The role of insulin-like growth factors and IGF-binding proteins in the physiological and pathological processes of the kidney

Prognostic significance of diabetes mellitus in localized renal cell carcinoma

OBJECTIVE

We investigated whether diabetes mellitus is associated with the cancer-related outcomes in patients with localized clear cell renal cell carcinoma treated with radical or partial nephrectomy.

METHODS

We reviewed data from 950 patients who received radical or partial nephrectomy for localized clear cell renal cell carcinoma from 1988 to 2009. We analyzed potential association of patients' diabetic status and various clinicopathologic features. Univariate and multivariate analyses were performed to identify independent predictors of cancer-specific survival, overall survival and non-cancer-related survival.

RESULTS

Of 950 patients, 108 (11.4%) reported having diabetes mellitus pre-operatively. Patients with and without diabetes mellitus demonstrated no significant differences regarding various clinicopathologic features except for age (P < 0.001), pre-existing hypertension (P < 0.001), pre-existing cardiovascular disease (P < 0.001) and performance status (P = 0.019). In terms of cancer-specific, overall and non-cancer-related survival, the Kaplan-Meier curves showed that non-diabetic patients had superior survival rates than diabetics (P = 0.012, <0.001 and <0.001, respectively). Meanwhile, although diabetes mellitus was shown to be an independent predictor of overall survival (P = 0.022) and non-cancer-related survival (P = 0.034), it was not observed to be a significant predictor of cancer-specific survival (P = 0.234) in multivariate analyses.

CONCLUSIONS

Diabetes mellitus may not be directly associated with disease-specific outcome in patients who receive surgical management for localized renal cell carcinoma. However, since diabetes mellitus was observed to be associated with overall survival in such patients, diabetic patients undergoing surgery for localized renal cell carcinoma should be counseled on the potential impact of diabetes mellitus. Institutional review board (IRB) approval number H-1106-062-366.

Stimulatory effect of IGF-I and VEGF on eNOS message, protein expression, eNOS phosphorylation and nitric oxide production in rat glomeruli, and the involvement of PI3-K signaling pathway

Nitric oxide (NO) is reported to be involved in the pathogenesis of renal hyperfiltration in the early stage of diabetic nephropathy. We set out to determine whether IGF-I and/or VEGF165 directly stimulate NO production in rat glomeruli and whether the expression of NO synthase (NOS) isoforms as well as eNOS phosphorylation contribute to NO generation by IGF-I and VEGF. Long-term exposure to IGF-I and/or VEGF165 augments NO production through increased eNOS mRNA, protein expression and phosphatidylinositol 3-kinase (PI3-K) signaling pathway plays a major role in this process; short-term exposure to IGF-I and/or VEGF(165) activates eNOS activity via phosphorylation by a PI3-K/Akt dependent pathway. Our data suggest the great possibility that increased endogenous IGF-I and VEGF may be responsible for the up-regulation of eNOS expression and NO production which contributes to glomerular hyperfiltration in early diabetic kidneys. IGF-I is a newly described growth factor that up-regulates eNOS expression and PI3-K plays a major role in this process.

The expression of insulin-like growth factor-I receptor correlates with Fuhrman grading of renal cell carcinomas

Recent reports have shown significant correlation between Fuhrman nuclear grade of renal cell carcinoma (RCC) and patient survival. However, no one specific gene alteration has yet been described to account for this correlation. This study investigated the expression of the insulin-like growth factor-I receptor (IGF-IR) in RCC and correlated the results to the tumor Fuhrman nuclear grade. Formalin-fixed, paraffin-embedded sections from 68 cases of RCC were stained using the immunohistochemical avidin-biotin-peroxidase method. An anti-human IGF-IR rabbit polyclonal antibody was used. The stains were semiquantitatively evaluated using the Allred score system, assessing intensity of stain and percentage of positive tumor cells. Statistical analysis was performed using the Kruskal-Wallis test. Strong and diffuse cytoplasmic IGF-IR stain (Allred score 7 to 8) was identified in 25 of 25 (100%) of grade 3 and 4 RCCs. Grade 2 RCCs had a median IGF-IR Allred score of 4. Ten of 10 (100%) grade 1 RCCs were negative. Even in the positive high-nuclear-grade tumors, areas of low nuclear grade, when present, were IGF-IR negative. Statistical analysis using the Kruskal-Wallis test demonstrated significant correlation between increasing Fuhrman nuclear grade and increasing IGF-IR Allred score (P <0.0001). Thus we report the novel finding of significant statistical correlation between IGF-IR protein expression and Fuhrman nuclear grade of RCC, and consequentially with patient survival.

Overweight, obesity, and cancer risk

Over the past few decades the proportion of people with excess body weight has been increasing in both developed and less developed countries. About 50% of men and 35% of women in Europe are currently estimated to be overweight or obese. In addition to an increase in the risk of cardiovascular disease and type II diabetes, the evidence summarised here shows that excess body weight is directly associated with risk of cancer at several organ sites, including colon, breast (in postmenopausal women), endometrium, oesophagus, and kidney. In part, these associations with cancer risk may be explained by alterations in the metabolism of endogenous hormones-including sex steroids, insulin, and insulin-like growth factors-which can lead to distortion of the normal balance between cell proliferation, differentiation, and apoptosis. Avoidance of weight gain thus seems to be an important factor for cancer prevention.

Pregnancy and risk of renal cell cancer: a population-based study in Sweden

Epidemiological findings indicate that hormonal influences may play a role in the etiology of renal cell cancer (RCC). The possible effect of childbearing remains enigmatic; while some investigators have reported a positive association between number of births and renal cell cancer risk, others have not. A case-control study, nested within a nation-wide Fertility Register covering Swedish women born 1925 and later, was undertaken to explore possible associations between parity and age at first birth and the risk of renal cell cancer. Among these women a total of 1465 cases of RCC were identified in the Swedish Cancer Register between 1958 and 1992 and information on the number of live childbirths and age at each birth was obtained by linkage to the Fertility Database. For each case, five age-matched controls were randomly selected from the same register. Compared to nulliparous women, ever-parous women were at a 40% increased risk of RCC (Odds Ratio [OR]=1.42; 95% CI 1.19-1.69). The corresponding OR for women of high parity (five or more live births) was 1.91 (95% CI 1.40-2.62). After controlling for age at first birth among parous women, each additional birth was associated with a 15% increase in risk (OR=1.15; 95% CI 1.08-1.22). The observed positive association between parity and renal cell cancer risk is unlikely to be fully explained by uncontrolled confounding, but warrants further evaluation in large studies, with allowance for body mass index.

Biology of kidney cells: ontogeny-recapitulating phylogeny

Biology of kidney cells can be used as a model for further understanding of ontogeny-recapitulating phylogeny. The common and species-specific structural and functional relationship between blood capillaries and the environment via a filtration barrier of nephrons is a biological phenomenon resulting from renal cell memory acquired through evolution. Genetically programmed development, a subsequent series of gene expression, and inductive interactions played a key role in differentiation and maintenance of specific activities of kidneys in birds and mammals. Various environmental factors may alter kidney development and specific activities at the levels of gene expression, repression, or derepression, and defensive mechanisms involved in reaction to risk factors are developed. Autoimmunity and cancerogenesis are closely dependent on a variety of environmental agents, such as antigens originating from infections with some viruses and toxins, or irradiation, advanced industrialization, and progress of civilization. As a result of gene mutation, delation, rearrangement, and/or susceptibility to different agents, renal cell memory is altered. Instead of cell-specific activities, the abilities for regeneration, and other genetically programmed activities, the genesis of kidney diseases are common. Balkan endemic nephropathy, as regional disease, is an important example of the role, of environmental agents, at the level of genes. Research programs on molecular genetics will contribute to our efforts both to prevent infections and to elucidate the genesis, diagnosis, prognosis, prevention, and therapy of kidney diseases.

Expression profiling of renal epithelial neoplasms: a method for tumor classification and discovery of diagnostic molecular markers

The expression patterns of 7075 genes were analyzed in four conventional (clear cell) renal cell carcinomas (RCC), one chromophobe RCC, and two oncocytomas using cDNA microarrays. Expression profiles were compared among tumors using various clustering algorithms, thereby separating the tumors into two categories consistent with corresponding histopathological diagnoses. Specifically, conventional RCCs were distinguished from chromophobe RCC/oncocytomas based on large-scale gene expression patterns. Chromophobe RCC/oncocytomas displayed similar expression profiles, including genes involved with oxidative phosphorylation and genes expressed normally by distal nephron, consistent with the mitochondrion-rich morphology of these tumors and the theory that both lesions are related histogenetically to distal nephron epithelium. Conventional RCCs underexpressed mitochondrial and distal nephron genes, and were further distinguished from chromophobe RCC/oncocytomas by overexpression of vimentin and class II major histocompatibility complex-related molecules. Novel, tumor-specific expression of four genes-vimentin, class II major histocompatibility complex-associated invariant chain (CD74), parvalbumin, and galectin-3-was confirmed in an independent tumor series by immunohistochemistry. Vimentin was a sensitive, specific marker for conventional RCCs, and parvalbumin was detected primarily in chromophobe RCC/oncocytomas. In conclusion, histopathological subtypes of renal epithelial neoplasia were characterized by distinct patterns of gene expression. Expression patterns were useful for identifying novel molecular markers with potential diagnostic utility.

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.

The phylogeny of the insulin-like growth factors

The insulin-like growth factors are major regulators of growth and development in mammals and their presence in lower vertebrates suggests that they played a similarly fundamental role throughout vertebrate evolution. While originally perceived simply as mediators of growth hormone, on-going research in mammals has revealed several hierarchical layers of complexity in the regulation of ligand bioavailability and signal transduction. Our understanding of the biological role and mechanisms of action of these important growth factors in mammals patently requires further elucidation of the IGF hormone system in the simple model systems that can be found in lower vertebrates and protochordates. This review contrasts our knowledge of the IGF hormone system in mammalian and nonmammalian models through comparison of tissue and developmental distributions and gene structures of IGF system components in different taxa. We also discuss the evolutionary origins of the system components and their possible evolutionary pathways.

Role of insulin-like growth factor binding proteins in human post-nephrectomy proximal tubule cells

1. In order to determine the role of the insulin-like growth factor-I (IGF-I)/IGF binding protein (IGFBP) axis in the augmentation of tubule growth and function following reductions in nephron mass, primary cultures of human proximal tubule cells (PTCs) were generated from the histologically normal sections of ten surgically removed kidneys. 2. PTC hypertrophy (cellular protein content), DNA synthesis (thymidine incorporation) and apical sodium-hydrogen exchange (NHE) activity (ethylisopropylamiloride-sensitive apical 22Na+ uptake) were measured following 24 h incubation in media supplemented with 10 % pre- or post-nephrectomy sera obtained from these patients. The results were compared with the effects of pre- and post-operative control sera collected from seven patients undergoing retroperitoneal operations not involving removal of renal tissue. 3. Day 1 post-nephrectomy sera promoted a significant 73 % increase in apical NHE activity, which was accompanied by a significant increase in PTC binding of 125I-IGF-I (post- vs. pre-nephrectomy, 163 +/- 6 vs. 142 +/- 4 fmol (mg protein)-1; P < 0.05). Subsequent post-nephrectomy sera significantly stimulated PTC protein content and thymidine incorporation, peaking at day 7 (127.7 +/- 14.0 and 118.4 +/- 9.0 % of pre-nephrectomy values, respectively; P < 0.05). The growth effects were cell specific, as they were not observed with renal cortical fibroblasts. No change was detected in any of these measured variables following exposure to control sera. 4. Serum IGF-I and IGFBP-1 levels did not significantly change over time or between groups. IGFBP-3 levels progressively decreased in both control and nephrectomized sera from pre-operative values of 3580 +/- 305 and 3360 +/- 217 ng ml-1, respectively, to 2670 +/- 341 and 2600 +/- 347 ng ml-1 at 1 week post-operation. Serum IGFBP-2 levels increased to a comparable extent in both controls (day 0 vs. day 7, 2940 +/- 1024 vs. 7010 +/- 2520 ng ml-1; P < 0.01) and nephrectomized patients (day 0 vs. day 7, 3070 +/- 656 vs. 9130 +/- 2010 ng ml-1; P < 0.01). 5. The results indicate that nephrectomy engenders the elaboration of one or more humoral factor(s), which promotes increased binding of IGF-I to PTCs and which may in turn specifically stimulate PTC Na+ transport and growth.

Human renal fibroblasts modulate proximal tubule cell growth and transport via the IGF-I axis

To determine the paracrine interactions involved in the tubulointerstitial response to progressive renal disease, the role of insulin-like growth factor-I (IGF-I) and its binding proteins (IGFBPs) in in vitro interactions between human proximal tubule cells (PTC) and renal cortical fibroblasts (CF) were studied in primary cell culture. PTC growth and transport were increased in the presence of CF-conditioned media (CF-CM), as shown by increased thymidine incorporation, cellular protein content and sodium-hydrogen exchange (NHE) activity, to 185 +/- 31% (P < 0.01), 150 +/- 18% (P < 0.05) and 195 +/- 27% (P < 0.01) of the control values, respectively. IGF-I was produced by cultured CF at a rate of 64.6 +/- 7.5 ng/mg protein/day. Exogenous IGF-I applied to PTC provoked similar enhancement of growth and NHE activity as CF-CM and the stimulatory effect of CF-CM was blocked by specific immunoneutralization of IGF-I receptors. These receptors were threefold more abundant on PTC basolateral versus apical membranes. IGF binding proteins (IGFBP)-2 and IGFBP-3 were secreted by CF at rates of 694 +/- 88 and 1769 +/- 45 ng/mg/day, with the release of IGFBP-3 being enhanced in the presence of PTC-CM (120.0 +/- 9.7% of control, P < 0.01). Moreover, the addition of CF-CM to PTC increased cell-associated IGFBP-3 on PTC surfaces, without changes in IGF-I receptor numbers or affinity and without changes in PTC mRNA for IGFBP-3. Des(1-3)IGF-I, an analog that binds to the IGF-I receptor but not to IGFBPs, provided a less potent stimulus for PTC growth compared with IGF-I, indicating that cell-associated IGFBP-3 facilitates the action of IGF-I on PTC. The results support important paracrine roles for both IGF-I and IGFBPs in the interstitial regulation of proximal tubule growth and transport.

Insulin-like growth factor I receptor gene expression during postnatal development of rabbit kidney

BACKGROUND

Insulin-like growth factor-I (IGF-I) is a peptide growth factor whose biological effects are mediated through a specific receptor (IGF-IR). IGF-I and IGF-IR are detected in both fetal and adult kidneys and have both metabolic and growth effects. IGF-IR expression during postnatal kidney development is not well defined and the biological role of this receptor during the postnatal stage is not clearly established. The purpose of the present study was to analyze IGF-IR gene expression during the postnatal development of rabbit kidney to achieve a better understanding of the correlation between growth and differentiation of kidney tissues and IGF-IR expression.

METHODS

Using in situ hybridization, we studied changes in IGF-IR expression in the kidneys of newborn rabbits and those up to 35 days old. Evaluation of the stage of kidney development and morphological maturation was made on histological sections stained with hematoxylin-eosin.

RESULTS

High levels of IGF-IR gene expression in the rabbit kidney occurred in the last stages of postnatal development and in the adult stages; during the development of the subcapsular metanephrogenic zone, IGF-IR gene expression was not observed. IGF-IR mRNA was expressed by proximal and distal tubules and by collecting ducts after these tissues attained morphological maturation. The appearance of IGF-IR mRNA in these kidney structures followed a precise temporo-spatial sequence. IGF-IR was not expressed by renal corpuscles, Henle's loops, inner medullary collecting ducts, vessels, or interstitial cells at any study stage.

CONCLUSIONS

The temporal and spatial patterns of IGF-IR gene expression during postnatal development of the rabbit kidney suggest that IGF-IR and its ligands are relevant for the acquisition of the function, and not for development events, by proximal and distal tubules and collecting ducts. This study also suggests that IGF-IR mRNA localization constitutes a useful marker to determine the functional maturation of these renal structures.

Gene expression of the insulin-like growth factor system during mouse kidney development

Expression of the insulin-like growth factor (IGF) system was investigated in mouse renal development and physiology, using non radioactive in situ hybridization and quantitative RT-PCR. IGF-I mRNA levels increased after birth and were confined to distal tubules and peritubular capillaries in the outer medulla. IGF-II mRNA levels were high in developing kidneys and peaked after birth. The type I receptor mRNA expression pattern mostly parallelled those of IGF-I and IGF-II. The IGF binding proteins (IGFBP's) showed weak mRNA expression for IGFBP-1 and -6. High fetal mRNA levels were measured for IGFBP-2, showing a similar profile in time as observed for IGF-II. Low fetal IGFBP-3 and -5 mRNA levels increased after birth. IGFBP-2, -4 and -5 mRNA expression was localized to differentiating cells. In the mature kidney predominant expression was confined to proximal tubules (IGFBP-4), thin limbs of Henle's Loop (IGFBP-2), glomerular mesangial cells (IGFBP-5) and peritubular capillaries of the medulla (IGFBP-5). IGFBP-3 mRNA was exclusively expressed in endothelial cells of the renal capillary system. Distinct mRNA expression for each member of the IGF system may point to specific roles in development and physiology of the mouse kidney.

Regulation by nutrition and age of insulin-like growth factor binding sites in ovine kidney

The insulin-like growth factors (IGFs) are considered to have a role in the regulation of renal growth and development. The purpose of the present study was to evaluate the effect of nutritional stress on IGF binding in ovine kidney at different postnatal ages. Binding of IGF-I and IGF-II to kidneys of fed and fasted sheep was characterised using histological autoradiography, competitive binding assays, and SDS-PAGE. Nutritional regulation of IGF-I binding was restricted to cells of the proximal tubules of two and 14-day-old lambs where we identified an IGF binding protein which was upregulated in response to fasting and where IGF-II binding was also slightly enhanced. Ontogenetic changes occurred in the glomeruli where IGF-I binding peaked at 6 months (P < or = 0.001), and IGF-II binding increased to 4 months and then plateaued (P < or = 0.01). In the medulla, IGF-II binding was highest at 4 and 6 months (P < or = 0.05). From these studies, we conclude that the IGF axis may play a role in the regulation of the metabolic response to fasting in the kidney of young lambs. Furthermore, the changes with age which are described may reflect a transition period at 4-6 months, from an initial promotion of kidney growth and development in young lambs to establishment of the metabolic and clearance functions in the adult animal.

The effect of insulin-like growth factors on brain myelination and their potential therapeutic application in myelination disorders

Degenerative disorders of the cerebral white matter, leukodystrophies and demyelination diseases, are characterized by the faulty formation or excessive breakdown of myelin. Insulin-like growth factors (IGFs) promote the proliferation of oligodendrocytes as well as their myelin synthesis. IGF-I overexpressing mice show a significant increase in brain weight associated with increased myelin content. In contrast, the brains of IGF-binding protein-1 transgenic mice show a dramatic decrease in myelination. Furthermore, IGFs and IGF-binding proteins are among the factors that are induced by brain injury and have neuroprotective effects. IGFs also induce neurite growth and survival, in particular in glial cells of the peripheral nervous system. In demyelinating diseases, IGF-I may be useful for reducing myelin breakdown and promoting myelin regeneration. These observations may lead to new therapeutic applications for IGFs, for example promoting remyelination or limiting damage following brain injury.

Characterization of insulin-like growth factor binding proteins and regulation of IGFBP3 in human mesangial cells

IGF-I regulates renal growth and development. Insulin-like growth factor binding proteins (IGFBPs) are synthesized by the kidney and may modulate the local autocrine and/or paracrine actions of IGF-I. We have previously demonstrated that mesangial cells (MC) release IGF-I and IGF-binding activity; however, the specific IGFBPs produced by these cells and the factors involved in their regulation are unknown. We examined MC for expression of IGFBP-1 to -6 mRNAs and proteins. RNase protection assays using total RNA demonstrated that MC express all of the IGFBPs. [125I]IGF-I Western ligand blot of conditioned medium demonstrated that MC release IGFBPs of 24, 29, 32 kDa, and a doublet at 46 kDa, consistent with IGFBP-4, -5, -2 and -3, respectively. IGFBP species of 28 and 34 kDa were also detected. Since IGF-I and TGF-beta are implicated in glomerular hypertrophy and matrix expansion, we tested their effect on IGFBPs released by MC. IGF-I (100 ng/ml), TGF-beta (2 ng/ml) and forskolin (10(-5) M) differentially regulated the abundance of IGFBPs released in the conditioned medium in a time-dependent manner. IGF-I and TGF-beta were potent inducers of the release of IGFBP3 protein; however, TGF-beta, but not IGF-I, increased IGFBP3 mRNA levels. Recombinant IGFBP3 was tested for its effect on IGF-I-induced mitogenesis. IGFBP3 inhibited IGF-I-stimulated DNA synthesis in a dose-dependent manner with a peak effect observed at 50 nM IGFBP3. Although TGF-beta is a potent inhibitor of IGF-I-stimulated DNA synthesis, this effect is not mediated via IGFBPs. Expression of IGFBP-1 to -6 by MC suggests that these proteins may modulate IGF-I bioavailability in the glomerulus. IGF-I itself, TGF-beta and cAMP agonists may indirectly modulate the effects of IGF-I via the release of IGFBPs by MC.

Response of the intrarenal insulin-like growth factor-I axis to acute ischemic injury and treatment with growth hormone and epidermal growth factor

We previously reported that following bilateral acute tubular necrosis (ATN) profound changes in the intrarenal insulin-like growth factor-I axis occurs which are unrelated to altered nutritional intake. In this current report we studied rats with unilateral ATN to assess whether these changes reflect a response to acute injury or the accompanying uremia. Compared to the contralateral kidney, the injured kidney showed an increase in IGF-I receptor number without a change in IGF-I receptor mRNA levels, a decrease in IGF-I mRNA and IGF-I protein levels, a decrease in growth hormone (GH) receptor mRNA abundance and receptor binding. There was also a decrease in IGF binding protein-2, -3 and -5 mRNA levels together with a fall in protein products. Since this unilateral ATN model excludes the influence of uremia and reduced nutritional intake, we surmised that these changes reflect a direct response to injury. Next, because of the reduced GH receptor binding noted above and the reported decrease in epidermal growth factor (EGF) expression in ATN, we tested the thesis that the low kidney IGF-I mRNA levels in ATN are partly due to a relative or absolute deficiency of these hormones. Administration of EGF or GH promptly increased ATN kidney IGF-I mRNA levels to control kidney values, lending support to the thesis. The response to EGF also suggests that the salutary effect of EGF treatment in ATN may partly be mediated by stimulating IGF-I production.

IGF-II dependent autocrine growth in cell lines derived from renal tumours of childhood

Aims-To determine the role of insulin-like growth factors (IGF) in the proliferation of tumour cells, by studying the mitogenic response to IGFs of three cell lines of differing phenotype established from both malignant rhabdoid and Wilms tumour, representing a range of cell types (GOS 4, G401, and T3/73).Methods-Production of IGF-II and IGF-I was measured by radioimmunoassay, and the presence of IGF binding protein complexes was observed by gel exclusion chromatography. Following growth analyses in serum-free media to ascertain the dependence of the cell lines on exogenous IGFs, the generation of autocrine growth was measured by a density dependence assay of proliferation in culture. Receptors were measured by radioligand cross linking and autocrine growth through these receptors assayed by the use of blocking antibodies.Results-While GOS 4 and G401 were able to proliferate in serum-free medium over a period of 5 d, T3/73 showed an absolute dependence on IGFs added daily at 1-10 ng/ml. Plating at clonal density showed that cell growth was directly density dependent in serum-free medium. The serum independent proliferation of G401 and GOS 4 was blocked by the addition of an antibody to the type 1 IGF receptor (alpha-IR3) suggesting that the effects of autocrine factors are mediated through type 1 IGF receptors. S1 nuclease protection analysis indicated that all three cell lines produced significant amounts of mRNA derived mainly from the P3 IGF-II promoter, but transcripts for IGF-I were undetectable. Radioimmunoassay of IGFs from conditioned media showed that all the lines made assayable IGF-II (8.6, 8.4, and 6.1 ng/ml/24 h/10(6) cells for GOS 4, G401, and T3/73 respectively). The presence of species consistent with both type 1 and type II IGF receptors was demonstrated using radioligand binding to cell membranes followed by cross linking.Conclusions-Autocrine IGF-II may contribute to the serum independence of GOS 4 and G401 cells, whereas T3/73 may depend on exogenous IGF-II for proliferation.

Renal growth hormone--insulin-like growth factor-I system in acute renal failure

The renal growth hormone--insulin-like growth factor-I system in acute ischemic renal failure. Recovery from acute tubular necrosis (ATN) is accelerated by IGF-I therapy. Furthermore, the local renal growth hormone-IGF-I system may participate in the natural repair. We examined the IGF-I system in rat kidneys subjected to 60 minute ischemia compared to sham operated controls. Two days after injury, growth hormone receptor mRNA and IGF-I mRNA levels fell approximately 9 to 33% of control values. This was associated with a reduction in kidney immunoreactive IGF-I levels. In contrast, IGF-I receptor mRNA abundance was unchanged. However, plasma membrane IGF-I receptor binding on day 2 and day 7 was near double the control values (P < 0.01). Scatchard analysis revealed a near twofold increase in receptor number. Since receptor mRNA levels were unchanged, this implies receptor protein up-regulation. In contrast to unchanged IGF-I receptor mRNA levels, the abundance of mRNA levels of insulin-like growth factor binding proteins (IGFBP) -2, -3, -4 and -5 fell approximately 14 to 62% of control levels day 2 after injury (P < 0.05), suggesting reduced IGFBP production. Thus, the renal response to ischemic ATN, namely, low IGFBP mRNA levels and high IGF-I receptor number, may function to increase IGF-I bioavailability and thereby enhance the reparative actions of local and circulating IGF-I in ischemic ATN.

Expression of insulin-like growth factor and binding protein genes during nephrogenesis

To study the role of insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) in human nephrogenesis, we examined the temporal and spatial pattern of expression of these genes using in situ hybridization. The uninduced metanephric blastema (MB) expressed abundant IGF-II mRNA. With induction by the ureteric duct (UD), the aggregated MB additionally expressed IGFBP-2 and IGFBP-4 mRNAs. The mature UD expressed IGFBP-3 mRNA while the ampulla in contact with the MB lacked IGFBP-3 mRNA and expressed IGFBP-2 exclusively. Upon formation of the S-shape nephron, IGFBP-2 mRNA was expressed in the committed glomerular and epithelial cells which also expressed IGF-II and IGFBP-4, and the mesenchyme of the vascular cleft expressed IGFBP-5 mRNA. In the maturing glomerulus, the glomerular epithelial cells expressed IGF-II mRNA together with IGFBP-2 and IGFBP-4 mRNAs, while IGFBP-5 mRNA was localized to the mesangium and supporting mesenchyme. As the proximal tubule was formed the epithelium expressed less of IGFBP-2 mRNA and more of IGFBP-4 mRNA. The renal mesenchyme in the cortex and medulla expressed abundant IGF-II mRNA, and lower levels of IGFBP-4 and -5 mRNAs. The epithelium of the collecting ducts and pelvicalyceal system expressed abundant IGFBP-3. In contrast, IGF-I, IGFBP-1, and IGFBP-6 mRNAs were expressed at low levels. The specific temporal and spatial pattern of expression of IGFBP genes on the background of abundant IGF-II gene expression suggests that the IGFBP peptides, as modulators of IGF action, are expressed locally at specific points of nephrogenesis to interact with IGF-II to regulate mesenchymal induction, renal epithelial cell commitment, differentiation and growth.

Direct demonstration of insulin-like growth factor-I-induced nitric oxide production by endothelial cells

Several lines of evidence indicate that insulin-like growth factor-I (IGF-I) is a potent mediator of vasodilation. To elucidate the mechanism and site of action of IGF-I, we performed continuous monitoring of nitric oxide (NO) release from endothelial cells using a highly-sensitive amperometric NO-sensor. Two types of cultured cells were used: human umbilical vein endothelial cells and immortalized rat renal interlobar artery endothelial cells. In separate experiments, [Ca2+]i changes in response to IGF-I were measured spectrofluorometrically in fura-2-loaded cells. Stimulation with IGF-I resulted in a rapid, dose-dependent increase in [NO] as detected by the NO-probe positioned 1 mm above the monolayers, followed by a sustained elevation lasting for at least five minutes. The effect of IGF-I was significantly suppressed by pretreatment with anti-IGF-I antibody, suggesting that it was specific for IGF-I. NG-nitro-L-arginine methyl ester, an inhibitor of NO synthesis, significantly blunted responses to IGF-I, but dexamethasone preincubation did not reduce the IGF-I-induced release of NO. These results indicate that the observed IGF-I-induced release of NO is a result of activation of the constitutive, rather than the inducible type of NO synthase in endothelial cells. Genistein, a tyrosine kinase inhibitor, resulted in a profound suppression of the IGF-I-induced release of NO. IGF-I did not affect [Ca2+]i in either type of cells. Therefore, IGF-I-induced NO production by both types of endothelial cells is mediated via a tyrosine kinase-dependent mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-like growth factor (IGF)-I, -II and IGF binding protein-2 (IGFBP-2) in the plasma of children with Wilms' tumour

Insulin-like growth factors (IGF)-I, -II and IGF binding protein-2 (IGFBP-2) have been measured in plasma of children with Wilms' tumour. The mean levels for total serum IGF-I and -II were not significantly altered in Wilms' tumour as compared with normal control plasma. However, the chromatographic profiles for IGF-I and -II in these groups were different with regard to the presence of IGF binding proteins and high molecular weight forms of IGFs; the high molecular weight form (9-15 kD) of IGF-II was significantly reduced in Wilms' tumour. Levels of IGFBP-2 were substantially elevated in serum from Wilms' tumour patients (1025 +/- 112 ng/ml compared with 416 +/- 44 ng/ml in controls), and inversely correlated with the levels of high molecular weight forms of IGF-II. We suggest that IGFBP-2 measurements might be of value as a marker for monitoring this type of tumour, either as an adjunct to diagnosis or surveillance of tumour growth during therapy.