Insulin-like growth-factor-binding protein gene expression and protein production by human tumour cell lines

Risk of cancer in patients treated with recombinant human growth hormone in childhood

Recombinant human growth hormone (GH) has been in use for over 30 years, and its indications have gradually expanded from the classical replacement therapy in GH deficiency (GHD) to pharmacological therapy in patients with normal GH secretion. The insulin-like growth factor-I (IGF-I ) is closely GH dependent and is the effector of GH biological actions in peripheral tissues. Since IGF-I has potent mitogenic and antiapoptotic effects, the use of GH, especially outside GHD, has raised safety concern regarding cancer risk. The results of experimental, epidemiological and observational studies are not univocal and a number of biases and confounders affect the interpretation of data. The aim of this review is to critically review the data linking GH therapy during childhood with cancer risk, highlighting strengths and weaknesses of the available evidence.

IGFBP-2 - taking the lead in growth, metabolism and cancer

The activity of the Insulin-like Growth Factors (IGFs) ligands elicited via their receptors and transduced by various intracellular signal pathways is modulated by the IGF Binding Proteins (IGFBPs). Among all the IGFBPs, IGFBP-2 has been implicated in the regulation of IGF activity in most tissue and organs. Besides binding to IGFs in the circulation these IGF-regulatory activities of IGFBP-2 involve interactions with components of the extracellular matrix, cell surface proteoglycans and integrin receptors. In addition to these local peri-cellular activities, IGFBP-2 exerts other key functions within the nucleus, where IGFBP-2 directly or indirectly promotes transcriptional activation of specific genes. All of these IGFBP-2 activities, intrinsic or dependent on IGFs, contribute to its functional roles in growth/development, metabolism and malignancy as evidenced by studies in IGFBP-2 animal models and also by many in vitro studies. Finally, preclinical studies have demonstrated that IGFBP-2 administration can be beneficial in improving metabolic responses (inhibition of adipogenesis and enhanced insulin sensitivity), while blockade of IGFBP-2 appears to be an effective approach to inhibiting tumour growth and metastasis.

The insulin and igf-I pathway in endocrine glands carcinogenesis

Endocrine cancers are a heterogeneous group of diseases that may arise from endocrine cells in any gland of the endocrine system. These malignancies may show an aggressive behavior and resistance to the common anticancer therapies. The etiopathogenesis of these tumors remains mostly unknown. The normal embryological development and differentiation of several endocrine glands are regulated by specific pituitary tropins, which, in adult life, control the function and trophism of the endocrine gland. Pituitary tropins act in concert with peptide growth factors, including the insulin-like growth factors (IGFs), which are considered key regulators of cell growth, proliferation, and apoptosis. While pituitary TSH is regarded as tumor-promoting factor for metastatic thyroid cancer, the role of other pituitary hormones in endocrine cancers is uncertain. However, multiple molecular abnormalities of the IGF system frequently occur in endocrine cancers and may have a role in tumorigenesis as well as in tumor progression and resistance to therapies. Herein, we will review studies indicating a role of IGF system dysregulation in endocrine cancers and will discuss the possible implications of these findings for tumor prevention and treatment, with a major focus on cancers from the thyroid, adrenal, and ovary, which are the most extensively studied.

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.

The role of the insulin-like growth factor system in colorectal cancer: review of current knowledge

BACKGROUND

The insulin-like growth factor system, which includes insulin-like growth factors (IGF-I and IGF-II), IGF receptors (IGF-IR and IGF-IIR) and IGF binding proteins (IGFBPs), plays an important role in epithelial growth, anti-apoptosis and mitogenesis. There is a growing body of evidence showing that IGFs control growth and proliferation of several types of cancer. This review introduces the latest information on the biology of the IGF system and its pathophysiological role in the development of colorectal cancer.

DISCUSSION

The growth promoting effects of IGF-I and IGF-II on cancer cells are mediated through the IGF-IR, which is a tyrosine kinase and cancer cells with a strong tendency to metastasise have a higher expression of the IGF-IR. Most of the IGFs in circulation are bound to the IGFBPs, which regulate the bioavailability of the IGFs. All IGFBPs inhibit IGF action by high affinity binding, while some of them also potentiate the effects of IGFs. Colon cancer cells produce specific proteases that degrade the IGFBP so that the IGF will be free to act on the cancer cell in an autocrine manner. Therefore, the IGFBPs play a crucial role in the development of the cancer.

CONCLUSION

The current knowledge about the link between IGFs and colon cancer is mainly based on in vitro investigations. Further in vivo study is needed to understand the exact role of the IGF system, especially its binding proteins, so that they can be manipulated for the prevention and treatment of colorectal cancer.

Insulin-like growth factor-binding protein 3 inhibits growth of experimental colocarcinoma

BACKGROUND

We have previously shown that an important cell growth regulatory protein, insulin-like growth factor-binding protein 3 (IGFBP-3) is depleted in peripheral blood after open--but not laparoscopic--surgery. We have also demonstrated that IGFBP-3 induces apoptosis of human colon cancer cells in vitro. We report here the effect of IGFBP-3 on the growth of colonic epithelial cells in vivo.

METHODS

Two tumor models were used: chemically induced carcinogenesis with azoxymethane (AOM) and inoculation of syngeneic colon cancer cells. In AOM-induced carcinogenesis, wild type (WT) and IGFBP-3 transgenic (IGFBP-3-TG) CD1 mice were injected with AOM and the number of aberrant crypt foci (ACF) in the colon studied. In the syngeneic model, BALB/c mice were inoculated with CT26 cells. The control group received saline, while the test group was administered IGFBP-3 weekly. Tumor weight was assessed 2.5 weeks after establishment.

RESULTS

The number of aberrant crypt foci was significantly lower in IGFBP-3 transgenic mice (1.3 +/- 1.1) compared to WT controls (6.8 +/- 6.0) (P < .001). Further, CT26 tumors were significantly smaller in BALB/c mice that received IGFBP-3 (0.364 +/- 0.165 g) than in WT controls (0.742 +/- 0.261 g) (P < .01).

CONCLUSIONS

IGFBP-3 inhibits the development of colonic tumors in experimental models and may hold promise as an adjuvant therapy for patients with neoplasms.

Circulating insulin-like growth factor II and colorectal adenomas

Circulating insulin-like growth factor I (IGF-I) and IGF-binding protein-3 (IGFBP-3) may be risk factors for the development of colorectal cancer. On the other hand, IGF-II and IGFBP-2 are overexpressed in colorectal carcinomas. These contrasting backgrounds led us to investigate the relationship between serum IGF-I, IGF-II, IGFBP-2, and IGFBP-3 and the presence of colorectal adenomas, known precursors of colorectal carcinoma, in 345 volunteers attending a screening flexible sigmoidoscopy trial (entry criteria: healthy, aged 55-64 yr). The most striking finding was an elevated mean serum IGF-II in individuals with adenomas (n = 52) compared with controls (mean difference, 139 ng/mL; 95% confidence intervals, 82, 196; P < 0.0001). Logistic regression adjusting for confounding factors confirmed the significant association between IGF-II and adenoma occurrence (P < 0.0001) and revealed an additional positive association with serum IGFBP-2 (P < 0.0001). However, there was no association found between either serum IGF-I and/or IGFBP-3 and the presence of adenomas. Additionally, in 31 individuals with adenomas in whom levels were determined pre- and postpolypectomy, there was a significant fall in mean IGF-II (P < 0.001) and IGFBP-2 (P < 0.001) after adenoma removal, but no difference in IGF-II and IGFBP-2 concentrations between repeated samples in 20 individuals without adenomas. Immunohistochemical studies demonstrated IGF-II expression in 83% of all adenomas, which contrasted with absent expression in normal colonic expression and hyperplastic polyps. This study has shown for the first time that serum IGF-II may be a tumor marker in individuals with colorectal adenomas. Further studies are needed to validate these relationships in larger populations, including individuals undergoing colonoscopy.

Gene expression and serum levels of insulin-like growth factors (IGFs) and IGF-binding proteins in a case of non-islet cell tumour hypoglycaemia

We describe a case of non-islet cell tumour hypoglycaemia (NICTH) associated with a renal cell carcinoma. Serum insulin-like growth factors (IGFs) (including IGF-II E peptide), IGF-binding proteins (IGFBPs), insulin and C-peptide were measured before and after surgical removal of the tumour. IGFBPs were visualized by Western ligand blotting. Preoperatively 'big' IGF-II and IGFBP-2 levels were raised. IGF-I, IGFBP-1 and IGFBP-3 were low, while insulin, C-peptide and GH were undetectable. These changes were reversed by 2 days postoperatively. Protease assays showed little IGFBP-3 protease activity preoperatively. Preoperatively, neutral chromatography demonstrated most of the immunoassayable IGFBP-3 in a high molecular weight form with a small amount of IGF-II. Most of the IGF-II and big IGF-II eluted in lower molecular weight forms. Postoperative samples showed a shift in IGF-II which became increasingly associated with IGFBP-3 in both low and high molecular weight complexes. By Northern blotting, expression of all species of IGF-II mRNA in the tumour was 10-fold greater than in normal human liver. The tumour did not express IGFBP-1 or IGFBP-2. IGFBP-3 was expressed in small amounts, while the expression of IGFBP-4 was two-fold higher than in liver. In conclusion, we have confirmed high levels of big IGF-II and IGFBP-2 in NICTH, changes which are reversed postoperatively. The IGF-II is derived from the tumour which overexpresses these genes but IGFBP-2 probably arises from extratumour upregulation.

Elevated serum levels of IGFBP-2 found in children suffering from acute leukaemia is accompanied by the occurrence of IGFBP-2 mRNA in the tumour clone

Insulin-like growth factor-binding proteins (IGFBPs) are important modulators of IGF action. In 50 children suffering from acute lymphoblastic leukaemia (ALL), we studied the serum levels of IGFBP-1,-2 and-3. The mean standard deviation score (SDS) values were estimated to be 0.7, 3.1 and -1.7 for the IGFBP-1,-2 and-3, respectively, compared with the normal range defined by a SDS from -2 to +2. IGFBP-1 and-3 were normal, but for IGFBP-2 we found a significantly elevated serum level compared with control groups (P < 0.05). However, during chemotherapy this increased serum IGFBP-2 normalized. In addition, we found a correlation between higher serum levels and the detection rate of the IGFBP-2 transcript in corresponding cells. In patients with ALL, the detection rates of IGFBP-2 mRNA were estimated to be 72% and 35% at the time of diagnosis and at day 33 of chemotherapy respectively; in the control groups (healthy children and children at their initial presentation of diabetes mellitus), the values were 28% and 33% respectively. Based on the correlation between IGFBP-2 serum levels and the corresponding gene expression as well as the normalization of IGFBP-2 levels during chemotherapy, we concluded that the increased serum level mainly originated from the tumour clone itself. Furthermore, possible functional consequences of elevated IGFBP-2 were outlined.

Activation-dependent expression of the insulin-like growth factor binding protein-2 in human lymphocytes

The expression of the insulin-like growth factor binding protein-2 (IGFBP-2) was assayed in mononuclear cells originating from different organs of the immune system. All mononuclear cells studied did express IGFBP-2, but the expression level was found to be dependent on the cell type and origin of the cell. T cells showed a higher expression of IGFBP-2 mRNA than did B cells, and CD34+ stem cells expressed IGFBP-2 mRNA at a high level. Expression was highest in bone marrow and thymus. Stimulation of peripheral mononuclear cells resulted in a marked increase of IGFBP-2 mRNA and also intracellular IGFBP-2, as analysed by fluorescence staining. This increase parallels the increase of other known T-cell activation markers. Furthermore, the increase of intracellular IGFBP-2 seems to precede T-cell blast formation and all T cells in active phases of the cell cycle have high levels of IGFBP-2. Our results provide a basis for further investigations on the contribution of the IGF-system to the regulation of T-cell proliferation and differentiation. IGFBP-2, in particular, may have an important influence in the regulation of T-cell activation and proliferation.

Molecular regulation of insulin-like growth factor-I and its principal binding protein, IGFBP-3

The insulin-like growth factors (IGFs) have diverse anabolic cellular functions, and structure similar to that of proinsulin. The distribution of IGFs and their receptors in a wide variety of organs and tissues enables the IGFs to exert endocrine, paracrine, and autocrine effects on cell proliferation and differentiation, caloric storage, and skeletal elongation. IGF-I exhibits particular metabolic responsiveness, and circulating IGF-I originates predominantly in the liver. Hepatic IGF-I production is controlled at the level of gene transcription, and transcripts are initiated largely in exon 1. Hepatic IGF-I gene transcription is reduced in conditions of protein malnutrition and diabetes mellitus, and our laboratory has used in vitro transcription to study mechanisms related to diabetes. We find that the presence of sequences downstream from the major transcription initiation sites in exon 1 is necessary for the diabetes-induced decrease in IGF-I transcription. Six nuclear factor binding sites have been identified within the exon 1 downstream region, and footprint sites III and V appear to be necessary for metabolic regulation; region V probes exhibit a decrease in nuclear factor binding with hepatic nuclear extracts from diabetic animals. IGFs in biological fluids are associated with IGF binding proteins, and IGFs circulate as a 150-kDa complex that consists of an IGF, an IGFBP-3, and an acid-labile subunit. Circulating IGFBP-3 originates mainly in hepatic nonparenchymal cells, where IGF-I increases IGFBP-3 mRNA stability, but insulin increases IGFBP-3 gene transcription. Regulation of IGFBP-3 gene transcription by insulin appears to be mediated by an insulin-responsive element, which recognizes insulin-responsive nuclear factors in both gel mobility shift assays and southwestern blots. Studies of mechanisms underlying the modulation of IGF-I and IGFBP-3 gene transcription, and identification of critical nuclear proteins involved, should lead to new understanding of the role and regulation of these important growth factors in diabetes mellitus and other metabolic disorders.

In vitro effects of growth hormone (GH) and insulin-like growth factor I and II (IGF-I and -II) on chromosome fragility and p53 protein expression in human lymphocytes

BACKGROUND

We have reported previously that growth hormone (GH) therapy increases cell radiosensitivity; in this study we tested whether GH itself or IGFs induce chromosome aberrations and investigated the expression of p53 protein in response to DNA damage.

METHODS

Human peripheral blood lymphocytes were incubated with GH [100 and 1000 microg L(-1)], insulin-like growth factor I [IGF-I; 150 and 1000 microg L(-1)] and IGF-II [600 and 1200 microg L(-1)] for 24 h. The radiomimetic agent bleomycin [BLM; 5 microgm L(-1)] was added in the last 3 h. Cytogenetic analysis was performed by assessing the percentages of damaged cells (%DC) and chromosome aberrations (%CA). The expression of p53 was investigated by flow cytometric assay using the monoclonal antibody DO-7, and expressed as percentage positive cells and mean fluorescence intensity.

RESULTS

BLM significantly increased both percentage DC and percentage CA and p53 expression (P < 0.01). The %DC was unaffected by the tested peptides. IGF-I [150 microg L(-1)] increased spontaneous percentage CA (P < 0.01). All peptides further increased the BLM-induced chromosome breakage: GH 100 and 1000 microg L(-1) by 30% and 73% respectively, IGF-I 150 and 1000 microg L(-1) by 41% and 96% respectively and IGF-II 600 and 1200 microg L(-1) by 89% and 45% respectively. The spontaneous and BLM-induced expression of p53 was unaffected by GH, whereas it was significantly increased by IGFs (P < 0001).

CONCLUSIONS

These results indicate that the DNA-damaging effect of BLM is amplified by GH and, more markedly, IGF-I and -II. IGF-I and -II also stimulate p53 protein expression that, taking part in DNA repair, may counteract the IGF action on genome stability.

Increased insulin-like growth factor binding protein-2 (IGFBP-2) gene expression and protein production lead to high IGFBP-2 content in malignant ovarian cyst fluid

Expression of insulin-like growth factor-I (IGF-I), its receptor and IGF-binding proteins (IGFBPs) by ovarian cancer cells and its mitogenic effect on these cells in vitro, suggest that IGF-I may have a role in regulation of human ovarian cancer. We have recently shown IGFBP-2 to be markedly elevated in malignant ovarian cyst fluid in vivo. To identify the origin of increased IGFBP-2 in these cyst fluids, the gene expression and protein content of IGFBP-2 were investigated in 14 malignant and four benign epithelial ovarian neoplasms. IGFBP-2 mRNA was detected in all ovarian specimens and was 2- to 30-fold higher in malignant than in benign neoplasms. Within the malignant tissues IGFBP-2 mRNA levels correlated with the aggressiveness of the tumour and were higher in invasive tumours than in those with borderline pathology. Southern blot analysis revealed no amplification of IGFBP-2 gene in the DNA samples from ovarian tumours regardless of their nature. IGFBP-2 was the major binding protein in tissue extracts, as measured by both Western ligand blotting and immunoblotting, and was significantly higher in malignant than in benign neoplasms. These findings were further supported by immunohistochemical detection of IGFBP-2 in tumour sections. Our data suggest that increased local production by the tumour in vivo is responsible for the increased IGFBP-2 levels in the cyst fluid bathing the ovarian malignancy. This may represent an autocrine regulatory mechanism for IGF-I proliferative effect of ovarian cancer.

Intracellular levels and secretion of insulin-like-growth-factor-binding proteins in MCF-7/6, MCF-7/AZ and MDA-MB-231 breast cancer cells. Differential modulation by estrogens in serum-free medium

The synthesis and secretion of insulin-like growth factor binding proteins (IGFBPs) were studied in MDA-MB-231 (estrogen-receptor-negative), MCF-7/6 (estrogen-receptor-positive, invasive) and in MCF-7/AZ (estrogen-receptor-positive, non-invasive) human breast carcinoma cell lines. Cells were grown or maintained in a chemically defined medium. Under these conditions, we found different patterns of IGFBPs in the three cell types. MDA-MB-231 cells secrete most of the IGFBPs they produce whereas MCF-7/6 and MCF-7/AZ cells maintain a high intracellular level. In MDA-MB-231 cells, the major IGFBP is IGFBP-4 which is the minor form in MCF-7/6 and MCF-7/AZ cells. IGFBP-2 and IGFBP-5 are predominant in MCF-7/6 cells while MCF-7/AZ cells produce far less IGFBPs and do not contain detectable amounts of 29-32-kDa forms (IGFBP-5). In MCF-7/6 cells, estradiol-17 beta specifically decreases both the intracellular content and secretion of IGFBP-2 and IGFBP-5. Estrogen regulation of IGFBPs cell content and secretion was found to be tamoxifen-resistant, and only slightly antagonized by ICI 182,780, a pure antiestrogen. The function of these regulations relative to the invasive phenotype and proliferation has now to be determined.

The insulin-like growth factor system in regulation of normal and malignant hematopoiesis

The published data available on the insulin-like growth factor (IGF) family of peptides, its receptors and binding proteins in connection with normal and neoplastic hematopoietic processes are reviewed. It is found that nearly all the different hematopoietic cells, either normal or neoplastic, express IGF receptors. The IGFs are involved in normal erythropoiesis, granulopoiesis and lymphopoiesis. IGFs, especially IGF-1, are mitogenic for cell lines of myeloid and lymphoid leukemias and Burkitt's lymphoma. Differentiation of certain immature malignant cell lines is associated with a decrease in the number and affinity of IGF receptors. It might be concluded that the IGFs have an important role in the physiologic and neoplastic processes of the hematopoietic system, and the expanding knowledge of this issue will contribute to the understanding of proliferation and differentiation processes in specific hematologic disorders.

Expression and down-regulation by retinoic acid of IGF binding protein-2 and -4 in medium from human neuroblastoma cells

Insulin-like growth factors (IGFs) regulate the autocrine/paracrine growth of neuroblastomas. The IGFs bind to specific binding proteins (IGFBPs) which modulate their biological activity. We investigated, by Western ligand blotting (WLB), the presence of IGFBPs and their possible modulation by retinoic acid (RA), IGF-I, IGF-II and truncated Des(1-3)IGF-I in conditioned medium (CM) of the human neuroblastoma SK-N-BE(2) cell line. We demonstrated the presence of two IGFBPs, with MW 37 kDa and 25 kDa. Following immunoprecipitation, they turned out to be IGFBP-2 and -4, respectively. The RA-induced differentiation in SK-N-BE(2) cells was accompanied by a marked reduction of the intensity of both IGFBP bands after 48 h (32% and 24% of control, respectively) and 72 h (2% and 0% of control, respectively) incubation. The addition of exogenous IGFs, which did not induce cell differentiation, did not change the IGFBP pattern significantly, except for the truncated form of IGF-I, which induced a marked decrease in both the 37 kDa and 25 kDa bands after 72 h incubation (45% and 18% of control, respectively). These findings suggest that IGFBPs have a role in RA-induced differentiation in human neuroblastoma cells.

Insulin-like growth factor (IGF)-I, -II and IGF binding protein-2 (IGFBP-2) in the plasma of children with Wilms' tumour

Insulin-like growth factors (IGF)-I, -II and IGF binding protein-2 (IGFBP-2) have been measured in plasma of children with Wilms' tumour. The mean levels for total serum IGF-I and -II were not significantly altered in Wilms' tumour as compared with normal control plasma. However, the chromatographic profiles for IGF-I and -II in these groups were different with regard to the presence of IGF binding proteins and high molecular weight forms of IGFs; the high molecular weight form (9-15 kD) of IGF-II was significantly reduced in Wilms' tumour. Levels of IGFBP-2 were substantially elevated in serum from Wilms' tumour patients (1025 +/- 112 ng/ml compared with 416 +/- 44 ng/ml in controls), and inversely correlated with the levels of high molecular weight forms of IGF-II. We suggest that IGFBP-2 measurements might be of value as a marker for monitoring this type of tumour, either as an adjunct to diagnosis or surveillance of tumour growth during therapy.