Insulin-like growth factor ligands, receptors, and binding proteins in cancer

Akt1-mediated intracellular oxidation after UVB irradiation suppresses apoptotic cell death induced by cell detachment and serum starvation

Apoptosis is an important cell death system that deletes damaged and mutated cells to prevent cancer. We have previously reported that a certain dose of UVB irradiation inhibited the apoptosis induced by serum starvation and cell detachment, leading to cell transformation. This antiapoptotic effect was partially inhibited by phosphatidylinositol 3-kinase (PI3-kinase) inhibitors. UVB irradiation is known to cause the phosphorylation of Akt via the activation of PI3-kinase; however, the Akt isoform-specific relationship has not yet been clarified. Notably, the role in antiapoptotic effect of UVB has yet to be elucidated. In this study, the role of Akt1 in the UVB-induced inhibition of apoptosis was examined by Akt1 knockdown using small interfering RNA (siRNA). NIH3T3 cells showed typical apoptotic cell death by serum starvation and cell detachment, which was significantly inhibited by UVB irradiation. Akt1 knockdown decreased the antiapoptotic effect of UVB. Hydrogen peroxide-induced suppression of cell death was also decreased in Akt1 knockdown cells. An antioxidant, N-acetylcysteine, inhibited the antiapoptotic effect by UVB irradiation, whereas no inhibition was observed in Akt1 knockdown cells. Furthermore, UVB-induced intracellular peroxidation was not observed in the knockdown cells, indicating that Akt1 played an important role in mediating the intracellular redox status. Treatment with insulin had a similar antiapoptotic effect as UVB irradiation involving intracellular peroxidation, which was also attenuated in Akt1 knockdown cells. These findings suggest that appropriate intracellular oxidation after UVB irradiation prevented apoptosis, a process which might be partially regulated by the production of reactive oxygen species mediated by Akt1.

Enhanced sensitivity to IGF-II signaling links loss of imprinting of IGF2 to increased cell proliferation and tumor risk

Loss of imprinting (LOI) of the insulin-like growth factor-II gene (IGF2), leading to abnormal activation of the normally silent maternal allele, is a common human epigenetic population variant associated with a 5-fold increased frequency of colorectal neoplasia. Here, we show first that LOI leads specifically to increased expression of proliferation-related genes in mouse intestinal crypts. Surprisingly, LOI(+) mice also have enhanced sensitivity to IGF-II signaling, not simply increased IGF-II levels, because in vivo blockade with NVP-AEW541, a specific inhibitor of the IGF-II signaling receptor, showed reduction of proliferation-related gene expression to levels half that seen in LOI(-) mice. Signal transduction assays in microfluidic chips confirmed this enhanced sensitivity with marked augmentation of Akt/PKB signaling in LOI(+) cells at low doses of IGF-II, which was reduced in the presence of the inhibitor to levels below those found in LOI(-) cells, and was associated with increased expression of the IGF1 and insulin receptor genes. We exploited this increased IGF-II sensitivity to develop an in vivo chemopreventive strategy using the azoxymethane (AOM) mutagenesis model. LOI(+) mice treated with AOM showed a 60% increase in premalignant aberrant crypt foci (ACF) formation over LOI(-) mice. In vivo IGF-II blockade with NVP-AEW541 abrogated this effect, reducing ACF to a level 30% lower even than found in exposed LOI(-) mice. Thus, LOI increases cancer risk in a counterintuitive way, by increasing the sensitivity of the IGF-II signaling pathway itself, providing a previously undescribed epigenetic chemoprevention strategy in which cells with LOI are "IGF-II addicted" and undergo reduced tumorigenesis in the colon upon IGF-II pathway blockade.

Growth-inhibitory effects of human anti-insulin-like growth factor-I receptor antibody (A12) in an orthotopic nude mouse model of anaplastic thyroid carcinoma

PURPOSE

The insulin-like growth factor-I receptor (IGF-IR) and its ligands have been implicated in the pathogenesis and progression of various cancers, including those arising in the thyroid gland. We therefore evaluated whether the IGF-IR could serve as a potential target for therapy of anaplastic thyroid carcinoma (ATC).

EXPERIMENTAL DESIGN

The expression and activation of the IGF-IR and some of its downstream signaling pathway components were evaluated in both human thyroid cancer specimens and thyroid cancer cell lines. The therapeutic potential of a humanized monoclonal antibody (A12) directed against IGF-IR was assessed in vitro and in vivo in an orthotopic model of ATC. Tumor volume and overall survival time were analyzed to evaluate the efficacy of A12 in vivo.

RESULTS

IGF-IR was overexpressed in 94% of the thyroid cancers. Blockade of IGF-IR with A12 was effective in attenuating IGF-IR signaling both in vitro and in vivo. However, the inhibitory effects of A12 on cell proliferation were cell line dependent, as those ATC cell lines that had detectable levels of pIGF-IR were more sensitive to A12 treatment. A12 was equally effective in vivo, where it brought approximately 57% (P = 0.041) inhibition in tumor volume. The concomitant use of A12 and irinotecan produced additive effects and resulted in a 93% (P < 0.001) reduction in tumor volume. Blocking IGF-IR blocked Akt phosphorylation and decreased proliferation and microvessel density but increased apoptosis within the tumor xenografts. Our results also highlighted a previously undefined IGF-IR-mediated antiangiogenic effect on tumor-associated endothelium in thyroid cancers.

CONCLUSION

Blocking the IGF-IR with A12 seems to be a potential avenue for treating patients with ATC by its direct antitumor effects and its effects on the tumor vasculature.

Structure and functional analysis of the IGF-II/IGF2R interaction

Embryonic development and normal growth require exquisite control of insulin-like growth factors (IGFs). In mammals the extracellular region of the cation-independent mannose-6-phosphate receptor has gained an IGF-II-binding function and is termed type II IGF receptor (IGF2R). IGF2R sequesters IGF-II; imbalances occur in cancers and IGF2R is implicated in tumour suppression. We report crystal structures of IGF2R domains 11-12, 11-12-13-14 and domains 11-12-13/IGF-II complex. A distinctive juxtaposition of these domains provides the IGF-II-binding unit, with domain 11 directly interacting with IGF-II and domain 13 modulating binding site flexibility. Our complex shows that Phe19 and Leu53 of IGF-II lock into a hydrophobic pocket unique to domain 11 of mammalian IGF2Rs. Mutagenesis analyses confirm this IGF-II 'binding-hotspot', revealing that IGF-binding proteins and IGF2R have converged on the same high-affinity site.

Transcriptional regulation of subtilisin-like proprotein convertase PACE4 by E2F: Possible role of E2F-mediated upregulation of PACE4 in tumor progression

PACE4, a member of the subtilisin-like proprotein convertase (SPC) family, is expressed at high levels in certain tumor cells and plays a role in metastatic progression through activation of matrix metalloproteinases. The mechanism leading to overexpression of PACE4 in tumor cells remains unclear. In this study, we show that the E2F1 transcription factor, which is implicated in carcinoma invasiveness, upregulates the expression of PACE4. HT1080 (highly tumorigenic and invasive) cells expressed much higher levels of PACE4 and E2F family (E2F1 and E2F2) transcripts than IMR90 (normal fibroblast) cells. Expression levels of other SPCs (furin and PC6) remained unchanged in these cells. Promoter analysis indicated that two E2F consensus binding sites (-117/-110 and -86/-79) in the 5'-flanking region of the human PACE4 gene function as positive regulatory elements. Mutation of these sites abolished PACE4 promoter response to E2F1 as well as binding of E2F1 in electrophoretic mobility-shift assays. Other E2F members, E2F2 and E2F3, also activated PACE4 expression, as in the case of E2F1. These results indicate a novel mechanism for E2F family-mediated promotion of carcinoma invasiveness through PACE4.

Duplication of the paternal IGF2 allele in trisomy 11 and elevated expression levels of IGF2 mRNA in congenital mesoblastic nephroma of the cellular or mixed type

In a metaphase comparative genomic hybridization and fluorescence in situ hybridization study of 13 congenital mesoblastic nephroma (CMN) tumors, trisomy 11 was found in seven cellular or mixed type tumors, disomy 11 with other chromosome changes in two cellular type tumors, and no chromosome changes in four classical type tumors. Reverse-transcription (RT)-PCR analysis detected the ETV6-NTRK3 fusion transcript in all eight cellular or mixed type tumors examined, but not in four classical type tumors. All seven tumors with trisomy 11 showed duplication of the paternal IGF2 allele, and six cellular or classical type tumors with disomy 11 showed one paternal and one maternal allele of IGF2, analyzing the methylation status of the sixth CTCF site of the H19-differentially methylated region. Allelic expression study using the ApaI/AvaII polymorphism site at exon 9 of IGF2 showed retention of imprinting in all seven tumors examined. Quantitative real-time RT-PCR analysis showed higher expression levels of IGF2 mRNA in three of three cellular type tumors with trisomy 11, in one cellular type tumor with disomy 11, and in three of four classical tumors than in fetal kidneys or normal kidney tissues. Thus, duplicated paternal IGF2 resulted in elevated IGF2 mRNA levels, and may provide CMN or its precursor cells with a proliferative advantage. The mechanism explaining that some cellular or classical type tumors with disomy 11 also showed elevated IGF2 mRNA levels remains unresolved. IGF2 clearly plays an important role in the tumorigenic process of CMN, although it is difficult to assess its exact role.

Pyrazolo[3,4-d]pyrimidines as potent inhibitors of the insulin-like growth factor receptor (IGF-IR)

A high throughput screen of Abbott's compound repository revealed that the pyrazolo[3,4-d]pyrimidine class of kinase inhibitors possessed moderate potency for IGF-IR, a promising target for cancer chemotherapy. The synthesis and subsequent optimization of this class of compounds led to the discovery of 14, a compound that possesses in vivo IGF-IR inhibitory activity.

To be or not to be—Determinants of embryonic survival following heat shock

Elevated temperature can reduce developmental competence of the preimplantation embryo. Whether an embryo survives elevated temperature depends on its genotype, stage of development, exposure to regulatory molecules and redox status. Following fertilization, the embryo is very sensitive to heat shock. By Days 4-5 after insemination, however, the embryo has acquired increased resistance to elevated temperature. One system that may potentiate embryonic survival at later stages of embryonic development is the apoptosis response-inhibition of apoptosis responses at Day 4 exacerbated effects of heat shock on development. Embryo responses to heat shock at Days 4-5 also depend upon genotype because Bos indicus embryos are more resistant than embryos from non-adapted B. taurus. Some experiments (although not all) indicate that survival following heat shock can be increased by reducing oxygen tension, suggesting involvement of reactive oxygen species or hypoxia-induced factors. Embryonic responses to heat shock are also affected by regulatory molecules that act to modify cellular physiology and improve cell survival. The best characterized of these is insulin-like growth factor-1 (IGF-1). Actions of IGF-1 to allow development following heat shock are independent of its anti-apoptotic actions because inhibition of the phosphatidylinositol-3 kinase pathway through which IGF-1 blocks apoptosis does not prevent thermoprotective effects of IGF-1 on development. Identification of specific determinants of embryonic survival creates the opportunity for new strategies to improve pregnancy rates in animals exposed to heat stress. Many environmental perturbations activate similar cellular responses. Therefore, molecular and cellular systems that improve embryonic survival to heat shock may confer protection from other embryotoxic conditions.

Novel role for insulin as an autocrine growth factor for malignant brain tumour cells

AT/RTs (atypical teratoid/rhabdoid tumours) of the CNS (central nervous system) are childhood malignancies associated with poor survival rates due to resistance to conventional treatments such as chemotherapy. We characterized a panel of human AT/RT and MRT (malignant rhabdoid tumour) cell lines for expression of RTKs (receptor tyrosine kinases) and their involvement in tumour growth and survival. When compared with normal brain tissue, AT/RT cell lines overexpressed the IR (insulin receptor) and the IGFIR (insulin-like growth factor-I receptor). Moreover, insulin was secreted by AT/RT cells grown in serum-free medium. Insulin potently activated Akt (also called protein kinase B) in AT/RT cells, as compared with other growth factors, such as epidermal growth factor. Pharmacological inhibitors, neutralizing antibodies, or RNAi (RNA interference) targeting the IR impaired the growth of AT/RT cell lines and induced apoptosis. Inhibitors of the PI3K (phosphoinositide 3-kinase)/Akt pathway also impaired basal and insulin-stimulated AT/RT cell proliferation. Experiments using RNAi and isoform-specific pharmacological inhibitors established a key role for the class I(A) PI3K p110alpha isoform in AT/RT cell growth and insulin signalling. Taken together, our results reveal a novel role for autocrine signalling by insulin and the IR in growth and survival of malignant human CNS tumour cells via the PI3K/Akt pathway.

Biología celular y genética en el cáncer de hígado

Hepatocellular carcinoma (HCC) is the main cause of death in cirrhotic patients and has become a major health problem in developed countries. Analysis of the somatic alterations and gene expression profiles in patients with HCC have provided important information the genes involved in liver carcinogenesis. Nevertheless, the most important molecular alterations in the initial stages of the disease are currently unknown. The application of high resolution technologies to other forms of cancer (genome analysis with oligo microarrays and SNP arrays) should lead to greater insight into the pathogenesis of this neoplasm. In the last few years, distinct signaling pathways involved in hepatocarcinogenesis have been identified. Among these, the Wnt, EGFR and PI3k/akt/mTOR pathways are constitutively altered in numerous studies, providing the molecular basis for the molecular treatment of this tumor. As in other neoplasms, the original tumor cell in HCC is controversial. The most widely accepted hypothesis suggests that numerous genomic alterations in the hepatocyte cells lead to a neoplastic phenotype. Alternatively, it has been postulated that at least a subgroup of tumors could be of stem cell origin. Both hypotheses agree on the existence of cancer stem cells, arising from the original tumor cell; these cancer stem cells would then perpetuate and disseminate the neoplasm. This review summarizes the most important information on the structural and functional alterations in HCC and describes some of the main signaling pathways implicated in liver cancer.

A comprehensive salivary analysis for oral cancer diagnosis

PURPOSE

This study utilized comprehensive salivary analysis to evaluate biochemical and immunological parameters in the saliva of oral squamous cell carcinoma (OSCC) patients.

METHODS

Whole saliva was collected from 25 otherwise healthy OSCC patients and compared to 25 healthy, age- and gender-matched individuals. All OSCC lesions were located at the lateral aspect of the mobile tongue. The salivary parameters analyzed included: sodium (Na), potassium (K), calcium (Ca), inorganic phosphate (P), magnesium (Mg), total protein (TP), albumin (Alb), lactate dehydrogenase (LDH), amylase (Amy), total immunoglobulin G (IgG), secretory immunoglobulin A (Sec. IgA), epidermal growth factor, insulin growth factor I (IGF-I) and metalloproteinases MMP-2 and MMP-9.

RESULTS

In cancer patients, salivary median total protein concentration was significantly higher by 26% (P = 0.01), as were concentrations of Na, Ca, P and Mg by 14% (P = 0.05), 59% (P = 0.05), 39% (P = 0.08) and 28% (P = 0.12), respectively. Amy and K concentrations were lower by 25% (P = 0.12) and 15% (P = 0.03), respectively. Alb was 108% higher (P = 0.0007), as were salivary LDH (88%, P = 0.002) and total IgG (125%, P = 0.01), while Sec. IgA was lower by 45% (P = 0.001). Concentrations of IGF, MMP-2 and MMP-9 were significantly higher by 117% (P = 0.03), 75% (P = 0.0003) and 35% (P = 0.05), respectively.

CONCLUSIONS

Comprehensive salivary analysis revealed an overall altered salivary composition in OSCC, indicating a compromised oral environment in these patients and suggesting salivary analysis as a new diagnostic tool for oral cancer. Local therapeutic agents can be easily applied to the oral mucosa, altering its "bathing medium"-the saliva.

Matrix metalloproteinase-7 triggers the matricrine action of insulin-like growth factor-II via proteinase activity on insulin-like growth factor binding protein 2 in the extracellular matrix

Many growth factors and cytokines are immobilized on the extracellular matrix (ECM) by binding to glycosaminoglycans and are stored in an inactive form in the cellular microenvironment. However, the mechanisms of ECM-bound growth factor or cytokine activation have not been well documented. We showed that the insulin-like growth factor type-1 receptor (IGF-1R) was rapidly phosphorylated after the addition of matrix metalloproteinase (MMP)-7 to a serum-starved human colon cancer cell line (HT29) and that phosphorylation was completely inhibited by an IGF-II neutralizing antibody. In the ECM of this cell line, IGF-II and IGF binding protein (BP)-2 coexisted, but IGFBP-2 disappeared from the ECM fraction after treatment with MMP-7 or heparinase III. On the other hand, in a cell line in which IGF-1R was overexpressed, IGF-1R was phosphorylated by supernatant from the MMP-7-treated ECM fraction of HT29 but not by that from a heparinase-III-treated ECM fraction. We also demonstrated that MMP-7 degrades IGFBP-2 in vitro at three cleavage sites (peptide bonds E(151)-L(152), G(175)-L(176) and K(181)-L(182)), which have not been documented previously. Taken together, these results demonstrate that MMP-7 generates bioactive IGF-II by degrading the IGF-II/IGFBP-2 complex binding to heparan sulfate proteoglycan in the ECM, resulting in IGF-II-induced signal transduction. This evidence indicates that some ECM-associated growth factors enhance their ability to bind to their receptors by some proteases in the tumor microenvironment. This mechanism of action ('protease-triggered matricrine') represents an attractive model for understanding ECM-tumor interactions.

Antisense treatment of IGF-IR induces apoptosis and enhances chemosensitivity in central nervous system atypical teratoid/rhabdoid tumours cells

Central nervous system (CNS) atypical teratoid/rhabdoid tumours (AT/RT) are among the paediatric malignant tumours with the worst prognosis and fatal outcome. Insulin-like growth factor I receptor (IGF-IR) protects cancer cells from apoptosis induced by a variety of anticancer drugs and radiation. In the present study, IGF-IR was expressed in 8/8 primary AT/RT as detected by immunohistochemistry. Moreover, we found IGF-I and IGF-II mRNA in BT-16 CNS AT/RT cells and IGF-II mRNA in BT-12 CNS AT/RT cells, and autophosphorylated IGF-IR in both cell lines, indicating the potential presence of an autocrine/paracrine IGF-I/II/IGF-IR loop in CNS AT/RT. IGF-IR antisense oligonucleotide treatment of human CNS AT/RT cells resulted in significant down-regulation of IGF-IR mRNA and protein expression, induction of apoptosis, and chemosensitisation to doxorubicin and cisplatin. These studies provide evidence for the influence of IGF-IR on cellular responses to chemotherapy and raise the possibility that curability of selected CNS AT/RT may be improved by pharmaceutical strategies directed towards the IGF-IR.

High-grade neuroendocrine carcinomas of the lung express K homology domain containing protein overexpressed in cancer but carcinoid tumors do not

K homology domain containing protein overexpressed in cancer (KOC) is a member of the insulin-like growth factor (IGF) messenger RNA-binding protein family and is expressed during embryogenesis and in certain malignancies. KOC, known as L523S and IGF messenger RNA-binding protein 3, was shown to be frequently expressed in high-grade neuroendocrine carcinomas of the lung in our immunohistochemical studies using a monoclonal antibody against human KOC. Specifically, all 10 small cell lung carcinomas (SCLCs) exhibited strong cytoplasmic staining, 9 with diffuse positivity and 1 with focal positivity. Among 14 large cell neuroendocrine carcinomas (LCNECs), 9 exhibited strong and diffuse cytoplasmic staining, and 5 cases showed focal immunoreactivity. In contrast, no KOC was detected in 21 typical and atypical carcinoids, except for one atypical carcinoid with oncocytic cells showing weak cytoplasmic staining. Although SCLCs exhibited a strong and diffuse staining pattern more frequently (90%) than LCNECs (64%), the difference did not reach statistical significance (P = .3408). Interestingly, our immunohistochemical studies demonstrated that IGF-II, reportedly regulated by KOC, was comparably expressed in SCLC, LCNEC, and typical and atypical carcinoids, irrespective of KOC expression status of the tumors. These results support the formulation that KOC may play an important role in the regulation of biologic behavior of high-grade neuroendocrine carcinomas. In addition, detection of KOC expression may be diagnostically useful in distinguishing high-grade neuroendocrine carcinomas from carcinoid tumors. Our findings of equivalent IGF-II expression in KOC-positive SCLC and LCNEC and KOC-negative carcinoid tumors suggest different regulatory mechanisms involved in the control of IGF-II expression in these tumors.

Allometric growth ratios are independent of Igf2 gene dosage during development

In the mouse, allelic dosage of the paternally expressed gene coding for insulin-like growth factor II (Igf2), from null to bi-allelic, results in dose-dependent growth, an effect which appears to be fully established during a discrete period of embryogenesis that then persists throughout life. Here, we specifically quantify the influence of Igf2 allelic dosage on the proportionality of regional embryonic growth rather than overall growth. Remarkably, preservation of allometric growth ratios between head and body regions were observed throughout development, irrespective of the range of overall growth phenotype (60-130% of wild type). Evaluation of log-log plots suggests that each allele of Igf2 expressed corresponds to the equivalent of 2-4 days of relative growth. Igf2 is predominantly expressed in extra-embryonic mesoderm (E7.5-E8.25), 24 h before alterations in cell number are known to occur in embryos with disruption of the paternally expressed allele. We hypothesized that the preservation of proportionality may result from modification of extra-embryonic development and subsequent alteration of systemic nutritional supply. Morphological analyses of chorio-allantoic and placental development between E9 and E9.5 appeared Igf2 independent. This suggests either an intrinsic but systemic Igf2-dependent activity within the embryo or a more complex developmental mechanism accounts for the proportional phenotype. Allelic IGF2 expression is subject to stochastic variation in humans, with 10% of the population estimated to be functionally bi-allelic. Evaluation of allometric growth of normal and pathological human embryos, suggest intra-uterine growth phenotypes associated with altered IGF2 imprinting are also likely to be proportionate.

Functional evaluation of novel soluble insulin-like growth factor (IGF)-II–specific ligand traps based on modified domain 11 of the human IGF2 receptor

Ligands transported by the mannose 6-phosphate/insulin-like growth factor (IGF)-II receptor (IGF2R) include IGF-II- and mannose 6-phosphate-modified proteins. Increased extracellular supply of IGF-II, either secondary to loss of the clearance function of IGF2R, loss of IGF binding protein function, or increased IGF2 gene expression, can lead to embryonic overgrowth and cancer promotion. Reduced supply of IGF-II is detrimental to tumor growth, and this suggests that gain of function of IGF-II is a molecular target for human cancer therapy. Domain 11 of IGF2R binds IGF-II with high specificity and affinity. Mutagenesis studies have shown that substitution of glutamic acid for lysine at residue 1554 results in a 6-fold higher affinity for IGF-II (20.5 nmol/L) than native domain 11 (119 nmol/L). Here, we generate a novel high-affinity IGF-II ligand trap by fusion of mutated human 11(E1554K) to a COOH-terminal human IgG1 Fc domain (11(E1554K)-Fc). The resulting homodimer has a significantly increased affinity for IGF-II (1.79 nmol/L) when measured by surface plasmon resonance. IGF-II signaling via the IGF-I receptor and the proliferative effect of IGF-II were specifically inhibited by 11(E1554K)-Fc in both HaCaT and Igf2(-/-) mouse embryonic fibroblast cells. These data confirm that a novel engineered and soluble IGF2R-11(E1554K)-Fc protein functions as an IGF-II-specific and high-affinity ligand trap in vitro and that this protein has potential application as an IGF-II antagonist for cancer therapy following in vivo experimental evaluation.

In the absence of IGF-1 signaling, IFN-gamma suppresses human malignant T-cell growth

Several approaches to target insulin-like growth factor-1 (IGF-1) signaling have resulted in the inhibition of the growth of a broad range of tumor cells. Malignant T cells are insensitive to the antiproliferative effects of the interferon-gamma (IFN-gamma)/signal transducer and activator of transcription 1 (STAT1) pathway because of the IGF-1-dependent internalization of the IFN-gammaR2 signaling chain. Here we show that human malignant T cells are also resistant to the growth inhibitory effect of both the IGF-1 receptor-specific inhibitor picropodophyllin (PPP) and retrovirus-mediated gene transfer of a dominant negative IGF-1 receptor. However, blockade of IGF-1 receptor perturbs IFN-gammaR2 internalization and induces its cell surface accumulation in malignant T cells. This allows the reinstatement of the IFN-gamma-induced STAT1 activation, a high expression of proapoptotic molecules, and the suppression of malignant T-cell growth both in vitro and in vivo in a severe combined immunodeficiency (SCID) mouse model. These data indicate that the inhibition of IGF-1 signaling combined with IFN-gamma administration could be a promising approach to suppress the growth of neoplastic T cells resistant to each treatment on its own.

Blastemal Expression of Type I Insulin-Like Growth Factor Receptor in Wilms' Tumors Is Driven by Increased Copy Number and Correlates with Relapse

Most Wilms' tumors are of low stage, favorable histology, and have a high likelihood of cure with current multimodal therapy. Despite this, there remains a group of patients whose tumors recur for whom intensive salvage regimens result in survival of only 50%. Fitting a Cox proportional hazards model to microarray-based comparative genomic hybridization (aCGH) data on 68 Wilms' tumor samples, we identified a significant correlation between increased copy number at chromosome 15q26.3 insulin-like growth factor I receptor (IGFIR) and tumor relapse (adjusted P = 0.014). Wilms' tumors (13%) exhibited a low-level gain corresponding to three to four copies of the gene by aCGH analysis, 9 of 10 of which exhibited high IGFIR mRNA levels. Although IGFIR protein expression was restricted to the epithelial cells of fetal kidney and Wilms' tumors in most cases, 12% of tumors were also found to express IGFIR in the blastemal compartment. Blastemal IGFIR protein expression was associated with an increased copy number and a shorter relapse-free survival time (P = 0.027, log-rank test). In addition to the membrane localization, IGFIR was localized to the perinuclear region of the blastemal cells in 6% of Wilms' tumors. These data provide evidence that an increase in IGFIR gene copy number results in aberrant expression in the blastemal compartment of some Wilms' tumors and is associated with an adverse outcome in these patients. These findings suggest the possibility of use of targeted agents in the therapy of these children.

Tumor lymphangiogenesis and metastatic spread-new players begin to emerge

The metastatic spread of tumor cells is the most lethal aspect of cancer and can occur via various routes, including the lymphatic vasculature. Studies of tumor models in animals and clinicopathological data have indicated that growth of lymphatic vessels (lymphangiogenesis) in the vicinity of solid tumors may contribute to lymphatic metastasis. Research over the past 5 years has identified a range of lymphangiogenic growth factors that could conceivably play a role in promoting tumor lymphangiogenesis and lymphatic metastasis. The most extensively studied signaling system that promotes lymphangiogenesis in tumors involves the secreted lymphangiogenic proteins vascular endothelial growth factor-C (VEGF-C) and VEGF-D, and their cognate receptor on lymphatic endothelium VEGF receptor-3 (VEGFR-3). More recent studies have identified other signaling molecules that can also promote lymphangiogenesis in vivo, including hepatocyte growth factor and members of the fibroblast growth factor, angiopoietin, platelet-derived growth factor and insulin-like growth factor families of secreted proteins. This article provides an overview of the molecular mechanisms that control lymphangiogenic signaling, emphasizing the more recently identified lymphangiogenic growth factors and the roles they may play in cancer biology. Molecular approaches for inhibiting lymphangiogenic signaling in cancer, designed to restrict tumor metastasis, are also examined.

INSULIN‐LIKE GROWTH FACTOR‐I RECEPTOR AS A CANDIDATE FOR A NOVEL MOLECULAR TARGET IN GASTROINTESTINAL CANCERS

Abnormal activation of growth factor receptors and their signal pathways are required for neoplastic transformation and tumor progression. The concept of targeting specific tumorigenic receptors has been validated by successful clinical application of multiple new drugs, such as those acting against HER2/neu, epidermal growth factor receptor 1, and c‐Kit. In this review, we focus on the next promising therapeutic molecular target of insulin‐like growth factor (IGF)‐I receptor (IGF‐Ir). The IGF/IGF‐Ir system is an important modifier of cancer cell proliferation, survival, growth, and treatment sensitivity in a number of neoplastic diseases, including human gastrointestinal carcinomas. Preclinical studies demonstrated that downregulation of IGF‐Ir signals reversed the neoplastic phenotype and sensitized cells to antitumor treatments. We summarize a variety of ways to disrupt IGF‐Ir function. Then, we introduce our strategy of adenoviruses expressing dominant negative of IGF‐Ir (IGF‐Ir/dn) against gastrointestinal cancers, including stomach, colon, and pancreas. IGF‐Ir/dn suppresses tumorigenicity both in vitro and in vivo and increases stressor‐induced apoptosis. IGF‐Ir/dn expression upregulates chemotherapy‐induced apoptosis and these combination therapies with chemotherapy are very effective against tumors in mice. Some drugs blocking IGF‐Ir function are now entering clinical trial, thus IGF‐Ir might be a candidate for a therapeutic target in several gastrointestinal malignancies.

Insulin-like growth factor-I promotes resistance of bovine preimplantation embryos to heat shock through actions independent of its anti-apoptotic actions requiring PI3K signaling

For the bovine preimplantation embryo, insulin-like growth factor-I (IGF-I) is a survival factor that blocks the induction of apoptosis and reduces the decrease in development caused by heat shock. The first objective was to determine the signaling pathways whereby IGF-I acts to increase embryo cell number while inhibiting heat-shock induced apoptosis. Exposure of embryos to heat shock reduced cell number and increased percent apoptosis, but IGF-I increased cell number and blocked induction of apoptosis caused by heat shock. Actions of IGF-I to increase cell number were blocked by treatment with the mitogen activated protein kinase kinase (MAPKK) inhibitor PD 98059 whereas the phosphatidylinositol 3-kinase (PI3K) inhibitor LY 294002 had no effect. Conversely, LY 294002 but not PD 98059 blocked actions of IGF-I to inhibit induction of apoptosis caused by heat shock. The second objective was to determine whether IGF-I blocks effects of heat shock on development to the blastocyst stage by preventing apoptosis. Culture of embryos with IGF-I was effective in blocking the reduction in blastocyst development caused by heat shock-this action occurred even in the presence of LY 294002. Addition of another inhibitor of apoptosis, the caspase-3 inhibitor z-DEVD-fmk, did not mimic the protective effects of IGF-I on blastocyst development. Surprisingly, IGF-I was not effective in blocking the reduction in blastocyst development caused by heat shock when cultured with z-DEVD-fmk. In conclusion, the anti-apoptotic actions of IGF-I require PI3K signaling while actions to promote proliferation require MAPKK signaling. Moreover, actions of IGF-I to allow heat-shocked embryos to continue development to the blastocyst stage are independent of its anti-apoptotic effects.

Insulin-Like Growth Factor-I Receptor Expression Regulates Neuroblastoma Metastasis to Bone

Neuroblastoma is a pediatric tumor that preferentially metastasizes to bone. Patients with bone metastases have a mortality rate >93%, indicating a need for novel treatment targets. Our laboratory has shown that type I insulin-like growth factor receptor (IGF-IR) expression and activation regulate neuroblastoma cell proliferation, motility, invasion, and survival, and that expression of the IGF-IR correlates with neuroblastoma tumorigenicity. Bone expresses large amounts of IGF ligands, and the IGF system is required for normal bone physiology. The current study addresses the role of the IGF system in neuroblastoma metastasis to bone. Upon reaching the bone marrow through the circulation, neuroblastoma cells must dock at the bone marrow endothelium, extravasate into the bone microenvironment, and destroy bone tissue to allow for tumor growth. This report examines the effects of high IGF-IR expression on neuroblastoma cell interaction with bone. The current data show that neuroblastoma cells with high IGF-IR expression, either endogenously or through transfection, adhere to human bone marrow endothelial cells and subsequently migrate toward both IGF-I and human bone stromal cells. High IGF-IR-expressing neuroblastoma cells adhere tightly to bone stromal cells, flatten, and extend processes. When neuroblastoma cells are injected directly into the tibiae of mice, those cells with increased IGF-IR form both osteolytic lesions within the tibiae and secondary tumors within other sites. These results support the hypothesis that IGF-IR expression in neuroblastoma cells increases tumor cell interaction with the bone microenvironment, resulting in greater formation of metastases.

Modulation of the growth hormone-insulin-like growth factor (GH-IGF) axis by pharmaceutical, nutraceutical and environmental xenobiotics: an emerging role for xenobiotic-metabolizing enzymes and the transcription factors regulating their expression. A review

The growth hormone-insulin-like growth factor (GH-IGF) axis has gained considerable focus over recent years. One cause of this increased interest is due to a correlation of age-related decline in plasma GH/IGF levels with age-related degenerative processes, and it has led to the prescribing of GH replacement therapy by some practitioners. On the other hand, however, research has also focused on the pro-carcinogenic effects of high GH-IGF levels, providing strong impetus for finding regimes that reduce its activity. Whereas the effects of GH/IGF activity on the action of xenobiotic-metabolizing enzyme systems is reasonably well appreciated, the effects of xenobiotic exposure on the GH-IGF axis has not received substantial review. Relevant xenobiotics are derived from pharmaceutical, nutraceutical and environmental exposure, and many of the mechanisms involved are highly complex in nature, not easily predictable from existing in vitro tests and do not always predict well from in vivo animal models. After a review of the human and animal in vivo and in vitro literature, a framework for considering the different levels of direct and indirect modulation by xenobiotics is developed herein, and areas that still require further investigation are highlighted, i.e. the actions of common endocrine disruptors such as pesticides and phytoestrogens, as well as the role of xenobiotic-metabolizing enzymes and the transcription factors regulating their expression. It is anticipated that a fuller appreciation of the existing human paradigms for GH-IGF axis modulation gained through this review may help explain some of the variation in levels of plasma IGF-1 and its binding proteins in the population, aid in the prescription of particular dietary regimens to certain individuals such as those with particular medical conditions, guide the direction of long-term drug/nutraceutical safety trials, and stimulate ideas for future research. It also serves to warn athletes that using compounds touted as performance enhancing because they promote short-term GH release could in fact be detrimental to performance in the long-run.

Dysregulation of growth factor signaling in human hepatocellular carcinoma

Dysregulation of pleiotropic growth factors, receptors and their downstream signaling pathway components represent a central protumorigenic principle in human hepatocarcinogenesis. Especially the Insulin-like Growth Factor/IGF-1 receptor (IGF/IGF-1R), Hepatocyte Growth Factor (HGF/MET), Wingless (Wnt/beta-catenin/FZD), Transforming Growth Factor alpha/Epidermal Growth Factor receptor (TGFalpha/EGFR) and Transforming Growth Factor beta (TGFbeta/TbetaR) pathways contribute to proliferation, antiapoptosis and invasive behavior of tumor cells. This review focuses on the relevant alterations in these pathways identified in human human hepatocellular carcinomas (HCCs). Resultant functional effects are modulated by multiple cross-talks between the different signaling pathways and additional tumor-relevant factors, such as cyclooxygenase-2 and p53. Several specific strategies are currently under development such as receptor kinase inhibitors, neutralizing antibodies and antagonistic proteins, which may improve the systemic treatment of human HCCs.

Kinetics of Insulin-like Growth Factor II (IGF-II) Interaction with Domain 11 of the Human IGF-II/Mannose 6-phosphate Receptor: Function of CD and AB Loop Solvent-exposed Residues

Ligands of the IGF-II/mannose 6-phosphate receptor (IGF2R) include IGF-II and mannose 6-phosphate modified proteins. Disruption of the negative regulatory effects of IGF2R on IGF-II-induced growth can lead to embryonic lethality and cancer promotion. Of the 15 IGF2R extracellular domains, domains 1-3 and 11 are known to have a conserved beta-barrel structure similar to that of avidin and the cation-dependent mannose 6-phosphate receptor, yet only domain 11 binds IGF-II with high specificity and affinity. In order to define the functional basis of this critical biological interaction, we performed alanine mutagenesis of structurally determined solvent-exposed loop residues of the IGF-II-binding site of human domain 11, expressed these mutant forms in Pichia pastoris, and determined binding kinetics with human IGF-II using isothermal calorimetry and surface plasmon resonance with transition state thermodynamics. Two hydrophobic residues in the CD loop (F1567 and I1572) were essential for binding, with a further non-hydrophobic residue (T1570) that slows the dissociation rate. Aside from alanine mutations of AB loop residues that decrease affinity by modifying dissociation rates (e.g. Y1542), a novel mutation (E1544A) of the AB loop enhanced affinity by threefold compared to wild-type. Conversion from an acidic to a basic residue at this site (E1544K) results in a sixfold enhancement of affinity via modification principally of the association rate, with enhanced salt-dependence, decreased entropic barrier and retained specificity. These data suggest that a functional hydrophobic binding site core is formed by I1572 and F1567 located in the CD loop, which initially anchors IGF-II. Within the AB loop, residues normally act to either stabilise or function as negative regulators of the interaction. These findings have implications for the molecular architecture and evolution of the domain 11 IGF-II-binding site, and the potential interactions with other domains of IGF2R.

Frequent IGF2/H19 domain epigenetic alterations and elevated IGF2 expression in epithelial ovarian cancer

Overexpression of the imprinted insulin-like growth factor-II (IGF2) is a prominent characteristic of gynecologic malignancies. The purpose of this study was to determine whether IGF2 loss of imprinting (LOI), aberrant H19 expression, and/or epigenetic deregulation of the IGF2/H19 imprinted domain contributes to elevated IGF2 expression in serous epithelial ovarian tumors. IGF2 LOI was observed in 5 of 23 informative serous epithelial ovarian cancers, but this did not correlate with elevated expression of IGF2 H19 RNA expression levels were also found not to correlate with IGF2 transcript levels. However, we identified positive correlations between elevated IGF2 expression and hypermethylation of CCCTC transcription factor binding sites 1 and 6 at the H19 proximal imprint center (P = 0.05 and 0.02, respectively). Hypermethylation of CCCTC transcription factor sites 1 and 6 was observed more frequently in cancer DNA compared with lymphocyte DNA obtained from women without malignancy (P < 0.0001 for both sites 1 and 6). Ovarian cancers were also more likely to exhibit maternal allele-specific hypomethylation upstream of the imprinted IGF2 promoters when compared with normal lymphocyte DNA (P = 0.004). This is the same region shown previously to be hypomethylated in colon cancers with IGF2 LOI, but this was not associated with LOI in ovarian cancers. Elevated IGF2 expression is a frequent event in serous ovarian cancer and this occurs in the absence of IGF2 LOI. These data indicate that the epigenetic changes observed in these cancers at the imprint center may contribute to IGF2 overexpression in a novel mechanistic manner.

Molecular approaches in pediatric oncology

The use of molecular approaches has become part of the standard of care in the management of pediatric cancer patients. Molecular approaches are now included in the initial diagnosis, definition of prognostically distinct patient subgroups, selection of patients for specific therapies, prediction of risk for toxicities to therapy, and monitoring of patients receiving both conventional and novel targeted therapies. This clinical application of molecular medicine has been based on a growing molecular understanding of cancer biology. Studies of pediatric cancers have contributed to this understanding in many ways. We present a model for understanding cancer biology, using specific examples taken from pediatric oncology, and then discuss the application of molecular techniques to the clinical management of pediatric cancer patients.

Insulin-like growth factor 1 receptor signaling regulates skin development and inhibits skin keratinocyte differentiation

The insulin-like growth factor 1 receptor (IGF-1R) is a multifunctional receptor that mediates signals for cell proliferation, differentiation, and survival. Genetic experiments showed that IGF-1R inactivation in skin results in a disrupted epidermis. However, because IGF-1R-null mice die at birth, it is difficult to study the effects of IGF-1R on skin. By using a combined approach of conditional gene ablation and a three-dimensional organotypic model, we demonstrate that IGF-1R-deficient skin cocultures show abnormal maturation and differentiation patterns. Furthermore, IGF-1R-null keratinocytes exhibit accelerated differentiation and decreased proliferation. Investigating the signaling pathway downstream of IGF-1R reveals that insulin receptor substrate 2 (IRS-2) overexpression compensates for the lack of IGF-1R, whereas IRS-1 overexpression does not. We also demonstrate that phosphatidylinositol 3-kinase and extracellular signal-regulated kinase 1 and 2 are involved in the regulation of skin keratinocyte differentiation and take some part in mediating the inhibitory signal of IGF-1R on differentiation. In addition, we show that mammalian target of rapamycin plays a specific role in mediating IGF-1R impedance of action on keratinocyte differentiation. In conclusion, these results reveal that IGF-1R plays an inhibitory role in the regulation of skin development and differentiation.

Soluble IGF2 receptor rescues Apc(Min/+) intestinal adenoma progression induced by Igf2 loss of imprinting

The potent growth-promoting activity of insulin-like growth factor-II (IGF-II) is highly regulated during development but frequently up-regulated in tumors. Increased expression of the normally monoallelic (paternally expressed) mouse (Igf2) and human (IGF2) genes modify progression of intestinal adenoma in the Apc(Min/+) mouse and correlate with a high relative risk of human colorectal cancer susceptibility, respectively. We examined the functional consequence of Igf2 allelic dosage (null, monoallelic, and biallelic) on intestinal adenoma development in the Apc(Min/+) by breeding with mice with either disruption of Igf2 paternal allele or H19 maternal allele and used these models to evaluate an IGF-II-specific therapeutic intervention. Increased allelic Igf2 expression led to elongation of intestinal crypts, increased adenoma growth independent of systemic growth, and increased adenoma nuclear beta-catenin staining. By introducing a transgene expressing a soluble form of the full-length IGF-II/mannose 6-phosphate receptor (sIGF2R) in the intestine, which acts as a specific inhibitor of IGF-II ligand bioavailability (ligand trap), we show rescue of the Igf2-dependent intestinal and adenoma phenotype. This evidence shows the functional potency of allelic dosage of an epigenetically regulated gene in cancer and supports the application of an IGF-II ligand-specific therapeutic intervention in colorectal cancer.

Infection of human cancer cells with myxoma virus requires Akt activation via interaction with a viral ankyrin-repeat host range factor

We demonstrate that the susceptibility of human cancer cells to be infected and killed by an oncolytic poxvirus, myxoma virus (MV), is related to the basal level of endogenous phosphorylated Akt. We further demonstrate that nonpermissive tumor cells will switch from resistant to susceptible for MV infection after expression of ectopically active Akt (Myr-Akt) and that permissive cancer cells can be rendered nonpermissive by blocking Akt activation with a dominant-negative inhibitor of Akt. Finally, the activation of Akt by MV involves the formation of a complex between the viral host range ankyrin-repeat protein, M-T5, and Akt. We conclude that the Akt pathway is a key restriction determinant for permissiveness of human cancer cells by MV.

Distinct roles of Akt1 and Akt2 in regulating cell migration and epithelial-mesenchymal transition

The Akt family of kinases are activated by growth factors and regulate pleiotropic cellular activities. In this study, we provide evidence for isoform-specific positive and negative roles for Akt1 and -2 in regulating growth factor–stimulated phenotypes in breast epithelial cells. Insulin-like growth factor-I receptor (IGF-IR) hyperstimulation induced hyperproliferation and antiapoptotic activities that were reversed by Akt2 down-regulation. In contrast, Akt1 down-regulation in IGF-IR–stimulated cells promoted dramatic neomorphic effects characteristic of an epithelial–mesenchymal transition (EMT) and enhanced cell migration induced by IGF-I or EGF stimulation. The phenotypic effects of Akt1 down-regulation were accompanied by enhanced extracellular signal–related kinase (ERK) activation, which contributed to the induction of migration and EMT. Interestingly, down-regulation of Akt2 suppressed the EMT-like morphological conversion induced by Akt1 down-regulation in IGF-IR–overexpressing cells and inhibited migration in EGF-stimulated cells. These results highlight the distinct functions of Akt isoforms in regulating growth factor–stimulated EMT and cell migration, as well as the importance of Akt1 in cross-regulating the ERK signaling pathway.

Expression of IGF-I, IGF-II, and IGF-IR in gallbladder carcinoma. A systematic analysis including primary and corresponding metastatic tumours

AIMS

The insulin-like growth factor (IGF) system has been implicated in tumour development and progression. This study was designed to analyse the expression of the IGF-I receptor (IGF-IR) and its ligands (IGF-I, IGF-II) in gallbladder cancer.

METHODS

IGF-I, IGF-II, and IGF-IR immunoreactivity was investigated in 57 gallbladder carcinomas and corresponding lymph node (n = 11) and hepatic (n = 7) metastases using a tissue microarray technique and correlated with tumour stage, grade, and patient outcome.

RESULTS

Cancer tissue allowing a reliable evaluation of IGF-I, IGF-II, and IGF-IR was present in 55 of 57 primary tumours and 17 of 18 metastases. IGF-I and IGF-II immunoreactivity was seen in 25 and 14 of the 55 primary tumours, in addition to six and three of the 17 metastases, respectively. No associations with tumour stage, grade, or prognosis were detected. IGF-IR was expressed in 52 of 55 primary tumours and all 17 metastases. IGF-IR staining intensity decreased with tumour cell dedifferentiation. Moreover, IGF-IR expression in less than 50% of cancer cells was an independent marker of poor prognosis in multivariate analysis (risk ratio, 4.0; 95% confidence interval, 1.4 to 11.2; p = 0.01).

CONCLUSIONS

The expression of IGF-IR and its ligands provides evidence for the existence of an auto/paracrine loop of tumour cell stimulation in gallbladder cancer and makes this type of cancer a candidate for therapeutic strategies aimed at interfering with the IGF pathway. The recognition of IGF-IR as a new independent prognostic biomarker may help to identify patients who might benefit from adjuvant treatment.

Loss of imprinting of IGF2: a common epigenetic modifier of intestinal tumor risk

Epigenetic alterations in cancer occur at least as commonly as genetic mutations, but epigenetic alterations could occur secondarily to the tumor process itself. To establish a causal role of epigenetic changes, investigators have turned to genetically engineered mouse models. Here, we review a recent study showing that a mouse model of loss of imprinting (LOI) of the insulin-like growth factor II gene (Igf2), which shows aberrant activation of the normally silent maternal allele, modifies the risk of intestinal neoplasia caused by mutations of the adenomatous polyposis coli (Apc) gene. This increased risk corresponds to the apparent increased risk of colorectal cancer in patients with LOI of IGF2. The model suggests that preexisting epigenetic alterations in normal cells increase tumor risk by expanding the target cell population and/or modulating the effect of subsequent genetic alterations on these cells, providing a novel idea for cancer risk management.

An obligatory caravanserai stop on the silk road to neural induction: Inhibition of BMP/GDF signaling

Work in Xenopus laevis produced the first molecular explanation for neural specification, the default model, where inactivation of the BMP pathway in ectodermal cells changes fates from epidermal to neural. This review covers the present status of our understanding of neural specification, with emphasis on Xenopus, but including relevant facts in other model systems. While recent experiments have increased the complexity of the molecular picture, they have also provided additional support for the default model and the central position of the BMP pathway. We conclude that synergy between accumulated knowledge and technical progress will maintain Xenopus at the forefront of research in neural development.

IFNgammaR2 trafficking tunes IFNgamma-STAT1 signaling in T lymphocytes

Ligand-dependent downregulation of the interferon gamma receptor signaling chain (IFNgammaR2) has always been seen as a key mechanism for shielding T lymphocytes from the antiproliferative effects of the IFNgamma-signal transducer and activator of transcription 1 (STAT1) pathway. Now, however, a ligand-independent mechanism of IFNgammaR2 internalization is emerging as a more general way of limiting IFNgamma-STAT1 signaling in T cells, with insulin-like growth factor-1 (IGF-1) and iron as the main players. Here, we review the array of immunomodulatory effects exerted by these two factors on different cell types involved in the immune response; these effects suggest that an inflammatory environment generates signals that favor IFNgammaR2 cell-surface accumulation and IFNgamma-induced apoptosis in T cells, whereas an anti-inflammatory environment promotes IFNgammaR2 internalization and induces T cell unresponsiveness to IFNgamma signaling.

Up-regulation of insulin-like growth factor axis components in human primary prostate cancer correlates with tumor grade

There is an evidence that components of the insulin-like growth factor (IGF)-signaling pathway are involved in the development and progression of prostate cancer. The aim of the present study was to provide a comprehensive analysis of the expression levels of proteins of the IGF axis in prostate cancer. We studied expression of the ligands IGF-I and IGF-II, the inhibitory IGF binding protein-3, the type I IGF receptor (IGF-IR), and the downstream mediator insulin receptor substrate-1 by immunohistochemistry in 56 tissue specimens (28 low-grade and 28 high-grade prostate adenocarcinomas). Protein expression in tumor areas, prostatic intraepithelial neoplasias (PINs), and adjacent benign prostatic tissue were evaluated regarding staining intensity and fraction of positive cells. An immunoreactivity score was established from staining intensity and fraction of positive cells, and correlated with the prognostic clinicopathologic parameters prostate-specific antigen serum levels, Gleason score, and TNM stage. The expression levels of all proteins investigated, except IGF binding protein-3, were up-regulated in PIN and in cancer. IGF-I and IGF-II expression showed a higher expression in high-grade compared with low-grade tumor areas. IGF-I and IGF-II and insulin receptor substrate-1 immunoreactivity was higher in tumors from patients with preoperative prostate-specific antigen serum levels 10 ng/mL or greater, and IGF-II expression was correlated with Gleason score. The data indicate significant alterations in the IGF system as prostate cancer develops. Differential expression of growth-stimulating components of the IGF system may be associated with the malignant phenotype and more aggressive tumor behavior. Expression of IGFs, especially IGF-II, may be predictors of the outcome of prostate cancer.

GH/IGF e neoplasia: o que há de novo nesta associação

Estudos in vitro e em animais sugerem que os membros do sistema insulin-like growth factors (IGFs), incluindo IGF-I, IGF-II, receptores de IGF-I e IGF-II (IGF-IR e IGF-IIR), e as IGF-binding proteins (IGFBPs) podem ter um importante envolvimento no desenvolvimento e na progressão de neoplasias. Mais especificamente, as IGFs promovem a progressão do ciclo celular e inibem a apoptose tanto por ação direta com outros fatores de crescimento como por ação indireta interagindo com outros sistemas moleculares intracelulares envolvidos na promoção e/ou progressão do câncer. Além disso, inúmeros estudos epidemiológicos têm sugerido que concentrações elevadas das IGFs, independente das alterações nas IGFBPs, podem estar associadas a um aumento no risco de desenvolver determinadas neoplasias. Esta revisão tem como objetivo apresentar o envolvimento do sistema IGF na regulação tumoral, os principais estudos epidemiológicos realizados e o risco de desenvolvimento de neoplasia em pacientes (com ou sem história pessoal de neoplasia prévia) que receberam hormônio de crescimento (rhGH). É importante salientar que o uso clínico de rhGH, nas indicações aprovadas internacionalmente, é seguro e não existem evidências, até o momento, da associação com o desenvolvimento de neoplasias.

Matrix metalloproteinase-7 degrades all insulin-like growth factor binding proteins and facilitates insulin-like growth factor bioavailability

Proteolytic modification of insulin-like growth factor binding proteins (IGFBPs) plays an important physiological role in regulating insulin-like growth factor (IGF) bioavailability. Recently, we demonstrated that matrix metalloproteinase-7 (MMP-7)/Matrilysin produced by various cancer cells catalyzes the proteolysis of IGFBP-3 in vitro and regulates IGF bioavailability, resulting in an anti-apoptotic effect against anchorage-independent culture. In the present study, we investigated whether MMP-7 contributes to proteolysis of the other five IGFBPs, IGFBP-1, IGFBP-2, IGFBP-4, IGFBP-5, and IGFBP-6, and whether this results in phosphorylation of the IGF type 1 receptor (IGF-1R). MMP-7 cleaved all six IGFBPs, resulting in IGF-mediated IGF-1R phosphorylation, which was inhibited by EDTA treatment. These results suggest that MMP-7 derived from cancer cells can regulate IGF bioavailability in the microenvironment surrounding the tumor, where various kinds of IGF/IGFBP complexes are found, thereby favoring cancer cell growth and survival during the processes of invasion and metastasis.