卵巢中的胰岛素样生长因子系统

本文详细阐述了胰岛素样生长因子（IGFs)系统各个成员的结构及其在卵巢中的表达和作用机制。IGFs是这一系统的中间环节,与IGFs受体作用刺激卵巢细胞中类固醇激素的生产和DNA合成,能够介导和扩大促性腺激素对卵巢功能的作用。IGFs与胰岛素样生长因子结合蛋白（IGFBPs)发生高亲和性结合,卵巢中自由的IGFs的水平受IGFBPs的调节。而IGFBPs蛋白酶能够降低IGFBPs和IGFs的亲和性,从而参与调节IGFs在卵巢中的作用。深入的研究这一系统,对于进一步了解卵巢卵泡生长发育、分化以及闭锁,卵泡细胞的增殖和凋亡的内在机制,以及提高动物的繁殖力有重要意义。     

Insulin-like growth factor and interacting proteins

Insulin-like growth factor - IGF-I is a small, 70 aminoacid mitogenic peptide, contributing to processes of growing, cancerogenesis, apoptosis, wound healing and many others. It constitutes so called 'somatotropic axis GH-IGF', composed of many other components. This axis is responsible for regulation of metabolic processes, and its proper functioning conditions organism's homeostasis. Presented work describes concise review of publications concerning IGF-I structure, function, expression and proteins affecting its activity, synthesis and circulation.     

Insulin-like growth factor inhibition of growth hormone secretion

Somatomedins-insulin-like growth factors (SM/IGF) are growth hormone (GH) dependent serum growth factors. There is some evidence that IGF inhibit GH release (negative feedback) in 3- to 24-h incubations of cultured rat adenohypophysial cells. We have used acutely dispersed noncultured rat adenohypophysial cells to study the dynamics of IGF on GH secretion. In this system both IGF-I and IGF-II (100 ng/mL) slightly, but significantly, decrease the cumulative GH released by human pancreas growth hormone releasing factor 1-40 (GRF) and the phosphodiesterase inhibitor 3-isobutyl-1-methyl xanthine. The inhibition is small (16%) and usually not statistically significant until 2 h of incubation. The inhibition with IGF is additive to that produced with low concentrations of somatostatin. The IGF also significantly decrease the rate of GH release in all time periods tested (0-1, 1-2, 2-3 h). In addition, the IGF decrease the quantity of [14C]leucine protein eluted at the position of labelled rat GH on Sephadex G75, which would include newly synthesized GH extracted from the cells. Thus we conclude that the decreased GH released may be due to an effect of IGF on both rate of release and on GH synthesis.     

Insulin-like growth factor I and erythropoiesis.

The bone marrow, the primary site of hematopoiesis, is a self-renewing system consisting of a unique micro-environment that promotes the differentiation and proliferation of the various hematopoietic cell lines. While many critical factors necessary for red cell production have been identified, the regulation of erythropoiesis has not been completely elucidated. In addition to multi-lineage growth factors (e.g. interleukin 3 or 4) and lineage-specific hematopoietic growth factors (e.g. erythropoietin), several lines of evidence suggest a key role for insulin-like growth factor I (IGF-I). First, growth hormone stimulates erythropoiesis and IGF-I is known to mediate many of growth hormone's actions (somatomedin hypothesis). Second, factors in bovine serum and in serum from an anephric human with erythropoietic activity distinct from erythropoietin have been identified as IGFs. Third, IGF receptors are found on both erythrocyte precursors as well as mature erythrocytes. Fourth, in vitro IGF-I stimulates erythropoiesis in bone marrow cultures. Fifth, IGF-I administration to neonatal or hypophysectomized animals results in increased erythropoiesis in vivo. Recent studies indicate that IGF-I at physiologic concentrations stimulates erythropoiesis and that growth hormone's action is indirect, occurring via IGF-I. The physiologic source of IGF-I for the bone marrow may be delivery from the serum (an endocrine mechanism) or synthesis within the bone marrow by stromal or other cells (a paracrine mechanism). Our recent studies have shown that mouse bone marrow stromal cells secrete both IGF-I and IGF binding proteins (IGFBPs). The role of IGFBPs in erythropoiesis is not known, but they might modulate the local concentration of IGF-I.(ABSTRACT TRUNCATED AT 250 WORDS)     

Insulin-like growth factor binding protein expression in human small cell lung cancer cell lines

Insulin-like growth factor binding proteins (IGF-BP) are secreted by several human small cell lung cancer cell lines (SCLC). In order to identify the IGF-BPs from SCLC cell lines the RNA from 10 different SCLC cell lines was analyzed by Northern blot analysis with the probes for three different IGF-BPs, IGFBP-1, IGFBP-2, and IGFBP-3. No hybridization signal could be detected with the probes encoding for IGFBP-1 and IGFBP-3. The hybridization with different IGFBP-2-specific oligodeoxynucleotide probes and with the corresponding full-length cDNA showed that all SCLC cell lines which secreted IGF-BPs express IGFBP-2.     

Insulin-like growth factor I and insulin-like growth factor binding protein 5 in Crohn's disease

Insulin-like growth factor (IGF)-I and its binding protein IGF binding protein 5 (IGFBP-5) were highly expressed in inflamed and fibrotic intestine in experimental Crohn's disease. IGF-I induced proliferation and increased collagen synthesis by smooth muscle cells and fibroblasts/myofibroblasts in vitro. Here we studied IGF-I and IGFBP-5 in Crohn's disease tissue. Tissue was collected from patients undergoing intestinal resection for Crohn's disease. IGF-I and IGFBP-5 mRNAs were quantitated by RNase protection assay and Northern blot analysis, respectively. In situ hybridization was performed to localize mRNA expression, and Western immunoblot was performed to quantitate protein expression. IGF-I and IGFBP-5 mRNAs were increased in inflamed/fibrotic intestine compared with normal-appearing intestine. IGF-I mRNA was expressed in multiple cell types in the lamina propria and fibroblast-like cells of the submucosa and muscularis externa. IGFBP-5 mRNA was highly expressed in smooth muscle of the muscularis mucosae and muscularis externa as well as fibroblast-like cells throughout the bowel wall. Tissue IGFBP-5 protein correlated with collagen type I (r = 0.82). These findings are consistent with a mechanism whereby IGF-I acts on smooth muscle and fibroblasts/myofibroblasts to increase collagen synthesis and cellular proliferation; its effects may be modulated by locally expressed IGFBP-5.     

Insulin-like growth factor I levels in healthy adults

Insulin-like growth factor I (IGF-I) levels mainly reflect secretion of growth hormone (GH) in the body. The aims of this study were to compare different IGF-I assay methods in healthy individuals, test the reliability of the methods and discuss the utility of IGF-I measurement in adults. The Nichols Institute Diagnostics radioimmunoassay was used to evaluate IGF-I in two random population samples of men and women (aged 25-64 years, n = 392) taken 10 years apart, in 1985 and 1995. This method for IGF-I testing was also compared with an immunoradiometric assay (IRMA) method in 387 men and women participating in the World Health Organization MONICA (MONItoring of trends and determinants for CArdiovascular diseases) Project, Goteborg, Sweden, in 1995. Serum IGF-I decreased with increasing age in both men and women. IGF-I was higher in young women compared with young men in both cohorts, while the opposite was found in the highest age group. Age-adjusted significant correlations were found between IGF-I and smoking, fibrinogen, coffee consumption, lipoprotein (a), osteocalcin and IGF-binding protein 3. The two cohorts showed similar mean IGF-I concentrations irrespective of method. The correlation between the Nichols and the IRMA methods was high: r = 0.93 (p < 0.0001). Based on this and previous studies, population-based IGF-I measurements are robust irrespective of which commercially available method of assay is used. IGF-I levels can be used in diagnosing acromegaly as well as providing target values. IGF-I assay can be used as a complement to stimulation testing in the diagnosis of GH deficiency, and as a tool for GH dose titration.     

Insulin-like growth factor I levels in healthy children

Measurement of insulin-like growth factor I (IGF-I) levels is used during the assessment of a child for the presence of growth hormone (GH) deficiency and to monitor the efficacy of GH replacement therapy. In either case, robust normative data are required to allow IGF-I values to be expressed as standard deviation scores, enabling comparison between individuals and assessment of change over time. However, IGF-I levels in healthy children are affected by a number of parameters, including age, gender, pubertal status, height, nutrient intake, body composition, intercurrent illness and ethnicity, and the generation of such data requires the collection of samples from significant numbers of healthy children. As external quality assurance schemes for IGF-I and an international standard based on authentic recombinant IGF-I are not widely used, it is imperative for the clinician to understand the performance characteristics and limitations of the IGF-I assay used and to be aware of the source and quality of control data. It must also be recognized that IGF-I measurement is only one component of the diagnostic process and has its limitations, as tissue sensitivity to circulating serum IGF-I levels will differ between individuals.     

Insulin-like growth factor I and impaired glucose tolerance

The effects of circulating insulin-like growth factor I (IGF-I) on glucose metabolism are well recognized. IGF-I is also important in maintaining beta-cell mass and regulating endogenous growth hormone (GH) levels. Low IGF-I levels could explain links between small birth size and the risk of developing type 2 diabetes mellitus in short, obese adults. In a recent prospective study, childhood insulin secretion was related to IGF-I levels and statural growth, whereas insulin sensitivity was related to early post-natal weight gain. Common genetic polymorphisms in the IGF1 gene have been linked to small birth size, post-natal growth and future diabetes risk, but these results have been inconsistent. Recent adult studies have demonstrated that lower baseline IGF-I levels predict the subsequent development of impaired glucose tolerance (IGT), type 2 diabetes and cardiovascular disease. Administration of low-dose GH therapy, at a dose that minimizes the lipolytic effects of GH and has the ability to increase IGF-I levels, enhances insulin sensitivity in young healthy adults and in GH-deficient adults and increases insulin secretion in individuals with IGT. Whether the administration of low-dose GH, recombinant IGF-I or combined IGF-I/IGF-binding protein 3 therapy prevents future development of IGT or type 2 diabetes in high-risk normoglycaemic and GH-deficient individuals merits further long-term studies.     

Insulin-like growth factor binding proteins and mammary gland development

Mammary gland development is dependent upon insulin-like growth factors (IGFs) as survival factors. The actions of the IGFs are modulated by a family of IGF-binding proteins (IGFBP1-6). Expression of the IGFBPs is both time-dependent and cell-specific during both the developmental phases and the involution of the mammary gland. Although studied extensively in vitro, understanding the roles of IGFBPs in vivo has been difficult, largely due to the fact that IGFBP knock-out mice have no dramatic phenotypes. This review examines the evidence from in vitro studies and the attempts to examine in vivo actions utilising models with IGFBP deficiency or over-expression. In vitro studies demonstrate that IGFBPs can act by inhibition of the survival effects of IGFs, as well as by enhancing the effects of IGFs. Because the IGFBPs are found associated with the extracellular matrix, a role for IGFBPs as a reservoir of IGFs or, alternatively as a potential barrier to IGFs, thereby restricting their entry into particular tissues or cellular compartments was postulated. We also provide evidence with respect to the IGF-independent actions of the IGFBPs which include receptors, nuclear localization, and interaction with the extracellular matrix and cell surface proteins including integrins. We believe that recent findings place some of the IGFBPs in a larger family of extracellular proteins, the secreted cysteine-rich protein (CCN) family, which have similar structural domains (involved in binding to IGFs, extracellular matrix and integrins) and are heavily implicated in tissue re-modeling and morphogenesis.     

Insulin-like growth factor binding protein-3 stimulates phosphatidylinositol 3-kinase in MCF-7 breast carcinoma cells

Insulin-like growth factor binding protein-3 (IGFBP-3) is the most abundant IGFBP in serum and other biological fluids. Apart from its capacity for specific and high-affinity binding to IGFs, it also has so-called "IGF-independent" activities that modulate cell proliferation and survival/apoptosis. However, the molecular elements of the IGFBP-3 signalling pathway remain obscure. In this study, we investigated the possible implication of phosphatidylinositol 3-kinase (PI 3-kinase) activity in MCF-7 breast carcinoma cells. In cells incubated with IGFBP-3, both total and insulin receptor substrate-1 (IRS-1)-associated PI 3-kinase activities were rapidly stimulated, with maximal effects after 3 and 10min of incubation, respectively. IGFBP-3-induced PI 3-kinase activity was unaffected by the state of IRS-1 tyrosine phosphorylation. Since IGFBP-3 failed to stimulate PI 3-kinase activity in MDA-MB 231 breast carcinoma cells, its effects in MCF-7 cells could be considered as cell-type-specific. Pertussis toxin abolished IGFBP-3-stimulation of PI 3-kinase activity, suggesting that this IGFBP-3 signalling pathway depends upon a pertussis toxin-sensitive G protein. Our results provide further evidence that IGFBP-3 directly triggers a specific intracellular signal in MCF-7 cells.     

Insulin-like growth factor binding protein-3 increases intracellular calcium concentrations in MCF-7 breast carcinoma cells

Insulin-like growth factor binding protein-3, IGFBP-3, specifically binds to IGFs with high affinity, but it is also capable of modulating the IGF-I signalling pathway or inducing apoptosis independently of its binding to IGFs. The molecular mechanisms underlying the action of IGFBP-3 have not been elucidated. In this study, we have demonstrated that binding of IGFBP-3 to a cell surface receptor in MCF-7 breast carcinoma cells induces a rapid and transient increase in intracellular free calcium. This increase was mediated via a pertussis toxin-sensitive pathway, indicating that the IGFBP-3 receptor may be specifically coupled to a Gi protein. The effect of IGFBP-3 on calcium concentrations was dose-dependent and also occurred when IGFBP-3 was complexed with either IGF-I or heparin, suggesting that the receptor binding site is probably located in the least conserved central domain of IGFBP-3. Neither IGFBP-1, nor IGFBP-5 (structurally the closest to IGFBP-3) altered intracellular calcium concentrations. These results provide evidence that a specific intracellular signal is triggered by IGFBP-3 binding to a cell surface receptor.     

Insulin-like growth factor II acts as an autocrine growth and motility factor in human rhabdomyosarcoma tumors

Rhabdomyosarcoma is the most common soft tissue sarcoma of childhood and appears to arise from developing striated muscle-forming cells. Since insulin-like growth factor II (IGF-II) is involved in normal muscle growth and maturation and elevated IGF-II mRNA levels have previously been reported in rhabdomyosarcomas, we have been studying the possible role of IGF-II in the unregulated growth and invasive potential of these embryonal tumors. In this study, we demonstrate that 13 of 14 rhabdomyosarcoma tumors express high levels of IGF-II mRNA relative to normal adult muscle and also express mRNA for the type I IGF receptors on their cell surface, the receptor thought to mediate the effects of IGF-II on muscle cells. We have established several rhabdomyosarcoma cell lines in mitogen-free media and demonstrate that these cells express type I IGF receptors on their cell surface and secrete IGF-II into the media. Exogenous IGF-II is able to stimulate cellular motility in these cell lines as assayed in a modified Boyden chamber. Finally, alpha IR-3, a type I receptor antagonist, inhibits the growth of these cell lines in serum-free media but does not inhibit IGF-II-induced motility of these cells. These data suggest that endogenously produced IGF-II functions as an autocrine growth and motility factor in many rhabdomyosarcoma tumors. The mitogenic actions of IGF-II are mediated through a domain of the type I IGF receptor that is blocked by alpha IR-3. IGF-II-induced motility may be mediated through an alternative signaling pathway.     

Insulin-like growth factor (IGF) induced proliferation of human lung fibroblasts is enhanced by neurotensin

Fibroblasts are key cells in tissue repair and important contributors to the inflammatory response. Insulin-like growth factors (IGFs) have been shown to participate in growth, in immune responses and in tissue repair where they stimulate cell growth. Neurotensin (NT) has been suggested to participate in inflammation and in tissue repair and is an autocrine or paracrine growth factor for several cancer cell types. Here we show that IGF-induced proliferation of fibroblasts is enhanced by NT in a concentration and type 1 NT-receptor dependent manner. This action of NT was blocked by inhibitors of phospholipase C and protein kinase C but not by inhibitors of phosphoinositide-3-kinase. An inhibitor of MEK 1/2 significantly reduced the proliferative effects of the IGFs but NT's ability to enhance IGF-induced proliferation was not effected. The ability of NT to enhance IGF-induced proliferation did not involve an autocrine factor. These results suggest that interactions between NT and the IGFs may contribute to the regulation of fibroblasts in for example, inflamed or injured tissues.