229 glioma cells via a process that may involve the upregulation of alphaVbeta3 integrin expression. Furthermore, we have defined a novel pathway for hepatocyte growth factor (HGF)-induced glioma cell migration and invasion which requires the induction of TGF-beta2 expression. Here, we demonstrate that TGF-beta2 induces MMP-2 expression and suppresses tissue inhibitor of metalloproteinases (TIMP)-2 expression and that concentration-dependently promotes the invasion of U87MG and LN-229 glioma cells in a matrigel invasion assay. Similarly, ectopic expression of the anti-apoptotic BCL-x, protein leads to enhanced matrigel invasion by LN-18 and LN-229 glioma cells. We outline the possible interrelations of TGF-beta, proteins of the BCL-2 family, integrins and metalloprotease activity. By virtue of its promotion of glioma invasion and its growth regulatory and immunomodulatory properties. TGF-beta continues to be one of the most promising targets for the experimental therapy of human malignant glioma.

L1 expressed by glioma cells promotes adhesion but not migration

L1 is an adhesion molecule of the immunoglobulin superfamily expressed by several types of cancer, including gliomas. It has been shown that L1 can act as chemoattractant to glioma cells, while the effects of L1 expressed by glioma cells themselves are unknown to date. We established a C6 rat glioma clone, conditionally expressing murine L1 under control of a tetracycline responsive promoter. In vitro experiments revealed increased adhesion on matrigel as well as increased intercellular adhesion in the presence of L1, whereas no L1-dependent effects on proliferation or migration on either matrigel or myelin were observed. In vivo experiments using transplantation into nude mouse striatum, where L1 expression by glioma cells was regulated by tetracycline via drinking water, did not show effects of L1 on tumor size or brain invasion. Our data suggest that L1 expressed on the surface of glioma cells increases cell-matrix and intercellular adhesion, but has no apparent effects on proliferation and invasion.

Glioma cell invasion: regulation of metalloproteinase activity by TGF-beta

Matrix metalloproteinases (MMPs) are a family of extracellular endopeptidases that selectively degrade components of the extracellular matrix. MMPs are implicated in tumor cell invasion because they mediate the breakdown of the basal membrane. In addition, they seem to be important for the creation and maintenance of a microenvironment that facilitates tumor cell survival. Among the essential characteristics of human malignant gliomas are infiltrative growth, angiogenesis and suppression of antitumor immune surveillance. Transforming growth factor-beta (TGF-beta) is intimately involved in the regulation of these processes. We have previously demonstrated that TGF-beta promotes the migration of LN- 18 and LN-229 glioma cells via a process that may involve the upregulation of alphaVbeta3 integrin expression. Furthermore, we have defined a novel pathway for hepatocyte growth factor (HGF)-induced glioma cell migration and invasion which requires the induction of TGF-beta2 expression. Here, we demonstrate that TGF-beta2 induces MMP-2 expression and suppresses tissue inhibitor of metalloproteinases (TIMP)-2 expression and that concentration-dependently promotes the invasion of U87MG and LN-229 glioma cells in a matrigel invasion assay. Similarly, ectopic expression of the anti-apoptotic BCL-x, protein leads to enhanced matrigel invasion by LN-18 and LN-229 glioma cells. We outline the possible interrelations of TGF-beta, proteins of the BCL-2 family, integrins and metalloprotease activity. By virtue of its promotion of glioma invasion and its growth regulatory and immunomodulatory properties. TGF-beta continues to be one of the most promising targets for the experimental therapy of human malignant glioma.

Malignant glioma biology: role for TGF-beta in growth, motility, angiogenesis, and immune escape

Characteristics of human malignant glioma are excessive proliferation, infiltrative growth, angiogenesis and suppression of anti-tumor immune surveillance. Transforming growth factor-beta (TGF-beta), a versatile cytokine, is intimately involved in the regulation of these processes. Here, we discuss the interactions of TGF-beta with growth factors, such as basic fibroblast growth factor (bFGF), epidermal growth factor (EGF) and platelet derived growth factor (PDGF), metalloproteinases (MMP-2, MMP-9) and their inhibitor, plasmin activator inhibitor-1 (PAI-1), and immune cells, like natural killer cells, T-cells and microglia. The differential effects of TGF-beta in glioma biology are outlined with emphasis on the induction of a survival advantage for glioma cells by enforced cell growth, migration, invasion, angiogenesis and immune paralysis. By virtue of its growth regulatory and immunomodulatory properties, TGF-beta promises to become a novel target for the experimental therapy of human malignant glioma.