Synthesis and characterization of IGF-II analogs: applications in the evaluation of IGF receptor function and IGF-independent actions of IGFBPs

Differential production of insulin-like growth factor-binding proteins in liver fibrosis progression

Noninvasive methods for liver disease diagnoses offer great advantages over biopsy, but they cannot be utilized in all cases. Therefore, specific indicators for chronic liver disease management are necessary. The aim was to assess the production of insulin-like growth factor-binding proteins (IGFBPs) 1-7 and their correlation with the different stages of fibrosis in chronic hepatitis C (CHC). A prospective, cross-sectional, multicenter study was conducted. CHC patients were categorized by FibroTest® and/or FibroScan®. Serum concentrations of IGFBPs 1-7 were determined through multiple suspension arrangement array technology. Significant differences were validated by the Kruskal-Wallis and Mann-Whitney U tests. Logistic regression models were performed to assess the association between the IGFBPs and fibrosis stages. The association was determined utilizing odds ratios (ORs), and receiver operating characteristic (ROC) curves were constructed to distinguish the IGFBPs in relation to the diagnosis of fibrosis. IGFBP-1 and IGFBP-7 concentrations were higher in CHC than in the healthy individuals, whereas IGFBP-3, IGFBP-5, and IGFBP-6 were downregulated in the patients. An apparent increase of all the IGFBPs was found at fibrosis stage F4, but with different regulations. IGFBP-2, -4, -6, and -7 had the best OR, showing the relation to fibrosis progression. The ROC curves showed that IGFBP-7 was the only protein that distinguished F1 from F3 and F2 from F3. IGFBPs participate in liver fibrosis progression and could be employed as circulating novel protein panels for diagnosis and as possible therapeutic targets in liver fibrosis progression.

The insulin-like growth factor mutation database (IGFmdb)

Insulin-like growth factors (IGF-I and IGF-II), and insulin are evolutionarily conserved hormonal regulators of eukaryotic growth and development. Through interactions with their cognate receptors, all three molecules can influence cellular growth, proliferation, differentiation, migration, and survival, as well as metabolic processes. As such, perturbations in signaling by IGFs and insulin are a well-documented cause of altered growth, development and survival during both embryonic and post-natal life. A key approach in understanding how IGFs and insulin elicit their biological effects has been through identifying structural features of the ligands that influence their receptor interactions. Over the years, the study of many hundreds of specifically engineered IGF and insulin analogues has provided a wealth of knowledge about how specific residues of these ligands contribute to ligand:receptor interactions. Some analogues have even provided the basis for designing therapeutic agents for the treatment of IGF and insulin-related diseases. As the list of IGF and insulin analogues continues to grow we find that, while many have been produced and studied, it would be of considerable value to have a central repository from which information about specific analogues and their receptor binding data were readily available in an easily searchable and comparable format. To address this, we have created the "Insulin-like growth factor mutation database" (IGFmdb). The IGFmdb is a web-based curated database of annotated ligand analogues and their receptor binding affinities that can be accessed via http://www.adelaide.edu.au/igfmutation. Currently the IGFmdb contains receptor-binding data for 67 IGF-II analogues that were publicly accessible prior to 2012, as well as 67 IGF-I analogues, including all of those produced and characterised in our laboratory. A small number of these are IGF species homologues. There are also 32 insulin analogues within IGFmdb that were reported within the included IGF analogue studies, representing only a small fraction of existing insulin mutants. Future developments of the IGFmdb will incorporate receptor-binding data for all publicly accessible IGF-I analogues and the data will be expanded to include IGF-binding protein (IGFBP) binding affinities.

Activation of IGF-2R stimulates cardiomyocyte hypertrophy in the late gestation sheep fetus

In vitro studies using rat and fetal sheep cardiomyocytes indicate that, in addition to its role as a clearance receptor, the insulin-like growth factor 2 receptor (IGF-2R) can induce cardiomyocyte hypertrophy. In the present study, we have determined the effect of specific activation of the IGF-2R in the heart of the late gestation fetus on cardiomyocyte development. Leu(27)IGF-2, an IGF-2R agonist, was infused into the fetal left circumflex coronary artery for 4 days beginning at 128.1 ± 0.4 days gestation. Ewes were humanely killed at 132.2 ± 1.2 days gestation (term, 150 days). Fetuses were delivered and hearts dissected to isolate the cardiomyocytes and to collect and snap-freeze tissue. Leu(27)IGF-2 infusion into the left circumflex coronary artery of fetal sheep increased the area of binucleated cardiomyocytes in the left, but not the right, ventricle. However, this infusion of Leu(27)IGF-2 did not change fetal weight, heart weight, blood pressure, blood gases or cardiomyocyte proliferation/binucleation. The increase in cardiomyocyte size in the Leu(27)IGF-2-infused group was associated with increased expression of proteins in the Gαs, but not the Gαq, signalling pathway. We concluded that infusion of Leu(27)IGF-2 into the left circumflex coronary artery causes cardiac IGF-2R activation in the left ventricle of the heart, and this stimulates cardiomyocyte hypertrophy in a Gαs-dependent manner.

Effect of IGFBP-3 on IGF- and IGF-analogue-induced insulin-like growth factor-I receptor (IGFIR) signalling

Insulin-like growth factor binding protein-3 (IGFBP-3) binds IGF-I and IGF-II with high affinity, at least an order of magnitude higher than the affiniy of the IGFs for the IGFIR. It has been hypothesized that IGFBP-3 inhibits IGF binding to the IGFIR via a mechanism independent of its ability to sequester IGFs. In the present study, we examined the effects of IGFBP-3 and its proteolytic fragments on the initial events of the IGFIR signalling pathway. IGFBP-3 inhibited IGF-I-, IGF-II-, Des(1-3)IGF-I- and Long(R3)IGF-I-induced IGFIR phosphorylation in a dose-dependent manner at similar concentration range but not QAYL-induced IGFIR-P. The((1-97))IGFBP-3 fragment was able to inhibit only IGF-I-induced IGFIR-P. The((1-97))IGFBP-3 fragment but not intact IGFBP-3 inhibited insulin-induced IGFIR-P. Monolayer cross-linking with [(125)I]IGFBP-3 indicated that there is no direct interaction of IGFBP-3 with the IGFIR. This study demonstrates that the effect on the initial step of IGFIR signalling by IGFBP-3 is largely due to its ability to sequester IGF and the IGF analogues in the extracellular milieu and not the result of any interaction of IGFBP-3 with the IGFIR or a mechanism independent of its ability to bind IGFs.

Identification of a family of low-affinity insulin-like growth factor binding proteins (IGFBPs): characterization of connective tissue growth factor as a member of the IGFBP superfamily

The insulin-like growth factor (IGF) binding proteins (IGFBPs) modulate the actions of the insulin-like growth factors in endocrine, paracrine, and autocrine settings. Additionally, some IGFBPs appear to exhibit biological effects that are IGF independent. The six high-affinity IGFBPs that have been characterized to date exhibit 40-60% amino acid sequence identity overall, with the most conserved sequences in their NH2 and COOH termini. We have recently demonstrated that the product of the mac25/IGFBP-7 gene, which shows significant conservation in the NH2 terminus, including an "IGFBP motif' (GCGCCXXC), exhibits low-affinity IGF binding. The closely related mammalian genes connective tissue growth factor (CTGF) gene, nov, and cyr61 encode secreted proteins that also contain the conserved sequences and IGFBP motifs in their NH2 termini. To ascertain if these genes, along with mac25/IGFBP-7, encode a family of low-affinity IGFBPs, we assessed the IGF binding characteristics of recombinant human CTGF (rhCTGF). The ability of baculovirus-synthesized rhCTGF to bind IGFs was demonstrated by Western ligand blotting, affinity cross-linking, and competitive affinity binding assays using 125I-labeled IGF-I or IGF-II and unlabeled IGFs. CTGF, like mac25/IGFBP-7, specifically binds IGFs, although with relatively low affinity. On the basis of these data, we propose that CTGF represents another member of the IGFBP family (IGFBP-8) and that the CTGF gene, mac25/IGFBP-7, nov, and cyr61 are members of a family of low-affinity IGFBP genes. These genes, along with those encoding the high-affinity IGFBPs 1-6, together constitute an IGFBP superfamily whose products function in IGF-dependent or IGF-independent modes to regulate normal and neoplastic cell growth.

Synthesis and characterization of insulin-like growth factor-binding protein (IGFBP)-7. Recombinant human mac25 protein specifically binds IGF-I and -II

The mac25 cDNA was originally cloned from leptomeningial cells and subsequently reisolated through differential display as a sequence preferentially expressed in senescent human mammary epithelial cells. The deduced amino acid sequence of the human mac25 propeptide shares a 20-25% identity to human insulin-like growth factor-binding proteins (IGFBPs), suggesting that mac25 could be another member of the IGFBP family. In the present study, we have generated recombinant human mac25 (rh-mac25) in a baculovirus expression system and assessed its affinity for IGFs and have evaluated the pattern of expression of the mac25 gene in human tissues. Binding of 125I-IGF-I and 125I-IGF-II to rh-mac25 was demonstrated by Western ligand blotting after nondenaturing polyacrylamide gel electrophoresis and by affinity cross-linking with as little as 2 nM rh-mac25. Specificity of rh-mac25 binding to 125I-IGFs was demonstrated by competition for rh-mac25 binding with unlabeled IGFs, but not with [QAYLL]IGF-II analog, which has 100-fold less affinity for IGFBPs. In comparison with IGFBP-3, rh-mac25 has at least a 5-6-fold lower affinity for IGF-I and 20-25-fold lower affinity for IGF-II. mac25 mRNA was detectable in a wide range of normal human tissues, with decreased expression in breast, prostate, colon, and lung cancer cell lines. In conclusion, mac25 specifically binds IGFs and constitutes a new member of the IGFBP family, IGFBP-7. Its wider distribution in normal tissue and lower expression in several cancer cells indicate that IGFBP-7 may function as a growth-suppressing factor, as well as an IGF-binding protein.

Transforming growth factor-beta-induced cell growth inhibition in human breast cancer cells is mediated through insulin-like growth factor-binding protein-3 action

Most estrogen receptor-negative breast cancer cells, including Hs578T cells, express mRNAs encoding insulin-like growth factor-binding protein (IGFBP)-3, as well as transforming growth factor (TGF)-beta receptors. Our previous studies (Oh, Y., Muller, H. L., Lamson, G., and Rosenfeld, R. G. (1993) J. Biol. Chem. 268, 14964-14971; Oh, Y., Muller, H. L., Pham, H. M., and Rosenfeld, R. G. (1993) J. Biol. Chem. 268, 26045-26048) have demonstrated a significant inhibitory effect of exogenous IGFBP-3 on Hs578T cell growth and existence of IGFBP-3-specific receptors that may mediate those direct inhibitory effect of IGFBP-3. TGF-beta is also a potent growth inhibitor in human breast cancer cells in vitro and regulates IGFBP-3 production in different cell systems, suggesting that IGFBP-3 is a major anti-proliferative factor and a key element for TGF-beta-induced growth inhibition in human breast cancer cells. In support of this hypothesis, we have demonstrated using Hs578T cells that: 1) TGF-beta stimulates IGFBP-3 gene expression and production prior to its inhibition of cell growth, 2) treatment with an IGFBP-3 antisense oligodeoxynucleotide selectively inhibits TGF-beta-induced IGFBP-3 synthesis and cell growth inhibition, and 3) treatment with IGF-II and IGF-II analogs diminish TGF-beta effects by blocking TGF-beta-induced binding of IGFBP-3 to the cell surface. These findings suggest that IGFBP-3 is a major anti-proliferative factor and a key element in TGF-beta-induced growth inhibition in human breast cancer cells.