Insulin-like growth factors in central nervous system tumors

Preclinical Models and Technologies in Glioblastoma Research: Evolution, Current State, and Future Avenues

Glioblastoma is the most common malignant primary central nervous system tumor and one of the most debilitating cancers. The prognosis of patients with glioblastoma remains poor, and the management of this tumor, both in its primary and recurrent forms, remains suboptimal. Despite the tremendous efforts that are being put forward by the research community to discover novel efficacious therapeutic agents and modalities, no major paradigm shifts have been established in the field in the last decade. However, this does not mirror the abundance of relevant findings and discoveries made in preclinical glioblastoma research. Hence, developing and utilizing appropriate preclinical models that faithfully recapitulate the characteristics and behavior of human glioblastoma is of utmost importance. Herein, we offer a holistic picture of the evolution of preclinical models of glioblastoma. We further elaborate on the commonly used in vitro and vivo models, delving into their development, favorable characteristics, shortcomings, and areas of potential improvement, which aids researchers in designing future experiments and utilizing the most suitable models. Additionally, this review explores progress in the fields of humanized and immunotolerant mouse models, genetically engineered animal models, 3D in vitro models, and microfluidics and highlights promising avenues for the future of preclinical glioblastoma research.

Type 1 Insulin-Like Growth Factor Receptor Nuclear Localization in High-Grade Glioma Cells Enhances Motility, Metabolism, and In Vivo Tumorigenesis

Gliomas are the most frequent solid tumors in children. Among these, high-grade gliomas are less common in children than in adults, though they are similar in their aggressive clinical behavior. In adults, glioblastoma is the most lethal tumor of the central nervous system. Insulin-like growth factor 1 receptor (IGF1R) plays an important role in cancer biology, and its nuclear localization has been described as an adverse prognostic factor in different tumors. Previously, we have demonstrated that, in pediatric gliomas, IGF1R nuclear localization is significantly associated with high-grade tumors, worst clinical outcome, and increased risk of death. Herein we explore the role of IGF1R intracellular localization by comparing two glioblastoma cell lines that differ only in their IGF1R capacity to translocate to the nucleus. In vitro, IGF1R nuclear localization enhances glioblastoma cell motility and metabolism without affecting their proliferation. In vivo, IGF1R has the capacity to translocate to the nucleus and allows not only a higher proliferation rate and the earlier development of tumors but also renders the cells sensitive to OSI906 therapy. With this work, we provide evidence supporting the implications of the presence of IGF1R in the nucleus of glioma cells and a potential therapeutic opportunity for patients harboring gliomas with IGF1R nuclear localization.

Type 1 IGF Receptor Localization in Paediatric Gliomas: Significant Association with WHO Grading and Clinical Outcome

Nuclear localization of insulin-like growth factor receptor type 1 (IGF-1R) has been described as adverse prognostic factor in some cancers. We studied the expression and localization of IGF-1R in paediatric patients with gliomas, as well as its association with World Health Organization (WHO) grading and survival. We conducted a single cohort, prospective study of paediatric patients with gliomas. Samples were taken at the time of the initial surgery; IGF-1R expression and localization were characterized by immunohistochemistry (IHC), subcellular fractionation and western blotting. Tumours (47/53) showed positive staining for IGF-1R by IHC. IGF-1R nuclear labelling was observed in 10/47 cases. IGF-1R staining was mostly non-nuclear in low-grade tumours, while IGF-1R nuclear labelling was predominant in high-grade gliomas (p = 0.0001). Survival was significantly longer in patients with gliomas having non-nuclear IGF-1R localization than in patients with nuclear IGF-1R tumours (p = 0.016). In gliomas, IGF-1R nuclear localization was significantly associated with both high-grade tumours and increased risk of death. Based on a prospective design, we provide evidence of a potential usefulness of intracellular localization of IGF-1R as prognostic factor in paediatric patients with gliomas.

Secondary Intracranial Tumors Following Radiotherapy for Pituitary Adenomas: A Systematic Review

Pituitary adenomas are often treated with radiotherapy for the management of tumor progression or recurrence. Despite the improvement in cure rates, patients treated by radiotherapy are at risk of development of secondary malignancies. We conducted a comprehensive literature review of the secondary intracranial tumors that occurred following radiotherapy to pituitary adenomas to obtain clinicopathological characteristics. The analysis included 48 neuroepithelial tumors, 37 meningiomas, and 52 sarcomas which were published between 1959–2017, although data is missing regarding overall survival and type of irradiation in a significant proportion of the reports. The average onset age for the pituitary adenoma was 37.2 ± 14.4 years and the average latency period before the diagnosis of the secondary tumor was 15.2 ± 8.7 years. Radiotherapy was administered in pituitary adenomas at an average dose of 52.0 ± 19.5 Gy. The distribution of pituitary adenomas according to their function was prolactinoma in 10 (7.2%) cases, acromegaly in 37 (27.0%) cases, Cushing disease in 4 (2.9%) cases, PRL+GH in 1 (0.7%) case, non-functioning adenoma in 57 (41.6%) cases. Irradiation technique delivered was lateral opposing field in 23 (16.7%) cases, 3 or 4 field technique in 27 (19.6%) cases, rotation technique in 10 (7.2%) cases, radio surgery in 6 (4.3%) cases. Most of the glioma or sarcoma had been generated after lateral opposing field or 3/4 field technique. Fibrosarcomas were predominant before 1979 (p < 0.0001). The median overall survival time for all neuroepithelial tumors was 11 months (95% confidence intervals (CI), 3–14). Patients with gliomas treated with radiotherapy exhibited a non-significant positive trend with longer overall survival. The median overall survival time for sarcoma cases was 6 months (95% CI, 1.5–9). The median survival time in patients with radiation and/or chemotherapy for sarcomas exhibited a non-significant positive trend with longer overall survival. In patients treated with radiotherapy for pituitary adenomas, the risk of secondary tumor incidence warrants a longer follow up period. Moreover, radiation and/or chemotherapy should be considered in cases of secondary glioma or sarcoma following radiotherapy to the pituitary adenomas.

A phosphatase-independent gain-of-function mutation in PTEN triggers aberrant cell growth in astrocytes through an autocrine IGF-1 loop

Loss-of-function mutations in the phosphatase PTEN (phosphatase and tensin homolog deleted on chromosome10) contribute to aberrant cell growth in part through upregulation of the mitogenic IGF-1/PI3K/Akt pathway. In turn, this pathway exerts a homeostatic feedback over PTEN. Using mutagenesis analysis to explore a possible impact of this mutual control on astrocyte growth, we found that truncation of the C-terminal region of PTEN (Δ51) associates with a marked increase in NFκB activity, a transcription factor overactivated in astrocyte tumors. Whereas mutations of PTEN are considered to lead to a loss-of-function, PTENΔ51, a truncation that comprises a region frequently mutated in human gliomas, displayed a neomorphic (gain-of-function) activity that was independent of its phosphatase activity. This gain-of-function of PTENΔ51 includes stimulation of IGF-1 synthesis through protein kinase A activation of the IGF-1 promoter. Increased IGF-1 originates an autocrine loop that activates Akt and NFκB. Constitutive activation of NFκB in PTENΔ51-expressing astrocytes leads to aberrant cell growth; astrocytes expressing this mutant PTEN generate colonies in vitro and tumors in vivo. Mutations converting a tumor suppressor such as PTEN into a tumor promoter through a gain-of-function involving IGF-1 production may further our understanding of the role played by this growth factor in glioma growth and help us define druggable targets for personalized therapy.

Genetic analysis in a patient presenting with meningioma and familial isolated pituitary adenoma (FIPA) reveals selective involvement of the R81X mutation of the AIP gene in the pathogenesis of the pituitary tumor

Familial isolated pituitary adenoma (FIPA), defined as the occurrence of at least two cases of pituitary adenoma in a family that does not exhibit features of syndromic diseases, such as Carney complex or Multiple Endocrine Neoplasia type 1 or 4, is a rare autosomal dominant disease with low penetrance. About 20 % of the families with FIPA harbor inactivating mutation in aryl hydrocarbon receptor-interacting protein gene (AIP) associated with loss of heterozygosity of the same genetic locus (11q13) in the tumor. Rarely different types of extra-pituitary tumors have been described in the setting of AIP mutation-positive FIPA. We present the case of a patient who was diagnosed with acromegaly due to the AIP mutation c.241C>T (p.R81X) at the age of 34 years, and treated by transsphenoidal surgery. At the age of 43 years she was diagnosed with a meningioma, and at age 46 had recurrence of the somatotropinoma. Genetic studies demonstrated loss of the normal allele (by sequencing and microsatellite analysis) in DNA from the pituitary adenoma but not from the meningioma, suggesting a selective involvement of AIP mutation in the pathogenesis of the pituitary adenoma, and a casual association with the meningioma. Further investigations are required to define the exact role of AIP in non-pituitary tumorigenesis.

Concentrations of IGF-I and IGFBP-3 and brain tumor risk in the European Prospective Investigation into Cancer and Nutrition

BACKGROUND

Insulin-like growth factor-1 (IGF-I) is important in normal brain development but in the adult brain, IGF-I overexpression may be a risk factor for tumor development.

METHODS

We examined the association between circulating concentrations of IGF-I and IGFBP-3 in relation to risk of gliomas (74 low-grade, 206 high-grade gliomas), meningiomas (n = 174) and acoustic neuromas (n = 49) by using a case-control design nested in the European Prospective Investigation into Cancer and Nutrition. IGF-I and IGFBP-3 were measured by ELISAs.Conditional logistic regression was used to compute ORs and corresponding 95% CIs.

RESULTS

The risk of low-grade gliomas was elevated with increased IGF-I (OR = 3.60, 95% CI: 1.11-11.7; top vs. bottom quartile) and decreased with elevated IGFBP-3 concentrations (OR = 0.28, 95% CI: 0.09-0.84) after mutual adjustment of these two factors; these results became nonsignificant after exclusion of the first year of follow-up. No association was observed for high-grade gliomas or meningiomas. Both high IGF-I and IGFBP-3 concentrations were associated with risk of acoustic neuromas (IGF-I: OR = 6.63, 95% CI: 2.27-19.4, top vs. bottom tertile; IGFBP-3: OR = 7.07, 95% CI: 2.32-21.6), even after excluding the first year of follow-up.

CONCLUSION

High concentrations of IGF-I might be positively associated with risk of low-grade gliomas and acoustic neuromas, although we cannot exclude reverse causation, in particular for low-grade gliomas.

IMPACT

Factors of the IGF axis might be involved in the etiology of some types of brain tumors.

Birth weight and order as risk factors for childhood central nervous system tumors

OBJECTIVE

To determine whether birth characteristics related to maternal-fetal health in utero are associated with the development of childhood central nervous system tumors.

STUDY DESIGN

We identified, from the California Cancer Registry, 3733 children under age 15 diagnosed with childhood central nervous system tumors between 1988 and 2006 and linked these cases to their California birth certificates. Four controls per case, matched on birth date and sex, were randomly selected from the same birth files. We evaluated associations of multiple childhood CNS tumor subtypes with birth weight and birth order.

RESULTS

Low birth weight was associated with a reduced risk of low-grade gliomas (OR=0.67; 95% CI, 0.46 to 0.97) and high birth weight was associated with increased risk of high-grade gliomas (OR=1.57; 95% CI, 1.16 to 2.12). High birth order (fourth or higher) was associated with decreased risk of low-grade gliomas (OR=0.75; 95% CI, 0.56 to 0.99) and increased risk of high-grade gliomas (OR=1.32; 95% CI, 1.01 to 1.72 for second order).

CONCLUSIONS

Factors that drive growth in utero may increase the risk of low-grade gliomas. There may be a similar relationship in high-grade gliomas, although other factors, such as early infection, may modify this association. Additional investigation is warranted to validate and further define these findings.

Helianthin induces antiproliferative effect on human glioblastoma cells in vitro

A major focus of brain cancer research today is to translate understanding of glioma biology into advances in treatment, by exploring the potential of target therapy. Here we investigated the ability of three compounds belonging to the chemical class of azo dyes (methyl red, methyl yellow, and helianthin) to inhibit glioblastoma (GB) cell growth in vitro. Our results showed that helianthin induced cytotoxicity in two GB cell cultures, cell lines 18 and 38, whereas methyl red and methyl yellow were not cytotoxic. The effect of helianthin on EGFR, IGF-1R, and their common intracellular signaling via PI3-K and ERK1/2 was also analyzed. Treatment with helianthin down-regulated EGFR and IGF-1R activity in both cell lines. Helianthin treatment blocked ERK1/2 phosphorylation without affecting PI3K activity in cell line 18 and reduced both PI3K and ERK1/2 in GB 38 cell line. The cell death was accompanied by degradation of PARP without affecting BCL2 expression in both GB cell cultures. Because of the genetic heterogeneity of malignant gliomas, we tested the effect of helianthin on other two primary GB lines (11 and 15) and two early-passage GB cultures (BT1GB and BT2GB), to assess the general nature of the anti-tumor effect of the drug in GB cells. We found that helianthin treatment induced cell death in all the GB cell cultures analyzed. To our knowledge, this is the first report indicating that helianthin can reduce GB cell growth.

Acromegaly and anaplastic astrocytoma: coincidence or pathophysiological relation?

Insulin-like growth factor type I (IGF-I) is an important promoter in the tumorigenesis of several extracranial and intracranial neoplasms. In astrocytic-cell tumors, the role of autocrine and paracrine IGF-I expression in enhancing tumoral progression is well established. However, the influence of systemic IGF-I levels on the clinical behavior of astrocytic neoplasms remains an open subject of research. We report the case of a 28-year-old man who presented simultaneously with acromegaly and an anaplastic astrocytoma, which had rapidly progressed from a low-grade astrocytoma. The coexistence of systemic IGF-I hypersecretion with a quick progression in the histopathological grade of the astrocytoma raises the compelling question of whether the clinical behavior of the astrocytic tumor was influenced by the acromegalic status. The role of IGF-I signaling in the pathogenesis of astrocytic-cell tumors and the experience with therapeutic strategies addressing this pathway in astrocytomas are also discussed.

Glioma risk in relation to serum levels of insulin-like growth factors

Several studies have suggested that insulin-like growth factors (IGF) are related to cancer risk. We investigated the associations between serum levels of IGF-I and IGF-binding protein-3 and glioma risk. A nested case-control study was conducted within a cancer prevention study, including 29,133 men (ages 50-69 years). In total, 22 glioma cases and 400 randomly selected controls were included. Serum samples were collected a minimum of 5 years before cancer diagnosis. Serum concentrations were measured using ELISA and divided into tertiles based on measurements among controls. Odds ratios and 95% confidence intervals were calculated using the lowest tertile as the reference category. No statistical association was detected between glioma and IGF-binding protein-3. IGF-I was inversely associated with glioma when comparing the lowest tertile with the other tertiles combined (odds ratio, 0.3; 95% confidence interval, 0.1-0.7). The results encourage future research on IGFs in relation to brain tumors in larger studies.

Higher glioblastoma tumour burden reduces efficacy of chemotherapeutic agents: in vitro evidence

INTRODUCTION

Glioblastoma is the most common primary brain tumour with poor overall survival. Surgical resection followed by radiation and chemotherapy is the mainstay of treatment. The role of aggressive resection in improving overall survival remains contentious, although there is evolving data to suggest this trend. Definitive evidence will necessitate a well-designed randomized prospective trial, although it is not likely that this will be possible or feasible. One possible advantage of aggressive tumour resection is a rapid reduction in oncological burden which may augment the effect of adjuvant chemotherapy.

MATERIALS AND METHODS

Three glioblastoma cell lines were seeded in concentrations from 5000-20,000 cells per well onto 96-well plates. The cells were incubated for 24 hours before treatment with varying concentrations of 1,3-Bis(2- chloroethyl)-1-nitrosourea (BCNU) ranging from 25 to 175 microg/mL. After 24 hours of treatment with BCNU, the cells were then examined microscopically and subjected to a cell proliferation assay to determine cytotoxicity effects of BCNU.

RESULTS

The drug concentration required to achieve greater than 90% growth inhibition (IC90) was taken as the reference for efficacy of chemotherapy dose. With tumour loading of 5000 cells per well, BCNU concentrations of 75-100 microg/mL resulted in greater than IC90, whereas BCNU concentration of 150-175 microg/mL was required with tumour loading of 20,000 cells per well. A higher concentration of chemotherapeutic agent is therefore required to bring about cell death in the presence of greater tumour burden.

CONCLUSION

Higher glioblastoma loading confers chemoresistance to BCNU. This is possibly secondary to complex interactions between tumour cells and neighbouring cells acting via autocrine or paracrine signaling pathways.

The insulin-like growth factor system and its pleiotropic functions in brain

In recent years, much interest has been devoted to defining the role of the IGF system in the nervous system. The ubiquitous IGFs, their cell membrane receptors, and their carrier binding proteins, the IGFBPs, are expressed early in the development of the nervous system and are therefore considered to play a key role in these processes. In vitro studies have demonstrated that the IGF system promotes differentiation and proliferation and sustains survival, preventing apoptosis of neuronal and brain derived cells. Furthermore, studies of transgenic mice overexpressing components of the IGF system or mice with disruptions of the same genes have clearly shown that the IGF system plays a key role in vivo.

Genetic characterization of commonly used glioma cell lines in the rat animal model system

Object

Animal models have been used extensively to discern the molecular biology of diseases and to gain insight into treatments. Nevertheless, discrepancies in the effects of treatments and procedures have been encountered during the transition from these animal models to application of the information to clinical trials in humans. To assess the genetic similarities between human gliomas and four cell lines used routinely in animal models, the authors used microarray technology to characterize the similarities and differences in gene expression.

Methods

To define the changes in gene expression, normal rat astrocytes were compared with four rat glioma cell lines (C6, 9L, F98, and RG2). The data were analyzed using two different methods: fold-change analysis and statistical analysis with t statistics. The gene products that were highlighted after intersecting the lists generated by the two methods of analysis were scrutinized against changes in gene expression reported in the literature. Tumorigenesis involves three major steps: the accumulation of genetic alterations, uncontrolled growth, and selected survival of transformed cells. The discussion of the results focuses attention on genes whose primary function is in pathways involved in glioma proliferation, infiltration, and neovascularization. A comparative microarray analysis of differentially expressed genes for four of the commonly used rat tumor cell lines is presented here.

Conclusions

Due to the variances between the cell lines and results from analyses in humans, caution must be observed in interpreting as well as in the translation of information learned from animal models to its application in human trials.

Differential patterns of insulin-like growth factor-I and -II mRNA expression in medulloblastoma

Insulin-like growth factors (IGFs) play an important role in tumour growth and development. We hypothesized that this is also the case for medulloblastomas, which are highly malignant cerebellar brain tumours usually occurring in children. In these tumours the expression patterns of IGF-I and -II mRNA were studied. Tumour specimens obtained from 12 children and two adults at diagnosis were hybridized in situ with digoxigenin-labelled cRNA probes for hIGF-I and hIGF-II mRNAs. In all cases, tumour cells showed abundant expression of IGF-I mRNA. Nine of the 14 tumours showed variable but significant IGF-II expression. In these tumours, the hybridization signal almost exclusively colocalized with a subpopulation of Ki-M1P positive cells that were identified as ramified microglia (RM) cells. In the five tumours without IGF-II expression, microglia/brain macrophages with a more rounded amoeboid-like morphology predominated. RM cells in normal cerebellar tissues, residing abundantly in areas of the white and, to a less extent, in the grey matter, were IGF-II mRNA-negative. These RM cells showed a thinner and more extensively branched appearance and were more evenly distributed than those encountered in medulloblastoma. Probably, during the transformation from the resting ramified towards the amoeboid morphology (or vice versa) IGF-II mRNA expression is only temporarily induced. The physiological meaning of the induction of IGF-II mRNA expression by these cells in medulloblastoma remains unclear but any IGF-II peptide synthesized could exert unfavourable mitogenic and antiapoptotic effects on adjacent tumour cells. However, in this relatively small number of cases we could not find any indications for a relationship between clinical characteristics of the various cases and the extent of IGF-II mRNA expression.

Changes in expression of transferrin, insulin-like growth factor 1, and interleukin 4 receptors after irradiation of cells of primary malignant brain tumor cell lines

Various immunotoxins have been developed for the treatment of cancer. The toxin is internalized by target cells through cell-surface receptors, and it is essential for these receptors to be expressed for the immunotoxin to have specific anti-tumor activity. Radiation therapy is one of the main treatment modalities for primary malignant brain tumors. The purpose of this study was to determine whether radiation influences the expression of cell-surface receptors. Cells of one human medulloblastoma (Daoy) and two glioblastoma (U373-MG and T98-G) cell lines were tested by exposing the cells to a single dose of 5 Gy gamma rays. Expression of transferrin receptors, type-1 insulin-like growth factor receptors (IGF1R), and interleukin 4 receptors (IL4R) was measured by flow cytometry analysis on unirradiated cells and on cells 3 to 120 h after irradiation. In Daoy cells, the absolute expression index of transferrin receptors increased during the 24 h after irradiation with the greatest change of 26% above control at 9 h. The absolute expression index of IGF1R increased 26.5% above control at 12 h. The absolute expression index of IL4R decreased 9 h after irradiation. In U373-MG cells the absolute expression index of transferrin receptors increased during the 24 h after irradiation, and the greatest increase was 45% above control at 9 h. The absolute expression index of IGF1R increased during the 12 h after irradiation with a maximum increase of 33% above control at 6 h. The absolute expression index of IL4R decreased with time after irradiation. In T98-G cells, the absolute expression index of both transferrin receptors and IL4R decreased after irradiation. The results suggest that the expression of growth factor receptors on brain tumor cells may be influenced by radiation. The effect of ionizing radiation on receptor expression should be considered when administration of targeted toxin is combined with radiation. Similar studies with other growth factor receptors used in targeted toxin therapy are recommended.

Astrocyte differentiation states and glioma formation

Gliomas are the most common primary malignancy in human central nervous system. Many similarities in cell morphology and expression of markers exist between cancerous cells and normal undifferentiated progenitor cells. At the molecular level, many important gene products are causally implicated in both the glial differentiation process and glial neoplasm formation. These observations raise the question of to what degree cell differentiation state influences glioma formation. In this review, we discuss new insights into the parallels between glial differentiation and glioma formation as well as the potential application of differentiation-inducing therapy.

Molecular biology of nervous system tumors

Many genetic alterations that contribute to CNS tumorigenesis and progression have been identified. One goal of such studies is to identify loci that would serve as diagnostic prognostic markers or both. A significant advance is the observation that chromosome 1p loss identified anaplastic oligodendroglioma and a subset of high-grade glioma patients who responded to chemotherapy and had longer survival times. Combined 1p and 19q loss was a predictor of prolonged survival of patients having pure oligodendrogliomas. Such markers eventually may be used to identify patients upfront who would benefit from treatment, while sparing patients who would not benefit. Although many molecular participants involved in the biologic pathways that promote proliferation, angiogenesis, and invasion have been elucidated, there are still many gaps in clinicians' knowledge. It is expected that the use of the human genome project information and databases such as SAGEmap, in combination with techniques such as cDNA arrays and proteomics, will facilitate greatly the identification of novel genes that contribute to CNS tumors. cDNA arrays and tissue arrays will permit the construction of CNS-specific screening tools that will permit the identification of tumor-specific mutations and alterations so that patient-specific therapies can be designed.

The IGF/IGFBP system in CNS malignancy

The insulin-like growth factor (IGF) system includes IGF-I and IGF-II, the type I and type II IGF receptors, and specific IGF binding proteins (IGFBP-1 to IGFBP-6). These factors regulate both normal and malignant brain growth. Enhanced expression of IGF-I and IGF-II mRNA transcripts has been demonstrated in gliomas, meniningiomas, and other tumours. Abnormal imprinting of IGF-II occurs in gliomas, medulloblastomas, and meningiomas. Both types of IGF receptor are expressed in gliomas and, in particular, the type I IGF receptor appears to be upregulated in malignant brain tissue. Antisense IGF-I receptor mRNA induces an antitumour response, resulting in complete brain tumour regression. Clinical trials for the treatment of brain tumours in humans based on a gene transfer protocol using IGF-I receptor antisense are under way. All six IGFBPs are expressed to a variable extent in brain tumours. High concentrations of IGFBP-2 are found in cerebrospinal fluid from patients with malignant central nervous system tumours; therefore, IGFBP-2 might be a useful marker for these tumours. IGFBP-4 appears to be a negative regulator of tumour proliferation. Both in vitro and in vivo experiments suggest that the IGF system represents an important target for the treatment of malignant central nervous system tumours and the ongoing trials should provide valuable information for future therapeutic approaches.

Insulin-like growth factor I (IGF-I) protects cells from apoptosis by Alzheimer's V642I mutant amyloid precursor protein through IGF-I receptor in an IGF-binding protein-sensitive manner

It has been found that insulin-like growth factor I (IGF-I) exerts cytoprotection against Abeta amyloid-induced neuronal cell death. Deposits of Abeta amyloid are one of the pathological hallmarks of Alzheimer's disease (AD). Here, we examined whether IGF-I exerts protective activity against cell death induced by a familial AD (FAD)-linked mutant of amyloid precursor protein (APP), and we found that IGF-I protected cells from toxicity of FAD-associated V642I mutant of APP in multiple cell systems. IGFBP-3 blocked this action of IGF-I, but not of des(1-3)IGF-I, which was as active as IGF-I in the presence of IGFBP-3. The data also demonstrated that the IGF-I receptor (IGF-IR) mediates the protective activity of IGF-I. The antagonizing function of the IGF-I/IGF-IR system against V642I-APP, which is further antagonized by IGFBP-3, provides a molecular clue to the understanding of AD pathophysiology and to the establishment of potential therapy for AD.

Identification of cadherin-11 down-regulation as a common response of astrocytoma cells to transforming growth factor-alpha

Transforming growth factor-alpha (TGF-alpha) and its receptor are frequently co-expressed in high-grade astrocytomas, suggesting a role for TGF-alpha autocrine/paracrine loops in the malignant progression of astrocytomas. To identify genes that may be critical in mediating TGF-alpha impact on the malignant progression of astrocytomas, we have used cDNA arrays to investigate TGF-alpha effects on the gene expression profile of U-373 MG glioblastoma cells. We found that in these cells approximately 50% of the TGF-alpha regulated genes code for cell motility/invasion-related proteins. TGF-alpha action on the expression of four of these proteins, alpha-catenin, IQGAP1, RhoA, and cadherin-11, was further investigated by immunoblotting in four astrocytoma cell lines and in normal astrocytes. The results demonstrate that the effects of TGF-alpha on IQGAP1, alpha-catenin, and RhoA expression are cell-line dependent. On the other hand, under TGF-alpha treatment, cadherin-11 expression is consistently decreased in all astrocytoma cell lines tested but is increased in normal astrocytes. In addition, we found that cadherin-11 is consistently down-regulated in astrocytomas versus normal brain tissues. Altogether, these results suggest that the down-regulation of cadherin-11 is a frequent molecular event in the neoplastic transformation of astrocytes and that this down-regulation may be initiated and/or amplified by TGF-alpha autocrine/paracrine loops during tumor progression.