Insulin-like growth factor binding protein control secretion and mechanisms of action

Prediagnosis Circulating Insulin-Like Growth Factors and Pancreatic Cancer Survival

BACKGROUND

Prediagnosis obesity and diabetes are associated with survival from pancreatic cancer, but the underlying mechanisms have not been characterized. Because both are associated with dysregulation in circulating insulin-like growth factor (IGF) levels, we evaluated the associations of prediagnosis IGF levels (IGF-I, IGF-II) and IGF binding protein 3 (IGFBP-3) with pancreatic cancer survival.

METHODS

Participants were subjects enrolled in the intervention arm of the PLCO Cancer Screening Trial who developed exocrine pancreatic cancer during follow-up (N = 178, 116 men and 67 women). Participants provided blood samples at enrollment, before cancer diagnosis. Cox proportional hazards regression model, adjusted for confounders was used to investigate associations of IGF biomarkers with pancreatic cancer survival. Because of the well-documented, gender-specific differences in circulating IGF biomarkers, and differential associations of IGF biomarkers with mortality, we evaluated associations separately among males and females.

RESULTS

Median survival was 172 days. Higher IGF-II and IGFBP-3 levels were associated with pancreatic cancer survival among males but not among females. The hazard ratios (HR) of death among men in the highest tertiles of IGF-II and IGFBP-3 compared with men in the lowest tertiles were 0.40 (95% confidence interval (CI) 0.23-0.71, p < 0.01) and 0.59 (95% CI 0.35-0.97, p = 0.10), respectively. There were no statistically significant associations between IGF-I concentrations, IGF-I/IGFBP-3, and pancreatic cancer survival.

CONCLUSIONS

Higher prediagnosis circulating IGF-II and IGFBP-3 levels are associated with better pancreatic cancer survival among men but not women. A greater understanding of how IGF signaling is related to pancreatic cancer survival could have utility in improving pancreatic cancer prognosis.

Serum adiponectin levels may be associated with the pathogenesis of hepatocellular carcinoma

The aim of the meta-analysis described below was to investigate the correlation between serum levels of adiponectin (ADPN) and the pathogenesis of hepatocellular carcinoma (HCC). Relevant studies about serum ADPN levels and the pathogenesis of HCC were identified by searching electric databases and by manual search. The included studies were selected in strict accordance with the inclusion and exclusion criteria. Detailed criteria were described in "Materials and methods" section. Statistical analyses were conducted with the STATA 12.0 statistical software (StataCorp, College Station, TX, USA). A total of nine studies were incorporated into this meta-analysis after careful consideration, including 705 HCC patients and 1390 healthy controls. This meta-analysis demonstrated that the serum ADPN levels in HCC patients were significantly higher than those in healthy controls (standard mean difference (SMD) = 0.97, 95% confidence intervals (CI) = 0.02∼1.93, P < 0.05). The result of subgroup analysis by ethnicity revealed that serum ADPN levels in Caucasians and Asians were both obviously higher than those in healthy controls (Caucasians: SMD = 0.51, 95% CI = 0.30∼0.73, P < 0.001; Asians: SMD = 0.49, 95% CI = 0.06∼0.91, P < 0.05), but in Africans, the differences between HCC patients and controls had no statistical significance (SMD = 2.64, 95% CI = -3.01∼8.30, P = 0.36). The evidence obtained by this meta-analysis suggests that serum ADPN levels are associated with the pathogenesis of HCC. Further conclusion might be that increased serum levels of ADPN can inhibit tumor growth and play a protective role in the development of HCC.

Action, localization and structure-function relationship of growth factors and their receptors in the prostate

Whereas the direct action of sex steroids, namely of androgens, on prostate cell division was questioned as early as in the 1970s, and remains so, the interest in prostatic growth factors (GFs) is rather recent but has expanded tremendously in the last five years. This lag period can be partly explained by the fact that, at the time, androgen receptors had just been discovered, and newly developed hormonal regimens or strategies to treat patients with prostate carcinoma (PCa) or epithelioma had generated great enthusiasm and hopes in the medical and scientific community. Another point to consider was the difficulty in maintaining prostate tissues in organ cultures and the relative novelty of culturing prostate epithelial cells in monolayers. Failures of sex steroids to elicit a direct positive response on prostate cell divisionin vitro, as seenin vivo, were interpreted as resulting from inappropriate models or culture conditions. However, the increasing number of reports confirming the lack of mitogenic activity of sex steroidsin vitro, coupled with the powerful mitogenic activity of GFs displayed in other systems, the discovery of GF receptors (GF-Rs), and the elucidation of their signalling pathways showing sex steroid receptors as potential substrates of GF-activated protein kinases gradually led to an increased interest in the putative role of GFs in prostate physiopathology. Of utmost importance was the recognition that hormone refractiveness was responsible for PCa progression, and for the poor outcome of patients with advanced disease under endocrine therapies. This problem remains a major issue and it raises several key questions that need to be solved at the fundamental and clinical levels.

A reassessment of insulin-like growth factor binding protein gene expression in the human retinal pigment epithelium

The role of insulin-like growth factors (IGF) in regulating cell differentiation and proliferation is in part modulated by the IGF binding protein (IGFBP) family of genes. Previous studies of the human retinal pigment epithelium (RPE) have detected expression of IGFBP-2, -3, and -6. However, recent experiments in our lab have suggested a broader pattern of IGFBP gene family expression in the RPE cell than has previously been recognized. We have examined the gene expression profile of IGFBP-1 to -6 and the related protein, IGFBP-rP1, in RPE cell lines derived from ten donors eyes using RT-PCR, ELISA, and Western methods. Transcripts of IGFBP-1 to -6 and -rP1 were consistently detected in human RPE cells. IGFBP-3, -5, -6, and -rP-1, appear to be constitutively expressed in the RPE, whereas IGFBP-1, -2, and -4, were expressed at variable levels in the cell lines examined. IGFBP secretion by the RPE in vitro was confirmed by ELISA (IGFBP-1, -2, -3, -4, and -6) and Western blot analysis (IGFBP-5 and -rP1). There was, in general, a strong correlation between gene-specific transcription levels and protein secretion by the RPE. Our studies demonstrate that the major IGFBP family genes are ubiquitously expressed in explanted human RPE cells in vitro. This broad expression profile and the recent evidence that IGFBPs have IGF-independent biological activity suggest that the IGFBP family genes may constitute a previously unrecognized and complex regulatory system in the human retina and RPE.

Direct measurement of IGF-I and IGFBP-3 in bronchoalveolar lavage fluid from idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is characterized by the rearrangement of extracellular matrix and progressive increase in the amount of fibrotic tissue in the lung. IGF-I is a potent profibrogenic molecule and its bioavailability is dependent on at least 6 binding proteins called IGFBPs. Among these, IGFBP-3 is the most represented in serum and in different connective tissues. The purpose of this study was to identify and characterize IGFBP-3 in bronchoalveolar lavage (BAL) fluids. We studied 11 patients with IPF and 6 normal subjects by performing baseline pulmonary function test and BAL. IGF-I and IGFBP-3 were measured by RIA in BAL and serum. No significant differences were observed between serum IGF-I and IGFBP-3 from IPF patients and normal subjects. Instead, the direct measurement in BAL revealed a significant increase of IGF-I and IGFBP-3 in IPF patients compared to normal subjects. BAL IGF-I and IGFBP-3 concentrations were significantly related to inspiratory vital capacity (IVC) and carbon dioxide partial pressure (PaCO2): the higher the value of IVC and the lower the value of PaCO2, the higher the level of IGF-I and IGFBP-3. In conclusion, IGFBP3 and IGF-I could be important local mediators of IPF. Their direct measurement in BAL in IPF patients could be used as a clinical marker of the disease, since high levels of IGFBP-3 and IGF-I in BAL are associated to the initial phase of the disease.

Human glomerular endothelial cells IGFBPs are regulated by IGF-I and TGF-beta1

The release of insulin-like growth factor binding proteins (IGFBPs) and their regulation in human glomerular endothelial cells (GENC) was characterised. GENC produce IGFBP-4, IGFBP-2 and IGFBP-3 and express mRNA for IGFBP-2 to IGFBP-5. Due to the fact that IGF-I and TGF-beta1 modulate glomerular hypertrophy, their action on IGFBP release and GENC growth was studied. IGF-I increased IGFBP-3, IGFBP-2 and decreased IGFBP-4, while TGF-beta1 decreased IGFBP-3 and apparently increased IGFBP-4. All of the IGFBPs, except the TGF-beta1-regulated IGFBP-4, were modulated at mRNA level. IGF-I stimulated GENC proliferation, while TGF-beta1 inhibited their growth. It was demonstrated that an IGFBP-3 antibody reduced GENC proliferation. However, rhIGFBP-3 alone had no effect on GENC, but after 48 h pre-incubation the IGF-I stimulated GENC growth was increased, suggesting that IGFBP-3 could modulate the IGF-I induced GENC proliferation. It was concluded that the stimulatory IGFBP-3 and the inhibitory IGFBP-4 could regulate GENC growth, although the IGFBP-3 seems to have a predominant effect in this control.

Insulin-like growth factor binding protein production in bovine retinal endothelial cells

Retinopathy is the most frequent microangiopathic complication in diabetes. Many circulating hormones and locally produced mitogenic factors have been involved. Bovine retinal endothelial cells (BRECs) were cultured to investigate if insulin, insulin-like growth factors (IGFs), IGF binding proteins (IGFBPs), and a chronic high-glucose condition could control endothelial cell growth. Specific IGF-I receptors with two binding sites with high (Kd 0.03 nmol/L) and low (Kd 1.3 nmol/L) affinity were found when analyzing families of displacement curves between IGF-I versus IGF-I and IGF-I versus insulin. However, IGFs failed to be mitogenic factors in these cells. This could be explained by an inhibitory effect due to the presence of specific IGFBPs with a molecular weight between 24 and 43 kd. Using Western blot and immunoblot analysis, Northern blot study, and specific radioimmunoassay (RIA), these IGFBPs have been identified as IGFBP-3, -2, -5, and -4. Insulin, which does not bind to IGFBPs, was a potent mitogenic factor in these cells at a high concentration (10 nmol/L), suggesting a cross-reaction to IGF-I receptor. These IGFBPs, except the 24-kd form (IGFBP-4), were modulated by both IGF-I and IGF-II, with a maximum effect at 100 and 10 nmol/L, respectively. This regulation on IGFBPs was IGF-I receptor-independent. In fact, (1) IGFBP mRNA levels were not modified after stimulation with 100 nmol/L IGF-I, (2) 100 nmol/L IGF plus an equimolar concentration of alpha IR3 did not affect IGFBP production, (3) Des(1-3)IGF-I had no effect on IGFBP modulation, whereas at 10 nmol/L it enhanced BREC thymidine cell incorporation, and (4) 100 nmol/L insulin, which at this concentration can cross-react with the IGF-I receptor, did not modify the IGFBP pattern. Chronic exposure (4 weeks) of BRECs to 25 mmol/L glucose had no effect on cell growth. However, after 3 weeks, we observed a decreased IGFBP detection, and addition of 100 nmol/L IGF-I did not change IGFBP levels and did not modify cell growth. Conversely, BRECs grown in regular medium for 4 weeks showed increased IGFBP production. In conclusion, we showed that conditions mimicking hyperinsulinemia, rather than high levels of IGFs, could regulate BREC growth and that the IGF-I analog, Des(1-3), even with reduced affinity for IGFBPs but in part capable of binding to IGFBP-3, significantly stimulated BRECs growth only at 10 nmol/L. IGF actions are modulated by locally produced endothelial IGFBPs, and in turn, these endothelial IGFBPs are regulated, via in IGF-I receptor-independent mechanism, by the presence of IGFs. The autoregulatory IGF system together with the direct glucose modulation of IGFBPs could contribute in diabetic subjects to the retinal endothelial cell growth and metabolism through local changes in IGF bioavailability.

The role of the insulin-like growth factors in the central nervous system

Increasing evidence strongly supports a role for insulin-like growth factor-I (IGF-I) in central nervous system (CNS) development. IGF-I, IGF-II, the type IIGF receptor (the cell surface tyrosine kinase receptor that mediates IGF signals), and some IGF binding proteins (IGFBPs; secreted proteins that modulate IGF actions) are expressed in many regions of the CNS beginning in utero. The expression pattern of IGF system proteins during brain growth suggests highly regulated and developmentally timed IGF actions on specific neural cell populations. IGF-I expression is predominantly in neurons and, in many brain regions, peaks in a fashion temporally coincident with periods in development when neuron progenitor proliferation and/or neuritic outgrowth occurs. In contrast, IGF-II expression is confined mainly to cells of mesenchymal and neural crest origin. While expression of type I IGF receptors appears ubiquitous, that of IGFBPs is characterized by regional and developmental specificity, and often occurs coordinately with peaks of IGF expression. In vitro IGF-I has been shown to stimulate the proliferation of neuron progenitors and/or the survival of neurons and oligodendrocytes, and in some cultured neurons, to stimulate function. Transgenic (Tg) mice that overexpress IGF-I in the brain exhibit postnatal brain overgrowth without anatomic abnormality (20-85% increases in weight, depending on the magnitude of expression). In contrast, Tg mice that exhibit ectopic brain expression of IGFBP-1, an inhibitor of IGF action when present in molar excess, manifest postnatal brain growth retardation, and mice with ablated IGF-I gene expression, accomplished by homologous recombination, have brains that are 60% of normal size as adults. Taken together, these in vivo studies indicate that IGF-I can influence the development of most, if not all, brain regions, and suggest that the cerebral cortex and cerebellum are especially sensitive to IGF-I actions. IGF-I's growth-promoting in vivo actions result from its capacity to increase neuron number, at least in certain populations, and from its potent stimulation of myelination. These IGF-I actions, taken together with its neuroprotective effects following CNS and peripheral nerve injury, suggest that it may be of therapeutic benefit in a wide variety of disorders affecting the nervous system.

Human recombinant insulin-like growth factor I and -II stimulate the expression of basic fibroblast growth factor but suppress the division of bovine coronary smooth muscle cells

Insulin-like growth factor I and II (IGF-I and -II)--two 7.65- and 7.47-kDA polypeptides belonging to the somatomedine family--are regular constituents of human blood plasma. Both factors exert mitogenic activity on a variety of cell types including arterial smooth muscle cells. In the present study, the effect of IGF-I and -II on cultured bovine coronary smooth muscle cells (cSMC) was assessed. Human recombinant IGF-I and IGF-II added to cSMC cultured in a medium containing 10% fetal bovine serum (FBS) decreased the cell number and [3H]thymidine incorporation in a dose dependent fashion up to 40% and 43% compared to control cells (100%). At the same time, the expression of basic fibroblast growth factor (bFGF) increased from 60 pg/5 x 10(4) cells (control) to 75 (IGF-I) and 113 pg/5 x 10(4) cells (IGF-II). In parallel with enhanced bFGF expression, the bFGF receptor content per cell and the [35S]sulfate incorporation into extracellular and cell-associated proteoglycans also increased under the influence of IGF-I and -II. In contrast, with low serum concentration (0.1% FBS) the addition of IGF-I and -II to bovine cSMC cultures resulted in a slight increase in cell number, protein content and [3H]thymidine incorporation as described in previous studies. These results suggest that the mitogenic activity of IGF-I and -II towards coronary smooth muscle cells depends on culture conditions. In the presence of 10% fetal bovine serum that mimics in vivo conditions, IGF-I and -II did not necessarily act as mitogenic factors but inhibited the proliferation of cSMC in vitro possibly by modulating antagonizing the action of other growth factors. Irrespective of the inhibition of cell division, the cellular bFGF, the bFGF receptor and the bFGF activity-related proteoheparan sulfate were overexpressed under the influence of IGF.

Human insulin-like growth factor binding protein-1 (hIGFBP-1) transgenic mice: insights into hIGFBP-1 regulation and actions

Three hemizygous transgenic (Tg) mouse lines were generated with a fusion gene composed of the mouse metallothionein promoter (mMT-1) and a full length human insulin-like growth factor binding protein-1 (hIGFBP-1) cDNA that was truncated in its 3' untranslated (3'UT) region. The transgene was ectopically expressed in the brain of each line and resulted in postnatal brain-growth retardation that was manifested by 2 weeks of age. Despite the expression of the transgene in multiple other tissues and high serum hIGFBP-1 concentrations in two of the three lines, studies designed to detect alterations in somatic growth, in reproduction and in glucose metabolism revealed few other abnormalities. Unexpectedly, however, we found that the regulation of the transgene shared characteristics with that of the native gene, despite the fact that it lacked the endogenous gene's 5' regulatory region, as well as most of its 3' UT region. Our studies suggest that factors controlling mRNA stability are important to regulation of both the native and transgene, and that an AU-rich element 17 base pairs (bp) from the end of coding sequence is responsible for the instability of the transgene and in part for instability of the endogenous gene.

Expression of insulin-like growth factor-I in transgenic mice

The studies reviewed above provide strong evidence for the concept that IGF-I plays an essential role in mediating the growth-promoting actions of GH, and thus, they support the central elements of the "somatomedin hypothesis." The data, however, also point to actions of each GH and IGF-I that are not linked. Many hormones and factors, other than GH, are known to regulate the expression of IGF-I, as well as its binding proteins (modulators of its actions), in a tissue-specific fashion. Some of these influences, e.g., estrogens, thyroid hormone, and nutritional factors, also effect GH synthesis and/or secretion. This complex and precise regulation undoubtedly plays a key role in coordinating the somatic and visceral growth stimulated by GH and IGF-I. The evidence that GH and IGF-I actions are not always coupled, therefore, is not surprising. The challenge is to dissect the precise role(s) of GH and IGF-I, as well as other hormones and growth factors, in the control of growth. Study of transgenic animals provides a powerful way to approach these issues in vivo. These studies demonstrate that IGF-I is capable of stimulating in vivo brain growth. The transgene IGF-I-stimulated increase in brain size appears to result both from an increase in cell number and, as demonstrated by Carson et al., from an increase in myelin content, which in turn may result from proliferation of oligodendrocytes. Other roles for IGF-I in brain growth and development, however, are possible and amply supported by numerous studies of brain-derived cultured cells (see other papers herein). Because IGF-I is normally expressed in brain, it seems reasonable to assume that the IGF-I-stimulated brain growth observed in these transgenic mice represents a response to IGF-I overexpression rather than a pharmacologic response that is not indicative of a normal IGF-I function. Study of this IGF-I transgenic line cannot address the developmental period(s) when IGF-I normally stimulates brain growth, but this transgenic line provides a model to investigate IGF-I's specific role and its mechanisms of action.