Long R3 insulin-like growth factor-I (IGF-I) infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF binding protein concentrations in the guinea pig

Insulin-Like Growth Factor and SLC12A7 Dysregulation: A Novel Signaling Hallmark of Non-Functional Adrenocortical Carcinoma

BACKGROUND

Insulin-like growth factor (IGF) dysregulation and gene copy number variations (CNV) are hallmarks of adrenocortical carcinoma (ACC). The contribution of IGF CNVs in adrenal carcinogenesis has not been studied previously. In addition, studies demonstrating an association between SLC12A7 gene amplifications and enhanced metastatic behavior in ACC, as well as reported IGF-SLC12A7 signaling interactions in other cancers, suggest a potential IGF-SLC12A7 signaling circuitry in ACC. Here we investigate the potential complicity of IGF-SLC12A7 signaling in ACC.

STUDY DESIGN

Insulin-like growth factor CNVs were determined by whole-exome sequencing analysis in an exploratory cohort of ACC. Quantitative polymerase chain reaction methods determined IGF1 and IGF2 expression levels and were evaluated for correlation with SLC12A7 expression and tumor characteristics. Insulin-like growth factor CNVs and expression patterns were compared with The Cancer Genome Atlas. In vitro studies determined the relationship of IGF and SLC12A7 co-expression in 2 ACC cell lines, SW-13 and NCI-H295R. Immunohistochemistry assessed IGF1 receptor (IGF1R) activation.

RESULTS

The IGF1 gene was amplified in 9 of 19 ACC samples, similar to findings in The Cancer Genome Atlas database. The IGF1 overexpression was observed in 5 samples and was associated with SLC12A7 overexpression and non-functional, early-stage tumors (p < 0.05). In contrast, IGF2 overexpression was associated with larger tumors (p < 0.05). In vitro IGF treatment of ACC cell lines did not stimulate SLC12A7 expression, and endogenous overexpression and silencing of SLC12A7 significantly altered IGF1 and IGF1R expression without impacting other IGFs. The IGF1R activation was associated with IGF1 overexpression in ACC tumor samples.

CONCLUSIONS

These findings indicate that IGF1 overexpression, caused in part by gene amplifications, is correlated with SLC12A7 overexpression in non-functional, early-stage ACCs, suggesting a potentially targeted IGF1-SLC12A7 therapeutic opportunity for these tumors.

Both epidermal growth factor and insulin-like growth factor receptors are dispensable for structural intestinal adaptation

PURPOSE

Intestinal adaptation structurally represents increases in crypt depth and villus height in response to small bowel resection (SBR). Previously, we found that neither epidermal growth factor receptor (EGFR) nor insulin-like growth factor 1 receptor (IGF1R) function was individually required for normal adaptation. In this study, we sought to determine the effect of disrupting both EGFR and IGF1R expression on resection-induced adaptation.

METHODS

Intestinal-specific EGFR and IGF1R double knockout mice (EGFR/IGF1R-IKO) (n=6) and wild-type (WT) control mice (n=7) underwent 50% proximal SBR. On postoperative day (POD) 7, structural adaptation was scored by measuring crypt depth and villus height. Rates of crypt cell proliferation, apoptosis, and submucosal capillary density were also compared.

RESULTS

After 50% SBR, normal adaptation occurred in both WT and EGFR/IGF1R-IKO. Rates of proliferation and apoptosis were no different between the two groups. The angiogenic response was less in the EGFR/IGF1R-IKO compared to WT mice.

CONCLUSION

Disrupted expression of EGFR and IGF1R in the intestinal epithelial cells does not affect resection-induced structural adaptation but attenuates angiogenesis after SBR. These findings suggest that villus growth is driven by receptors and pathways that occur outside the epithelial cell component, while angiogenic responses may be influenced by epithelial-endothelial crosstalk.

Insulin-like growth factor 2 and its enterocyte receptor are not required for adaptation in response to massive small bowel resection

PURPOSE

Enhanced structural features of resection-induced intestinal adaptation have been demonstrated following the administration of multiple different growth factors and peptides. Among these, the insulin-like growth factor (IGF) system has been considered to be significant. In this study, we employ mutant mouse strains to directly test the contribution of IGF2 and its enterocyte receptor (IGF1R) toward the adaptation response to massive small bowel resection (SBR).

METHODS

IGF2-knockout (IGF2-KO) (n=8) and intestine specific IGF1R-knockout mice (IGF1R-IKO) (n=9) and their wild type (WT) littermates (n=5, n=7, respectively) underwent 50% proximal SBR. At post-operative day 7, structural adaptation was measured as crypt depth and villus height. Rates of enterocyte proliferation and apoptosis were also recorded.

RESULTS

The successful deletion of IGF2 and IGF1R expression in the enterocytes was confirmed by RT-PCR and Western blot, respectively. Normal adaptation occurred in both IGF2-KO and IGF1R-IKO mice after 50% SBR. Post-operative rates of proliferation and apoptosis in both IGF2-KO and IGF1R-IKO mice were no different than their respective controls.

CONCLUSION

IGF2 and functional IGF1R signaling in enterocytes are both dispensable for resection-induced adaptation responses. The mechanism for IGF-stimulation of intestinal adaptation may involve other ligands or cellular compartments within the intestine.

The IGF-1 receptor in cancer biology

The type 1 insulin-like growth factor receptor (IGF-1R) plays an important role in the establishment and maintenance of the transformed phenotype. It also has a strong antiapoptotic activity and has a significant influence on the control of cell and body size. Downregulation of the IGF-1R leads to massive apoptosis of cancer cells. These characteristics make it an attractive target for anticancer therapy.

Insulin-like growth factor binding protein 2 (IGFBP-2) separates hypertrophic and hyperplastic effects of growth hormone (GH)/IGF-I excess on adrenocortical cells in vivo

GH and IGF-I are capable of inducing cellular hypertrophy and/or hyperplasia. Chronic overexpression of GH in transgenic mice results in systemically and locally increased IGF-I levels and in disproportionate overgrowth, including adrenocortical enlargement and corticosterone hypersecretion. Using PEPCK-bovine GH transgenic (G) mice, we demonstrate that adrenal enlargement involves both hypertrophy (44%) and hyperplasia (50%) of zona fasciculata cells. To clarify whether IGFBP-2 affected cell volume and number, we crossed hemizygous G mice with hemizygous CMV-IGFBP-2 transgenic (B) mice, generating G mice, B mice, GB double transgenic mice, and nontransgenic controls (C). The absolute weight of the adrenal glands was significantly increased in 5-wk- and 4-month-old G mice vs. C and B mice. IGFBP-2 overexpression in GB mice reduced this effect of GH excess by 26% and 37% in 5-wk- and 4-month-old animals, respectively. GH-induced hypertrophy of zona fasciculata cells was completely abolished by IGFBP-2 overexpression in GB mice whereas hyperplasia was not affected. Basal and ACTH-induced plasma corticosterone levels of 4-month-old G mice, but not of GB mice, were two- to threefold increased compared with C mice. Plasma ACTH levels were similar in all groups. Our data show that IGFBP-2 potently separates hypertrophic and hyperplastic effects of GH/IGF-I excess on adrenocortical cells.

Short-term infusion of LongR(3) insulin-like growth factor (IGF)-I decreases hepatic IGF-I mRNA but not IGF binding protein-3 mRNA expression in pigs

Infusion of pigs with an insulin-like growth factor-I (IGF-I) analogue (LongR(3)IGF-I) that does not bind to IGF-binding proteins decreases growth rate and the plasma concentration of growth hormone (GH), IGF-I, IGFBP-3, and insulin. This study was designed to determine whether the decrease is due to changes in IGF-I and IGFBP-3 gene expression. IGF-I or LongR(3)IGF-I (180 microg/kg/day) was infused into 55-kg finisher pigs for 4 days using Travenol infuser pumps. Plasma IGF-I concentration was measured by radioimmunoassay and plasma IGFBP-3 and IGFBP-2 were estimated by Western ligand blotting. Steady-state levels of IGF-I and IGFBP-3 mRNA were measured by RNase protection assay. Neither IGF-I nor LongR(3)IGF-I had a significant effect on hepatic IGF-I class 1 mRNA expression, whereas hepatic IGF-I class 2 mRNA expression was significantly reduced by both peptides. Plasma IGFBP-3 levels were unaffected by IGF-I treatment but were reduced by LongR(3)IGF-I treatment. The decrease in IGFBP-3 was not due to decreased gene expression in porcine liver or kidney, since neither IGF-I nor LongR(3)IGF-I treatment altered IGFBP-3 mRNA. This study infers a direct effect of the IGF analogue LongR(3)IGF-I on GH through its inhibition of plasma IGF-I concentration and class 2 IGF-I mRNA. The decrease in plasma IGFBP-3 was not accompanied by a decrease in hepatic or renal IGFBP-3 mRNA, suggesting that in this case, plasma IGFBP-3 protein levels are posttranslationally regulated or are derived from tissues other than liver or kidney.

Maternal nutrition affects the ability of treatment with IGF-I and IGF-II to increase growth of the placenta and fetus, in guinea pigs

The aim of this study was to investigate how administration of IGF-I and IGF-II, during early to mid pregnancy, affects maternal growth and body composition as well as fetal and placental growth, in ad libitum fed, and in moderately, chronically food restricted guinea pigs. From day 20 of gestation, mothers (3-4 months old) were infused with IGF-I, IGF-II (565 microg/day) or vehicle for 17 days and then killed on day 40 of gestation. Maternal organ weights, fetal and placental weights were assessed. Treatment with IGFs did not alter body weight gain and had small effects on body composition in the mothers. Both IGF-I and IGF-II increased fetal and placental weights in ad libitum fed dams and IGF-I increased placental weight in food restricted dams. In conclusion, treatment with IGF-I during the first half of pregnancy stimulates placental growth in both ad libitum fed and food restricted guinea pigs without affecting maternal growth while fetal growth is stimulated by IGF treatment only in ad libitum fed animals.

Porcine growth hormone and LongR(3)IGF-I can improve recovery from surgery-induced weight loss in guinea pigs

In the present study, porcine growth hormone (pGH) and LongR(3)IGF-I (LR(3)IGF-I), a potent analogue of IGF-I, were infused continuously into 430-g guinea pigs for 7 days, either alone or in combination, to examine whether pGH can counteract the reduction in circulating IGF-I concentrations induced by LR(3)IGF-I administration. The pGH and LR(3)IGF-I were infused at rates of 400 microg/day (0.93 mg/kg/day) and 120 microg/day (0.28 mg/kg/day), respectively, by miniosmotic pumps. The same doses were infused in the combination treatment. During the first day of treatment, animals lost between 2 and 3% of body weight. Cumulative body weight gains as a percentage of initial body weight were significantly (P < 0.001) increased relative to vehicle-treated controls by the LR(3)IGF-I, pGH, and combination treatments when effects were analyzed across the whole 7-day treatment period. The increased weight gains relative to controls were largely made on day 2, but these gains were not associated with increased water or feed intakes, indicating that pGH and LR(3)IGF-I improved feed conversion efficiency. LR(3)IGF-I alone or in combination with pGH significantly increased the fractional weight of kidneys at the end of the 7-day treatment period, whereas LR(3)IGF-I alone increased the fractional weight of spleens. Concentrations of IGF-I in serum collected after 7 days of treatment were decreased by LR(3)IGF-I, but this decrease was not ameliorated by coinfusion with pGH. GH alone did not have any effects on IGF-I concentration. This study suggests that pGH does not have a strong influence on circulating IGF-I concentrations in the guinea pig. We have also demonstrated that pGH and LR(3)IGF-I are capable of enhancing the recovery of body weight lost in response to surgery in the guinea pig.

The effects of insulin-like growth factors on tumorigenesis and neoplastic growth

Several decades of basic and clinical research have demonstrated that there is an association between the insulin-like growth factors (IGFs) and neoplasia. We begin with a brief discussion of the function and regulation of expression of the IGFs, their receptors and the IGF-binding proteins (IGFBPs). A number of investigational interventional strategies targeting the GH or IGFs are then reviewed. Finally, we have assembled the available scientific knowledge about this relationship for each of the major tumor types. The tumors have been grouped together by organ system and for each of the major tumors, various key elements of the relationship between IGFs and tumor growth are discussed. Specifically these include the presence or absence of autocrine IGF-I and IGF-II production; presence or absence of IGF-I and IGF-II receptor expression; the expression and functions of the IGFBPs; in vitro and in vivo experiments involving therapeutic interventions; and available results from clinical trials evaluating the effect of GH/IGF axis down-regulation in various malignancies.

IGF-I but not the IGF-I variant long R(3)IGF-I increases serum IGFBP-3 in adolescent monkeys

Previous work in rhesus monkeys has shown that both acute or chronic subcutaneous (s.c.) administration of insulin-like growth factor (IGF)-I elevates serum concentrations of IGF binding protein (IGFBP)-3. In order to determine whether an analog of IGF-I, which has a reduced affinity for the IGFBPs, has similar effects, a series of studies using adolescent female rhesus monkeys were conducted. In the first study, an s.c. injection of IGF-I (110 mg/kg;n = 6) significantly elevated serum IGFBP-3 concentrations through 7 h following treatment. In contrast, serum IGFBP-3 decreased throughout the day following an injection of Long R(3)IGF-I (110 mg/kg, s.c., n = 5). However, this decrease was not due to the analog treatment as serum IGFBP-3 also declined in a similar fashion in untreated females (n = 5) sampled on the same schedule. Serum GH levels were acutely suppressed by both IGFs but were not altered in untreated females. In the second study, serum IGFBP-3 were compared between untreated control females (n = 6) and females treated continuously by s.c. infusion with either Long R(3)IGF-I (120 mg/kg/day, s.c.;n = 5) or IGF-I (120 mg/kg/day, s.c.;n = 5) or IGF-I s.c.;n = 4). Serum IGFBP-3 was consistently elevated by IGF-I infusion, whereas levels in analog-treated monkeys were similar to those in control females. Although acute or chronic administration of Long R(3)IGF-I did not elevate serum IGFBP-3, chronic administration of the analog did not block the acute facilitating effects of IGF-I on serum IGFBP-3. The increase in serum IGFBP-3 following an acute injection of IGF-I (110 mg/kg, s.c.) was not significantly different between untreated females and females receiving a constant s.c. infusion of Long R(3)IGF-I. These data indicate either acutely or chronically administered IGF-I but not its analog Long R(3)IGF-I can elevate serum concentrations of IGFBP-3. Although the analog fails to increase serum IGFBP-3, it does not block the facilitating effects of IGF-I on concentrations of this IGFBP. Taken together, these data suggest that the increase in serum IGFBP-3 by exogenous IGF-I may not be a receptor mediated event but may be the result of IGF-I binding to IGFBP-3 and forming the binary and ternary complex, slowing IGFBP-3 degradation.

The IGF-I receptor in cancer research

The type 1 insulin-like growth factor receptor (IGF-IR) plays an important role in both normal and abnormal growth. It is particularly important in anchorage-independent growth. Impairment of its function causes apoptosis of tumor cells and inhibition of tumor growth in experimental animals. However, the IGF-IR can also induce differentiation, and eventually cell death, of certain types of cells. Its major substrates, IRS-1 and Shc, determine whether the IGF-IR will transform cells or will cause their differentiation.

Influence of continuous growth hormone or insulin-like growth factor I administration in adult female chickens

A series of studies was conducted to determine whether growth hormone (GH) exerts effects on adult female chickens. Recombinant chicken GH (rcGH) was administered continuously via osmotic minipumps. No consistent effects of rcGH treatment were observed on reproductive indices. Hens receiving rcGH treatment for 10 days exhibited hepatomegaly and showed a tendency (P < 0.1) for increased spleen and thymus weights. Moreover, there were increases in the circulating concentrations of insulin-like growth factor-I (IGF-I) and IGF-binding proteins (IGF-BPs) (22-kDa IGF-BP after 2, 5, and 10 days; 28-kDa IGF-BP after 5 and 10 days; and 36-kDa IGF-BP after 10 days) with rcGH treatment. To determine whether the changes in IGF-BPs were due directly to GH or indirectly via IGF-I, the effects of the continuous administration of rcGH or recombinant human IGF-I (rhIGF-I) were compared. While rcGH again elevated the circulating levels of 28- and 36-kDa IGF-BPs, no such effect was observed with rhIGF-I treatment. However, both treatments exerted similar effects in depressing pituitary GH mRNA levels and elevating plasma concentrations of IGF-I. It is concluded that GH directly elevates circulating concentrations of IGF-I and IGF-BPs, but the negative feedback effect on GH synthesis is mediated via IGF-I.

Action of long(R3)-insulin-like growth factor-1 on protein metabolism in beef heifers

Insulin-like growth factor-1 (IGF-1) is perhaps the most important endogenous factor controlling growth. Most studies to date in livestock have shown that IGF-1 has greatest efficacy when animals are in a catabolic state. We have determined the effects of an i.v. infusion of the IGF-1 analog Long(R3)-IGF-1 on protein metabolism in beef heifers that were slowly losing liveweight because of restricted feeding. There was a tendency for both whole-body protein and skeletal muscle protein to be conserved in Long(R3)-IGF-1-treated heifers. Long(R3)-IGF-1 administration markedly reduced the plasma concentrations of all amino acids measured and glucose. There was a significant change in the profile differences of endogenous plasma IGF-1 concentrations during the 8-hr infusion period, with plasma IGF-1 decreasing sharply in the test group. There was a significant difference in mean profiles for plasma IGF-2 between the test and control groups. Overall, plasma IGF-2 for the control group decreased only slightly over time (about 40 ng/ml), whereas the test group decreased dramatically (by about 140 ng/ml). Increased plasma concentrations of a 31-32-kDa IGF-binding protein (possibly IGF-binding protein-1) in the treated group was detected by radioligand blot. We found that Long(R3)-IGF-1 infusion tended to preserve whole-body and muscle protein in beef heifers on a low-quality diet, and suggest that further investigation of this treatment may provide an alternative approach to reducing weight loss during the dry season.

Insulin-like growth factor (IGF)-I but not IGF-II promotes lean growth and feed efficiency in broiler chickens

The efficacy of exogenous IGFs to stimulate growth and modulate protein and fat deposition was examined in a number of broiler chicken lines. From around 600 g body weight the chickens received a continuous infusion of vehicle (0.1 M acetic acid), human recombinant IGF-I or [Gly1]IGF-II at 300 microg/kg body weight per day, or a combined infusion of 150 microg/kg/day of each IGF for 2 weeks. Experiment 1 used commercial broiler female chickens and included measurements of nitrogen balance, Ntau-methylhistidine excretion and muscle protein synthesis rates. In Experiment 2 the same treatments were applied to three experimental lines of chickens selected for high food consumption (relatively fat), high food utilisation efficiency (relatively lean), or at random (control). IGF-I, but not IGF-II, significantly increased growth rate and food utilisation efficiency by around 10-15% in each experiment, an effect which was consistent across all genotypes. Nitrogen balance was significantly increased by IGF-I in Experiment 1 as was carcass nitrogen content in Experiment 2, indicating that the increased growth was in lean tissue. Carcass fat was consistently reduced in chickens receiving IGF-I and was related to the levels of circulating IGF-I (r2 = 0.30, P < 0.01) but not triiodothyronine. Protein synthesis rates were unaffected by treatment and could not account for increased growth rate. However, there was a significant reduction in Ntau-methylhistidine excretion indicating a reduced rate of muscle protein breakdown in IGF-I-treated chickens (1. 56%/day vs 2.05%/day for IGF-I-treated vs controls, P < 0.05). The efficiency of feed utilisation was inversely related to the rate of protein breakdown (r2 = 0.25, P < 0.01). In conclusion, these experiments are the first to report an enhancement of growth and food utilisation efficiency by broiler chickens receiving exogenous IGF-I. Our results show that IGF-I may be important in controlling the growth and efficiency of food utilisation of young chickens at least in part by modulating the rates of protein breakdown.

The somatotropic axis in neonatal calves can be modulated by nutrition, growth hormone, and Long-R3-IGF-I

Effects on the somatotropic axis [plasma levels of insulin-like growth factors (IGFs) I and II, IGF-binding proteins (IGFBPs), and growth hormone (GH)] of feeding different amounts of colostrum or milk replacer, of Long-R3-IGF-I (administered subcutaneously or orally; 50 micrograms.kg body wt-1.day-1 for 7 days), and of subcutaneously injected recombinant bovine GH (rbGH; 1 mg.kg body wt-1.day-1 for 7 days) were evaluated in calves during the 1st wk of life. Plasma Long-R3-IGF-I increased after subcutaneous application but not with the oral dose. Endogenous IGF-I was higher in calves fed colostrum six times compared with those fed only milk replacer. Native IGF-I was highest in rbGH-injected calves but was lowered by the subcutaneous injection of Long-R3-IGF-I. IGF-II concentrations were not modified by any of the treatments. IGFBP-2 increased in calves fed only milk replacer and those receiving subcutaneous Long-R3-IGF-I. GH was not modulated by differences in nutrition but increased after rbGH administration and similarly in all groups after intravenous injection of GH-releasing factor analog GRF-(1-29). Parenteral administration of Long-R3-IGF-I decreased GH concentration but did not affect the secretory pattern. The data demonstrate that the somatotrophic axis is basically functioning in neonatal calves and is influenced by nutrition, GH, and Long-R3-IGF-I.