Molecular identification of grass carp igfbp2 and the effect of glucose, insulin, and glucagon on igfbp2 mRNA expression.

The GH (growth hormone)/IGFs (insulin-like growth factors) system has an important function in the regulation of growth. In this system, IGFBPs play a crucial regulatory role in IGF functions. As a member of the IGFBP family, IGFBP2 can bind to IGF and regulate IGF functions to regulate development and growth. In addition, IGFBP2 shows key regulatory functions in cell proliferation and metabolism. In this study, the igfbp2 gene was cloned from grass carp (Ctenopharyngodon idellus) liver. The ORF of grass carp igfbp2 is 834 bp long and encodes 277 amino acids. The tissue distribution results showed that igfbp2 is expressed in multiple tissues in grass carp and has a high expression level in the liver. In the OGTT, igfbp2 expression was significantly decreased in the liver and brain after 6 h of treatment with glucose. In vitro, igfbp2 expression in grass carp's primary hepatocytes was significantly suppressed by insulin after treatment for 6 and 12 h. Moreover, igfbp2 expression was markedly increased in a dose-dependent manner with glucagon incubation in grass carp's primary hepatocytes. To the best of our knowledge, this is the first report about Igfbp2 in grass carp. These results will provide a basis for the in-depth study of grass carp Igfbp2.

IGFBP2 promotes vasculogenic mimicry formation via regulating CD144 and MMP2 expression in glioma.

Vasculogenic mimicry (VM) refers to the fluid-conducting channels formed by aggressive tumor cells rather than endothelial cells (EC) with elevated expression of genes associated with vascularization. VM has been considered as one of the reasons that glioblastoma becomes resistant to anti-VEGF therapy. However, the molecular basis underlying VM formation remains unclear. Here we report that the insulin-like growth factor-binding protein 2 (IGFBP2) acts as a potent factor to enhance VM formation in glioma. Evidence showed that elevated IGFBP2 expression was positively related with VM formation in patients with glioma. Enforced expression of IGFBP2 increased network formation of glioma cells in vitro by activating CD144 and MMP2 (Matrix Metalloproteinase 2). U251 cells with stable knockdown of IGFBP2 led to decreased VM formation and tumor progression in orthotopic mouse model. Mechanistically, IGFBP2 interacts with integrin α5 and ß1 subunits and augments CD144 expression in a FAK/ERK pathway-dependent manner. Luciferase reporter and ChIP assay suggested that IGFBP2 activated the transcription factor SP1, which could bind to CD144 promoter. Thus, IGFBP2 acts as a stimulator of VM formation in glioma cells via enhancing CD144 and MMP2 expression.

Phenotype analysis of male transgenic mice overexpressing mutant IGFBP-2 lacking the Cardin-Weintraub sequence motif: Reduced expression of synaptic markers and myelin basic protein in the brain and a lower degree of anxiety-like behaviour.

Brain growth and function are regulated by insulin-like growth factors I and II (IGF-I and IGF-II) but also by IGF-binding proteins (IGFBPs), including IGFBP-2. In addition to modulating IGF activities, IGFBP-2 interacts with a number of components of the extracellular matrix and cell membrane via a Cardin-Weintraub sequence or heparin binding domain (HBD1). The nature and the signalling elicited by these interactions are not fully understood. Here, we examined transgenic mice (H1d-hBP2) overexpressing a mutant human IGFBP-2 that lacks a specific heparin binding domain (HBD1) known as the Cardin-Weintraub sequence. H1d-hBP2 transgenic mice have the genetic background of FVB mice and are characterized by severe deficits in brain growth throughout their lifetime (p<0.05). In tissue lysates from brain hemispheres of 12-21day old male mice, protein levels of the GTPase dynamin-I were significantly reduced (p<0.01). Weight reductions were also found in distinct brain regions in two different age groups (12 and 80weeks). In the younger group, impaired weights were observed in the hippocampus (-34%; p<0.001), cerebellum (-25%; p<0.0001), olfactory bulb (-31%; p<0.05) and prefrontal cortex (-29%; p<0.05). At an age of 12weeks expression of myelin basic protein was reduced (p<0.01) in H1d-BP-2 mice in the cerebellum but not in the hippocampus. At 80weeks of age, weight reductions were similarly present in the cerebellum (-28%; p<0.001) and hippocampus (-31; p<0.05). When mice were challenged in the elevated plus maze, aged but not younger H1d-hBP2 mice displayed significantly less anxiety-like behaviour, which was also observed in a second transgenic mouse model overexpressing mouse IGFBP-2 lacking HBD1 (H1d-mBP2). These in vivo studies provide, for the first time, evidence for a specific role of IGFBP-2 in brain functions associated with anxiety and risk behaviour. These activities of IGFBP-2 could be mediated by the Cardin-Weintraub/HBD1 sequence and are altered in mice expressing IGFBP-2 lacking the HBD1.

The roles of selenium, insulin-like growth factor binding protein 2 and suppressor of cytokine signaling 3 in the pathogenesis of Kashin-Beck disease.

We aimed to verify the levels of IGFBP2 and SOCS3 in cartilage and chondrocytes of Kashin-Beck disease (KBD) patients and the effects of different selenium concentrations on the protein expression levels. Chondrocytes were cultured with sodium selenite in vitro. Immunohistochemistry and western blotting were used to verify the protein expressions. IGFBP2 and SOCS3 were up-regulated in KBD chondrocytes and decreased with increasing selenium concentrations. IGFBP2 expressed highest in the middle zone of KBD cartilage, SOCS3 expressed higher in the middle and deep zone. IGFBP2 and SOCS3 may be the biomarkers for KBD diagnosis and evaluating the effect of selenium supplement.

Insulin-like growth factor axis in pregnancies affected by fetal growth disorders.

BACKGROUND: Insulin-like growth factors 1 and 2 (IGF1 and IGF2) and their binding proteins (IGFBPs) are expressed in the placenta and known to regulate fetal growth. DNA methylation is an epigenetic mechanism which involves addition of methyl group to a cytosine base in the DNA forming a methylated cytosine-phosphate-guanine (CpG) dinucleotide which is known to silence gene expression. This silences gene expression, potentially altering the expression of IGFs and their binding proteins. This study investigates the relationship between DNA methylation of components of the IGF axis in the placenta and disorders in fetal growth. Placental samples were obtained from cord insertions immediately after delivery from appropriate, small (defined as birthweight <10th percentile for the gestation [SGA]) and macrosomic (defined as birthweight > the 90th percentile for the gestation [LGA]) neonates. Placental DNA methylation, mRNA expression and protein levels of components of the IGF axis were determined by pyrosequencing, rtPCR and Western blotting. RESULTS: In the placenta from small for gestational age (SGA) neonates (n = 16), mRNA and protein levels of IGF1 were lower and of IGFBPs (1, 2, 3, 4 and 7) were higher (p < 0.05) compared to appropriately grown neonates (n = 37). In contrast, in the placenta from large for gestational age (LGA) neonates (n = 20), mRNA and protein levels of IGF1 was not different and those of IGFBPs (1, 2, 3 and 4) were lower (p < 0.05) compared to appropriately grown neonates. Compared to appropriately grown neonates, CpG methylation of the promoter regions of IGF1 was higher in SGA neonates. The CpG methylation of the promoter regions of IGFBP1, IGFBP2, IGFBP3, IGFBP4 and IGFBP7 was lower in the placenta from SGA neonates as compared to appropriately grown neonates, but was unchanged in the placenta from LGA neonates. CONCLUSIONS: Our results suggest that changes in CpG methylation contribute to the changes in gene expression of components of the IGF axis in fetal growth disorders. Differential methylation of the IGF1 gene and its binding proteins is likely to play a role in the pathogenesis of SGA neonates.

IGFBP2 potentiates nuclear EGFR-STAT3 signaling.

Insulin-like growth factor binding protein 2 (IGFBP2) is a pleiotropic oncogenic protein that has both extracellular and intracellular functions. Despite a clear causal role in cancer development, the tumor-promoting mechanisms of IGFBP2 are poorly understood. The contributions of intracellular IGFBP2 to tumor development and progression are also unclear. Here we present evidence that both exogenous IGFBP2 treatment and cellular IGFBP2 overexpression lead to aberrant activation of epidermal growth factor receptor (EGFR), which subsequently activates signal transducer and activator of transcription factor 3 (STAT3) signaling. Furthermore, we demonstrate that IGFBP2 augments the nuclear accumulation of EGFR to potentiate STAT3 transactivation activities, via activation of the nuclear EGFR signaling pathway. Nuclear IGFBP2 directly influences the invasive and migratory capacities of human glioblastoma cells, providing a direct link between intracellular (and particularly nuclear) IGFBP2 and cancer hallmarks. These activities are also consistent with the strong association between IGFBP2 and STAT3-activated genes derived from The Cancer Genome Atlas database for human glioma. A high level of all three proteins (IGFBP2, EGFR and STAT3) was strongly correlated with poorer survival in an independent patient data set. These results identify a novel tumor-promoting function for IGFBP2 of activating EGFR/STAT3 signaling and facilitating EGFR accumulation in the nucleus, thereby deregulating EGFR signaling by two distinct mechanisms. As targeting EGFR in glioma has been relatively unsuccessful, this study suggests that IGFBP2 may be a novel therapeutic target.

The RGD sequence present in IGFBP-2 is required for reduced glucose clearance after oral glucose administration in female transgenic mice.

Recent studies suggest that insulin-like growth factor-binding protein-2 (IGFBP-2) affects both growth and metabolism. Whereas negative growth effects are primarily due to negative interference with IGF-I, the mechanisms for metabolic interference of IGFBP-2 are less clear. As we demonstrate, overexpression of IGFBP-2 in transgenic mice is correlated with a decelerated clearance of blood glucose after oral administration. IGFBP-2 carries an integrin-binding domain (RGD motif), which has been shown to also mediate IGF-independent effects. We thus asked if higher serum levels of IGFBP-2 without an intact RGD motif would also partially block blood glucose clearance after oral glucose application. In fact, transgenic mice overexpressing mutated IGFBP-2 with higher levels of IGFBP-2 carrying an RGE motif instead of an RGD were not characterized by decelerated glucose clearance. Impaired glucose tolerance was correlated with lower levels of GLUT4 present in plasma membranes isolated from muscle tissues after glucose challenge. At the same time, activation of TBC1D1 was depressed in mice overexpressing wild-type but not mutated IGFBP-2. Although we do not have reason to assume altered activation of IGF-I receptor or PDK1/Akt activation in both models, we have identified increased levels of integrin-linked kinase and focal adhesion kinase dependent on the presence of the RGD motif. From our results we conclude that impaired glucose clearance in female IGFBP-2 transgenic mice is dependent on the presence of the RGD motif and that translocation of GLUT4 in the muscle may be regulated by IGFBP-2 via RGD-dependent mechanisms.

Serum IGF-BP2 strongly moderates age's effect on cognition: a MIMIC analysis.

We have used structural equation models to explicitly distinguish functional status and therefore "dementia-relevant" variance in cognitive task performance (i.e., "δ" for dementia). Our approach is modular and can be directed to other targets. In this analysis, we construct a δ ortholog representing the "cognitive correlates of age" (cAGE). cAGE largely mediates age's effects on dementia severity, as rated by the Clinical Dementia Rating Scale Sum of boxes and has an area under the receiver operating curve = 0.96 for the diagnosis of Alzheimer's Disease versus controls. We then test cAGE's association with serum insulin-like growth factor binding protein 2 (IGF-BP2), which has previously been associated with age-related cognitive changes in animals, and with cortical atrophy in older humans. IGF-BP2's adverse effects on cognition are largely mediated through cAGE, independent of education, ethnicity, gender, depression ratings, serum homocysteine levels, hemoglobin A1c, and apolipoprotein e4 status. This suggests that age-specific cognitive decline may be moderated by IGF-BP2 and that modulation of that protein's function(s) might ameliorate age-specific cognitive impairments.

Insulin-Like Growth Factor Binding Protein-2 Promotes Adhesion of Endothelial Progenitor Cells to Endothelial Cells via Integrin α5ß1.

The contribution of endothelial progenitor cells (EPCs) to new vessel formation has been studied in different physiological and pathological conditions for decades. As previously suggested, insulin-like growth factor binding protein-2 (IGFBP-2) may interact with integrins and promote cell migration. However, the role of IGFBP-2 in regulation of EPC functions remains largely unknown. In this present study, we found that overexpression of IGFBP-2 in human umbilical vein endothelial cells (HUVECs) promoted EPC-endothelial adhesion. Conversely, siRNA-mediated depletion of IGFBP-2 inhibited oxygen-glucose deprivation (OGD)-induced EPC-endothelial adhesion. Further, we demonstrated that the arginine-glycine-aspartic acid (RGD) motif in its C-domain is required for interaction with integrin α5ß1. In addition, treatment with IGFBP-2 significantly enhanced incorporation of EPCs into tubule networks formed by HUVECs. Thus, our findings suggest that exogenous administration of IGFBP-2 may facilitate neovascularization and improve treatment of ischemic conditions.

Insulin-Like Growth Factor Binding Proteins--an Update.

The insulin-like growth factor (IGF) system is essential for normal growth and development, and its perturbation is implicated in a number of diseases. IGF activity is finely regulated by a family of six high-affinity IGF binding proteins (IGFBPs). 1GFBPs usually inhibit IGF actions but may enhance them under certain conditions. Additionally, IGFBPs bind non-IGF ligands in the extracellular space, cell membrane, cytoplasm and nucleus, thereby modulating cell proliferation, survival and migration in an IGF-independent manner. IGFBP activity is regulated by transcriptional mechanisms as well as by post-translational modifications and proteolysis. Understanding the balance between the various actions of IGFBPs in vivo may lead to novel insights into disease processes and possible IGFBP-based therapeutics.

Exogenous IGFBP-2 promotes proliferation, invasion, and chemoresistance to temozolomide in glioma cells via the integrin ß1-ERK pathway.

BACKGROUND: Insulin-like growth factor binding protein-2 (IGFBP-2) is significantly increased in the serum of patients with malignant gliomas. High plasma IGFBP-2 levels are correlated with poor prognosis in glioma patients. However, the exact role of exogenous IGFBP-2 in gliomas is unclear. METHODS AND RESULTS: Using the MTT cell viability assay, cell cycle analysis, and the transwell migration assay, it was demonstrated that IGFBP-2 treatment stimulated proliferation and invasion in U87 and U251 cell lines and primary SU3 glioma cells. Western blot analysis and immunofluorescence staining revealed that IGFBP-2 promoted ERK phosphorylation and nuclear translocation. Moreover, blocking ERK activation using the inhibitor PD98059 markedly reduced the effects of IGFBP-2 in glioma cells. As IGFBP-2 has an integrin-binding domain, the contribution of integrin ß1 to these IGFBP-2-mediated processes was examined. Neutralisation or knockdown of the expression of integrin ß1 inhibited IGFBP-2-induced ERK activation, cell proliferation, and cell invasion. Significantly, IGFBP-2 induced temozolomide resistance in glioma cells in an integrin ß1/ERK-dependent manner. CONCLUSIONS: Exogenous IGFBP-2 induces proliferation, invasion, and chemoresistance in glioma cells via integrin ß1/ERK signaling, suggesting that targeting this pathway could represent a potential therapeutic strategy for the treatment of gliomas. The identification of this pathway in glioma progression provides insight into the mechanism by which serum IGFBP-2 levels can predict the prognosis of glioma patients.

Insulin-like growth factor binding protein 2 (IGFBP-2) promotes growth and survival of breast epithelial cells: novel regulation of the estrogen receptor.

In breast tumors IGF binding protein-2 (IGFBP-2) is elevated, and the presence of IGFBP-2 has been shown to correlate with malignancy. However, how IGFBP-2 contributes to the malignant state is still unclear. Silencing IGFBP-2 blocked cell proliferation and in MCF-7 cells increased cell death, indicating that IGFBP-2 was acting in both a mitogenic and a survival capacity. Exogenous IGFBP-2 acting via integrin receptors to reduce phosphatase and tensin homolog deleted from chromosome 10 (PTEN) levels protected these cells against death induced by various chemotherapeutic agents. This was dependent on a functional estrogen receptor (ER)-α because silencing ER-α blocked the ability of IGFBP-2 to confer cell survival. Loss of IGFBP-2 increased levels of PTEN and improved chemosensitivity of the cells, confirming its role as a survival factor. Silencing IGFBP-2 had no effect on the response to IGF-II, but responses to estrogen and tamoxifen were no longer observed due to loss of ER-α, which could be prevented by the inhibition of PTEN. Conversely, exogenous IGFBP-2 increased ER-α mRNA and protein in both normal and cancer cells via its interaction with integrin receptors. These actions of IGFBP-2 on ER-α involved the IGF-I receptor and activation of phosphatidylinositol 3-kinase in the cancer cells but were independent of this in normal breast cells. The production of IGFBP-2 by breast cancer cells enhances their proliferative potential, increases their survival, and protects them against chemotherapy-induced death. IGFBP-2 not only modulates IGFs and directly regulates PTEN but also has a role in maintaining ER-α expression.

Insulin-like growth factor binding protein-2 and neurotrophin 3 synergize together to promote the expansion of hematopoietic cells ex vivo.

Co-culture of Umbilical Cord Blood (UCB) CD34+ cells with irradiated Mesenchymal Stem Cells (MSCs) without contact increase the expansion of Hematopoietic Progenitor Cells (HPC). Neurotrophin-3 (NT-3) and insulin-like growth factor binding protein-2 (IGFBP-2) are two factors whose expressions were significantly elevated in conditioned media derived from irradiated MSCs. To determine whether these factors are partly responsible for the growth promoting potential of MSCs, we investigated their impact on the growth and differentiation of UCB-CD34+ cells. Addition of either factor alone had little impact on cell growth, however both factors synergized together to increase the expansion of total nucleated cells, erythroids, megakaryocytes (Mk) and CD34+ cells. However, in contrast to MSCs they failed to significantly improve the expansion of hematopoietic progenitors. Consistent with the impact of these factors on hematopoietic cells, both synergized to activate ERK1/2 and AKT in primary human UCB cells. In conclusion, the study demonstrates for the first time that a neurotrophin factor can synergize with IGFBP-2 to promote hematopoietic cell expansion.

Insulin-like growth factor-binding protein 2-driven glioma progression is prevented by blocking a clinically significant integrin, integrin-linked kinase, and NF-κB network.

Insulin-like growth factor-binding protein 2 (IGFBP2) is increasingly recognized as a glioma oncogene, emerging as a target for therapeutic intervention. In this study, we used an integrative approach to characterizing the IGFBP2 network, combining transcriptional profiling of human glioma with validation in glial cells and the replication-competent ASLV long terminal repeat with a splice acceptor/tv-a glioma mouse system. We demonstrated that IGFBP2 expression is closely linked to genes in the integrin and integrin-linked kinase (ILK) pathways and that these genes are associated with prognosis. We further showed that IGFBP2 activates integrin ß1 and downstream invasion pathways, requires ILK to induce cell motility, and activates NF-κB. Most significantly, the IGFBP2/integrin/ILK/NF-κB network functions as a physiologically active signaling pathway in vivo by driving glioma progression; interfering with any point in the pathway markedly inhibits progression. The results of this study reveal a signaling pathway that is both targetable and highly relevant to improving the survival of glioma patients.

IGFBP-2 at the interface of growth and metabolism--implications for childhood obesity.

The growth hormone/insulin-like growth factor-I (IGF-I) axis is at the centre of normal human childhood growth. Six well characterised binding proteins (IGFBP-1 to IGFBP-6) act as general carriers of IGF-I, but they also modulate IGF-I bioavailability and activity in a tissue-specific, and developmentally appropriate, manner. Recent findings also point to several binding proteins possessing specific 'lGF-independent' actions and, in particular, there is now substantial evidence linking IGFBP-2 with nutritional status and insulin sensitivity. IGFBP-2 concentrations are reduced in obesity, and further reductions are seen in those with Type 2 diabetes. As IGFBP-2 is the major IGFBP expressed in infancy, and is also the predominant IGFBP produced from adipocytes, it is ideally positioned to act as a keystone between nutrition, growth and metabolism. Childhood obesity is associated with an increased risk of long-term morbidity and mortality, but the factors that determine which obese children will develop these long-term complications are not fully understood. IGFBP-2 may be integrally involved in the molecular processes that govern the development of obesity and subsequent weight-related disease. Within this manuscript, we explore the associations between IGFBP-2 and obesity with a particular emphasis on how an increased understanding of the role of IGFBP-2 in metabolism may lead to improvements in the prevention and treatment of childhood obesity.

JNK mediates insulin-like growth factor binding protein 2/integrin alpha5-dependent glioma cell migration.

We have previously shown that a molecular interaction between insulin-like growth factor binding protein 2 (IGFBP2) and integrin alpha5 is necessary for the enhancement of cell migration in IGFBP2-overexpressing gliomas. In the present study, we examined the mechanism through which the IGFBP2/integrin alpha5 interaction mediates enhanced glioma cell migration. Although both ERK and JNK MAP kinases were activated, JNK was specifically involved in IGFBP2-mediated migration as shown by inhibitor analysis of IGFBP2-overexpressing cells. Because gliomas are solid tumors that require contact with a surface (e.g., other cells, extracellular matrix) for migration, we used the extracellular matrix (ECM) protein fibronectin, which is the sole ligand of the alpha5beta1 integrin receptor, to show that integrin alpha5 is an important mediator of JNK activation. In addition, we found the IGFBP2/integrin alpha5 pathway to be activated in a significantly shorter interval in cells seeded onto fibronectin-coated surfaces compared to cells seeded onto plastic alone. The activation of JNK was downstream of the IGFBP2/integrin alpha5 interaction, as shown by alpha5 knockdown experiments using IGFBP2-overexpressing cells. Based on these data we propose that the interaction between IGFBP2 and integrin alpha5 accelerates cell adhesion, and this, in turn, enhances JNK-mediated glioma cell migration.

Insulin-like growth factor binding protein: a possible marker for the metabolic syndrome?

Insulin-like growth factor (IGF) binding proteins (IGFBPs) moved on to contain both IGF high- and low-affinity binders, exerting mitogenic and metabolic actions through its complex interplay between IGF/insulin and its IGF/insulin-independent manner. Progress on the metabolic-related function of IGFBPs has been rapid in recent years. A wealth of studies in 3T3-L1 adipocytes and the transgenic mice models demonstrated that IGFBPs played important roles in the pathogenesis of obesity and insulin resistance. Studies conducted in humans demonstrated the close relation between IGFBPs and the components of the metabolic syndrome. Abnormal expression of IGFBP was detected in various states of the metabolic disorders, suggesting that it could be used as a convenient and sensitive marker of insulin resistance, identification of insulin-resistant individuals at high cardiovascular risk, and may be an earlier marker of the metabolic syndrome. These exciting findings bring us new insight into the elucidation of the metabolic syndrome, which may have important clinical implications.

The role of insulin-like growth factor (IGF) binding protein-2 in the insulin-mediated decrease in IGF-I bioactivity.

CONTEXT: Insulin interacts with the GH-IGF system by a reciprocal regulation of IGF-binding proteins (IGFBP) and GH, which in turn regulate insulin sensitivity via bioactive IGF-I. This network is linked to metabolic syndrome and cardiovascular diseases. OBJECTIVE: We evaluated the effect of glucose and insulin on IGFBP-1-4, particularly IGFBP-2, in the regulation of bioactive IGF-I and its relation to insulin resistance. SETTING: The study was conducted at an endocrinology center. RESEARCH DESIGN AND METHODS: Twenty-four healthy subjects (12 men; aged 21-72 yr; body mass index 25.9 +/- 0.9 kg/m(2)) and 19 subjects with impaired glucose tolerance (IGT; eight men; aged 26-71 yr; body mass index 28.9 +/- 1.2 kg/m(2)) were prospectively studied using oral glucose tolerance test and hyperinsulinemic euglycemic clamp. RESULTS: During the clamp, insulin decreased IGF-I bioactivity in both IGT subjects and controls (-16.2 +/- 2.8 and -13.9 +/- 3.3%, respectively; P < 0.01). In addition, insulin increased IGFBP-2 and GH and decreased IGFBP-1 and -4 but did not alter total IGF-I, IGF-II, or IGFBP-3 levels. During the oral glucose tolerance test, GH and IGFBP-1 were markedly suppressed. Subjects with IGT showed more pronounced insulin resistance and lower GH, IGFBP-1, and IGFBP-2 levels (P < 0.05). In multiple regression analysis, IGFBP-2 was an independent predictor of insulin sensitivity (beta = 0.36, P < 0.05) and IGF-I bioactivity (beta = -0.5, P < 0.05). CONCLUSIONS: Our data indicate that insulin acutely decreases IGF-I bioactivity through differential modulation of IGFBPs. Furthermore, IGFBP-2 plays a central role in the insulin-IGF system cross talk and is closely linked to insulin resistance, thereby providing a further explanation for its association with the metabolic syndrome.

Common carp (Cyprinus carpio) insulin-like growth factor binding protein-2 (IGFBP-2): molecular cloning, expression profiles, and hormonal regulation in hepatocytes.

In the present study, we cloned IGFBP-2 cDNA from common carp (Cyprinus carpio) liver. The 1879 bp full-length cDNA encodes 274 amino acid residues containing a putative signal peptide of 22 residues. Two IGFBP-2 transcripts with estimated sizes of 2.2 and 1.5 kb have been detected with Northern blot analysis in liver. Relatively high levels of IGFBP-2 mRNA were observed in all regions of brain, liver, pituitary, ovary and testis. Intermediate levels were observed in white muscle, thymus gland and head kidney, while in retina, heart and other tissues IGFBP-2 mRNA levels were very low. A significant level of IGFBP-2 mRNA was firstly detected at lens formation stage, and it continued to increase to the highest level at blood cycling stage, and fell to a relatively high level until hatching. The expression pattern of IGFBP-2 mRNA was similar during different stages of testis and ovary. At recrudescing stage the expression level was extremely low, but it sharply increased to a high level at matured stage, and finally brought back to the very low level at regressed stage. Hepatocytes IGFBP-2 mRNA was greatly reduced by growth hormone but increased by insulin. PD-98059 and LY-294002, the specific inhibitor of MEK and PI3K, increased IGFBP-2 mRNA expression level and completely blocked the inhibitory effect of GH. It is suggested that the MAPK and PI3 kinase-signaling pathways were involved in the decrease of IGFBP-2 mRNA expression induced by GH in primary cultured hepatocytes.

IGF-dependent and IGF-independent actions of IGF-binding protein-1 and -2: implications for metabolic homeostasis.

Insulin-like growth factor (IGF)-binding proteins (IGFBPs) confer temporospatial regulation to IGF bioactivity. Both stimulatory and inhibitory effects of IGFBPs on IGF actions have been described, and IGF-independent effects of several IGFBPs are emerging. Accumulating evidence indicates important roles for members of the IGFBP family in metabolic homeostasis. For example, IGFBP-1 concentrations fluctuate inversely in response to changes in plasma insulin levels, implicating IGFBP-1 in glucoregulation, and fasting levels of IGFBP-1 predict insulin sensitivity at the population level. IGFBP-2 concentrations reflect long-term insulin sensitivity and are reduced in the presence of obesity. Here, we review the evolving roles of IGFBP-1 and IGFBP-2 in metabolic homeostasis, summarize their effects on IGF bioactivity and explore putative mechanisms by which they might exert IGF-independent cellular actions.