Role of insulin-like growth factor-I (IGF-I) receptor, IGF-I, and IGF binding protein-2 in human colorectal cancers

Anti-Gene IGF-I Vaccines in Cancer Gene Therapy: A Review of a Case of Glioblastoma

OBJECTIVE

Vaccines for the deadliest brain tumor - glioblastoma (GBM) - are generally based on targeting growth factors or their receptors, often using antibodies. The vaccines described in the review were prepared to suppress the principal cancer growth factor - IGF-I, using anti-gene approaches either of antisense (AS) or of triple helix (TH) type. Our objective was to increase the median survival of patients treated with AS and TH cell vaccines.

METHODOLOGY

The cells were transfected in vitro by both constructed IGF-I AS and IGF-I TH expression episomal vectors; part of these cells was co-cultured with plant phytochemicals, modulating IGF-I expression. Both AS and TH approaches completely suppressed IGF-I expression and induced MHC-1 / B7 immunogenicity related to the IGF-I receptor signal.

RESULTS

This immunogenicity proved to be stronger in IGF-I TH than in IGF-I AS-prepared cell vaccines, especially in TH / phytochemical cells. The AS and TH vaccines generated an important TCD8+ and TCD8+CD11b- immune response in treated GBM patients and increased the median survival of patients up to 17-18 months, particularly using TH vaccines; in some cases, 2- and 3-year survival was reported. These clinical results were compared with those obtained in therapies targeting other growth factors.

CONCLUSION

The anti-gene IGF-I vaccines continue to be applied in current GBM personalized medicine. Technical improvements in the preparation of AS and TH vaccines to increase MHC-1 and B7 immunogenicity have, in parallel, allowed to increase in the median survival of patients.

The Insulin-like Growth Factor System and Colorectal Cancer

Insulin-like growth factors (IGFs) are peptides which exert mitogenic, endocrine and cytokine activities. Together with their receptors, binding proteins and associated molecules, they participate in numerous pathophysiological processes, including cancer development. Colorectal cancer (CRC) is a disease with high incidence and mortality rates worldwide, whose etiology usually represents a combination of the environmental and genetic factors. IGFs are most often increased in CRC, enabling excessive autocrine/paracrine stimulation of the cell growth. Overexpression or increased activation/accessibility of IGF receptors is a coinciding step which transmits IGF-related signals. A number of molecules and biochemical mechanisms exert modulatory effects shaping the final outcome of the IGF-stimulated processes, frequently leading to neoplastic transformation in the case of irreparable disbalance. The IGF system and related molecules and pathways which participate in the development of CRC are the focus of this review.

Insulin-Like Growth Factor 2 (IGF2) Signaling in Colorectal Cancer-From Basic Research to Potential Clinical Applications

Colorectal cancer (CRC) is one of the most common cancers in men and women worldwide as well as is the leading cause of death in the western world. Almost a third of the patients has or will develop liver metastases. While genetic as well as epigenetic mechanisms are important in CRC pathogenesis, the basis of the most cases of cancer is unknown. High spatial and inter-patient variability of the molecular alterations qualifies this cancer in the group of highly heterogeneous tumors, which makes it harder to elucidate the mechanisms underlying CRC progression. Determination of highly sensitive and specific early diagnosis markers and understanding the cellular and molecular mechanism(s) of cancer progression are still a challenge of the current era in oncology of solid tumors. One of the accepted risk factors for CRC development is overexpression of insulin-like growth factor 2 (IGF2), a 7.5-kDa peptide produced by liver and many other tissues. IGF2 is the first gene discovered to be parentally imprinted. Loss of imprinting (LOI) or aberrant imprinting of IGF2 could lead to IGF2 overexpression, increased cell proliferation, and CRC development. IGF2 as a mitogen is associated with increased risk of developing colorectal neoplasia. Higher serum IGF2 concentration as well as its tissue overexpression in CRC compared to control are associated with metastasis. IGF2 protein was one of the three candidates for a selective marker of CRC progression and staging. Recent research indicates dysregulation of different micro- and long non-coding RNAs (miRNAs and lncRNAs, respectively) embedded within the IGF2 gene in CRC carcinogenesis, with some of them indicated as potential diagnostic and prognostic CRC biomarkers. This review systematises the knowledge on the role of genetic and epigenetic instabilities of IGF2 gene, free (active form of IGF2) and IGF-binding protein (IGFBP) bound (inactive form), paracrine/autocrine secretion of IGF2, as well as mechanisms of inducing dysplasia in vitro and tumorigenicity in vivo. We have tried to answer which molecular changes of the IGF2 gene and its regulatory mechanisms have the most significance in initiation, progression (including liver metastasis), prognosis, and potential anti-IGF2 therapy in CRC patients.

Long non-coding RNA HOTAIR promotes cell migration by upregulating insulin growth factor-binding protein 2 in renal cell carcinoma

Renal cell carcinoma (RCC) is one of the most lethal urologic cancers. About one-third of RCC patients already have distal metastasis at the time of diagnosis. There is growing evidence that Hox antisense intergenic RNA (HOTAIR) plays essential roles in metastasis in several types of cancers. However, the precise mechanism by which HOTAIR enhances malignancy remains unclear, especially in RCC. Here, we demonstrated that HOTAIR enhances RCC-cell migration by regulating the insulin growth factor-binding protein 2 (IGFBP2) expression. HOTAIR expression in tumors was significantly correlated with nuclear grade, lymph-node metastasis, and lung metastasis. High HOTAIR expression was associated with a poor prognosis in both our dataset and The Cancer Genome Atlas dataset. Migratory capacity was enhanced in RCC cell lines in a HOTAIR-dependent manner. HOTAIR overexpression accelerated tumorigenicity and lung metastasis in immunodeficient mice. Microarray analysis revealed that IGFBP2 expression was upregulated in HOTAIR-overexpressing cells compared with control cells. The enhanced migration activity of HOTAIR-overexpressing cells was attenuated by IGFBP2 knockdown. IGFBP2 and HOTAIR were co-expressed in clinical RCC samples. Our findings suggest that the HOTAIR-IGFBP2 axis plays critical roles in RCC metastasis and may serve as a novel therapeutic target for advanced RCC.

Preoperative serum levels of insulin-like growth factor-binding protein 2 predict prognosis of gastric cancer patients

It has been reported that serum insulin-like growth factor-binding protein 2 (IGFBP2) levels are elevated in various types of cancers. However, the clinicopathologic and prognostic implications of circulating IGFBP2 have never been investigated in gastric cancer. We tested IGFBP2 levels in the sera of 118 gastric cancer patients and 34 healthy controls using enzyme-linked immunosorbent assay (ELISA). The mean serum IGFBP2 level was significantly elevated in the gastric cancer patients compared to controls (805.23 ± 590.56 ng/ml vs. 459.61 ± 277.01 ng/ml; P < 0.001). Serum IGFBP2 levels were significantly higher in larger (> 6 cm) tumors (956.8 ± 734.0 ng/ml vs. 548.6 ± 364.0 ng/ml; P = 0.007) and in higher (T3/4) T stages (854.8 ± 621.4 ng/ml vs. 546.5 ± 315.1 ng/ml; P = 0.037). Multivariate Cox analysis showed that higher serum IGFBP2 level (> 400.01 ng/ml) was an independent prognostic factor predicting worse overall survival in patients with gastric cancer (hazard ratio (HR): 3.749, P = 0.034). When we divided patients into four groups based on blood IGFBP2 levels, survival was stratified. The HRs for death in the 3rd and 4th quartiles of serum IGFBP2 levels in comparison to that in the 1st quartile were 2.527 (P = 0.043) and 3.092 (P = 0.012). In conclusion, circulating IGFBP2 has potential as a biomarker predicting prognosis for gastric cancer patients.

TRIB3 enhances cell viability during glucose deprivation in HEK293-derived cells by upregulating IGFBP2, a novel nutrient deficiency survival factor

Glucose deprivation occurs in several human diseases, including infarctions and solid tumors, and leads to cell death. In this article, we investigate the role of the pseudokinase Tribbles homolog 3 (TRIB3) in the cellular stress response to glucose starvation using cell lines derived from HEK293, which is highly glycolytic under standard conditions. Our results show that TRIB3 mRNA and protein levels are strongly upregulated in glucose-deprived cells via the induction of activating transcription factor 4 (ATF4) by the endoplasmic reticulum (ER) stress sensor kinase PERK. Cell survival in glucose-deficient conditions is enhanced by TRIB3 overexpression and reduced by TRIB3 knockdown. Genome-wide gene expression profiling uncovered approximately 40 glucose deprivation-responsive genes that are affected by TRIB3, including several genes involved in signaling processes and metabolism. Based on transcription factor motif analysis, the majority of TRIB3-downregulated genes are target genes of ATF4, which TRIB3 is known to inhibit. The gene most substantially upregulated by TRIB3 is insulin-like growth factor binding protein 2 (IGFBP2). IGFBP2 mRNA and protein levels are downregulated in cells subjected to glucose deprivation, and reduced IGFBP2 expression aggravates cell death during glucose deficiency, while overexpression of IGFBP2 prolongs cell survival. Moreover, IGFBP2 silencing abrogates the pro-survival effect of TRIB3. Since TRIB3 augments IGFBP2 expression in glucose-starved cells, the data indicate that IGFBP2 contributes to the attenuation of cell death by TRIB3. These results implicate TRIB3 and IGFBP2, both of which are known to be overexpressed in several types of cancers, as pro-survival modulators of cell viability in nutrient-deficient microenvironments.

Linking patient outcome to high throughput protein expression data identifies novel regulators of colorectal adenocarcinoma aggressiveness

A key question in cancer systems biology is how to use molecular data to predict the biological behavior of tumors from individual patients. While genomics data have been heavily used, protein signaling data are more directly connected to biological phenotype and might predict cancer phenotypes such as invasion, metastasis, and patient survival. In this study, we mined publicly available data for colorectal adenocarcinoma from the Cancer Genome Atlas and identified protein expression and signaling changes that are statistically associated with patient outcome. Our analysis identified a number of known and potentially new regulators of colorectal cancer. High levels of insulin growth factor binding protein 2 (IGFBP2) were associated with both recurrence and death, and this was validated by immunohistochemical staining of a tissue microarray for a secondary patient dataset. Interestingly, GATA binding protein 3 (GATA3) was the protein most frequently associated with death in our analysis, and GATA3 expression was significantly decreased in tumor samples from stage I-II deceased patients. Experimental studies using engineered colon cancer cell lines show that exogenous expression of GATA3 decreases three-dimensional colony growth and invasiveness of colon cancer cells but does not affect two-dimensional proliferation. These findings suggest that protein data are useful for biomarker discovery and identify GATA3 as a regulator of colorectal cancer  aggressiveness.

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.

mRNA expression of IGF-1 and IGF-1R in patients with colorectal adenocarcinoma and type 2 diabetes

BACKGROUND AND AIMS

Increasing studies show that messenger RNA (mRNA) levels of local IGF-system are overexpressed in cancer tissue of patients with colorectal cancer (CRC). However, the influence of type 2 diabetes (T2DM) on the expression of insulin-like growth factor-1 (IGF-1) and IGF-1 receptor (IGF-1R) mRNA in colorectal cancer tissue and adjacent non-cancerous tissue (ANCT) is unknown. The aim of this study was to assess mRNA expression of IGF-1 and IGF-1R in paired samples of cancer tissue and ANCT between colorectal adenocarcinoma (CA) patients with and without T2DM.

METHODS

To quantify the levels of IGF-1 and IGF-1R mRNA in CA, we analyzed the expression of IGF-1 and IGF-1R mRNA levels in paired samples of cancer tissue and ANCT in CA patients with and without T2DM using real-time reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

mRNA levels of IGF-1 and IGF-1R were significantly higher in cancer tissue compared with its ANCT in CA patients with and without T2DM. Compared with the CA group, significantly higher levels of IGF-1 and IGF-1R mRNA were observed in cancer tissue in CA with T2DM group. No significant differences were observed in the role of cancer locations, Dukes stages and diabetes duration on mRNA expression of IGF-1. After adjusting for age, gender and Dukes stages, multivariate analysis indicated IGF-1 mRNA level was a risk factor for prognosis (p <0.05).

CONCLUSIONS

Our results support the hypothesis that IGF system plays an important role in CRC. Further larger studies are needed.

IGFBP2/FAK pathway is causally associated with dasatinib resistance in non-small cell lung cancer cells

Insulin-like growth factor (IGF)-binding protein-2 (IGFBP2) expression is increased in various types of cancers, including in a subset of patients with lung cancer. Because IGFBP2 is involved in signal transduction of some critical cancer-related pathways, we analyzed the association between IGFBP2 and response to pathway-targeted agents in seven human non-small cell lung cancer (NSCLC) cell lines. Western blot analysis and ELISA showed that four of the seven NSCLC cell lines analyzed expressed high levels of IGFBP2, whereas the remaining three had barely detectable IGFBP2. Susceptibilities of those seven cell lines to nine anticancer agents targeting to IGF1R, Src, FAK, MEK, and AKT were determined by a dose-dependent cell viability assay. The results showed that high IGFBP2 levels were associated with resistance to dasatinib and, to a lesser degree, to sacaratinib, but not to other agents. Ectopic IGFBP2 overexpression or knockdown revealed that changing IGFBP2 expression levels reversed dasatinib susceptibility phenotype, suggesting a causal relationship between IGFBP2 expression and dasatinib resistance. Molecular characterization revealed that focal adhesion kinase (FAK) activation was associated with increased IGFBP2 expression and partially contributed to IGFBP2-mediated dasatinib resistance. Treatment with a combination of dasatinib and FAK inhibitor led to enhanced antitumor activity in IGFBP2-overexpressing and dasatinib-resistant NSCLC cells in vitro and in vivo. Our results showed that the IGFBP2/FAK pathway is causally associated with dasatinib resistance and may be used as biomarkers for identification of dasatinib responders among patients with lung cancer. Simultaneous targeting on Src and FAK will likely improve the therapeutic efficacy of dasatinib for treatment of lung cancer.

Insulin-like growth factor binding protein-2 level is increased in blood of lung cancer patients and associated with poor survival

Background

We recently showed that IGFBP2 is overexpressed in primary lung cancer tissues. This study aims to determine whether IGFBP2 is elevated in blood samples of lung cancer patients and whether its level is associated with clinical outcomes.

Methodology/Principal Findings

Plasma IGFBP2 levels were determined blindly by enzyme-linked immunosorbent assay in 80 lung cancer patients and 80 case-matched healthy controls for comparison. We analyzed blood samples for IGFBP2 levels from an additional 84 patients with lung cancer and then tested for associations between blood IGFBP2 levels and clinical parameters in all 164 lung cancer patients. All statistical tests were two-sided and differences with p<0.05 were considered significant. The mean plasma concentration of IGFBP2 in lung cancer patients was significantly higher than that in healthy controls (388.12±261.00 ng/ml vs 219.30±172.84 ng/ml, p<0.001). IGFBP2 was increased in all types of lung cancer, including adenocarcinoma, squamous cell cancer, and small-cell cancer, regardless of patients’ age, sex, or smoking status. IGFBP2 levels were mildly but significantly associated with tumor size and were significantly higher in stage IV than stage I or III disease. A multivariate analysis showed that lung cancer patients whose blood IGFBP2 was higher than 160.9 ng/ml had a poor survival outcome, with a hazard ratio of 8.76 (95% CI 1.12-68.34, p=0.038 after adjustment for tumor size, pathology, and stage). The median survival time for patients with blood IGFBP2 >160.9 ng/ml is 15.1 months; whereas median survival time was 128.2 months for the patients whose blood IGFBP2 was ≤160.9 ng/ml (p =0.0002).

Conclusions/Significance

Blood IGFBP2 is significantly increased in lung cancer patients. A high circulating level of IGFBP2 is significantly associated with poor survival, suggesting that blood IGFBP2 levels could be a prognostic biomarker for lung cancer.

The prognostic role of ephrin A2 and endothelial growth factor receptor pathway mediators in patients with advanced colorectal cancer treated with cetuximab

BACKGROUND

Patients with colorectal cancer (CRC) with wild-type KRAS mutations are often treated with the endothelial growth factor receptor (EGFR) monoclonal antibody cetuximab. Despite the presence of a specific molecular target, most patients still do not derive benefit from this biological treatment. Our study explores the role of ephrin A2 (EphA2) receptor expression and of EGFR pathway mediators as predictors of cetuximab benefit.

PATIENTS AND METHODS

Formalin-fixed paraffin-embedded (FFPE) tumor biopsy samples from 226 cetuximab-treated patients with CRC were studied for mRNA expression of insulin growth factor binding protein 2 (IGFBP2), insulin growth factor receptor 1 (IGF1R), cMET, EphA2, human epidermal growth factor receptor 2 (HER2), HER3, and HER4 by means of TaqMan reverse-transcribed polymerase chain reaction (RT-PCR).

RESULTS

Of the 226 patients evaluable for exploratory analysis, 222 had complete data from follow-up visits. The univariate analysis revealed the following significant adverse prognostic factors for risk of death: high EphA2 mRNA levels (hazard ratio [HR], 1.61; P = .015), high HER2 mRNA levels (HR, 1.51; P = .045), and high IGF1R mRNA levels (HR, 1.56; P = .021). Low EphA2 tumor expression was significantly associated with objective response to cetuximab therapy. In multivariate analysis of a broad biomarker panel, factors with independent prognostic value included EphA2 mRNA levels (HR, 1.67; P = .029), high amphiregulin (AREG) mRNA levels in KRAS wild-type tumors (HR, 0.17; P < .0001), and high epiregulin (EREG) mRNA levels (HR, 0.38; P = .006).

CONCLUSION

High EphA2 receptor expression in CRC was associated with a worse outcome in patients treated with cetuximab-based therapy. Prospective validation in treated and control patients is required to dissect the predictive from prognostic role in advanced CRC.

Regulation of protumorigenic pathways by insulin like growth factor binding protein2 and its association along with β-catenin in breast cancer lymph node metastasis

Background

Insulin like growth factor binding proteins modulate the mitogenic and pro survival effects of IGF. Elevated expression of IGFBP2 is associated with progression of tumors that include prostate, ovarian, glioma among others. Though implicated in the progression of breast cancer, the molecular mechanisms involved in IGFBP2 actions are not well defined. This study investigates the molecular targets and biological pathways targeted by IGFBP2 in breast cancer.

Methods

Transcriptome analysis of breast tumor cells (BT474) with stable knockdown of IGFBP2 and breast tumors having differential expression of IGFBP2 by immunohistochemistry was performed using microarray. Differential gene expression was established using R-Bioconductor package. For validation, gene expression was determined by qPCR. Inhibitors of IGF1R and integrin pathway were utilized to study the mechanism of regulation of β-catenin. Immunohistochemical and immunocytochemical staining was performed on breast tumors and experimental cells, respectively for β-catenin and IGFBP2 expression.

Results

Knockdown of IGFBP2 resulted in differential expression of 2067 up regulated and 2002 down regulated genes in breast cancer cells. Down regulated genes principally belong to cell cycle, DNA replication, repair, p53 signaling, oxidative phosphorylation, Wnt signaling. Whole genome expression analysis of breast tumors with or without IGFBP2 expression indicated changes in genes belonging to Focal adhesion, Map kinase and Wnt signaling pathways. Interestingly, IGFBP2 knockdown clones showed reduced expression of β- catenin compared to control cells which was restored upon IGFBP2 re-expression. The regulation of β-catenin by IGFBP2 was found to be IGF1R and integrin pathway dependent. Furthermore, IGFBP2 and β-catenin are co-ordinately overexpressed in breast tumors and correlate with lymph node metastasis.

Conclusion

This study highlights regulation of β-catenin by IGFBP2 in breast cancer cells and most importantly, combined expression of IGFBP2 and β-catenin is associated with lymph node metastasis of breast tumors.

Insulin-like growth factor binding protein-2 is a novel therapeutic target associated with breast cancer

PURPOSE

Insulin-like growth factor (IGF) binding proteins (IGFBP) modulate interactions of IGF ligands with the IGF-I receptor. The role of IGFBPs, and specifically IGFBP-2, in breast cancer progression has been poorly defined. This study assesses the effect of IGFBP-2 on the behavior of human breast cancer using clinical specimens as well as in vitro and in vivo experimental systems.

EXPERIMENTAL DESIGN

4,181 primary invasive breast cancers and 120 benign breast tissue samples were identified for tumor tissue microarray construction and immunostained with IGFBP-2 antibody. Estrogen receptor-negative MDA-MB-231 cells constitutively overexpressing IGFBP-2 (MDA-MB-231BP-2) were created to assess the effect of IGFBP-2 gain-of-function. MDA-MB-468 cells, naturally expressing IGFBP-2, were used to determine the effect of IGFBP-2 loss-of-function using OGX-225, an antisense oligonucleotide drug candidate.

RESULTS

IGFBP-2 expression was significantly higher in breast cancer tissue compared with benign breast tissue. MDA-MB-231BP-2 cells grew more rapidly and were more resistant to paclitaxel both in vitro and in vivo compared with parental cells. OGX-225 decreased IGFBP-2 expression and attenuated the associated aggressive phenotype of MDA-MB-231BP-2 cells both in vitro and in vivo. Furthermore, OGX-225 inhibited the in vitro and in vivo growth of MDA-MB-468 cells.

CONCLUSIONS

This study provides evidence that IGFBP-2 expression is associated with breast cancer. Novel therapeutics targeting IGFBP-2, such as OGX-225, merit further evaluation.

An HLA-DR-degenerate epitope pool detects insulin-like growth factor binding protein 2-specific immunity in patients with cancer

Recent studies have shown the importance of helper CD4 T cells in initiating and sustaining tumor-specific CD8 T-cell immunity. This has paved the way for identifying MHC class II epitopes that could be incorporated into class I-based vaccines. In this study, the goal was to identify an HLA-DR-degenerate epitope pool derived from insulin-like growth factor binding protein 2 (IGFBP-2). IGFBP-2, a regulator of insulin-like growth factor action, is overexpressed in the majority of breast and ovarian cancers. Using algorithms, we predicted 29 HLA-DR1-binding epitopes. Binding assays targeting 15 different HLA-DRs revealed that 10 epitopes were degenerate, binding to at least four different HLA-DR variants. An IFN-gamma enzyme-linked immunosorbent spot assay was used to assess immunity to these 10 epitopes in 48 patients with either breast or ovarian cancer and 18 controls. Elevated T-cell immunity in patients was detected in 4 of the 10 epitopes (IGFBP2.17, IGFBP2.22, IGFBP2.249, and IGFBP2.293). The cumulative T-cell frequency of these four epitopes was elevated in patients relative to controls. All four peptides are naturally processed and presented to CD4 T-cells. The degenerate pool of peptides covers nearly 80% of patients and may be useful for augmenting CD4 T-cell immunity in patients undergoing immunization.

Silencing of insulin-like growth factor-binding protein-2 in human glioblastoma cells reduces both invasiveness and expression of progression-associated gene CD24

Glioblastoma multiforme (GBM) is a malignant brain tumor characterized by rapid growth and extensive invasiveness. Overexpression of insulin-like growth factor-binding protein-2 (IGFBP-2) has been reported in GBM. However, it remains to be determined how IGFBP-2 is involved in the progression of GBM. We utilized short hairpin-RNA (shRNA) expression retroviral vectors to inactivate the IGFBP-2 gene permanently in two human GBM cell lines, U251 and YKG-1. The stable knockdown of IGFBP-2 resulted in decreased invasiveness, decreased saturation density of the cells in vitro, and decreased tumorigenicity in nude mice. Transcriptional profiling of both lines revealed several genes that were significantly down-regulated by inactivation of IGFBP-2. One such gene was CD24, which has been implicated in progression of various cancers. Indeed, CD24 was expressed in most GBM cases and the inactivation of CD24 in GBM cells suppressed cellular invasiveness, as was the case for IGFBP-2. Forced overexpression of CD24 led to increased invasiveness of both IGFBP-2-inactivated GBM cell lines and also A172, a human GBM cell line with low endogenous CD24. Further supporting the inter-relationship between IGFBP-2 and CD24, knockdown of IGFBP-2 suppressed the CD24 promoter activity. Moreover, both CD24 promoter activity and in vitro invasiveness were restored in knockdown cells by transfection with an IGFBP-2 expression plasmid. These results indicate that CD24 is modulated by IGFBP-2 and contributes to IGFBP-2-enhanced invasiveness of GBM cells.

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.

Overexpression of the insulin-like growth factor I receptor and activation of the AKT pathway in hyperplastic endometrium

PURPOSE

Although there is considerable information on the molecular aberrations associated with endometrial cancer, very little is known of the changes in gene expression associated with endometrial hyperplasia.

EXPERIMENTAL DESIGN

To address this, we have compared the level of expression of estrogen-regulated genes and components of the insulin-like growth factor I (IGF-I) signaling pathway in endometrial biopsies from subjects with normal endometrium, complex atypical endometrial hyperplasia, and endometrial adenocarcinoma (type I).

RESULTS

There was a significant increase in the expression of the IGF-I receptor (IGF-IR) in biopsies from hyperplastic endometrium and endometrial carcinoma compared with the proliferative endometrium. The receptor was also activated, as judged by increased tyrosine phosphorylation. In addition, in endometrial hyperplasia and carcinoma, the downstream components of the IGF-IR pathway are activated, as reflected in increased Akt phosphorylation. Loss of phosphatase and tensin homologue deleted on chromosome 10 (PTEN) expression in endometrial hyperplasia did not correlate with increased activation of IGF-IR. However, the simultaneous loss of PTEN expression and increased IGF-IR activation in hyperplasia was associated with an increased incidence of endometrial carcinoma.

CONCLUSIONS

These results suggest that up-regulation of IGF-IR and loss of PTEN may be independent events that give rise to complementary activation of the IGF-I pathway and increase the probability of the development of cancer. These studies suggest that increased expression of IGF-IR may be an important contributor to the risk of endometrial hyperplasia and cancer.

The insulin-like growth factor system and colorectal cancer: clinical and experimental evidence

OBJECTIVE

The aim of this review is to clarify the involvement of the insulin-like growth factor (IGF) system in the development of colorectal malignancy.

MATERIALS AND METHODS

Medline searches were used to identify key articles relating the IGF system with the development of colorectal cancer.

RESULTS

The IGF system has been linked to colorectal malignancy by a convergence of data from epidemiological, clinical and laboratory-based sources.

CONCLUSION

Further work is needed to characterise the IGF system expression in the colon. Such clarification could lead to the identification of targets that can be manipulated for clinical advantage.

A 14-kDa cathepsin L-derived carboxyl IGFBP-2 fragment is sequestered by cultured rat ileal crypt cells

IGF-II gut drives mucosal growth during gestation. IGF binding protein-2 (IGFBP-2) has a high affinity for IGF-II and tightly regulates IGF-II availability during fetal and early neonatal growth. We have previously demonstrated that glucocorticoids alter IGF homeostasis in the neonatal ileum, but the mechanism(s) by which this occurs is poorly understood. We hypothesized that dexamethasone alters proteolytic regulation of IGFBP-2 in ileal crypt cells. To test this, ileal crypt [ileal epithelial (IEC)-18] cells were cultured in serum-free media and used to study IGFBP-2 catabolism by immunochemistry, gene array analysis, and pharmacological perturbation with dexamethasone. In addition, isolated human IGFBP-2, IGF-II, and cathepsins B, D, and L were utilized for in vitro protease assays. We found IGFBP-2 to be highly abundant in IEC-18 culture, and sequestration of carboxyl IGFBP-2 antigen was seen within vesicular bodies of some cells. Dexamethasone significantly decreased the number of these cells and decreased IGFBP-2 in the media. On gene array analysis, cathepsin L's message abundance was significantly increased by dexamethasone, and, by in vitro assay, cathepsin L created a 14-kDa carboxyl fragment that corresponded to the sole antigen detected in IEC-18 cell lysates as well as a 16.5-kDa fragment found in the media. The sequestered fragment size was formed preferentially when IGF-II was present, whereas the larger fragment size was formed preferentially when IGF-II was absent. Cathepsins B and D did not produce these fragments in vitro and were not detected in IEC-18 media. We conclude that dexamethasone alters IGFBP-2 catabolism through its effects on cathepsin L.

Expression of the insulin-like growth factor-I receptor and proapoptotic Bax and Bak proteins in human colorectal cancer

Insulin-like growth factor-I (IGF-I) and IGF-I receptor (IGF-IR), despite their well-known roles in cell survival and proliferation, can also weakly enhance apoptosis. To study the relationships between the IGF-IR and Bax as well as Bak, 144 cases of colorectal cancer were examined by immunohistochemistry, using the avidin-biotin-peroxidase method. The results were correlated with selected clinicopathological features of colorectal cancer and with the expression of IGF-IR, Bax, and Bak in normal colon mucosa. In Bax-, Bak-, or IGF-IR-positive cancers, the adjacent colorectal mucosa revealed positive immunostaining for these proteins. In the majority of Bax-, Bak-, or IGF-IR-negative tumors, we observed no staining for these proteins in adjacent mucosa. The strong immunostaining for IGF-IR, Bax, and Bak was noted in 50.8, 55.5, and 49.3% of tumors, respectively. We observed positive correlations between IGF-IR and Bax (P < 0.002, r = 0.302), between IGF-IR and Bak (P < 0.0001, r = 0.407), and between Bax and Bak (P < 0.0001, r = 0.474). No relationship was noted between IGF-IR expression and tumor grade, stage, or lymph node status. We found negative associations between Bax, Bak, and tumor grade (P < 0.01 and P < 0.003, respectively), but no relationships between Bax and Bak and tumor stage or between Bax and Bak and lymph node status. Our results demonstrate that, in addition to overexpressed IGF-IR, there are relationships between IGF-IR and proapoptotic proteins in colorectal carcinomas that could contribute to increased cell turnover and the progression of colorectal cancer.

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.

Morphological and transcriptional responses of untransformed intestinal epithelial cells to an oncogenic β-catenin protein

Aberrant transactivation of a certain set of target genes by the beta-catenin and T-cell factor/lymphoid enhancer factor (TCF/LEF) transcription factor complexes has been implicated in the process of intestinal epithelial cells entering early colorectal carcinogenesis. A rat intestinal epithelial cell line IEC6 became elongated, extended protrusions at cell periphery, and increased stress fibers and focal contacts upon the induction of beta-catenin protein stabilized by deletion of the N-terminal glycogen synthase kinase-3beta (GSKbeta) phosphorylation sites (beta-catenin DeltaN89). We used the GeneChiptrade mark oligonucleotide microarray system to examine approximately 24 000 genes and identified 13 genes whose expression was altered during the course of this morphological transformation. Those genes included known negative regulators of the Wnt signaling pathway, Sfrp4 and Axin2; extracellular matrix and related molecule, Hxb and Crtl1; cell adhesion and cytoskeletal proteins, Podxl, Igaf4, and Itab6; and molecules involved in the insulin and insulin-like growth factor (IGF) signaling pathways, Enpp1, Igfbp2, and Sgk. We report the finding that insulin-like growth factor-binding protein-2 (IGFBP2) is a direct target gene of the beta-catenin and TCF/LEF complexes. The IGFBP2 protein interacts with integrins. Disruption of the multigene network system regulating cell adhesion and cytoskeleton may be crucial in the initiation of colorectal carcinogenesis.

Insulin-like growth factor binding protein 2 promotes ovarian cancer cell invasion

BACKGROUND

Insulin-like growth factor binding protein 2 (IGFBP2) is overexpressed in ovarian malignant tissues and in the serum and cystic fluid of ovarian cancer patients, suggesting an important role of IGFBP2 in the biology of ovarian cancer. The purpose of this study was to assess the role of increased IGFBP2 in ovarian cancer cells.

RESULTS

Using western blotting and tissue microarray analyses, we showed that IGFBP2 was frequently overexpressed in ovarian carcinomas compared with normal ovarian tissues. Furthermore, IGFBP2 was significantly overexpressed in invasive serous ovarian carcinomas compared with borderline serous ovarian tumors. To test whether increased IGFBP2 contributes to the highly invasive nature of ovarian cancer cells, we generated IGFBP2-overexpressing cells from an SKOV3 ovarian cancer cell line, which has a very low level of endogenous IGFBP2. A Matrigel invasion assay showed that these IGFBP2-overexpressing cells were more invasive than the control cells. We then designed small interference RNA (siRNA) molecules that attenuated IGFBP2 expression in PA-1 ovarian cancer cells, which have a high level of endogenous IGFBP2. The Matrigel invasion assay showed that the attenuation of IGFBP2 expression indeed decreased the invasiveness of PA-1 cells.

CONCLUSIONS

We therefore showed that IGFBP2 enhances the invasion capacity of ovarian cancer cells. Blockage of IGFBP2 may thus constitute a viable strategy for targeted cancer therapy.

trans-10, cis-12 conjugated linoleic acid reduces insulin-like growth factor-II secretion in HT-29 human colon cancer cells

We previously demonstrated that a mixture of conjugated linoleic acid (CLA) isomers decreases colon cancer incidence in rats treated with 1,2-dimethylhydrazine. Our in vitro studies have also shown that CLA inhibits the growth of HT-29 cells, a human colon cancer cell line. When we compared the individual potencies of the two main isomers found in the mixture of CLA isomers (e.g., cis-9, trans-11 [c9t11] and trans-10, cis-12 [t10c12]), t10c12 CLA decreased viable cell numbers in a dose-dependent manner. By contrast, c9t11 CLA had no effect. Therefore, the present study examined whether the decreased cell growth is related to changes in secretion of insulin-like growth factor (IGF)-II and/or IGF-binding proteins (IGFBPs) that have been shown to regulate HT-29 cell proliferation. Cells were incubated in serum-free medium with various concentrations of the individual CLA isomers, and immunoblot analysis of 24-hour, serum-free, conditioned media using a monoclonal anti-IGF-II antibody was performed. HT-29 cells secreted both mature 7,500 apparent molecular weight (M(r)) and higher-M(r) forms of IGF-II. t10c12 CLA decreased the levels of the higher-M(r) and the mature form of IGF-II in a dose-dependent manner, whereas c9t11 CLA had no effect. Ligand blot analysis of conditioned medium using (125)I-IGF-II revealed that the production of IGFBP-2 and IGFBP-4 was also decreased by t10c12 CLA, whereas c9t11 CLA had no effect. Exogenous IGF-II abrogated the growth inhibition induced by t10c12 CLA. These results indicate that inhibition of HT-29 cell growth by t10c12 CLA may be mediated by decreasing IGF-II secretion in these cells.

Insulin resistance and its contribution to colon carcinogenesis

The insulin resistance-colon cancer hypothesis, stating that insulin resistance may be associated with the development of colorectal cancer, represents a significant advance in colon cancer, as it emphasizes the potential for this cancer to become a modifiable disease. The fact that the incidence of insulin resistance has been increasing in the United States and much of the rest of the Western world where colon cancer remains the second leading cause of cancer death makes the exploration of the interrelationship of these conditions a subject of high priority. Here, we review the salient features of insulin resistance, defined as impaired biological response to the action of insulin. Recent epidemiological studies, evaluating potential associations between colon cancer risk and diabetes mellitus, dietary intake and metabolic factors, and IGF levels in several clinical settings, provide strong support of the insulin resistance-colon cancer hypothesis (without establishing causality). Mechanistically, insulin resistance has been associated with hyperinsulinemia, increased levels of growth factors including IGF-1, and alterations in NF-kappaB and peroxisome proliferator-activated receptor signaling, which may promote colon cancer through their effects on colonocyte kinetics. It is a reasonable expectation that in the not too distant future, critical interventions to the already mapped molecular sequence of events, which link two apparently disparate entities, combined with lifestyle changes could abrogate the development of colon cancer.

Cellular actions of the insulin-like growth factor binding proteins

In addition to their roles in IGF transport, the six IGF-binding proteins (IGFBPs) regulate cell activity in various ways. By sequestering IGFs away from the type I IGF receptor, they may inhibit mitogenesis, differentiation, survival, and other IGF-stimulated events. IGFBP proteolysis can reverse this inhibition or generate IGFBP fragments with novel bioactivity. Alternatively, IGFBP interaction with cell or matrix components may concentrate IGFs near their receptor, enhancing IGF activity. IGF receptor-independent IGFBP actions are also increasingly recognized. IGFBP-1 interacts with alpha(5)beta(1) integrin, influencing cell adhesion and migration. IGFBP-2, -3, -5, and -6 have heparin-binding domains and can bind glycosaminoglycans. IGFBP-3 and -5 have carboxyl-terminal basic motifs incorporating heparin-binding and additional basic residues that interact with the cell surface and matrix, the nuclear transporter importin-beta, and other proteins. Serine/threonine kinase receptors are proposed for IGFBP-3 and -5, but their signaling functions are poorly understood. Other cell surface IGFBP-interacting proteins are uncharacterized as functional receptors. However, IGFBP-3 binds and modulates the retinoid X receptor-alpha, interacts with TGFbeta signaling through Smad proteins, and influences other signaling pathways. These interactions can modulate cell cycle and apoptosis. Because IGFBPs regulate cell functions by diverse mechanisms, manipulation of IGFBP-regulated pathways is speculated to offer therapeutic opportunities in cancer and other diseases.

Overexpression of the insulin-like growth factor I receptor in human colon carcinomas

BACKGROUND

High concentrations of insulin-like growth factor (IGF)-I and IGF-II have been demonstrated in human colonic adenocarcinomas and exert mitogenic effects through paracrine/autocrine interactions with the IGF-I receptor (IGF-IR). However, definitive studies of IGF-IR expression in these tissues have not been performed.

METHODS

To study changes in the levels of the IGF-IR in colorectal carcinoma, we analyzed the expression of IGF-IR in 40 paired samples of normal and carcinomatous colonic tissue by quantitative reverse-transcription-polymerase chain reaction (RT-PCR), immunohistochemistry, and ligand binding.

RESULTS

As measured by RT-PCR, the IGF-IR mRNA ratio in paired tumor and adjacent normal mucosa was higher than 2.0 in 32 of 40 (80%) samples. The overall mean IGF-IR mRNA level was five-fold higher in tumor versus adjacent normal mucosa (P < 0.0001). Overexpression of IGF-IR in colon carcinomas was confirmed at the protein level by immunohistochemistry and receptor-binding studies. Colon carcinoma cells exhibited a positive staining for IGF-IR in 91% of all tumors (30 of 33) whereas the adjacent normal colonic epithelial cells showed only a very faint or no significant IGF-IR immunoreactivity. Radioligand assays and Scatchard analysis in both tissue types revealed a single class of high-affinity IGF-IR-binding sites with a similar dissociation constant (K(d;) 0.14 +/- 0.02 nmol/L, n = 18). However, specific (125)IGF-I-binding and receptor concentrations were elevated in tumor membranes compared with normal mucosa (33.6 +/- 5.6 vs. 22.7 +/- 3.4 fmol/mg protein, P < 0.05). IGF-I affinity crosslinking and sodium dodecyl sulfate-polyacrylamide gel electrophoresis displayed specific bands corresponding to the size of the normal alpha-subunit of the IGF-IR that were more intense in carcinomatous samples. IGF-II mRNA levels were significantly elevated in colorectal carcinomas (P < 0.0001). The IGF-II mRNA ratio in tumor versus normal tissue was elevated more than twofold in 28 of 40 paired samples and a positive correlation was observed between the overexpression of IGF-II and IGF-IR in the tumors.

CONCLUSIONS

Our results demonstrate that, in addition to IGF-II, a strong overexpression of IGF-IR is found in the majority of colorectal carcinomas, supporting the hypothesis of an important role of the IGF system in the pathogenesis of colorectal carcinoma.

Trans-10,cis-12-conjugated linoleic acid inhibits Caco-2 colon cancer cell growth

A commercially available mixture of conjugated linoleic acid (CLA) isomers decreases colon cancer cell growth. We compared the individual potencies of the two main isomers in this mixture [cis-9,trans-11 (c9t11) and trans-10,cis-12 (t10c12)] and assessed whether decreased cell growth is related to changes in secretion of insulin-like growth factor II (IGF-II) and/or IGF-binding proteins (IGFBPs), which regulate Caco-2 cell proliferation. Cells were incubated in serum-free medium with different concentrations of the individual CLA isomers. t10c12 CLA dose dependently decreased viable cell number (55 +/- 3% reduction 96 h after adding 5 microM t10c12 CLA). t10c12 CLA induced apoptosis and decreased DNA synthesis, whereas c9t11 CLA had no effect. Immunoblot analysis of 24-h serum-free conditioned medium using a monoclonal anti-IGF-II antibody revealed that Caco-2 cells secreted both a mature 7,500 molecular weight (M(r)) IGF-II and higher M(r) forms of IGF-II. The levels of the higher M(r) and the mature form of IGF-II were decreased 50 +/- 3% and 22 +/- 2%, respectively, by 5 microM t10c12 CLA. c9t11 CLA had no effect. Ligand blot analysis of conditioned medium using 125I-labeled IGF-II revealed that t10c12 CLA slightly decreased IGFBP-2 production; c9t11 CLA had no effect. Exogenous IGF-II reversed t10c12 CLA-induced growth inhibition and apoptosis. These results indicate that CLA-inhibited Caco-2 cell growth is caused by t10c12 CLA and may be mediated by decreasing IGF-II secretion in Caco-2 cells.

Decreased production of insulin-like growth factor-binding protein (IGFBP)-6 by transfection of colon cancer cells with an antisense IGFBP-6 cDNA construct leads to stimulation of cell proliferation

BACKGROUND

: Previously, we have observed that highly unsaturated dietary (n-3) fatty acids inhibit cell proliferation in conjunction with stimulation of insulin-like growth factor-binding protein (IGFBP)-6 secretion in Caco-2 cells, a human colon carcinoma cell line.

METHODS

: To test the converse hypothesis that inhibition of endogenous IGFBP-6 secretion stimulates Caco-2 cell proliferation, cells were transfected with the antisense IGFBP-6 expression construct or pcDNA3 vector only, and single colonies resistant to G418 sulfate were isolated.

RESULTS

: Our initial studies indicated that three antisense clones grew faster and produced less IGFBP-6 than two pcDNA3 clones, so antisense IGFBP-6 #5 and pcDNA3 #8 were selected for further detailed analysis. Both the control and antisense clones grew in serum-free medium reaching a plateau density at day eight. However, the antisense clone grew at a rate faster than that of the control and reached a final density that was 31 +/- 3% higher than the control. Northern blot, ligand blot and immunoblot analyses revealed that accumulation of IGFBP-6 mRNA and concentrations of IGFBP-6 peptide produced by the antisense clone were decreased by 80-90% compared to the control. The doubling times of the antisense and control clones were 21.9 +/- 0.4 and 24.8 +/- 0.3 h (P < 0.05), respectively. Exogenous IGF-I and IGF-II (0.2-200 nmol/L) stimulated proliferation of both the control and antisense clones in a dose-dependent manner, but the relative potency and efficacy of IGF-II was higher in the antisense clone compared to the control. These results indicate that suppression of IGFBP-6 secretion correlates with an increase in the basal rate of Caco-2 cell growth.

CONCLUSIONS

: Our findings are consistent with the hypothesis that IGFBP-6 inhibits cell growth by binding to endogenously produced IGF-II, thereby preventing IGF-II from interacting with the IGF-I receptor to stimulate cellular proliferation by an autocrine mechanism.

IGFs and IGFBPs: surrogate markers for diagnosis and surveillance of tumour growth?

Insulin-like growth factors (IGFs), IGF receptors, and IGF binding proteins (IGFBPs) constitute the IGF system. Comprehensive data indicate that these factors play a pivotal role in tumorigenesis. Epidemiological data indicate that cancer risk is associated with high serum IGF-I values. Because dysregulation of the IGF system is a frequent pattern in malignancy, IGFs/IGFBPs might represent novel tumour markers that could be useful both for diagnosis and surveillance.

The growth hormone-insulin-like growth factor-I axis and colorectal cancer

The growth hormone (GH)-insulin-like growth factor (IGF)-I axis is an important modulator of growth and development, but in addition to their classical role as endocrine hormones, its components also regulate a wide range of biological functions through paracrine and autocrine mechanisms. Their potent mitogenic and anti-apoptotic effects play a critical role in the regulation of rapidly renewing epithelial cell populations such as those found in the colon. Recent evidence suggests an association between inappropriate regulation of the GH-IGF-I axis and the development of colorectal cancer. However, the molecular mechanisms and signalling pathways responsible are only beginning to be unravelled, as are the relative contributions of the endocrine and autocrine or paracrine effects.

Insulin-like growth factor 1 and oestradiol promote cell proliferation of MCF-7 breast cancer cells: new insights into their synergistic effects

In MCF-7 breast cancer cells, the insulin-like growth factor 1 receptor (IGF-1R) and the oestrogen receptor (ER) are coexpressed and the two signalling systems are engaged in a crosstalk that results in synergistic growth. However, coupling between the signalling cascades is poorly understood. Oestradiol enhances IGF-1R signalling by inducing the expression of insulin receptor substrate 1 (IRS-1), a substrate of the IGF-1R. Oestradiol induced expression of IRS-1 results in enhanced tyrosine phosphorylation of IRS-1 after IGF-1 stimulation, followed by enhanced mitogen activated protein kinase, phosphoinositide 3' kinase, and Akt activation. Oestradiol can also potentiate the effect of IGF-1 on the expression of cyclin D1 and cyclin E, and on the phosphorylation of the retinoblastoma protein (RB). These effects are greatly diminished in SX13 cells, which exhibit a 50% reduction in IGF-1R expression but few functional IGF-1Rs at the surface. Oestradiol and IGF-1 regulate the expression of two cyclin dependent kinase inhibitors, p21 and p27, differently. Whereas IGF-1 increases p21 expression and reduces p27 expression, oestradiol has no effect on p21. In summary, in MCF-7 cells, oestrogen potentiates the effect of IGF-1 on IGF-1R signalling and its effects on certain cell cycle components.

Increased levels of insulin-like growth factor binding protein-2 in sera and tumours from patients with colonic neoplasia with and without acromegaly

OBJECTIVE

Patients with acromegaly are at increased risk of developing colorectal carcinoma and premalignant tubulovillous adenoma. The pathogenesis of these neoplasms could involve a stimulatory effect of serum growth factors on colonic epithelial cell proliferation. The aim of this study was to evaluate changes in (1) serum IGF-I, IGF-II, IGFBP-3 and IGFBP-2 and (2) changes in local expression of IGFBPs and p53 in colonic epithelium in patients with colonic neoplasia with and without acromegaly.

DESIGN

A cross-sectional retrospective study was performed. Fasting serum samples were obtained at the time of colonoscopy for patients with acromegaly and at the time of surgery for patients with colonic neoplasia without acromegaly.

MEASUREMENTS

Serum IGF-I, IGF-II, IGFBP-2 and IGFBP-3 were measured using specific immunoassays. Tissue expression of IGFBP-2, IGFBP-3 and p53 status were determined by immunohistochemistry.

PATIENTS

Group 1: 26 age- and sex-matched control subjects (range 40-69 years); group 2: 18 patients with acromegaly without colonic neoplasia (range 39-68 years); group 3: 18 patients with acromegaly and colonic neoplasia (range 41-74 years, 11 = adenoma, seven = carcinoma); group 4: 19 patients with colonic neoplasia without endocrine disease (range 43-91 years, four = adenoma, 15 = carcinoma). Immunohistochemical staining of colonic biopsies was performed for IGFBP-2, IGFBP-3 and p53 in groups 3 and 4.

RESULTS

Mean serum IGF-I and IGFBP-3 levels were significantly elevated in group 2 (371 +/- 131 microg/l and 6.5 +/- 1.8 mg/l, respectively) and group 3 (379 +/- 174 microg/l and 5.8 +/- 1.6 mg/l, respectively), and significantly reduced in group 4 (103 +/- 36 microg/l and 2.4 +/- 1 mg/l) compared to controls (165 +/- 40 microg/l and 4.7 +/- 1 mg/l; P < 0.0001, P < 0.001, respectively). However, median serum IGFBP-2 levels were significantly elevated in group 3 (P < 0.01) and group 4 (P < 0.0001). Immunostaining for IGFBP-2 showed strong areas of immunoreactivity in the cytoplasm of malignant colonic epithelium compared to benign epithelium. IGFBP-3 immunostaining showed strong areas of immunoreactivity in the cytoplasm and in the nucleus of malignant and benign colonic epithelium compared to the normal epithelium. Nuclear staining for p53 was observed in three patients from group 3 (two carcinoma, one adenoma) and four patients from group 4 (all carcinoma).

CONCLUSION

Our results describe changes in IGFBP-2 expression in colonic neoplasia in patients with and without acromegaly, which suggest that this binding protein may regulate local bioavailability of IGF, which in turn could modulate colonic cell proliferation and/or differentiation.