Insulin-like Growth Factor Binding Protein-4 Levels Research Articles

Insulin-like growth factor binding Protein-4: A novel indicator of pulmonary arterial hypertension severity and survival.

Proteomic analysis of patients with pulmonary arterial hypertension (PAH) has demonstrated significant abnormalities in the insulin-like growth factor axis (IGF). This study proposed to establish associations between a specific binding protein, insulin-like growth factor binding protein 4 (IGFBP4), and PAH severity as well as survival across varying study cohorts. In all cohorts studied, serum IGFBP4 levels were significantly elevated in PAH compared to controls (p < 0.0001). IGFBP4 concentration was also highest in the connective tissue-associated PAH (CTD-PAH) and idiopathic PAH subtypes (876 and 784 ng/mL, median, respectively). After adjustment for age and sex, IGFBP4 was significantly associated with worse PAH severity as defined by a decreased 6-min walk distance (6MWD), New York heart association functional class (NYHA-FC), REVEAL 2.0 score and higher right atrial pressures. In longitudinal analysis provided by one of the study cohorts, IGFBP4 was prospectively significantly associated with a shorter 6MWD, worse NYHA-FC classification, and decreased survival. Cox multivariable analysis demonstrated higher serum IGFBP4 as an independent predictor of survival in the overall PAHB cohort. Therefore, this study established that higher circulating IGFBP4 levels were significantly associated with worse PAH severity, decreased survival and disease progression. Dysregulation of IGF metabolism/growth axis may play a significant role in PAH cardio-pulmonary pathobiology.

IGFBP-4: A promising biomarker for lung cancer.

Background: Insulin-like growth factor binding protein-4 (IGFBP-4), a member of the insulin-like growth factor (IGF) family, transports, and regulates the activity of IGFs. The pregnancy-associated plasma protein-A (PAPP-A) has proteolytic activity towards IGFBP-4, and both proteins have been associated with a variety of cancers, including lung cancer. Thus, we aimed to evaluate the use of IGFBP-4 and PAPP-A as potential biomarkers for lung cancer. Methods: Eighty-three volunteers, including 60 patients with lung cancer and 23 healthy individuals, were included in this study. The patients with lung cancer were selected based on their treatment status, histological subgroup, and stage of the disease. Enzyme-linked immunosorbent assays were used to assess the serum levels of IGFBP-4 and PAPPA, whereas the IGF-1 levels were measured using a chemiluminescent immunometric assay. Results: The serum IGFBP-4 levels in all patient groups, regardless of the treatment status and histological differences, were significantly higher than those in the control group (p<0.005). However, the serum PAPP-A levels in the untreated patient group were found to be higher than those in the control group, but this difference was not statistically significant (p=0.086). Conclusions: The serum PAPP-A and IGFBP-4 levels are elevated in lung cancer. However, IGFBP-4 may have better potential than PAPP-A as a lung cancer biomarker.

Depot-specific and GH-dependent regulation of IGF binding protein-4, pregnancy-associated plasma protein-A, and stanniocalcin-2 in murine adipose tissue

IntroductionPregnancy-associated plasma protein-A (PAPP-A) stimulates insulin-like growth factor (IGF)-I action through proteolytic cleavage of IGF binding protein-4 (IGFBP-4). Recently, stanniocalcin-2 (STC2) was discovered as an inhibitor of PAPP-A. Most members of the IGF system are expressed in adipose tissue (AT), but there is a relative paucity of information on the distribution of IGFBP-4, PAPP-A, and STC2 in different AT depots. Since IGF-I expression in AT is highly GH-dependent, we used bovine GH transgenic (bGH) and GH receptor knockout (GHR−/−) mice to investigate AT depot-specific expression patterns of IGFBP-4, PAPP-A, and STC2, and whether the regulation is GH-dependent. MethodsSeven-month-old male bGH, GHR−/− and wild type (WT) control mice were used. Body composition was determined, and subcutaneous, epididymal, retroperitoneal, mesenteric and brown adipose tissue (BAT) depots were collected. RNA expression of Igfbp4, Pappa, and Stc2 was assessed by reverse transcription quantitative PCR and IGFBP-4 protein by Western blotting. ResultsIgfbp4, Pappa, and Stc2 RNA levels were differentially expressed in an AT depot-dependent manner in WT mice. Igfbp4 RNA levels were significantly higher in all white AT depots than in BAT. Pappa was most highly expressed in the mesenteric depot: levels were 7.5-fold higher in mesenteric than in subcutaneous AT (p < .001). Although intraabdominal in origin, epididymal and retroperitoneal Pappa expression levels were 69% and 68% lower, respectively, as compared to mesenteric levels (p < .001). Stc2 RNA expression was significantly higher in all intraabdominal white AT as compared to subcutaneous AT and BAT; levels in epididymal, retroperitoneal, and mesenteric were all more than three-fold higher than in subcutaneous AT (p < .001) and 12-fold higher than in BAT (p < .001). Gene expression patterns in bGH and GHR−/− mice mimicked those in WT mice, suggesting that GH does not affect the transcription of the STC2-PAPP-A-IGFBP-4-axis in AT. However, proteins levels of intact IGFBP-4 were significantly increased in bGH mice and decreased in GHR−/− mice, whereas the PAPP-A-generated IGFBP-4 fragment level was unaltered. ConclusionExpression of Igfbp4, Pappa, and Stc2 differ between AT depots and is generally higher in white AT than in BAT. The transcription appears to occur in a GH-independent manner, whereas IGFBP-4 protein levels are highly influenced by altered GH activity.

Pregnancy-associated plasma protein-A (PAPP-A) levels in patients with severe allergic asthma are reduced by omalizumab

ABSTRACTBackground: Remodeling is a crucial feature of severe asthma and may be associated with activation of the allergic cascade by immunoglobulin E (IgE). Omalizumab, an anti-IgE monoclonal antibody, effectively targets the severe allergic asthma phenotype. Pregnancy-associated plasma protein-A (PAPP-A) is an insulin-like growth factor binding protein-4 (IGFBP-4) protease, increasing local insulin-like growth factor (IGF)-1 concentrations, which in turn initiating a cascade involved in the regulation of cell growth, differentiation, and proliferation in various tissues. In the present study, we evaluated the effects of omalizumab on serum PAPP-A, IGFBP-4, and IGF-1 levels in subjects with severe allergic asthma. Methods: We studied 36 asthmatic subjects and 36 healthy controls. An ultrasensitive enzyme-linked immunosorbent assay (ELISA) kit was used to measure serum PAPP-A levels, and routine commercial ELISA kits were employed to assess serum levels of IGF-1, IGFBP-4 in control subjects and asthmatic subjects before therapy (baseline) and after six months of omalizumab therapy in patients with severe asthma. Results: Compared to control subjects, serum PAPP-A and IGFB-4 levels were significantly higher in asthmatic subjects (both p values < 0.001). However, the serum IGF-I levels of asthmatic subjects were similar to those of control subjects (p > 0.05). In asthma subjects, 6-month omalizumab treatment significantly decreased the serum PAPP-A (p < 0.001), IGF-I (p = 0.031), and IGFB4 (p = 0.025) levels. Conclusion: PAPP-A level may be a useful biomarker for predicting airway remodeling in patients with severe asthma receiving omalizumab, and may also reflect the response to treatment.

IGFBP-4 expression is adversely associated with lung cancer prognosis.

Insulin-like growth factor binding protein-4 (IGFBP-4) was reported to be associated with prognosis in several types of cancer; however, to the best of our knowledge, whether it is correlated with lung cancer has yet to be reported. In the present study, 102 pairs of lung cancer tissues and surrounding non-cancerous tissues (SNCTs) were collected. The IGFBP-4 levels in tissues were detected with immunohistochemistry. The relevance of IGFBP-4 to the survival of patients was assessed. The IGFBP-4 gene was knocked down, and its function in the proliferation of lung cancer cells was measured. The percentage of lung cancer tissues with higher IGFBP-4 expression than SNCTs (51.9%) was increased compared with the percentage with similar (11.76%) or lower (36.27%) IGFBP-4 expression. Patients with higher IGFBP-1 expression exhibited a shorter median survival time. IGFBP-1 was associated with metastasis, lung cancer stages and malignancy, but not with age, sex or tumor size. Lung cancer cells with stably knocked down IGFBP-4 showed an inhibitory proliferation rate. The present study identified that IGFBP-4 was adversely associated with the prognosis of lung cancer patients. IGFBP-4 knockdown prohibited lung cancer cell growth. The present study provides a potential marker for lung cancer diagnosis and a possible target for lung cancer therapy.

Insulin-Like Growth Factor Binding Protein-4 as a Marker of Chronic Lupus Nephritis.

Kidney biopsy remains the mainstay of Lupus Nephritis (LN) diagnosis and prognostication. The objective of this study is to identify non-invasive biomarkers that closely parallel renal pathology in LN. Previous reports have demonstrated that serum Insulin-like growth factor binding protein 4 (IGFBP-4) was increased in diabetic nephropathy in both animal models and patients. We proceeded to assess if IGFBP4 could be associated with LN. We performed ELISA using the serum of 86 patients with LN. Normal healthy adults (N = 23) and patients with other glomerular diseases (N = 20) served as controls. Compared to the healthy controls or other glomerular disease controls, serum IGFBP-4 levels were significantly higher in the patients with LN. Serum IGFBP-4 did not correlate well with systemic lupus erythematosus disease activity index (SLEDAI), renal SLEDAI or proteinuria, but it did correlate with estimated glomerular filtration rate (R = 0.609, P < 0.0001). Interestingly, in 18 patients with proliferative LN whose blood samples were obtained at the time of renal biopsy, serum IGFBP-4 levels correlated strongly with the chronicity index of renal pathology (R = 0.713, P < 0.001). IGFBP-4 emerges a potential marker of lupus nephritis, reflective of renal pathology chronicity changes.

Circulating Insulin-like Growth Factor Binding Protein-4

Objective: Insulin-like growth factor binding protein-4 (IGFBP-4), inhibits IGF actions under a variety of experimental conditions. Parathyroid hormone (PTH), 1.25-hydroxy(OH)vitamin D, IGF-I, IGF-II and transforming growth factor (TGF)-b are the major regulators of IGFBP-4 production in vitro. However, little is known about the in vivo regulation of circulating IGFBP-4 in humans.Methods: We measured serum concentrations of calcium (Ca), phosphorus (P), alkaline phosphatase (ALP), PTH, vitamin D, IGF-I, IGFBP-3, and IGFBP-4 in infants (n=22) with nutritional rickets before and after treatment of rickets with vitamin D (300 000 U single dose po).Results: The mean±SD age of the patients was 1.3±1.6 years (range 0.2-3). Serum Ca and P increased, whereas ALP and PTH decreased after treatment (Ca from 6.6±1.4 to 9.5±1.6 mg/dL, P from 3.9±1.4 to 5.4±0.8 mg/dL, ALP from 2590±2630 to 1072±776 IU/mL and PTH from 407±248 to 27.4±20.8 ng/dL, respectively). Vitamin D levels were low (7.8±2.5 ng/mL) and increased after treatment (18.1±4.0 ng/mL, p<0.001). Serum IGF-I and IGFBP-3 levels both increased after treatment (IGF-I: 13.5±12.2 vs. 23.7±14.2 ng/mL, p<0.001 and IGFBP-3: 1108±544 vs. 1652±424 ng/mL, p<0.001). However, serum IGFBP-4 levels did not change significantly after treatment (18.8±8.0 vs. 21.5±4.8 ng/mL). No correlation between PTH and IGF-I, IGFBP-3 or IGFBP-4 was detected. Significant correlations were observed between PTH and ALP (r=0.53, p<0.05), and between IGF-I and IGFBP-3 (r=0.46, p<0.05).Conclusion: The results demonstrate that contrary to in vivo studies, circulating IGFBP-4 levels are not influenced by secondary hyperparathyroidism in vitamin D deficiency rickets since IGFBP-4 levels did not change after normalization of PTH with vitamin D treatment.Conflict of interest:None declared.

Comparison of follicular fluid insulin-like growth factor II and insulin-like growth factor binding protein 4 levels between short 7-day and long gonadotropin-releasing hormone agonist protocols

OBJECTIVE: Insulin-like growth factor II (IGF-II) and Insulin-like growth factor binding protein 4 (IGFBP-4) play a major role in the autocrine and paracrine regulation of folliculogenesis. To explore the individual influence on the intrafollicular microenvironment between the short 7-day gonadotropin-releasing hormone agonist (GnRHa) protocol (7-day protocol) and GnRHa long protocol (long protocol) by comparing the concentrations of IGF-II, IGFBP-4, and the ratio of IGF-II/IGFBP-4 in follicular fluid. DESIGN: Prospective randomized controlled study. MATERIALS AND METHODS: 88 infertile patients with tubal factor who accepted IVF treatment from July to October 2007 were included in this study. 7-day protocol group (n=44): GnRHa (decapeptyl, Ferring) was injected 0.1 mg daily from day 2 of the menstrual cycle to day 8. At the same time gonadotropin (Gn) was injected daily from day 3. Long protocol group (n=44): GnRHa (diphereline, Ferring) was injected 1.88 mg singly in the mid-luteal phase of previous menstrual cycle. Once the patient was down regulated, gonadotropin injection was started. Follicular fluid was obtained from dominant follicles during oocyte retrieval. The levels of IGF-II and IGFBP-4 in follicular fluid were detected separately by radioimmunoassay and enzyme-linked immunosorbent assay. RESULTS: The durations of controlled ovarian stimulation was significantly shorter and total dose of Gn used were significantly lower in the 7-day protocol group. The levels of serum E2 and E2 per mature follicle on the day of hCG injection, the number of oocytes retrieved, fertilization rate, cleaved embryos rate, top-quality embryos rate, implantation rate, pregnancy rate, and clinical abortion rate were similar between the two groups. The concentrations of IGF-II (0.17±0.06ng/ml vs 0.20±0.07 ng/ml, P=0.020) and IGFBP-4 (2915.48±1443.02pg/ml vs 3646.64±1818.67pg/ml, P=0.040) in follicular fluid of the 7-day protocol group patients were significantly lower. There was no significant difference in the ratio of IGF-II/IGFBP-4 (0.07±0.04 vs 0.07±0.03, P=0.471) between the 7-day and long protocol group. Linear correlation analysis showed that the level of follicular fluid IGF-II was positively correlated to total dose of Gn used (r=0.316, P <0.05). CONCLUSIONS: The short 7-day and long GnRHa protocols may affect the concentrations of follicular fluid IGF-II and IGFBP-4. However, the changes of follicular fluid IGF-II and IGFBP-4 concentrations may not contribute to different clinical outcomes.

Insulin-like Growth Factor-Binding Protein 4 in Children with Acute Lymphoblastic Leukemia

Insulin-like growth factor-binding protein 4 (IGFBP-4) is a potent inhibitor of IGF-mediated cell proliferation. To investigate the functional relevance of IGFBP-4 in leukemia, we measured plasma IGFBP-4 levels and messenger RNA expression in leukemic cell clones of patients with acute lymphoblastic leukemia (ALL) and in control subjects. The IGFBP-4 levels of ALL patients at diagnosis were significantly lower than the levels of healthy control subjects. We evaluated the patients at diagnosis and after 33 days of chemotherapy and found plasma IGFBP-4 levels at day 33 to be significantly lower than the levels at diagnosis. There was no correlation of plasma IGFBP-4 level with age, sex, immunophenotype, or ALL risk group, and there was no correlation of IGFBP-4 level with plasma IGF-I, IGF-II, IGFBP-1, IGFBP-2, and IGFBP-3 levels. Gene expression analysis of the leukemic blast population at diagnosis revealed that the leukemic clones did not significantly contribute to systemic IGFBP-4 levels. The decrease in plasma IGFBP-4 levels during chemotherapy represents an indirect effect, probably caused by the chemotherapeutic effects on IGFBP-4-expressing cells of the liver and other organs. In addition, IGFBP-4 gene expression was investigated in 13 human immune cell-related cell lines by reverse transcription-polymerase chain reaction analysis. IGFBP-4 was exclusively expressed in cell lines derived either from B-cells or from myelomonocytic cells, whereas IGFBP-4 was not expressed in T-cell lines.

Targeted Expression of a Protease-resistant IGFBP-4 Mutant in Smooth Muscle of Transgenic Mice Results in IGFBP-4 Stabilization and Smooth Muscle Hypotrophy

The insulin-like growth factor-binding protein 4 (IGFBP-4), the most abundant IGF-binding protein produced by rodent smooth muscle cells (SMC), is degraded by specific protease(s) potentially releasing IGF-I for local bioactivity. IGFBP-4 protease(s) recognizes basic residues within the midregion of the molecule. We constructed a mutant IGFBP-4 with the cleavage domain substitution 119-KHMAKVRDRSKMK-133 to 119-AAMAAVADASAMA-133. Myc-tagged native and IGFBP-4.7A retained equivalent IGF-I binding affinity. Whereas native IGFBP-4 was cleaved by SMC-conditioned medium, IGFBP-4.7A was completely resistant to proteolysis. To explore the function of the protease-resistant IGFBP-4 in vivo, expression of the mutant and native proteins was targeted to SMC of transgenic mice by means of a smooth muscle alpha-actin promoter. Transgene expression was confined to SMC-rich tissues in all lines. Bladder and aortic immunoreactive IGFBP-4/transgene mRNA ratios in SMP8-BP4.7A mice were increased by 2- to 4-fold relative to SMP8-BP4 mice, indicating that the IGFBP-4.7A protein was stabilized in vivo. SMP8-BP4.7A mice had lower aortic, bladder, and stomach weight and intestinal length relative to SMP8-BP4 counterparts matched for protein expression by Western blotting. Thus, IGFBP-4.7A results in greater growth inhibition than equivalent levels of native IGFBP-4 in vivo, demonstrating a role for IGFBP-4 proteolysis in the regulation of IGF-I action.

Plasma levels of insulin-like growth factor binding protein-4 (IGFBP-4) under normal and pathological conditions.

Insulin-like growth factor binding protein-4 (IGFBP-4) belongs to a family of six structurally related IGF-binding proteins that are involved in the modulation of the biological effects of the IGFs. In order to obtain more insight into the clinical significance and regulation of IGFBP-4 in vivo we determined the levels of this protein by a specific radioimmunoassay in the human circulation under normal and various pathological conditions. Selected human biological fluids and plasma samples from 804 normal healthy males and females, ranging from 0 to 78 years of age, were analysed. In addition, plasma samples from patients with several disorders (i.e. hypothyroidism, hyperthyroidism, GH-deficiency, acromegaly, cancer, chronic renal failure corticosteroid-treatment) were investigated. A specific RIA for hIGFBP-4 was developed, using a rabbit polyclonal antibody raised against a synthetic peptide containing amino acids 80-103 of the mature hIGFBP-4 sequence. In normal individuals circulating IGFBP-4 levels in males did not change with age. For females the values tended to increase slightly in older age. Overall, the mean +/- SD for males and females (189 +/- 83 microg/l and 193 +/- 72 microg/l, respectively) were not different. Normative range values of IGFBP-4 correlated weakly with those of IGF-II (r = 0.31, P < 0.001). Neither hypothyroidism nor hyperthyroidism appeared to influence circulating IGFBP-4 levels since the levels were within the normal range. Both GH status and pharmacological doses of glucocorticoids, as employed in various chronic diseases, did not seriously affect plasma IGFBP-4 either. Under conditions with increased circulating PTH levels, i.e. dialysed adult patients with chronic renal failure (CRF) and subjects with hyperparathyroidism, a weak positive relationship was noted between the plasma contents of IGFBP-4 and PTH. An excess of IGFBP-4 was found in plasma of both nondialysed and dialysed prepubertal growth retarded children with chronic renal failure (CRF) (mean SDS: 10.75 and 5.78, respectively). IGFBP-4 levels were inversely related to glomerular filtration rate. Similar results were obtained for dialysed adults with CRF. In a group of CRF children who had undergone renal transplantation, circulating IGFBP-4 levels were markedly lower (mean SDS: 3.75). There was no evidence for an increased secretion of IGFBP-4 in the circulation of most of the cancer patients with solid tumours. Several children with acute lymphoblastic leukaemia, however, showed elevated plasma IGFBP-4 levels (mean SDS: 1.27). The presence of IGFBP-4 could also be demonstrated in other human biological fluids. The highest amounts were found in amniotic fluid (391-717 microg/l) and follicular fluid (249-500 microg/l). Measurement of plasma IGFBP-4 has been shown so far to be of minor clinical relevance. However, the results indicate that different concentration gradients between plasma and various other body fluids may exist. Therefore, it may well be that certain pathophysiological stimuli induce significant alterations in the local turnover rate of IGFBP-4 but that they are not reflected by changes in the circulating levels. The possibility of quantifying IGFBP-4 by RIA will facilitate further in vitro and in vivo studies on its regulation and function in humans.

A new radioimmunoassay to measure rat insulin-like growth factor binding protein-4 (IGFBP-4) in serum, wound fluid and conditioned media.

Insulin-like growth factor binding protein-4 (IGFBP-4) is, like the other five IGFBPs, a critical regulator of the activity of insulin-like growth factor-I (IGF-I) and IGF-II. Because of the possible role of IGFBP-4 in multiple systems including reproduction, pregnancy, bone formation and wound healing, we developed a radioimmunoassay (RIA) to measure the concentration of IGFBP-4 in the serum, extracellular fluid and conditioned media of cells of rodents so that these animal models could be better exploited. Rat IGFBP-4 was expressed in Escherichia coli and purified to homogeneity. The recombinant material was used to raise a rabbit polyclonal antibody against rat IGFBP-4 and for iodination and standards. The RIA developed was sensitive to less than 1 ng/mL of rat IGFBP-4 and IGF-I did not interfere. There was no cross-reactivity with other rat IGFBPs on immuno-Western analysis of serum and wound fluid. IGFBP-4 from mouse serum did cross-react in our assay; however, serum from horse, pig or human showed no cross-reaction. Human IGFBP-1 and IGFBP-3 showed a very weak cross-reactivity. Serum IGFBP-4 levels showed no gender difference but did reveal a significant 66% increase in older rats. During the course of wound healing, which is IGF-I dependent, IGFBP-4 showed no changes. In conclusion an RIA for rat IGFBP-4 has been developed that specifically measures the concentration of IGFBP-4 in the sera, extracellular fluid and conditioned media of rodents. With this assay, the role of IGFBP-4 and IGFs in growth, development and the function of multiple systems can be further investigated using rodent models.

Overexpression of insulin-like growth factor-binding protein-4 (IGFBP-4) in smooth muscle cells of transgenic mice through a smooth muscle alpha-actin-IGFBP-4 fusion gene induces smooth muscle hypoplasia.

Insulin-like growth factor I (IGF-I) has been postulated to function as a smooth muscle cell (SMC) mitogen and to play a role in the pathogenesis of bladder hypertrophy, estrogen-induced uterine growth, and restenosis after arterial angioplasty. IGF-binding protein-4 (IGFBP-4) inhibits IGF-I action in vitro and is the most abundant IGFBP in the rodent arterial wall. To explore the function of this binding protein in vivo, transgenic mouse lines were developed harboring fusion genes consisting of a rat IGFBP-4 complementary DNA cloned downstream of either a -724 bp fragment of the mouse smooth muscle alpha-actin 5'-flanking region (SMP2-BP-4) or -1074 bp, 63 bp of 5'-untranslated region, and 2.5 kb of intron 1 of smooth muscle alpha-actin (SMP8-BP-4). SMP2-BP-4 mice expressed low levels of the exogenous IGFBP-4 messenger RNA (mRNA), which was not specifically targeted to SMC-rich tissue environments, and were therefore not analyzed further. Six SMP8-BP-4 transgenic lines derived from separate founders were characterized. Mating of hemizygous SMP8-BP-4 mice with controls produced about 50% transgenic offspring, with equal sex distribution. Expression of IGFBP-4 mRNA in nontransgenic littermates was maximal in liver and kidney. By contrast, transgenic IGFBP-4 mRNA expression, distinguished because of a smaller transcript size, was confined to SMC-containing tissues, with the following hierarchy: bladder > aorta > stomach = uterus. There was no transgene expression in skeletal muscle, brain, or cardiac myocytes. The abundance of IGFBP-4 measured by Western ligand blotting or by immunoblotting, was 8- to 10-fold higher in aorta and bladder of SMP8-BP-4 mice than in their nontransgenic littermates, with no change in plasma IGFBP-4 levels. Transgenic mice exhibited a significant reduction in wet weight of SMC-rich tissues, including bladder, intestine, aorta, uterus, and stomach, with no change in total body or carcass weight. In situ hybridization showed that transgene expression was targeted exclusively to the muscular layers of the arteries, veins, bladder, ureter, stomach, intestine, and uterus. Overexpression of IGFBP-4 was associated with SMC hypoplasia, a reciprocal phenotype to that of transgenic mice overexpressing IGF-I under control of the same promoter (SMP8-IGF-I). Double transgenic mice derived from mating SMP8-BP-4 with SMP8-IGF-I animals showed a modest decrease in wet weight at selected SMC tissues. Although we cannot exclude that the effects of IGFBP-4 may be IGF independent, these data suggest that IGFBP-4 is a functional antagonist of IGF-I action on SMC in vivo.

Potent Inhibition of Human Ovarian Steroidogenesis by Insulin-Like Growth Factor Binding Protein-4 (IGFBP-4)

Several studies have now documented the existence of IGFBPs in follicular fluid and their correlation with the health of the follicle. In particular, increased levels of IGFBP-4 have been reported in androgen-dominant atretic follicles and those from polycystic ovaries. The aim of this study was to elucidate the role of IGFBP-4 in ovarian steroidogenesis. Granulosa cells and theca tissue were incubated with or without LH or FSH in the presence or absence of IGFBP-4 (0.5–50 ng/ml). Inhibition by IGFBP-4 of estradiol production in the presence of testosterone alone was seen in three of four experiments. IGFBP-4 completely inhibited FSH-stimulated estradiol production in three experiments and caused 67% inhibition in a fourth. Similar results were obtained for theca, in which concurrent incubation with IGFBP-4 completely negated the stimulatory effects of LH on androstenedione production. The mechanism by which IGFBP-4 exerts these potent effects and the possibility that this may be IGF-independent are currently being investigated.

Potent Inhibition of Human Ovarian Steroidogenesis by Insulin-Like Growth Factor Binding Protein-4 (IGFBP-4)

Several studies have now documented the existence of IGFBPs in follicular fluid and their correlation with the health of the follicle. In particular, increased levels of IGFBP-4 have been reported in androgen-dominant atretic follicles and those from polycystic ovaries. The aim of this study was to elucidate the role of IGFBP-4 in ovarian steroidogenesis. Granulosa cells and theca tissue were incubated with or without LH or FSH in the presence or absence of IGFBP-4 (0.5-50 ng/ml). Inhibition by IGFBP-4 of estradiol production in the presence of testosterone alone was seen in three of four experiments. IGFBP-4 completely inhibited FSH-stimulated estradiol production in three experiments and caused 67% inhibition in a fourth. Similar results were obtained for theca, in which concurrent incubation with IGFBP-4 completely negated the stimulatory effects of LH on androstenedione production. The mechanism by which IGFBP-4 exerts these potent effects and the possibility that this may by IGF-independent are currently being investigated.

Transforming growth factor- α stimulates insulin-like growth factor binding protein-4 (IGFBP-4) expression and blocks follicle-stimulating hormone regulation of IGFBP-4 production in rat granulosa cells

The ability of TGF- α to regulate insulin-like growth factor binding protein-4 (IGFBP-4), was investigated. Primary cultures of rat granulosa cells (GC) were grown in serum-free medium with rat (r) TGF- α and/or rFSH, and secreted IGFBP-4 protein and its steady state mRNA levels were measured by Western immunoblotting and Northern blotting, respectively. Control (untreated) cells secreted IGFBP-4 spontaneously, and the levels were increased by rTGF- α in a dose- and time-dependent manner. rTGF- α abolished FSH-induced IGFBP-4 protease activity and suppressed FSH-dependent effects on IGFBP-4 production. IGFBP-4 mRNA levels were decreased and increased by FSH and TGF- α, respectively, and TGF- α blocked the FSH effects. These results demonstrate that TGF- α is a potent stimulator of IGFBP-4 expression in rat GC and can overcome the regulatory effects of FSH on IGFBP-4 production. The consequence of these TGF- α effects is a marked, sustained increase in the levels of IGFBP-4 in the microenvironment.

Regulation of insulin-like growth factor-binding protein-4 protease activity by estrogen and parathyroid hormone in SaOS-2 cells: implications for the pathogenesis of postmenopausal osteoporosis.

The cellular mechanisms involved in the accelerated bone loss occurring in association with estrogen deprivation as seen following the menopause are not fully understood. Insulin-like growth factor-I (IGF-I) is the local regulator of osteoblasts and one of its binding proteins, insulin-like growth factor-binding protein-4 (IGFBP-4), binds to IGF-I and suppresses biological activity. Previous studies have shown that the binding activity of IGFBP-4 in the conditioned medium of parathyroid hormone (PTH)-treated SaOS-2 osteoblastic-like cells is enhanced twofold and that this PTH-enhanced IGFBP-4 binding activity is abolished by 17 beta-estradiol. Levels of IGFBP-4 in the conditioned medium have been reported to be regulated not only at the level of production but also at the level of degradation which is catalyzed by a protease that specifically cleaves IGFBP-4. We have, therefore, studied the effects of 17 beta-estradiol and PTH on IGFBP-4 protease activity using SaOS-2 cells. SaOS-2 cells produce a protease that specifically cleaves IGFBP-4 into two fragments of approximately 18 and 14 kilodaltons. IGFBP-4 protease activity in the conditioned medium from PTH-treated cells was suppressed, while this PTH-induced suppression of protease activity was reversed by the addition of 17 beta-estradiol to the cultures. IGFBP-4 proteolytic activity was stimulated by IGF-I or IGF-II added exogenously and was inhibited by EDTA or protease inhibitors. IGFBP-4 proteolyzed in the conditioned medium from cells treated with PTH and 17 beta-estradiol was less effective at inhibiting IGF-I-stimulated [3H]thymidine incorporation into DNA compared with that proteolyzed in the conditioned medium from PTH-treated cells. The simplest explanation is that 17 beta-estradiol suppressed the inhibitory effect of PTH on osteoblastic activity by inhibiting the PTH-induced suppression of IGFBP-4 protease activity.

Thyroid hormone and retinoic acid induce the synthesis of insulin-like growth factor-binding protein-4 in mouse osteoblastic cells.

Thyroid hormone (T3) is a known regulator of the transcription rate of specific genes. By subtractive hybridization of T2-treated osteoblastic cells, differentially expressed messenger RNAs (mRNAs) were enriched in the form of double stranded complementary DNA (cDNA) fragments. Sequencing of a differentially expressed cDNA that detects a 2.6-kilobase mRNA in Northern blots revealed to homology in the EMBL-Genebank data bases. A mouse genomic library was screened, and the isolated genomic DNA was identified as part of the insulin-like growth factor-binding protein-4 (IGFBP-4) gene including the 3'-untranslated region to which the cloned cDNA fragment was mapped by sequencing. We observed an up-regulation of the 2.6-kilobase IGFBP-4 mRNA transcript in the presence of T3 or retinoic acid. The induction of the IGFBP-4 transcript persisted up to 48 h. This response was inhibited by cycloheximide as well as actinomycin D. Long term induction studies revealed that the T3 effect is present during the complete culture period, with a constant rise in IGFBP-4 mRNA levels until 14 days. Under these culture conditions, the DNA content of MC3T3-E1 cells were significantly reduced by T3 and retinoic acid, indicating the repressive effect of both hormones on cell growth. Western immunoblots showed that the transcriptional induction is consequently transduced to increased IGFBP-4 levels in the conditioned medium of T3-treated cells. Our data show that thyroid hormone and retinoic acid stimulate transcription of IGFBP-4 mRNA in osteoblasts, resulting in increased IGFBP-4 secretion into the medium. IGFBP-4, a known inhibitor of cellular proliferation, might contribute to the antiproliferative effect of T3 and retinoic acid on osteoblasts.

Estrogen- but not androgen-dominant human ovarian follicular fluid contains an insulin-like growth factor binding protein-4 protease.

Estrogen-dominant follicular fluid (FFe) and granulosa-luteal cell conditioned media, in contrast to androgen-dominant FF (FFa), contain barely detectable levels of insulin-like growth factor binding protein-4 (IGFBP-4) by ligand binding techniques. The current study was designed to evaluate the possibility of an IGFBP-4 protease in FFe, which may alter the affinity of IGFBP-4 for insulin-like growth factors (IGFs), rendering IGFBP-4 undetectable by ligand binding techniques. FFe and FFa were obtained from regularly menstruating women, and FFe was also obtained during in vitro fertilization procedures. Mixing experiments were performed by using human recombinant IGFBP-4 or IGFBP-4 in nonpregnancy serum (NPS) as substrate and FF as the source of the putative protease. Incubation of NPS at 37C for 5 h in the presence of FFe resulted in the reduction of IGFBP-4 to barely detectable levels when analyzed by Western ligand blotting, with no change occurring in the levels of the other binding proteins present in NPS. In contrast, incubation of FFa with NPS under similar conditions had no effect on the levels of IGFBP-4. The disappearance of IGFBP-4 when NPS was mixed with FFe exhibited optimal pH-dependence at pH 7-9. Inhibition of the putative protease by aprotinin, ethylenediaminetetraacetic acid, and 1,10-phenanthroline supports its identification as a metalloserine protease. Western immunoblot analysis detected the presence of a proteolytic fragment of approximately 17-18 kDa after incubation of recombinant IGFBP-4 in the presence of FFe but not in the presence of FFa. Similar incubation of other recombinant human IGFBPs did not reveal their degradation, further suggesting that the protease in FFe is specific for IGFBP-4. These data demonstrate the presence of an IGFBP-4-specific metalloserine protease in FFe but not in FFa, and they suggest that proteolytic cleavage may be responsible for effectively decreasing levels of inhibitory IGFBP-4 and thus increasing bioavailability of IGF peptides within estrogen-dominant follicles. The importance of this mechanism may lie in providing the dominant follicle with more available IGFs to synergize with gonadotropins in stimulating estradiol production and in inhibiting this synergy in androgen-dominant and atretic follicles.

Regulation of insulin-like growth factor (IGF)-binding protein-4 availability in normal human osteoblast-like cells: role of endogenous IGFs.

Insulin-like growth factor-binding protein-4 (IGFBP-4) is an important regulator of insulin-like growth factor-I (IGF-I) anabolic activity in bone. Although cultured human osteoblast-like (hOB) cells have been reported to secrete IGFBP-4, we could not detect IGFBP-4 protein in 8 of 27 individual donor-derived hOB-cell conditioned medium (hOB-CM) samples examined by Western ligand blotting. Nonetheless, this subset of hOB cells had normal IGFBP-4 messenger ribonucleic acid expression and protein secretion. Regulation of IGFBP-4 levels in hOB cultures appeared to occur extracellularly. hOB cells produce an IGFBP-4 proteinase that requires the presence of IGF for cleavage of the IGFBP-4 molecule into 2 fragments of approximately 18 and 14 kilodaltons. These fragments are not detected by Western ligand blotting. Our data indicate that elevated endogenous levels of IGF can activate IGFBP-4 proteolysis, because in hOB cultures lacking detectable IGFBP-4 protein 1) basal IGF messenger ribonucleic acid expression was increased; 2) IGF-II peptide levels were elevated; 3) IGF-neutralizing antibodies added to hOB-CM attenuated the proteolysis of exogenous IGFBP-4; and 4) recombinant human IGFBP-4 was proteolyzed into 2 immunoreactive fragments of approximately 18 and 14 kilodaltons during cell-free incubations in these hOB-CM without the addition of exogenous IGF. In conclusion, elevated IGF expression and secretion can contribute to enhanced proteolysis of endogenous and exogenous IGFBP-4 via a proteinase secreted by cultured hOB cells. Levels of endogenous IGF peptide may determine IGFBP-4 availability in the bone microenvironment and, thus, modulate the local cell response to IGF-I.