Growth regulation by insulin-like growth factor-I in fish

Insulin-like growth factor-I (IGF-I) is a mitogenic polypeptide that plays an essential role in the regulation of development and somatic growth of vertebrates, mainly by mediating growth hormone actions. It has clearly been established that the structure of IGF-I and its biological function has been highly conserved among vertebrates. In this paper, we review the recent developments in the molecular, biochemical, and physiological properties of IGF-I in fish.     

Expression and regulation of mRNAs for insulin-like growth factor-I receptor and LH receptor in corpora lutea

Relationship between insulin-like growth factor-I receptor (IGF-IR) and luteinizing hormone receptor (LHR) mRNA expression as well as their regulation was determined in rat corpora lutea (CL) . In the CL of estrous cycle rat, LHR mRNA positive CL expressed high level of mRNA of IGF-IR. While the expression of LHR mRNA decreased on estrus, the CL still expressed relatively high level of IGF-IR mRNA. In pseudopregnant rat CL, the expression level of LHR mRNA was low on day 1, the most intense signals were detected on day 8, the signals of LHR mRNA became undetectable on day 14. In contrast to LHR expression, the high level of IGF-IR mRNA was observed in pseudopregnant CL of day 1, and thereafter its signals were detected from day 2 to day 14. Pregnant rat CL expressed both LHR and IGF-IR mRNAs. IGF-I stimulated LHR expression in CL. PGF2 inhibited expression of IGF-IR and LHR. PGE2 negated the inhibiting effects of PGF2. These data suggest that IGF-I may be involved in regulating CL function, and maintaining CL structure through changes in expression of its receptors. Inhibited expression of IGF-IR by PGF2 may be part of mechanisms for regression of CL.     

Expression and regulation of mRNAs for insulin-like growth factor-I receptor and LH receptor in corpora lutea

Relationship between insulin-like growth factor-l receptor (IGF-IR) and luteinizing hormone receptor (LHR) mRNA expression as well as their regulation was determined in rat corpora lutea (CL) . In the CL of estrous cycle rat, LHR mRNA positive CL expressed high level of mRNA of IGF-IR. While the expression of LHR mRNA decreased on estrus, the CL still expressed relatively high level of IGF-IR mRNA. In pseudopregnant rat CL, the expression level of LHR mRNA was low on day 1, the most intense signals were detected on day 8, the signals of LHR mRNA became undetectable on day 14. In contrast to LHR expression, the high level of IGF-IR mRNA was observed in pseudopregnant CL of day 1, and thereafter its signals were detected from day 2 to day 14. Pregnant rat CL expressed both LHR and IGF-IR mRNAs. IGF-I stimulated LHR expression in CL. PGF2ainhibited expression of IGF-IR and LHR. PGE2 negated the inhibiting effects of PGF2α. These data suggest that IGF-I may be involved in regulating CL function, and maintai     

Heterogeneity of insulin-like growth factor-I affinity for the insulin-like growth factor-II receptor: comparison of natural, synthetic and recombinant DNA-derived insulin-like growth factor-I

Although insulin-like growth factors (IGF) I and II bind with high affinity to structurally discrete receptors, they bind with a lesser affinity to each other's receptor. We have evaluated the affinity of five different IGF-I preparations (three natural IGF-I preparations, one synthetic preparation, and one recombinant DNA-derived) for the IGF-II receptor in rat placental membranes, 18-54,SF cells and BRL-3A cells. In all tissues tested, the natural IGF-I preparations demonstrated an affinity for the IGF-II receptor which was 10-20% that of IGF-II. However, the recombinant and synthetic IGF-I preparations exhibited substantially lower affinities than natural IGF-I for this receptor, with only 10-25% reduction in (125-I)iodo IGF-II binding at peptide concentrations up to 400 ng/ml. Radioimmunoassay of the natural IGF-I preparations with an antibody directed against the unique C-peptide region of IGF-II demonstrated that contamination of IGF-I preparations with immunoreactive IGF-II could not exceed 5%. These results demonstrate that IGF-I purified from human plasma has a different affinity for the IGF-II receptor than does synthetic or recombinant IGF-I. Furthermore, these data are consistent with the hypothesis that IGF-I, itself, may be heterogeneous, and that subforms may vary in their affinities for the IGF receptors. Alternatively, IGF-I preparations which have been considered to be pure may be contaminated with small amounts of IGF-II, resulting in overestimation of the affinity of IGF-I for the type II IGF receptor.     

Expression of insulin-like growth factor binding protein-4, insulin-like growth factor-I receptor, and insulin-like growth factor-I in the mouse uterus throughout the estrous cycle

Recent evidence suggests that a regulated insulin-like growth factor (IGF) system mediates the effects of estrogen, promoting the proliferation and differentiation of specific uterine cell types throughout the estrous cycle and during gestation in the rodent. Previous studies have shown that IGFs are differentially expressed in the mouse uterus during the periimplantation period. In the current study, we examined the expression of IGF binding protein-4 (IGFBP-4), IGF-I receptor (IGF-IR), and IGF-I in the mouse uterus throughout the estrous cycle. Ligand blot analysis was conducted on uterine homogenates using [125I]IGF-I. IGFBP-4 was detected in all uterine homogenates, varying in intensity throughout the estrous cycle. In situ hybridization studies at metestrus and diestrus demonstrated an intense IGFBP-4 mRNA signal in antimesometrial stromal cells between the luminal epithelium and the myometrium, but at proestrus and estrus, no IGFBP-4 signal was detected. No IGF-I mRNA was detected at any stage of the estrous cycle by in situ hybridization. However, by RT-PCR analysis, IGF-I mRNA was detected at all stages of the estrous cycle. RT-PCR analysis also showed IGF-IR mRNA throughout the estrous cycle. Using immunohistochemistry, IGF-IR immunostaining was detected throughout the estrous cycle and on days 2-7 of gestation, but was restricted to the glandular epithelium. These results suggest that uterine IGFBP-4 expression may not be dependent on uterine IGF-I expression. They also suggest that IGFBP-4 may play a role in uterine physiology independent of the inhibition of IGF-I action, and that IGF-IR is constitutively expressed in the mouse uterus.     

C-terminal Src kinase associates with ligand-stimulated insulin-like growth factor-I receptor

Increased expression of the insulin-like growth factor-I receptor (IGF-IR) protein-tyrosine kinase occurs in several kinds of cancer and induces neoplastic transformation in fibroblast cell lines. The transformed phenotype can be reversed by interfering with the function of the IGF-IR. The IGF-IR is required for transformation by a number of viral and cellular oncoproteins, including SV40 large T antigen, Ras, Raf, and Src. The IGF-IR is a substrate for Src in vitro and is phosphorylated in v-Src-transformed cells. We observed that the IGF-IR and IR associated with the C-terminal Src kinase (CSK) following ligand stimulation. We found that the SH2 domain of CSK binds to the tyrosine-phosphorylated form of IGF-IR and IR. We determined the tyrosine residues in the IGF-IR and in the IR responsible for this interaction. We also observed that fibroblasts stimulated with IGF-I or insulin showed a rapid and transient decrease in c-Src tyrosine kinase activity. The results suggest that c-Src and CSK are involved in IGF-IR and IR signaling and that the interaction of CSK with the IGF-IR may play a role in the decrease in c-Src activity following IGF-I stimulation.     

Regulation of survival signals from the insulin-like growth factor-I receptor

Suppression of apoptosis by survival factors is important for the maintenance of normal tissue homoeostasis and the response to infection or injury. Survival factors such as insulin-like growth factor-I (IGF-I) initiate a signalling cascade that starts by tyrosine phosphorylation of substrates leading to the activation of serine kinases that modulate the activity of members of the Bcl-2 family, which regulates the apoptotic machinery in most cells. Tumour cells often have enhanced survival mechanisms due either to up-regulation of the IGF-I receptor and its ligands or to loss of function of a phosphatase (PTEN) that regulates part of this survival pathway. The C-terminus of the IGF-I receptor appears to be a regulatory domain for the anti-apoptotic activity of this receptor, and certain residues within the C-terminus are essential for this regulatory activity. Knowledge of the proteins and pathways, which interact with these C-terminal domains, should lead us to ways of modulating IGF-I-mediated survival in tumours.     

Pubertal maturation modifies the regulation of insulin-like growth factor-I receptor signaling by estradiol in the rat prefrontal cortex

The transition from adolescence to adulthood is accompanied by substantial plastic modifications in the cerebral cortex, including changes in the growth and retraction of neuronal processes and in the rate of synaptic formation and neuronal loss. Some of these plastic changes are prevented in female rats by prepubertal ovariectomy. The ovarian hormone estradiol modulates neuronal differentiation and survival and these effects are in part mediated by the interaction with insulin-like growth factor-I (IGF-I). In this study, we have explored whether the activation by estradiol of some components of IGF-I receptor signaling is altered in the prefrontal cortex during puberty. Estradiol administration to rats ovariectomized after puberty resulted, 24 h after the hormonal administration, in a sustained phosphorylation of Akt and glycogen synthase kinase 3 beta in the prefrontal cortex. However, this hormonal effect was not observed in animals ovariectomized before puberty. These findings suggest that during pubertal maturation there is a programming by ovarian hormones of the future regulatory actions of estradiol on IGF-I receptor signaling in the prefrontal cortex. The modification in the regulation of IGF-I receptor signaling by estradiol during pubertal maturation may have implications for the developmental changes occurring in the prefrontal cortex in the transition from adolescence to adulthood.     

胰岛素样生长因子受体Ⅰ序列结构的生物信息学分析

胰岛素样生长因子受体Ⅰ的3'UTR长度大于7 kb,结构复杂,有多种mi RNAs的结合位点,参与信号通路中MAPK及PI3K/AKT的调节和多种肿瘤的形成和发展,通过生物信息学分析知道其结构特点,为后续研究提供思路。分析表明儿童神经胶质瘤中IGF1R的3'UTR与mi RNAs结合位点突变率最高。分析IGF1R序列3'UTR的结构,mi RNAs结合位点,氨基酸序列的理化性质,亲疏水性,糖基化和磷酸化位点,二级结构和三级结构建模。IGF1R三级结构与配体IGF1的三级结构模拟分子对接,得到2种蛋白相互作用的氨基酸位置及名称。因此,通过对IGF1R 3'UTR突变,降低与mi RNAs的结合,IGF1R表达上调,同时改变与IGF1的氨基酸结合位点,降低2种蛋白的相互作用,从而抑制IGF1R的作用。     

Characterization of a chimeric monoclonal antibody against the insulin-like growth factor-I receptor

The insulin-like growth factors (IGFs) signaling system has been shown to play important roles in neoplasia. The IGF receptor type 1 (IGF-IR) is overexpressed in many types of solid and hematopoietic malignancies, and there is substantial experimental and clinical evidence that targeting IGF-IR is a promising therapeutic strategy against cancer. It has been previously reported that a mouse monoclonal antibody (mAb), 4G11, blocked IGF-I binding to IGF-IR and downregulated the IGF-IR in MCF-7 cells. We cloned this antibody, constructed a human-mouse chimeric antibody, designated m590, and characterized it. The chimeric IgG1 m590 bound to cell-associated IGF-IR on NWT c43 stably transfected cells and MCF-7 breast cancer cells as efficiently as the parental murine antibody. Using purified IGF-IR extracellular domains, we found that both the chimeric m590 and the parental 4G11 antibodies bind to conformational epitopes on IGF-IR. Neither of these antibodies bound to the insulin receptor (IR) ectodomain. Furthermore, IgG1 m590 blocked the binding of IGF-I and IGF-II to IGF-IR, and inhibited both IGF-I and IGF-II induced phosphorylation of IGF-IR in MCF-7 cells. These results suggest that m590 could be an useful antibody in diagnosis and treatment of cancer, as well as a research tool.     

Differential expression of insulin-like growth factor-I and insulin-like growth factor binding protein-1 in the diabetic rat

Summary Multiple factors contribute to the growth retardation which is a characteristic feature of uncontrolled diabetes. In this report we have examined the effects of streptozotocin-induced (STZ) diabetes on expression of insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-1 (IGFBP-1) in various tissues. As early as 7 days after STZ administration there was a modest reduction in IGF-I mRNA abundance. The reduction (10–30%) was of similar magnitude in each of the 7 tissues examined; liver, kidney, lung, diaphragm, quadraceps, heart and adipose tissue. However, the reduction achieved statistical significance only in the lung (p < 0.05) and diaphragm (p < 0.01). A further reduction in IGF-I mRNA abundance was seen in many tissues, 32 and 91 days after STZ administration. In contrast to the decrease in IGF-I mRNA, IGFBP-1 mRNA was significantly increased in the liver and kidney of diabetic rats. IGFBP-1 mRNA was detectable at only very low levels in other tissues but was increased in diabetic rats compared non-diabetic rats. In diabetic rats, a highly significant correlation (R = 0.75, p < 0.001) between hepatic IGFBP-1 mRNA and glucose was observed whereas there was no significant correlation between serum glucose and hepatic IGF-I mRNA abundance (R = 0.24, p = NS). Treatment of diabetic rats with insulin resulted in a small, non significant increase in hepatic and renal IGF-I mRNA and a significant decrease in renal IGFBP-1 mRNA abundance. The observations reported here are consistent with the hypothesis that diminished IGF-I expression and inhibition of available IGF-1 by increased levels of IGFBP-1 may explain the impaired growth seen in diabetic animals.