Increase In IGF-II Research Articles

Ternary complex formation and IGFBP-3 proteolytic activity during childhood: age-dependent changes.

IGF-I is mainly sequestered in a 150-kDa ternary complex with IGF binding protein (IGFBP)-3 and the acid-labile subunit. Data on complex formation and factors influencing formation have not been established. Dissociation of IGF-I from the ternary complex is in part regulated by proteolysis of IGFBP-3, which reduces its affinity for IGF-I. Short small for gestational age (SGA) children have lower IGF-I and IGFBP-3 levels compared with healthy peers. The objective of the study was to determine complex formation in healthy normal-statured children and assess variables influencing complex formation. Second, we determined complex formation in short SGA children. Complex formation was assessed using (125)I-hIGF-I column chromatography in 70 controls (40 boys), median age 10.6 years, and 40 short SGA children (25 boys), median age 8.6 years. IGFBP-3 was determined by Western immunoblotting. (125)I-hIGF-I complex formation showed an age-specific pattern in healthy controls. Variables positively influencing ternary complex formation were higher serum IGF-I levels compared with IGFBP-3 levels (P < .001) and lower serum IGF-II (P < .001) and IGFBP-1 levels (P < .001). In addition, a higher presence of proteolyzed IGFBP-3 negatively influenced 150-kDa complex formation (P = .006). At a young age, healthy children showed considerable IGFBP-3 proteolytic activity, which declined with aging (P < .001). IGFBP-3 proteolytic activity was negatively correlated with IGF-I levels (P < .001). Compared with healthy controls, short SGA children showed reduced IGF-I levels (-1.3 vs 0.1 SD score) and increased proteolyzed IGFBP-3 (35.1% vs 12.2%). Age-specific normative values for (125)I-hIGF-I 150-kDa ternary complex formation are presented. A decrease in IGF-I and an increase in IGF-II, IGFBP-1, and IGFBP-3 proteolytic activity associate with reduced (125)I-hIGF-I ternary complex formation. Our results suggest that in conditions in which IGF-I levels are low, such as young age and in short SGA children, IGFBP-3 proteolytic activity is increased to ensure IGF-I bioavailability.

MRNA expression pattern of insulin-like growth factor components of granulosa cells and cumulus cells in women with and without polycystic ovary syndrome according to oocyte maturity

The mRNA expression of insulin-like growth factor (IGF) components was investigated in granulosa cells (GCs) and cumulus cells (CCs) sampled from immature and mature follicles in women with and without polycystic ovary syndrome (PCOS). Gene expression for IGF-binding protein (IGFBP) 3 in GCs definitely differed between normal women and women with PCOS, whereas increase in IGF-I and IGF receptor (IGFR) 2 mRNA in mature-follicle GCs, increase in IGF-II, IGFR-1, and IGFBP-4 mRNA in immature-follicle GCs, increase in IGFR-2 and IGFBP-2 mRNA in mature-follicle CCs, and increase IGFBP-6 mRNA in immature-follicle CCs were observed in both normal women and women with PCOS.

P46 Studies on the bivalent interaction of IGF-II with the insulin and type 1 IGF receptors

demonstrated the role of the IGF system in the regulation of trophoblast proliferation and survival and alterations in the IGF ligands or the receptors could have implications in the pathogenesis of trophoblastic diseases. The aim of this study was to investigate the role of the IGF system in trophoblast cell differentiation by evaluating the expression of genes of the IGF system during the process. We utilized the HTR8/Svneo extra villous trophoblast cell line and induced differentiation by stimulation with forskolin (FSK), an agonist of adenylyl cyclase, We found that cells treated with FSK 25mM for 72 hours secreted high levels of chorionic gonadotropin (hCG), a common differentiation marker of syncitiotrophoblast. Interestingly we found a hCG related increase in IGF-II and IGF-IIR mRNAs expression, suggesting an important role of this growth factor and its receptor during differentiation. To investigate the potential role of an autocrine IGF-II/IGF-IIR loop we obtained a stable IGF-IIR silenced HTR8/Svneo cell line by shRNA tranfection and induced differentiation aspreviously. After 72 hours of treatment with FSK we found a marked reduction in IGF-II mRNA levels, in comparison with the non-silenced cell line, together with a decrease in the expression in the IGF-I and Insulin receptors. In addition we observed a direct relation between IGF-IIR silencing with a delayed kinetic pattern of differentiation. In conclusion this study presents a first approximation to the autocrine role of IGFII/IGF-IIR system in trophoblastic cell differentiation.

Association of Elevated IGFBP-1 with Increased IGF-II Concentration in Patients with Carcinoma of the Liver

Insulin-like growth factors (IGFs) are mitogens for numerous types of cells including cancer cells. The aim of this work was to analyze some of the components of the IGF system to assess which could be potential clinical biomarkers for monitoring patients diagnosed with liver cancer. Compared to healthy persons, patients with liver cancer had a lower concentration of IGF-I and a higher concentration of IGFBP-1, whereas the concentrations of IGF-II and IGFBP-3 remained unchanged. The IGF-I:IGFBP-3 ratio decreased in patients with cancer, while the IGF-II:IGFBP-1 ratio was not altered. Patients with primary carcinoma and those scheduled for surgery had lower IGF-I and higher IGF-II and IGFBP-1 concentrations than patients with secondary carcinoma and those not eligible for surgery. It may be postulated that a liver with primary cancer is induced to increase IGF-II and IGFBP-1 synthesis more than a liver involved in metastatic response. Similarly, in patients eligible for liver surgery an increase in IGF-II may reflect a gradual change in the concentration associated with a different stage of disease. As increased synthesis of certain IGFBPs is necessary to compensate decreased production of the others or increased IGF production, determination of serum IGF-II, IGFBP-1 and their ratio may aid in estimating the compensatory capacity of the liver affected by cancer.

Association of elevated IGFBP-1 with increased IGF-II concentration in patients with carcinoma of the liver

Insulin-like growth factors (IGFs) are mitogens for numerous types of cells including cancer cells. The aim of this work was to analyze some of the components of the IGF system to assess which could be potential clinical biomarkers for monitoring patients diagnosed with liver cancer. Compared to healthy persons, patients with liver cancer had a lower concentration of IGF-I and a higher concentration of IGFBP-1, whereas the concentrations of IGF-II and IGFBP-3 remained unchanged. The IGF-I:IGFBP-3 ratio decreased in patients with cancer, while the IGF-II:IGFBP-1 ratio was not altered. Patients with primary carcinoma and those scheduled for surgery had lower IGF-I and higher IGF-II and IGFBP-1 concentrations than patients with secondary carcinoma and those not eligible for surgery. It may be postulated that a liver with primary cancer is induced to increase IGF-II and IGFBP-1 synthesis more than a liver involved in metastatic response. Similarly, in patients eligible for liver surgery an increase in IGF-II may reflect a gradual change in the concentration associated with a different stage of disease. As increased synthesis of certain IGFBPs is necessary to compensate decreased production of the others or increased IGF production, determination of serum IGF-II, IGFBP-1 and their ratio may aid in estimating the compensatory capacity of the liver affected by cancer.

Disruption of insulin-like growth factor-II imprinting during embryonic development rescues the dwarf phenotype of mice null for pregnancy-associated plasma protein-A

Pregnancy-associated plasma protein-A (PAPP-A), an insulin-like growth factor-binding protein (IGFBP) protease, increases insulin-like growth factor (IGF) activity through cleavage of inhibitory IGFBP-4 and the consequent release of IGF peptide for receptor activation. Mice homozygous for targeted disruption of the PAPP-A gene are born as proportional dwarfs and exhibit retarded bone ossification during fetal development. Phenotype and in vitro data support a model in which decreased IGF-II bioavailability during embryogenesis results in growth retardation and reduction in overall body size. To test the hypothesis that an increase in IGF-II during embryogenesis would overcome the growth deficiencies, PAPP-A-null mice were crossed with DeltaH19 mutant mice, which have increased IGF-II expression and fetal overgrowth due to disruption of IgfII imprinting. DeltaH19 mutant mice were 126% and PAPP-A-null mice were 74% the size of controls at birth. These size differences were evident at embryonic day 16.5. Importantly, double mutants were indistinguishable from controls both in terms of size and skeletal development. Body size programmed during embryo development persisted post-natally. Thus, disruption of IgfII imprinting and consequent elevation in IGF-II during fetal development was associated with rescue of the dwarf phenotype and ossification defects of PAPP-A-null mice. These data provide strong genetic evidence that PAPP-A plays an essential role in determining IGF-II bioavailability for optimal fetal growth and development.

The influence of dietary intake on the insulin-like growth factor (IGF) system across three ethnic groups: a population-based study.

The insulin-like growth factor (IGF) system has been implicated in the aetiopathogenesis of cancer, cardiovascular disease and diabetes. Since dietary factors and ethnicity are considered contributory to the development of these diseases, we examined the IGF system in relation to nutritional intake by ethnic group. Dietary intake in 257 subjects of White European, African-Caribbean and Pakistani ethnic origin living in Manchester, UK was assessed using ethnic-group-specific food-frequency questionnaires to assess habitual nutrient intake over the previous 12 months. Fasting IGF-I, IGF-II and IGF-binding protein-1 (IGFBP-1) concentrations were determined and their relationship to specific dietary constituents was analysed. Analysis by quintiles of nutrient intake showed a significant increase in circulating IGF-I concentration with increasing dietary fat intake (F for trend=3.9, ), saturated fat intake and for protein intake There was also a significant increase in IGF-II by quintiles of dietary protein intake There was a trend for increasing IGF-I with increasing energy intake. The relationships between circulating concentration of IGFBP-1, an acute regulator of IGF action, and fat/protein intake were opposite to those for IGF-I and IGF-II. Multiple linear regression modelling showed that people of Pakistani origin and older subjects had lower levels of IGF-I (Pakistani origin vs. others, ) (age, for both). There was an independent inverse relationship between IGF-I and dietary carbohydrate intake This study provides evidence for a dietary contribution to regulation of the IGF system, although the effects of ethnicity on circulating IGF levels remain dominant. We propose that the IGF system's influences on cancer risk in specific ethnic groups are potentially modifiable by dietary intervention.

Characterization of the growth hormone receptor in human dermal fibroblasts and liver during development.

Human tissues express growth hormone receptors (hGHR) by the 3rd mo of gestation. We assessed developmental changes in hGHR function in fibroblasts and liver, testing binding and hormonal response. Fetal cells showed low but reproducible hGH binding. No age-related changes occurred in fibroblasts (9 wk-34 yr). In contrast, there was a fourfold increase in hGH binding in postnatal liver, with a sixfold increase in hGHR mRNA. Both full-length and truncated hGHR mRNAs were detected in all livers. Cross-linking revealed a larger hGH/receptor complex in fetal liver. Fetal hepatocytes produced 10 times more insulin-like growth factor (IGF)-II than IGF-I, and responded to hGH (150 ng/ml) with a significant increase in IGF-II. Fetal hepatocytes secreted three IGF-binding proteins (IGFBPs), including IGFBP1, but not IGFBP3. hGH did not alter fetal hepatocyte IGFBPs but stimulated glucose uptake. Exposure of fibroblasts to hGH decreased hGH binding only in >1-yr postnatal fibroblasts, whereas treatment with dexamethasone (100-400 nM) increased binding only in postnatal cells. Thus, although fetal hepatocytes and fibroblasts possess functional hGHR, these receptors (and/or their signaling pathways) are immature or have adapted to the in utero environment.

Hypoxia increases insulinlike growth factor gene expression in rat osteoblasts.

Vascular disruption secondary to fracture leads to a hypoxic zone of injury where the oxygen tension at the center of the wound is quite low. In this dynamic microenvironment, a number of growth factors are elaborated to stimulate the synthetic processes of fracture repair. Previously the authors have shown the hypoxia-induced increase of vascular endothelial growth factor expression in osteoblasts. The purpose of these experiments was to examine osteoblast expression of insulinlike growth factors (IGF) I and II--cytokines believed to play a role in increased collagen synthesis, chemotaxis, and proliferation of osteoblasts in response to hypoxia. Primary cell cultures of osteoblasts isolated from neonatal rat calvaria were subjected to hypoxia (PO2 = 35 mmHg) for 0, 3, 6, 24, and 48 hours. Northern blot analysis of ribonucleic acid (RNA) from resulting cultures demonstrated a more than 60% increase in IGF-II messenger RNA (mRNA) expression after 3 hours of hypoxia. IGF-II mRNA expression continued to increase through later time points to 200% and 260% of baseline at 24 and 48 hours respectively. In contrast, IGF-I demonstrated no significant change in mRNA expression compared with baseline control (normoxia) cultures. In these experiments the authors have demonstrated a hypoxia-induced increase in IGF-II but not IGF-I in primary osteoblasts. The differential expression of these two growth factors may underscore important differences in the behavior of osteoblasts in the hypoxic fracture microenvironment. Taken together, these data add additional support to the theory that hypoxia induces gene-specific changes in expression of molecules important to extracellular matrix formation for successful bone healing.

Ontogeny of growth hormone (GH), insulin-like growth factors (IGF-I and IGF-II) and IGF binding protein-2 (IGFBP-2) in genetically lean and obese swine

Serum GH, IGF-I, IGF-II and IGFBP-2 concentrations were determined by radioimmunoassay in swine of genetic lines which were selected for high (obese) and low (lean) backfat. Blood samples were collected at birth, before and after nursing, at 1 and 3 days of age and at weekly or fortnightly intervals until 30 weeks of age. Overall, GH, IGF-I, IGF-II and IGFBP-2 were highest at birth and declined during the first week of postnatal life. An age-by-line interaction was apparent for GH and IGF-I during the early neonatal period with levels being higher in the lean line than the obese line at 1 day of age and similar at 1 week of age. At 3 to 5 weeks of age there was an elevation in GH which was greater in lean than obese pigs. IGFBP-2 concentration patterns were characterized by a nadir at 5 to 7 weeks of age and a decline from an apex at 8 weeks of age in both lines. IGF-II declined steadily from birth until about 10 weeks of age. A subsequent increase in IGF-II was then observed between 12 and 22 weeks, which was greater in the obese line and in male pigs but not apparent in lean females. At birth, pigs which had not nursed had higher GH and IGFBP-2 and lower IGF-I and IGF-II concentrations. The effect of nursing on IGF-I was significantly influenced by line. These data indicate that the endocrine milieu and developmental changes in the endocrine milieu of pigs with differing propensities for obesity differs, suggesting that there is an association between growth factors and physiological traits such as the development of obesity.

Retinoic acid regulates insulin-like growth factor II expression in a neuroblastoma cell line.

Insulin-like growth factors (IGF-I and IGF-II) are mitogenic polypeptides that play an important role in normal growth and development. IGF-II has been shown to stimulate the growth of neuroblastoma tumors in an autocrine and paracrine fashion. Critical in determining the role of IGF-II in tumorigenesis is the necessity to delineate factors affecting the transcription of IGF-II in normal and tumor tissues. To date such factors are poorly characterized. In this study we find that retinoic acid (RA), a naturally occurring morphogen, that has been shown to be indispensable in the development of the chick limb bud, stimulates an increase in IGF-II messenger RNA (mRNA) in the Lan-1-15N neuroblastoma cell line. This increase in IGF-II is coincident with RA mediated inhibition of DNA synthesis. An increase in the steady state levels of IGF-II mRNA is detectable within 2 h of RA treatment and maximal by 24 h. In RA-treated Lan-1-15N cells, IGF-II mRNA levels are regulated at the level of new gene transcription and result in an increase in IGF-II protein in the culture supernatant. These studies suggest one mechanism affecting the production of IGF-II in vivo may be mediated by RA and detail a model system by which transcriptional regulation of IGF-II mRNA can be analyzed.