Hepatic Insulin-like Growth Factor-binding Protein-1 Research Articles

Abstract 3490: IGFBP1 mediates musculoskeletal defects in colorectal cancer

Abstract Colorectal cancer (CRC) is frequently accompanied by cachexia, an uncured multi-systemic wasting syndrome that affects the majority of patients, especially when the disease recurs with liver metastases (LMs). Muscle and bone loss are amongst the most detrimental symptoms of cachexia and directly cause increased morbidity and mortality. We and others have shown that CRC also promotes metabolic and genomic perturbations of the liver, and further, that formation of LMs exacerbates muscle and bone wasting. These observations, along with evidence that liver-derived factors (i.e., hepatokines) may poorly influence musculoskeletal health, suggest an endocrine role of the liver in mediating cancer-induced cachexia. In the present study, we identified the hepatokine insulin-like growth factor binding protein 1 (IGFBP1) as a novel mediator of musculoskeletal wasting in CRC. Plasma from CRC patients and preclinical mouse models of CRC (C26, MC38, HCT116, ApcMin/+) were assessed for circulating IGFBP1 levels. AML12 hepatocytes were cultured with CRC cells (C26, MC38, HCT116) to assess tumor induced hepatic IGFBP1 production, while C2C12 myotubes and osteoclast precursor cells were cultured to examine the in vitro effects of IGFBP1 on myotube atrophy and osteoclastogenesis. 8-week-old male wild-type (WT) C57BL/6J and IGFBP1-KO mice were intrasplenically injected with MC38 tumor cells (mMC38) to mimic hepatic dissemination of cancer cells, while sham-operated animals received saline. Animals were assessed for muscle force 24-hours prior to euthanasia, and skeletal muscles and bone were collected for molecular and morphological analyses. CRC patients and CRC tumor-bearing mice demonstrated markedly elevated circulating plasma IGFBP1, also supported by increased liver IGFBP1 mRNA expression in C26, MC38 and HCT116 hosts. Follow-up in vitro studies demonstrated that co-culturing CRC cells (lacking IGFBP1 expression) with AML12 hepatocytes promotes IGFBP1 production, thereby suggesting that IGFBP1 is purely host-derived. Further, treatment with recombinant IGFBP1 was sufficient to stimulate osteoclastogenesis, while also promoting atrophy of C2C12 myotubes. Conversely, use of anti-IGFBP1 neutralizing antibodies prevented osteoclastogenesis and preserved C2C12 myotube size when exposed to plasma from mice bearing CRCs. Notably, WT mMC38 bearers displayed reductions in muscle mass and strength, as well as in trabecular bone volume fraction (BV/TV) and trabecular number (Tb.N). Conversely, IGFBP1-KO tumor hosts exhibited preserved skeletal muscle and bone mass. Altogether, our data implicate IGFBP1, an exquisitely liver-derived factor, as a novel mediator of musculoskeletal deficits in CRC cachexia, and supports novel strategies to counteract host-derived factors in the treatment of cancer-associated multi-organ complications. Citation Format: Joshua R. Huot, Fabrizio Pin, Andrea Bonetto. IGFBP1 mediates musculoskeletal defects in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3490.

A Mixture of Valine and Isoleucine Restores the Growth of Protein-Restricted Pigs Likely through Improved Gut Development, Hepatic IGF-1 Pathway, and Plasma Metabolomic Profile.

Valine (Val) alone or in combination with isoleucine (Ile) improves the growth under severe protein restriction; however, the underlying mechanisms remain unknown. In this study, we assessed whether Val/Ile-induced growth in protein-restricted pigs is associated with changes in gut development, hepatic insulin-like growth factor 1 (IGF-1) production, and blood metabolomics. Forty piglets were assigned to five dietary groups: positive control (PC) with standard protein content; low protein (LP) with very low protein content; and LP supplemented with Val (LPV), Ile (LPI), and Val and Ile (LPVI). LPVI reversed the negative effects of VLP diets on growth and gut morphology. Both LPV and LPVI restored the reduced transcript of IGF-1 while decreasing the transcript of insulin-like growth factor binding protein 1 (IGFBP1) in the liver. LPV and LPVI recovered the reduced plasma Val, glycine, and leucine concentrations, which were positively correlated with improved gut morphology and the hepatic IGF-1 gene expression and negatively correlated with hepatic IGFBP1 mRNA abundance. In conclusion, supplementation with a combination of Val and Ile into the VLP diets restored the decreased growth performance of pigs fed with these diets likely through improved gut development, hepatic IGF-1 expression and bioavailability, and plasma metabolomics profile.

Direct regulation of IGF-binding protein 1 promoter by interleukin-1β via an insulin- and FoxO-1-independent mechanism.

The level of insulin-like growth factor-binding protein 1 (IGFBP1), a liver-produced serum protein that regulates insulin-like growth factor-I bioactivity, glucose homeostasis, and tissue regeneration, increases during inflammation. This manuscript describes a novel pathway for the regulation of hepatic IGFBP1 mRNA and protein levels by interleukin (IL)-1β. Experiments with the luciferase reporter system show that IL-1β stimulates transcriptional activity from the 1-kb promoter region of IGFBP1. Although IL-1β stimulation suppresses the insulin activation of protein kinase B, the major upstream regulator of IGFBP1 mRNA transcription, the induction of IGFBP1 by IL-1β did not require an intact insulin response element. Furthermore, neither overexpression nor silencing of FoxO-1 had any effect on the IL-1β-induced increase in IGFBP1 mRNA levels and promoter activity. However, inhibition of the ERK MAP kinases effectively prevented the IL-1β effects. Inhibition of neutral sphingomyelinase, a key player in the IL-1β signaling cascade that acts upstream of ERK, also suppressed the IL-1β effects, while increasing the ceramide, through the addition of C2-ceramide or via treatment with exogenous sphingomyelinase, was sufficient to induce IGFBP1 promoter-driven luciferase activity. Studies in primary rat hepatocytes where the levels of neutral sphingomyelinase were either elevated or suppressed using adenoviral constructs affirmed the key role of neutral sphingomyelinase and ceramide (exerted likely through ERK activation) in the IL-1β-induced IGFBP1 production. Finally, the IL-1β effects on IGFBP1 mRNA production and protein secretion could be abolished by the addition of insulin, either at very late time points or at very high doses.

Effect of alternative lipids and temperature on growth factor gene expression in yellowtail kingfish (Seriola lalandi)

This study was undertaken to assess the efficacy of utilizing insulin-like growth factor 1 (IGF-I) and insulin-like growth factor binding protein 1 (IGFBP-1) as endocrine biomarkers to provide a rapid indication of yellowtail kingfish growth using real-time, reverse-transcriptase quantitative PCR (RT-qPCR). Two experiments were conducted separately (5 weeks each) at an optimal water temperature (22°C) using fish weighing 95.6 ± 0.1 g (mean ± standard deviation, n = 3) and at a sub-optimal water temperature (18°C) using similar-sized fish (101 ± 0.1 g, n = 3). Four experimental diets were formulated to contain poultry oil (PO) or canola oil (CO) at 50% or 100% inclusion as a substitute for fish oil (FO). A diet containing 100% FO was used as a control. Irrespective of diet, fish grew faster at 22°C than at 18°C. The 100% replacement of FO by CO resulted in the poorest fish growth at both temperatures. IGF-I expression correlated with growth rate at 22°C, but the same trend was not seen at 18°C. Hepatic IGF-I and IGFBP-1 mRNA expression were also positively correlated. This study suggests that hepatic IGF-I mRNA assessed by RT-qPCR with additional methodological development may be used to accurately assess the influence of diet on growth of some fish species used in aquaculture.

Reconstitution of Insulin Action in Muscle, White Adipose Tissue, and Brain of Insulin Receptor Knock-out Mice Fails to Rescue Diabetes

Type 2 diabetes results from an impairment of insulin action. The first demonstrable abnormality of insulin signaling is a decrease of insulin-dependent glucose disposal followed by an increase in hepatic glucose production. In an attempt to dissect the relative importance of these two changes in disease progression, we have employed genetic knock-outs/knock-ins of the insulin receptor. Previously, we demonstrated that insulin receptor knock-out mice (Insr(-/-)) could be rescued from diabetes by reconstitution of insulin signaling in liver, brain, and pancreatic β cells (L1 mice). In this study, we used a similar approach to reconstitute insulin signaling in tissues that display insulin-dependent glucose uptake. Using GLUT4-Cre mice, we restored InsR expression in muscle, fat, and brain of Insr(-/-) mice (GIRKI (Glut4-insulin receptor knock-in line 1) mice). Unlike L1 mice, GIRKI mice failed to thrive and developed diabetes, although their survival was modestly extended when compared with Insr(-/-). The data underscore the role of developmental factors in the presentation of murine diabetes. The broader implication of our findings is that diabetes treatment should not necessarily target the same tissues that are responsible for disease pathogenesis.

Induction of Hepatic Insulin-Like Growth Factor Binding Protein-1 (IGFBP-1) in Rats by Dietary n-6 Polyunsaturated Fatty Acids

Abstract. The insulin-like growth factors (IGFs) are mitogenic polypeptides that have been linked to a variety of normal physiological processes as well as neoplasia. Overexpression of several components of the IGF system is associated with hepatocarcinogenesis in humans and rodents. In rat liver, diets rich in n-6 polyunsaturated fatty acid (PUFA) enhance the development of preneoplastic lesions and tumors. Therefore, the objective of this study was to determine the effect of these dietary fatty acids on the hepatic expression of the various components of the IGF system. The mRNA levels of IGF-1 and the type 1 receptor were not different in livers of rats fed a diet containing 20% corn oil (CO) compared with those fed 5% CO. Analysis of the IGF binding proteins revealed that insulin-like growth factor binding protein-1 (IGFBP-1) levels were altered by the amount and type of dietary fat. A 2.5-fold induction of IGFBP-1 mRNA occurred within 1 week after the animals were fed the 20% corn oil diet compared with those fed 5% CO and was further enhanced to over 6-fold after 1 month. Furthermore, IGFBP-1 protein was only detectable in the livers of animals fed the 20% CO diet. Induction of IGFBP-1 mRNA (4.5-fold) also occurred in rats fed a high-fat diet containing safflower (rich in n-6 PUFAs) compared with those fed a high-fat diet containing menhaden oil (rich in n-3 PUFAs). The induction of IGFBP-1 mRNA was independent of serum insulin levels and the development of insulin resistance. Since IGFBP-1 mRNA is upregulated in regenerating liver, we reasoned that the induction of IGFBP-1 mRNA may be associated with an increase in cell proliferation; however, no difference was observed in the hepatic labeling index of rats fed the 20% CO compared with the 5% CO diet. In summary, these studies show a striking induction by dietary n-6 PUFAs of hepatic IGFBP-1, a protein that has been implicated in liver cancer development.

Hepatic IGFBP1 is a prosurvival factor that binds to BAK, protects the liver from apoptosis, and antagonizes the proapoptotic actions of p53 at mitochondria

Liver is generally refractory to apoptosis induced by the p53 tumor suppressor protein, but the molecular basis remains poorly understood. Here we show that p53 transcriptional activation leads to enhanced expression of hepatic IGFBP1 (insulin-like growth factor-binding protein-1). Exhibiting a previously unanticipated role, a portion of intracellular IGFBP1 protein localizes to mitochondria where it binds to the proapoptotic protein BAK and hinders BAK activation and apoptosis induction. Interestingly, in many cells and tissues p53 also has a direct apoptotic function at mitochondria that includes BAK binding and activation. When IGFBP1 is in a complex with BAK, formation of a proapoptotic p53/BAK complex and apoptosis induction are impaired, both in cultured cells and in liver. In contrast, livers of IGFBP1-deficient mice exhibit spontaneous apoptosis that is accompanied by p53 mitochondrial accumulation and evidence of BAK oligomerization. These data support the importance of BAK as a mediator of p53's mitochondrial function. The results also identify IGFBP1 as a negative regulator of the BAK-dependent pathway of apoptosis, whose expression integrates the transcriptional and mitochondrial functions of the p53 tumor suppressor protein.

Regulation of Hepatic Insulin-Like Growth Factor-Binding Protein-1 Gene Expression by Insulin: Central Role for Mammalian Target of Rapamycin Independent of Forkhead Box O Proteins

The expression of IGF-binding protein-1 (IGFBP-1) is induced in rat liver by dexamethasone and glucagon and is completely inhibited by 100 nM insulin. Various studies have implicated phosphatidylinositol 3-kinase, protein kinase B (Akt), phosphorylation of the transcription factors forkhead in rhabdomyosarcoma 1 (Foxo1)/Foxo3, and the mammalian target of rapamycin (mTOR) in insulin's effect. In this study we examined insulin regulation of IGFBP-1 in both subconfluent and confluent hepatocytes. In subconfluent hepatocytes, insulin inhibition of IGFBP-1 mRNA levels was blocked by inhibiting PI3 kinase activation, and there was a corresponding inhibition of Foxo1/Foxo3 phosphorylation. In these same cells, inhibition of the insulin effect by rapamycin occurred in the presence of insulin-induced Foxo1/Foxo3 phosphorylation. In confluent hepatocytes, insulin could not activate the phosphatidylinositol 3-kinase (PI3 kinase)-Akt-Foxo1/Foxo3 pathway, but still inhibited IGFBP-1 gene expression in an mTOR-dependent manner. In subconfluent hepatocytes, the serine/threonine phosphatase inhibitor okadaic acid (100 nM) partially inhibited IGFBP-1 gene expression by 40%, but did not produce phosphorylation of either Akt or Foxo proteins. In contrast, 1 nm insulin inhibited the IGFBP-1 mRNA level by 40% and correspondingly activated Akt and Foxo1/Foxo3 phosphorylation to a level comparable to that observed with 100 nM insulin. These results suggest a potential role for a serine/threonine phosphatase(s) in the regulation of IGFBP-1 gene transcription, which is not downstream of mTOR and is independent of Akt. In conclusion, we have found that in rat liver, insulin inhibition of IGFBP-1 mRNA levels can occur in the absence of the phosphorylation of Foxo1/Foxo3, whereas activation of the mTOR pathway is both necessary and sufficient.

The serum levels of proinsulin and their relationship with IGFBP‐1 in obese children

Serum proinsulin (PI) levels were investigated in obese children to determine whether PI is a sensitive indicator of insulin resistance, as previously shown in adults with type 2 diabetes mellitus (DM), and to evaluate their relationship with insulin-like growth factor-binding protein-1 (IGFBP-1) known as a predictor of the development of cardiovascular disease in diabetic adults. Forty-two obese children without DM (age, 12.1 +/- 1.5 year) and 42 age-matched control children were included in the study. The serum levels of PI, immunoreactive insulin (IRI), IGFBP-1 and free insulin-like growth factor-1 (IGF-1) were measured in the fasting state. The fasting levels of serum PI and IRI were significantly higher in obese children than in controls (PI, 10.5 +/- 6.8 vs. 5.6 +/- 2.0 pmol/l, p < 0.001; IRI, 72.0 +/- 41.8 vs. 32.7 +/- 19.5 pmol/l, p < 0.001). Serum IGFBP-1 levels were significantly lower in obese children than in controls (37.7 +/- 24.6 vs. 76.3 +/- 26.5 microg/l, p < 0.001). The ratio of PI to IRI (calculated as molar ratios) did not differ significantly between obese and control subjects (0.16 +/- 0.08 vs. 0.19 +/- 0.11, p = 0.08). For the whole group, serum PI levels correlated positively with IRI and inversely with IGFBP-1 (IRI, r = 0.67, p < 0.001; IGFBP-1, r = -0.49, p < 0.001). Serum IGFBP-1 levels correlated inversely with both BMI and IRI (BMI, r = -0.73, p < 0.001; IRI, r = -0.60, p < 0.001). Multiple regression analysis revealed that the best predictive parameters for IGFBP-1 were BMI and PI (R2 = 0.57, p < 0.001 and p < 0.05, respectively). These findings suggest that fasting serum PI levels may be a better predictor than fasting insulin levels for the future development of type 2 DM and cardiovascular disease in obese children, and PI, in addition to insulin, contributes to the suppression of hepatic IGFBP-1 production.

Insulin regulation of hepatic insulin-like growth factor-binding protein-1 (IGFBP-1) gene expression and mammalian target of rapamycin (mTOR) signalling is impaired by the presence of hydrogen peroxide.

Hepatic expression of insulin-like growth factor-binding protein-1 (IGFBP-1) is rapidly and completely inhibited by insulin. The signalling pathway that mediates this effect of insulin requires the activation of phosphoinositide 3-kinase (PI 3-kinase). Many of the cellular actions of insulin, including activation of PI 3-kinase, can be 'mimicked' by oxidative stresses, such as H(2)O(2). In the present study, we demonstrate that H(2)O(2) does not 'mimic' but rather antagonizes insulin repression of IGFBP-1 gene expression in H4IIE cells. This effect is accompanied by a decrease in the insulin-induced activation of mammalian target of rapamycin (mTOR)-dependent signalling. However, insulin-induced phosphorylation and regulation of protein kinase B, glycogen synthase kinase-3 and FKHR (forkhead in rhabdomyosarcoma) are not affected by H(2)O(2) in the same cells. In addition, H(2)O(2) strongly activates the p42/p44 mitogen-activated protein kinases, but the presence of PD184352 (an inhibitor of this pathway) does not block the effect of H(2)O(2) on IGFBP-1 gene expression. Our results support the view that the insulin-mediated repression of IGFBP-1 gene expression is partly mTOR-dependent, and demonstrate that H(2)O(2) selectively antagonizes mTOR-dependent insulin action. The implications for the use of H(2)O(2)-generating agents as therapeutics for the treatment of insulin resistance, as well as the role of oxidative stress in the development of insulin resistance, are discussed.

Insulin Regulation of Insulin-like Growth Factor-binding Protein-1 Gene Expression Is Dependent on the Mammalian Target of Rapamycin, but Independent of Ribosomal S6 Kinase Activity

Insulin inhibits the expression of the hepatic insulin-like growth factor-binding protein-1 (IGFBP-1) and glucose-6-phosphatase (G6Pase) genes. The signaling pathway that mediates these events requires the activation of phosphatidylinositol 3-kinase, whereas transfection studies have suggested an involvement of Akt (protein kinase B) and FKHR, a transcription factor regulated by Akt. We now demonstrate that insulin repression of endogenous IGFBP-1 gene transcription was blocked by rapamycin or by amino acid starvation. Rapamycin inhibited the mammalian target of rapamycin (mTOR) and the subsequent activation of p70/p85 S6 protein kinase-1 (S6K1) by insulin, whereas amino acid depletion prevented insulin induction of these signaling molecules. Importantly, we demonstrate that insulin regulation of the thymine-rich insulin response element of the IGFBP-1 promoter was also inhibited by rapamycin. However, sustained activation of S6K1 did not repress this promoter. In addition, rapamycin did not affect insulin regulation of G6Pase expression or Akt activation. We propose that these observations indicate that an mTOR-dependent, but S6K-independent mechanism regulates the suppression of IGFBP-1 (but not G6Pase) gene expression by insulin. Therefore, although the insulin-responsive sequence of the G6Pase gene promoter is related to that of the IGFBP-1 promoter, the signaling pathways that mediate suppression of these genes are distinct.

Time course changes in IGFBP-1 after treadmill exercise and postexercise food intake in rats.

Prolonged exercise increases circulating insulin-like growth factor binding protein-1 (IGFBP-1) in humans and animals, but its physiological significance is unknown. This study examined 1) time-course changes in plasma IGFBP-1 and hepatic IGFBP-1 mRNA expression after exercise, 2) changes in IGFBP-1 in relation to plasma glucose, insulin, and IGF-I, and 3) the impact of feeding a postexercise meal on the IGFBP-1 response. Food-deprived male rats were vigorously run on a treadmill and compared with nonexercised controls at 15 min and 1, 4, 8, and 12 h after exercise. Circulating insulin concentrations in exercised rats were lower than in controls at 15 min and 1 h, whereas plasma glucose and IGF-I remained unaffected. Circulating and hepatic expression of IGFBP-1 was markedly increased above that of controls at 15 min, 1 h, and 12 h. In a separate experiment, one-half of the exercised animals received a nutritionally complete meal immediately after the experimental run. The meal elevated plasma insulin and glucose concentrations at 15 min and 1 h. Despite this change in nutritional status, serum IGFBP-1 concentrations and hepatic IGFBP-1 abundance remained elevated at 15 min and 1 h. These results demonstrate that the IGFBP-1 response to a single bout of treadmill exercise is short in duration and independent of insulin, glucose, and amino acid availability.

Interleukin-6-induced STAT3 and AP-1 amplify hepatocyte nuclear factor 1-mediated transactivation of hepatic genes, an adaptive response to liver injury.

Following hepatic injury or stress, gluconeogenic and acute-phase response genes are rapidly upregulated to restore metabolic homeostasis and limit tissue damage. Regulation of the liver-restricted insulin-like growth factor binding protein 1 (IGFBP-1) gene is dramatically altered by changes in the metabolic state and hepatectomy, and thus it provided an appropriate reporter to assess the transcriptional milieu in the liver during repair and regeneration. The cytokine interleukin-6 (IL-6) is required for liver regeneration and repair, and it transcriptionally upregulates a vast array of genes during liver growth by unknown mechanisms. Evidence for a biologic role of IL-6 in IGFBP-1 upregulation was demonstrated by increased expression of hepatic IGFBP-1 in IL-6 transgenic and following injection of IL-6 into nonfasting animals and its reduced expression in IL-6(-/-) livers posthepatectomy. In both hepatic and nonhepatic cells, IL-6 -mediated IGFBP-1 promoter activation was via an intact hepatocyte nuclear factor 1 (HNF-1) site and was dependent on the presence of endogenous liver factor HNF-1 and induced factors STAT3 and AP-1 (c-Fos/c-Jun). IL-6 acted through the STAT3 pathway, as dominant negative STAT3 completely blocked IL-6-mediated stimulation of the IGFBP-1 promoter via the HNF-1 site. HNF-1/c-Fos and HNF-1/STAT3 protein complexes were detected in mouse livers and in hepatic and nonhepatic cell lines overexpressing STAT3/c-Fos/HNF-1. Similar regulation was demonstrated using glucose-6-phosphatase and alpha-fibrinogen promoters, indicating that HNF-1/IL-6/STAT3/AP-1-mediated transactivation of hepatic gene expression is a general phenomenon after liver injury. These results demonstrate that the two classes of transcription factors, growth induced (STAT3 and AP-1) and tissue specific (HNF-1), can interact as an adaptive response to liver injury to amplify expression of hepatic genes important for the homeostatic response during organ repair.

Induction of hepatic insulin-like growth factor binding protein-1 (IGFBP-1) in rats by dietary n-6 polyunsaturated fatty acids.

The insulin-like growth factors (IGFs) are mitogenic polypeptides that have been linked to a variety of normal physiological processes as well as neoplasia. Overexpression of several components of the IGF system is associated with hepatocarcinogenesis in humans and rodents. In rat liver, diets rich in n-6 polyunsaturated fatty acid (PUFA) enhance the development of preneoplastic lesions and tumors. Therefore, the objective of this study was to determine the effect of these dietary fatty acids on the hepatic expression of the various components of the IGF system. The mRNA levels of IGF-1 and the type 1 receptor were not different in livers of rats fed a diet containing 20% corn oil (CO) compared with those fed 5% CO. Analysis of the IGF binding proteins revealed that insulin-like growth factor binding protein-1 (IGFBP-1) levels were altered by the amount and type of dietary fat. A 2.5-fold induction of IGFBP-1 mRNA occurred within 1 week after the animals were fed the 20% corn oil diet compared with those fed 5% CO and was further enhanced to over 6-fold after 1 month. Furthermore, IGFBP-1 protein was only detectable in the livers of animals fed the 20% CO diet. Induction of IGFBP-1 mRNA (4.5-fold) also occurred in rats fed a high-fat diet containing safflower (rich in n-6 PUFAs) compared with those fed a high-fat diet containing menhaden oil (rich in n-3 PUFAs). The induction of IGFBP-1 mRNA was independent of serum insulin levels and the development of insulin resistance. Since IGFBP-1 mRNA is upregulated in regenerating liver, we reasoned that the induction of IGFBP-1 mRNA may be associated with an increase in cell proliferation; however, no difference was observed in the hepatic labeling index of rats fed the 20% CO compared with the 5% CO diet. In summary, these studies show a striking induction by dietary n-6 PUFAs of hepatic IGFBP-1, a protein that has been implicated in liver cancer development.

Hepatic regeneration in insulin-like growth factor binding protein-1 transgenic mice

Background/Aims: Partial hepatectomy results in activation of genes in the residual liver tissue which serve to restore glucose homeostasis and regenerate liver mass. Expression of insulin-like growth factor binding protein-1 (IGFBP-1) is up-regulated following partial hepatectomy and IGFBP-1 can modulate both the metabolic and mitogenic effects of insulin-like growth factor-1 (IGF-I). The aim of the study was to compare the effects of partial hepatectomy on blood glucose levels and hepatic regeneration in wild-type and transgenic mice which constitutively overexpress IGFBP-1. Methods: Hepatic IGFBP-1 mRNA, blood glucose concentrations, liver mass and hepatic DNA synthesis were compared in sham-operated and partially hepatectomized transgenic and wild-type mice. Results: Hepatic IGFBP-1 mRNA was higher in sham-operated transgenic than wild-type mice, but in both groups of mice, partial hepatectomy was associated with a significant rise in IGFBP-1 mRNA. The absolute decline in blood glucose levels following partial hepatectomy was greater in transgenic mice. Basal DNA synthesis and the response to IGF-I in isolated hepatocytes from both groups of mice were similar, and DNA synthesis in the regenerating liver in vivo was not significantly different in transgenic as compared to wild-type mice: 449.3±63.9 vs. 321.6±52.3 cpm/ μg DNA. Hepatic regeneration as measured by liver weight after hepatectomy was not different between transgenic and wild-type mice. Conclusions: Constitutive overexpression of IGFBP-1 does not enhance hepatic regeneration and does not prevent the decline in blood glucose following partial hepatectomy.

Protein Kinase B/Akt Mediates Effects of Insulin on Hepatic Insulin-like Growth Factor-binding Protein-1 Gene Expression through a Conserved Insulin Response Sequence

Insulin regulates the expression of multiple hepatic genes through a conserved insulin response sequence (IRS) (CAAAAC/TAA) by an as yet undetermined mechanism. Protein kinase B/Akt (PKB/Akt), a member of the PKA/PKC serine/threonine kinase family, functions downstream from phosphatidylinositol 3'-kinase (PI3K) in mediating effects of insulin on glucose transport and glycogen synthesis. We asked whether PKB/Akt mediates sequence-specific effects of insulin on hepatic gene expression using the model of the insulin-like growth factor binding protein-1 (IGFBP-1) promoter. Insulin lowers IGFBP-1 mRNA levels, inhibits IGFBP-1 promoter activity, and activates PKB/Akt in HepG2 hepatoma cells through a PI3K-dependent, rapamycin-insensitive mechanism. Constitutively active PI3K and PKB/Akt are each sufficient to mediate effects of insulin on the IGFBP-1 promoter in a nonadditive fashion. Dominant negative K179 PKB/Akt disrupts the ability of insulin and PI3K to activate PKB/Akt and to inhibit promoter activity. The IGFBP-1 promoter contains two IRSs each of which is sufficient to mediate sequence-specific effects of insulin, PI3K, and PKB/Akt on promoter activity. Highly related IRSs from the phosphoenolpyruvate carboxykinase and apolipoprotein CIII genes also are effective in this setting. These results indicate that PKB/Akt functions downstream from PI3K in mediating sequence-specific effects of insulin on the expression of IGFBP-1 and perhaps multiple hepatic genes through a conserved IRS.

Growth hormone modulates insulin regulation of hepatic insulin-like growth factor binding protein-1 transcription.

Hepatic transcription of insulin-like growth factor-binding protein-1 (IGFBP-1) is enhanced in hypophysectomized (hypox) rats and can be rapidly down-regulated by GH administration. Here we examined the effect of insulin on IGFBP-1 messenger RNA abundance in hypox rats and the effects of insulin and GH on IGFBP-1/chloramphenicol acetyltransferase (CAT) reporter plasmids transiently transfected into isolated hepatocytes from pituitary-intact and hypox rats. Unlike GH, administration of insulin to hypox rats in doses of 10 or 50 micrograms/100 g BW had no effect on hepatic IGFBP-1 messenger RNA abundance. Insulin at 10(-7) M resulted in a 42.1 +/- 9.8% suppression of CAT activity in hepatocytes from pituitary-intact animals transfected with a CAT reporter plasmid containing 1671 bp of the 5'-flanking region of the rat IGFBP-1 gene. In the same assay, GH at a concentration of 2.3 x 10(-8) M significantly reduced CAT activity. In contrast, insulin had no effect on CAT activity in hepatocytes from hypox rats, whereas GH resulted in comparable suppression of CAT activity in hepatocytes from hypox rats and pituitary-intact rats, 13.6 +/- 2.3% vs. 18.2 +/- 3.2%. Deletional analysis and mobility shift assays were used to identify the GH-responsive regions in the IGFBP-1 gene. GH suppression of CAT activity was lost when the IGFBP-1 5'-flanking region was deleted down to -277 bp, whereas insulin suppression was retained for all but the smallest fragment of the IGFBP-1 gene. Mobility shift assays were used to compare nuclear extracts from sham-operated, hypox, and GH-treated hypox rats. When hepatic nuclear extracts from hypox rats were incubated with the -277 to -82 and the -556 to -368 bp fragments, retarded bands were apparent that were not present in the extracts from sham-operated rats. GH treatment of hypox rats 15 or 30 min before death completely normalized the retardation pattern seen with the -277 to -82 bp fragment, but did not affect the pattern seen with the -556 to -368 bp fragment. A 20-bp fragment corresponding to the previously identified insulin response element, -108 to -89 bp, was also analyzed. An additional retarded band, not seen with nuclear extracts from sham-operated rats, was apparent when nuclear extracts of hypox rats or GH-treated hypox rats were used. These data provide the first in vitro evidence that GH directly regulates transcription of IGFBP-1 expression. In addition, our findings suggest that GH modulates insulin regulation of IGFBP-1 transcription, possibly by altering the milieu of trans-acting factors that interact with both the insulin response element and distinct upstream sites.

Stimulation of hepatic insulin-like growth factor-binding protein-1 and -3 gene expression by octreotide in rats

It has recently been demonstrated in various clinical experiments that native somatostatin and its long-acting analogues increase circulating levels of insulin-like growth factor-binding protein-1 (IGFBP-1) within 1-2 h, independent of effects on circulating insulin or glucose levels. Using human hepatoma cells in vitro the somatostatin analogue, octreotide, has been shown to increase IGFBP-1 mRNA within 24 h indicative of a direct stimulatory effect of octreotide on IGFBP-1 synthesis. In order to ascertain whether octreotide acutely stimulates IGFBP-1 mRNA in vivo, placebo or two doses of octreotide were injected subcutaneously into three groups of rats. One hour after saline or octreotide administration, liver, kidney and serum were obtained for the measurement of IGFBPs-1 to -6 mRNA in tissue and IGFBPs and IGF-I in serum. Octreotide increased liver IGFBP-1 (562%) and IGFBP-3 (23%) mRNA expression with a concomitant rise in the circulating 30 kDa (106%) and 38-42 kDa (23%) IGFBPs. No detectable changes were seen in other liver IGFBP transcripts, other circulating IGFBPs or in any of the kidney IGFBP transcripts. Serum IGF-I increased by 37% in the animals receiving the high octreotide dose. No concomitant changes were observed in glucose or insulin levels. These data show that octreotide acutely stimulates hepatic IGFBP-1 and -3 mRNA in vivo in rats. The stimulating effect on IGFBP-3 presents a possible hitherto unknown form of regulation of IGFBP-3 whilst the effect on IGFBP-1 indicates that the stimulatory effect of octreotide on circulating IGFBP-1 described in clinical trials may be due to increased hepatic production. The present findings may be of importance in the clinical use of octreotide.

Ethanol induces a paradoxical simultaneous increase in circulating concentrations of insulin-like growth factor binding protein-1 and insulin

The aim of this study was to examine the effect of acute alcohol intake on circulating concentrations of insulin, C-peptide, insulin-like growth factor (IGF) binding protein-1 (IGFBP-1), and plasma glucose levels. We measured these parameters for 12 hours after administration of 0, 0.5, or 1.0 g ethanol/kg body weight to nine healthy volunteers between 7:00 and 7:45 pm according to a randomized, double-blind, crossover design. Following a snack at 9:00 pm, plasma insulin ( P < .05) and C-peptide ( P < .01) concentrations were significantly increased at 10:00 pm in the 1.0-g group as compared with the control group. C-peptide to insulin molar ratios were significantly higher ( P < .05) in both ethanol groups at 10:00 pm and 2:00 am than in the control group. No differences were observed in plasma glucose levels between the three groups. Plasma IGFBP-1 levels showed a dose-dependent increase in the ethanol groups, and remained increased from 10:00 pm for 3 hours ( P < .05 or less) at the lower dose and for 6 hours ( P < .05 or less) at the higher dose. These observations indicate that ethanol-induced postprandial hyperinsulinemia is due to increased insulin secretion and that alcohol may increase hepatic insulin extraction. The lack of any effect on plasma glucose levels suggests that alcohol intake must be associated with decreased insulin sensitivity. Alcohol intake results in a paradoxical increase in peripheral concentrations of IGFBP-1 despite simultaneous hyperinsulinemia. This implies that ethanol has a direct stimulatory effect on hepatic IGFBP-1 synthesis.

Effects of glucocorticoids on circulating levels and hepatic expression of insulin-like growth factor (IGF)-binding proteins and IGF-I in the adrenalectomized streptozotocin-diabetic rat

Circulating levels and hepatic expression of insulin-like growth factor-binding protein-1 (IGFBP-1) are increased in insulin-deficient streptozotocin (STZ)-diabetic rats. Glucocorticoids stimulate and insulin suppresses hepatocellular expression of IGFBP-1 in vitro. We asked whether increased IGFBP-1 expression in STZ-diabetic animals is due to an effect of insulin deficiency per se or whether insulin deficiency represents a permissive state where glucocorticoids may play an important role in the regulation of IGFBP-1 and other circulating peptides involved in the modulation of IGF bioactivity. Intact female Sprague-Dawley-derived rats and rats undergoing bilateral adrenalectomy (ADNX) were injected with STZ (140 mg/kg) or buffer. Corticosterone acetate (50 mg/kg) or vehicle was administered to diabetic and nondiabetic animals immediately after ADNX and 24 h later. All rats were killed 48 h after surgery and/or STZ administration. Serum [125I]IGF-I-binding activity was increased 4-fold (P < 0.01), and Western ligand and immunoblotting demonstrated that levels of IGFBP-1 were high in intact STZ-diabetic animals. ADNX prevented these effects of STZ-diabetes, and corticosterone treatment restored serum IGF-binding activity and IGFBP-1 to intact diabetic levels. Similarly, Northern analysis demonstrated that the abundance of hepatic IGFBP-1 mRNA was increased 6-fold in intact STZ-diabetic animals (P < 0.01), but not in adrenalectomized diabetic animals. Corticosterone treatment restored hepatic IGFBP-1 mRNA to intact diabetic levels, and serum concentrations of corticosterone correlated with the abundance of IGFBP-1 mRNA (r = 0.475; P < 0.01), indicating that glucocorticoids play an important role in the regulation of expression of IGFBP-1 in insulin-deficient animals. In contrast, neither ADNX nor corticosterone altered the abundance of hepatic IGFBP-1 mRNA levels in nondiabetic animals. This pattern of regulation appeared to be specific; serum levels of immunoreactive IGFBP-2 and -4 tended to rise in adrenalectomized animals, and levels of IGFBP-3 were not affected by either ADNX or corticosterone treatment. Of note, serum levels of IGF-I by RIA were reduced in STZ-diabetic animals compared to control values (168 +/- 16 vs. 587 +/- 55 ng/ml, respectively; P < 0.01), were partially restored toward control values with ADNX (320 +/- 22 ng/ml), and were reduced again by corticosterone treatment (195 +/- 26 ng/ml), indicating that glucocorticoids also contribute to the regulation of IGF-I levels in insulin-deficient animals. The abundance of IGF-I mRNA was reduced in STZ-diabetic animals, and ADNX also partially prevented this effect of diabetes.