Insulin-like growth factor-binding protein-3 activates a phosphotyrosine phosphatase. Effects on the insulin-like growth factor signaling pathway

Signaling Pathways of the Insulin-like Growth Factor Binding Proteins

The 6 high-affinity insulin-like growth factor binding proteins (IGFBPs) are multifunctional proteins that modulate cell signaling through multiple pathways. Their canonical function at the cellular level is to impede access of insulin-like growth factor (IGF)-1 and IGF-2 to their principal receptor IGF1R, but IGFBPs can also inhibit, or sometimes enhance, IGF1R signaling either through their own post-translational modifications, such as phosphorylation or limited proteolysis, or by their interactions with other regulatory proteins. Beyond the regulation of IGF1R activity, IGFBPs have been shown to modulate cell survival, migration, metabolism, and other functions through mechanisms that do not appear to involve the IGF-IGF1R system. This is achieved by interacting directly or functionally with integrins, transforming growth factor β family receptors, and other cell-surface proteins as well as intracellular ligands that are intermediates in a wide range of pathways. Within the nucleus, IGFBPs can regulate the diverse range of functions of class II nuclear hormone receptors and have roles in both cell senescence and DNA damage repair by the nonhomologous end-joining pathway, thus potentially modifying the efficacy of certain cancer therapeutics. They also modulate some immune functions and may have a role in autoimmune conditions such as rheumatoid arthritis. IGFBPs have been proposed as attractive therapeutic targets, but their ubiquity in the circulation and at the cellular level raises many challenges. By understanding the diversity of regulatory pathways with which IGFBPs interact, there may still be therapeutic opportunities based on modulation of IGFBP-dependent signaling.

GIPC-Regulated IGFBP-3 Promotes HSC Migration In Vitro and Portal Hypertension In Vivo Through a β1-Integrin Pathway

BACKGROUND & AIMS

Transforming growth factor (TGF-β)-induced activation of quiescent hepatic stellate cells (HSCs) and their transformation to myofibroblasts is a key event in liver fibrosis and portal hypertension. GIPC (also referred to as synectin) is a downstream signal activation molecule of TGF-β and other receptors. In this study, we sought to identify novel genes targeted by TGF-β and GIPC and elucidate if and how they may contribute to liver fibrosis.

METHODS

We performed sequential messenger RNA sequencing analysis on TGF-β-stimulated HSCs and then on TGF-β-stimulated HSCs in the presence and absence of GIPC also referred to as synectin (GIPC) knockdown. Insulin-like growth factor binding protein-3 (IGFBP-3) transport protein emerged as a top activation target of both TGF-β and GIPC. Quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, targeted chromatin immunoprecipitation, and Western blot analysis were done for further confirmation.

RESULTS

IGFBP-3, an insulin growth factor transport protein, emerged as a top activation target of both TGF-β and GIPC, which was confirmed by quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, and Western blot analysis. Targeted chromatin immunoprecipitation showed that GIPC increases the histone 3 lysine 27 (H3K27) acetylation activating mark and concurrently decreases the H3K27 inhibitory trimethylation (H3K27m3) mark, providing an epigenetic correlate to the gene regulation changes. In vivo, global knockout of IGFBP-3 mice resulted in attenuation of HSC activation markers and attenuation of portal pressure in response to chronic liver injury models. Analysis of serum levels from cirrhotic patients also showed an IGFBP-3 increase of more than 2-fold compared with healthy controls. Finally, in vitro mechanism studies showed that IGFBP-3 promotes HSC migration through integrin-dependent phosphorylation of protein kinase B.

CONCLUSIONS

TGF-β up-regulates IGFBP-3 through GIPC, leading to increased HSC migration in vitro and promotes portal hypertension in vivo. These studies support the role of IGFBP-3 as a potential pathophysiologic target or biomarker in chronic liver disease.

HOXC6 predicts invasion and poor survival in hepatocellular carcinoma by driving epithelial-mesenchymal transition

Aberrant expression of HOXC6 has been reported in several malignant tumors, yet little is known about the value of HOXC6 in invasion and prognosis of hepatocellular carcinoma (HCC). HOXC6 expression was positively correlated with high AFP level, liver cirrhosis, larger tumor, vascular invasion and BCLC stage. Kaplan-Meier analysis revealed that HOXC6 was an independent predictor for overall survival (OS) and time to recurrence (TTR). In addition, HOXC6 status could act as prognostic predictor in different risk subgroups. Moreover, HOXC6 maintained its prognostic value in different ability of invasiveness. Furthermore, combination of HOXC6 and serum AFP could be a potential predictor for survival in HCC patients. Additionally, further study showed that HOXC6 may promote invasion of HCC by driving epithelial-mesenchymal transition (EMT). Knockdown of HOXC6 significantly decreased the migration and invasion of HCC cells and changed the expression pattern of EMT markers. An opposite expression pattern of EMT markers was observed in HOXC6-transfected cells. In addition, immunohistochemistry and RT-PCR results further confirmed this correlation. In conclusion, HOXC6 contributes to invasion by inducing EMT pathway and predicts poor prognosis of HCC. HOXC6/AFP expression may help to distinguish the different risks of HCC patients after hepatectomy.

Role of IGF-binding proteins in regulating IGF responses to changes in metabolism

The IGF-binding protein family contains six members that share significant structural homology. Their principal function is to regulate the actions of IGF1 and IGF2. These proteins are present in plasma and extracellular fluids and regulate access of both IGF1 and II to the type I IGF receptor. Additionally, they have functions that are independent of their ability to bind IGFs. Each protein is regulated independently of IGF1 and IGF2, and this provides an important mechanism by which other hormones and physiologic variables can regulate IGF actions indirectly. Several members of the family are sensitive to changes in intermediary metabolism. Specifically the presence of obesity/insulin resistance can significantly alter the expression of these proteins. Similarly changes in nutrition or catabolism can alter their synthesis and degradation. Multiple hormones such as glucocorticoids, androgens, estrogen and insulin regulate IGFBP synthesis and bioavailability. In addition to their ability to regulate IGF access to receptors these proteins can bind to distinct cell surface proteins or proteins in extracellular matrix and several cellular functions are influenced by these interactions. IGFBPs can be transported intracellularly and interact with nuclear proteins to alter cellular physiology. In pathophysiologic states, there is significant dysregulation between the changes in IGFBP synthesis and bioavailability and changes in IGF1 and IGF2. These discordant changes can lead to marked alterations in IGF action. Although binding protein physiology and pathophysiology are complex, experimental results have provided an important avenue for understanding how IGF actions are regulated in a variety of physiologic and pathophysiologic conditions.

Silencing homeobox C6 inhibits colorectal cancer cell proliferation

Homeobox C6 (HOXC6), a member of the homeobox family that encodes highly conserved transcription factors, plays a vital role in various carcinomas. In this study, we used a tissue microarray (TMA) consisting of 462 CRC samples to demonstrate that HOXC6 is more abundantly expressed in colorectal cancer (CRC) tissues than adjacent normal mucosa. Clinicopathological data indicated that higher HOXC6 expression correlated with poor overall survival and was associated with primary tumor location in the right colon, primary tumor (pT) stage 3/4 and primary node (pN) stage 1/2. Multivariate analysis showed that high HOXC6 expression was an independent risk factor for poor CRC patient prognosis. HOXC6 downregulation via lentivirus-mediated expression of HOXC6-targeting shRNA reduced HCT116 cell viability and colony formation in vitro, and reduced growth of subcutaneous xenografts in nude mouse. HOXC6 thus appears to promote CRC cell proliferation and tumorigenesis through autophagy inhibition and mTOR pathway activation.

Role of IGF Binding Proteins in Regulating Metabolism

Insulin-like growth factors (IGFs) circulate in extracellular fluids bound to a family of binding proteins. Although they function in a classical manner to limit the access of the IGFs to their receptors they also have a multiplicity of actions that are independent of this property; they bind to their own receptors or are transported to intracellular and intranuclear sites to influence cellular functions that may directly or indirectly modify IGF actions. The availability of genetically modified animals has helped to determine their functions in a physiological context. These results show that many of their actions are cell type- and context-specific, and have led to a broader understanding of how these proteins function coordinately with IGF-I and -II to regulate growth and metabolism.

Bisphenol-A induces expression of HOXC6, an estrogen-regulated homeobox-containing gene associated with breast cancer

HOXC6 is a homeobox-containing gene associated with mammary gland development and is overexpressed in variety of cancers including breast and prostate cancers. Here, we have examined the expression of HOXC6 in breast cancer tissue, investigated its transcriptional regulation via estradiol (E2) and bisphenol-A (BPA, an estrogenic endocrine disruptor) in vitro and in vivo. We observed that HOXC6 is differentially over-expressed in breast cancer tissue. E2 induces HOXC6 expression in cultured breast cancer cells and in mammary glands of Sprague Dawley rats. HOXC6 expression is also induced upon exposure to BPA both in vitro and in vivo. Estrogen-receptor-alpha (ERα) and ER-coregulators such as MLL-histone methylases are bound to the HOXC6 promoter upon exposure to E2 or BPA and that resulted in increased histone H3K4-trimethylation, histone acetylation, and recruitment of RNA polymerase II at the HOXC6 promoter. HOXC6 overexpression induces expression of tumor growth factors and facilitates growth 3D-colony formation, indicating its potential roles in tumor growth. Our studies demonstrate that HOXC6, which is a critical player in mammary gland development, is upregulated in multiple cases of breast cancer, and is transcriptionally regulated by E2 and BPA, in vitro and in vivo.

A model to explain specific cellular communications and cellular harmony:- a hypothesis of coupled cells and interactive coupling molecules

BACKGROUND

The various cell types and their relative numbers in multicellular organisms are controlled by growth factors and related extracellular molecules which affect genetic expression pathways. However, these substances may have both/either inhibitory and/or stimulatory effects on cell division and cell differentiation depending on the cellular environment. It is not known how cells respond to these substances in such an ambiguous way. Many cellular effects have been investigated and reported using cell culture from cancer cell lines in an effort to define normal cellular behaviour using these abnormal cells.A model is offered to explain the harmony of cellular life in multicellular organisms involving interacting extracellular substances.

METHODS

A basic model was proposed based on asymmetric cell division and evidence to support the hypothetical model was accumulated from the literature. In particular, relevant evidence was selected for the Insulin-Like Growth Factor system from the published data, especially from certain cell lines, to support the model. The evidence has been selective in an attempt to provide a picture of normal cellular responses, derived from the cell lines.

RESULTS

The formation of a pair of coupled cells by asymmetric cell division is an integral part of the model as is the interaction of couplet molecules derived from these cells. Each couplet cell will have a receptor to measure the amount of the couplet molecule produced by the other cell; each cell will be receptor-positive or receptor-negative for the respective receptors. The couplet molecules will form a binary complex whose level is also measured by the cell. The hypothesis is heavily supported by selective collection of circumstantial evidence and by some direct evidence. The basic model can be expanded to other cellular interactions.

CONCLUSIONS

These couplet cells and interacting couplet molecules can be viewed as a mechanism that provides a controlled and balanced division-of-labour between the two progeny cells, and, in turn, their progeny. The presence or absence of a particular receptor for a couplet molecule will define a cell type and the presence or absence of many such receptors will define the cell types of the progeny within cell lineages.

Effects of raloxifene and estrogen on bioactive IGF1 in GH-deficient women

CONTEXT

GH action is attenuated by estrogens and selective estrogen receptor modulators (SERMs) administered orally. During GH therapy in hypopituitary women, co-treatment with raloxifene, a SERM, induced a smaller gain in lean body mass (LBM) compared with estrogen, despite an equal reduction in IGF1. As a higher IGF-binding protein-3 (IGFBP3) level was observed with raloxifene co-treatment, we hypothesize that an increase in IGFBP3 reduced IGF1 bioactivity causing the attenuated anabolic effect.

OBJECTIVE

To assess the effects of 17β-estradiol (E₂) and raloxifene on bioactive IGF1.

DESIGN

In study 1, 12 GH-deficient (GHD) women were randomized to raloxifene 120 mg/day or E₂ 4 mg/day for 1 month. In study 2, 16 GHD women were randomized to 1 month GH treatment alone (0.5 mg/day) and in combination with raloxifene (60 mg/day) or E₂ (2 mg/day). We measured bioactive IGF1, immunoreactive IGF1 and IGF2, and IGFBP3 immunoreactivity and fragmentation.

RESULTS

Raloxifene and estrogen suppressed (P<0.05) total IGF1 equally in GHD and GH-replaced hypopituitary women. In GHD patients, neither raloxifene nor estrogen affected bioactive IGF1. GH significantly increased IGF1 bioactivity, an effect attenuated by co-treatment with raloxifene (Δ -23 ± 7%, P<0.01) and estrogen (Δ -26 ± 3%, P=0.06). Total IGF1 correlated (r(2)=0.54, P<0.001) with bioactive IGF1, which represented 3.1 ± 0.2% of the total IGF1, irrespective of the treatments. Total IGF2 was unchanged by raloxifene and estrogen treatment. IGFBP3 was significantly higher during raloxifene administration, whereas no differences in IGFBP3 fragmentation were observed.

CONCLUSION

Raloxifene effect on bioactive IGF1 is similar to that of estrogen despite higher IGFBP3 levels during raloxifene administration. We conclude that the observed different effects on LBM between raloxifene and estrogen treatments cannot be explained by differences in IGF1 bioactivity.

TGF-β-induced expression of IGFBP-3 regulates IGF1R signaling in human osteosarcoma cells

Signaling pathways initiated by transforming growth factor-β (TGF-β) and insulin-like growth factors (IGFs) are important in osteosarcoma cell growth. We have investigated a role for endogenous IGF binding protein-3 (IGFBP-3) in mediating cross-talk between TGF-β receptor and type I IGF receptor (IGF1R) signaling pathways in MG-63 osteosarcoma cells. TGF-β1 indirectly activated the Ras/Raf/MAPK pathway and induced the expression of IGFBP-3, an important regulator of IGF1R activity. IGFBP-3 attenuated TGF-β1 activation of ERK1/2 and Akt in MG-63 cells, and inhibited TGF-β1-induced cell cycle progression and proliferation. This effect of IGFBP-3 was blocked by inhibiting IGF1R signaling. TGF-β1 phosphorylated Smad2 on the non-receptor substrate sites (Ser245/250/255). Blocking the TGF-β1-induced expression of IGFBP-3 enhanced pSmad2(Ser245/250/255) and increased its nuclear accumulation. These results suggest an important role for TGF-β1 in osteosarcoma cell growth, with the induction of IGFBP-3 by TGF-β1 serving in a negative-feedback loop to control cell growth by preventing activation of the IGF1R.

Insulin-like growth factor binding protein-3 (IGFBP-3): Novel ligands mediate unexpected functions

In addition to its important role in the regulation of somatic growth by acting as the major circulating transport protein for the insulin-like growth factors (IGFs), IGF binding protein-3 (IGFBP-3) has a variety of intracellular ligands that point to its function within major signaling pathways. The discovery of its interaction with the retinoid X receptor has led to the elucidation of roles in regulating the function of several nuclear hormone receptors including retinoic acid receptor-α, Nur77 and vitamin D receptor. Its interaction with the nuclear hormone receptor peroxisome proliferator-activated receptor-γ is believed to be involved in regulating adipocyte differentiation, which is also modulated by IGFBP-3 through an interaction with TGFβ/Smad signaling. IGFBP-3 can induce apoptosis alone or in conjunction with other agents, and in different systems can activate caspases -8 and -9. At least two unrelated proteins (LRP1 and TMEM219) have been designated as receptors for IGFBP-3, the latter with a demonstrated role in inducing caspase-8-dependent apoptosis. In contrast, IGFBP-3 also has demonstrated roles in survival-related functions, including the repair of DNA double-strand breaks through interaction with the epidermal growth factor receptor and DNA-dependent protein kinase, and the induction of autophagy through interaction with GRP78. The ability of IGFBP-3 to modulate the balance between pro-apoptotic and pro-survival sphingolipids by regulating sphingosine kinase 1 and sphingomyelinases may be integral to its role at the crossroads between cell death and survival in response to a variety of stimuli. The pleiotropic nature of IGFBP-3 activity supports the idea that IGFBP-3 itself, or pathways with which it interacts, should be investigated as targets of therapy for a variety of diseases.

Adipokines, insulin-like growth factor binding protein-3 levels, and insulin sensitivity in women with polycystic ovary syndrome

BACKGROUND/AIMS

Many women with polycystic ovary syndrome (PCOS) exhibit insulin resistance. Adipose tissue plays an important role in insulin resistance, and adipokines including tumor necrosis factor (TNF)-α and adiponectin are altered in PCOS. Insulin-like growth factor binding protein-3 (IGFBP-3), alone or in conjunction with other adipokines, is also associated with insulin resistance. We evaluated the effects of TNF-α, adiponectin, and IGFBP-3 on insulin sensitivity and the relationships among these proteins in women with PCOS.

METHODS

We recruited 40 women with PCOS and 40 age- and body mass index (BMI)-matched regular cycling women (controls). The women were divided into obese (BMI ≥ 25 kg/m(2)) and nonobese (BMI < 25 kg/m(2)) groups. Anthropometric measurements were performed, and serum levels of TNF-α, adiponectin, and IGFBP-3 were determined. Insulin sensitivity was estimated using the metabolic clearance rate (MCR) of glucose calculated from the oral glucose tolerance test.

RESULTS

Serum levels of TNF-α and IGFBP-3 did not differ between the PCOS and control groups, but adiponectin levels in the PCOS group were lower than those in control women in the nonobese group (p < 0.05). TNF-α, adiponectin, and IGFBP-3 levels were not correlated with each other in women with PCOS, but a significant positive correlation was observed between adiponectin levels and MCR (p < 0.05). Multiple regression analysis revealed that adiponectin levels were significantly associated with insulin sensitivity (p < 0.05) in women with PCOS.

CONCLUSIONS

IGFBP-3 and TNF-α levels were not associated with insulin sensitivity, but adiponectin levels were related to insulin sensitivity in women with PCOS.

Transcriptional regulation of MDR-1 by HOXC6 in multidrug-resistant cells

Resistance to chemotherapeutic drugs is a significant clinical problem in the treatment of cancer and this resistance has been linked to the cellular expression of multidrug-efflux transporters. The aim of this study was to explore the role of HOXC6 in the regulation of multidrug resistance (MDR) to chemotherapeutic drugs. The HOXC6 gene was identified as being overexpressed in drug-resistant cells compared with parental cell lines. Transfection assays demonstrated that HOXC6 activated MDR-1 promoter activity. A series of MDR-1 promoter deletion mutants was examined and the minimal HOXC6-responsive region was identified to be in the TAAT motif (-2243 bp) of the MDR-1 promoter. Interestingly, overexpression of HOXC6 in the parental cell lines resulted in the upregulation of MDR-1 expression. The inhibition of HOXC6 using small interfering RNA led to the repression of MDR-1. We determined that knockdown of HOXC6 expression in MDR cells increased their sensitivity to paclitaxel. Flow cytometry analysis suggested that siHOXC6 could induce paclitaxel-induced apoptosis and that this was accompanied by an increased accumulation and a decreased release of paclitaxel. Taken together, our findings suggest that HOXC6 expression is an important mechanism of chemotherapeutic drug resistance via its regulation of MDR-1.

HOXC6 is deregulated in human head and neck squamous cell carcinoma and modulates Bcl-2 expression

Homeobox C6 (HOXC6) genes belong to the homeoprotein family of transcription factors, which play an important role in morphogenesis and cellular differentiation during embryonic development. The aim of this study was to explore the role of HOXC6 in the regulation of Bcl-2 in human head and neck squamous cell carcinoma (HNSCC). The HOXC6 and Bcl-2 gene were identified as being overexpressed in HNSCC tissue and cell lines. Transfection assays demonstrated that HOXC6 increased the levels of Bcl-2 mRNA and protein. A luciferase reporter assay suggested that HOXC6 induced activity of the Bcl-2 promoter. A series of Bcl-2 promoter deletion mutants were examined and the minimal HOXC6-responsive region was identified to be in the TAAT motif (-420 bp) of the Bcl-2 promoter. Interestingly, the inhibition of HOXC6 using siRNA led to the repression of Bcl-2 expression and induced caspase-3-dependent apoptosis; overexpression of HOXC6 in HNSCC cells increased the resistance to paclitaxel-induced apoptosis. Together, our findings suggest that HOXC6 is an important mechanism of the anti-apoptotic pathway via regulation of Bcl-2 expression.

Serum IGFBP-3 is a more effective predictor than IGF-1 and IGF-2 for the development of hepatocellular carcinoma in patients with chronic HCV infection

Hepatocellular carcinoma (HCC) contributes to 14.8% of all cancer mortality in Egypt, which has a high prevalence of hepatitis C virus (HCV). We have previously shown alterations in the insulin-like growth factor-1 (IGF-1) receptor signalling pathway during experimental hepatocarcinogenesis. The aim of this study was to determine whether serum levels of IGF-1, IGF-2 and IGFBP-3 can be used to discriminate between HCC and the stages of hepatic dysfunction in patients with liver cirrhosis assessed by the Child-Pugh (CP) score, and to correlate these levels with HCC stages. We recruited 241 subjects to the present study; 79 with liver cirrhosis, 62 with HCV-induced HCC and 100 age-matched controls. Results showed that serum levels of IGF-1, IGF-2 and IGFBP-3 were reduced significantly in cirrhosis and HCC patients in comparison to the controls, and that this reduction negatively correlated with the CP scores. However, only IGFBP-3 levels showed significant negative correlation with α-fetoprotein levels. The reduction in IGF-1 and IGFBP-3 but not IGF-2 levels was significant in HCC in comparison to patients with cirrhosis. None of the parameters significantly correlated with the HCC stage. IGFBP-3 levels discriminated between cirrhosis and HCC at a sensitivity of 87%, a specificity of 80% and a cut-off value of <682.6 ng/ml. In conclusion, although our results showed that serum IGF-1, IGF-2 and IGFBP-3 are reduced with the progression of hepatic dysfunction, only IGFBP-3 may be considered as the most promising serological marker for the prediction of the development of HCC in the chronic HCV patients with liver cirrhosis.

Insulin-like growth factor II in hepatocellular carcinoma

Hepatocellular carcinoma is one of the most common malignant human tumors. Hepatocarcinogenesis is a multistep process with a multifactorial etiology. Chronic hepatitis B and hepatitis C virus infection, alcohol drinking and cirrhosis of any etiology are the major risk factors for hepatocellular carcinoma. Growth factors, their receptors and related proteins are involved in the process of malignant transformation. The IGF axis is involved in the proliferation and differentiation of normal, transformed and malignant hepatocytes. In the context of hepatocarcinogenesis, IGF-II has, in particular, been investigated thoroughly. Increased IGF-II bioavailability, protease activity of IGF-binding proteins and IGF-I receptor expression, decreased expression of IGF-II receptor and IGF-binding proteins are thought to contribute to hepatocellular carcinoma genesis. This review will first focus on the role of the IGF axis in hepatocarcinogenesis. In the second part it will emphasize circulating IGF-II levels in chronic liver disease and hepatocellular carcinoma, and diagnostic application of serum IGF-II level in both small and larger hepatocellular carcinoma.

Insulin-like growth factor-I regulation of immune function: a potential therapeutic target in autoimmune diseases?

This topically limited review explores the relationship between the immune system and insulin-like growth factors (IGF-I and IGF-II) and the proteins through which they act, including IGF-I receptor (IGF-IR) and the IGF-I binding proteins. The IGF/IGF-IR pathway plays important and diverse roles in tissue development and function. It regulates cell cycle progression, apoptosis, and the translation of proteins. Many of the consequences ascribed to IGF-IR activation result from its association with several accessory proteins that are either identical or closely related to those involved in insulin receptor signaling. Relatively recent awareness that IGF-I and IGF-IR regulate immune function has cast this pathway in an unexpected light; it may represent an important switch governing the quality and amplitude of immune responses. IGF-I/IGF-IR signaling may also participate in the pathogenesis of autoimmune diseases, although its relationship with these processes seems complex and relatively unexplored. On the one hand, IGF-I seems to protect experimental animals from developing insulin-deficient diabetes mellitus. In contrast, activating antibodies directed at IGF-IR have been detected in patients with Graves' disease, where the receptor is overexpressed by multiple cell types. The frequency of IGF-IR+ B and T cells is substantially increased in patients with that disease. Potential involvement of IGF-I and IGF-IR in the pathogenesis of autoimmune diseases suggests that this pathway might constitute an attractive therapeutic target. IGF-IR has been targeted in efforts directed toward drug development for cancer, employing both small-molecule and monoclonal antibody approaches. These have been generally well-tolerated. Recognizing the broader role of IGF-IR in regulating both normal and pathological immune responses may offer important opportunities for therapeutic intervention in several allied diseases that have proven particularly difficult to treat.

Growth factors as active participants in carcinogenesis: a perspective

Growth factors are low molecular peptides active in the stimulation of cell proliferation and in the regulation of embryonic development and cellular differentiation. Significant progress has been made in developing effective strategies to treat human malignancies with new chemical compounds based on a rationale directed against various components of signaling pathways. Many of these drugs target a growth factor receptor--for instance, in the form of monoclonal antibodies or inhibitors of tyrosine kinases, such as monoclonal antibodies against epidermal growth factor receptors used in treating certain types of breast cancer. Imatinib mesylate [Gleevec]) is an excellent example of mediators of signal transduction, such as tyrosine kinases. Growth factors proper are used to ameliorate various and sometimes fatal side effects of cytotoxic and/or myelosuppressive chemotherapy. Basic characteristics of several growth families are discussed with therapeutic modalities based on growth factor activity or, more often, inhibition of such activity.

The Sex-determining region Y-box 4 and homeobox C6 transcriptional networks in prostate cancer progression: crosstalk with the Wnt, Notch, and PI3K pathways

The transforming growth factor beta, Hedgehog, Notch, and Wnt signaling pathways all play critical roles in the development and progression of prostate cancer. It is becoming increasingly apparent that these pathways may intersect with developmentally important transcription factors such as the sex-determining region Y-box 4 (SOX4), homeobox C6, enhancer of zeste 2, and ETS-related gene, which are up-regulated in prostate cancers. For example, identification of the downstream targets of SOX4 and homeobox C6 suggests that these factors may cooperate to activate the Notch pathway and the PI3K/AKT pathway, possibly in response to Wnt signals. PI3K/AKT activation likely occurs indirectly via up-regulation of growth factor receptors, while Notch activation is secondary to up-regulation of Notch pathway components. In addition, SOX4 may affect terminal differentiation via regulation of other transcription factors such as NKX3.1 and MLL, and regulation of components of the microRNA pathway such as Dicer and Argonaute 1. The evidence supporting activation of these pathways in prostate cancer progression suggests that combinations of compounds targeting them may be of benefit to patients with aggressive, metastatic disease.

Perspectives in mammalian IGFBP-3 biology: local vs. systemic action

Insulin-like growth factor (IGF) binding protein (IGFBP)-3 has traditionally been defined by its role as a binding protein and its association with IGF delivery and availability. Development of non-IGF binding IGFBP-3 analogs and the use of cell lines devoid of type 1 IGF receptors (IGF-R) have led to critical advances in the field of IGFBP-3 biology. These studies show that IGFBP-3 has IGF-independent roles in inhibiting cell proliferation in cancer cell lines. Nuclear transcription factor, retinoid X receptor (RXR)-alpha, and IGFBP-3 functionally interact to reduce prostate tumor growth and prostate-specific antigen in vivo. Moreover, IGFBP-3 inhibits insulin-stimulated glucose uptake into adipocytes independent of IGF. The purpose of this review is to highlight IGFBP-3 as a novel effector molecule and not just another "binding protein" by discussing its IGF-independent actions on metabolism and cell growth. Although this review presents studies that assume the role of IGFBP-3 as either an endocrine or autocrine/paracrine molecule, these systems may not exist as distinct entities, justifying the examination of IGFBP-3 in an integrated model. Also, we provide an overview of factors that regulate IGFBP-3 availability, including its production, methylation, and ubiquitination. We conclude with the role of IGFBP-3 in whole body systems and possible future applications of IGFBP-3 in physiology.

Genome-wide analysis of the homeobox C6 transcriptional network in prostate cancer

Homeobox transcription factors are developmentally regulated genes that play crucial roles in tissue patterning. Homeobox C6 (HOXC6) is overexpressed in prostate cancers and correlated with cancer progression, but the downstream targets of HOXC6 are largely unknown. We have performed genome-wide localization analysis to identify promoters bound by HOXC6 in prostate cancer cells. This analysis identified 468 reproducibly bound promoters whose associated genes are involved in functions such as cell proliferation and apoptosis. We have complemented these data with expression profiling of prostates from mice with homozygous disruption of the Hoxc6 gene to identify 31 direct regulatory target genes of HOXC6. We show that HOXC6 directly regulates expression of bone morphogenic protein 7, fibroblast growth factor receptor 2, insulin-like growth factor binding protein 3, and platelet-derived growth factor receptor alpha (PDGFRA) in prostate cells and indirectly influences the Notch and Wnt signaling pathways in vivo. We further show that inhibition of PDGFRA reduces proliferation of prostate cancer cells, and that overexpression of HOXC6 can overcome the effects of PDGFRA inhibition. HOXC6 regulates genes with both oncogenic and tumor suppressor activities as well as several genes such as CD44 that are important for prostate branching morphogenesis and metastasis to the bone microenvironment.

IGFBP-3 sensitizes prostate cancer cells to interferon-gamma-induced apoptosis

OBJECTIVE

Insulin-like growth factor binding protein-3 (IGFBP-3) has been shown to exhibit diverse biological actions, including IGF-independent effects on cell growth and cell death. Here we report that IGFBP-3 sensitizes prostate cancer cells to interferon-gamma (IFN-gamma)-induced apoptosis and inhibition of cell proliferation.

DESIGN

The cell growth or cell death of prostate cells in response to the treatments of IGFBPs and/or IFN-gamma was measured, and the signaling pathways mediating these actions assessed.

RESULTS

Cell proliferation was minimally affected when M12 prostate cancer cells were treated with exogenous IGFBP-3 (1-5 microg/ml), IGFBP-1 (1-5 microg/ml) or IFN-gamma (20 U/ml). However, strong inhibition of cell growth and significant apoptosis were observed when M12 cells were co-treated with IGFBP-3 and IFN-gamma, but not with IGFBP-1 and IFN-gamma. These effects were IGF-independent and appear not to require intracellular localization of IGFBP-3, as similar results were obtained with mutants of IGFBP-3 that either could not bind IGF or has impaired ability to be internalized. Further analyses revealed that IGFBP-3, but not IGFBP-1, could significantly enhance the weak tyrosine phosphorylation of STAT1 induced by IFN-gamma (20 U/ml) alone. The IGFBP-3-promoted apoptosis in the presence of IFN-gamma could also be abrogated by blockade of the mTOR pathway with its pharmacological inhibitors, LY294002 or rapamycin.

CONCLUSIONS

These results demonstrated that in a cancer cell line not responsive to exogenous IGFBP-3 alone, IGFBP-3 sensitized the cells to the anti-proliferative, proapoptotic actions of IFN-gamma through an IGF-independent, STAT1- and mTOR-dependent mechanism.

Contribution of the orphan nuclear receptor Nur77 to the apoptotic action of IGFBP-3

Tumor suppression by insulin-like growth factor-binding protein-3 (IGFBP-3) has been demonstrated to occur via insulin-like growth factor-dependent and -independent mechanisms in vitro and in vivo. We have recently described IGFBP-3-induced mitochondrial translocation of the nuclear receptors RXRalpha/Nur77 in the induction of prostate cancer (CaP) cell apoptosis. Herein, we demonstrate that IGFBP-3 and Nur77 associate in the cytoplasmic compartment in 22RV1 CaP cells. Nur77 is a major component of IGFBP-3-induced apoptosis as shown by utilizing mouse embryonic fibroblasts (MEFs) derived from Nur77 wild-type and knockout (KO) mice. However, dose-response experiments revealed that a small component of IGFBP-3-induced apoptosis is Nur77 independent. Reintroduction of Nur77 into Nur77 KO MEFs restores full responsiveness to IGFBP-3. IGFBP-3 induces phosphorylation of Jun N-terminal kinase and inhibition of Akt phosphorylation and activity, which have been associated with Nur77 translocation. Finally, IGFBP-3 administration to CaP xenografts on SCID mice induced apoptosis and translocated Nur77 out of the nucleus. Taken together, our results verify an important role for the orphan nuclear receptor Nur77 in the apoptotic actions of IGFBP-3.

Aberrant promoter methylation of insulin-like growth factor binding protein-3 gene in human cancers

Insulin-like growth factor binding protein-3 (IGFBP-3) is postulated to be a mediator of growth suppression signals. Here, we examined the methylation status of IGFBP-3 to correlate to clinicopathological factors in human cancers. The methylation status of IGFBP-3 was determined by bisulfite DNA sequencing and was correlated with expression semi-quantified by real-time RT-PCR to develop a methylation-specific PCR (MSP) assay for IGFBP-3. Using the MSP assay, we examined the methylation status of IGFBP-3 in gastric cancer (GC), colorectal cancer (CRC), breast cancer (BC) and malignant mesothelioma (MM). IGFBP-3 methylation was detected in 6 of 13 (46%) and 16 of 24 (67%) GC cell lines and tumors, respectively; 4 of 8 (50%) and 15 of 26 (58%) CRC cell lines and tumors, respectively; 3 of 11 (27%) and 7 of 39 (18%) BC cell lines and tumors, respectively and 1 of 5 (20%) and 18 of 56 (32%) MM cell lines and tumors, respectively. Interestingly, the methylation status of MM specimens from Japanese patients (75%, 12 out of 16 patients) was significantly higher than those from the USA (15%, 6 out of 40 patients) (p < 0.0001), suggesting the presence of ethnic differences in the IGFBP-3 methylation status. We also found that IGFBP-3 methylation was preferentially present in GCs arising in the lower-third of the stomach (p = 0.079). In summary, our results showed that IGFBP-3 methylation played an important role in the silencing of its expression, suggesting that IGFBP-3 may act as a tumor suppressor gene in several human cancers examined.

Insulin-like growth factor binding protein-3 induces insulin resistance in adipocytes in vitro and in rats in vivo

Insulin-like growth factor binding protein (IGFBP)-3 binds to IGF and modulates their actions and also possesses intrinsic activities. We investigated its effects on insulin action and found that when IGFBP-3 was added to fully differentiated 3T3-L1 adipocytes in culture, insulin-stimulated glucose transport was significantly inhibited to 60% of control in a time- and dose-dependent manner. Tumor necrosis factor (TNF)-alpha treatment also inhibited glucose transport to the same degree as IGFBP-3 and, in addition, increased IGFBP-3 levels 3-fold. Co-treatment with TNF-alpha and IGFBP-3 antisense partially prevented the inhibitory effect of TNF-alpha on glucose transport, indicating a role for IGFBP-3 in cytokine-induced insulin resistance. Insulin-stimulated phosphorylation of the insulin receptor was markedly decreased by IGFBP-3 treatment. IGFBP-3 treatment suppressed adiponectin expression in 3T3-L1 adipocytes. Infusion of IGFBP-3 to Sprague-Dawley rats for 3 h decreased peripheral glucose uptake by 15% compared with controls as well as inhibiting glycogen synthesis. Systemic administration of IGFBP-3 to rats for 7 d resulted in a dramatic 40% decrease in peripheral glucose utilization and glycogen synthesis. These in vitro and in vivo findings demonstrate that IGFBP-3 has potent insulin-antagonizing capability and suggest a role for IGFBP-3 in cytokine-induced insulin resistance and other mechanisms involved in the development of type-2 diabetes.

The role of the IGF system in cancer growth and metastasis: overview and recent insights

IGF-I receptor (IGF-IR) signaling and functions are mediated through the activities of a complex molecular network of positive (e.g., type I IGF) and negative (e.g., the type II IGF receptor, IGF-IIR) effectors. Under normal physiological conditions, the balance between the expression and activities of these molecules is tightly controlled. Changes in this delicate balance (e.g., overexpression of one effector) may trigger a cascade of molecular events that can ultimately lead to malignancy. In recent years, evidence has been mounting that the IGF axis may be involved in human cancer progression and can be targeted for therapeutic intervention. Here we review old and more recent evidence on the role the IGF system in malignancy and highlight experimental and clinical studies that provide novel insights into the complex mechanisms that contribute to its oncogenic potential. Controversies arising from conflicting evidence on the relevance of IGF-IR and its ligands to human cancer are discussed. Our review highlights the importance of viewing the IGF axis as a complex multifactorial system and shows that changes in the expression levels of any one component of the axis, in a given malignancy, should be interpreted with caution and viewed in a wider context that takes into account the expression levels, state of activation, accessibility, and functionality of other interacting components. Because IGF targeting for anticancer therapy is rapidly becoming a clinical reality, an understanding of this complexity is timely because it is likely to have an impact on the design, mode of action, and clinical outcomes of newly developed drugs.

The GH-IGF-IGFBP axis is changed in Turner syndrome: partial normalization by HRT

BACKGROUND

We recently described increased insulin-like growth factor binding protein 3 (IGFBP-3) proteolysis in the circulation in adult Turner syndrome (TS), with normalization during sex hormone replacement therapy (HRT), suggesting the presence of a sex hormone regulated IGFBP-3 proteolytic activity.

OBJECTIVE

To study the GH-IGF-IGFBP axis in TS without and during HRT, and to further characterize the nature of the IGFBP-3 proteolytic activity.

MATERIAL

23 women with TS before and during HRT, and 24 healthy age-matched women.

METHODS

The study included measurements of the acid-labile subunit (ALS), IGFBP-1, -2 and -3 (immunoreactive and Western ligand blot (WLB)), IGFBP-4 (WLB) and IGF-I bioactivity. To determine the molecular distribution of IGFBP-3, serum from patient and controls was subjected to neutral size-exclusion chromatography followed by determination of the IGFBP profile by WLB and immunoassay. Finally, the inhibitor characteristic of in vitro IGFBP-3 proteolytic activity in serum was determined.

RESULTS

Immunoreactive IGF-I was normal, while IGF-I bioactivity was decreased in TS. Immunoreactive IGFBP-1, -2 and -3 were normal, while WLB-IGFBPs were all reduced, but increased in response to HRT. The IGFBP-3 ternary complex was significantly reduced in TS, and increased in response to HRT, while the non-ternary complexed IGFBP-3 remained unaffected by treatment. In vitro IGFBP-3 proteolytic activity in serum was abolished by aprotinin, while EDTA and zinc chloride had no inhibitory effects, suggesting the presence of a serine protease. 17beta-estradiol had no direct inhibitory effect on the IGFBP-3 proteolytic activity in vitro. Size-exclusion chromatography showed that the protease had a molecular mass of more than 500 kDa.

CONCLUSION

The GH-IGF-IGFBP axis is profoundly disturbed in TS, with a partly normalizing effect of HRT. A sex hormone-dependent IGFBP-3 proteolytic activity (serine protease) leads to destabilization of the 150 kDa IGFBP-3 ternary complex in TS. During HRT both IGFBP-3 proteolytic activity and ternary complex formation is normalized.

Central and opposing effects of IGF-I and IGF-binding protein-3 on systemic insulin action

IGF-I is recognized as an insulin sensitizer at the liver and muscle, while recent evidence suggests that IGF-binding protein (IGFBP)-3 acts as an insulin antagonist. As there is a paucity of IGF-I receptors in the liver and as the IGF-IGFBP system in the central nervous system is emerging as physiologically relevant, we examined whether the effects of IGF-I and IGFBP-3 on insulin action are mediated through central mechanisms. Intracerebroventricular (ICV) infusion of IGF-I during the insulin clamp (3 mU x kg(-1) x min(-1)) resulted in significant improvement in hepatic insulin action (50%, P < 0.05). In contrast, ICV infusion of IGFBP-3 significantly impaired insulin action at the liver (45% increase in hepatic glucose production, P < 0.01). While IGF-I marginally increased peripheral glucose uptake, IGFBP-3 significantly decreased peripheral glucose uptake (approximately 30%, P < 0.01). As the nuclear localization signal mutant IGFBP-3, which has a normal affinity to IGFs but binds other IGFBP-3 partners poorly and fails to normally internalize, has reduced central activity on metabolism, we conclude that the effects of IGFBP-3 on the hypothalamus involve activity mediated by interfacing with other molecules in addition to IGFs. Marked, opposing, and independent physiological effects of IGF-I and IGFBP-3 through central mechanisms may have implications on potential strategies in specific modulation of peripheral insulin action.

Insulin-like growth factor binding protein-3 in extracellular matrix stimulates adhesion of breast epithelial cells and activation of p44/42 mitogen-activated protein kinase

IGF-binding protein-3 (IGFBP-3) is a multifunctional protein that regulates the potent mitogenic and antiapoptotic effects of IGF-I and IGF-II and exerts bioactivity independent of modulating IGF receptor activation. Previous studies have shown that in solution, IGFBP-3 binds constituent proteins of the extracellular matrix (ECM) such as fibronectin and collagen and is present in ECM deposited by fibroblasts in vitro; however, binding of IGFBP-3 to matrix has not been characterized, nor has its function in this environment been investigated. In this study, we show that IGFBP-3 binds to ECM deposited by human breast epithelial and cancer cells and neonatal human fibroblasts. IGF-I and heparin blocked binding of IGFBP-3 to matrix when added with the binding protein but were unable to displace IGFBP-3 already bound to the matrix. IGF-I bound to matrix-immobilized IGFBP-3 with approximately 25-fold reduced affinity compared with IGFBP-3 in solution. Mutation of the C-terminal basic domain of IGFBP-3 (228KGRKR-->MDGEA) resulted in markedly reduced binding to matrix compared with wild-type IGFBP-3, whereas mutation of the adjacent consensus heparin-binding domain (220KKK-->HSR) had relatively little effect. In the presence of matrix-bound IGFBP-3, adhesion of breast epithelial cells was increased by approximately 25%, and activation of the signaling pathway intermediate p44/42 MAPK was enhanced greater than 3-fold. These results indicate a previously unrecognized and potentially important role for IGFBP-3 in the extracellular matrix.

Einfluss von Ischämie/Hypoxie auf die HIF-1-Aktivität und Expression von hypoxieabhängigen Genen in der Kochlea der neugeborenen Ratte

BACKGROUND

Transcription factor HIF-1 (hypoxia-inducible factor-1) regulates the expression of genes which are involved in glucose supply, growth, metabolism, redox reactions and blood supply. Hypoxia and ischemia play an important role in the pathogenesis of tinnitus and hearing loss. Therefore, HIF-1 activity and the expression of HIF-1 dependent genes in the cochlea were examined under ischemic and hypoxic conditions.

MATERIAL AND METHODS

For the HIF-1 analysis, single-cell cultures of the organ of Corti (OC), stria vascularis (SV) and modiolus (MOD) were used. mRNA expression was analyzed in the organotypic culture using a microarray technique (RN U34-chip, Affymetrix).

RESULTS

Ischemia (hypoxia without glucose) and pure hypoxia increase the HIF-1 activity identically, with the highest increase found in MOD and OC. The HIF-1 alpha mRNA levels were found to be higher in SV than in the OC and MOD. During culturing, there is a clear increase in HIF-1 alpha mRNA and the expression of a number of HIF-1 dependent genes, such as Gapdh/glyceraldehyde-3-phosphate dehydrogenase, Slc2a1/solute carrier family 2 (facilitated glucose transporter), member 1, Tf/transferrin and Tfrc/transferrin receptor, in all three regions. In SV, MOD and OC, increase in the expression of Hmox1/hemoxygenase 1, Nos2/nitric oxide synthase, inducible and Tfrc is particularly high. Hypoxia (5 h) results in an increased expression of Igf2/Insulin-like growth factor 2.

CONCLUSION

The present data underline the contribution of radical forming processes to the pathogenesis of inner ear diseases. For experimental research, it is important to note that organotypic culture may be coupled with hypoxia.

Effects of insulin-like growth factor (IGF) binding protein-3 (IGFBP-3) on endometrial cancer (HHUA) cell apoptosis and EGF stimulated cell proliferation in vitro

OBJECTIVE

IGFBP-3 has been demonstrated to stimulate or inhibit cell proliferation independently of its ability to bind IGF and a specific IGFBP-3 receptor has been proposed. EGF has been implicated in the cancer development and carcinogenesis. Only limited data are available on the crosstalk between IGFBP-3 signaling and EGF induced cell survival and signal transduction. The current studies were undertaken to characterize IGFBP-3 binding to endometrial cancer cells (HHUA) and determine its biological effects, as well as whether IGFBP-3 exposure alters the cell proliferation stimulated by EGF.

METHODS

Cell proliferation and apoptosis were analyzed by ELISA using specific antibodies. The interaction between HHUA cell and IGFBP-3 was analyzed using a biosensor. The phosphorylation abundance of specific proteins and their phosphorylation in response to EGF and IGFBP-3 was analyzed by immunoprecipitation followed by immunoblotting.

RESULTS

Biosensor analysis showed that IGFBP-3 could bind to HHUA cell surface. IGFBP-3 inhibited BrdU uptake, potentiated ssDNA production and induced p53 in HHUA cells. Although EGF stimulated HHUA cell proliferation and Akt phosphorylation, IGFBP-3 inhibited cell proliferation and Akt phosphorylation that had been stimulated by EGF. However, EGF receptor phosphorylation and expression were not reduced by IGFBP-3. Since HHUA cells lack IGF receptors and do not show biological response to IGF these results suggest that IGFBP-3 can bind to HHUA cells, inhibit cell proliferation and induce apoptosis independently of its ability to bind to IGFs possibly by binding to an IGFBP-3 receptor.

CONCLUSIONS

Taken together these findings demonstrate that IGFBP-3 binds to HHUA cell surface, and inhibits cell division induced by EGF, possibly by modulating the EGF-mediated signal transduction system.

Insulin-like growth factor-I, insulin-like growth factor binding protein-3 and the risk of fibrocystic breast conditions among Chinese women

We investigated whether circulating insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-3 (IGFBP-3) levels are associated with the risk of fibrocystic breast conditions (FBC), in a case-control study nested within a randomized trial of breast self-examination conducted in Shanghai, China. Participants were enrolled during 1989-1991 and were followed over 10 years for the development of breast diseases. Controls (n = 897) were frequency-matched by age to cases (n = 451), who were diagnosed with FBC between 1995 and 2000. Circulating IGF-I and IGFBP-3 levels and their molar ratio were positively associated with risk of FBC. The odds ratios (ORs) and 95% confidence intervals (CI) for the upper fourth of the distribution compared to the lowest fourth for IGF-I, IGFBP3 and their molar ratio were 3.02 (2.02-4.52), 1.92 (1.37-2.71) and 2.26 (1.52-3.36), respectively. The strength of the association between IGF-I levels and FBC was attenuated after adjustment for IGFBP-3 and that for IGFBP-3 was largely eliminated after adjustment for IGF-I. Increasing levels of IGF-I were particularly associated with increasing risk of FBC with proliferative elements (ORs and 95% CIs for the 2nd, 3rd and upper fourth of the distribution of IGF-I: 3.13 (1.50-6.53), 4.57 (2.22-9.39) and 6.30 (3.08-12.89), compared with the lowest fourth. Our results suggest that elevated levels of IGF-I may contribute to the development of FBC.

Global gene expression analysis in time series following N-acetyl L-cysteine induced epithelial differentiation of human normal and cancer cells in vitro

Background

Cancer prevention trials using different types of antioxidant supplements have been carried out at several occasions and one of the investigated compounds has been the antioxidant N-acetyl-L-cysteine (NAC). Studies at the cellular level have previously demonstrated that a single supplementation of NAC induces a ten-fold more rapid differentiation in normal primary human keratinocytes as well as a reversion of a colon carcinoma cell line from neoplastic proliferation to apical-basolateral differentiation [1]. The investigated cells showed an early change in the organization of the cytoskeleton, several newly established adherens junctions with E-cadherin/β-catenin complexes and increased focal adhesions, all features characterizing the differentiation process.

Methods

In order to investigate the molecular mechanisms underlying the proliferation arrest and accelerated differentiation induced by NAC treatment of NHEK and Caco-2 cells in vitro, we performed global gene expression analysis of NAC treated cells in a time series (1, 12 and 24 hours post NAC treatment) using the Affymetrix GeneChip™ Human Genome U95Av2 chip, which contains approximately 12,000 previously characterized sequences. The treated samples were compared to the corresponding untreated culture at the same time point.

Results

Microarray data analysis revealed an increasing number of differentially expressed transcripts over time upon NAC treatment. The early response (1 hour) was transient, while a constitutive trend was commonly found among genes differentially regulated at later time points (12 and 24 hours). Connections to the induction of differentiation and inhibition of growth were identified for a majority of up- and down-regulated genes. All of the observed transcriptional changes, except for seven genes, were unique to either cell line. Only one gene, ID-1, was mutually regulated at 1 hour post treatment and might represent a common mediator of early NAC action.

The detection of several genes that previously have been identified as stimulated or repressed during the differentiation of NHEK and Caco-2 provided validation of results. In addition, real-time kinetic PCR analysis of selected genes also verified the differential regulation as identified by the microarray platform.

Conclusion

NAC induces a limited and transient early response followed by a more consistent and extensively different expression at later time points in both the normal and cancer cell lines investigated. The responses are largely related to inhibition of proliferation and stimulation of differentiation in both cell types but are almost completely lineage specific. ID-1 is indicated as an early mediator of NAC action.

IGF-binding proteins mediate TGF-beta 1-induced apoptosis in bovine mammary epithelial BME-UV1 cells

TGF-beta 1 is an antiproliferative and apoptogenic factor for mammary epithelial cells (MEC) acting in an auto/paracrine manner and thus considered an important local regulator of mammary tissue involution. However, the apoptogenic signaling pathway induced by this cytokine in bovine MEC remains obscure. The present study was focused on identification of molecules involved in apoptogenic signaling of transforming growth factor-beta 1 (TGF-beta 1) in the model of bovine mammary epithelial cell line (BME-UV1). Laser scanning cytometry (LSC), Western blot and electrophoretic mobility shift assay (EMSA) were used for analysis of expression and activity of TGF-beta 1-related signaling molecules. The earliest response occurring within 1-2 h after TGF-beta 1 administration was an induction and activation of R-Smads (Smad2 and Smad3) and Co-Smad (Smad4). An evident formation of Smad-DNA complexes began from 2nd hour after MEC exposure to TGF-beta 1. Similarly to Smads, proteins of AP1 complex: phosphorylated c-Jun and JunD appeared to be early reactive molecules; however, an increase in their expression was detected only in cytosolic fraction. In the next step, an increase of IGF binding protein-3 (IGFBP-3) and IGFBP-4 expression was observed from 6th hour followed by a decrease in the activity of protein kinase B (PKB/Akt), which occurred after 24 h of MEC exposure to TGF-beta 1. The decrease in PKB/Akt activity coincided in time with the decline of phosphorylated Bad expression (inactive form). Present study supported additional evidence that stimulation of insulin-like growth factor I (IGF-I) was associated with complete abrogation of TGF-beta 1-induced activation of Bad and Bax and in the consequence protection against apoptosis. In conclusion, apoptotic effect of TGF-beta 1 in bovine MEC is mediated by IGFBPs and occurs through IGF-I sequestration, resulting in inhibition of PKB/Akt-dependent survival pathway.

Free insulin-like growth factors -- measurements and relationships to growth hormone secretion and glucose homeostasis

IGF-I is a multipotent growth factor with important actions on normal tissue growth and regeneration. In addition, IGF-I has been suggested to have beneficial effects on glucose homeostasis due to its glucose lowering and insulin sensitizing actions. However, not all effects of IGF-I are considered to be favorable; thus, epidemiological studies suggest that IGF-I is also involved in the development of common cancers, atherosclerosis and type 2 diabetes. The biological actions of IGF-I are modulated by at least six IGF-binding proteins, which bind approximately 99% of the circulating IGF-I pool. So far, most in vivo studies have used serum or plasma total (extractable IGF-I) as an estimate of the bioactivity of IGF-I in vivo. However, within the last decade, validated assays for measurement of free IGF-I have been described. This review aims to discuss the current assays for free IGF-I and their advances in relation to the traditional measurement of total IGF-I. The literature overview will focus on the role of circulating free versus total IGF-I in the feedback regulation of GH release, and the possible involvement of the circulating IGF-system in glucose homeostasis.

An evaluation of the role of insulin-like growth factors (IGF) and of type-I IGF receptor signalling in hepatocarcinogenesis and in the resistance of hepatocarcinoma cells against drug-induced apoptosis

Strong evidence emphasizes the role of the insulin-like growth factor (IGF) system and of type-I IGF receptor (IGF-IR) signalling in tumourigenesis. In this connection: (i) changes in the expression pattern of components of the IGF system (autocrine/paracrine expression of IGF-I and -II, overexpression of IGF-IR, decreased expression of IGF-binding proteins (IGFBPs) and of type-II IGF receptor/cation-independent mannose-6-phosphate receptor (IGF-II/M6PR) and (ii) increased serum concentrations of proteases that cleave the IGFBPs (e.g., cathepsin D) were observed in patients with hepatocellular carcinomas (HCC), in human hepatoma cell lines and in their conditioned culture medium, as well as in rodent models of hepatocarcinogenesis. Accordingly, studies carried out with animal models do suggest that the IGF system and IGF-IR signalling may play a role in hepatocarcinogenesis and in deregulated proliferation and apoptosis of HCC cells. Finally the instrumental role of Raf/MEK/ERK, one of the signalling cascades stimulated by IGF-IR, in anthracycline-induced apoptosis of HepG2 and Huh-7 human hepatoma cell lines emphasizes that care must be taken when designing combinations of antitumoural molecules for antineoplastic treatment. This review addresses the putative roles of the IGF system in primary HCC, with a special focus on the underlying molecular mechanisms. In a second part it emphasizes the putative interference of IGF-IR signalling with chemotherapeutic drug-induced apoptosis in human hepatoma cells.

Identification of insulin receptor substrate proteins as key molecules for the TβR‐V/LRP‐1‐mediated growth inhibitory signaling cascade in epithelial and myeloid cells

The type V TGF-beta receptor (TbetaR-V) mediates IGF-independent growth inhibition by IGFBP-3 and mediates growth inhibition by TGF-beta1 in concert with the other TGF-beta receptor types. TbetaR-V was recently found to be identical to LRP-1. Here we find that insulin and (Q3A4Y15L16) IGF-I (an IGF-I analog that has a low affinity for IGFBP-3) antagonize growth inhibition by IGFBP-3 in mink lung epithelial cells (Mv1Lu cells) stimulated by serum. In these cells, IGFBP-3 induces serine-specific dephosphorylation of IRS-1 and IRS-2. The IGFBP-3-induced dephosphorylation of IRS-2 is prevented by cotreatment of cells with insulin, (Q3A4Y15L16) IGF-I, or TbetaR-V/LRP-1 antagonists. The magnitude of the IRS-2 dephosphorylation induced by IGFBP-3 positively correlates with the degree of growth inhibition by IGFBP-3 in Mv1Lu cells and mutant cells derived from Mv1Lu cells. Stable transfection of murine 32D myeloid cells (which lack endogenous IRS proteins and are insensitive to growth inhibition by IGFBP-3) with IRS-1 or IRS-2 cDNA confers sensitivity to growth inhibition by IGFBP-3; this IRS-mediated growth inhibition can be completely reversed by insulin in 32D cells stably expressing IRS-2 and the insulin receptor. These results suggest that IRS-1 and IRS-2 are key molecules for the TbetaR-V/LRP-1-mediated growth inhibitory signaling cascade.

Dual effects of IGFBP-3 on endothelial cell apoptosis and survival: involvement of the sphingolipid signaling pathways

Insulin-like growth factor binding protein (IGFBP)-3 has both growth-inhibiting and growth-promoting effects at the cellular level. The cytotoxic action of several anticancer drugs is linked to increased ceramide generation through sphingomyelin hydrolysis or de novo biosynthesis. Herein, we investigated the role of IGFBP-3 on apoptosis of human umbilical vein endothelial cells (HUVEC) and its relationship with ceramide levels. We report that IGFBP-3 exerts dual effects on HUVEC, potentiating doxorubicin-induced apoptosis but enhancing survival in serum-starved conditions. Ceramide was increased by IGFBP-3 in the presence of doxorubicin and decreased when IGFBP-3 was added alone to cells cultured in serum-free medium. The protection exerted by the ceramide synthase inhibitor fumonisin B1 over doxorubicin-induced apoptosis was enhanced by IGFBP-3 with concomitant reduction of ceramide levels. IGFBP-3 alone activated sphingosine kinase (SK) and increased SK1 mRNA; the SK inhibitor N,N-dimethylsphingosine (DMS) blocked IGFBP-3 antiapoptotic effect. Moreover, IGFBP-3 increased IGF-I mRNA and dramatically enhanced IGF-I release. IGF-I receptor (IGF-IR) and its downstream signaling pathways Akt and ERK were phosphorylated by IGFBP-3, whereas inhibition of IGF-IR phosphorylation with tyrphostin AG1024 suppressed the antiapopoptic effect of IGFBP-3. Finally, IGFBP-3 increased endothelial cell motility in all experimental conditions. These findings provide evidence that IGFBP-3 differentially regulates endothelial cell apoptosis by involvement of the sphingolipid signaling pathways. Moreover, the survival effect of IGFBP-3 seems to be mediated by the IGF-IR.

Insulin-like growth factor binding protein-3 is a novel mediator of apoptosis in insulin-secreting cells

Insulin-like growth factor binding protein-3 (IGFBP-3) is emerging as a critical regulator of cell survival. There has been no study which directly examined the potential role for this major growth factor in the programmed cell death (apoptosis) of insulin-secreting cells. To determine whether IGFBP-3 mediates apoptosis in insulin-secreting cells, we performed a rigorous series of experiments with the rat insulinoma (RIN) cell line m5F and the hamster insulin-secreting tumor (HIT) T-15. Within 24 h exogenous IGFBP-3 induced significant DNA fragmentation in RIN and HIT cells, at doses ranging from 4.4 to 2000 ng/ml (P<0.05) without a classic dose-response relationship. DNA fragmentation induced by rhIGFBP-3 occurred in the presence of immunoglobulin to block the type 1 IGF receptor. As detected by flow cytometry for Annexin V exposure to the cell surface, rhIGFBP-3 treatment doubled the proportion of apoptotic HIT cells from 1.7 +/- 0.4% (serum-free control) to 3.4 +/- 0.2% (P<0.02), an effect completely reversed by co-treatment with 1000 ng/ml rhIGF-I. Immunofluorescent microscopy disclosed that pro-inflammatory Th1 cytokines increased intranuclear aggregation of endogenous IGFBP-3. Cytokine-induced DNA fragmentation was completely blocked by relatively brief pre-treatment with antisense IGFBP-3 phosphorothioate oligodeoxynucleotides. In conclusion, we have presented the first evidence that IGFBP-3 contributes to cytokine-mediated apoptosis in insulin-secreting cells.

The roles of IGF-I and IGFBP-3 in the regulation of proximal tubule, and renal cell carcinoma cell proliferation

BACKGROUND

Insulin-like growth factor I (IGF-I), a potent proximal tubule cell (PTC) mitogen, has been implicated in the progression of many human cancers. Our previous work on human renal tissues has suggested that IGF-I and several of its binding proteins (IGFBP-3 and -6) are up-regulated in clear cell renal cell carcinoma (RCC).

METHODS

To further elucidate the role of IGF-I and IGFBPs in RCC growth, immunohistochemistry, thymidine incorporation, and Western analysis were performed in primary cultures of normal PTC (priPTC) and clear-cell RCC (priRCC), as well as in SN12K1 cells (a cell line derived from metastatic RCC).

RESULTS

By immunohistochemistry, IGFBP-3 and IGF-I were prominently expressed in SN12K1 cells, and weakly expressed in priPTC and priRCC. Incubation with 100 ng/mL IGF-I significantly augmented DNA synthesis by priPTC (mean +/- SD 120.7%+/- 19.7% of controls, P < 0.05), priRCC (238.7%+/- 279.9% of controls, P < 0.01), and SN12K1(120.0%+/- 22.9% of controls, P < 0.05). Neutralizing antibodies to IGF-I and IGF-I receptor significantly suppressed SN12K1 growth (81.9%+/- 13.5% of control, P < 0.01 and 87.4%+/- 16.2% of control, P < 0.05, respectively). Removal of endogenous IGFBP-3 by an anti-IGFBP-3 increased SN12K1 DNA synthesis (243.9%+/- 35.3% of control, P < 0.001), which was partially abrogated by coincubation with exogenous IGFBP-3 (135.97%+/- 5.9% of controls, P < 0.001). Using Western analysis, IGFBP-3 expression was enhanced in IGF-I-stimulated SN12K1 cells exposed to exogenous IGF-I. Coincubation with anti-IGFBP-3 further enhanced IGF-I-induced DNA synthesis.

CONCLUSION

RCC cells express IGF-I and IGFBP-3, and are responsive to exogenous IGF-I stimulation. Moreover, in SN12K1 cells (derived from metastatic RCC), autocrine IGF-I and IGFBP-3 actions, respectively, stimulated and inhibited growth. These results suggest that IGF-I and IGFBP-3 may be potential candidates for therapeutic manipulation in patients with advanced RCC.

Insulin-like growth factor binding protein-3 stimulates phosphatidylinositol 3-kinase in MCF-7 breast carcinoma cells

Insulin-like growth factor binding protein-3 (IGFBP-3) is the most abundant IGFBP in serum and other biological fluids. Apart from its capacity for specific and high-affinity binding to IGFs, it also has so-called "IGF-independent" activities that modulate cell proliferation and survival/apoptosis. However, the molecular elements of the IGFBP-3 signalling pathway remain obscure. In this study, we investigated the possible implication of phosphatidylinositol 3-kinase (PI 3-kinase) activity in MCF-7 breast carcinoma cells. In cells incubated with IGFBP-3, both total and insulin receptor substrate-1 (IRS-1)-associated PI 3-kinase activities were rapidly stimulated, with maximal effects after 3 and 10min of incubation, respectively. IGFBP-3-induced PI 3-kinase activity was unaffected by the state of IRS-1 tyrosine phosphorylation. Since IGFBP-3 failed to stimulate PI 3-kinase activity in MDA-MB 231 breast carcinoma cells, its effects in MCF-7 cells could be considered as cell-type-specific. Pertussis toxin abolished IGFBP-3-stimulation of PI 3-kinase activity, suggesting that this IGFBP-3 signalling pathway depends upon a pertussis toxin-sensitive G protein. Our results provide further evidence that IGFBP-3 directly triggers a specific intracellular signal in MCF-7 cells.

Cellular internalization of insulin-like growth factor binding protein-3: distinct endocytic pathways facilitate re-uptake and nuclear localization

Insulin-like growth factor binding protein-3 (IGFBP-3) is well established as a growth-inhibitory, apoptosis-inducing secreted molecule that acts via insulin-like growth factor (IGF)-independent as well as IGF-dependent pathways. Nuclear localization of IGFBP-3 has been observed and nuclear binding partners for IGFBP-3 demonstrated. However, little is known about the mechanism of IGFBP-3 internalization. We hypothesized that IGFBP-3 is first secreted then taken up again into cells and that its internalization could occur via binding to transferrin or caveolin. Incubation of cells with an IGFBP-3-neutralizing antibody demonstrated that nuclear translocation of endogenous IGFBP-3 requires IGFBP-3 secretion and re-uptake. Nuclear localization of exogenously added IGFBP-3 was rapid, occurring within 15 min, inhibited by co-incubation and extracellular sequestration with IGF-I, and dependent on the transferrin-binding C-terminal peptide region of IGFBP-3. Co-immunoprecipitation assays confirmed that IGFBP-3 binds transferrin but not directly to the transferrin receptor (TfR1); however, transferrin binds TfR1 and a ternary complex is formed. Specific binding to caveolin scaffolding docking sequence was confirmed utilizing radiolabeled IGFBP-3. Blocking TfR1-mediated endocytosis prevents both endogenous and exogenous IGFBP-3 re-uptake and inhibitors of caveolae formation also retard IGFBP-3 nuclear entry. Co-treatment with anti-transferrin receptor antibody and cholesterol depletion agents completely abolished endogenous and exogenous IGFBP-3 uptake. Suppression of IGFBP-3 internalization by TfR1 blockade inhibited IGFBP-3-induced apoptosis. Together, these data indicate that the actions of IGFBP-3 are mediated by internalization via distinct endocytic pathways.

Insulin-like growth factor-binding protein-3 potentiates epidermal growth factor action in MCF-10A mammary epithelial cells. Involvement of p44/42 and p38 mitogen-activated protein kinases

Insulin-like growth factor-binding protein-3 (IGFBP-3) is inhibitory to the growth of many breast cancer cells in vitro; however, a high level of expression of IGFBP-3 in breast tumors correlates with poor prognosis, suggesting that IGFBP-3 may be associated with growth stimulation in some breast cancers. We have shown previously in MCF-10A breast epithelial cells that chronic activation of Ras-p44/42 mitogen-activated protein (MAP) kinase confers resistance to the growth-inhibitory effects of IGFBP-3 (Martin, J. L., and Baxter, R. C. (1999) J. Biol. Chem. 274, 16407-16411). Here we show that, in the same cell line, IGFBP-3 potentiates DNA synthesis and cell proliferation stimulated by epidermal growth factor (EGF), a potent activator of Ras. A mutant of IGFBP-3, which fails to translocate to the nucleus and has reduced ability to cell-associate, similarly enhanced EGF action in these cells. By contrast, the structurally related IGFBP-5, which shares many functional features with IGFBP-3, was slightly inhibitory to DNA synthesis in the presence of EGF. IGFBP-3 primes MCF-10A cells to respond to EGF because pre-incubation caused a similar degree of EGF potentiation as co-incubation. In IGFBP-3-primed cells, EGF-stimulated EGF receptor phosphorylation at Tyr-1068 was increased relative to unprimed cells, as was phosphorylation and activity of p44/42 and p38 MAP kinases, but not Akt/PKB. Partial blockade of the p44/42 and p38 MAP kinase pathways abolished the potentiation by IGFBP-3 of EGF-stimulated DNA synthesis. Collectively, these findings indicate that IGFBP-3 enhances EGF signaling and proliferative effects in breast epithelial cells via increased EGF receptor phosphorylation and activation of p44/42 and p38 MAP kinase signaling pathways.