Growth and differentiation signals by the insulin-like growth factor 1 receptor in hemopoietic cells are mediated through different pathways

Evolutionary analysis and functional characterization reveal the role of the insulin-like growth factor system in a diversified selection of chickens (Gallus gallus)

The insulin-like growth factor (IGF) system plays an indispensable role in embryonic and postnatal development in mammals. However, the effects of the system on growth, carcass, and egg-laying traits, and diversified selection have not been systematically studied in chickens. In the present study, firstly the composition and gene structures of the chicken IGF system were investigated using phylogenetic tree and conserved synteny analysis. Then the effects of the genetic variations in the IGF system genes on breeding of specialized varieties were explored by principal component analysis. In addition, the spatiotemporal expression properties of the genes in this system were analyzed by RT-qPCR and the functions of the genes in egg production performance and growth were explored by association study. Moreover, the effects of IGF-binding proteins 3 (IGFBP3) on skeletal muscle development in chicken were investigated by cell cycle analysis, 5-ethynyl-2'-deoxyuridine (EdU) and Cell Counting Kit-8 (CCK-8) assays. The results showed that the chicken IGF system included 13 members which could be classified into 3 groups based on their amino acid sequences: IGF binding proteins 1 to 5 and 7 (IGFBP1-5 and 7) belonged to the first group; IGF 1 and 2 (IGF1 and IGF2), and IGF 1 and 2 receptor (IGF1R and IGF2R) belonged to the second group; and IGF2 binding proteins 1-3 (IGF2BP1-3) belonged to the third group. The IGF2BP1 and 3, and IGFBP2, 3, and 7 genes likely contributed more to the formation of both the specialized meat-type and egg-type lines, whereas IGFBP1 and 5 likely contributed more to the formation of the egg-type lines. The SNPs in the IGF2BP3 and IGFBP2 and 5 genes were significantly associated with egg number, and SNPs in the IGFBP3 promoter region were significantly associated with body weight, breast muscle weight and leg muscle weight. The IGFBP3 inhibited proliferation but promoted differentiation of chicken primary myoblasts (CPMs). These results provide insights into the roles of the IGF system in the diversified selection of chickens. The SNPs associated with egg-laying performance, growth, and carcass traits could be used as genetic markers for breeding selection of chickens in the future.

Genomic Survey of Tyrosine Kinases Repertoire in Electrophorus electricus With an Emphasis on Evolutionary Conservation and Diversification

Tyrosine kinases (TKs) play key roles in the regulation of multicellularity in organisms and involved primarily in cell growth, differentiation, and cell-to-cell communication. Genome-wide characterization of TKs has been conducted in many metazoans; however, systematic information regarding this superfamily in Electrophorus electricus (electric eel) is still lacking. In this study, we identified 114 TK genes in the E electricus genome and investigated their evolution, molecular features, and domain architecture using phylogenetic profiling to gain a better understanding of their similarities and specificity. Our results suggested that the electric eel TK (EeTK) repertoire was shaped by whole-genome duplications (WGDs) and tandem duplication events. Compared with other vertebrate TKs, gene members in Jak, Src, and EGFR subfamily duplicated specifically, but with members lost in Eph, Axl, and Ack subfamily in electric eel. We also conducted an exhaustive survey of TK genes in genomic databases, identifying 1674 TK proteins in 31 representative species covering all the main metazoan lineages. Extensive evolutionary analysis indicated that TK repertoire in vertebrates tended to be remarkably conserved, but the gene members in each subfamily were very variable. Comparative expression profile analysis showed that electric organ tissues and muscle shared a similar pattern with specific highly expressed TKs (ie, epha7, musk, jak1, and pdgfra), suggesting that regulation of TKs might play an important role in specifying an electric organ identity from its muscle precursor. We further identified TK genes exhibiting tissue-specific expression patterns, indicating that members in TKs participated in subfunctionalization representing an evolutionary divergence required for the performance of different tissues. This work generates valuable information for further gene function analysis and identifying candidate TK genes reflecting their unique tissue-function specializations in electric eel.

Targeting the IGF-Axis for Cancer Therapy: Development and Validation of an IGF-Trap as a Potential Drug

The insulin-like growth factor (IGF)-axis was implicated in cancer progression and identified as a clinically important therapeutic target. Several IGF-I receptor (IGF-IR) targeting drugs including humanized monoclonal antibodies have advanced to phase II/III clinical trials, but to date, have not progressed to clinical use, due, at least in part, to interference with insulin receptor signaling and compensatory signaling by the insulin receptor (IR) isoform A that can bind IGF-II and initiate mitogenic signaling. Here we briefly review the current state of IGF-targeting biologicals, discuss some factors that may be responsible for their poor performance in the clinic and outline the stepwise bioengineering and validation of an IGF-Trap—a novel anti-cancer therapeutic that could bypass these limitations. The IGF-Trap is a heterotetramer, consisting of the entire extracellular domain of the IGF-IR fused to the Fc portion of human IgG₁. It binds human IGF-I and IGF-II with a three-log higher affinity than insulin and could inhibit IGF-IR driven cellular functions such as survival, proliferation and invasion in multiple carcinoma cell models in vitro. In vivo, the IGF-Trap has favorable pharmacokinetic properties and could markedly reduce metastatic outgrowth of colon and lung carcinoma cells in the liver, outperforming IGF-IR and ligand-binding monoclonal antibodies. Moreover, IGF-Trap dose-response profiles correlate with their bio-availability profiles, as measured by the IGF kinase receptor-activation (KIRA) assay, providing a novel, surrogate biomarker for drug efficacy. Our studies identify the IGF-Trap as a potent, safe, anti-cancer therapeutic that could overcome some of the obstacles encountered by IGF-targeting biologicals that have already been evaluated in clinical settings.

IGF1 regulates RUNX1 expression via IRS1/2: Implications for antler chondrocyte differentiation

Although IGF1 is important for the proliferation and differentiation of chondrocytes, its underlying molecular mechanism is still unknown. Here we addressed the physiologic function of IGF1 in antler cartilage and explored the interplay of IGF1, IRS1/2 and RUNX1 in chondrocyte differentiation. The results showed that IGF1 was highly expressed in antler chondrocytes. Exogenous rIGF1 could increase the proliferation of chondrocytes and cell proportion in the S phase, whereas IGF1R inhibitor PQ401 abrogated the induction by rIGF1. Simultaneously, IGF1 could stimulate the expression of IHH which was a well-known marker for prehypertrophic chondrocytes. Further analysis evidenced that IGF1 regulated the expression of IRS1/2 whose silencing resulted in a rise of IHH mRNA levels, but the regulation was impeded by PQ401. Knockdown of IRS1 or IRS2 with specific siRNA could greatly enhance rIGF1-induced chondrocyte differentiation and reduce the expression of RUNX1. Extraneous rRUNX1 might rescue the effects of IRS1 or IRS2 siRNA on the differentiation. In antler chondrocytes, IGF1 played a role in modulating the expression of RUNX1 through IGF1R. Moreover, attenuation of RUNX1 expression advanced the differentiation elicited by rIGF1, while administration of rRUNX1 to chondrocytes treated with IGF1 siRNA or PQ401 reduced their differentiation. Additionally, siRNA-mediated downregulation of IRS1 or IRS2 in the chondrocytes impaired the interaction between IGF1 and RUNX1. Collectively, IGF1 could promote the proliferation and differentiation of antler chondrocytes. Furthermore, IRS1/2 might act downstream of IGF1 to regulate chondrocyte differentiation through targeting RUNX1.

Preparation of the Full Set of Recombinant Mouse- and Human-Secreted Phospholipases A2

A family of 14-20kDa, disulfide-rich, calcium-dependent secreted phospholipases A₂ (sPLA₂s) that release fatty acids from the sn-2 position of glycerophospholipids can be found in mammals. They have a diverse array of tissue distribution and biological functions. In this chapter we provide detailed protocols for production of nearly all of the mouse and human sPLA₂s mainly by expression in bacteria and in vitro refolding or by expression in insect cells. High-resolution mass spectrometry and enzymatic assays were, respectively, used to show that all disulfides are formed and that the enzymes are active, strongly suggesting that each sPLA₂ was prepared in the structurally native form. The availability of these proteins has allowed kinetic studies to be carried out, to prepare highly selective antisera, to screen for selective inhibitors, to study receptor binding, and to study the action of each enzyme on mammalian cell membranes and their in vivo biological roles.

[Transcriptomics and proteomics in studies of induced differentiation of leukemia cells]

Induced differentiation of leukemia cells is in the focus of basic and applied biomedical studies medicine and biology for more than 30 years. During this period specific regulatory molecules involved in the maturation process have been identified by biochemical and molecular biological methods. Recent developments of high-throughput transcriptomic and proteomic techniques made it possible to analyze large sets of mRNA and proteins; this resulted in identification of functionally important signal transduction pathways and networks of molecular interactions, and thus extent existing knowledge on the molecular mechanisms of induced differentiation. Despite significant advances in mechanisms of induced differentiation, many problems related to the molecular mechanism of cell maturation, a phenomenon of therapeutic resistance of leukemic cells need better understanding and thus require further detailed study. Transcriptomics and proteomics methods provide a suitable methodological platform for the implementation of such studies. This review highlights the use of transcriptomic and proteomic methods in studies aimed at various aspects of the induced differentiation. Special attention is paid to the employment of the systems approach for investigation of various aspects of cell maturation. The use of the systems approach in studies of induced differentiation is an important step for the transition from the formal data accumulation on expression of mRNA and proteins towards creating models of biological processes in silico.

Insulin-like growth factor receptor-1 (IGF-IR) as a target for prostate cancer therapy

Prostate cancer is the most commonly diagnosed cancer in men and is the second leading cause of cancer-related deaths in men each year. Androgen deprivation therapy is and has been the gold standard of care for advanced or metastatic prostate cancer for decades. While this treatment strategy initially shows benefit, eventually tumors recur as castration-resistant prostate cancer for which there are limited treatment options with only modest survival benefit. Upregulation of the insulin-like growth factor receptor type I (IGF-IR) signaling axis has been shown to drive the survival of prostate cancer cells in many studies. As many IGF-IR blockades have been developed, few have been tested preclinically and even fewer have entered clinical trials for prostate cancer therapy. In this review, we will update the most recent preclinical and clinical studies of IGF-IR therapy for prostate cancer. We will also discuss the challenges for IGF-IR targeted therapies to achieve clinical benefit for prostate cancer.

Transforming growth factor-β, insulin-like growth factor I/insulin-like growth factor I receptor and vascular endothelial growth factor-A: prognostic and predictive markers in triple-negative and non-triple-negative breast cancer

In the current study, the prognostic and predictive values of serum transforming growth factor-β1 (TGF-β1), insulin-like growth factor I (IGF-I)/IGF-I receptor (IGF-IR) and vascular endothelial growth factor-A (VEGF-A) were evaluated in triple-negative and non-triple-negative breast cancer (TNBC and non-TNBC). The aim was to identify a group of serological biomarkers and to identify possible candidates for targeted therapy in patients with TNBC and non-TNBC. Protein levels of TGF-β1, IGF-I/IGF-IR and VEGF-A in the serum were measured in 43 TNBC, 53 non-TNBC and 20 normal control participants using quantitative ELISA assays. Results were correlated against standard prognostic factors, response to treatment and survival. TNBC was identified to be associated with poor prognosis and serum levels of VEGF-A and IGF/IGF-IR were significantly higher in the TNBC group compared with the non-TNBC group. IGF-IR and VEGF-A overexpression was observed to be correlated with TGF-β1 expression and all of the markers investigated were associated with metastasis and disease progression. In the multivariate analysis, VEGF-A, IGF-I and IGF-IR were observed to be independent predictors for overall survival, whereas TGF-β1 and lymph node status were identified as independent predictors for disease-free survival. The overall response rate was significantly lower in patients with TNBC and those with high levels of TGF-β1, IGF-I/IGF-IR and VEGF-A. In view of the present results, it was concluded that TGF-β1, IGF-I/IGF-IR and VEGF-A overexpression is associated with the presence of aggressive tumors, which exhibit an increased probability of metastasis, a poor response to treatment and reduced survival rate. This indicates that VEGF-A, IGF-IR and IGF-I have the potential to be used as surrogate biomarkers and are promising candidates for targeted therapy, particularly in patients with TNBC.

Soy isoflavones and prostate cancer: a review of molecular mechanisms

Soy isoflavones are dietary components for which an association has been demonstrated with reduced risk of prostate cancer (PCa) in Asian populations. However, the exact mechanism by which these isoflavones may prevent the development or progression of PCa is not completely understood. There are a growing number of animal and in vitro studies that have attempted to elucidate these mechanisms. The predominant and most biologically active isoflavones in soy products, genistein, daidzein, equol, and glycetin, inhibit prostate carcinogenesis in some animal models. Cell-based studies show that soy isoflavones regulate genes that control cell cycle and apoptosis. In this review, we discuss the literature relevant to the molecular events that may account for the benefit of soy isoflavones in PCa prevention or treatment. These reports show that although soy isoflavone-induced growth arrest and apoptosis of PCa cells are plausible mechanisms, other chemo protective mechanisms are also worthy of consideration. These possible mechanisms include antioxidant defense, DNA repair, inhibition of angiogenesis and metastasis, potentiation of radio- and chemotherapeutic agents, and antagonism of estrogen- and androgen-mediated signaling pathways. Moreover, other cells in the cancer milieu, such as the fibroblastic stromal cells, endothelial cells, and immune cells, may be targeted by soy isoflavones, which may contribute to soy-mediated prostate cancer prevention. In this review, these mechanisms are discussed along with considerations about the doses and the preclinical models that have been used.

Expression levels of insulin receptor substrate-1 modulate the osteoblastic differentiation of mesenchymal stem cells and osteosarcoma cells

The insulin-like growth factor-1 system, including its critical mediator insulin receptor substrate-1 (IRS-1), is involved in regulating osteosarcoma (OS) cell proliferation or differentiation. The aim of this study is to define the role of IRS-1 in OS cells by assessing the contribution of IRS-1 in the differentiation of human and murine OS cell lines and mouse mesenchymal stem cells (MSCs) and found that the basal level of IRS-1 is important for the initiation of differentiation. Both down-regulation and over-expression of IRS-1 inhibited osteoblastic differentiation. In vivo studies showed that OS cells over-expressing IRS-1 have increased metastatic potential and tumor growth. The proteasome inhibitor MG-132 led to an increase in IRS-1 protein level that inhibited osteoblastic differentiation, suggesting a role for proteasomal regulation in maintaining the appropriate expression level of IRS-1. Thus, precise regulation of IRS-1 expression level is critical for determining the differentiating capacity of MSCs and OS cells, and that derangement of IRS-1 levels can be a critical step in OS transformation.

Anticarcinogenic effect of quercetin by inhibition of insulin-like growth factor (IGF)-1 signaling in mouse skin cancer

It has been shown that dysregulation of IGF-1 signaling is associated with tumor incidence and progression, whereas blockade of the signaling can effectively inhibit carcinogenesis. Although several mechanisms of anticancer activity of quercetin were proposed, molecular targets of quercetin have not been identified yet. Hence, we assessed the effect of quercetin on IGF-1 signaling inhibition in BK5.IGF-1 transgenic (Tg) mice, which over-expresses IGF-1 in the skin epidermis. A quercetin diet (0.02% wt/wt) for 20 weeks remarkably delayed the incidence of skin tumor by 2 weeks and reduced tumor multiplicity by 35% in a 7,12-dimethylbenz(a)anthracene (DMBA)-tetradecanoyl phorbol-13-acetate (TPA) two stage mouse skin carcinogenesis protocol. Moreover, skin hyperplasia in Tg mice was significantly inhibited by a quercetin supplementation. Further analysis of the MT1/2 skin papilloma cell line showed that a quercetin treatment dose dependently suppressed IGF-1 induced phosphorylation of the IGF-1 receptor (IGF-1R), insulin receptor substrate (IRS)-1, Akt and S6K; however, had no effect on the phosphorylation of PTEN. Additionally, the quercetin treatment inhibited IGF-1 stimulated cell proliferation in a dose dependent manner. Taken together, these data suggest that quercetin has a potent anticancer activity through the inhibition of IGF-1 signaling.

IGF-1 promotes the development and cytotoxic activity of human NK cells

Insulin-like growth factor 1 (IGF-1) is a critical regulator of many physiological functions, ranging from longevity to immunity. However, little is known about the role of IGF-1 in natural killer cell development and function. Here, we identify an essential role for IGF-1 in the positive regulation of human natural killer cell development and cytotoxicity. Specifically, we show that human natural killer cells have the ability to produce IGF-1 and that differential endogenous IGF-1 expression leads to disparate cytotoxicity in human primary natural killer cells. Moreover, miR-483-3p is identified as a critical regulator of IGF-1 expression in natural killer cells. Overexpression of miR-483-3p has an effect similar to IGF-1 blockade and decreased natural killer cell cytotoxicity, whereas inhibition of miR-483-3p has the opposite effect, which is reversible with IGF-1 neutralizing antibody. These findings indicate that IGF-1 and miR-483-3p belong to a new class of natural killer cell functional modulators and strengthen the prominent role of IGF-1 in innate immunity.

Insulin-like growth factor (IGF)-1 regulates many physiological functions including growth and metabolism. Ni et al. show that human natural killer cells secrete IGF-1 and that IGF-1 enhances the development and cytotoxicity of these cells.

Genome-wide DNA methylation analysis reveals a potential mechanism for the pathogenesis and development of uterine leiomyomas

Background

The pathogenesis of uterine leiomyomas, the most common benign tumor in women, remains unclear. Since acquired factors such as obesity, hypertension and early menarche place women at greater risk for uterine leiomyomas, uterine leiomyomas may be associated with epigenetic abnormalities that are caused by unfavorable environmental exposures.

Principal Findings

Profiles of genome-wide DNA methylation and mRNA expression were investigated in leiomyomas and in myometrium with and without leiomyomas. Profiles of DNA methylation and mRNA expression in the myometrium with and without leiomyomas were quite similar while those in leiomyomas were distinct. We identified 120 genes whose DNA methylation and mRNA expression patterns differed between leiomyomas and the adjacent myometrium. The biological relevance of the aberrantly methylated and expressed genes was cancer process, including IRS1 that is related to transformation, and collagen-related genes such as COL4A1, COL4A2 and COL6A3. We also detected 22 target genes of estrogen receptor (ER) alpha, including apoptosis-related genes, that have aberrant DNA methylation in the promoter, suggesting that the aberrant epigenetic regulation of ER alpha-target genes contributes to the aberrant response to estrogen.

Conclusions

Aberrant DNA methylation and its related transcriptional aberration were associated with cancer processes, which may represent a critical initial mechanism that triggers transformation of a single tumor stem cell that will eventually develop into a monoclonal leiomyoma tumor. The aberrant epigenetic regulation of ER alpha-target genes also may contribute to the aberrant response to estrogen, which is involved in the development of uterine leiomyomas after menarche.

Growth factors polymerized within fibrin hydrogel promote amylase production in parotid cells

Salivary gland cell differentiation has been a recurring challenge for researchers as primary salivary cells show a loss of phenotype in culture. Particularly, parotid cells show a marked decrease in amylase expression, the loss of tight junction organization and proper cell function. Previously, Matrigel has been used successfully as an extracellular matrix; however, it is not practical for in vivo applications as it is tumorigenic. An alternative method could rely on the use of fibrin hydrogel (FH), which has been used extensively in biomedical engineering applications ranging from cardiovascular tissue engineering to wound-healing experiments. Although several groups have examined the effects of a three-dimensional (3D) environment on salivary cell cultures, little is known about the effects of FH on salivary cell cultures. The current study developed a 3D cell culture model to support parotid gland cell differentiation using a combination of FH and growth factor-reduced Matrigel (GFR-MG). Furthermore, FH polymerized with a combination of EGF and IGF-1 induced formation of 3D spheroids capable of amylase expression and an agonist-induced increase in the intracellular Ca(2+) concentration ([Ca(2+)]i) in salivary cells. These studies represent an initial step toward the construction of an artificial salivary gland to restore salivary gland dysfunction. This is necessary to reduce xerostomia in patients with compromised salivary function.

VEGF/neuropilin-2 regulation of Bmi-1 and consequent repression of IGF-IR define a novel mechanism of aggressive prostate cancer

We show that the VEGF receptor neuropilin-2 (NRP2) is associated with high-grade, PTEN-null prostate cancer and that its expression in tumor cells is induced by PTEN loss as a consequence of c-Jun activation. VEGF/NRP2 signaling represses insulin-like growth factor-1 receptor (IGF-IR) expression and signaling, and the mechanism involves Bmi-1-mediated transcriptional repression of the IGF-IR. This mechanism has significant functional and therapeutic implications that were evaluated. IGF-IR expression positively correlates with PTEN and inversely correlates with NRP2 in prostate tumors. NRP2 is a robust biomarker for predicting response to IGF-IR therapy because prostate carcinomas that express NRP2 exhibit low levels of IGF-IR. Conversely, targeting NRP2 is only modestly effective because NRP2 inhibition induces compensatory IGF-IR signaling. Inhibition of both NRP2 and IGF-IR, however, completely blocks tumor growth in vivo.

Proline-rich tyrosine kinase 2 (Pyk2) regulates IGF-I-induced cell motility and invasion of urothelial carcinoma cells

The insulin-like growth factor receptor I (IGF-IR) plays an essential role in transformation by promoting cell growth and protecting cancer cells from apoptosis. We have recently demonstrated that the IGF-IR is overexpressed in invasive bladder cancer tissues and promotes motility and invasion of urothelial carcinoma cells. These effects require IGF-I-induced Akt- and MAPK-dependent activation of paxillin. The latter co-localizes with focal adhesion kinases (FAK) at dynamic focal adhesions and is critical for promoting motility of urothelial cancer cells. FAK and its homolog Proline-rich tyrosine kinase 2 (Pyk2) modulate paxillin activation; however, their role in regulating IGF-IR-dependent signaling and motility in bladder cancer has not been established. In this study we demonstrate that FAK was not required for IGF-IR-dependent signaling and motility of invasive urothelial carcinoma cells. On the contrary, Pyk2, which was strongly activated by IGF-I, was critical for IGF-IR-dependent motility and invasion and regulated IGF-I-dependent activation of the Akt and MAPK pathways. Using immunofluorescence and AQUA analysis we further discovered that Pyk2 was overexpressed in bladder cancer tissues as compared to normal tissue controls. Significantly, in urothelial carcinoma tissues there was increased Pyk2 localization in the nuclei as compared to normal tissue controls. These results provide the first evidence of a specific Pyk2 activity in regulating IGF-IR-dependent motility and invasion of bladder cancer cells suggesting that Pyk2 and the IGF-IR may play a critical role in the invasive phenotype in urothelial neoplasia. In addition, Pyk2 and the IGF-IR may serve as novel biomarkers with diagnostic and prognostic significance in bladder cancer.

Functional roles and clinical values of insulin-like growth factor-binding protein-5 in different types of cancers

Insulin-like growth factor-binding proteins (IGFBPs) are critical regulators of the mitogenic activity of insulin-like growth factors (IGFs). IGFBP5, one of these IGFBPs, has special structural features, including a nuclear transport domain, heparin-binding motif, and IGF/extracellular matrix/acid-labile subunit-binding sites. Furthermore, IGFBP5 has several functional effects on carcinogenesis and even normal cell processes, such as cell growth, death, motility, and tissue remodeling. These biological effects are sometimes related with IGF (IGF-dependent effects) and sometimes not (IGF-independent effects). The functional role of IGFBP5 is most likely determined in a cell-type and tissue-type specific manner but also depends on cell context, especially in terms of the diversity of interacting proteins and the potential for nuclear localization. Clinical findings show that IGFBP5 has the potential to be a useful clinical biomarker for predicting response to therapy and clinical outcome of cancer patients. In this review, we summarize the functional diversity and clinical importance of IGFBP5 in different types of cancers.

LIP expression is regulated by IGF-1R signaling and participates in suppression of anoikis

Background

The transcription factor, CCAAT enhancer binding protein-β (C/EBPβ), is expressed as several distinct protein isoforms (LAP1, LAP2 and LIP) that have opposing actions in cellular proliferation and differentiation. Increases in the ratio of LIP/LAP are associated with aggressive, metastatic breast cancer; however, little is known regarding the molecular mechanisms that regulate LIP expression or the biological actions of an increase in the LIP/LAP ratio. Metastasis is highly dependent upon the suppression of anoikis and the role of C/EBPβ and LIP in this anchorage-independent, survival process is currently not known in mammary epithelial cells. IGF-1R signaling is important for the survival of breast cancer cells and crosstalk between IGF-1R and EGFR signaling pathways have been implicated in the development of more aggressive disease. We therefore evaluated in mammary epithelial cells whether IGF-1R signaling regulates the LIP/LAP ratio, analyzed the potential interplay between EGFR and IGF-1R signaling and addressed the biological significance of increased LIP expression in cellular survival and suppression of anoikis.

Results

Our data provide the first evidence that IGF-1R signaling regulates LIP expression in an EGFR independent manner to increase the LIP/LAP ratio in mammary epithelial cells. Although crosstalk between IGF-1R signaling and EGFR signaling is detectable in MCF10A cells, this crosstalk is not required for the IGF-1 mediated regulation of LIP expression. Rather, the critical regulator of IGF-1 induced LIP expression appears to be EGFR-independent, Akt activity. Our data also demonstrate that increases in LIP expression promote cell survival via suppression of anoikis. Likewise, knockdown of total C/EBPβ leads to increased cell death and suggest that C/EBPβ expression is important for survival and resistance to anoikis. IGF-1 treatment can partially rescue vector control cells from anoikis; however, cells with reduced C/EBPβ expression do not survive anoikis.

Conclusions

Taken together, our data demonstrate that IGF-1R signaling regulates LIP expression in an EGFR independent manner to increase the LIP/LAP ratio in mammary epithelial cells. C/EBPβ expression and elevations in LIP play an important role in regulating cellular survival via suppression of anoikis, in an IGF-1R mediated context or in a manner independent of IGF-1R signaling.

Progress in the treatment of intestinal barrier dysfunction

Intestinal barrier function plays a pivotal role in the development and progression of some severe diseases such as severe burn, severe acute pancreatitis, tumors, and severe liver disease. With a gradual understanding of the role of intestinal barrier dysfunction in the pathophysiology of various severe diseases, scholars have paid more attention to the basic and clinical research of the treatment of intestinal barrier function. This paper will review the latest advance in the treatment of intestinal barrier dysfunction.

The prognostic significance of the insulin-like growth factor-1 ligand and receptor expression in breast cancer tissue

BACKGROUND AND OBJECTIVES

Previous in vitro studies have suggested that IGF-1 stimulation can lead a more aggressive breast cancers and subsequent poor prognosis in breast cancer patients. We aim to how IGF-1 and IGF-1R mRNA levels in breast cancer are associated with disease-free survival (DFS) and other clinicopathological factors.

METHODS

IGF-1 and IGF-1R mRNA levels were measured in breast cancer tissue from 132 patients using real-time PCR. DFS and clinicopathological information were obtained from patient case notes.

RESULTS

IGF-1 and IGF-1R mRNA levels did not correlate with any clinicopathological factors. Patients who relapsed had lower IGF-1 mRNA levels in their tumour tissue compared to those who remained disease-free during the 5-year follow-up period. Patients who had ER-positive breast cancers with high IGF-1 mRNA levels had longer DFS compared to those with low IGF-1 mRNA levels. IGF-1 mRNA levels was not associated with DFS in patients with ER-negative cancers. IGF-1R mRNA levels was not associated with DFS in any subgroup analysis. Multivariate analysis showed that IGF-1 mRNA levels and histopathological grade were independent predictors of DFS.

CONCLUSIONS

Breast cancer tissue IGF-1 expression is a favourable prognostic indicator and could be used in clinical setting in planning for adjuvant treatment.

IGFBP-rP1, a potential molecule associated with colon cancer differentiation

BACKGROUND

In our previous studies, we have demonstrated that insulin-like growth factor binding protein-related protein1 (IGFBP-rP1) played its potential tumor suppressor role in colon cancer cells through apoptosis and senescence induction. In this study, we will further uncover the role of IGFBP-rP1 in colon cancer differentiation and a possible mechanism by revealing responsible genes.

RESULTS

In normal colon epithelium, immunohistochemistry staining detected a gradient IGFBP-rP1 expression along the axis of the crypt. IGFBP-rP1 strongly expressed in the differentiated cells at the surface of the colon epithelium, while weakly expressed at the crypt base. In colon cancer tissues, the expression of IGFBP-rP1 correlated positively with the differentiation status. IGFBP-rP1 strongly expressed in low grade colorectal carcinoma and weakly expressed in high grade colorectal carcinoma. In vitro, transfection of PcDNA3.1(IGFBP-rP1) into RKO, SW620 and CW2 cells induced a more pronounced anterior-posterior polarity morphology, accompanied by upregulation with alkaline phosphatase (AKP) activity. Upregulation of carcino-embryonic antigen (CEA) was also observed in SW620 and CW2 transfectants. The addition of IGFBP-rP1 protein into the medium could mimic most but not all effects of IGFBP-rP1 cDNA transfection. Seventy-eight reproducibly differentially expressed genes were detected in PcDNA3.1(IGFBP-rP1)-RKO transfectants, using Affymetrix 133 plus 2.0 expression chip platform. Directed Acyclic Graph (DAG) of the enriched GO categories demonstrated that differential expression of the enzyme regulator activity genes together with cytoskeleton and actin binding genes were significant. IGFBP-rP1 could upreguate Transgelin (TAGLN), downregulate SRY (sex determining region Y)-box 9(campomelic dysplasia, autosomal sex-reversal) (SOX9), insulin receptor substrate 1(IRS1), cyclin-dependent kinase inhibitor 2B (p15, inhibits CDK4) (CDKN2B), amphiregulin(schwannoma-derived growth factor) (AREG) and immediate early response 5-like(IER5L) in RKO, SW620 and CW2 colon cancer cells, verified by Real time Reverse Transcription Polymerase Chain Reaction (rtRT-PCR). During sodium butyrate-induced Caco2 cell differentiation, IGFBP-rP1 was upregulated and the expression showed significant correlation with the AKP activity. The downregulation of IRS1 and SOX9 were also induced by sodium butyrate.

CONCLUSION

IGFBP-rP1 was a potential key molecule associated with colon cancer differentiation. Downregulation of IRS1 and SOX9 may the possible key downstream genes involved in the process.

Mutual interaction and reciprocal down-regulation between c-met and insulin receptor substrate-1

The insulin receptor substrate-1 (IRS-1) and c-met, the receptor for the hepatocyte growth factor (HGF) co-immuno-precipitate from lysates treated with the respective antibodies. The interaction between IRS-1 and c-met requires a tyrosyl phosphorylated IRS-1 and results in reciprocal down-regulation. IRS-1 inhibits cell motility, while the activated c-met promotes it. These and other results suggest an explanation for reports in the literature indicating that c-met levels are high and IRS-1 levels are low in human cancer metastases.

Subcellular localization of IRS-1 in IGF-I-mediated chondrogenic proliferation, differentiation and hypertrophy of bone marrow mesenchymal stem cells

Bone marrow derived mesenchymal stem cells (BM-MSC) can differentiate into chondrocytes. Understanding the mechanisms and growth factors that control the MSC stemness is critical to fully implement their therapeutic use in cartilage diseases. The activated type 1 insulin-like growth factor receptor (IGF-IR), interacting with the insulin receptor substrate-1 (IRS-1), can induce cancer cell proliferation and transformation. In cancer or transformed cells, IRS-1 has been shown to localize in the cytoplasm where it activates the canonical Akt pathway, as well as in the nucleus where it binds to nuclear proteins. We have previously demonstrated that IGF-I has distinct time-dependent effect on primary BM-MSC chondrogenic pellets: initially (2-day culture), IGF-I induces proliferation; subsequently, IGF-I promotes chondrocytic differentiation (7-day culture). In the present study, by using MSC from the BM of IRS-1(- / - ) mice we show that IRS-1 mediates almost 50% of the IGF-I mitogenic response and the MAPK-MEK/ERK signalling accounts for the other 50%. After stimulation with IGF-I, we found that in 2-day old human and mouse derived BM-MSC pellets, IRS-1 (total and phosphorylated) is nuclearly localized and that proliferation prevails over differentiation. The IGF-I mitogenic effect is Akt-independent. In 7-day MSC pellets, IGF-I stimulates the chondrogenic differentiation of MSC into chondrocytes, pre-hypertrophic and hypertrophic chondrocytes and IRS-1 accumulates in the cytoplasm. IGF-I-dependent differentiation is exclusively Akt-dependent. Our data indicate that in the physiologically relevant model of primary cultured MSC, IGF-I induces a temporally regulated nuclear or cytoplasmic localization of IRS-1 that correlate with the transition from proliferation to chondrogenic differentiation.

Molecular predictors of response to a humanized anti-insulin-like growth factor-I receptor monoclonal antibody in breast and colorectal cancer

The insulin-like growth factor-I receptor (IGF-IR) pathway is required for the maintenance of the transformed phenotype in neoplastic cells and hence has been the subject of intensive drug discovery efforts. A key aspect of successful clinical development of targeted therapies directed against IGF-IR will be identification of responsive patient populations. Toward that end, we have endeavored to identify predictive biomarkers of response to an anti-IGF-IR-targeting monoclonal antibody in preclinical models of breast and colorectal cancer. We find that levels of the IGF-IR itself may have predictive value in these tumor types and identify other gene expression predictors of in vitro response. Studies in breast cancer models suggest that IGF-IR expression is both correlated and functionally linked with estrogen receptor signaling and provide a basis for both patient stratification and rational combination therapy with antiestrogen-targeting agents. In addition, we find that levels of other components of the signaling pathway such as the adaptor proteins IRS1 and IRS2, as well as the ligand IGF-II, have predictive value and report on the development of a pathway-focused panel of diagnostic biomarkers that could be used to test these hypotheses during clinical development of IGF-IR-targeting therapies.

Overexpression of SOCS-2 and SOCS-3 genes reverses erythroid overgrowth and IGF-I hypersensitivity of primary polycythemia vera (PV) cells

Polycythemia vera (PV), an acquired, chronic, clonal disorder arising in a multipotential hematopoietic progenitor cell, is characterized by hyperplasia of three major myeloid lineages, with a pronounced increase in cells of the erythroid lineage. Erythroid progenitor cells in PV are strikingly hypersensitive to insulin-like growth factor-I (IGF-I); this effect is specific and is mediated through the IGF-I receptor. To investigate the possibility that in PV the increase in number of erythroid progenitors and their hypersensitivity to IGF-I result from a defect in negative regulation of cytokine activity, we examined the expression of members of the SOCS gene family. Circulating mononuclear cells, grown in serum-free methylcellulose medium in the presence of IGF-I, produced BFU-E-derived colonies whose cells revealed a reduction of SOCS-2 and SOCS-3 expression in PV only. Overexpression of these genes in transfected PV cells reduced their erythroid overgrowth and IGF-I hypersensitivity. We hypothesize that a defect in expression of SOCS-2 and SOCS-3 genes may be crucial for the IGF-I hypersensitivity and progressive increase in erythroid cell population size characteristic of PV.

Adipogenesis licensing and execution are disparately linked to cell proliferation

Coordination of cell differentiation and proliferation is a key issue in the development process of multi-cellular organisms and stem cells. Here we provide evidence that the establishment of adipocyte differentiation of 3T3-L1 cells requires two processes: the licensing of an adipogenesis gene-expression program within a particular growth-arrest stage, i.e., the contact-inhibition stage, and then the execution of this program in a cell-cycle-independent manner, by which the licensed progenitors are differentiated into adipocytes in the presence of inducing factors. Our results showed that differentiation licensing of 3T3-L1 cells during the contact-inhibition stage involved epigenetic modifications such as DNA methylation and histone modifications, whereas disturbing these epigenetic modifications by DNA methylation inhibitors or RNAi during the contact-inhibition stage significantly reduced adipogenesis efficiency. More importantly, when these licensed 3T3-L1 cells were re-cultured under non-differentiating conditions or treated only with insulin, this adipogenesis commitment could be maintained from one cell generation to the next, whereby the licensed program could be activated in a cell-cycle-independent manner once these cells were subjected to adipogenesis-inducing conditions. This result suggests that differentiation licensing and differentiation execution can be uncoupled and disparately linked to cell proliferation. Our findings deliver a new concept that cell-fate decision can be subdivided into at least two stages, licensing and execution, which might have different regulatory relationships with cell proliferation. In addition, this new concept may provide a clue for developing new strategies against obesity.

Insulin-like growth factor (IGF) 1 and 2 help to predict disease outcome in GIST patients

BACKGROUND

The expression of the insulin-like growth factor (IGF) system has never been studied in gastrointestinal stromal tumors (GISTs).

PATIENTS AND METHODS

We studied the immunohistochemical expression of IGF1 receptor (IGFR-I), IGF1 and IGF2 in 94 samples of GISTs. IGF1 and IGF2 expression was scored in three classes: negative (N), moderate (M) and strong (S), according to staining intensity and extent.

RESULTS

IGFR-I was overexpressed in all cases. IGF1 and IGF2 expression was absent in 25 and 48 cases, moderate in 29 and 16 cases and strong in 40 and 30 cases, respectively. Strong IGF1 expression significantly correlated with higher mitotic index (P = 0.0001), larger (P = 0.01), higher risk (P = 0.0002), metastatic (P = 0.0001) and relapsed (P = 0.04) GISTs. Strong IGF2 expression correlated with higher mitotic index (P = 0.05) and higher risk GISTs (P = 0.001). The Kaplan-Meier analysis (N versus M versus S) showed a significant worsening of the disease-free survival (DFS) with the increase of IGF1 (P = 0.02) and IGF2 (P = 0.02) expression. In the subgroup of patients with operated high-risk GISTs, there was a better trend in DFS for patients affected by GISTs with negative IGF1 and IGF2.

CONCLUSIONS

The expression of IGF1 and IGF2 seems to predict relapse in GIST patients.

Insulin receptor substrate (IRS)-1 regulates murine embryonic stem (mES) cells self-renewal

Mouse embryonic stem (mES) cells are pluripotent cells that can be propagated in vitro with leukemia inhibitory factor (LIF) and serum. Intracellular signaling by LIF is principally mediated by activation of STAT-3, although additional pathways for self-renewal have been described. Here, we identified a novel role for Insulin receptor substrate-1 (IRS-1) as a critical factor in mES cells self-renewal and differentiation. IRS-1 is expressed and tyrosyl phosphorylated during mES cells self-renewal. Differentiation of mES cells, by LIF withdrawal, is associated with a marked reduction in IRS-1 expression. Targeting of IRS-1 by si-IRS-1 results in a severe reduction of Oct-4 protein expression and alkaline phosphatase activity, markers of undifferentiated mES cells. IRS-1 targeting does not interfere with LIF-induced STAT-3 phosphorylation, but negatively affects protein kinase B (PKB/AKT) and glycogen synthase kinase-3 (GSK-3beta) phosphorylation, which are downstream effectors of the LIF-mediated PI3K signaling cascade. Targeting of IRS-1 also results in a marked down regulation of Id-1 and Id-2 proteins expression, which are important components for self-renewal of ES cells. Conversely, over expression of IRS-1 inhibits mES cell differentiation. Taken together, these results suggest that expression and activity of IRS-1 are critical to the maintenance of the self-renewal program in mES cells.

Neuroprotective effects of short peptides derived from the Insulin-like growth factor 1

Insulin-like growth factor I (IGF-1) is a peptide synthesized in response to growth hormone stimulation. While most of the circulating IGF-1 comes from the liver, it can also be produced in other tissues and both its expression and processing undergo tissue-specific regulation. The predominant form, IGF-1Ea is a circulating factor while two others, IGF-1Eb and IGF-1Ec (MGF), are mostly expressed in different tissues or in response to various stimuli and show some preferences with respect to the signal transduction pathways they activate. In skeletal muscle specific forms of IGF-1 play a role in development and growth and in addition to these physiological roles IGF-1 functions in the damaged muscle. IGF-1 is also important for the developing and adult brain and can reduce neuronal death caused by different types of injuries. Like many other peptide hormones IGF-1 originates from a precursor pro-hormone that undergoes extensive post-translational modifications. Processing liberates the mature peptide, which acts via the specific IGF-1 receptor but additional short peptides can arise from both N- and C-termini of various IGF-1 isoforms. These derivatives function as autonomous biologically active peptides and extremely potent neuroprotective agents. Their biological effects are independent of the activation of the IGF-1 receptor. Unfortunately, little is known about their mechanism(s) of action. Likewise, the existence of the endogenous production and wider biological effects of these short peptides are uncertain. However, considering the difference in the modes of action it might be possible to dissociate the unwanted and potentially dangerous mitogenic activity of the full-length IGF-1 exerted via its receptor from the neuroprotective effects of short derivatives mediated through different pathways. Such small molecules show good penetration through the blood brain barrier, can be inexpensively manufactured and modified to increase their stability. Therefore, they are good candidates for development into a neuroprotective therapeutic modality.

Dual regulation of upstream binding factor 1 levels by IRS-1 and ERKs in IGF-1-receptor signaling

The Upstream Binding Factor 1 (UBF1) is a nucleolar protein that participates in the regulation of RNA polymerase I activity and ribosomal RNA (rRNA) synthesis. In 32D myeloid cells expressing the type 1 insulin-like growth factor receptor (IGF-IR), the UBF1 protein (but not its mRNA) is down regulated when the cells are shifted from Interleukin-3 (IL-3) to IGF-1. Ectopic expression of insulin receptor substrate-1 (IRS-1) in these cells inhibits the down-regulation of UBF1. We now show that the stability of UBF1 in 32D-derived cells requires also a signal from the extracellular regulated kinases (ERKs). When ERKs signaling is defective, as in cells over-expressing the insulin receptor (InR) or selected mutants of the IGF-1R, UBF1 is down-regulated, even in the presence of IRS-1. The down-regulation is corrected by the expression of an activated Ha-ras, which stimulates ERKs activity. Mutations at threonines 117 and 201 of UBF1, known to be phosphorylated by ERKs, cause its down-regulation. However, when IRS-2, instead of IRS-1, is ectopically expressed in 32D InR cells, ERKs phosphorylation is increased and UBF is stabilized. Taken together, these results indicate that in 32D-derived myeloid cells expressing either the IGF-IR or the InR, UBF1 levels are regulated by signaling from both IRS proteins and ERKs.

Micro RNA 145 targets the insulin receptor substrate-1 and inhibits the growth of colon cancer cells

The insulin receptor substrate-1 (IRS-1), a docking protein for both the type 1 insulin-like growth factor receptor (IGF-IR) and the insulin receptor, is known to send a mitogenic, anti-apoptotic, and anti-differentiation signal. Several micro RNAs (miRs) are suggested by the data base as possible candidates for targeting IRS-1. We show here that one of the miRs predicted by the data base, miR145, whether transfected as a synthetic oligonucleotide or expressed from a plasmid, causes down-regulation of IRS-1 in human colon cancer cells. IRS-1 mRNA is not decreased by miR145, while it is down-regulated by an siRNA targeting IRS-1. Targeting of the IRS-1 3'-untranslated region (UTR) by miR145 was confirmed using a reporter gene (luciferase) expressing the miR145 binding sites of the IRS-1 3'-UTR. In agreement with the role of IRS-1 in cell proliferation, we show that treatment of human colon cancer cells with miR145 causes growth arrest comparable to the use of an siRNA against IRS-1. Taken together, these results identify miR145 as a micro RNA that down-regulates the IRS-1 protein, and inhibits the growth of human cancer cells.

Downregulation of the upstream binding factor1 by glycogen synthase kinase3beta in myeloid cells induced to differentiate

The upstream binding factor 1 (UBF1), one of the proteins that regulate the activity of RNA polymerase I, is downregulated in 32D myeloid cells induced to differentiate into granulocytes, either by the type 1 insulin-like growth factor (IGF-1) or the granulocytic colony stimulating factor (G-CSF). Downregulation of UBF1 is largely due to protein degradation, while mRNA levels are not affected. Inhibition of UBF1 degradation by lithium chloride (LiCl)and lactacystin suggest a role of glycogen synthase kinase beta (GSK3beta) in a proteasome-dependent degradation of UBF. GSK3beta phosphorylates in vitro and in vivo the UBF protein, which has five putative motifs for phosphorylation by GSK3beta. Elimination and/or mutations of these motifs stabilize the UBF1 protein even in cells induced to differentiate. Conversely, a stably transfected, constitutively active GSK3beta accelerates the downregulation of UBF1. We show further that activation of the differentiating protein C/EPBalpha in 32D cells transformed by the oncogenic BCR/ABL protein causes downregulation of UBF1. Finally, inhibition of differentiation of myeloid cells by a dominant negative mutant of Stat3 stabilizes the UBF1 protein, while rapamycin-induced differentiation of myeloid cells downregulates UBF1 levels. Taken together, our results indicate that the induction of granulocytic differentiation in 32D murine myeloid cells causes the degradation of UBF1, via GSK3beta and the proteasome pathway.

Insulin Receptor Substrate-1 Regulates the Transformed Phenotype of BT-20 Human Mammary Cancer Cells

Although originating from a human breast cancer, BT-20 cells do not form colonies in soft agar. BT-20 cells do not express insulin receptor substrate-1 (IRS-1), which is known to promote both normal and abnormal growth and to inhibit differentiation. Stable expression of IRS-1 confers to BT-20 cells the ability to form colonies in soft agar. BT-20 cells form tumors in xenografts in mice, but the size of tumors is twice as large when the cells express IRS-1. The increased transformed phenotype is characterized by occupancy of the rDNA and cyclin D1 promoters by IRS-1 and the activation of the cyclin D1, c-myc, and rDNA promoters. In addition, the retinoblastoma protein, which is detectable in the rDNA promoter of quiescent BT-20/IRS-1 cells, is replaced by IRS-1 after insulin-like growth factor-I stimulation. Our results indicate that in BT-20 human mammary cancer cells, expression of IRS-1 activates promoters involved in cell growth and cell proliferation, resulting in a more transformed phenotype. Targeting of IRS-1 could be effective in inhibiting the proliferation of mammary cancer cells. [Cancer Res 2007;67(5):2124–30]

A Mechanism for Cell Size Regulation by the Insulin and Insulin-Like Growth Factor-I Receptors

Deletion of the type 1 insulin-like growth factor receptor (IGF-IR) or of the insulin receptor substrate-1 (IRS-1) genes in animals causes a 50% reduction in body size at birth. Decrease in body size is due to both a decreased number of cells and a decreased cell size. Deletion of the insulin receptor (InR) genes results in mice that are normal in size at birth. We have used 32D-derived myeloid cells to study the effect of IGF-IR and InR signaling on cell size. 32D cells expressing the IGF-IR and IRS-1 are almost twice as large as 32D cells expressing the InR and IRS-1. A mechanism for the difference in size is provided by the levels of the upstream binding factor 1 (UBF1), a nucleolar protein that participates in the regulation of RNA polymerase I activity and rRNA synthesis and therefore cell size. When shifted to the respective ligands, UBF1 levels decrease in cells expressing the InR and IRS-1, whereas they remain stable in cells expressing the IGF-IR and IRS-1. The expression of the IGF-IR and IRS-1 is crucial to the stability of UBF1.

Recruitment of insulin receptor substrate-1 and activation of NF-kappaB essential for midkine growth signaling through anaplastic lymphoma kinase

Anaplastic lymphoma kinase (ALK) is a transmembrane receptor tyrosine kinase in the insulin receptor superfamily. We recently demonstrated that the growth factors pleiotrophin (PTN) and midkine (MK) are ligands for ALK and that upon ALK activation, insulin receptor substrate-1 (IRS-1) and other substrates are phosphorylated. Here, the role of IRS-1 in ligand-mediated ALK signaling is investigated in interleukin-3 (IL-3)-dependent 32D murine myeloid cells. These cells do not express ALK and IRS family members, and do not respond to exogenously added PTN or MK. We show that expression of ALK plus IRS-1 renders these cells independent of IL-3 owing to the activation of ALK by endogenous MK. Mutational analysis reveals that this transformed phenotype of 32D cells requires kinase-active ALK as well as the interaction of ALK with IRS-1. Furthermore, 32D/IRS-1/ALK cells display an enhanced activation of mitogen-activated protein kinase and PI3-kinase pathways, and a selective transcriptional activation of nuclear factor (NF)-kappaB. Small interfering RNA-mediated knockdown of the endogenous MK or p65/NF-kappaB revealed that both these are rate limiting for the transformed phenotype induced by ALK plus IRS-1. We conclude that the recruitment of IRS-1 to activated ALK and the activation of NF-kappaB are essential for the autocrine growth and survival signaling of MK.

Epidermal growth factor induces insulin receptor substrate-2 in breast cancer cells via c-Jun NH(2)-terminal kinase/activator protein-1 signaling to regulate cell migration

The epidermal growth factor (EGF) and insulin-like growth factor (IGF) signaling pathways are critically involved in cancer development and progression. However, how these two signals cross-talk with each other to regulate cancer cell growth is not clearly understood. In this study, we found that EGF remarkably induced expression of major IGF signaling components, insulin receptor substrate (IRS)-1 and IRS-2, an effect that could be blocked by EGF receptor (EGFR) tyrosine kinase inhibitors. Although both extracellular signal-regulated kinase and c-Jun NH(2)-terminal kinase (JNK) signaling pathways were involved in the EGF up-regulation of IRS-1, the IRS-2 induction by EGF was specifically mediated by JNK signaling. Consistent with this, EGF increased IRS-2 promoter activity, which was associated with recruitment of activator protein-1 (AP-1) transcription factors and was inhibited by blocking AP-1 activity. Moreover, EGF treatment enhanced IGF-I and integrin engagement-elicited tyrosine phosphorylation of IRS and their downstream signaling, such as binding to phosphatidylinositol 3'-kinase regulatory subunit p85. Finally, repressing the induction of IRS-2 levels abolished the EGF enhancement of cell motility, suggesting that increased IRS-2 is essential for the EGF regulation of breast cancer cell migration. Taken together, our results reveal a novel mechanism of cross-talk between the EGF and IGF signaling pathways, which could have implications in therapeutic applications of targeting EGFR in tumors. Because AP-1 activity is involved in breast cancer progression, our work may also suggest IRS-2 as a useful marker for aggressive breast cancer.

Expression profiles of micro RNA in proliferating and differentiating 32D murine myeloid cells

32D cells are murine myeloid cells that grow indefinitely in Interleukin-3 (IL-3). In these cells, the type 1 insulin-like growth factor (IGF-I) and granulocytic-colony stimulating factor (G-CSF) induce differentiation to granulocytes. 32D cells do not express insulin receptor substrate-1 (IRS-1) or IRS-2, docking proteins of the IGF-I receptor. Ectopic expression of IRS-1 in these cells inhibits differentiation, the cells become IL-3 independent and IGF-1 dependent and can form tumors in mice. 32D and 32D-derived cells offer a good model in which to study the expression profiles of Micro Rna (miR) related to sustained proliferation or differentiation. We present here the data obtained with miR micro-arrays and identify the miR that are regulated by IGF-1 or G-CSF and are associated with either differentiation or indefinite cell proliferation of 32D murine myeloid cells.

IGF-I mediated survival pathways in normal and malignant cells

The type-I and -II insulin-like growth factors (IGF-I, II) are now established as survival- or proliferation-factors in many in vitro systems. Of note IGFs provide trophic support for multiple cell types or organ cultures explanted from various species, and delay the onset of programmed cell death (apoptosis) through the mitochondrial (intrinsic pathway) or by antagonizing activation of cytotoxic cytokine signaling (extrinsic pathway). In some instances, IGFs protect against other forms of death such as necrosis or autophagy. The effect of IGFs on cell survival appears to be context specific, being determined both by the cell origin (tissue specific) and the cellular stress that induces loss of cellular viability. In many human cancers, there is a strong association with dysregulated IGF signaling, and this association has been extensively reviewed recently. IGF-regulation is also disrupted in childhood cancers as a consequence of chromosomal translocations. IGFs are implicated also in acute renal failure, traumatic injury to brain tissue, and cardiac disease. This article focuses on the role of IGFs and their cellular signaling pathways that provide survival signals in stressed cells.

Evidence that insulin-like growth factor-1 requires protein kinase C-epsilon, PI3-kinase and mitogen-activated protein kinase pathways to protect human vascular smooth muscle cells from apoptosis

Insulin-like growth factor (IGF)-1 has been implicated in the development of occlusive vascular lesions. Although its role in vascular smooth muscle cell (VSMC) growth and migration are fairly well characterized, anti-apoptotic signals of IGF-1 in human VSMC remain largely unknown. In this study, we examined IGF-1 signals that protect human and rat VSMC from staurosporine (STAU)- and c-myc- induced apoptosis, respectively. Treatment with STAU resulted in apoptotic DNA fragmentation, phosphatidylserine externalization and cell shrinkage, but only occasional VSMC 'blebbing'. STAU-induced death and IGF-1-mediated survival were concentration dependent, while time-lapse video microscopy showed that IGF-1 inhibited c-myc-induced apoptosis by 90%. Pretreatment with mitogen-activated protein kinase/extracellular signal regulated kinase kinase (MEK) inhibitors UO126 and PD098059, or with the phosphatidylinositol 3-kinase (PI3-K) inhibitor wortmannin, reversed IGF-1-mediated human VSMC survival by 25-27% and 66%, respectively. Translocation studies showed that IGF-1 activated protein kinase C (PKC)-epsilon, but not PKC-alpha or PKC-delta, even in the presence of STAU, while pharmacological PKC inhibition (Ro-318220 or Go6976) implicated PKC-zeta or a novel PKC isozyme in IGF-1-mediated survival. Transient expression of activated PKC-epsilon but not activated PKC-zeta decreased myc-induced apoptosis in rat VSMC. In human VSMC, antisense oligodeoxynucleotides to PKC-epsilon partially reversed IGF-1-induced survival. In addition, IGF-1 elicited a mild but sustained activation of extracellular signal regulated kinase (ERK)1/2 in human VSMC that was abolished after 1 h in the presence of STAU. PKC downregulation reversed both IGF-1- and PMA-induced ERK activity, but platelet-derived growth factor (PDGF)-induced activity was unchanged. These results indicate for the first time that IGF-1 can protect human VSMC via multiple signals, including PKC-epsilon, PI3-K and mitogen-activated protein kinase pathways.

Transformation by the simian virus 40 T antigen is regulated by IGF-I receptor and IRS-1 signaling

Previous work has shown that the Simian Virus 40 T antigen (T antigen) cannot transform mouse embryo fibroblasts (MEFs) that do not express the type 1 insulin-like growth factor receptor (IGF-IR). We have now investigated the mechanism(s) by which the transforming activity of T antigen is affected by IGF-IR signaling. We demonstrate that transformation by T antigen of MEFs and several other cell lines requires an insulin receptor substrate-1 (IRS-1) phosphorylated on tyrosines. If IRS-1 is not expressed, or is serine phosphorylated or otherwise inactive, T antigen fails to transform cells in culture. For instance, while T antigen cannot transform 32D myeloid cells (that do not express IRS-1), its transforming activity is restored by the expression of a wild-type IRS-1, but not of an IRS-1 mutated at the PI3K binding sites. The importance of IRS-1 activation of PI3K in T-antigen transformation is supported by the finding that a constitutively activated p110 subunit of PI3K, a target of IRS-1, overcomes the inability of T antigen to transform MEFs with a serine phosphorylated IRS-1. Taken together, these results indicate that the IRS-1/PI3K signaling is one of the mechanisms regulating transformation by the SV40 T antigen. We propose that the requirement for a tyrosyl-phosphorylated IRS-1 provides a mechanism to explain the failure of T antigen to transform MEFs with deleted IGF-IR genes.

Proteomic analysis on insulin signaling in human hematopoietic cells: identification of CLIC1 and SRp20 as novel downstream effectors of insulin

Insulin/IGF-I-dependent signals play important roles for the regulation of proliferation, differentiation, metabolism, and autophagy in various cells, including hematopoietic cells. Although the early protein kinase activation cascade has been intensively studied, the whole picture of intracellular signaling events has not yet been clarified. To identify novel downstream effectors of insulin-dependent signals in relatively early phases, we performed high-resolution two-dimensional electrophoresis (2-DE)-based proteomic analysis using human hematopoietic cells 1 h after insulin stimulation. We identified SRp20, a splicing factor, and CLIC1, an intracellular chloride ion channel, as novel downstream effectors besides previously reported effectors of Rho-guanine nucleotide dissociation inhibitor 2 and glutathione S-transferase-pi. Reduction in SRp20 was confirmed by one-dimensional Western blotting. Moreover, MG-132, a proteasome inhibitor, prevented this reduction. By contrast, upregulation of CLIC1 was not observed in one-dimensional Western blotting, unlike the 2-DE results. As hydrophilic proteins were predominantly recovered in 2-DE, the discrepancy between the 1-DE and 2-DE results may indicate a certain qualitative change of the protein. Indeed, the nuclear localization pattern of CLIC1 was remarkably changed by insulin stimulation. Thus insulin induces the proteasome-dependent degradation of SRp20 as well as the subnuclear relocalization of CLIC1.

Gene expression profiles in cells transformed by overexpression of the IGF-I receptor

To identify genes associated with insulin-like growth factor-I receptor (IGF-IR)-mediated cellular transformation, we isolated genes that are differentially expressed in R- cells (derived from the IGF-IR knockout mouse) and R+ cells (R- cells that overexpress the IGF-IR). From these, 45 genes of known function were expressed at higher levels in R+ cells and 22 were expressed at higher levels in R- cells. Differential expression was confirmed by Northern blot analysis of R+ and R- cells. Genes expressed more abundantly in R+ cells are associated with (1) tumour growth and metastasis including, betaigH3, mts1, igfbp5 protease, and mystique; (2) cell division, including cyclin A1 and cdk1; (3) signal transduction, including pkcdeltabp and lmw-ptp; and (4) metabolism including ATPase H+ transporter and ferritin. In MCF-7 cells IGF-I induced expression of two genes, lasp-1 and mystique, which could contribute to metastasis. Lasp-1 expression required activity of the PI3-kinase signalling pathway. Mystique was highly expressed in metastatic but not in androgen-dependent prostate cancer cell lines and Mystique overexpression in MCF-7 cells promoted cell migration and invasion. We conclude that genes identified in this screen may mediate IGF-IR function in cancer progression.

The ELAV RNA-stability factor HuR binds the 5'-untranslated region of the human IGF-IR transcript and differentially represses cap-dependent and IRES-mediated translation

The type I insulin-like growth factor receptor (IGF-IR) is an integral component in the control of cell proliferation, differentiation and apoptosis. The IGF-IR mRNA contains an extraordinarily long (1038 nt) 5'-untranslated region (5'-UTR), and we have characterized a diverse series of proteins interacting with this RNA sequence which may provide for intricate regulation of IGF-IR gene expression at the translational level. Here, we report the purification and identification of one of these IGF-IR 5'-UTR-binding proteins as HuR, using a novel RNA crosslinking/RNase elution strategy. Because HuR has been predominantly characterized as a 3'-UTR-binding protein, enhancing mRNA stability and generally increasing gene expression, we sought to determine whether HuR might serve a different function in the context of its binding the IGF-IR 5'-UTR. We found that HuR consistently repressed translation initiation through the IGF-IR 5'-UTR. The inhibition of translation by HuR was concentration dependent, and could be reversed in trans by addition of a fragment of the IGF-IR 5'-UTR containing the HuR binding sites as a specific competitor, or abrogated by deletion of the third RNA recognition motif of HuR. We determined that HuR repressed translation initiation through the IGF-IR 5'-UTR in cells as well, and that siRNA knockdown of HuR markedly increased IGF-IR protein levels. Interestingly, we also found that HuR potently inhibited IGF-IR translation mediated through internal ribosome entry. Kinetic assays were performed to investigate the mechanism of translation repression by HuR and the dynamic interplay between HuR and the translation apparatus. We found that HuR, occupying a cap-distal position, significantly delayed translation initiation mediated by cap-dependent scanning, but was eventually displaced from its binding site, directly or indirectly, as a consequence of ribosomal scanning. However, HuR perpetually blocked the activity of the IGF-IR IRES, apparently arresting the IRES-associated translation pre-initiation complex in an inactive state. This function of HuR as a 5'-UTR-binding protein and dual-purpose translation repressor may be critical for the precise regulation of IGF-IR expression essential to normal cellular homeostasis.

A modified tandem affinity purification tag technique for the purification of protein complexes in mammalian cells

The tandem affinity purification (TAP) tag technique has been used with success to identify under nondenaturing conditions protein complexes in yeast. The technique can be used in mammalian cells, but we found that the original technique does not yield enough recovery for the identification of proteins when mammalian cells growing in monolayer have to be used. We present here a modified TAP tag technique that allows sufficient recovery of proteins from mouse fibroblasts growing in monolayer cultures. The recovery allows protein identification by mass spectrometry.

Regulation of Upstream Binding Factor 1 Activity by Insulin-like Growth Factor I Receptor Signaling

The upstream binding factor 1 (UBF1) is one of the proteins in a complex that regulates the activity of RNA polymerase I, which controls the rate of ribosomal RNA (rRNA) synthesis. We have shown previously that insulin receptor substrate-1 (IRS-1) can translocate to the nuclei and nucleoli of cells and bind UBF1. We report here that activation of the type I insulin-like growth factor receptor (IGF-IR) by IGF-I increases transcription from the ribosomal DNA (rDNA) promoter in both myeloid cells and mouse fibroblasts. The increased activity of the rDNA promoter is accompanied by increased phosphorylation of UBF1, a requirement for UBF1 activation. Phosphorylation occurs on a number of UBF1 peptides, most prominently on the highly acidic, serine-rich C terminus. In myeloid cells (but not in mouse embryo fibroblasts) IRS-1 signaling stabilizes the levels of UBF1 protein. These findings demonstrate that IGF-IR signaling can increase the activity of UBF1 and transcription from the rDNA promoter, providing one explanation for the reported effects of the IGF/IRS-1 axis on cell and body size in animals and cells in culture.