Growth regulation of human glioblastoma T98G cells by insulin-like growth factor-1 and its receptor

Glioma Cell Secretion: A Driver of Tumor Progression and a Potential Therapeutic Target

Cellular secretion is an important mediator of cancer progression. Secreted molecules in glioma are key components of complex autocrine and paracrine pathways that mediate multiple oncogenic pathologies. In this review, we describe tumor cell secretion in high-grade glioma and highlight potential novel therapeutic opportunities. Cancer Res; 78(21); 6031-9. ©2018 AACR.

Anatomic localization of O6-methylguanine DNA methyltransferase (MGMT) promoter methylated and unmethylated tumors: a radiographic study in 358 de novo human glioblastomas

Promoter methylation of O6-methylguanine DNA methyltransferase (MGMT) is associated with a favorable prognosis in glioblastoma multiforme (GBM) and has been hypothesized to occur early in tumor transformation of glial cells. Thus, a possible link exists between the site of malignant transformation and MGMT promoter methylation status. Using the Analysis of Differential Involvement (ADIFFI) statistical mapping technique in a total of 358 patients with GBM, we demonstrate that human de novo GBMs occur in a high frequency contiguous with the posterior subventricular zone (SVZ); MGMT promoter methylated GBMs are lateralized to the left hemisphere, while MGMT unmethylated GBMs are lateralized to the right hemisphere; and tumors near the left temporal lobe have a significantly longer overall survival compared with tumors occurring elsewhere, independent of treatment or MGMT methylation status.

Dual targeting of IGF-1R and PDGFR inhibits proliferation in high-grade gliomas cells and induces radiosensitivity in JNK-1 expressing cells

Increased expression and activation of receptor tyrosine kinases frequently occur in human brain tumors, mediating a variety of growth-promoting pathways and leading to radioresistance; however, little is known about their motogenic potency relative to one another. In this study, we found co-expression of Insulin like growth factor-1 receptor (IGF-1R) and platelet derived growth factor receptor (PDGFR) in two high-grade gliomas (HGG) cell lines 18 and 38. Dual targeting of IGF-1R and PDGFR increased cell death in both 18 and 38 cell lines in comparison to inhibition of either receptor alone. In addition, co-inhibition of IGF-1R and PDGFR increased radiosensitivity in 18 cells but failed to intensify the effect of radiation in 38 cells. In HGG cells, radiation-induced cell death has been connected to the activation of c-Jun-NH2-terminal kinase-1 (JNK1). We found that JNK1 was weakly expressed in 38 cells while it had an elevated expression in 18 cells. Exposure to ionizing radiation induced JNK1 activation only in 18 cells without affecting the protein activity in 38 cells. These results suggest that in 18 cell line radiation-activated JNK1 may provide an anti-proliferative signaling, parallel to receptors co-targeting. To test this hypothesis, HGG cells were treated with dominant negative JNK1 (dnJNK1) and the response to radiation was assayed in presence or absence of receptors co-inhibition. Indeed dnJNK protected 18 cells against gamma-irradiation-induced cell death. dnJNK treatment did not influence radiation response of the 38 cell line, which expressed low levels of JNK1. In conclusion we found that IGF-1R and PDGFR co-inhibition caused an increased cell death in two HGG cell line and induced the radiosensitization of the JNK1 expressing cell line.

Treatment of hematologic malignancies and solid tumors by inhibiting IGF receptor signaling

Insulin-like growth factors (IGF) and their receptors (IGF-1R) constitute a complex biologic system implicated in diverse regulatory levels of cell proliferation, viability, differentiation and metabolism. Extensive epidemiologic data have implicated the IGF/IGF-1R pathway in the establishment of human malignancies, consistent with experimental data on the role of this signaling cascade in promoting cell transformation, resistance to apoptosis, metastases and other aspects of the biology of human cancers. However, historically, the IGF/IGF-1R pathway has not been viewed as an attractive target for therapeutic intervention. The widespread IGF-1R expression in normal tissues and its close homology to the insulin receptor had led to the assumption that IGF-1R inhibition would cause unacceptable toxicities in vivo. Even though neutralizing antibodies against human IGF-1R have been efficacious against xenograft tumors, a lack of reactivity against the host rodent receptor has confounded the assessment of its therapeutic index. Furthermore, the lack of a clear understanding of the relevant significance for neoplastic cells in the function of IGF-1R versus other growth factor receptors provided an additional disincentive for the study of this pathway. However, recent reports from the authors' group and others have shown that small molecule inhibitors of tyrosine kinase activity of IGF-1R can be safely and efficaciously administered in vivo in clinically relevant orthotopic models of human neoplasias, such as multiple myeloma. This article reviews the data that validated IGF-1R as a therapeutic target for a broad spectrum of malignancies and provides in vivo proof-of-concept for the use of selective IGF-1R kinase inhibitors as primary antitumor therapy or in synergistic combination as chemosensitizers. These results have not only provided the rationale for clinical trials of small molecule IGF-1R inhibitors, but have also rekindled interest in other therapeutic modalities (e.g., monoclonal antibodies) aimed at suppressing the function of this critical pathway for tumor cell pathophysiology.

Modification of insulin-like growth factor 1 receptor, c-Src, and Bcl-XL protein expression during the progression of Barrett's neoplasia

Oncogenes, growth factors, cell surface receptors, and cell-cycle and apoptotic regulatory proteins have been implicated in the growth regulation and progression of Barrett's-associated neoplasia. Among these, insulin-like growth factor 1 receptor (IGF1-R) and c-Src are reported to be key regulators of mitogenesis and tumorigenesis. In addition, c-Src may exert its transforming capability by inducing increased expression of IGF1-R on the neoplastic cells. Bcl-X(L), a member of the Bcl-2 family, blocks apoptosis and has been reported to increase in Barrett's-associated neoplasia. To study the modifications in IGF1-R, c-Src, and Bcl-X(L) protein expression during the progression of Barrett's-associated neoplasia, we analyzed 34 resected gastroesophagectomy specimens by immunohistochemistry using antibodies to human IGF1-R, c-Src, and Bcl-X(L). In these cases, we found 22 intestinal (Barrett's) metaplasias (IMs), 25 low-grade dysplasias (LGDs), 28 high-grade dysplasias (HGDs), 34 invasive adenocarcinomas (CAs), and 19 lymph node metastases. High IGF1-R cytoplasmic staining was present in 14 of 19 (74%) node metastases, in 28 of 34 (82%) CAs, in 18 of 28 (64%) HGDs, in 13 of 25 (52%) LGDs, and in 5 of 22 (23%) IMs. Strong and diffuse c-Src expression was identified in 17 of 19 (89%) node metastases, in 29 of 34 (85%) Cas, in 26 of 28 (93%) HGDs, in 18 of 25 (72%) LGDs, and in 9 of 22 (41%) IMs. Bcl-X(L) cytoplasmic staining was evident in 12 of 19 (63%) node metastases, in 20 of 34 (59%) Cas, in 20 of 28 (71%) HGDs, in 15 of 25 (60%) LGDs, and in 6 of 22 (27%) IMs. In 11 cases, c-Src activity was measured by kinase assay and reflected the immunohistochemical results. Our data indicate that expression levels of IGF1-R, c-Src, and Bcl-X(L) proteins are coordinately elevated in Barrett's-associated neoplasia. These findings indicate important roles of these growth regulatory proteins in the malignant progression of Barrett's-associated neoplasia.

Development of new insulin-like growth factor-1 receptor kinase inhibitors using catechol mimics

Because insulin-like growth factor-1 (IGF-1) and its receptor play a pivotal role in many cancers, it is an attractive target for the design of inhibitors. Here we present a new family of bioisostere inhibitors, based on the structure of AG 538. AG 538 is a substrate-competitive inhibitor of the IGF-1 receptor (IGF-1R), with an IC50 = 61 nM in a cell-free kinase assay (Blum, G., Gazit, A., and Levitzki, A. (2000) Biochemistry 39, 15705-15712). AG 538 is a low molecular weight compound containing two catechol rings, which are sensitive to oxidation in cells. We have therefore prepared and examined catechol bioisosteres of AG 538. These AG 538 bioisosteres possess similar biological properties to AG 538; they inhibit IGF-1R by a substrate-competitive mechanism and are non-competitive vis à vis ATP. They inhibit IGF-1R kinase activity in the sub-micromolar concentration range in cell-free assays. IGF-1 induced IGF-1R autophosphorylation; IRS-1 phosphorylation and protein kinase B activation are inhibited at a low micromolar concentration range when applied to intact cells. These inhibitors also block the formation of colonies in soft agar by prostate and breast cancer cells. The ability to replace catechol groups with a moiety that is more stable in cells may aid in developing non-catechol-containing substrate-competitive inhibitors targeted toward IGF-1R and possibly against other protein-tyrosine kinases.

Expression and distribution of insulin-like growth factor-1 receptor in human carcinomas

The insulin-like growth factor-1 receptor (IGF1-R) is a cellular receptor overexpressed in many tumor cell lines and in some human tumors that seems to play a critical role in transformation, tumorigenicity, and metastasis. To date, a comprehensive evaluation of tissue distribution of IGF1-R in human carcinomas from different anatomical sites has been lacking. Using stage-oriented human cancer tissue microarrays, we studied IGF1-R expression and distribution in a group of 152 human carcinomas from a variety of anatomical sites and from 63 normal tissues through immunohistochemistry. The tumors included carcinomas from breast (8), ovary (9), endometrium (7), esophagus (5), stomach (7), pancreas (7), liver (4), colon (10), kidney (14), bladder (17), prostate (11), head and neck (31), salivary glands (8), lung (13), and skin (1). Formalin-fixed, paraffin embedded tissues of each case were immuno-stained using the avidin-biotin peroxidase method and an anti-IGF1-R rabbit polyclonal antibody. High-membranous IGF1-R staining was observed in 7 of 8 (87.5%) breast carcinomas, in 9 of 9 (100%) ovarian carcinomas, in 7 of 7 (100%) endometrial carcinomas, in 5 of 7 (71.1%) gastric carcinomas, in 4 of 7 (57.1%) pancreatic carcinomas, in 9 of 10 (90%) colon adenocarcinomas, in 11 of 13 (84.6%) lung carcinomas, in 6 of 11 (54.5%) prostatic adenocarcinomas, and in 17 of 17 (100%) transitional cell carcinomas of the bladder. Only a minority of squamous cell carcinomas of the head and neck and esophagus (34), salivary gland tumors (5), and renal cell carcinomas (14) were IGF1-R positive. This study demonstrates the overexpression of IGF1-R across a wide variety of human carcinomas of glandular or transitional cell origin.

Treatment of murine breast cancer cells with antisense RNA to the type I insulin-like growth factor receptor decreases the level of plasminogen activator transcripts, inhibits cell growth in vitro, and reduces tumorigenesis in vivo

AIMS

To establish that cells from the murine mammary carcinoma cell line, EMT6, express type I insulin-like growth factor receptor (IGF-IR), tissue-type plasminogen activator (tPA), and urokinase-type plasminogen activator (uPA). To investigate the role of IGF-IR in growth, transformation, and tumorigenesis in addition to its relation to tPA and uPA in EMT6 cells. To assess the suitability of the EMT6/syngeneic mouse model for studying the role of IGF-IR in tumorigenesis.

METHODS

The presence of transcripts for IGF-IR, tPA, and uPA was determined by northern blot analysis using poly (A(+)) RNA derived from EMT6 cells transfected with an antisense IGF-IR construct or a construct lacking the antisense IGF-IR insert. Flow cytometry was used to measure IGF-IR protein. Assays were performed to determine cell proliferation, transformation, and the tumorigenicity of antisense IGF-IR transfected EMT6 cells and control transfected EMT6 cells.

RESULTS

There was strong expression of IGF-IR, tPA, and uPA in EMT6 cells. EMT6 cells from clones carrying antisense IGF-IR displayed a significant decrease in cell proliferation and lost the ability to form colonies in soft agar. A decrease in tumour size occurred when cells carrying the antisense IGF-IR were injected into syngeneic mice. Reduced expression of tPA and uPA was seen in EMT6 cells carrying the antisense IGF-IR construct.

CONCLUSIONS

The IGF-IR plays a role in the progression, transformation, and tumorigenesis of EMT6 murine mammary carcinoma cells. The suppression of IGF-IR mRNA in EMT6 cells decreases tPA and uPA expression. EMT6 cells and the syngeneic mouse provide a suitable model for studying the role of IGF-IR in breast tumour progression.

Antiproliferative and apoptotic effect of ascorbyl stearate in human glioblastoma multiforme cells: modulation of insulin-like growth factor-I receptor (IGF-IR) expression

Human glioblastomas (gliomas) are characterized as highly invasive and rapidly growing brain tumors. In this study, we present data on in vitro effect of ascorbyl stearate (Asc-S), a liphophilic derivative of ascorbic acid on cell proliferation, transformation, apoptosis and modulation of expression of insulin-like growth factor-I receptor (IGF-IR) in human glioblastoma multiforme (T98G) cells. Asc-S showed significant inhibition of fetal bovine serum and human recombinant insulin-like growth factor-I (IGF-I) dependent cell proliferation in a dose dependent manner. Treatment of T98G cells with 0, 50, 100 and 150 microM Asc-S for 24h slowed down the cell multiplication cycle with significant accumulation of cells at late S/G2-M phase of cycle. Asc-S treatment (100 microM) reversed the transformed phenotype as determined by clonogenecity in soft agar and also induced apoptosis of T98G. These changes were found to be associated with significant decrease in IGF-IR expression in dose and time dependent manner compared to untreated controls. The data clearly demonstrate that Asc-S has antiproliferative and apoptotic effect on T98G cells probably through modulation of IGF-IR expression and consequent facilitation of programmed cell death.

Inhibition of growth and increased expression of insulin-like growth factor-binding protein-3 (IGFBP-3) and -6 in prostate cancer cells stably transfected with antisense IGFBP-4 complementary deoxyribonucleic acid

Insulin-like growth factor-binding proteins (IGFBPs) both stimulate and inhibit IGF activity, and in the M12 prostate cancer cell line, overexpression of IGFBP-4 was shown to delay tumorigenesis while decreasing the production of IGFBP-2. We have performed the reverse experiment, inhibition of IGFBP-4 expression with antisense complementary DNA, in two prostate tumor cell lines, ALVA-31 and M12. Expression of antisense messenger RNA transcripts was verified by RNase protection assays, and inhibition of mature IGFBP-4 in cell medium was demonstrated by Western blotting. Both transfected lines (ALVA-31asBP4 and M12asBP4) proliferated more slowly in monolayer culture than parental controls. Colony formation in soft agar was strongly inhibited in both cases, and the rate of tumor formation and growth in male athymic nude mice injected with M12asBP4 was markedly reduced relative to that in mice receiving M12 control cells. Apoptosis induced by the topoisomerase inhibitor etoposide was also enhanced in transfected cells. The effects on colony formation in soft agar and tumor formation in mice were maintained for the duration of the experiments, in contrast to the delayed growth observed in the previous study of IGFBP-4 overexpression. A significant difference was found in the patterns of IGFBP expression; production of both messenger RNA and protein for IGFBP-3 and IGFBP-6 was greatly increased in the M12asBP4 and ALVA31asBP4 cell lines. Up-regulation of these binding proteins has been observed in association with actions of 1,25-dihydroxyvitamin D(3) in prostate cancer cells, and the data suggest a role for IGFBP-3 and IGFBP-6 in the suppression of prostate tumor cell growth.

IGF-I receptor activation and BCL-2 overexpression prevent early apoptotic events in human neuroblastoma

The type I insulin-like growth factor receptor (IGF-IR) is important for mitogenesis, transformation, and survival of tumor cells. The current study examines the effect of IGF-IR expression and activation on apoptosis in SHEP human neuroblastoma cells. SHEP cells undergo apoptosis which is prevented by IGF-I addition or overexpression of the IGF-IR (SHEP/IGF-IR cells). High mannitol treatment activates caspase-3 by 1 h in SHEP cells while caspase-3 activation is delayed by 3 h in SHEP/IGF-IR cells. Transfection with Bcl-2 (SHEP/Bcl-2 cells) prevents serum withdrawal and mannitol induced apoptosis and caspase-3 activation. Mannitol induces mitochondrial membrane depolarization in both SHEP and SHEP/IGF-IR cells. IGF-IR activation or overexpression of Bcl-2 in SHEP cells prevents mitochondrial membrane depolarization. Collectively, these results suggest that IGF-IR or Bcl-2 overexpression in neuroblastoma cells promotes cell survival by preventing mitochondrial membrane depolarization and caspase-3 activation, ultimately leading to increased tumor growth.

Emerging translational therapies for mesothelioma

Malignant pleural mesothelioma remains a therapeutic and diagnostic problem. Translational mechanisms for treatment of the disease are emerging from newly learned characteristics of the tumor on a molecular, cellular, and extracellular basis. Although slow to reach the clinical arena, these potential strategies do show proof of principle in the in vitro and in vivo settings, and some, including adenoviral molecular chemotherapy, have completed phase I testing. This review describes the rationale and status of these newer treatment ideas.

Expression of insulin-like growth factor-1 receptor in human colorectal cancer

The activation of the insulinlike growth factor 1/IGF-1 receptor system (IGF1/IGF1-R) has recently emerged as critical event in transformation and tumorigenicity of several murine and human tumors. Expression of IGF1 and of IGF1-R has been demonstrated in normal and neoplastic intestinal cell lines of rats and humans. However, the modulation of IGF1-R expression during the progression from normal colonic mucosa to adenoma, to carcinoma, and to metastasis, has not been evaluated. In this retrospective study, we investigated the expression of IGF1-R in 12 colonic adenomas (AD), 36 primary colorectal adenocarcinomas (CA), and in 27 corresponding metastases (MT). Normal colonic mucosa (N) was adjacent to the CA in 34 cases. Formalin-fixed, paraffin-embedded tissues of each case were immunostained using the avidin-biotin-peroxidase method. We used an anti-IGF1-R rabbit polyclonal antibody (Santa Cruz Biotechnology, CA; dilution 1:100). Positive staining was quantitated by CAS-200. Moderate to strong cytoplasmic immunostaining was observed in 34 of 36 CA (96%), and in 25 of 27 MT (93%). In all of the positive MTs, the intensity of the staining was always strong. In 10 of 12 ADs (83%), only a faint cytoplasmic stain was identified. Normal mucosa when present was negative. Strong IGF1-R positivity correlated with higher grade and higher-stage tumors (P < .01). These data suggest a role of IGF1-R expression during the progression of colorectal adenoma to carcinoma. An increased number of IGF1-R receptors may favor the metastasis of colorectal cancer.

Overexpression of insulin-like growth factor-binding protein-2 in C6 glioma cells results in conditional alteration of cellular growth

To examine the relationship between the expression of insulin-like growth factor (IGF)-binding protein-2 (IGFBP-2) and cell growth in a cell type with a defined IGF/IGFBP system, an ovine IGFBP-2 complementary DNA was overexpressed in C6 glioma cells. C6 cells produce IGFBP-3, IGFBP-4, a negligible amount of IGFBP-2, and IGF-I. An ovine IGFBP-2 complementary DNA was transfected into C6 cells, and nine colonies that stably expressed variable levels of IGFBP-2 messenger RNA were selected. Synthesis of corresponding levels of IGFBP-2 was confirmed by ligand blot and immunoblot analyses of conditioned media. Three clones exhibited significantly reduced growth rates, and the remainder showed growth rates similar to those of the wild-type C6 cells. The clones, which overexpressed high levels of IGFBP-2 and IGF-I, had growth rates similar to the wild-type cells, whereas the three clones that overexpressed IGFBP-2 without a concomitant increase in IGF-I had reduced growth rates. In addition, a cell-associated IGFBP was identified in the slow growing clones, but not in the wild-type or the fast growing clones. This cell-associated IGFBP was deduced to be IGFBP-5 based on its molecular size, detection of IGFBP-5 messenger RNA only in slow growing clones, and competition of its binding by heparin. Growth of the slow growing clone, C6BP2-1, could not be overcome by the addition of exogenous IGF-I, suggesting that the cell-associated IGFBP-5 was the dominant regulator of IGF action. These observations suggested that 1) in C6 glioma cells cellular growth is altered by a disturbance in the equilibrium between IGF-I and IGFBPs and/or the functional properties of the IGFBPs; and 2) C6 cells may have a limited capacity to modulate IGF/IGFBP expression in response to changes in endogenous expression of IGFBPs. Endogenous regulation of the balance between IGFs and IGFBPs may be a model of regulation of cellular growth in tumor cells.

In situ visualization of intratumor growth factor signaling: immunohistochemical localization of activated ERK/MAP kinase in glial neoplasms

Abnormal growth factor signaling is implicated in the pathogenesis of gliomas. The extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) pathway is a likely target, linking receptor tyrosine kinase activation to downstream serine/threonine phosphorylation events regulating proliferation and differentiation. Signaling within heterogeneous cell populations of gliomas cannot be adequately assessed by traditional biochemical enzyme assays. Immunohistochemical detection of doubly phosphorylated (activated) ERK/MAPK permitted visualization of spatially discrete cellular patterns of ERK/MAPK activation, compared with the relatively uniform expression of total ERK/MAPK protein. The astrocytic tumors, regardless of grade, had the highest overall degree of enzyme activation, whereas oligodendrogliomas had the least. Anaplastic progression in oligodendrogliomas resulted in a larger number of cells with active ERK/MAPK. Within glioblastomas, microvascular hyperplasia and necrosis were associated with ERK/MAPK activation in adjacent tumor cells. In addition to spatial patterns of intratumor paracrine signaling, a possible cell-cycle-associated regulation was detected: mitotic and actively cycling tumor cells showed diminished activation relative to cells in G0. Although ERK/MAPK activation was not restricted to neoplastic glia, consistent patterns of selective activation in tumor cells suggests that sustained activation may contribute to the neoplastic glial phenotype.

Growth factors in gliomas: antisense and dominant negative mutant strategies

Antisense and dominant negative mutant strategies were developed as 'magic bullets' to suppress the function of a particular gene while preserving the remaining cellular activities. While experience with these techniques has dispelled some of the 'magic', these strategies remain useful for understanding the function of particular gene products. Antisense strategies involve the administration of either a synthetic oligodeoxynucleotide or a plasmid construct which produces a sequence that is complementary to the DNA or mRNA of the gene of interest. Antisense binding should inhibit transcription or translation of the gene, and thus decrease synthesis of the protein for which the gene encodes. Conversely, dominant negative mutations inhibit activity of a gene product by encoding for a second protein which suppresses the function of the gene of interest. For example, a single mutant subunit in a multimeric protein might allow normal assembly of the protein while inhibiting its activity. The use of these techniques for investigating the role of various growth factor pathways in glial neoplasia and their potential therapeutic applications are reviewed below.

Insulin-like growth factor receptor cooperates with integrin alpha v beta 5 to promote tumor cell dissemination in vivo

Tumor cell interactions with adhesion proteins and growth factors likely contribute to the metastatic cascade. Evidence is provided that insulin or insulin-like growth factor-mediated signals cooperate with the commonly expressed integrin alpha v beta 5 to promote spontaneous pulmonary metastasis of multiple tumor cell types in both the chick embryo and severe combined immune deficiency mouse/human chimeric models. Expression of alpha v beta 5 in tumor cells promoted their adhesion to vitronectin in vitro. However, cell motility required cytokine stimulation, which caused redistribution of alpha-actinin to membrane-adhesive sites containing alpha v beta 5. Significantly, ligation of alpha v beta 5 and cytokine receptors were both required for spontaneous pulmonary metastasis of multiple tumor types even though it was not necessary for primary tumor growth. Thus, tumor cell metastasis can be regulated by a functional cooperation between cytokine signaling events and the adhesion receptor alpha v beta 5 in a manner independent of tumor cell growth. These findings provide evidence that integrin ligation, in conjunction with cytokine activation, plays an important role in the dissemination of malignant tumor cells.

Ethanol-induced inhibition of cell proliferation is modulated by insulin-like growth factor-I receptor levels

Ethanol inhibits the tyrosine autophosphorylation of the insulin-like growth factor (IGF)-I receptor, an action that correlates with the inhibition of IGF-I-stimulated cell proliferation [J. Biol. Chem. 268:21777-21782 (1993)]. In the current study, the IGF-I-dependent proliferation of mouse BALB/c3T3 cells was completely inhibited by ethanol, but the growth of BALB/c3T3 cells that overexpress the IGF-I receptor (p6 cells) was only partially inhibited by ethanol BALB/ c3T3 cells that simultaneously overexpress both the IGF-I receptor and IGF-I were insensitive to growth inhibition by ethanol. In p6 cells, increasing concentrations of IGF-I overcame the inhibition of IGF-I receptor tyrosine autophosphorylation in the presence of ethanol. The importance of the IGF-I receptor as a specific target for ethanol was further investigated in C6 rat giloblastoma cells that respond mitogenically to both epidermal growth factor (EGF) and IGF-I. The mitogenic response of C6 cells to EGF was abrogated in cells expressing antisense mRNA to the IGF-I receptor. Thus, EGF action in these cells is dependent on activation of an IGF-I/IGF-I receptor autocrine pathway. Indeed, EGF stimulated an increase in IGF-I receptor levels by more than 100%. Ethanol completely inhibited the proliferation of C6 cells in response to either EGF or IGF-I. However, ethanol did not directly interfere with EGF receptor function, because EGF-induced cell proliferation was unaffected by ethanol when added exclusively during a 1-hr exposure to EGF. Ethanol did not interfere with the EGF-induced increase in IGF-I receptor expression. The addition of both EGF and IGF-I overcame the inhibitory action of ethanol. In conclusion, the potency of ethanol as an inhibitor of IGF-I-mediated cell proliferation correlates with the level of IGF-I receptors. In contrast to its effect on the IGF-I-receptor, ethanol has no direct effect on EGF receptor activation.

Regulation of insulin-like growth factor I receptor gene expression by the Wilms' tumor suppressor WT1

THe insulin-like growth factor I receptor (IGF-I-R) has been implicated in the etiology and/or progression of Wilms' tumor, or nephroblastoma, a pediatric neoplasm of the kidney that is often associated with deletion or mutation of the WT1 tumor suppressor gene. The levels of IGF-I-R mRNA in the tumors were sixfold higher than in normal adjacent kidney tissue and were inversely correlated to the levels of WT1 mRNA, suggesting that the expression of the IGF-I-R gene is under inhibitory control by WT1. Cotransfection of an IGF-I-R promoter-luciferase reporter construct together with a WT1 expression vector resulted in a dose-dependent suppression of promoter activity. Multiple WT1 binding sites were mapped in the 5'-flanking and 5'-untranslated regions of the IGF-I-R gene using gel retardation and DNaseI footprinting assays. Thus, suppression of the IGF-I-R promoter by WT1 involves multiple interactions of its zinc finger domain with sites located both upstream and downstream of the transcription initiation site. Finally, we showed that expression of the endogenous IGF-I-R gene is decreased in G401 cells stably transfected with a WT1 expression vector. Reduction in expression of the IGF-I-R gene is associated with a decrease in a number of IGF-I-mediated biological effects. Thus, deletion or mutation of the WT1 gene in Wilms' tumor and other malignancies can result in overexpression of the receptor, with enhanced autocrine/paracrine activation by locally produced or circulating IGFs.

Neurotensin-mediated effects on astrocytic tumor cell proliferation

Neurotensin (NT) and neurotensin receptors (NTRs) are widely found in the brain, NT may be considered as a mitogen factor in some tissues. However, no NT-mediated effects on glioma cell proliferation have been reported so far. In our present study we investigated the influence of NT on the proliferation of astrocytic tumor cell lines. To this end we used a synthetic NT agonist (JMV-449), a protease inhibitor which blocks the natural degradation of NT (JMV-531), and NT. The in vitro biological models used in the present study included the low grade SW1088, and the high grade U87, U373 and A172 astrocytic tumor cell lines. The peptide-induced influence on astrocytic tumor cell proliferation was investigated by means of the colorimetric MTT assay. Our results show that the NT and the NT agonist significantly stimulated the proliferation in 2/4 and 3/4 of the astrocytic cell lines respectively. Similarly, compound JMV-531 also induced an increase in the proliferation of 2/4 of the astrocytic cell lines. This marked influence of the NT and NT agonists, or the enzyme-endogenous prevention of its degradation on the regulation of astrocytic tumor growth therefore suggests that NT antagonists might be used to treat certain patients with high grade astrocytic tumors that do not respond to chemotherapy and/or radiotherapy.

The GC factor regulates the expression of the insulin-like growth factor-I receptor

We have transfected a plasmid expressing the transcriptional regulator GC Factor (GCF) into cell lines and have found that the GCF: 1 causes a decrease in the levels of insulin-like growth factor I receptor (IGF-IR) mRNA; 2 causes a decrease in the number of IGF-IRs; and 3 represses the activity of the IGF-IR promoter. In addition, we show that the regulation of IGF-IR expression by GCF plays a physiological role in the control of cellular proliferation in vitro.