Insulinlike growth factor binding proteins

Metallothionein 2A Expression in Cancer-Associated Fibroblasts and Cancer Cells Promotes Esophageal Squamous Cell Carcinoma Progression

Simple Summary

Cancer-associated fibroblasts (CAFs) are tumor promoters in various cancers. We previously reported a correlation between the high expression of the CAF marker fibroblast activation protein and poor prognosis of esophageal squamous cell carcinoma (ESCC). We also found that metallothionein 2A (MT2A) is highly expressed in CAF-like cells that we established. In the current study, we explored the role of MT2A in ESCC progression. MT2A expression in the CAF-like cells induced expression and secretion of insulin-like growth factor binding protein 2 (IGFBP2), which promoted the migration and invasiveness of ESCC cells through the NFκB, Akt, and Erk signaling pathways. Furthermore, MT2A was involved in ESCC cell growth, migration, and invasiveness. Moreover, high expression of MT2A in the cancer tissue correlated with poor prognosis of ESCC patients. Briefly, we demonstrate that MT2A and IGFBP2 are potential novel therapeutic targets in ESCC.

Abstract

Esophageal cancer has the sixth highest mortality rate worldwide. Cancer-associated fibroblasts (CAFs) are involved in the progression of various cancers. Previously, we demonstrated an association between high expression of the CAF marker, fibroblast activation protein, and poor prognosis of esophageal squamous cell carcinoma (ESCC). We also established CAF-like cells by indirect co-culture of bone marrow-derived mesenchymal stem cells with ESCC cell lines and found metallothionein 2A (MT2A) to be highly expressed in them. Here, to explore the function of MT2A in CAFs, we silenced MT2A in the CAF-like cells and ESCC cell lines using small interfering RNA. MT2A knockdown in the CAF-like cells suppressed expression and secretion of insulin-like growth factor binding protein 2 (IGFBP2); recombinant IGFBP2 promoted migration and invasiveness of ESCC cells via NFκB, Akt, and Erk signaling pathways. Furthermore, MT2A knockdown in the ESCC cell lines inhibited their growth, migration, and invasiveness. Immunohistochemistry demonstrated that high MT2A expression in the cancer stroma and cancer nest of ESCC tissues correlated with poor prognosis of ESCC patients. Hence, we report that MT2A in CAFs and cancer cells contributes to ESCC progression. MT2A and IGFBP2 are potential novel therapeutic targets in ESCC.

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 EGFR, which subsequently activates 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 TCGA database for human glioma. A high level of all 3 proteins (IGFBP2, EGFR and STAT3) was strongly correlated with poorer survival in an independent patient dataset. 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 2 distinct mechanisms. As targeting EGFR in glioma has been relatively unsuccessful, this study suggests that IGFBP2 may be a novel therapeutic target.

Fetal and amniotic insulin-like growth factor-I supplements improve growth rate in intrauterine growth restriction fetal sheep

To date, there is no known prenatal treatment for intrauterine growth restriction (IUGR). IGF-I is an important regulator of fetal growth and circulating IGF-I concentrations are reduced in IUGR fetuses. We investigated whether any of three different methods of fetal IGF-I administration would reverse IUGR in sheep. Animals were randomized into five groups: control (n = 17), IUGR + saline (SAL, n = 17), IUGR + iv IGF-I (IGF-IV, n = 14), IUGR + intraamniotic IGF-I (IGF-AF, n = 14), or IUGR + intraamniotic IGF-I with nutrients (IGF-NUT, n = 16). Weekly IGF-I dose was 360 microg in each treatment group. IUGR was induced by placental embolization between 93 and 99 d and treatment was from 100-128 d gestation (term = 147 d). Embolization caused asymmetrical IUGR with reduced fetal growth rates and body and organ weights, but increased brain to liver weight ratio, at post mortem. Embolized fetuses were also hypoxemic and hypoglycemic and had reduced circulating IGF-I and insulin concentrations. IGF-AF and IGF-IV significantly increased fetal growth rates, but only IGF-AF significantly increased fetal liver weight, compared with saline-treated fetuses. Fetal weights and brain to liver weight ratios in all IGF-I-treated fetuses were intermediate between the control and SAL groups. Addition of nutrients reduced the effects of amniotic IGF-I treatment and increased fetal hemoglobin and lactate concentrations. Treatments did not change fetal plasma IGF-I and insulin concentrations. This is the first report of an intrauterine treatment significantly increasing fetal growth rate in established IUGR. Amniotic IGF-I administration may provide the basis for a clinically applicable prenatal treatment for the IUGR fetus.

Blood-brain barrier drug targeting enables neuroprotection in brain ischemia following delayed intravenous administration of neurotrophins

The blood-brain barrier (BBB) is the rate-limiting step in the translation of neurotrophin neuroscience into clinically effective neurotherapeutics. Since neurotrophins do not cross the BBB, these proteins cannot be used for neuroprotection following intravenous administration, and it is not feasible to administer these molecules by intra-cerebral injection in human stroke. The present studies describe the development of the chimeric peptide brain drug targeting technology and the use of brain-derived neurotrophic factor (BDNF) chimeric peptides in either global or regional brain ischemia. The BDNF chimeric peptide is formed by conjugation of BDNF to a monoclonal antibody (MAb) to the BBB transferrin receptor, and the MAb acts as a molecular Trojan Horse to ferry the BDNF across the BBB via transport on the endogenous BBB transferrin receptor. High degrees of neuroprotection in transient forebrain ischemia, permanent middle cerebral artery occlusion, or reversible middle cerebral artery occlusion are achieved with the delayed intravenous administration of BDNF chimeric peptides. In contrast, no neuroprotection is observed following the intravenous administration of unconjugated BDNF, because the neurotrophin does not cross the BBB in vivo.

Fate of (125)I-IGF-I administered into the amniotic fluid of late-gestation fetal sheep

Large amounts of amniotic fluid (AF) are swallowed in late gestation. AF is the most accessible fetal compartment and provides a possible paraplacental route for the therapeutic administration of hormones and nutrients to the fetus. We therefore wished to investigate the fate of the predominant fetal growth factor, IGF-I, administered into AF of late-gestation ovine fetuses. Seven chronically catheterized fetuses at 124 d gestation had approximately 800 x 10(6) dpm of (125)I-IGF-I injected into the AF. AF and blood samples were withdrawn for up to 6 d. At 131 d gestation a postmortem examination was performed. All AF, blood, and tissue samples were counted. Selected samples of AF, blood, and gut contents underwent size-separation chromatography. (125)I-IGF-I was rapidly mixed in AF, with a significant difference in counts from different regions of the cavity persisting for only 3 h (p < 0.05). In vivo binding of (125)I-IGF-I in AF correlated highly with AF IGF binding protein 3 concentrations (r(2) = 0.93, p < 0.0001). In some animals, free (125)I-IGF-I persisted in AF and in plasma for the duration of the experiments. Chromatography of plasma samples demonstrated that intact (125)I-IGF-I was taken up from the fetal gut. Only fetal gut and thyroid contained appreciable counts at postmortem examination. Gut contents had more counts than gut wall, and the number of counts in gut contents increased distally (p < 0.05 for colon contents versus other regions). We conclude that there is sustained delivery of (125)I-IGF-I from the AF to the gut and systemic circulation of the ovine fetus after a single intraamniotic injection.

Liver mRNA expression of IGF-I and IGFBPs in adult undernourished diabetic rats

To investigate the role played by factors other than GH, such as nutrients and insulin, on IGF-I secretion, adult male rats of 200 g.b.w. were food-restricted for 7 days and then made diabetic by streptozotocin administration (UD). Different groups of UD rats were submitted to the following four day treatments: left untreated (UD), refed (UD+R), treated with insulin (UD+I), or a combination of both refeeding and insulin (UD+R+I). Serum concentration of IGF-I and liver mRNA expression of IGF-I, IGF-binding proteins and GH receptor were measured. Insulin treatment alone partially recovered liver IGF-I and IGFBPs mRNA expression, while refeeding alone had no effect. Only a combination of both insulin and refeeding recovered both parameters. Contrary to the results obtained with a longer period of recovery, these experiments show that serum and mRNA expression of IGF-I and IGFBPs in adult undernourished diabetic rats can be restored by insulin and nutrients administration with no prior restoration of serum and pituitary GH to control values and no compensatory changes in GH receptor gene expression.

Role of insulin-like growth factor-I (IGF-I) receptor, IGF-I, and IGF binding protein-2 in human colorectal cancers

The identification of novel autocrine/paracrine signaling pathways and possible markers represents an important component in the understanding of tumor growth control. In this study, we assessed the potential role of insulin-like growth factor-I (IGF-I), the IGF-I receptor (IGF-IR) and IGF binding protein-2 (IGFBP-2) in human colorectal cancer. Initial studies demonstrating increased IGF-I binding and IGF-IR density in human colon cancer tissue revealed that a component of iodinated (3-[125-I]iodotyrosyl) IGF-I (125I-ICGF-I) binding was not attributable to IGF-IR. Binding studies and Western blot analysis suggested that this second component of 125I-IGF-I binding could be due to IGFBP-2. Further analysis by a specific solution hybridization/RNase protection assay for IGF-IR mRNA levels, IGFBP-2 mRNA levels and in situ hybridization for IGFBP-2 localization, was carried out in nine patients with colon cancer. IGF-IR mRNA levels by RNAse protection assays were unchanged, whereas IGFBP-2 mRNA levels were increased 4-8-fold in patients with colon cancer compared to controls. Three patients with Dukes stage C disease had the highest levels of IGFBP-2 mRNA. In situ hybridization studies localized IGFBP-2 mRNA to malignant cells and not to the surrounding stromal cells, suggesting an autocrine role for IGFBP-2. The discrepancy between increased IGF-I binding, IGF-IR density, IGFBP-2 mRNA and the minimal modulation of the IGF-IR mRNA implies post-transcriptional regulation of IGF-IRs. Our results suggest that IGFBP-2 may be implicated in colon cancer metastases and prognosis. Its usefulness as a potential tumor marker should be further investigated.

Insulin-like growth factor-I and insulin-like growth factor binding protein-1 in a representative population of type 2 diabetic patients in Sweden

OBJECTIVE

To study the influence of type 2 diabetes on the insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-1 (IGFBP-1) serum levels in an area-based population of type 2 patients previously described.

RESULTS

The patients (n = 151) were elderly (70.6 +/- 0.7 years of age) and moderately overweight (BMI 27.0 +/- 0.4 kg/m2). Most patients (83%) were treated with either diet alone or diet in combination with sulphonylurea. Metabolic control measured as HbAlc deteriorated with duration (p < 0.001) and between groups treated with diet (HbA1c 5.8 +/- 0.6), sulphonylurea (7.5 +/- 0.2) and insulin (7.7 +/- 0.4). Mean levels of IGF-I were within reported normal range, but were lower in the insulin-treated as compared to the non-insulin-treated patients. Levels of IGF-I decreased with diabetes duration and with increased blood glucose. There was a positive correlation between IGF-I and insulin levels and also an inverse correlation between IGF-I and IGFBP-1 levels. The IGFBP-1 levels were twofold higher than reported in non-diabetic individuals. In multiple stepwise correlation analysis, 37% of the variability in IGFBP-1 could be explained by BMI, IGF-I SD score, age, IGF-I, and fasting blood glucose.

CONCLUSION

Our study indicates that influence of type 2 diabetes on IGF-I bioavailability in individual patients is modulated by insulin, body weight (presumably reflecting insulin sensitivity) and metabolic control. Furthermore, increased levels of IGFBP-1 are strongly associated with decreased b-cell function in type 2 diabetes mellitus.

Effects of GH on IGF-II-induced progesterone accumulation by cultured porcine granulosa cells

A total of seven experiments were conducted to investigate the potential facilitative interaction of growth hormone (GH) and insulin-like growth factor II (IGF-II) in stimulating steroidogenesis by cultured porcine granulosa cells and to examine the possible nature of this action. Porcine granulosa cells were cultured in serum-free medium in the presence or absence of GH or prolactin, with or without IGF-II or IGF-I. IGF-II by itself dose (with peak progesterone production of 498 ng/mg DNA/24 h being observed at 100 ng of IGF-II/mL) and time- (with minimum time requirement of 24-48 h) dependently increased progesterone accumulation (P < 0.01). Neither GH (dose range 0, 5, 10, 50, 100, and 150 ng/mL) nor prolactin (dose range 0, 0.01, 0.1, 1, 5, 10 micrograms/mL) alone stimulated progesterone accumulation when compared with the control (P > 0.05). However, in the presence of IGF-II, GH proved to be a potent amplifier of IGF-II in progesterone production (P < 0.01) with a minimum GH time requirement of 24-48 h. In contrast, prolactin did not influence IGF-II-induced progesterone accumulation (P > 0.05). An inhibitory study showed that the presence of cycloheximide (3 micrograms/mL) or actinomycin D (1 microgram/mL) blocked both the stimulatory effect of IGF-II on progesterone accumulation and the amplification of GH on IGF-II induced production (P > 0.01), suggesting GH amplification of IGF-II-induced progesterone accumulation is a process involving gene transcription and translation. Northern blot analysis further demonstrated that GH amplification of IGF-II-induced steroidogenesis can be attributed, at least partially, to enhanced IGF-II-induced cytochrome P450 cholesterol side-chain cleavage mRNA by GH.

Impaired brain development and reduced astrocyte response to injury in transgenic mice expressing IGF binding protein-1

Numerous reports indicate that insulin-like growth factor-I (IGF-I) has a critical role in brain development, that it contributes to neuronal survival and that its activity is regulated by a family of IGF binding proteins (IGFBPs). In the present study, brain development was investigated in transgenic (Tg) mice that overexpress rat IGFBP-1 under the control of phosphoglycerate kinase promoter. Adult Tg mice had significantly decreased brain weight (299 +/- 17 vs. 499 +/- 11 mg), brain DNA content (684 +/- 8 vs. 810 +/- 31 microg) and brain protein (37 +/- 1 vs. 48 +/- 2 mg) compared with wild-type (Wt) mice and these deficits were already evident at birth. In Tg mice, myelin staining was generally reduced and there was a diminished thickness of the corpus callosum. The total area of hippocampus and dentate gyrus were significantly reduced by 55% and 72%, respectively. Bromodeoxyuridine labeling of proliferating cells in 3-day-old mice was markedly reduced by 41% in the dentate gyrus and by 19% in ventricular zones of Tg mice. Reactive astrogliosis reflected by morphology and glial fibrillary acidic protein expression of astrocytes in response to a mechanical lesion was substantially less in Tg compared with Wt mice. Mixed glial cell cultures from Tg animals were significantly less responsive to stimulation of proliferation by IGF-I than cultures from Wt mice. We conclude that overexpression of IGFBP-1 impairs brain development and reduces glial cell proliferation in response to injury.

Induction of cell proliferation in avian inner ear sensory epithelia by insulin-like growth factor-I and insulin

Postembryonic production of inner-ear hair cells occurs both normally and after insult in lower vertebrates and avians. To determine how this proliferation is controlled, several growth factors were tested for effects on progenitor-cell division in cultured avian vestibular sensory epithelium. Mitogenic effects of bombesin, epidermal growth factor, insulin-like growth factor-I (IGF-I), insulin, and transforming growth factor-alpha were assayed in organo-typic cultures of utricles from the mature, undamaged (normal) chicken inner ear. Tritiated thymidine and autoradiographic techniques and 5-bromo-2'-deoxyuridine (BrdU) immunocytochemistry were used to identify cells synthesizing DNA. IGF-I stimulated DNA synthesis in the vestibular sensory receptor epithelium in a dose-dependent manner. DNA synthesis was also stimulated by insulin. These results suggest that stimulation of the IGF-I receptors by IGF-I or insulin binding stimulates cell proliferation in the mature avian vestibular sensory epithelium.

Oxidation of human insulin-like growth factor I in formulation studies: kinetics of methionine oxidation in aqueous solution and in solid state

PURPOSE

The aim of this work was to study the kinetics of oxidation of methionine in human Insulin-like Growth Factor I (hIGF-I)1 in aqueous solution and in the solid state by the aid of quantification of oxygen.

METHODS

The oxidized from of hIGF-I was characterized by tryptic peptide analysis, RP-HPLC and FAB-MS and quantified by RP-HPLC. The oxygen content was quantified polarographically by a Clark-type electrode.

RESULTS

Second-order kinetics with respect to amount of protein and dissolved oxygen was found to be appropriate for the oxidation of methionine in hIGF-I. The rate constants ranged from 1 to 280 M-1 month-1 and had an activation energy of 95 (+/-4) kl/mole. Light exposure, storage temperature and oxygen content were found to have a considerable impact on the oxidation rates. No significant difference in reaction rates was found for the oxidation of hIGF-I in aqueous solution or in the solid state. A method for decreasing the oxygen content in aqueous solution without purging is described.

CONCLUSIONS

Polarographic quantification of dissolved oxygen makes it possible to establish the kinetics for oxidation of proteins. The oxidation of methionine in hIGF-I appears to follow second-order kinetics.

Influence of thyroxine in vivo on preadipocyte development and insulin-like growth factor-I and IGF binding protein secretion in fetal stromal vascular cell cultures

Studies were conducted to determine the influence of thyroxine (T4) in vivo on preadipocyte development and insulin-like growth factor-I (IGF-I) and IGF binding proteins (IGFBPs) secretion in stromal-vascular (S-V) cultures. Fetal pigs were hypophysectomized (hypox) at 70 days of gestation, implanted with T4 pellets, and fetuses from the dam at 75 days of gestation. In a second experiment, hypox and T4 implantation were performed at 75 days and fetal pigs removed at 95 days of gestation. Primary cultures of stromal vascular (S-V) cells derived from fetal adipose tissue were established. Cultures were stained for morphological analysis and conditioned media were collected for IGF-1 determination by radioimmunoassay (RIA) and IGFBP analysis by Western blotting. After only 5 days of T4 treatment, fat cell cluster number and size and lipid deposition in cultures were significantly increased compared to cultures from untreated hypox fetuses. Fetal hypox reduced IGF-I secretion by preadipocytes at both ages and T4 treatment completely normalized IGF-I secretion (p < 0.05). Four IGFBPs (BP-1, BP-2, BP-3 & BP-4) detected in S-V cultures derived from 95-day fetuses were decreased in concentration by hypox by 44 +/- 9.4%, 32 +/- 9.7%, 42 +/- 12% and 53 +/- 6.9%. In cultures derived from T4 treated hypox fetuses, the levels of these four IGFBPs were increased by 187 +/- 25%, 239 +/- 38%, 190 +/- 5% and 347 +/- 43% over control values, respectively. In cultures from 75-day fetuses, only IGFBP-2 (major one) and BP-1 (minor one) were detected and their secretion was also decreased by hypox and elevated by T4 treatment (190 +/- 49.5%, 156 +/- 30%, respectively, of controls). The results provide direct evidence that T4 has a major influence on fetal preadipocyte development. T4 stimulated production of IGF-I and IGFBP in fetal S-V cultures, which in turn, may have mediated the capability of T4 to enhance fetal adipose tissue development.

Insulin-like growth factor 2 and insulin-like growth factor binding protein 2 expression in hepatoblastoma

The expression of insulin-like growth factor 2 (IGF2) and insulin-like growth factor binding protein 2 (IGFBP2) in 11 cases of hepatoblastoma was studied by means of in situ mRNA hybridization using digoxigenin (DIG)-labeled riboprobes. The results showed that both IGF2 and IGFBP2 transcripts are present in hepatoblastoma and that their expression is inversely correlated with the degree of tumor cell differentiation. The data suggested that IGF2 and IGFBP2 gene expression could be regarded as a marker for assessment of the degree of differentiation in hepatoblastoma.

The insulin-like growth factor system in regulation of normal and malignant hematopoiesis

The published data available on the insulin-like growth factor (IGF) family of peptides, its receptors and binding proteins in connection with normal and neoplastic hematopoietic processes are reviewed. It is found that nearly all the different hematopoietic cells, either normal or neoplastic, express IGF receptors. The IGFs are involved in normal erythropoiesis, granulopoiesis and lymphopoiesis. IGFs, especially IGF-1, are mitogenic for cell lines of myeloid and lymphoid leukemias and Burkitt's lymphoma. Differentiation of certain immature malignant cell lines is associated with a decrease in the number and affinity of IGF receptors. It might be concluded that the IGFs have an important role in the physiologic and neoplastic processes of the hematopoietic system, and the expanding knowledge of this issue will contribute to the understanding of proliferation and differentiation processes in specific hematologic disorders.

Insulin-like growth factor I treatment reduces clinical deficits and lesion severity in acute demyelinating experimental autoimmune encephalomyelitis

Our goal was to test the effects of insulin-like growth factor I (IGF-I) treatment on clinical deficits, lesion number and lesion size in acute demyelinating experimental autoimmune encephalomyelitis (EAE) induced in Lewis rats with an emulsion containing guinea pig spinal cord. In this EAE model, there is severe immune-mediated demyelination, which resembles that seen in actively demyelinating MS lesions. On day 12-13 after EAE induction, a total of 23 pairs of rats with the same mild degree of tail and hind limb weakness were given either intravenous IGF-I or placebo twice daily for 8 days. The daily IGF-I dose used in the first trial was 200 micrograms (about 0.6 mg kg-1) and in the second and third trials was 1 mg (about 3.0 mg kg-1). IGF-I treatment reduced permeability of the blood-spinal cord barrier to Evans blue-albumin. Maximum clinical deficit scores of IGF-I-treated rats were significantly lower and treated rats recovered faster than controls. IGF-I treatment produced significant reductions in weight loss and hind limb weakness. Treatment also improved treadmill walking, stride length and climbing performance. Morphometric analysis showed that spinal cord inflammatory lesions were significantly smaller and fewer in IGF-I-treated rats. The higher IGF-I dose produced a greater reduction in clinical and pathological deficits. We conclude that IGF-I treatment promotes clinical recovery by reducing EAE-induced blood-spinal cord barrier changes and the associated immune-mediated inflammatory lesions. Our results suggest that IGF-I may be useful in treating patients with multiple sclerosis and other demyelinating diseases.

Insulin and insulin-like growth factor system components gene expression in the chicken retina from early neurogenesis until late development and their effect on neuroepithelial cells

To better understand the role of insulin-related growth factors in neural development, we have characterized by in situ hybridization in chicken embryonic retina the patterns of gene expression for insulin, insulin-like growth factor I (IGF-I), their respective receptors and the IGF binding protein 5 (IGFBP5) from early stages (E6) until late stages (E18)--an analysis not performed yet in any species. In addition, we studied the effect of insulin and IGF-I on cultured neuroepithelial cells. Insulin receptor mRNA and IGF-I receptor mRNA were both present and showed a similar, widespread pattern throughout retina development. Insulin mRNA could be detected only by reverse transcription coupled to polymerase chain reaction. IGF-I mRNA was concentrated in the ciliary processes and extraocular muscles early in development (embryonic day 6; E6) and in maturing retinal ganglion cells subsequently (E9-15). IGFBP5 mRNA was preferentially localized in the more differentiated central retinal zone and was maximally concentrated in the inner nuclear and ganglion cell layers at E9. These findings suggest a near constitutive expression of insulin receptor and IGF-I receptor genes, while IGF-I and IGFBP5 showed a highly focal spatiotemporal regulation of gene expression. Insulin and IGF-I, already at 10(-8) M, increased the proportion of PM1-positive neuroepithelial cells found in E5 retinal cultures without affecting significantly the total number of proliferating cells. Together, these data support the finding that, during early neurogenesis in chicken retina, insulin and IGF-I have a specific paracrine/autocrine action. This action, as well as possible effects elicited subsequently, may be dictated by restricted-local synthesis of the ligands and limited access to the factors contained in the vitreous humour. In the case of IGF's role, local IGFBPs expression can contribute to the fine modulation.

Culture of intact Sertoli/germ cell units and isolated Sertoli cells from Squalus testis. II. Stimulatory effects of insulin and IGF-I on DNA synthesis in premeiotic stages

To investigate growth control mechanisms during spermatogenesis in vitro, [3H]thymidine incorporation into acid-insoluble macromolecules was used to quantify DNA synthesis in cultured spermatocysts (intact Sertoli cell/germ cell clones) derived from premeiotic (PrM), meiotic (M), and postmeiotic (PoM) regions of dogfish (Squalus acanthias) testis. Forty-eight hours after seeding in basal medium, DNA synthesis was > 7-fold higher in PrM cysts than in other stages, thus verifying the staging procedure. In autoradiograms, germ cells of PrM cysts (e.g., spermatogonial and preleptotene stages) were labeled all-or-none, but not all cysts were labeled, and later developmental stages (e.g., cysts with round or elongating spermatids) were never labeled. Fetal bovine serum (FBS, 10%) and insulin-transferrin-selenite (ITS, 10 micrograms-10 ng/ml) doubled DNA synthesis in PrM cyst cultures but had no effect at other stages. Bovine insulin (10 micrograms/ml) and human recombinant insulin-like growth factor-I (IGF-I, 15 ng/ml) also doubled [3H]thymidine uptake in PrM cultures, but lower doses were less effective and estradiol-17 beta, transferrin, adult shark serum, purified shark relaxin, and a variety of other known growth factors were neither stimulatory nor inhibitory at the doses and conditions tested. Sertoli cell monolayers derived from PrM- or M-stage spermatocysts displayed a dose-response increase in DNA synthesis after addition of IGF-I (15-75 ng/ml), with a maximal increment significantly greater than with 10% FBS. Using [3H]thymidine incorporation by PrM cysts as an end-point, stimulatory bioactivity was detected in the < 30,000 kDa fraction of spent media from PrM Sertoli cells, whereas the low molecular weight fraction of M-stage Sertoli cells was inhibitory. Gel electrophoretic analysis of the two fractions revealed qualitative and quantitative differences in protein banding patterns, reinforcing the view that secretory activity of Sertoli cells is stage related. Results of these studies implicate insulin/IGF-I in mechanisms governing proliferation of male germ cells and support the view that Sertoli cells have an autocrine or paracrine role as both targets and sources of growth regulatory factors.

Insulin-like growth factors and their receptors in normal physiology and pathological states

The insulin-like growth factor system, which includes the IGFs, IGF-binding proteins and IGF receptors, plays an essential role in normal growth and development, as well as the cellular differentiation of a number of other important systems, including the reproductive and immune systems. IGF action has also been implicated in several pathological conditions, including tissue repair, malnutrition, diabetes and malignancy.

Hormonal Ergogenic Aids

Most hormonal agents used for nonmedical purposes in athletes have legitimate medical uses. This review introduces each compound by its pharmacology, clinical pharmacology, and legitimate medical use and reviews information on its abuse. Human growth hormone is presently available in virtually unlimited quantities due to its production by recombinant DNA technology. Its use in athletes is considered for its muscle-building, fat-depleting properties. Erythropoietin is a kidney hormone that increases red cell mass. It is used for renal dialysis patients to avoid blood transfusions. Its use in athletes is to raise red blood cell mass in an attempt to augment maximal oxygen capacity and the ability to do endurance work. Human chorionic gonadotropin has the biological activity of luteinizing hormone to increase testosterone synthesis and to maintain (partially) testicular volume when exogenous androgens are taken. Clenbuterol is a beta2adrenergic agonist with muscle-building properties that are seemingly specific to striated muscle; clenbuterol may cause reduction in body fat.

Circulating binding proteins for the insulinlike growth factors

Six distinct insulinlike growth factor-binding proteins (IGFBP-1 to IGFBP-6) of core molecular mass 20-30 II have been identified, of which one, IGFBP-3, carries most o f the circulating IGF-I and IGF-II in ternary complexes that also contain an acid-labile glycoprotein subunit. Although the role of circulating IGFBP-3 in IGF stabilization and transport is becoming increasingly well understood, the functions of the other IGFBPs in the circulation are less clear, and some redundancy of function is possible. IGFBP-l, which is metabolically regulated by insulin and carbohydrates, may act as a counterregulator in blood glucose regulation and could also be important in targeting IGF delivery from the circulation to the tissues, while recent studies of IGFBP-2 physiology suggest that this protein may function as an additional IGF carrier when IGFBP-3 levels are inadequate. Research into the roles of circulating IGFBP-4, -5, and -6 is, as yet, poorly developed and will depend on the ready availability of analytical methods for these proteins.

Localization of insulin-like growth factor binding protein-2 messenger RNA during postnatal brain development: correlation with insulin-like growth factors I and II

Insulin-like growth factor binding protein-2 binds insulin-like growth factors I and II with high affinity and modulates the interaction of these ligands with the type I insulin-like growth factor receptor. Previously we have shown that insulin-like growth factor binding protein-2 and insulin-like growth factor-I gene expression are spatiotemporally co-ordinated in the developing retina and cerebellum. The present study examined other brain regions and found a similar correlation in insulin-like growth factor binding protein-2 and insulin-like growth factor-I gene expression in relay stations of developing sensory and cerebellar networks of the rat. In these sites, as in the cerebellum and retina, insulin-like growth factor-I messenger RNA is localized in the principal or projection neurons and insulin-like growth factor binding protein-2 messenger RNA is localized in surrounding astroglia. Outside these sensory relay centers, the relationship of insulin-like growth factor binding protein-2 to insulin-like growth factor-I gene expression is not so well defined. In the hippocampal formation, insulin-like growth factor-I messenger RNA is present in large interneurons and insulin-like growth factor binding protein-2 messenger RNA in regional astrocytes; their timing is co-ordinated, with peak levels seen about postnatal day 12, but their anatomical association is not apparent. The least degree of correlation between local insulin-like growth factor-I and insulin-like growth factor binding protein-2 gene expression is found in the neocortex, where insulin-like growth factor-I is abundant in scattered large neurons from postnatal days 3 to 20. In contrast, insulin-like growth factor binding protein-2 messenger RNA is widely expressed throughout the neocortex from before birth to about postnatal day 12, in a pattern consistent with expression by nascent astroglia. Insulin-like growth factor binding protein-2 gene expression is greatly reduced throughout the brain by the third week after birth; in response to optic nerve transection, however, there is a resurgence of gene expression for this factor by activated astrocytes in affected retinal target regions. Insulin-like growth factor binding protein-2 and insulin-like growth factor-II messenger RNAs are co-localized in the choroid plexus and leptomeninges from the time of birth onward without diminution. In summary, insulin-like growth factor binding protein-2 demonstrates complex patterns of gene expression during postnatal brain development--some of which appear to be closely related to local insulin-like growth factor synthesis and some of which appear independent of it.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of insulin-like growth factor binding proteins secreted by cultured bovine theca and granulosa cells

Insulin-like growth factor binding proteins (IGFBPs) secreted by bovine granulosa and theca interna cells cultured in the presence of different luteinizing factors--insulin (2 micrograms/ml), forskolin (10 microM), or a combination of the two were examined and characterized. Direct binding of [125I]IGF to the conditioned media was compared to progesterone production under these different treatments. In theca cells, maximal secretion of IGFBPs was achieved using forskolin alone, whereas maximal progesterone production was induced by the insulin+forskolin treatment. In contrast, maximal secretion of both IGFBPs and progesterone in granulosa cells was achieved using forskolin alone. IGFBP species secreted by the two cell types under the different treatments were detected by ligand blotting. Conditioned media from theca cells in serum-free medium collected on the seventh day of culture exhibited three bands of 34, 40 and 44 kDa when treated with insulin or forskolin. The intensity of the 40-44 kDa complex was enhanced and a 21 kDa band appeared when cells were treated with a combination of insulin plus forskolin. Conditioned media of granulosa cells stimulated with insulin or forskolin exhibited 21, 27, 29, 34 and 40-44 kDa bands. Treatment with insulin+forskolin greatly increased the intensity of a 40-44 kDa complex. A similar shift towards high molecular weight binding proteins was observed when these media were analyzed by high-performance liquid chromatography gel filtration. These findings substantiate the secretion of IGFBPs by bovine theca and granulosa cells and show it to be dependent on culture treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental regulation of insulin-like growth factor binding protein production: studies in fetal, postnatal, and pregnant sheep

To assess the roles of developmental factors in the regulation of sheep IGFBP production at the cellular level, we characterized and compared the IGFBPs released by fetal, postnatal, and maternal sheep skin fibroblasts in culture with those in fetal, postnatal, and maternal sheep plasma. Sheep fibroblasts produced seven IGFBPs: a 36.5-41 kDa protein induced in vitro by IGF-I, likely representing oIGFBP-3; a 28.5 kDa protein that reacted with antisera to human IGFBP-2, likely representing oIGFBP-2; 25 and 27 kDa proteins induced in fetal fibroblasts by IGF-I; a 22 kDa protein that was inhibited by IGF-I, likely representing oIGFBP-4; and 21 and 23 kDa proteins labelled only by IGF-II, suggesting their similarities to IGFBP-6. The developmental pattern of IGFBP production by sheep fibroblasts in culture was similar in several respects to that observed in sheep plasma. For example, relative amounts of the 21, 22, and 28.5 kDa IGFBPs exceeded that of the 36.5-41 kDa protein in early fetal fibroblast conditioned media and in fetal plasma, while the relative concentrations of the 36.5-41 kDa protein increased markedly during the perinatal period. Sheep plasma differed, however, in two major respects from fibroblast conditioned media: First, fetal, and to a far lesser extent maternal, plasma contained a 200 kDa IGF-II-selective BP, likely to be the circulating form of the IGF-II receptor; and second, plasma, unlike conditioned media, contained a 26 kDa IGFBP, likely to be oIGFBP-1. The results of our studies suggest that the production and release of IGFBPs by isolated sheep fibroblasts is regulated by developmental factors operative under in vitro culture conditions. The differences in the relative levels of IGFBPs in conditioned media from fetal, postnatal, and maternal sheep fibroblasts resemble in several respects the differences in the relative concentrations of the various IGFBPs in fetal, postnatal, and maternal sheep plasma. Thus, sheep fibroblasts provide a useful though imperfect model system by which to examine the nutritional and hormonal regulation of sheep IGFBP production at various developmental stages.

Insulin-like growth factor I and II and insulin-like growth factor binding protein-2 RNAs are expressed in adjacent tissues within rat embryonic and fetal limbs

Since the rapid proliferation of cells in a directed manner is a necessary component of limb formation, the distribution of locally produced mitogenic molecules within the developing limb is of considerable interest. We have used in situ hybridization to localize transcripts for both insulin-like growth factor binding protein-2 (IGFBP-2) and its ligands, the insulin-like growth factors I and II (IGF-I and IGF-II), within limb buds of rat embryos 10-16 days after conception (equivalent to stages 1-12 of mouse limb morphogenesis, Wanek et al, 1989. J. Exp. Zool. 249, 41-49). The mRNA for IGFBP-2 is very abundant in an anterior-posterior strip of ectoderm along the distal edge of the limb bud (the progenitor of the apical ectodermal ridge or AER) from as early as limb stage 1 (Embryonic Day 10) and is much less abundant in the rest of the limb ectoderm. A high level of IGFBP-2 expression continues to characterize the AER following its definitive appearance (stage 3) and throughout its existence (until stage 7). This is a period of rapid outgrowth during which the rate of mesodermal cell division is highest in cells nearest to the AER. The AER is known to have mitogenic activity in vitro and to direct limb outgrowth in vivo, but, until recently, few putative molecular correlates of these activities have been detected. The transcripts for IGF-I and IGF-II are also present at high abundance in developing limbs, especially in mesodermally derived cells. IGF-I mRNA is abundant in presumptive limb mesoderm from the beginning of limb outgrowth (just before stage 1), but is very low or undetectable in much of the rest of the embryo, while IGF-II mRNA becomes very abundant in limb mesoderm at stage 2. The distribution in limbs of both IGF-I and IGF-II mRNA changes dramatically during outgrowth and differentiation, so that their expression characterizes complementary populations of cells by stage 11. Taken together, these data suggest that IGFs and the IGF binding proteins, which may modulate IGF action, contribute to limb outgrowth and patterning.

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

Insulin-like growth factor binding proteins (IGFBPs) in pregnant baboon serum and tissue culture media obtained following explant culture of uteri from pregnant baboons were characterized by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (2D SDS-PAGE) followed by Western ligand blot analysis using 125I-labeled IGF-I. IGFBP-1 (Mr 30,000; pI 4-4.2), IGFBP-2 (Mr 34,000, pI 5.7-6.2), IGFBP-3 (doublet Mr 42-48,000; pI 6.2-6.8), and IGFBP-4 (Mr 24,000; pI 5.7-6.0) were clearly separated from one another. The authenticity of IGFBP-1, -2, and -3 was verified by immunoprecipitation using polyclonal antibodies followed by ligand blotting. Specificity of 125I-labeled IGF-I binding to IGFBPs was also determined by competitive binding studies using unlabeled IGF-I and -II. This technique allows for the identification of IGFBPs in complex biological fluids on the basis of their characteristic Mr and pI with or without the availability of specific antibodies and can be done rapidly using the mini 2D SDS-PAGE systems.