Interaction of Insulin-like Growth Factor II (IGF-II) with Multiple Plasma Proteins

The IGF-II-Insulin Receptor Isoform-A Autocrine Signal in Cancer: Actionable Perspectives

Insulin receptor overexpression is a common event in human cancer. Its overexpression is associated with a relative increase in the expression of its isoform A (IR^A), a shorter variant lacking 11 aa in the extracellular domain, conferring high affinity for the binding of IGF-II along with added intracellular signaling specificity for this ligand. Since IGF-II is secreted by the vast majority of malignant solid cancers, where it establishes autocrine stimuli, the co-expression of IGF-II and IR^A in cancer provides specific advantages such as apoptosis escape, growth, and proliferation to those cancers bearing such a co-expression pattern. However, little is known about the exact role of this autocrine ligand–receptor system in sustaining cancer malignant features such as angiogenesis, invasion, and metastasis. The recent finding that the overexpression of angiogenic receptor kinase EphB4 along with VEGF-A is tightly dependent on the IGF-II/IR^A autocrine system independently of IGFIR provided new perspectives for all malignant IGF2omas (those aggressive solid cancers secreting IGF-II). The present review provides an updated view of the IGF system in cancer, focusing on the biology of the autocrine IGF-II/IR^A ligand–receptor axis and supporting its underscored role as a malignant-switch checkpoint target.

Current Experimental Methods for Characterizing Protein-Protein Interactions

Protein molecules often interact with other partner protein molecules in order to execute their vital functions in living organisms. Characterization of protein-protein interactions thus plays a central role in understanding the molecular mechanism of relevant protein molecules, elucidating the cellular processes and pathways relevant to health or disease for drug discovery, and charting large-scale interaction networks in systems biology research. A whole spectrum of methods, based on biophysical, biochemical, or genetic principles, have been developed to detect the time, space, and functional relevance of protein-protein interactions at various degrees of affinity and specificity. This article presents an overview of these experimental methods, outlining the principles, strengths and limitations, and recent developments of each type of method.

Current Experimental Methods for Characterizing Protein-Protein Interactions

Protein molecules often interact with other partner protein molecules in order to execute their vital functions in living organisms. Characterization of protein-protein interactions thus plays a central role in understanding the molecular mechanism of relevant protein molecules, elucidating the cellular processes and pathways relevant to health or disease for drug discovery, and charting large-scale interaction networks in systems biology research. A whole spectrum of methods, based on biophysical, biochemical, or genetic principles, have been developed to detect the time, space, and functional relevance of protein-protein interactions at various degrees of affinity and specificity. This article presents an overview of these experimental methods, outlining the principles, strengths and limitations, and recent developments of each type of method.

Hyaluronan and hyaluronidase, which is better for embryo development?

Our aim was to examine size-specific effects of Hyaluronan (HA) on preimplantation embryo development. We investigated the effects of Hyalovet (HA, 500-750 kDa; the size produced by HA synthase-3, which is abundant in the oviduct), or HA treated with Hyaluronidase-2 (Hyal2; also expressed in the oviduct that breaks down HA into 20 kDa fragments). In experiment 1 (in vivo), oviducts of synchronized and superovulated ewes (n = 20) were surgically exposed on Day 2 post-mating, ligated, and infused with either Hyalovet, Hyalovet + Hyal2, Hyal2, or PBS (control). Ewes were killed 5 days later for recovery of embryos and oviductal epithelial cells (OEC). Blastocyst rates were significantly higher in Hyal2 and Hyalovet + Hyal2 oviducts. Hyaluronidase-2 infusion resulted in higher blastocyst cell numbers and hatching rates. This was associated with increased HSP70 expression in OEC. In contrast, Hyalovet resulted in the lowest development to blastocyst stage and lowest hatching rates, and decreased IGF2 and IGFBP2 expression in OEC. IGF1 and IL1α expression were not affected. In experiment 2, to rule out indirect effects of oviductal factors, ovine embryos were produced and cultured with the same treatments in vitro from Day 2 to 8. Hyaluronidase-2, but not Hyalovet, enhanced blastocyst formation and reduced inner cell mass apoptosis. Hyalovet inhibited hatching. In conclusion, the presence of large-size HA (500-750 kDa) in the vicinity of developing embryos appears to disturb the oviductal environment and embryo development in vivo and in vitro. In contrast, we show evidence that breakdown of HA into smaller fragments is required to maximize embryo development and blastocyst quality.

Loss of androgen receptor promotes adipogenesis but suppresses osteogenesis in bone marrow stromal cells

Gender differences have been described in osteoporosis with females having a higher risk of osteoporosis than males. The differentiation of bone marrow stromal cells (BMSCs) into bone or fat is a critical step for osteoporosis. Here we demonstrated that loss of the androgen receptor (AR) in BMSCs suppressed osteogenesis but promoted adipogenesis. The mechanism dissection studies revealed that AR deficiency suppressed osteogenesis-related genes to inhibit osteoblast differentiation from BMSCs. Knockout of AR promoted adipogenesis of BMSCs via Akt activation through IGFBP3-mediated IGF signaling, and the 5' promoter assay and chromatin immunoprecipitation assays further proved that AR could modulate IGFBP3 expression at the transcriptional level. Finally, addition of IGF inhibitors successfully masked the AR deficiency-induced Akt activation, and inhibitions of Akt, IGF1, and IGF2 pathways reversed the AR depletion effects on the adipogenesis process. These results suggested that AR-mediated changes in IGFBP3 might modulate the IGF-Akt axis to regulate adipogenesis in BMSCs.

IGFBP-3 can either inhibit or enhance EGF-mediated growth of breast epithelial cells dependent upon the presence of fibronectin

Progression of breast cancer is associated with remodeling of the extracellular matrix, often involving a switch from estrogen dependence to a dependence on EGF receptor (EGFR)/HER-2 and is accompanied by increased expression of the main binding protein for insulin-like growth factors (IGFBP-3). We have examined the effects of IGFBP-3 on EGF responses of breast epithelial cells in the context of changes in the extracellular matrix. On plastic and laminin with MCF-10A normal breast epithelial cells, EGF and IGFBP-3 each increased cell growth and together produced a synergistic response, whereas with T47D breast cancer cells IGFBP-3 alone had no effect, but the ability of EGF to increase cell proliferation was markedly inhibited in the presence of IGFBP-3. In contrast on fibronectin with MCF-10A cells, IGFBP-3 alone inhibited cell growth and blocked EGF-induced proliferation. With the cancer cells, IGFBP-3 alone had no effect but enhanced the EGF-induced increase in cell growth. The insulin-like growth factor-independent effects of IGFBP-3 alone on cell proliferation were completely abrogated in the presence of an EGFR, tyrosine kinase inhibitor, Iressa. Although IGFBP-3 did not affect EGFR phosphorylation [Tyr(1068)], it was found to modulate receptor internalization and was associated with activation of Rho and subsequent changes in MAPK phosphorylation. The levels of fibronectin and IGFBP-3 within breast tumors may determine their dependence on EGFR and their response to therapies targeting this receptor.

Fresh-frozen plasma as a source of exogenous insulin-like growth factor-I in the extremely preterm infant

CONTEXT

Preterm birth is followed by a decrease in circulatory levels of IGF-I and IGF binding protein (IGFBP)-3, proteins with important neurogenic and angiogenic properties.

OBJECTIVE

Our objective was to evaluate the effects of iv administration of fresh-frozen plasma (FFP) from adult donors on circulatory levels of IGF-I and IGFBP-3 in extremely preterm infants.

DESIGN, SETTING, AND PATIENTS

A prospective cohort study was performed in 20 extremely preterm infants [mean (SD) gestational age 25.3 (1.3) wk] with clinical requirement of FFP during the first postnatal week. Sampling was performed before initiation of transfusion, directly after, and at 6, 12, 24, and 48 h after completed FFP transfusion.

MAIN OUTCOME MEASURES

Concentrations of IGF-I and IGFBP-3 before and after transfusion of FFP were determined.

RESULTS

FFP with a mean (SD) volume of 11 ml/kg (3.1) was administered at a median postnatal age of 2 d (range 1-7). Mean (SD) IGF-I and IGFBP-3 concentrations in administered FFP were 130 (39) and 2840 microg/liter (615), respectively. Immediately after FFP transfusion, mean (SD) concentrations of IGF-I increased by 133% from 11 (6.4) to 25 microg/liter (9.3) (P < 0.001) and IGFBP-3 by 61% from 815 (451) to 1311 microg/liter (508) (P < 0.001). Concentrations of IGF-I and IGFBP-3 remained higher at 6 (P < 0.001, P = 0.009) and 12 h (P = 0.017, P = 0.018), respectively, as compared with concentrations before FFP transfusion. Typical half-life of administrated IGF-I was 3.4 h for a 1-kg infant.

CONCLUSION

Transfusion of FFP to extremely preterm infants during the first postnatal week elevates levels of IGF-I and IGFBP-3.

Methods for the detection and analysis of protein-protein interactions

A large number of methods have been developed over the years to study protein-protein interactions. Many of these techniques are now available to the nonspecialist researcher thanks to new affordable instruments and/or resource centres. A typical protein-protein interaction study usually starts with an initial screen for novel binding partners. We start this review by describing three techniques that can be used for this purpose: (i) affinity-tagged proteins (ii) the two-hybrid system and (iii) some quantitative proteomic techniques that can be used in combination with, e.g., affinity chromatography and coimmunoprecipitation for screening of protein-protein interactions. We then describe some public protein-protein interaction databases that can be searched to identify previously reported interactions for a given bait protein. Four strategies for validation of protein-protein interactions are presented: confocal microscopy for intracellular colocalization of proteins, coimmunoprecipitation, surface plasmon resonance (SPR) and spectroscopic studies. Throughout the review we focus particularly on the advantages and limitations of each method.

Modeling growth factor activity during proinflammatory stress: methodological considerations in assessing cytokine modulation of IGF binding proteins released by cultured bovine kidney epithelial cells

The present research was conducted to model potential mechanisms through which IGFBPs might be affected by a key proinflammatory response initiating cytokine tumor necrosis factor (TNF-)-alpha. Madin-Darby bovine kidney epithelial (MDBK) cells, known to release IGFBPs in response to several stimuli, were grown under several conditions and challenged with forskolin (F) or recombinant TNF-alpha for 24h. Forskolin increased IGFBP-3 gene expression and media content of BP-3 protein. TNF-alpha increased basal and augmented F-mediated IGFBP-3 gene expression. However, TNF-alpha effects on the measurable media content of IGFBPs were influenced by culture conditions; in the absence of added protease inhibitors (PIs) or sufficient media albumin concentration (high BSA, 1mg/ml), the effect of TNF-alpha was to decrease (P<0.02) measurable IGFBPs. In the presence of PI and high BSA, media IGFBP-3 levels were shown to be increased by TNF-alpha consistent with the gene expression data. Changes in media IGFBP-3 protease activity were examined further to explain the observed effects of TNF-alpha on production and destruction of IGFBPs in media. When recombinant human IGFBP-3 (500 ng/ml) was added to PI-free, low BSA 100 microg/ml) media from TNF-treated MDBK cells, less than 10% of the BP-3 was recognizable by Western blot in 30 min; conversely, inclusion of High BSA and PI in media resulted in attenuation of the protease effect on the IGFBPs. The data suggest that the MDBK model of cellular response to proinflammatory stimulus is affected by culture conditions and that TNF-alpha affects media content of IGFBPs through effects on IGFBP gene expression coupled with degradation of IGFBPs via enhanced proteolytic enzyme release.

Early effects of imatinib mesylate on the expression of insulin-like growth factor binding protein-3 and positron emission tomography in patients with gastrointestinal stromal tumor

BACKGROUND

Imatinib has demonstrated marked clinical efficacy against gastrointestinal stromal tumor (GIST). Microarray technology, real-time polymerase chain reaction (PCR) validation, and fluorodeoxyglucose-positron emission tomography (FDG-PET) imaging were used to study the early molecular effects of imatinib antitumor activity in GIST.

METHODS

After exposure of sensitive and resistant sarcoma cell lines to imatinib for 24 to 48 hours, the changes in gene expression were evaluated using a 1146 unique pathway array with Western blot validation. Real-time PCR was used to confirm changes in gene expression in human GIST samples (preimatinib biopsy and postimatinib surgical specimen after 3-7 days of therapy). FDG-PET was performed to correlate radiographic findings with the effects of imatinib on gene expression in GIST.

RESULTS

In all, 55 genes demonstrated a > or = 2-fold change after imatinib treatment of the GIST882 cells. Among these genes there was up-regulation of insulin-like growth factor binding protein-3 (IGFBP-3), a protein that modulates proliferation and apoptosis. Western blot analysis confirmed the increase of IGFBP-3 only in imatinib-sensitive GIST882 cells. Up to a 7-fold induction (49% mean increase; P = .08) of IGFBP-3 mRNA was found in tumor samples from patients with low residual FDG uptake, whereas there was an up to 12-fold reduction (-102% mean decrease; P = .03) in IGFBP-3 in those patients with high residual FDG uptake after imatinib therapy.

CONCLUSIONS

In the current study, imatinib appears to regulate numerous genes and specifically induces IGFBP-3 in GIST cells and tumor samples. IGFBP-3 levels also were found to be inversely correlated with residual FDG uptake in GIST patients early in imatinib therapy. These initial observations suggest that IGFBP-3 is an important early marker of antitumor activity of imatinib in GIST.

Novel actions of IGFBP-3 on intracellular signaling pathways of insulin-secreting cells

Understanding mechanisms underlying apoptotic destruction of insulin-secreting cells is critical to validate therapeutic targets for type 1 diabetes mellitus. We recently reported insulin-like growth factor binding protein-3 (IGFBP-3) as a novel mediator of apoptosis in insulin-secreting cells. In light of emerging IGF-independent roles for IGFBP-3, we investigated the mechanisms underlying actions of the novel, recombinant human mutant G(56)G(80)G(81)-IGFBP-3, which lacks intrinsic IGF binding affinity. Using the rat insulinoma RINm5F cell line, we report the first studies in insulin-secreting cells that IGFBP-3 selectively suppresses multiple, key intracellular phosphorelays. By immunoblot, we demonstrate that G(56)G(80)G(81)-IGFBP-3 suppresses phosphorylation of c-raf-MEK-ERK pathway and p38 kinase in time-dependent and dose-dependent manners. SAPK/JNK signaling was unaffected. These data delineate several novel intracellular sites of action for IGFBP-3 in insulin-secreting cells.

Survey of the year 2005 commercial optical biosensor literature

We identified 1113 articles (103 reviews, 1010 primary research articles) published in 2005 that describe experiments performed using commercially available optical biosensors. While this number of publications is impressive, we find that the quality of the biosensor work in these articles is often pretty poor. It is a little disappointing that there appears to be only a small set of researchers who know how to properly perform, analyze, and present biosensor data. To help focus the field, we spotlight work published by 10 research groups that exemplify the quality of data one should expect to see from a biosensor experiment. Also, in an effort to raise awareness of the common problems in the biosensor field, we provide side-by-side examples of good and bad data sets from the 2005 literature.

The role of insulin-like growth factor binding proteins

Insulin-like growth factors (IGFs) are fundamental cell regulators with an evolutionary conserved role synchronising tissue growth, development and function according to metabolic conditions. Although structurally very similar to insulin, the IGFs act in a very different way as cell regulators. Whereas insulin is stored in a specific gland and released when needed, the IGFs are stored outside of cells with soluble binding proteins. A very complex system of six IGF binding proteins, each of which exists in various modified states and interacts with other proteins, provides a sophisticated system for conferring specificity to provide a finely tuned system for local regulation at the tissue level.