Increased levels of circulating free insulin-like growth factors in patients with non-islet cell tumour hypoglycaemia

Summary Non-islet cell tumour hypoglycaemia (NICTH) is characterised by severe and recurrent fasting hypoglycaemia, and is usually caused by secretion of insulin-like growth factor-II (IGF-II) by the tumour. This induces secondary changes in the circulating levels of insulin, growth hormone (GH), and the IGF-binding proteins (IGFBPs), resulting in an increased insulin-like hypoglycaemic activity of IGF-II. A participating role of IGF-I is not established. We measured serum levels of free IGF-I and free IGF-II, total IGF-I, total IGF-II, big IGF-II and IGFBP-1, IGFBP-2 and IGFBP-3 in patients with NICTH before (n = 14) and after surgical removal of the tumour (n = 3). A control group (n = 20) was included for comparison. In NICTH patients, free IGF-II was 20-fold increased (26.8 ± 8.1 [mean ± SEM] vs. 1.3 ± 0.1 μg/l), and free IGF-I was four fold increased (2.8 ± 0.4 vs. 0.7 ± 0.1 μg/l), as compared to control subjects (p < 0.0001). In accordance with earlier observations levels of total IGF-I, total IGF-II, and IGFBP-3 were decreased, whereas IGFBP-1 and IGFBP-2 were increased in NICTH (all p-values < 0.05). The highly elevated levels of free IGF-I and free IGF-II most likely imply a considerable hypoglycaemic insulin-like activity, and may, by negative feedback explain the marked suppression of the GH/IGF-I axis observed in NICTH. Finally, free IGF-II seems to be a powerful biochemical marker in the diagnosis of NICTH. [Diabetologia (1998) 41: 589–594] Received: 21 October 1997 and in final revised form: 15 December 1997     

Abnormal serum IGF-II transport in non-islet cell tumor hypoglycemia results from abnormalities of both IGF binding protein-3 and acid labile subunit and leads to elevation of serum free IGF-II

The syndrome of non-islet cell tumor hypoglycemia (NICTH) is the result of hypersecretion of IGF-II by a tumor although serum IGF-II is seldom elevated. This is attributable to abnormalities of the IGF binding proteins (IGFBPs) present in NICTH which is characterized by a marked decrease in the fraction of IGFBP-3 present in the 150 kD complex with acid labile subunit (ALS) and a 2- to 4-fold increase in IGFBP-2. We studied the impact of these changes in IGFBPs on the concentration of free IGF-II using a neutral C-18 Sep-Pak extraction procedure. We found that free IGF-II was increased 8- to 20-fold in NICTH. Thus there is no limitation of free IGF-II for complex formation. Additional experiments were conducted to determfine whether ALS deficiency limits 150 kD complex formation. We observed that addition of purified ALS to NICTH sera only partially succeeded in converting smaller complexes containing IGFBP-3 to large 150 kD complexes. We conclude that both a functional deficiency of ALS and IGFBP-3 are present in NICTH sera. The increased free IGF-II in NICTH sera contributes greatly to bioactivity and largely explains the marked hypoglycemia of NICTH patients even when total serum IGF-II concentrations may remain within normal limits.     

Serum "big insulin-like growth factor II" from patients with tumor hypoglycemia lacks normal E-domain O-linked glycosylation, a possible determinant of normal propeptide processing.

The insulin-like growth factor II (IGF-II) gene is overexpressed in many mesenchymal tumors and can lead to non-islet-cell tumor hypoglycemia (NICTH). ProIGF-II consists of the 67 aa of IGF-II with a carboxyl 89-aa extension, the E domain. A derivative of proIGF-II containing only the first 21 aa of the E domain [proIGF-II-(E1-21)] has been isolated by others from normal serum and has O-linked glycosylation. We found that the "big IGF-II" of normal serum, as detected by an RIA directed against residues 1-21 of the E domain of proIGF-II, was reduced in size by treatment with neuraminidase and O-glycosidase. The big IGF-II, which is greatly increased in NICTH sera, was unaffected by neuraminidase and O-glycosidase treatment. We have also shown that big IGF-II from normal serum is retained by jacalin lectin columns and that big IGF-II from NICTH serum was not retained, indicating that it lacked O-glycosylation. Normal O-linked glycosylation may be required for proper peptidase processing of proIGF-II. The lack of normal O-linked glycosylation by tumors may explain the predominance of big IGF-II in NICTH sera. In normal serum, most of the IGF-II is present in a 150-kDa ternary complex with IGF-II binding protein (IGFBP) 3 and alpha subunit. In NICTH serum, however, the complexes carrying big IGF-II are < 50 kDa. We investigated whether big IGF-II of NICTH was responsible for this abnormality. Tumor big IGF-II and IGF-II were equally effective in forming the 150-kDa complex with purified IGFBP-3 and 125I-labeled alpha subunit. Both 125I-labeled IGF-II and 125I-labeled proIGF-II-(E1-21), when incubated with normal serum, formed the 150-kDa complex as detected by Superose 12 exclusion chromatography. We conclude that the nonglycosylated big IGF-II of NICTH serum can form normal complexes with serum IGFBPs. The defective binding in NICTH is attributable to defective IGFBP-3 binding.     

Alterations of the 11p15 imprinted region and the IGFs system in a case of recurrent non-islet-cell tumour hypoglycaemia (NICTH)

BACKGROUND: AND OBJECTIVE: Non-islet-cell tumour hypoglycaemia (NICTH) is a rare disorder and has been explained by oversecretion of non mature IGF-II and dysregulation of the IGFs sytem. The mechanisms responsible for tumoural IGF-II overexpression in NICTH have been rarely studied. We report an extensive study of IGF-II and IGFBPs as well as chromosome 11p15 gene expression regulation in a case of a pleural fibrosarcoma in a 63-year-old patient presenting with NICTH. METHODS AND RESULTS: Abnormal high molecular weight precusor forms of IGF-II were present in the patient's serum and were associated with dramatic alterations in the circulating levels of IGF-I, IGF-II and their binding proteins, as well as an inhibition of the somatotroph axis. These alterations returned to normal following complete surgical removal of the tumour. No structural change in chromosome 11p15 region was apparent in the tumour. However, dysregulation of this imprinted region was demonstrated, leading to the loss of imprinting of the IGF-II gene associated with high IGF-II expression, and by contrast decreased level of expression of H19 and p57KIP2 genes. Recurrence of the tumour four years latter was not associated with hypoglycaemia or changes in the levels of circulating IGFs or IGFBPs, despite IGF-II overexpression by the tumour. This suggests that a large tumour volume is required to reach high enough levels to cause changes in the levels of circulating IGFs and IGFBPs, and to cause hypoglycaemia. CONCLUSION: These results suggest that a dysregulation of gene expression and imprinting of chromosome 11p15 region is associated with tumour growth and IGF-II overexpression in non-islet-cell tumour hypoglycaemia.     

Column chromatographic characterization of complex formation of pro-IGF-II isoforms with acid labile subunit and IGF-binding proteins associated with non-islet cell tumour induced hypoglycaemia

Objective and designNon-islet cell tumour induced hypoglycaemia (NICTH) is a paraneoplastic phenomenon that is associated with the formation of several isoforms of pro-insulin like growth factor 2 (pro-IGF-II), or so called “big” IGF-II. Disturbance of ternary complex formation by big IGF-II is assumed to be a crucial early event in the pathogenic cascade of hypoglycaemia.By size-exclusion chromatography, we investigated complex formation by adding different naturally occurring isoforms of pro-IGF-II to pooled normal adult serum. Results were compared with the analysis of the serum from a patient with NICTH.ResultsGel filtration experiments with the serum of a patient with NICTH demonstrated that ternary complex formation was severely compromised.The various forms of pro-IGF-II did not induce a shift of IGF-binding protein 3 (IGFBP-3) from 150 kD towards smaller binary complexes in the normal adult serum, suggesting that they did not interfere with the interaction between the acid labile subunit and IGFBP-3. Instead, unglycosylated recombinant pro-IGF-II[1–104] was capable of forming a 150 kD complex. In contrast, predominantly glycosylated and unglycosylated pro-IGF-II[1–87] eluted in the free unbound form. We showed that mature IGF-II and isoforms of pro-IGF-II were able to phosphorylate the IGF-I receptors of MC7 cells, albeit to a markedly lesser extent than IGF-I. When the patient's serum was tested in this system, the IGF-I receptor phosphorylation activity was considerably less than that in sera from age matched healthy individuals.ConclusionWe postulate that, alongside the presence of big IGF-II in the circulation, additional steps are required to stimulate the release of IGF-II and pro-IGF-II isoforms from IGFBPs in vivo. These factors may be proteases, that are present in the local environment of the tumour and in insulin-sensitive tissues.     

Altered expression of IGFs and IGF-binding proteins during intrauterine growth restriction in guinea pigs

The IGF system is one of the most important endocrine and paracrine growth factor systems that regulate fetal and placental growth. We hypothesized that intrauterine growth restriction (IUGR) in guinea pigs is mediated by the altered expression of IGFs and/or IGF binding protein (BP) mRNAs in tissues and is related to growth of specific tissues. IUGR was induced by unilateral uterine artery ligation on day 30 of gestation, and fetal plasma, amniotic fluid and tissue samples were collected at 55-57 days (term about 68 days) from paired IUGR and control fetuses (n=6). Western ligand blotting and immunoblotting were used to compare IGFBP levels in plasma and amniotic fluid. Total RNA was extracted from placenta and fetal tissues, and the relative abundance of IGF-II and IGFBP-1-6 mRNA was determined by Northern blotting, using species-specific probes where available. IUGR fetuses had decreased (P<0.01, by Student's t-test) placental weight and body weight with an increase in the brain:liver weight ratio. The principal IGFBPs in fetal plasma migrated at 40-35, 30 and 25 kDa and were identified as IGFBP-3, -2 and -4 respectively. IUGR was associated with elevated plasma IGFBP-2 and IGFBP-4 and reduced IGFBP-3 levels. IGFBPs were detected at low levels in amniotic fluid of control fetuses but at higher levels in IUGR fetuses. In IUGR placentae, there was a small increase in IGFBP-4 mRNA (P<0.05). IGFBP-2 mRNA increased (P<0.001) in liver of IUGR fetuses. IGF-II and IGFBP mRNA expression did not change in fetal muscle. The results are consistent with reduced IGF action, directly or through inhibition by IGFBPs, particularly by circulating and tissue IGFBP-2, as a potential causal factor in decreased growth of the placenta and certain fetal tissues.     

Inflammation is a modulator of the insulin-like growth factor (IGF)/IGF-binding protein system inducing reduced bioactivity of IGFs in cystic fibrosis

OBJECTIVE: In inflammatory bowel diseases, increased serum interleukin (IL)-6 levels are associated with high serum insulin-like growth factor-binding protein 2 (IGFBP-2) levels, and cytokines modify the insulin-like growth factor (IGF)/IGFBP system in models in vitro. In cystic fibrosis (CF) the IGF/IGFBP system has not been extensively studied, and relationships with proinflammatory cytokines have not been explored. The aim of this study was to investigate the IGF/IGFBP system and verify changes dependent on IL-1beta, IL-6, tumour necrosis factor alpha (TNFalpha), and insulin. METHODS: Eighteen subjects with CF (mean age 26.6 +/- 1.1 years) and 18 controls, comparable for age, sex, and body mass index, were enrolled. Serum IGF-I, IGF-II, IGFBP-2, IGFBP-3, IL-1beta, IL-6, TNFalpha, insulin and C-peptide were measured. Different molecular forms of IGFBP-2 and IGFBP-3 were investigated by Western immunoblotting. The patients were analysed as a whole and as two subgroups depending on established clinical criteria (Swachman-Kulczycki score). RESULTS: Patients had higher serum concentrations of IL-1beta, IL-6, TNFalpha and IGFBP-2 than controls. Serum concentrations of IGF-I and IGF-II were significantly lower and insulin and C-peptide levels significantly increased in CF compared with healthy controls whereas IGFBP-3 serum concentrations were similar, with comparable IGF-I/IGFBP-3 and decreased IGF-I/IGFBP-2 and IGF-II/IGFBP-2 molar ratios. From correlation analysis we detected a significant positive correlation between IGFBP-2 and IL-6 and a negative correlation between IGFBP-2 and IGFBP-3. CONCLUSIONS: Our findings suggest that inflammation is an important modulator of the IGF/IGFBP system with an overall reduction in IGF bioactivity in CF.     

Characterization of human insulin-like growth factor-binding proteins by two-dimensional polyacrylamide gel electrophoresis and Western ligand blot analysis.

The insulin-like growth factor (IGF)-binding proteins (IGFBPs) from adult human serum, amniotic fluid, and cerebrospinal fluid were analyzed by a modified two-dimensional gel electrophoresis followed by Western ligand blotting. The samples were subjected to immobilized pH gradient isoelectric focusing in the first dimension, followed by nondenaturing SDS-PAGE in the second dimension and autoradiography after ligand blotting with [125I]IGF-I or [125I]IGF-II. The identity of the binding proteins was confirmed by immunoblotting and immunoprecipitation with specific antibodies. Using this method, all six human high affinity IGFBPs could be clearly separated from each other according to their molecular mass and isoelectric points (pI). All IGFBPs exhibited a variety of specific pI isoforms, which presumably represent posttranslational modifications. In adult human serum, glycosylated IGFBP-3 is found as a broad band of spots with molecular masses of 41 and 45 kDa and a pI in the range of 4.8-8.2. The two IGFBP-3 bands could be reduced to a single 36-kDa band after deglycosylation (pI 6-9). Furthermore, the specific spots for IGFBP-2 (33 kDa; pI 6.2-7.1) and deglycosylated IGFBP-4 (24 kDa; pI 6.3, 6.5, and 6.8) were found with their expected molecular masses. Additionally, the diffuse bands around 30 kDa, found in one-dimensional Western ligand blotting, could be clearly separated into distinct groups of specific spots representing IGFBP-1 (30 kDa; pI 4.0-4.8), IGFBP-6 (30 kDa; pI 4.8-5.8), glycosylated IGFBP-4 (29 kDa; pI 6.1 and 6.3), and IGFBP-5 (30/31 kDa; pI 6.4-8). As expected, IGFBP-6 was visible only when IGF-II was used as radioligand. In conclusion, two-dimensional gel electrophoresis followed by Western ligand blotting allows identification of all six high affinity IGFBPs with their isoforms on the basis of their characteristic molecular masses and pI, especially in the range of 30 kDa. This technique can be rapidly performed with small amounts of complex biological fluids and is a powerful tool for the detection and analysis of posttranslational modifications of IGFBPs.     

The insulin-like growth factors and their binding proteins in a case of non-islet-cell tumour-associated hypoglycaemia.

Non-islet-cell tumours which induce hypoglycaemia are rare. Insulin-like growth factor-II (IGF-II) produced by some tumours is thought to be responsible for the hypoglycaemia and other systemic effects, despite normal or even low serum IGF-II levels. We studied a 44-year-old woman presenting with symptomatic hypoglycaemia associated with a large intraabdominal haemangiopericytoma. The serum IGF-II level was 455 micrograms/l when measured after acid-ethanol extraction (normal range (NR) 450-750 micrograms/l) and 1063 micrograms/l after acid chromatography (normal human serum pool 1068 micrograms/l). Levels of fasting plasma insulin, C-peptide, glucose and serum IGF-I levels were low before the operation (less than 2 mU/l (NR less than 2-14), 0.23 nmol/l (NR 0.4-1.2), 3.1 mmol/l, (NR 3.7-5.9) and 0.02 U/ml respectively). After tumour removal, the symptoms resolved rapidly and the patient made a full recovery. Secretion of both insulin and growth hormone was suppressed before the operation in response to a 75 g glucose meal and to an infusion of 100 micrograms GH-releasing hormone (GHRH) respectively in comparison with studies after the operation. Serum IGF-II levels 6 weeks and 12 weeks after the operation fell to 385 micrograms/l (777 micrograms/l; acid chromatography) and 280 micrograms/l (647 micrograms/l; acid chromatography) and serum IGF-I levels increased to 0.35 U/ml and 0.26 U/ml. Serum before the operation and tumour extract contained chiefly a large molecular weight precursor IGF-II (molecular weight 15,000-20,000) which disappeared from the serum after the operation. The IGF-binding proteins (IGFBP-1, IGFBP-2, IGFBP-3 and IGFBP-4) were examined.(ABSTRACT TRUNCATED AT 250 WORDS)     

Clinical features of insulin-like growth factor-II producing non-islet-cell tumor hypoglycemia.

In some patients with non-islet-cell tumor hypoglycemia (NICTH), a high molecular weight form of IGF-II (big IGF-II) derived from tumors is present in the circulation and might be associated with recurrent hypoglycemia. In this study, in order to survey the clinical characteristics of patients with IGF-II producing NICTH, we analyzed the medical records of 78 patients with NICTH (M/F 44/34, age 62+/-1.8, range; 9-86 years.) whose serum contained a large amount of big IGF-II. Hepatocellular carcinoma and gastric carcinoma were the most common causes of NICTH. The diameters of the tumors were more than 10 cm in 70% of the patients. Basal immunoreactive insulin (IRI) levels were less than 3 microU/dl in 79% of the patients. Hypoglycemic attack was the onset of disease in 31 of 65 cases (48%), but the tumor was revealed prior to the occurrence of hypoglycemia in 34 cases (52%). Twenty-five of 47 (53%) patients had decreased serum potassium levels. These data suggested that hypoinsulinemic hypoglycemia associated with the presence of a large tumor supports the diagnosis of IGF-II producing NICTH. Hypokalemia was associated with hypoglycemia in some patients. The BMI (21.4+/-0.6 kg/m2) and serum total protein levels (6.6+/-0.1g/dl) were preserved at the occurrence of first hypoglycemic attack suggesting that malnutrition might not be the main cause of hypoglycemia in most patients.     

The effectiveness of different treatment options for non-islet cell tumour hypoglycaemia

OBJECTIVE: To compare the outcome of different treatment options used in several cases of non-islet cell tumour hypoglycaemia (NICTH). PATIENTS: Eight cases of NICTH were referred for diagnosis and monitoring following either surgical or medical treatment. METHODS: Serum samples collected throughout the time-course of each case were analysed for glucose, insulin, C-peptide, IGF-I, total IGF-II, total IGF-II to IGF-I ratio and, in most of the cases, big IGF-II. RESULTS: Surgical excision was successful in the relief of symptoms and normalization of the biochemical parameters. Therapeutic treatment with glucocorticoids confirmed previous studies showing the suppressive effect on tumour (big) IGF-II production. The present data show that the effect was dose-dependent and reversible if doses were below a critical level. CONCLUSIONS: Within the limits of the cases studied, and the time-scales involved, moderate- to high-dose glucocorticoid therapy had immediate beneficial influence on symptomatic hypoglycaemia and, if tolerated in the long term, was effective in correcting the underlying biochemical dysfunction, unlike other therapeutic regimens. This effectiveness was only achieved when the dose exceeded a threshold level specific to the patient. In addition, reduction of the dose or withdrawal of the drug caused a return of the abnormal biochemical profile. Surgical removal of the malignancy, where this was an option, was successful within the periods studied.     

Insulin-like growth factors (IGFs) and IGF-binding proteins in the developing rhesus monkey.

Rhesus monkeys follow a developmental pattern of serum insulin-like growth factor-I (IGF-I) levels similar to that found in humans. In these monkeys, serum IGF-I levels peak during puberty (2.5-4.5 yr of age in males). We have examined the developmental pattern of IGF-binding protein-1 (IGFBP-1), -2, and -3 in serum by Western ligand blotting, the levels of IGFBP-3, IGF-I, and IGF-II in serum by RIA, and the IGFBP mRNA levels of IGFBP-1, -2, and -3 in the livers of rhesus monkeys from fetal life through adulthood by Northern analysis. The pattern of the serum levels of the IGFBPs reflected the liver mRNA levels of the IGFBPs. The IGFBP-1 and IGFBP-2 liver mRNA and serum levels were highest in the fetus and first year of life and were very low after 4 yr of age. Conversely, the IGFBP-3 liver mRNA and serum levels were relatively low early in life and peaked during puberty. The serum levels of IGF-I and IGF-II were strongly correlated with the level of IGFBP-3. We conclude that the developmental pattern of IGFBPs in the rhesus monkey is similar to that in the human, and that serum IGFBP levels are probably regulated by the rate of IGFBP mRNA synthesis.     

Severe Hypoglycemia Caused by Recurrent Sarcomatoid Carcinoma in the Pelvic Cavity: A Case Report

Nonislet cell tumor hypoglycemia (NICTH) is a paraneoplastic syndrome characterized by persistent, severe hypoglycemia in different tumor types of mesochymal or epithelial origin; however, NICTH is infrequently induced by sarcomatoid carcinoma (SC). Despite some sarcomatoid and epithelioid characteristics in few cases of malignancies from epithelium, NICTH induced by recurrent SC in pelvic cavity in this report is extremely rare.We report a case in which NICTH caused by recurrence and pulmonary metastases from SC in the pelvic cavity, and the computed tomography scan revealed multiple pelvic masses and multiple large masses in the pulmonary fields. During the treatment of intestinal obstruction, the patient presented paroxysmal loss of consciousness and sweating. Her glucose even reached 1.22 mmol/L while the serum glycosylated hemoglobin was normal and previous history of diabetes or use of oral hypoglycemic agents and insulin denied.The laboratory examination showed that the low level of insulin, C-peptide, and growth hormone levels in the course of hypoglycemic episodes suggesting to the diagnosis of hypoglycemia induced by nonislet cell tumor, and the decreased levels of insulin-like growth factor (IGF)-I and IGFBP3 and the high expression of big IGF-II in the serum further confirmed the diagnosis of NICTH. Because of the widely pelvic recurrence and pulmonary metastases were unresected, the patient was discharged from the hospital after 2 weeks treatment with dexamethasone and glucose and unfortunately died 1 week later.NICTH caused by SC in the pelvic cavity is extremely rare case in clinical. The aim of this report was to present the importance to examine big IGF-II expression in patient''s serum in order to reach the diagnosis of NICTH in cases of intractable cancer-associated hypoglycemia.     

Effect of thyroxine administration on the IGF/IGF binding protein system in neonatal and adult thyroidectomized rats

The effects of different doses of thyroxine (T(4)) delivered by injection or s.c. pellet implantation on alterations of the IGF/IGF binding protein (IGFBP) system were studied in neonatal and adult thyroidectomized (Tx) rats. Body weight, blood glucose, plasma insulin, TSH and GH and pituitary GH content, as well as serum IGF-I, IGF-II, IGFBP-1, -2 and -3 and their liver mRNA expression were assayed. Pellet implantation with the smaller dose of T(4) (1.5 microg/100 g body weight (b.w.) per day) in Tx neonatal rats decreased serum IGF-I, -II and the 30 kDa complex of IGFBPs (IGFBP-1 and -2), and increased serum IGFBP-3. Only the larger dose of T(4) (3 microg/100 g b.w. per day) recovered liver mRNA expression of IGF-I and ensured euthyroid status as shown by the normalized levels of plasma TSH. The rapid increase of body weight and serum GH after T(4) administration indicated a high sensitivity to T(4) during the neonatal period. Serum and liver mRNA expression of IGFs and plasma insulin and GH recovered in adult Tx rats after pellet implantation of 1.75 microg/100 g b.w. per day throughout 10 days. The continuous replacement of T(4) by pellet seems to be the most suitable method for thyroid rehabilitation. A very good correlation was found between insulin and IGF-II in Tx neonates treated with T(4) but not between insulin and IGF-I in Tx adults. IGFBP-2 seems to be up-regulated by T(4) deprivation in neonatal and adult rats. Finally, a good correlation as well as a partial correlation were found between IGFs and thyroid hormones in both neonatal and adult Tx populations, suggesting a direct effect in vivo of T(4) on the hepatic secretion of IGFs, as previously suggested in vitro.     

Binding characteristics of pro-insulin-like growth factor-II from cancer patients: binary and ternary complex formation with IGF binding proteins-1 to -6

Many tumours secrete IGF-II in incompletely processed precursor forms. The ability of these pro-IGF-II forms to complex with the six IGF binding proteins (IGFBPs) is poorly understood. In this study, pro-IGF-II has been extracted from the serum and tumour tissue of two patients with non-islet cell tumour hypoglycaemia. These samples were used to study binary complex formation with IGFBPs-1 to -6 using competitive IGF-II binding assays and ternary complex formation with IGFBP-3 and IGFBP-5. In each case, IGFBPs-1 to -6 showed little difference in their ability to form binary complexes with recombinant IGF-II or tumour-derived pro-IGF-II forms, when the preparations were standardised according to IGF-II immunoreactivity. As previously described, ternary complex formation by acid-labile subunit (ALS) with IGFBP-3 and pro-IGF-II was greatly decreased compared with complex formation with mature IGF-II. In contrast, ALS bound similarly to IGFBP-5 in the presence of pro-IGF-II and mature IGF-II. These studies suggest that pro-IGF-II preferentially forms binary complexes with IGFBPs, and ternary complexes with IGFBP-5, rather than ternary complexes with IGFBP-3 as seen predominantly in normal serum. This may increase the tissue availability of serum pro-IGF-II, allowing its insulin-like potential to be realised.     

Insulin-like growth factor (IGF) binding proteins modulate the glucocorticoid-dependent biological effects of IGF-II in cultured fetal rat hepatocytes

The role of insulin-like growth factor binding proteins (IGFBPs) in regulation by IGF-II of glycogenesis and DNA synthesis was investigated in hepatocytes isolated from fetal rat livers at days 15 and 18 of gestation and grown in the presence or absence of cortisol. IGFBP-1 was clearly revealed by Western ligand blot and immunoblot analysis of IGFBPs secreted into conditioned media. Its production and cellular messenger RNA (mRNA) were positively regulated by cortisol and increased in older cells. In the absence of IGFBP (fresh medium), glycogenesis, and DNA synthesis were stimulated by IGF-II and insulin. In each case, cortisol enhanced this stimulation. In the presence of IGFBPs (cell-conditioned media), IGF-II stimulation of DNA synthesis and to a lesser extent glycogenesis was inhibited. The degree of inhibition was directly related to IGFBP-1 production. IGFBPs had no effect on stimulation of glycogenesis and DNA synthesis by des(1-6)IGF-II, a structural analog of IGF-II that does not bind to IGFBPs. Insulin, whose biological effects were not modified by conditioned media, inhibited IGFBP-1 production. Comparison of the dose dependence of the two bioactivities showed that DNA synthesis was more sensitive to IGF-II than glycogenesis. Our results suggest that in the case of DNA synthesis the effects of IGF-II are mediated via the IGF-I receptor and those of insulin via the insulin receptor, whereas in the case of glycogenesis both are mediated via the insulin receptor. In conclusion, IGF-II and insulin stimulation of glycogenesis and DNA synthesis in cultured fetal hepatocytes depends on the presence of glucocorticoid and the stage of development. IGF-II action is negatively regulated by IGFBP-1 whose synthesis increases in the presence of glucocorticoids.     

Insulin-like growth factors (IGFs) reduce IGF-binding protein-4 (IGFBP-4) concentration and stimulate IGFBP-3 independently of IGF receptors in human fibroblasts and epidermal cells.

Recent studies have provided a consensus that insulin-like growth factor-I (IGF-I) stimulates IGF-binding protein-3 (IGFBP-3) in vivo and in vitro. While it also appears well established that IGFBP-1 is inversely related to insulin concentrations, evidence regarding regulation of other IGFBP is inconclusive. Using immunoprecipitation and Western ligand blot, we have characterized the IGFBPs released into conditioned medium (CM) by cells from the adult human fibroblast cell line N3652 and the human epidermal squamous cell carcinoma line SCL-1. N3652 cells expressed IGFBP-3, IGFBP-2, a 24-kilodalton (kDa) IGFBP presumed to be IGFBP-4, and IGFBPs at 30 and 28 kDa. SCL-1 expressed IGFBP-3 and a putative IGFBP-4, with intermediate bands at 34 and 30 kDa. As determined by ligand blot of CM from confluent cells 72 h after the addition of peptides to serum-free medium, IGF-I and IGF-II potently stimulated IGFBP-3 in both cell lines, but otherwise IGFBP regulation in the two cells diverged. In N3652 cells, IGFBP-3 concentrations in CM increased to 700% and 800% of basal levels in the presence of IGF-I and IGF-II (at 100 ng/ml; n = 5 experiments), respectively. IGFBP-3 was not affected by insulin up to 10 micrograms/ml. In contrast, IGFBP-4 levels were diminished 54% and 73% by 100 ng/ml IGF-I and IGF-II, respectively, with no response to insulin. In SCL-1 cells, IGF-I and IGF-II were virtually identical in stimulating a mean 200% increase in IGFBP-3 (n = 5 experiments). Insulin was less potent, but caused a significant stimulation of IGFBP-3 levels. IGF-I, IGF-II, and insulin all stimulated an approximately 50% increase in IGFBP-4 concentrations. To test the hypothesis that IGF-induced alterations in IGFBP-3 and IGFBP-4 concentrations were regulated via the type 1 IGF receptor, we attempted to block IGFBP changes with type 1 IGF receptor antibody alpha IR-3 and to induce IGFBP changes with an IGF-II analog, [Leu27]IGF-II, with little affinity for the type 1 receptor. alpha IR-3 failed to block either the IGF-induced rise in IGFBP-3 in each cell line or the decline in IGFBP-4 in N3652 CM. [Leu27]IGF-II was as potent as IGF-II or IGF-I in inducing changes in IGFBP-3 and IGFBP-4 concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)     

Characterization of the high molecular weight insulin-like growth factor complex in term pregnancy serum.

Insulin-like growth factors (IGFs) circulate in human adult serum predominantly as a high mol wt complex of 150 kilodaltons (kDa), which is made up of three subunits: alpha, the acid-labile subunit, a glycoprotein of around 85-100 kDa; beta, the acid-stable IGF-binding protein subunit, which is the 40-kDa GH-dependent glycoprotein IGF-binding protein-3 (IGFBP-3); and gamma, the 7.5 IGF-I or -II peptide subunit. During human pregnancy, all three subunits are elevated when measured by RIA. However, recent ligand blotting studies have shown that IGFBP-3 is markedly reduced during pregnancy. When pregnancy serum is acidified and neutralized to inactivate endogenous alpha-subunit, ternary complex formation is normal with exogenous radiolabeled alpha-subunit, indicating functional IGFBP-3. We have attempted to clarify the status of IGFBP-3 and the high mol wt (alpha beta gamma) complex in human term pregnancy serum by further analyses. Term pregnancy (TP) or nonpregnancy (NP) pooled sera were fractionated on a S-300 neutral column. The high mol wt (125-150 kDa) and the low mol wt (30-40 kDa) IGF-IGFBP complexes were identified by both RIA for IGFBP-3 and ligand blotting; each was pooled separately. Half of each pool was lyophilized and rechromatographed in acid to separate the IGF-I peptides from their IGFBPs. The IGFBP fractions were recovered for further studies. When the IGFBPs from the high mol wt complex were cross-linked to [125I]IGF-I or -II, bands of 48, 34, 26, and 21 kDa, which were more intense with [125I]IGF-II, were observed, and all were immunoprecipitable by anti-IGFBP-3 antibody. The smaller forms were elevated in TP serum. Affinity cross-linking analysis with [125I]alpha-subunit showed that the IGFBPs from the high mol wt, but not the low mol wt, complex can reform the ternary 150-kDa complex when cold IGF-I or IGF-II is added exogenously. A smaller 130-kDa complex was also present, and it was the predominant form in TP serum. Both bands were immunoprecipitable by anti-IGFBP-3 antibody. When purified alpha-subunit or fractions from neutral Sephacryl S-300 chromatography were cross-linked to covalent [125I]IGF-II:IGFBP-3, a specific band at 150 kDa was observed with pure alpha-subunit as well as with S-300 150- to 100-kDa serum fractions. These results suggest that 1) functional alpha-subunit is present in TP serum; 2) intact as well as smaller fragments of IGFBP-3 are present in the big complex of TP serum and are able to bind IGF and complex with alpha-subunit; and 3) IGFBP-3 in TP serum has reduced binding to [125I]IGF-I, but not to [125I]IGF-II.